19 - PART 12 Endocrinology and Metabolism

01 - SECTION 1 Endocrinology

SECTION 1 Endocrinology

Section 1 Endocrinology J. Larry Jameson

Approach to the

Patient with Endocrine

Disorders The management of endocrine disorders has applied principles of precision medicine before the term was commonly used (Chap. 5). A general goal is to maintain or restore homeostasis using precise homone measurements to titrate treatment regimens. Effective patient management requires a broad understanding of intermediary metabo­ lism, reproductive physiology, bone metabolism, and growth. Accord­ ingly, the practice of endocrinology is intimately linked to a conceptual framework for understanding hormone secretion, hormone action, and principles of feedback control (Chap. 389). The endocrine system is evaluated primarily by measuring hormone concentrations, arming the clinician with valuable diagnostic information. Most disorders of the endocrine system are amenable to effective treatment once the cor­ rect diagnosis is established. Endocrine deficiency disorders are treated with physiologic hormone replacement; hormone excess conditions, which usually are caused by benign glandular adenomas, are managed by removing tumors surgically or reducing hormone levels medically. SCOPE OF ENDOCRINOLOGY Classically, the specialty of endocrinology encompasses the study of glands and the hormones they produce. Over time, the field has expanded because of the discovery of hormones and growth factors produced by the brain, gastrointestinal (GI) tract, musculoskeletal system, and other nonglandular organs. The term endocrine was coined by Starling to contrast the actions of hormones secreted internally (endocrine) with those secreted externally (exocrine) or into a lumen, such as the GI tract. The term hormone, derived from a Greek phrase meaning “to set in motion,” aptly describes the dynamic actions of hormones as they elicit cellular responses and regulate physiologic processes through feedback mechanisms. Unlike many other specialties in medicine, it is not possible to define endocrinology strictly along anatomic lines. The classic endocrine glands—pituitary, thyroid, parathyroid, pancreatic islets, adrenals, and gonads—communicate broadly with other organs through the nervous system, hormones, cytokines, and growth factors. In addition to its traditional synaptic functions, the brain produces a vast array of peptide hormones, and this has led to the discipline of neuroendo­ crinology. Through the production of hypothalamic releasing factors, the central nervous system (CNS) exerts a major regulatory influence over pituitary hormone secretion (Chap. 390). The peripheral nervous system stimulates the adrenal medulla. The immune and endocrine systems are also intimately intertwined. The adrenal hormone cortisol is a powerful immunosuppressant. Cytokines and interleukins (ILs) have profound effects on the functions of the pituitary, adrenal, thy­ roid, and gonads. Common endocrine diseases such as autoimmune thyroid disease and type 1 diabetes mellitus are caused by dysregulation of immune surveillance and tolerance. Less common diseases such as polyglandular failure, Addison’s disease, and lymphocytic hypophysitis also have an immunologic basis. Immune therapies for cancer and vari­ ous autoimmune diseases can initiate autoimmune endocrine disease as a side effect of treatment. The interdigitation of endocrinology with physiologic processes in other specialties sometimes blurs the role of hormones. For example, hormones play an important role in maintenance of blood pressure,

Endocrinology and Metabolism PART 12 intravascular volume, and peripheral resistance in the cardiovascular system. Vasoactive substances such as catecholamines, angiotensin II, endothelin, and nitric oxide are involved in dynamic changes of vascu­ lar tone in addition to their multiple roles in other tissues. The heart is the principal source of atrial natriuretic peptide, which acts in classic endocrine fashion to induce natriuresis at a distant target organ (the kidney). Erythropoietin, a traditional circulating hormone, is made in the kidney and stimulates erythropoiesis in bone marrow (Chap. 66). The kidney is also integrally involved in the renin-angiotensin axis (Chap. 398) and is a primary target of several hormones, including parathyroid hormone (PTH), mineralocorticoids, fibroblast growth factor 23 (FGF23), and vasopressin. The GI tract produces a vast array of peptide hormones, such as glucagon-like peptide 1 (GLP1), chole­ cystokinin, ghrelin, gastrin, secretin, and vasoactive intestinal peptide, among many others. Carcinoid and islet tumors can secrete excessive amounts of these hormones, leading to specific clinical syndromes (Chap. 89). Many of these GI hormones are also produced in the CNS, where their functions are poorly understood. Adipose tissue produces leptin, which acts centrally to control appetite, along with adiponectin, resistin, and other hormones that regulate metabolism. As hormones such as inhibin, ghrelin, and leptin are discovered, they become inte­ grated into the science and practice of medicine on the basis of their functional roles rather than their tissues of origin. Characterization of hormone receptors frequently reveals unex­ pected relationships to factors in nonendocrine disciplines. The growth hormone (GH) and leptin receptors, for example, are members of the cytokine receptor family. The G protein–coupled receptors (GPCRs), which mediate the actions of many peptide hormones, are used in numerous physiologic processes, including vision, smell, and neurotransmission. PATHOLOGIC MECHANISMS OF ENDOCRINE DISEASE Endocrine diseases can be divided into three major types of condi­ tions: (1) hormone excess, (2) hormone deficiency, and (3) hormone resistance (Table 388-1). ■ ■CAUSES OF HORMONE EXCESS Syndromes of hormone excess can be caused by neoplastic growth of endocrine cells, autoimmune disorders, and excess hormone admin­ istration. Benign endocrine tumors, including parathyroid, pituitary, and adrenal adenomas, often retain the capacity to produce hormones, reflecting the fact that these tumors are relatively well differentiated. Many endocrine tumors exhibit subtle defects in their “set points” for feedback regulation. For example, in Cushing’s disease, impaired feed­ back inhibition of adrenocorticotropic hormone (ACTH) secretion is associated with autonomous function. However, the tumor cells are less sensitive to feedback inhibition, as evidenced by ACTH suppression at higher doses of dexamethasone (e.g., high-dose dexamethasone test) (Chap. 398). Similar set point defects are also typical of parathyroid adenomas and autonomously functioning thyroid nodules. The molecular basis of some endocrine tumors, such as the multiple endocrine neoplasia (MEN) syndromes (MEN1, 2A, 2B), has provided important insights into tumorigenesis (Chap. 402). MEN1 is char­ acterized primarily by the triad of parathyroid, pancreatic islet, and pituitary tumors. MEN2 predisposes to medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism. The MEN1 gene, located on chromosome 11q13, encodes a tumor-suppressor gene, menin. Analogous to the paradigm first described for retinoblastoma, the affected individual inherits a mutant copy of the MEN1 gene, and tumorigenesis ensues after a somatic “second hit” leads to loss of func­ tion of the normal MEN1 gene (through deletion or point mutations). In contrast to inactivation of a tumor-suppressor gene, as occurs in MEN1 and most other inherited cancer syndromes, MEN2 is caused by activating mutations in a single allele. In this case, activating mutations of the RET protooncogene, which encodes a receptor tyrosine kinase,

02 - 388 Approach to the Patient with Endocrine Disorders

388 Approach to the Patient with Endocrine Disorders

Section 1 Endocrinology J. Larry Jameson

Approach to the

Patient with Endocrine

Disorders The management of endocrine disorders has applied principles of precision medicine before the term was commonly used (Chap. 5). A general goal is to maintain or restore homeostasis using precise homone measurements to titrate treatment regimens. Effective patient management requires a broad understanding of intermediary metabo­ lism, reproductive physiology, bone metabolism, and growth. Accord­ ingly, the practice of endocrinology is intimately linked to a conceptual framework for understanding hormone secretion, hormone action, and principles of feedback control (Chap. 389). The endocrine system is evaluated primarily by measuring hormone concentrations, arming the clinician with valuable diagnostic information. Most disorders of the endocrine system are amenable to effective treatment once the cor­ rect diagnosis is established. Endocrine deficiency disorders are treated with physiologic hormone replacement; hormone excess conditions, which usually are caused by benign glandular adenomas, are managed by removing tumors surgically or reducing hormone levels medically. SCOPE OF ENDOCRINOLOGY Classically, the specialty of endocrinology encompasses the study of glands and the hormones they produce. Over time, the field has expanded because of the discovery of hormones and growth factors produced by the brain, gastrointestinal (GI) tract, musculoskeletal system, and other nonglandular organs. The term endocrine was coined by Starling to contrast the actions of hormones secreted internally (endocrine) with those secreted externally (exocrine) or into a lumen, such as the GI tract. The term hormone, derived from a Greek phrase meaning “to set in motion,” aptly describes the dynamic actions of hormones as they elicit cellular responses and regulate physiologic processes through feedback mechanisms. Unlike many other specialties in medicine, it is not possible to define endocrinology strictly along anatomic lines. The classic endocrine glands—pituitary, thyroid, parathyroid, pancreatic islets, adrenals, and gonads—communicate broadly with other organs through the nervous system, hormones, cytokines, and growth factors. In addition to its traditional synaptic functions, the brain produces a vast array of peptide hormones, and this has led to the discipline of neuroendo­ crinology. Through the production of hypothalamic releasing factors, the central nervous system (CNS) exerts a major regulatory influence over pituitary hormone secretion (Chap. 390). The peripheral nervous system stimulates the adrenal medulla. The immune and endocrine systems are also intimately intertwined. The adrenal hormone cortisol is a powerful immunosuppressant. Cytokines and interleukins (ILs) have profound effects on the functions of the pituitary, adrenal, thy­ roid, and gonads. Common endocrine diseases such as autoimmune thyroid disease and type 1 diabetes mellitus are caused by dysregulation of immune surveillance and tolerance. Less common diseases such as polyglandular failure, Addison’s disease, and lymphocytic hypophysitis also have an immunologic basis. Immune therapies for cancer and vari­ ous autoimmune diseases can initiate autoimmune endocrine disease as a side effect of treatment. The interdigitation of endocrinology with physiologic processes in other specialties sometimes blurs the role of hormones. For example, hormones play an important role in maintenance of blood pressure,

Endocrinology and Metabolism PART 12 intravascular volume, and peripheral resistance in the cardiovascular system. Vasoactive substances such as catecholamines, angiotensin II, endothelin, and nitric oxide are involved in dynamic changes of vascu­ lar tone in addition to their multiple roles in other tissues. The heart is the principal source of atrial natriuretic peptide, which acts in classic endocrine fashion to induce natriuresis at a distant target organ (the kidney). Erythropoietin, a traditional circulating hormone, is made in the kidney and stimulates erythropoiesis in bone marrow (Chap. 66). The kidney is also integrally involved in the renin-angiotensin axis (Chap. 398) and is a primary target of several hormones, including parathyroid hormone (PTH), mineralocorticoids, fibroblast growth factor 23 (FGF23), and vasopressin. The GI tract produces a vast array of peptide hormones, such as glucagon-like peptide 1 (GLP1), chole­ cystokinin, ghrelin, gastrin, secretin, and vasoactive intestinal peptide, among many others. Carcinoid and islet tumors can secrete excessive amounts of these hormones, leading to specific clinical syndromes (Chap. 89). Many of these GI hormones are also produced in the CNS, where their functions are poorly understood. Adipose tissue produces leptin, which acts centrally to control appetite, along with adiponectin, resistin, and other hormones that regulate metabolism. As hormones such as inhibin, ghrelin, and leptin are discovered, they become inte­ grated into the science and practice of medicine on the basis of their functional roles rather than their tissues of origin. Characterization of hormone receptors frequently reveals unex­ pected relationships to factors in nonendocrine disciplines. The growth hormone (GH) and leptin receptors, for example, are members of the cytokine receptor family. The G protein–coupled receptors (GPCRs), which mediate the actions of many peptide hormones, are used in numerous physiologic processes, including vision, smell, and neurotransmission. PATHOLOGIC MECHANISMS OF ENDOCRINE DISEASE Endocrine diseases can be divided into three major types of condi­ tions: (1) hormone excess, (2) hormone deficiency, and (3) hormone resistance (Table 388-1). ■ ■CAUSES OF HORMONE EXCESS Syndromes of hormone excess can be caused by neoplastic growth of endocrine cells, autoimmune disorders, and excess hormone admin­ istration. Benign endocrine tumors, including parathyroid, pituitary, and adrenal adenomas, often retain the capacity to produce hormones, reflecting the fact that these tumors are relatively well differentiated. Many endocrine tumors exhibit subtle defects in their “set points” for feedback regulation. For example, in Cushing’s disease, impaired feed­ back inhibition of adrenocorticotropic hormone (ACTH) secretion is associated with autonomous function. However, the tumor cells are less sensitive to feedback inhibition, as evidenced by ACTH suppression at higher doses of dexamethasone (e.g., high-dose dexamethasone test) (Chap. 398). Similar set point defects are also typical of parathyroid adenomas and autonomously functioning thyroid nodules. The molecular basis of some endocrine tumors, such as the multiple endocrine neoplasia (MEN) syndromes (MEN1, 2A, 2B), has provided important insights into tumorigenesis (Chap. 402). MEN1 is char­ acterized primarily by the triad of parathyroid, pancreatic islet, and pituitary tumors. MEN2 predisposes to medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism. The MEN1 gene, located on chromosome 11q13, encodes a tumor-suppressor gene, menin. Analogous to the paradigm first described for retinoblastoma, the affected individual inherits a mutant copy of the MEN1 gene, and tumorigenesis ensues after a somatic “second hit” leads to loss of func­ tion of the normal MEN1 gene (through deletion or point mutations). In contrast to inactivation of a tumor-suppressor gene, as occurs in MEN1 and most other inherited cancer syndromes, MEN2 is caused by activating mutations in a single allele. In this case, activating mutations of the RET protooncogene, which encodes a receptor tyrosine kinase,

TABLE 388-1  Causes of Endocrine Dysfunction TYPE OF ENDOCRINE DISORDER EXAMPLES Hyperfunction Neoplastic   Benign   Malignant   Ectopic   Genetic predisposition Autoimmune Iatrogenic Infectious/inflammatory Activating receptor mutations   Pituitary adenomas, hyperparathyroidism, autonomous thyroid or adrenal nodules Adrenal cancer, medullary thyroid cancer, carcinoid Ectopic ACTH, SIADH secretion MEN1, MEN2 Graves’ disease Cushing’s syndrome, hypoglycemia Subacute thyroiditis LH, TSH, Ca2+, PTH receptors, Gsα PART 12 Endocrinology and Metabolism Hypofunction Autoimmune Iatrogenic Infectious/inflammatory Hormone mutations Enzyme defects Developmental defects Nutritional/vitamin deficiency Hemorrhage/infarction Hashimoto’s thyroiditis, type 1 diabetes mellitus, Addison’s disease, polyglandular failure Radiation-induced hypopituitarism, hypothyroidism, surgical Adrenal insufficiency, hypothalamic sarcoidosis GH, LHβ, FSHβ, vasopressin 21-Hydroxylase deficiency Kallmann’s syndrome, Turner’s syndrome, transcription factors Vitamin D deficiency, iodine deficiency Sheehan’s syndrome, adrenal insufficiency Hormone Resistance   Receptor mutations   Membrane   Nuclear Signaling pathway mutations Postreceptor   GH, vasopressin, LH, FSH, ACTH, GnRH, GHRH, PTH, leptin, Ca2+ AR, TR, VDR, ER, GR, PPARγ Albright’s hereditary osteodystrophy Type 2 diabetes mellitus, leptin resistance Abbreviations: ACTH, adrenocorticotropic hormone; AR, androgen receptor; ER, estrogen receptor; FSH, follicle-stimulating hormone; GH, growth hormone; GHRH, growth hormone–releasing hormone; GnRH, gonadotropin-releasing hormone; GR, glucocorticoid receptor; LH, luteinizing hormone; MEN, multiple endocrine neoplasia; PPAR, peroxisome proliferator activated receptor; PTH, parathyroid hormone; SIADH, syndrome of inappropriate antidiuretic hormone; TR, thyroid hormone receptor; TSH, thyroidstimulating hormone; VDR, vitamin D receptor. lead to thyroid C-cell hyperplasia in childhood before the develop­ ment of medullary thyroid carcinoma. Elucidation of this pathogenic mechanism has allowed early genetic screening for RET mutations in individuals at risk for MEN2, permitting identification of those who may benefit from prophylactic thyroidectomy and biochemical screen­ ing for pheochromocytoma and hyperparathyroidism. Mutations that activate hormone receptor signaling have been identified in several GPCRs. For example, activating mutations of the luteinizing hormone (LH) receptor cause a dominantly transmitted form of male-limited precocious puberty, reflecting premature stimu­ lation of testosterone synthesis in Leydig cells (Chap. 403). Activating mutations in these GPCRs are located predominantly in the trans­ membrane domains and induce receptor coupling to Gsα even in the absence of hormone. Consequently, adenylate cyclase is activated, and cyclic adenosine monophosphate (AMP) levels increase in a manner that mimics hormone action. A similar phenomenon results from acti­ vating mutations in Gsα. When these mutations occur early in develop­ ment, they cause McCune-Albright syndrome. When they occur only in somatotropes, the activating Gsα mutations cause GH-secreting tumors and acromegaly (Chap. 392). In autoimmune Graves’ disease, antibody interactions with the thyroid-stimulating hormone (TSH) receptor mimic TSH action, lead­ ing to hormone overproduction (Chap. 394). Analogous to the effects of activating mutations of the TSH receptor, these stimulating auto­ antibodies induce conformational changes in the TSH receptor that release it from a constrained state, thereby triggering receptor coupling to G proteins, and signaling induces excess thyroid hormone synthesis and secretion. ■ ■CAUSES OF HORMONE DEFICIENCY Most examples of hormone deficiency states can be attributed to glandular destruction caused by autoimmunity, surgery, infection, inflammation, infarction, hemorrhage, or tumor infiltration (Table 388-1). Autoimmune damage to the thyroid gland (Hashimoto’s thyroiditis)

and pancreatic islet β cells (type 1 diabetes mellitus) are examples of relatively common endocrine diseases. Mutations in a number of hor­ mones, hormone receptors, transcription factors, enzymes, and chan­ nels can also lead to hormone deficiencies. ■ ■HORMONE RESISTANCE Most severe hormone resistance syndromes are due to inherited defects in membrane receptors, nuclear receptors, or the pathways that transduce receptor signals. These disorders are characterized by defective hormone action despite the presence of increased hormone levels. In complete androgen resistance, for example, mutations in the androgen receptor result in a female phenotypic appearance in genetic (XY) males, even though LH and testosterone levels are increased (Chap. 402). In addition to these relatively rare genetic disorders, more common acquired forms of functional hormone resistance include insulin resistance in type 2 diabetes mellitus, leptin resistance in obesity, and GH resistance in catabolic states. The pathogenesis of functional resistance involves receptor downregulation and postrecep­ tor desensitization of signaling pathways; functional forms of resis­ tance are generally reversible. ■ ■CLINICAL EVALUATION OF ENDOCRINE DISORDERS Because most glands are relatively inaccessible, the physical exami­ nation usually focuses on the manifestations of hormone excess or deficiency as well as direct examination of palpable glands, such as the thyroid and gonads. For these reasons, it is important to evaluate patients in the context of their presenting symptoms, review of systems, family and social history, and exposure to medications that may affect the endocrine system. Astute clinical skills are required to detect subtle symptoms and signs suggestive of underlying endocrine disease. For example, a patient with Cushing’s syndrome may manifest specific findings, such as central fat redistribution, skin striae, and proximal muscle weakness, in addition to features seen commonly in the general

population, such as obesity, plethora, hypertension, and glucose intol­ erance. Similarly, the insidious onset of hypothyroidism—with fatigue, mental slowing, dry skin, and other features—can be difficult to dis­ tinguish from similar, nonspecific findings in the general population. Clinical judgment that is based on knowledge of disease prevalence TABLE 388-2  Examples of Prevalent Endocrine and Metabolic Disorders in the Adult DISORDER APPROXIMATE PREVALENCE IN ADULTSa SCREENING/TESTING RECOMMENDATIONSb CHAPTER(S) Obesity 40% Obese, BMI ≥30 70% Overweight, BMI ≥25 Type 2 diabetes mellitus

10% Beginning at age 45, screen every 3 years, or earlier in high-risk groups: FPG >126 mg/dL Random plasma glucose >200 mg/dL An elevated HbA1c Consider comorbid complications Hyperlipidemia 20–25% Cholesterol screening at least every 5 years; more often in high-risk groups Lipoprotein analysis (LDL, HDL) for increased cholesterol, CAD, diabetes Consider secondary causes Metabolic syndrome 35% Measure waist circumference, FPG, BP, lipids

Hypothyroidism 5–10%, women 0.5–2%, men Graves’ disease 1–3%, women 0.1%, men Thyroid nodules and neoplasia 2–5% palpable

25% by ultrasound Osteoporosis 5–10%, women 2–5%, men Hyperparathyroidism 0.1–0.5%, women > men Serum calcium PTH, if calcium is elevated Assess comorbid conditions Infertility 10%, couples Investigate both members of couple Semen analysis in male Assess ovulatory cycles in female Specific tests as indicated Polycystic ovarian syndrome 5–10%, women Free testosterone, DHEAS Consider comorbid conditions Hirsutism 5–10% Free testosterone, DHEAS Exclude secondary causes Additional tests as indicated Menopause Median age, 51 FSH

Hyperprolactinemia 15% in women with amenorrhea or galactorrhea Erectile dysfunction 10–25% Careful history, PRL, testosterone Consider secondary causes (e.g., diabetes) Hypogonadism, male 1–2% Testosterone, LH

Gynecomastia 15% Often, no tests are indicated Consider Klinefelter’s syndrome Consider medications, hypogonadism, liver disease Klinefelter’s syndrome 0.2%, men Karyotype Testosterone Vitamin D deficiency 10% Measure serum 25-OH vitamin D Consider secondary causes Turner’s syndrome 0.03%, women Karyotype Consider comorbid conditions aThe prevalence of most disorders varies among ethnic groups and with aging. Data based primarily on U.S. population. bSee individual chapters for additional information on evaluation and treatment. Early testing is indicated in patients with signs and symptoms of disease and in those at increased risk. Abbreviations: BMI, body mass index; BP, blood pressure; CAD, coronary artery disease; DHEAS, dehydroepiandrosterone; FPG, fasting plasma glucose; FSH, folliclestimulating hormone; HbA1C, hemoglobin A1C; HDL, high-density lipoprotein; LDL, low-density lipoprotein; LH, luteinizing hormone; MRI, magnetic resonance imaging; PRL, prolactin; PTH, parathyroid hormone; TSH, thyroid-stimulating hormone.

and pathophysiology is required to decide when to embark on more extensive evaluation of these disorders. Laboratory testing plays an essential role in endocrinology by allowing quantitative assessment of hormone levels and dynamics. Radiologic imaging tests such as computed tomography (CT) scan, magnetic resonance imaging (MRI),

Calculate BMI Measure waist circumference Exclude secondary causes Consider comorbid complications

Approach to the Patient with Endocrine Disorders
CHAPTER 388

TSH; confirm with free T4

TSH, free T4

Physical examination or ultrasound of thyroid Fine-needle aspiration biopsy

Bone mineral density measurements in women >65 years or in postmenopausal women or men at risk Exclude secondary causes

403,404

PRL level MRI, if not medication-related

03 - 389 Mechanisms of Hormone Action

389 Mechanisms of Hormone Action

ultrasound, and thyroid scan are also used for the diagnosis of endo­ crine disorders. However, these tests generally are employed only after a hormonal abnormality has been established by biochemical testing.

■ ■HORMONE MEASUREMENTS AND ENDOCRINE TESTING Immunoassays are the most important diagnostic tool in endocrinol­ ogy, as they allow sensitive, specific, and quantitative determination of steady-state and dynamic changes in hormone concentrations. Immu­ noassays use antibodies to detect specific hormones. For many peptide hormones, these measurements are now configured to use two differ­ ent antibodies to increase binding affinity and specificity. There are many variations of these assays; a common format involves using one antibody to capture the antigen (hormone) onto an immobilized sur­ face and a second antibody, coupled to a chemiluminescent (immuno­ chemiluminescent assay [ICMA]) or radioactive (immunoradiometric assay [IRMA]) signal, to detect the antigen. These assays are sensitive enough to detect plasma hormone concentrations in the picomolar to nanomolar range, and they can readily distinguish structurally related proteins, such as PTH from PTH-related peptide (PTHrP). A variety of other techniques are used to measure specific hormones, including mass spectroscopy, various forms of chromatography, and enzymatic methods; bioassays are now used rarely. Mass spectroscopy is increas­ ingly being used given its ability to quantitatively measure large num­ bers of peptides or steroids simultaneously. PART 12 Endocrinology and Metabolism Most hormone measurements are based on plasma or serum sam­ ples. However, urinary hormone determinations remain useful for the evaluation of some conditions. Urinary collections over 24 h provide an integrated assessment of the production of a hormone or metabolite, many of which vary during the day. It is important to ensure complete collections of 24-h urine samples; simultaneous measurement of creati­ nine provides an internal control for the adequacy of collection and can be used to normalize some hormone measurements. A 24-h urine-free cortisol measurement largely reflects the amount of unbound cortisol, thus providing a reasonable index of biologically available hormone. Other commonly used urine determinations include 17-hydroxycor­ ticosteroids, 17-ketosteroids, vanillylmandelic acid, metanephrine, catecholamines, 5-hydroxyindoleacetic acid, and calcium. The value of quantitative hormone measurements lies in their correct interpretation in a clinical context. The normal range for most hormones is relatively broad, often varying by a factor of two- to tenfold. The wide normal range reflects the effects of binding proteins as well as circadian rhythms and other physiologic variables. The normal ranges for many hormones are sex- and age-specific. Thus, using the correct normative database is an essential part of interpreting hormone tests. The pulsatile nature of hormones and factors that can affect their secretion, such as sleep, meals, and medications, must also be considered. Cortisol values increase fivefold between midnight and dawn; reproductive hormone levels vary dramatically during the female menstrual cycle. For many endocrine systems, much information can be gained from basal hormone testing, particularly when different components of an endocrine axis are assessed simultaneously. For example, low testoster­ one and elevated LH levels suggest a primary gonadal disease, whereas a hypothalamic-pituitary disorder is likely if both LH and testosterone are low. Because TSH is a sensitive indicator of thyroid function, it is generally recommended as a first-line test for thyroid disorders. An elevated TSH level is almost always the result of primary hypothyroid­ ism, whereas a low TSH is most often caused by thyrotoxicosis. These predictions can be confirmed by determining the free thyroxine level. In the less common circumstance when free thyroxine and TSH are both low, it is important to consider secondary hypopituitarism caused by hypothalamic-pituitary disease. Elevated calcium and PTH levels suggest hyperparathyroidism, whereas PTH is suppressed in hypercal­ cemia caused by malignancy or granulomatous diseases. A suppressed ACTH in the setting of hypercortisolemia, or increased urine free cor­ tisol, is seen with hyperfunctioning adrenal adenomas. It is not uncommon, however, for baseline hormone levels associ­ ated with pathologic endocrine conditions to overlap with the normal range. In this circumstance, dynamic testing is useful to separate

the two groups further. There are a multitude of dynamic endocrine tests, but all are based on principles of feedback regulation, and most responses can be rationalized based on principles that govern the regulation of endocrine axes. Suppression tests are used in the setting of suspected endocrine hyperfunction. An example is the dexamethasone suppression test used to evaluate Cushing’s syndrome (Chaps. 392 and 398). Stimulation tests generally are used to assess endocrine hypo­ function. The ACTH stimulation test, for example, is used to assess the adrenal gland response in patients with suspected adrenal insuffi­ ciency. Other stimulation tests use hypothalamic-releasing factors such as corticotropin-releasing hormone (CRH) and growth hormone– releasing hormone (GHRH) to evaluate pituitary hormone reserve (Chap. 392). Insulin-induced hypoglycemia evokes pituitary ACTH and GH responses. Stimulation tests based on reduction or inhibition of endogenous hormones are now used infrequently. Examples include metyrapone inhibition of cortisol synthesis and clomiphene inhibition of estrogen feedback. ■ ■SCREENING AND ASSESSMENT OF COMMON ENDOCRINE DISORDERS Many endocrine disorders are prevalent in the adult population (Table 388-2) and can be diagnosed and managed by general inter­ nists, family practitioners, or other primary health care providers. The high prevalence and clinical impact of certain endocrine diseases justify vigilance for features of these disorders during routine physical examinations; laboratory screening is indicated in selected high-risk populations. ■ ■FURTHER READING Endocrine Society: The Endocrine Society Clinical Practice Guidelines. Available from https://www.endocrine.org/clinical-practice-guidelines. Loriaux DL: A Biographical History of Endocrinology. Hoboken, Wiley Blackwell, 2016. Robertson RP (ed): DeGroot’s Endocrinology: Adult and Pediatric, 8th ed. Philadelphia, Elsevier, 2023. J. Larry Jameson

Mechanisms of

Hormone Action The endocrine system, composed of various glands and the hormones they produce, regulates growth, metabolism, homeostasis, and repro­ duction. Because hormones circulate and act via receptors in target tissues, they serve to coordinate physiologic responses to external or internal cues. For example, the light-dark cycle, sensed through the visual system, modulates hypothalamic corticotropin-releasing hor­ mone (CRH), which increases pituitary adrenocorticotropin hormone (ACTH) production, leading to increased adrenal cortisol production before the time of waking in the morning. Increased cortisol, in turn, circulates throughout the body, acting via the nuclear glucocorticoid receptor, to activate numerous genetic programs that influence metab­ olism, the cardiovascular system, behavior, and the immune system. This chapter provides an overview of the different types of hormones and how they function at the cellular level to control myriad physi­ ologic processes. CLASSES OF HORMONES Hormones can be divided into five major types: (1) amino acid deriva­ tives such as dopamine, catecholamine, and thyroid hormone; (2) small neuropeptides such as gonadotropin-releasing hormone (GnRH),

thyrotropin-releasing hormone (TRH), somatostatin, and vasopres­ sin; (3) large proteins such as insulin, luteinizing hormone (LH), and parathyroid hormone (PTH); (4) steroid hormones such as cortisol and estrogen that are synthesized from cholesterol-based precursors; and (5) vitamin derivatives such as retinoids (vitamin A) and vitamin D. A variety of peptide growth factors, such as insulin-like growth factor 1 (IGF1), share actions with hormones but often act more locally. As a rule, amino acid derivatives and peptide hormones interact with cellsurface membrane receptors. Steroids, thyroid hormones, vitamin D, and retinoids are lipid-soluble and bind to intracellular nuclear recep­ tors, although many also interact with membrane receptors or intracel­ lular signaling proteins as well. ■ ■HORMONE AND RECEPTOR FAMILIES Hormones and receptors can be grouped into families, reflecting struc­ tural similarities and evolutionary origins (Table 389-1). The evolution of these families generates diverse but highly selective pathways of hor­ mone action. Understanding these relationships is useful to extrapolate structural and mechanistic insights gleaned from one hormone or receptor to other family members. The glycoprotein hormone family, consisting of thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), LH, and human chorionic gonadotropin (hCG), illustrates many features of evolution­ arily related hormones. The glycoprotein hormones are heterodimers that share the α subunit in common; the β subunits are distinct and confer specific biologic actions. The overall three-dimensional archi­ tecture of the β subunits is similar, reflecting the locations of conserved disulfide bonds that constrain protein conformation. Evolutionary analysis suggests that the β-subunit genes arose from a common ancestral gene through gene duplication and divergence to evolve new biologic functions. As hormone families expand and diverge, their receptors have coevolved to create new biologic functions. Related G protein–coupled receptors (GPCRs), for example, have evolved for each of the glyco­ protein hormones. These receptors are also structurally similar, and each is coupled predominantly to the Gsα signaling pathway. Because of co-evolution with respective hormones to achieve specificity, there TABLE 389-1  Examples of Membrane Receptor Families and Signaling Pathways RECEPTORS EFFECTORS SIGNALING PATHWAYS G Protein–Coupled Seven-Transmembrane Receptor (GPCR) LH, FSH, TSH, β-adrenergic Stimulation of cyclic AMP production, protein kinase A Gsα, adenylate cyclase Glucagon, PTH, PTHrP, ACTH, MSH, GHRH, CRH Ca2+ channels Calmodulin, Ca2+-dependent kinases Somatostatin, α-adrenergic Giα Inhibition of cyclic AMP production Activation of K+, Ca2+ channels TRH, GnRH Gq, G11 Phospholipase C, diacylglycerol, IP3, protein kinase C, voltage-dependent Ca2+ channels Receptor Tyrosine Kinase Insulin, IGF-I  Tyrosine kinases, IRS  MAP kinases, PI 3-kinase; AKT  Cytokine Receptor–Linked Kinase GH, PRL JAK, tyrosine kinases STAT, MAP kinase, PI 3-kinase, IRS-1 Serine Kinase Activin, TGF-β, MIS Serine kinase Smads Abbreviations: IP3, inositol triphosphate; IRS, insulin receptor substrates; MAP, mitogen-activated protein; MSH, melanocyte-stimulating hormone; PI, phosphatidylinositol; RSK, ribosomal S6 kinase; TGF-β, transforming growth factor β. For all other abbreviations, see text. Note that most receptors interact with multiple effectors and activate networks of signaling pathways.

is minimal overlap of hormone binding. For example, TSH binds with high specificity to the TSH receptor but interacts minimally with the LH or FSH receptors. Nonetheless, there can be subtle physiologic con­ sequences of hormone cross-reactivity with other receptors. Very high levels of hCG during pregnancy weakly stimulate the TSH receptor and increase thyroid hormone levels, resulting in feedback inhibition and a compensatory decrease in TSH.

IGF1 and IGF2 have structural similarities that are most apparent when precursor forms of the proteins are compared. In contrast to the high degree of specificity seen with the glycoprotein hormones, there is moderate cross-talk among the members of the insulin/IGF family. High concentrations of an IGF2 precursor produced by certain tumors (e.g., sarcomas) can cause hypoglycemia, partly because of binding to insulin and IGF1 receptors. High concentrations of insulin also bind to the IGF1 receptor, accounting for some of the clinical manifestations seen in conditions with chronic hyperinsulinemia. Mechanisms of Hormone Action CHAPTER 389 Another important example of receptor cross-talk is seen with PTH and parathyroid hormone–related peptide (PTHrP) (Chap. 422). PTH is produced by the parathyroid glands, whereas PTHrP is expressed at high levels during development and by a variety of tumors (Chap. 98). These hormones have amino acid sequence similarity, particularly in their amino-terminal regions. Both hormones bind to the PTH1R receptor that is expressed in bone and kidney. Excessive production of either hormone results in hypercalcemia and hyperphosphatemia, making it difficult to distinguish hyperparathyroidism from hypercal­ cemia of malignancy solely on the basis of serum chemistries. However, sensitive and specific assays for PTH and PTHrP now allow these dis­ orders to be distinguished. Based on their specificities for DNA-binding sites, the nuclear receptor family can be subdivided into type 1 receptors (glucocorti­ coid receptor, mineralocorticoid receptor, androgen receptor, estrogen receptor, progesterone receptor) that bind steroids and type 2 receptors (thyroid hormone receptor, vitamin D receptor, retinoic acid receptor, peroxisome proliferator activated receptor) that bind thyroid hormone, vitamin D, retinoic acid, or lipid derivatives, respectively. Certain functional domains in nuclear receptors, such as the zinc finger DNAbinding domains, are highly conserved. However, selective amino acid differences within this domain confer DNA sequence specificity. The hormone-binding domains are more variable, providing great diversity in the array of small molecules that bind to different nuclear recep­ tors. With few exceptions, hormone binding is highly specific for a single type of nuclear receptor. One exception involves the glucocor­ ticoid and mineralocorticoid receptors. Because the mineralocorticoid receptor also binds glucocorticoids with high affinity, an enzyme (11β-hydroxysteroid dehydrogenase) in renal tubular cells inactivates glucocorticoids, allowing selective renal responses to mineralocorti­ coids such as aldosterone. However, when very high glucocorticoid concentrations occur, as in Cushing’s syndrome, the glucocorticoid degradation pathway becomes saturated, allowing excessive cortisol levels to bind mineralocorticoid receptors leading to sodium retention and potassium wasting. This phenomenon is particularly pronounced in ectopic ACTH syndromes (Chap. 398). Another example of relaxed nuclear receptor specificity involves the estrogen receptor, which can bind an array of compounds, some of which have little apparent struc­ tural similarity to the high-affinity ligand estradiol. This feature of the estrogen receptor makes it susceptible to activation by “environmental estrogens” such as resveratrol, octylphenol, and many other aromatic hydrocarbons. However, this lack of specificity provides an opportu­ nity to synthesize clinically useful antagonists (e.g., tamoxifen) and selective estrogen response modulators (SERMs) such as raloxifene. These compounds generate distinct estrogen receptor conformations that alter receptor interactions with components of the transcription machinery (see below), thereby conferring their unique actions. ■ ■HORMONE SYNTHESIS AND PROCESSING The synthesis of peptide hormones and their receptors occurs through a classic pathway of gene expression: transcription → mRNA → protein → posttranslational protein processing → intracellular sorting, followed by membrane integration or secretion.

Many hormones are embedded within larger precursor polypep­ tides that are proteolytically processed to yield the biologically active hormone. Examples include proopiomelanocortin (POMC) → ACTH; proglucagon → glucagon; proinsulin → insulin; and pro-PTH → PTH, among others. In many cases, such as POMC and proglucagon, these precursors generate multiple biologically active peptides. For example, proglucagon generates glucagon, as well as glucagon-like peptide 1 (GLP1), among other peptides. It is provocative that hormone precur­ sors are typically inactive, presumably adding an additional level of control through peptide processing. Prohormone conversion occurs not only for peptide hormones but also for certain steroids (testosterone → dihydrotestosterone) and thyroid hormone (T4 → T3).

PART 12 Endocrinology and Metabolism Peptide precursor processing is intimately linked to intracellular sorting pathways that transport proteins to appropriate vesicles and enzymes, resulting in specific cleavage steps, followed by protein fold­ ing and translocation to secretory vesicles. Hormones destined for secretion are translocated across the endoplasmic reticulum guided by an amino-terminal signal sequence that subsequently is cleaved. Cell-surface receptors are inserted into the membrane via short seg­ ments of hydrophobic amino acids that remain embedded within the lipid bilayer. During translocation through the Golgi and endoplasmic reticulum, hormones and receptors are subject to a variety of post­ translational modifications, such as glycosylation and phosphorylation, which can alter protein conformation, modifying circulating half-life and biological activity. Synthesis of most steroid hormones is based on modifications of the precursor, cholesterol. Multiple regulated enzymatic steps are required for the synthesis of testosterone (Chap. 403), estradiol (Chap. 404), cortisol (Chap. 398), and vitamin D (Chap. 421). This large number of synthetic steps predisposes to multiple genetic and acquired disorders of steroidogenesis. Endocrine genes contain regulatory DNA elements similar to those found in many other genes, but their exquisite control by hormones reflects the presence of specific hormone response elements. For example, the TSH genes are repressed directly by thyroid hormones acting through the thyroid hormone receptor (TR), a member of the nuclear receptor family. Steroidogenic enzyme gene expression requires specific transcription factors, such as steroidogenic factor 1 (SF1), acting in conjunction with signals transmitted by trophic hor­ mones (e.g., ACTH or LH). Once activated, SF1 functions as a master regulator, inducing a large array of genes required for steroidogenic and metabolic pathways required for steroid synthesis. For some hormones, substantial regulation occurs at the level of translational efficiency. Insulin biosynthesis, although it requires ongoing gene transcription, is regulated primarily at the translational and secretory levels in response to the levels of glucose or amino acids. ■ ■HORMONE SECRETION, TRANSPORT, AND DEGRADATION The circulating level of a hormone is determined by its rate of secre­ tion and its half-life. After protein processing, peptide hormones (e.g., GnRH, insulin, growth hormone [GH]) are stored in secretory gran­ ules. As these granules mature, they are poised beneath the plasma membrane for imminent release into the circulation. In most instances, the stimulus for hormone secretion is a releasing factor or neural signal that induces rapid changes in voltage-gated channel activity or intracel­ lular calcium concentrations, leading to secretory granule fusion with the plasma membrane and release of its contents into the extracellular environment and bloodstream. Steroid hormones, in contrast, diffuse into the circulation as they are synthesized. Thus, their secretory rates are closely aligned with rates of synthesis. For example, ACTH and LH induce steroidogenesis by stimulating the activity of the steroidogenic acute regulatory (StAR) protein, which transports cholesterol into the mitochondrion. These hormones also induce other rate-limiting enzy­ matic steps (e.g., cholesterol side-chain cleavage enzyme, CYP11A1) in specific steroidogenic pathways. Hormone transport and degradation dictate the rapidity with which a hormonal signal decays. Some hormone signals are evanescent (e.g., somatostatin), whereas others are longer-lived (e.g., TSH). Because

somatostatin exerts effects in virtually every tissue, a short half-life allows its concentrations and actions to be controlled locally. Structural modifications that impair somatostatin degradation have been useful for generating long-acting therapeutic analogues such as octreotide (Chap. 392). In contrast, the actions of TSH are highly specific for the thyroid gland. Its prolonged half-life generates relatively constant serum levels even though TSH is secreted in discrete pulses. An understanding of circulating hormone half-life is important for achieving physiologic hormone replacement, as the frequency of dosing and the time required to reach steady state are intimately linked to rates of hormone decay. T4, for example, has a circulating half-life of 7 days. Consequently, >1 month is required to reach a new steady state, and single daily doses are sufficient to achieve constant hormone levels. T3, in contrast, has a half-life of 1 day. Its administration is associated with more dynamic serum levels, and it must be administered two to three times per day. Similarly, synthetic glucocorticoids vary widely in their half-lives; those with longer half-lives (e.g., dexamethasone) are associ­ ated with greater suppression of the hypothalamic-pituitary-adrenal (HPA) axis. Most protein hormones (e.g., ACTH, GH, prolactin [PRL], PTH, LH) have relatively short half-lives (<20 min), leading to sharp peaks of secretion and decay. The only accurate way to profile the pulse frequency and amplitude of these hormones is to measure levels in frequently sampled blood (every 10 min or less) over long durations (8–24 h). Because this is not practical in a clinical setting, an alternative strategy is to pool three to four blood samples drawn at about 30-min intervals or interpret the results in the context of a relatively wide nor­ mal range. Rapid hormone decay is useful in certain clinical settings. For example, the short half-life of PTH allows the use of intraoperative PTH levels to confirm successful removal of a parathyroid adenoma. This is particularly valuable diagnostically when there is a possibility of multicentric disease or parathyroid hyperplasia, as occurs with mul­ tiple endocrine neoplasia (MEN) or renal insufficiency. Many hormones circulate in association with serum-binding pro­ teins. Examples include (1) T4 and T3 binding to thyroxine-binding globulin (TBG), albumin, and thyroxine-binding prealbumin (TBPA); (2) cortisol binding to cortisol-binding globulin (CBG); (3) androgen and estrogen binding to sex hormone–binding globulin (SHBG); (4) IGF1 and IGF2 binding to multiple IGF-binding proteins (IGFBPs); (5) GH interactions with GH-binding protein (GHBP), a circulating fragment of the GH receptor extracellular domain; and (6) activin binding to follistatin. These interactions provide a hormone reservoir, prevent otherwise rapid degradation of unbound hormones, restrict hormone access to certain sites (e.g., IGFBPs), and modulate the levels of unbound, or “free,” hormone concentrations. Although a variety of binding protein abnormalities have been identified, most have little clinical consequence aside from creating diagnostic problems. For example, TBG deficiency can reduce total thyroid hormone levels greatly, but the free concentrations of T4 and T3 remain normal. Liver disease and certain medications can also influence binding protein lev­ els (e.g., estrogen increases TBG) or cause displacement of hormones from binding proteins (e.g., salsalate displaces T4 from TBG). In gen­ eral, only unbound hormone is available to interact with receptors and thus elicit a biologic response. Short-term perturbations in binding proteins change the free hormone concentration, which in turn induces compensatory adaptations through feedback loops. SHBG changes in women are an exception to this self-correcting mechanism. When SHBG decreases because of insulin resistance or androgen excess, the unbound testosterone concentration is increased, potentially contrib­ uting to hirsutism in women with polycystic ovary syndrome (PCOS) (Chap. 406). The increased unbound testosterone level does not result in an adequate compensatory feedback correction because estrogen, not testosterone, is the primary regulator of the reproductive axis. An additional exception to the unbound hormone hypothesis involves megalin, a member of the low-density lipoprotein (LDL) receptor family that serves as an endocytotic receptor for thyroglobu­ lin, carrier-bound vitamins A and D, and SHBG-bound androgens and estrogens. After internalization, the carrier proteins are degraded in lysosomes and release their bound ligands within the cells. Other membrane transporters have also been identified for thyroid hormones.

Hormone degradation can be an impor­ tant mechanism for regulating concentrations locally. As noted above, 11β-hydroxysteroid dehydrogenase inactivates glucocorticoids in renal tubular cells, preventing actions through the mineralocorticoid receptor. Thyroid hormone deiodinases convert T4 to T3 and can inactivate T3. During devel­ opment, degradation of retinoic acid by Cyp26b1 prevents primordial germ cells in the male from entering meiosis, as occurs in the female ovary. Activin/MIS/BMP TGF-β Serine kinase ■ ■HORMONE ACTION THROUGH RECEPTORS Receptors for hormones are divided into two major classes: membrane and nuclear. Mem­ brane receptors primarily bind peptide hor­ mones and catecholamines. Nuclear receptors bind small molecules that can diffuse across the cell membrane, such as steroids and vitamin D. Certain general principles apply to hormone-receptor interactions regardless of the class of receptor. Hormones bind to receptors with specificity and an affinity that generally coincides with the dynamic range of circulating hormone concentrations. Low con­ centrations of free hormone (usually 10−12 to 10−9 M) rapidly associate and dissociate from receptors in a bimolecular reaction such that the occupancy of the receptor at any given moment is a function of hor­ mone concentration and the receptor’s affinity for the hormone. Recep­ tor numbers vary greatly in different target tissues, providing one of the major determinants of tissue-specific responses to circulating hor­ mones. For example, ACTH receptors are located almost exclusively in the adrenal cortex, and LH receptors are found predominantly in the gonads. In contrast, insulin and TRs are widely distributed, reflecting the need for metabolic responses in all tissues. FIGURE 389-1  Membrane receptor signaling. MAPK, mitogen-activated protein kinase; PKA, C, protein kinase A, C; TGF, transforming growth factor. For other abbreviations, see text. ■ ■MEMBRANE RECEPTORS Membrane receptors for hormones can be divided into several major groups: (1) seven-transmembrane GPCRs, (2) tyrosine kinase receptors, (3) cytokine receptors, and (4) serine kinase receptors (Fig. 389-1). The seven-transmembrane GPCR family binds a huge array of hormones, including large proteins (e.g., LH, PTH), small pep­ tides (e.g., TRH, somatostatin), catecholamines (epinephrine, dopa­ mine), and even minerals (e.g., calcium). The extracellular domains of GPCRs vary widely in size and are the major binding site for large hormones. The transmembrane-spanning regions are composed of hydrophobic α-helical domains that traverse the lipid bilayer. Like some channels, these domains are thought to circularize and form a hydrophobic pocket into which certain small ligands fit. Hormone binding induces conformational changes in these domains, transduc­ ing structural changes to the intracellular domain, which is a docking site for G proteins. The large family of G proteins, so named because they bind guanine nucleotides (guanosine triphosphate [GTP], guanosine diphosphate [GDP]), provides great diversity for coupling receptors to different signaling pathways. G proteins form a heterotrimeric complex that is composed of various α and βγ subunits (Fig. 389-2). The α subunit contains the guanine nucleotide–binding site and an intrinsic GTPase that hydrolyzes GTP → GDP. The βγ subunits are tightly associated and modulate the activity of the α subunit as well as mediating their own effector signaling pathways. G protein activity is regulated by a cycle that involves GTP hydrolysis and dynamic interactions between the α and βγ subunits. Hormone binding to the receptor induces GDP dissociation, allowing Gα to bind GTP and dissociate from the βγ com­ plex. Under these conditions, the Gα subunit is activated and mediates signal transduction through various enzymes, such as adenylate cyclase and phospholipase C. GTP hydrolysis to GDP allows reassociation with the βγ subunits and restores the inactive state. G proteins interact with

G protein–coupled Seven transmembrane Cytokine/GH/PRL Insulin/IGF-I Tyrosine kinase Membrane Mechanisms of Hormone Action CHAPTER 389 G protein PKA, PKC JAK/STAT Signaling pathways Ras/Raf MAPK Smads Nucleus Target gene other cellular proteins, including kinases, channels, G protein–coupled receptor kinases (GRKs), and arrestins, that mediate signaling as well as receptor desensitization and recycling. A variety of endocrinopathies result from mutations in GPCRs that alter their interactions with G proteins (Table 389-2). Loss-of-function mutations are generally recessive and inactivate the relevant hormone signaling pathway. Because many of these receptors are important for development as well as signaling, patient presentations resemble glandular failure syndromes (e.g., mutations in LH-R, FSH-R, TSH-R). Gain-of-function (GOF) mutations are more complex. Selected GOF mutations induce conformational changes in the GPCR that mimic the activated state normally induced by hormone binding. These GOF mutations result in a constitutively active state in which G protein coupling stimulates cell signaling pathways, most commonly via cyclic adenosine 5′-monophosphate (cAMP) and protein kinase A. When mutations occur in the germline, the conditions are heritable and pres­ ent in early life (e.g., LH-R, TSH-R). Sporadic, somatic mutations can also occur and result in clonal expansion of hyperfunctioning cells. Mutations in the TSH-R illustrate the range of possible clinical con­ sequences of GPCR mutations. Recessive inactivating mutations in the TSH-R cause congenital hypothyroidism with thyroid gland hypoplasia and resistance to TSH. Clinically, the hormone profile resembles pri­ mary hypothyroidism with low T4 and high TSH. On the other hand, germline activating mutations cause congenital hyperthyroidism. The disorder is autosomal dominant because an activating mutation of one TSH-R allele is sufficient to induce cellular hyperfunction and disease. Because the TSH-R is activated in every cell of the thyroid, there is hyperplastic growth and hyperfunction that resembles the pathology seen in Graves’ disease. This unusual disorder presents in infancy and must be distinguished from the more common clinical circumstance in which maternal antibodies in women with active or previously treated Graves’ disease cross the placenta and stimulate the thyroid gland of the fetus. If an activating TSH-R mutation occurs later in life, in the somatic tissue, there is clonal expansion of the thyrocyte harboring the mutation, ultimately leading to an autonomous hyperfunctioning thyroid nodule. Of note, a similar condition can be caused by somatic mutations in Gsα. In this case, the Gsα GTPase is inactivated and GTP cannot be converted to GDP. Consequently, the Gsα signaling pathway in this particular cell is constitutively active, mimicking chronic TSH stimulation and again leading to clonal expansion and an autonomous hyperfunctioning thyroid nodule. About one-third of hyperfunction­ ing “hot” thyroid nodules harbor sporadic mutations in either the TSH-R or Gsα (TSH-R mutations are more common). Gsα mutations in tissues other than the thyroid can also cause endo­ crine disease. For example, Gsα mutations in pituitary somatotropes

G protein-coupled receptor Ligand bound Membrane β γ Gαs GTP GTP GDP PART 12 Endocrinology and Metabolism cAMP Cycling Cell growth and signaling FIGURE 389-2  G protein signaling. G protein–coupled receptors (GPCRs) signal via the family of G proteins, so named because they bind guanylyl nucleotides. In the example shown, a GPCR bound to a ligand induces GDP dissociation, allowing Gsα to bind GTP and dissociate from the βγ complex. GTP-bound Gsα increases cAMP production by adenylyl cyclase and activates the protein kinase A pathway. Not shown are separate signaling pathways activated by the βγ complex. When GTP is converted to GDP by an intrinsic GTPase, the βγ subunits reassociate with GDP-bound Gsα and the complex returns to an inactive state. As noted in the text, mutations in Gsα that eliminate GTPase activity result in constitutive activation of receptor signaling pathways because GTPbound Gsα cannot be converted to its GDP-bound inactive state. cAMP, cyclic adenosine 5′-monophosphate; GDP, guanosine diphosphate; Gsα, G protein α; GTP, guanosine triphosphate. mimic activation of the growth hormone–releasing hormone (GHRH) pathway and lead to GH-producing adenomas and acromegaly. Rarely, mutations in other components of the protein kinase A pathway in somatotropes can also cause GH-producing adenomas. Gsα mutations that occur early in development (typically mosaic) cause McCuneAlbright syndrome (Chap. 424), and the clinical features are mani­ fest because the activated G protein pathway mimics the actions of various hormones (PTH, melanocyte-stimulating hormone [MSH], TSH, GHRH) in different tissues. Germline inactivating Gsα muta­ tions cause a range of disorders that are transmitted and expressed in a complex manner because the locus is imprinted (Chap. 422). These conditions include Albright’s hereditary osteodystrophy (AHO), pseu­ dopseudohypoparathyroidism (PPHP), and pseudohypoparathyroid­ ism types 1b, 1c, and 2. The tyrosine kinase receptors transduce signals for insulin and a variety of growth factors, such as IGF1, epidermal growth factor (EGF), nerve growth factor, platelet-derived growth factor, and fibro­ blast growth factors. The cysteine-rich extracellular domains contain binding sites for the growth factors. After ligand binding, this class of receptors undergoes autophosphorylation, inducing interactions with intracellular adaptor proteins such as Shc and insulin receptor sub­ strates (IRS). In the case of the insulin receptor, multiple kinases are activated, including the Raf-Ras-MAPK and the Akt/protein kinase B pathways. The tyrosine kinase receptors play a prominent role in cell growth and differentiation as well as in intermediary metabolism. The GH and PRL receptors belong to the cytokine receptor family. Analogous to the tyrosine kinase receptors, ligand binding induces receptor interaction with intracellular kinases—the Janus kinases (JAKs), which phosphorylate members of the signal transduction and activators of transcription (STAT) family—as well as with other signal­ ing pathways (Ras, PI3-K, MAPK). The activated STAT proteins trans­ locate to the nucleus and stimulate expression of target genes. The serine kinase receptors mediate the actions of activins, trans­ forming growth factor β, müllerian-inhibiting substance (MIS; also known as anti-müllerian hormone [AMH]), and bone morphogenic proteins (BMPs). This family of receptors (consisting of type I and II subunits) signals through proteins termed smads (fusion of terms for Caenorhabditis elegans sma + mammalian mad). Like the STAT proteins, the smads serve a dual role of transducing the receptor signal and acting as transcription factors. The pleomorphic actions of these

growth factors dictate that they act primarily in a local (paracrine or autocrine) manner. Bind­ ing proteins such as follistatin (which binds activin and other members of this family) func­ tion to inactivate the growth factors and restrict their distribution. Ligand unbound Disease-causing mutations also occur in each of these classes of receptors. For example, insulin receptor mutations cause an extreme form of insulin resistance. GH receptor muta­ tions cause Laron-type dwarfism, character­ ized by low IGF1 and high GH. AMH receptor mutations cause persistent müllerian duct syn­ drome. These hormone resistance syndromes are autosomal recessive and relatively uncom­ mon. Unlike the GPCRs, activating mutations are unusual, although they do occur for the RET tyrosine kinase receptor, which causes the autosomal dominant disorder MEN type 2 (MEN2) (Chap. 400). Gαs β γ GDP ■ ■NUCLEAR RECEPTORS The family of nuclear receptors has nearly 100 members, many of which are still classified as orphan receptors because their ligands, if they exist, have not been identified (Fig. 389-3). Otherwise, most nuclear receptors are classi­ fied on the basis of their ligands. Although all nuclear receptors ultimately act to increase or decrease gene transcription, some (e.g., glucocorticoid receptor) reside primarily in the cytoplasm, whereas others (e.g., TR) are located in the nucleus. After ligand binding, the cytoplasmically localized recep­ tors translocate to the nucleus. There is growing evidence that certain ligands and their nuclear receptors (e.g., glucocorticoid, estrogen) can also act at the membrane or in the cytoplasm to modulate signal transduction pathways, providing a mechanism for cross-talk between membrane and nuclear receptors. The structures of nuclear receptors have been studied extensively, including by x-ray crystallography. The DNA-binding domain, consist­ ing of two zinc fingers, contacts specific DNA recognition sequences in target genes. Most nuclear receptors bind to DNA as dimers. Conse­ quently, each monomer recognizes an individual DNA motif, referred to as a “half-site.” The steroid receptors, including the glucocorticoid, estrogen, progesterone, and androgen receptors, bind to DNA as homodimers. Consistent with this twofold symmetry, their DNA rec­ ognition half-sites are palindromic. The thyroid, retinoid, peroxisome proliferator activated, and vitamin D receptors bind to DNA pref­ erentially as heterodimers in combination with retinoid X receptors (RXRs). Their DNA half-sites are typically arranged as direct repeats. The carboxy-terminal hormone-binding domains mediate tran­ scriptional control. For type II receptors such as TR and retinoic acid receptor (RAR), co-repressor proteins bind to the receptor in the absence of ligand and silence gene transcription. Hormone binding induces conformational changes in the receptor, triggering the release of co-repressors and the recruitment of coactivators that stimulate transcription. Thus, these receptors are capable of mediating dynamic changes in the level of gene activity. Disease states can be associated with defective regulation of these events. For example, in promy­ elocytic leukemia, fusion of RARα to other nuclear proteins causes aberrant gene silencing that prevents normal cellular differentiation. Treatment with retinoic acid reverses this repression and allows cellular differentiation and apoptosis to occur. Most type 1 steroid receptors interact weakly with co-repressors, but ligand binding still induces interactions with an array of coactivators. X-ray crystallography shows that various SERMs induce distinct estrogen receptor conforma­ tions. The tissue-specific responses caused by these agents in breast, bone, and uterus appear to reflect distinct interactions with various coactivators. The receptor-coactivator complex stimulates gene tran­ scription by several pathways, including (1) recruitment of enzymes

TABLE 389-2  Genetic Causes of G protein Receptor Disorders RECEPTOR DISORDER GENETICS LH Leydig cell hypoplasia (male) Primary amenorrhea, resistance to LH (female) Familial male precocious puberty (male) Leydig cell adenoma, precocious puberty (male) AR, inactivating AR, inactivating AD, activating Sporadic, activating FSH Hypergonadotropic ovarian failure (female) Hypospermia (male) Ovarian hyperstimulation (female) AR, inactivating AR, inactivating Sporadic, activating TSH Congenital hypothyroidism, TSH resistance Nonautoimmune familial hyperthyroidism Hyperfunctioning thyroid adenoma AR, AD, inactivating AD, activating Sporadic, activating GnRH Hypogonadotropic hypogonadism AR, inactivating Kisspeptin Hypogonadotropic hypogonadism Precocious puberty AR, inactivating AD, activating Prokineticin Precocious puberty Sporadic, activating TRH Central hypothyroidism AR, inactivating GHRH GH deficiency AR, inactivating PTH Blomstrand chondrodysplasia Jansen metaphyseal chondrodysplasia AR, inactivating AD, activating Calcium sensing receptor Familial hypocalciuric hypercalcemia Neonatal severe hyperparathyroidism Familial hypocalcemic hypercalciura AD, inactivating AR, inactivating AD, activating Arginine vasopressin receptor 2 Nephrogenic diabetes insipidus Nephrogenic SIADH XL, inactivating XL, activating ACTH Familial ACTH resistance ACTH-independent Cushing syndrome AR, inactivating Sporadic, activating Melanocortin 4 Severe obesity Codominant, inactivating Abbreviations: ACTH, adrenocorticotropin hormone; AD, autosomal dominant; AR, autosomal recessive; FSH, follicle-stimulating hormone; GH, growth hormone; GHRH, growth hormone–releasing hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; PTH, parathyroid hormone; SIADH, syndrome of inappropriate antidiuretic hormone secretion; TRH, thyrotropin-releasing hormone; TSH, thyroid-stimulating hormone; XL, X-linked. Homodimer Steroid Heterodimer Receptors Receptors ER, AR, PR, GR Ligands DNA response elements Ligand induces coactivator binding Ligand dissociates corepressors and induces coactivator binding Constitutive activator or repressor binding Gene Expression Activated Activated + – + – + – Basal Hormone Receptor Hormone FIGURE 389-3  Nuclear receptor signaling. AR, androgen receptor; DAX, dosage-sensitive sex-reversal, adrenal hypoplasia congenita, X chromosome; ER, estrogen receptor; GR, glucocorticoid receptor; HNF4α, hepatic nuclear factor 4α; PPAR, peroxisome proliferator activated receptor; PR, progesterone receptor; RAR, retinoic acid receptor; SF-1, steroidogenic factor-1; TR, thyroid hormone receptor; VDR, vitamin D receptor.

(histone acetyl transferases) that modify chromatin structure, (2) inter­ actions with additional transcription factors on the target gene, and (3) direct interactions with components of the general transcription apparatus to enhance the rate of RNA polymerase II–mediated tran­ scription. Studies of nuclear receptor–mediated transcription reveal relatively rapid (e.g., 30–60 min) cycling of transcription complexes on any specific target gene.

Nuclear receptor mutations are an important cause of endocrine dis­ ease. Androgen receptor mutations cause androgen insensitivity syn­ drome (AIS) (Chap. 402). Because the androgen receptor is located on the X chromosome, phenotypic expression is more commonly manifest than with other nuclear receptor disorders. Affected individuals with AIS are XY phenotypic females with retained testes and male-range testosterone levels. Tissue insensitivity to androgens varies based on the severity of the mutation. Müllerian structures are absent because Sertoli cells of the testis produce AMH during development. Female carriers of androgen receptor mutations are phenotypically normal. Recessive mutations of the estrogen, glucocorticoid, and vitamin D receptors occur but are rare. Mechanisms of Hormone Action CHAPTER 389 Thyroid hormone receptor β (TRβ) mutations have an unusual pathophysiology. They are autosomal dominant and function via a “dominant negative” mechanism to cause resistance to thyroid hor­ mone (RTH) (Chap. 394). The mutations occur in selected regions of the TRβ hormone-binding domain and preserve the ability of the mutant receptor to heterodimerize with RXR, interact with corepressors, and bind to DNA regulatory sites. The mutant receptors function as antagonists of receptors from the normal copy of the TRβ gene. Affected patients have high T4 and T3 and inappropriately ele­ vated (unsuppressed) TSH, reflecting impaired feedback regulation of the hypothalamic-pituitary-thyroid axis. Organ systems are vari­ ably resistant to thyroid hormones based on the relative expression of TRβ and TRα. Mutations in the genes encoding TRα and PPARγ can also cause disease by functioning in an analogous dominant negative manner. FUNCTIONS OF HORMONES The functions of individual hormones are described in detail in subsequent chapters. Nevertheless, it is useful to illustrate how most biologic responses require the integration of several different hormone pathways. The physiologic functions of hormones can be divided into three general types: (1) growth and differentiation, (2) maintenance of homeostasis, and (3) reproduction. Orphan Receptors SF-1, DAX-1, HNF4α TR, VDR, RAR, PPAR Activated Silenced

■ ■GROWTH Multiple hormones and nutritional factors mediate the complex phe­ nomenon of growth (Chap. 390). Short stature may be caused by GH deficiency, hypothyroidism, Cushing’s syndrome, precocious puberty, malnutrition, chronic illness, or genetic abnormalities that affect the epiphyseal growth plates (e.g., FGFR3 and SHOX mutations). Many factors (GH, IGF1, thyroid hormones) stimulate growth, whereas others (sex steroids) lead to epiphyseal closure. Understanding these hormonal interactions is important in the diagnosis and management of growth disorders. For example, delaying exposure to high levels of sex steroids may enhance the efficacy of GH treatment.

PART 12 Endocrinology and Metabolism ■ ■MAINTENANCE OF HOMEOSTASIS Although virtually all hormones affect homeostasis, the most impor­ tant among them are the following:

  1. Thyroid hormone—controls ~25% of basal metabolism in most tissues.
  2. Cortisol—exerts a permissive action for many hormones in addition to its own direct effects.
  3. PTH—regulates calcium and phosphorus levels.
  4. Vasopressin—regulates serum osmolality by controlling renal freewater clearance.
  5. Mineralocorticoids—control vascular volume and serum electrolyte (Na+, K+) concentrations.
  6. Insulin—maintains euglycemia in the fed and fasted states. The defense against hypoglycemia is an impressive example of inte­ grated hormone action (Chap. 418). In response to the fasting state and falling blood glucose, insulin secretion is suppressed, resulting in decreased glucose uptake and enhanced glycogenolysis, lipolysis, proteolysis, and gluconeogenesis to mobilize fuel sources. If hypogly­ cemia develops (usually from insulin administration or sulfonylureas), an orchestrated counterregulatory response occurs—glucagon and epinephrine rapidly stimulate glycogenolysis and gluconeogenesis, whereas GH and cortisol act over several hours to raise glucose levels and antagonize insulin action. Although free-water clearance is controlled primarily by vasopres­ sin, cortisol and thyroid hormone are also important for facilitating renal tubular responses to vasopressin (Chap. 393). PTH and vitamin D function in an interdependent manner to control calcium metabo­ lism (Chap. 421). PTH stimulates renal synthesis of 1,25-dihydroxyvi­ tamin D, which increases calcium absorption in the gastrointestinal tract and enhances PTH action in bone. Increased calcium, along with vitamin D, feeds back to suppress PTH, thus maintaining calcium balance. Depending on the severity of a specific stress and whether it is acute or chronic, multiple endocrine and cytokine pathways are activated to mount an appropriate physiologic response. In severe acute stress such as trauma or shock, the sympathetic nervous system is activated, and catecholamines are released, leading to increased cardiac output and a primed musculoskeletal system. Catecholamines also increase mean blood pressure and stimulate glucose production. Multiple stressinduced pathways converge on the hypothalamus, stimulating several hormones, including vasopressin and CRH. These hormones, in addi­ tion to cytokines (tumor necrosis factor α, interleukin [IL] 2, IL-6), increase ACTH and GH production. ACTH stimulates the adrenal gland, increasing cortisol, which in turn helps sustain blood pressure and dampen the inflammatory response. Increased vasopressin acts to conserve free water. ■ ■REPRODUCTION The stages of reproduction include (1) sex determination during fetal development (Chap. 402); (2) sexual maturation during puberty (Chaps. 403 and 404); (3) conception, pregnancy, lactation, and child rearing (Chap. 404); and (4) cessation of reproductive capability at menopause (Chap. 407). Each of these stages involves an orchestrated interplay of multiple hormones, a phenomenon well illustrated by the dynamic hormonal changes that occur during each 28-day menstrual cycle. In the early follicular phase, pulsatile secretion of LH and FSH

stimulates the progressive maturation of the ovarian follicle. This results in gradually increasing estrogen and progesterone levels, lead­ ing to enhanced pituitary sensitivity to GnRH, which, when combined with accelerated GnRH secretion, triggers the LH surge and rupture of the mature follicle. Inhibin, a protein produced by the granulosa cells, enhances follicular growth and feeds back to the pituitary to selectively suppress FSH without affecting LH. Growth factors such as EGF and IGF1 modulate follicular responsiveness to gonadotropins. Vascular endothelial growth factor and prostaglandins play a role in follicle vascularization and rupture. During pregnancy, the increased production of PRL, in combina­ tion with placentally derived steroids (e.g., estrogen and progesterone), prepares the breast for lactation. Estrogens induce the production of progesterone receptors, allowing for increased responsiveness to pro­ gesterone. In addition to these and other hormones involved in lacta­ tion, the nervous system and oxytocin mediate the suckling response and milk release. HORMONAL FEEDBACK REGULATORY SYSTEMS Feedback control, both negative and positive, is a fundamental feature of endocrine systems. Each of the major hypothalamic-pituitaryhormone axes is governed by negative feedback, a process that main­ tains hormone levels within a relatively narrow range (Chap. 390). Examples of hypothalamic-pituitary negative feedback include (1) thy­ roid hormones on the TRH-TSH axis, (2) cortisol on the CRH-ACTH axis, (3) gonadal steroids on the GnRH-LH/FSH axis, and (4) IGF1 on the GHRH-GH axis (Fig. 389-4). These regulatory loops include both positive (e.g., TRH, TSH) and negative (e.g., T4, T3) components, allowing for exquisite control of hormone levels. As an example, a small reduction of thyroid hormone triggers a rapid increase of TRH and TSH secretion, resulting in thyroid gland stimulation and increased thyroid hormone production. When thyroid hormone reaches a nor­ mal level, it feeds back to suppress TRH and TSH, and a new steady state is attained. Feedback regulation also occurs for endocrine systems that do not involve the pituitary gland, such as calcium feedback on PTH, glucose inhibition of insulin secretion, and leptin feedback on the hypothalamus. An understanding of feedback regulation provides important insights into endocrine testing paradigms (see below). Hypothalamus CNS Releasing factors – + – Pituitary Target hormone feedback inhibition Trophic hormones + Adrenal Gonads Thyroid FIGURE 389-4  Feedback regulation of endocrine axes. CNS, central nervous system.

04 - 390 Physiology of Anterior Pituitary Hormones

390 Physiology of Anterior Pituitary Hormones

Positive feedback control also occurs but is not well understood. The primary example is estrogen-mediated stimulation of the midcycle LH surge. Although chronic low levels of estrogen are inhibitory, gradu­ ally rising estrogen levels stimulate LH secretion. This effect, which is illustrative of an endocrine rhythm (see below), involves activation of the hypothalamic GnRH pulse generator. In addition, estrogen-primed gonadotropes are extraordinarily sensitive to GnRH, leading to ampli­ fication of LH release. ■ ■PARACRINE AND AUTOCRINE CONTROL The previously mentioned examples of feedback control involve classic endocrine pathways in which hormones are released by one gland and act on a distant target gland. However, local regulatory systems, often involving growth factors, are increasingly recognized. Paracrine regu­ lation refers to factors released by one cell that act on an adjacent cell in the same tissue. For example, somatostatin secretion by pancreatic islet δ cells inhibits insulin secretion from nearby β cells. Autocrine regulation describes the action of a factor on the same cell from which it is produced. IGF1 acts on many cells that produce it, including chondrocytes, breast epithelium, and gonadal cells. Unlike endocrine actions, paracrine and autocrine control are difficult to document because local growth factor concentrations cannot be measured readily. Anatomic relationships of glandular systems also greatly influence hormonal exposure: the physical organization of islet cells enhances their intercellular communication; the portal vasculature of the hypo­ thalamic-pituitary system exposes the pituitary to high concentrations of hypothalamic releasing factors; testicular seminiferous tubules gain exposure to high testosterone levels produced by the interdigitated Leydig cells; the pancreas receives nutrient information and local expo­ sure to peptide hormones (incretins) from the gastrointestinal tract; and the liver is the proximal target of insulin action because of portal drainage from the pancreas. ■ ■HORMONAL RHYTHMS The feedback regulatory systems described above are superimposed on hormonal rhythms that are used for adaptation to the environment. Seasonal changes, the daily occurrence of the light-dark cycle, sleep, meals, and stress are examples of the many environmental events that affect hormonal rhythms. The menstrual cycle is repeated on average every 28 days, reflecting the time required to follicular maturation, ovulation, and potential implantation (Chap. 390). Essentially all pitu­ itary hormone rhythms are entrained to sleep and to the circadian cycle, generating reproducible patterns that are repeated approximately every 24 h. The HPA axis, for example, exhibits characteristic peaks of ACTH and cortisol production in the early morning, with a nadir during the night. Recognition of these rhythms is important for endocrine testing and treatment. Patients with Cushing’s syndrome characteristically exhibit increased midnight cortisol levels compared with normal indi­ viduals (Chap. 398). In contrast, morning cortisol levels are similar in these groups, as cortisol is normally high at this time of day in normal individuals. The HPA axis is more susceptible to suppression by glu­ cocorticoids administered at night as they blunt the early-morning rise of ACTH. Understanding these rhythms allows glucocorticoid replace­ ment that mimics diurnal production by administering larger doses in the morning than in the afternoon. Disrupted sleep rhythms can alter hormonal regulation. For example, sleep deprivation causes mild insulin resistance, food craving, and hypertension, which are revers­ ible, at least in the short term. Emerging evidence indicates that circa­ dian clock pathways not only regulate sleep-wake cycles but also play important roles in virtually every cell type. For example, tissue-specific deletion of clock genes alters rhythms and levels of gene expression, as well as metabolic responses in liver, adipose, and other tissues. Other endocrine rhythms occur on a more rapid time scale. Many peptide hormones are secreted in discrete bursts every few hours. LH and FSH secretion are exquisitely sensitive to GnRH pulse frequency. Intermittent pulses of GnRH are required to maintain pituitary sensitivity, whereas continuous exposure to GnRH causes pituitary gonadotrope desensitization. This feature of the hypothalamic-pitu­ itary-gonadotrope axis forms the basis for using long-acting GnRH

agonists to treat central precocious puberty or to decrease testosterone levels in the management of prostate cancer. It is important to be aware of the pulsatile nature of hormone secretion and the rhythmic patterns of hormone production in relating serum hormone measurements to normal values. For some hormones, integrated markers have been developed to circumvent hormonal fluctuations. Examples include 24-h urine collections for cortisol, the measurement of IGF1 as a bio­ logic marker of GH action, and HbA1c as an index of long-term (weeks to months) blood glucose control.

Often, one must interpret endocrine data only in the context of other hormones. For example, PTH levels typically are assessed in combina­ tion with serum calcium concentrations. A high serum calcium level in association with elevated PTH is suggestive of hyperparathyroidism, whereas a suppressed PTH in the setting of hypercalcemia is more likely to be caused by hypercalcemia of malignancy, or other causes of hypercalcemia. Similarly, when T4 and T3 concentrations are low, TSH should be elevated, reflecting reduced feedback inhibition. When this is not the case, it is important to consider secondary hypothyroidism, which is caused by a defect at the level of the pituitary. Physiology of Anterior Pituitary Hormones CHAPTER 390 ■ ■FURTHER READING Fukami M et al: Gain-of-function mutations in G-protein-coupled receptor genes associated with human endocrine disorders. Clin Endocrinol 88:351, 2018. Herbison AE: A simple model of estrous cycle negative and positive feedback regulation of GnRH secretion. Frontiers Neuroendocrinol 57:100837, 2020. Kim YH, Lazar MA: Transcriptional control of circadian rhythms and metabolism: A matter of time and space. Endocr Rev 41:707, 2020. Robertson RP (ed): DeGroot’s Endocrinology: Adult and Pediatric, 8th ed. Philadelphia, Elsevier, 2023. Scholtes C, Giguère V: Transcriptional control of energy metabo­ lism by nuclear receptors. Nature Rev Mol Cell Biol 23:750, 2022. Shlomo Melmed, J. Larry Jameson

Physiology of Anterior

Pituitary Hormones The anterior pituitary often is referred to as the “master gland” because, together with the hypothalamus, it orchestrates the complex regula­ tory functions of many other endocrine glands. The anterior pituitary gland produces six major hormones: (1) prolactin (PRL), (2) growth hormone (GH), (3) adrenocorticotropic hormone (ACTH), (4) lutein­ izing hormone (LH), (5) follicle-stimulating hormone (FSH), and

(6) thyroid-stimulating hormone (TSH) (Table 390-1). Pituitary

hormones are secreted in a pulsatile manner, reflecting regulation by an array of specific hypothalamic releasing factors. Each of these pitu­ itary hormones elicits specific trophic responses in peripheral target tissues including the adrenal, thyroid, and gonads, as well as tissues involved in metabolism (e.g., liver, breast, bone). Elicited hormonal products of peripheral glands, in turn, exert feedback control at the level of the hypothalamus and pituitary to modulate pituitary function (Fig. 390-1). Pituitary tumors cause characteristic hormone excess syn­ dromes. Hormone deficiency may be inherited or acquired. Fortunately, there are efficacious treatments for many pituitary hormone excess and deficiency syndromes. Nonetheless, these diagnoses are often elusive; this emphasizes the importance of recognizing subtle clinical manifes­ tations and performing the correct laboratory diagnostic tests. For dis­ cussion of disorders of the posterior pituitary or neurohypophysis, see Chap. 393.

TABLE 390-1  Anterior Pituitary Hormone Expression and Regulation CELL CORTICOTROPE SOMATOTROPE LACTOTROPE THYROTROPE GONADOTROPE Tissue-specific transcription factor T-Pit Prop-1, Pit-1 Prop-1, Pit-1 Prop-1, Pit-1, TEF SF-1, DAX-1 Developmental timing 6 weeks 8 weeks 12 weeks 12 weeks 12 weeks Hormone POMC GH PRL TSH FSH, LH Protein Polypeptide Polypeptide Polypeptide Glycoprotein α, β subunits Glycoprotein α, β subunits Amino acids 266 (ACTH 1–39)

210, 204 Stimulators CRH, AVP, cytokines GHRH, ghrelin Estrogen, TRH, VIP TRH GnRH, activins, estrogen Inhibitors Glucocorticoids Somatostatin, IGF-1 Dopamine T3, T4, dopamine, somatostatin, glucocorticoids PART 12 Endocrinology and Metabolism Target gland Adrenal Liver, bone, other tissues Breast, other tissues Thyroid Ovary, testis Trophic effect Steroid production IGF-1 production, growth induction, insulin antagonism Normal range ACTH, 4–22 pg/L <0.5 μg/La M <15 μg/L; F <20 μg/L 0.1–5 mU/L M, 5–20 IU/L; F (basal), 5–20 IU/L aHormone secretion integrated over 24 h. Abbreviations: F, female; M, male. For other abbreviations, see text. Source: Courtesy of Elsevier. ANATOMY AND DEVELOPMENT ■ ■ANATOMY The pituitary gland weighs ~600 mg and is located within the sella turcica ventral to the diaphragma sella; it consists of anatomically and functionally distinct anterior and posterior lobes. The bony sella is con­ tiguous to vascular and neurologic structures, including the cavernous sinuses, cranial nerves, and optic chiasm. Thus, expanding intrasellar pathologic processes may have significant central mass effects in addi­ tion to their endocrinologic impact. Hypothalamic neural cells synthesize specific releasing and inhibit­ ing hormones that are secreted directly into the portal vessels of the pituitary stalk. Blood supply of the pituitary gland comes from the superior and inferior hypophyseal arteries (Fig. 390-2). The hypotha­ lamic-pituitary portal plexus provides the major blood source for the anterior pituitary, allowing reliable transmission of hypothalamic pep­ tide pulses without significant systemic dilution; consequently, anterior pituitary cells are exposed to specific releasing or inhibiting factors and in turn release their respective hormones as discrete pulses into the systemic circulation (Fig. 390-3). The posterior pituitary is supplied by the inferior hypophyseal arter­ ies. In contrast to the anterior pituitary, the posterior lobe is directly innervated by hypothalamic neurons (supraopticohypophyseal and tuberohypophyseal nerve tracts) via the pituitary stalk (Chap. 393). Thus, posterior pituitary production of arginine vasopressin (AVP) and oxytocin is particularly sensitive to neuronal damage by lesions that affect the pituitary stalk or hypothalamus. ■ ■PITUITARY DEVELOPMENT The embryonic differentiation and maturation of anterior pituitary cells have been elucidated in considerable detail. Pituitary develop­ ment from Rathke’s pouch involves a complex interplay of lineagespecific transcription factors expressed in pluripotent Sox2-expressing precursor cells and gradients of locally produced growth factors (Table 390-1). The transcription factor Prop-1 induces pituitary development of Pit-1-specific lineages as well as gonadotropes. The transcrip­ tion factor Pit-1 determines cell-specific expression of GH, PRL, and TSH in somatotropes, lactotropes, and thyrotropes. Expression of high levels of estrogen receptors in cells that contain Pit-1 favors PRL expression, whereas thyrotrope embryonic factor (TEF) induces TSH expression. Pit-1 binds to GH, PRL, and TSH gene regulatory elements, providing a mechanism for determining specific pituitary hormone phenotypic stability. Gonadotrope cell development is fur­ ther defined by the cell-specific expression of the nuclear receptors steroidogenic factor (SF-1) and dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX-1). Devel­ opment of corticotrope cells, which express the proopiomelanocortin

Sex steroids, inhibin Milk production T4 synthesis and secretion Sex steroid production, follicle growth, germ cell maturation (POMC) gene, requires the T-Pit transcription factor. Abnormalities of pituitary development can be caused by inherited mutations of devel­ opmental transcription factors including Pit-1, Prop-1, SF-1, DAX-1, and T-Pit, resulting in selective or combined pituitary hormone deficit syndromes. ANTERIOR PITUITARY HORMONES Each anterior pituitary hormone is under unique control, and each exhibits highly specific normal and dysregulated secretory characteristics. ■ ■PROLACTIN Synthesis  PRL consists of 198 amino acids and has a molecular mass of 21,500 kDa; it is weakly homologous to GH and human pla­ cental lactogen (hPL), reflecting the duplication and divergence of a common GH-PRL-hPL precursor gene. PRL is synthesized in lacto­ tropes, which constitute ~20% of anterior pituitary cells. Lactotropes and somatotropes are derived from a common precursor cell that may give rise to a tumor that secretes both PRL and GH. Lactotrope cell hyperplasia develops during pregnancy and the first few months of lactation. These transient functional changes in the lactotrope popula­ tion are induced by estrogen to increase PRL production. Secretion  Normal adult serum PRL levels are about 10–25 μg/L in women and 10–20 μg/L in men. PRL secretion is pulsatile, with the highest secretory peaks occurring during non–rapid eye move­ ment (non-REM) sleep. Peak serum PRL levels (up to 30 μg/L) occur between 4:00 and 6:00 a.m. The circulating half-life of PRL is ~50 min. PRL is unique among the pituitary hormones in that the predomi­ nant hypothalamic control mechanism is inhibitory, reflecting tonic dopamine-mediated suppression of PRL release. This regulatory path­ way accounts for the spontaneous PRL hypersecretion that occurs with pituitary stalk section, often a consequence of head trauma or com­ pressive mass lesions at the skull base. Pituitary dopamine type 2 (D2) receptors mediate inhibition of PRL synthesis and secretion. Targeted disruption (gene knockout) of the murine D2 receptor in mice results in hyperprolactinemia and lactotrope proliferation. As discussed below, dopamine agonists play a central role in the management of hyperpro­ lactinemic disorders. Thyrotropin-releasing hormone (TRH) (pyro Glu-His-Pro-NH2) is a hypothalamic tripeptide that elicits PRL release within 15–30 min after intravenous injection. TRH primarily regulates TSH, and the physiologic relevance of TRH for PRL regulation is unclear (Chap. 394). Serum PRL levels rise transiently after exercise, meals, sexual intercourse, minor surgical procedures, general anesthesia, chest wall injury, acute myocardial infarction, and other forms of acute stress. PRL levels increase markedly (about tenfold) during pregnancy and

TRH GHRH SRIF GnRH CRH Dopamine Hypothalamus – + – – + – + + Pituitary – ACTH Target organs + TSH Cortisol GH LH PRL Cell homeostasis and function Adrenal glands FSH + + + T4/T3 Thermogenesis metabolism Thyroid glands + Testosterone Inhibin Lactation Spermatogenesis Secondary sex characteristics Testes + Estradiol Progesterone Inhibin Chondrocytes Linear and organ growth Ovaries Ovulation Secondary sex characteristics IGF-1 FIGURE 390-1  Diagram of pituitary axes. Hypothalamic hormones regulate anterior pituitary trophic hormones that in turn determine target gland secretion. Peripheral hormones feed back to negatively regulate hypothalamic and pituitary hormones. For abbreviations, see text. decline rapidly within 2 weeks of parturition. If breast-feeding is initi­ ated, basal PRL levels remain elevated; suckling stimulates transient reflex increases in PRL levels that last for ~30–45 min. Breast suckling activates afferent neural pathways in the hypothalamus that induce PRL release. With time, suckling-induced responses diminish and interfeeding PRL levels return to normal. Action  The PRL receptor is a member of the type I cytokine recep­ tor family that also includes GH and interleukin (IL) 6 receptors. Ligand binding induces receptor dimerization and intracellular signal­ ing by Janus kinase (JAK), which stimulates translocation of the signal transduction and activators of transcription (STAT) family to activate target genes. Mutations of the PRL receptor result in PRL insensitivity, hyperprolactinemia, and oligomenorrhea. When homozygous, PRL receptor mutations cause agalactia, demonstrating that PRL action is necessary for lactation. In the breast, the lobuloalveolar epithelium proliferates in response to PRL, placental lactogens, estrogen, pro­ gesterone, and local paracrine growth factors, including insulin-like growth factor 1 (IGF-1).

Third ventricle Neuroendocrine cell nuclei Hypothalamus Physiology of Anterior Pituitary Hormones CHAPTER 390 Stalk Superior hypophyseal artery Inferior hypophyseal artery Long portal vessels Trophic hormone secreting cells Posterior pituitary Anterior pituitary Short portal vessel Hormone secretion FIGURE 390-2  Diagram of hypothalamic-pituitary vasculature. The hypothalamic nuclei produce hormones that traverse the portal system and impinge on anterior pituitary cells to regulate pituitary hormone production. Posterior pituitary hormones are derived from direct neural extensions. Liver PRL acts to induce and maintain lactation and to suppress both reproductive function and sexual drive. These functions are geared toward ensuring that maternal lactation is sustained and not inter­ rupted by pregnancy. PRL inhibits reproductive function by sup­ pressing hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary gonadotropin secretion and by impairing gonadal steroidogenesis in both women and men. In the ovary, PRL blocks fol­ liculogenesis and inhibits granulosa cell aromatase activity, leading to hypoestrogenism and anovulation. PRL also has a luteolytic effect, gen­ erating a shortened, or inadequate, luteal phase of the menstrual cycle. In men, attenuated LH secretion leads to low testosterone levels and decreased spermatogenesis. These hormonal changes decrease libido and reduce fertility in patients with hyperprolactinemia. ■ ■GROWTH HORMONE Synthesis  GH is the most abundant anterior pituitary hormone, and GH-secreting somatotrope cells constitute up to 50% of the total anterior pituitary cell population. Mammosomatotrope cells, which coexpress PRL with GH, can be identified by using double immunos­ taining techniques. Somatotrope development and GH transcription LH mlU/mL GnRH pg/mL GnRH pulses LH pulses FIGURE 390-3  Hypothalamic gonadotropin-releasing hormone (GnRH) pulses induce secretory pulses of luteinizing hormone (LH).

are determined by expression of the cell-specific Pit-1 nuclear tran­ scription factor. Five distinct genes encode GH and related proteins. The pituitary GH gene (hGH-N) produces two alternatively spliced products that give rise to 22-kDa GH (191 amino acids) and a less abundant 20-kDa GH molecule with similar biologic activity. Placen­ tal syncytiotrophoblast cells express a GH variant (hGH-V) gene; the related hormone human chorionic somatotropin (HCS) is expressed by distinct members of the gene cluster.

Secretion  GH secretion is controlled by complex hypothalamic and peripheral factors. GH-releasing hormone (GHRH) is a 44-amino-acid hypothalamic peptide that stimulates GH synthesis and release. Ghrelin, an octanoylated gastric-derived peptide, and synthetic ago­ nists of the GHS-R induce GHRH and also directly stimulate GH release. Somatostatin (somatotropin-release inhibiting factor [SRIF]) is synthesized in the medial preoptic area of the hypothalamus and inhibits GH secretion. GHRH is secreted in discrete spikes that elicit GH pulses, whereas SRIF sets basal GH secretory tone. SRIF also is expressed in many extrahypothalamic tissues, including the central nervous system (CNS), gastrointestinal tract, and pancreas, where it also acts to inhibit islet hormone secretion. IGF-1, the peripheral tar­ get hormone for GH, feeds back to inhibit GH; estrogen induces GH, whereas chronic glucocorticoid excess suppresses GH release, leading to growth delay in children. PART 12 Endocrinology and Metabolism Surface receptors on the somatotrope regulate GH synthesis and secretion. The GHRH receptor is a G protein–coupled receptor (GPCR) that signals through the intracellular cyclic AMP pathway to stimulate somatotrope cell proliferation as well as GH production. Inactivating mutations of the GHRH receptor cause profound growth deficiency (dwarfism). A distinct surface receptor for ghrelin, the gastric-derived GH secretagogue, is expressed in both the hypothalamus and pituitary. Somatostatin binds to five distinct receptor subtypes (SST1 to SST5); SST2 and SST5 subtypes preferentially suppress GH (and TSH) secre­ tion, while SST5 predominantly suppresses ACTH secretion. GH secretion is pulsatile, with highest peak levels occurring at night, generally correlating with sleep onset. GH secretory rates decline markedly with age so that hormone levels in middle age are ~15% of pubertal levels. These changes are paralleled by an age-related decline in lean muscle mass. GH secretion is also reduced in obese individuals, although IGF-1 levels may not be suppressed, suggesting a change in the setpoint for feedback control. Elevated GH levels occur within an hour of deep sleep onset as well as after exercise, physical stress, and trauma and during sepsis. Integrated 24-h GH secretion is higher in women and is also enhanced by estrogen replacement, likely reflective of increased peripheral GH resistance. Using standard assays, random GH measurements are undetectable in ~50% of daytime samples obtained from healthy subjects and are also undetectable (<1 μg/L) in most obese and elderly subjects. Thus, single random GH measure­ ments do not distinguish patients with adult GH deficiency from those with GH levels in the normal range. GH secretion is profoundly influenced by nutritional factors. Using ultrasensitive GH assays with a sensitivity of 0.002 μg/L, a glucose load suppresses GH to <0.7 μg/L in women and to <0.07 μg/L in men. Increased GH pulse frequency and peak amplitudes occur with chronic malnutrition or prolonged fasting. GH is stimulated by oral ghrelin receptor agonists, intravenous l-arginine, dopamine, and apo­ morphine (a dopamine receptor agonist), as well as by α-adrenergic pathways. β-Adrenergic blockade induces basal GH and enhances GHRH- and insulin-evoked GH release. Action  The pattern of GH secretion may affect tissue responses. The higher GH pulsatility observed in men compared with the rela­ tively continuous basal GH secretion in women may be an important biologic determinant of linear growth patterns and liver enzyme induction. The 70-kDa peripheral GH receptor protein has structural homol­ ogy with the cytokine/hematopoietic superfamily. A fragment of the receptor extracellular domain generates a soluble GH binding protein (GHBP) that binds to circulating GH. The liver and cartilage express

the greatest number of GH receptors. GH binding to preformed receptor dimers is followed by internal rotation and subsequent signal­ ing through the JAK/STAT pathway. Activated STAT proteins translo­ cate to the nucleus, where they modulate expression of GH-regulated target genes. GH analogues that bind to the receptor but are incapable of mediating receptor signaling are potent antagonists of GH action. A GH receptor antagonist (pegvisomant) is approved for treatment of acromegaly. GH induces protein synthesis and nitrogen retention and also impairs glucose tolerance by antagonizing insulin action. GH also stimulates lipolysis, leading to increased circulating fatty acid levels, reduced omental fat mass, and enhanced lean body mass. GH promotes sodium, potassium, and water retention and elevates serum levels of inorganic phosphate. Linear bone growth occurs as a result of complex hormonal and growth factor actions, including those of IGF-1. GH stimulates epiphyseal prechondrocyte differentiation. These precursor cells produce IGF-1 locally, and their proliferation is also responsive to the growth factor. Insulin-Like Growth Factors  Although GH exerts direct effects in target tissues, many of its physiologic effects are mediated indirectly through IGF-1, a potent growth and differentiation factor. The liver is the major source of circulating IGF-1. In peripheral tissues, IGF-1 also exerts local paracrine actions that appear to be both dependent on and independent of GH. Thus, GH administration induces circulating IGF-1 as well as stimulating local IGF-1 production in multiple tissues. Both IGF-1 and IGF-2 are bound to high-affinity circulating IGFbinding proteins (IGFBPs) that regulate IGF availability and bioactiv­ ity. Levels of IGFBP3 are GH dependent, and it serves as the major carrier protein for circulating IGF-1. GH deficiency and malnutrition usually are associated with low IGFBP3 levels. IGFBP1 and IGFBP2 regulate local tissue IGF action but do not bind appreciable amounts of circulating IGF-1. Serum IGF-1 concentrations are profoundly affected by physi­ ologic factors. Levels increase during puberty, peak at 16 years, and subsequently decline by >80% during the aging process. IGF-1 con­ centrations are higher in women than in men. Because GH is the major determinant of hepatic IGF-1 synthesis, abnormalities of GH synthesis or action (including pituitary failure, GHRH receptor defect, GH receptor defect, or pharmacologic GH receptor blockade) lead to reduced IGF-1 levels. Hypocaloric states are associated with GH resistance; IGF-1 levels are therefore low with cachexia, malnutrition, and sepsis. In acromegaly, IGF-1 levels are high and reflect a log-linear relationship with circulating GH concentrations. IGF-1 PHYSIOLOGY  Injected IGF-1 (100 μg/kg) induces hypoglyce­ mia, and lower doses improve insulin sensitivity in patients with severe insulin resistance and diabetes. In cachectic subjects, IGF-1 infusion (12 μg/kg per h) enhances nitrogen retention and lowers cholesterol levels. Longer-term subcutaneous IGF-1 injections enhance protein synthesis and are anabolic. Although bone formation markers are induced, bone turnover also may be stimulated by IGF-1. IGF-1 is approved for use in patients with GH-resistance syndromes. IGF-1 side effects are dose dependent, and overdose may result in hypoglycemia, hypotension, fluid retention, temporomandibular jaw pain, and increased intracranial pressure, all of which are revers­ ible. Retinal damage and avascular femoral head necrosis have been reported. Chronic excess IGF-1 administration presumably would result in features of acromegaly. ■ ■ADRENOCORTICOTROPIC HORMONE (See also Chap. 398). Synthesis  ACTH-secreting corticotrope cells constitute ~20% of the pituitary cell population. ACTH (39 amino acids) is derived from the POMC precursor protein (266 amino acids) that also generates several other peptides, including β-lipotropin, β-endorphin, met-enkephalin, α-melanocyte-stimulating hormone (α-MSH), and corticotropin-like intermediate lobe protein (CLIP). The POMC gene is potently sup­ pressed by glucocorticoids and induced by corticotropin-releasing

hormone (CRH), AVP, and proinflammatory cytokines, including IL-6, as well as leukemia inhibitory factor. CRH, a 41-amino-acid hypothalamic peptide synthesized in the paraventricular nucleus as well as in higher brain centers, is the predominant stimulator of ACTH synthesis and release. The CRH receptor is a GPCR that is expressed on the corticotrope and signals to induce POMC transcription. Secretion  ACTH secretion is pulsatile and exhibits a characteristic circadian rhythm, peaking at about 6:00 a.m. and reaching a nadir about midnight. Adrenal glucocorticoid secretion, which is driven by ACTH, follows a parallel diurnal pattern. ACTH circadian rhythmicity is determined by variations in secretory pulse amplitude rather than changes in pulse frequency. Superimposed on this endogenous rhythm, ACTH levels are increased by physical and psychological stress, exer­ cise, acute illness, and insulin-induced hypoglycemia. Glucocorticoid-mediated negative regulation of the hypothalamicpituitary-adrenal (HPA) axis occurs as a consequence of both hypotha­ lamic CRH suppression and direct attenuation of pituitary POMC gene expression and ACTH release. In contrast, loss of cortisol feedback inhibition, as occurs in primary adrenal failure, results in extremely high ACTH levels. Acute inflammatory or septic insults activate the HPA axis through the integrated actions of proinflammatory cytokines, bacterial toxins, and neural signals. The overlapping cascade of ACTH-inducing cyto­ kines (tumor necrosis factor [TNF]; IL-1, -2, and -6; and leukemia inhibitory factor) activates hypothalamic CRH and AVP secretion, pituitary POMC gene expression, and local pituitary paracrine cytokine networks. The resulting cortisol elevation restrains the inflammatory response and enables host protection. Concomitantly, cytokine-mediated central glucocorticoid receptor resistance impairs glucocorticoid sup­ pression of the HPA. Thus, the neuroendocrine stress response reflects the net result of highly integrated hypothalamic, intrapituitary, and peripheral hormone and cytokine signals acting to regulate cortisol secretion. Action  The major function of the HPA axis is to maintain meta­ bolic homeostasis and mediate the neuroendocrine stress response, largely by inducing adrenal cortisol production. ACTH induces adre­ nocortical steroidogenesis by sustaining adrenal cell proliferation and function. The receptor for ACTH, designated melanocortin-2 receptor, is a GPCR that induces steroidogenesis by stimulating a cascade of steroidogenic enzymes (Chap. 398). ■ ■GONADOTROPINS: FSH AND LH Synthesis and Secretion  Gonadotrope cells constitute ~10% of anterior pituitary cells and produce two gonadotropin hormones—LH and FSH. Like TSH and human chorionic gonadotropin, LH and FSH are glycoprotein hormones that contain α and β subunits. The α subunit is common to these glycoprotein hormones; specificity of hormone function is conferred by the β subunits, which are expressed by separate genes. Gonadotropin synthesis and release are dynamically regulated. This is particularly true in women, in whom rapidly fluctuating gonadal steroid levels vary throughout the menstrual cycle. Hypo­ thalamic GnRH, a 10-amino-acid peptide, regulates the synthesis and secretion of both LH and FSH. Brain kisspeptin, a product of the KISS1 gene, regulates hypothalamic GnRH release. GnRH is secreted in discrete pulses every 60–120 min, and the pulses in turn elicit LH and FSH pulses (Fig. 390-3). The pulsatile mode of GnRH input is essen­ tial to its action; pulses prime gonadotrope responsiveness, whereas continuous GnRH exposure induces desensitization. Based on this phenomenon, long-acting GnRH agonists are used to suppress gonad­ otropin levels in children with precocious puberty and in men with prostate cancer (Chap. 92) and are used in some ovulation-induction protocols to reduce levels of endogenous gonadotropins (Chap. 404). Estrogens act at both the hypothalamus and the pituitary to modulate gonadotropin secretion. Chronic estrogen exposure is inhibitory,

whereas rising estrogen levels, as occur during the preovulatory surge, exert positive feedback to enhance pituitary responsiveness and to increase gonadotropin pulse frequency and amplitude. Progesterone slows GnRH pulse frequency but enhances gonadotropin responses to GnRH. Testosterone feedback in men also occurs at the hypotha­ lamic and pituitary levels and is mediated in part by its conversion to estrogens.

Although GnRH is the main regulator of LH and FSH secretion, FSH synthesis is also under distinct control by the gonadal peptides inhibin and activin, members of the transforming growth factor β (TGF-β) family. Inhibin selectively suppresses FSH, whereas activin stimulates FSH synthesis (Chap. 404). Physiology of Anterior Pituitary Hormones CHAPTER 390 Action  The gonadotropin hormones interact with their respective GPCRs expressed in the ovary and testis, evoking germ cell develop­ ment and maturation and steroid hormone biosynthesis. In women, FSH regulates ovarian follicle development and stimulates ovarian estrogen production. LH mediates ovulation and maintenance of the corpus luteum. In men, LH induces Leydig cell testosterone synthesis and secretion, and FSH stimulates seminiferous tubule development and regulates spermatogenesis. ■ ■THYROID-STIMULATING HORMONE Synthesis and Secretion  TSH-secreting thyrotrope cells consti­ tute 5% of the anterior pituitary cell population. TSH shares a common α subunit with LH and FSH but contains a specific TSH β subunit. TRH is a hypothalamic tripeptide (pyroglutamyl histidylprolinamide) that acts through a pituitary GPCR to stimulate TSH synthesis and secretion; it also stimulates the lactotrope cell to secrete PRL. TSH secretion is stimulated by TRH, whereas thyroid hormones, dopamine, somatostatin, and glucocorticoids suppress TSH by overriding TRH induction. Thyroid hormones are the predominant negative regulator of TSH production. Thyrotrope cell proliferation and TSH secretion are both induced when negative feedback inhibition by thyroid hormones is removed. Thus, thyroid damage (including surgical thyroidectomy), radia­ tion-induced hypothyroidism, chronic thyroiditis, and prolonged goitrogen exposure are associated with increased TSH levels. Longstanding untreated hypothyroidism can lead to elevated TSH levels, which may be associated with thyrotrope hyperplasia and pituitary enlargement and may sometimes be evident on magnetic resonance imaging. Action  TSH is secreted in pulses, although the excursions are modest in comparison to other pituitary hormones because of the low amplitude of the pulses and the relatively long half-life of TSH. Consequently, single determinations of TSH suffice to precisely assess its circulating levels. TSH binds to a GPCR on thyroid follicular cells to stimulate thyroid hormone synthesis and release (Chap. 394). ■ ■FURTHER READING Bernard V et al: Prolactin: A pleiotropic factor in health and disease. Nat Rev Endocrinol 15:356, 2019. Das N, Kumar TR: Molecular regulation of follicle-stimulating hor­ mone synthesis, secretion and action. J Mol Endocrinol 60:R131, 2018. Langlais D et al: Adult pituitary cell maintenance: Lineage-specific contribution of self-duplication. Mol Endocrinol 27:1103, 2013. Le Tissier P et al: The process of anterior pituitary hormone pulse generation. Endocrinology 159:3524, 2018. Ho KY et al: The physiology of growth hormone (GH) in adults: Translational journey to GH replacement therapy. J Endocrinol 257:e220197, 2023. Ranke MB, Wit JM: Growth hormone: Past, present and future. Nat Rev Endocrinol 14:285, 2018. Zhang S et al: Single-cell transcriptomics identifies divergent develop­ mental lineage trajectories during human pituitary development. Nat Commun 11:5275, 2020.

05 - 391 Hypopituitarism

391 Hypopituitarism

Shlomo Melmed, J. Larry Jameson

Hypopituitarism Deficient production of anterior pituitary hormones leads to features of hypopituitarism. Impaired production of one or more of the anterior pituitary trophic hormones can result from inherited disorders; more commonly, adult hypopituitarism is acquired and reflects the com­ pressive mass effects of tumors or the consequences of local pituitary or hypothalamic traumatic, autoimmune, inflammatory, or vascular damage. These processes also may impair synthesis or secretion of hypothalamic hormones, with resultant pituitary failure (Table 391-1). PART 12 Endocrinology and Metabolism ■ ■DEVELOPMENTAL CAUSES OF HYPOPITUITARISM Pituitary dysplasia may result in aplastic, hypoplastic, or ectopic pituitary gland development. Because pituitary development follows midline cell migration from the nasopharyngeal Rathke’s pouch, mid­ line craniofacial disorders may be associated with pituitary dysplasia. Acquired pituitary failure in the newborn also can be caused by birth trauma, including cranial hemorrhage, asphyxia, and breech delivery. A large number (>50) of transcription factors and growth factors are critical for the development of the hypothalamus and pituitary gland and the function of differentiated anterior pituitary cell lineages. Muta­ tions have been described in the HESX1, SOX2, SOX3, LHX3, LHX4, OTX, GLI2, PAX6, BMP4, ARNT2, FGF8, FGFR1, SHH, PROKR2, GPR161, IGSF1, PITX2, and CHD7 genes, among others. Heterozygous loss-of-function or autosomal recessive mutations disrupt hypothalamic and pituitary development at different developmental stages, causing a wide array of phenotypes ranging from severe syndromic midline and other defects to combined pituitary hormone defects or isolated hor­ mone deficiencies. Depending on the gene involved, the pituitary may be hypoplastic, hyperplastic, or ectopic. Midline defects include variable combinations of abnormal development of the eyes, corpus collosum, vertebrae, and genital systems. Pituitary dysfunction ranges from iso­ lated hormone deficiency to combined pituitary hormone deficiency (CPHD) and arginine vasopressin deficiency (AVP-D). In addition to these syndromic developmental disorders, some mutations affect specific pituitary cell lineages. For example, Pit-1 mutations cause combined growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) deficiencies. These patients usually present with growth failure and varying degrees of hypothy­ roidism. The pituitary may appear hypoplastic on magnetic resonance imaging (MRI). Prop-1 is expressed early in pituitary development and appears to be required for Pit-1 function. Familial and sporadic PROP1 mutations result in combined GH, PRL, TSH, and gonado­ tropin deficiency. Over 80% of these patients have growth retarda­ tion; by adulthood, all are deficient in TSH and gonadotropins, and a small minority later develop adrenocorticotropic hormone (ACTH) deficiency. Because of gonadotropin deficiency, these individuals do not enter puberty spontaneously. In some cases, the pituitary gland appears enlarged on MRI. TPIT mutations result in ACTH deficiency associated with hypocortisolism. Mutations in NR5A1 (also known as steroidogenic factor 1 [SF1]) impair development of gonadotropes, as well as adrenal/gonadal development. ■ ■HYPOTHALAMIC ENDOCRINE DYSFUNCTION Hypothalamic disorders can affect temperature regulation, appetite, sleep-wake cycles, autonomic systems, behavior, and memory, as well as multiple endocrine systems. Selected examples of hypothalamic dis­ orders that affect the endocrine system are described below. Kallmann Syndrome  Kallmann syndrome results from defective hypothalamic gonadotropin-releasing hormone (GnRH) synthesis and is associated with anosmia or hyposmia due to olfactory bulb agenesis or hypoplasia (Chap. 403). Classically, the syndrome may also be asso­ ciated with color blindness, optic atrophy, nerve deafness, cleft palate, renal abnormalities, cryptorchidism, and neurologic abnormalities

TABLE 391-1  Etiology of Hypopituitarisma Development/structural   Midline cerebral defect syndromes   Pituitary dysplasia/aplasia   Primary empty sella   Congenital hypothalamic disorders (septo-optic dysplasia, Prader-Willi syndrome, Bardet-Biedl syndrome, Kallmann syndrome)   Congenital central nervous system mass, encephalocele Genetic   Combined pituitary hormone deficiencies   Isolated primary hormone deficiencies Traumatic   Surgical resection   Radiotherapy damage   Head injuries Neoplastic   Pituitary adenoma   Parasellar mass (germinoma, ependymoma, glioma)   Rathke’s cyst   Craniopharyngioma   Hypothalamic hamartoma, gangliocytoma   Pituitary metastases (breast, lung, colon carcinoma)   Lymphoma and leukemia   Meningioma Infiltrative/inflammatory   Lymphocytic hypophysitis   Hemochromatosis   Sarcoidosis   Histiocytosis X   Granulomatous hypophysitis   Transcription factor antibodies   Immunotherapy Vascular   Pituitary apoplexy   Pregnancy-related (infarction with diabetes; postpartum necrosis)   Subarachnoid hemorrhage   Sickle cell disease   Arteritis   Snake bite venom Infections   Fungal (histoplasmosis)   Parasitic (toxoplasmosis)   Tuberculosis   Pneumocystis jirovecii Drug-induced   CTLA-4 inhibitors   PD-1/PD-L1 inhibitors  aTrophic hormone failure associated with pituitary compression or destruction usually occurs sequentially: growth hormone > follicle-stimulating hormone > luteinizing hormone > thyroid-stimulating hormone > adrenocorticotropic hormone. During childhood, growth retardation is often the presenting feature, and in adults, hypogonadism is the earliest symptom. Abbreviations: CTLA-4, cytotoxic T lymphocyte antigen 4; PD-1, programmed cell death protein 1; PD-L1, programmed cell death protein ligand 1. such as mirror movements. The initial genetic cause was the X-linked KAL gene, mutations of which impair embryonic migration of GnRH neurons from the hypothalamic olfactory placode to the hypothala­ mus. Since then, more than a dozen additional genetic abnormalities, in addition to KAL mutations, have been found to cause isolated GnRH deficiency. Autosomal recessive (i.e., GPR54, KISS1) and dominant (i.e., FGFR1) modes of transmission have been described, and there is a growing list of genes associated with GnRH deficiency (including GNRH1, PROK2, PROKR2, CHD7, PCSK1, FGF8, NELF, WDR11, TAC3, TACR3, and SEMA3E). Some patients have oligogenic

mutations in which mutations in a combination of different genes lead to the phenotype. Associated clinical features, in addition to GnRH deficiency, vary depending on the genetic cause. GnRH deficiency prevents progression through puberty. Males present with delayed puberty and pronounced hypogonadal features, including micro­ penis, probably the result of low testosterone levels during infancy. Females present with primary amenorrhea and failure of secondary sexual development. Kallmann syndrome and other causes of congenital GnRH defi­ ciency are characterized by low luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels and low concentrations of sex steroids (testosterone or estradiol). In sporadic cases of isolated gonadotropin deficiency, the diagnosis is often one of exclusion after other known causes of hypothalamic-pituitary dysfunction have been eliminated. Repetitive GnRH administration restores normal pituitary gonadotropin responses, pointing to a hypothalamic defect in these patients. Long-term treatment of males with human chorionic gonadotropin (hCG) or testosterone restores pubertal development and secondary sex characteristics; women can be treated with cyclic estrogen and progestin. Fertility may be restored by the administration of gonado­ tropins or by using a portable infusion pump to deliver subcutaneous, pulsatile GnRH. Bardet-Biedl Syndrome  This very rare genetically heterogeneous disorder is characterized by intellectual disability, renal abnormalities, obesity, and hexadactyly, brachydactyly, or syndactyly. Central AVP-D may or may not be associated. GnRH deficiency occurs in 75% of males and half of affected females. Retinal degeneration begins in early childhood, and most patients are blind by age 30. Numerous subtypes of Bardet-Biedl syndrome have been identified, with genetic linkage to at least nine different loci. Several of the loci encode genes involved in basal body cilia function, and this may account for the diverse clinical manifestations. Leptin and Leptin Receptor Mutations  Deficiencies of leptin or its receptor cause a broad spectrum of hypothalamic abnormalities, including hyperphagia, obesity, and central hypogonadism (Chap. 413). Decreased GnRH production in these patients results in attenuated pituitary FSH and LH synthesis and release. Prader-Willi Syndrome  This is a contiguous gene syndrome that results from deletion of the paternal copies of the imprinted SNRPN gene, the NECDIN gene, and possibly other genes on chromosome 15q. Prader-Willi syndrome is associated with hypogonadotropic hypogo­ nadism, hyperphagia-obesity, chronic muscle hypotonia, intellectual disability, and adult-onset diabetes mellitus. Multiple somatic defects also involve the skull, eyes, ears, hands, and feet. Diminished hypo­ thalamic oxytocin- and AVP-producing nuclei have been reported. Deficient GnRH synthesis is suggested by the observation that chronic GnRH treatment restores pituitary LH and FSH release. ■ ■ACQUIRED HYPOPITUITARISM Hypopituitarism may be caused by accidental or neurosurgical trauma; vascular events such as apoplexy; pituitary or hypothalamic neoplasms, craniopharyngioma, lymphoma, or metastatic tumors; inflammatory disease such as lymphocytic hypophysitis; autoimmune hypophysitis associated with checkpoint inhibitor cancer immunotherapy; infiltra­ tive disorders such as sarcoidosis, hemochromatosis (Chap. 426), and tuberculosis; or irradiation. Patients with brain injury, including from contact sports trauma, motor vehicle accidents, explosive causes, subarachnoid hemorrhage, and irradiation, can experience transient or long-term hypopituita­ rism. These traumatic and vascular conditions likely account for about 5% of hypopituitarism, reflecting the growing prevalence and recogni­ tion of these disorders. Long-term periodic endocrine follow-up is indicated because hypothalamic or pituitary dysfunction will develop in 25–40% of these patients. Hypothalamic Infiltration Disorders  Sarcoidosis, histiocy­ tosis X, amyloidosis, and hemochromatosis frequently involve both

hypothalamic and pituitary neuronal and neurochemical tracts. Con­ sequently, AVP-D is a common presentation, reported in half of patients with these disorders. Growth retardation is seen if attenuated GH secretion occurs before puberty. Hypogonadotropic hypogonad­ ism and hyperprolactinemia are also common.

Inflammatory Lesions  Pituitary damage and subsequent secre­ tory dysfunction can be seen with chronic site infections such as tuber­ culosis, with opportunistic fungal infections associated with AIDS, and in tertiary syphilis. Other inflammatory processes, such as granulomas and sarcoidosis, should be considered in the differential diagnosis of imaging studies suggestive of a pituitary adenoma. These lesions may cause extensive hypothalamic and pituitary damage, leading to hor­ mone deficiencies. Hypopituitarism CHAPTER 391 Cranial Irradiation  Cranial irradiation may result in long-term hypothalamic and pituitary dysfunction, especially in children and adolescents, as they are more susceptible to damage after whole-brain or head and neck therapeutic irradiation. The development of sub­ sequent hormonal abnormalities correlates strongly with irradiation dosage and the time interval after completion of radiotherapy. Up to two-thirds of patients ultimately develop hormone insufficiency after a median dose of 50 Gy (5000 rad) directed at the skull base. The devel­ opment of hypopituitarism occurs over 5–15 years and usually reflects hypothalamic damage rather than primary destruction of pituitary cells. Although the pattern of hormone loss is variable, GH deficiency is most common, followed by gonadotropin, TSH, and ACTH defi­ ciency. When deficiency of one or more hormones is documented, the possibility of diminished reserve of other hormones is likely. Accord­ ingly, anterior pituitary function should be continually evaluated over the long term in previously irradiated patients, and replacement therapy instituted when appropriate (see below). Lymphocytic Hypophysitis  This occurs most often in post­ partum women; it usually presents with hyperprolactinemia and MRI evidence of a prominent pituitary mass that often resembles an adenoma, with mildly elevated PRL levels. Pituitary failure caused by diffuse lymphocytic infiltration may be transient or permanent but requires immediate evaluation and treatment. Rarely, isolated pituitary hormone deficiencies have been described, suggesting a selective auto­ immune process targeted to specific cell types. Most patients manifest symptoms of progressive mass effects with headache and visual distur­ bance. The erythrocyte sedimentation rate often is elevated. Because it may be indistinguishable from a pituitary adenoma on MRI, hypophy­ sitis should be considered in a postpartum woman with a newly diagnosed pituitary mass before an unnecessary surgical intervention is undertaken. The inflammatory process often resolves after several months of glucocorticoid treatment, and pituitary function may be restored, depending on the extent of damage. Immunotherapy and Hypophysitis  Pituitary cells express cyto­ toxic T lymphocyte antigen-4 (CTLA-4), and up to 20% of patients receiving cancer immunotherapy with CTLA-4 inhibitors (e.g., ipi­ limumab) may develop hypophysitis with heterogeneously associ­ ated thyroid, adrenal, islet, and gonadal failure. Hypophysitis is also reported with PD-1/PD-L1 inhibitors (e.g., pembrolizumab and nivolumab) and may show delayed presentation. HLA type DQ0602 is associated with checkpoint inhibitor–associated hypophysitis in 39% of such patients. Pituitary hormone replacement, with or without high-dose glucocorticoids, may be safely tolerated with continued immunotherapy. Pituitary Apoplexy  Acute intrapituitary hemorrhagic vascular events can cause substantial damage to the pituitary and surround­ ing sellar structures. Pituitary apoplexy may occur spontaneously in a preexisting pituitary adenoma; postpartum (Sheehan’s syndrome); or in association with diabetes, hypertension, sickle cell anemia, or acute shock. The hyperplastic enlargement of the pituitary, which occurs normally during pregnancy, increases the risk for hemorrhage and infarction. Apoplexy is an endocrine emergency that may result in severe hypoglycemia, hypotension and shock, central nervous system

(CNS) hemorrhage, and death. Acute symptoms may include severe headache with signs of meningeal irritation, bilateral visual changes, ophthalmoplegia, and, in severe cases, cardiovascular collapse and loss of consciousness. Pituitary computed tomography (CT) or MRI may reveal signs of intratumoral or sellar hemorrhage, with pituitary stalk deviation and compression of pituitary tissue.

Patients with no evident visual loss or impaired consciousness can be observed and managed conservatively with high-dose glucocorti­ coids. Those with significant or progressive visual loss, cranial nerve palsy, or loss of consciousness require urgent surgical decompression. Visual recovery after sellar surgery is inversely correlated with the length of time after the acute event. Therefore, severe ophthalmoplegia or visual deficits are indications for early surgery. Hypopituitarism is common after apoplexy. PART 12 Endocrinology and Metabolism Empty Sella  A partial or apparently totally empty sella is often an incidental MRI finding and may sometimes be associated with intracranial hypertension. These patients usually have normal pitu­ itary function, implying that the surrounding rim of pituitary tissue is fully functional. Hypopituitarism, however, may develop insidiously. Pituitary adenomas also may undergo clinically silent infarction and involution with development of a partial or totally empty sella by cerebrospinal fluid (CSF) filling the dural herniation. Rarely, small but functional pituitary adenomas may arise within the rim of normal pituitary tissue, and they are not always visible on MRI. ■ ■PRESENTATION AND DIAGNOSIS The clinical manifestations of hypopituitarism depend on which hormones are lost and the extent of the hormone deficiency (see below). GH deficiency causes growth disorders in children and leads to abnormal body composition in adults. Gonadotropin deficiency causes menstrual disorders and infertility in women and decreased sexual function, infertility, and loss of secondary sexual characteris­ tics in men. TSH and ACTH deficiencies usually develop later in the course of pituitary failure. TSH deficiency causes growth retardation in children and features of hypothyroidism in children and adults. Secondary adrenal insufficiency caused by ACTH deficiency leads to hypocortisolism with relative preservation of mineralocorticoid production. PRL deficiency causes failure of lactation. When lesions involve the posterior pituitary, polyuria and polydipsia reflect loss of AVP secretion. In patients with long-standing pituitary damage, epi­ demiologic studies document an increased mortality rate, primarily from increased cardiovascular and cerebrovascular disease. Previous head or neck irradiation is also a determinant of increased mortality rates in patients with hypopituitarism, especially from cerebrovascular disease. ■ ■LABORATORY INVESTIGATION Biochemical diagnosis of pituitary insufficiency is made by demon­ strating low levels of respective pituitary trophic hormones in the setting of low levels of target organ hormones. For example, low free thyroxine in the setting of a low or inappropriately normal TSH level suggests secondary hypothyroidism. Similarly, a low testosterone level without elevation of gonadotropins suggests hypogonadotropic hypogonadism. Provocative tests may be required to assess pituitary reserve (Table 391-2). GH responses to insulin-induced hypogly­ cemia, arginine, glucagon, l-dopa, growth hormone–releasing hor­ mone (GHRH), or growth hormone–releasing orally active ghrelin receptor agonist macimorelin can be used to assess GH reserve. Corticotropin-releasing hormone (CRH) administration induces ACTH release, and administration of synthetic ACTH (cosyntropin) evokes adrenal cortisol release as an indirect indicator of pituitary ACTH reserve (Chap. 398). ACTH reserve is most reliably assessed by measuring ACTH and cortisol levels during insulin-induced hypoglycemia. However, this test should be performed cautiously in patients with suspected adrenal insufficiency because of enhanced susceptibility to hypoglycemia and hypotension. Administering insu­ lin to induce hypoglycemia is contraindicated in patients with active coronary artery disease or known seizure disorders.

TREATMENT Hypopituitarism Hormone replacement therapy, including glucocorticoids, thyroid hormone, sex steroids, GH, and AVP, is usually safe and free of complications. Treatment regimens that mimic physiologic hor­ mone production allow for maintenance of satisfactory clinical homeostasis. Effective dosage schedules are outlined in Table 391-3. Patients in need of glucocorticoid replacement require especially careful dose adjustments during stressful events such as acute ill­ ness, dental procedures, trauma, and hospitalization. ■ ■DISORDERS OF GROWTH AND DEVELOPMENT Skeletal Maturation and Somatic Growth  The growth plate is dependent on a variety of hormonal stimuli, including GH, insulinlike growth factor (IGF)-1, sex steroids, thyroid hormones, paracrine and circulating growth factors (e.g., fibroblast growth factor family), and cytokines. The growth-promoting process also requires caloric energy, amino acids, vitamins, and trace metals and consumes ~10% of normal energy production. Malnutrition impairs chondrocyte activity, increases GH resistance, and leads to reduced circulating IGF-1 and IGF binding protein (IGFBP)-3 levels. Linear bone growth rates are very high in infancy and are pituitary dependent. Mean growth velocity is ~6 cm/year in later childhood and usually is maintained within a given range on a standardized percen­ tile chart. Peak growth rates occur during midpuberty when bone age is 12 (girls) or 13 (boys). Secondary sexual development is associated with elevated sex steroids that cause progressive epiphyseal growth plate closure. Bone age is delayed in patients with all forms of true GH deficiency or GH receptor defects that result in attenuated GH action. Short stature may occur as a result of constitutive intrinsic growth defects or because of acquired extrinsic factors that impair growth. In general, delayed bone age in a child with short stature is suggestive of a hormonal or systemic disorder, whereas normal bone age in a short child is more likely to be caused by a genetic cartilage dysplasia or growth plate disorder (Chap. 425). GH Deficiency in Children  Isolated GH deficiency is character­ ized by short stature, micropenis, increased fat, high-pitched voice, and a propensity to hypoglycemia due to relatively unopposed insulin action. Familial modes of inheritance are seen in at least one-third of these individuals and may be autosomal dominant, recessive, or X-linked. About 10% of children with GH deficiency have mutations in the GH-N gene, including gene deletions and a wide range of point mutations. Mutations in transcription factors Pit-1 and Prop-1, which control somatotrope development (see above), result in GH deficiency in combination with other pituitary hormone deficiencies, which may become manifest only in adulthood. The diagnosis of idiopathic GH deficiency should be made only after known molecular defects have been rigorously excluded. GHRH RECEPTOR MUTATIONS  Recessive mutations of the GHRH receptor gene in subjects with severe proportionate dwarfism are asso­ ciated with low basal GH levels that cannot be stimulated by exogenous GHRH, GH-releasing peptide, or insulin-induced hypoglycemia, as well as anterior pituitary hypoplasia. The syndrome exemplifies the importance of the GHRH receptor for determining somatotrope pro­ liferation and hormonal responsiveness. GH INSENSITIVITY  This is caused by defects of GH receptor structure or signaling. Homozygous or heterozygous mutations of the GH recep­ tor are associated with partial or complete GH insensitivity and growth failure (Laron syndrome). The diagnosis is based on normal or high GH levels, with decreased circulating GH-binding protein (GHBP), and low IGF-1 levels. Very rarely, defective IGF-1, IGF-1 receptor, or IGF-1 signaling defects are also encountered. STAT5B mutations result in both immunodeficiency as well as abrogated GH signaling, leading to short stature with normal or elevated GH levels and low IGF-1 levels. Circulat­ ing GH receptor antibodies may rarely cause peripheral GH insensitivity.

TABLE 391-2  Tests of Pituitary Sufficiency HORMONE TEST BLOOD SAMPLES INTERPRETATION GH Insulin tolerance test: Regular insulin (0.05–0.15 U/kg IV) –30, 0, 30, 60, 120 min for glucose and GH GHRH/L-arginine test: GHRH 1 μg/kg IV and arginine 30 g IV over 30 min 0, 15, 30, 45, 60, 120 min for GH Normal GH response is BMI dependent: 11 μg/L if BMI

<25 kg/m2, 8 μg/L if BMI 25-20, and 4 μg/L if BMI ≥30 Not available in the United States Ghrelin receptor agonist test: 0.5 mg/kg PO 0, 30, 45, 60, 90 min for GH Normal response is GH >2.8 μg/L Glucagon test: 1 mg IM (1.5 mg if body weight >90 kg) 0, 30, 60, 90, 120, 150, 180, 210, 240 for GH l-Dopa test: 500 mg PO 0, 30, 60, 120 min for GH Normal response is GH >3 μg/L PRL TRH test: 200–500 μg IV 0, 20, and 60 min for TSH and PRL Normal PRL is >2 μg/L and increase >200% of baseline ACTH           Insulin tolerance test: Regular insulin (0.05–0.15 U/kg IV) –30, 0, 30, 60, 90 min for glucose and cortisol CRH test: 1 μg/kg CRH IV at 8 a.m. 0, 15, 30, 60, 90, 120 min for ACTH and cortisol Metyrapone test: Metyrapone (30 mg/kg) at midnight Plasma 11-deoxycortisol and cortisol at 8 a.m.; ACTH can also be measured Standard ACTH stimulation test: ACTH 1-24 (cosyntropin), 0.25 mg IM or IV 0, 30, 60 min for cortisol and aldosterone Low-dose ACTH test: ACTH 1-24 (cosyntropin), 1 μg IV 0, 30, 60 min for cortisol Cortisol should be >21 μg/dL 3-day ACTH stimulation test consists of 0.25 mg ACTH 1-24 given IV over 8 h each day   Cortisol >21 μg/dL TSH   Basal thyroid function tests: T4, T3, TSH Basal measurements Low free thyroid hormone levels in the setting of TSH levels that are not appropriately increased indicate pituitary insufficiency TRH test: 200–500 μg IV 0, 20, 60 min for TSH and PRLa TSH should increase by >5 mU/L unless thyroid hormone levels are increased LH, FSH   LH, FSH, testosterone, estrogen Basal measurements Basal LH and FSH should be increased in postmenopausal women Low testosterone levels in the setting of low LH and FSH indicate pituitary insufficiency GnRH test: GnRH (100 μg) IV 0, 30, 60 min for LH and FSH In most adults, LH should increase by 10 IU/L and FSH by 2 IU/L Normal responses are variable Multiple hormones Combined anterior pituitary test: GHRH (1 μg/kg), CRH (1 μg/kg), GnRH (100 μg), TRH (200 μg) are given IV –30, 0, 15, 30, 60, 90, 120 min for GH, ACTH, cortisol, LH, FSH, and TSH aEvoked PRL response indicates lactotrope integrity. Abbreviations: T3, triiodothyronine; T4, thyroxine; TRH, thyrotropin-releasing hormone. For other abbreviations, see text. NUTRITIONAL SHORT STATURE  Caloric deprivation and malnutri­ tion, uncontrolled diabetes, and chronic renal failure represent sec­ ondary causes of abrogated GH receptor function. These conditions also stimulate production of proinflammatory cytokines, which act to exacerbate the block of GH-mediated signal transduction. Children with these conditions typically exhibit features of acquired short stature with normal or elevated GH and low IGF-1 levels. PSYCHOSOCIAL SHORT STATURE  Emotional and social deprivation lead to growth retardation accompanied by delayed speech, discordant hyperphagia, and an attenuated response to administered GH. A nur­ turing environment restores growth rates. ■ ■PRESENTATION AND DIAGNOSIS Short stature is commonly encountered in clinical practice, and the decision to evaluate these children requires clinical judgment in asso­ ciation with auxologic data and family history. Short stature should be evaluated comprehensively if a patient’s height is >3 standard deviations below the mean for age or if the growth rate has decelerated. Skeletal maturation is best evaluated by measuring a radiologic bone

Glucose <40 mg/dL; GH should be >3 μg/L Normal response is GH >3.0 µg/L if BMI <25 kg/m2 or if BMI 25-30 and low pretest probability, and GH >1.0 µg/L if BMI 25-30 and high pretest probability or if BMI >30 Hypopituitarism CHAPTER 391 Glucose <40 mg/dL Cortisol should increase by >7 μg/dL or to >20 μg/dL Basal ACTH increases 2- to 4-fold and peaks at

20–100 pg/mL Cortisol levels >20–25 μg/dL Plasma cortisol should be <4 g/dL to assure an adequate response Normal response is 11-deoxycortisol >7.5 μg/dL or

ACTH >75 pg/mL Normal response is cortisol >21 μg/dL and aldosterone response >4 ng/dL above baseline Combined or individual releasing hormone responses must be elevated in the context of basal target gland hormone values and may not be uniformly diagnostic

(see text) age, which is based mainly on the degree of wrist bone growth plate fusion. Final height can be predicted using standardized scales (BayleyPinneau or Tanner-Whitehouse) or estimated by adding 6.5 cm (boys) or subtracting 6.5 cm (girls) from the midparental height. ■ ■LABORATORY INVESTIGATION Because GH secretion is pulsatile, GH deficiency is best assessed by examining the response to provocative stimuli, including exercise, insulin-induced hypoglycemia, and other pharmacologic tests that normally increase GH to >7 μg/L in children. Random GH measure­ ments do not distinguish children with normal GH levels from those with true GH deficiency. Adequate adrenal and thyroid hormone replacement should be assured before testing. Age-matched IGF-1 levels are not sufficiently sensitive or specific to make the diagno­ sis but can be useful to confirm GH deficiency. Pituitary MRI may reveal pituitary mass lesions or structural defects. Molecular analyses for known mutations should be undertaken when the cause of short stature remains cryptic or when additional clinical features suggest a genetic cause.

TABLE 391-3  Hormone Replacement Therapy for Adult Hypopituitarisma HORMONE DEFICIT HORMONE REPLACEMENT ACTH     Hydrocortisone (10–20 mg/d in divided doses) Cortisone acetate (15–25 mg/d in divided doses) Prednisone (5 mg a.m.) TSH l-Thyroxine (0.075–0.15 mg daily) FSH/LH                 Males   Testosterone gel (5–10 g/d)   Testosterone skin patch (5 mg/d) PART 12 Endocrinology and Metabolism   Testosterone enanthate (200 mg IM every 2 weeks) Females   Conjugated estrogen (0.65–1.25 mg qd for 25 days)   Progesterone (5–10 mg qd) on days 16–25   Estradiol skin patch (0.025–0.1 mg every week), adding progesterone on days 16–25 if uterus intact   For fertility: menopausal gonadotropins, human chorionic gonadotropins GH   Adults: Somatotropin (0.1–1.25 mg SC qd) Children: Somatotropin (0.02–0.05 mg/kg per day) AVP Intranasal desmopressin (5–20 g twice daily) Oral 300–600 μg qd aAll doses shown should be individualized for specific patients and should be reassessed during stress, surgery, or pregnancy. Male and female fertility requirements should be managed as discussed in Chaps. 403 and 404. Note: For abbreviations, see text. TREATMENT Disorders of Growth and Development Replacement therapy with recombinant GH (0.02–0.05 mg/kg per day SC) restores growth velocity in GH-deficient children to ~10 cm/year. If pituitary insufficiency is documented, other associ­ ated hormone deficits should be corrected, especially adrenal ste­ roids. In selected situations, GH treatment may be combined with strategies to delay puberty (e.g., GnRH agonist) or reduce sex ste­ roids (e.g., aromatase inhibitors) as a means to mitigate sex steroid effect on epiphyseal closure. GH treatment is also moderately effec­ tive for accelerating growth rates in children with Turner syndrome and chronic renal failure. Treating psychosocial or constitutional (idiopathic) short stature with GH is not uniformly recommended as these children may only experience modest additive growth, which should be weighed against GH cost and side effect profiles. In patients with GH insensitivity and growth retardation due to mutations of the GH receptor, treatment with IGF-1 bypasses the dysfunctional GH receptor. ADULT GH DEFICIENCY Adult GH deficiency (AGHD) usually is caused by acquired hypotha­ lamic or pituitary somatotrope damage. Acquired pituitary hormone deficiency follows a typical pattern in which loss of adequate GH reserve foreshadows subsequent hormone deficits. The sequential order of hormone loss is usually GH → FSH/LH → TSH → ACTH. Patients previously diagnosed with childhood-onset GH deficiency should be retested as adults to affirm the diagnosis. ■ ■PRESENTATION AND DIAGNOSIS The clinical features of AGHD include changes in body composi­ tion, lipid metabolism, and quality of life as well as cardiovascular dysfunction (Table 391-4). Body composition changes are common and include reduced lean body mass, increased fat mass with selective deposition of intraabdominal visceral fat, and increased waist-to-hip ratio. Hyperlipidemia, left ventricular dysfunction, hypertension, and increased plasma fibrinogen levels also may be present. Bone mineral content is reduced, with resultant increased fracture rates. Patients

TABLE 391-4  Features of Adult Growth Hormone Deficiency Clinical Impaired quality of life   Decreased energy and drive   Poor concentration   Low self-esteem   Social isolation Body composition changes   Increased body fat mass   Central fat deposition   Increased waist-to-hip ratio   Decreased lean body mass Reduced exercise capacity   Reduced maximum O2 uptake   Impaired cardiac function   Reduced muscle mass Cardiovascular risk factors   Impaired cardiac structure and function   Abnormal lipid profile   Decreased fibrinolytic activity   Atherosclerosis   Omental obesity Imaging Pituitary: mass or structural damage Bone: reduced bone mineral density Abdomen: excess omental adiposity Laboratory Evoked GH <3 ng/mL IGF-1 and IGFBP-3 low or normal Increased LDL cholesterol Concomitant gonadotropin, TSH, and/or ACTH reserve deficits may be present Abbreviation: LDL, low-density lipoprotein. For other abbreviations, see text. may experience social isolation, depression, and difficulty maintain­ ing gainful employment. Adult hypopituitarism is associated with a threefold increase in cardiovascular mortality rates in comparison to age- and sex-matched controls, and this may be due to GH deficiency, as patients in these studies were replaced with other deficient pituitary hormones. ■ ■LABORATORY INVESTIGATION AGHD is rare, and in light of the nonspecific nature of associated clinical symptoms, patients appropriate for testing should be selected carefully on the basis of well-defined criteria. With few exceptions, testing should be restricted to patients with the following predisposing factors: (1) pituitary surgery, (2) pituitary or hypothalamic tumor or granulomas, (3) history of cranial irradiation, (4) radiologic evidence of a pituitary lesion, and (5) childhood requirement for GH replace­ ment therapy. The transition of a GH-deficient adolescent to adult­ hood requires retesting to document subsequent AGHD. Up to 20% of patients previously treated for childhood-onset GH deficiency are found to be GH sufficient on repeat testing as adults. A significant proportion (~25%) of truly GH-deficient adults have low-normal IGF-1 levels. Thus, as in the evaluation of GH deficiency in children, valid age-matched IGF-1 measurements provide a use­ ful index of therapeutic responses but are not sufficiently precise for diagnostic purposes. The most validated test to distinguish pituitarysufficient patients from those with AGHD is insulin-induced (0.05– 0.1 U/kg) hypoglycemia. After glucose reduction to ~40 mg/dL, most individuals experience neuroglycopenic symptoms (Chap. 418), and peak GH release occurs at 60 min and remains elevated for up to 2 h. About 90% of healthy adults exhibit GH responses >5 μg/L; AGHD is defined by a peak GH response to hypoglycemia of <3 μg/L. Although insulininduced hypoglycemia is safe when performed under appropriate

History of pituitary pathology Clinical features present Evoked GH <3 µg/L Exclude contraindications Treat with GH 0.1–0.3 mg/d Check IGF-1 after 1 mo Titrate GH dose up to 1.25 mg/d 6 mo No response Response Discontinue Rx Monitor IGF-1 Levels FIGURE 391-1  Management of adult growth hormone (GH) deficiency. IGF, insulinlike growth factor; Rx, treatment. supervision, it is contraindicated in patients with diabetes, ischemic heart disease, cerebrovascular disease, or epilepsy and in elderly patients. Alternative stimulatory tests include intravenous arginine (30 g), GHRH (1 μg/kg), oral ghrelin receptor agonist (0.5 mg/kg), and glucagon (1 mg). Combinations of these tests may evoke GH secretion in subjects who are not responsive to a single test. TREATMENT Adult GH Deficiency Once the diagnosis of AGHD is unequivocally established, replace­ ment of GH may be indicated. Contraindications to therapy include the presence of an active neoplasm, intracranial hypertension, and uncontrolled diabetes and retinopathy. The starting adult dose of 0.1–0.2 mg/d should be titrated (up to a maximum of 1.25 mg/d) to maintain IGF-1 levels in the mid-normal range for age- and sexmatched controls (Fig. 391-1). Women require higher doses than men, and elderly patients require less GH. Long-term GH mainte­ nance sustains normal IGF-1 levels and is associated with persistent body composition changes (e.g., enhanced lean body mass and lower body fat). High-density lipoprotein cholesterol increases, but total cholesterol and insulin levels may not change significantly. Lumbar spine bone mineral density increases, but this response is gradual (>1 year). Many patients note significant improvement in quality of life when evaluated by standardized questionnaires. The effect of GH replacement on mortality rates in GH-deficient patients is currently the subject of long-term prospective investigation. Recently approved long-acting GH preparations for patients with AGHD require weekly injections. Ideally, dosing should be titrated to achieve normal but not supra-normal IGF-1 levels. Early reports indicate that side effects appear similar to subcutaneous formulations. About 30% of patients exhibit reversible dose-related fluid reten­ tion, joint pain, and carpal tunnel syndrome, and up to 40% exhibit myalgias and paresthesia. Patients receiving insulin require careful monitoring for dosing adjustments, as GH is a potent counterregulatory hormone for insulin action. Patients with type 2 diabetes mellitus may initially develop further insulin resistance. However, glycemic control usually improves with the sustained loss of abdominal fat associated with long-term GH replacement. Headache, increased intracranial pressure, hypertension, and tin­ nitus occur rarely. Pituitary tumor regrowth and progression of skin lesions or other tumors have not been encountered in long-term surveillance programs with appropriate replacement doses.

ACTH DEFICIENCY

■ ■PRESENTATION AND DIAGNOSIS Secondary adrenal insufficiency occurs as a result of pituitary ACTH deficiency. It is characterized by fatigue, weakness, anorexia, nausea, vomiting, and, occasionally, hypoglycemia. In contrast to primary adrenal failure, hypocortisolism associated with pituitary failure usu­ ally is not accompanied by hyperpigmentation or mineralocorticoid deficiency. ACTH deficiency is commonly due to glucocorticoid withdrawal after treatment-associated suppression of the hypothalamic-pituitaryadrenal (HPA) axis. Isolated ACTH deficiency may occur after surgical resection of an ACTH-secreting pituitary adenoma that has suppressed the HPA axis; this phenomenon is in fact suggestive of a surgical cure. The mass effects of other pituitary adenomas or sellar lesions may lead to ACTH deficiency, usually in combination with other pituitary hor­ mone deficiencies. Partial ACTH deficiency may be unmasked in the presence of an acute medical or surgical illness, when clinically signifi­ cant hypocortisolism reflects diminished ACTH reserve. Rarely, TPIT or POMC mutations result in primary ACTH deficiency. Hypopituitarism CHAPTER 391 ■ ■LABORATORY DIAGNOSIS Inappropriately low ACTH levels in the setting of low cortisol levels are characteristic of diminished ACTH reserve. Low basal serum cortisol levels are associated with blunted cortisol responses to ACTH stimula­ tion and impaired cortisol response to insulin-induced hypoglycemia or testing with metyrapone or CRH. For a description of provocative ACTH tests, see Chap. 398. TREATMENT ACTH Deficiency Glucocorticoid replacement therapy improves most features of ACTH deficiency. The total daily dose of hydrocortisone replace­ ment preferably should not exceed 20 mg daily, divided into two or three doses. Prednisone (5 mg each morning) is longer acting and has fewer mineralocorticoid effects than hydrocortisone. Some authorities advocate lower maintenance doses in an effort to avoid cushingoid side effects. Doses should be increased severalfold dur­ ing periods of acute illness or stress. Patients should wear medical alert bracelets and/or carry identification cards with information about their glucocorticoid requirements. GONADOTROPIN DEFICIENCY Hypogonadism is the most common presenting feature of adult hypo­ pituitarism even when other pituitary hormones are also deficient. It is often a harbinger of hypothalamic or pituitary lesions that impair GnRH production or delivery through the pituitary stalk. As noted below, hypogonadotropic hypogonadism is a common presenting fea­ ture of hyperprolactinemia. A variety of inherited and acquired disorders are associated with isolated hypogonadotropic hypogonadism (Chap. 403). Hypothalamic defects associated with GnRH deficiency include Kallmann syndrome and mutations in more than a dozen genes that regulate GnRH neu­ ron migration, development, and function (see above). Mutations in GPR54, DAX1, NR5A1, kisspeptin, the GnRH receptor, and the LHβ or FSHβ subunit genes also cause pituitary gonadotropin deficiency. Acquired forms of GnRH deficiency leading to hypogonadotropism are seen in association with anorexia nervosa, stress, starvation, and extreme exercise but also may be idiopathic. Hypogonadotropic hypo­ gonadism in these disorders is reversed by removal of the stressful stimulus or by caloric replenishment. ■ ■PRESENTATION AND DIAGNOSIS In premenopausal women, hypogonadotropic hypogonadism presents as diminished ovarian function leading to oligomenorrhea or amenor­ rhea, infertility, decreased vaginal secretions, decreased libido, and breast atrophy. In hypogonadal adult men, secondary testicular failure

06 - 392 Pituitary Tumor Syndromes

392 Pituitary Tumor Syndromes

is associated with decreased libido and potency, infertility, decreased muscle mass with weakness, reduced beard and body hair growth, soft testes, and characteristic fine facial wrinkles. Osteoporosis occurs in both untreated hypogonadal women and men.

■ ■LABORATORY INVESTIGATION Central hypogonadism is associated with low or inappropriately normal serum gonadotropin levels in the setting of low sex hormone concentrations (testosterone in men, estradiol in women). Because gonadotropin secretion is pulsatile, valid assessments may require repeated measurements or the use of pooled serum samples. Men have reduced sperm counts. PART 12 Endocrinology and Metabolism Intravenous GnRH (100 μg) stimulates gonadotropes to secrete LH (which peaks within 30 min) and FSH (which plateaus during the ensuing 60 min). Normal responses vary according to menstrual cycle stage, age, and sex of the patient. Generally, LH levels increase about threefold, whereas FSH responses are less pronounced. In the setting of gonadotropin deficiency, a normal gonadotropin response to GnRH indicates intact pituitary gonadotrope function and suggests a hypo­ thalamic abnormality. An absent response, however, does not reliably distinguish pituitary from hypothalamic causes of hypogonadism. For this reason, GnRH testing usually adds little to the information gained from baseline evaluation of the hypothalamic-pituitary-gonadotrope axis except in cases of isolated GnRH deficiency (e.g., Kallmann syndrome). MRI examination of the sellar region and assessment of other pituitary functions usually are indicated in patients with documented central hypogonadism. TREATMENT Gonadotropin Deficiency In males, testosterone replacement is necessary to achieve and maintain normal growth and development of the external genitalia, secondary sex characteristics, male sexual behavior, and androgenic anabolic effects, including maintenance of muscle function and bone mass. Testosterone may be administered by intramuscular injections every 1–4 weeks or by using skin patches or testoster­ one gels (Chap. 403). Gonadotropin injections (hCG or human menopausal gonadotropin [hMG]) over 12–18 months are used to restore fertility. Pulsatile GnRH therapy (25–150 ng/kg every 2 h), administered by a subcutaneous infusion pump, is also effective for treatment of hypothalamic hypogonadism when fertility is desired. In premenopausal women, cyclical replacement of estrogen and progesterone maintains secondary sexual characteristics and integ­ rity of genitourinary tract mucosa and prevents premature osteo­ porosis (Chap. 404). Gonadotropin therapy is used for ovulation induction. Follicular growth and maturation are initiated using hMG or recombinant FSH; hCG or human luteinizing hormone is subsequently injected to induce ovulation. As in men, pulsatile GnRH therapy can be used to treat hypothalamic causes of gonado­ tropin deficiency. ARGININE VASOPRESSIN DEFICIENCY See Chap. 393 for diagnosis and treatment of AVP-D. ■ ■FURTHER READING Fleseriu M et al: Hormonal replacement in hypopituitarism in adults: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 101:3888, 2016. Gregory LC, Dattani MT: The molecular basis of congenital hypopi­ tuitarism and related disorders. J Clin Endocrinol Metab 105:e2103, 2020. Melmed S: Pathogenesis and diagnosis of growth hormone deficiency in adults. N Engl J Med 380:2551, 2019. Miller BS et al: Long-acting growth hormone preparations-current status and future considerations. J Clin Endocrinol Metab 105:e2121, 2020.

Prodam F et al: Insights into non-classic and emerging causes of hypo­ pituitarism. Nat Rev Endocrinol 17:114, 2021. Quandt Z et al: Spectrum of clinical presentations, imaging findings, and HLA types in immune checkpoint inhibitor-induced hypophysi­ tis. J Endocr Soc 7:bvad012, 2023. Tanriverdi F et al: Pituitary dysfunction after traumatic brain injury: A clinical and pathophysiological approach. Endocr Rev 36:305, 2015. Yamamoto M et al: Autoimmune pituitary disease: New concepts with clinical implications. Endocr Rev 41:261, 2020. Shlomo Melmed, J. Larry Jameson

Pituitary Tumor

Syndromes HYPOTHALAMIC, PITUITARY, AND OTHER SELLAR MASSES ■ ■EVALUATION OF SELLAR MASSES Local Mass Effects  Clinical manifestations of sellar lesions vary, depending on the anatomic location of the mass and the direction of its extension (Table 392-1). The dorsal sellar diaphragm presents the least resistance to soft tissue expansion from the sella; consequently, pituitary adenomas frequently extend in a suprasellar direction. Bony invasion may occur as well, especially through the sellar floor to the sphenoid sinus (Fig. 392-1). Headaches are common features of small intrasellar tumors, even with no demonstrable suprasellar extension. Because of the confined nature of the pituitary, small changes in intrasellar pressure stretch the dural plate; however, headache severity correlates poorly with adenoma size or extension. Suprasellar extension can lead to visual loss by several mechanisms, the most common being compression of the optic chiasm. Rarely, direct invasion of the optic nerves or obstruction of cerebrospinal fluid (CSF) flow leading to secondary visual disturbances can occur. Pitu­ itary stalk compression by a hormonally active or inactive intrasellar mass may compress the portal vessels, disrupting pituitary access to hypothalamic hormones and dopamine; this results in early hyperpro­ lactinemia and later concurrent loss of other pituitary hormones. This “stalk section” phenomenon may also be caused by trauma, whiplash injury with posterior clinoid stalk compression, or skull base fractures. Lateral mass invasion may impinge on the cavernous sinus and com­ press its neural contents, leading to cranial nerve III, IV, and VI palsies as well as effects on the ophthalmic and maxillary branches of the fifth cranial nerve (Chap. 452). Patients may present with diplopia, ptosis, ophthalmoplegia, and decreased facial sensation, depending on the extent of neural damage. Extension into the sphenoid sinus indicates that the pituitary mass has eroded through the sellar floor (Fig. 392-1). Aggressive tumors rarely invade the palate roof and cause nasopharyn­ geal obstruction, infection, and CSF leakage. Temporal and frontal lobe involvement may rarely lead to uncinate seizures, personality disor­ ders, and anosmia. Direct hypothalamic encroachment by an invasive pituitary mass may cause important metabolic sequelae, including precocious puberty or hypogonadism, arginie vasopressin deficiency (AVP-D), sleep disturbances, dysthermia, and appetite disorders. Magnetic Resonance Imaging  Sagittal and coronal T1-weighted magnetic resonance imaging (MRI) before and after administration of gadolinium allows precise visualization of the pituitary gland with

TABLE 392-1  Features of Sellar Mass Lesionsa IMPACTED STRUCTURE CLINICAL IMPACT Pituitary Hypogonadism Hypothyroidism Growth failure, adult growth hormone deficiency Hypoadrenalism Hyperprolactinema (stalk compression) Optic chiasm Loss of red perception Bitemporal hemianopia Superior or bitemporal field defect Scotoma Blindness Hypothalamus Temperature dysregulation Appetite and thirst disorders Obesity Arginine vasopression deficiency Sleep disorders Behavioral dysfunction Autonomic dysfunction Cavernous sinus Ophthalmoplegia with or without ptosis or diplopia Facial numbness Frontal lobe Personality disorder Anosmia Brain Headache Hydrocephalus Psychosis Dementia Laughing seizures aAs the intrasellar mass expands, it first compresses intrasellar pituitary tissue, then usually invades dorsally through the dura to lift the optic chiasm or laterally to the cavernous sinuses. Bony erosion is rare, as is direct brain compression. Microadenomas may present with headache. clear delineation of the hypothalamus, pituitary stalk, pituitary tissue and surrounding suprasellar cisterns, cavernous sinuses, sphenoid sinus, and optic chiasm. Pituitary gland height ranges from 6 mm in children to 8 mm in adults; during pregnancy and puberty, the height may reach 10–12 mm. The upper aspect of the adult pituitary is flat or slightly concave, but in adolescent and pregnant individuals, this sur­ face may be convex, reflecting physiologic pituitary enlargement. The stalk should be midline and vertical. Anterior pituitary gland soft tissue consistency is slightly hetero­ geneous on MRI, and signal intensity resembles that of brain matter on T1-weighted imaging (Fig. 392-2). Adenoma density is usually lower than that of surrounding normal tissue on T1-weighted imaging, and the signal intensity increases with T2-weighted images. Computed tomography (CT) scan is reserved to define the extent of bony erosion or the presence of calcification. Sellar masses are encountered commonly as incidental findings on MRI, and most are pituitary adenomas (incidentalomas). In the absence of hormone hypersecretion, these small intrasellar lesions can be monitored safely with MRI, which is performed annually and then less often if there is no evidence of further growth. Resection should be considered for incidentally discovered larger macroadenomas, because about one-third become invasive or cause local pressure effects. If hormone hypersecretion is identified, specific therapies are indicated as described below. When larger masses (>1 cm) are encountered, they should also be distinguished from nonadenomatous lesions. Meningio­ mas often are associated with bony hyperostosis; craniopharyngiomas may have calcifications and are usually hypodense, whereas gliomas are hyperdense on T2-weighted images. Ophthalmologic Evaluation  Because optic tracts may be con­ tiguous to an expanding pituitary mass, reproducible visual field assessment using perimetry techniques should be performed on all patients with sellar mass lesions that impinge the optic chiasm (Chap. 34).

Bitemporal hemianopia, often more pronounced superiorly, is observed classically. It occurs because nasal ganglion cell fibers, which cross in the optic chiasm, are especially vulnerable to compression of the ventral optic chiasm. Occasionally, homonymous hemianopia occurs from postchiasmal compression or monocular temporal field loss from prechiasmal compression. Invasion of the cavernous sinus can produce diplopia from ocular motor nerve palsy. Early diagnosis reduces the risk of optic atrophy, vision loss, or eye misalignment.

Laboratory Investigation  The presenting clinical features of functional pituitary adenomas (e.g., acromegaly, prolactinoma, or Cushing’s disease) should guide the laboratory studies (Table 392-2). However, for a sellar mass with no obvious clinical features of hormone excess, laboratory studies are geared toward determining the nature of the tumor and assessing the possible presence of hypopituitarism. When a pituitary adenoma is suspected based on MRI, initial hormonal evaluation usually includes (1) basal prolactin (PRL); (2) insulin-like growth factor (IGF)-1; (3) 24-h urinary free cortisol (UFC) and/or overnight oral dexamethasone (1 mg) suppression test; (4) α subunit, follicle-stimulating hormone (FSH), and luteinizing hormone (LH); and (5) thyroid function tests. Additional hormonal evaluation may be indicated based on the results of these tests. Pending more detailed assessment of hypopituitarism, a menstrual history, measurement of testosterone and 8 A.M. cortisol levels, and thyroid function tests usu­ ally identify patients with pituitary hormone deficiencies that require hormone replacement before further testing or surgery (Chap. 391). Pituitary Tumor Syndromes CHAPTER 392 Histologic Evaluation  Immunohistochemical staining of pitu­ itary tumor specimens obtained at transsphenoidal surgery for hor­ mones as well as cell-type specific transcription factors confirms clinical and laboratory studies and provides a histologic diagnosis when hormone studies are equivocal and in cases of clinically non­ functioning tumors. TREATMENT Hypothalamic, Pituitary, and Other Sellar Masses OVERVIEW Successful management of sellar masses requires accurate diagnosis as well as selection of optimal therapeutic modalities. Most pitu­ itary tumors are benign and slow growing. Clinical features result from local mass effects and hormonal hyper- or hyposecretion syndromes caused directly by the adenoma or occurring as a conse­ quence of treatment. Thus, lifelong management and follow-up are necessary for these patients. MRI with gadolinium enhancement for pituitary visualiza­ tion, new advances in transsphenoidal surgery and in stereotactic radiotherapy, and novel therapeutic agents have improved pitu­ itary tumor management. The goals of pituitary tumor treatment include normalization of excess pituitary secretion, amelioration of symptoms and signs of hormonal hypersecretion syndromes, and shrinkage or ablation of large tumor masses with relief of adjacent structure compression. Residual anterior pituitary function should be preserved during treatment and sometimes can be restored by removing the tumor mass. Ideally, adenoma recurrence should be prevented. TRANSSPHENOIDAL SURGERY Transsphenoidal resection is the desired surgical approach for pituitary tumors, except for the rare invasive suprasellar mass sur­ rounding the frontal or middle fossa or the optic nerves or invad­ ing posteriorly behind the clivus, which may require transcranial approaches. Intraoperative microscopy facilitates visual distinc­ tion between adenomatous and normal pituitary tissue as well as microdissection of small tumors that may not be visible by MRI (Fig. 392-3). Endoscopic techniques with three-dimensional intraoperative localization enable better visualization and access to tumor tissue. Transsphenoidal surgery also avoids cranial invasion and manipulation of brain tissue required by subfrontal surgical

PART 12 Endocrinology and Metabolism A B FIGURE 392-1  Expanding pituitary mass. Pituitary mass expansion may (A) impinge vital soft tissue structures and (B) invade the sphenoid sinus. (Reproduced with permission from P Cappabianca et al: Size does not matter. The intrigue of giant adenomas: a true surgical challenge. Acta Neurochir (Wien) 156:2217, 2014.) FIGURE 392-2  Pituitary adenoma. Coronal T1-weighted postcontrast magnetic resonance image shows a homogeneously enhancing mass (arrowheads) in the sella turcica and suprasellar region compatible with a pituitary adenoma; the small arrows outline the carotid arteries.

approaches. Individual surgical experience is a major determinant of outcome efficacy with these techniques. In addition to correction of hormonal hypersecretion, pituitary surgery is indicated for mass lesions that impinge on surround­ ing structures. Surgical decompression and resection are required for an expanding pituitary mass, which may be asymptomatic or accompanied by persistent headache, progressive visual field defects, cranial nerve palsies, hydrocephalus, and, occasionally, intrapituitary hemorrhage and apoplexy. Transsphenoidal surgery rarely is used for pituitary tissue biopsy to establish a histologic diagnosis. Whenever possible, the pituitary mass lesion should be selectively excised; normal pituitary tissue should be manipulated or resected only when critical for effective mass dissection. Non­ selective hemihypophysectomy or total hypophysectomy may be indicated if no hypersecreting mass lesion is clearly discernible, multifocal lesions are present, or the remaining nontumorous pitu­ itary tissue is obviously necrotic. This strategy, however, increases the likelihood of postoperative hypopituitarism and the need for lifelong hormone replacement. Preoperative mass effects, including visual field defects and compromised pituitary function, may be reversed by surgery, par­ ticularly when the deficits are not long-standing. For large and invasive tumors, it is necessary to determine the optimal balance between maximal tumor resection and preservation of anterior pituitary hormonal function, especially for preserving growth and

TABLE 392-2  Screening Tests for Functional Pituitary Adenomas   TEST COMMENTS Acromegaly Serum IGF-1 Oral glucose tolerance test with GH obtained at 0, 30, and 60 min Interpret IGF-1 relative to age- and sex-matched controls Normal subjects should suppress growth hormone to <1 μg/L Prolactinoma Serum PRL Exclude medications MRI of the sella should be ordered if PRL is elevated Cushing’s disease 24-h urinary free cortisol Dexamethasone (1 mg) at 11 P.M. and fasting plasma cortisol measured at 8 A.M. Late night salivary cortisol ACTH assay CRH stimulation test with measurements of cortisol and ACTH from peripheral and/or petrosal sinus blood  Ensure urine collection is total and accurate Normal subjects suppress to <5 μg/dL Distinguishes adrenal adenoma (ACTH suppressed) from ectopic ACTH or Cushing’s disease (ACTH normal or elevated) The CRH test is used primarily to distinguish pituitary adenomas from ectopic ACTH sources Gonadotropinoma Baseline FSH, LH, free α subunit, ovarian hyperstimulation, estrogen (females), testosterone (males) TRH stimulation test with assays for LH, FSH, free α subunit, free LHβ, free FSHβ subunits Rare; more commonly nonfunctioning adenomas Consider screening for hypopituitarism Some gonadotropinomas exhibit an inappropriate gonadotropin response to TRH TSH-producing adenoma Free T4, free T3, TSH, free α subunit Key feature is an inappropriately normal or high TSH in the setting of elevated free T4 and T3 Abbreviations: ACTH, adrenocorticotropin hormone; CRH, corticotropin-releasing hormone; FSH, follicle-stimulating hormone; GH, growth hormone; IGF-1, insulin-like growth factor 1; LH, luteinizing hormone; MRI, magnetic resonance imaging; PRL, prolactin; TSH, thyroid-stimulating hormone. reproductive function in younger patients. Tumor invasion outside the sella is rarely amenable to surgical cure, and the surgeon must judge the risk-versus-benefit ratio of extensive tumor resection. Side Effects  Tumor size, the degree of invasiveness, and experi­ ence of the surgeon largely determine the incidence of surgical com­ plications. Operative mortality rate is ~1%. Transient AVP-D and hypopituitarism occur in up to 20% of patients. Permanent AVP-D, cranial nerve damage, nasal septal perforation, or visual distur­ bances may be encountered in up to 10% of patients. CSF leaks occur in 4% of patients. Less common complications include carotid artery injury, loss of vision, hypothalamic damage, and meningitis. Permanent side effects are rare after surgery for microadenomas. RADIATION Radiation is used either as a primary therapy for pituitary or parasellar masses or, more commonly, as an adjunct to surgery or medical therapy. Focused megavoltage irradiation is achieved by precise MRI localization, using a high-voltage linear accelerator and accurate isocentric rotational arcing. A major determinant of accu­ rate irradiation is reproduction of the patient’s head position during multiple visits and maintenance of absolute head immobility. A total of <50 Gy (5000 rad) is given as 180 cGy (180 rad) fractions divided over ~6 weeks. Stereotactic radiosurgery delivers a large single high-energy dose from a cobalt-60 source (Gamma Knife), linear accelerator, or cyclotron. Long-term effects of Gamma Knife sur­ gery appear to be similar to those encountered with conventional radiation. Proton beam therapy is available in some centers and provides concentrated radiation doses within a localized region.

Optic chiasm Pituitary tumor Internal carotid artery Oculomotor nerve Venus plexus of cavernous sinus Trochlear nerve Trigeminal nerve Sphenoid sinus Pituitary Tumor Syndromes CHAPTER 392 Sphenoid bone Nasal septum Surgical curette Pituitary tumor Sphenoid sinus FIGURE 392-3  Transsphenoidal resection of pituitary mass via the endonasal approach. The role of radiation therapy in pituitary tumor management depends on the nature and anatomic location of the tumor, the age of the patient, and the availability of surgical and radiation exper­ tise. Because of its relatively slow onset of action, radiation therapy is usually reserved for postsurgical management. As an adjuvant to surgery, radiation is used to treat residual tumor in an attempt to prevent persistent growth or recurrence. Irradiation offers the only means for potentially ablating significant postoperative residual nonfunctioning tumor tissue. By contrast, PRL-, growth hormone (GH)–, adrenocorticotropin hormone (ACTH)–, and thyrotropin (thyroid-stimulating hormone [TSH])–secreting residual tumor tis­ sues are amenable to medical therapy. Side Effects  In the short term, radiation may cause transient nau­ sea and weakness. Alopecia and loss of taste and smell may be more long-lasting. Failure of pituitary hormone synthesis is common in patients who have undergone head and neck or pituitary-directed irradiation. More than 50% of patients develop loss of GH, ACTH, TSH, and/or gonadotropin secretion within 10 years, usually due to hypothalamic damage. Lifelong follow-up with testing of anterior pituitary hormone reserve is therefore required after radiation treatment. Optic nerve damage with impaired vision due to optic neuritis is reported in ~2% of patients who undergo pituitary irradi­ ation. Cranial nerve damage is uncommon now that radiation doses are <2 Gy (200 rad) at any one treatment session and the maximum dose is <50 Gy (5000 rad). The use of stereotactic radiotherapy reduces the risk of damage to adjacent structures. Conventional

radiotherapy for pituitary tumors has been associated with adverse mortality rates, mainly from cerebrovascular disease. The cumula­ tive risk of developing a secondary tumor after conventional radia­ tion is 1.3% after 10 years and 1.9% after 20 years. MEDICAL Medical therapy for pituitary tumors is highly specific and depends on tumor type. For prolactinomas, dopamine agonists are the treatment of choice. For acromegaly, somatostatin receptor ligands (SRLs) and a GH receptor antagonist are indicated. For TSHsecreting tumors, SRLs and occasionally dopamine agonists are indicated. ACTH-secreting tumors may respond to SRLs, and adrenal-directed therapy may also be of benefit. Nonfunctioning tumors are generally not responsive to medications and require surgery and/or irradiation.

PART 12 Endocrinology and Metabolism ■ ■SELLAR MASSES Sellar masses may arise from brain, hypothalamic, or pituitary tissues. Each exhibit features related to the lesion location but also unique to the specific etiology. Unique MRI characteristics inform the differen­ tial diagnosis of pituitary masses (Fig. 392-4). Lesions involving the anterior and preoptic hypothalamic regions cause paradoxical vasoconstriction, tachycardia, and hyperthermia. Acute hyperthermia usually is due to a hemorrhagic insult, but poi­ kilothermia may also occur. Central disorders of thermoregulation result from posterior hypothalamic damage. The periodic hypothermia syndrome is characterized by episodic attacks of rectal temperatures <30°C (86°F), sweating, vasodilation, vomiting, and bradycardia (Chap. 477). Damage to the ventromedial hypothalamic nuclei by cra­ niopharyngiomas, hypothalamic trauma, or inflammatory disorders may be associated with hyperphagia and obesity. This region appears to contain an energy-satiety center where melanocortin receptors are influenced by leptin, insulin, pro-opiomelanocortin (POMC) products, and gastrointestinal peptides (Chap. 413). Polydipsia and hypodipsia are associated with damage to central osmoreceptors located in preoptic nuclei (Chap. 393). Slow-growing hypothalamic lesions can cause increased somnolence and disturbed sleep cycles as well as obesity, hypothermia, and emotional outbursts. Lesions of the central hypothalamus may stimulate sympathetic neurons, leading to A B C FIGURE 392-4  Imaging differential diagnosis of sellar masses. A. Microadenoma. B. Macroadenoma. C. Craniopharyngioma. D. Hypophysitis with stalk thickening. (A, B, D: Used with permission from Vivien Bonert, MD. C: Reproduced with permission from Muller HL: Childhood craniopharyngioma. Recent advances in diagnosis, treatment and follow-up. Horm Res 69:193, 2008.)

elevated serum catecholamine and cortisol levels. These patients are predisposed to cardiac arrhythmias, hypertension, and gastric erosions. Craniopharyngiomas are benign, suprasellar cystic masses that present with headaches, visual field deficits, and variable degrees of hypopituitarism. They are derived from Rathke’s pouch and arise near the pituitary stalk, commonly extending into the suprasellar cistern. Craniopharyngiomas are often large, cystic, and locally invasive. Many are partially calcified, exhibiting a characteristic appearance on skull x-ray and CT images. More than half of all patients present before age 20, usually with signs of increased intracranial pressure, includ­ ing headache, vomiting, papilledema, and hydrocephalus. Associated symptoms include visual field abnormalities, personality changes and cognitive deterioration, cranial nerve damage, sleep difficulties, and weight gain accompanied by features of the metabolic syndrome. Hypopituitarism is documented in ~90%, and AVP-D occurs in ~10% of patients. About half of affected children present with growth retar­ dation. MRI is generally superior to CT for evaluating cystic structure and tissue components of craniopharyngiomas. CT is useful to define calcifications and evaluate invasion into surrounding bony structures and sinuses. Treatment usually involves transcranial or transsphenoidal surgi­ cal resection followed by postoperative radiation of residual tumor. Surgery alone is curative in less than half of patients because of recur­ rences due to adherence to vital structures or because of small tumor deposits in the hypothalamus or brain parenchyma. The goal of surgery is to remove as much tumor as possible without risking complications associated with efforts to remove firmly adherent or inaccessible tissue. In the absence of radiotherapy, ~75% of craniopharyngiomas recur, and 10-year survival is <50%. In patients with incomplete resection, radiotherapy improves 10-year survival to 70–90% but is associated with increased risk of secondary malignancies. Most patients require lifelong pituitary hormone replacement. As some craniopharyngiomas (particularly papillary) are associated with activated BRAF V600E mutations, use of BRAF inhibitors (dabrafenib or vemurafenib) either alone or in combination with MEK inhibitors (trametinib or cobi­ metinib) has resulted in long-term growth responses in some patients. Developmental failure of Rathke’s pouch obliteration may lead to Rathke’s cysts, which are small (<5 mm) cysts entrapped by squamous epithelium and are found in ~20% of individuals at autopsy. Although D

Rathke’s cysts do not usually grow and are often diagnosed inciden­ tally, about a third present in adulthood with compressive symptoms, AVP-D, and hyperprolactinemia due to stalk compression. Rarely, hydrocephalus develops. The diagnosis is suggested preoperatively by visualizing the cyst wall on MRI, which distinguishes these lesions from craniopharyngiomas. Cyst contents range from CSF-like fluid to mucoid material. Arachnoid cysts are rare and generate an MRI image that is isointense with CSF. Sellar chordomas usually present with bony clival erosion, local invasiveness, and, on occasion, calcification. Normal pituitary tissue may be visible on MRI, distinguishing chordomas from aggressive pitu­ itary adenomas. Mucinous material may be obtained by fine-needle aspiration. Meningiomas arising in the sellar region may be difficult to distin­ guish from nonfunctioning pituitary adenomas. Meningiomas typi­ cally enhance on MRI and may show evidence of calcification or bony erosion. Meningiomas may cause compressive symptoms. Histiocytosis X includes a variety of syndromes associated with foci of eosinophilic granulomas. AVP-D, exophthalmos, and punched-out lytic bone lesions (Hand-Schüller-Christian disease) are associated with granulomatous lesions visible on MRI, as well as a characteristic axil­ lary skin rash. Rarely, the pituitary stalk may be involved. Pituitary metastases occur in ~3% of cancer patients. Bloodborne metastatic deposits are found almost exclusively in the posterior pitu­ itary. Accordingly, AVP-D can be a presenting feature of lung, gastro­ intestinal, breast, and other pituitary metastases. About half of pituitary metastases originate from breast cancer; ~25% of patients with meta­ static breast cancer have such deposits. Rarely, pituitary stalk involve­ ment results in anterior pituitary insufficiency. The MRI diagnosis of a metastatic lesion may be difficult to distinguish from an aggressive pituitary adenoma; the diagnosis may require histologic examination of excised tumor tissue. Primary or metastatic lymphoma, leukemias, and plasmacytomas also occur within the sella. Hypothalamic hamartomas and gangliocytomas may arise from astrocytes, oligodendrocytes, and neurons with varying degrees of differentiation. These tumors may overexpress hypothalamic neuro­ peptides, including gonadotropin-releasing hormone (GnRH), growth hormone–releasing hormone (GHRH), and corticotropin-releasing hormone (CRH). With GnRH-producing tumors, children present with precocious puberty, psychomotor delay, and laughing-associated seizures. Medical treatment of GnRH-producing hamartomas with long-acting GnRH analogues effectively suppresses gonadotropin secretion and controls premature pubertal development. Rarely, ham­ artomas also are associated with craniofacial abnormalities; imperfo­ rate anus; cardiac, renal, and lung disorders; and pituitary failure as features of Pallister-Hall syndrome, which is caused by mutations in the carboxy terminus of the GLI3 gene. Hypothalamic hamartomas are often contiguous with the pituitary, and preoperative MRI diagnosis may not be possible. Histologic evidence of hypothalamic neurons in tissue resected at transsphenoidal surgery may be the first indication of a primary hypothalamic lesion. Hypothalamic gliomas and optic gliomas occur mainly in childhood and usually present with visual loss. Adults have more aggressive tumors; about a third are associated with neurofibromatosis. Brain germ cell tumors may arise within the sellar region. They include dysgerminomas, which frequently are associated with AVP-D and visual loss. They rarely metastasize. Germinomas, embryonal car­ cinomas, teratomas, and choriocarcinomas may arise in the parasellar region and produce human chorionic gonadotropin (hCG). These germ cell tumors present with precocious puberty, AVP-D, visual field defects, and thirst disorders. Many patients are GH deficient with short stature. ■ ■PITUITARY ADENOMAS AND HYPERSECRETION SYNDROMES Pituitary adenomas are the most common cause of pituitary hormone hypersecretion and hyposecretion syndromes in adults. They account for ~15% of all intracranial neoplasms and have been identified with a population prevalence of ~80/100,000. At autopsy, up to one-quarter

of all pituitary glands harbor an unsuspected microadenoma (<10 mm diameter). Similarly, pituitary imaging detects small clinically inappar­ ent pituitary lesions in at least 10% of individuals.

Pathogenesis  Pituitary adenomas are benign neoplasms that arise from one of the five anterior pituitary cell types. The clinical and bio­ chemical phenotypes of pituitary adenomas depend on the cell type from which they are derived. Thus, tumors arising from lactotrope (PRL), somatotrope (GH), corticotrope (ACTH), thyrotrope (TSH), or gonadotrope (LH, FSH) cells hypersecrete their respective hormones (Table 392-3). Plurihormonal tumors express various combinations of GH, PRL, TSH, ACTH, or the glycoprotein hormone α or β subunits. They may be diagnosed by careful immunocytochemistry of specific hormone and transcription factor expression or may manifest as clini­ cal syndromes that combine features of these hormonal hypersecretory syndromes. Morphologically, these tumors may arise from a single polysecreting cell type or include cells with mixed function within the same tumor. Pituitary Tumor Syndromes CHAPTER 392 Hormonally active tumors are characterized by autonomous hor­ mone secretion with diminished feedback responsiveness to physi­ ologic inhibitory pathways. Hormone production does not always correlate with tumor size. Small hormone-secreting adenomas may cause significant clinical perturbations, whereas larger adenomas that produce less hormone may be clinically silent and remain undiagnosed (if no central compressive effects occur). About one-third of all adeno­ mas are clinically nonfunctioning and produce no distinct clinical hypersecretory syndrome. Most of them arise from gonadotrope cells and may secrete small amounts of α- and β-glycoprotein hormone subunits or, very rarely, intact circulating gonadotropins. True pituitary carcinomas with documented extracranial metastases are exceedingly rare. Almost all pituitary adenomas are monoclonal in origin, implying the acquisition of one or more somatic mutations that confer a selec­ tive growth advantage. Consistent with their clonal origin, complete surgical resection of small pituitary adenomas usually cures hormone hypersecretion. Nevertheless, hypothalamic hormones such as GHRH and CRH also enhance mitotic activity of their respective pituitary tar­ get cells in addition to their role in pituitary hormone regulation. Thus, patients who harbor rare abdominal or chest tumors that produce ectopic GHRH or CRH may present with somatotrope or corticotrope hyperplasia with GH or ACTH hypersecretion. TABLE 392-3  Classification of Pituitary Adenomasa HORMONE PRODUCT CLINICAL SYNDROME ADENOMA CELL ORIGIN Lactotrope PRL Hypogonadism, galactorrhea Gonadotrope FSH, LH, subunits Silent/nonfunctioning, ovarian hyperstimulation, hypogonadism Somatotrope GH Acromegaly/gigantism Corticotrope ACTH/none Cushing’s disease or silent Mixed lactotrope and somatotrope GH, PRL Acromegaly, hypogonadism, galactorrhea Other plurihormonal cell Any Mixed Acidophil stem cell PRL, GH Hypogonadism, galactorrhea, acromegaly Mammosomatotrope PRL, GH Hypogonadism, galactorrhea, acromegaly Thyrotrope TSH Thyrotoxicosis Null cell None Hypopituitarism/none Oncocytoma None Hypopituitarism/none aHormone-secreting tumors are listed in decreasing order of frequency. All tumors may cause local pressure effects, including visual disturbances, cranial nerve palsy, and headache. Note: For abbreviations, see text. Source: Reproduced with permission from S Melmed: Pathogenesis of pituitary tumors. Nat Rev Endocrinol 7:257, 2011.

Several etiologic genetic events have been implicated in the develop­ ment of pituitary tumors. The pathogenesis of sporadic forms of acro­ megaly has been particularly informative as a model of tumorigenesis. GHRH, after binding to its G protein–coupled somatotrope receptor, uses cyclic adenosine monophosphate (AMP) as a second messenger to stimulate GH secretion and somatotrope proliferation. A subset (~35%) of GH-secreting pituitary tumors contains sporadic mutations in Gsα. These mutations attenuate intrinsic GTPase activity, resulting in constitutive elevation of cyclic AMP, Pit-1 induction, and activation of cyclic AMP response element binding protein (CREB), thereby pro­ moting somatotrope cell proliferation and GH secretion.

Growth factors may also promote pituitary tumor proliferation. Basic fibroblast growth factor (bFGF) is abundant in the pituitary and stimulates pituitary cell mitogenesis, whereas epidermal growth factor receptor (EGFR) signaling induces both hormone synthesis and cell proliferation. Mutations of USP8 may result in overexpressed EGFR in a subset of ACTH-secreting tumors. Other factors involved in initiation and promotion of pituitary tumors include loss of negativefeedback inhibition (as seen with primary hypothyroidism or hypo­ gonadism) and estrogen-mediated or paracrine angiogenesis. Growth characteristics and neoplastic behavior also may be influenced by activated oncogenes, including RAS and pituitary tumor transforming gene (PTTG), or inactivation of growth suppressor genes, including MEG3. Pituitary adenomas exhibit lineage-specific features of cellcycle disruption, including cellular senescence, with chromosomal instability and copy number alterations as well as elevated levels of CDK inhibitors. These features underlie the invariably benign nature of these adenomas. PART 12 Endocrinology and Metabolism Genetic Syndromes Associated with Pituitary Tumors  Several familial syndromes are associated with pituitary tumors, and the genetic mechanisms for some of them have been unraveled (Table 392-4). Multiple endocrine neoplasia (MEN) 1 is an autosomal dominant syndrome characterized primarily by a genetic predisposition to para­ thyroid, pancreatic islet, and pituitary adenomas (Chap. 400). MEN 1 is caused by inactivating germline mutations in MENIN, a consti­ tutively expressed tumor-suppressor gene located on chromosome 11q13. Loss of heterozygosity or a somatic mutation of the remaining normal MENIN allele leads to tumorigenesis. About half of affected patients develop prolactinomas; acromegaly and Cushing’s disease are less commonly encountered. Carney complex is characterized by spotty skin pigmentation, myxo­ mas, and endocrine tumors, including testicular, adrenal, and pituitary adenomas. Acromegaly occurs in ~20% of these patients. A subset of patients has mutations in the R1α regulatory subunit of protein kinase A (PRKAR1A). TABLE 392-4  Familial Pituitary Tumor Syndromes (See Chap. 400)   GENE MUTATED CLINICAL FEATURES Multiple endocrine neoplasia 1 (MEN 1) MEN1 (11q13) Hyperparathyroidism Pancreatic neuroendocrine tumors Foregut carcinoids Adrenal adenomas Skin lesions Pituitary adenomas (40%) Multiple endocrine neoplasia 4 (MEN 4) CDKNIB (12p13) Hyperparathyroidism Pituitary adenomas Other tumors Carney complex PRKAR1A (17q23-24) Pituitary hyperplasia and adenomas (10%) Atrial myxomas Schwannomas Adrenal hyperplasia Lentigines Familial pituitary adenomas AIP (11q13.2) Acromegaly/gigantism (~15% of afflicted families)

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, pigmented skin patches, and a variety of endocrine disorders, includ­ ing acromegaly, adrenal adenomas, and autonomous ovarian function (Chap. 424). Hormonal hypersecretion results from constitutive cyclic AMP production caused by inactivation of the GTPase activity of Gsα. The Gsα mutations occur postzygotically, leading to a mosaic pattern of mutant expression. Familial acromegaly is a rare disorder in which family members may manifest either acromegaly or gigantism. A subset of families with a predisposition for familial pituitary tumors, especially acromegaly, has been found to harbor germline mutations in the AIP gene, which encodes the aryl hydrocarbon receptor interacting protein. ■ ■HYPERPROLACTINEMIA Etiology  Hyperprolactinemia is the most common pituitary hor­ mone hypersecretion syndrome in both men and women. PRL-secret­ ing pituitary adenomas (prolactinomas) are the most common cause of PRL levels >200 μg/L (see below). Less pronounced PRL elevation can also be seen with microprolactinomas but is more commonly caused by drugs, pituitary stalk compression, hypothyroidism, or renal failure (Table 392-5). Pregnancy and lactation are the important physiologic causes of hyperprolactinemia. Sleep-associated hyperprolactinemia reverts to normal within an hour of awakening. Nipple stimulation and sexual orgasm also may increase PRL. Chest wall stimulation or trauma (including chest surgery and herpes zoster) invokes the reflex suckling arc with resultant hyperprolactinemia. Chronic renal failure elevates PRL by decreasing peripheral clearance. Primary hypothyroidism is associated with mild hyperprolactinemia, probably because of com­ pensatory TRH secretion. Mutation of the PRL receptor is a rare cause of hyperprolactinemia. Lesions of the hypothalamic-pituitary region that disrupt hypo­ thalamic dopamine synthesis, portal vessel delivery, or lactotrope responses are associated with hyperprolactinemia. Thus, hypothalamic tumors, cysts, infiltrative disorders, and radiation-induced dam­ age cause elevated PRL levels, usually in the range of 30–100 μg/L. Plurihormonal adenomas (including GH and ACTH tumors) may hypersecrete PRL directly. Pituitary masses, including clinically non­ functioning pituitary tumors, may compress the pituitary stalk to cause hyperprolactinemia. Drug-induced inhibition or disruption of dopaminergic receptor function is a common cause of hyperprolactinemia (Table 392-5). Thus, antipsychotics and antidepressants are a relatively common cause of mild hyperprolactinemia. Most patients receiving risperidone have elevated PRL levels, sometimes exceeding 200 μg/L. Methyldopa inhibits dopamine synthesis, and verapamil blocks dopamine release, also leading to hyperprolactinemia. Hormonal agents that induce PRL include estrogens and thyrotropin-releasing hormone (TRH). Presentation and Diagnosis  Amenorrhea, galactorrhea, and infertility are the hallmarks of hyperprolactinemia in women. If hyper­ prolactinemia develops before menarche, primary amenorrhea results. More commonly, hyperprolactinemia develops later in life and leads to oligomenorrhea and ultimately to amenorrhea. If hyperprolactinemia is sustained, vertebral bone mineral density can be reduced compared with age-matched controls, particularly when it is associated with pro­ nounced hypoestrogenemia. Galactorrhea is present in up to 80% of hyperprolactinemic women. Although usually bilateral and spontane­ ous, it may be unilateral or expressed only manually. Patients also may complain of decreased libido, weight gain, and mild hirsutism. In men with hyperprolactinemia, diminished libido, infertility, and visual loss (from optic nerve compression) are the usual presenting symptoms. Gonadotropin suppression leads to reduced testosterone, impotence, and oligospermia. True galactorrhea is uncommon in men with hyperprolactinemia. If the disorder is long-standing, secondary effects of hypogonadism are evident, including osteopenia, reduced muscle mass, and decreased beard growth. The diagnosis of idiopathic hyperprolactinemia is made by exclu­ sion of known causes of hyperprolactinemia in the setting of a normal

TABLE 392-5  Etiology of Hyperprolactinemia I.  Physiologic hypersecretion   Pregnancy   Lactation   Chest wall stimulation   Sleep   Stress II.  Hypothalamic-pituitary stalk damage Pituitary adenoma with stalk compression Suprasellar mass   Craniopharyngioma   Meningioma   Dysgerminoma   Metastases Empty sella Lymphocytic hypophysitis Granulomas Rathke’s cyst Irradiation Trauma   Pituitary stalk section   Suprasellar surgery III.  Pituitary adenoma hypersecretion   Prolactinoma   Acromegaly IV.  Systemic disorders Chronic renal failure Hypothyroidism Cirrhosis Pseudocyesis Epileptic seizures V.  Drug-induced hypersecretion Dopamine receptor blockers   Atypical antipsychotics: risperidone   Phenothiazines: chlorpromazine, perphenazine   Butyrophenones: haloperidol   Thioxanthenes   Metoclopramide Dopamine synthesis inhibitors   α-Methyldopa Catecholamine depletors   Reserpine Opiates H2 antagonists   Cimetidine, ranitidine Imipramines   Amitriptyline, amoxapine Serotonin reuptake inhibitors   Fluoxetine Calcium channel blockers   Verapamil   Estrogens   Thyrotropin-releasing hormone Note: Hyperprolactinemia >200 μg/L almost invariably is indicative of a prolactinsecreting pituitary adenoma. Physiologic causes, hypothyroidism, and drug-induced hyperprolactinemia should be excluded before extensive evaluation. pituitary MRI. Some of these patients may harbor small microadeno­ mas below visible MRI sensitivity (~2 mm). ■ ■GALACTORRHEA Galactorrhea, the inappropriate discharge of milk-containing fluid from the breast, is considered abnormal if it persists longer than 6 months after childbirth or discontinuation of breast-feeding. Postpartum

galactorrhea associated with amenorrhea is a self-limiting disorder usually associated with moderately elevated PRL levels. Galactorrhea may occur spontaneously, or it may be elicited by nipple pressure. In both men and women, galactorrhea may vary in color and consistency (transparent, milky, or bloody) and arise either unilaterally or bilater­ ally. Mammography or ultrasound is indicated for bloody discharges (particularly from a single nipple), which may be caused by breast cancer. Galactorrhea is commonly associated with hyperprolactinemia caused by any of the conditions listed in Table 392-5. Acromegaly is associated with galactorrhea in about one-third of patients. Treatment of galactorrhea usually involves managing the underlying disorder (e.g., replacing T4 for hypothyroidism, discontinuing a medication, treating prolactinoma).

Pituitary Tumor Syndromes CHAPTER 392 Laboratory Investigation  Basal, fasting morning PRL levels (normally <20 μg/L) should be measured to assess hypersecretion. Both false-positive and false-negative results may be encountered. In patients with markedly elevated PRL levels (>1000 μg/L), reported results may be falsely lowered because of assay artifacts; sample dilution is required to measure these high values accurately. Falsely elevated values may be caused by aggregated forms of circulating PRL, which are usually biologically inactive (macroprolactinemia). Hypo­ thyroidism should be excluded by measuring TSH and T4 levels. TREATMENT Hyperprolactinemia Treatment of hyperprolactinemia depends on the cause of elevated PRL levels. Regardless of the etiology, however, treatment should be aimed at normalizing PRL levels to alleviate suppressive effects on gonadal function, halt galactorrhea, and preserve bone mineral density. Dopamine agonists are effective for most causes of hyper­ prolactinemia (see the treatment section for prolactinoma, below) regardless of the underlying cause. If the patient is taking a medication known to cause hyperprolac­ tinemia, the drug should be withdrawn, if possible. For psychiatric patients who require neuroleptic agents, supervised dose titration or the addition of a dopamine agonist can help restore normopro­ lactinemia and alleviate reproductive symptoms. However, dopa­ mine agonists may worsen the underlying psychiatric condition, especially at high doses. Hyperprolactinemia usually resolves after adequate thyroid hormone replacement in hypothyroid patients or after renal transplantation in patients undergoing dialysis. Resec­ tion of hypothalamic or sellar mass lesions can reverse hyperprolac­ tinemia caused by stalk compression and reduced dopamine tone. Granulomatous infiltrates occasionally respond to glucocorticoid administration. In patients with irreversible hypothalamic dam­ age, no treatment may be warranted. In up to 30% of patients with hyperprolactinemia—usually without a visible pituitary microad­ enoma—the condition may resolve spontaneously. ■ ■PROLACTINOMA Etiology and Prevalence  Tumors arising from lactotropes account for about half of all functioning pituitary tumors, with a popu­ lation prevalence of ~10/100,000 in men and ~30/100,000 in women. Mixed tumors that secrete combinations of GH and PRL, ACTH and PRL, and rarely TSH and PRL are also seen. These plurihormonal tumors are usually recognized by immunohistochemistry, sometimes without apparent clinical manifestations from the production of addi­ tional hormones. Microadenomas are classified as <1 cm in diameter and usually do not invade the parasellar region. Macroadenomas are ≥1 cm in diameter and may be locally invasive and impinge on adjacent structures. The female-to-male ratio for microprolactinomas is 20:1, whereas the sex ratio is near 1:1 for macroadenomas. Tumor size generally correlates directly with PRL concentrations; values

250 μg/L usually are associated with macroadenomas. Men tend to present with larger tumors than women, possibly because the features of male hypogonadism are less readily evident. PRL levels remain stable

in most patients, reflecting the slow growth of these tumors. About 5% of microadenomas progress in the long term to macroadenomas.

Presentation and Diagnosis  Women usually present with amen­ orrhea, infertility, and galactorrhea. If the tumor extends outside the sella, visual field defects or other mass effects may be seen. Men often present with impotence, loss of libido, infertility, or signs of central nervous system (CNS) compression, including headaches and visual defects. Assuming that physiologic and medication-induced causes of hyperprolactinemia are excluded (Table 392-5), the diagnosis of pro­ lactinoma is likely with a PRL level >200 μg/L. PRL levels <100 μg/L may be caused by microadenomas, other sellar lesions that decrease dopamine inhibition, or nonneoplastic causes of hyperprolactinemia. For this reason, an MRI should be performed in all patients with hyperprolactinemia. It is important to remember that hyperprolac­ tinemia caused secondarily by the mass effects of nonlactotrope lesions is also corrected by treatment with dopamine agonists despite failure to shrink the underlying mass. Consequently, PRL suppression by dopa­ mine agonists does not necessarily indicate that the underlying lesion is a prolactinoma. PART 12 Endocrinology and Metabolism TREATMENT Prolactinoma Because microadenomas rarely progress to become macroadeno­ mas, no treatment may be needed if patients are asymptomatic and fertility is not desired; these patients should be monitored by regular serial PRL measurements and MRI scans. For symptomatic microadenomas, therapeutic goals include control of hyperprolac­ tinemia, reduction of tumor size, restoration of menses and fertility, and resolution of galactorrhea. Dopamine agonist doses should be titrated to achieve maximal PRL suppression and restoration of reproductive function (Fig. 392-5). A normalized PRL level does not ensure reduced tumor size. However, tumor shrinkage usually is not seen in those who do not respond with lowered PRL levels. For macroadenomas, formal visual field testing should be performed before initiating dopamine agonists. MRI and visual fields should be assessed at 6- to 12-month intervals until the mass shrinks and annually thereafter until maximum size reduction has occurred. ELEVATED PROLACTIN LEVELS Exclude secondary causes of hyperprolactinemia MRI evidence for pituitary mass Symptomatic Prolactinoma Microadenoma Macroadenoma Titrate dopamine agonist Drug intolerance Titrate dopamine agonist Change dopamine agonist Serum PRL <20

50 (µg/L) 20–50 Maintenance Rx Consider Surgery Reassess diagnosis Increase dose FIGURE 392-5  Management of prolactinoma. MRI, magnetic resonance imaging; PRL, prolactin.

Oral dopamine agonists (cabergoline and bromocriptine) are the mainstay of therapy for patients with micro- or macroprolactinomas. Dopamine agonists suppress PRL secretion and synthesis as well as lactotrope proliferation. In patients with microadenomas who have achieved normoprolactinemia and significant reduction of tumor mass, the dopamine agonist may be withdrawn after 2 years. These patients should be monitored carefully for evidence of prolactinoma recurrence. About 20% of patients (especially males) are resistant to dopaminergic treatment; these adenomas may exhibit decreased D2 dopamine receptor numbers or a postreceptor defect. D2 receptor gene mutations in the pituitary have not been reported. Cabergoline  An ergoline derivative, cabergoline is a long-acting dopamine agonist with high D2 receptor affinity. The drug effectively suppresses PRL for >14 days after a single oral dose and induces prolactinoma shrinkage in most patients. Cabergoline (0.5–1.0 mg twice weekly) achieves normoprolactinemia and resumption of normal gonadal function in ~80% of patients with microadenomas; galactorrhea improves or resolves in 90% of patients. Cabergoline normalizes PRL and shrinks ~70% of macroprolactinomas. Mass effect symptoms, including headaches and visual disorders, usu­ ally improve dramatically within days after cabergoline initiation; improvement of sexual function requires several weeks of treat­ ment but may occur before complete normalization of PRL levels. MRI should be repeated within 16 weeks after initial therapy of macroadenomas as shrinkage of invasive adenomas may be striking (Fig. 392-6). After initial control of PRL levels has been achieved, cabergoline should be reduced to the lowest effective maintenance dose. In ~5% of treated patients harboring a microadenoma, hyper­ prolactinemia may resolve and not recur when dopamine agonists are discontinued after long-term treatment. Cabergoline also may be effective in patients resistant to bromocriptine. Adverse effects and drug intolerance are encountered less commonly than with bromocriptine. Bromocriptine  The ergot alkaloid bromocriptine mesylate is a dopamine receptor agonist that suppresses PRL secretion. Because it is short-acting, the drug is preferred when pregnancy is desired. Therapy is initiated by administering a low bromocriptine dose (0.625–1.25 mg) at bedtime with a snack, followed by gradually Test visual fields Test pituitary reserve function Repeat MRI within 4 months Tumor shrinkage and prolactin normalized No tumor shrinkage or tumor growth or persistent hyperprolactinemia Monitor PRL and repeat MRI annually

A B C D FIGURE 392-6  Large invasive prolactinoma successfully treated with cabergoline. A–B. Prolactin-secreting macroadenoma in a 32-year-old male measuring 5.6 × 6.9 cm invading the skull base. PRL level was 122,260 μg/L. Four days after cabergoline was started, PRL was 10,823 μg/L and dropped to 772 μg/L after 3 weeks. C–D. Substantial tumor regression after 40 months of treatment, with PRL levels stable at 25 μg/L. (Reproduced with permission from M Ahmed, O Al-Nozha: Images in clinical medicine. Large prolactinoma. N Engl J Med 363:177, 2010.) increasing the dose. Most patients are controlled with a daily dose of <7.5 mg (2.5 mg tid). SIDE EFFECTS Side effects of dopamine agonists include constipation, nasal stuffi­ ness, dry mouth, nightmares, insomnia, and vertigo; decreasing the dose usually alleviates these problems. Nausea, vomiting, and postural hypotension with faintness may occur in ~25% of patients after the initial dose. These symptoms may persist in some patients. In general, fewer side effects are reported with cabergoline. For the ~15% of patients who are intolerant of oral bromocriptine, cabergoline may be better tolerated. Intravaginal administration of bromocriptine is often efficacious in patients with intractable gastrointestinal side effects. Auditory hallucinations, delusions, mood swings, and impulse control disorders have been reported in up to 5% of patients and may be due to the dopamine agonist properties or to the lysergic acid derivative of the compounds. Rare reports of leukopenia, thrombocytopenia, pleural fibrosis, car­ diac arrhythmias, and hepatitis have been described. Patients with Parkinson disease who receive at least 3 mg of cabergoline daily have been reported to be at risk for development of cardiac valve

Pituitary Tumor Syndromes CHAPTER 392 regurgitation. Studies analyzing >500 prolactinoma patients receiv­ ing recommended doses of cabergoline (up to 2 mg weekly) have shown no evidence for an increased incidence of valvular disorders. Nevertheless, because no controlled prospective studies in pituitary tumor patients are available, it is prudent to perform echocardio­ grams before initiating standard-dose cabergoline therapy. Surgery  Surgical adenoma debulking may be indicated for dopa­ mine resistance or intolerance as well as the presence of an invasive macroadenoma with compromised vision that fails to improve after drug treatment. Initial PRL normalization is achieved in ~70% of microprolactinomas after surgical resection, but only 40% of mac­ roadenomas can be resected successfully. Follow-up studies have shown that hyperprolactinemia recurs in up to 20% of patients within the first year after surgery; long-term recurrence rates may exceed 50% for macroadenomas. Radiotherapy for prolactinomas is reserved for patients with aggressive tumors that do not respond to maximally tolerated dopamine agonists and/or surgery. PREGNANCY The pituitary increases in size during pregnancy, reflecting the stimulatory effects of estrogen and perhaps other growth factors

on pituitary vascularity and lactotrope hyperplasia. About 5% of microadenomas significantly increase in size, but 15–30% of macroadenomas grow during pregnancy. Bromocriptine has been used for >30 years to restore fertility in women with hyperprolac­ tinemia, without evidence of teratogenic effects. Nonetheless, most authorities recommend strategies to minimize fetal exposure to the drug. For women taking bromocriptine who desire pregnancy, mechanical contraception should be used through three regular menstrual cycles to allow for conception timing. When pregnancy is confirmed, bromocriptine should be discontinued and PRL levels followed serially, especially if headaches or visual symptoms occur. For women harboring macroadenomas, regular visual field test­ ing is recommended, and the drug should be reinstituted if tumor growth is apparent. Although pituitary MRI may be safe during pregnancy, this procedure should be reserved for symptomatic patients with severe headache and/or visual field defects. Surgical decompression may be indicated if vision is threatened. Although comprehensive data support the efficacy and relative safety of bromocriptine-facilitated fertility, patients should be advised of potential unknown deleterious effects and the risk of tumor growth during pregnancy. Because cabergoline is long-acting with a high D2-receptor affinity, it is not recommended for use in women when fertility is desired.

PART 12 Endocrinology and Metabolism ■ ■ACROMEGALY Etiology  GH hypersecretion is usually the result of a somato­ trope adenoma but may rarely be caused by extrapituitary lesions (Table 392-6). In addition to the more common GH-secreting somato­ trope adenomas, mixed mammosomatotrope tumors and acidophilic stem cell adenomas secrete both GH and PRL. In patients with acido­ philic stem cell adenomas, features of hyperprolactinemia (hypogo­ nadism and galactorrhea) predominate over the less clinically evident signs of acromegaly. Occasionally, mixed plurihormonal tumors are encountered that also secrete ACTH, the glycoprotein hormone α subunit, or TSH in addition to GH. Patients with partially empty sel­ lae may present with GH hypersecretion due to a small GH-secreting adenoma within the compressed rim of pituitary tissue; some of these may reflect the spontaneous necrosis of tumors that were previously TABLE 392-6  Causes of Acromegaly   PREVALENCE, % Excess Growth Hormone Secretion Pituitary   Densely or sparsely granulated GH cell adenoma   Mixed GH cell and PRL cell adenoma   Mammosomatotrope cell adenoma   Plurihormonal adenoma   GH cell carcinoma or metastases   Multiple endocrine neoplasia 1 (GH cell adenoma)   McCune-Albright syndrome   Ectopic sphenoid or parapharyngeal sinus pituitary

adenoma Extrapituitary tumor   Pancreatic islet cell tumor   Lymphoma   <1 Excess Growth Hormone–Releasing Hormone Secretion Central   Hypothalamic hamartoma, choristoma, ganglioneuroma Peripheral   Bronchial carcinoid, pancreatic islet cell tumor, small- <1   <1 cell lung cancer, adrenal adenoma, medullary thyroid carcinoma, pheochromocytoma Abbreviations: GH, growth hormone; PRL, prolactin. Source: Data from S Melmed: Medical progress: Acromegaly. N Engl J Med 355:2558, 2006.

larger. GH-secreting tumors rarely arise from ectopic pituitary tissue remnants in the nasopharynx or midline sinuses. There are case reports of ectopic GH secretion by tumors of pan­ creatic, ovarian, lung, or hematopoietic origin. Rarely, excess GHRH production may cause acromegaly because of chronic stimulation of somatotropes. These patients present with classic features of acromeg­ aly, elevated GH levels, pituitary enlargement on MRI, and pathologic characteristics of pituitary hyperplasia. The most common cause of GHRH-mediated acromegaly is a chest or abdominal carcinoid tumor. Although these tumors usually express positive GHRH immunoreac­ tivity, clinical features of acromegaly are evident in only a minority of patients with carcinoid disease. Excessive GHRH also may be elabo­ rated by hypothalamic tumors, usually choristomas or neuromas. Presentation and Diagnosis  Protean manifestations of GH and IGF-1 hypersecretion are indolent and often are not clinically diag­ nosed for 10 years or more. Acral bony overgrowth results in frontal bossing, increased hand and foot size, mandibular enlargement with prognathism, and widened space between the lower incisor teeth. In children and adolescents, initiation of GH hypersecretion before epiphyseal long bone closure is associated with development of pitu­ itary gigantism (Fig. 392-7). Soft tissue swelling results in increased heel pad thickness, increased shoe or glove size, ring tightening, characteristic coarse facial features, and a large fleshy nose. Other commonly encountered clinical features include hyperhidrosis, a deep and hollow-sounding voice, oily skin, arthropathy, kyphosis, carpal tunnel syndrome, proximal muscle weakness and fatigue, acanthosis nigricans, and skin tags. Generalized visceromegaly occurs, including cardiomegaly, macroglossia, and thyroid gland enlargement. The most significant clinical impact of GH excess occurs with respect to the cardiovascular system. Cardiomyopathy with arrhyth­ mias, left ventricular hypertrophy, decreased diastolic function, and hypertension ultimately occur in most patients if untreated. Upper airway obstruction with sleep apnea occurs in >60% of patients and is associated with both soft tissue laryngeal airway obstruction and central sleep dysfunction. Diabetes mellitus develops in 25% of patients with acromegaly, and most patients are intolerant of a glucose load (as GH counteracts the action of insulin). Acromegaly is associated with an increased risk of colon polyps and mortality from colonic malig­ nancy; polyps are diagnosed in up to one-third of patients. Overall mortality is increased about threefold and is due primarily to cardio­ vascular and cerebrovascular disorders and respiratory disease. Unless GH levels are controlled, survival is reduced by an average of 10 years compared with an age-matched control population. Laboratory Investigation  Age-matched serum IGF-1 levels are elevated in acromegaly. Consequently, an IGF-1 level provides a use­ ful laboratory screening measure when clinical features raise the possibility of acromegaly. Owing to the pulsatility of GH secretion, measurement of a single random GH level is not useful for the diag­ nosis or exclusion of acromegaly and does not correlate with disease severity. The diagnosis of acromegaly is confirmed by demonstrating the failure of GH suppression to <0.4 μg/L within 1–2 h of an oral glucose load (75 g). When ultrasensitive GH assays are used, normal nadir GH levels are even lower (<0.05 μg/L). About 20% of patients exhibit a paradoxical GH rise after glucose. PRL should be measured, as it is elevated in ~25% of patients with acromegaly. Thyroid function, gonadotropins, and sex steroids may be attenuated because of tumor mass effects. Because most patients will undergo surgery with gluco­ corticoid coverage, tests of ACTH reserve in asymptomatic patients are more efficiently deferred until after surgery. TREATMENT Acromegaly The goal of treatment is to control GH and IGF-1 hypersecretion, ablate or arrest tumor growth, ameliorate comorbidities, restore mortality rates to normal, and preserve pituitary function. Surgical resection of GH-secreting adenomas is the initial treat­ ment for most patients (Fig. 392-8). SRLs are used as adjuvant

A FIGURE 392-7  Features of acromegaly/gigantism. A 22-year-old man with gigantism due to excess growth hormone is shown to the left of his identical twin. The increased height and prognathism (A) and enlarged hand (B) and foot (C) of the affected twin are apparent. Their clinical features began to diverge at the age of ~13 years. (Reproduced with permission from RF Gagel, IE McCutcheon. Images in clinical medicine. Pituitary gigantism. N Engl J Med 340:524, 1999.) treatment for preoperative shrinkage of large invasive macroadeno­ mas, immediate relief of debilitating symptoms, and reduction of GH hypersecretion; in frail patients experiencing morbidity; and in patients who decline surgery or when surgery fails to achieve bio­ chemical control. Irradiation or repeat surgery may be required for patients who cannot tolerate or do not respond to adjunctive medi­ cal therapy. The high rate of late hypopituitarism and the slow rate (5–15 years) of biochemical response are the main disadvantages of radiotherapy. Irradiation is also relatively ineffective in normal­ izing IGF-1 levels. Stereotactic ablation of GH-secreting adenomas by Gamma Knife radiotherapy is promising, but long-term results and side effects appear similar to those observed with conventional radiation. SRLs may be required while awaiting the full benefits of radiotherapy. Systemic comorbid sequelae of acromegaly, including cardiovascular disease, diabetes, and arthritis, should be managed aggressively. Mandibular surgical repair may be indicated. SURGERY Transsphenoidal surgical resection by an experienced surgeon is the preferred primary treatment for both microadenomas (remission rate ~70%) and macroadenomas (<50% in remission). Soft tissue swelling improves immediately after tumor resection. GH levels return to normal within an hour, and IGF-1 levels are normalized within 3–4 days. In ~10% of patients, acromegaly may recur several years after apparently successful surgery; hypopituitarism develops in up to 15% of patients after surgery. SOMATOSTATIN RECEPTOR LIGANDS SRLs exert their therapeutic effects through SST2 and SST5 receptor subtypes, both expressed by GH-secreting tumors. The preferred medical treatments for patients with acromegaly include long-acting injectable SRL depot formulations of octreo­ tide and lanreotide as well as oral octreotide capsules. Although responses vary widely in individual patients, meta-analyses indi­ cate that GH and IGF-1 levels are normalized in ~50% of patients. Octreotide acetate is an eight-amino-acid synthetic somatosta­ tin analogue. In contrast to native somatostatin, the analogue is

Pituitary Tumor Syndromes CHAPTER 392 B C relatively resistant to plasma degradation. It has a 2-h serum halflife and possesses 40-fold greater potency than native somatostatin to suppress GH. Octreotide LAR is a sustained-release, long-acting formulation of octreotide incorporated into microspheres that sus­ tain drug levels for several weeks after intramuscular injection. GH suppression occurs for as long as 6 weeks after a 30-mg intra­ muscular injection; long-term monthly treatment sustains GH and IGF-1 suppression and also reduces pituitary tumor size in ~50% of patients. Lanreotide, in a slow-release depot SRL preparation, is a cyclic somatostatin octapeptide analogue that suppresses GH and IGF-1 hypersecretion after a 60-mg subcutaneous injection. Longterm (every 4–6 weeks) administration controls GH hypersecretion in about two-thirds of treated patients and improves patient compli­ ance because of the long interval required between drug injections. Oral octreotide capsules (40–80 mg daily) maintain biochemical control in patients previously maintained on injectable formula­ tions. Rapid relief of headache and soft tissue swelling occurs in ~75% of patients within days to weeks of SRL initiation. Most patients report symptomatic improvement, including amelioration of headache, perspiration, obstructive apnea, and cardiac failure. Pasireotide LAR, a multireceptor ligand with preferential SST5 bind­ ing, has been shown to exhibit efficacy in achieving biochemical control in patients resistant to octreotide or lanreotide preparations. Side Effects  SRLs are well tolerated in most patients. Adverse effects are similar for injectable octreotide and lanreotide as well as for oral octreotide formulation. They are short-lived and mostly relate to drug-induced suppression of gastrointestinal motility and secretion. Transient nausea, abdominal discomfort, fat malabsorp­ tion, diarrhea, and flatulence occur in one-third of patients, and these symptoms usually remit within 2 weeks. Gallbladder contrac­ tility and emptying are attenuated; up to 30% of patients develop long-term echogenic sludge or asymptomatic cholesterol gallstones. Other side effects include mild glucose intolerance due to transient insulin suppression, asymptomatic bradycardia, hypothyroxinemia, and local injection site discomfort. Pasireotide is associated with similar gastrointestinal side effects but with a higher prevalence of glucose intolerance and new-onset diabetes mellitus.

GH-secreting pituitary tumor Surgery Well controlled Cabergolineb Monitor IGF-1 Well controlled Not controlled Not controlled PART 12 Endocrinology and Metabolism SRL Not controlled Well controlled Increase SRL dose Monitor IGF-1 Pegvisomant Reoperation Well controlled Monitor IGF-1 Radiotherapy Pasireotide + pegvisomant FIGURE 392-8  Management of acromegaly. aIf curative surgery is not feasible. bConsider in cases of mild postoperative GH/IGF-1 elevations. GH, growth hormone; IGF, insulin-like growth factor; SRL, somatostatin receptor ligand (injectable or oral octreotide, or lanreotide). GH RECEPTOR ANTAGONIST Pegvisomant antagonizes endogenous GH action by blocking peripheral GH binding to its receptor. Consequently, serum IGF-1 levels are suppressed, reducing the deleterious effects of excess endogenous GH. Pegvisomant is administered by daily subcu­ taneous injection (10–30 mg) and normalizes IGF-1 in ~70% of patients. GH levels, however, remain elevated as the drug does not target the pituitary adenoma. Side effects include reversible liver enzyme elevation, lipodystrophy, and injection site pain. Tumor size should be monitored by MRI. Combined treatment with monthly SRLs and weekly or biweekly pegvisomant injections has been used effectively in treatmentresistant patients. DOPAMINE AGONISTS Very high doses of cabergoline (0.5 mg/d) may achieve short-lived and modest GH therapeutic efficacy. Combined treatment with octreotide and cabergoline may induce additive biochemical con­ trol compared with either drug alone. RADIATION THERAPY External radiation therapy or high-energy stereotactic techniques are used as adjuvant therapy for acromegaly. An advantage of radiation is that patient compliance with long-term treatment is not required. Tumor mass is reduced, and GH levels are attenuated over time. However, 50% of patients require at least 8 years for GH levels to be suppressed to <5 μg/L; this level of GH reduction is achieved in ~90% of patients after 18 years but represents suboptimal GH

Primary SRLa Monitor IGF-1 Not controlled SRL + pegvisomant Pasireotide Well controlled Monitor IGF-1 Not controlled Re-operation suppression. Patients may require interim medical therapy for several years before attaining maximal radiation benefits. Most patients also experience hypothalamic-pituitary damage, leading to gonadotropin, ACTH, and/or TSH deficiency within 10 years of therapy. SUMMARY Surgery is the preferred primary treatment for GH-secreting micro­ adenomas (Fig. 392-8). The high frequency of residual GH hyperse­ cretion after macroadenoma resection usually necessitates adjuvant or primary medical therapy for these larger tumors. Patients unable to receive or respond to unimodal medical treatment may benefit from combined treatments, or they can be offered radiation. Very rarely, repeat surgery may be required. ■ ■CUSHING’S DISEASE (ACTH-PRODUCING ADENOMA) (See also Chap. 398) Etiology and Prevalence  Pituitary corticotrope adenomas (Cushing’s disease) account for 70% of patients with endogenous causes of Cushing’s syndrome. However, it should be emphasized that iatrogenic hypercortisolism is the most common cause of cushingoid features. Ectopic tumor ACTH production, cortisol-producing adrenal adenomas, adrenal carcinoma, and adrenal hyperplasia account for the other causes; rarely, ectopic tumor CRH production is encountered. ACTH-producing adenomas account for ~10–15% of all pituitary tumors. Because the clinical features of Cushing’s syndrome often lead to early diagnosis, most ACTH-producing pituitary tumors are

TABLE 392-7  Clinical Features of Cushing’s Syndrome (All Ages) SYMPTOMS/SIGNS FREQUENCY, % Obesity or weight gain (>115% ideal body weight)

Thin skin

Moon facies

Hypertension

Purple skin striae

Hirsutism

Menstrual disorders (usually amenorrhea)

Plethora

Abnormal glucose tolerance

Impotence

Proximal muscle weakness

Truncal obesity

Acne

Bruising

Mental changes

Osteoporosis

Edema of lower extremities

Hyperpigmentation

Hypokalemic alkalosis

Diabetes mellitus

Source: Adapted with permission from MA Magiokou et al, in Wierman ME: Diseases of the Pituitary. Totowa, NJ: Humana; 1997. relatively small microadenomas. However, macroadenomas also are seen and some ACTH-expressing adenomas are clinically silent. Cush­ ing’s disease is 5–10 times more common in women than in men. These pituitary adenomas exhibit unrestrained ACTH secretion, with resultant hypercortisolemia. However, they retain partial suppress­ ibility in the presence of high doses of administered glucocorticoids, providing the basis for dynamic testing to distinguish pituitary from nonpituitary causes of Cushing’s syndrome. Presentation and Diagnosis  The diagnosis of Cushing’s syn­ drome presents two great challenges: (1) to distinguish patients with pathologic cortisol excess from those with physiologic or other dis­ turbances of cortisol production and (2) to determine the etiology of pathologic cortisol excess. Typical features of chronic cortisol excess include thin skin, central obesity, hypertension, plethoric moon facies, purple striae and easy bruisability, glucose intolerance or diabetes mellitus, gonadal dysfunc­ tion, osteoporosis, proximal muscle weakness, signs of hyperandrogen­ ism (acne, hirsutism), and psychological disturbances (depression, mania, and psychoses) (Table 392-7). Hematopoietic features of hypercortisolism include leukocytosis, lymphopenia, and eosinopenia. Immune suppression includes delayed hypersensitivity and infection propensity. These protean yet commonly encountered manifestations of hypercortisolism make it challenging to decide which patients man­ date formal laboratory evaluation. Certain features make pathologic causes of hypercortisolism more likely; they include characteristic central redistribution of fat, thin skin with striae and bruising, and proximal muscle weakness. In children and young females, early osteo­ porosis may be particularly prominent. The primary cause of death is cardiovascular disease, but life-threatening infections and risk of suicide are also increased. Rapid development of features of hypercortisolism associated with skin hyperpigmentation and severe myopathy suggests an ectopic tumor source of ACTH. Hypertension, hypokalemic alkalosis, glucose intolerance, and edema are also more pronounced in these patients. Serum potassium levels <3.3 mmol/L are evident in ~70% of patients with ectopic ACTH secretion but are seen in <10% of patients with pituitary-dependent Cushing’s syndrome. Laboratory Investigation  The diagnosis of Cushing’s disease is based on laboratory documentation of endogenous hypercortisolism.

Measurement of 24-h UFC is a precise and cost-effective screening test. Alternatively, the failure to suppress plasma cortisol after an overnight 1-mg dexamethasone suppression test can be used to identify patients with hypercortisolism. As nadir levels of cortisol occur at night, ele­ vated midnight serum or salivary samples of cortisol are suggestive of Cushing’s disease. Basal plasma ACTH levels often distinguish patients with ACTH-independent (adrenal or exogenous glucocorticoid) from those with ACTH-dependent (pituitary, ectopic ACTH) Cushing’s syn­ drome. Mean basal ACTH levels are about eightfold higher in patients with ectopic ACTH secretion than in those with pituitary ACTHsecreting adenomas. However, extensive overlap of ACTH levels in these two disorders precludes using ACTH measurements to make the distinction. Preferably, dynamic testing based on differential sensitiv­ ity to glucocorticoid feedback or ACTH stimulation in response to CRH or cortisol reduction is used to distinguish ectopic from pituitary sources of excess ACTH (Table 392-8). Very rarely, circulating CRH levels are elevated, reflecting ectopic tumor-derived secretion of CRH and often ACTH. For further discussion of dynamic testing for Cushing’s syndrome, see Chap. 398.

Pituitary Tumor Syndromes CHAPTER 392 Most ACTH-secreting pituitary tumors are <5 mm in diameter, and about half are undetectable by sensitive MRI. The high prevalence of incidental pituitary microadenomas diminishes the ability to distin­ guish ACTH-secreting pituitary tumors accurately from nonsecreting incidentalomas. Inferior Petrosal Venous Sampling  Because pituitary MRI with gadolinium enhancement is insufficiently sensitive to detect small (<2 mm) pituitary ACTH-secreting adenomas, bilateral inferior petrosal sinus ACTH sampling before and after CRH administration may be required to distinguish these lesions from ectopic ACTH-secreting tumors that may have similar clinical and biochemical characteristics. Simultaneous assessment of ACTH in each inferior petrosal vein and TABLE 392-8  Differential Diagnosis of ACTH-Dependent Cushing’s Syndromea ACTH-SECRETING PITUITARY TUMOR ECTOPIC ACTH SECRETION   Etiology Pituitary corticotrope adenoma Plurihormonal adenoma Bronchial, abdominal carcinoid Small-cell lung cancer Thymoma, other sources Sex F > M M > F Clinical features Slow onset Rapid onset Pigmentation Severe myopathy Serum potassium

<3.3 μg/L <10% 75% 24-h UFC High High Basal ACTH level Inappropriately high Very high Dexamethasone suppression 1 mg overnight   Low-dose (0.5 mg q6h)         Cortisol >5 μg/dL Cortisol >5 μg/dL   High-dose (2 mg q6h) Cortisol <5 μg/dL Cortisol >5 μg/dL UFC >80% suppressed Microadenomas: 90% Macroadenomas: 50% 10% Inferior petrosal sinus sampling       Basal     central: peripheral  

2   <2   CRH-induced     central: peripheral   3   <3 aACTH-independent causes of Cushing’s syndrome are diagnosed by suppressed ACTH levels and an adrenal mass in the setting of hypercortisolism. Iatrogenic Cushing’s syndrome is excluded by history. Abbreviations: ACTH, adrenocorticotropic hormone; CRH, corticotropin-releasing hormone; F, female; M, male; UFC, urinary free cortisol.

in the peripheral circulation provides a strategy for confirming and localizing pituitary ACTH production. Sampling is performed at base­ line and 2, 5, and 10 min after intravenous CRH (1 μg/kg) injection. An increased central:peripheral ACTH ratio (>2) before and a peak central:peripheral ACTH ratio >3 after CRH injection confirm the presence of a pituitary ACTH-secreting adenoma. The sensitivity of this test is >95%, with very rare false-positive results. False-negative results may be encountered in patients with aberrant venous drainage. Petrosal sinus catheterizations are technically difficult, and ~0.05% of patients develop neurovascular complications. The procedure should not be performed in patients with hypertension, in patients with known cerebrovascular disease, or in the presence of a well-visualized pituitary adenoma on MRI.

PART 12 Endocrinology and Metabolism TREATMENT Cushing’s Disease Selective transsphenoidal resection is the treatment of choice for Cushing’s disease (Fig. 392-9). The remission rate for this proce­ dure is ~80% for microadenomas but <50% for macroadenomas. However, surgery is rarely successful when the adenoma is not vis­ ible on MRI. After successful tumor resection, most patients experi­ ence a postoperative period of symptomatic ACTH deficiency that may last up to 12 months. This usually requires low-dose cortisol replacement, as patients experience steroid withdrawal symptoms and have a suppressed hypothalamic-pituitary-adrenal axis. Bio­ chemical recurrence occurs in ~5% of patients in whom surgery was initially successful. As persistent hypercortisolemia may cause blood clotting defects, prophylactic postoperative thromboembolic management has been advocated for vulnerable patients. When initial surgery is unsuccessful, repeat surgery is sometimes indicated, particularly when a pituitary source for ACTH is well documented. In older patients, in whom issues of growth and fertil­ ity are less important, hemi- or total hypophysectomy may be nec­ essary if a discrete pituitary adenoma is not recognized. Pituitary irradiation may be used after unsuccessful surgery, but it cures only ~15% of patients. Because the effects of radiation are slow and only partially effective in adults, adrenal-targeted steroidogenic inhibi­ tors are used in combination with pituitary irradiation to block adrenal responses to persistently high ACTH levels. ACTH-dependent hypercortisolism Pituitary MRI Petrosal sinus ACTH sampling* Consider chest/abdomen imaging Ectopic ACTH excluded ACTH-secreting pituitary adenoma Pasireotide and/or Glucocorticoid receptor antagonist Transsphenoidal surgical resection and/or Steroidogenic inhibitors Biochemical cure Persistent hypercortisolism and/or Pituitary irradiation Glucocorticoid replacement, if needed ?Irradiation Follow-up: Adrenalectomy Serial biochemical and MRI evaluation Risk of Nelson’s syndrome FIGURE 392-9  Management of Cushing’s disease. ACTH, adrenocorticotropin hormone; MRI, magnetic resonance imaging; ∗, Not usually required.

Pasireotide LAR 10–40 mg intramuscularly, an SRL with high affinity for SST5 > SST2 receptor subtypes, may control hypercor­ tisolemia in a subset of patients with ACTH-secreting pituitary tumors when surgery is not an option or has not been successful. The drug lowers plasma ACTH levels and normalizes 24-h UFC levels in ~20% of patients, and up to 40% of patients may experience pituitary tumor shrinkage. Side effects are similar to those encoun­ tered for other SRLs and include transient abdominal discomfort, diarrhea, nausea, and gallstones (20% of patients). Notably, hyper­ glycemia and new-onset diabetes develop in up to 70% of patients, likely due to suppressed pancreatic secretion of insulin and incre­ tins. Because patients with hypercortisolism are insulin-resistant, hyperglycemia should be rigorously managed. The drug requires consistent long-term administration. Osilodrostat (2 mg twice daily titrated up to 30 mg twice daily), an oral 11β-hydroxylase inhibitor that blocks adrenal gland cortisol biosynthesis, normalized 24-h UFC in 86% of patients. Mild, mostly transient gastrointestinal symptoms are common. Patients should be closely monitored for development of hypocortisolism and adre­ nal insufficiency. Elevated adrenal hormone precursors may lead to hypokalemia and hypertension. QTc prolongation and possibly increased tumor volume are also reported. Ketoconazole, an imidazole derivative antimycotic agent, inhib­ its several P450 enzymes and effectively lowers cortisol in most patients with Cushing’s disease when administered twice daily (600–1200 mg/d). Elevated hepatic transaminases, gynecomastia, impotence, gastrointestinal upset, and edema are common side effects. Levoketoconazole, a 2S,4R enantiomer of ketoconazole, is admin­ istered at the same dose/schedule as ketoconazole and has a similar side effect profile. Mifepristone (300–1200 mg/d), a glucocorticoid receptor antago­ nist, blocks peripheral cortisol action and is approved to treat hyperglycemia in Cushing’s disease. Because the drug does not target the pituitary tumor, both ACTH and cortisol levels remain elevated, thus obviating a reliable circulating biomarker. Side effects are largely due to general antagonism of other steroid hormones and include hypokalemia, endometrial hyperplasia, hypoadrenal­ ism, and hypertension. Metyrapone (2–4 g/d) inhibits 11β-hydroxylase activity and nor­ malizes plasma cortisol in up to 75% of patients. Side effects include nausea and vomiting, rash, and exacerbation of acne or hirsutism. Mitotane (3–6 g/d orally in four divided doses) suppresses cortisol hypersecretion by inhibiting 11β-hydroxylase and cholesterol sidechain cleavage enzymes and by destroying adrenocortical cells. Side effects of mitotane include gastrointestinal symptoms, dizziness, gynecomastia, hyperlipidemia, skin rash, and hepatic enzyme eleva­ tion. It also may lead to hypoaldosteronism. Other agents include aminoglutethimide (250 mg tid), trilostane (200–1000 mg/d), cypro­ heptadine (24 mg/d), and IV etomidate (0.3 mg/kg per h). Glucocor­ ticoid insufficiency is a potential side effect of agents used to block steroidogenesis. The use of steroidogenic inhibitors has decreased the need for bilateral adrenalectomy. Surgical removal of both adrenal glands corrects hypercortisolism but may be associated with significant morbidity rates and necessitates permanent glucocorticoid and min­ eralocorticoid replacement. Adrenalectomy in the setting of residual corticotrope adenoma tissue predisposes to the development of Nelson’s syndrome, a disorder characterized by rapid pituitary tumor enlargement and increased pigmentation secondary to high ACTH levels. Prophylactic radiation therapy may be indicated to prevent the development of Nelson’s syndrome after adrenalectomy. ■ ■NONFUNCTIONING AND GONADOTROPINPRODUCING PITUITARY ADENOMAS Etiology and Prevalence  Nonfunctioning pituitary adenomas include those that secrete little or no pituitary hormones into the systemic circulation, as well as tumors that produce too little hormone

to result in recognizable clinical features. They are the most common type of pituitary adenoma and are usually macroadenomas at the time of diagnosis because clinical features are not apparent until tumor mass effects occur. Based on immunohistochemistry, most clinically non­ functioning adenomas can be shown to originate from gonadotrope cells or from pituitary null cells. These tumors typically produce small amounts of intact gonadotropins (usually FSH) as well as uncombined α, LH β, and FSH β subunits. Tumor secretion may lead to elevated α and FSH β subunits and, very rarely, to increased LH β subunit lev­ els. Some adenomas express α subunits without FSH or LH. A TRH stimulation test often induces an atypical increase of tumor-derived gonadotropins or subunits. Presentation and Diagnosis  Clinically nonfunctioning tumors often present with optic chiasm pressure and other symptoms of local expansion or may be incidentally discovered on an MRI performed for another indication (incidentaloma). Rarely, menstrual disturbances or ovarian hyperstimulation occur in women with large tumors that pro­ duce FSH and LH. In these cases, ovaries may have features that resem­ ble polycystic ovarian syndrome and may produce very high levels of estrogen. More commonly, adenoma compression of the pituitary stalk or surrounding pituitary tissue leads to attenuated LH and features of hypogonadism. PRL levels are usually slightly increased, also because of stalk compression. It is important to distinguish this circumstance from true prolactinomas, as nonfunctioning tumors do not shrink in response to treatment with dopamine agonists. Laboratory Investigation  The goal of laboratory testing in clini­ cally nonfunctioning tumors is to classify the type of tumor, identify hormonal markers of tumor activity, and detect possible hypopituita­ rism. Free α subunit levels may be elevated in 10–15% of patients with nonfunctioning tumors. In female patients, peri- or postmenopausal basal FSH concentrations are difficult to distinguish from tumorderived FSH elevation. Premenopausal women have cycling FSH levels, also preventing clear-cut diagnostic distinction from tumor-derived FSH. In men, gonadotropin-secreting tumors may be diagnosed because of slightly increased gonadotropins (FSH > LH) in the setting of a pituitary mass. Testosterone levels are usually low despite the nor­ mal or increased LH level, perhaps reflecting reduced LH bioactivity or the loss of normal LH pulsatility. Because this pattern of hormone test results is also seen in primary gonadal failure and, to some extent, with aging (Chap. 403), the finding of increased gonadotropins alone is insufficient for the diagnosis of a gonadotropin-secreting tumor. In the majority of patients with gonadotrope adenomas, TRH adminis­ tration stimulates LH β subunit secretion; this response is not seen in Nonfunctioning Pituitary Mass Differential diagnosis based on MRI and clinical features Dynamic pituitary reserve testing Nonfunctioning adenoma Microadenoma Macroadenoma Low risk of visual loss Observe Surgery Follow-up: MRI MRI Trophic hormone testing and replacement FIGURE 392-10  Management of a nonfunctioning pituitary mass. MRI, magnetic resonance imaging.

normal individuals. GnRH testing, however, is not helpful for making the diagnosis. For nonfunctioning and gonadotropin-secreting tumors, the diagnosis usually rests on immunohistochemical analyses of surgi­ cally resected tumor tissue, as the mass effects of these tumors usually necessitate resection.

Although acromegaly or Cushing’s disease usually presents with unique clinical features, clinically inapparent (silent) somatotrope or corticotrope adenomas may only be diagnosed by immunostaining of resected tumor tissue. These silent tumors usually grow more aggres­ sively and account for up to 20% of all nonfunctioning adenomas. If PRL levels are <100 μg/L in a patient harboring a pituitary mass, a nonfunctioning adenoma causing pituitary stalk compression should be considered. Pituitary Tumor Syndromes CHAPTER 392 TREATMENT Nonfunctioning and Gonadotropin-Producing Pituitary Adenomas As the probability of nonfunctioning microadenoma growth is very low, asymptomatic small nonfunctioning microadenomas with no threat to vision may be followed with an MRI after 3 years, with serial MRI and visual field testing thereafter as needed. However, for macroadenomas, transsphenoidal surgery is indicated to reduce tumor size and relieve compressive mass effects (Fig. 392-10). Although it is not usually possible to remove all adenoma tissue surgically, vision improves in 70% of patients with preoperative visual field defects. Preexisting hypopituitarism that results from tumor mass effects may improve or resolve completely. Beginning ~6 months postoperatively, MRI scans should be performed yearly to detect whether tumor regrowth is occurring. Within 5–6 years after successful surgical resection, ~15% of nonfunctioning tumors recur. When substantial tumor remains after transsphenoidal sur­ gery, adjuvant radiotherapy may be indicated to prevent persistent tumor regrowth. Radiotherapy may be deferred if no postoperative residual mass is evident. Nonfunctioning pituitary tumors respond poorly to dopamine agonist treatment, and SRLs are largely ineffec­ tive for shrinking these tumors. ■ ■TSH-SECRETING ADENOMAS TSH-producing macroadenomas are very rare but are often large and locally invasive when they occur. Patients usually present with thyroid goiter and hyperthyroidism, reflecting chronic overproduction of TSH. Other sellar mass (not adenoma) Exclude aneurysm Surgery Histologic diagnosis May require disease-specific therapy MRI Trophic hormone testing and replacement

07 - 393 Disorders of the Neurohypophysis

393 Disorders of the Neurohypophysis

Diagnosis is based on demonstrating elevated serum free T4 levels, inappropriately normal or high TSH secretion, and MRI evidence of a pituitary adenoma. Elevated free glycoprotein hormone α subunits are seen in many patients.

It is important to exclude other causes of inappropriate TSH secre­ tion, such as resistance to thyroid hormone, an autosomal dominant disorder caused by mutations in the thyroid hormone β receptor (Chap. 394). The presence of a pituitary mass and elevated β subunit levels are suggestive of a TSH-secreting tumor. Dysalbuminemic hyperthyroxinemia syndromes, caused by mutations in serum thyroid hormone binding proteins, are also characterized by elevated thyroid hormone levels, but with normal rather than suppressed TSH levels. Moreover, free thyroid hormone levels are normal in these disorders, most of which are familial. PART 12 Endocrinology and Metabolism TREATMENT TSH-Secreting Adenomas The initial therapeutic approach is to remove or debulk the tumor mass surgically, usually using a transsphenoidal approach. Total resection is not often achieved as most of these adenomas are large and locally invasive. Normal circulating thyroid hormone levels are achieved in about two-thirds of patients after surgery. Thyroid ablation or antithyroid drugs (methimazole and propylthioura­ cil) can be used to reduce thyroid hormone levels. SRL treatment effectively normalizes TSH and α subunit hypersecretion, shrinks the tumor mass in 50% of patients, and improves visual fields in 75% of patients; euthyroidism is restored in most patients. Because SRLs markedly suppress TSH, biochemical hypothyroidism often requires concomitant thyroid hormone replacement, which may also further control tumor growth. ■ ■AGGRESSIVE ADENOMAS Despite the rarity of malignant transformation and metastatic lesions, a subset of pituitary adenomas undergoes aggressive local growth and central nervous system invasion with high Ki67 levels (>4%). Silent corticotrope and somatotrope tumors, as well as pro­ lactinomas occurring in middle-aged men, are particularly prone to aggressive growth and recurrence. Patients with these tumors usually require an integrated management approach including repeat surger­ ies and irradiation. Temozolomide has also been used with variable responses. ■ ■FURTHER READING Coopmans EC et al: Multivariable prediction model for biochemical response to first-generation somatostatin receptor ligands in acro­ megaly. J Clin Endocrinol Metab 105:2964, 2020. Elbelt U et al: Efficacy of temozolomide therapy in patients with aggressive pituitary adenomas and carcinomas: A German survey. J Clin Endocrinol Metab 105:e660, 2020. Fleseriu M et al: Acromegaly: Pathogenesis, diagnosis, and manage­ ment. Lancet Diabetes Endocrinol 10:804, 2022. Fleseriu M et al: An individualized approach to the management of Cushing disease. Nat Rev Endocrinol 19:581, 2023. Hamblin R et al: Natural history of non-functioning pituitary micro­ adenomas: Results from the UK non-functioning pituitary adenoma consortium. Eur J Endocrinol 189:87, 2023. Melmed S: Pituitary-tumor endocrinopathies. N Engl J Med 382:937, 2020. Neou M et al: Pangenomic classification of pituitary neuroendocrine tumors. Cancer Cell 37:123, 2020. Petersenn S et al: Diagnosis and management of prolactin-secreting pituitary adenomas: A Pituitary Society international Consensus Statement. Nat Rev Endocrinol 19:722, 2023. Samson SL et al: Maintenance of acromegaly control in patients switching from injectable somatostatin receptor ligands to oral octreotide. J Clin Endocrinol Metab 105:e3785, 2020.

Mirjam Christ-Crain, Mark Sherlock

Disorders of the Neurohypophysis The posterior pituitary consists of the distal axons of the hypothalamic magnocellular neurons that make up the neurohypophysis. The peri­ karya (cell bodies) of these axons are located in paired paraventricular and supraoptic nuclei of the hypothalamus. Some of these neurons produce arginine vasopressin (AVP), also known as antidiuretic hor­ mone (ADH); others produce oxytocin. AVP acts on the renal tubules to reduce water loss by concentrating the urine. Oxytocin stimulates postpartum milk letdown in response to suckling, and also elicits socioemotional responses. A deficiency of AVP secretion or action causes a syndrome characterized by the production of large amounts of dilute urine. Excessive or inappropriate AVP production impairs urinary water excretion and predisposes to hyponatremia. VASOPRESSIN ■ ■SYNTHESIS AND SECRETION AVP is a nonapeptide composed of a six-member disulfide ring and a tripeptide tail (Fig. 393-1). It is synthesized via a polypeptide precursor that includes AVP, neurophysin, and copeptin, all encoded by a single gene on chromosome 20. After preliminary processing and folding, the precursor is packaged in neurosecretory vesicles, where it is trans­ ported down the axon. It is further processed to AVP, neurophysin, and copeptin, and stored in neurosecretory vesicles in the posterior pituitary until it is released by exocytosis into peripheral blood. In healthy individuals, AVP secretion is regulated primarily by the “effective” osmotic pressure, which is determined largely by the plasma concentration of sodium and its anions. This regulation is mediated by specialized cells in the anteromedial hypothalamus, known as osmo­ receptors. The osmoreceptors receive blood from small perforating branches of the anterior communicating artery. They are extremely sensitive to small changes in the plasma concentration of sodium and its anions but normally are insensitive to other naturally occurring plasma solutes such as urea and glucose. This osmoregulatory system includes inhibitory as well as stimulatory components that function in concert to create an osmotic threshold, or set point, control system. Below this osmotic threshold, plasma AVP is suppressed to levels that permit the development of a maximum water diuresis. Above the threshold, plasma AVP rises steeply in direct proportion to plasma osmolarity, quickly reaching levels sufficient to produce maximum antidiuresis. The absolute levels of plasma osmolarity/sodium at which minimally and maximally effective levels of plasma AVP occur differ from person to person, apparently due to genetic influences on the set and sensitivity of the system. However, the average threshold, or set point, for AVP release corresponds to a plasma osmolarity and sodium of ~275 mosmol/L and 135 meq/L, respectively; levels only 2–4% higher normally result in maximum antidiuresis. AVP is also secreted in response to a decrease in blood pressure or by volume loss of >10–20%. These hemodynamic (baroregulated) influ­ ences are mediated by neuronal afferents that originate in transmural pressure receptors of the heart and large arteries and project via the vagus and glossopharyngeal nerves to the brainstem, which sends post­ synaptic projections to the hypothalamus. AVP secretion also can be stimulated by nausea, acute hypoglycemia, glucocorticoid deficiency, smoking, and possibly angiotensin. Emetic stimuli are extremely potent in comparison to osmotic stimuli; they typically elicit immediate, 50- to 100-fold increases in plasma AVP even when the nausea is transient and not associated with vomiting or other symptoms. They act via the emetic center in the medulla and can be blocked completely by treat­ ment with antiemetics such as fluphenazine. There is no evidence that pain or other noxious stresses have any effect on AVP unless they elicit a vasovagal reaction and its associated nausea and hypotension.

DNA Vasopressin Neurophysin II Copeptin Oxytocin Neurophysin I FIGURE 393-1  Primary structure, production, and release of arginine vasopressin (AVP). AVP is a nonapeptide composed of a six-member disulfide ring and a tripeptide tail. It is synthesized via a polypeptide precursor that includes AVP, neurophysin, and copeptin, all encoded by a single gene on chromosome 20. The precursor hormone, pre-pro-vasopressin consists of three peptides: AVP, neurophysin 2, and copeptin. ■ ■ACTION The most important physiologic action of AVP is to reduce water excretion by promoting the concentration of urine. Other physiologic actions of AVP include stimulating ACTH and vasoconstriction. This antidiuretic effect is achieved primarily by increasing the hydroosmotic permeability of principal cells that line the distal tubule and medullary collecting ducts of the kidney (Fig. 393-2). In the absence of AVP, these cells are impermeable to water and reabsorb little, if any, of the relatively large volume of dilute filtrate that enters from the proximal nephron. In this condition, the rate of urine output can be as high as 0.2 mL/kg per min and the specific gravity and osmolarity as low as ~1.000 and 50 mOsmol/L, respectively. When AVP is secreted, it binds to V2 receptors on the basal surface of principal cells causing water channels composed of aquaporin-2 (AQ-2) to be inserted into the apical surface of the cell. These channels allow water to flow pas­ sively from the lumen through the cell down the osmotic gradient cre­ ated by the hypertonicity of the renal medulla. The magnitude of this antidiuretic effect varies in direct proportion to plasma AVP, the rate of solute excretion, and the level of hypertonicity in the renal medulla. The maximum antidiuresis achievable in healthy humans occurs at plasma AVP concentrations in the range of 1 to 3 pg/mL and results in a urine osmolarity as high as 1200 mOsmol/L. However, maximum concentrating capacity varies considerably depending on the level of hypertonicity in the renal medulla and that, in turn, is a function of the level and duration of AVP receptor 2 (AVPR2)–stimulated reabsorp­ tion of urea in the distal nephron. Hence, if basal AVP stimulation of AVPR2 is low (e.g., a high basal fluid intake in primary polydipsia), the rise in urine osmolarity that occurs immediately after an increase in AVP concentrations may be so blunted as to suggest a defect in antidi­ uretic function. This reduced concentrating capacity accounts for the shortcomings of the traditional indirect methods for the differential diagnosis of polyuric states (see below). At high concentrations, AVP also causes contraction of smooth muscle in blood vessels in the skin and gastrointestinal tract, induces glycogenolysis in the liver, and potentiates ACTH release by

Thirst Brainstem Osmoreceptor Disorders of the Neurohypophysis CHAPTER 393 Hypothalamus Baroreceptor Vagus nerve Posterior pituitary Luminal membrane AQ2 channel Migration to the luminal membrane mRNA for AQ2 channels Pre-formed AQ2 channels ATP cAMP Basolateral membrane V2 receptor AVP FIGURE 393-2  Antidiuretic effect of arginine vasopressin (AVP) in the regulation of urine volume. In a typical 70-kg adult, the kidney filters ~180 L/d of plasma. Of this, ~144 L (80%) is reabsorbed isosmotically in the proximal tubule and another 8 L (4–5%) is reabsorbed without solute in the descending limb of Henle’s loop. In the presence of AVP, solute-free water is reabsorbed osmotically through the principal cells of the collecting ducts, resulting in the excretion of a much smaller volume of concentrated urine. This antidiuretic effect is mediated via a G protein–coupled V2 receptor that increases intracellular cyclic AMP, thereby inducing translocation of aquaporin 2 (AQP 2) water channels into the apical membrane. The resultant increase in permeability permits an influx of water that diffuses out of the cell through AQP 3 and AQP 4 water channels on the basal-lateral surface. The net rate of flux across the cell is determined by the number of AQP 2 water channels in the apical membrane and the strength of the osmotic gradient between tubular fluid and the renal medulla.

NORMAL AVP AND THIRST RESPONSE TO 5% SALINE INFUSION

Plasma AVP (pg/mL)

PART 12 Endocrinology and Metabolism

LD

Plasma osmolality (mosm/kg) FIGURE 393-3  The relationship of plasma osmolality to arginine vasopressin (AVP) secretion and thirst. VAS, visual analogue scale. corticotropin-releasing factor. These effects are mediated by V1a or V1b receptors that are coupled to phospholipase C. They may also affect the sensitivity of the baroreceptor and influence sympathetic and parasym­ pathetic outflows to a variety of target organs, including the heart, the peripheral vasculature, and the kidneys. ■ ■METABOLISM AVP distributes rapidly into a space approximately equal to the extra­ cellular fluid volume. It is cleared irreversibly with a half-life (t1/2) of 10–30 min. Most AVP clearance is due to degradation in the liver and kidneys. During pregnancy, the metabolic clearance of AVP is increased three- to fourfold due to placental production of an N-terminal peptidase (vasopressinase). Importantly, the synthetic vasopressin analogue desmopressin (DDAVP) is more resistant to N-terminal pep­ tidases, resulting in a longer half-life. THIRST Because AVP cannot reduce water loss below a certain minimum level obligated by urinary solute load and evaporation from skin and lungs, a mechanism for ensuring adequate water intake is essential for preventing dehydration. This vital function is performed by the thirst mechanism. Like AVP, thirst and fluid intake are regulated primarily by an osmostat that is localized in the anteromedial hypothalamus and detects very small changes in the plasma concentration of sodium and its anions. The thirst osmostat appears to be “set” about 3% higher than the AVP osmostat (Fig. 393-3). This relationship ensures that thirst, polydipsia, and dilution of body fluids do not occur until plasma osmolarity/sodium exceeds the defensive capacity of the antidiuretic mechanism. Defects in thirst result in hypodipsia/adipsia. The gas­ trointestinal tract also has a mechanism that detects fluid intake and inhibits thirst and AVP secretion before water is absorbed sufficiently to lower plasma osmolarity/sodium. However, the resultant inhibition of thirst and AVP is transient unless plasma osmolarity/sodium is reduced, and the role of this system in clinical disorders of water bal­ ance has not been determined. OXYTOCIN Oxytocin (OXT) is also a nonapeptide that differs from AVP at posi­ tions 3 and 8 (Fig. 393-1). However, it has relatively little antidiuretic effect and seems to act mainly on mammary ducts to facilitate milk letdown during nursing. It also may help initiate or facilitate labor by stimulating contraction of uterine smooth muscle, but it is not clear if this action is physiologic or necessary for normal delivery. In addition to its release from axonal terminals, OXT is dendritically released into

Thirst (cm/VAS)

Plasma osmolality (mosm/kg)

the central extracellular space and directly projected to other brain regions, where it acts as a neurotransmitter. The central oxytocinergic system is key in regulating socioemotional functioning, including attachment and pair bonding, fear extinction, emotion recognition, and empathy. DEFICIENCIES OF AVP SECRETION AND ACTION ■ ■DIABETES INSIPIDUS (AVP DEFICIENCY AND AVP RESISTANCE) Clinical Characteristics  Deficiencies in AVP secretion or action result in the excretion of abnormally large volumes of dilute urine. The 24-h urine volume exceeds 40–50 mL/kg body weight and conse­ quently leads to polydipsia. Signs and symptoms of dehydration (and biochemical hypernatremia) are uncommon unless thirst and/or water intake are also impaired. Etiology  AVP deficiency and AVP resistance should be differenti­ ated from increased AVP metabolism in pregnancy and from primary polydipsia. Primary deficiency of AVP secretion was formerly called neurogenic, pituitary, cranial, or central diabetes insipidus but is now referred to as AVP deficiency. It can be caused by a variety of acquired, congenital, or genetic disorders but is often idiopathic (Table 393-1). The most common genetic form is transmitted in an autosomal domi­ nant mode and is caused by diverse mutations in the coding region of one allele of the AVP–neurophysin II (or AVP-NPII) gene. Renal insensitivity to the antidiuretic action of AVP leads to AVP resistance, which was formerly known as nephrogenic diabetes insipidus. It can be caused by a drug such as lithium, a disorder such as hypokalemia and hypercalcemia, or by a genetic mutation. In pregnancy, increased metabolism of AVP may occur due to AVP degradation by an N-terminal aminopeptidase (vasopressinase) pro­ duced in the placenta. This is referred to as gestational AVP deficiency because the signs and symptoms manifest during pregnancy and usu­ ally remit several weeks after delivery. These forms of AVP deficiency and AVP resistance should be dif­ ferentiated from excessive intake of fluids, which is commonly referred to as primary polydipsia. This disorder is common in patients with neu­ rodevelopmental or psychotic disorders, particularly chronic schizo­ phrenia. Outside the psychiatric setting, it is increasingly seen in the general population owing to the popularity of lifestyle programs and the belief that drinking large amounts of water is healthy and improves cognition (Table 393-1).

TABLE 393-1  Etiology of Polyuria–Polydipsia Syndromes BASIC DEFECT ACQUIRED CAUSES HEREDITARY CAUSES AVP Deficiency Deficiency in AVP synthesis or secretion • Trauma (surgery, deceleration injury) • Neoplasia (craniopharyngioma, meningioma, germinoma, metastases) • Vascular (cerebral or hypothalamic hemorrhage, infarction or ligation of anterior communicating artery aneurysm) • Granulomatous (histiocytosis, sarcoidosis) • Infectious (meningitis, encephalitis, tuberculosis) • Inflammatory or autoimmune (lymphocytic infundibuloneurohypophysitis, IgG4 neurohypophysitis) • Drug or toxin exposure • Osmoreceptor dysfunction (adipsic DI) • Others (hydrocephalus, ventricular or suprasellar cyst, trauma, and degenerative diseases) • Idiopathic AVP Resistance Reduced renal sensitivity to antidiuretic effect of physiologic AVP levels • Drug exposure (lithium, demeclocycline, cisplatin, etc.) • Hypercalcemia or hypokalemia • Infiltrating lesions (sarcoidosis, amyloidosis, multiple myeloma, etc.) • Vascular disorders (sickle cell anemia) • Mechanical (polycystic kidney disease and urethral obstruction) Primary Polydipsia Excessive fluid intake at a diminished set point  • Dipsogenica (idiopathic or similar lesions as with central DI) • Psychosis intermittent hyponatremia–polydipsia (PIP) syndrome • Compulsive water drinking • Health enthusiasts Gestational AVP Deficiency Increased enzymatic metabolism of circulating AVP hormone Pregnancy NA aDownward resetting of the thirst threshold. Abbreviations: AVP, arginine vasopressin; AVPR, AVP receptor; DI, diabetes insipidus; NA, not applicable; PCSK1, proprotein convertase subtilisin/kexin type 1; WFS1, Wolfram syndrome 1. Source: Reproduced with permission from M Christ-Crain et al: Diabetes insipidus. Nat Rev Dis Primers 5:54, 2019. Pathophysiology  In AVP deficiency and resistance, the defect in urine concentration increases the rate of water excretion and causes a small (1–2%) decrease in body water and a commensurate increase in plasma osmolarity/sodium, which stimulates thirst and a compensa­ tory increase in water intake. The severity of the defect in antidiuretic function varies significantly from patient to patient. In some patients, AVP deficiency is nearly complete and cannot be overcome by even an intense stimulus such as nausea or severe dehydration. In others, AVP deficiency is incomplete, and a modest stimulus such as a few hours of fluid deprivation, smoking, or a vasovagal reaction is sufficient to concentrate the urine. However, even in patients with a partial defect, the maximum level of urine osmolarity produced by these stimuli is usually less than normal partly because the prior deficiency in basal AVP stimulation temporarily diminishes renal concentrating capacity. Nevertheless, the underlying cause of the AVP deficiency/resistance can be determined by analyzing the relationship of urine osmolar­ ity to plasma AVP/copeptin and of plasma AVP/copeptin to plasma osmolarity/sodium. The pathophysiology of primary polydipsia is the reverse of that in AVP deficiency or resistance. The increase in fluid intake reduces plasma osmolarity/sodium and leads to a physiologic decrease in AVP secretion. The resultant urinary dilution produces a compensa­ tory increase in urinary free-water excretion that usually offsets the increase in intake and stabilizes plasma osmolarity/sodium at a level below basal. Thus, hyponatremia is uncommon unless the polydipsia is very severe or the compensatory water diuresis is impaired (by another contributory factor that causes AVP release). In diagnostic tests, fluid deprivation or hypertonic saline infusion produces a normal rise in plasma AVP, but the resultant increase in urine concentration is usually subnormal because the capacity of the kidney to concentrate the urine

• Autosomal dominant: AVP mutations • Autosomal recessive, type a and b: AVP mutations • Autosomal recessive, type c: WFS1 mutations • Autosomal recessive, type d: PCSK1 Disorders of the Neurohypophysis CHAPTER 393 mutations • X-linked recessive: gene unknown • X-linked: AVPR2 mutations • Autosomal recessive or dominant: AQP2 mutations  NA is temporarily diminished by the prior lack of AVP stimulation. Thus, the maximum level of urine osmolarity achieved is often indistinguish­ able from that produced by fluid deprivation and/or administration of ADH in partial pituitary or partial nephrogenic diabetes insipidus. However, unlike AVP deficiency or resistance, the relationships of the rise in plasma AVP to the rise in plasma and urine osmolarity are both normal in primary polydipsia. Differential Diagnosis  If symptoms of polyuria, nocturia, and/or persistent thirst are present in the absence of glucosuria, the possibility of AVP deficiency or AVP resistance should be evaluated by collecting a 24-h urine on unrestricted fluid intake. If the volume is >40–50 mL/kg per day and/or >3 L/d, further investigations are indicated. If sodium levels are below the normal reference range (<135 mmol/L), this sug­ gests primary polydipsia since these patients can drink themselves into hyponatremia. If sodium levels are above the normal reference range, the diagnosis of AVP deficiency or resistance is likely, and a test with desmopressin (2 μg) followed by a repeat measurement of urine osmo­ larity will determine if hypotonic polyuria is due to a AVP deficiency or AVP resistance. This is subcutaneous and should be done in hospital to allow reassessment of urinary osmolality. However, in most patients, sodium levels will be in the normal range, making further tests for dif­ ferential diagnosis necessary (Fig. 393-4). The indirect water deprivation test was the gold standard for dif­ ferential diagnosis for many years. This test is based on indirect assessment of AVP activity by measurement of the urine concentra­ tion capacity during a prolonged period of dehydration and again after a subsequent injection of an exogenous synthetic AVP analogue, desmopressin. However, the published criteria for interpretation were based on post hoc data from a small number of patients with an overall

Suspected hypotonic polyuria Confirm the presence of polyuria (>40–50 mL/kg/24 h) GU evaluation Urine osmolality <800 mosm/kg Measure serum sodium, plasma osmolality Low serum sodium (<135 mmol/L) PART 12 Endocrinology and Metabolism Primary polydipsia Normal serum sodium (136–146 mmol/L) Baseline copeptin level Water deprivation test Urine osmolality <300 mosm/kg Copeptin

21.4 pmol/L Copeptin <21.4 pmol/L Urine osmolality 300–800 mosm/kg Urine osmolality 800 mosm/kg Mild primary polydipsia Desmopressin test Desmopressin test Stimulated copeptin 4.9 pmol/L (at plasma sodium 150 mmol/L) <50% increase 50% increase 9% increase <9% increase Primary polydipsia Complete or partial central DI Nephrogenic DI Complete central DI Partial central DI Primary polydipsia FIGURE 393-4  Algorithm for differential diagnosis of polyuria polydipsia syndrome. If symptoms of polyuria, nocturia, and/or persistent thirst are present in the absence of glucosuria, the possibility of arginine vasopressin (AVP) deficiency or AVP resistance should be evaluated by collecting a 24-h urine on unrestricted fluid intake. If the volume is >50 mL/kg per day with a concomitant urinary osmolality <800 mOsm/kg, serum sodium and plasma osmolality should be measured. If sodium levels are below the normal reference range, it suggests primary polydipsia since these patients can drink themselves into hyponatremia. If sodium levels are above the normal reference range, the diagnosis of AVP deficiency or resistance can be made, and a test with desmopressin (2 μg) followed by a repeat measurement of urine osmolarity will determine if hypotonic polyuria is due to a AVP deficiency or AVP resistance. However, in most patients, sodium levels will be in the normal range, making further tests for differential diagnosis necessary. If copeptin measurement is available, a copeptin-based diagnostic algorithm is used. High baseline copeptin level of >21.4 pmol/L without prior water deprivation identifies AVP resistance. For the more difficult differential diagnosis of AVP deficiency and primary polydipsia, a copeptin level of >4.9 pmol/L at a high sodium level (≥150 mmol/L) after hypertonic saline infusion has an overall diagnostic accuracy of 97% to diagnose AVP deficiency. DI, diabetes insipidus; GU, genitourinary. diagnostic accuracy of 70% and only 41% for patients with primary polydipsia. To overcome these limitations, direct measurement of AVP was proposed, but despite initial promising results, this method is not in routine clinical use, mainly because of technical limitations of the AVP assay. Copeptin is the C-terminal segment of the AVP prohormone and is an AVP surrogate that is very stable ex vivo (Fig. 393-1). Studies have shown that a high baseline copeptin level of >21.4 pmol/L, without prior water deprivation, unequivocally identifies AVP resistance. For the more difficult differential diagnosis of AVP deficiency and primary polydipsia, a copeptin level of >4.9 pmol/L at a high sodium level (≥150 mmol/L) after hypertonic saline infusion has an overall diagnostic accuracy of 96.5%. Importantly, this test requires close monitoring of sodium levels. Copeptin levels after arginine infusion have also shown promising results in differentiating AVP deficiency from primary poly­ dipsia, but with a lower diagnostic accuracy. Currently, copeptin assays are commercially available in Europe, Australia, India, and Mexico, and tests are pending in several other countries. Once AVP deficiency has been diagnosed, the underlying pathology must be identified by magnetic resonance imaging (MRI) of the sella and suprasellar regions. Also, assessment of the posterior pituitary and the pituitary stalk can be helpful in the differential diagnosis of AVP deficiency. The pituitary bright spot on MRI (a radiologic marker of neurosecretory vesicles containing AVP) is an area of hyperintensity

Urinary volume <50 mL/kg/24 h High serum sodium (>147 mmol/L) Central or nephrogenic DI Complete or partial nephrogenic DI Hypertonic saline test Stimulated copeptin <4.9 pmol/L (at plasma sodium

150 mmol/L) seen in most healthy individuals, but may be lacking in patients with AVP deficiency. However, the absence of the pituitary bright spot is not sufficient to establish a diagnosis of AVP deficiency since it can be present in early stages of AVP deficiency or can be absent in elderly patients. Treatment  The signs and symptoms of uncomplicated AVP defi­ ciency can be eliminated by treatment with DDAVP, a synthetic ana­ logue of AVP. DDAVP acts selectively at V2 receptors to increase urine concentration and decrease urine flow in a dose-dependent manner. It is also more resistant to degradation than is AVP and has a three- to fourfold longer duration of action. The dose of DDAVP impacts on the duration of action (i.e., the higher the dose, the greater the duration of action). DDAVP can be given by IV or SC injection, nasal inhalation, or orally by means of a tablet or melt. The doses required to treat AVP deficiency vary depending on the patient and the route of administra­ tion. Among adults, doses usually range from 1–2 μg qd or bid by injec­ tion, 10–20 μg bid or tid by nasal spray, or 100–400 μg bid or tid orally. The onset of antidiuresis is rapid, ranging from as little as 15 min after injection to 60 min after oral administration. Hyponatremia is the most common complication of desmopressin therapy, with mild depres­ sion of plasma sodium concentration (131–134 mmol/L) reported in about a quarter of patients with intact thirst. In 15% of patients,

hyponatremia is more severe, with plasma sodium concentration of <130 mmol/L. Desmopressin escape, which involves intermittently delaying DDAVP for a number of hours to allow a transient aquaresis, reduces the risk of hyponatremia. Treatment of primary polydipsia focuses on the reduction of exces­ sive fluid intake, optimally in a graded fashion to allow patients to slowly reduce fluids. Treatments to reduce mouth dryness (e.g., ice chips, hard candy to stimulate salivary flow) are also useful to reduce thirst. Pharmacologic therapies have been tried without consistent success. A recent study suggests that glucagon-like peptide 1 (GLP-1) analogues reduce fluid intake, urine output, and thirst perception. AVP resistance is difficult to treat. Patients typically do not respond to desmopressin treatment; however, some patients may respond to high doses if their resistance is only partial. Treatment with conventional doses of a thiazide diuretic and/or amiloride in conjunction with a lowsodium diet and coadministration of nonsteroidal anti-inflammatory drugs (NSAIDs) usually reduces the polyuria and polydipsia, but this combination is nephrotoxic, and careful monitoring of renal function is important. Drug-induced AVP resistance should be treated by dis­ continuation of the causative agent—most commonly lithium—where possible. Persistent lithium-induced AVP resistance can be treated by hydrochlorothiazide and amiloride. It important to be aware that plasma volume contraction produced by thiazide diuretics can decrease lithium excretion and predispose to lithium toxicity. ■ ■HYPODIPSIC/ADIPSIC HYPERNATREMIA An increase in plasma osmolarity/sodium above the normal range (hypertonic hypernatremia) can be due to a decrease in total body water or an increase in total body sodium. The former results from a failure to drink enough water to replace normal or increased urinary and insensible loss due either to water deprivation or a lack of thirst (hypodipsia/adipsia). Clinical Characteristics  Hypodipsic/adipsic hypernatremia is a rare syndrome characterized by chronic or recurrent hypertonic dehydration that most frequently coexists with AVP deficiency (adipsic diabetes insipidus or adipsic AVP deficiency). The hypernatremia var­ ies widely in severity and is often associated with signs of hypovolemia such as tachycardia, postural hypotension, azotemia, hyperuricemia, and hypokalemia due to secondary hyperaldosteronism. Muscle weak­ ness, pain, rhabdomyolysis, hyperglycemia, hyperlipidemia, thrombo­ embolic disease, acute renal failure, and obtundation can also occur. Etiology  Hypodipsia/adipsia is usually due to abnormalities of osmoreceptors in the anterior hypothalamus that regulate thirst. The defect can result from various congenital malformations of midline brain structures or may be acquired due to diseases such tumors (pri­ mary or secondary, and their associated surgery) or aneurysms of the anterior communicating artery, head trauma, granulomatous diseases such as sarcoidosis and histiocytosis, AIDS, and cytomegalovirus encephalitis. Adipsic hypernatremia without demonstrable hypotha­ lamic lesions has also been associated with autoantibodies directed against the subfornical organ. Pathophysiology  A deficiency in osmotically induced thirst results in a failure to drink enough water to replenish obligatory renal and extrarenal losses with resultant significant hypernatremia. Rarely, the regulation of AVP secretion is completely normal, suggesting that the lack of thirst is due to a defect in postosmoreceptor neural path­ ways to higher cognitive centers. Differential Diagnosis  Hypodipsic/adipsic hypernatremia with or without coexisting AVP deficiency usually can be distinguished from other causes of inadequate fluid intake (e.g., coma, paralysis, restraints, absence of fresh water) by the clinical history and setting as well as measurements of serum and urine osmolality. Previous episodes and/ or denial of thirst and failure to drink spontaneously when the patient is conscious, unrestrained, and hypernatremic are virtually diagnostic. Treatment  Hypodipsic hypernatremia can be corrected by admin­ istering water orally if the patient is alert and cooperative or by infusing

TABLE 393-2  Approach to the Management of Water Balance for Patients with Adipsic Arginine Vasopressin (AVP) Deficiency

  1. Replace AVP with sufficient vasopressin (DDAVP).
  2. Monitor fluid input/output initially as an inpatient to achieve eunatremia.
  3. Weigh and record patient’s eunatremic weight.
  4. Recommend 1.5–2 L of fluid intake per day assuming urinary losses are less.
  5. Weigh daily.
  6. If below eunatremic weight, then replace with equivalent volume of fluid to restore eunatremic weight.
  7. Recommend increased fluid intake in times of increased perspiration or Disorders of the Neurohypophysis CHAPTER 393 ambient temperatures.
  8. Regular plasma sodium measurements.  hypotonic fluids (0.45% saline or 5% dextrose) if the patient is not. The amount of free water in liters required to correct the free water deficit should be estimated from body weight in kg and the serum sodium concentration in mmol/L. This amount plus an allowance for continuing insensible and urinary losses should be given over a 24- to 48-h period with close monitoring of serum sodium to ensure that it does not correct too rapidly. Plasma urea/creatinine should be moni­ tored closely for signs of acute renal failure caused by rhabdomyolysis, hypovolemia, and hypotension. Once the patient has been rehydrated, an MRI of the brain and tests of anterior pituitary function should be performed to look for the cause and collateral defects in other hypothalamic functions. A long-term management plan to prevent or minimize recurrence of the fluid and electrolyte imbalance also should be developed. This should include a practical method to regulate fluid intake in accordance with variations in water balance as indicated by changes in body weight or serum sodium determined by home moni­ toring analyzers, if available. Another potential treatment approach is summarized in Table 393-2. ■ ■INAPPROPRIATE ANTIDIURESIS (SEE IN MORE DETAIL CHAP. 56) Clinical Characteristics  Syndrome of inappropriate antidiuresis (SIAD) is produced when plasma levels of AVP are elevated at times when the physiologic secretion of AVP from the posterior pituitary would normally be osmotically suppressed. The clinical abnormality is a decrease in the osmotic pressure of body fluids, such that the hall­ mark of SIAD is hypoosmolality. If hyponatremia is severe or develops acutely, it can cause a variety of neurologic symptoms and signs, such as headache, confusion, anorexia, nausea, vomiting, coma, and con­ vulsions. If the hyponatremia develops gradually or exists for more than a few days, it may be apparently asymptomatic, but even mild hyponatremia is associated with an increased rate of falls and fractures, neurocognitive and neuromuscular symptoms, and increased morbid­ ity and mortality. Etiology  SIAD has many different etiologies, which are summa­ rized in Chap. 56. Pathophysiology  In SIAD, the failure to mount a water diuresis when intake exceeds urinary and insensible loss results in a slight expansion of total body water followed by a modest increase in urinary sodium excretion. As a result, expansion of extracellular volume is minimal, and clinically detectable edema does not develop. However, intracellular volume increases in proportion to the severity and rapid­ ity of the change in plasma sodium. In the brain, this cellular swelling causes an increase in pressure that triggers a variety of symptoms. After several days, the swelling and symptoms may subside due to inactiva­ tion of some intracellular solutes and resultant decrease in cellular volume. Differential Diagnosis  Evaluation of urine and serum osmo­ lality and sodium is the most useful investigation in establishing whether the diagnostic criteria for SIAD are met, alongside clinical assessment of volume status. Measurement of serum osmolality is important to exclude non-hypotonic causes of hyponatremia, such

08 - 394 Thyroid Gland Physiology and Testing

394 Thyroid Gland Physiology and Testing

as pseudohyponatremia (due to raised lipids or protein) or translo­ cational hyponatremia (due to raised glucose or exogenous effective osmolytes [e.g., mannitol]). SIAD must then be differentiated from other types of hypotonic hyponatremia. Measurement of urinary osmolality helps to distinguish SIAD from primary polydipsia where urinary osmolality is usually <100–200 mosm/L. Measurement of urinary sodium levels are useful to differentiate hyponatremia with low effective arterial blood volume from hyponatremia with normal effective arterial blood volume. In hypovolemic or hypervolemic hyponatremia with low effective blood volume, the mechanisms to conserve sodium remain intact, resulting in low urine sodium excretion, whereas in SIAD, there is ongoing renal sodium loss. According to guidelines, levels of <30 mmol/L argue for low effec­ tive arterial blood volume. Assessment of volume status has been used to classify hyponatremia into hypo-, hyper-, or euvolemic hyponatremia, though the accuracy of the clinical examination is poor. Hypervolemic hyponatremia typically occurs in patients with generalized edema due to severe congestive heart failure or cirrhosis. Hypovolemic hyponatremia occurs in patients with loss of sodium and water due to severe vomiting, diarrhea, diuretic use or primary adrenal insufficiency. In case of euvolemic hyponatremia, secondary adrenal insufficiency should be excluded before SIAD is diagnosed. Measurement of plasma AVP or copeptin has no diagnostic value. It is widely recommended to evaluate thyroid function in the workup of hyponatremia. There is, however, limited evidence for hypothyroid­ ism as a significant cause of hyponatremia.

PART 12 Endocrinology and Metabolism TREATMENT Syndrome of Inappropriate Antidiuresis The management of SIAD differs depending on the underlying etiology as well as the severity and duration of symptoms. In the presence of severe neurologic symptoms, urgent intervention and treatment with hypertonic saline are indicated, aiming for an ini­ tial sodium rise of 4–6 mmol with a 100-mL bolus of hypertonic (3%) sodium chloride administered over ~15 min. An initial dose should be followed by clinical reassessment and a repeat dose if there is no clinical response until this target increment has been achieved. First-line treatment of chronic hyponatremia is fluid restriction, usually in the range of 500 to 1000 mL/d including all liquids, not solely water. However, fluid restriction is often ineffective, espe­ cially if urinary osmolality is >500 mosm/L. Second-line treatments when fluid restriction is inadequate are urea or tolvaptan. Urea is a product of hepatic nitrogen metabolism that is renally excreted and exerts an osmotic effect to promote free water excretion. Usually, doses of 30–60 g are sufficient to raise sodium levels. Tolvaptan is an oral vasopressin V2-receptor antagonist that blocks AVP action in the kidney, inducing a water diuresis and raising sodium levels. Due to the risk of overly rapid correction, low-dose tolvaptan (7.5 mg) has become more widely prescribed in recent years. Other concerns with tolvaptan include cost and risk of liver function derangement seen with sustained higher-dose therapy as used for autosomal dominant polycystic kidney disease. Demeclocycline is recommended by some as an alternative therapy, but European guidelines do not recommend it due to side effects. Demeclocycline can induce renal AVP resistance, thereby promoting dilute urine excretion. This effect is unpredictable and potential adverse effects include gastrointestinal intolerance, neph­ rotoxicity, and a photosensitive skin rash. According to a recent study, oral sodium chloride tablets and loop diuretics have a ques­ tionable efficacy. SGLT-2 inhibitors act at the sodium-glucose cotransporter in the proximal tubule to reduce resorption of glucose and sodium. SGLT-2 inhibitors induce glycosuria, which is accom­ panied by increased water excretion due to an osmotic diuresis. This has been shown to increase sodium levels in hospitalized as well as in outpatients with SIAD.

Acknowledgments The authors are grateful to Gary L. Robertson and Daniel G. Bichet for their contributions to this chapter in previous editions of Harrison's. ■ ■FURTHER READING Adrogué HJ, Madias NE: The syndrome of inappropriate antidiure­ sis. N Engl J Med 389:1499, 2023. Christ-Crain M et al: Diabetes insipidus. Nat Rev Dis Primers 5:54, 2019. Fenske W et al: A copeptin based approach in the diagnosis of diabetes insipidus. N Engl J Med 379:428, 2018. Refardt J et al: Arginine or hypertonic saline-stimulated copeptin to diagnose AVP deficiency. N Engl J Med 389:1877, 2023. Tomkins M et al: Diagnosis and management of central diabetes insipidus in adults. J Clin Endocrinol Metab 107:2701, 2022. Warren A et al: Syndrome of inappropriate antidiuresis: From patho­ physiology to management. Endocr Rev 44:819, 2023. J. Larry Jameson, Anthony P. Weetman,

Susan J. Mandel

Thyroid Gland

Physiology and Testing The thyroid gland produces two related hormones, thyroxine (T4) and triiodothyronine (T3) (Fig. 394-1). Acting through thyroid hormone receptors (TR) α and β, these hormones play a critical role in cell dif­ ferentiation and organogenesis during development and help maintain thermogenic and metabolic homeostasis in the adult. Autoimmune disorders of the thyroid gland can stimulate overproduction of thyroid hormones (thyrotoxicosis) (Chap. 396) or cause glandular destruction and hormone deficiency (hypothyroidism) (Chap. 395). Benign nod­ ules and various forms of thyroid cancer are relatively common and amenable to detection by physical examination, ultrasound, and other imaging techniques (Chap. 397). ANATOMY AND DEVELOPMENT The thyroid (Greek thyreos, shield, plus eidos, form) consists of two lobes connected by an isthmus. It is located anterior to the trachea between the cricoid cartilage and the suprasternal notch. The normal thyroid is 12–20 g in size, highly vascular, and soft in consistency. Four parathyroid glands, which produce parathyroid hormone (Chap. 422), are located posterior to each pole of the thyroid. The recurrent laryngeal nerves traverse the lateral borders of the thyroid gland and must be identified during thyroid surgery to avoid injury and vocal cord paralysis. The thyroid gland develops from the floor of the primitive pharynx during the third week of gestation. The developing gland migrates along the thyroglossal duct to reach its final location in the neck. This feature accounts for the rare ectopic location of thyroid tissue at the base of the tongue (lingual thyroid) as well as the occurrence of thy­ roglossal duct cysts along this developmental tract. Thyroid hormone synthesis begins at about 11 weeks’ gestation. Neural crest derivatives from the ultimobranchial body give rise to thyroid medullary C cells that produce calcitonin, a calcium-lowering hormone. The C cells are interspersed throughout the thyroid gland, although their density is greatest in the juncture of the upper onethird and lower two-thirds of the gland. Calcitonin plays a minimal role in calcium homeostasis in humans, but the C cells are clinically important because they are the cellular origin of medullary thyroid cancer (Chap. 400).

I I NH2

3' 5' CH HO O CH2 COOH I I Thyroxine (T4) 3,5,3',5'-Tetraiodothyronine Deiodinase 1 or 2 (5'-Deiodination) Deiodinase 3>2 (5-Deiodination) I I I I NH2 O CH2 CH HO COOH O CH2 CH HO I I Triiodothyronine (T3) 3,5,3'-Triiodothyronine Reverse T3 (rT3) 3,3',5'-Triiodothyronine FIGURE 394-1  Structures of thyroid hormones. Thyroxine (T4) contains four iodine atoms. Deiodination leads to production of the potent hormone triiodothyronine (T3) or the inactive hormone reverse T3. Thyroid gland development is orchestrated by the coordinated expression of several developmental transcription factors. Thyroid transcription factor genes TTF1, TTF2, NKX2-1, FOXE1, and paired homeobox-8 (PAX8) are expressed selectively, but not exclusively, in the thyroid gland. In combination, they dictate thyroid cell development and the induction of thyroid-specific proteins such as thyroglobulin (Tg), thyroid peroxidase (TPO), the sodium iodide symporter (Na+/I–, NIS), and the thyroid-stimulating hormone (TSH) receptor (TSH-R). Mutations in these developmental transcription factors or their downstream target genes are rare causes of thyroid agenesis or dyshormonogenesis, although the causes of most forms of congenital hypothyroidism remain unknown (see Chap. 395, Table 395-1). Because congenital hypothyroidism occurs in ~1 in 4000 newborns, neonatal screening is now performed in most industrialized countries. Transplacental passage of maternal thyroid hormone occurs before the fetal thyroid gland begins to function and provides significant hormone support to a fetus with congenital hypo­ thyroidism. Early thyroid hormone replacement in newborns with congenital hypothyroidism prevents potentially severe developmental abnormalities. The thyroid gland consists of numerous spherical follicles com­ posed of thyroid follicular cells that surround secreted colloid, a proteinaceous fluid containing large amounts of thyroglobulin, the protein precursor of thyroid hormones (Fig. 394-2). The thyroid fol­ licular cells are polarized—the basolateral surface is apposed to the bloodstream and an apical surface faces the follicular lumen. Increased demand for thyroid hormone is regulated by TSH, which binds to its receptor on the basolateral surface of the follicular cells. This binding leads to Tg reabsorption from the follicular lumen and proteolysis within the cytoplasm, yielding thyroid hormones for secretion into the bloodstream. REGULATION OF THE THYROID AXIS TSH, secreted by the thyrotrope cells of the anterior pituitary, plays a pivotal role in control of the thyroid axis and serves as the most use­ ful physiologic marker of thyroid hormone action. TSH is a 31-kDa hormone composed of α and β subunits; the α subunit is common to the other glycoprotein hormones (luteinizing hormone, folliclestimulating hormone, human chorionic gonadotropin [hCG]), whereas the TSH β subunit is unique to TSH. The extent and nature of carbo­ hydrate modification are modulated by thyrotropin-releasing hormone (TRH) and influence the biologic activity of the hormone. The thyroid axis is a classic example of an endocrine feedback loop (Chap. 389). Hypothalamic TRH stimulates pituitary production of TSH, which, in turn, stimulates thyroid hormone synthesis and secre­ tion. Thyroid hormones act via negative feedback predominantly through thyroid hormone receptor β2 (TRβ2) to inhibit TRH and TSH production (Fig. 394-2). The “set point” in this axis is established by

TSH. TRH is the major positive regulator of TSH synthesis and secretion. Peak TSH secretion occurs ~15 min after administration of exogenous TRH. Dopamine, gluco­ corticoids, and somatostatin suppress TSH but are not of major physiologic importance except when these agents are administered in pharmacologic doses. Reduced levels of thyroid hormone increase basal TSH production and enhance TRH-mediated stimulation of TSH. High thyroid hormone levels rapidly and directly suppress TSH gene expression and inhibit TRH stimulation of TSH secretion, indicating that thyroid hormones are the dominant regu­ lator of TSH production. Like other pituitary hormones, TSH is released in a pulsatile manner and exhibits a diurnal rhythm; its highest levels occur at night. However, these TSH excursions are modest in comparison to those of other pituitary hormones, in part, because TSH has a relatively long plasma half-life (50 min). Consequently, single measurements of TSH are adequate for assessing its circulating level. TSH is measured using immunoradio­ metric assays that are highly sensitive and specific. These assays readily distinguish between normal and suppressed TSH values; thus, TSH can be used for the diagnosis of primary hyper­ thyroidism (low TSH) or primary hypothyroidism (high TSH).

Thyroid Gland Physiology and Testing CHAPTER 394 NH2 COOH THYROID HORMONE SYNTHESIS, METABOLISM, AND ACTION ■ ■THYROID HORMONE SYNTHESIS Thyroid hormones are derived from Tg, a large iodinated glycoprotein. After secretion into the thyroid follicle, Tg is iodinated on tyrosine T3 T4 Hypothalamus – TSH-R Basal NIS II- cAMP TRH + – Tg Pituitary Apical TPO DIT Follicular cell Tg-MIT

Thyroid Thyroid follicle T3 T4 Peripheral actions FIGURE 394-2  Regulation of thyroid hormone synthesis. Left. Thyroid hormones T4 and T3 feed back to inhibit hypothalamic production of thyrotropin-releasing hormone (TRH) and pituitary production of thyroid-stimulating hormone (TSH). TSH stimulates thyroid gland production of T4 and T3. Right. Thyroid follicles are formed by thyroid epithelial cells surrounding proteinaceous colloid, which contains thyroglobulin. Follicular cells, which are polarized, synthesize thyroglobulin and carry out thyroid hormone biosynthesis (see text for details). DIT, diiodotyrosine; MIT, monoiodotyrosine; NIS, sodium iodide symporter; Tg, thyroglobulin; TPO, thyroid peroxidase; TSH-R, thyroid-stimulating hormone receptor.

residues that are subsequently coupled via an ether linkage. Reuptake of Tg into the thyroid follicular cell allows proteolysis and the release of newly synthesized T4 and T3.

Iodine Metabolism and Transport  Iodide uptake is a critical first step in thyroid hormone synthesis. Ingested iodine is bound to serum proteins, particularly albumin. Unbound iodine is excreted in the urine. The thyroid gland extracts iodine from the circulation in a highly efficient manner. For example, 10–25% of radioactive tracer (e.g., 123I) is taken up by the normal thyroid gland over 24 h in an iodine-replete state; this value can rise to 70–90% in Graves’ disease. Iodide uptake is mediated by NIS, which is expressed at the basolateral membrane of thyroid follicular cells. NIS is most highly expressed in the thyroid gland, but low levels are present in the salivary glands, lac­ tating breast, and placenta. The iodide transport mechanism is highly regulated, allowing adaptation to variations in dietary supply. Low iodine levels increase the amount of NIS and stimulate uptake, whereas high iodine levels suppress NIS expression and uptake. The selective expression of NIS in the thyroid allows isotopic scanning, treatment of hyperthyroidism, and ablation of thyroid cancer with radioisotopes of iodine, without significant effects on other organs. Mutation of the NIS gene is a rare cause of congenital hypothyroidism, underscoring its importance in thyroid hormone synthesis. Another iodine transporter, pendrin, is located on the apical surface of thyroid cells and mediates PART 12 Endocrinology and Metabolism Global scorecard of iodine nutrition in 2021 Iodine intake in the general population assessed by median urinary iodine concentration (mUIC) in school-age children (SAC)a Studies conducted in 2005–2020 Insufficient mUIC <100 µg/L

National data

Sub-national data No recent data

FIGURE 394-3  Worldwide iodine nutrition. aIn population monitoring of iodine status using urinary iodine concentration (UIC), school-age children (SAC) serve as a proxy for the general population; therefore, preference has been given to studies carried out in SAC. The UIC data have been selected for each country in the following order of priority: data from the most recent known nationally representative survey carried out between 2005 and 2020 in (1) SAC, (2) SAC and adolescents, (3) adolescents, (4) women of reproductive age, (5) other adults (excluding pregnant or lactating women), and (6) other eligible populations. In the absence of recent national surveys, subnational data were used in the same order of priority. Subnational UIC surveys are commonly carried out to provide a rapid assessment of population iodine status, but due to a lack of sampling rigor, they may over- or underestimate the iodine status at the national level and should be interpreted with caution. bAdequate iodine intake in SAC corresponds to median UIC values in the range of 100–299 μg/L and includes categories previously referred to as “adequate” (100–199 μg/L) and “more than adequate” (200–299 μg/L). (Reproduced with permission from The Iodine Global Network. Global scorecard of iodine nutrition in 2021 in the general population based on data in schoolage children (SAC). IGN: Ottawa, Canada. 2021.)

iodine efflux into the lumen. Mutation of the pendrin gene causes Pen­ dred syndrome, a disorder characterized by defective organification of iodine, goiter, and sensorineural deafness. Iodine deficiency is prevalent in many mountainous regions and in central Africa, central South America, and northern Asia (Fig. 394-3). Europe remains mildly iodine-deficient, and health surveys indicate that iodine intake has been falling in the United States and Australia. The World Health Organization (WHO) estimates that about 2 billion people are iodine-deficient, based on urinary excretion data. In areas of relative iodine deficiency, there is an increased prevalence of goi­ ter and, when deficiency is severe, hypothyroidism and cretinism. Cretinism is characterized by intellectual disability and growth retarda­ tion and occurs when children who live in iodine-deficient regions are not treated with iodine or thyroid hormone to restore normal thyroid hormone levels during early life. These children are often born to mothers with iodine deficiency, and it is likely that maternal thyroid hormone deficiency worsens the condition. The physiologic iodine requirement is higher in lactating women, and iodine turnover is high in infants. Concomitant selenium deficiency may also contribute to the neurologic manifestations of cretinism. Iodine supplementation of salt, bread, and other food substances has markedly reduced the preva­ lence of cretinism. Unfortunately, however, iodine deficiency remains a common cause of preventable intellectual disability, often because of societal resistance to food additives or the cost of supplementation. In Iodine intake Adequateb mUIC 100–299 µg/L Excess mUIC ≥300 µg/L

addition to overt cretinism, mild iodine deficiency can lead to subtle reduction of IQ. Oversupply of iodine, through supplements or foods enriched in iodine (e.g., shellfish, kelp), is associated with an increased incidence of autoimmune thyroid disease. The Recommended Dietary Allowance (RDA) is 220 μg iodine per day for pregnant women and 290 μg iodine per day for breastfeeding women. Because the effects of iodine deficiency are most severe in pregnant women and their babies, the American Thyroid Association has recommended that all pregnant and breastfeeding women in the United States and Canada take a pre­ natal multivitamin containing 150 μg iodine per day. Urinary iodine is

100 μg/L in iodine-sufficient populations. Organification, Coupling, Storage, and Release  After iodide enters the thyroid, it is trapped and transported to the apical mem­ brane of thyroid follicular cells, where it is oxidized in an organifica­ tion reaction that involves TPO and hydrogen peroxide produced by dual oxidase (DUOX) and DUOX maturation factor (DUOXA). The reactive iodine atom is added to specific tyrosyl residues within Tg, a large (660 kDa) dimeric protein that consists of 2769 amino acids. The iodotyrosines in Tg are then coupled via an ether linkage in a reaction that is also catalyzed by TPO. Either T4 or T3 can be produced by this reaction, depending on the number of iodine atoms present in the iodotyrosines. After coupling, Tg is taken back into the thyroid cell, where it is processed in lysosomes to release T4 and T3. Uncoupled mono- and diiodotyrosines (MIT, DIT) can be deiodinated by the enzyme iodotyrosine deiodinase, thereby recycling any iodide that is not converted into thyroid hormones. Disorders of thyroid hormone synthesis are rare causes of congenital hypothyroidism (Chap. 395). The vast majority of these disorders are due to recessive mutations in TPO or Tg, but defects have also been identified in the TSH-R, NIS, pendrin, hydrogen peroxide generation, and iodotyrosine deiodinase, as well as genes involved in thyroid gland development. In the case of biosynthetic defects, the gland is incapable of synthesizing adequate amounts of hormone, leading to increased TSH and a large goiter. TSH Action  TSH regulates thyroid gland function through the TSH-R, a seven-transmembrane G protein–coupled receptor (GPCR). The TSH-R is coupled to the α subunit of stimulatory G protein (GSα), which activates adenylyl cyclase, leading to increased production of cyclic adenosine monophosphate (cAMP). TSH also stimulates phos­ phatidylinositol turnover by activating phospholipase C. Recessive lossof-function TSH-R mutations cause thyroid hypoplasia and congenital hypothyroidism. Dominant gain-of-function mutations are rare causes of sporadic or familial hyperthyroidism that is characterized by goiter, thyroid cell hyperplasia, and autonomous function (Chap. 396). Most of these activating mutations occur in the transmembrane domain of the receptor. They mimic the conformational changes induced by TSH binding or the interactions of thyroid-stimulating immunoglobulins (TSIs) in Graves’ disease. Activating TSH-R mutations also occur as somatic events, leading to clonal selection and expansion of the affected thyroid follicular cell and autonomously functioning thyroid nodules. Other Factors That Influence Hormone Synthesis and Release  Although TSH is the dominant hormonal regulator of thyroid gland growth and function, a variety of growth factors, most produced locally in the thyroid gland, also influence thyroid hormone synthesis. These include insulin-like growth factor 1 (IGF-1), epider­ mal growth factor, transforming growth factor β (TGF-β), endothelins, and various cytokines. The quantitative roles of these factors are not well understood, but they are important in selected disease states. In acromegaly, for example, increased levels of growth hormone and IGF-1 are associated with goiter and predisposition to multinodular goiter (MNG). Certain cytokines and interleukins (ILs) produced in association with autoimmune thyroid disease induce thyroid growth, whereas others lead to apoptosis. Iodine deficiency increases thyroid blood flow and upregulates the NIS, stimulating more efficient iodine uptake. Excess iodide transiently inhibits thyroid iodide organification, a phenomenon known as the Wolff-Chaikoff effect. In individuals with

a normal thyroid, the gland escapes from this inhibitory effect and iodide organification resumes; the suppressive action of high iodide may persist, however, in patients with underlying autoimmune thyroid disease.

THYROID FUNCTION IN PREGNANCY Five factors alter thyroid function in pregnancy: (1) the transient increase in hCG during the first trimester, which weakly stimulates the TSH-R; (2) the estrogen-induced rise in thyroxine-binding globulin (TBG) during the first trimester, which is sustained dur­ ing pregnancy; (3) alterations in the immune system, leading to the onset, exacerbation, or amelioration of an underlying autoimmune thyroid disease; (4) increased thyroid hormone metabolism by the placental type III deiodinase; and (5) increased urinary iodide excre­ tion, which can cause impaired thyroid hormone production in areas of marginal iodine sufficiency. Women with a precarious iodine intake (<50 μg/d) are most at risk of developing a goiter during pregnancy or giving birth to an infant with a goiter and hypothyroid­ ism. The WHO recommends a daily iodine intake of 250 μg during pregnancy and lactation, and prenatal vitamins should contain 150 μg per tablet. Thyroid Gland Physiology and Testing CHAPTER 394 The rise in circulating hCG levels during the first trimester is accompanied by a reciprocal fall in TSH that persists into the middle of pregnancy. This reflects the weak binding of hCG, which is present at very high levels, to the TSH-R. Rare individuals have variant TSH-R sequences that enhance hCG binding and TSH-R activation. hCGinduced changes in thyroid function can result in transient gestational hyperthyroidism that may be associated with hyperemesis gravidarum, a condition characterized by severe nausea and vomiting and risk of volume depletion. However, antithyroid drugs are not indicated unless concomitant Graves’ disease is suspected. Parenteral fluid replacement usually suffices until the condition resolves. Normative values for most thyroid function tests differ during pregnancy, and if available, trimester-specific reference ranges should be used when diagnosing thyroid dysfunction during pregnancy. TSH levels decrease at the end of the first trimester and then rise as gesta­ tion progresses so that the nonpregnant reference ranges can be used from mid-gestation to delivery. Total T4 and T3 levels are ~1.5× higher throughout pregnancy, but the free T4, which is the same or slightly higher at the end of the first trimester, progressively decreases so that by the third trimester, values are often below the nonpregnant lower reference cutoff. During pregnancy, subclinical hypothyroidism occurs in 2% of women, but overt hypothyroidism is present in only 1 in 500. Prospec­ tive randomized controlled trials have not shown a benefit for univer­ sal thyroid disease screening in pregnancy. Targeted TSH testing for hypothyroidism is recommended for women planning a pregnancy if they have a strong family history of autoimmune thyroid disease, other autoimmune disorders (e.g., type 1 diabetes), infertility, prior preterm delivery or recurrent miscarriage, or signs or symptoms of thyroid disease, or are older than 30 years. Thyroid hormone requirements are increased by up to 45% during pregnancy in levothyroxine-treated hypothyroid women. ■ ■THYROID HORMONE TRANSPORT AND METABOLISM Serum-Binding Proteins  T4 is secreted from the thyroid gland in about 15-fold excess over T3 (Table 394-1). Both hormones are bound to plasma proteins, including TBG, transthyretin (TTR, formerly known as thyroxine-binding prealbumin [TBPA]), and albumin. The plasma-binding proteins increase the pool of circulating hormone, delay hormone clearance, and may modulate hormone delivery to selected tissue sites. The concentration of TBG is relatively low (1–2 mg/dL), but because of its high affinity for thyroid hormones (T4 > T3), it carries ~80% of the bound hormones. Albumin has relatively low affinity for thyroid hormones but has a high plasma concentration (~3.5 g/dL), and it binds up to 10% of T4 and 30% of T3. TTR carries ~10% of T4 but little T3. When the effects of the various binding proteins are combined, ~99.98% of T4 and 99.7% of T3 are protein-bound. Because T3 is less

TABLE 394-1  Characteristics of Circulating T4 and T3 HORMONE PROPERTY T4 T3 Serum concentrations   Total hormone 8 μg/dL 0.14 μg/dL   Fraction of total hormone in the unbound form 0.02% 0.3%   Unbound (free) hormone 21 × 10–12M 6 × 10–12M Serum half-life 7 d 2 d Fraction directly from the thyroid 100% 20% Production rate, including peripheral conversion 90 μg/d 32 μg/d PART 12 Endocrinology and Metabolism Intracellular hormone fraction ~20% ~70% Relative metabolic potency 0.3

Receptor binding 10–10M 10–11M tightly bound than T4, the fraction of unbound T3 is greater than unbound T4, but there is less unbound T3 in the circulation because it is produced in smaller amounts and cleared more rapidly than T4. The unbound or “free” concentrations of the hormones are ~2 × 10−11 M for T4 and ~6 × 10−12 M for T3, which roughly correspond to the thyroid hormone receptor–binding constants for these hormones (see below). The unbound hormone is thought to be biologically available to tissues. The homeostatic mechanisms that regulate the thyroid axis are directed toward maintenance of normal concentrations of unbound hormones. Abnormalities of Thyroid Hormone–Binding Proteins  A number of inherited and acquired abnormalities affect thyroid hor­ mone–binding proteins. X-linked TBG deficiency is associated with very low levels of total T4 and T3. However, because unbound hormone levels are normal, patients are euthyroid and TSH levels are normal. It is important to recognize this disorder to avoid efforts to normal­ ize total T4 levels, because this leads to thyrotoxicosis and is futile because of rapid hormone clearance in the absence of TBG. TBG levels are elevated by estrogen, which increases sialylation and delays TBG clearance. Consequently, in women who are pregnant or taking estrogen-containing contraceptives, elevated TBG increases total T4 and T3 levels; however, unbound T4 and T3 levels are normal. These features are part of the explanation for why women with hypothyroid­ ism require increased amounts of L-thyroxine replacement as TBG levels are increased by pregnancy or estrogen treatment. Mutations in TBG, TTR, and albumin may increase the binding affinity for T4 and/ or T3 and cause disorders known as euthy­ roid hyperthyroxinemia or familial dys­ albuminemic hyperthyroxinemia (FDH) (Table 394-2). These disorders result in increased total T4 and/or T3, but unbound hormone levels are normal. The familial nature of the disorders, and the fact that TSH levels are normal rather than sup­ pressed, should suggest this diagnosis. Unbound hormone levels (ideally mea­ sured by dialysis) are normal in FDH. The diagnosis can be confirmed by using tests that measure the affinities of radiolabeled hormone binding to specific transport proteins or by performing DNA sequence analyses of the abnormal transport protein genes. TABLE 394-2  Conditions Associated with Euthyroid Hyperthyroxinemia DISORDER CAUSE TRANSMISSION CHARACTERISTICS Familial dysalbuminemic hyperthyroxinemia (FDH) AD Increased T4 Normal unbound T4 Rarely increased T3 TBG         Familial excess Increased TBG production XL Increased total T4, T3 Normal unbound T4, T3   Acquired excess Medications (estrogen), pregnancy, cirrhosis, hepatitis Acquired Increased total T4, T3 Normal unbound T4, T3 Transthyretina         Excess Islet tumors Acquired Usually normal T4, T3   Mutations Increased affinity for T4 or T3 AD Increased total T4, T3 Normal unbound T4, T3 Medications: propranolol, ipodate, iopanoic acid, amiodarone Certain medications, such as salicylates and salsalate, can displace thyroid hor­ mones from circulating binding proteins. Although these drugs transiently perturb the thyroid axis by increasing free thyroid hormone levels, TSH is suppressed until a new steady state is reached, thereby restor­ ing euthyroidism. Circulating factors asso­ ciated with acute illness may also displace thyroid hormone from binding proteins (Chap. 396). Resistance to thyroid hormone (RTH) aAlso known as thyroxine-binding prealbumin (TBPA). Abbreviations: AD, autosomal dominant; TBG, thyroxine-binding globulin; TSH, thyroid-stimulating hormone; XL, X-linked.

Deiodinases  T4 may be thought of as a precursor for the more potent T3. T4 is converted to T3 by the deiodinase enzymes (Fig. 394-1). Type I deiodinase, which is located primarily in thyroid, liver, and kid­ neys, has a relatively low affinity for T4. Type II deiodinase has a higher affinity for T4 and is found primarily in the pituitary gland, brain, brown fat, and thyroid gland. Expression of type II deiodinase allows it to regulate T3 concentrations locally, a property that may be important in the context of levothyroxine (T4) replacement. Type II deiodinase is also regulated by thyroid hormone; hypothyroidism induces the enzyme, resulting in enhanced T4 → T3 conversion in tissues such as brain and pituitary. T4 → T3 conversion is impaired by fasting, systemic illness or acute trauma, oral contrast agents, and a variety of medications (e.g., propylthiouracil, propranolol, amiodarone, gluco­ corticoids). Type III deiodinase inactivates T4 and T3 and is the most important source of reverse T3 (rT3), including in the sick euthyroid syndrome. This enzyme is expressed in the human placenta but is not active in healthy individuals. In the sick euthyroid syndrome, especially with hypoperfusion, the type III deiodinase is activated in muscle and liver. Massive hemangiomas and other tumors that express type III deiodinase are a rare cause of consumptive hypothyroidism. ■ ■THYROID HORMONE ACTION Thyroid Hormone Transport  Circulating thyroid hormones enter cells by passive diffusion and via specific transporters such as the monocarboxylate 8 transporter (MCT8), MCT10, and organic aniontransporting polypeptide 1C1. Mutations in the MCT8 gene have been identified in patients with X-linked psychomotor retardation and thyroid function abnormalities (low T4, high T3, and high TSH). After entering cells, thyroid hormones act primarily through nuclear recep­ tors, although they also have nongenomic actions through stimulating mitochondrial enzymatic responses and may act directly on blood ves­ sels and the heart through integrin receptors. Nuclear Thyroid Hormone Receptors  Thyroid hormones bind with high affinity to nuclear TRs α and β. Both TRα and TRβ are expressed in most tissues, but their relative expression levels vary among organs; TRα is particularly abundant in brain, kidneys, gonads, muscle, and heart, whereas TRβ expression is relatively high in the pituitary and liver. Both receptors are variably spliced to form unique isoforms. The TRβ2 isoform, which has a unique amino terminus, is selectively expressed in the hypothalamus and pituitary, where it plays a role in feedback control of the thyroid axis (see above). The TRα2 Albumin mutations, usually R218H Decreased T4 → T3 conversion Acquired Increased T4 Decreased T3 Normal or increased TSH AD Increased unbound T4, T3 Normal or increased TSH Some patients clinically thyrotoxic Thyroid hormone receptor β mutations

Nucleus T3 T3 T4 CoR

CoA T3 CoA

RXR TR Cytoplasm Gene TRE

Gene expression FIGURE 394-4  Mechanism of thyroid hormone receptor action. The thyroid hormone receptor (TR) and retinoid X receptor (RXR) form heterodimers that bind specifically to thyroid hormone response elements (TRE) in the promoter regions of target genes. In the absence of hormone, TR binds co-repressor (CoR) proteins that silence gene expression. The numbers refer to a series of ordered reactions that occur in response to thyroid hormone: (1) T4 or T3 enters the nucleus; (2) T3 binding dissociates CoR from TR; (3) co-activators (CoA) are recruited to the T3-bound receptor; and (4) gene expression is altered. isoform contains a unique carboxy terminus that precludes thyroid hormone binding. The TRs contain a central DNA-binding domain and a C-terminal ligand-binding domain. They bind to specific DNA sequences, termed thyroid response elements (TREs), in target genes (Fig. 394-4). The receptors bind as homodimers or, more commonly, as heterodimers with retinoic acid X receptors (RXRs) (Chap. 389). The activated receptor can either stimulate gene transcription (e.g., myosin heavy chain α) or inhibit transcription (e.g., TSH β-subunit gene), depending on the nature of the regulatory elements in the target gene. Thyroid hormones (T3 and T4) bind with similar affinities to TRα and TRβ. However, structural differences in the ligand-binding domains provide the potential for developing receptor-selective ago­ nists or antagonists, and these are under investigation. T3 is bound with 10–15 times greater affinity than T4, which explains its increased potency. Although T4 is produced in excess of T3, receptors are occu­ pied mainly by T3, reflecting T4 → T3 conversion by peripheral tissues, T3 bioavailability in the plasma, and the greater affinity of receptors for T3. After binding to TRs, thyroid hormone induces conformational changes in the receptors that modify its interactions with accessory transcription factors. Importantly, in the absence of thyroid hormone binding, the aporeceptors bind to co-repressor proteins that inhibit gene transcription. Hormone binding dissociates the co-repressors and allows the recruitment of co-activators that enhance transcription. The discovery of TR interactions with co-repressors explains the fact that TR silences gene expression in the absence of hormone binding. Consequently, hormone deficiency has a profound effect on gene expression because it causes gene repression as well as loss of hormoneinduced stimulation. This concept has been corroborated by the find­ ing that targeted deletion of the TR genes in mice has a less pronounced phenotypic effect than hormone deficiency. Thyroid Hormone Resistance  Resistance to thyroid hormone (RTH) is an autosomal dominant disorder characterized by elevated thyroid hormone levels and inappropriately normal or elevated TSH. Individuals with RTH do not, in general, exhibit signs and symptoms that are typical of hypothyroidism because hormone resistance is par­ tial and is compensated by increased levels of thyroid hormone. The clinical features of RTH can include goiter, attention deficit disorder, mild reduction in IQ, delayed skeletal maturation, tachycardia, and impaired metabolic responses to thyroid hormone.

Classical forms of RTH are caused by mutations in the TRβ gene. These mutations, located in restricted regions of the ligand-binding domain, cause loss of receptor function. However, because the mutant receptors retain the capacity to dimerize with RXRs, bind to DNA, and recruit co-repressor proteins, they function as antagonists of the remaining normal TRβ and TRα receptors. This property, referred to as “dominant negative” activity, explains the autosomal dominant mode of transmission. The diagnosis is suspected when unbound thy­ roid hormone levels are increased without suppression of TSH. Similar hormonal abnormalities are found in other affected family members, although the TRβ mutation arises de novo in ~20% of patients. DNA sequence analysis of the TRβ gene provides a definitive diagnosis. RTH must be distinguished from other causes of euthyroid hyperthyroxin­ emia (e.g., FDH) and inappropriate secretion of TSH by TSH-secreting pituitary adenomas (Chap. 392). In most patients, no treatment is indicated; the importance of making the diagnosis is to avoid inappro­ priate treatment of mistaken hyperthyroidism and to provide genetic counseling.

Thyroid Gland Physiology and Testing CHAPTER 394 A distinct form of RTH is caused by mutations in the TRα gene. Affected patients have many clinical features of congenital hypo­ thyroidism including growth retardation, skeletal dysplasia, severe constipation, and delayed neurocognitive development. In contrast to RTH caused by mutations in TRβ, thyroid function tests include normal TSH, low or normal T4, and normal or elevated T3 levels. These distinct clinical and laboratory features underscore the different tissue distribution and functional roles of TRβ and TRα. Thyroxine treatment appears to alleviate some of the clinical manifestations of patients with RTH caused by TRα mutations. ■ ■PHYSICAL EXAMINATION In addition to the examination of the thyroid itself, the physical exami­ nation should include a search for signs of abnormal thyroid function and the extrathyroidal features of ophthalmopathy and dermopathy (Chap. 396). Examination of the neck begins by inspecting the seated patient from the front and side and noting any surgical scars, obvious masses, or distended veins. The thyroid can be palpated with both hands from behind or while facing the patient, using the thumbs to palpate each lobe. It is best to use a combination of these methods, especially when nodules are small. The patient’s neck should be slightly flexed to relax the neck muscles. After locating the cricoid cartilage, the isthmus, which is attached to the lower one-third of the thyroid lobes, can be identified and then followed laterally to locate either lobe (normally, the right lobe is slightly larger than the left). By asking the patient to swallow sips of water, thyroid consistency can be better appreciated as the gland moves beneath the examiner’s fingers. Features to be noted include thyroid size, consistency, nodularity, and any tenderness or fixation. An estimate of thyroid size (normally 12–20 g) should be made, and a drawing is often the best way to record findings. Ultrasound imaging provides the most accurate measure­ ment of thyroid volume and nodularity and is useful for assessment of goiter prevalence in iodine-deficient regions. However, ultrasound is not indicated if the thyroid physical examination is normal. The size, location, and consistency of any nodules should also be defined. A bruit or thrill over the gland, located over the insertion of the supe­ rior and inferior thyroid arteries (supero- or inferolaterally), indicates increased vascularity, associated with turbulent rather than laminar blood flow, as occurs in hyperthyroidism. If the lower borders of the thyroid lobes are not clearly felt, a goiter may be retrosternal. Large retrosternal goiters can cause venous distention over the neck and difficulty breathing, especially when the arms are raised (Pemberton’s sign). With any central mass above the thyroid, the tongue should be extended, as thyroglossal cysts then move upward. The thyroid exami­ nation is not complete without assessment for lymphadenopathy in the supraclavicular and cervical regions of the neck. ■ ■LABORATORY EVALUATION Measurement of Thyroid Hormones  The enhanced sensitivity and specificity of TSH assays have greatly improved laboratory assess­ ment of thyroid function. Because TSH levels change dynamically

in response to alterations of T4 and T3, a logical approach to thyroid testing is to first determine whether TSH is suppressed, normal, or elevated. With rare exceptions (see below), a normal TSH level excludes a primary abnormality of thyroid function. This strategy depends on the use of assays for TSH that are sensitive enough to discriminate between the lower limit of the reference interval and the suppressed val­ ues that occur with thyrotoxicosis. Extremely sensitive assays can detect TSH levels ≤0.004 mIU/L, but, for practical purposes, assays sensitive to ≤0.01 mIU/L are sufficient. The widespread availability of sensitive TSH assays has rendered the TRH stimulation test obsolete, because the failure of TSH to rise after an intravenous bolus of 200–400 μg TRH has the same implications as a suppressed basal TSH. Because the antibod­ ies used in many TSH assays are biotinylated, biotin supplements con­ taining 1000 μg or more, including biotin in some multivitamins, can interfere with TSH measurements, resulting in falsely low TSH values and falsely high T4 or T3 levels. Therefore, patients should be advised to stop taking biotin for at least 2 days prior to thyroid function testing.

PART 12 Endocrinology and Metabolism The finding of an abnormal TSH level must be followed by measure­ ments of circulating thyroid hormone levels to confirm the diagnosis of hyperthyroidism (suppressed TSH) or hypothyroidism (elevated TSH). Automated immunoassays are widely available for serum total T4 and total T3. T4 and T3 are highly protein-bound, and numerous fac­ tors (illness, medications, genetic factors) can influence protein bind­ ing. It is useful, therefore, to measure the free, or unbound, hormone levels, which correspond to the biologically available hormone pool. Two direct methods are used to measure unbound thyroid hormones: (1) unbound thyroid hormone competition with radiolabeled T4 (or an analogue) for binding to a solid-phase antibody, and (2) physical separation of the unbound hormone fraction by ultracentrifugation or equilibrium dialysis. Although early unbound hormone immunoassays suffered from artifacts, newer assays correlate well with the results of the more technically demanding and expensive physical separation methods. An indirect method that is now less commonly used to esti­ mate unbound thyroid hormone levels is to calculate the free T3 or free T4 index from the total T4 or T3 concentration and the thyroid hormone binding ratio (THBR). The latter is derived from the T3-resin uptake test, which determines the distribution of radiolabeled T3 between an absorbent resin and the unoccupied thyroid hormone–binding proteins in the sample. The binding of the labeled T3 to the resin is increased when there is reduced unoccupied protein binding sites (e.g., TBG deficiency) or increased total thyroid hormone in the sample; it is decreased under the opposite circumstances. The product of THBR and total T3 or T4 provides the free T3 or T4 index. In effect, the index corrects for anomalous total hormone values caused by variations in hormone-protein binding. Total thyroid hormone levels are elevated when TBG is increased due to estrogens (pregnancy, oral contraceptives, hormone therapy, tamoxifen, selective estrogen receptor modulators, inflammatory liver disease) and decreased when TBG binding is reduced (androgens, nephrotic syndrome). Genetic disorders and acute illness can also cause abnormalities in thyroid hormone–binding proteins, and various drugs (phenytoin, carbamazepine, salicylates, and nonsteroidal antiinflammatory drugs [NSAIDs]) can interfere with thyroid hormone binding. Because unbound thyroid hormone levels are normal and the patient is euthyroid in all of these circumstances, assays that measure unbound hormone are preferable to those for total thyroid hormones. For most purposes, the unbound T4 level is sufficient to confirm thyrotoxicosis, but 2–5% of patients have only an elevated T3 level (T3 toxicosis). Thus, unbound T3 levels should be measured in patients with a suppressed TSH but normal unbound T4 levels. There are several clinical conditions in which the use of TSH as a screening test may be misleading, particularly without simultaneous unbound T4 determinations. Any severe nonthyroidal illness can cause abnormal TSH levels. Although hypothyroidism is the most common cause of an elevated TSH level, rare causes include a TSH-secreting pituitary tumor (Chap. 392), thyroid hormone resistance, and assay artifact. Conversely, a suppressed TSH level, particularly <0.01 mIU/L, usually indicates thyrotoxicosis. However, subnormal TSH levels between 0.01 and 0.1 mIU/L may be seen during the first trimester of

pregnancy (due to hCG secretion), after treatment of hyperthyroid­ ism (because TSH can remain suppressed for several months), and in response to certain medications (e.g., high doses of glucocorticoids or dopamine). As above, biotin supplements, generally those containing more than 1000 ug, taken <18 h prior to a blood draw can interfere with biotinylated TSH antibodies and the subsequent streptavidin capture. Importantly, secondary hypothyroidism, caused by hypothalamicpituitary disease, is associated with a variable (low to high-normal) TSH level, which is inappropriate for the low T4 level. Thus, TSH should not be used as an isolated laboratory test to assess thyroid function in patients with suspected or known hypothalamic or pituitary disease. Tests for the end-organ effects of thyroid hormone excess or deple­ tion, such as estimation of basal metabolic rate, tendon reflex relax­ ation rates, or serum cholesterol, are relatively insensitive and are not useful as clinical determinants of thyroid function. Tests to Determine the Etiology of Thyroid Dysfunction 

Autoimmune thyroid disease is detected most easily by measuring circulating antibodies against TPO and Tg. Because antibodies to Tg alone are less common, it is reasonable to measure only TPO anti­ bodies. About 5–15% of euthyroid women and up to 2% of euthyroid men have thyroid antibodies; such individuals are at increased risk of developing thyroid dysfunction. Almost all patients with autoimmune hypothyroidism, and up to 80% of those with Graves’ disease, have TPO antibodies, usually at high levels. TSIs are antibodies that stimulate the TSH-R in Graves’ disease. They are most commonly measured by commercially available tracer displacement assays called TRAb (TSH receptor antibody) with the assumption that elevated levels in the setting of clinical hyperthyroid­ ism reflect stimulatory effects on the TSH receptor. A bioassay is less commonly used. Remission rates in patients with Graves’ disease after antithyroid drug cessation are higher in patients with disappearance TRAb. Furthermore, the TRAb assay is used to predict both fetal and neonatal thyrotoxicosis caused by transplacental passage of high maternal levels of TRAb or TSI (>3× upper limit of normal) in the last trimester of pregnancy. Serum Tg levels are increased in all types of thyrotoxicosis except thyrotoxicosis factitia caused by self-administration of thyroid hor­ mone. Tg levels are particularly increased in thyroiditis, reflecting thyroid tissue destruction and release of Tg. The main role for Tg mea­ surement, however, is in the follow-up of thyroid cancer patients. After total thyroidectomy and radioablation for patients with thyroid cancer, Tg levels should be <0.2 ng/mL in the absence of anti-Tg antibodies; measurable levels indicate incomplete ablation or recurrent cancer. Radioiodine Uptake and Thyroid Scanning  The thyroid gland selectively transports and organifies radioisotopes of iodine (123I, 125I, 131I) and transports 99mTc pertechnetate, allowing thyroid imaging for all these isotopes, but quantitation of radioactive tracer fractional uptake for iodine isotopes only. Nuclear imaging of Graves’ disease is characterized by an enlarged gland and increased tracer uptake that is distributed homogeneously. Toxic adenomas appear as focal areas of increased uptake, with suppressed tracer uptake in the remainder of the gland (reflecting suppressed TSH). In toxic MNG, the gland is enlarged—often with dis­ torted architecture—and there are multiple areas of relatively increased (functioning nodules) or decreased tracer uptake (suppressed thyroid parenchyma or nonfunctioning nodules). Subacute, viral, and postpar­ tum thyroiditis are associated with very low uptake because of follicular cell damage and TSH suppression. Thyrotoxicosis factitia is also asso­ ciated with low uptake because exogenous hormone suppresses TSH. In addition, excessive circulating exogenous iodine (e.g., from dietary sources of iodinated contrast dye) reduces radionuclide uptake even in the presence of increased thyroid hormone production. Thyroid scintigraphy is not used in the routine evaluation of patients with thyroid nodules but should be performed if the serum TSH level is subnormal to determine if functioning thyroid nodules are pres­ ent. Functioning or “hot” nodules are almost never malignant, and fine-needle aspiration (FNA) biopsy is not indicated (see Chap. 397,

Fig. 397-3B). The vast majority of thyroid nodules do not produce thyroid

09 - 395 Hypothyroidism

395 Hypothyroidism

hormone (“cold” nodules, see Chap. 397, Fig 397-3A), and these are more likely to be malignant (~5–10%). Whole-body and thyroid scanning is also used in the treatment and, now less frequently, in the surveillance of thyroid cancer. After thyroidectomy for thyroid cancer, the TSH level is raised by either using a thyroid hormone withdrawal protocol or recombinant human TSH injection (Chap. 397). Admin­ istration of either 131I or 123I (in higher activities than used to image the thyroid gland alone) allows whole-body scanning (WBS) to detect the thyroid remnant. WBS imaging is also performed after therapeutic administration of 131I, which confirms remnant ablation and may reveal iodine-avid metastases. Thyroid Ultrasound  Ultrasonography is the most valuable tool for the diagnosis and evaluation of patients with nodular thyroid disease (Chap. 397). Evidence-based guidelines recommend thyroid ultrasonography for all patients suspected of having thyroid nodules by either physical examination or another imaging study. Using 10- to 12-MHz linear transducers, resolution and image quality are excellent, allowing the characterization of nodules and cysts >3 mm. Sonographic patterns that combine suspicious sonographic features are highly sug­ gestive of malignancy (e.g., hypoechoic solid nodules with irregular borders and punctate echogenic foci >90% cancer risk), whereas other patterns correlate with a lower likelihood of cancer (isoechoic solid nodules, 5–10% cancer risk). Some patterns suggest benignity (e.g., spongiform nodules, defined as those with multiple small internal cys­ tic areas, or simple cysts, <3% cancer risk) (see Chap. 397, Fig. 397-2). These patterns have been incorporated into validated risk stratification systems (RSSs) for sonographic imaging of thyroid nodules (American College of Radiology [ACR] Thyroid Imaging Reporting and Data System [TI-RADS], American Thyroid Association, European Thyroid Association [EU-TIRADS] and others) (see Chap. 397, Fig. 397-1). These systems are relatively concordant in the classification of thyroid nodules; they differ in size cutoff recommendations for FNA. Not sur­ prisingly, the RSSs with lower size cutoffs have higher sensitivity and lower specificity for thyroid cancer diagnosis than those with higher cutoffs. Nevertheless, all have been shown to reduce unnecessary FNAs by at least 45%, in part due to the recommendation not to perform FNA of spongiform nodules. In addition to evaluating thyroid nodules, ultrasound is useful for monitoring nodule size and for the aspiration of nodules or cystic lesions. Ultrasound-guided FNA biopsy of thyroid lesions lowers the rate of inadequate sampling and decreases sample error, thereby reduc­ ing both the nondiagnostic and false-negative rates of FNA cytology. Ultrasonography of the central and lateral cervical lymph node com­ partments is indispensable in the evaluation of thyroid cancer patients, preoperatively and during follow-up. In addition, the all of the RSSs recommend a survey of the cervical lymph nodes as part of every diag­ nostic thyroid sonographic examination. ■ ■FURTHER READING Alexander EK et al: 2017 Guidelines of the American Thyroid Asso­ ciation for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid 27:315, 2017. Andersson M, Braegger CP: The role of iodine for thyroid function in lactating women and infants. Endocr Rev 43:469, 2022. Carvalho DP, Dupuy C: Thyroid hormone biosynthesis and release. Mol Cell Endocrinol 458:S0303, 2017. Groeneweg S et al: Thyroid hormone transporters. Endocr Rev 41:146, 2020. Lee SY, Pearce EN: Testing, monitoring, and treatment of thyroid dysfunction in pregnancy. J Clin Endocrinol Metab 106:883, 2021. Mio C et al: Molecular defects in thyroid dysgenesis. Clin Genet 97:222, 2020. Moran C et al: Genetic disorders of thyroid development, hormone biosynthesis and signalling. Clin Endocrinol 97:502, 2022. Pappa T, Refetoff S: Resistance to thyroid hormone beta: a focused review. Front Endocrinol 12:1, 2021. Rugge JB et al: Screening and treatment of thyroid dysfunction: An evidence review for the U.S. Preventive Services Task Force. Ann Intern Med 162:35, 2015.

Anthony P. Weetman, Susan J. Mandel,

J. Larry Jameson

Hypothyroidism HYPOTHYROIDISM Iodine deficiency remains a common cause of hypothyroidism world­ wide. In areas of iodine sufficiency, autoimmune disease (Hashimoto’s thyroiditis) and iatrogenic causes (treatment of hyperthyroidism) are most common (Table 395-1). Hypothyroidism CHAPTER 395 ■ ■CONGENITAL HYPOTHYROIDISM Prevalence  Hypothyroidism occurs in about 1 in 2000–4000 new­ borns, and neonatal screening is performed in most industrialized countries. It may be transient, especially if the mother has thyroidstimulating hormone (TSH) receptor (TSH-R)–blocking antibodies or has received antithyroid drugs, but permanent hypothyroidism occurs in the majority. The causes of neonatal hypothyroidism include thyroid gland dysgenesis in 65%, inborn errors of thyroid hormone synthesis in 30%, and TSH-R antibody mediated in 5% of affected newborns. The developmental abnormalities are twice as common in girls. Mutations that cause congenital hypothyroidism are being increasingly identi­ fied, but most remain idiopathic (Chap. 394). These can be broadly categorized as mutations causing (1) central hypothyroidism because of abnormal hypothalamic-pituitary development or the loss of spe­ cific components of the thyrotropin-releasing hormone (TRH)/TSH hormonal pathways; (2) abnormal thyroid gland development or dys­ genesis; or (3) abnormal thyroid hormone synthesis and processing, or dyshormonogenesis (Table 395-2). Transplacental passage of maternal thyroid hormone occurs before the fetal thyroid gland begins to func­ tion and provides partial hormone support to a fetus with congenital hypothyroidism. TABLE 395-1  Causes of Hypothyroidism Primary Autoimmune hypothyroidism: Hashimoto’s thyroiditis, atrophic thyroiditis Iatrogenic: 131I treatment, subtotal or total thyroidectomy, external irradiation of neck for lymphoma or cancer Drugs: iodine excess (including iodine-containing contrast media), amiodarone, lithium, antithyroid drugs, p-aminosalicylic acid, interferon a and other cytokines, aminoglutethimide, tyrosine kinase inhibitors (e.g., sunitinib), immune checkpoint inhibitors (e.g., ipilimumab, nivolumab, pembrolizumab) Congenital hypothyroidism: absent or ectopic thyroid gland, dyshormonogenesis, TSH-R mutation Iodine deficiency Infiltrative disorders: amyloidosis, sarcoidosis, hemochromatosis, scleroderma, cystinosis, Riedel’s thyroiditis Overexpression of type 3 deiodinase in infantile hemangioma and other tumors Transient Silent thyroiditis, including postpartum thyroiditis Subacute thyroiditis Withdrawal of supraphysiologic thyroxine treatment in individuals with an intact thyroid After 131I treatment or subtotal thyroidectomy for Graves’ disease Secondary Hypopituitarism: tumors, pituitary surgery or irradiation, infiltrative disorders, Sheehan’s syndrome, trauma, genetic forms of combined pituitary hormone deficiencies Isolated TSH deficiency or inactivity Drugs: bexarotene, mitotane Hypothalamic disease: tumors, trauma, infiltrative disorders, Prader-Willi syndrome Abbreviations: TSH, thyroid-stimulating hormone; TSH-R, TSH receptor.

TABLE 395-2  Examples of Genetic Causes of Congenital Hypothyroidism DEFECTIVE GENE PROTEIN TYPE OF HYPOTHYROIDISM INHERITANCE CONSEQUENCES PROP-1 Central, hypothyroidism Homozygous recessive Combined pituitary hormone deficiencies, including thyroid-stimulating hormone (TSH), with preservation of adrenocorticotropic hormone PIT-1 Central, hypothyroidism Homozygous or heterozygous loss of function IGSF1 Central, hypothyroidism X-linked loss of function Loss of TSH receptor (TSH-R) expression, testicular enlargement TSHb Central, hypothyroidism Heterozygous loss of function TSH deficiency TTF-1 (TITF-1) Primary, thyroid dysgenesis Heterozygous loss of function Variable thyroid hypoplasia, choreoathetosis, pulmonary problems PART 12 Endocrinology and Metabolism TTF-2 (FOXE-1) Primary, thyroid dysgenesis Homozygous recessive Thyroid agenesis, choanal atresia, spiky hair PAX-8 Primary, thyroid dysgenesis Heterozygous loss of function Thyroid dysgenesis, kidney abnormalities NKX2-1 Primary, thyroid dysgenesis Heterozygous loss of function Thyroid dysgenesis, brain, lung abnormalities NKX2-5 Primary, thyroid dysgenesis Heterozygous loss of function Thyroid dysgenesis, heart abnormalities GLIS3 Primary, thyroid dysgenesis Homozygous recessive Thyroid dysgenesis, neonatal diabetes, facial abnormalities JAG-1 Primary, thyroid dysgenesis Heterozygous loss of function Thyroid dysgenesis, Alagille syndrome type 1, heart abnormalities TSH receptor Primary, thyroid dysgenesis and dyshormonogenesis Homozygous recessive Resistance to TSH Primary, thyroid dyshormonogenesis Heterozygous loss of function, imprinting GSa (Albright hereditary osteodystrophy) Na+/I– symporter (SLC5A5) Primary, thyroid dyshormonogenesis Homozygous recessive Inability to transport iodide DUOX2 (THOX2) Primary, thyroid dyshormonogenesis Heterozygous loss of function Organification defect DUOXA2 Primary, thyroid dyshormonogenesis Homozygous recessive Organification defect Thyroid peroxidase Primary, thyroid dyshormonogenesis Homozygous recessive Defective organification of iodide Thyroglobulin Primary, thyroid dyshormonogenesis Homozygous recessive Defective synthesis of thyroid hormone Pendrin (SLC26A4) Primary, thyroid dyshormonogenesis Homozygous recessive Pendred syndrome: sensorineural deafness and partial organification defect in thyroid Dehalogenase 1 (IYD) Primary, thyroid dyshormonogenesis Homozygous recessive Loss of iodide reutilization Clinical Manifestations  The majority of infants appear normal at birth, and with the use of biochemical screening, few cases are now diagnosed based on clinical features, which include prolonged jaundice, feeding problems, hypotonia, enlarged tongue, delayed bone maturation, and umbilical hernia. Importantly, permanent neuro­ logic damage results if treatment is delayed. Typical features of adult hypothyroidism may also be present (Table 395-3). Other congenital malformations, especially cardiac, are four times more common in congenital hypothyroidism. Diagnosis and Treatment  Because of the severe neurologic con­ sequences of untreated congenital hypothyroidism, neonatal screening programs have been established. These are generally based on mea­ surement of TSH or T4 levels in heel-prick blood specimens. When the TABLE 395-3  Signs and Symptoms of Hypothyroidism (Descending Order of Frequency) SYMPTOMS SIGNS Tiredness, weakness Dry skin Feeling cold Hair loss Difficulty concentrating and poor memory Constipation Weight gain with poor appetite Dyspnea Hoarse voice Menorrhagia (later oligomenorrhea or amenorrhea) Paresthesia Impaired hearing Dry coarse skin; cool peripheral extremities Puffy face, hands, and feet (myxedema) Diffuse alopecia Bradycardia Peripheral edema Delayed tendon reflex relaxation Carpal tunnel syndrome Serous cavity effusions

Combined deficiencies of growth hormone, prolactin, TSH Resistance to TSH diagnosis is confirmed, T4 is instituted at a dose of 10–15 μg/kg per d, and the dose is adjusted by close monitoring of TSH levels. T4 require­ ments are relatively great during the first year of life, and a high cir­ culating T4 level is usually needed to normalize TSH. Early treatment with T4 results in normal IQ levels, but subtle neurodevelopmental abnormalities may occur in those with the most severe hypothyroidism at diagnosis or when treatment is delayed or suboptimal. If transient hypothyroidism is suspected, or the diagnosis is unclear, treatment can be stopped safely after the age of 3 years followed by further evaluation. ■ ■AUTOIMMUNE HYPOTHYROIDISM Classification  Autoimmune hypothyroidism (Hashimoto’s thy­ roiditis) may be associated with a goiter (goitrous thyroiditis) or minimal residual thyroid tissue (atrophic thyroiditis). Because the auto­ immune process gradually reduces thyroid function, there is a phase of compensation when normal thyroid hormone levels are maintained by a rise in TSH. Although some patients may have minor symptoms, this state is called subclinical hypothyroidism. Later, unbound T4 levels fall and TSH levels rise further; symptoms become more readily apparent at this stage (usually TSH >10 mIU/L), which is referred to as clinical hypothyroidism or overt hypothyroidism. Prevalence  The mean annual incidence rate of autoimmune hypo­ thyroidism is up to 4 per 1000 women and 1 per 1000 men. It is more common in certain populations, such as the Japanese, probably because of genetic factors and chronic exposure to a high-iodine diet. Hypothy­ roidism typically occurs between 30 and 50 years of age, and the preva­ lence of increases with age. The mean age at diagnosis is 60 years, and the prevalence of overt hypothyroidism increases with age. Subclinical hypothyroidism is found in 6–8% of women (10% over the age of 60) and 3% of men. The annual risk of developing clinical hypothyroidism is ~4% when subclinical hypothyroidism is associated with positive thyroid peroxidase (TPO) antibodies.

Pathogenesis  In Hashimoto’s thyroiditis, there is a marked lym­ phocytic infiltration of the thyroid with germinal center formation, atrophy of the thyroid follicles accompanied by oxyphil metaplasia, absence of colloid, and mild to moderate fibrosis. In atrophic thy­ roiditis, the fibrosis is much more extensive, lymphocyte infiltration is less pronounced, and thyroid follicles are almost completely absent. Atrophic thyroiditis usually represents the end stage of Hashimoto’s thyroiditis rather than a separate disorder, although a distinct form of marked fibrosis occurs in which the gland is infiltrated with IgG4positive plasma cells. As with most autoimmune disorders, susceptibility to autoimmune hypothyroidism is determined by a combination of genetic and envi­ ronmental factors, and the risk of either autoimmune hypothyroidism or Graves’ disease is increased among siblings. HLA-DR polymor­ phisms are the best documented genetic risk factors for autoimmune hypothyroidism, especially HLA-DR3, DR4, and DR5 in Caucasians. A weak association also exists between polymorphisms in PTPN22 and CTLA-4, which have immunoregulatory functions, and autoimmune hypothyroidism. All these genetic associations are shared by other autoimmune diseases, which may explain the relationship between autoimmune hypothyroidism and other autoimmune diseases, espe­ cially type 1 diabetes mellitus, Addison’s disease, pernicious anemia, and vitiligo. The role of other contributory loci remains to be clarified. A gene on chromosome 21 may be responsible for the association between autoimmune hypothyroidism and Down’s syndrome. The female preponderance of thyroid autoimmunity is most likely due to sex steroid effects on the immune response, but an X chromosome– related genetic factor is also possible and may account for the high frequency of autoimmune hypothyroidism in Turner’s syndrome. Envi­ ronmental susceptibility factors are poorly defined at present. A high iodine or low selenium intake and decreased exposure to microorgan­ isms in childhood increase the risk of autoimmune hypothyroidism. Smoking cessation transiently increases incidence, whereas alcohol intake seems protective. These factors may account for the increase in prevalence over the past two to three decades. The thyroid lymphocytic infiltrate in autoimmune hypothyroid­ ism is composed of activated T cells as well as B cells. Thyroid cell destruction is primarily mediated by the CD8+ cytotoxic T cells, but local production of cytokines, such as tumor necrosis factor (TNF), interleukin-1 (IL-1), and interferon γ (IFN-γ), derived from the inflammatory infiltrate may render thyroid cells more susceptible to apoptosis mediated by death receptors, such as Fas, and by oxidative stress. These cytokines also impair thyroid cell function directly and induce the expression of other proinflammatory molecules by the thyroid cells themselves, such as cytokines, human leukocyte antigen (HLA) class I and class II molecules, adhesion molecules, CD40, and nitric oxide. Administration of high concentrations of cytokines for therapeutic purposes (especially IFN-α) is associated with increased autoimmune thyroid disease, possibly through mechanisms similar to those in sporadic disease. Novel anticancer and immunomodulatory treatments, such as tyrosine kinase inhibitors, immune checkpoint inhibitors, and alemtuzumab, can also induce thyroiditis via their effects on T-cell regulation. Antibodies to TPO and thyroglobulin (Tg) are clinically useful mark­ ers of thyroid autoimmunity, but any pathogenic effect is restricted to a secondary role in amplifying an ongoing autoimmune response. TPO antibodies fix complement, and complement membrane-attack complexes are present in the thyroid in autoimmune hypothyroidism. However, transplacental passage of Tg or TPO antibodies has no effect on the fetal thyroid, which suggests that T cell–mediated injury is required to initiate autoimmune damage to the thyroid. Up to 20% of patients with autoimmune hypothyroidism have anti­ bodies against the TSH-R, which, in contrast to thyroid-stimulating immunoglobulin (TSI), do not stimulate the receptor but prevent the binding of TSH. These TSH-R-blocking antibodies, therefore, cause hypothyroidism and, especially in Asian patients, thyroid atrophy. Their transplacental passage may induce transient neonatal hypothy­ roidism. Rarely, patients have a mixture of TSI and TSH-R-blocking antibodies, and thyroid function can oscillate between hyperthyroidism

and hypothyroidism as one or the other antibody becomes dominant. Predicting the course of disease in such individuals is difficult, and they require close monitoring of thyroid function. Bioassays can be used to document that TSH-R-blocking antibodies reduce the cyclic AMP–inducing effect of TSH on cultured TSH-R-expressing cells, but these assays are difficult to perform. Immunoassays for TSH receptor antibodies, which measure whether the patient’s serum contains an antibody that can displace either labeled TSH or a monoclonal TSH receptor antibody from the TSH receptor, do not distinguish between these types of functional antibodies, but a positive result in a patient with spontaneous hypothyroidism is strong evidence for the presence of blocking antibodies. The use of these assays does not generally alter clinical management, although it may be useful to confirm the cause of transient neonatal hypothyroidism.

Hypothyroidism CHAPTER 395 Clinical Manifestations  The main clinical features of hypothy­ roidism are summarized in Table 395-3. The onset is usually insidious, and the patient may become aware of symptoms only when euthy­ roidism is restored. Patients with Hashimoto’s thyroiditis may present because of goiter rather than symptoms of hypothyroidism. The goiter may not be large, but it is usually irregular and firm in consistency. Rarely, uncomplicated Hashimoto’s thyroiditis is associated with pain. Patients with atrophic thyroiditis or the later stage of Hashimoto’s thyroiditis present with symptoms and signs of hypothyroidism. The skin is dry, and there is decreased sweating, thinning of the epider­ mis, and hyperkeratosis of the stratum corneum. Increased dermal glycosaminoglycan content traps water, giving rise to skin thickening without pitting (myxedema). Typical features include a puffy face with edematous eyelids and nonpitting pretibial edema (Fig. 395-1). There is pallor, often with a yellow tinge to the skin due to carotene accumula­ tion. Nail growth is retarded, and hair is dry, brittle, difficult to manage, and falls out easily. In addition to diffuse alopecia, there is thinning of the outer third of the eyebrows, although this is not a specific sign of hypothyroidism. Other common features include constipation and weight gain (despite a poor appetite). In contrast to popular perception, the weight gain is usually modest and due mainly to fluid retention in the myxedematous tissues. Libido is decreased in both sexes, and there may be oligomenorrhea or amenorrhea in long-standing disease, but FIGURE 395-1  Facial appearance in hypothyroidism. Note puffy eyes and thickened skin.

menorrhagia may occur at an early stage. Fertility is reduced, and the incidence of miscarriage is increased. Prolactin levels are often mod­ estly increased (Chap. 392) and may contribute to alterations in libido and fertility and cause galactorrhea.

Myocardial contractility and pulse rate are reduced, leading to a reduced stroke volume and bradycardia. Increased peripheral resis­ tance may be accompanied by hypertension, particularly diastolic. Blood flow is diverted from the skin, producing cool extremities. Peri­ cardial effusions occur in up to 30% of patients but rarely compromise cardiac function. Although alterations in myosin heavy chain isoform expression have been documented, cardiomyopathy is rare. Fluid may also accumulate in other serous cavities and in the middle ear, giving rise to conductive deafness; sensorineural deafness may also occur. Pulmonary function is generally normal, but dyspnea may be caused by pleural effusion, impaired respiratory muscle function, diminished ventilatory drive, or sleep apnea. PART 12 Endocrinology and Metabolism Carpal tunnel and other entrapment syndromes are common, as is impairment of muscle function with stiffness, cramps, and pain. On examination, there may be slow relaxation of tendon reflexes and pseu­ domyotonia. Memory and concentration are impaired. Experimentally, positron emission tomography (PET) scans examining glucose metab­ olism in hypothyroid subjects show lower regional activity in the amyg­ dala, hippocampus, and perigenual anterior cingulate cortex, among other regions, and this activity corrects after thyroxine replacement. Rare neurologic problems include reversible cerebellar ataxia, demen­ tia, psychosis, and myxedema coma. Hashimoto’s encephalopathy has been defined as a steroid-responsive syndrome associated with TPO antibodies, myoclonus, and slow-wave activity on electroencephalog­ raphy, but the relationship with thyroid autoimmunity or hypothyroid­ ism is not established, and if a patient is euthyroid, levothyroxine (LT4) therapy has not been shown to be efficacious in treatment. The hoarse voice and occasionally clumsy speech of hypothyroidism reflect fluid accumulation in the vocal cords and tongue. The features described above are the consequence of thyroid hor­ mone deficiency. However, autoimmune hypothyroidism may be associated with signs or symptoms of other autoimmune diseases, particularly vitiligo, pernicious anemia, Addison’s disease (Schmidt’s syndrome), alopecia areata, and type 1 diabetes mellitus (T1DM). In the polygenic disorder autoimmune polyendocrine syndrome type 2, autoimmune thyroid disease is present in 70–75%, T1DM in 40–60%, and Addison’s disease in 40–50%. Less common associations include celiac disease, dermatitis herpetiformis, chronic active hepatitis, rheu­ matoid arthritis, systemic lupus erythematosus (SLE), myasthenia Elevated Measure unbound T4 Normal Measure unbound T4 Mild hypothyroidism Primary hypothyroidism TPOAb+ TPOAb– TPOAb+ or symptomatic TPOAb–, no symptoms Autoimmune hypothyroidism Rule out other causes of hypothyroidism Consider T4 treatment Annual follow-up T4 treatment FIGURE 395-2  Evaluation of hypothyroidism. TPOAb+, thyroid peroxidase antibodies present; TPOAb–, thyroid peroxidase antibodies not present; TSH, thyroid-stimulating hormone.

gravis, autoimmune hypoparathyroidism, primary hypogonadism, and Sjögren’s syndrome. Thyroid-associated ophthalmopathy usually occurs in Graves’ disease (Chap. 396), but in ~5% of patients, it is associated with autoimmune hypothyroidism. Autoimmune hypothyroidism is uncommon in children and usually presents with slow growth and delayed facial and dental maturation. The pituitary may be enlarged due to thyrotroph hyperplasia. Myopa­ thy, with muscle swelling, is more common in children than in adults. In most cases, puberty is delayed, but precocious puberty sometimes occurs. There may be intellectual impairment if the onset is before 3 years and the hormone deficiency is severe. Laboratory Evaluation  A summary of the investigations used to determine the existence and cause of hypothyroidism is provided in Fig. 395-2. A normal TSH level excludes primary (but not secondary or central) hypothyroidism. If the TSH is elevated, a free or unbound T4 level (FT4) is needed to confirm the presence of clinical hypothyroid­ ism, but T4 is inferior to TSH when used as a screening test because it will not detect subclinical hypothyroidism. Circulating unbound T3 levels are normal in ~25% of patients, reflecting adaptive deiodinase responses to hypothyroidism. T3 measurements are, therefore, not indicated. Once clinical or subclinical hypothyroidism is confirmed, the etiol­ ogy is usually easily established by demonstrating the presence of TPO and Tg antibodies, which are present in >95% of patients with autoim­ mune hypothyroidism. Other abnormal laboratory findings in hypo­ thyroidism may include increased creatine phosphokinase, elevated cholesterol and triglycerides, and anemia (usually normocytic or mac­ rocytic) depending upon the degree and duration of hypothyroidism. Except when accompanied by iron deficiency or B12 deficiency from concomitant pernicious anemia, the anemia and other abnormalities gradually resolve with thyroxine replacement. Differential Diagnosis  An asymmetric goiter in Hashimoto’s thy­ roiditis may be confused with a multinodular goiter (MNG) or thyroid carcinoma, in which thyroid antibodies may also be present. Primary thyroid lymphoma (Chap. 397) is rare but strongly associated with pre­ existing autoimmune thyroiditis. Ultrasound can be used to show the presence of solitary or multiple nodules rather than the thyroid enlarge­ ment with heterogeneous echogenicity typical of Hashimoto’s thyroid­ itis. However, ultrasound imaging may also detect pseudonodules, hypoechoic areas likely representing areas of lymphocytic infiltrates, which need to be distinguished from true superimposed nodules as fine-needle aspirate is not warranted for these. Fine-needle aspiration Measure TSH Normal Pituitary disease suspected? Low Yes No No further tests Normal Low No further tests Rule out drug effects, sick euthyroid syndrome, then evaluate anterior pituitary function

(FNA) biopsy should be performed for all true nodules meeting FNA criteria (Chap. 397). Other causes of hypothyroidism are discussed below and in Table 395-1 but rarely cause diagnostic confusion. ■ ■OTHER CAUSES OF HYPOTHYROIDISM Iatrogenic hypothyroidism is a common cause of hypothyroidism and can often be detected by screening before symptoms develop. In the first 3–4 months after radioiodine treatment for Graves’ disease, tran­ sient hypothyroidism may occur due to reversible radiation damage. Low-dose thyroxine treatment can be withdrawn if recovery occurs. Because TSH levels are suppressed by hyperthyroidism, unbound T4 levels are a better measure of thyroid function than TSH in the months following radioiodine treatment. Mild hypothyroidism after subtotal thyroidectomy or lobectomy may also resolve after several months, as the gland remnant is stimulated by increased TSH levels. Iodine deficiency is responsible for endemic goiter and cretinism but is an uncommon cause of adult hypothyroidism unless the iodine intake is very low or there are complicating factors, such as the con­ sumption of thiocyanates in cassava or selenium deficiency. Although hypothyroidism due to iodine deficiency can be treated with thyroxine, public health measures to improve iodine intake should be advocated to eliminate this problem. Iodized salt or bread or a single bolus of oral or intramuscular iodized oil have all been used successfully. Paradoxically, chronic iodine excess can also induce goiter and hypothyroidism. The intracellular events that account for this effect are unclear, but individuals with autoimmune thyroiditis are especially susceptible. Iodine excess is responsible for the hypothyroidism that occurs in patients treated with amiodarone (Chap. 396). Other drugs, particularly lithium, may also cause hypothyroidism. Transient hypo­ thyroidism may also be caused by thyroiditis (Chap. 396). Secondary or central hypothyroidism is usually diagnosed in the context of other anterior pituitary hormone deficiencies; isolated TSH deficiency is very rare (Chap. 391). TSH levels may be low, normal, or even slightly increased in secondary hypothyroidism; the latter is due to secretion of immunoactive but bioinactive forms of TSH. The diagnosis is confirmed by detecting a low unbound T4 level. The goal of treatment is to maintain free T4 levels in the upper half of the reference interval because TSH levels cannot be used to monitor therapy. TREATMENT Hypothyroidism CLINICAL HYPOTHYROIDISM If there is no residual thyroid function, the daily replacement dose of LT4 is usually 1.6 μg/kg body weight (typically 100–150 μg), ide­ ally taken at least 30 min before breakfast. In many patients, how­ ever, lower doses suffice until residual thyroid tissue is destroyed. In patients who develop hypothyroidism after the treatment of Graves’ disease, there is often underlying autonomous function, necessitat­ ing lower replacement doses (typically 75–125 μg/d). Adult patients under 60 years old without evidence of heart disease may be started on 50–100 μg of LT4 daily. The dose is adjusted on the basis of TSH levels, with the goal of treatment being a normal TSH, ideally in the lower half of the reference range. TSH responses are gradual and should be measured about 6–8 weeks after instituting treatment or after any subsequent change in LT4 dosage. The clinical effects of LT4 replacement are slow to appear. Patients may not experience full relief from symptoms until several months after normal TSH levels are restored. Adjustment of LT4 dosage is made in 12.5- or 25-μg increments if the TSH is high; decrements of the same magnitude should be made if the TSH is suppressed. Patients with a suppressed TSH of any cause, including LT4 overtreatment, have an increased risk of atrial fibrillation and reduced bone density. About 10–15% of patients may have persistent symptoms despite restoration of euthyroidism with LT4 for reasons that remain unclear. Although desiccated animal thyroid preparations (thyroid extract USP) are available, they are not recommended because the

ratio of T3 to T4 is nonphysiologic. The use of LT4 combined with liothyronine (triiodothyronine, T3) has been investigated, but ben­ efit has not been confirmed in prospective studies. There is no place for liothyronine alone as long-term replacement, because the short half-life necessitates three or four daily doses and is associated with fluctuating T3 levels.

Once full replacement is achieved and TSH levels are stable, fol­ low-up measurement of TSH is recommended at annual intervals. It is important to ensure ongoing adherence as patients do not feel any symptomatic difference after missing a few doses of LT4, and this sometimes leads to self-discontinuation. Hypothyroidism CHAPTER 395 In patients of normal body weight who are taking ≥200 μg of LT4 daily, an elevated TSH level is often a sign of poor adherence to treatment. This is also the likely explanation for fluctuating TSH levels, despite a constant LT4 dosage. Such patients often have normal or high free T4 levels, despite an elevated TSH, because they remember to take medication for a few days before testing; this is sufficient to normalize T4, but not TSH levels. It is impor­ tant to consider variable adherence because this pattern of thyroid function tests is otherwise suggestive of disorders associated with inappropriate TSH secretion (Chap. 394). Because T4 has a long half-life (7 days), patients who miss a dose can be advised to take two doses of the skipped tablets at once. Other causes of increased LT4 requirements must be excluded, particularly malabsorption (e.g., celiac disease, small-bowel surgery, atrophic or Helicobacter pylori–related gastritis), oral estrogen-containing medications or selective estrogen receptor modulator therapy, ingestion with a meal, and drugs that interfere with T4 absorption or metabolism such as bile acid sequestrants, ferrous sulfate, calcium supplements, sevelamer, sucralfate, proton pump inhibitors, lovastatin, aluminum hydroxide, rifampicin, amiodarone, carbamazepine, phenytoin, and tyrosine kinase inhibitors. SUBCLINICAL HYPOTHYROIDISM Subclinical hypothyroidism refers to biochemical evidence of thy­ roid hormone deficiency in patients who have few or no appar­ ent clinical features of hypothyroidism. There are no universally accepted recommendations for the management of subclinical hypothyroidism, but LT4 is recommended if the patient is a woman who wishes to conceive or is pregnant or when TSH levels are

10 mIU/L. Most other patients can simply be monitored annually. A trial of treatment may be considered when young or middle-aged patients have symptoms of hypothyroidism or risk of heart disease. It is important to confirm that any elevation of TSH is sustained over a 3-month period before treatment is given. Treatment is administered by starting with a low dose of LT4 (25–50 μg/d) with the goal of normalizing TSH. SPECIAL TREATMENT CONSIDERATIONS Rarely, LT4 replacement is associated with pseudotumor cerebri in children. Presentation appears to be idiosyncratic and occurs months after treatment has begun. Because maternal hypothyroidism may both adversely affect fetal neural development and be associated with adverse gestational outcomes (miscarriage, preterm delivery), thyroid function should be monitored to preserve euthyroidism in women with a history or a high risk of hypothyroidism. Although epidemiologic studies have demonstrated the association of miscarriage and preterm delivery with the presence of thyroid autoantibodies detected either during or prior to gestation in euthyroid women, randomized controlled multicenter trials evaluating LT4 therapy prior to conception in this population have not demonstrated benefit. Because of the known increase in thyroid hormone requirements during preg­ nancy in hypothyroid women, LT4 therapy should be targeted to maintain a serum TSH in the normal range but <2.5 mIU/L prior to conception. In women without evidence of thyroid dysfunction, serum TSH decreases in the late first trimester, and if trimester-specific ranges are not available, an appropriate range for 7–12 weeks’ gestation can

10 - 396 Hyperthyroidism and Other Causes of Thyrotoxicosis

396 Hyperthyroidism and Other Causes of Thyrotoxicosis

be approximated by decreasing the upper limit of the nonpregnant reference range by 0.5 mIU/L (~4.0 mIU/L) and the lower limit by 0.4 mIU/L (~0.1 mIU/L). However, it is important to recognize that the normal TSH range in pregnancy for the second and third trimesters is not significantly different from the nonpregnancy ref­ erence range. Therefore, when caring for LT4-replaced women with hypothyroidism, thyroid function should be evaluated immediately after pregnancy is confirmed and every 4 weeks during the first half of the pregnancy, with less frequent testing after 20 weeks’ gestation (every 6–8 weeks depending on whether LT4 dose adjustment is ongoing). The increment of LT4 dosage increase depends upon the etiology of hypothyroidism, with athyreotic women requiring more (~45%) than those with Hashimoto’s who may have some residual thyroid function. Women should increase LT4 from once-daily dosing to nine doses per week as soon as pregnancy is confirmed to anticipate this change. Thereafter, dosage should be closely moni­ tored with a goal TSH in the lower half of the trimester-specific normative range, if available, or <2.5 mIU/L, which allows for reserve if additional LT4 dosage increases are required as pregnancy progresses. After delivery, LT4 doses typically return to prepreg­ nancy levels. Pregnant women should be counseled to separate ingestion of prenatal vitamins and iron supplements from LT4.

PART 12 Endocrinology and Metabolism Elderly patients may require 20% less thyroxine than younger patients. In the elderly, especially patients with known coronary artery disease, the starting dose of LT4 is 12.5–25 μg/d with similar increments every 2–3 months until TSH is normalized. In some patients, it may be impossible to achieve full replacement despite optimal antianginal treatment. Emergency surgery is generally safe in patients with untreated hypothyroidism, although routine sur­ gery in a hypothyroid patient should be deferred until euthyroidism is achieved. Myxedema coma still has a 20–40% mortality rate, despite inten­ sive treatment, and outcomes are independent of the T4 and TSH levels. Clinical manifestations include reduced level of conscious­ ness, sometimes associated with seizures, as well as the other features of hypothyroidism (Table 395-3). Hypothermia can reach 23°C (74°F). There may be a history of treated hypothyroidism with poor compliance, or the patient may be previously undiagnosed. Myxedema coma almost always occurs in the elderly and is usu­ ally precipitated by factors that impair respiration, such as drugs (especially sedatives, anesthetics, and antidepressants), pneumo­ nia, congestive heart failure, myocardial infarction, gastrointestinal bleeding, or cerebrovascular accidents. Sepsis should also be sus­ pected. Exposure to cold may also be a risk factor. Hypoventilation, leading to hypoxia and hypercapnia, plays a major role in pathogen­ esis; hypoglycemia and dilutional hyponatremia also contribute to the development of myxedema coma. LT4 can initially be administered as a single IV bolus of 200– 400 μg, which serves as a loading dose, followed by a daily oral dose of 1.6 μg/kg per d, reduced by 25% if administered IV. If a suitable IV preparation is not available, the same initial dose of LT4 can be given by nasogastric tube (although absorption may be impaired in myxedema). Because T4 → T3 conversion is impaired in myxedema coma, there is a rationale for adding liothyronine (T3) intravenously or via nasogastric tube to LT4 treatment, although excess liothyro­ nine has the potential to provoke arrhythmias. An initial loading dose of 5–20 μg liothyronine should be followed by 2.5–10 μg every 8 h, with lower doses chosen for smaller or older patients and those at cardiovascular risk. Supportive therapy should be provided to correct any associated metabolic disturbances. External warming is indicated only if the temperature is <30°C, as it can result in cardiovascular collapse (Chap. 477). Space blankets should be used to prevent further heat loss. Parenteral hydrocortisone (50 mg every 6 h) should be administered because there is impaired adrenal reserve in pro­ found hypothyroidism. Any precipitating factors should be treated, including the early use of broad-spectrum antibiotics, pending the exclusion of infection. Ventilatory support with regular blood gas analysis is usually needed during the first 48 h. Hypertonic saline

or IV glucose may be needed if there is severe hyponatremia or hypoglycemia; hypotonic IV fluids should be avoided because they may exacerbate water retention secondary to reduced renal perfu­ sion and inappropriate vasopressin secretion. The metabolism of most medications is impaired, and sedatives should be avoided if possible or used in reduced doses. Medication blood levels should be monitored, when available, to guide dosage. ■ ■FURTHER READING Biondi B et al: Subclinical hypothyroidism in older individuals. Lancet Diabetes Endocrinol 10:129, 2022. Chaker L et al: Hypothyroidism. Nature Rev Dis Primers 8:30, 2022. Hegedüs L et al: Primary hypothyroidism and quality of life. Nature Rev Endocrinol 18:230, 2022. Jonklaas J et al: Guidelines for the treatment of hypothyroidism: Pre­ pared by the American Thyroid Association Task Force on thyroid hormone replacement. Thyroid 24:1670, 2014. Lee SY et al: Assessment and treatment of thyroid disorders in preg­ nancy and the postpartum period. Nat Rev Endocrinol 18:158, 2022. van Trotsenburg P et al: Congenital hypothyroidism: A 2020-2021 consensus guidelines update-an ENDO-European reference network initiative endorsed by the European Society for Pediatric Endocrinol­ ogy and the European Society for Endocrinology. Thyroid 31:387, 2021.

Hyperthyroidism and

Other Causes of

Thyrotoxicosis Anthony P. Weetman, Susan J. Mandel,

J. Larry Jameson
THYROTOXICOSIS Thyrotoxicosis is defined as the state of thyroid hormone excess and is not synonymous with hyperthyroidism, which is the result of excessive thyroid function. However, the major etiologies of thyrotoxicosis are hyperthyroidism caused by Graves’ disease, toxic multinodular goiter (MNG), and toxic adenomas. Other causes are listed in Table 396-1. ■ ■GRAVES’ DISEASE Epidemiology  Graves’ disease accounts for 60–80% of thyro­ toxicosis. The prevalence varies among populations, reflecting genetic factors and iodine intake (high iodine intake is associated with an increased prevalence of Graves’ disease). Graves’ disease occurs in up to 2% of women but is one-tenth as frequent in men. The disorder rarely begins before adolescence and typically occurs between 20 and 50 years of age; it also occurs in the elderly. Pathogenesis  As in autoimmune hypothyroidism, a combina­ tion of environmental and genetic factors, including polymorphisms in HLA-DR, the immunoregulatory genes CTLA-4, CD25, CD40, PTPN22, FCRL3, and CD226, as well as the gene encoding the thyroidstimulating hormone (TSH) receptor (TSH-R), contributes to Graves’ disease susceptibility. The concordance for Graves’ disease in monozy­ gotic twins is 20–30%, compared to <5% in dizygotic twins. Indirect evidence suggests that stress is an important environmental factor, presumably operating through neuroendocrine effects on the immune system. Smoking is a moderate risk factor for Graves’ disease and a major risk factor for the development of ophthalmopathy. Sudden increases in iodine intake may precipitate Graves’ disease, and there is

TABLE 396-1  Causes of Thyrotoxicosis Primary Hyperthyroidism Graves’ disease Toxic multinodular goiter Toxic adenoma Functioning thyroid carcinoma metastases Activating mutation of the TSH receptor Activating mutation of GSa (McCune-Albright syndrome) Struma ovarii Drugs: iodine excess (Jod-Basedow phenomenon) Thyrotoxicosis without Hyperthyroidism Subacute thyroiditis Silent thyroiditis Other causes of thyroid destruction: drugs (amiodarone, cytokines, tyrosine kinase inhibitors, immune checkpoint inhibitors), radiation, infarction of adenoma Ingestion of excess thyroid hormone (thyrotoxicosis factitia) or thyroid tissue Secondary Hyperthyroidism TSH-secreting pituitary adenoma Thyroid hormone resistance syndrome: occasional patients may have features of thyrotoxicosis Chorionic gonadotropin-secreting tumorsa Gestational thyrotoxicosisa aCirculating TSH levels are low in these forms of secondary hyperthyroidism. Abbreviation: TSH, thyroid-stimulating hormone. a threefold increase in the occurrence of Graves’ disease in the post­ partum period. Graves’ disease may occur during the immune recon­ stitution phase after highly active antiretroviral therapy (HAART) or alemtuzumab treatment and following treatment with immune check­ point inhibitors (e.g., nivolumab, pembrolizumab). The hyperthyroidism of Graves’ disease is caused by thyroidstimulating immunoglobulins (TSIs) that are synthesized by lympho­ cytes in the thyroid gland as well as in bone marrow and lymph nodes. Such antibodies can be detected by bioassays or by using the more widely available immunoassays (TSH receptor antibodies [TRAb]) that measure whether the patient’s serum contains an antibody that can dis­ place either labeled TSH or a monoclonal TSH receptor antibody from the TSH receptor. The presence of TRAb in a patient with thyrotoxi­ cosis implies the existence of TSI, and these assays are useful in moni­ toring pregnant Graves’ patients in whom high levels of TSI can cross the placenta and cause neonatal thyrotoxicosis. Other thyroid autoim­ mune responses, similar to those in autoimmune hypothyroidism (see above), occur concurrently in patients with Graves’ disease. In particu­ lar, thyroid peroxidase (TPO) and thyroglobulin (Tg) antibodies occur in up to 80% of cases. Because the coexisting lymphocytic thyroiditis can also affect thyroid function, there is no direct correlation between the level of TSI and thyroid hormone levels in Graves’ disease. Cytokines appear to play a major role in thyroid-associated ophthal­ mopathy. There is infiltration of the extraocular muscles by activated T cells; the release of cytokines such as interferon γ (IFN-γ), tumor necrosis factor (TNF), and interleukin 1 (IL-1) results in fibroblast activation and increased synthesis of glycosaminoglycans that trap water, thereby leading to characteristic muscle swelling. Late in the disease, there is irreversible fibrosis of the muscles. Increased fat is an additional cause of retrobulbar tissue expansion. The increase in intra­ orbital pressure can lead to proptosis, diplopia, and optic neuropathy. Although the pathogenesis of thyroid-associated ophthalmopathy is incompletely understood, the TSH-R is a thyroid autoantigen and is expressed in orbital tissues. In addition, aberrant signaling via insulinlike growth factor 1 receptors (IGF-1R) on orbital fibroblasts has also been implicated. These mechanisms are the basis for new monoclonal antibody treatments (e.g., teprotumumab) that reduce the levels of TSH-R/IGF-1R complexes and attenuate signaling. Clinical Manifestations  Signs and symptoms include features that are common to any cause of thyrotoxicosis (Table 396-2) as well

TABLE 396-2  Signs and Symptoms of Thyrotoxicosis (Descending Order of Frequency) SYMPTOMS SIGNSa Hyperactivity, irritability, dysphoria Heat intolerance and sweating Palpitations Fatigue and weakness Weight loss with increased appetite Diarrhea Polyuria Oligomenorrhea, loss of libido Tachycardia; atrial fibrillation in the elderly Tremor Goiter Warm, moist skin Muscle weakness, proximal myopathy Lid retraction or lag Gynecomastia Hyperthyroidism and Other Causes of Thyrotoxicosis
CHAPTER 396 aExcludes the signs of ophthalmopathy and dermopathy specific for Graves’ disease. as those specific for Graves’ disease. The clinical presentation depends on the severity of thyrotoxicosis, the duration of disease, individual susceptibility to excess thyroid hormone, and the patient’s age. In the elderly, features of thyrotoxicosis may be subtle or masked, and patients may present mainly with fatigue and weight loss, a condition known as apathetic thyrotoxicosis. Thyrotoxicosis may cause unexplained weight loss, despite an enhanced appetite, due to the increased metabolic rate. Weight gain occurs in 5% of patients, however, because of increased food intake. Other prominent features include hyperactivity, nervousness, and irritability, ultimately leading to a sense of easy fatigability in some patients. Insomnia and impaired concentration are common; apathetic thyrotoxicosis may be mistaken for depression in the elderly. Fine tremor is a frequent finding, best elicited by having patients stretch out their fingers while feeling the fingertips with the palm. Common neurologic manifestations include hyperreflexia, muscle wasting, and proximal myopathy without fasciculation. Chorea is rare. Thyro­ toxicosis is sometimes associated with a form of hypokalemic periodic paralysis; this disorder is particularly common in Asian males with thyrotoxicosis, but it occurs in other ethnic groups as well. The most common cardiovascular manifestation is sinus tachycar­ dia, often associated with palpitations, occasionally caused by supra­ ventricular tachycardia. The high cardiac output produces a bounding pulse, widened pulse pressure, and an aortic systolic murmur and can lead to worsening of angina or heart failure in the elderly or those with preexisting heart disease. Atrial fibrillation is more common in patients

50 years of age. Treatment of the thyrotoxic state alone converts atrial fibrillation to normal sinus rhythm in up to 75% of patients without an underlying cardiac problem. The skin is usually warm and moist, and the patient may complain of sweating and heat intolerance, particularly during warm weather. Palmar erythema, onycholysis, and, less commonly, pruritus, urticaria, and diffuse hyperpigmentation may be evident. Hair texture may become fine, and diffuse alopecia occurs in up to 40% of patients, per­ sisting for months after restoration of euthyroidism. Gastrointestinal transit time is decreased, leading to increased stool frequency, often with diarrhea and occasionally mild steatorrhea. Women frequently experience oligomenorrhea or amenorrhea; in men, there may be impaired sexual function and, rarely, gynecomastia. The direct effect of thyroid hormones on bone resorption leads to osteopenia in longstanding thyrotoxicosis; mild hypercalcemia occurs in up to 20% of patients, but hypercalciuria is more common. There is a small increase in fracture rate in patients with a previous history of thyrotoxicosis. In Graves’ disease, the thyroid is usually diffusely enlarged to two to three times its normal size. The consistency is firm, but not nodular. There may be a thrill or bruit, best detected at the inferolateral margins of the thyroid lobes, due to the increased vascularity of the gland and the hyperdynamic circulation. Lid retraction, causing a staring appearance, can occur in any form of thyrotoxicosis and is the result of sympathetic overactivity. However, Graves’ disease is associated with specific eye signs that comprise Graves’ ophthalmopathy (Fig. 396-1A). This condition is also called thyroid eye disease (TED) because it occurs in the absence

PART 12 Endocrinology and Metabolism A B C FIGURE 396-1  Features of Graves’ disease. A. Ophthalmopathy in Graves’ disease; lid retraction, periorbital edema, conjunctival injection, and proptosis are marked. B. Thyroid dermopathy over the lateral aspects of the shins. C. Thyroid acropachy. of hyperthyroidism in 10% of patients. Most of these individuals have autoimmune hypothyroidism or thyroid antibodies. The onset of Graves’ ophthalmopathy occurs within the year before or after the diagnosis of thyrotoxicosis in 75% of patients but can sometimes precede or follow thyrotoxicosis by several years, accounting for some cases of euthyroid ophthalmopathy. About one-third of patients with Graves’ disease have clinical evi­ dence of ophthalmopathy. However, the enlarged extraocular muscles typical of the disease, and other subtle features, can be detected in most patients when investigated by ultrasound or computed tomography (CT) imaging of the orbits. Unilateral signs are found in up to 10% of ophthalmopathy patients. The earliest manifestations of ophthalmopa­ thy are usually a sensation of grittiness, eye discomfort, and excess tearing. About one-third of patients have proptosis, best detected by visualization of the sclera between the lower border of the iris and the lower eyelid, with the eyes in the primary position. Proptosis can be measured using an exophthalmometer. In severe cases, proptosis may cause corneal exposure and damage, especially if the lids fail to close during sleep. Periorbital edema, scleral injection, and chemosis are also frequent. In 5–10% of patients, the muscle swelling is so severe that diplopia results, typically, but not exclusively, when the patient looks up and laterally. The most serious manifestation is compression of the optic nerve at the apex of the orbit, leading to papilledema; peripheral field defects; and, if left untreated, permanent loss of vision. The “NO SPECS” scoring system to evaluate ophthalmopathy is an acronym derived from the following changes: 0 = No signs or symptoms 1 = Only signs (lid retraction or lag), no symptoms 2 = Soft tissue involvement (periorbital edema) 3 = Proptosis (>22 mm) 4 = Extraocular muscle involvement (diplopia) 5 = Corneal involvement 6 = Sight loss Although useful as a mnemonic, the NO SPECS scheme is inad­ equate to describe the eye disease fully, and patients do not necessarily progress from one class to another; alternative scoring systems (e.g., the EUGOGO system developed by the European Group on Graves’ Orbitopathy) that assess disease activity are preferable for monitor­ ing and treatment purposes. When Graves’ eye disease is active and

moderate to severe, evaluation and management with an ophthal­ mologist is indicated, and objective measurements are needed, such as lid-fissure width; corneal staining with fluorescein; evaluation of extraocular muscle function (e.g., Hess chart), intraocular pressure and visual fields, acuity, and color vision; and orbital imaging with CT or magnetic resonance imaging (MRI). Thyroid dermopathy occurs in <5% of patients with Graves’ disease (Fig. 396-1B), almost always in the presence of moderate or severe ophthalmopathy. Although most frequent over the anterior and lateral aspects of the lower leg (hence the term pretibial myxedema), skin changes can occur at other sites, particularly after trauma. The typical lesion is a noninflamed, indurated plaque with a deep pink or purple color and an “orange skin” appearance. Nodular involvement can occur, and the condition can rarely extend over the whole lower leg and foot, mimicking elephantiasis. Thyroid acropachy refers to a form of clubbing found in <1% of patients with Graves’ disease (Fig. 396-1C). It is so strongly associated with thyroid dermopathy that an alternative cause of clubbing should be sought in a Graves’ patient without coinci­ dent skin and orbital involvement. Ophthalmopathy, dermopathy, and acropachy have declined in incidence, probably due to better recogni­ tion and prompt treatment of the underlying thyroid disease. Laboratory Evaluation  Investigations used to determine the existence and cause of thyrotoxicosis are summarized in Fig. 396-2. In Graves’ disease, the TSH level is suppressed, and total and unbound thyroid hormone levels are increased. In 2–5% of patients (and more in areas of borderline iodine intake), only T3 is increased (T3 toxicosis). The converse state of T4 toxicosis, with elevated total and unbound T4 and normal T3 levels, is occasionally seen when hyperthyroidism is induced by excess iodine, providing surplus substrate for thyroid hormone synthesis. Measurement of TRAb is also useful. Associated abnormalities that may cause diagnostic confusion in thyrotoxicosis include elevation of bilirubin, liver enzymes, and ferritin. Microcytic anemia and thrombocytopenia may occur. Differential Diagnosis  Diagnosis of Graves’ disease is straightfor­ ward in a patient with biochemically confirmed thyrotoxicosis, diffuse goiter on palpation, ophthalmopathy, and often a personal or family history of autoimmune disorders. TRAb measurement is usually used to confirm the diagnosis of Graves’ disease in patients with thyrotoxi­ cosis who lack these features, but the diagnosis can also be established by a radionuclide (99mTc, 123I, or 131I) scan and uptake of the thyroid, which will distinguish the diffuse, high uptake of Graves’ disease from destructive thyroiditis, ectopic thyroid tissue, and factitious thyrotoxi­ cosis, as well as diagnose a toxic adenoma or toxic MNG. Alternatively, color-flow Doppler ultrasonography distinguishes between hyperthy­ roidism (with increased blood flow) and destructive thyroiditis and avoids using radioactivity. In secondary hyperthyroidism due to a TSH-secreting pituitary tumor, there is also a diffuse goiter. The pres­ ence of a nonsuppressed TSH level and the finding of a pituitary tumor on CT or MRI scan suggest this diagnosis. Clinical features of thyrotoxicosis can mimic certain aspects of other disorders, including panic attacks, mania, pheochromocytoma, and weight loss associated with malignancy. The diagnosis of thyrotoxi­ cosis can be easily excluded if the TSH and unbound T4 and T3 levels are normal. A normal TSH also excludes Graves’ disease as a cause of diffuse goiter. Clinical Course  Clinical features generally worsen without treat­ ment; mortality was 10–30% before the introduction of satisfactory therapy. Some patients with mild Graves’ disease experience spontane­ ous relapses and remissions. Rarely, there may be fluctuation between hypo- and hyperthyroidism due to changes in the functional activity of TSH-R antibodies. About 15% of patients who enter remission after treatment develop hypothyroidism 10–15 years later because of the destructive autoimmune process. The clinical course of ophthalmopathy does not follow that of the thyroid disease, although thyroid dysfunction can worsen eye signs. Ophthalmopathy typically worsens over the initial 3–6 months, fol­ lowed by a plateau phase over the next 12–18 months, and then some

Measure TSH, unbound T4 TSH low, unbound T4 normal TSH and unbound T4 normal TSH low, unbound T4 high Measure unbound T3 Primary thyrotoxicosis High T3 toxicosis Subclinical hyperthyroidism Features of Graves’ diseasea? Yes No Graves’ disease Multinodular goiter or toxic adenomab? Yes No Toxic nodular hyperthyroidism Low radionuclide uptake? Yes No Destructive thyroiditis, iodine excess or excess thyroid hormone Rule out other causes including stimulation by chorionic gonadotropin FIGURE 396-2  Evaluation of thyrotoxicosis. aDiffuse goiter, positive thyroid peroxidase (TPO) antibodies or thyroid-stimulating hormone (TSH) receptor antibody (TRAb), ophthalmopathy, dermopathy. bCan be confirmed by radionuclide scan. spontaneous improvement, particularly in the soft tissue changes. However, the course is more fulminant in up to 5% of patients, requir­ ing intervention in the acute phase if there is optic nerve compression or corneal ulceration. Diplopia may appear late in the disease due to fibrosis of the extraocular muscles. Radioiodine treatment for hyper­ thyroidism worsens the eye disease in a small proportion of patients (especially smokers). Antithyroid drugs and surgery have no adverse effects on the clinical course of ophthalmopathy. Thyroid dermopathy, when it occurs, usually appears 1–2 years after the development of Graves’ hyperthyroidism; it may improve spontaneously. TREATMENT Graves’ Disease The hyperthyroidism of Graves’ disease is treated by reducing thy­ roid hormone synthesis, using an antithyroid drug, or reducing the amount of thyroid tissue with radioiodine (131I) treatment or by thyroidectomy. Antithyroid drugs are the predominant initial therapy in many centers in Europe, Latin America, and Japan, whereas radioiodine is more often the first line of treatment in North America. These differences reflect the fact that no single approach is optimal and that patients may require multiple treat­ ments to achieve remission. The main antithyroid drugs are thionamides: propylthiouracil, carbimazole (not available in the United States), and the active metabolite of the latter, methimazole. All inhibit the function of TPO, reducing oxidation and organification of iodide. These drugs also reduce thyroid antibody levels by mechanisms that remain unclear, and they appear to enhance spontaneous rates of remission. Propylthiouracil inhibits deiodination of T4 → T3. However, this effect is of minor benefit, except in the most severe thyrotoxicosis, and is offset by the much shorter half-life of this drug (90 min) compared to methimazole (6 h). Due to the hepatotoxicity of pro­ pylthiouracil, the U.S. Food and Drug Administration (FDA) has limited indications for its use to the first trimester of pregnancy,

TSH normal or increased, high unbound T4 TSH-secreting pituitary adenoma or thyroid hormone resistance syndrome Normal Hyperthyroidism and Other Causes of Thyrotoxicosis
CHAPTER 396 No further tests Follow up in 6–12 weeks the treatment of thyroid storm, and patients with minor adverse reactions to methimazole. If propylthiouracil is used, monitoring of liver function tests is recommended. There are many variations of antithyroid drug regimens. The initial dose of carbimazole or methimazole is usually 10–20 mg every 12 h, but once-daily dosing is possible after euthyroidism is restored. Propylthiouracil is given at a dose of 100–200 mg every 6–8 h, and divided doses are usually given throughout the course. Lower doses of each drug may suffice in areas of low iodine intake. The starting dose of an antithyroid drug can be gradually reduced (titration regimen) as thyrotoxicosis improves. Less commonly, high doses may be given combined with levothyroxine (LT4) supplementation (block-replace regimen) to avoid drug-induced hypothyroidism. The titration regimen is often preferred to mini­ mize the dose of antithyroid drug and provide an index of treatment response. Thyroid function tests and clinical manifestations are reviewed 4–6 weeks after starting treatment, and the dose is titrated based on unbound T4 levels. Most patients do not achieve euthyroidism until 6–8 weeks after treatment is initiated. TSH levels often remain suppressed for several months and therefore do not provide a sen­ sitive index of treatment response. The usual daily maintenance doses of antithyroid drugs in the titration regimen are 2.5–10 mg of carbimazole or methimazole and 50–100 mg of propylthiouracil. In the block-replace regimen, the initial dose of antithyroid drug is held constant, and the dose of LT4 is adjusted to maintain normal unbound T4 levels. When TSH suppression is alleviated, TSH levels can also be used to monitor therapy. Maximum remission rates (30–60%) are achieved by 12–18 months for the titration regimen and are higher in patients in whom TRAb levels are no longer detected than in those with TRAb persistence. For unclear reasons, remission rates appear to vary in different geographic regions. Younger patients, males, smokers, and patients with a history of allergy, severe hyperthyroidism, or large goiters are most likely to relapse when treatment stops, as are those with enduring TRAb, but outcomes are difficult to predict. All patients

should be followed closely for relapse during the first year after treatment and at least annually thereafter. Prolonged treatment for up to 10 years with small doses of an antithyroid drug has been used as an alternative to ablative therapies following relapse.

The common minor side effects of antithyroid drugs are rash, urticaria, fever, and arthralgia (1–5% of patients). These may resolve spontaneously or after substituting an alternative antithy­ roid drug; rashes may respond to an antihistamine. Rare but major side effects include hepatitis (especially with propylthiouracil; avoid use in children) and cholestasis (methimazole and carbimazole); vasculitis; and, most important, agranulocytosis (<1%). It is essen­ tial that antithyroid drugs are stopped and not restarted if a patient develops major side effects. Written instructions should be pro­ vided regarding the symptoms of possible agranulocytosis (e.g., sore throat, fever, mouth ulcers) and the need to stop treatment pending an urgent complete blood count to confirm that agranulocytosis is not present. Management of agranulocytosis is described in Chap. 107. It is not useful to monitor blood counts prospectively, because the onset of agranulocytosis is idiosyncratic and abrupt. PART 12 Endocrinology and Metabolism Propranolol (20–40 mg every 6 h) or longer-acting selective β1 receptor blockers such as atenolol may be helpful to control adren­ ergic symptoms, especially in the early stages before antithyroid drugs take effect. Beta blockers are also useful in patients with thy­ rotoxic periodic paralysis, pending correction of thyrotoxicosis. In consultation with a cardiologist or using a risk score like CHA2DS2VASc, anticoagulation should be considered in all patients with atrial fibrillation; the majority revert spontaneously to sinus rhythm with control of hyperthyroidism, and long-term anticoagulation is not usually needed. Decreased warfarin doses are required when patients are thyrotoxic. If digoxin is used, increased doses are often needed in the thyrotoxic state. Radioiodine causes progressive destruction of thyroid cells and can be used as initial treatment or for relapses after a trial of anti­ thyroid drugs. There is a small risk of thyrotoxic crisis (see below) after radioiodine, which can be minimized by pretreatment with antithyroid drugs for at least a month before treatment. Antecedent treatment with an antithyroid drug and a beta blocker should be considered for all elderly patients or for those with cardiac prob­ lems. Carbimazole or methimazole must be stopped 2–3 days before radioiodine administration to achieve optimum iodine uptake and can be restarted 3–7 days after radioiodine in those at risk of com­ plications from worsening thyrotoxicosis. Propylthiouracil appears to have a prolonged radioprotective effect and should be stopped for a longer period before radioiodine is given, or a larger dose of radioiodine will be necessary. Efforts to calculate an optimal dose of radioiodine that achieves euthyroidism without a high incidence of relapse or progression to hypothyroidism have not been successful. Some patients inevitably relapse after a single dose because the biologic effects of radiation vary between individuals, and hypothyroidism cannot be uniformly avoided even using accurate dosimetry. A practical strategy is to give a fixed dose based on clinical features, such as the severity of thyrotoxicosis, the size of the goiter (larger goiters need a higher dosage) and the radioiodine uptake (higher uptake decreases the dosage needed). 131I dosage generally ranges between 370 MBq (10 mCi) and 555 MBq (15 mCi). Most authorities favor an approach aimed at thyroid ablation (as opposed to euthyroidism), given that LT4 replacement is straightforward and most patients ultimately prog­ ress to hypothyroidism over 5–10 years. Certain radiation safety precautions are necessary in the first few days after radioiodine treatment, but the exact guidelines vary depending on local protocols. In general, patients need to avoid close, prolonged contact with children and pregnant women for 5–7 days because of possible transmission of residual isotope and exposure to radiation emanating from the gland. Rarely, there may be mild pain due to radiation thyroiditis 1–2 weeks after treatment. Hyperthyroidism can persist for 2–3 months before radioiodine takes full effect. For this reason, β-adrenergic blockers or anti­ thyroid drugs, which can be restarted 5–7 days after radioiodine

administration, can be used to control symptoms during this inter­ val. Persistent hyperthyroidism can be treated with a second dose of radioiodine, usually 6 months after the first dose. The risk of hypothyroidism after radioiodine depends on the dosage but is at least 10–20% in the first year and 5% per year thereafter and 5% per year thereafter, with higher rates after ablative treatment. Patients should be informed of this possibility before treatment and require close follow-up during the first year followed by annual thyroid function testing. Pregnancy and breast-feeding are absolute contraindications to radioiodine treatment, but patients can conceive safely 6 months after treatment. The presence of ophthalmopathy, especially in smokers, requires caution. Prednisone, 0.2–0.5 mg/kg per d (depending on ophthalmopathy severity), at the time of radioiodine treatment, tapered over 6–12 weeks, may prevent exacerbation of ophthalmopathy, but radioiodine should generally be avoided in patients with active moderate-to-severe eye disease. Although many physicians avoid radioiodine in children and adolescents because of the potential risks of malignancy, others have advocated radioio­ dine use in older children. There is no overall increase in cancer risk after radioiodine. Patients may be advised that the risks are small enough to be indistinguishable from antithyroid drugs or surgery. Total or near-total thyroidectomy is an option for patients who relapse after antithyroid drugs and prefer this treatment to radio­ iodine. Some experts recommend surgery in young individuals, particularly when the goiter is very large. Careful control of thy­ rotoxicosis with antithyroid drugs, followed by potassium iodide (SSKI; 1–2 drops orally tid for 10 days), is needed prior to surgery to avoid thyrotoxic crisis and to reduce the vascularity of the gland. The major complications of surgery—bleeding, laryngeal edema, hypoparathyroidism, and damage to the recurrent laryngeal nerves—are unusual when the procedure is performed by highly experienced surgeons. Recurrence rates in the best series are <2%, but the rate of hypothyroidism is similar to that following radioio­ dine treatment, especially with the current trend away from subtotal thyroidectomy. Antithyroid drugs should be used to manage active Graves’ disease in pregnancy. Because transplacental passage of these drugs may produce fetal hypothyroidism and goiter if the maternal dose is excessive, maternal antithyroid dose titration should target serum free or total T4 levels at or just above the pregnancy reference range. If available, propylthiouracil should be used until 14–16 weeks’ gestation because of the risk of rare cases of methimazole/carbimazole embryopathy, including aplasia cutis and other defects, such as choanal atresia and tracheoesophageal fistulae. Because of the potential for teratogenic effects, antithyroid medication should be discontinued in any newly pregnant woman with Graves’ disease who is euthyroid on a low dose of methimazole (<5–10 mg/d) or propylthiouracil (<100–200 mg/d), after evaluating recent thyroid function tests, disease history, goiter size, duration of therapy, and TRAb measurement. Following cessation, careful monitoring of maternal thyroid function tests is essential. On the other hand, for women at high risk of developing thyrotoxicosis if antithyroid drugs are discontinued (large goiter, requirement for higher antithyroid drug dosage, elevated TRAb), continued therapy is necessary, with propylthiouracil (if available) administration in the first trimester. Because of its rare association with hepatotoxicity, propylthiouracil should be limited to the first trimester and then maternal therapy should be converted to methimazole (or carbimazole) at a ratio of 15–20 mg of propylthiouracil to 1 mg of methimazole. It is often possible to stop treatment in the last trimester because TSI tend to decline in pregnancy. Nonetheless, the transplacental transfer of these antibodies, if present, at levels three times higher than the normative range may rarely cause fetal or neonatal thyrotoxicosis. Poor intrauterine growth, a fetal heart rate of >160 beats/min, advanced bone age, fetal goiter, and high levels of maternal TSI after 26 weeks’ gestation may herald this complication. Antithyroid drugs given to the mother can be used to treat the fetus and may be needed for 1–3 months after delivery, until the maternal antibodies

disappear from the baby’s circulation. The postpartum period is a time of major risk for relapse of Graves’ disease. Breast-feeding is safe with low doses of antithyroid drugs. Graves’ disease in children is usually managed initially with methimazole or carbimazole (avoid propylthiouracil), often given as a course of the titration regi­ men for at least 3 years. Surgery or radioiodine may be indicated for severe or relapsing disease. Thyrotoxic crisis, or thyroid storm, is rare and presents as a life-threatening exacerbation of hyperthyroidism, accompanied by fever, delirium, seizures, coma, vomiting, diarrhea, and jaundice. The mortality rate due to cardiac failure, arrhythmia, or hyper­ thermia is high (4–17%) even with treatment. Thyrotoxic crisis is usually precipitated by acute illness (e.g., stroke, infection, trauma, diabetic ketoacidosis), surgery (especially on the thyroid), or radio­ iodine treatment of a patient with partially treated or untreated hyperthyroidism. Management requires intensive monitoring and supportive care, identification and treatment of the precipitating cause, and measures that reduce thyroid hormone synthesis. Large doses of propylthiouracil (500–1000 mg loading dose and 250 mg every 4 h) should be given orally or by nasogastric tube or per rec­ tum; the drug’s inhibitory action on T4 → T3 conversion makes it the antithyroid drug of choice. If not available, methimazole can be used in doses of 20 mg every 6 h. One hour after the first dose of propylthiouracil or methimazole, stable iodide (5 drops SSKI every 6 h) is given to block thyroid hormone synthesis via the WolffChaikoff effect (the delay allows the antithyroid drug to prevent the excess iodine from being incorporated into new hormone). Propranolol should also be given to reduce tachycardia and other adrenergic manifestations (60–80 mg PO every 4 h, or 2 mg IV every 4 h). Although other β-adrenergic blockers can be used, high doses of propranolol decrease T4 → T3 conversion, and the doses can be easily adjusted. Caution is needed to avoid acute negative inotropic effects, but controlling the heart rate is important, as some patients develop a form of high-output heart failure. Short-acting IV esmolol can be used to decrease heart rate while monitoring for signs of heart failure. Additional therapeutic measures include glucocorticoids (e.g., hydrocortisone 300 mg IV bolus, then 100 mg every 8 h), antibiotics if infection is present, cholestyramine to sequester thyroid hormones, cooling, oxygen, and IV fluids. Mild ophthalmopathy requires no active treatment, because there is usually spontaneous improvement. General measures include meticulous control of thyroid hormone levels, cessation of smoking, and an explanation of the natural history of ophthalmopathy. Dis­ comfort can be relieved with artificial tears (e.g., hypromellose 0.3% or carbomer 0.2% ophthalmic gel), paraffin-based eye ointment, and the use of dark glasses with side frames. Periorbital edema may respond to a more upright sleeping position or a diuretic. Corneal exposure during sleep can be avoided by using patches or taping the eyelids shut. Minor degrees of diplopia improve with prisms fitted to spectacles. Some authorities also advocate selenium 100 μg bid. Moderate-to-severe ophthalmopathy, in which the eye disease has sufficient impact on daily life to justify the risks of treatment, is usually treated with IV methylprednisolone (e.g., 500 mg of methylprednisolone once weekly for 6 weeks, then 250 mg once weekly for 6 weeks). This is preferable to oral glucocorticoids. A poor response at 6 weeks generally indicates the need for alternative treatment. Once the eye disease has stabilized, surgery may be indi­ cated for relief of diplopia and correction of appearance. External beam radiotherapy of the orbits has been used for many years, but the efficacy of this therapy remains unclear, and it is best reserved for those who are not responsive to glucocorticoid therapy. Tepro­ tumumab, a monoclonal antibody inhibitor of the IGF-1 receptor, improves proptosis, diplopia, clinical activity score, and quality of life and is recommended as first-line treatment in patients with active moderate-to-severe ophthalmopathy with significant pro­ ptosis or diplopia, but use may be limited by availability and cost. Relapse rates are similar to glucocorticoids (30%). Rituximab and tocilizumab are other monoclonal antibodies that have been used as second-line treatment after glucocorticoids. Sight-threatening

ophthalmopathy due to optic nerve compression or corneal damage is an emergency that requires immediate high-dose IV glucocorti­ coids (e.g., methylprednisolone 500–1000 mg on alternate days). If there is a poor response after 2 weeks, surgical orbital decom­ pression should be considered by removing bone from the medial and inferior orbital wall, thereby allowing displacement of fat and swollen extraocular muscles. In addition to nerve decompression, proptosis recedes an average of 5 mm, but there may be residual or even worsened diplopia.

Thyroid dermopathy does not usually require treatment, but it can cause cosmetic problems or interfere with the fit of shoes. Surgical removal is not indicated. If necessary, treatment consists of topical, high-potency glucocorticoid ointment under an occlusive dressing or compression dressing. Teprotumumab has been benefi­ cial in some cases. Hyperthyroidism and Other Causes of Thyrotoxicosis
CHAPTER 396 ■ ■OTHER CAUSES OF THYROTOXICOSIS Destructive thyroiditis (subacute or silent thyroiditis) typically presents with a short thyrotoxic phase due to the release of preformed thyroid hormones and catabolism of Tg (see “Subacute Thyroiditis,” below). True hyperthyroidism is absent, as demonstrated by a low radionuclide uptake. Circulating Tg levels are typically increased. Other causes of thyrotoxicosis with low or absent thyroid radionuclide uptake include thyrotoxicosis factitia, iodine excess, and, rarely, ectopic thyroid tissue, particularly teratomas of the ovary (struma ovarii) and functional metastatic follicular carcinoma. Whole-body radionuclide studies can demonstrate ectopic thyroid tissue, and thyrotoxicosis factitia can be distinguished from destructive thyroiditis by the clinical features and low levels of Tg. Amiodarone treatment is associated with thyrotoxico­ sis in up to 10% of patients, particularly in areas of low iodine intake (see below). TSH-secreting pituitary adenoma is a rare cause of thyrotoxicosis. It is characterized by the presence of an inappropriately normal or increased TSH level in a patient with hyperthyroidism, diffuse goiter, and elevated T4 and T3 levels (Chap. 392). Elevated levels of the α subunit of TSH, released by the TSH-secreting adenoma, support this diagnosis, which can be confirmed by demonstrating the pituitary tumor on MRI or CT scan. A combination of transsphenoidal surgery, sella irradiation, and octreotide may be required to normalize TSH, because many of these tumors are large and locally invasive at the time of diagnosis. Radioiodine or antithyroid drugs can be used to control thyrotoxicosis. Thyrotoxicosis caused by toxic MNG and hyperfunctioning solitary nodules is discussed below (Chap. 396). THYROIDITIS There are several classification systems to describe the clinical syn­ dromes of thyroiditis. One is based on the onset and duration of disease (Table 396-3); others are based on the absence or presence of pain. ■ ■ACUTE THYROIDITIS Acute thyroiditis is rare and due to suppurative infection of the thyroid. In children and young adults, the most common cause is the presence of a piriform sinus, a remnant of the fourth branchial pouch that con­ nects the oropharynx with the thyroid. Such sinuses are predominantly left-sided. A long-standing goiter and degeneration in a thyroid malig­ nancy are risk factors in the elderly. The patient presents with thyroid pain, often referred to the throat or ears, and a small, tender goiter that may be asymmetric. Fever, dysphagia, and erythema over the thyroid are common, as are systemic symptoms of a febrile illness and lymphadenopathy. The differential diagnosis of thyroid pain includes subacute or, rarely, chronic thyroiditis; hemorrhage into a cyst; malignancy includ­ ing lymphoma; and, rarely, amiodarone-induced thyroiditis or amyloi­ dosis. However, the abrupt presentation and clinical features of acute thyroiditis rarely cause confusion. The erythrocyte sedimentation rate (ESR) and white cell count are usually increased, but thyroid func­ tion is generally normal. Fine-needle aspiration (FNA) biopsy shows infiltration by polymorphonuclear leukocytes; culture of the sample

TABLE 396-3  Causes of Thyroiditis Acute Bacterial infection: especially Staphylococcus, Streptococcus, and Enterobacter Fungal infection: Aspergillus, Candida, Coccidioides, Histoplasma, and Pneumocystis Radiation thyroiditis after 131I treatment Amiodarone (may also be subacute or chronic) Subacute Viral (or granulomatous) thyroiditis Silent thyroiditis (including postpartum thyroiditis) PART 12 Endocrinology and Metabolism Mycobacterial infection Drug-induced (interferon, amiodarone, tyrosine kinase inhibitors, immune checkpoint inhibitors) Chronic Autoimmunity: focal thyroiditis, Hashimoto’s thyroiditis, atrophic thyroiditis FIGURE 396-3  Clinical course of subacute thyroiditis. The release of thyroid hormones is initially associated with a thyrotoxic phase and suppressed thyroidstimulating hormone (TSH). A hypothyroid phase then ensues, with low T4 and TSH levels that are initially low but gradually increase. During the recovery phase, increased TSH levels combined with resolution of thyroid follicular injury lead to normalization of thyroid function, often several months after the beginning of the illness. ESR, erythrocyte sedimentation rate; UT4, free or unbound T4. can identify the organism. Caution is needed in immunocompromised patients as fungal, mycobacterial, or Pneumocystis thyroiditis can occur in this setting. Antibiotic treatment is guided initially by Gram stain and, subsequently, by cultures of the FNA biopsy. Surgery may be needed to drain an abscess, which can be localized by CT scan or ultrasound. Tracheal obstruction, septicemia, retropharyngeal abscess, mediastinitis, and jugular venous thrombosis may complicate acute thyroiditis but are uncommon with prompt use of antibiotics. Riedel’s thyroiditis Parasitic thyroiditis: echinococcosis, strongyloidiasis, cysticercosis Traumatic: after palpation ■ ■SUBACUTE THYROIDITIS This is also termed de Quervain’s thyroiditis, granulomatous thyroid­ itis, or viral thyroiditis. Many viruses have been implicated, including mumps, coxsackie, influenza, adenoviruses, and echoviruses. Subacute thyroiditis may also occur with the SARS-CoV-2 illness or after receiv­ ing the COVID vaccine. The diagnosis may be overlooked because the symptoms can mimic pharyngitis. Attempts to identify the causative virus in an individual patient are often unsuccessful and do not influ­ ence management. The peak incidence occurs at 30–50 years, and women are affected three times more frequently than men. Pathophysiology  The thyroid shows a characteristic patchy inflammatory infiltrate with disruption of the thyroid follicles and multinucleated giant cells within some follicles. The follicular changes progress to granulomas accompanied by fibrosis. Finally, the thyroid returns to normal, usually several months after onset. During the ini­ tial phase of follicular destruction, there is release of Tg and thyroid hormones, leading to increased circulating T4 and T3 and suppres­ sion of TSH (Fig. 396-3). During this destructive phase, radioactive iodine uptake is low or undetectable. After several weeks, the thyroid is depleted of stored thyroid hormone and a phase of hypothyroid­ ism typically occurs, with low unbound T4 (and sometimes T3) and moderately increased TSH levels. Radioactive iodine uptake returns to normal or is even increased as a result of the rise in TSH. Finally, thy­ roid hormone and TSH levels return to normal as the disease subsides. Clinical Manifestations  The patient usually presents with a pain­ ful and enlarged thyroid, sometimes accompanied by fever. There may be features of thyrotoxicosis or hypothyroidism, depending on the phase of the illness. Malaise and symptoms of an upper respiratory tract infec­ tion may precede the thyroid-related features by several weeks. In other patients, the onset is acute, severe, and without obvious antecedent. The patient typically complains of a sore throat, and examination reveals a small goiter that is exquisitely tender. Pain is often referred to the jaw or ear. Complete resolution is the usual outcome, but late-onset permanent hypothyroidism occurs in 15% of cases, particularly in those with coin­ cidental thyroid autoimmunity. A prolonged course over many months, with one or more relapses, occurs in a small percentage of patients.

ESR TSH

UT4

UT4 (pmol/L) ESR (mm/h) TSH (mU/L)

0.5

0.01

Time (weeks) Thyrotoxic Hypothyroid Recovery Clinical Phases Laboratory Evaluation  As depicted in Fig. 396-3, thyroid func­ tion tests characteristically evolve through three distinct phases over about 6 months: (1) thyrotoxic phase, (2) hypothyroid phase, and (3) recovery phase. In the thyrotoxic phase, T4 and T3 levels are increased, reflecting their discharge from the damaged thyroid cells, and TSH is suppressed. The T4/T3 ratio is lower than in Graves’ or thyroid auton­ omy, in which T3 is often disproportionately increased. The diagnosis is confirmed by a high ESR and low uptake of radioiodine (<5%) or 99mTc pertechnetate (as compared to salivary gland pertechnetate con­ centration). The white blood cell count may be increased, and thyroid antibodies are negative. If the diagnosis is in doubt, FNA biopsy may be useful, particularly to distinguish unilateral involvement from bleeding into a cyst or neoplasm. TREATMENT Subacute Thyroiditis Relatively large doses of aspirin (e.g., 600 mg every 4–6 h) or nonsteroidal anti-inflammatory drugs (NSAIDs) are sufficient to control symptoms in many cases. Generally, gastroprotective medi­ cations, such as proton pump inhibitors, are also prescribed. If this treatment is inadequate, or if the patient has marked local or systemic symptoms, glucocorticoids should be given. The usual starting dose is 15–40 mg of prednisone, depending on sever­ ity. The dose is gradually tapered over 6–8 weeks, in response to improvement in symptoms and the ESR. If a relapse occurs during glucocorticoid withdrawal, the dosage should be increased and then withdrawn more gradually. Thyroid function should be moni­ tored every 2–4 weeks using TSH and free T4 levels. Symptoms of thyrotoxicosis improve spontaneously but may be ameliorated by β-adrenergic blockers; antithyroid drugs play no role in treatment of the thyrotoxic phase. LT4 replacement may be needed if the hypothyroid phase is prolonged, but doses should be low enough (50–100 μg daily) to allow TSH-mediated recovery. ■ ■SILENT THYROIDITIS Painless thyroiditis, or “silent” thyroiditis, occurs in patients with under­ lying autoimmune thyroid disease and has a clinical course similar to that of subacute thyroiditis. The condition occurs in up to 5% of women 3–6 months after pregnancy and is then termed postpartum thyroiditis. Typically, patients have a brief phase of thyrotoxicosis last­ ing 2–4 weeks, followed by hypothyroidism for 4–12 weeks, and then resolution; often, however, only one phase is apparent. The condition is associated with the presence of TPO antibodies antepartum, and it is

three times more common in women with type 1 diabetes mellitus. As in subacute thyroiditis, the uptake of 99mTc pertechnetate or radioactive iodine is initially suppressed. In addition to the painless goiter, silent thyroiditis can be distinguished from subacute thyroiditis by a normal ESR and the presence of TPO antibodies. Glucocorticoid treatment is not indicated for silent thyroiditis. Severe thyrotoxic symptoms can be managed with a brief course of propranolol, 20–40 mg three or four times daily. Thyroxine replacement may be needed for the hypothyroid phase but should be withdrawn after 6–9 months, as recovery is the rule. Annual follow-up thereafter is recommended because a propor­ tion of these individuals develop permanent hypothyroidism. The condition may recur in subsequent pregnancies. ■ ■DRUG-INDUCED THYROIDITIS Patients receiving cytokines, such as IFN-α, tyrosine kinase inhibitors, such as sorafenib, and immune checkpoint inhibitors may develop painless thyroiditis. IFN-α, which is used to treat chronic hepatitis B or C and hematologic and skin malignancies, causes thyroid dysfunction in up to 5% of treated patients. It has been associated with painless thyroiditis, hypothyroidism, and Graves’ disease and is most common in women with TPO antibodies prior to treatment. Thyroiditis occurs in 5–20% of cancer patients treated with the immune checkpoint inhibitors pembrolizumab or nivolumab. In all cases, treatment is the same as silent thyroiditis. Routine monitoring of thyroid function tests is recommended by the American Society of Clinical Oncology. For discussion of amiodarone, see “Amiodarone Effects on Thyroid Func­ tion,” below. ■ ■CHRONIC THYROIDITIS Focal thyroiditis is present in 20–40% of euthyroid autopsy cases and is associated with serologic evidence of autoimmunity, particularly the presence of TPO antibodies. The most common clinically apparent cause of chronic thyroiditis is Hashimoto’s thyroiditis, an autoimmune disorder that often presents as a firm or hard goiter of variable size (Chap. 395). Riedel’s thyroiditis is a rare disorder that typically occurs in middle-aged women. It presents with an insidious, painless goiter with local symptoms due to compression of the esophagus, trachea, neck veins, or recurrent laryngeal nerves. Dense fibrosis disrupts normal gland architecture and can extend outside the thyroid cap­ sule. Despite these extensive histologic changes, thyroid dysfunction is uncommon. The goiter is hard, nontender, often asymmetric, and fixed, leading to suspicion of a malignancy. Diagnosis requires open biopsy as FNA biopsy is usually inadequate. Treatment is with gluco­ corticoids, other immunomodulatory treatments, tamoxifen, or surgi­ cal relief of compressive symptoms. There is an association between Riedel’s thyroiditis and IgG4-related disease causing idiopathic fibrosis at other sites (retroperitoneum, mediastinum, biliary tree, lung, and orbit) (Chap. 380). SICK EUTHYROID SYNDROME (NONTHYROIDAL ILLNESS) Any acute, severe illness can cause abnormalities of circulating TSH or thyroid hormone levels in the absence of underlying thyroid disease, making these measurements potentially misleading. The major cause of these hormonal changes is the release of cytokines such as IL-6. Unless a thyroid disorder is strongly suspected, the routine testing of thyroid function should be avoided in acutely ill patients. The most common hormone pattern in sick euthyroid syndrome (SES), also called nonthyroidal illness (NTI), is a decrease in total and unbound T3 levels (low T3 syndrome) with normal levels of T4 and TSH. The magnitude of the fall in T3 correlates with the severity of the illness. T4 conversion to T3 via peripheral 5′ (outer ring) deiodination is impaired, leading to increased reverse T3 (rT3). Since rT3 is metabolized by 5′ deiodination, its clearance is also reduced. Thus, decreased clear­ ance rather than increased production is the major basis for increased rT3. Also, T4 is alternately metabolized to the hormonally inactive T3 sulfate. It is generally assumed that this low T3 state is adaptive, because it can be induced in normal individuals by fasting. Teleologically, the fall in T3 may limit catabolism in starved or ill patients.

Very sick patients may exhibit a dramatic fall in total T4 and T3 levels (low T4 syndrome). With decreased tissue perfusion, muscle and liver expression of the type 3 deiodinase leads to accelerated T4 and T3 metabolism. This state has a poor prognosis. Another key factor in the fall in T4 levels is altered binding to thyroxine-binding globulin (TBG). The commonly used free T4 assays are subject to artifact when serum binding proteins are low and underestimate the true free T4 level. Fluctuation in TSH levels also creates challenges in the interpretation of thyroid function in sick patients. TSH levels may range from 0.01 to 0.1 mIU/L in very ill patients, especially with dopamine or glucocor­ ticoid therapy, to >20 mIU/L during the recovery phase of SES. The exact mechanisms underlying the subnormal TSH seen in 10% of sick patients and the increased TSH seen in 5% remain unclear but may be mediated by cytokines including IL-12 and IL-18. However, if the serum TSH is undetectable (<0.01 mIU/L), primary thyroid disease is more likely and endocrine evaluation should be done.

Hyperthyroidism and Other Causes of Thyrotoxicosis
CHAPTER 396 Any severe illness can induce changes in thyroid hormone levels, but certain disorders exhibit a distinctive pattern of abnormalities. Acute liver disease is associated with an initial rise in total (but not unbound) T3 and T4 levels due to TBG release; these levels become subnormal with progression to liver failure. A transient increase in total and unbound T4 levels, usually with a normal T3 level, is seen in 5–30% of acutely ill psychiatric patients. TSH values may be transiently low, normal, or high in these patients. In the early stage of HIV infection, T3 and T4 levels rise, even if there is weight loss. T3 levels fall with progres­ sion to AIDS, but TSH usually remains normal. Renal disease is often accompanied by low T3 concentrations, but with normal rather than increased rT3 levels, due to an unknown factor that increases uptake of rT3 into the liver. The diagnosis of NTI is challenging. Historic information may be limited, and patients often have multiple metabolic derangements. Use­ ful features to consider include previous history of thyroid disease and thyroid function tests, evaluation of the severity and time course of the patient’s acute illness, documentation of medications that may affect thyroid function or thyroid hormone levels, and measurements of rT3 together with unbound thyroid hormones and TSH. The diagnosis of NTI is frequently presumptive, given the clinical context and pattern of laboratory values; only resolution of the test results with clinical recovery can clearly establish this disorder. Treatment of NTI with thyroid hormone (T4 and/or T3) is controversial, but most authorities recommend monitoring the patient’s thyroid function tests during recovery, without administering thyroid hormone, unless there is historic or clinical evidence suggestive of hypothyroidism. Sufficiently large randomized controlled trials using thyroid hormone are unlikely to resolve this therapeutic controversy in the near future, because clini­ cal presentations and outcomes are highly variable. AMIODARONE EFFECTS ON THYROID FUNCTION Amiodarone is a commonly used type III antiarrhythmic agent (Chap. 259). It is structurally related to thyroid hormone and contains 39% iodine by weight. Thus, typical doses of amiodarone (200 mg/d) are associated with very high iodine intake, leading to greater than 40-fold increases in plasma and urinary iodine levels. Moreover, because amiodarone is stored in adipose tissue, high iodine levels persist for

6 months after discontinuation of the drug. Amiodarone inhibits deiodinase activity, and its metabolites function as weak antagonists of thyroid hormone action. Amiodarone has the following effects on thy­ roid function: (1) acute, transient suppression of thyroid function; (2) inhibition of T4 to T3 conversion causing either euthyroid hyperthyrox­ inemia or increased dosage requirement in LT4-treated hypothyroid patients; (3) hypothyroidism in patients susceptible to the inhibitory effects of a high iodine load; and (4) thyrotoxicosis that may be caused by either a Jod-Basedow effect from the iodine load, in the setting of MNG or incipient Graves’ disease, or a thyroiditis-like condition due to a toxic effect on thyroid follicular cells. The initiation of amiodarone treatment is associated with a transient decrease of T4 levels, reflecting the inhibitory effect of iodine on T4 release. Soon thereafter, most individuals escape from iodide-dependent

11 - 397 Thyroid Nodular Disease and Thyroid Cancer

397 Thyroid Nodular Disease and Thyroid Cancer

suppression of the thyroid (Wolff-Chaikoff effect), and the inhibitory effects on deiodinase activity and thyroid hormone receptor action become predominant. These events lead to the following pattern of thyroid function tests: increased T4, decreased T3, increased rT3, and a transient TSH increase (up to 20 mIU/L). TSH levels normalize or are slightly suppressed within 1–3 months.

The incidence of hypothyroidism from amiodarone varies geo­ graphically, apparently correlating with iodine intake. Hypothyroidism occurs in up to 13% of amiodarone-treated patients in iodine-replete countries, such as the United States, but is less common (<6% inci­ dence) in areas of lower iodine intake, such as Italy or Spain. The pathogenesis appears to involve an inability of the thyroid gland to escape from the Wolff-Chaikoff effect in autoimmune thyroiditis. Consequently, amiodarone-associated hypothyroidism is more com­ mon in women and individuals with positive TPO antibodies. It is usually unnecessary to discontinue amiodarone for this side effect, because LT4 can be used to normalize thyroid function. TSH levels should be monitored, because T4 levels are often increased for the rea­ sons described above. In addition, TSH levels need to be monitored in LT4-replaced hypothyroid patients because a dosage increase is often required. PART 12 Endocrinology and Metabolism The management of amiodarone-induced thyrotoxicosis (AIT) is complicated by the fact that there are different causes of thyrotoxicosis and because the increased thyroid hormone levels exacerbate underly­ ing arrhythmias and coronary artery disease. Amiodarone treatment causes thyrotoxicosis in 10% of patients living in areas of low iodine intake and in 2% of patients in regions of high iodine intake. There are two major forms of AIT, although some patients have features of both. Type 1 AIT is associated with an underlying thyroid abnormal­ ity (preclinical Graves’ disease or nodular goiter). Thyroid hormone synthesis becomes excessive as a result of increased iodine exposure (Jod-Basedow phenomenon). Type 2 AIT occurs in individuals with no intrinsic thyroid abnormalities and is the result of drug-induced lyso­ somal activation leading to destructive thyroiditis with histiocyte accu­ mulation in the thyroid; the incidence rises as cumulative amiodarone dosage increases. Mild forms of type 2 AIT can resolve spontaneously or can occasionally lead to hypothyroidism. Color-flow Doppler ultra­ sonography shows increased vascularity in type 1 AIT but decreased vascularity in type 2 AIT. Thyroid scintiscans are difficult to interpret in this setting because the high endogenous iodine levels diminish tracer uptake. However, the presence of normal or rarely increased uptake favors type 1 AIT. In AIT, because of amiodarone’s prolonged half-life and storage in adipose tissue, there is no immediate benefit from discontinuing the drug. Treatment studies have reported a similar time course for AIT type 2 resolution whether amiodarone was continued or stopped. Therefore, the decision to discontinue the drug should be based upon the severity of the arrhythmia. High doses of antithyroid drugs can be used in type 1 AIT but are often ineffective. Potassium perchlorate, 500 mg bid, has been used to reduce thyroidal iodide content. Perchlorate treatment has been associated with agranulocytosis, although the risk appears relatively low with short-term use. This drug is also no longer available in many countries. Glucocorticoids (initial dose usually 40–60 mg/d of prednisone) are effective in treating in type 2 AIT. Near-total thyroid­ ectomy rapidly decreases thyroid hormone levels and may be the most effective long-term solution if the patient can undergo the procedure safely. ■ ■FURTHER READING Alexander EK et al: 2017 Guidelines of the American Thyroid Asso­ ciation for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid 27:315, 2017. Biondi B, Cooper DS: Subclinical hyperthyroidism. N Engl J Med 378:2411, 2018. Burch HB et al: Management of thyroid eye disease: A Consensus Statement by the American Thyroid Association and European Thyroid Association. Thyroid 32:1439, 2022. Kim BW: Does radioactive iodine therapy for hyperthyroidism cause cancer? J Clin Endocrinol Metab 107:e448, 2022.

Ross DS et al: 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid 26:1343, 2016. Wiersinga WM et al: Hyperthyroidism: Aetiology, pathogenesis, diag­ nosis, management, complications, and prognosis. Lancet Diabetes Endocrinol 11:282, 2023. Susan J. Mandel, Anthony P. Weetman,

J. Larry Jameson

Thyroid Nodular Disease

and Thyroid Cancer ■ ■GOITER AND THYROID NODULAR DISEASE Goiter refers to an enlarged thyroid gland. Biosynthetic defects, iodine deficiency, autoimmune disease, and nodular diseases can each lead to goiter, although by different mechanisms. Biosynthetic defects and iodine deficiency are associated with reduced efficiency of thyroid hormone synthesis, leading to increased thyroid-stimulat­ ing hormone (TSH), which stimulates thyroid growth as a compensa­ tory mechanism to overcome the block in hormone synthesis. Graves’ disease and Hashimoto’s thyroiditis are also associated with goiter. In Graves’ disease, the goiter results mainly from the TSH-R–medi­ ated effects of thyroid-stimulating immunoglobulins. The goitrous form of Hashimoto’s thyroiditis occurs because of acquired defects in hormone synthesis, leading to elevated levels of TSH and its con­ sequent growth effects. Lymphocytic infiltration and immune sys­ tem–induced growth factors also contribute to thyroid enlargement in Hashimoto’s thyroiditis. Thyroid nodular disease is characterized by the disordered growth of thyroid cells, which can be either hyperplastic or neoplastic. A patient may have a multinodular goiter (MNG) in which thyroid nodules (generally hyperplastic) replace the majority of the normal thyroid parenchyma; this presentation is more common in areas of borderline iodine deficiency. Or, the thyroid gland may be normal in size and contain discrete thyroid nodules. Because the management of goiter depends on the etiology, the detection of thyroid enlarge­ ment on physical examination should prompt further evaluation to identify its cause. Nodular thyroid disease is common, occurring in about 3–7% of adults when assessed by physical examination. Using ultrasound, nod­ ules are present in up to 50% of adults, with the majority being <1 cm in diameter. Thyroid nodules may be solitary or multiple, and they may be functional or nonfunctional. ■ ■DIFFUSE NONTOXIC (SIMPLE) GOITER Etiology and Pathogenesis  When diffuse enlargement of the thyroid occurs in the absence of nodules and hyperthyroidism, it is referred to as a diffuse nontoxic goiter. This is sometimes called simple goiter and is characterized by the presence of uniform follicles that are filled with colloid. Worldwide, diffuse goiter is most commonly caused by iodine deficiency and is termed endemic goiter when it affects >5% of the population. In nonendemic regions, sporadic goiter occurs, and the cause is usually unknown. Thyroid enlargement in teenagers is sometimes referred to as juvenile goiter. In general, goiter is more com­ mon in women than men, probably because of the greater prevalence of underlying autoimmune disease and the increased iodine demands associated with pregnancy.

In iodine-deficient areas, thyroid enlargement reflects a compen­ satory effort to trap iodide and produce sufficient hormone under conditions in which hormone synthesis is relatively inefficient. Somewhat surprisingly, TSH levels are usually normal or only slightly increased, suggesting increased sensitivity to TSH or activa­ tion of other pathways that lead to thyroid growth. Iodide appears to have direct actions on thyroid vasculature and may indirectly affect growth through vasoactive substances such as endothelins and nitric oxide. Endemic goiter may also be caused by exposure to environmental goitrogens such as cassava root, which contains a thiocyanate; vegetables of the Cruciferae family (known as crucifer­ ous vegetables) (e.g., Brussels sprouts, cabbage, and cauliflower); and milk from regions where goitrogens are present in grass. Although relatively rare, inherited defects in thyroid hormone synthesis lead to a diffuse nontoxic goiter. Abnormalities at each step of hormone syn­ thesis, including iodide transport (sodium/iodide symporter [NIS]), thyroglobulin (Tg) synthesis, organification and coupling (thyroid peroxidase [TPO]), and the regeneration of iodide (dehalogenase), have been described. ■ ■CLINICAL MANIFESTATIONS AND DIAGNOSIS If thyroid function is preserved, most goiters are asymptomatic. Exami­ nation of a diffuse goiter reveals a symmetrically enlarged, nontender, generally soft gland without palpable nodules. Goiter is defined, some­ what arbitrarily, as a lateral lobe with a volume greater than the thumb of the individual being examined. On ultrasound, total thyroid volume exceeding 30 mL is considered abnormal. If the thyroid is markedly enlarged, it can cause tracheal or esophageal compression. These features are unusual, however, in the absence of nodular disease and fibrosis. Substernal goiter may obstruct the thoracic inlet. Pemberton’s sign refers to facial and neck congestion due to jugular venous obstruc­ tion when the arms are raised above the head, a maneuver that draws the thyroid into the thoracic inlet. Respiratory flow measurements and computed tomography (CT) or magnetic resonance imaging (MRI) should be used to evaluate substernal goiter in patients with obstructive signs or symptoms. Thyroid function tests should be performed in all patients with goiter to exclude thyrotoxicosis or hypothyroidism. It is not unusual, particularly in iodine deficiency, to find a low total T4, with normal T3 and TSH, reflecting enhanced T4 → T3 conversion, as well as preferential T3 production. A low TSH with a normal free T3 and free T4, particularly in older patients, suggests the possibility of thyroid autonomy or undiagnosed Graves’ disease, and is termed subclinical thyrotoxicosis. The benefit of treatment (typically with radioiodine) in subclinical thyrotoxicosis, versus follow-up and implementing treatment if free T3 or free T4 levels become abnormal, is unclear, but treatment is increasingly recommended in the elderly to reduce the risk of atrial fibrillation and bone loss. Low urinary iodine levels

(<50 μg/L) support a diagnosis of iodine deficiency. Thyroid scanning is not generally necessary for euthyroid patients. If preformed, scintig­ raphy demonstrates increased uptake in iodine deficiency and most cases of dyshormonogenesis. TREATMENT Diffuse Nontoxic (Simple) Goiter Iodine replacement induces variable regression of goiter in iodine deficiency, depending on duration and the degree of hyperplasia, with accompanying fibrosis, and autonomous function that may have developed. Surgery is rarely indicated for diffuse goiter. Exceptions include documented evidence of tracheal compres­ sion or obstruction of the thoracic inlet, which are more likely to be associated with substernal MNGs (see below). Subtotal or near-total thyroidectomy for these or cosmetic reasons should be performed by an experienced surgeon to minimize complication rates. Surgery should be followed by replacement with levothy­ roxine (LT4).

■ ■NONTOXIC MULTINODULAR GOITER

Etiology and Pathogenesis  Depending on the population stud­ ied, MNG or the presence of nodules in a thyroid of normal size occurs in up to 12% of adults. MNG should be distinguished from the presence of nodules in a normal-size thyroid gland (see “Approach to the Patient with Thyroid Nodules”). MNG is more common in women than men and increases in prevalence with age. It is more common in iodine-deficient regions but also occurs in regions of iodine sufficiency, reflecting multiple genetic, autoimmune, and environmental influences on the pathogenesis. Thyroid Nodular Disease and Thyroid Cancer CHAPTER 397 There is typically wide variation in nodule size. Histology reveals a spectrum of morphologies ranging from hypercellular, hyperplastic regions to cystic areas filled with colloid. Fibrosis is often extensive, and areas of hemorrhage or lymphocytic infiltration may be seen. Using molecular techniques, most nodules within an MNG are poly­ clonal in origin, suggesting a hyperplastic response to locally produced growth factors and cytokines. TSH, which is usually not elevated, may play a permissive or contributory role. Monoclonal neoplastic lesions may also occur, reflecting mutations in genes that confer a selective growth advantage to the progenitor cell. Clinical Manifestations  Most patients with nontoxic MNG are asymptomatic and euthyroid. MNG typically develops over many years and is detected on routine physical examination, when an individual notices an enlargement in the neck, or as an incidental finding on imag­ ing. If the goiter is large enough, it can ultimately lead to compressive symptoms including difficulty swallowing, respiratory distress (tracheal compression), or plethora (venous congestion), but these symptoms are uncommon. Symptomatic MNGs are usually large and/or develop fibrotic areas that cause compression. Sudden pain in an MNG is usually caused by hemorrhage into a nodule. Hoarseness, reflecting laryngeal nerve involvement, may suggest malignancy but more commonly is due to others causes such as gastroesophageal reflux. Diagnosis  On examination, thyroid architecture is distorted, and multiple nodules of varying size can be appreciated. Because many nodules are deeply embedded in thyroid tissue or reside in posterior or substernal locations, it is not possible to palpate all nodules. Pem­ berton’s sign, characterized by facial suffusion when the patient’s arms are elevated above the head, suggests that the goiter has increased pressure in the thoracic inlet. A TSH level should be measured to exclude subclinical hyper- or hypothyroidism, but thyroid function is usually normal. Tracheal deviation is common, but compression must usually exceed 70% of the tracheal diameter before there is significant airway compromise. Pulmonary function testing can be used to assess the functional effects of compression, which characteristically causes inspiratory stridor. CT or MRI can be used to evaluate the anatomy of the goiter and the extent of substernal extension or tracheal nar­ rowing. A barium swallow may reveal the extent of esophageal com­ pression. The risk of malignancy in MNG is similar to that in solitary nodules. Ultrasonography should be used to identify which nodules should be biopsied based on a combination of size and sonographic pattern (Fig. 397-1) (Chap. 394). For nodules with more suspicious sonographic patterns (e.g., hypoechoic solid nodules with irregular borders), biopsy is recommended at a lower size cutoff than those with less suspicious imaging features (Figs. 397-1 and 397-2). TREATMENT Nontoxic Multinodular Goiter Most nontoxic MNGs can be managed conservatively. T4 sup­ pression is rarely effective for reducing goiter size and introduces the risk of subclinical or overt thyrotoxicosis, particularly if there is underlying autonomy or if it develops during treatment. Contrast agents and other iodine-containing substances should be avoided because of the risk of inducing the Jod-Basedow effect, characterized by enhanced thyroid hormone production by autonomous nodules. Radioiodine has been used when surgery

ACR TI-RADS COMPOSITION ECHOGENICITY (Choose 1) (Choose 1) Cystic or almost
0 points completely cystic Anechoic
0 points Wider-than-tall
0 points Hyperechoic or
1 point isoechoic Taller-than-wide
3 points Spongiform
0 points Mixed cystic
1 point and solid Hypoechoic
2 points Very hypoechoic
3 points Solid or almost
2 points completely solid PART 12 Endocrinology and Metabolism Add Points From All Categories to Determine TI-RADS Level 0 Points 2 Points TR1 Benign No FNA TR2 Not Suspicious No FNA TR3 Mildly Suspicious FNA if ≥ 2.5 cm Follow if ≥ 1.5 cm COMPOSITION ECHOGENICITY SHAPE MARGIN ECHOGENIC FOCI Anechoic: Applies to cystic or almost completely cystic nodules. Taller-than-wide: Should be assessed on a transverse image with measurements parallel to sound beam for height and perpendicular to sound beam for width. Spongiform: Composed predominantly (>50%) of small cystic spaces. Do not add further points for other categories. Hyperechoic/isoechoic/hypoechoic: Compared to adjacent parenchyma. Mixed cystic and solid: Assign points for predominant solid component. Very hypoechoic: More hypoechoic than strap muscles. This can usually be assessed by visual inspection. Assign 1 point if echogenicity cannot be determined. Assign 2 points if composition cannot be determined because of calcification. *Refer to discussion of papillary microcarcinomas for 5-9 mm TR5 nodules. FIGURE 397-1  American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TI-RADS). TI-RADS is a five-tiered system categorizing the sonographic appearance of thyroid nodules based on increased risk for malignancy. For each level (TR1–5), there are recommendations for both fine-needle aspiration (FNA) minimum size cutoffs and follow-up. (Reproduced with permission from FN Tessler et al: ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. J Am Coll Radiol 14:587, 2017.) is contraindicated in areas where large nodular goiters are more prevalent (e.g., some areas of Europe and Brazil) because it can decrease MNG volume and may selectively ablate regions of autonomy. Dosage of 131I depends on the size of the goiter and radioiodine uptake but is usually about 3.7 MBq (0.1 mCi) per gram of tissue, corrected for uptake (typical dose 370–1070 MBq [10–29 mCi]). Repeat treatment may be needed, and effective­ ness may be increased by concurrent administration of low-dose recombinant TSH (0.1 mg IM). It is possible to achieve a 40–50% reduction in goiter size in most patients. Earlier concerns about radiation-induced thyroid swelling and tracheal compression have diminished, as studies have shown this complication to be rare. When acute compression occurs, glucocorticoid treatment or surgery may be needed. Radiation-induced hypothyroidism is less common than after treatment for Graves’ disease. However, posttreatment autoimmune thyrotoxicosis may occur in up to 5% of patients treated for nontoxic MNG. Surgery remains highly effective but is not without risk, particularly in older patients with underlying cardiopulmonary disease. ■ ■TOXIC MULTINODULAR GOITER The pathogenesis of toxic MNG appears to be similar to that of nontoxic MNG; the major difference is the presence of functional autonomy in toxic MNG. The molecular basis for autonomy in toxic MNG remains unknown. As in nontoxic goiters, many nodules are polyclonal, whereas others are monoclonal and vary in their clonal

SHAPE (Choose 1) MARGIN (Choose 1) ECHOGENIC FOCI (Choose All That Apply) Smooth
0 points None or large
0 points comet-tail artifacts Ill-defined
0 points Macrocalcifications
1 point Lobulated or
2 points irregular Peripheral (rim) 2 points calcifications Extra-thyroidal
3 points extension Punctate echogenic 3 points foci 4 to 6 Points 7 Points or More 3 Points TR4 Moderately Suspicious FNA if ≥ 1.5 cm Follow if ≥ 1 cm TR5 Highly Suspicious FNA if ≥ 1 cm Follow if ≥ 0.5 cm* Large comet-tail artifacts: V-shaped, >1 mm, in cystic components. Lobulated: Protrusions into adjacent tissue. Irregular: Jagged, spiculated, or sharp angles. Macrocalcifications: Cause acoustic shadowing. Extrathyroidal extension: Obvious invasion = malignancy. Peripheral: Complete or incomplete along margin. Assign 0 points if margin cannot be determined. Punctate echogenic foci: May have small comet-tail artifacts. origins. Genetic abnormalities known to confer functional autonomy, such as activating TSH-R or GSα mutations (see below), are not usually found in the autonomous regions of toxic MNG goiter. In addition to features of goiter, the clinical presentation of toxic MNG includes subclinical or mild overt hyperthyroidism. The patient is usually elderly and may present with atrial fibrillation or palpitations, tachycardia, nervousness, tremor, or weight loss. Recent exposure to iodine, from contrast dyes or other sources, may precipitate or exacer­ bate thyrotoxicosis. The TSH level is low. The free T4 level may be normal or minimally increased; T3 is often elevated to a greater degree than T4. Thyroid scan shows heterogeneous uptake with multiple regions of increased and decreased uptake; 24-h uptake of radioiodine may not be increased but is usually in the upper normal range in the presence of the low TSH level. Prior to definitive treatment of the hyperthyroidism, ultrasound imaging should be performed to assess the presence of discrete nodules corresponding to areas of decreased uptake (“cold” nodules) (Fig. 397-3A). If present, fine-needle aspiration (FNA) may be indicated based on sonographic patterns and size cutoffs (see “Approach to the Patient with Thyroid Nodules”). The cytology results, if indeterminate or sus­ picious, may direct the therapy to surgery. TREATMENT Toxic Multinodular Goiter Antithyroid drugs normalize thyroid function and are particu­ larly useful in the elderly or ill patients with limited life span.

A B FIGURE 397-2  Sonographic patterns of thyroid nodules. A. High suspicion ultrasound pattern for thyroid malignancy ACR TI-RADS TR5 (hypoechoic solid nodule with irregular borders and punctate echogenic foci). B. Very low suspicion ultrasound pattern for thyroid malignancy ACR TI-RADS TR1 (spongiform nodule with microcystic areas comprising >50% of nodule volume). ACR TI-RADS, American College of Radiology Thyroid Imaging Reporting and Data System. Panel A Panel B FIGURE 397-3  Scintigraphic scans of thyroid nodules. I123 scan (anterior view) of right lower pole nonfunctioning “cold” nodule (A) in a euthyroid patient and left hyperfunctioning “hot” nodule (B) causing thyrotoxicosis with suppression of I123 uptake in the extranodular thyroid. (Courtesy of Dan Pryma.)

In contrast to Graves’ disease, spontaneous remission does not occur, and low-dose antithyroid drug therapy is well tolerated for years. Radioiodine is generally the treatment of choice; it treats areas of autonomy as well as decreasing the mass of the goiter by ablating the functioning nodules. Sometimes, however, a degree of autonomy may persist, presumably because multiple autonomous regions may emerge after others are treated, and further radio­ iodine treatment may be necessary. Surgery provides definitive treatment of underlying thyrotoxicosis as well as goiter. Patients should be rendered euthyroid using an antithyroid drug before operation.

Thyroid Nodular Disease and Thyroid Cancer CHAPTER 397 ■ ■HYPERFUNCTIONING SOLITARY NODULE A solitary, autonomously functioning thyroid nodule is referred to as toxic adenoma. The pathogenesis of this disorder has been unraveled by demonstrating the functional effects of mutations that stimulate the TSH-R signaling pathway. Most patients with solitary hyperfunc­ tioning nodules have acquired somatic, activating mutations in the TSH-R (Fig. 397-4). These mutations, located primarily in the recep­ tor transmembrane domain, induce constitutive receptor coupling to GSα, increasing cyclic adenosine monophosphate (AMP) levels and leading to enhanced thyroid follicular cell proliferation and func­ tion. Less commonly, somatic mutations are identified in GSα. These mutations, which are similar to those seen in McCune-Albright syndrome (Chap. 424) or in a subset of somatotrope adenomas (Chap. 392), impair guanosine triphosphate (GTP) hydrolysis, caus­ ing constitutive activation of the cyclic AMP signaling pathway. In most series, activating mutations in either the TSH-R or the GSα subunit genes are identified in >90% of patients with solitary hyper­ functioning nodules. Thyrotoxicosis is usually mild and is generally only detected when a nodule is >3 cm. The disorder is suggested by a subnormal TSH level; the presence of the thyroid nodule, often large enough to be palpable; and the absence of clinical features suggestive of Graves’ disease or other causes of thyrotoxicosis. A thyroid scan provides a definitive diagnostic test, demonstrating focal uptake in the hyperfunctioning nodule and diminished uptake in the remainder of the gland, as activity of the normal thyroid is suppressed. TREATMENT Hyperfunctioning Solitary Nodule Radioiodine ablation is usually the treatment of choice. Because normal thyroid function is suppressed, 131I is concentrated in the

Extracellular domain TSH-R PART 12 Endocrinology and Metabolism

Transmembrane domains GSα AC Activating mutations Cell growth, differentiation Hormone synthesis cyclic AMP FIGURE 397-4  Activating mutations of the thyroid-stimulating hormone receptor (TSH-R). Mutations (*) that activate TSH-R reside mainly in transmembrane 5 and intracellular loop 3, although mutations have occurred in a variety of different locations. The effect of these mutations is to induce conformational changes that mimic TSH binding, thereby leading to coupling to stimulatory G protein (GSα) and activation of adenylate cyclase (AC), an enzyme that generates cyclic AMP. hyperfunctioning nodule with minimal uptake and damage to normal thyroid tissue. Relatively large radioiodine doses (e.g., 370– 1110 MBq [10–29.9 mCi] 131I) have been shown to correct thyrotox­ icosis in ~75% of patients within 3 months. Hypothyroidism occurs in <10% of those patients over the next 5 years. Surgical resection is also effective and is usually limited to lobectomy, thereby preserv­ ing thyroid function and minimizing risk of hypoparathyroidism or damage to the recurrent laryngeal nerves. Medical therapy using antithyroid drugs and beta blockers can normalize thyroid function but is not an optimal long-term treatment. Using ultrasound guid­ ance, percutaneous radiofrequency ablation has been used success­ fully in some centers to ablate hyperfunctioning nodules, and this technique has also been used to reduce the size of nonfunctioning thyroid nodules. BENIGN LESIONS The various types of benign thyroid nodules are listed in Table 397-1. Benign nodules may be hyperplastic and reflect a combination of both macro- and microfollicular architecture, or they may be neoplastic, encapsulated adenomas that generally have a more monotonous microfollicular pattern. If the adenoma is composed of oncocytic follicular cells arranged in a follicular pattern, this is termed an oncocytic (formerly termed Hürthle cell) adenoma. Hyperplastic nodules generally appear as mixed cystic/solid or spongiform lesions on ultrasound. The definition of spongiform requires the presence of microcystic areas comprising >50% of the nodule volume, with the concept that this microcystic sonographic pattern recapitulates the histology of macrofollicles containing colloid (Fig. 397-2B). However, the majority of solid nodules (whether hypo-, iso-, or hyperechoic) are also benign. FNA, usually performed with ultrasound guidance, is the diagnostic procedure of choice to evaluate thyroid nodules (see the “Approach to the Patient with Thyroid Nodules” section). Pure thyroid cysts, <1% of all thyroid growths, consist of colloid and are benign as well. Cysts frequently recur, even after repeated

TABLE 397-1  WHO Classification of Thyroid Neoplasms Developmental abnormalities

  1. Thyroglossal duct cyst
  2. Other congenital thyroid abnormalities Follicular cell–derived neoplasms
  3. Benign tumors a. Thyroid follicular nodular disease b. Follicular adenoma c. Follicular adenoma with papillary architecture d. Oncocytic adenoma of the thyroid
  4. Low-risk neoplasms a. Noninvasive follicular thyroid neoplasm with papillary-like nuclear features b. Thyroid tumors of uncertain malignant potential c. Hyalinizing trabecular tumor
  5. Malignant neoplasms a. Follicular thyroid carcinoma b. Invasive encapsulated follicular variant papillary carcinoma c. Papillary thyroid carcinoma d. Oncocytic carcinoma of the thyroid e. Follicular-derived carcinomas, high-grade

i. Differentiated high-grade thyroid carcinoma

ii. Poorly differentiated thyroid carcinoma f. Anaplastic follicular cell–derived thyroid carcinoma Thyroid C-cell–derived carcinoma

  1. Medullary thyroid carcinoma Mixed medullary and follicular cell–derived carcinomas Salivary gland–type carcinomas of the thyroid
  2. Mucoepidermoid carcinoma of the thyroid
  3. Secretory carcinoma of salivary gland type Thyroid tumors of uncertain histogenesis
  4. Sclerosing mucoepidermoid carcinoma with eosinophilia
  5. Cribriform morular thyroid carcinoma Thymic tumors within the thyroid
  6. Thymoma family
  7. Spindle epithelial tumor with thymus-like elements
  8. Thymic carcinoma family Embryonal thyroid neoplasms
  9. Thyroblastoma  Abbreviation: WHO, World Health Organization. Source: Reprinted from International Agency for Research on Cancer, WHO Classification of Tumours, https://whobluebooks.iarc.fr/structures/ endocrine-and-neuroendocrine-tumours/ aspiration, and may require surgical excision if they are large. Ethanol ablation to sclerose the cyst has been used successfully for patients who are symptomatic. TSH suppression with LT4 therapy does not decrease thyroid nodule size in iodine-sufficient populations. However, if there is relative iodine deficiency, both iodine and LT4 therapy have been demonstrated to decrease nodule volume. If LT4 is administered in this situation, the TSH should be maintained at or just below the lower limit of normal, but not frankly suppressed. If the nodule has not decreased in size after 6–12 months of therapy, treatment should be discontinued because little benefit is likely to accrue from long-term treatment; the risk of iatrogenic subclinical thyrotoxicosis should also be considered.

THYROID CANCER Thyroid carcinoma is the most common malignancy of the endocrine system. Malignant tumors derived from the follicular epithelium are classified according to histologic features. Differentiated tumors, such as papillary thyroid cancer (PTC) or follicular thyroid cancer (FTC), are often curable, and the prognosis is good for patients identified with early-stage disease. In contrast, anaplastic thyroid cancer (ATC) is aggressive, responds poorly to treatment, and is associated with a bleak prognosis. Over the past 30 years, the incidence of thyroid cancer has increased from 4.9 to >15 cases per 100,000 individuals in the United States. However, disease-specific mortality has only minimally increased. The increased incidence is predominantly attributable to small T1 papillary cancer tumors (<2 cm) and has led experts to consider that thyroid cancer is being overdiagnosed, suggesting that cancers are being detected that would otherwise be unlikely to harm a patient. The concept of cancer overdiagnosis is predicated upon the presence of a disease reservoir (the autopsy prevalence of PTC is ~25%), activi­ ties leading to disease detection (increased diagnostic imaging with incidental detection of nodules), and a mismatch in the directional rate between diagnosis and mortality (thyroid cancer disease-specific mortality not changed in 40 years). Similar trends have been observed worldwide, especially in countries with a higher proportion of privately financed health care, leading to increased resource utilization includ­ ing imaging. The 20-year disease-specific mortality for low-risk thy­ roid cancer is 1%. Fortunately, epidemiologic data in the United States document a decrease in new thyroid cancer diagnoses (62,450 cases in 2015 and 43,720 cases in 2023), and this trend correlates with the implementation of evidence-based guidelines that recommend higher size thresholds for nodule FNA. Current trends in thyroid cancer care focus on (1) avoiding over­ diagnosis by limiting FNA by sonographic risk stratification with size cutoffs; (2) limiting surgery, radioiodine, and subsequent surveillance for low-risk tumors; and (3) identifying patients at higher recurrence risk for more aggressive treatment and monitoring. Prognosis is gen­ erally worse in older persons (>65 years). Thyroid cancer is twice as common in women as men, but male gender is associated with a worse prognosis. Additional important risk factors include a history of child­ hood (before age 18) head or neck irradiation, evidence for local tumor fixation or gross metastatic involvement of lymph nodes, and the pres­ ence of distant metastases (Table 397-2). Several unique features of thyroid cancer facilitate its management: (1) thyroid nodules are amenable to biopsy by FNA; (2) iodine radioisotopes can be used to diagnose (123I and 131I) and potentially treat (131I) differen­ tiated thyroid cancer, reflecting the unique uptake of this anion by the thyroid gland; and (3) serum markers allow the detection of residual or recurrent disease, including the use of Tg levels for PTC FTC and onco­ cytic carcinoma and calcitonin for medullary thyroid cancer (MTC). ■ ■CLASSIFICATION Thyroid neoplasms can arise in each of the cell types that populate the gland, including thyroid follicular cells, calcitonin-producing C cells, TABLE 397-2  Risk Factors for Thyroid Carcinoma in Patients with Thyroid Nodule from History and Physical Examination History of head and neck irradiation before the age of 18, including mantle radiation for Hodgkin’s disease and brain radiation for childhood leukemia or other cranial malignancies Exposure to ionizing radiation from fallout in childhood or adolescence Age <20 or >65 years Rapidly enlarging neck mass Male gender Family history of papillary thyroid cancer in two or more first-degree relatives, MEN 2, or other genetic syndromes associated with thyroid malignancy (e.g., Cowden’s syndrome, familial adenomatous polyposis, Carney complex, PTEN [phosphatase and tensin homolog] hamartoma tumor) Vocal cord paralysis, hoarse voice Nodule fixed to adjacent structures Lateral cervical lymphadenopathy (ipsilateral to the nodule) 18FDG or Ga-68 Dotatate PET avidity  Abbreviations: FDG, fluorodeoxyglucose; MEN, multiple endocrine neoplasia; PET, positron emission tomography.

lymphocytes, and stromal and vascular elements, as well as metastases from other sites (Table 397-1). The American Joint Committee on Cancer (AJCC) staging system using the tumor, node, metastasis (TNM) classi­ fication is most commonly used. This system classifies different types of thyroid cancers (papillary, follicular, poorly differentiated, oncocytic cell, or anaplastic) based upon: 1) tumor size and extrathyroidal invasion; 2) regional lymph node metastases; and 3) distant metastases.1

■ ■PATHOGENESIS AND GENETIC BASIS Radiation  Early studies of the pathogenesis of thyroid cancer focused on the role of external radiation, which predisposes to chromosomal breaks, leading to genetic rearrangements and loss of tumor-suppressor genes. External radiation of the mediastinum, face, head, and neck region was administered in the past to treat an array of conditions, including acne and enlargement of the thymus, tonsils, and adenoids. Radiation exposure increases the risk of benign and malig­ nant thyroid nodules, is associated with multicentric cancers, and shifts the incidence of thyroid cancer to an earlier age group. Radiation from nuclear fallout also increases the risk of thyroid cancer through absorp­ tion of radioactive iodine isotopes. Children seem more predisposed to the effects of radiation than adults. Thyroid Nodular Disease and Thyroid Cancer CHAPTER 397 TSH and Growth Factors  Many differentiated thyroid cancers express TSH receptors and, therefore, remain responsive to TSH. Higher serum TSH levels, even within normal range, are associated with increased thyroid cancer risk in patients with thyroid nodules. These observations provide the rationale for T4 suppression of TSH in patients with thyroid cancer. Residual expression of TSH receptors also allows TSH-stimulated uptake of 131I therapy (see below). Oncogenes and Tumor-Suppressor Genes  Thyroid cancers are monoclonal in origin, consistent with the idea that they originate as a consequence of mutations that confer a growth advantage, or resistance to cell death, to a single progenitor cell. In addition to increased rates of proliferation, some thyroid cancers exhibit impaired apoptosis and features that enhance invasion, angiogenesis, and metastasis. Thyroid neoplasms have been analyzed for a variety of genetic alterations, but without clear evidence of an ordered acquisition of somatic mutations as they progress from the benign to the malignant state. On the other hand, certain mutations, such as RET/PTC and PAX8-PPARγ1 rear­ rangements, are relatively specific for thyroid neoplasia. As described above, activating mutations of the TSH-R and the GSα subunit are associated with autonomously functioning nodules. Muta­ tions in the enhancer of zeste homolog 1 (EZH1), which plays a role in chromatin remodeling, are also seen in about a quarter of autonomous nodules. Although these mutations induce thyroid cell growth, this type of nodule is almost always benign, likely because they drive dif­ ferentiation pathways. Activation of the RET-RAS-BRAF signaling pathway is seen in up to 70% of PTCs, although the types of mutations are heterogeneous. A variety of rearrangements involving the RET gene on chromosome 10 bring this receptor tyrosine kinase under the control of other promot­ ers, leading to receptor overexpression. RET rearrangements occur in 15% of PTCs in different series and were observed with increased fre­ quency in tumors developing after the Chernobyl radiation accident. Rearrangements in PTC have also occurred for another tyrosine kinase gene, TRK1, which is located on chromosome 1. BRAF V600E muta­ tions are a common genetic alteration, occurring in up to 60% of PTC. These mutations activate the kinase, which stimulates the mitogenactivated protein kinase (MAPK) cascade. RAS mutations, which also stimulate the MAPK cascade, are found in ~15% of thyroid neoplasms (NRAS > HRAS > KRAS), including both PTC follicular variant and FTC. Of note, simultaneous RET, BRAF, and RAS mutations rarely occur in the same tumor, suggesting that activation of the MAPK 1RM Tuttle et al: Updated American Joint Committee on Cancer/Tumor-NodeMetastasis Staging System for Differentiated and Anaplastic Thyroid Cancer (Eighth Edition): What changed and why? Thyroid 27:751, 2017.

cascade is critical for tumor development, independent of the step that initiates the cascade. Activation of the phosphatidylinositol 3-kinase (PI3K) pathway, often by deletion of the PTEN phosphatase gene, also occurs in both differentiated thyroid cancers.

BRAF and RAS mutations also occur in FTCs. In addition, a rear­ rangement of the thyroid developmental transcription factor PAX8 with the nuclear receptor PPARγ is identified in a significant fraction of FTCs, usually independent of RAS pathway mutations. Overall, ~70% of follicular cancers have mutations or genetic rearrangements. Loss of heterozygosity of 3p or 11q, consistent with deletions of tumor-suppressor genes, is also common in FTCs. Upregulation and downregulation of various microRNAs also influence gene expression patterns in both differentiated and dedifferentiated thyroid cancers. PART 12 Endocrinology and Metabolism Oncocytic tumors, which contain large numbers of mitochondria, are characterized by mutations in mitochondrial genes, primarily encoding enzymes in the electron transport chain. They also exhibit chromosomal copy number alterations and near haploidization. Most of the mutations seen in differentiated thyroid cancers have also been detected in ATCs. TERT promoter mutations occur in <10% of differentiated PTCs but are more common in ATC. BRAF mutations are seen in up to 50% of ATCs. Mutations in CTNNB1, which encodes β-catenin, occur in about two-thirds of ATCs, but not in PTC or FTC. Mutations of the tumor-suppressor P53 also play an important role in the development of ATC. Because P53 plays a role in cell-cycle surveillance, DNA repair, and apoptosis, its loss may contribute to the rapid acquisi­ tion of genetic instability as well as poor treatment responses (Chap. 77). MTC, when associated with multiple endocrine neoplasia (MEN) type 2, harbors an inherited mutation of the RET gene. Unlike the rearrangements of RET seen in PTC, the mutations in MEN 2 are point mutations that induce constitutive activity of the tyrosine kinase (Chap. 400). MTC is preceded by hyperplasia of the C cells, raising the likelihood that as-yet-unidentified “second hits” lead to cellular transformation. A subset of ~40% of sporadic MTC contains somatic mutations that activate RET. Molecular diagnostics are being used more commonly in the clini­ cal management of thyroid nodules, particularly to distinguish benign from malignant lesions after FNA and to reduce the number of diag­ nostic surgeries for indeterminate nodules. These tools are now offered as diagnostic panels by specialized referral laboratories. The panels also distinguish parathyroid and medullary nodules from thyroid follicular cell–derived lesions. ■ ■WELL-DIFFERENTIATED THYROID CANCER Papillary  PTC is the most common type of thyroid cancer, account­ ing for 80–85% of well-differentiated thyroid malignancies. Micro­ scopic PTC is present in up to 25% of thyroid glands at autopsy, but most of these lesions are very small (several millimeters) and are not clinically significant. Characteristic cytologic features of PTC help make the diagnosis by FNA or after surgical resection; these include large, clear nuclei with powdery chromatin (described as an “Orphan Annie eye” appearance) with nuclear grooves and prominent nucleoli. The histologic finding of these cells arranged in either papillary struc­ tures or follicles distinguishes the classic and follicular variants of PTC, respectively. There are several subtypes of papillary thyroid cancer. The more differentiated classic and follicular variants are likely to have an indolent course in the absence of angioinvasion or metastatic adenopa­ thy. The aggressive variants (tall cell, columnar cell, hobnail, poorly differentiated) require more intensive therapy and closer follow-up. Recently, a subtype previously known as the encapsulated PTC follicu­ lar variant, without capsular or angioinvasion, is no longer considered malignant and has been renamed noninvasive follicular thyroid neo­ plasm with papillary-like nuclear features (NIFTP). PTC may be multifocal and invade locally within the thyroid gland as well as through the thyroid capsule and into adjacent structures in the neck. It has a propensity to spread via the lymphatic system but can metastasize hematogenously as well, particularly to bone and lung. Because of the relatively slow growth of the tumor, a significant burden of pulmonary metastases may accumulate, sometimes with

1.0 Disease-specific survival probability 0.8 0.6 p <0.001 0.4 Stage = I Stage = II Stage = III Stage = IV 0.2 0.0

Time from diagnosis (months)

108 120 132 FIGURE 397-5  Unadjusted disease-specific survival curves for patients with papillary thyroid cancer in the American Joint Commission on Cancer/Union for International Cancer Control eighth edition TNM staging system. (Reproduced with permission from LN Pontius et al: Projecting survival in papillary thyroid cancer: A comparison of the seventh and eighth editions of the American Joint Commission on Cancer/Union for International Cancer Control Staging Systems in two contemporary national patient cohorts. Thyroid 27:1408, 2017. The publisher for this copyrighted material is MaryAnn Liebert, Inc. publishers.) remarkably few symptoms. The prognostic implication of lymph node spread depends on the volume of metastatic disease. Micrometastases, defined as <2 mm of cancer in a lymph node, do not affect prognosis. However, gross metastatic involvement of multiple 2- to 3-cm lymph nodes indicates a 25–30% chance of recurrence and may increase mortality in older patients. Most papillary cancers are identified in the early stages (>95% stages I or II) and have an excellent prognosis, with survival curves similar to expected survival (Fig. 397-5). Mortality is markedly increased in stage IV disease, especially in the presence of distant metastases (stage IVB), but this group comprises only about 1% of patients. The treatment of PTC is described below. Follicular  The incidence of FTC varies widely in different parts of the world; it is more common in iodine-deficient regions. Currently, FTC accounts for only about 5% of all thyroid cancers diagnosed in the United States. FTC is difficult to diagnose by FNA because the dis­ tinction between benign and malignant follicular neoplasms requires histology because the nuclear features of follicular adenomas and car­ cinomas do not differ. Rather, follicular carcinoma is diagnosed by the presence of capsular and/or vascular invasion. Follicular carcinomas with only capsular invasion have a very low risk of metastasis, and lobectomy alone suffices. Angioinvasive FTC is more aggressive and may metastasize to bone, lung, and the central nervous system. Mor­ tality rates associated with angioinvasive FTC are less favorable than for PTC, in part because a larger proportion of patients present with stage IV disease. Poor prognostic features include distant metastases, age >55 years, primary tumor size >4 cm, and the presence of marked vascular invasion. TREATMENT Surgery for Well-Differentiated Thyroid Cancer All well-differentiated thyroid cancers >1–1.5 cm (T1b or larger) should be surgically excised. Active surveillance is an option for small (up to 1.5 cm) intrathyroidal micropapillary thyroid cancers without cervical lymph node metastases, extrathyroidal extension, or location near the posterior thyroid capsule (near the recurrent laryngeal nerve). In addition to removing the primary lesion, surgery allows accurate histologic diagnosis and staging. Because there is no compelling evidence that bilateral thyroid surgery improves survival, the initial surgical procedure may be either a unilateral (lobectomy) or bilateral (near-total thyroidectomy) pro­ cedure for patients with intrathyroidal cancers >1 cm and <4 cm

(T1b and T2 tumors) in the absence of metastatic disease and after a careful sonographic evaluation for metastatic cervical adenopathy. For patients at high risk for recurrence, bilateral surgery allows administration of radioiodine for remnant ablation and potential treatment of iodine-avid metastases, if indicated, as well as for monitoring of serum Tg levels. Therefore, near-total thyroidectomy is appropriate in the presence of metastases or clinical evidence of extrathyroidal invasion and for most tumors >4 cm. In addition, for patients found to have a high-risk tumor after lobectomy based upon aggressive pathology features (e.g., vascular invasion or a less differentiated subtype), completion surgery should be performed to allow for effective radioiodine administration. Surgical complica­ tion rates are acceptably low if the surgeon is highly experienced in the procedure. Preoperative sonography should be performed in all patients to assess the central and lateral cervical lymph node compartments for suspicious adenopathy, which if present, should undergo FNA and be removed, as indicated, at surgery. TSH SUPPRESSION THERAPY Because most tumors are still TSH-responsive, LT4 suppression of TSH has been mainstay of thyroid cancer treatment. The degree of TSH suppression should be individualized based on a patient’s risk of recurrence. It should be adjusted over time as surveillance blood tests and imaging confirm absence of disease or, alternatively, indicate pos­ sible residual/recurrent cancer. For patients at low risk of recurrence, TSH should be maintained in the lower normal limit (0.5–2.0 mIU/L). For patients either at intermediate or high risk of recurrence, TSH levels should be kept to 0.1–0.5 mIU/L and <0.1 mIU/L, respectively, if there are no strong contraindications to mild thyrotoxicosis. TSH should be <0.1 mIU/L for those with known metastatic disease. RADIOIODINE TREATMENT After near-total thyroidectomy, <1 g of thyroid tissue remains in the thyroid bed. Postsurgical radioablation of the remnant thyroid eliminates residual normal thyroid, facilitating the use of Tg deter­ minations. In addition, well-differentiated thyroid cancer often incorporates radioiodine, although less efficiently than normal thyroid follicular cells. Radioiodine uptake is determined primar­ ily by expression of the NIS and is stimulated by TSH, requiring expression of the TSH-R. The retention time for radioactivity is influenced by the extent to which the tumor retains differentiated functions such as iodide trapping and organification. Consequently, for patients at higher risk of recurrence and for those with known distant metastatic disease, 131I therapy may provide an adjuvant role and potentially treat residual tumor cells. Indications  Not all patients benefit from radioiodine therapy. Neither recurrence nor survival rates are improved in stage I patients with T1 tumors (≤2 cm) confined to the thyroid. No benefit has been demonstrated for larger (>2 cm but <4 cm) lowrisk tumors. However, in higher risk patients (larger tumors, more aggressive variants of papillary cancer, tumor vascular invasion, extrathyroidal invasion, presence of large-volume lymph node metastases), radioiodine may reduce recurrence and may increase survival for older patients. 131I Thyroid Ablation and Treatment  As noted above, the decision to use 131I for thyroid ablation should be coordinated with the sur­ gical approach, because radioablation is much more effective when there is minimal remaining normal thyroid tissue. Radioiodine is administered after iodine depletion (patient follows a low-iodine diet for 1–2 weeks) and in the presence of elevated serum TSH levels to stimulate uptake of the isotope into both the remnant and potentially any residual tumor. To achieve high serum TSH levels, there are two approaches. A patient may be withdrawn from thy­ roid hormone so that endogenous TSH is secreted and, ideally, the serum TSH level is >25 mIU/L at the time of 131I therapy. A typical strategy is to treat the patient for several weeks postoperatively with liothyronine (25 μg qd or bid), followed by thyroid hormone withdrawal for 2 weeks. Alternatively, recombinant human TSH

(rhTSH) is administered as two daily consecutive injections (0.9 mg) with administration of 131I 24 h after the second injection. The patient can continue to take LT4 and remains euthyroid. Both approaches have equal success in achieving remnant ablation.

A pretreatment scanning dose of 131I (usually 111 MBq [3 mCi]) or 123I (74 MBq [2 mCi]) can reveal the amount of residual tis­ sue and provides guidance about the dose needed to accomplish ablation. However, because of concerns about radioactive “stun­ ning” that impairs subsequent treatment, there is a trend to avoid pretreatment scanning with 131I and use either 123I or proceed directly to ablation, unless there is suspicion that the amount of residual tissue will alter therapy or that there is distant metastatic disease. In the United States, outpatient doses of up to 6475 MBq (175 mCi) can be given at most centers. The administered dose depends on the indication for therapy, with lower doses of 1100 MBq (30 mCi) given for remnant ablation but higher doses of up to 5500 MBq (150 mCi) reserved for use as adjuvant therapy when residual disease is suspected or present. Whole-body scanning (WBS) following radioiodine treatment is used to confirm the 131I uptake in the remnant and to identify possible metastatic disease. Thyroid Nodular Disease and Thyroid Cancer CHAPTER 397 Surveillance Testing  Serum thyroglobulin (Tg) is a sensitive marker of residual/recurrent thyroid cancer after ablation of the residual postsurgical thyroid tissue. Current Tg assays have func­ tional sensitivities as low as 0.1 ng/mL, as opposed to older assays with functional sensitivities of 1–2 ng/mL, reducing the number of patients with truly undetectable serum Tg levels. Because the vast majority of PTC recurrences are in cervical lymph nodes, a neck ultrasound should be performed about 6 months after thyroid abla­ tion; ultrasound has been shown to be more sensitive than WBS in this scenario. In low-risk patients who have no clinical evidence of residual disease after ablation, negative cervical sonography, and a basal Tg <0.2 ng/mL on LT4, the risk of structural recurrence is <3% at 5 years, and the frequency of follow-up testing can be decreased to annual TSH and Tg testing, with only periodic ultrasound examina­ tion. The serum TSH should be maintained in the lower half of the normal range. The use of WBS for thyroid cancer surveillance is reserved for patients with known iodine-avid metastases or those with elevated serum thyroglobulin levels and negative imaging with ultrasound, chest CT, neck cross-sectional imaging, and positron emission tomography (PET) CT who may require additional 131I therapy. In addition to radioiodine, external beam radiotherapy is also used to treat gross residual neck disease or specific metastatic lesions, particularly when they cause bone pain or threaten neuro­ logic injury (e.g., vertebral metastases). New Potential Therapies  Kinase inhibitors target pathways known to be active in thyroid cancer, including the RAS, BRAF, RET, EGFR, VEGFR, and angiogenesis pathways. Treatment has been shown to stabilize progressive metastatic disease that is refractory to radioiodine therapy, although only one study has demonstrated improved survival. Given the significant associated toxicities and the need for ongoing therapy, patient selection is critical to limit systemic therapy to those with significant morbid­ ity risk. The American Thyroid Association guidelines recommend active surveillance for asymptomatic patients with metastatic tumors between 1 and 2 cm and then intervention as the rate of tumor growth increases. In addition, based on genetic analyses of metastases, mutation-selective kinase inhibitors are now being used. In addition to multikinase inhibitors, new therapies target tumor-specific mutational changes including BRAF V600E point mutations and NTRK and RET gene fusions. Immune checkpoint inhibitors have also shown efficacy for some thyroid cancers with high tumor mutation burden (TMB-H). Ongoing trials are also exploring whether differentiation protocols, targeting the MAPK pathway, might enhance radioiodine uptake and efficacy.

■ ■ANAPLASTIC AND OTHER FORMS OF THYROID CANCER

Anaplastic Thyroid Cancer  As noted above, ATC is a poorly differentiated and aggressive cancer. The prognosis is poor, and most patients die within 6 months of diagnosis. Because of the undifferentiated state of these tumors, the uptake of radioiodine is usually negligible, but it can be used therapeutically if there is resid­ ual uptake. Chemotherapy has been attempted with multiple agents, including anthracyclines and paclitaxel, but it is usually ineffective. External beam radiation therapy can be attempted and continued if tumors are responsive. Both multitargeted and mutation-directed kinase inhibitors are in clinical trials and may prolong survival by a few months. Thyroid Lymphoma  Lymphoma in the thyroid gland often arises in the background of Hashimoto’s thyroiditis. A rapidly expanding thyroid mass suggests the possibility of this diagnosis. Diffuse large-cell lymphoma is the most common type in the thyroid. Biopsies reveal sheets of lymphoid cells that can be difficult to dis­ tinguish from small-cell lung cancer or ATC. These tumors are often highly sensitive to external radiation. Surgical resection should be avoided as initial therapy because it may spread disease that is oth­ erwise localized to the thyroid. If staging indicates disease outside of the thyroid, treatment should follow guidelines used for other forms of lymphoma (Chap. 113). PART 12 Endocrinology and Metabolism ■ ■MEDULLARY THYROID CARCINOMA MTC can be sporadic or familial and accounts for ~5% of thyroid can­ cers. There are three familial forms of MTC: MEN 2A, MEN 2B, and familial MTC without other features of MEN (Chap. 400). In general, MTC is more aggressive in MEN 2B than in MEN 2A, and familial MTC is more aggressive than sporadic MTC. Elevated serum calcito­ nin provides a marker of residual or recurrent disease. All patients with MTC should be tested for RET mutations, because genetic counseling and testing of family members can be offered to those individuals who test positive for mutations. The management of MTC is primarily surgical. Prior to surgery, pheochromocytoma should be excluded in all patients with a RET mutation. Unlike tumors derived from thyroid follicular cells, these tumors do not take up radioiodine. External radiation treatment and targeted kinase inhibitors may provide palliation in patients with advanced disease (Chap. 400). APPROACH TO THE PATIENT Thyroid Nodules Palpable thyroid nodules are found in ~5% of adults, but the preva­ lence varies considerably worldwide. Given this high prevalence rate, practitioners may identify thyroid nodules on physical exami­ nation. However, the increased usage of diagnostic medical imaging (e.g., carotid ultrasound, cervical spine MRI) has led to an increased frequency of incidental nodule detection, accounting for the major­ ity of patients currently presenting for nodule evaluation. The main goal of this evaluation is to identify, in a cost-effective manner, the small subgroup of individuals with malignant lesions that have the potential to be clinically significant. Nodules are more common in iodine-deficient areas, in women, and with aging. Most palpable nodules are >1 cm in diameter, but the ability to feel a nodule is influenced by its location within the gland (superficial vs deeply embedded), the anatomy of the patient’s neck, and the experience of the examiner. More sensitive methods of detection, such as CT, thyroid ultrasound, and pathologic studies, reveal thyroid nodules in up to 50% of glands in individuals aged

50 years. The presence of these thyroid incidentalomas has led to much debate about how to detect nodules and which nodules to investigate further. An approach to the evaluation of thyroid nodules detected by either palpation or imaging is outlined in Fig. 397-6. Most patients

with thyroid nodules have normal thyroid function tests. None­ theless, thyroid function should be assessed by measuring a TSH level, which may be suppressed by one or more autonomously functioning nodules. If the TSH is suppressed, a radionuclide scan is indicated to determine if the identified nodule is “hot,” as lesions with increased uptake are almost never malignant and FNA is unnecessary (Fig. 397-3B). Otherwise, the next step in evaluation is performance of a thyroid ultrasound for three reasons: (1) For nodules detected on physical examination, ultrasound will confirm if the palpable nodule is indeed a nodule. About 15% of “palpable” nodules are not confirmed on imaging, and therefore no further evaluation is required. (2) Ultrasound will assess if there are addi­ tional nonpalpable nodules for which FNA may be recommended based on imaging features and size. (3) Ultrasound will characterize the imaging pattern of the nodule, which, combined with the nod­ ule’s size, facilitates decision-making about FNA. There are several validated risk stratification systems (RSS) for sonographic imaging of thyroid nodules (American College of Radiology [ACR] Thyroid Imaging Reporting and Data System [TI-RADS], American Thy­ roid Association, European Thyroid Association [EU-TIRADS], among others). These demonstrate consistent risk estimates for thyroid cancer based on certain sonographic patterns. All provide size cutoff recommendations for nodule FNA based on sonographic patterns, with lower size cutoffs for nodules with more suspicious ultrasound patterns, but the specific size cutoff criteria differ among the RSS. Not surprisingly, the RSSs with lower size cutoffs have higher sensitivity and lower specificity for thyroid cancer diagnosis than those with higher cutoffs. Nevertheless, all have been shown to reduce unnecessary FNAs by at least 45%, in part due to the recom­ mendation not to perform FNA for spongiform nodules. ACR TIRADS is currently the most widely used RSS in the United States, and nodules are classified from TR1 to TR5 (Fig. 397-1). For example, a spongiform nodule (TR1, Fig. 397-2B) has a <3% chance of cancer, and observation rather than FNA is generally recommended by all RSSs, whereas 10–20% of solid hypoechoic nodules with smooth borders (TR4) are malignant and FNA is recommended at size cutoffs ranging from 1 to 1.5 cm. All the RSSs recommend FNA at 1 cm for the highest suspicion pattern nodule, TR5 (Figs. 397-1 and 397-2A). Given what is known about the prevalence and generally indolent behavior of small thyroid cancers <1 cm, none of the RSSs recommend routine FNA for any nodule <1 cm unless metastatic cervical lymph nodes are present. FNA biopsy, ideally performed with ultrasound guidance, is the best diagnostic test when performed by physicians familiar with the procedure and when the results are interpreted by experienced cyto­ pathologists. The technique is particularly useful for detecting PTC. However, the distinction between benign and malignant follicular patterned lesions is often not possible using cytology alone because of the absence of characteristic nuclear features in follicular carci­ noma. Using the current ultrasound RSS for FNA decision-making, FNA biopsies yield the following spectrum of cytology diagnoses: 50–60% benign, 5% malignant or suspicious for malignancy, 5–7% nondiagnostic or yielding insufficient material for diagnosis, and 25–40% indeterminate. The Bethesda System is now widely used to provide more uniform terminology for reporting thyroid nodule FNA cytology results. This six-tiered classification system (newest version 3) with the respective estimated malignancy rates is shown in Table 397-3. Importantly, because NIFTP can only be diagnosed by surgical pathology, NIFTP is included in the malignancy esti­ mates. Specifically, the Bethesda System subcategorized cytology specimens previously labeled as indeterminate into three catego­ ries: atypia undetermined significance (AUS), follicular neoplasm (FN), and suspicious for malignancy (SFM). Cytology results indicative of malignancy generally mandate surgery, after performing preoperative sonography to evaluate the cervical lymph nodes. Nondiagnostic cytology specimens most often result from cystic lesions but may also occur in fibrous longstanding nodules or very vascular nodules where a longer needle

EVALUATION OF THYROID NODULES DETECTED BY PALPATION OR IMAGING History, physical examination, TSH Normal or high TSH Low TSH Diagnostic US with LN assessment Nodule not functioning Radionuclide scanning Nodule(s) detected on US Do FNA based upon US imaging features and size Results of FNA cytology Nondiagnostic Nondiagnostic Repeat US-guided FNA Malignant Bethesda System Cytology Reporting Suspicious for PTC Follicular neoplasm Consider molecular testing Surgery if indicated Atypia or follicular lesion of undetermined significance (AUS/FLUS) Benign Follow FIGURE 397-6  Approach to the patient with a thyroid nodule. See text and references for details. FNA, fine-needle aspiration; LN, lymph node; PTC, papillary thyroid cancer; Rx, therapy; TSH, thyroid-stimulating hormone; US, ultrasound. dwell time may result in a hemorrhagic specimen. Ultrasoundguided FNA is indicated when a repeat FNA is necessary. Repeat FNA will yield a diagnostic cytology in ~50% of cases. Given the low false-negative rate of a benign cytology (<3%), benign nodules with a lower suspicion sonographic pattern (TR2, TR3, TR4) can be followed. Those with more worrisome ultrasound features, espe­ cially TR5 nodules, should undergo repeat FNA because of a higher likelihood of a missed malignancy. The use of LT4 to suppress TABLE 397-3  Bethesda Classification for Thyroid Cytology Version 3 RISK OF MALIGNANCY

(INCLUDING NIFTP)

MEAN % (RANGE) DIAGNOSTIC CATEGORY  I.  Nondiagnostic or unsatisfactory 13 (5–20) II.  Benign 4 (2–7) III.  Atypia of unknown significance (AUS) 22 (13–30) IV.  Follicular neoplasm (FN) 30 (23–34)  V.  Suspicious for malignancy (SFM) 74 (67–83) VI.  Malignant 97 (97–100) Abbreviation: NIFTP, noninvasive follicular thyroid neoplasm with papillary-like nuclear features.

Thyroid Nodular Disease and Thyroid Cancer CHAPTER 397 Hyperfunctioning nodule Evaluate and Rx for hyperthyroidism Close follow-up or surgery Surgery Repeat US-guided FNA or consider molecular testing Surgery if indicated serum TSH is not effective in shrinking nodules in iodine-replete populations, and therefore, LT4 suppression should not be used. The three indeterminate cytology classifications introduced by the Bethesda System are associated with different risks of malignancy (Table 397-3). For nodules with suspicious for malignancy cytology, surgery is recommended after ultrasound assessment of cervical lymph nodes. Options to be discussed with the patient include lobectomy versus total thyroidectomy. On the other hand, the majority of nodules with AUS and FN cytology results are benign; the range of malignancy (ROM) var­ ies from 13 to 34%. The traditional approach for these patients is diagnostic lobectomy for histopathologic diagnosis. Therefore, many patients undergo surgery for benign nodules. Over the past decade, the uncertainty about the ROM for indeterminate cytology nodules has been the driver for the development of molecular test­ ing, which can better differentiate benign from malignant nodules. Based on results from next-generation sequencing, which includes point mutations, small insertions/deletions, and gene fusions, as well as results from microRNA analyses and gene expression, the cur­ rent validated and commercially available molecular tests combine these techniques with the following two goals: (1) risk stratification of thyroid nodules based on a positive result; and (2) reduction in cancer risk to an acceptable level for nonsurgical surveillance based

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398 Disorders of the Adrenal Cortex

on a negative result. Assuming a 25–30% ROM for nodules with indeterminate cytology, the negative predictive values for the cur­ rently validated molecular tests are >95%. The evaluation of a thyroid nodule is stressful for most patients. They are concerned about the possibility of thyroid cancer, whether verbalized or not. It is constructive, therefore, to review the diag­ nostic approach and to reassure patients when no malignancy is found. When a suspicious lesion or thyroid cancer is identified, the generally favorable prognosis and available treatment options can be reassuring. PART 12 Endocrinology and Metabolism ■ ■FURTHER READING Ali SZ et al: The 2023 Bethesda system for reporting thyroid cytopa­ thology. Thyroid 33:1039, 2023. Baloch ZW et al: Overview of the 2022 WHO classification of thyroid neoplasms. Endocr Pathol 33:27, 2022. Davies L, Hoang J: Thyroid cancer in the USA: Current trends and outstanding questions. Lancet Diab Endocrinol 9:11, 2021. Dunn LA et al: Vemurafenib redifferentiation of BRAF mutant, RAI-refractory thyroid cancers. J Clin Endocrinol Metab 104:1417,

Durante C et al: The diagnosis and management of thyroid nodules: A review. JAMA 319:914, 2018. Fagin JA, Nikirov YE: Progress in thyroid cancer genomics: A 40-year journey. Thyroid 33:1271, 2023. Haugen BR et al: 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid 26:1, 2016. Tessler FN et al: ACR Thyroid Imaging Reporting and Data System (TI-RADS): White paper of the ACR TI-RADS committee. J Am Coll Radiol 14:587, 2017. Tuttle RM et al: Updated American Joint Committee and Cancer/ Tumor-Node-Metastasis Staging System for differentiated and ana­ plastic thyroid cancer (eighth edition): What changed and why? Thyroid 27:751, 2017. Wiebke Arlt, Alessandro Prete

Disorders of the

Adrenal Cortex The adrenal cortex produces three classes of corticosteroid hormones: glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), and adrenal androgen precursors (e.g., dehydroepiandrosterone [DHEA]) (Fig. 398-1). Glucocorticoids and mineralocorticoids act through specific nuclear receptors, regulating aspects of the physi­ ologic stress response as well as blood pressure and electrolyte homeo­ stasis. Adrenal androgen precursors are converted in the gonads and peripheral target cells to sex steroids that act via nuclear androgen and estrogen receptors. Disorders of the adrenal cortex are characterized by deficiency or excess of one or several of the three major corticosteroid classes. Hormone deficiency can be caused by inherited glandular or enzy­ matic disorders or by destruction of the pituitary or adrenal gland

by autoimmune disorders, infection, infarction, or iatrogenic events such as surgery or hormonal suppression. Hormone excess is usually the result of neoplasia, leading to increased production of adreno­ corticotropic hormone (ACTH) by the pituitary or neuroendocrine ectopic ACTH-producing cells or increased production of glucocorti­ coids, mineralocorticoids, or adrenal androgen precursors by adrenal nodules or hyperplasia. Adrenal nodules are increasingly identified incidentally during cross-sectional imaging of the chest or abdomen performed for other reasons. ■ ■ADRENAL ANATOMY AND DEVELOPMENT The normal adrenal glands weigh 6–11 g each. They are located above the kidneys and have their own blood supply. Arterial blood flows initially to the subcapsular region and then meanders from the outer cortical zona glomerulosa through the intermediate zona fasciculata to the inner zona reticularis and eventually to the adrenal medulla. The right adrenal (or suprarenal) vein drains directly into the vena cava, while the left adrenal vein drains into the left renal vein. During early embryonic development, the adrenals originate from the urogenital ridge and then separate from gonads and kidneys at about the sixth week of gestation. Concordant with the time of sexual differentiation (seventh to ninth week of gestation, Chap. 402), the adrenal cortex starts to produce cortisol and the adrenal sex steroid precursor DHEA. The orphan nuclear receptors SF1 (steroidogenic factor 1; encoded by the gene NR5A1) and DAX1 (dosage-sensitive sex reversal gene 1; encoded by the gene NR0B1), among others, play a cru­ cial role during this period of development, as they regulate a multitude of adrenal genes involved in steroidogenesis. ■ ■REGULATORY CONTROL OF STEROIDOGENESIS Production of glucocorticoids and adrenal androgens is under the control of the hypothalamic-pituitary-adrenal (HPA) axis, whereas mineralocorticoids are regulated by the renin-angiotensin-aldosterone (RAA) system. Glucocorticoid synthesis is under inhibitory feedback control by the hypothalamus and the pituitary (Fig. 398-2). Hypothalamic release of corticotropin-releasing hormone (CRH) occurs in response to endogenous or exogenous stress. CRH stimulates the cleavage of the 241–amino acid polypeptide proopiomelanocortin (POMC) by pituitary-specific prohormone convertase 1 (PC1), yielding the 39–amino acid peptide ACTH. ACTH is released by the corticotrope cells of the anterior pituitary and acts as the pivotal regulator of adrenal cortisol synthesis, with additional short-term effects on mineralocor­ ticoid and adrenal androgen synthesis. The release of CRH, and sub­ sequently ACTH, occurs in a pulsatile fashion that follows a circadian rhythm under the control of the hypothalamus, specifically its supra­ chiasmatic nucleus (SCN), with additional regulation by a complex network of cell-specific clock genes. The circadian release of ACTH is mostly regulated by the CRH, but arginine-vasopressin (AVP) also exerts a secretagogue role. Reflecting the pattern of ACTH secretion, adrenal cortisol secretion exhibits a distinct circadian rhythm, starting to rise in the early morning hours prior to awakening, with peak levels in the morning and low levels in the evening (Fig. 398-3). Diagnostic tests assessing the HPA axis make use of the fact that it is regulated by negative feedback. Glucocorticoid excess is diagnosed by employing a dexamethasone suppression test. Dexamethasone, a potent synthetic glucocorticoid, suppresses CRH/ACTH by binding hypothalamic-pituitary glucocorticoid receptors (GRs) and, therefore, results in downregulation of endogenous cortisol synthesis. Various versions of the dexamethasone suppression test are described in detail in Chap. 392. If cortisol production is autonomous (e.g., adrenal nod­ ule), ACTH is already suppressed, and dexamethasone has little addi­ tional effect. If cortisol production is driven by an ACTH-producing pituitary adenoma, dexamethasone suppression is ineffective at lower doses but usually induces suppression at higher doses. If cortisol production is driven by an ectopic source of ACTH, the tumors are usually resistant to dexamethasone suppression. Thus, the dexametha­ sone suppression test is useful to establish the diagnosis of Cushing’s syndrome and assist with the differential diagnosis of cortisol excess.

H3C H3C H CH3 H3C H H3C H H HO Cholesterol Mineralocorticoids Mineralocorticoid precursors Glucocorticoid precursors CYP11A1 ADX O O CH3 CH3 H3C H3C H3C H3C H3C H H H3C H H H H H H H O O CYP21A2 POR HO HSD3B2 Deoxycorticosterone Corticosterone 18OH-Corticosterone Aldosterone Pregnenolone Progesterone CYP17A1 POR CYP17A1 POR O O H3C CH3 CH3 H3C H3C OH OH H3C H H3C H H3C H H H H H H H HO O O CYP21A2 POR HSD11B2 17-hydroxypregnenolone 17-hydroxyprogesterone (17OHP) HSD3B2 11Deoxycortisol Cortisol CYP17A1 POR CYP17A1 POR O O H3C H3C CH3 H H3C H3C H H H H H H H O HSD3B2 O HO HSD17B HSD17B SRD5A Androstenedione Testosterone 5-Dihydrotestosterone DHEA SULT2A1 PAPSS2 CYP11B1 ADX O CH3 CH3 H O O HO H H HSD11B2 H O O S H H HSD17B2/4 HSD11B1 DHEAS O OO O H6PDH 11-hydroxyandrostenedione 11-ketoandrostenedione 11-ketotestosterone Adrenal androgen precursors Androgens FIGURE 398-1  Adrenal steroidogenesis. ADX, adrenodoxin; AKR1C3, aldo-keto reductase 1C3; CYP11A1, side chain cleavage enzyme; CYP11B1, 11b-hydroxylase; CYP11B2, aldosterone synthase; CYP17A1, 17a-hydroxylase/17,20 lyase; CYP21A2, 21-hydroxylase; DHEA, dehydroepiandrosterone; DHEAS, dehydroepiandrosterone sulfate; H6PDH, hexose-6-phosphate dehydrogenase; HSD11B1, 11b-hydroxysteroid dehydrogenase type 1; HSD11B2, 11b-hydroxysteroid dehydrogenase type 2; HSD17B, 17b-hydroxysteroid dehydrogenase; HSD3B2, 3b-hydroxysteroid dehydrogenase type 2; PAPSS2, PAPS synthase type 2; POR, P450 oxidoreductase; SRD5A, 5a-reductase; SULT2A1, DHEA sulfotransferase. Conversely, to assess glucocorticoid deficiency, ACTH stimulation of cortisol production is used. The ACTH peptide contains 39 amino acids, but the first 24 are sufficient to elicit a physiologic response. The standard ACTH stimulation test involves the administration of cosyn­ tropin (ACTH 1-24), 250 μg IM or IV, and collection of blood samples at 0, 30, and optionally 60 min for cortisol. A normal response is defined as a cortisol level >15–20 μg/dL (>400–550 nmol/L) 30–60 min after cosyn­ tropin stimulation, with the precise cutoff dependent on the assay used. A low-dose (1 μg cosyntropin IV) version of this test has been advo­ cated; however, it has no superior diagnostic value and is more cumber­ some to carry out due to the lack of commercially available preparations of 1 μg cosyntropin. Alternatively, an insulin tolerance test (ITT) can be used to assess adrenal function. It involves injection of insulin to induce hypoglycemia, which represents a strong stress signal that triggers hypothalamic CRH release and activation of the entire HPA axis. The ITT involves administration of regular insulin 0.1 U/kg IV (dose should be lower if hypopituitarism is likely) and collection of blood samples at 0, 30, 60, and 120 min for glucose, cortisol, and growth hormone (GH),

O O O O HO Disorders of the Adrenal Cortex CHAPTER 398 CHO H3C OH HO OH HO HO OH OH H3C H3C H H H3C H H H H H H H O O O CYP11B2 ADX CYP11B2 ADX CYP11B2 ADX CYP11B1 ADX O O O H3C HO H3C O OH OH OH OH OH OH H3C H3C H H H H H H O O CYP11B1 ADX Cortisone HSD11B1 H6PDH Glucocorticoids OH OH CH3 H3C H3C H H H H O H OH O O AKR1C3 AKR1C3 H H H H H H HSD17B2/4 O if also assessing the GH axis. Oral or IV glucose is administered after the patient has achieved symptomatic hypoglycemia (usually plasma glu­ cose <40 mg/dL). A normal response is defined as a cortisol >20 μg/dL

and GH >5.1 μg/L, again with assay-specific cutoff variability. The ITT requires careful clinical monitoring and sequential measurements of glucose. It is contraindicated in patients with coronary disease, cerebro­ vascular disease, or seizure disorders, which has made the cosyntropin test the commonly accepted first-line test. The overnight metyrapone test is alternatively used in some centers: metyrapone—a drug blocking the conversion of 11-deoxycortisol to cortisol by 11β-hydroxylase (see treatment of Cushing’s syndrome)—is administered orally at midnight (2500 mg or 30 mg/kg). In healthy individuals, the decrease in corti­ sol stimulates CRH and ACTH production, resulting in an increase in 11-deoxycortisol. A normal response consists of an early morning serum 11-deoxycortisol concentration >287 nmol/L (10 µg/dL). The use of home-waking salivary cortisone as a measure of adrenal cortisol reserve looks highly promising and represents a potential alternative noninvasive test that can be undertaken at home.

Stressors (physical, emotional, including fever, hypoglycemia, hypotension) Circadian rhythm Neurotransmitters Hypothalamus PART 12 Endocrinology and Metabolism – + CRH Anterior pituitary – + Circulating cortisol ACTH Adrenal cortex FIGURE 398-2  Regulation of the hypothalamic-pituitary-adrenal (HPA) axis. ACTH, adrenocorticotropic hormone; CRH, corticotropin-releasing hormone. Mineralocorticoid production is controlled by the RAA regulatory cycle, which is initiated by the release of the enzyme renin from the juxtaglomerular cells in the kidney, resulting in cleavage of hepatic angiotensinogen to angiotensin I (Fig. 398-4). The angiotensin-converting enzyme (ACE) cleaves angiotensin I to angiotensin II, which binds and activates the angiotensin II receptor type 1 (AT1 receptor [AT1R]), resulting in increased adrenal aldosterone production and vasocon­ striction. Aldosterone enhances renal sodium retention and potassium excretion resulting in volume expansion and increased renal perfusion, which in turn regulates renin release. Because mineralocorticoid synthesis is primarily under the control of the RAA system, hypothalamicpituitary damage does not significantly impact the capacity of the adrenal to synthesize aldosterone.

Cortisol (nmol/L) Similar to the HPA axis, the assessment of the RAA system can be used for diagnostic purposes. If mineralocorticoid excess is present, there is a counterregulatory downregulation of plasma renin (see below for testing). Conversely, in min­ eralocorticoid deficiency, plasma renin is mark­ edly increased. Physiologically, oral or IV sodium loading results in suppression of aldosterone, a response that is attenuated or absent in patients with autonomous mineralocorticoid excess.

Nadir: 0015 h

22 23 24 1

9 10 11 12 13 14 15 16 17 18 19 20 21 Clock time ■ ■STEROID HORMONE BIOSYNTHESIS, METABOLISM, AND ACTION ACTH stimulation is required for the initiation of steroidogenesis. The ACTH receptor MC2R (melanocortin 2 receptor) interacts with the FIGURE 398-3  Physiologic cortisol circadian rhythm. Circulating cortisol concentrations (geometrical mean ± standard deviation values and fitted cosinor) drop under the rhythm-adjusted mean (MESOR) in the early evening hours, with nadir levels around midnight and a rise in the early morning hours; peak levels are observed ~8:30 A.M. (acrophase). (Reproduced with permission from M Debono et al: Modified-release hydrocortisone to provide circadian cortisol profiles. J Clin Endocrinol Metab 94:1548, 2009.)

MC2R-accessory protein MRAP, and the complex is transported to the adrenocortical cell membrane, where it binds to ACTH (Fig. 398-5). ACTH stimulation generates cyclic AMP (cAMP), which upregulates the protein kinase A (PKA) signaling pathway. Inactive PKA is a tetra­ mer of two regulatory and two catalytic subunits that is dissociated by cAMP into a dimer of two regulatory subunits bound to cAMP and two free and active catalytic subunits. PKA activation impacts steroidogen­ esis in three distinct ways: (1) increases the import of cholesterol esters; (2) increases the activity of hormone-sensitive lipase, which cleaves cholesterol esters to cholesterol for import into the mitochondrion; and (3) increases the availability and phosphorylation of CREB (cAMP response element binding), a transcription factor that enhances tran­ scription of CYP11A1 and other enzymes required for glucocorticoid synthesis. Adrenal steroidogenesis occurs in a zone-specific fashion, with mineralocorticoid synthesis occurring in the outer zona glomerulosa, glucocorticoid synthesis in the zona fasciculata, and adrenal androgen biosynthesis in the inner zona reticularis serving as precursors for both classic and 11-oxygenated androgens (Fig. 398-1). All steroidogenic pathways require cholesterol import into the mitochondrion, a process initiated by the action of the steroidogenic acute regulatory (StAR) pro­ tein, which shuttles cholesterol from the outer to the inner mitochon­ drial membrane. The majority of steroidogenic enzymes are cytochrome P450 (CYP) enzymes, which are either located in the mitochondrion (side chain cleavage enzyme, CYP11A1; 11β-hydroxylase, CYP11B1; aldosterone synthase, CYP11B2) or in the endoplasmic reticulum mem­ brane (17α-hydroxylase, CYP17A1; 21-hydroxylase, CYP21A2; aroma­ tase, CYP19A1). These enzymes require electron donation via specific redox cofactor enzymes, P450 oxidoreductase (POR), and adrenodoxin/ adrenodoxin reductase (ADX/ADR) for the microsomal and mitochon­ drial CYP enzymes, respectively. In addition, the short-chain dehy­ drogenase 3β-hydroxysteroid dehydrogenase type 2 (3β-HSD2), also termed Δ4, Δ5 isomerase, plays a major role in adrenal steroidogenesis. The cholesterol side chain cleavage enzyme CYP11A1 gener­ ates pregnenolone. Glucocorticoid synthesis requires conversion of pregnenolone to progesterone by 3β-HSD2, followed by conversion to 17-hydroxyprogesterone (17OHP) by CYP17A1, further hydroxyl­ ation at carbon 21 by CYP21A2, and eventually, 11β-hydroxylation by CYP11B1 to generate active cortisol (Fig. 398-1). Mineralocor­ ticoid synthesis also requires progesterone, which is first converted to deoxycorticosterone (DOC) by CYP21A2 and then converted via corticosterone and 18-hydroxycorticosterone to aldosterone in three steps catalyzed by CYP11B2. For adrenal androgen synthesis, pregnen­ olone undergoes conversion by CYP17A1, which uniquely catalyzes two enzymatic reactions. Via its 17α-hydroxylase activity, CYP17A1 Acrophase: 0830 h MESOR: 5.25 µg/dL (145 nmol/L)

Circulating blood volume Renal sodium retention (and potassium excretion) Renal perfusion pressure Adrenal Aldosterone release Activation of Angiotensin II receptor type 1 (AT1 receptor) Angiotensin II FIGURE 398-4  Regulation of the renin-angiotensin-aldosterone (RAA) system. converts pregnenolone to 17-hydroxypregnenolone, followed by gen­ eration of the universal sex steroid precursor DHEA via CYP17A1 17,20 lyase activity. The majority of DHEA is secreted by the adrenal in the form of its sulfate ester, DHEAS, generated by DHEA sulfotrans­ ferase (SULT2A1). DHEA is converted to androstenedione, which can be activated to testosterone or channeled into the 11-oxygenated androgen pathway by 11β-hydroxylation (CYP11B1). Following its release from the adrenal, cortisol circulates in the bloodstream mainly bound to cortisol-binding globulin (CBG) and, Cell membrane ACTH ATP Protein kinase A cAMP Adenylate cyclase ACTH γ β Gsα N MC2R N C C N C C N C Mitochondrion Mitochondrion N Endoplasmic reticulum Nucleus N MRAP MRAP C P CRE CREB Transcription of CYP11A1 and other steroidogenic enzymes FIGURE 398-5  ACTH effects on adrenal steroidogenesis. ACTH, adrenocorticotropic hormone; CREB, cAMP response element–binding protein; HSL, hormone-sensitive lipase; MRAP, MC2R-accessory protein; protein kinase A catalytic subunit (C; PRKACA), PKA regulatory subunit (R; PRKAR1A); SOAT1, sterol O-acyltransferase 1; StAR, steroidogenic acute regulatory (protein); TSPO, translocator protein.

Kidney Disorders of the Adrenal Cortex CHAPTER 398 Vasoconstriction Juxtaglomerular cells Angiotensinogen Renin release Angiotensin I Angiotensinconverting enzyme (ACE) to a lesser extent, to albumin, with only a minor fraction circulating as free, unbound hormone. Free cortisol is thought to enter cells directly, not requiring active transport. In addition, in a multitude of peripheral target tissues of glucocorticoid action, including adipose, liver, muscle, and brain, cortisol is generated from inactive cortisone within the cell by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) (Fig. 398-6). Thereby, 11β-HSD1 functions as a tissue-specific prere­ ceptor regulator of glucocorticoid action. For the conversion of inactive cortisone to active cortisol, 11β-HSD1 requires nicotinamide adenine Adrenal cortex cell Cholesterol ester Scavenger receptor B1 R C R C Cytosol Cholesterol ester R R HSL SOAT1 Cholesterol C C cAMP Translocator protein TSPO CREB StAR CYP11A1 Pregnenolone

Glucocorticoid target cell Cortisone Cortisol 11β-HSD1 Endoplasmic reticulum PART 12 Endocrinology and Metabolism NADPH NADP+ AP-1 GR G6P No transcription 6PGL H6PDH GR transrepression GR transactivation FIGURE 398-6  Prereceptor activation of cortisol and glucocorticoid receptor (GR) action. AP-1, activator protein-1; G6P, glucose-6-phosphate; GREs, glucocorticoid response elements; HSPs, heat shock proteins; NADPH, nicotinamide adenine dinucleotide phosphate (reduced form); 6PGL, 6-phosphogluconate. dinucleotide phosphate (NADPH [reduced form]), which is provided by the enzyme hexose-6-phosphate dehydrogenase (H6PDH). Like the catalytic domain of 11β-HSD1, H6PDH is located in the lumen of the endoplasmic reticulum and converts glucose-6-phosphate (G6P) to 6-phosphogluconate (6PGL), thereby regenerating NADP+ to NADPH, which drives the activation of cortisol from cortisone by 11β-HSD1. In the cytosol of target cells, cortisol binds and activates the GR, which results in dissociation of heat shock proteins (HSPs) from the receptor and subsequent dimerization (Fig. 398-6). Cortisol-bound GR dimers translocate to the nucleus and activate glucocorticoid response elements (GREs) in the DNA sequence, thereby enhancing transcrip­ tion of glucocorticoid-regulated genes (GR transactivation). However, cortisol-bound GR can also form heterodimers with transcription factors such as AP-1 or nuclear factor-κB (NF-κB), resulting in transre­ pression of proinflammatory genes, a mechanism of major importance for the anti-inflammatory action of glucocorticoids. It is important to note that corticosterone also exerts glucocorticoid activity, albeit much weaker than cortisol itself. However, in rodents, corticosterone is the major glucocorticoid, and in patients with 17-hydroxylase deficiency, lack of cortisol can be compensated for by higher concentrations of corticosterone that accumulates as a consequence of the enzymatic block. Cortisol is inactivated to cortisone by the microsomal enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) (Fig. 398-7), mainly in the kidney, but also in the colon, salivary glands, and other mineralocorticoid target tissues. Cortisol and aldosterone bind the mineralocorticoid receptor (MR) with equal affinity; however, cortisol circulates in the bloodstream at about a 1000-fold higher concentra­ tion. Thus, only rapid inactivation of cortisol to cortisone by 11β-HSD2 prevents MR activation by excess cortisol, thereby acting as a tissuespecific modulator of the MR pathway. In addition to cortisol and aldo­ sterone, DOC (Fig. 398-1) also exerts mineralocorticoid activity. DOC accumulation due to 11β-hydroxylase deficiency or due to tumorrelated excess production can result in mineralocorticoid excess. Aldosterone synthesis in the adrenal zona glomerulosa cells is driven by the enzyme aldosterone synthase (CYP11B2). The bind­ ing of angiotensin II to the AT1 receptor causes glomerulosa cell membrane depolarization by increasing intracellular sodium through inhibition of sodium-potassium (Na+/K+) ATPase enzymes as well as potassium channels. This drives an increase in intracellular calcium by opening voltage-dependent calcium channels or inhibition of

calcium (Ca2+) ATPase enzymes. Consequently, the calcium signaling

Cytosol GR GR HSP GR Coactivator complex Nucleus Nucleus GR GR GRE or Transcription pathway is triggered, resulting in upregulation of CYP11B2 transcrip­ tion (Fig. 398-8). Analogous to cortisol action via the GR, aldosterone (or cortisol) binding to the MR in the kidney tubule cell dissociates the HSP-receptor complex, allowing homodimerization of the MR and translocation of the hormone-bound MR dimer to the nucleus (Fig. 398-7). The activated MR enhances transcription of the epithelial sodium channel (ENaC) and serum glucocorticoid-inducible kinase 1 (SGK-1). In the cytosol, interaction of ENaC with Nedd4 prevents cell surface expression of ENaC. However, SGK-1 phosphorylates serine residues within the Nedd4 protein, reduces the interaction between Nedd4 and ENaC, and consequently, enhances the trafficking of ENaC to the cell surface, where it mediates sodium retention at the expense of potassium extrusion through the renal outer medullary potassium channel (ROMK) channel. ■ ■CUSHING’S SYNDROME (See also Chap. 392) Cushing’s syndrome reflects a constellation of clinical features that result from chronic exposure to excess glucocorti­ coids of any etiology. The disorder can be ACTH-dependent (e.g., pitu­ itary corticotrope adenoma, ectopic secretion of ACTH by nonpituitary tumor) or ACTH-independent (e.g., adrenocortical adenoma, adreno­ cortical carcinoma [ACC], nodular adrenal hyperplasia), as well as iatro­ genic (e.g., administration of exogenous glucocorticoids to treat various inflammatory conditions). The term Cushing’s disease refers specifically to Cushing’s syndrome caused by a pituitary corticotrope adenoma. Epidemiology  Iatrogenic (or exogenous) Cushing’s syndrome is by far the most common etiology, considering that around 1% of the population uses chronic glucocorticoid treatments for their antiinflammatory and immunosuppressive properties. On the contrary, endogenous Cushing’s syndrome is generally considered a rare disease; it occurs with an incidence of 1.8–3.2 per million population per year. However, it is debated whether mild cortisol excess may be more prevalent among patients with features of Cushing’s such as centripetal obesity, type 2 diabetes, and osteoporotic vertebral fractures, recogniz­ ing that these are relatively nonspecific and common in the population. Etiology  In the overwhelming majority of patients with endog­ enous Cushing’s syndrome, the underlying cause is an ACTH-producing pituitary neuroendocrine tumor, i.e., a corticotrope adenoma (Table 398-1), as initially described by Harvey Cushing in 1912. Cush­ ing’s disease more frequently affects women, with the exception of pre­ pubertal cases, where it is more common in boys. By contrast, ectopic

Kidney distal convoluted tubule cell Blood (basal site) Lumen (apical site) Aldosterone Cytosol Cortisol Cortisone 11β_HSD2 NAD+ NADH Nucleus ER Lumen MR MR HRE Na+ ATP K+ FIGURE 398-7  Prereceptor inactivation of cortisol and mineralocorticoid receptor action. ENaC, epithelial sodium channel; HRE, hormone response element; Na+/K+- ATPase, sodium-potassium adenosine triphosphatase; NADH, nicotinamide adenine dinucleotide; ROMK, renal outer medullary potassium channel; SGK-1, serum glucocorticoid-inducible kinase-1. ACTH syndrome is more frequently identified in men. Only 10% of patients with Cushing’s syndrome have a primary, adrenal cause of their disease (i.e., autonomous cortisol excess independent of ACTH), and most of these patients are women. In at least 90% of patients with Cushing’s disease, ACTH excess is caused by a corticotrope pituitary microadenoma, often only a few millimeters in diameter. Pituitary macroadenomas (i.e., tumors >1 cm Adrenal zona glomerulosa cell Na+, K+– ATPase Na+, Ca2+ exchanger Ca2+ channel Ca2+– ATPase Na+ Ca2+ AT1R Ang II Ca2+ Na+ K+ K+ Depolarization channel K+ Nucleus CYP11B2 Aldosterone FIGURE 398-8  Regulation of adrenal aldosterone synthesis. Ang II, angiotensin II; AT1R, angiotensin II receptor type 1; CYP11B2, aldosterone synthase.

K+ ROMK MR HSP MR MR K+ ROMK Disorders of the Adrenal Cortex CHAPTER 398 MR MR SGK-1 MR ENaC Na+ Nedd4 Na+ ENaC ENaC Nedd4 Transcription of and ENaC ENaC SGK-1 in size) are found in only 5–10% of patients and may have invasive features and affect the optic chiasm and the cavernous sinuses. Pitu­ itary corticotrope adenomas usually occur sporadically but very rarely can be found in the context of multiple endocrine neoplasia type 1 (MEN 1) (Chap. 400), MEN 4, familial isolated pituitary adenomas, Carney complex, DICER 1 syndrome, and Lynch syndrome. Pituitary adenomas causative of Cushing’s disease frequently harbor activating somatic variants in the USP8 gene, encod­ ing the deubiquitinating enzyme ubiquitinspecific protease 8, which lead to constitutive activation of epidermal growth factor (EGF) signaling and consequent upregulated expression of the ACTH precursor POMC. USP8 mutations are found in 11–62% of corticotrope adenomas and more frequently in adults and women with Cushing’s disease. Less frequently, somatic variants of the glu­ cocorticoid receptor gene (NR3C1), BRAF, USP48, and TP53 are observed in the tumor tissue of USP8 wild-type Cushing’s disease cases. Ca2+ Ectopic ACTH production is predomi­ nantly caused by occult carcinoid tumors, most frequently in the lung, but also in the thymus or pancreas. Because of their small size, these tumors are often difficult to locate. Advanced small-cell lung cancer can cause ectopic ACTH production. In rare cases, ectopic CRH and/or ACTH pro­ duction has been found to originate from medullary thyroid carcinoma or pheochro­ mocytoma, the latter co-secreting catechol­ amines and ACTH. The majority of patients with endogenous ACTH-independent cortisol excess harbor a cortisol-producing adrenal adenoma, and

TABLE 398-1  Causes of Endogenous Cushing’s Syndrome FEMALE:MALE RATIO %   ACTH-Dependent Cushing’s Syndrome  

Cushing’s disease (= ACTH-producing pituitary adenoma) 4:1

Ectopic ACTH syndrome (due to ACTH secretion by bronchial or pancreatic carcinoid tumors, smallcell lung cancer, medullary thyroid carcinoma, pheochromocytoma, and others) 1:1

ACTH-Independent Cushing’s Syndrome 4:1

PART 12 Endocrinology and Metabolism Adrenocortical adenoma   5–10 Adrenocortical carcinoma  

Rare causes: macronodular adrenal hyperplasia; primary pigmented nodular adrenal disease (micro- and/or macronodular); McCune-Albright syndrome   <1 Abbreviation: ACTH, adrenocorticotropic hormone. activating somatic mutations in the PKA catalytic subunit PRKACA have been identified as the cause of disease in 40% of these tumors. Somatic inactivating defects of PRKAR1A, encoding one of the regula­ tory subunits of PKA, and GNAS, encoding the stimulatory G protein alpha subunit 1 GNAS-1 (guanine nucleotide-binding protein alpha stimulating activity polypeptide 1), have been observed less frequently in unilateral cortisol-producing adenomas. ACCs may also cause ACTH-independent cortisol excess and are often large, with excess production of several corticosteroid classes. A rare but notable cause of adrenal cortisol excess is primary bilat­ eral macronodular adrenal hyperplasia (PBMAH) with low circulat­ ing ACTH but with evidence for autocrine stimulation of cortisol production via intra-adrenal ACTH production. These hyperplastic nodules are often also characterized by aberrant expression of G pro­ tein–coupled receptors not usually found in the adrenal, including receptors for luteinizing hormone, vasopressin, serotonin, interleukin 1, catecholamines, or gastric inhibitory peptide (GIP), the cause of food-dependent Cushing’s. Activation of these receptors results in upregulation of PKA signaling, as physiologically occurs with ACTH, with a subsequent increase in cortisol production. A combination of germline and somatic mutations in the tumor-suppressor gene ARMC5 have been identified as a prevalent cause of Cushing’s due to bilateral macronodular adrenal hyperplasia; these patients often pres­ ent with biochemical evidence of Cushing’s but lack specific clinical signs, which develop slowly over decades and accelerate cardiovascu­ lar risk. Constitutively activating PRKACA mutations and inactivat­ ing KDM1A variants (lysine-specific histone demethylase 1A) can also be a rare cause of bilateral macronodular adrenal hyperplasia, the latter associated with GIP-dependent Cushing’s syndrome. Bilateral macronodular adrenal hyperplasia with cortisol excess has also been described in other familial syndromes: MEN 1, hereditary leiomyo­ matosis and renal cell cancer (FH gene), and familial adenomatous polyposis (APC gene). Germline mutations in PRKAR1A are found in patients with pri­ mary pigmented nodular adrenal disease (PPNAD) as part of Carney’s complex, an autosomal dominant multiple neoplasia condition associ­ ated with cardiac and cutaneous myxomas, hyperlentiginosis, Sertoli cell tumors, ovarian tumors, breast tumors, thyroid nodules, Schwannomas, and PPNAD. PPNAD can present as micronodular or macronodular hyperplasia, or both. Phosphodiesterases can influence intracellular cAMP and can thereby impact PKA activation. Mutations in PDE11A and PDE8B have been identified in patients with bilateral adrenal hyper­ plasia and Cushing’s, with and without evidence of PPNAD. Another rare cause of ACTH-independent Cushing’s is McCuneAlbright syndrome, also associated with polyostotic fibrous dys­ plasia, unilateral café-au-lait spots, and precocious puberty. McCune-Albright syndrome is caused by GNAS activating mutations (Table 398-1; Chap. 424).

TABLE 398-2  Signs and Symptoms of Cushing’s Syndrome BODY COMPARTMENT/ SYSTEM SIGNS AND SYMPTOMS Body fat Weight gain, central obesity, rounded face, fat pad on back of neck (“buffalo hump”) Skin Facial plethora, thin and brittle skin, easy bruising, broad and purple stretch marks, acne, hirsutism Bone Osteopenia, osteoporosis (vertebral fractures), decreased linear growth in children Muscle Weakness, proximal myopathy (prominent atrophy of gluteal and upper leg muscles with difficulty climbing stairs or getting up from a chair) Cardiovascular system Hypertension, hypokalemia, edema, atherosclerosis Metabolism Glucose intolerance/diabetes, dyslipidemia Reproductive system Decreased libido; in women, amenorrhea (due to cortisol-mediated inhibition of gonadotropin release) Central nervous system Irritability, emotional lability, depression, insomnia and disrupted sleep, sometimes cognitive defects; in severe cases, paranoid psychosis Blood and immune system Increased susceptibility to infections, increased white blood cell count, eosinopenia, hypercoagulation with increased risk of deep vein thrombosis and pulmonary embolism Clinical Manifestations  Glucocorticoids affect almost all cells of the body; thus, signs of cortisol excess impact multiple physiologic systems (Table 398-2), with upregulation of gluconeogenesis, lipoly­ sis, and protein catabolism causing the most prominent features. In addition, excess glucocorticoid secretion overcomes the ability of 11β-HSD2 to rapidly inactivate cortisol to cortisone in the kidney, thereby exerting mineralocorticoid actions, manifest as hypertension, hypokalemia, and edema. Excess glucocorticoids also interfere with central regulatory systems, leading to suppression of gonadotropins with subsequent hypogonadism and amenorrhea and suppression of the hypothalamic-pituitary-thyroid axis, resulting in decreased thyroid-stimulating hormone (TSH) secretion. The majority of clinical signs and symptoms observed in Cushing’s syndrome are relatively nonspecific and include features such as obe­ sity, diabetes, diastolic hypertension, hirsutism, and depression that are commonly found in patients who do not have Cushing’s. There­ fore, careful clinical assessment is an important aspect of evaluating suspected cases. A diagnosis of Cushing’s should be considered when several clinical features are found in the same patient, particularly when more specific features are found or manifest at an unusual age, e.g., osteoporosis in a young patient. Distinct features include thinning and fragility of the skin, with easy bruising and broad (>1 cm), purplish striae (Fig. 398-9), and signs of proximal myopathy, which becomes most obvious when trying to stand up from a chair without the use of hands or when climbing stairs. Clinical manifestations of Cushing’s do not differ substantially among the different causes of Cushing’s. In ectopic ACTH syndrome, hyperpigmentation of the knuckles, scars, or skin areas exposed to increased friction can be observed (Fig. 398-9) and is caused by stimulatory effects of excess ACTH and other POMC cleavage products on melanocyte pigment production. Furthermore, patients with ectopic ACTH syndrome, and some with ACC as the cause of Cushing’s, may have a more rapid onset and progression of clinical signs and symptoms, namely edema, hypokalemia, and hypertension. Patients with Cushing’s syndrome can be acutely endangered by deep vein thrombosis, with subsequent pulmonary embolism, due to a hypercoagulable state associated with cortisol excess. The majority of patients also experience psychiatric symptoms, mostly in the form of anxiety or depression, but acute paranoid or depressive psychosis may occur. Even after cure, long-term health may be affected by persistently impaired health-related quality of life and increased risk of cardiovas­ cular disease and osteoporosis with vertebral fractures, depending on the duration and degree of exposure to significant cortisol excess.

A B FIGURE 398-9  Clinical features of Cushing’s syndrome. A. Note central obesity and broad, purple stretch marks (B. close-up). C. Note thin and brittle skin in an elderly patient with Cushing’s syndrome. D. Hyperpigmentation of the knuckles in a patient with ectopic adrenocorticotropic hormone (ACTH) excess. Diagnosis  The most important first step in the management of patients with suspected Cushing’s syndrome is to establish the correct diagnosis. Most mistakes in clinical management, leading to unneces­ sary imaging or surgery, are made because the diagnostic protocol is not followed (Fig. 398-10). This protocol requires establishing the diagnosis of Cushing’s beyond doubt prior to employing any tests used for the differential diagnosis of the condition. In principle, after exclud­ ing exogenous glucocorticoid use as the cause of clinical signs and symptoms, suspected cases should be tested if there are multiple and progressive features of Cushing’s, particularly features with a poten­ tially higher discriminatory value. Exclusion of cortisol excess is also indicated in patients with incidentally discovered adrenal masses. A diagnosis of Cushing’s can be considered as established if the results of several tests are consistently suggestive of Cushing’s. These tests may include increased 24-h urinary free cortisol excretion in three separate collections, failure to appropriately suppress morning serum cortisol after overnight exposure to dexamethasone, and evidence of loss of diurnal cortisol secretion with high levels of serum or salivary cortisol at midnight, the time of the physiologically lowest secretion (Fig. 398-10). Factors potentially affecting the outcome of these diagnostic tests have to be excluded such as incomplete 24-h urine collection or rapid inactiva­ tion of dexamethasone due to concurrent intake of CYP3A4-inducing drugs (e.g., antiepileptics, rifampicin). Concurrent intake of oral con­ traceptives that raise CBG and thus total cortisol can cause failure to suppress after dexamethasone. If in doubt, testing should be repeated after 4–6 weeks off oral estrogens. Patients with pseudo-Cushing states, e.g., alcohol-related nonneoplastic hypercortisolism or associated with major depression or morbid obesity, as well as those with cyclic Cushing’s syndrome, may require further testing to safely confirm or exclude the diagnosis of Cushing’s. In addition, the biochemical assays employed can affect the test results, with specificity representing a common problem with antibody-based assays for the measurement of urinary free cortisol. These assays have been greatly improved by the introduction of highly specific tandem mass spectrometry.

Disorders of the Adrenal Cortex CHAPTER 398 C D Differential Diagnosis  The evaluation of patients with confirmed Cushing’s should be carried out by an endocrinologist and begins with the differential diagnosis of ACTH-dependent and ACTHindependent cortisol excess (Fig. 398-10). Generally, plasma ACTH levels are suppressed in cases of autonomous adrenal cortisol excess, consequent to enhanced negative feedback to the hypothalamus and pituitary. By contrast, patients with ACTH-dependent Cushing’s have normal or increased plasma ACTH, with very high levels being found in some patients with ectopic ACTH syndrome. Importantly, imaging should only be used after it is established whether the cortisol excess is ACTH-dependent or ACTH-independent because nodules in the pitu­ itary or the adrenal are a common finding in the general population. In patients with confirmed ACTH-independent excess, adrenal imaging is indicated (Fig. 398-11), preferably using an unenhanced computed tomography (CT) scan. This allows assessment of adrenal morphol­ ogy and also the determination of tumor density, i.e., the attenuation value measured in Hounsfield units (HUs), which helps to distinguish between benign and malignant adrenal lesions (note, this only applies to unenhanced CT; postcontrast CT does not convey this information). For ACTH-dependent cortisol excess (Chap. 392), a magnetic resonance image (MRI) of the pituitary is the investigation of choice, but it may not show an abnormality in up to 40% of cases because of small tumors below the sensitivity of detection. Characteristically, pituitary corticotrope adenomas fail to enhance following gadolinium administration on T1-weighted MRI images. In all cases of confirmed ACTH-dependent Cushing’s, further tests are required for the dif­ ferential diagnosis of pituitary Cushing’s disease and ectopic ACTH syndrome. These tests exploit the fact that most pituitary corticotrope adenomas still display regulatory features, including residual ACTH suppression by high-dose glucocorticoids and responsiveness to CRH or desmopressin, a synthetic analog of vasopressin. In contrast, ectopic sources of ACTH are typically resistant to dexamethasone suppression and unresponsive to CRH or desmopressin (Fig. 398-10). However, it should be noted that a small minority of ectopic ACTH-producing

Clinical suspicion of Cushing’s (Central adiposity, proximal myopathy, striae, amenorrhea, hirsutism, impaired glucose tolerance, diastolic hypertension, and osteoporosis) Screening/confirmation of diagnosis • 24-h urinary free cortisol excretion increased above normal (≥2x) • Dexamethasone overnight test (Plasma cortisol >50 nmol/L at 8–9 am after 1 mg dexamethasone at 11 pm) • Midnight salivary cortisol (≥2x) If further confirmation needed/desired: • Low dose DEX test (Plasma cortisol >50 nmol/L after 0.5 mg DEX q6h for 2 days) PART 12 Endocrinology and Metabolism Differential diagnosis 1: Plasma ACTH ACTH normal or high

15 pg/mL ACTH-dependent Cushing’s

Differential diagnosis 2 • MRI pituitary • CRH test (ACTH increase >40% at 15–30 min + cortisol increase >20% at 45–60 min after CRH 100 µg IV) • High dose DEX test (Cortisol suppression >50% after q6h 2 mg DEX for 2 days or a single dose of 8 mg overnight) • Desmopressin test (ACTH increase

33% + >18% cortisol increase after 10 µg IV of desmopressin) Positive test results + pituitary lesion >6–9 mm at MRI Negaitive test results Equivocal results Ectopic ACTH production Cushing’s disease Inferior petrosal sinus sampling (petrosal/peripheral ACTH ratio >2 at baseline, >3 at 2–5 min after CRH 100 µg IV) Transsphenoidal pituitary surgery Pos. Neg. FIGURE 398-10  Management of the patient with suspected Cushing’s syndrome. ACTH, adrenocorticotropic hormone; CRH, corticotropin-releasing hormone; CT, computed tomography; DEX, dexamethasone; MRI, magnetic resonance imaging. tumors exhibit dynamic responses similar to pituitary corticotrope tumors. If the tests show discordant results or if there is any other reason for doubt, the differential diagnosis can be further clarified by performing bilateral inferior petrosal sinus sampling (IPSS) with con­ current blood sampling for ACTH in the right and left inferior petrosal sinus and a peripheral vein. An increased central/peripheral plasma ACTH ratio >2 at baseline and >3 at 2–5 min after CRH injection is indicative of Cushing’s disease (Fig. 398-10), with very high sensitivity and specificity. Of note, the results of the IPSS cannot be reliably used for lateralization (i.e., prediction of the location of the tumor within the pituitary) because there is broad interindividual variability in the venous drainage of the pituitary region. Importantly, no cortisollowering agents should be used prior to IPSS.

Exclude iatrogenic Cushing’s due to exogenous glucocorticoids (any form) Positive Negative ACTH suppressed to <5 pg/mL ACTH-independent Cushing’s Unenhanced CT adrenals Bilateral micronodular or macronodular adrenal hyperplasia Unilateral adrenal mass Adrenal tumor workup Unilateral adrenalectomy Bilateral adrenalectomy Locate and remove ectopic ACTH source Neg. If the differential diagnostic testing indicates ectopic ACTH syndrome, then further imaging should include high-resolution, fine-cut CT scanning of the chest and abdomen for scrutiny of the lung, thymus, and pancreas. If no lesions are identified, an MRI of the chest can be considered because carcinoid tumors usually show high signal intensity on T2-weighted images. Furthermore, octreotide scintigraphy and 68Ga DOTATATE positron emission tomography (PET)/CT can be helpful in some cases because ecto­ pic ACTH-producing tumors often express somatostatin recep­ tors. Depending on the suspected cause, patients with ectopic ACTH syndrome should also undergo blood sampling for fasting gut hormones, chromogranin A, calcitonin, and biochemical exclusion of pheochromocytoma.

A C B D FIGURE 398-11  Adrenal imaging in Cushing’s syndrome. A. Adrenal computed tomography (CT) showing normal bilateral adrenal morphology (arrows). B. CT scan depicting a right adrenocortical adenoma (arrow) causing Cushing’s syndrome. C. Magnetic resonance imaging (MRI) showing bilateral adrenal hyperplasia due to excess adrenocorticotropic hormone stimulation in Cushing’s disease. D. MRI showing bilateral macronodular hyperplasia causing Cushing’s syndrome. TREATMENT Cushing’s Syndrome Overt Cushing’s is associated with a poor prognosis if left untreated. In ACTH-independent disease, treatment consists of surgical removal of the adrenal tumor or nodular hyperplasia. For benign tumors, a minimally invasive laparoscopic approach can be used, whereas for those suspected of malignancy, an open approach is preferred. In Cushing’s disease, the treatment of choice is selective removal of the pituitary corticotrope tumor, usually via an endo­ scopic transsphenoidal approach. This results in an initial cure rate of 60–80% when performed by a highly experienced surgeon, although remission rates are much lower (12–70%) in patients presenting with larger or invasive tumors. Even after initial remis­ sion following surgery, long-term follow-up is important because late relapse occurs in a significant number of patients. If pituitary disease persists after surgery or recurs after initial remission, there are several options including second surgery, fractionated radiotherapy, stereotactic radiosurgery, pharmacologic therapy, and bilateral adrenalectomy. These options need to be applied in a highly individualized fashion. In some patients with very severe, overt Cushing’s (e.g., dif­ ficult-to-control hypokalemic hypertension, acute psychosis, or life-threatening infections), it may be necessary to introduce medi­ cal therapy to rapidly control the cortisol excess during the period leading up to surgery, which also can help to alleviate hypercoagula­ bility and, thus, operative risk. Similarly, patients with metastasized, glucocorticoid-producing carcinomas may require long-term anti­ glucocorticoid drug treatment. In the case of ectopic ACTH syn­ drome, in which the tumor cannot be located, one must carefully

Disorders of the Adrenal Cortex CHAPTER 398 weigh whether drug treatment or bilateral adrenalectomy is the most appropriate choice, with the latter facilitating immediate cure but requiring life-long corticosteroid replacement. In this instance, it is paramount to ensure regular imaging follow-up for identifica­ tion of the ectopic ACTH source. Oral agents with established efficacy in Cushing’s syndrome are osilodrostat, metyrapone, ketoconazole, levoketoconazole, and mifepristone. Osilodrostat and metyrapone inhibit cortisol synthe­ sis at the level of 11β-hydroxylase (Fig. 398-1). The antimycotic drug ketoconazole, and its stereoisomer levoketoconazole, inhibit the early steps of steroidogenesis. Mifepristone is a GR blocker, hence mitigating the effects of cortisol excess on target tissues. Typical starting doses are 1–2 mg bid for osilodrostat (maximum daily dose, 60 mg), 500 mg tid for metyrapone (maximum daily dose, 6 g), 200 mg tid for ketoconazole (maximum daily dose, 1200 mg),

150 mg bid for levoketoconazole (maximum daily dose, 1200 mg), and 300 mg for mifepristone (maximum daily dose, 1200 mg). Mito­ tane, a derivative of the insecticide o,p’DDD, is an adrenolytic agent that is also effective for reducing cortisol. Because of its side effect profile, it is most commonly used in the context of ACC, but low-dose treatment (500–1000 mg/d) has also been used in benign Cushing’s. In severe cases of cortisol excess, etomidate, an agent that potently blocks 11β-hydroxylase and aldosterone synthase, can be used to rapidly lower cortisol. It is administered by continu­ ous IV infusion in low, nonanesthetic doses. For Cushing’s disease, the subcutaneous or intramuscular administration of pasireotide, a somatostatin receptor agonist, represents another therapeutic option, if surgical cure cannot be achieved. The dopamine agonist cabergoline is also used off-label to treat certain patients with Cushing’s disease, especially those with mild cortisol excess and/or residual tumor due to the potential for tumor shrinkage.

After the successful removal of an ACTH- or cortisol-producing tumor, the HPA axis will remain suppressed. Thus, hydrocortisone replacement needs to be initiated at the time of surgery and slowly tapered following recovery, to allow physiologic adaptation to nor­ mal cortisol levels. Depending on the degree and duration of corti­ sol excess, the HPA axis may require many months or even years to resume normal function and sometimes does not recover. Gener­ ally, ectopic ACTH syndrome shows the best recovery rate (80%; median time to recovery 7 months) and adrenal Cushing’s has the lowest (40%; median time to recovery 30 months), with Cushing’s disease intermediate (60%; median time to recovery 17 months).

PART 12 Endocrinology and Metabolism ■ ■PRIMARY MINERALOCORTICOID EXCESS Epidemiology  Following the first description of a patient with an aldosterone-producing adrenal adenoma (Conn’s syndrome), mineralo­ corticoid excess was thought to represent a rare cause of hypertension. However, in studies systematically screening all patients with hyper­ tension, a much higher prevalence is now recognized, ranging from 5 to 12%. The prevalence is higher when patients are preselected for hypokalemic hypertension or drug-resistant hypertension. TABLE 398-3  Causes of Primary Mineralocorticoid Excess CAUSES OF PRIMARY MINERALOCORTICOID EXCESS MECHANISM % Sporadic Primary Aldosteronism  94–99 Adrenal (Conn’s) adenoma Autonomous aldosterone excess can be caused by somatic (intratumor) mutations in the potassium channel GIRK4 (encoded by KCNJ5; identified as cause of disease in 40–70% of aldosterone-producing adenomas and associated with overproduction of hybrid steroids). Further causes include somatic mutations affecting the α-subunit of the Na+/K+-ATPase (encoded by ATP1A1), the plasma membrane calcium-transporting ATPase 3 (encoded by ATP2B3), the voltage-gated calcium channel CaV1.3 and CaV3.2 (encoded by CACNA1D and CACNA1H, respectively), and the ClC-2 chloride channel (encoded by CLCN2). All mutations result in the upregulation of CYP11B2 and hence aldosterone synthesis. Rarely, somatic mutations affecting β-catenin (encoded by CTNNB1) have been observed alone or in combination with CACNA1D mutations and are presumed to promote an increase in the number of aldosterone-producing cells. Bilateral adrenal hyperplasia Bilateral autonomous aldosterone excess due to aldosterone-producing diffuse hyperplasia and/or multiple aldosteroneproducing micronodules. CACNA1D somatic mutations have been described in 58% of aldosterone-producing micronodules of patients with bilateral aldosterone excess who underwent unilateral adrenalectomy as a nonstandard treatment. Familial Primary Aldosteronism  1–6 Type 1 (also known as glucocorticoid-remediable hyperaldosteronism or dexamethasone-suppressible hyperaldosteronism) Autosomal dominant. Crossover between the CYP11B1 and CYP11B2 genes results in ACTH-driven aldosterone production. Characterized by severe hypertension in childhood or young adults (often <20 years), with a high risk of cardiovascular events including hemorrhagic stroke at a young age due to ruptured intracranial aneurysm. Analysis of adrenal steroidogenesis shows overproduction of hybrid steroids. Type 2 Autosomal dominant. The most common form (1–6% of adults with primary aldosteronism). Due to germline CLCN2 mutations. Variable phenotypic presentation, which typically includes early-onset hypertension. Type 3 Autosomal dominant. Germline KCNJ5 mutations. Characterized by severe early-onset hypertension (<20 years) with massive bilateral macronodular adrenal hyperplasia. Analysis of adrenal steroidogenesis shows overproduction of hybrid steroids. Type 4 Autosomal dominant. Germline CACNA1H mutations. Characterized by severe early-onset hypertension (<20 years), which can be associated with developmental disorders in some cases. Primary aldosteronism, seizures, and neurologic abnormalities (PASNA) De novo CACNA1D mutations. Characterized by childhood-onset hypertension, seizures, neurologic abnormalities, congenital hyperinsulinism, and cardiac abnormalities. Other Causes (Rare)  <1 Syndrome of apparent mineralocorticoid excess (SAME) Mutations in HSD11B2 result in lack of renal inactivation of cortisol to cortisone, leading to excess activation of the MR by cortisol (inhibition of 11β-hydroxysteroid dehydrogenase type 2 by excess licorice ingestion can have similar effects). Cushing’s syndrome Cortisol excess overcomes the capacity of HSD11B2 to inactivate cortisol to cortisone, consequently flooding the MR.   Glucocorticoid resistance Upregulation of cortisol production due to GR mutations results in flooding of the MR by cortisol.   Adrenocortical carcinoma Autonomous aldosterone and/or DOC excess.   Congenital adrenal hyperplasia Accumulation of DOC due to mutations in CYP11B1 or CYP17A1.   Progesterone-induced hypertension Progesterone acts as an abnormal ligand due to mutations in the MR gene.   Liddle’s syndrome Mutant ENaC β or γ subunits resulting in reduced degradation of ENaC keeping the membrane channel in open conformation for longer, enhancing mineralocorticoid action. Abbreviations: ACTH, adrenocorticotropic hormone; DOC, deoxycorticosterone; ENaC, epithelial sodium channel; GR, glucocorticoid receptor; HSD11B2, 11β-hydroxysteroid dehydrogenase type 2; MR, mineralocorticoid receptor.

Etiology  The most common cause of primary (i.e., adrenal) miner­ alocorticoid excess is primary aldosteronism, reflecting excess produc­ tion of aldosterone by the adrenal zona glomerulosa. Traditionally, the main subtypes of the disease are bilateral primary aldosteronism due to bilateral micronodular adrenal hyperplasia (the most common form) and unilateral aldosterone-producing adenoma (Conn’s syndrome) (Table 398-3). Although recent evidence has shown that primary aldosteronism exists on a spectrum blurring the line between bilateral and unilateral forms, their binary distinction underpins clinical man­ agement because unilateral forms are amenable to potentially curative surgery, whereas mineralocorticoid receptor antagonist therapy is the treatment of choice for bilateral forms. Somatic mutations in channels and enzymes responsible for increasing sodium and calcium influx in adrenal zona glomerulosa cells have been identified as prevalent causes of aldosterone-producing adrenal adenomas (Table 398-3) and, in the case of germline mutations, also of familial forms of primary aldoste­ ronism. Sporadic bilateral adrenal hyperplasia as a cause of mineralo­ corticoid excess is usually micronodular but can also contain larger nodules that might be mistaken for a unilateral adenoma. Genetic forms of primary aldosteronism, which account for up to 6% of cases, should be suspected in patients with severe hypertension diagnosed 30–40 60–70

during childhood or young adulthood (Table 398-3). In rare instances, primary aldosteronism is caused by an ACC. Carcinomas should be considered in younger patients and in those with larger tumors because benign aldosterone-producing adenomas usually measure <2 cm in diameter. A rare cause of aldosterone excess is glucocorticoid-remediable aldosteronism (GRA), or type 1 familial primary aldosteronism, which is caused by a chimeric gene resulting from the crossover of promoter sequences between the CYP11B1 and CYP11B2 genes that are involved in glucocorticoid and mineralocorticoid synthesis, respectively (Fig. 398-1). This rearrangement brings CYP11B2 transcription under the control of ACTH receptor signaling; consequently, aldosterone production is regulated by ACTH rather than by renin. The family history can be helpful because there may be evidence for dominant transmission of hypertension. Recognition of the disorder is important because it can be associated with early-onset hypertension and strokes. In addition, glucocorticoid suppression can reduce aldosterone pro­ duction. The adrenal glands of patients with GRA produce high levels of the hybrid steroids 18-oxocortisol and 18-hydroxycortisol due to the coexistence of CYP11B1 and CYP11B2 enzymatic activities in the same steroidogenic cells, which are normally segregated to the zona fasciculata and glomerulosa, respectively. Similarly, high hybrid steroid levels are observed in patients with aldosterone-producing adenomas harboring somatic KCNJ5 mutations (encoding the potassium channel GIRK4) and type 3 familial primary aldosteronism due to germline KCNJ5 mutations (Table 398-3). Hybrid steroids are produced by normal adrenal glands in very low concentrations and can therefore be measured in the blood and urine to identify these conditions. Other rare causes of primary mineralocorticoid excess are listed in Table 398-3. An important cause is excess binding and activation of the MR by a steroid other than aldosterone. Cortisol acts as a potent mineralocorticoid if it escapes efficient inactivation to cortisone by 11β-HSD2 in the kidney (Fig. 398-7). This can be caused by inac­ tivating mutations in the HSD11B2 gene resulting in the syndrome of apparent mineralocorticoid excess (SAME) that characteristi­ cally manifests with severe hypokalemic hypertension in childhood. However, milder mutations may cause normokalemic hypertension manifesting in adulthood (type II SAME). Inhibition of 11β-HSD2 by excess licorice ingestion also results in hypokalemic hypertension, as does overwhelming of 11β-HSD2 conversion capacity by cortisol excess in Cushing’s syndrome. DOC also binds and activates the MR and can cause hypertension if its circulating concentrations are increased. This can arise through autonomous DOC secretion by an ACC, but also when DOC accumulates as a consequence of an adrenal enzymatic block, as seen in congenital adrenal hyperplasia (CAH) due to CYP11B1 (11β-hydroxylase) or CYP17A1 (17α-hydroxylase) defi­ ciency (Fig. 398-1). Progesterone can cause hypokalemic hypertension in rare individuals who harbor a MR mutation that enhances binding and activation by progesterone; physiologically, progesterone normally exerts antimineralocorticoid activity. Finally, excess mineralocorti­ coid activity can be caused by mutations in the β or γ subunits of the ENaC, disrupting its interaction with Nedd4 (Fig. 398-7), and thereby decreasing receptor internalization and degradation. The constitutively active ENaC drives hypokalemic hypertension, resulting in an autoso­ mal dominant disorder termed Liddle’s syndrome. Clinical Manifestations  Excess activation of the MR leads to potassium depletion and increased sodium retention, with the latter causing an expansion of extracellular and plasma volume. Increased ENaC activity also results in hydrogen depletion, which can cause metabolic alkalosis. Aldosterone also has direct effects on the vascular system, where it increases cardiac remodeling and decreases compli­ ance. Aldosterone excess may cause direct damage to the myocardium and the kidney glomeruli, in addition to secondary damage due to systemic hypertension. The clinical hallmark of mineralocorticoid excess is hypokalemic hypertension; however, only 10–40% of patients with primary aldo­ steronism exhibit hypokalemia. Serum sodium tends to be normal due to the concurrent fluid retention, which in some cases can lead

to peripheral edema. Hypomagnesemia is also a common finding. Hypokalemia can be exacerbated by thiazide drug treatment, which leads to increased delivery of sodium to the distal renal tubule, thereby driving potassium excretion. Severe hypokalemia can be associated with polyuria, glucose intolerance, muscle weakness, overt proximal myopathy, or even arrhythmias, rhabdomyolysis, and hypokalemic paralysis. Severe alkalosis contributes to muscle cramps and, in severe cases, can cause tetany.

Of note, patients with primary aldosteronism show increased rates of osteoporosis, type 2 diabetes, and cognitive dysfunction. A sig­ nificant proportion of patients with primary aldosteronism suffer from concurrent mild autonomous cortisol secretion (MACS), a constella­ tion also termed Connshing syndrome. Diagnosis  Diagnostic screening for mineralocorticoid excess is not currently recommended for all patients with hypertension but should be restricted to those who exhibit hypertension associated with drug resistance, hypokalemia, an adrenal mass, onset of disease before the age of 40 years, or family history of primary aldosteronism (Fig. 398-12). The accepted screening test is concurrent measurement of plasma renin and aldosterone with subsequent calculation of the aldosterone-renin ratio (ARR) (Fig. 398-12); serum potassium needs to be normalized prior to testing. Stopping antihypertensive medication can be cumber­ some, particularly in patients with severe hypertension. Thus, for prac­ tical purposes, in the first instance, the patient can remain on the usual antihypertensive medications, with the exception that MR antagonists need to be ceased at least 4–6 weeks prior to ARR measurement. The remaining antihypertensive drugs may also affect the outcome of ARR testing (e.g., beta-blocker treatment can cause false-positive results and ACE/AT1R inhibitors can cause false-negative results in milder cases and may have to be discontinued for 2–4 weeks in case of repeat test­ ing) (Table 398-4). The decision to arrange washout from potentially interfering medications should be individualized. Disorders of the Adrenal Cortex CHAPTER 398 Current international guidelines suggest a positive ARR screening result is >750 pmol/L per ng/mL per hour, with a concurrently high normal or increased aldosterone (Fig. 398-12). However, lower ARR cutoffs are routinely used in clinical practice since it is increasingly recognized that milder forms of primary aldosteronism may otherwise be missed. Another consideration is that if one relies on the ARR only, the likelihood of a false-positive ARR becomes greater when renin lev­ els are very low. The characteristics of the biochemical assays are also important. Some labs measure plasma renin activity, whereas others measure plasma renin concentrations. Antibody-based assays for the measurement of serum aldosterone lack the reliability of tandem mass spectrometry assays, but these are not yet ubiquitously available. Diagnostic confirmation of mineralocorticoid excess in a patient with a positive ARR screening result should be undertaken by an endo­ crinologist as the tests lack optimized validation. The most straightfor­ ward is the saline infusion test, which involves the IV administration of 2 L of physiologic saline over a 4-h period. Failure of aldosterone to suppress <170 pmol/L (6 ng/dL) in the seated position or <140 pmol/L (5 ng/dL) in the recumbent position is indicative of autono­ mous mineralocorticoid excess. Alternative tests are the oral sodium loading test (300 mmol NaCl/d for 3 days) or the fludrocortisone suppression test (0.1 mg q6h with 30 mmol NaCl q8h for 4 days); the latter can be difficult because of the risk of profound hypokalemia and increased hypertension. In patients with overt hypokalemic hyperten­ sion, strongly positive ARR, and concurrently increased aldosterone levels, confirmatory testing is usually not necessary. Differential Diagnosis and Treatment  After the diagnosis of hyperaldosteronism is established, the next step is to use adrenal imag­ ing to further assess the cause. Fine-cut CT scanning of the adrenal region is the method of choice because it provides excellent visualiza­ tion of adrenal morphology, and most aldosterone-producing adeno­ mas are <2 cm. CT will readily identify larger tumors suspicious of malignancy but may miss lesions <5 mm. The differentiation between bilateral micronodular hyperplasia and a unilateral adenoma is only required if a surgical approach is feasible and desired. Consequently, selective adrenal vein sampling (AVS) should only be carried out in

Clinical suspicion of mineralocorticoid excess Patients with hypertension and • Severe hypertension (>3 BP drugs, drug-resistant) or • Hypokalemia (spontaneous or diuretic-induced) or • Adrenal mass or • Family history of early-onset hypertension or cerebrovascular events at <40 years of age • Hypertension and a personal/family history of early-onset hypertension or cerebrovascular accident at a young age (<40 years) • Hypertension and a family history of primary aldosteronism in a first-degree relative PART 12 Endocrinology and Metabolism Negative Positive

Screening Measurement of aldosterone-renin ratio (ARR) on current blood pressure medication (stop spironolactone for 4–6 weeks) and with hypokalemia corrected (ARR screen positive if ARR >750 pmol/L: ng/mL/h) (consider repeat off interfering medications for 2–4 weeks if results are equivocal) Negative Confirmation of diagnosis E.g., saline infusion test (2 L physiologic saline over 4 h IV), oral sodium loading, fludrocortisone suppression Negative Unenhanced CT scan of the adrenals Unilateral mass Age >35 years Is the patient fit for/agrees to surgery? Age <35 years Yes Positive No Adrenal vein sampling Negative Medical treatment (MR antagonists, amiloride) Unilateral adrenalectomy FIGURE 398-12  Management of patients with suspected mineralocorticoid excess. Perform adrenal tumor workup (see Fig. 398-13). BP, blood pressure; CAH, congenital adrenal hyperplasia; CT, computed tomography; ENaC, epithelial sodium channel; GC/MS, gas chromatography/mass spectrometry; MR, mineralocorticoid receptor; PRA, plasma renin activity. TABLE 398-4  Effects of Medications and Other Conditions on the Aldosterone-Renin Ratio (ARR) EFFECT ON THE ARR ANTIHYPERTENSIVE DRUGS OTHER MEDICATIONS OTHER CONDITIONS Possible false-negative results (due to increase of renin and/or aldosterone) MR antagonists; diuretics; DHPcalcium antagonists; ACE inhibitors; AT1R blockers; aliskirena Possible false-positive results (due to reduction of renin and/or aldosterone) β-Blockers; clonidine; α-methyldopa; aliskirena Negligible effect Non-DHP-calcium antagonists; α1adrenergic receptor antagonists; hydralazine aThe direct renin inhibitor aliskiren can cause false-negative results if the direct renin concentration is measured, as it causes a reduction of plasma renin activity. Abbreviations: ACE, angiotensin-converting enzyme; AT1R, angiotensin II receptor type 1; DHP, dihydropyridine; MR, mineralocorticoid receptor; NSAID, nonsteroidal antiinflammatory drug; SGLT2, sodium-glucose cotransporter 2; SSRI, selective serotonin reuptake inhibitor.

Rare: Both renin and aldosterone suppressed 24-h urinary steroid profile (GC/MS) Normal adrenals, micronodularity, or bilateral masses*/ hyperplasia*

Diagnostic for • Apparent mineralocorticoid excess (HSD11B2 def.) • CAH (CYP11B1 or CYP17A1 def.) • Adrenal tumor-related desoxycorticosterone excess If negative, consider • Liddle’s syndrome (ENaC mutations) (responsive to amiloride trial) Consider glucocorticoid remediable aldosteronism and other familial forms of primary aldosteronism SGLT2 inhibitors; SSRIs Hypokalemia; dietary salt restriction; malignant hypertension; renovascular hypertension; pregnancy NSAIDs; estrogen-containing oral contraceptives Impaired renal function with hyperkalemia; luteal phase of the menstrual cycle in premenopausal women / /

surgical candidates with either no obvious lesion on CT or evidence of a unilateral lesion but with age >35 years because the latter patients have a higher likelihood of harboring a coincidental, endocrine-inactive adrenal adenoma (Fig. 398-12). AVS is used to compare aldosterone levels in the inferior vena cava and between the right and left adrenal veins. AVS requires concurrent measurement of cortisol to document the correct placement of the catheter in the adrenal veins and should demonstrate a cortisol gradient >2–3 in baseline conditions between the vena cava and each adrenal vein. Lateralization is confirmed by an aldosterone/cortisol ratio that is at least twofold higher on one side than the other in baseline conditions. AVS is a complex procedure that requires a highly skilled interventional radiologist. Even then, the right adrenal vein can be difficult to cannulate correctly, which, if not achieved, invalidates the procedure. There is also no agreement as to whether the two adrenal veins should be cannulated simultaneously or successively and whether ACTH stimulation enhances the diagnostic value of AVS. Recently, PET-CT with a labeled form of metomidate, a methyl analogue of etomidate that binds to both CYP11B1 and CYP11B2, has been validated as a noninvasive alternative to AVS. [11C] metomidate PET-CT with dexamethasone pretreatment to suppress CYP11B1 activity can differentiate unilateral from bilateral forms of primary aldosteronism and has similar performance to AVS in predict­ ing biochemical and clinical success following adrenalectomy. Patients <35 years with confirmed primary aldosteronism, a uni­ lateral lesion on CT, and no clinical suspicion of familial forms can go straight to surgery, which is also indicated in patients with confirmed lateralization documented by a valid AVS procedure or [11C]metomi­ date PET-CT. Laparoscopic adrenalectomy is the preferred approach. Patients who are not surgical candidates, or with evidence of bilateral hyperplasia based on CT or AVS, should be treated medically

(Fig. 398-12). Medical treatment, which can also be considered prior to surgery to avoid postsurgical hypoaldosteronism, consists primarily of the MR antagonist spironolactone. It can be started at 12.5–50 mg daily and titrated up to a maximum of 400 mg/d to control blood pressure and normalize potassium. Side effects include menstrual irregularity, decreased libido, and gynecomastia. The more selective MR antagonist eplerenone can also be used. Doses start at 25 mg bid, and it can be titrated up to 200 mg/d. Another useful drug is the potassium-sparing diuretic amiloride (5–10 mg bid). In patients with normal adrenal morphology and family history of early-onset, severe hypertension, a diagnosis of GRA should be con­ sidered and can be evaluated using genetic testing. Treatment of GRA consists of administering dexamethasone, using the lowest dose pos­ sible to control blood pressure. Some patients also require additional MR antagonist treatment. The diagnosis of non-aldosterone-related mineralocorticoid excess is based on documentation of suppressed renin and suppressed aldoste­ rone in the presence of hypokalemic hypertension. This testing is best carried out by employing urinary steroid metabolite profiling by gas chromatography/mass spectrometry (GC/MS). An increased free cor­ tisol over free cortisone ratio is suggestive of SAME and can be treated with dexamethasone. Steroid profiling by GC/MS also detects the ste­ roids associated with CYP11B1 and CYP17A1 deficiency or the irregular steroid secretion pattern in a DOC-producing ACC (Fig. 398-12). If the GC/MS profile is normal, Liddle’s syndrome should be considered. It is very sensitive to amiloride treatment but will not respond to MR antago­ nist treatment because the defect is due to a constitutively active ENaC. ■ ■APPROACH TO THE PATIENT: INCIDENTALLY DISCOVERED ADRENAL MASS Epidemiology  Incidentally discovered adrenal masses, commonly termed adrenal “incidentalomas,” are common, with a prevalence of 2–5% in the general population as documented in CT and autopsy series. The prevalence increases with age, with 1% of 40-year-olds and 7% of 70-year-olds harboring an adrenal mass. The widespread use of cross-sectional imaging has also increased the recognized prevalence. Etiology  Most solitary adrenal tumors are monoclonal neo­ plasms. Several genetic syndromes, including MEN 1 (MEN1), MEN

TABLE 398-5  Classification of Unilateral Adrenal Masses APPROXIMATE PREVALENCE (%) MASS Benign Adrenocortical adenoma     Endocrine-inactive 40–70   Cortisol-producing (mild autonomous cortisol secretion) 20–50   Aldosterone-producing 2–5   Cortisol-producing (overt Cushing’s syndrome) 1–4 Disorders of the Adrenal Cortex CHAPTER 398 Pheochromocytoma 1–5 Adrenal myelolipoma 3-6 Adrenal ganglioneuroma

Adrenal cyst and pseudocyst

Adrenal hematoma/hemorrhagic infarction <1 Adrenal hemangioma <0.1 Indeterminate   Adrenocortical oncocytoma <1 Malignant   Metastases (most frequent: breast, lung) 3–7 Adrenocortical carcinoma 0.4–4 Malignant pheochromocytoma <1 Adrenal neuroblastoma <0.1 Lymphomas (including primary adrenal lymphoma) <0.1 Note: Bilateral adrenal enlargement/masses may be caused by congenital adrenal hyperplasia, bilateral macronodular hyperplasia, bilateral hemorrhage (due to antiphospholipid syndrome or sepsis-associated Waterhouse-Friderichsen syndrome), granuloma, amyloidosis, or infiltrative disease including tuberculosis. 2 (RET), Carney’s complex (PRKAR1A), McCune-Albright (GNAS1), Li Fraumeni (TP53), Lynch (MLH1, MSH2, MSH6, PMS2, EPCAM), and familial adenomatous polyposis (APC) can have adrenocortical tumors as one of their features. On the other hand, Von-HippelLindau disease (VHL), MEN 2, paraganglioma syndrome type 1/4/5 (SDHD/SDHB/SDHA), neurofibromatosis type 1 (NF1), and hereditary leiomyomatosis and renal cell cancer (FH) are among the genetic syn­ dromes associated with pheochromocytomas. Up to 50% of adrenal nodules are hormonally active, due to a cor­ tisol- or aldosterone-producing adrenocortical adenoma or a pheo­ chromocytoma associated with catecholamine excess (Table 398-5). ACC is rare but is the cause of an adrenal mass in up to 4% of patients. However, metastases originating from another solid tissue tumor are an additional cause of adrenal incidentaloma and account for up to 40% of adrenal masses in patients undergoing imaging for tumor staging or follow-up monitoring (Table 398-5). Differential Diagnosis and Treatment  Patients with an adrenal mass >1 cm require a diagnostic evaluation. Two key questions need to be addressed: (1) Does the tumor autonomously secrete hormones that could have a detrimental effect on health? (2) Is the adrenal mass benign or malignant? Hormone secretion by an adrenal mass occurs along a continuum, with a gradual increase in clinical manifestations in parallel with hormone levels. Exclusion of catecholamine excess from a pheochro­ mocytoma arising from the adrenal medulla is a mandatory part of the diagnostic workup of lipid-poor masses (Fig. 398-13). In case of hypertension, primary aldosteronism should be ruled out. Over­ production of adrenal androgen precursors, DHEA and its sulfate, is rare and most frequently seen in the context of ACC, as are increased levels of steroid precursors such as 17OHP. Cortisol excess is the most observed hormonal abnormality in adrenal masses, ranging from rare clinically overt Cushing’s syndrome to much more prevalent MACS (early-morning cortisol >50 nmol/L [1.8 μg/dL] after overnight admin­ istration of dexamethasone 1 mg in the absence of clinical features of Cushing’s). Patients with MACS may exhibit one or more components of the metabolic syndrome (e.g., obesity, type 2 diabetes, hypertension,

Adrenal mass Review imaging and assess hormone excess in parallel Assess for malignancy: Unenhanced CT imaging (tumor diameter and attenuation value)

40 mm mass with HU >201 PART 12 Endocrinology and Metabolism Any size mass with HU <10 or <40 mm mass with HU 10–20 40 mm mass with HU 10–20 or <40 mm mass with HU >201 Multidisciplinary team discussion Urine steroid metabolomics (if available) Interval imaging2 after 6–12 months No further imaging required Positive Negative FDG-PET/CT2 Negative Positive Positive Surgery3,4 Interval imaging2 after 3–6 months Negative No further imaging 1 Homogeneous mass >40 mm diameter with HU >20 on unenhanced CT or heterogeneous mass on unenhanced CT (which prevents HU measurement). 2 Interval imaging usually by unenhanced CT (or MRI); in selected cases, FDG-PET/CT may also be considered. 3 If ACC is suspected, surgery should be preceded by staging for ACC including CT chest, abdomen, and pelvis. 4 If a non-adrenal pathology is suspected, a biopsy may be considered after phaeochromocytoma has been excluded. 5 Cases of Cushing’s syndrome have to be confirmed as ACTH-independent by measurement of plasma ACTH. FIGURE 398-13  Management of the patient with an incidentally discovered adrenal mass. This pathway is primarily designed for adrenal incidentalomas; in adrenal nodules identified by screening or staging for an extra-adrenal primary malignancy, the likelihood of a metastasis needs to be considered when arranging further imaging or a biopsy. ACC, adrenocortical carcinoma; ACTH, adrenocorticotropic hormone; CT, computed tomography; DD, differential diagnosis; DHEAS, dehydroepiandrosterone sulfate; 1 mg-DST, 1 mg dexamethasone overnight suppression test; FDG-PET, fluorodeoxyglucose positron emission tomography; HU, Hounsfield Units; 17-OHP, 17-hydroxyprogesterone; MACS, mild autonomous cortisol excess secretion; MRI, magnetic resonance imaging; UFC, urinary free cortisol. dyslipidemia), osteoporosis, increased risk of cardiovascular events, frailty, and impaired quality of life, and have increased mortality risk. There is an ongoing debate about the optimal treatment for these patients, which includes adrenalectomy or conservative management with long-term monitoring and treatment of comorbidities potentially attributable to the cortisol excess. For the differentiation of benign from malignant adrenal masses, imaging is relatively sensitive, although specificity is suboptimal. Unenhanced CT is the procedure of choice for imaging the adrenal glands (Fig. 398-11). A diagnosis of ACC, pheochromocytoma, and benign adrenal myelolipoma becomes more likely with increasing diameter of the adrenal mass. However, size alone is of poor predictive value, with only 80% specificity for the differentiation of benign from malignant masses when using a 4-cm cutoff. Metastases are rare but are found with similar frequency in adrenal masses of all sizes. The tumor attenuation value on unenhanced CT is of high diagnostic value,

Assess for hormone excess Assess clinically for manifestations of adrenal hormone excess and carry out biochemical testing: • 1 mg-DST (all patients) • If clinical suspicion of Cushing’s: 24-hour UFC; salivary cortisol • If HU >10: plasma (or urinary) metanephrines • If hypertension: paired plasma renin & aldosterone; serum potassium • If ACC suspected (size ≥4 cm with HU >20 or heterogeneous density): serum 17OHP, DHEAS, A4; in women also testosterone and in men and postmenopausal women estradiol • If bilateral masses: serum 17OHP (DD congenital adrenal hyperplasia) • If clinical suspicion of bilateral adrenal metastases: paired early- morning ACTH and cortisol (to rule out adrenal insufficiency) No evidence of hormone excess Clinically overt hormone excess: multidisciplinary Mild autonomous cortisol secretion (MACS): abnormal 1 mg-DST + absent clinical features of Cushing’s team discussion Consider proceeding swiftly to surgery3,4,5 No further biochemical workup Assess comorbidities potentially attributable to cortisol excess (hypertension; type 2 diabetes; dyslipidemia; osteoporosis) Individualized treatment decision: adrenalectomy vs. long-term monitoring for development of comorbidities as many adrenocortical adenomas are lipid rich and thus present with low attenuation values (i.e., densities of <20 HUs). However, similar numbers of adrenocortical adenomas are lipid poor and present with higher HUs, making it difficult to differentiate them from ACCs, as well as pheochromocytomas, both of which invariably have high atten­ uation values (i.e., densities >20 HU on precontrast scans). Generally, benign lesions are rounded and homogenous, whereas most malignant lesions appear lobulated and inhomogeneous. Pheochromocytoma and adrenomyelolipoma may also exhibit lobulated and inhomogeneous features. MRI also allows for the visualization of the adrenal glands with somewhat lower resolution than CT. However, because it does not involve exposure to ionizing radiation, it is preferred in children, young adults, and during pregnancy. MRI has a valuable role in the character­ ization of indeterminate adrenal lesions using chemical shift analysis, with malignant tumors rarely showing loss of signal on opposed-phase MRI; however, this may also be observed in a proportion of benign

adrenocortical adenomas, and chemical shift analysis results usually are similar to those obtained by measuring tumor attenuation on unen­ hanced CT. The evidence base for the utility of fluorodeoxyglucose (FDG)-PET was initially scarce but is now expanding, with recent data indicating that a lack of FDG uptake reliably indicates a benign adre­ nocortical mass; however, care has to be taken in patients with a history of extra-adrenal cancer as adrenal metastases arising from those some­ times do not take up FDG, i.e., as typically seen in renal cell carcinoma. Adrenocortical carcinoma is invariably FDG avid; however, specificity is poor, with many benign adrenal adenomas also taking up FDG. Fine-needle aspiration (FNA) or CT-guided biopsy of an adrenal mass is very rarely indicated. FNA of a pheochromocytoma can cause a life-threatening hypertensive crisis. FNA of an ACC violates the tumor capsule and can cause needle track metastasis. FNA should only be considered in a patient with a history of nonadrenal malignancy and a newly detected adrenal mass, after careful exclusion of pheochromocy­ toma, and if the outcome will influence therapeutic management. It is important to recognize that in 25% of patients with a previous history of nonadrenal malignancy, a newly detected mass on CT is not a metas­ tasis. While FNA can diagnose extra-adrenal malignancies, it has very limited ability to differentiate between benign and malignant adreno­ cortical lesions and hence should not be used for the diagnosis of ACC. Adrenal masses associated with confirmed hormone excess or sus­ pected malignancy are usually treated surgically (Fig. 398-13) or, if adrenalectomy is not feasible or desired, with medication. Preoperative exclusion of glucocorticoid excess is particularly important for the pre­ diction of postoperative suppression of the contralateral adrenal gland, which requires glucocorticoid replacement peri- and postoperatively. Adrenal masses of any size with normal endocrine biochemistry at diagnosis and an attenuation value of <10 HU on unenhanced CT can be considered benign (malignancy rate <0.5%) and do not require fur­ ther follow-up (Fig. 398-13). This similarly applies to adrenal masses <4 cm in diameter and an attenuation value of 10–20 HU. In adrenal masses <4 cm and >20 HU attenuation as well as in masses >4 cm and 10–20 HU, the likelihood of malignancy is still very low (<5%) and can be mitigated by arranging for interval imaging (Fig. 398-13). The overwhelming majority of risk of malignancy applies to adrenal masses

4 cm with an attenuation >20 HU, and these masses require swift attention (Fig. 398-13), with a 50% risk of underlying malignancy. The risk of adrenocortical carcinoma is higher in young patients (<40 years), whereas metastases of extra-adrenal primaries occur at all ages. In adrenal masses with suspicious imaging findings (>4 cm and >20 HU), surgery and/or biopsy are feasible options; however, the latter will still result in unnecessary surgery for many benign tumors. A recently introduced diagnostic test, urine steroid metabolomics, has a twofold higher positive predictive value than imaging in detecting adrenocorti­ cal carcinoma, based on a distinct “malignant steroid fingerprint” with accumulating precursor steroid metabolites in 24-h urine. ■ ■ADRENOCORTICAL CARCINOMA ACC is a rare malignancy with an annual incidence of 1–2 per mil­ lion population. ACC is generally considered a highly malignant tumor; however, it presents with broad interindividual variability with regard to biologic characteristics and clinical behavior. Somatic mutations in the tumor-suppressor gene TP53 are found in 25% of apparently sporadic ACC. Germline TP53 mutations are the cause of the Li-Fraumeni syndrome associated with multiple solid organ can­ cers including ACC and are found in 25% of pediatric ACC cases; the TP53 mutation R337H is found in almost all pediatric ACC in Brazil. Other genetic changes identified in ACC include germline mutations of genes affecting DNA mismatch repair (Lynch syndrome), PRKAR1A (Carney complex), MEN1, APC (familial adenomatous polyposis), and somatic alterations in the Wnt/β-catenin pathway and in the insulinlike growth factor 2 (IGF2) cluster. IGF2 overexpression is found in 90% of ACCs. Patients with large adrenal tumors suspicious of malignancy should be managed by a multidisciplinary specialist team, including an endocrinologist, an oncologist, a surgeon, a radiologist, and a histo­ pathologist. FNA is not indicated in suspected ACC: first, cytology

TABLE 398-6  Classification System for Staging of Adrenocortical Carcinoma ENSAT STAGE TNM STAGE TNM DEFINITIONS I T1,N0,M0 T1, tumor ≤5 cm     N0, no positive lymph node     M0, no distant metastases II T2,N0,M0 T2, tumor >5 cm     N0, no positive lymph node     M0, no distant metastases Disorders of the Adrenal Cortex CHAPTER 398 III T1–T2,N1,M0 N1, positive lymph node(s)   T3–T4,N0–N1,M0 M0, no distant metastases     T3, tumor infiltration into surrounding tissue     T4, tumor invasion into adjacent organs or venous tumor thrombus in vena cava or renal vein IV T1–T4,N0–N1,M1 M1, presence of distant metastases Abbreviations: ENSAT, European Network for the Study of Adrenal Tumors; TNM, tumor, node, metastasis. and also histopathology of a core biopsy cannot differentiate between benign and malignant primary adrenal masses; second, FNA violates the tumor capsule and may even cause needle canal metastasis. Even when the entire tumor specimen is available, the histopathologic dif­ ferentiation between benign and malignant adrenocortical lesions is a diagnostic challenge. The most common histopathologic classification is the Weiss score, taking into account high nuclear grade; mitotic rate (>5/high-power field [HPF]); atypical mitosis; <25% clear cells; diffuse architecture; and presence of necrosis, venous invasion, and invasion of sinusoidal structures and tumor capsule. The presence of three or more elements suggests ACC. However, FNA is a feasible option if looking for metastases of an extra-adrenal primary or other adrenal tumor enti­ ties, such as ganglioneuroma. Although 60–70% of ACCs show biochemical evidence of steroid overproduction, in many patients, this is not clinically apparent due to the relatively inefficient steroid production by the adrenocortical can­ cer cells. Excess production of glucocorticoids and adrenal androgen precursors are most common and indicative of malignancy. Tumor staging at ACC diagnosis (Table 398-6) has important prognostic implications and requires scanning of the chest and abdo­ men for local organ invasion, lymphadenopathy, and metastases. Intravenous contrast medium is necessary for maximum sensitivity for hepatic metastases. An adrenal origin may be difficult to determine on standard axial CT imaging if the tumors are large and invasive, but CT reconstructions and MRI are more informative (Fig. 398-14) using multiple planes and different sequences. Vascular and adjacent organ invasion is diagnostic of malignancy. 18-Fluoro-2-deoxy-D-glucose PET (18-FDG-PET) is highly sensitive for the detection of malignancy and can be used to detect small metastases or local recurrence that may not be obvious on CT (Fig. 398-14). However, FDG-PET has limited specificity and therefore cannot be used for differentiating benign from malignant adrenal lesions. Metastasis in ACC most frequently occurs to liver and lung. There is no established grading system for ACC, and the Weiss score carries no prognostic value; the most important prognostic his­ topathologic parameter is the Ki67 proliferation index, with Ki67 <10% indicative of slow to moderate growth velocity, whereas a Ki67 ≥10% is associated with poor prognosis including high risk of recurrence and rapid progression. Cure of ACC can only be achieved by early detection and complete surgical removal. Capsule violation during primary surgery, metastasis at diagnosis, and primary treatment in a nonspecialist center and by a nonspecialist surgeon are major determinants of poor survival. If the primary tumor invades adjacent organs, en bloc removal of kidney and spleen should be considered to reduce the risk of recurrence, and regional lymph node dissection may further reduce this risk. Surgery

PART 12 Endocrinology and Metabolism A B FIGURE 398-14  Imaging in adrenocortical carcinoma (ACC). Magnetic resonance imaging scan with (A) frontal and (B) lateral views of a right ACC that was detected incidentally. Computed tomography (CT) scan with (C) coronal and (D) transverse views depicting a right-sided ACC. Note the irregular border and inhomogeneous structure. CT scan (E) and positron emission tomography/CT (F) visualizing a peritoneal metastasis of an ACC in close proximity to the right kidney (arrow). can also be considered in a patient with metastases if there is severe tumor-related hormone excess. This indication needs to be carefully weighed against surgical risk, including thromboembolic complications, and the resulting delay in the introduction of other therapeutic options. Patients with confirmed ACC and successful removal of the primary tumor should receive adjuvant treatment with mitotane (o,p’DDD), particularly in patients with a high risk of recurrence as determined by European Network for the Study of Adrenal Tumors (ENSAT) stage III and IV or Ki67 proliferation index ≥10%. Adjuvant mitotane should be continued for at least 2 years, if side effects are tolerated. Regular monitoring of plasma mitotane levels is mandatory (therapeutic range 14–20 mg/L; neurotoxic complications more frequent at >20 mg/L). Mitotane is usually started at 500 mg tid, with stepwise increases to a maximum dose of 2000 mg tid in days (high-dose saturation) or weeks (low-dose saturation) as tolerated. Once therapeutic range plasma mitotane levels are achieved, the dose can be tapered to maintenance doses mostly ranging from 1000 to 1500 mg tid. Mitotane treatment results in disruption of cortisol synthesis and thus requires glucocor­ ticoid replacement; glucocorticoid replacement dose should be at least double of that usually used in adrenal insufficiency (i.e., 40–60 mg daily in two to three divided doses) because mitotane induces hepatic CYP3A4 activity, resulting in rapid inactivation of glucocorticoids. Mitotane also increases circulating CBG, thereby decreasing the avail­ able free cortisol fraction. Single metastases can be addressed surgically or with radiofrequency ablation as appropriate. If the tumor recurs or progresses during mitotane treatment, cytotoxic chemotherapy should be considered; the established first-line chemotherapy regimen is the combination of cisplatin, etoposide, and doxorubicin plus continuing mitotane. Painful bone metastasis responds to irradiation. Overall survival in ACC is still poor, with 5-year survival rates of 30–40% and a median survival of 15 months in metastatic ACC. ■ ■ADRENAL INSUFFICIENCY Epidemiology  The prevalence of well-documented, permanent adrenal insufficiency is 5 in 10,000 in the general population. Hypotha­ lamic-pituitary origin of the disease is most frequent, with a prevalence of 3 in 10,000, whereas primary adrenal insufficiency has a prevalence of 2 in 10,000. Approximately one-half of the latter cases are acquired, mostly caused by autoimmune destruction of the adrenal glands; the other one-half are genetic, most commonly caused by distinct enzymatic blocks in adrenal steroidogenesis affecting glucocorticoid synthesis (i.e., CAH). Adrenal insufficiency arising from suppression of the HPA axis consequent to exogenous glucocorticoid treatment is much more com­ mon, occurring in 0.5–2% of the population in developed countries.

C D E F Etiology  Primary adrenal insufficiency is most commonly caused by autoimmune adrenalitis. Isolated autoimmune adrenalitis accounts for 30–40%, whereas 60–70% develop adrenal insufficiency as part of autoimmune polyglandular syndromes (APSs) (Chap. 400) (Table 398-7). APS1, also termed APECED (autoimmune polyendo­ crinopathy-candidiasis-ectodermal dystrophy), is the underlying cause in 10% of patients affected by APS. APS1 is transmitted in an autoso­ mal recessive manner and is caused by mutations in the autoimmune regulator gene AIRE. Associated autoimmune conditions overlap with those seen in APS2 but may also include total alopecia, primary hypo­ parathyroidism, and, in rare cases, lymphoma. APS1 patients invariably develop chronic mucocutaneous candidiasis, usually manifested in childhood and preceding adrenal insufficiency by years or decades. The much more prevalent APS2 is of polygenic inheritance, with confirmed associations with the HLA-DR3 gene region in the major histocompat­ ibility complex and distinct gene regions involved in immune regula­ tion (CTLA-4, PTPN22, CLEC16A). Coincident autoimmune disease most frequently includes thyroid autoimmune disease, vitiligo, and pre­ mature ovarian failure. Less commonly, additional features may include type 1 diabetes and pernicious anemia caused by vitamin B12 deficiency. X-linked adrenoleukodystrophy has an incidence of 1:20,000 males and is caused by mutations in the X-ALD gene encoding the peroxi­ somal membrane transporter protein ABCD1; its disruption results in the accumulation of very-long-chain (>24 carbon atoms) fatty acids. Approximately 50% of cases manifest in early childhood with rapidly progressive white matter disease (cerebral adrenoleukodystrophy); 35% present during adolescence or in early adulthood with neurologic features indicative of myelin and peripheral nervous system involve­ ment (adrenomyeloneuropathy [AMN]). In the remaining 15%, adre­ nal insufficiency is the sole manifestation of disease. Of note, distinct mutations manifest with variable penetrance and phenotypes within affected families. Rarer causes of adrenal insufficiency involve the destruction of the adrenal glands as a consequence of infection, hemorrhage, or infiltra­ tion (Table 398-7); tuberculous adrenalitis is still a frequent cause of disease in developing countries. Adrenal metastases rarely cause adre­ nal insufficiency, and this occurs only with bilateral, bulky metastases. Inborn causes of primary adrenal insufficiency other than CAH are rare, causing <1% of cases. However, their elucidation provides important insights into adrenal gland development and physiology. Mutations causing primary adrenal insufficiency (Table 398-7) include factors regulating adrenal development and steroidogenesis (DAX-1, SF-1), cholesterol synthesis, import and cleavage (DHCR7, StAR, CYP11A1), elements of the adrenal ACTH response pathway (MC2R, MRAP) (Fig. 398-5), and factors involved in redox regulation (NNT, TXNRD2) and DNA repair (MCM4, CDKN1C).

TABLE 398-7  Causes of Primary Adrenal Insufficiency DIAGNOSIS GENE ASSOCIATED FEATURES Autoimmune polyglandular syndrome 1 (APS1) AIRE Hypoparathyroidism, chronic mucocutaneous candidiasis, other autoimmune disorders, rarely lymphomas Autoimmune polyglandular syndrome 2 (APS2) Associations with HLA-DR3, CTLA-4 Hypothyroidism, hyperthyroidism, premature ovarian failure, vitiligo, type 1 diabetes mellitus, pernicious anemia Isolated autoimmune adrenalitis Associations with HLA-DR3, CTLA-4   Congenital adrenal hyperplasia (CAH) CYP21A2, CYP11B1, CYP17A1, HSD3B2, POR Congenital lipoid adrenal hyperplasia (CLAH) STAR, CYP11A1 46,XY DSD, gonadal failure (see also Chap. 402) Adrenal hypoplasia congenita (AHC) NR0B1 (DAX-1), NR5A1 (SF-1) 46,XY DSD, gonadal failure (see also Chap. 402) Adrenoleukodystrophy (ALD), adrenomyeloneuropathy (AMN) ABCD1 Demyelination of central nervous system (ALD) or spinal cord and peripheral nerves (AMN) Familial glucocorticoid deficiency MC2R Tall stature   MRAP None   STAR None   NNT TXNRD2   MCM4 Growth retardation, natural killer cell deficiency Triple A syndrome AAAS Alacrima, achalasia, neurologic impairment Smith-Lemli-Opitz syndrome SLOS Cholesterol synthesis disorder associated with mental retardation, craniofacial malformations, growth failure Kearns-Sayre syndrome Mitochondrial DNA deletions Progressive external ophthalmoplegia, pigmentary retinal degeneration, cardiac conduction defects, gonadal failure, hypoparathyroidism, type 1 diabetes, IMAGe syndrome CDKN1C Intrauterine growth retardation, metaphyseal dysplasia, genital anomalies MIRAGE syndrome SAMD9 Myelodysplasia, infection, restriction of growth, genital phenotypes, and enteropathy Sphingosine-1-phosphate lyase deficiency SGPL1 Steroid-resistant nephrotic syndrome, immunodeficiency, neurologic defects, ichthyosis, primary hypothyroidism, cryptorchidism Adrenal infections   Tuberculosis, HIV, CMV, cryptococcosis, histoplasmosis, coccidioidomycosis Adrenal infiltration   Metastases, lymphomas, sarcoidosis, amyloidosis, hemochromatosis Adrenal hemorrhage   Meningococcal sepsis (Waterhouse-Friderichsen syndrome), primary antiphospholipid syndrome Drug-induced   Mitotane, aminoglutethimide, abiraterone, trilostane, etomidate, ketoconazole, levoketoconazole, osilodrostat, suramin, mifepristone (RU486), interferonalpha, immune checkpoint inhibitors (rare) Bilateral adrenalectomy   E.g., in the management of Cushing’s syndrome or after bilateral nephrectomy Abbreviations: AIRE, autoimmune regulator; CMV, cytomegalovirus; DSD, disordered sex development; MC2R, ACTH receptor; MCM4, mini chromosome maintenancedeficient 4 homologue; MRAP, MC2R-accessory protein; NNT, nicotinamide nucleotide transhydrogenase. Secondary (or central) adrenal insufficiency is the consequence of dysfunction of the hypothalamic-pituitary component of the HPA axis (Table 398-8). Excluding iatrogenic suppression, the overwhelming majority of cases are caused by pituitary or hypothalamic tumors or their treatment by surgery or irradiation (Chap. 392). Rarer causes include pituitary apoplexy, either as a consequence of an infarcted pituitary adenoma or transient reduction in the blood supply of the pituitary during surgery or after rapid blood loss associated with par­ turition, also termed Sheehan’s syndrome. Isolated ACTH deficiency is rarely caused by autoimmune disease or pituitary infiltration (Table 398-8). Mutations in the ACTH precursor POMC or in factors regu­ lating pituitary development are genetic causes of ACTH deficiency (Table 398-8). Clinical Manifestations  In principle, the clinical features of primary adrenal insufficiency (Addison’s disease) are character­ ized by the loss of both glucocorticoid and mineralocorticoid secretion (Table 398-9). In secondary adrenal insufficiency, only glucocorticoid deficiency is present, as the adrenal itself is intact and thus still ame­ nable to regulation by the RAA system. Adrenal androgen secretion is disrupted in both primary and secondary adrenal insufficiency (Table 398-9). Hypothalamic-pituitary disease can lead to additional clinical manifestations due to involvement of other endocrine axes (thyroid, gonads, GH, prolactin) or visual impairment with bitem­ poral hemianopia caused by chiasmal compression. It is important to

See Table 398-10 (see also Chap. 402) Disorders of the Adrenal Cortex CHAPTER 398 None None recognize that iatrogenic adrenal insufficiency caused by exogenous glucocorticoid suppression of the HPA axis may result in all symptoms associated with glucocorticoid deficiency (Table 398-9), if exogenous glucocorticoids are stopped abruptly. However, patients will appear clinically cushingoid as a result of the preceding overexposure to glucocorticoids. Chronic adrenal insufficiency manifests with relatively nonspecific signs and symptoms, such as fatigue and loss of energy, often result­ ing in delayed or missed diagnoses (e.g., as depression or anorexia). A distinguishing feature of primary adrenal insufficiency is hyperpig­ mentation, which is caused by excess ACTH stimulation of melano­ cytes. Hyperpigmentation is most pronounced in skin areas exposed to increased friction or shear stress and is increased by sunlight (Fig. 398-15). Conversely, in secondary adrenal insufficiency, the skin has an alabaster-like paleness due to lack of ACTH secretion. Hyponatremia is a characteristic biochemical feature in primary adrenal insufficiency and is found in 80% of patients at presenta­ tion. Hyperkalemia is present in 40% of patients at initial diagnosis. Hyponatremia is primarily caused by mineralocorticoid deficiency but can also occur in secondary adrenal insufficiency due to diminished inhibition of antidiuretic hormone (ADH) release by cortisol, resulting in mild syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Glucocorticoid deficiency also results in slightly increased TSH concentrations that normalize within days to weeks after initia­ tion of glucocorticoid replacement.

TABLE 398-8  Causes of Secondary Adrenal Insufficiency DIAGNOSIS GENE ASSOCIATED FEATURES Pituitary tumors (endocrine active and inactive adenomas, very rare: carcinoma)   Depending on tumor size and location: visual field impairment (bilateral hemianopia), hyperprolactinemia, secondary hypothyroidism, hypogonadism, growth hormone deficiency Other mass lesions affecting the hypothalamic-pituitary region   Craniopharyngioma, meningioma, ependymoma, metastases PART 12 Endocrinology and Metabolism Pituitary irradiation   Radiotherapy administered for pituitary tumors, brain tumors, or craniospinal irradiation in leukemia Autoimmune hypophysitis   Often associated with pregnancy; may present with panhypopituitarism or isolated ACTH deficiency; can be associated with autoimmune thyroid disease, more rarely with vitiligo, premature ovarian failure, type 1 diabetes, pernicious anemia Pituitary apoplexy/ hemorrhage   Hemorrhagic infarction of large pituitary adenomas or pituitary infarction consequent to traumatic major blood loss (e.g., surgery or pregnancy: Sheehan’s syndrome) Pituitary infiltration   Tuberculosis, actinomycosis, sarcoidosis, histiocytosis X, granulomatosis with polyangiitis (Wegener’s), metastases Drug-induced   Chronic glucocorticoid excess (endogenous or exogenous), immune check point inhibitors, opioids, interferon alpha, ribavirin, megestrol acetate Congenital isolated ACTH deficiency TBX19 (Tpit)   Combined pituitary hormone deficiency (CPHD) PROP-1 Progressive development of CPHD in the order GH, PRL, TSH, LH/FSH, ACTH   HESX1 CPHD and septo-optic dysplasia   LHX3 CPHD and limited neck rotation, sensorineural deafness   LHX4 CPHD and cerebellar abnormalities   SOX3 CPHD and variable mental retardation Proopiomelanocortin (POMC) deficiency POMC Early-onset obesity, red hair pigmentation Abbreviations: ACTH, adrenocorticotropic hormone; GH, growth hormone; LH/ FSH, luteinizing hormone/follicle-stimulating hormone; PRL, prolactin; TSH, thyroidstimulating hormone. Acute adrenal insufficiency, also termed adrenal crisis, usually occurs after a prolonged period of nonspecific complaints and is more fre­ quently observed in patients with primary adrenal insufficiency, due to the loss of both glucocorticoid and mineralocorticoid secretion. Postural hypotension may progress to hypovolemic shock. Adrenal insufficiency may mimic features of acute abdomen with abdominal tenderness, nau­ sea, vomiting, and fever. In some cases, the primary presentation may resemble neurologic disease, with decreased responsiveness progressing to stupor and coma. An adrenal crisis can be triggered by an intercur­ rent illness, surgical or other stress, or increased glucocorticoid inactiva­ tion (e.g., hyperthyroidism). Prospective data indicate 8.3 adrenal crises and 0.5 adrenal crisis–related deaths per 100 patient-years. Diagnosis  The diagnosis of adrenal insufficiency is established by the short cosyntropin test, a safe and reliable tool with excellent pre­ dictive diagnostic value (Fig. 398-16). The cutoff for failure is usually defined at cortisol levels of <450–500 nmol/L (16–18 μg/dL) sampled 30–60 min after ACTH stimulation; the exact cutoff is dependent on the locally available assay, with generally lower cutoffs for mass spec­ trometry–based assays. During the early phase of HPA disruption (e.g., within 4 weeks of pituitary insufficiency), patients may still respond

TABLE 398-9  Signs and Symptoms of Adrenal Insufficiency Signs and Symptoms Caused by Glucocorticoid Deficiency Fatigue, lack of energy Weight loss, anorexia Myalgia, joint pain Fever Normochromic anemia, lymphocytosis, eosinophilia Slightly increased TSH (due to loss of feedback inhibition of TSH release) Hypoglycemia (more frequent in children) Low blood pressure, postural hypotension Hyponatremia (due to loss of feedback inhibition of AVP release) Signs and Symptoms Caused by Mineralocorticoid Deficiency (Primary Adrenal Insufficiency Only) Abdominal pain, nausea, vomiting Dizziness, postural hypotension Salt craving Low blood pressure, postural hypotension Increased serum creatinine (due to volume depletion) Hyponatremia Hyperkalemia Signs and Symptoms Caused by Adrenal Androgen Deficiency Lack of energy Dry and itchy skin (in women) Loss of libido (in women) Loss of axillary and pubic hair (in women) Other Signs and Symptoms Hyperpigmentation (primary adrenal insufficiency only) (due to excess of proopiomelanocortin [POMC]-derived peptides) Alabaster-colored pale skin (secondary adrenal insufficiency only) (due to deficiency of POMC-derived peptides) Abbreviations: AVP, arginine vasopressin; TSH, thyroid-stimulating hormone. to exogenous ACTH stimulation. In this circumstance, the ITT is an alternative choice but is more invasive and should be carried out only under a specialist’s supervision (see above). Induction of hypoglycemia is contraindicated in individuals with diabetes mellitus, cardiovascular disease, or history of seizures. Random serum cortisol measurements are of limited diagnostic value because baseline cortisol levels may be coincidentally low due to the physiologic diurnal rhythm of cortisol secretion (Fig. 398-3). Similarly, many patients with secondary adrenal insufficiency have relatively normal baseline cortisol levels but fail to mount an appropriate cortisol response to ACTH, which can only be revealed by stimulation testing. Importantly, tests to establish the diag­ nosis of adrenal insufficiency should never delay treatment. Thus, in a patient with suspected adrenal crisis, it is reasonable to draw baseline cortisol levels, provide replacement therapy, and defer formal stimula­ tion testing until a later time. Once adrenal insufficiency is confirmed, measurement of plasma ACTH is the next step, with increased or inappropriately low levels defining primary and secondary origin of disease, respectively (Fig. 398-16). In primary adrenal insufficiency, increased plasma renin will confirm the presence of mineralocorticoid deficiency. At initial presentation, patients with primary adrenal insufficiency should undergo screening for steroid autoantibodies as a marker of autoim­ mune adrenalitis. If these tests are negative, adrenal imaging by CT is indicated to investigate possible hemorrhage, infiltration, or masses. In male patients with negative autoantibodies in the plasma, verylong-chain fatty acids should be measured to exclude X-ALD. Patients with inappropriately low ACTH, in the presence of confirmed cortisol deficiency, should undergo hypothalamic-pituitary imaging by MRI. Features suggestive of preceding pituitary apoplexy, such as suddenonset severe headache or history of previous head trauma, should be carefully explored, particularly in patients with no obvious MRI lesion.

A B C D FIGURE 398-15  Clinical features of Addison’s disease. Note the hyperpigmentation in areas of increased friction including (A) palmar creases, (B) dorsal foot, (C) nipples and axillary region, and (D) patchy hyperpigmentation of the oral mucosa. TREATMENT Acute Adrenal Insufficiency Acute adrenal insufficiency requires immediate initiation of rehy­ dration, usually carried out by saline infusion at initial rates of 1 L/h with continuous cardiac monitoring. Glucocorticoid replacement should be initiated by bolus injection of 100 mg hydrocortisone, followed by the administration of 200 mg hydrocortisone over 24 h, preferably by continuous infusion or alternatively by bolus IV or IM injections. Mineralocorticoid replacement can be initiated once the daily hydrocortisone dose has been reduced to <50 mg because at higher doses hydrocortisone provides sufficient stimulation of MRs. Glucocorticoid replacement for the treatment of chronic adrenal insufficiency should be administered at a dose that replaces the physiologic daily cortisol production, which is usually achieved by the oral administration of 15–25 mg hydrocortisone in two to three divided doses. Pregnancy may require an increase in hydrocorti­ sone dose by 50% during the last trimester. In all patients, at least one-half of the daily dose should be administered in the morning upon awakening. Long-acting glucocorticoids such as predniso­ lone or dexamethasone are not preferred because they result in increased glucocorticoid exposure due to extended GR activation at times of physiologically low cortisol secretion. There are no wellestablished dose equivalencies, but as a guide, equipotency can be assumed for 1 mg hydrocortisone, 1.6 mg cortisone acetate, 0.2 mg

Disorders of the Adrenal Cortex CHAPTER 398 prednisolone, 0.25 mg prednisone, and 0.025 mg dexamethasone. Currently available standard glucocorticoid preparations fail to mimic the physiologic cortisol secretion rhythm (Fig. 398-3). How­ ever, this is overcome by recent modified release hydrocortisone preparations, with promising results emerging from the treatment of patients with primary adrenal insufficiency due to congenital adrenal hyperplasia. Monitoring of glucocorticoid replacement is mainly based on the history and examination for signs and symptoms suggestive of glucocorticoid over- or underreplacement, including assessment of body weight and blood pressure. Plasma ACTH, 24-h urinary free cortisol, or serum cortisol day curves reflect whether hydrocorti­ sone has been taken or not but do not convey reliable information about replacement quality. In patients with isolated primary adrenal insufficiency, monitoring should include screening for autoimmune thyroid disease, and female patients should be made aware of the possibility of premature ovarian failure. Supraphysiologic gluco­ corticoid treatment with doses equivalent to 30 mg hydrocortisone or more will affect bone metabolism, and these patients should undergo regular bone mineral density evaluation. All patients with adrenal insufficiency need to be instructed about the requirement for stress-related glucocorticoid dose adjustments. These gener­ ally consist of doubling the routine oral glucocorticoid dose in the case of intercurrent illness with fever and bed rest and the need for immediate IV or IM injection of 100 mg hydrocortisone followed

Clinical suspicion of adrenal insufficiency (weight loss, fatigue, postural hypotension, hyperpigmentation, hyponatremia) Screening/confirmation of diagnosis • Plasma cortisol 30–60 min after 250 µg cosyntropin IM or IV (Cortisol post cosyntropin <450–500 nmol/L [assay-specific]) • CBC, serum sodium, potassium, creatinine, urea, TSH Differential diagnosis Plasma ACTH, plasma renin, serum aldosterone PART 12 Endocrinology and Metabolism Primary adrenal insufficiency (High ACTH, high renin, low aldosterone) Glucocorticoid + mineralocorticoid replacement Glucocorticoid replacement Adrenal autoantibodies Negative Positive Negative Positive • Autoimmune adrenalitis; • Autoimmune polyglandular syndrome (APS) • Chest x-ray • Serum 17-OHP • In men: plasma very- long-chain fatty acids (VLCFA) • Adrenal CT Positive Negative • Adrenal infection (tuberculosis), • Infiltration (e.g., lymphoma) • Hemorrhage • Congenital adrenal hyperplasia (17-OHP↑) • Autoimmune adrenalitis most likely diagnosis • In men, consider adrenoleukodystrophy (VLCFA↑) FIGURE 398-16  Management of the patient with suspected adrenal insufficiency. ACTH, adrenocorticotropic hormone; CBC, complete blood count; CT, computed tomography; MRI, magnetic resonance imaging; 17-OHP, 17-hydroxyprogesterone; PRA, plasma renin activity; TSH, thyroid-stimulating hormone. by intravenous infusion of 200 mg hydrocortisone/24 h in cases of prolonged vomiting, surgery, or trauma. All patients, but in particu­ lar those living or traveling in regions with delayed access to acute health care, should carry a hydrocortisone self-injection emergency kit, in addition to their usual steroid emergency cards and bracelets, and should receive training in its use. Mineralocorticoid replacement in primary adrenal insufficiency should be initiated at a dose of 100–150 μg fludrocortisone. The adequacy of treatment can be evaluated by measuring blood pres­ sure, sitting and standing, to detect a postural drop indicative of hypovolemia. In addition, serum sodium, potassium, and plasma renin should be measured regularly. Renin levels should be kept in the upper normal reference range. Changes in glucocorticoid dose may also impact on mineralocorticoid replacement as cortisol also binds the MR; 40 mg of hydrocortisone is equivalent to 100 μg of fludro­ cortisone. It is important to note that prednisone and prednisolone have reduced mineralocorticoid activity and dexamethasone has none. In patients living or traveling in areas with hot or tropical weather conditions, the fludrocortisone dose should be increased by 50–100 μg during the summer. Mineralocorticoid dose may also

Secondary adrenal insufficiency (Low-normal ACTH, normal renin, normal aldosterone) MRI pituitary • History of exogenous glucocorticoid treatment? • History of head trauma? • Consider isolated ACTH deficiency Hypothalamicpituitary mass lesion need to be adjusted during pregnancy due to the anti-mineralocor­ ticoid activity of progesterone, but this is less often required than hydrocortisone dose adjustment. Plasma renin cannot serve as a monitoring tool during pregnancy because renin rises physiologi­ cally during gestation. Adrenal androgen replacement is an option in patients with lack of energy, despite optimized glucocorticoid and mineralocorticoid replacement. It may also be indicated in women with features of androgen deficiency, including loss of libido. Adrenal androgen replacement can be achieved by once-daily administration of 25–50 mg DHEA. Treatment is monitored by measurement of DHEAS, androstenedione, testosterone, and sex hormone–binding globulin (SHBG) 24 h after the last DHEA dose. ■ ■GLUCOCORTICOID-INDUCED ADRENAL INSUFFICIENCY A possible unwanted effect of glucocorticoid treatment is suppression of the hypothalamic-pituitary-adrenal axis. Glucocorticoid-induced adrenal insufficiency (GI-AI) can be observed with any route of

exogenous administration, including oral, topical, inhaled, intranasal, and intraarticular. Factors affecting the risk of GI-AI include the dura­ tion of glucocorticoid therapy, mode of administration, glucocorticoid dose and potency, concomitant drugs that interfere with glucocorticoid metabolism, and individual susceptibility. Up to half of long-term oral glucocorticoid users (0.5–1.8% of the general population in Western countries) develop GI-AI: patients treated with supraphysiologic doses for longer than 3–4 weeks carry the highest risk, whereas short-term therapy is generally safe. GI-AI has been described in around 8% of inhaled glucocorticoid users, but the risk increases substantially (21–27%) when high doses are used and for treatment duration >1 year. GI-AI has also been reported in approximately half of patients receiving intra-articular steroid injections, but evidence in this population is very limited. The use of multiple glucocorticoid formulations at the same time and the concomitant administration of strong cytochrome P450 3A4 inhibitors, which include several antibiotics, antifungals, and the protease inhibitor ritonavir, are among the factors dramatically increasing the risk of developing GI-AI. Ritonavir is the most reported offending medication, used as part of antiviral combinations to treat HIV infection, hepatitis C infection, and COVID-19. Other drugs that can increase the risk are opioids, which can also blunt the HPA axis response. Clinicians who prescribe glucocorticoids should educate patients about the different aspects of glucocorticoid therapy, including the risk of GI-AI. If glucocorticoids are no longer required for the control of the underlying disease and the treatment duration is <3–4 weeks, glucocorticoids can be stopped abruptly. Conversely, patients on longterm treatment should be tapered down gradually until approach­ ing a physiologic dose (e.g., 3–5 mg of prednisone). Patients who have developed a dependence on supraphysiologic glucocorticoid doses can develop withdrawal symptoms during tapering including malaise, fatigue, nausea, muscle and joint pain, and sleep and mood disturbances. Symptoms can be severe, and patients can sometimes benefit from a temporary increase in their glucocorticoid dose and a subsequent slower taper. Once a physiologic glucocorticoid dose has been achieved, patients should be tested for HPA axis recovery through an early-morning serum cortisol measurement, which pro­ vides information on the likelihood of GI-AI. There are no established cortisol cutoffs, which are influenced by the assay used and other fac­ tors including concurrent major stress and altered CBG levels leading to falsely elevated (e.g., oral estrogens, pregnancy) or falsely reduced (e.g., advanced liver cirrhosis, nephrotic syndrome) cortisol levels. Current international guidelines suggest that an early-morning cortisol <150 nmol/L (or 5 µg/dL) is highly suggestive of GI-AI, whereas values

300 nmol/L (or 10 µg/dL) are in keeping with HPA axis recovery. For indeterminate values, cosyntropin stimulation may be considered. Several clinicians do not routinely measure cortisol levels in patients tapering glucocorticoids; in such cases, patients must be educated and closely monitored for clinical manifestations of adrenal insufficiency, and biochemical testing should be swiftly arranged if there are any clinical concerns. Patients with established GI-AI must be treated as any other patient with secondary adrenal insufficiency. Other than daily glucocorticoid TABLE 398-10  Variants of Congenital Adrenal Hyperplasia VARIANT GENE IMPACT ON STEROID SYNTHESIS DIAGNOSTIC MARKER STEROIDS IN SERUM (AND URINE) 21-Hydroxylase deficiency (21OHD) CYP21A2 Glucocorticoid deficiency, mineralocorticoid deficiency, adrenal androgen excess 11β-Hydroxylase deficiency (11OHD) CYP11B1 Glucocorticoid deficiency, mineralocorticoid excess, adrenal androgen excess 17α-Hydroxylase deficiency (17OHD) CYP17A1 (Glucocorticoid deficiency), mineralocorticoid excess, androgen deficiency HSD3B2 Glucocorticoid deficiency, (mineralocorticoid deficiency), adrenal androgen excess (females and males), gonadal androgen deficiency (males) 3β-Hydroxysteroid dehydrogenase deficiency (3bHSDD) P450 oxidoreductase deficiency (PORD) POR Glucocorticoid deficiency, (mineralocorticoid excess), prenatal androgen excess and postnatal androgen deficiency, skeletal malformations

replacement, patients should receive stress dose coverage when they are exposed to stress to avoid acute adrenal insufficiency. Mineralocor­ ticoid therapy is not required due to preserved aldosterone production.

■ ■CONGENITAL ADRENAL HYPERPLASIA (See also Chap. 402) CAH is caused by mutations in genes encoding steroidogenic enzymes involved in glucocorticoid synthesis (CYP21A2, CYP17A1, HSD3B2, CYP11B1) or in the cofactor enzyme P450 oxido­ reductase that serves as an electron donor to CYP21A2 and CYP17A1 (Fig. 398-1). Invariably, patients affected by CAH exhibit glucocorti­ coid deficiency. Depending on the exact step of enzymatic block, they may also have excess production of mineralocorticoids or deficient production of sex steroids (Table 398-10). The diagnosis of CAH is readily established by measurement of the steroids accumulating before the distinct enzymatic block, either in serum or in urine, preferably by the use of mass spectrometry–based assays (Table 398-10). Disorders of the Adrenal Cortex CHAPTER 398 Mutations in CYP21A2 are the most prevalent cause of CAH, responsible for 90–95% of cases. 21-Hydroxylase deficiency disrupts glucocorticoid and mineralocorticoid synthesis (Fig. 398-1), result­ ing in diminished negative feedback via the HPA axis. This leads to increased pituitary ACTH release, which drives increased synthesis of adrenal androgen precursors and subsequent androgen excess. The degree of impairment of glucocorticoid and mineralocorticoid secre­ tion depends on the severity of mutations. Major loss-of-function mutations result in combined glucocorticoid and mineralocorticoid deficiency (classic CAH, neonatal presentation), whereas less severe mutations affect glucocorticoid synthesis only (simple virilizing CAH, neonatal or early childhood presentation). The mildest mutations result in the least severe clinical phenotype, nonclassic CAH, usually presenting during adolescence and early adulthood and with preserved glucocorticoid production. Androgen excess is present in all patients and manifests with broad phenotypic variability, ranging from severe virilization of the external genitalia in neonatal girls (e.g., 46,XX disordered sex development [DSD]) to hirsutism and oligomenorrhea resembling a polycystic ovary syndrome phenotype in young women with nonclassic CAH. In coun­ tries without neonatal screening for CAH, boys with classic CAH usu­ ally present with life-threatening adrenal crisis in the first few weeks of life (salt-wasting crisis); a simple-virilizing genotype manifests with precocious pseudo-puberty and advanced bone age in early childhood, whereas men with nonclassic CAH are usually detected only through family screening. Glucocorticoid treatment is more complex than for other causes of primary adrenal insufficiency as it not only needed to replace miss­ ing glucocorticoids but also to control the increased ACTH drive and subsequent androgen excess. Current treatment is hampered by the lack of glucocorticoid preparations that mimic the diurnal cortisol secretion profile, resulting in a prolonged period of ACTH stimulation and subsequent androgen production during the early morning hours. In childhood, optimization of growth and pubertal development are important goals of glucocorticoid treatment, in addition to prevention of adrenal crisis and treatment of 46,XX DSD. In adults, the focus shifts 17-Hydroxyprogesterone, 21-deoxycortisol (pregnanetriol, 17-hydroxypregnanolone, pregnanetriolone) 11-deoxycortisol, 11-deoxycorticosterone (tetrahydro-11deoxycortisol, tetrahydro-11-deoxycorticosterone) 11-Deoxycorticosterone, corticosterone, pregnenolone, progesterone (tetrahydro-11-deoxycorticosterone, tetrahydrocorticosterone, pregnenediol, pregnanediol) 17-Hydroxypregnanolone (pregnanetriol) Pregnenolone, progesterone, 17-hydroxyprogesterone (pregnanediol, pregnanetriol)

PART 12 Endocrinology and Metabolism B A D C FIGURE 398-17  Imaging in congenital adrenal hyperplasia (CAH). Adrenal computed tomography scans showing homogenous bilateral hyperplasia in a young patient with classic CAH (A) and macronodular bilateral hyperplasia (B) in a middle-aged patient with classic CAH with longstanding poor disease control. Magnetic resonance imaging scan with T1-weighted (C) and T2-weighted (D) images showing bilateral testicular adrenal rest tumors (arrows) in a young patient with salt-wasting CAH. (Used with permission from N. Reisch.) to preserving fertility and preventing side effects of glucocorticoid overtreatment, namely, the metabolic syndrome and osteoporosis. Fertility can be compromised in women due to oligomenorrhea/amen­ orrhea with chronic anovulation as a consequence of androgen excess. Men may develop testicular adrenal rest tissue (TART) (Fig. 398-17) consisting of hyperplastic cells with shared adrenal and gonadal char­ acteristics located in the rete testis, which should not be confused with testicular tumors. TART can compromise sperm production and induce testicular fibrosis that may be irreversible. TREATMENT Congenital Adrenal Hyperplasia Hydrocortisone is a good treatment option for the prevention of adrenal crisis, but longer acting prednisolone may be needed to control androgen excess. In children, hydrocortisone is given in divided doses at 1–1.5 times the normal cortisol production rate (~10–13 mg/m2 per day). In adults, if hydrocortisone does not suf­ fice, intermediate-acting glucocorticoids (e.g., prednisone) may be given, using the lowest dose necessary to suppress excess androgen production. For achieving fertility, dexamethasone treatment may be required but should only be given for the shortest possible time period to limit adverse metabolic side effects. The recent intro­ duction of modified and delayed-release hydrocortisone, which mimics the endogenous physiologic cortisol release pattern, is promising, providing effective control of steroid precursor excess while the daily hydrocortisone dose is lower than required for immediate-release hydrocortisone. An oral corticotropin-releasing factor antagonist, Crinecerfont, has shown efficacy to reduce gluco­ corticoid replacement doses needed to suppress adrenal androgens. Biochemical monitoring should include androstenedione and testosterone, aiming for the normal sex-specific reference range. 17OHP is a useful marker of overtreatment, indicated by 17OHP levels within the normal range of healthy controls. Glucocorticoid overtreatment may suppress the hypothalamic-pituitary-gonadal axis. Thus, treatment needs to be carefully titrated against clinical

features of disease control. Stress-dose glucocorticoids should be given at double or triple the daily dose for surgery, acute illness, or severe trauma. Poorly controlled CAH can result in adrenocorti­ cal hyperplasia, which gave the disease its name, and may present as macronodular hyperplasia subsequent to long-standing ACTH excess (Fig. 398-17). The nodular areas can develop autonomous adrenal androgen production and may be unresponsive to glu­ cocorticoid treatment. The prevalence of adrenomyelolipomas is increased in CAH; these are benign but can require surgical inter­ vention due to lack of self-limiting growth. Mineralocorticoid requirements change during life and are higher in children, explained by relative mineralocorticoid resistance that diminishes with ongoing maturation of the kidney. Children with CAH usually receive mineralocorticoid and salt replacement. How­ ever, young adults with CAH should undergo reassessment of their mineralocorticoid reserve. Plasma renin should be regularly moni­ tored and kept within the upper half of the normal reference range. ■ ■FURTHER READING Bancos I et al: Urine steroid metabolomics for the differential diagno­ sis of adrenal incidentalomas in the EURINE-ACT study: A prospec­ tive test validation study. Lancet Diabetes Endocrinol 8:773, 2020. Beuschlein F et al: European Society of Endocrinology and Endo­ crine Society Joint Clinical Guideline: Diagnosis and therapy of glucocorticoid-induced adrenal insufficiency. Eur J Endocrinol 109:1657, 2024. Claahsen-Van Der Grinten HL et al: Congenital adrenal hyperplasia: Current insights in pathophysiology, diagnostics and management. Endocr Rev 43:91, 2022. Debono M et al: Home waking salivary cortisone to screen for adrenal insufficiency. NEJM Evid 2:EVIDoa2200182, 2023. Fassnacht M et al: European Society of Endocrinology clinical prac­ tice guidelines on the management of adrenal incidentalomas, in collaboration with the European Network for the Study of Adrenal Tumors. Eur J Endocrinol 189:G1, 2023.

13 - 399 Pheochromocytoma

399 Pheochromocytoma

Fleseriu M et al: Consensus on diagnosis and management of Cushing’s disease: A guideline update. Lancet Diabetes Endocrinol 9:847, 2021. Hahner S et al: Adrenal insufficiency. Nat Rev Dis Primers 7:19, 2021. Merke DP et al: Modified-release hydrocortisone in congenital adre­ nal hyperplasia. J Clin Endocrinol Metab 106:e2063, 2021. Prete A et al: Prevention of adrenal crisis: Cortisol responses to major stress compared to stress dose hydrocortisone delivery. J Clin Endo­ crinol Metab 105:2262, 2020. Prete A et al: Cardiometabolic disease burden and steroid excretion in benign adrenal tumors: A cross-sectional multicenter study. Ann Intern Med 175:325, 2022. Wu X et al: [11C]metomidate PET-CT versus adrenal vein sampling for diagnosing surgically curable primary aldosteronism: a prospective, within-patient trial. Nat Med 29:190, 2023. Frederic Castinetti,

Hartmut P. H. Neumann

Pheochromocytoma Pheochromocytomas and paragangliomas (PPGLs) are catecholamineproducing tumors derived from the sympathetic or parasympathetic nervous system. These tumors may arise sporadically or be inherited as features of multiple endocrine neoplasia type 2 (MEN 2), von Hippel–Lindau (VHL) disease, or several other pheochromocy­ toma-associated syndromes. The diagnosis of pheochromocytomas identifies a potentially correctable cause of hypertension, and their removal can prevent hypertensive crises that can be lethal. The clini­ cal presentation is variable, ranging from an adrenal incidentaloma to a hypertensive crisis with associated cerebrovascular or cardiac complications. Given the wide range of clinical signs, diagnosis may be delayed for years. ■ ■EPIDEMIOLOGY The incidence of PPGL ranges from 0.04 to 0.95 cases per 100,000 per year, with a gradual increase over time probably due to genetic familial screening, changes in imaging modalities, and more frequent A Adrenal pheochromocytoma B Extra-adrenal pheochromocytoma C Head and neck paraganglioma FIGURE 399-1  The paraganglial system and topographic sites (in red) of pheochromocytomas and paragangliomas. (Parts A and B reproduced with permission from WM Manger, RW Gifford: Clinical and experimental pheochromocytoma. Cambridge: Blackwell Science; 1996.)

diagnosis as an incidentaloma. About ~0.1% of hypertensive patients harbor a pheochromocytoma. The mean age at diagnosis is ~40 years, although the tumors can be detected from early childhood, particularly when genetically determined, until late in life. The classic “rule of tens” for pheochromocytomas states that ~10% are bilateral, 10% are extraadrenal, and 10% are metastatic.

■ ■ETIOLOGY AND PATHOGENESIS PPGLs are well-vascularized tumors that arise from cells derived from the sympathetic (e.g., adrenal medulla or sympathetic trunk) or para­ sympathetic (e.g., carotid body, glomus tympanicum, glomus jugulare, glomus vagale) paraganglia (Fig. 399-1). The name pheochromocytoma reflects the formerly used black-colored staining caused by chromaffin oxidation of catecholamines. The World Health Organization (WHO) applies the term pheochromocytoma to adrenal tumors (usually secret­ ing) and the term paraganglioma to tumors at all other sites including head and neck, thoracic, extra-adrenal retroperitoneal, and pelvic sites. Pheochromocytoma CHAPTER 399 The etiology of sporadic PPGLs is unknown. However, 25–33% of patients have an inherited condition, including germline mutations in the classically recognized RET (rearranged during transfection), VHL, NF1 (neurofibromatosis type 1), SDHB, SDHC, and SDHD (subunits of SDH) genes or in the more recently recognized SDHA, SDHAF2, TMEM127 (transmembrane protein 127), MAX (myc-associated factor X), FH (fumarate hydratase), PDH1, PDH2 (pyruvate dehydro­ genase), HIF1α and HIF2α (hypoxia-inducible factor), MDH2 (malate dehydrogenase), KIF1Bβ (kinesin family member), IDH1, (isocitrate dehydrogenase 1), SLC25A11 (oxoglutarate/malate), H-RAS (trans­ forming protein p21), and DNMTA3 (DNA methyltransferase 3 alpha) genes. Biallelic gene inactivation, a characteristic of tumor-suppressor genes, has been demonstrated for the VHL, NF1, SDHx, TMEM127, MAX, FH, PDH1, PDH2, MDH2, and KIF1Bβ genes. In contrast, RET is a protooncogene, and mutations activate receptor tyrosine kinase activity. Succinate dehydrogenase (SDH) is an enzyme of the Krebs cycle and the mitochondrial respiratory chain. The VHL protein is a component of a ubiquitin E3 ligase. VHL mutations reduce protein degradation, resulting in upregulation of components involved in cellcycle progression, glucose metabolism, and oxygen sensing. In addition to germline mutations, somatic mutations have been observed in >20 genes, broadly grouped into three different clusters of pathogenetically relevant genes: cluster 1, the pseudohypoxia group comprising mainly the genes SDHx (subunits of SDH), FH, VHL, and HIF2A; cluster 2, the kinase signaling group (RET, NF1, TMEM127, MAX, HRAS, KIF1Bβ, PDH); and cluster 3, the Wnt signaling group (CSDE1, MAML3). Vagus n. Tympanic n. Jugular p. Jugular ganglion Nodose ganglion Jugular v. Intravagal p. Glossopharyngeal n. Sup. laryngeal a. Intercarotid p. Sup. laryngeal p. Int. laryngeal a. Inf. laryngeal p. Recurrent laryngeal n. Aorticopulmonary p. Coronary p. Subclavian p. Pulmonary p. Descending aorta

TABLE 399-1  Clinical Features Associated with Pheochromocytoma, Listed by Frequency of Occurrence

  1. Headaches
  2. Profuse sweating
  3. Palpitations and tachycardia
  4. Hypertension, sustained or
  5. Weight loss
  6. Paradoxical response to antihypertensive drugs
  7. Polyuria and polydipsia
  8. Constipation
  9. Orthostatic hypotension
  10. Dilated cardiomyopathy
  11. Erythrocytosis
  12. Elevated blood sugar
  13. Hypercalcemia paroxysmal
  14. Anxiety and panic attacks
  15. Pallor
  16. Nausea
  17. Abdominal pain
  18. Weakness PART 12 Endocrinology and Metabolism ■ ■CLINICAL FEATURES Its clinical presentation is so variable that pheochromocytoma has been termed “the great masquerader” (Table 399-1). Among the presenting manifestations, episodes of palpitation, headache, and profuse sweating are typical, and these manifestations constitute a classic triad that is seen in roughly a third of patients with pheochromocytoma. The pres­ ence of all three manifestations in association with hypertension makes pheochromocytoma a likely diagnosis. However, a pheochromocytoma can be asymptomatic for years or can be identified through imaging screening in a patient presenting with a hereditary syndrome. Some tumors grow to a considerable size before patients note symptoms. The dominant sign is hypertension. Classically, patients have episodic hypertension, but sustained hypertension is also common. Catecholamine crises can lead to heart failure, pulmonary edema, arrhythmias, and intracranial hemorrhage. During episodes of hor­ mone release, which can occur at widely divergent intervals, patients are anxious and pale, and they experience tachycardia and palpita­ tions. These paroxysms generally last <1 h and may be precipitated by surgery, positional changes, exercise, pregnancy, urination (particularly with bladder pheochromocytomas), and various medications (e.g., tri­ cyclic antidepressants, opiates, metoclopramide). Patients may present with true panic attacks that may be mistakenly attributed to psychiatric illness. ■ ■DIAGNOSIS The diagnosis is based on documentation of catecholamine excess by biochemical testing and localization of the tumor by imaging. These two criteria are of equal importance, although measurement of cat­ echolamines or metanephrines (their methylated metabolites) is tradi­ tionally the first step in diagnosis. Biochemical Testing  PPGLs synthesize and store catecholamines, which include norepinephrine (noradrenaline), epinephrine (adrena­ line), and dopamine. Elevated plasma and urinary levels of catechol­ amines and metanephrines form the cornerstone of diagnosis. The characteristic fluctuations in the hormonal activity of tumors result in considerable variation in serial catecholamine measurements. How­ ever, most tumors continuously leak O-methylated metabolites, which are detected by measurement of metanephrines. Catecholamines and metanephrines can be measured by differ­ ent methods, including high-performance liquid chromatography, enzyme-linked immunosorbent assay, and liquid chromatography/ mass spectrometry. When pheochromocytoma is suspected on clinical grounds (i.e., when values are three times the upper limit of normal), this diagnosis is highly likely regardless of the assay used. However, as summarized in Table 399-2, the sensitivity and specific­ ity of available biochemical tests vary greatly, and these differences are important in assessing patients with borderline elevations of different compounds. Urinary tests for metanephrines (total or fractionated) and catecholamines are widely available and are used commonly for initial evaluation. Among these tests, those for the fractionated metanephrines and catecholamines are the most sensi­ tive. Plasma tests are more convenient and include measurements of catecholamines and metanephrines. Measurements of plasma

TABLE 399-2  Biochemical and Imaging Methods Used for Diagnosis of Pheochromocytoma and Paraganglioma DIAGNOSTIC METHOD SENSITIVITY SPECIFICITY 24-h urinary tests       Catecholamines +++ +++   Fractionated metanephrines ++++ ++   Total metanephrines +++ ++++ Plasma tests       Catecholamines +++ ++   Free metanephrines ++++ +++ Imaging       CT ++++ +++   MRI ++++ +++ MIBG scintigraphy ++ ++++ Somatostatin receptor scintigraphya ++ ++ 18Fluoro-DOPA PET/CT ++++ ++++ 68Gallium-DOTATOC or DOTATATE PET/CT ++++ ++++ aValues are particularly high in head and neck paragangliomas. Abbreviations: CT, computed tomography; MIBG, metaiodobenzylguanidine; MRI, magnetic resonance imaging; PET/CT, positron emission tomography plus CT. For the biochemical tests, the ratings correspond globally to sensitivity and specificity rates as follows: ++, <85%; +++, 85–95%; and ++++, >95%. metanephrines are the most sensitive and are less susceptible to falsepositive elevations from stress, including venipuncture. Although the incidence of false-positive test results has been reduced by the introduction of newer assays, physiologic stress responses and medications that increase catecholamine levels still can confound testing. Because the tumors are relatively rare, borderline elevations are likely to represent false-positive results. In this circumstance, it is important to exclude dietary or drug-related factors (withdrawal of levodopa or use of sympathomimetics, diuretics, tricyclic antidepres­ sants, alpha and beta blockers) that might cause false-positive results and then to repeat testing. Diagnostic Imaging  A variety of methods have been used to local­ ize PPGLs (Table 399-2, Figs. 399-2, 399-3, and 399-4). Computed tomography (CT) and magnetic resonance imaging (MRI) are similar in sensitivity and should be performed with contrast. T2-weighted MRI with gadolinium contrast is optimal for detecting pheochromocytomas and is somewhat better than CT for imaging extra-adrenal PPGLs. About 5% of adrenal incidentalomas, which usually are detected by CT or MRI, prove to be pheochromocytomas upon endocrinologic evaluation, but the presence of pheochromocytomas is unlikely if unenhanced CT reveals an attenuation of <10 Hounsfield units (HU). Tumors also can be localized by procedures using radioactive tracers, including 131I- or 123I-metaiodobenzylguanidine (MIBG) scintigraphy, 18F-DOPA positron emission tomography (PET), 68Ga-DOTATATE PET, or 18F-fluorodeoxyglucose (FDG) PET (Fig. 399-2B and 399-4A and B). For PET-CT with both 68Ga-DOTATATE and 18F-DOPA, the sensitivity and specificity are very high (>95%). These agents are par­ ticularly useful in the documentation of hereditary syndromes but also in metastatic pheochromocytoma, because uptake is exhibited also in paragangliomas and metastases. Pathology  PPGLs are found at the classical sites of the adrenal medulla (Fig. 399-2) and paraganglia (Fig. 399-3). Histologically, the tumors often show a characteristic “Zellballen” pattern, consisting of nests of neuroendocrine chief cells with peripheral glial-like susten­ tacular cells. However, a broad spectrum of architectural and cytologic features can be seen. Immunohistochemistry is positive for chromo­ granin and synaptophysin in the chief cells and S-100 in the susten­ tacular cells (Fig. 399-5A–D). Increasingly, staining with antibodies against the proteins encoded by susceptibility genes for hereditary pheochromocytomas, such as SDHB, is used to histologically demon­ strate defects of these proteins, thereby making germline mutations more likely (Fig. 399-5E and F).

A B FIGURE 399-2  Typical pheochromocytoma (adrenal unilateral). A. Magnetic resonance imaging. B. 18F-DOPA positron emission tomography (PET). Tumor marked by arrows. (Part A was provided courtesy of Dr. Tobias Krauss, Freiburg. Part B was provided courtesy of Dr. Juri Ruf, Freiburg.) Differential Diagnosis  When the possibility of a pheochromocy­ toma is being entertained, other disorders to consider include essential hypertension, anxiety attacks, use of cocaine or amphetamines, mastocy­ tosis or carcinoid syndrome (usually without hypertension), intracranial lesions, clonidine withdrawal, autonomic epilepsy, and factitious crises (usually from use of sympathomimetic amines). When an asymptomatic adrenal mass is identified, likely diagnoses other than pheochromocy­ toma include a nonfunctioning adrenal adenoma, an aldosteronoma, and a cortisol-producing adenoma (Cushing’s syndrome). ■ ■TREATMENT Complete tumor removal, the ultimate therapeutic goal, can be achieved by partial or total adrenalectomy. It is important to preserve A C D FIGURE 399-3  Paragangliomas (extra-adrenal pheochromocytomas). A. Carotid body tumor. B. Thoracic tumor. C. Paraaortal tumor. D. Pelvic tumor at the anterior wall of the urinary bladder. Tumors marked by arrows. (Part A was provided courtesy of Dr. Carsten Boedeker, Stralsund. Parts B and D were provided courtesy of Dr. Tobias Krauss, Freiburg. Part C was provided courtesy of Dr. Martin Walz, Essen.)

Pheochromocytoma CHAPTER 399 the normal adrenal cortex in order to prevent Addison’s disease, particularly in hereditary disorders in which bilateral pheochro­ mocytomas are most likely. Preoperative preparation of the patient has to be considered, and blood pressure should be consistently <160/90 mmHg. Classically, blood pressure has been controlled by α-adrenergic blockers (oral phenoxybenzamine, 0.5–4 mg/kg

of body weight). Because patients are volume-constricted, liberal salt intake and hydration are necessary to avoid severe orthostasis. Oral prazosin or intravenous phentolamine can be used to manage parox­ ysms while adequate alpha blockade is awaited. Beta blockers (e.g., 10 mg of propranolol three or four times per day) should not be used as first-line treatment because of the risk of increased hyper­ tension. Other antihypertensives, such as calcium channel blockers B

PART 12 Endocrinology and Metabolism FIGURE 399-4  Multiple and metastatic pheochromocytoma. A. Paraganglioma syndrome. A patient with the SDHD W5X mutation and PGL1 68Ga-DOTATATE positron emission tomography (PET) demonstrating tumor uptake in the right jugular glomus, the right and left carotid body, both adrenal glands, and an interaortocaval paraganglion (arrows). Note the physiologic accumulation of the radiopharmaceutical agent in the kidneys and the liver. B. 18F-DOPA PET of a patient with metastatic pheochromocytoma. Several metastases marked by arrows. (Parts A and B were provided courtesy of Dr. Juri Ruf, Freiburg.) A C B D E F FIGURE 399-5  Histology and immunohistochemistry of pheochromocytoma. A. Hematoxylin and eosin, B. chromogranin, C. synaptophysin, C and B stain chief cells; D. S-100 stains sustentacular cells. E, F. Immunohistochemistry with SDHB antibody: positive staining (granular cytoplasmic staining) indicates intact SDHB (E), whereas negative staining (endothelial cells positive as internal control) (F) indicates structurally changed or absent SDHB due to a germline mutation in the SDHB gene, which was confirmed by molecular genetic analysis of a blood sample. (Parts A–D and F were used with permission from Dr. Helena Leijon, Helsinki. Part E was provided courtesy of Dr. Kurt Werner Schmid, Essen.) A B

or angiotensin-converting enzyme inhibitors, have also been used effectively. Surgery should be performed by teams of surgeons and anesthesi­ ologists with experience in the management of pheochromocytomas. Blood pressure can be labile during surgery, particularly at the outset of intubation or when the tumor is manipulated. Nitroprusside infusion is useful for intraoperative hypertensive crises, and hypotension usually responds to volume infusion. The latter side effect can, however, be avoided in normotensive pheochromocytoma patients by having only standby intraoperative nitroprusside, which has been shown to be safe and avoids postoperative hypotension often caused by alpha blockers. The long-lasting guideline for obligatory preoperative treatment with alpha blockers is under discussion and seemingly not needed. Minimally invasive techniques (laparoscopy or retroperitoneos­ copy) have become the standard approaches in pheochromocytoma surgery. They are associated with fewer complications, a faster recov­ ery, and optimal cosmetic results. Extra-adrenal abdominal and most thoracic pheochromocytomas can also be removed endoscopically. In this setting, adrenal sparing surgery should be considered. Post­ operatively, catecholamine normalization should be documented. An adrenocorticotropic hormone (ACTH) test should be used to exclude cortisol deficiency when bilateral adrenal cortex–sparing surgery has been performed. Head and neck paragangliomas are a challenge for surgeons, since damage of adjacent tissue, mainly vessels or cranial nerves II, VII, IX, X, XI, and XII, is a frequent permanent side effect. Careful con­ sideration of best management is important, and radiotherapy may be an alternative, especially for large head and neck paragangliomas. Tympanic paragangliomas are symptomatic early, and most of these tumors can easily be resected, with subsequent improvement of hear­ ing and alleviation of tinnitus. Asymptomatic paraganglial tumors, now often detected in patients with hereditary tumors and their rela­ tives, are challenging to manage. Watchful waiting strategies have been introduced, but they should consider any genetic syndrome, such as SDHB, that might be associated with a higher degree of malignancy (see below). ■ ■METASTATIC PHEOCHROMOCYTOMA About 5–10% of PPGLs are metastatic. The diagnosis of malignant pheochromocytoma is problematic. The typical histologic criteria of cellular atypia, presence of mitoses, and invasion of vessels or adjacent tissues are insufficient for the diagnosis of malignancy in pheochro­ mocytoma. Size >5 cm, high pheochromocytoma of the adrenal gland scaled score (PASS) and grading system for adrenal pheochromocy­ toma and paraganglioma (GAPP) score, and SDHB-positive status have been considered as markers of risk of recurrence, but they remain controversial. Thus, the term malignant pheochromocytoma has been replaced by metastatic pheochromocytoma as suggested by the WHO and is restricted to tumors with lymph node or distant metastases, the latter most commonly found by nuclear medicine imaging in lungs, bone, or liver locations, suggesting a vascular pathway of spread (Fig. 399-4B). Because hereditary syndromes are associated with multifocal tumor sites, these features should be anticipated in patients with germ­ line mutations, especially of SDHB, SDHD, VHL, and RET. However, distant metastases also occur in these syndromes, especially in carriers of SDHB mutations. Treatment of metastatic pheochromocytoma or paraganglioma is challenging. Options include tumor mass reduction, alpha blockers for symptoms, chemotherapy including tyrosine kinase inhibitors, nuclear medicine radiotherapy, and stereotactic radiation. Nuclear medicine therapy is the treatment of choice for scintigraphically documented metastases, preferably with 131I-MIBG in 100–300 mCi doses over 3–6 cycles, or somatostatin receptor ligands, e.g., DOTATOC labeled with yttrium-90 or lutetium-177. Averbuch’s chemotherapy protocol includes dacarbazine (600 mg/m2 on days 1 and 2), cyclophospha­ mide (750 mg/m2 on day 1), and vincristine (1.4 mg/m2 on day 1), all repeated every 21 days for 3–6 cycles. Palliation (stable disease to shrinkage) is achieved in about one-half of patients. Due to increasing insights in the genetics of pheochromocytoma and their molecular

pathways, new targeted chemotherapeutic options such as sunitinib and temozolomide are under investigation. The prognosis of metastatic pheochromocytoma or paraganglioma is variable, with 5-year survival rates of 30–60%.

■ ■PHEOCHROMOCYTOMA IN PREGNANCY Pheochromocytomas occasionally are diagnosed in pregnancy and can be very challenging to manage. The pathogenesis of adrenergic crises during pregnancy in previously asymptomatic women might be linked to human chorionic gonadotropin (hCG)-induced stimulation of epinephrine production by pheochromocytoma, as some of these express luteinizing hormone/chorionic gonadotropin (LHCG) recep­ tors. Endoscopic removal, preferably in the fourth to sixth month of gestation, is possible and can be followed by uneventful childbirth. Regular screening in families with inherited pheochromocytomas pro­ vides an opportunity to identify and remove such tumors in women of reproductive age. Pheochromocytoma CHAPTER 399 ■ ■PHEOCHROMOCYTOMA-ASSOCIATED SYNDROMES About 25–33% of patients with a PPGL have an inherited syndrome. At diagnosis, patients with inherited syndromes are a mean of ~15 years younger than patients with sporadic tumors. The best-known pheochromocytoma-associated syndrome is the autosomal dominant disorder MEN 2 (Chap. 400). Both types of MEN 2 (2A and 2B) are caused by mutations in RET, which encodes a tyrosine kinase. The locations of RET mutations correlate with the age of disease onset, the aggressiveness, and the type of MEN 2 (Chap. 400). MEN 2A is characterized by medullary thyroid carci­ noma (MTC), pheochromocytoma, and hyperparathyroidism. MEN 2B also includes MTC (more aggressive than in MEN 2A), pheochro­ mocytoma, and multiple mucosal neuromas, marfanoid habitus, and other developmental disorders, although it typically lacks hyperpara­ thyroidism. MTC is found in virtually all patients with MEN 2, but pheochromocytoma occurs in only ~50% of these patients. Nearly all pheochromocytomas in MEN 2 are benign and located in the adrenals, often bilaterally. Pheochromocytoma may be symptomatic before the diagnosis of MTC is made. Prophylactic thyroidectomy is being per­ formed in many carriers of RET mutations, and the recommended age to perform thyroidectomy usually depends on the mutation and/or the level of calcitonin; pheochromocytomas should be excluded before any surgery in these patients. VHL is an autosomal dominant disorder that predisposes to retinal and cerebellar hemangioblastomas, which also occur in the brainstem and spinal cord (Fig. 399-6). Other important features of VHL are clear cell renal carcinomas, pancreatic neuroendocrine tumors, endo­ lymphatic sac tumors of the inner ear, cystadenomas of the epididymis and broad ligament, and multiple pancreatic or renal cysts. Although the VHL gene can be inactivated by all types of mutations, patients with pheochromocytoma predominantly have missense mutations. About 20–30% of patients with VHL have pheochromocytomas, but in some families, the incidence can reach 90%. The recognition of pheo­ chromocytoma as a VHL-associated feature provides an opportunity to diagnose retinal, central nervous system, renal, and pancreatic tumors at a stage when effective treatment may still be possible. NF1 was the first described pheochromocytoma-associated syn­ drome. The NF1 gene functions as a tumor suppressor by regulating the Ras signaling cascade. Classic features of neurofibromatosis include multiple neurofibromas, café au lait spots, axillary freckling of the skin, and Lisch nodules of the iris. Pheochromocytomas occur in only ~1% of these patients and are located predominantly in the adrenals. Meta­ static pheochromocytoma is not uncommon in NF1. The paraganglioma syndromes (PGLs) have been classified by genetic analyses of families with head and neck paragangliomas. The susceptibility genes encode subunits of the enzyme SDH, a component in the Krebs cycle and the mitochondrial electron transport chain. SDH is formed by four subunits (A–D). Mutations of SDHA (PGL5), SDHB (PGL4), SDHC (PGL3), SDHD (PGL1), and SDHAF2 (PGL2) predispose to the PGLs. The transmission of the disease in carriers of

PART 12 Endocrinology and Metabolism A C E G H D F B FIGURE 399-6  von Hippel–Lindau disease. Tumors and cysts marked by arrows. A. Retinal angioma (arrows with a pair of feeding vessels). All subsequent panels show findings on magnetic resonance imaging. B–D. Hemangioblastomas of the cerebellum (large cyst and a solid mural tumor) (B) in brainstem (in part cystic) (C) and spinal cord (thoracic) (D). E. Bilateral renal clear cell carcinomas with two tumors on each side F. Multiple pancreatic cysts. G. Microcystic serous pancreatic cystadenoma (with multiple tiny spaces). H. Two pancreatic islet cell tumors. (Part A was provided courtesy of Dr. Dieter Schmidt. Part B was provided courtesy of Dr. Christian Taschner, Freiburg. Part C was provided courtesy of Dr. Sven Glaesker, Brussels. Part D was used with permission from Dr. Jan-Helge Klingler, Freiburg. Part E was provided courtesy of Dr. Cordula Jilg, Freiburg. Parts F–H were provided courtesy of Dr. Tobias Krauss, Freiburg.) SDHA, SDHB, and SDHC germline mutations is autosomal dominant. In contrast, in virtually all SDHD and SDHAF2 families, only the prog­ eny of affected fathers develops tumors if they inherit the mutation. PGL1 is most common, followed by PGL4; PGL2, PGL3, and PGL5 are rare. Adrenal, extra-adrenal abdominal, and thoracic pheochro­ mocytomas, which are components of PGL1, PGL4, and PGL5, are rare in PGL3 and absent in PGL2 (Fig. 399-4A). About one-third of patients with PGL4 develop metastases, which is the highest rate in pheochromocytoma-associated syndromes. However, the penetrance of the disease is usually low, raising questions about the optimal way to monitor asymptomatic carriers on a long-term basis. Other syndromes with metastatic pheochromocytomas are mainly VHL, NF1, and PGL1. Other familial pheochromocytoma has been attributed to heredi­ tary, mainly adrenal tumors in patients with germline mutations in the genes TMEM127 and MAX. Transmission is also autosomal domi­ nant, and mutations of MAX, like those of SDHD, cause tumors only if inherited from the father. Pituitary neuroendocrine tumors have been described as an association with SDHx (pituitary adenoma and pheochromocytoma/paraganglioma 3PA syndrome) as well as MAX mutations (MEN 5), but they seem to occur very rarely. ■ ■GENETIC SCREENING OF PATIENTS WITH PHEOCHROMOCYTOMA OR PARAGANGLIOMA Universal germline panel testing is now the gold standard to char­ acterize the genetic factors involved in PPGL. It usually identifies a genetic etiology in up to 30% of the cases. This rate can be even higher in patients with early age of onset, extra-adrenal location, multiple tumors, metastatic tumors, or family history of PPGL. Effective pre­ ventive medicine for pheochromocytoma and pheochromocytomaassociated diseases requires management according to identified germline mutations in susceptibility genes (Table 399-3). Because of the relatively high prevalence of familial syndromes among patients who present with pheochromocytoma or paraganglioma, it is useful to identify germline mutations even in patients without a known family history. Despite the use of a universal germline panel testing performed for all patients with a PPGL, a first step remains to search for clinical features of inherited syndromes and to obtain an in-depth, multigen­ erational family history. Each of these syndromes exhibits autosomal dominant transmission with variable penetrance, but a proband with a mother affected by paraganglial tumors is not predisposed to PLG1 and PGL2 (SDHD and SDHAF2 mutation carrier). Cutaneous neurofi­ bromas, café au lait spots, and axillary freckling suggest neurofibroma­ tosis. Germline mutations in NF1 have nearly never been reported in patients with sporadic pheochromocytomas. Thus, NF1 testing is not needed in the absence of other clinical features of neurofibromatosis. A personal or family history of MTC or an elevation of serum calcitonin strongly suggests MEN 2 and should prompt testing for RET muta­ tions. A history of visual impairment or tumors of the cerebellum, brainstem, spinal cord, or the kidney suggests the possibility of VHL. A personal and/or family history of head and neck paraganglioma suggests PGL1 or PGL4. Of note, sequencing protocols may not detect large deletions of one or more exons.

14 - 400 Multiple Endocrine Neoplasia Syndromes

400 Multiple Endocrine Neoplasia Syndromes

TABLE 399-3  Patterns of Occurrence in Inherited Pheochromocytoma and Paraganglioma–Associated Syndromes EXTRA-ADRENAL RETROPERITONEAL OR PELVIC TUMORS MUTATED GENE ADRENAL TUMORS HEAD AND NECK TUMORS MAX +++++ <x + <x +++++ ++++ ++ +++ NF1 +++++ <+ + <+ + ++ + ++ RET +++++ <+ <+ <+ ++++ ++++ <+ + SDHA ++ ++++ ++ + + <+ + + SDHB ++++ +++ +++ + ++ <+ +++ ++ SDHC <+ +++++ <+ + + <+ <+ ++ SDHD ++ +++++ + + ++++ <+ + +++ VHL +++++ <+ + + ++++ +++ + ++++ TMEM127 +++++ + + + ++ ++ <+ + Note: Frequencies in percentage (<+: 0–4%; +: 5–19%; ++: 20–39%; +++: 40–59%; ++++: 60–79%; +++++: 80–100%) of clinical characteristics of pheochromocytomas/ paragangliomas of patients with germline mutations of the genes MAX, NF1, RET, SDHA, SDHB, SDHC, SDHD, VHL, and TMEM127; for other genes, the data are too limited to include in this summary. A single adrenal pheochromocytoma in a patient with an otherwise unremarkable history may still be associated with mutations of VHL, RET, SDHB, or SDHD (in decreasing order of frequency). Two-thirds of extra-adrenal tumors are associated with one of these syndromes, and multifocal tumors occur with decreasing frequency in carriers of RET, SDHD, VHL, SDHB, and MAX mutations. About 30% of head and neck paragangliomas are associated with germline mutations of one of the SDH subunit genes (most often SDHD) and are rare in carriers of VHL, RET, MAX, and TMEM127 mutations. Immunohistochemistry is helpful in the preselection of hereditary pheochromocytoma. Negative immunostaining with antibodies to SDHB (Fig. 399-5F), TMEM127, and MAX may predict mutations of the SDHx (PGL1-5), TMEM127, and MAX genes, respectively. Once the underlying syndrome is diagnosed, the benefit of genetic testing can be extended to relatives. For this purpose, it is necessary to identify the germline mutation in the proband and, after genetic counseling, to perform DNA sequence analyses of the responsible gene in relatives to determine whether they are affected. Other family mem­ bers may benefit when individuals who carry a germline mutation are biochemically screened for paraganglial tumors. ■ ■FUTURE PERSPECTIVES About 15% of sporadic PPGLs present with recurrence, including some ocurring >10 years after initial management; this rate is higher in genetically determined PPGL. Defining the clinical outcome of a PPGL remains difficult, and machine learning models including several fac­ tors might be helpful in the future to personalize the follow-up of these patients. The recent American Joint Committee on Cancer tumornode-metastasis classification could help select patients at risk of recur­ rence. The pathogenesis of PPGL remains imperfectly understood, and as for other endocrine tumors, microenvironment and immune cells might influence PPGL aggressiveness or metastatic behavior; they could also constitute some new therapeutic targets in the future. ■ ■FURTHER READING Al Subhi AR et al: Systematic review: Incidence of pheochromocy­ toma and paraganglioma over 70 years. J Endocr Soc 6:bvac105, 2022. Amar L et al: International consensus on initial screening and followup of asymptomatic SDHx mutation carriers. Nat Rev Endocrinol 17:435, 2021. Bancos I et al: Maternal and fetal outcomes in pheochromocytoma and pregnancy: A multi-center retrospective cohort study and sys­ tematic review of literature. Lancet Diabetes Endocrinol 2021; 9:13. Calsina B et al: Genomic and immune landscape of metastatic pheo­ chromocytoma and paraganglioma. Nat Commun 14:1122, 2023. Castinetti F et al: Controversies about the systematic preoperative pharmacological treatment before pheochromocytoma or paragan­ glioma surgery. Eur J Endocrinol 186:D17, 2022. Horton C et al: Universal germline panel testing for individuals with pheochromocytoma and paraganglioma produces high diagnostic yield. J Clin Endocrinol Metab 107:e1917, 2022.

BILATERAL ADRENAL TUMORS FAMILY HISTORY IN PROBANDS FOR COMPONENTS OF THE GIVEN SYNDROME THORACIC TUMORS MULTIPLE

TUMORS METASTATIC TUMORS Multiple Endocrine Neoplasia Syndromes CHAPTER 400 Lenders JW et al: Genetics, diagnosis, management and future direc­ tions of research of phaeochromocytoma and paraganglioma: A posi­ tion statement and consensus of the Working Group on Endocrine Hypertension of the European Society of Hypertension. J Hypertens 38:1443, 2020. Lopez AG et al: Expression of LHCGR in pheochromocytomas unveils an endocrine mechanism connecting pregnancy and epi­ nephrine overproduction. Hypertension 79:1006, 2022. Neumann HPH et al: Comparison of pheochromocytoma-specific morbidity and mortality among adults with bilateral pheochromocy­ tomas undergoing total adrenalectomy vs cortical-sparing adrenalec­ tomy. JAMA Netw Open 2:e198898, 2019. Pamporaki C et al: Prediction of metastatic pheochromocytoma and paraganglioma: A machine learning modelling study using data from a cross-sectional cohort. Lancet Digit Health 5:e551, 2023. Taïeb D et al: European Association of Nuclear Medicine Practice Guideline/Society of Nuclear Medicine and Molecular Imaging Procedure Standard 2019 for radionuclide imaging of phaeochromo­ cytoma and paraganglioma. Eur J Nucl Med Mol Imaging 46:2112, 2019. Taïeb D et al: Clinical consensus guideline on the management of phaeochromocytoma and paraganglioma in patients harbouring germline SDHD pathogenic variants. Lancet Diabetes Endocrinol 11:345, 2023. Rajesh V. Thakker

Multiple Endocrine

Neoplasia Syndromes Multiple endocrine neoplasia (MEN) is characterized by a predilection for tumors involving two or more endocrine glands. Five major forms of MEN are recognized and referred to as MEN types 1–5 (MEN 1–5) (Table 400-1). Each type of MEN is inherited as an autosomal domi­ nant syndrome or may occur sporadically, that is, without a family history. However, this distinction between familial and sporadic forms is often difficult because family members with the disease may have died before symptoms developed. In addition to MEN 1–5, at least six other syndromes are associated with multiple endocrine and other organ neoplasias (MEONs) (Table 400-2). These MEONs include the hyperparathyroidism-jaw tumor (HPT-JT) syndrome, Carney com­ plex, von Hippel–Lindau disease (Chap. 399), neurofibromatosis

TABLE 400-1  Multiple Endocrine Neoplasia (MEN) Syndromes TYPE (CHROMOSOMAL LOCATION) GENE AND MOST FREQUENTLY MUTATED CODONS TUMORS (ESTIMATED PENETRANCE) MEN 1 (11q13) Parathyroid adenoma (90%) Enteropancreatic tumor (30–70%) • Gastrinoma (>50%) • Insulinoma (10–30%) • Nonfunctioning and PPoma MEN1 83/84, 4-bp del (≈4%) 119, 3-bp del (≈3%) 209-211, 4-bp del (≈8%) 418, 3-bp del (≈4%) 514-516, del or ins (≈7%) Intron 4 ss (≈10%) (20–55%) • Glucagonoma (<3%) • VIPoma (<1%) Pituitary adenoma (15–50%) • Prolactinoma (60%) • Somatotrophinoma (25%) • Corticotrophinoma (<5%) • Nonfunctioning (<5%) Associated tumors • Adrenal cortical tumor (20–70%) • Pheochromocytoma (<1%) • Bronchopulmonary NET (2%) • Thymic NET (2%) • Gastric NET (10%) • Lipomas (>33%) • Angiofibromas (85%) • Collagenomas (70%) • Meningiomas (8%) PART 12 Endocrinology and Metabolism MEN 2 (10 cen-10q11.2)   MEN 2A     MTC (90%) Pheochromocytoma (>50%) Parathyroid adenoma (10–25%)   RET 634, e.g., Cys → Arg (~85%)   MTC only MTC (100%) RET 618, missense (>50%)   MEN 2B (also MTC (>90%) Pheochromocytoma (>50%) Associated abnormalities (40–50%) • Mucosal neuromas • Marfanoid habitus • Medullated corneal nerve RET 918, Met → Thr (>95%) known as MEN 3) fibers • Megacolon MEN 4 (12p13)         Parathyroid adenomaa CDKN1B; no common mutations identified to date     Pituitary adenomaa Reproductive organ tumorsa (e.g., testicular cancer, neuroendocrine cervical carcinoma) ?Adrenal + renal tumorsa MEN5 (14q23.3) Pheochromocytomaa MAX; no common mutations identified to date Pituitary adenomaa Parathyroid adenomas?a Neural crest tumors (e.g., ganglioneuroma, neuroblastoma) (other tumors? – renal cell carcinoma, renal oncocytoma, pancreatic NETs, chondrosarcoma)  aInsufficient numbers reported to provide prevalence information. Note: Autosomal dominant inheritance of the MEN syndromes has been established. Abbreviations: del, deletion; ins, insertion; MTC, medullary thyroid cancer; NET, neuroendocrine tumor; PPoma, pancreatic polypeptide–secreting tumor; VIPoma, vasoactive intestinal polypeptide–secreting tumor. Source: Adapted with permission from Thakker RV. Multiple endocrine neoplasia– syndromes of the twentieth century. J Clin Endocrinol Metab 83:2617, 1998.

TABLE 400-2  Multiple Endocrine and Other Organ Neoplasia (MEON) Syndromes CHROMOSOMAL LOCATION DISEASEa GENE PRODUCT Hyperparathyroidism-jaw tumor (HPT-JT) Parafibromin 1q31.2 Carney complex       CNC1 PRAKAR1A 17q24.2   CNC2 ?b 2p16 von Hippel–Lindau disease (VHL) pVHL (elongin) 3p25 Neurofibromatosis type 1 (NF1) Neurofibromin 17q11.2 Cowden’s syndrome (CWS)       CWS1 PTEN 10q23.31   CWS2 SDHB 1p36.13   CWS3 SDHD 11q23.1   CWS4 KLLN 10q23.31   CWS5 PIK3CA 3q26.32   CWS6 AKT1 14q32.33   CWS7 SEC23B 20p11.23 McCune-Albright syndrome (MAS) Gsα 20q13.32 aThe inheritance for these disorders is autosomal dominant, except MAS, which is due to mosaicism that results from the postzygotic somatic cell mutation of the GNAS1 gene, encoding Gsα. b?, unknown. type 1 (Chap. 95), Cowden’s syndrome (CWS), and McCune-Albright syndrome (MAS) (Chap. 424); all of these are inherited as autoso­ mal dominant disorders, except for MAS, which is caused by mosaic expression of a postzygotic somatic cell mutation (Table 400-2). A diagnosis of a MEN or MEON syndrome may be established in an individual by one of three criteria: (1) clinical features (two or more of the associated tumors [or lesions] in an individual); (2) familial pattern (one of the associated tumors [or lesions] in a firstdegree relative of a patient with a clinical diagnosis of the syndrome); and (3) genetic analysis (a germline mutation in the associated gene in an individual, who may be clinically affected or asymptomatic). Mutational analysis in MEN and MEON syndromes is helpful in clinical practice to (1) confirm the clinical diagnosis; (2) identify family members who harbor the mutation and require screening for relevant tumor detection and early/appropriate treatment; and (3) identify the ~50% of family members who do not harbor the germline mutation and can, therefore, be alleviated of the anxiety of developing associated tumors. This latter aspect also helps to reduce health care costs by reducing the need for unnecessary biochemical and radio­ logic investigations. ■ ■MULTIPLE ENDOCRINE NEOPLASIA TYPE 1 Clinical Manifestations  MEN type 1 (MEN 1), which is also referred to as Wermer’s syndrome, is characterized by the triad of tumors involving the parathyroids, pancreatic islets, and anterior pituitary. In addition, adrenal cortical tumors, carcinoid tumors usually of the fore­ gut, meningiomas, facial angiofibromas, collagenomas, and lipomas may also occur in some patients with MEN 1. Combinations of the affected glands and their pathologic features (e.g., hyperplastic adenomas of the parathyroid glands) may differ in members of the same family and even between identical twins. In addition, a nonfamilial (e.g., sporadic) form occurs in 8–14% of patients with MEN 1, and molecular genetic studies have confirmed the occurrence of de novo mutations of the MEN1 gene in ~10% of patients with MEN 1. The prevalence of MEN 1 is ~0.25% based on randomly chosen postmortem studies but is 1–18% among patients with primary hyperparathyroidism, 16–38% among patients with pancreatic islet tumors, and <3% among patients with pituitary tumors. The disorder affects all age groups, with a reported age range of 5–81 years, with clinical and biochemical manifestations developing in the vast majority by the fifth decade. The clinical manifestations of MEN 1 are related to the sites of tumors and their hormonal products. In the absence of treatment, endocrine tumors are associated with an earlier

TABLE 400-3  Biochemical and Radiologic Screening in Multiple Endocrine Neoplasia Type 1 TUMOR AGE TO BEGIN (YEARS) BIOCHEMICAL TEST (PLASMA OR SERUM) ANNUALLY IMAGING TEST (TIME INTERVAL) Parathyroid

Calcium, PTH None Pancreatic NETs         Gastrinoma

Gastrin (± gastric pH) None   Insulinoma

Fasting glucose, insulin None   Other pancreatic NET <10 Chromogranin A; pancreatic polypeptide, glucagon, vasoactive intestinal peptide Anterior pituitary

Prolactin, IGF-I MRI (every 3 years) Adrenal <10 None unless symptoms or signs of functioning tumor and/or tumor >1 cm identified on imaging Thymic and bronchial carcinoid

None CT or MRI (every 1–2 years) Abbreviations: CT, computed tomography; EUS, endoscopic ultrasound; IGF-I, insulin-like growth factor I; MRI, magnetic resonance imaging; NET, neuroendocrine tumor; PTH, parathyroid hormone. Source: Data from PJ Newey, RV Thakker: Role of multiple endocrine neoplasia type 1 mutational analysis in clinical practice. Endocr Pract 17, 2011 and RV Thakker: Multiple endocrine neoplasia type 1 (MEN1). Translational Endocrinology and Metabolism, Vol 2. Chevy Chase, MD: The Endocrine Society; 2011. mortality in patients with MEN 1, with a 50% probability of death by the age of 50 years. The cause of death is usually a malignant tumor, often from a pancreatic neuroendocrine tumor (NET) or foregut carcinoid. In addition, the treatment outcomes of patients with MEN 1–associated tumors are not as successful as those in patients with non–MEN 1 tumors. This is because MEN 1–associated tumors, with the exception of pituitary NETs, are usually multiple, making it difficult to achieve a successful surgical cure. Occult metastatic disease is also more prevalent in MEN 1, and the tumors may be larger, more aggressive, and resistant to treatment. Parathyroid Tumors (See also Chap. 422)  Primary hyper­ parathyroidism occurs in ~90% of patients and is the most common feature of MEN 1. Patients may have asymptomatic hypercalcemia or vague symptoms associated with hypercalcemia (e.g., polyuria, poly­ dipsia, constipation, malaise, or dyspepsia). Nephrolithiasis and osteitis fibrosa cystica (less commonly) may also occur. Biochemical investiga­ tions reveal hypercalcemia, usually in association with elevated circu­ lating parathyroid hormone (PTH) (Table 400-3). The hypercalcemia is usually mild, and severe hypercalcemia or parathyroid cancer is a rare occurrence. Additional differences in the primary hyperparathy­ roidism of patients with MEN 1, as opposed to those without MEN 1, include an earlier age at onset (20–25 vs 55 years) and an equal maleto-female ratio (1:1 vs 1:3). Preoperative imaging (e.g., neck ultrasound with 99mTc-sestamibi parathyroid scintigraphy) is of limited benefit because all parathyroid glands may be affected, and neck exploration may be required irrespective of preoperative localization studies. TREATMENT Parathyroid Tumors Surgical removal of the abnormally overactive parathyroids in patients with MEN 1 is the definitive treatment, and most special­ ist centers recommend performing a subtotal (e.g., removal of 3.5 glands) parathyroidectomy. Minimally invasive parathyroidec­ tomy is not recommended because all four parathyroid glands are usually affected with multiple adenomas or hyperplasia. Surgical experience should be taken into account given the variability in pathology in MEN 1. Calcimimetics (e.g., cinacalcet), which act via the calcium-sensing receptor, have been used to treat primary hyperparathyroidism in some patients when surgery is unsuccessful or contraindicated. Pancreatic Tumors (See also Chap. 89)  The incidence of pancreatic islet cell tumors, which are NETs, in patients with MEN 1 ranges from 30 to 80% in different series. Most of these tumors (Table 400-1) produce excessive amounts of hormone (e.g., gastrin, insulin, glucagon, vasoactive intestinal polypeptide [VIP]) and are associated with distinct clinical syndromes, although some are nonfunctioning or

MRI, CT, or EUS (annually) Multiple Endocrine Neoplasia Syndromes CHAPTER 400 MRI or CT (annually with pancreatic imaging) nonsecretory. These pancreatic islet cell tumors have an earlier age at onset in patients with MEN 1 than in patients without MEN 1. Gastrinoma  Gastrin-secreting tumors (gastrinomas) are associated with marked gastric acid production and recurrent peptic ulcerations, a combination referred to as Zollinger-Ellison syndrome. Gastrinomas occur more often in patients with MEN 1 who are aged >30 years. Recurrent severe multiple peptic ulcers, which may perforate, and cachexia are major contributors to the high mortality. Patients with Zollinger-Ellison syndrome may also suffer from diarrhea and steat­ orrhea. The diagnosis is established by demonstration of an elevated fasting serum gastrin concentration in association with increased basal gastric acid secretion (Table 400-3). However, the diagnosis of Zollinger-Ellison syndrome may be difficult in hypercalcemic MEN 1 patients because hypercalcemia can also cause hypergastrinemia. Ultrasonography, endoscopic ultrasonography, computed tomography (CT), nuclear magnetic resonance imaging (MRI), selective abdominal angiography, venous sampling, and somatostatin receptor scintigraphy (SRS) are helpful in localizing the tumor prior to surgery. Gastrinomas represent >50% of all pancreatic NETs in patients with MEN 1, and ~20% of patients with gastrinomas will be found to have MEN 1. Gas­ trinomas, which may also occur in the duodenal mucosa, are the major cause of morbidity and mortality in patients with MEN 1. TREATMENT Gastrinoma Medical treatment of patients with MEN 1 and Zollinger-Ellison syndrome is directed toward reducing basal acid output to <10 mmol/L. Parietal cell H+-K+-adenosine triphosphatase (ATPase) inhibitors (e.g., omeprazole or lansoprazole) reduce acid output and are the drugs of choice for gastrinomas. Some patients may also require additional treatment with the histamine H2 receptor antagonists cimetidine or ranitidine. The role of surgery in the treatment of gastrinomas in patients with MEN 1 is controversial. The goal of surgery is to reduce the risk of distant metastatic disease and improve survival. For a nonmetastatic gastrinoma situated in the pancreas, surgical excision is often effective. However, the risk of hepatic metastases increases with tumor size, such that 25–40% of patients with pancreatic NETs >4 cm develop hepatic metastases, and 50–70% of patients with tumors 2–3 cm in size have lymph node metastases. Survival in MEN 1 patients with gastrinomas <2.5 cm in size is 100% at 15 years, but 52% at 15 years, if metastatic disease is present. The presence of lymph node metastases does not appear to adversely affect survival. Surgery for gastrinomas that are >2–2.5 cm has been recommended, because the disease-related survival in these patients is improved following surgery. In addition, duodenal gastrinomas, which occur more frequently in patients with MEN 1, have been treated successfully with surgery. However,

in most patients with MEN 1, gastrinomas are multiple or extrapan­ creatic, and with the exception of duodenal gastrinomas, surgery is rarely successful. For example, the results of one study revealed that only ~15% of patients with MEN 1 were free of disease immediately after surgery, and at 5 years, this number had decreased to ~5%; the respective outcomes in patients without MEN 1 were better, at 45 and 40%. Given these findings, most specialists recommend a nonsurgical management for gastrinomas in MEN 1, except as noted earlier for smaller, isolated lesions. Treatment of dissemi­ nated gastrinomas is difficult. Chemotherapy with streptozotocin and 5-fluorouracil; hormonal therapy with octreotide or lanreotide, which are human somatostatin analogues (SSAs); selected internal radiation therapy (SIRT); radiofrequency ablation; peptide radio receptor therapy (PRRT); hepatic artery embolization; administra­ tion of human leukocyte interferon; and removal of all resectable tumor have been successful in some patients.

PART 12 Endocrinology and Metabolism Insulinoma  These β islet cell insulin-secreting tumors represent 10–30% of all pancreatic tumors in patients with MEN 1. Patients with an insulinoma present with hypoglycemic symptoms (e.g., weakness, headaches, sweating, faintness, seizures, altered behavior, weight gain) that typically develop after fasting or exertion and improve after glucose intake. The most reliable test is a supervised 72-h fast. Biochemical inves­ tigations reveal increased plasma insulin concentrations in association with hypoglycemia (Table 400-3). Circulating concentrations of C pep­ tide and proinsulin, which are also increased, are useful in establishing the diagnosis. It also is important to demonstrate the absence of sulfo­ nylureas in plasma and urine samples obtained during the investigation of hypoglycemia (Table 400-3). Surgical success is greatly enhanced by preoperative localization by endoscopic ultrasonography, CT scanning, or celiac axis angiography. Additional localization methods may include preoperative and perioperative percutaneous transhepatic portal venous sampling, selective intraarterial stimulation with hepatic venous sam­ pling, and intraoperative direct pancreatic ultrasonography. Insulinomas occur in association with gastrinomas in 10% of patients with MEN 1, and the two tumors may arise at different times. Insulinomas occur more often in patients with MEN 1 who are aged <40 years, and some arise in individuals aged <20 years. In contrast, in patients without MEN 1, insu­ linomas generally occur in those aged >40 years. Insulinomas may be the first manifestation of MEN 1 in 10% of patients, and ~4% of patients with insulinomas will have MEN 1. TREATMENT Insulinoma Medical treatment, which consists of frequent carbohydrate meals and diazoxide or octreotide, is not always successful, and surgery is the optimal treatment. Surgical treatment, which ranges from enucleation of a single tumor to a distal pancreatectomy or partial pancreatectomy, has been curative in many patients. Chemotherapy (streptozotocin, 5-fluorouracil, and doxorubicin), PRRT (e.g., with 177Lu-DOTATATE), or hepatic artery embolization has been used for metastatic disease. Glucagonoma  These glucagon-secreting pancreatic NETs occur in <3% of patients with MEN 1. The characteristic clinical manifestations of a skin rash (necrolytic migratory erythema), weight loss, anemia, and stomatitis may be absent. The tumor may have been detected in an asymptomatic patient with MEN 1 undergoing pancreatic imaging or by the finding of glucose intolerance and hyperglucagonemia. TREATMENT Glucagonoma Surgical removal of the glucagonoma is the treatment of choice. However, treatment may be difficult because ~50–80% of patients have metastases at the time of diagnosis. Medical treatment with SSAs (e.g., octreotide or lanreotide) or chemotherapy with

streptozotocin and 5-fluorouracil has been successful in some patients, and hepatic artery embolization has been used to treat metastatic disease. Vasoactive Intestinal Peptide (VIP) Tumors (VIPomas) 

VIPomas have been reported in only a few patients with MEN 1. This clinical syndrome is characterized by watery diarrhea, hypokalemia, and achlorhydria (WDHA syndrome), which is also referred to as the Verner-Morrison syndrome, or the VIPoma syndrome. The diagnosis is established by excluding laxative and diuretic abuse, confirming a stool volume in excess of 0.5–1.0 L/d during a fast, and documenting a markedly increased plasma VIP concentration. TREATMENT VIPomas Surgical management of VIPomas, which are mostly located in the tail of the pancreas, can be curative. However, in patients with unresectable tumor, SSAs, such as octreotide and lanreotide, may be effective. Streptozotocin with 5-fluorouracil may be ben­ eficial, along with hepatic artery embolization for the treatment of metastases. Pancreatic Polypeptide-Secreting Tumors (PPomas) and Nonfunctioning Pancreatic NETs  PPomas are found in a large number of patients with MEN 1. No pathologic sequelae of excessive polypeptide (PP) secretion are apparent, and the clinical significance of PP is unknown. Many PPomas may have been unrecognized or clas­ sified as nonfunctioning pancreatic NETs, which likely represent the most common enteropancreatic NET associated with MEN 1 (Fig. 400-1). The absence of both a clinical syndrome and specific biochemical abnormalities may result in a delayed diagnosis of nonfunctioning pancreatic NETs, which are associated with a worse prognosis than other functioning tumors, including insulinoma and gastrinoma. The optimum screening method and its timing interval for nonfunctioning pancreatic NETs remain to be established. At present, endoscopic ultra­ sound likely represents the most sensitive method of detecting small pancreatic tumors, but SRS is the most reliable method for detecting metastatic disease (Table 400-3). FIGURE 400-1  Pancreatic nonfunctioning neuroendocrine tumor (NET) in a 32-year-old patient with multiple endocrine neoplasia type 1 (MEN 1). An abdominal magnetic resonance imaging (MRI) scan revealed a low-intensity >3.0 cm (anteroposterior maximal diameter) tumor within the body of pancreas. There was no evidence of invasion of adjacent structures or metastases. The tumor is indicated by white dashed circle.

TREATMENT PPomas and Nonfunctioning Pancreatic NETs The management of nonfunctioning pancreatic NETs in the asymp­ tomatic patient is controversial. One recommendation is to under­ take surgery irrespective of tumor size after biochemical assessment is complete. Alternatively, other experts recommend surgery based on tumor size, using either >1 cm or >2 cm at different centers. Pan­ creatoduodenal surgery is successful in removing the tumors in 80% of patients, but >40% of patients develop complications, including diabetes mellitus, frequent steatorrhea, early and late dumping syn­ dromes, and other gastrointestinal symptoms. However, ~50–60% of patients treated surgically survive >5 years. When considering these recommendations, it is important to consider that occult met­ astatic disease (e.g., tumors not detected by imaging investigations) is likely to be present in a substantial proportion of these patients at the time of presentation. Inhibitors of tyrosine kinase receptors (TKRs) and of the mammalian target of rapamycin (mTOR) signal­ ing pathway have been reported to be effective in treating pancre­ atic NET metastases and in doubling the progression-free survival time. Additional treatments for metastatic disease include PRRT using 177Lu-DOTATATE, chemotherapy, radiofrequency ablation, transarterial chemoembolization, and SIRT. Other Pancreatic NETs  NETs secreting growth hormone–releasing hormone (GHRH), GHRHomas, have been reported rarely in patients with MEN 1. It is estimated that ~33% of patients with GHRHomas have other MEN 1–related tumors. GHRHomas may be diagnosed by demonstrating elevated serum concentrations of growth hormone and GHRH. More than 50% of GHRHomas occur in the lung, 30% occur in the pancreas, and 10% are found in the small intestine. Somatostati­ nomas secrete somatostatin, a peptide that inhibits the secretion of a variety of hormones, resulting in hyperglycemia, cholelithiasis, low acid output, steatorrhea, diarrhea, abdominal pain, anemia, and weight loss. Although 7% of pancreatic NETs secrete somatostatin, the clinical fea­ tures of somatostatinoma syndrome are unusual in patients with MEN 1. Pituitary Tumors (See also Chap. 392)  Pituitary tumors occur in 15–50% of patients with MEN 1 (Table 400-1), and ~75% of these are microadenomas (<1 cm diameter). The tumors occur as early as 5 years of age or as late as the ninth decade. MEN 1 pituitary adenomas are more frequent in women than men, in whom they are often macroad­ enomas (>1 cm diameter). There are no specific histologic parameters that differentiate between MEN 1 and non–MEN 1 pituitary tumors. Approximately 60% of MEN 1–associated pituitary tumors secrete pro­ lactin, <25% secrete growth hormone, 5% secrete adrenocorticotropic hormone (ACTH), and the remainder appear to be nonfunctioning, with some secreting glycoprotein subunits (Table 400-1). However, pituitary tumors derived from MEN 1 patients may exhibit immunore­ activity to several hormones. In particular, there is a greater frequency of somatolactotrope tumors. Prolactinomas are the first manifestation of MEN 1 in ~15% of patients, whereas somatotrope tumors occur more often in patients aged >40 years. Fewer than 3% of patients with anterior pituitary tumors will have MEN 1. Clinical manifestations are similar to those in patients with sporadic pituitary tumors without MEN 1 and depend on the hormone secreted and the size of the pitu­ itary tumor. Thus, patients may have symptoms of hyperprolactinemia (e.g., amenorrhea, infertility, and galactorrhea in women, or impotence and infertility in men) or have features of acromegaly or Cushing’s disease. In addition, enlarging pituitary tumors may compress adjacent structures such as the optic chiasm or normal pituitary tissue, causing visual disturbances and/or hypopituitarism. In asymptomatic patients with MEN 1, periodic biochemical monitoring of serum prolactin and insulin-like growth factor 1 (IGF-1) levels, as well as MRI of the pitu­ itary, can lead to early identification of pituitary tumors (Table 400-3). In patients with abnormal results, hypothalamic-pituitary testing should characterize the nature of the pituitary lesion and its effects on the secretion of other pituitary hormones.

TREATMENT Pituitary Tumors Treatment of pituitary tumors in patients with MEN 1 consists of therapies similar to those used in patients without MEN 1 and includes appropriate medical therapy (e.g., bromocriptine or caber­ goline for prolactinoma; or octreotide or lanreotide for somatotrope tumors) or selective transsphenoidal adenomectomy, if feasible, with radiotherapy reserved for residual unresectable tumor tissue. Multiple Endocrine Neoplasia Syndromes CHAPTER 400 Associated Tumors  Patients with MEN 1 may also develop carci­ noid tumors, adrenal cortical tumors, facial angiofibromas, collageno­ mas, thyroid tumors, and lipomatous tumors. Carcinoid Tumors (See also Chap. 89)  Carcinoid tumors occur in >3% of patients with MEN 1 (Table 400-1). The carcinoid tumor may be located in the bronchi, gastrointestinal tract, pancreas, or thymus. At the time of diagnosis, most patients are asymptomatic and do not have clinical features of the carcinoid syndrome. Impor­ tantly, no hormonal or biochemical abnormality (e.g., plasma chro­ mogranin A) is consistently observed in individuals with thymic or bronchial carcinoid tumors. Thus, screening for these tumors is depen­ dent on radiologic imaging. The optimum method for screening has not been established. Low-dose CT and MRI are sensitive for detecting thymic and bronchial tumors (Table 400-3), although repeated CT scanning raises concern about exposure to repeated doses of ionizing radiation. Octreotide scintigraphy may also reveal some thymic and bronchial carcinoids, although there is insufficient evidence to recom­ mend its routine use. Gastric carcinoids, of which the type II gastric enterochromaffin-like (ECL) cell carcinoids (ECLomas) are associated with MEN 1 and Zollinger-Ellison syndrome, may be detected inci­ dentally at the time of gastric endoscopy for dyspeptic symptoms in MEN 1 patients. These tumors, which may be found in >10% of MEN 1 patients, are usually multiple and sized <1.5 cm. Bronchial carcinoids in patients with MEN 1 occur predominantly in women (male-tofemale ratio, 1:4). In contrast, thymic carcinoids in European patients with MEN 1 occur predominantly in men (male-to-female ratio, 20:1), with cigarette smokers having a higher risk for these tumors; thymic carcinoids in Japanese patients with MEN 1 have a less marked sex dif­ ference (male-to-female ratio 2:1). The course of thymic carcinoids in MEN 1 appears to be particularly aggressive. The presence of thymic tumors in patients with MEN 1 is associated with a median survival after diagnosis of ~9.5 years, with 70% of patients dying as a direct result of the tumor. TREATMENT Carcinoid Tumors If resectable, surgical removal of carcinoid tumors is the treatment of choice. For patients with unresectable tumors and those with metastatic disease, treatment with SSAs, radiotherapy, chemothera­ peutic agents (e.g., fluorouracil, temozolomide, cisplatin, etopo­ side), mTOR inhibitors (e.g., everolimus), or PRRT therapy has resulted in symptom improvement and regression of some tumors. Little is known about the malignant potential of gastric type II ECLomas, but treatment with SSAs has resulted in regression of these ECLomas. Adrenocortical Tumors (See also Chap. 398)  Asymptom­ atic adrenocortical tumors occur in 20–70% of patients with MEN 1 depending on the radiologic screening methods used (Table 400-1). Most of these tumors, which include cortical adenomas, hyperplasia, multiple adenomas, nodular hyperplasia, cysts, and carcinomas, are nonfunctioning. Indeed, <10% of patients with enlarged adrenal glands have hormonal hypersecretion, with primary hyperaldosteronism and ACTH-independent Cushing’s syndrome being encountered most commonly. Occasionally, hyperandrogenemia may occur in association with adrenocortical carcinoma. Pheochromocytoma in association

with MEN 1 is rare. Biochemical investigation (e.g., plasma renin and aldosterone concentrations, low-dose dexamethasone suppression test, urinary catecholamines, and/or metanephrines) should be undertaken in those with symptoms or signs suggestive of functioning adrenal tumors or in those with tumors >1 cm. Adrenocortical carcinoma occurs in ~1% of MEN 1 patients but increases to >10% for adrenal tumors >1 cm.

TREATMENT Adrenocortical Tumors PART 12 Endocrinology and Metabolism Consensus has not been reached about the management of MEN 1–associated nonfunctioning adrenal tumors, because the majority are benign. However, the risk of malignancy increases with size, particularly for tumors with a diameter >4 cm. Indications for surgery for adrenal tumors include size >4 cm in diameter, atypical or suspicious radiologic features (e.g., increased Hounsfield unit on unenhanced CT scan) and size of 1–4 cm in diameter, or significant measurable growth over a 6-month period. The treatment of func­ tioning (e.g., hormone-secreting) adrenal tumors is similar to that for tumors occurring in non–MEN 1 patients. Meningioma  Central nervous system (CNS) tumors, including ependymomas, schwannomas, and meningiomas, have been reported in MEN 1 patients (Table 400-1). Meningiomas are found in <10% of patients with other clinical manifestations of MEN 1 (e.g., primary hyperparathyroidism) for >15 years. The majority of meningiomas are not associated with symptoms, and 60% do not enlarge. The treatment of MEN 1–associated meningiomas is similar to that in non–MEN 1 patients. Lipomas  Subcutaneous lipomas occur in >33% of patients with MEN 1 (Table 400-1) and are frequently multiple. In addition, visceral, pleural, or retroperitoneal lipomas may occur in patients with MEN 1. Management is conservative. However, when surgically removed for cosmetic reasons, they typically do not recur. Facial Angiofibromas and Collagenomas  The occurrence of multiple facial angiofibromas in patients with MEN 1 may range from

20 to >90%, and occurrence of collagenomas may range from 0 to 70% (Table 400-1). These cutaneous findings may allow presymp­ tomatic diagnosis of MEN 1 in the relatives of a patient with MEN 1. Treatment for these cutaneous lesions is usually not required. Thyroid Tumors  Thyroid tumors, including adenomas, colloid goiters, and carcinomas, have been reported to occur in >25% of patients with MEN 1. However, the prevalence of thyroid disorders in the general population is high, and it has been suggested that the association of thyroid abnormalities in patients with MEN 1 may be incidental. The treatment of thyroid tumors in MEN 1 patients is simi­ lar to that for non–MEN 1 patients. Genetics and Screening  The MEN1 gene is located on chromo­ some 11q13 and consists of 10 exons, which encode a 610–amino acid protein, menin, that regulates transcription, genome stability, cell division, and proliferation. The pathophysiology of MEN 1 follows the Knudson two-hit hypothesis with a tumor-suppressor role for menin. Inheritance of a germline MEN1 mutation predisposes an individual to developing a tumor that arises following a somatic mutation, which may be a point mutation or more commonly a deletion, leading to loss of heterozygosity (LOH) in the tumor DNA. The germline mutations of the MEN1 gene are scattered throughout the entire 1830-bp coding region and splice sites, and there is no apparent correlation between the location of MEN1 mutations and clinical manifestations of the disor­ der, in contrast with the situation in patients with MEN 2 (Table 400-1). More than 10% of MEN1 germline mutations arise de novo and may be transmitted to subsequent generations. Some families with MEN 1 mutations develop parathyroid tumors as the sole endocrinopathy, and this condition is referred to as familial isolated hyperparathyroid­ ism (FIHP). However, between 5 and 25% of patients with MEN 1 do

not harbor germline mutations or deletions of the MEN1 gene. Such patients with MEN 1–associated tumors but without MEN1 mutations may represent phenocopies or have mutations involving other genes. Other genes associated with MEN 1–like features include CDKN1B, which encodes p27kip1; mutations result in MEN4 (see below) (Table 400-1). Mutations in CDC73, which encodes parafibromin, result in the HPT-JT syndrome; mutations in the calcium-sensing receptor gene (CaSR) result in familial benign hypocalciuric hypercalcemia (FBHH); mutations in MAX, which encodes Myc-associated factor X, result in MEN5, and mutations in the aryl hydrocarbon receptor interacting protein gene (AIP), a tumor suppressor located on chromosome 11q13, are associated with familial isolated pituitary adenomas (FIPA). Genetic testing to determine the MEN1 mutation status in symptomatic family members within a MEN 1 kindred, as well as in all index cases (e.g., patients) with two or more endocrine tumors, is advisable. If a MEN1 mutation is not identified in the index case with two or more endocrine tumors, clinical and genetic tests for other disorders such as HPT-JT syn­ drome, FBHH, FIPA, MEN 2, or MEN 4 should be considered because these patients may represent phenocopies for MEN 1. The current guidelines recommend that MEN1 mutational analysis should be undertaken in (1) an index case with two or more MEN 1– associated endocrine tumors (e.g., parathyroid, pancreatic, or pituitary tumors); (2) asymptomatic first-degree relatives of a known MEN1 mutation carrier; and (3) first-degree relatives of a MEN1 mutation carrier with symptoms, signs, or biochemical or radiologic evidence for one or more MEN 1–associated tumors. In addition, MEN1 mutational analysis should be considered in patients with suspicious or atypical MEN 1. This would include individuals with parathyroid adenomas before the age of 30 years or multigland parathyroid disease; individuals with gastrinoma or multiple pancreatic NETs at any age; or individuals who have two or more MEN 1–associated tumors that are not part of the classical triad of parathyroid, pancreatic islet, and anterior pituitary tumors (e.g., parathyroid tumor plus adrenal tumor). Family members, including asymptomatic individuals who have been identified to harbor a MEN1 mutation, will require biochemical and radiologic screening (Table 400-3). In contrast, relatives who do not harbor the MEN1 muta­ tion have a risk of developing MEN 1–associated endocrine tumors that is similar to that of the general population; thus, relatives without the MEN1 mutation do not require repeated screening. Mutational analysis in asymptomatic individuals should be under­ taken at the earliest opportunity and, if possible, in the first decade of life because tumors have developed in some children by the age of 5 years. Appropriate biochemical and radiologic investigations (Table 400-3) aimed at detecting the development of tumors should then be under­ taken in affected individuals. Mutant gene carriers should undergo biochemical screening at least once per annum and also have baseline pituitary and abdominal imaging (e.g., MRI or CT), which should then be repeated at 1- to 3-year intervals (Table 400-3). Screening should commence after 5 years of age and should continue for life because the disease may develop as late as the eighth decade. The screening history and physical examination elicit the symptoms and signs of hypercalcemia; nephrolithiasis; peptic ulcer disease; neuroglycopenia; hypopituitarism; galactorrhea and amenorrhea in women; acromegaly; Cushing’s disease; and visual field loss and the presence of subcutane­ ous lipomas, angiofibromas, and collagenomas. Biochemical screening should include measurements of serum calcium, PTH, gastrointestinal hormones (e.g., gastrin, insulin with a fasting glucose, glucagon, VIP, PP), chromogranin A, prolactin, and IGF-1 in all individuals. More specific endocrine function tests should be undertaken in individuals who have symptoms or signs suggestive of a specific clinical syndrome. Biochemical screening for the development of MEN 1 tumors in asymptomatic members of families with MEN 1 is of great importance to reduce morbidity and mortality from the associated tumors. ■ ■MULTIPLE ENDOCRINE NEOPLASIA TYPE 2 AND TYPE 3 Clinical Manifestations  MEN type 2 (MEN 2), which is also called Sipple’s syndrome, is characterized by the association of medullary

TABLE 400-4  Recommendations for Tests and Surgery in MEN 2 and MEN 3a RET MUTATION, EXON (EX) LOCATION, AND CODON INVOLVED RISKb RET MUTATIONAL ANALYSIS Ex8 (533)c; Ex10 (609, 611, 618, 620)c; Ex11 (630, 631, 666)c; Ex13 (768, 790)c; Ex14 (804)c; Ex15 (891)c; EX16 (912)c + <3–5

<5d 16e

Ex11 (634)c; Ex15 (883)c ++ <3 <3 <5f 11e

Ex15 (883)g; Ex16 (918)g +++ ASAP and by <1 ASAP and by <0.5–1 ASAP and by <1 11e —h aData from American Thyroid Association Guidelines Task Force, RT Kloos et al: Medullary thyroid cancer: management guidelines of the American Thyroid Association. Thyroid 19:565, 2009 and revised from SA Wells Jr et al: Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma. Thyroid 25:567, 2015. bRisk for early development of metastasis and aggressive growth of medullary thyroid cancer: +++, highest; ++, high; and + moderate. cMutations associated with MEN 2A (or medullary thyroid carcinoma only). dTiming of surgery to be based on elevation of serum calcitonin and/or joint discussion with pediatrician, surgeon, and parent/family. Later surgery may be appropriate if serum calcitonin and neck ultrasound are normal. ePresence of pheochromocytoma must be excluded prior to any surgical intervention and also in women with RET mutation who are planning pregnancy or are pregnant. fSurgery earlier than 5 years based on elevation of serum calcitonin. Optimal timing of surgery should be decided by the surgeon and pediatrician, in consultation with the child’s parent. gMutations associated with MEN 2B (MEN 3). hNot required because PHPT is not a feature of MEN 2B (MEN 3). Abbreviations: ASAP, as soon as possible; MEN, multiple endocrine neoplasia; PHPT, primary hyperparathyroidism. thyroid carcinoma (MTC), pheochromocytomas, and parathyroid tumors (Table 400-1). Three clinical variants of MEN 2 are recognized: MEN 2A, MEN 2B, and MTC only. MEN 2A, which is often referred to as MEN 2, is the most common variant. In MEN 2A, MTC is associated with pheochromocytomas in 50% of patients (may be bilateral) and with parathyroid tumors in 20% of patients. MEN 2A may rarely occur in association with Hirschsprung’s disease, caused by the absence of autonomic ganglion cells in the terminal hindgut, resulting in colonic dilatation, severe constipation, and obstruction. MEN 2A may also be associated with cutaneous lichen amyloidosis, which is a pruritic lichenoid lesion that is usually located on the upper back. MEN 2B, which is also referred to as MEN 3, represents 5% of all cases of MEN 2 and is characterized by the occurrence of MTC and pheochromocy­ toma in association with a Marfanoid habitus; mucosal neuromas of the lips, tongue, and eyelids; medullated corneal fibers; and intestinal autonomic ganglion dysfunction leading to multiple diverticulae and megacolon. Parathyroid tumors do not usually occur in MEN 2B. MTC only (FMTC) is a variant in which MTC is the sole manifestation of the syndrome. However, the distinction between FMTC and MEN 2A is difficult and should only be considered if there are at least four family members aged >50 years who are affected by MTC but not pheochro­ mocytomas or primary hyperparathyroidism. All of the MEN 2 vari­ ants are due to mutations of the rearranged during transfection (RET) protooncogene, which encodes a TKR. Moreover, there is a correlation between the locations of RET mutations and MEN 2 variants. Thus, ~95% of MEN 2A patients have mutations involving the cysteine-rich extracellular domain, with mutations of codon 634 accounting for ~85% of MEN 2A mutations; FMTC patients also have mutations of the cysteine-rich extracellular domain, with most mutations occurring in codon 618. In contrast, ~95% of MEN 2B/MEN 3 patients have mutations of codon 918 of the intracellular tyrosine kinase domain (Table 400-1 and Table 400-4). Medullary Thyroid Carcinoma  MTC is the most common feature of MEN 2A and MEN 2B and occurs in almost all affected individuals. MTC represents 5–10% of all thyroid gland carcinomas, and 20% of MTC patients have a family history of the disorder. The use of RET mutational analysis to identify family members at risk for hereditary forms of MTC has altered the presentation of MTC from that of symptomatic tumors to a preclinical disease for which prophylactic thyroidectomy (Table 400-4) is undertaken to improve the prognosis and ideally result in cure. However, in patients who do not have a known family history of MEN 2A, FMTC, or MEN 2B, and therefore have not had RET mutational analysis, MTC may present as a palpable mass in the neck, which may be asymptomatic or associated with symptoms of pressure or dysphagia in >15% of patients. Diar­ rhea occurs in 30% of patients and is associated either with elevated circulating concentrations of calcitonin or tumor-related secretion of serotonin and prostaglandins. Some patients may also experience flushing. In addition, ectopic ACTH production by MTC may cause

[H] FDG avid MTC in neck PART 12 Endocrinology and Metabolism Metastatic MTC in liver FDG avid adrenal pheochromocytoma [F] FIGURE 400-2  Fluorodeoxyglucose (FDG) positron emission tomography scan in a patient with multiple endocrine neoplasia type 2A, showing medullary thyroid cancer (MTC) with hepatic and skeletal (left arm) metastasis and a left adrenal pheochromocytoma. Note the presence of excreted FDG compound in the bladder. (Reproduced with permission from A Naziat et al: Confusing genes: A patient with MEN2A and Cushing’s disease. Clin Endocrinol (Oxf) 78:966, 2013.) Pheochromocytoma (See also Chap. 399)  These noradrena­ line- and adrenaline-secreting tumors occur in >50% of patients with MEN 2A and MEN 2B and are a major cause of morbidity and mortal­ ity. Patients may have symptoms and signs of catecholamine secretion (e.g., headaches, palpitations, sweating, poorly controlled hyperten­ sion), or they may be asymptomatic with detection through biochemi­ cal screening based on a history of familial MEN 2A, MEN 2B, or MTC. Pheochromocytomas in patients with MEN 2A and MEN 2B differ significantly in distribution when compared with patients with­ out MEN 2A and MEN 2B. Extra-adrenal pheochromocytomas, which occur in 10% of patients without MEN 2A and MEN 2B, are observed rarely in patients with MEN 2A and MEN 2B. Malignant pheochromo­ cytomas are much less common in patients with MEN 2A and MEN 2B. The biochemical and radiologic investigation of pheochromocy­ toma in patients with MEN 2A and MEN 2B is similar to that in non– MEN 2 patients and includes the measurement of plasma (obtained from supine patients) and urinary free fractionated metanephrines (e.g., normetanephrine and metanephrines measured separately), CT or MRI scanning, radionuclide scanning with meta-iodo-(123I or 131I)- benzyl guanidine (MIBG), and PET using (18F)-fluorodopamine or (18F)-fluoro-2-dexoxy-D-glucose (Fig. 400-2). TREATMENT Pheochromocytoma Surgical removal of pheochromocytoma, using α and β adreno­ receptor blockade before and during the operation, is the rec­ ommended treatment. Other antihypertensive agents, including calcium channel blockers, are sometimes required for adequate blood pressure control. Endoscopic adrenal-sparing surgery, which

decreases postoperative morbidity, hospital stay, and expense, as opposed to open surgery, has become the method of choice. Parathyroid Tumors (See also Chap. 422)  Parathyroid tumors occur in 10–25% of patients with MEN 2A. However, >50% of these patients do not have hypercalcemia. The presence of abnormally enlarged parathyroids, which are unusually hyperplastic, is often seen in the normocalcemic patient undergoing thyroidectomy for MTC. The biochemical investigation and treatment of hypercalcemic patients with MEN 2A is similar to that of patients with MEN 1. Genetics and Screening  To date, ~50 different RET muta­ tions have been reported, and these are located in exons 5, 8, 10, 11, 13, 14, 15, and 16. RET germline mutations are detected in

95% of MEN 2A, FMTC, and MEN 2B families, with Cys634Arg being most common in MEN 2A, Cys618Arg being most common in FMTC, and Met918Thr being most common in MEN 2B (Tables 400-1 and 400-4). Between 5 and 10% of patients with MTC or MEN 2A– associated tumors have de novo RET germline mutations, and ~50% of patients with MEN 2B have de novo RET germline mutations. These de novo RET germline mutations always occur on the paternal allele. Approximately 5% of patients with sporadic pheochromocytoma have a germline RET mutation, but such germline RET mutations do not appear to be associated with sporadic primary hyperparathyroidism. Thus, RET mutational analysis should be performed in (1) all patients with MTC who have a family history of tumors associated with MEN 2, FMTC, or MEN 3, such that the diagnosis can be confirmed and genetic testing offered to asymptomatic relatives; (2) all patients with MTC and pheochromocytoma without a known family history of MEN 2 or MEN 3; (3) all patients with MTC, but without a family history of MEN 2, FMTC, or MEN 3, because these patients may have a de novo germline RET mutations; (4) all patients with bilateral pheochromocy­ toma; and (5) patients with unilateral pheochromocytoma, particularly if this occurs with increased calcitonin levels. Screening for MEN 2/MEN 3–associated tumors in patients with RET germline mutations should be undertaken annually and include serum calcitonin measurements, a neck ultrasound for MTC, plasma (or 24-h urinary) fractionated metanephrines for pheochromocytoma, and albumin-corrected serum calcium or ionized calcium with PTH for primary hyperparathyroidism. In patients with MEN 2–associated RET mutations, screening for MTC should begin by 1–5 years, for pheochromocytoma by 11–16 years, and for primary hyperparathy­ roidism by 11–16 years of age (Table 400-4). ■ ■MULTIPLE ENDOCRINE NEOPLASIA TYPE 4 Clinical Manifestations  Patients with MEN 1–associated tumors, such as parathyroid adenomas, pituitary adenomas, and pancreatic NETs, occurring in association with gonadal, adrenal, renal, and thy­ roid tumors have been reported to have mutations of the gene encod­ ing the 196–amino acid cyclin-dependent kinase inhibitor (CK1) p27 kip1 (CDKN1B). Such families with MEN 1–associated tumors and CDKN1B mutations are designated to have MEN 4 (Table 400-1). The investigations and treatments for the MEN 4–associated tumors are similar to those for MEN 1 and non–MEN 1 tumors. Genetics and Screening  To date, 50 MEN patients (from <20 kindreds) with mutations of CDKN1B, which is located on chromo­ some 12p13, have been reported, and all of these are predicted to result in a loss of function. These MEN 4 patients may represent ~3% of the 5–10% of patients with MEN 1 who do not have mutations of the MEN1 gene. Germline CDKN1B mutations may rarely be found in patients with sporadic (i.e., nonfamilial) forms of primary hyperparathyroidism. ■ ■MULTIPLE ENDOCRINE NEOPLASIA TYPE 5 Clinical Manifestations  Two kindreds in whom multiple endo­ crine tumors were associated with heterozygous germline MAX mutations have been reported. Although MAX mutations have been described in rare cases of hereditary pheochromocytoma and para­ ganglioma, the occurrence of these tumors in these kindreds was also

associated with pituitary adenomas, parathyroid adenomas, and non­ endocrine tumors including chondrosarcoma, lung adenocarcinoma, ganglioneuroma, and neuroblastoma. Additional tumors reported in patients with germline MAX mutations include pancreatic NETs, renal oncocytomas, and renal carcinoma. Genetics and Screening  The MAX gene is located on chromo­ some 14q23.3 and encodes the ubiquitously expressed MYC-associated factor X transcription factor, which is presumed to act as a tumor suppressor. The spectrum of clinical manifestations associated with germline MAX mutations and MEN 5 remains to be fully defined, although most patients appear to have development of early-onset pheochromocytoma. ■ ■HYPERPARATHYROIDISM-JAW TUMOR SYNDROME (SEE ALSO CHAP. 422) Clinical Manifestations  Hyperparathyroidism-jaw tumor (HPTJT) syndrome is an autosomal dominant disorder characterized by the development of parathyroid tumors (15% are carcinomas) and fibroosseous jaw tumors. In addition, some patients may also develop Wilms’ tumors, renal cysts, renal hamartomas, renal cortical adenomas, renal cell carcinoma (RCC), pancreatic adenocarcinomas, uterine tumors, testicular mixed germ cell tumors with a major seminoma component, and Hürthle cell thyroid adenomas. The parathyroid tumors may occur in isolation and without any evidence of jaw tumors, and this may cause confusion with other hereditary hypercalcemic disorders, such as MEN 1. However, genetic testing to identify the causative mutation will help to establish the correct diagnosis. The investigation and treatment for HPT-JT–associated tumors are similar to those in non-HPT-JT patients, except that early parathyroidectomy is advisable because of the increased frequency of parathyroid carcinoma. Genetics and Screening  The gene that causes HPT-JT is located on chromosome 1q31.2 and encodes a 531–amino acid protein, parafibromin (Table 400-2). Parafibromin is also referred to as cell division cycle protein 73 (CDC73) and has a role in transcrip­ tion. Genetic testing in families helps to identify mutation carriers who should be periodically screened for the development of tumors (Table 400-5). ■ ■VON HIPPEL–LINDAU DISEASE (SEE ALSO CHAP. 399) Clinical Manifestations  von Hippel–Lindau (VHL) disease is an autosomal dominant disorder characterized by hemangioblasto­ mas of the retina and CNS; cysts involving the kidneys, pancreas, and epididymis; RCC; pheochromocytomas; and pancreatic islet cell tumors. The retinal and CNS hemangioblastomas are benign vascular tumors that may be multiple; those in the CNS may cause symptoms TABLE 400-5  HPT-JT Screening Guidelines TUMORa TEST FREQUENCYb Parathyroid Serum Ca, PTH 6–12 months Ossifying jaw fibroma Panoramic jaw x-ray with neck shieldingc 5 years Renal Abdominal MRIc,d 5 years Uterine Ultrasound (transvaginal or transabdominal) and additional imaging ± D&C if indicatede Annual aScreening for most common HPT-JT–associated tumors is considered. Assessment for other reported tumor types may be indicated (e.g., pancreatic, thyroid, testicular tumors). bFrequency of repeating test after baseline tests performed. cX-rays and imaging involving ionizing radiation should ideally be avoided to minimize risk of generating subsequent mutations. dUltrasound scan recommended if MRI unavailable. eSuch selective pelvic imaging should be considered after obtaining a detailed menstrual history. Abbreviations: Ca, calcium; D&C, dilation and curettage; HPT-JT, hyperparathyroidism-jaw tumor syndrome; MRI, magnetic resonance imaging; PTH, parathyroid hormone. Source: Reproduced with permission from PJ Newey, MR Bowl, T Cranston et al: Cell division cycle protein 73 homolog (CDC73) mutations in the hyperparathyroidism-jaw tumor syndrome (HPT-JT) and parathyroid tumors. Hum Mutat 31:295, 2010.

by compressing adjacent structures and/or increasing intracranial pressure. In the CNS, the cerebellum and spinal cord are the most fre­ quently involved sites. The renal abnormalities consist of cysts and car­ cinomas, and the lifetime risk of RCC in VHL is 70%. The endocrine tumors in VHL consist of pheochromocytomas and pancreatic islet cell tumors. The clinical presentation of pheochromocytoma in VHL disease is similar to that in sporadic cases, except that there is a higher frequency of bilateral or multiple tumors, which may involve extraadrenal sites in VHL disease. The most frequent pancreatic lesions in VHL are multiple cyst-adenomas, which rarely cause clinical disease. However, nonsecreting pancreatic islet cell tumors occur in <10% of VHL patients, who are usually asymptomatic. The pancreatic tumors in these patients are often detected by regular screening using abdominal imaging. Pheochromocytomas should be investigated and treated as described earlier for MEN 2. The pancreatic islet cell tumors frequently become malignant, and early surgery is recommended.

Multiple Endocrine Neoplasia Syndromes CHAPTER 400 Genetics and Screening  The VHL gene, which is located on chromosome 3p26-p25, is widely expressed in human tissues and encodes a 213–amino acid protein (pVHL) (Table 400-2). A wide variety of germline VHL mutations have been identified. VHL acts as a tumor-suppressor gene. A correlation between the type of mutation and the clinical phenotype has been reported; large deletions and proteintruncating mutations are associated with a low incidence of pheochro­ mocytomas, whereas some missense mutations in VHL patients are associated with pheochromocytoma (referred to as VHL type 2C). Other missense mutations may be associated with hemangioblastomas and RCC but not pheochromocytoma (referred to as VHL type 1), whereas distinct missense mutations are associated with hemangioblastomas, RCC, and pheochromocytoma (VHL type 2B). VHL type 2A, which refers to the occurrence of hemangioblastomas and pheochromocytoma without RCC, is associated with rare missense mutations. The basis for these complex genotype-phenotype relationships remains to be eluci­ dated. One major function of pVHL, which is also referred to as elongin, is to downregulate the expression of vascular endothelial growth factor (VEGF) and other hypoxia-inducible mRNAs. Thus, pVHL, in complex with other proteins, regulates the expression of hypoxia-inducible factors (HIF-1 and HIF-2) such that loss of functional pVHL leads to a stabiliza­ tion of the HIF protein complexes, resulting in VEGF overexpression and tumor angiogenesis. Screening for the development of pheochromo­ cytomas and pancreatic islet cell tumors is as described earlier for MEN 2 and MEN 1, respectively (Tables 400-3 and 400-4). ■ ■NEUROFIBROMATOSIS Clinical Manifestations  Neurofibromatosis type 1 (NF1), which is also referred to as von Recklinghausen’s disease, is an autosomal dominant disorder characterized by the following manifestations: neurologic (e.g., peripheral and spinal neurofibromas); ophthalmo­ logic (e.g., optic gliomas and iris hamartomas such as Lisch nodules); dermatologic (e.g., café au lait macules); skeletal (e.g., scoliosis, mac­ rocephaly, short stature, pseudoarthrosis); vascular (e.g., stenoses of renal and intracranial arteries); and endocrine (e.g., pheochromocy­ toma, carcinoid tumors, precocious puberty). Neurofibromatosis type 2 (NF2) is also an autosomal dominant disorder but is characterized by the development of bilateral vestibular schwannomas (acoustic neuromas) that lead to deafness, tinnitus, or vertigo. Some patients with NF2 also develop meningiomas, spinal schwannomas, peripheral nerve neurofibromas, and café au lait macules. Endocrine abnormali­ ties are not found in NF2 and are associated solely with NF1. Pheo­ chromocytomas, carcinoid tumors, and precocious puberty occur in ~1% of patients with NF1, and growth hormone deficiency has also been reported. The features of pheochromocytomas in NF1 are simi­ lar to those in non-NF1 patients, with 90% of tumors being located within the adrenal medulla and the remaining 10% at an extra-adrenal location, which often involves the para-aortic region. Primary carci­ noid tumors are often periampullary and may also occur in the ileum but rarely in the pancreas, thyroid, or lungs. Hepatic metastases are associated with symptoms of the carcinoid syndrome, which include flushing, diarrhea, bronchoconstriction, and tricuspid valve disease.

Precocious puberty is usually associated with the extension of an optic glioma into the hypothalamus with resultant early activation of gonad­ otropin-releasing hormone secretion. Growth hormone deficiency has also been observed in some NF1 patients, who may or may not have optic chiasmal gliomas, but it is important to note that short stature is frequent in the absence of growth hormone deficiency in patients with NF1. The investigation and treatment for tumors are similar to those undertaken for each respective tumor type in non-NF1 patients. Genetics and Screening  The NF1 gene, which is located on chro­ mosome 17q11.2 and acts as a tumor suppressor, consists of 60 exons that span >350 kb of genomic DNA (Table 400-2). Mutations in NF1 are of diverse types and are scattered throughout the exons. The NF1 gene product is the protein neurofibromin, which has homologies to the p120GAP (GTPase activating protein) and acts on p21ras by converting the active GTP bound form to its inactive GDP form. Mutations of NF1 impair this downregulation of the p21ras signaling pathways, which in turn results in abnormal cell proliferation. Screening for the develop­ ment of pheochromocytomas and carcinoid tumors is as described earlier for MEN 2 and MEN 1, respectively (Tables 400-3 and 400-4).

PART 12 Endocrinology and Metabolism ■ ■CARNEY COMPLEX Clinical Manifestations  Carney complex (CNC) is an autosomal dominant disorder characterized by spotty skin pigmentation (usually of the face, labia, and conjunctiva), myxomas (usually of the eyelids and heart, but also the tongue, palate, breast, and skin), psammoma­ tous melanotic schwannomas (usually of the sympathetic nerve chain and upper gastrointestinal tract), and endocrine tumors that involve the adrenals, Sertoli cells, somatotropes, thyroid, and ovary. Cushing’s syndrome, the result of primary pigmented nodular adrenal disease (PPNAD), is the most common endocrine manifestation of CNC and may occur in one-third of patients. Patients with CNC and Cushing’s syndrome often have an atypical appearance by being thin (as opposed to having truncal obesity). In addition, they may have short stature, muscle and skin wasting, and osteoporosis. These patients often have levels of urinary free cortisol that are normal or increased only margin­ ally. Cortisol production may fluctuate periodically with days or weeks of hypercortisolism; this pattern is referred to as “periodic Cushing’s syndrome.” Patients with Cushing’s syndrome usually have loss of the circadian rhythm of cortisol production. Acromegaly, the result of a somatotrope tumor, affects ~10% of patients with CNC. Testicular tumors may also occur in one-third of patients with CNC. These may either be large-cell calcifying Sertoli cell tumors, adrenocortical rests, or Leydig cell tumors. The Sertoli cell tumors occasionally may be estrogen-secreting and lead to precocious puberty or gynecomastia. Some patients with CNC have been reported to develop thyroid fol­ licular tumors, ovarian cysts, or breast duct adenomas. Genetics and Screening  CNC type 1 (CNC1) is due to mutations of the protein kinase A (PKA) regulatory subunit 1 α (R1α) (PRAKAR1A), a tumor suppressor, whose gene is located on chromosome 17q.24.2 (Table 400-2). The gene causing CNC type 2 (CNC2) is located on chromosome 2p16 and has not yet been identi­ fied. It is interesting to note, however, that some tumors do not show LOH of 2p16 but instead show genomic instability, suggesting that this CNC gene may not be a tumor suppressor. Screening and treatment of these endocrine tumors are similar to those described earlier for patients with MEN 1 and MEN 2 (Tables 400-3 and 400-4). ■ ■COWDEN’S SYNDROME Clinical Manifestations  Multiple hamartomatous lesions, espe­ cially of the skin, mucous membranes (e.g., buccal, intestinal, colonic), breast, and thyroid, are characteristic of Cowden’s syndrome (CWS), which is an autosomal dominant disorder. Thyroid abnormalities occur in two-thirds of patients with CWS, and these usually consist of multinodular goiters or benign adenomas, although <10% of patients may have a follicular thyroid carcinoma. Breast abnormalities occur in

75% of patients and consist of either fibrocystic disease or adenocar­ cinomas. The investigation and treatment for CWS tumors are similar to those undertaken for non-CWS patients.

Genetics and Screening  CWS is genetically heterogenous, and seven types (CWS1–7) are recognized (Table 400-2). CWS1 is due to mutations of the phosphate and tensin homologue deleted on chromosome 10 (PTEN) gene, located on chromosome 10q23.31. CWS2 is caused by mutations of the succinate dehydrogenase subunit B (SDHB) gene, located on chromosome 1p36.13; and CWS3 is caused by mutations of the SDHD gene, located on chromosome 11q13.1. SDHB and SDHD mutations are also associated with pheochromocy­ toma. CWS4 is caused by hypermethylation of the Killin (KLLN) gene, the promoter of which shares the same transcription site as PTEN on chromosome 10q23.31. CWS5 is caused by mutations of the phospha­ tidylinositol 3-kinase catalytic alpha (PIK3CA) gene on chromosome 3q26.32. CWS6 is caused by mutations of the V-Akt murine thymoma viral oncogene homolog 1 (AKT1) gene on chromosome 14q32.33, and CWS7 is caused by mutations of the saccharomyces cerevisiae homol­ ogy of B (SEC23B) gene on chromosome 20p11.23. Screening for thy­ roid abnormalities entails neck ultrasonography and fine-needle aspiration with analysis of cell cytology. ■ ■MCCUNE-ALBRIGHT SYNDROME (SEE ALSO CHAP. 424) Clinical Manifestations  McCune-Albright syndrome (MAS) is characterized by the triad of polyostotic fibrous dysplasia, which may be associated with hypophosphatemic rickets; café au lait skin pigmentation; and peripheral precocious puberty. Other endocrine abnormalities include thyrotoxicosis, which may be associated with a multinodular goiter, somatotrope tumors, and Cushing’s syndrome (due to adrenal tumors). Investigation and treatment for each endocri­ nopathy are similar to those used in patients without MAS. Genetics and Screening  MAS is a disorder of mosaicism that results from postzygotic somatic cell mutations of the G protein α-stimulating subunit (Gsα), encoded by the GNAS1 gene, located on chromosome 20q13.32 (Table 400-2). The Gsα mutations, which include Arg201Cys, Arg201His, Glu227Arg, or Glu227His, are activating and are found only in cells of the abnormal tissues. Screening for hyper­ function of relevant endocrine glands and development of hypophospha­ temia, which may be associated with elevated serum fibroblast growth factor 23 (FGF23) concentrations, is undertaken in MAS patients. Acknowledgment The author is grateful to the National Institute of Health Research (NIHR) Oxford Biomedical Research Centre Programme for support and to Mrs. Tracey Walker for typing the manuscript. ■ ■FURTHER READING Binderup MLM et al: von Hippel-Lindau disease: Updated guideline for diagnosis and surveillance. Eur J Med Genet 65:104538, 2022. Bouys L, Bertherat J: Management of endocrine disease: Carney complex: Clinical and genetic update 20 years after the identification of the CNC1 (PRKAR1A) gene. Eur J Endocrinol 184:R99, 2021. Brandi ML et al: Multiple endocrine neoplasia type 1: Latest insights. Endocr Rev 42:133, 2021. Legius E et al: Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: An international consensus recommendation. Genet Med 23:1506, 2021. Hadoux J et al: Phase 3 trial of selpercatinib in advanced RET-mutant medullary thyroid cancer. N Engl J Med 389:1851, 2023. Minisola S et al: Epidemiology, pathophysiology, and genetics of pri­ mary hyperparathyroidism. J Bone Miner Res 37:2315, 2022. Ruggeri RM et al: Multiple endocrine neoplasia type 4 (MEN4): A thorough update on the latest and least known MEN syndrome. Endocrine 82:480, 2023. Seabrook AJ et al: Multiple endocrine tumors associated with germ­ line MAX mutations: Multiple endocrine neoplasia type 5? J Clin Endocrinol Metab 106:1163, 2021. Thakker RV et al: Clinical practice guidelines for multiple endocrine neoplasia type 1 (MEN1). J Clin Endocrinol Metab 97:2990, 2012.

15 - 401 Autoimmune Polyendocrine Syndromes

401 Autoimmune Polyendocrine Syndromes

Peter A. Gottlieb, Aaron W. Michels

Autoimmune

Polyendocrine Syndromes Polyglandular deficiency syndromes have been given many differ­ ent names, reflecting the wide spectrum of disorders that have been associated with these syndromes and the heterogeneity of their clinical presentations. The name used in this chapter for this group of disorders is autoimmune polyendocrine syndrome (APS). In general, these disor­ ders are divided into two major categories, APS type 1 (APS-1) and APS type 2 (APS-2). Some groups have further subdivided APS-2 into APS type 3 (APS-3) and APS type 4 (APS-4) depending on the type of autoimmunity involved. For the most part, this additional classification does not clarify our understanding of disease pathogenesis or preven­ tion of complications in individual patients. Importantly, there are many nonendocrine disease associations included in these syndromes, suggesting that although the underlying autoimmune disorder predomi­ nantly involves endocrine targets, it does not exclude other tissues. The disease associations found in APS-1 and APS-2 are summarized in Table 401-1. Understanding these syndromes and their disease manifestations can lead to early diagnosis and treatment of additional disorders in patients and their family members. TABLE 401-1  Disease Associations with Autoimmune Polyendocrine Syndromes AUTOIMMUNE POLYENDOCRINE SYNDROME TYPE 1 AUTOIMMUNE POLYENDOCRINE SYNDROME TYPE 2 OTHER AUTOIMMUNE POLYENDOCRINE DISORDERS Endocrine Endocrine IPEX (immune dysfunction polyendocrinopathy X-linked)   Addison’s disease Addison’s disease Thymic tumors   Hypoparathyroidism Type 1 diabetes Anti-insulin receptor antibodies   Hypogonadism Graves’ disease or autoimmune thyroiditis POEMS syndrome   Graves’ disease or Hypogonadism Insulin autoimmune syndrome (Hirata’s syndrome) autoimmune thyroiditis   Type 1 diabetes   Adult combined pituitary hormone deficiency (CPHD) with anti-Pit1 autoantibodies     Kearns-Sayre syndrome     DIDMOAD syndrome Nonendocrine Nonendocrine Congenital rubella associated with thyroiditis and/or diabetes   Mucocutaneous Celiac disease, dermatitis herpetiformis   candidiasis   Chronic active Pernicious anemia   hepatitis   Pernicious anemia Vitiligo     Vitiligo Alopecia     Asplenism Myasthenia gravis     Ectodermal dysplasia IgA deficiency     Alopecia Parkinson’s disease     Malabsorption Idiopathic thrombocytopenia   syndromes   IgA deficiency     Abbreviations: DIDMOAD, diabetes insipidus, diabetes mellitus, progressive bilateral optic atrophy, and sensorineural deafness; POEMS, polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes. Note: Italics denote less common disorders.

■ ■APS-1 APS-1 (Online Mendelian Inheritance in Man [OMIM] 240300) has also been called autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy (APECED). Mucocutaneous candidiasis, hypoparathyroid­ ism, and Addison’s disease form the three major components of this disorder. However, as summarized in Table 401-1, many other organ systems can be involved over time. APS-1 is rare, with <500 cases reported in the literature.

The classical form of APS-1 is an autosomal recessive disorder caused by mutations in the AIRE gene (autoimmune regulator gene) found on chromosome 21. This gene is most highly expressed in thy­ mic medullary epithelial cells (mTECs) where it controls the expression of tissue-specific self-antigens (e.g., insulin). Deletion of this regulator leads to decreased expression of tissue-specific self-antigens and is hypothesized to allow autoreactive T cells to avoid central deletion, which normally occurs during T-cell maturation in the thymus. The AIRE gene is also expressed in epithelial cells found in peripheral lymphoid organs, but its role in these extrathymic cells remains con­ troversial. To date, >100 mutations have been described in this gene, and there is a higher frequency within certain ethnic groups includ­ ing Iranian Jews, Sardinians, Finns, Norwegians, and Irish. Recently, several autosomal dominant mutations have been identified and are localized primarily in the PHD1 domain of the AIRE gene, rather than the CARD region, where the autosomal recessive mutations have been found. Individuals with this nonclassical form of APS-1 may have a later onset of symptoms and less aggressive disease, without the full spectrum of autoimmune components being expressed. Autoimmune Polyendocrine Syndromes CHAPTER 401 Clinical Manifestations  Classical APS-1 develops very early in life, often in infancy (Table 401-2). Chronic mucocutaneous candi­ diasis without signs of systemic disease is often the first manifesta­ tion. It affects the mouth and nails more frequently than the skin and esophagus. Chronic oral candidiasis can result in atrophic disease with areas suggestive of leukoplakia, which can pose a risk for future carcinoma. The etiology is associated with anticytokine autoantibodies (anti-interleukin [IL] 17A, IL-17F, and IL-22) related to T helper (TH) 17 T cells and depressed production of these cytokines by peripheral blood mononuclear cells. Hypoparathyroidism usually develops next, followed by adrenal insufficiency. The time from development of one component of the disorder to the next can be many years, and the order of disease appearance is variable. Chronic candidiasis is nearly always present and is not very respon­ sive to treatment. Hypoparathyroidism is found in >85% of cases, and Addison’s disease is found in nearly 80%. Gonadal failure appears to affect women more than men (70 vs 25%, respectively), and hypo­ plasia of the dental enamel also occurs frequently (77% of patients). TABLE 401-2  Comparison of APS-1 and APS-2 APS-1 APS-2 Early onset: infancy Later onset Siblings often affected and at risk Multigenerational Equivalent sex distribution Females > males affected Monogenic: AIRE gene, chromosome 21, autosomal recessive Polygenic: HLA, MICA, PTNP22, CTLA4 Not HLA associated for entire syndrome, some specific component risk DR3/DR4 associated; other HLA class III gene associations noted Autoantibodies to type 1 interferons and IL-17 and IL-22 No autoantibodies to cytokines Autoantibodies to specific target organs Autoantibodies to specific target organs Asplenism No defined immunodeficiency Mucocutaneous candidiasis Association with other nonendocrine immunologic disorders like myasthenia gravis and idiopathic thrombocytopenic purpura Abbreviations: APS, autoimmune polyendocrine syndrome; HLA, human leukocyte antigen; IL, interleukin.

Other endocrine disorders that occur less frequently include type 1 diabetes (23%) and autoimmune thyroid disease (18%). Nonendocrine manifestations that present less frequently include alopecia (40%), vitiligo (26%), intestinal malabsorption (18%), pernicious anemia (31%), chronic active hepatitis (17%), and nail dystrophy. An unusual and debilitating manifestation of the disorder is the development of refractory diarrhea/obstipation that may be related to autoantibodymediated destruction of enterochromaffin or enterochromaffin-like cells. The incidence rates for many of these disorders peak in the first or second decade of life, but the individual disease components con­ tinue to emerge over time. Therefore, prevalence rates may be higher than originally reported.

PART 12 Endocrinology and Metabolism Diagnosis  The diagnosis of APS-1 is usually made clinically when two of the three major component disorders are found in an indi­ vidual patient. Siblings of individuals with APS-1 should be considered affected even if only one component disorder has been detected due to the known inheritance of the syndrome. Genetic analysis of the AIRE gene should be undertaken to identify mutations. Detection of anti–interferon α and anti–interferon ω antibodies can identify nearly 100% of cases with APS-1. The autoantibody arises independent of the type of AIRE gene mutation and is not found in other autoimmune disorders. Diagnosis of each underlying disorder should be done based on their typical clinical presentations (Table 401-3). Mucocutaneous candidiasis may present throughout the gastrointestinal tract, and it may be detected in the oral mucosa or from stool samples. Evaluation by a gastroenterologist to examine the esophagus for candidiasis or secondary stricture may be merited based on symptoms. Other gas­ trointestinal manifestations of APS-1, including malabsorption and obstipation, may also bring these young patients to the attention of gastroenterologists for first evaluation. Specific physical examination findings of hyperpigmentation, vitiligo, alopecia, tetany, and signs of hyper- or hypothyroidism should be considered as signs of develop­ ment of component disorders. The development of disease-specific autoantibody assays can help confirm disease and also detect risk for future disease. For example, where possible, detection of anticytokine antibodies to IL-17 and IL-22 would confirm the diagnosis of mucocutaneous candidiasis due to APS-1. The presence of anti-21-hydroxylase antibody or anti17-hydroxylase antibody (which may be found more commonly in adrenal insufficiency associated with APS-1) would confirm the pres­ ence or risk for Addison’s disease. Other autoantibodies found in type 1 diabetes (e.g., anti-GAD65), pernicious anemia, and other component conditions should be screened for on a regular basis (6- to 12-month intervals depending on the age of the subject). Laboratory tests, including a complete metabolic panel, phospho­ rous and magnesium, thyroid-stimulating hormone (TSH), adreno­ corticotropic hormone (ACTH; morning), hemoglobin A1c, plasma vitamin B12 level, and complete blood count with peripheral smear looking for Howell-Jolly bodies (asplenism), should also be performed at these time points. Detection of abnormal physical findings or test results should prompt subsequent examinations of the relevant organ system (e.g., presence of Howell-Jolly bodies indicates need for ultra­ sound of spleen). TREATMENT APS-1 Therapy of individual disease components is carried out as outlined in other relevant chapters. Replacement of deficient hormones (e.g., adrenal, pancreas, ovaries/testes) will treat most of the endo­ crinopathies noted. Several unique issues merit special emphasis. Adrenal insufficiency can be masked by primary hypothyroidism by prolonging the half-life of cortisol. The caveat therefore is that replacement therapy with thyroid hormone can precipitate an adrenal crisis in an undiagnosed individual. Hence, all patients with hypothyroidism and the possibility of APS should be screened

TABLE 401-3  Clinical Features and Recommended Follow-Up for APS-1 and APS-2 COMPONENT DISEASE RECOMMENDED EVALUATION APS-1 Addison’s disease Sodium, potassium, ACTH, cortisol, 21- and 17-hydroxylase autoantibodies Diarrhea History Ectodermal dysplasia Physical examination Hypoparathyroidism Serum calcium, phosphate, PTH Hepatitis Liver function tests Hypothyroidism/Graves’ disease TSH; thyroid peroxidase and/or thyroglobulin autoantibodies and anti-TSH receptor Ab Male hypogonadism FSH/LH, testosterone Malabsorption Physical examination, anti-IL-17 and anti-IL-22 autoantibodies Mucocutaneous candidiasis Physical examination, mucosal swab, stool samples Obstipation History Ovarian failure FSH/LH, estradiol Pernicious anemia CBC, vitamin B12 levels Splenic atrophy Blood smear for Howell-Jolly bodies; platelet count; ultrasound if positive Type 1 diabetes Glucose, hemoglobin A1c, diabetes-associated autoantibodies (insulin, GAD65, IA-2, ZnT8) APS-2 Addison’s disease 21-Hydroxylase autoantibodies, ACTH stimulation testing if positive Alopecia Physical examination Autoimmune hyper- or hypothyroidism TSH; thyroid peroxidase and/or thyroglobulin autoantibodies, anti-TSH receptor Ab Celiac disease Transglutaminase autoantibodies; small intestine biopsy if positive Cerebellar ataxia Dictated by signs and symptoms of disease Chronic inflammatory demyelinating polyneuropathy Dictated by signs and symptoms of disease Hypophysitis Dictated by signs and symptoms of disease, anti-Pit1 autoantibody Idiopathic heart block Dictated by signs and symptoms of disease IgA deficiency IgA level Myasthenia gravis Dictated by signs and symptoms of disease, antiacetylcholinesterase Ab Myocarditis Dictated by signs and symptoms of disease Pernicious anemia Anti–parietal cell autoantibodies   CBC, vitamin B12 levels if positive Serositis Dictated by signs and symptoms of disease Stiff man syndrome Dictated by signs and symptoms of disease Vitiligo Physical examination, NALP-1 polymorphism Abbreviations: Ab, antibody; ACTH, adrenocorticotropic hormone; APS, autoimmune polyendocrine syndrome; CBC, complete blood count; FSH, follicle-stimulating hormone; IL, interleukin; LH, luteinizing hormone; PTH, parathyroid hormone; TSH, thyroid-stimulating hormone. for adrenal insufficiency to allow treatment with glucocorticoids prior to the initiation of thyroid hormone replacement. Treatment of mucocutaneous candidiasis with ketoconazole in an individual with subclinical adrenal insufficiency may also precipitate adrenal crisis. Furthermore, mucocutaneous candidiasis may be difficult to eradicate entirely. Severe cases of disease involvement may require systemic immunomodulatory therapy, but this is not commonly needed. ■ ■APS-2 APS-2 (OMIM 269200) is more common than APS-1, with a preva­ lence of 1–2 in 100,000. It has a gender bias and occurs more often in

female patients, with a ratio of at least 3:1 compared to male patients. In contrast to APS-1, APS-2 often has its onset in adulthood, with a peak incidence between 20 and 60 years of age. It shows a familial, multigenerational heritage (Table 401-2). The presence of two or more of the following endocrine deficiencies in the same patient defines the presence of APS-2: primary adrenal insufficiency (Addison’s dis­ ease; 50–70%), Graves’ disease or autoimmune thyroiditis (15–69%), type 1 diabetes mellitus (T1D; 40–50%), and primary hypogonadism. Frequently associated autoimmune conditions include celiac disease (3–15%), myasthenia gravis, vitiligo, alopecia, serositis, and pernicious anemia. These conditions occur with increased frequency in affected patients but are also found in their family members (Table 401-3). Genetic Considerations  The overwhelming risk factor for APS-2 has been localized to the genes in the human lymphocyte antigen (HLA) complex on chromosome 6. Primary adrenal insufficiency in APS-2, but not APS-1, is strongly associated with both HLA-DR3 and HLA-DR4. Other class I and class II genes and alleles, such as HLA-B8, HLA-DQ2 and HLA-DQ8, and HLA-DR subtypes such as DRB1∗04:04, appear to contribute to organ-specific disease susceptibility (Table 401-4). HLA-B8- and HLA-DR3-associated ill­ nesses include selective IgA deficiency, juvenile dermatomyositis, der­ matitis herpetiformis, alopecia, scleroderma, autoimmune thrombocytopenia purpura, hypophysitis, metaphyseal osteopenia, and serositis. Several other immune genes have been proposed to be associated with Addison’s disease and therefore with APS-2 (Table 401-3). The “5.1” allele of a major histocompatibility complex (MHC) gene is an atypical class I HLA molecule MIC-A. The MIC-A5.1 allele has a very strong association with Addison’s disease that is not accounted for by linkage disequilibrium with DR3 or DR4. Its role is complicated because certain HLA class I genes can offset this effect. PTPN22 codes for a polymorphism in a protein tyrosine phosphatase, which acts on intracellular signaling pathways in both T and B lymphocytes. It has been implicated in T1D, Addison’s disease, and other autoimmune con­ ditions. CTLA4 is a receptor on the T-cell surface that modulates the activation state of the cell as part of the signal 2 pathway (i.e., binding to CD80/86 on antigen presenting cells). Polymorphisms of this gene TABLE 401-4  APS-2 and Other Polyendocrine Disorder Associations DISEASE HLA ASSOCIATION INITIATING FACTOR MECHANISM AUTOANTIGEN Graves’ disease DR3 Iodine Anti-CD52 Myasthenia gravis DR3, DR7 Thymoma Penicillamine Anti-insulin receptor ? SLE or other autoimmune disease Antibody Insulin receptor Hypoparathyroidism ? ? Antibody Cell surface inhibitor Insulin autoimmune syndrome DR4, DRB10406 Methimazole Sulfhydryl-containing drugs Celiac disease DQ2/DQ8 Gluten diet T cell Transglutaminase Type 1 diabetes DR3/DR4 DQ2/DQ8 ? Congenital rubella Addison’s disease DR3/DR4 DRB10404 Unknown T cell 21-Hydroxylase P450-5cc Thyroiditis DR3/DQB10201 DQA10301 Iodine Interferon α Pernicious anemia ? ? T cell Intrinsic factor H+/K+ ATPase Vitiligo ? Melanoma Antigen Immunization Chromosome dysgenesis–trisomy 21 and Turner’s syndrome DQA1*0301 ? ? Thyroid, islet, transglutaminase Hypophysitis ? Pit-1, TDRD6 ? Pituitary, Pit-1 Abbreviations: APS, autoimmune polyendocrine syndrome; SLE, systemic lupus erythematosus; TSH, thyroid-stimulating hormone.

appear to cause downregulation of the cell surface expression of the receptor, leading to decreased T-cell activation and proliferation. This appears to contribute to Addison’s disease and potentially other com­ ponents of APS-2. Allelic variants of the IL-2Rα are linked to develop­ ment of T1D and autoimmune thyroid disease and could contribute to the phenotype of APS-2 in certain individuals.

Diagnosis  When one of the component disorders is present, a second associated disorder occurs more commonly than in the general population (Table 401-3). There is controversy as to which tests to use and how often to screen individuals for disease. A strong family history of autoimmunity should raise suspicion in an individual with an initial component diagnosis. The development of a rarer form of autoimmu­ nity, such as Addison’s disease, should prompt more extensive screen­ ing for other linked disorders, as ~50% of Addison’s disease patients develop another autoimmune disease during their lifetime. Autoimmune Polyendocrine Syndromes CHAPTER 401 Circulating autoantibodies, as previously discussed, can precede the development of clinical disease by many years but would allow the clinician to follow the patient and identify the disease onset at its earliest time point (Tables 401-3 and 401-4). For each of the endocrine components of the disorder, appropriate autoantibody assays are listed and, if positive, should prompt physiologic testing to diagnose clinical or subclinical disease. For Addison’s disease, antibodies to 21-hydroxylase

antibodies are highly diagnostic for risk of adrenal insufficiency. However, individuals may take many years to develop overt symptoms of hypoadrenalism. Screening of 21-hydroxylase antibody–positive patients can be performed measuring morning ACTH and cortisol on a yearly basis. Rising ACTH values over time or low morning cortisol in association with signs or symptoms of adrenal insufficiency should prompt testing via the cosyntropin stimulation test (Chap. 398). T1D can be screened for by measuring autoantibodies directed against insulin, GAD65, IA-2, and ZnT8. Risk for progression to disease is based on the number of antibodies (≥2 islet autoantibodies with nor­ mal glucose tolerance is now defined as stage 1 of T1D as the lifetime risk for developing clinical symptoms is nearly 100%) and metabolic factors (impaired oral glucose tolerance test). Many efforts are ongo­ ing and underway to screen relatives of T1D patients and those in the general population for islet autoantibodies to identify individuals with Antibody TSH receptor Antibody Acetylcholine receptor Antibody Insulin T cell Insulin, GAD65, IA-2, ZnT8, IGRP T cell Thyroglobulin Thyroid peroxidase ? Melanocyte

preclinical disease who may elect to have treatment with teplizumab, anti-CD3 monoclonal antibody, to delay the clinical onset of diabetes.

Screening tests for thyroid disease can include anti–thyroid peroxi­ dase (TPO) or anti-thyroglobulin autoantibodies or anti-TSH receptor antibodies for Graves’ disease. Yearly measurements of TSH can then be used to follow these individuals. Celiac disease can be screened for using the anti–tissue transglutaminase (tTg) antibody test. For those <20 years of age, testing every 1–2 years should be performed, whereas less frequent testing is indicated after the age of 20 because the major­ ity of individuals who develop celiac disease have the antibody earlier in life. Positive tTg antibody test results should be confirmed on repeat testing, followed by small-bowel biopsy to document pathologic changes of celiac disease. Many patients have asymptomatic celiac disease that is nevertheless associated with osteopenia and impaired growth. If left untreated, symptomatic celiac disease has been reported to be associated with an increased risk of gastrointestinal malignancy, especially lymphoma, and osteoporosis later in life. PART 12 Endocrinology and Metabolism The knowledge of the particular disease associations should guide other autoantibody or laboratory testing. A complete history and physical examination should be performed every 1–3 years including complete blood count, metabolic panel, TSH, and vitamin B12 levels to screen for most of the possible abnormalities. More specific tests should be based on specific findings from the history and physical examination. TREATMENT APS-2 With the exception of Graves’ disease, the management of each endocrine component of APS-2 involves hormone replacement and is covered in detail in the chapters on adrenal (Chap. 398), thyroid (Chap. 394), gonadal (Chaps. 403 and 404), and para­ thyroid diseases (Chap. 422). As noted for APS-1, adrenal insuf­ ficiency can be masked by primary hypothyroidism and should be considered and treated as discussed above. In patients with T1D, decreasing insulin requirements or hypoglycemia, without obvious secondary causes, may indicate the emergence of adrenal insuf­ ficiency. Hypocalcemia in APS-2 patients is more likely due to malabsorption, potentially from undiagnosed celiac disease, than hypoparathyroidism. Immunotherapy for autoimmune endocrine disease has been reserved for T1D, for the most part, reflecting the lifetime burden of the disease for the individual patient and society. Although several immunotherapies (e.g., modified anti-CD3, rituximab, abatacept, alefacept, low-dose antithymocyte globulin, TNF-α inhibitors, and JAK inhibitors) can prolong the honeymoon phase of T1D, none has achieved long-term success. Notably, the antiCD3 monoclonal antibody (teplizumab) does delay the onset of clinical diabetes by an average of 3 years when administered to individuals with stage 2 T1D (e.g., those with autoantibodies and impaired glucose tolerance) and is now approved for clinical use in the United States. Active basic and clinical research using novel therapies and combinations may change the treatment landscape of this disease and other autoimmune conditions that share similar pathways. ■ ■IMMUNE CHECKPOINT INHIBITOR–INDUCED ENDOCRINE AUTOIMMUNITY Therapies that block immune checkpoints, such as programmed cell death protein 1 (PD-1), its ligand (PD-L1), or CTLA-4, are beneficial immunotherapies for many advanced-stage cancers. These immune checkpoint inhibitors (ICIs) block negative immune regulation, thereby allowing for an immune response directed against tumor cells. However, immune-related adverse events also occur, especially autoimmunity directed toward self-tissues. ICI-induced T1D, thy­ roid disease, hypophysitis, and adrenal insufficiency have all been reported with these therapies and in combination. Hypothyroidism

occurs in ~10% and T1D in 1–2% of those receiving monoclonal antibodies directed against PD-1 or PD-L1, and hypophysitis and adrenal insufficiency occur in <1% of treated patients. These autoim­ mune side effects can develop during or after therapy, mostly within a few weeks to months following the start of therapy. ICI-induced T1D has a very rapid onset, presents with diabetic ketoacidosis, is permanent, and requires lifelong exogenous insulin therapy for treat­ ment. There is a strong genetic association, with HLA-DR4 being present in ~70% of patients, and islet autoantibodies may be present at diagnosis. The pathogenesis is immune mediated as T lymphocyte infiltration has been documented in the pancreatic islets of an ICIT1D patient. Determining the mechanisms of autoimmune disease development following ICI therapies and developing biomarkers to stratify risk for autoimmune side effects prior to therapy are active areas of research. ■ ■IPEX Immune dysregulation, polyendocrinopathy, enteropathy, and X-linked disease (IPEX; OMIM 304790) is a rare X-linked recessive disorder. The disease onset is in infancy and is characterized by severe enteropathy, T1D, and skin disease, as well as variable association with several other autoimmune disorders. Many infants die within the first days of life, but the course is variable, with some children surviving for 12–15 years. Early onset of T1D, often at birth, is highly sugges­ tive of the diagnosis because nearly 80% of IPEX patients develop T1D. Although treatment of the individual disorders can temporarily improve the situation, treatment of the underlying immune deficiency is required and includes immunosuppressive therapy generally fol­ lowed by hematopoietic stem cell transplantation. Transplantation is the only life-saving form of therapy and can be fully curative by normalizing the imbalanced immune system found in this disorder. IPEX is caused by mutations in the FOXP3 gene, which is also mutated in the Scurfy mouse, an animal model that shares much of the same phenotype of IPEX patients. The FOXP3 transcription fac­ tor is expressed in regulatory T cells designated CD4+CD25+FOXP3+ (Treg). Lack of this factor causes a profound deficiency of this Treg population and results in rampant autoimmunity due to the lack of peripheral tolerance normally provided by these cells. Certain muta­ tions may lead to varying forms of expression of the full syndrome, and there are rare cases where the FOXP3 gene is intact but other genes involved in this pathway (e.g., CD25, IL-2Rα) may be causative. Future therapy with autologous CD4+ T cells transfected with a func­ tioning FOXP3 gene may offer a better long-term outcome than has been seen in those treated with stem cell transplantation. ■ ■THYMIC TUMORS Thymomas and thymic hyperplasia are associated with several auto­ immune diseases, with the most common being myasthenia gravis (44%) and red cell aplasia (20%). Graves’ disease, T1D, and Addison’s disease may also be associated with thymic tumors. Patients with myasthenia gravis and thymoma may have unique anti–acetylcholine receptor autoantibodies. Most thymomas lack AIRE expression within the thymoma, and this could be a potential factor in the development of autoimmunity. In support of this concept, thymoma is the one other disease with “frequent” development of anticytokine antibodies and mucocutaneous candidiasis in adults. The majority of tumors are malignant, and temporary remissions of the autoimmune condition can occur with resection of the tumor. ■ ■ANTI-INSULIN RECEPTOR ANTIBODIES This is a very rare disorder where severe insulin resistance (type B) is caused by the presence of anti-insulin receptor antibodies. It is associated with acanthosis nigricans, which can also be associated with other forms of less severe insulin resistance. About one-third of patients have an associated autoimmune illness such as systemic lupus erythematosus or Sjögren’s syndrome. Therefore, the presence of anti­ nuclear antibodies, elevated erythrocyte sedimentation rate, hyper­ globulinemia, leukopenia, and hypocomplementemia may accompany

the presentation. The presence of anti-insulin receptor autoantibodies leads to marked insulin resistance, requiring >100,000 units of insulin to be given daily with only partial control of hyperglycemia. Patients can also have severe hypoglycemia due to partial activation of the insulin receptor by the antibody. The course of the disease is variable, and several patients have had spontaneous remissions. A therapeutic approach that targets B lymphocytes, including rituximab, cyclophosphamide, and pulse steroids, has been validated in follow-on case reports to induce remission of the disease. ■ ■INSULIN AUTOIMMUNE SYNDROME (HIRATA’S SYNDROME) The insulin autoimmune syndrome, associated with Graves’ disease and methimazole therapy (or other sulfhydryl-containing medications), is of particular interest due to a remarkably strong association with a specific HLA haplotype. Such patients with elevated titers of anti-insulin antibodies frequently present with hypoglycemia. In Japan, the disease is restricted to HLA-DR4-positive individuals with DRB1∗04:06, while Caucasian patients predominantly have DRB1∗04:03 (which is related to DRB1∗04:06). In Hirata’s syndrome, the anti-insulin antibodies are often polyclonal. Discontinuation of the medication generally leads to resolution of the syndrome over time. There are very rare cases of insulin autoimmune syndrome not associated with sulfhydryl-containing medications that result in profound, life-threatening hypoglycemia. Treatment involves treating the underlying condition that causes anti-insulin antibodies, such as a B lymphocyte lymphoma (tend to have monoclonal insulin antibodies) or systemic lupus erythematosus. As hypoglycemia is profound when elevated titers of high-affinity insulin antibodies bind secreted insulin and then release it into circulation, treatment that begins with highdose glucocorticoids and rituximab to target B lymphocytes has been shown to be effective. ■ ■POEMS SYNDROME POEMS (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes; also known as Crow-Fukase syndrome; OMIM 192240) patients usually present with a progressive sensorimotor polyneuropathy, diabetes mellitus (50%), primary gonadal failure (70%), and a plasma cell dyscrasia with sclerotic bony lesions. Associated findings can be hepatosplenomegaly, lymphadenopathy, and hyperpigmentation. Patients often present in the fifth to sixth decade of life and have a median survival after diagnosis of <3 years. The syndrome is assumed to be secondary to circulating immunoglobulins, but patients have excess vascular endothelial growth factor as well as elevated levels of other inflammatory cytokines such as IL-1β, IL-6, and tumor necrosis factor α. Patients have been treated with thalidomide, and more recently lenalidomide, leading to a decrease in vascular endothelial growth factor. Hyperglycemia responds to small, subcutaneous doses of insulin. The hypogonadism is due to primary gonadal disease with elevated plasma levels of follicle-stimulating hormone and luteinizing hormone. Temporary resolution of the features of POEMS, including normalization of blood glucose, may occur after radiotherapy for localized plasma cell lesions of bone or after chemotherapy, lenalidomide and dexamethasone, or autologous stem cell transplantation. ■ ■OTHER DISORDERS Other diseases can exhibit polyendocrine deficiencies, including Kearns-Sayre syndrome, DIDMOAD syndrome (diabetes insipidus, diabetes mellitus, progressive bilateral optic atrophy, and sensorineural deafness; also termed Wolfram’s syndrome), Down’s syndrome or trisomy 21 (OMIM 190685), Turner’s syndrome (monosomy X, 45,X0), and congenital rubella. Kearns-Sayre syndrome (OMIM 530000) is a rare mitochondrial DNA disorder characterized by myopathic abnormalities leading to ophthalmoplegia and progressive weakness in association with several endocrine abnormalities, including hypoparathyroidism, primary

gonadal failure, diabetes mellitus, and hypopituitarism. Crystalline mitochondrial inclusions are found in muscle biopsy specimens, and such inclusions have also been observed in the cerebellum. Antiparathyroid antibodies have not been described; however, antibodies to the anterior pituitary gland and striated muscle have been identified, and the disease may have autoimmune components. These mitochondrial DNA mutations occur sporadically and do not appear to be associated with a familial syndrome.

Wolfram’s syndrome (OMIM 222300, chromosome 4; OMIM 598500, mitochondrial) is a rare autosomal recessive disease that is also called DIDMOAD. Neurologic and psychiatric disturbances are prominent in most patients and can cause severe disability. The disease is caused by defects in the Wolfram syndrome 1 (WFS1) gene, which encodes a 100-kDa transmembrane protein that has been localized to the endoplasmic reticulum and is found in neuronal and neuroendocrine tissue. Its expression induces ion channel activity with a resultant increase in intracellular calcium and may play an important role in intracellular calcium homeostasis. Wolfram’s syndrome appears to be a slowly progressive neurodegenerative process, and there is nonautoimmune selective destruction of the pancreatic beta cells. Diabetes mellitus with an onset in childhood is usually the first manifestation. Diabetes mellitus and optic atrophy are present in all reported cases, but expression of the other features is variable. Treatments targeting endoplasmic reticulum dysfunction are being tested and may be a bridge until gene therapy can be developed to treat the most severely affected cases. Autoimmune Polyendocrine Syndromes CHAPTER 401 Down’s syndrome, or trisomy 21 (OMIM 190685), is associated with the development of T1D, thyroiditis, and celiac disease. Patients with Turner’s syndrome also appear to be at increased risk for the development of thyroid disease and celiac disease. It is recommended to screen patients with trisomy 21 and Turner’s syndrome for associated autoimmune diseases on a regular basis. ■ ■GLOBAL CONSIDERATIONS Identification of these syndromes requires access to central laboratories with the ability to detect unique autoantibodies and to sequence the specific genes that may underlie these disorders. Early recognition of the clinical features of these disorders and timely referral and/or consultation with tertiary care centers to confirm the diagnosis and initiate therapy are important to improving outcomes. The AIRE recessive gene mutations found in APS-1 were originally described in high frequency in several populations including Finns, Iranian Jews, Sardinians, Norwegians, and Irish. Although individuals from many other countries have now been found to have these mutations and the newly identified dominant AIRE gene mutations, understanding the frequency in the background population may raise the clinician’s level of suspicion for these rare disorders. Hirata’s syndrome was originally reported in Japanese populations but also may be found in other populations, as noted. ■ ■FURTHER READING Anderson MS, Su MA: AIRE expands: New roles in immune tolerance and beyond. Nat Rev Immunol 16:247, 2016. Dispenzieri A: POEMS syndrome: 2021 update on diagnosis, riskstratification, and management. Am J Hematol 96:872, 2021. Husebye ES et al: Autoimmune polyendocrine syndromes. N Engl J Med 378:1132, 2018. Oftedal BE et al: A partial form of AIRE deficiency underlies a mild form of autoimmune polyendocrine syndrome type 1. J Clin Invest 133:e169704, 2023. Postow MA et al: Immune-related adverse events associated with immune checkpoint blockade. N Engl J Med 378:158, 2018. Ramos EL et al: Teplizumab and β-cell function in newly diagnosed type 1 diabetes. N Engl J Med 389:2151, 2023. Zhao Z et al: Autoimmune polyendocrine syndrome induced by immune checkpoint inhibitors: A systematic review. Cancer Immunol Immunother 70:1527, 2021.

16 - SECTION 2 Sex- and Gender-Based Medicine

SECTION 2 Sex- and Gender-Based Medicine

Section 2 Sex- and Gender-Based Medicine Courtney Finlayson, J. Larry Jameson,

John C. Achermann

Sex Development PART 12 Endocrinology and Metabolism Sex development begins in utero but continues into young adulthood with the achievement of sexual maturity and reproductive capability. The major determinants of sex development can be divided into three components: chromosomal sex, gonadal sex (sex determination), and phenotypic sex (sex differentiation) (Fig. 402-1). Variations at each of these stages can result in differences (or disorders) of sex develop­ ment (DSDs) (Table 402-1). In the newborn period, ~1 in 5000 babies undergo investigation because of atypical or ambiguous genitalia. Urgent assessment is indicated, because some causes such as congeni­ tal adrenal hyperplasia (CAH) can be associated with life-threatening adrenal crises. An experienced multidisciplinary team is important for counseling, planning appropriate investigations, discussing long-term well-being, supporting parents, and providing clear communication about the diagnosis and management options. DSDs can also present at other ages and to a range of health professionals, including with either absent puberty, primary amenorrhea, or androgenization in the teen years (Table 402-2). Other forms of gonadal dysfunction (e.g., Klinefelter syndrome [KS], Turner syndrome [TS]) often are diagnosed later in life by internists. Because DSDs are associated with a variety of psychological, reproductive, and potential medical consequences, an open dialogue must be established between the patient and health care providers to ensure continuity and attention to these issues across the life span. Gender variance and gender dysphoria are more common among some individuals with DSD than in the general population, though not high. Thus, attention to and comfort discussing gender identity is important. Support groups also have a valuable role to play for many patients and families. Care of individuals with DSDs should be holistic, often involving medical, psychosocial, and urogynecologic expertise, while acknowl­ edging that the best way to care for individuals with DSD is not always clear and should be individualized. There are many controversies, particularly concerning whether genitoplasty or prophylactic gonadec­ tomy in selected conditions should be performed for infants and young children prior to the age of consent. Accepted nomenclature is also Chromosomal Sex XX XY Ovary-determining genes Testis-determining genes Gonadal Sex Gonadal steroids & peptides (T, DHT, AMH/MIS) Gonadal steroids (E2) Phenotypic Sex FIGURE 402-1  Sex development can be divided into three major components: chromosomal sex, gonadal sex, and phenotypic sex. AMH, anti-müllerian hormone also known as Müllerian-inhibiting substance, MIS; DHT, dihydrotestosterone;

T, testosterone.

controversial. Previous terms such as intersex and hermaphrodite were changed by the 2006 Consensus Statement to disorder of sex develop­ ment and ovotesticular DSD. The term “disorder” is often considered negative and stigmatizing and thus has shifted toward difference of sex development, but no term is universally accepted. SEX DEVELOPMENT Chromosomal sex, defined by a karyotype, describes the X and/or Y chromosome complement (46,XY; 46,XX) established at the time of fertilization. The presence of a normal Y chromosome determines that testis development will occur even in the presence of multiple X chromosomes (e.g., 47,XXY). Loss of an X chromosome impairs gonad development (45,X or 45,X/46,XY mosaicism). Fetuses with no X chro­ mosome (45,Y) are not viable. Gonadal sex refers to the histologic and functional characteristics of gonadal tissue as testis or ovary. The embryonic gonad is initially “bipotential” and can develop into either a testis or an ovary (Fig. 402-2). Testis development is initiated by expression of the gene SRY (sexdetermining region on the Y chromosome) (from ~42 days after conception). Disruption of SRY prevents testis development in 46,XY individuals, whereas translocation of SRY in 46,XX individuals induces testis development and a male phenotype. SRY regulates SOX9 (SRYrelated HMG-box gene 9), leading to expression of a cascade of genes involved in testis development, including in Sertoli cell maturation and Leydig cell differentiation/steroidogenesis. Disruption of some of these genes can influence both the development of the testis and other organs, such as kidney (WT1), adrenal/spleen (SF1, NR5A1), brain (PPP1R12A), or heart (GATA4). Chromosomal segment duplications (e.g., Xp21 containing DAX1/NR0B1) can also impair testis develop­ ment, revealing the sensitivity of testis-determining pathway to gene dosage effects. Ovarian development is not a “passive” process. Many specific genes are expressed during early ovary development, some of which may repress testis development (e.g., WNT4, R-spondin-1) (Fig. 402-2). Once the ovary has formed, additional factors are required for normal follicular development (e.g., follicle-stimulating hormone [FSH] recep­ tor). Steroidogenesis in the ovary requires the development of follicles that contain granulosa cells and theca cells surrounding the oocytes (Chap. 404). Thus, there is relatively limited ovarian steroidogenesis until puberty. Germ cells also develop in a sex dimorphic manner. In the develop­ ing ovary, primordial germ cells (PGCs) show marked proliferation and enter meiosis, whereas they undergo mitotic arrest in the develop­ ing testis. Approximately 7 million germ cells are present in the fetal ovary toward the end of the second trimester, and 1 million remain at birth. Only 400 are ovulated during a woman’s reproductive life span (Chap. 404). Phenotypic sex refers to the structures of the external and internal genitalia and secondary sex characteristics. In early gestation, internal and external genitalia are initially similar in both sexes (“indifferent”). Sex-specific development occurs as a result of hormone action (Fig. 402-3). The developing testis releases anti-müllerian hormone (AMH; also known as müllerian-inhibiting substance [MIS]) from Sertoli cells and testosterone from Leydig cells. AMH acts through specific receptors to cause regression of the müllerian structures from 60–80 days after conception. At ~60–140 days after conception, tes­ tosterone supports the maintenance of wolffian structures, including the epididymides, vasa deferentia, and seminal vesicles. Testosterone is the precursor for dihydrotestosterone (DHT), a potent androgen that promotes development of the external genitalia, including the penis and scrotum (60–100 days, and thereafter) (Fig. 402-3). The urogenital sinus develops into the prostate and prostatic urethra in the male and into the urethra and lower portion of the vagina in the female. The genital tubercle becomes the glans penis in the male and the clitoris in the female. The urogenital swellings form the scrotum or the labia majora, and the urethral folds fuse to form the shaft of the penis and the male urethra or the labia minora. In the female, wolffian ducts regress and the müllerian ducts form the fallopian tubes, uterus, and upper segment of the vagina. A female phenotype will develop in the

17 - 402 Sex Development

402 Sex Development

Section 2 Sex- and Gender-Based Medicine Courtney Finlayson, J. Larry Jameson,

John C. Achermann

Sex Development PART 12 Endocrinology and Metabolism Sex development begins in utero but continues into young adulthood with the achievement of sexual maturity and reproductive capability. The major determinants of sex development can be divided into three components: chromosomal sex, gonadal sex (sex determination), and phenotypic sex (sex differentiation) (Fig. 402-1). Variations at each of these stages can result in differences (or disorders) of sex develop­ ment (DSDs) (Table 402-1). In the newborn period, ~1 in 5000 babies undergo investigation because of atypical or ambiguous genitalia. Urgent assessment is indicated, because some causes such as congeni­ tal adrenal hyperplasia (CAH) can be associated with life-threatening adrenal crises. An experienced multidisciplinary team is important for counseling, planning appropriate investigations, discussing long-term well-being, supporting parents, and providing clear communication about the diagnosis and management options. DSDs can also present at other ages and to a range of health professionals, including with either absent puberty, primary amenorrhea, or androgenization in the teen years (Table 402-2). Other forms of gonadal dysfunction (e.g., Klinefelter syndrome [KS], Turner syndrome [TS]) often are diagnosed later in life by internists. Because DSDs are associated with a variety of psychological, reproductive, and potential medical consequences, an open dialogue must be established between the patient and health care providers to ensure continuity and attention to these issues across the life span. Gender variance and gender dysphoria are more common among some individuals with DSD than in the general population, though not high. Thus, attention to and comfort discussing gender identity is important. Support groups also have a valuable role to play for many patients and families. Care of individuals with DSDs should be holistic, often involving medical, psychosocial, and urogynecologic expertise, while acknowl­ edging that the best way to care for individuals with DSD is not always clear and should be individualized. There are many controversies, particularly concerning whether genitoplasty or prophylactic gonadec­ tomy in selected conditions should be performed for infants and young children prior to the age of consent. Accepted nomenclature is also Chromosomal Sex XX XY Ovary-determining genes Testis-determining genes Gonadal Sex Gonadal steroids & peptides (T, DHT, AMH/MIS) Gonadal steroids (E2) Phenotypic Sex FIGURE 402-1  Sex development can be divided into three major components: chromosomal sex, gonadal sex, and phenotypic sex. AMH, anti-müllerian hormone also known as Müllerian-inhibiting substance, MIS; DHT, dihydrotestosterone;

T, testosterone.

controversial. Previous terms such as intersex and hermaphrodite were changed by the 2006 Consensus Statement to disorder of sex develop­ ment and ovotesticular DSD. The term “disorder” is often considered negative and stigmatizing and thus has shifted toward difference of sex development, but no term is universally accepted. SEX DEVELOPMENT Chromosomal sex, defined by a karyotype, describes the X and/or Y chromosome complement (46,XY; 46,XX) established at the time of fertilization. The presence of a normal Y chromosome determines that testis development will occur even in the presence of multiple X chromosomes (e.g., 47,XXY). Loss of an X chromosome impairs gonad development (45,X or 45,X/46,XY mosaicism). Fetuses with no X chro­ mosome (45,Y) are not viable. Gonadal sex refers to the histologic and functional characteristics of gonadal tissue as testis or ovary. The embryonic gonad is initially “bipotential” and can develop into either a testis or an ovary (Fig. 402-2). Testis development is initiated by expression of the gene SRY (sexdetermining region on the Y chromosome) (from ~42 days after conception). Disruption of SRY prevents testis development in 46,XY individuals, whereas translocation of SRY in 46,XX individuals induces testis development and a male phenotype. SRY regulates SOX9 (SRYrelated HMG-box gene 9), leading to expression of a cascade of genes involved in testis development, including in Sertoli cell maturation and Leydig cell differentiation/steroidogenesis. Disruption of some of these genes can influence both the development of the testis and other organs, such as kidney (WT1), adrenal/spleen (SF1, NR5A1), brain (PPP1R12A), or heart (GATA4). Chromosomal segment duplications (e.g., Xp21 containing DAX1/NR0B1) can also impair testis develop­ ment, revealing the sensitivity of testis-determining pathway to gene dosage effects. Ovarian development is not a “passive” process. Many specific genes are expressed during early ovary development, some of which may repress testis development (e.g., WNT4, R-spondin-1) (Fig. 402-2). Once the ovary has formed, additional factors are required for normal follicular development (e.g., follicle-stimulating hormone [FSH] recep­ tor). Steroidogenesis in the ovary requires the development of follicles that contain granulosa cells and theca cells surrounding the oocytes (Chap. 404). Thus, there is relatively limited ovarian steroidogenesis until puberty. Germ cells also develop in a sex dimorphic manner. In the develop­ ing ovary, primordial germ cells (PGCs) show marked proliferation and enter meiosis, whereas they undergo mitotic arrest in the develop­ ing testis. Approximately 7 million germ cells are present in the fetal ovary toward the end of the second trimester, and 1 million remain at birth. Only 400 are ovulated during a woman’s reproductive life span (Chap. 404). Phenotypic sex refers to the structures of the external and internal genitalia and secondary sex characteristics. In early gestation, internal and external genitalia are initially similar in both sexes (“indifferent”). Sex-specific development occurs as a result of hormone action (Fig. 402-3). The developing testis releases anti-müllerian hormone (AMH; also known as müllerian-inhibiting substance [MIS]) from Sertoli cells and testosterone from Leydig cells. AMH acts through specific receptors to cause regression of the müllerian structures from 60–80 days after conception. At ~60–140 days after conception, tes­ tosterone supports the maintenance of wolffian structures, including the epididymides, vasa deferentia, and seminal vesicles. Testosterone is the precursor for dihydrotestosterone (DHT), a potent androgen that promotes development of the external genitalia, including the penis and scrotum (60–100 days, and thereafter) (Fig. 402-3). The urogenital sinus develops into the prostate and prostatic urethra in the male and into the urethra and lower portion of the vagina in the female. The genital tubercle becomes the glans penis in the male and the clitoris in the female. The urogenital swellings form the scrotum or the labia majora, and the urethral folds fuse to form the shaft of the penis and the male urethra or the labia minora. In the female, wolffian ducts regress and the müllerian ducts form the fallopian tubes, uterus, and upper segment of the vagina. A female phenotype will develop in the

TABLE 402-1  Classification of Differences (Disorders) of Sex Development (DSDs) SEX CHROMOSOME DSD 46,XY DSD (SEE TABLE 402-3) 46,XX DSD (SEE TABLE 402-4) 47,XXY (Klinefelter syndrome and variants) 45,X (Turner syndrome and variants) 45,X/46,XY mosaicism (mixed gonadal dysgenesis) 46,XX/46,XY (chimerism/mosaicism) Gonadal (testis) development Complete or partial gonadal dysgenesis Impaired fetal Leydig cell function Ovotesticular DSD Testis regression Disruption in androgen synthesis or action Disruption of androgen biosynthesis   LH receptor (LHCGR)   Smith-Lemli-Opitz syndrome (DHCR7)   Steroidogenic acute regulatory (StAR) protein   Cholesterol side-chain cleavage (CYP11A1)   3β-Hydroxysteroid dehydrogenase II (HSD3B2)   17α-Hydroxylase/17,20-lyase (CYP17A1)   P450 oxidoreductase (POR)   Cytochrome b5 (CYB5A)   17β-Hydroxysteroid dehydrogenase III (HSD17B3)   5α-Reductase II (SRD5A2)   Aldo-keto reductase 1C2 (AKR1C2) Disruption of androgen action   Androgen insensitivity syndrome  Others include: Syndromic associations of male genital development Associated with fetal growth restriction Persistent müllerian duct syndrome Vanishing testis syndrome Isolated hypospadias Congenital hypogonadotropic hypogonadism Cryptorchidism Environmental influences Abbreviations: LH, luteinizing hormone; MODY, maturity-onset diabetes of the young; MRKH, Mayer-Rokitansky-Küster-Hauser syndrome. Source: Reproduced with permission from IA Hughes et al: Consensus statement on management of intersex disorders. J Pediatr Urol 2:148, 2006. absence of the gonad, but estrogen is needed for maturation of the uterus and breast at puberty. The prenatal hormone environment is likely one of many factors influencing aspects of gender identity and behavior. This is an area of ongoing research and is beyond the scope of this chapter. DIFFERENCES OF CHROMOSOMAL SEX Variations in sex chromosome number and structure can present as DSDs (e.g., 45,X/46,XY). KS (47,XXY) and TS (45,X) do not usually present with genital ambiguity but are associated with gonadal dys­ function (Table 402-3). TABLE 402-2  Presentation of Differences of Sex Development (DSD) at Different Stages of Life PRESENTATION FEATURES PROFESSIONAL EXAMPLES Prenatal Karyotype-phenotype discordance Obstetrician; fetal medicine Many Neonatal Atypical genitalia Obstetrician; neonatal medicine Many   Salt-losing crisis Pediatrician CAH (CYP21A2) Childhood Hernia Surgeon CAIS   Androgenization Endocrinologist CAH (CYP21A2, CYP11B1)   Poor growth Pediatrician Turner, 45,X/46,XY   Associated features Oncologist/nephrologist Wilms’ tumor Puberty Androgenization Estrogenization   Absent puberty Endocrinologist Gonadal dysgenesis, CAH (CYP17A1), Turner Post-puberty Amenorrhea Gynecologist CAIS Adult Infertility Andrologist Klinefelter, 45,X/46,XY, SF1 Abbreviations: CAH, congenital adrenal hyperplasia; CAIS, complete androgen insensitivity syndrome; 17β-HSD, 17β-hydroxysteroid dehydrogenase deficiency; SF1, steroidogenic factor 1 (NR5A1).

Gonadal (ovary) development Gonadal dysgenesis Ovotesticular DSD Testicular DSD Androgen excess Fetal   3β-Hydroxysteroid dehydrogenase II (HSD3B2)   21-Hydroxylase (CYP21A2)   P450 oxidoreductase (POR)   11β-Hydroxylase (CYP11B1) Fetoplacental   Aromatase deficiency (CYP19A1)   Oxidoreductase deficiency (POR) Maternal Maternal virilizing tumors (e.g., luteomas) Androgenic drugs Others include: Syndromic associations (e.g., cloacal anomalies) Müllerian agenesis/hypoplasia (e.g., MRKH) Uterine abnormalities (e.g., MODY5) Vaginal atresia (e.g., McKusick-Kaufman) Labial adhesions Sex Development CHAPTER 402 ■ ■KLINEFELTER SYNDROME (47,XXY)

(SEE ALSO CHAP. 403) Pathophysiology  The classic form of KS (47,XXY) occurs after meiotic nondisjunction of the sex chromosomes during gametogenesis (40% during spermatogenesis, 60% during oogenesis). Other forms of aneuploidy have similar features to KS (including mosaic 46,XY/47,XXY, 48,XXYY, and 48,XXXY) but are less common. KS has an incidence of at least 1 in 1000 men, but ~75% of cases are not diagnosed. Of those diagnosed, historically only 10% were identified prepubertally. How­ ever, noninvasive prenatal testing is leading to increased early detection. Endocrinologist Endocrinologist 17β-HSD, 5α-reductase, SF1 Ovotestis

WT1 Urogenital ridge SF1 SRY Bipotential gonad WNT4 RSPO1 FOXL2 46,XX 46,XY SOX9 Other genes Ovary Testis PART 12 Endocrinology and Metabolism Leydig cells Sertoli cells Granulosa cells AMH Testosterone DHT Müllerian regression Follicle development Male sexual differentiation FIGURE 402-2  The genetic regulation of gonadal development. See text for additional genes involved. AMH, anti-müllerian hormone (müllerian-inhibiting substance); DHT, dihydrotestosterone; FOXL2, forkhead transcription factor L2; RSPO1, R-spondin 1; SF1, steroidogenic factor 1 (also known as NR5A1); SOX9, SRYrelated HMG-box gene 9; SRY, sex-determining region on the Y chromosome; WNT4, wingless-type MMTV integration site 4; WT1, Wilms’ tumor–related gene 1. Ovary Fallopian tube Uterus Vagina Female Male A Clitoris Labia minora Labia majora Vagina B Female Male FIGURE 402-3  Sex development. A. Internal urogenital tract. B. External genitalia.

Clinical Features  KS is most commonly characterized by small testes, infertility, gynecomastia, tall stature/increased leg length, and hypogonadism in phenotypic males. At birth, most infants with KS do not have clinical features, although there are higher rates of cryptorchi­ dism and hypospadias. Most patients present in puberty with arrested pubertal development caused by testicular insufficiency. Others are diagnosed after puberty, based on low androgens, gynecomastia, or infertility. Testes are small and firm (median length 2.5 cm [4 mL volume]; almost always <3.5 cm [12 mL]) and typically seem inap­ propriately small for the degree of androgenization. Biopsies are not usually necessary but typically reveal seminiferous tubule hyaliniza­ tion and azoospermia. Other clinical features of KS are listed in Table 402-3. Plasma concentrations of FSH and luteinizing hormone (LH) are increased in most adults with 47,XXY, and plasma testosterone is decreased (50–75%), reflecting primary gonadal insufficiency. Estra­ diol is often increased, resulting in gynecomastia (Chap. 403). Those with mosaic forms of KS have less severe clinical features, have larger testes, and sometimes achieve spontaneous fertility. TREATMENT Klinefelter Syndrome Growth, endocrine function, and bone mineralization should be monitored, especially from adolescence. Educational and psy­ chological support is important for many individuals with KS. Gonad Epididymis Mesonephros Mullerian duct .. Testis Wolffian duct Vas deferens Urogenital sinus Seminal vesicle Prostate Genital tubercle Genital swelling Urethral fold and groove Glans penis Shaft of penis Scrotum Penoscrotal raphe

TABLE 402-3  Possible Associated Clinical Features of Sex Chromosome Variations DISORDER COMMON CHROMOSOMAL COMPLEMENT GONAD Klinefelter syndrome 47,XXY or 46,XY/47,XXY Hyalinized testes Male Male Increased incidence of gynecomastia Small testes, azoospermia, decreased facial and axillary hair, decreased libido, tall stature and increased leg length, decreased penile length, increased risk of breast tumors, thromboembolic disease, learning difficulties, anxiety, speech delay and decreased verbal IQ, obesity, diabetes mellitus, metabolic syndrome, varicose veins, hypothyroidism, systemic lupus erythematosus, epilepsy Turner syndrome 45,X or 45,X/46,XX Streak gonad or immature ovary   Clinical Features Infancy: lymphedema, web neck, shield chest, low-set hairline, cardiac defects and coarctation of the aorta, urinary tract malformations, and horseshoe kidney Childhood: short stature, cubitus valgus, short neck, short fourth metacarpals, hypoplastic nails, micrognathia, scoliosis, otitis media and sensorineural hearing loss, ptosis and amblyopia, multiple nevi and keloid formation, autoimmune thyroid disease, visuospatial learning difficulties Adulthood: absent puberty and primary amenorrhea, hypertension, obesity, dyslipidemia, impaired glucose tolerance and insulin resistance, autoimmune thyroid disease, cardiovascular disease, aortic root dilation, osteoporosis, inflammatory bowel disease, chronic hepatic dysfunction, increased risk of colon cancer, hearing loss 45,X/46,XY mosaicism 45,X/46,XY Testis or streak gonad Variable Variable Usually male     Short stature, increased risk of gonadal tumors, some Turner syndrome features Ovotesticular DSD 46,XX/46,XY Testis and ovary or ovotestis   Clinical Features   Possible increased risk of gonadal tumors Abbreviation: DSD, difference of sex development. Androgen supplementation improves virilization, libido, energy, hypofibrinolysis, and bone mineralization in men with low testos­ terone levels but may occasionally worsen gynecomastia (Chap. 403). Gynecomastia can be treated by surgical reduction if it causes concern (Chap. 403). Fertility has been achieved by using in vitro fertilization in men with oligospermia or with intracytoplasmic sperm injection (ICSI) after retrieval of spermatozoa by testicular sperm extraction techniques (Chap. 403). Long-term monitoring of men with KS is important given the increased risk of breast cancer, cardiovascular disease, metabolic syndrome, osteoporosis, and autoimmune disorders. Because most men with KS are never diagnosed, it is important that all internists consider this diagnosis in men with such features. ■ ■TURNER SYNDROME (GONADAL DYSGENESIS; 45,X) Pathophysiology  TS is caused by complete or partial loss of one X chromosome and affects ~1 in 2500 women. Approximately one-half of women with TS have a 45,X karyotype, ~20% have 45,X/46,XX mosa­ icism, and the remainder have structural abnormalities of the X chro­ mosome, or Y chromosome material. The clinical features of TS likely result at least in part from haploinsufficiency of X chromosomal genes (especially in the pseudoautosomal region), but the exact mechanisms remain poorly understood. Clinical Features  TS is characterized by female-typical external genitalia, short stature, hypergonadotropic hypogonadism, infertility, and other phenotypic features (Table 402-3). Infants may present with lymphedema, nuchal folds, low hairline, or left-sided cardiac defects or later in childhood with unexplained growth failure or delayed puberty. Although limited spontaneous pubertal development occurs in up to 30% of girls with TS (10%, 45,X; 60%, 45,X/46,XX) and up to 20% have menarche, the vast majority of women with TS develop complete ovarian insufficiency. Therefore, this diagnosis should be considered in all women who present with primary or secondary amenorrhea and elevated gonadotropin levels.

GENITALIA BREAST DEVELOPMENT EXTERNAL INTERNAL Clinical Features Sex Development CHAPTER 402 Female Hypoplastic female Immature female Clinical Features Variable Variable Gynecomastia TREATMENT Turner Syndrome The management of girls and women with TS requires a multi­ disciplinary approach to address many potentially affected organ systems according to TS practice guidelines. Individuals require long-term monitoring by an experienced cardiologist to follow con­ genital heart defects (CHDs) (30%) (bicuspid aortic valve, 30–50%; coarctation of the aorta, 30%; aortic root dilation, 5%), antibiotic prophylaxis for dental or surgical procedures, and serial magnetic resonance imaging (MRI) of aortic root dimensions, as progres­ sive aortic root dilation is associated with increased risk of aortic dissection. Individuals found to have congenital renal and urinary tract malformations (30%) are at risk for urinary tract infections, hypertension, and nephrocalcinosis. Hypertension can occur inde­ pendently of cardiac and renal malformations and should be moni­ tored and treated as in other patients with essential hypertension. Regular assessment of thyroid function, weight, dentition, hearing, speech, vision, and educational issues should be performed during childhood. Counseling about long-term growth and fertility issues should be provided. Patient support groups are active throughout the world and can play an invaluable role. Short stature is common, and untreated final height rarely exceeds 150 cm in nonmosaic 45,X TS. Recombinant growth hormone is used to increase adult height. Girls with evidence of ovarian insufficiency require estrogen replacement to induce breast and uterine development, support growth, and maintain bone mineralization. Most physicians now initiate low-dose estrogen therapy to induce puberty at an age-appropriate time (~11 years). Doses of estrogen are increased gradually to allow development over a 2- to 4-year period. Progestins are added later to regulate withdrawal bleeds. A very small percentage of women with TS have had spontaneous pregnancy, whereas others have achieved success­ ful pregnancy after ovum donation and in vitro fertilization, but the risks of cardiac complications are high, and expert counseling and

management are needed. The existence of Y chromosome mate­ rial in individuals with TS increases the risk for germ cell tumors, and gonadectomy has traditionally been advised. Increasingly, it is recommended that this decision also weigh potential for gonadal function and the importance of autonomous decision-making. Long-term follow-up of women with TS includes careful surveil­ lance of sex hormone replacement and reproductive function, bone mineralization, cardiac function and aortic root dimensions, blood pressure, weight and glucose tolerance, hepatic and lipid profiles, thyroid function, celiac disease screening, skin examination, and hearing. This service is provided by a dedicated TS clinic in some centers.

PART 12 Endocrinology and Metabolism ■ ■45,X/46,XY MOSAICISM The phenotype of individuals with 45,X/46,XY mosaicism (sometimes called mixed gonadal dysgenesis) can vary considerably. Some have a predominantly female phenotype (see TS above). Most 45,X/46,XY individuals have a male phenotype and testes, and the diagnosis is made incidentally after amniocentesis or during investigation of infertility. In practice, most newborns referred for assessment have atypical genitalia and variable somatic features. There is often marked asymmetry, with a streak gonad and hemiuterus on one side and a partially descended dysgenetic testis and hemiscrotum on the other side. Many children are raised as boys, but in some children, sex desig­ nation (whether to raise the baby as male or female) must be decided by parents and the multidisciplinary team. There is an increased risk of germ cell cancer (GCC), up to 35% in intraabdominal gonads, so prophylactic removal of intraabdominal gonads is usually consid­ ered. Individuals raised as males often have hypospadias surgery and removal of dysgenetic or streak gonads if the gonads cannot be brought down into the scrotum. Scrotal testes can be preserved but require regular examination for tumor development and sonography (and possibly biopsy) at the time of puberty. Testosterone supplementation may be required in puberty or adulthood if low testosterone is detected. Potential associated features (e.g., cardiac, renal) should be monitored according to TS guidelines. Infertility is typical, but non-azoospermia or focal spermatogenesis has been reported, highlighting the impor­ tance of individualized approaches to management. ■ ■OVOTESTICULAR DSD Ovotesticular DSD (OTDSD) is a condition in which an individual has both ovarian and testicular tissue, either by having both an ovary and a testis or by having an ovotestis. Most individuals with this diagnosis have a 46,XX karyotype (especially in individuals of African ancestry), although 46,XX/46,XY chimerism and very rarely a 46,XY karyotype is also possible. OTDSD usually presents with atypical genitalia at birth and sometimes breast development, cyclical hematuria, and/or phallic development at puberty. Progressive regression of the ovarian and/or testicular component can occur over time. Gender identity varies in OTDSD but often aligns with assigned sex. Risk of GCC is also elevated in OTDSD (~3%). Infertility is typical (especially in 46,XX testes with no Y chromosome), but births have occurred via ovum or sperm from individuals with other forms of OTDSD. DIFFERENCES OF GONADAL AND PHENOTYPIC SEX Differences of gonadal and phenotypic sex can result in reduced andro­ gen production or action in individuals with a 46,XY karyotype (46,XY DSD) or excess androgen production in individuals with a 46,XX karyotype (46,XX DSD) (Table 402-1). These conditions cover a spec­ trum of phenotypes ranging from phenotypic females with a Y chro­ mosome to phenotypic males with a 46,XX karyotype to individuals with atypical genitalia. Karyotype is a useful starting investigation for diagnosis with basic biochemical profiling. High-throughput genetic testing can help in reaching a definitive diagnosis. ■ ■46,XY DSD Underandrogenization of the 46,XY fetus reflects defects in andro­ gen production or action. It can result from disruption of testis

development, defects of androgen synthesis, or resistance to testoster­ one and DHT (Table 402-1). Disruption of Testis Development  •  TESTICULAR DYSGENESIS 

Complete gonadal dysgenesis (CGD, Swyer’s syndrome) is associated with streak gonads, müllerian structures (due to insufficient AMH/ MIS secretion), and a complete absence of androgenization. Pheno­ typic females with this condition usually present because of absent pubertal development and are found to have a 46,XY karyotype. Serum sex steroids, AMH/MIS, and inhibin B are low, and LH and FSH are elevated. Individuals with CGD typically identify as female. The risk of GCC is high, and intraabdominal gonads should be removed. In con­ trast, patients with partial gonadal dysgenesis (PGD, dysgenetic testes) may produce enough MIS to regress the uterus and sufficient testoster­ one for partial androgenization and, therefore, usually present in the newborn period with atypical genitalia, highlighting the spectrum of features that are typically seen with many DSDs. Testicular dysgenesis can result from disruption of testis-promoting genes (e.g., WT1, SF1, SRY, SOX9, MAP3K1, DHH, DHX37, and oth­ ers) or, rarely, duplication of chromosomal loci containing “antitestis” genes (e.g., DAX1) (Table 402-4). Among these, deletions or mutations of SRY and heterozygous mutations of SF1 (NR5A1) or DHX37 appear to be most common but still account collectively for <30% of cases. Associated clinical features may be present (Table 402-4). A family history of DSD, hypospadias, infertility, or early menopause is impor­ tant because variations in some genes (e.g., SF1/NR5A1, SOX8) can be associated with a range of reproductive phenotypes. SF1 variants are sometimes inherited from a mother in a sex-limited dominant man­ ner (which can mimic X-linked inheritance), and a woman may later develop primary ovarian insufficiency because of the effect of SF1 on the ovary. Gender identity can be variable in PGD. Dysgenetic testes have an increased risk of GCC. For descended testes, monitoring via physical examination is appropriate. If testes are intraabdominal and not able to be brought down, they may be removed to prevent GCC (risk up to 35% if intraabdominal). Dysgenetic testes may or may not produce sufficient testosterone for puberty. In those who identify as male, testosterone replacement may be needed. In those who identify as female, estrogen replacement will be needed for female-typical pubertal development and ongoing sex steroid requirements. Absent (vanishing) testis syndrome (bilateral anorchia) reflects regression of the testis during development. The absence of müllerian structures indi­ cates adequate secretion of AMH early in utero. Usually, androgeniza­ tion of the external genitalia is normal. The etiology is often unknown but sometimes associated with pathogenic variants in DHX37. These individuals can be offered testicular prostheses and androgen replace­ ment in adolescence and typically identify as male. Disruption of Androgen Synthesis  Defects in the pathway that regulates androgen synthesis (Fig. 402-4) cause underandrogenization of the 46,XY fetus (Table 402-1). Müllerian regression is unaffected because Sertoli cell function is preserved, and no uterus is found. These conditions can present with a spectrum of genital appearances, ranging from female-typical external genitalia or clitoromegaly in some individuals to penoscrotal hypospadias or a small phallus in others. LH RECEPTOR  Pathogenic variants in the LH receptor (LHCGR) cause Leydig cell hypoplasia and testosterone insufficiency due to LH resistance. STEROIDOGENIC ENZYME PATHWAYS  Mutations in steroidogenic acute regulatory protein (StAR) and CYP11A1 affect both adrenal and gonadal steroidogenesis (Fig. 402-4) (Chap. 398). Affected individuals (46,XY) usually have severe early-onset salt-losing adrenal failure and a female phenotype, although later-onset milder variants are increasingly reported. Defects in 3β-hydroxysteroid dehydrogenase type 2 (HSD3B2) also cause adrenal insufficiency in severe cases, but the accumula­ tion of dehydroepiandrosterone (DHEA) has a mild androgenizing effect, resulting in atypical genitalia or hypospadias. Salt loss occurs in many but not all children. Patients with CAH due to 17α-hydroxylase (CYP17A1) deficiency have variable underandrogenization and develop hypertension and hypokalemia due to the potent salt-retaining effects

TABLE 402-4  Selected Genetic Causes of 46,XY Differences of Sex Development (DSDs) GENE INHERITANCE GONAD UTERUS EXTERNAL GENITALIA ASSOCIATED FEATURES Disruption of Testis Development WT1 AD Dysgenetic testis +/– Female or ambiguous Wilms’ tumor, renal abnormalities, gonadal tumors (WAGR, DenysDrash and Frasier syndromes) SF1/NR5A1 AR/AD (SL) Dysgenetic testis/ Leydig dysfunction +/– Female, ambiguous or male SRY Y Dysgenetic testis or ovotestis +/– Female or ambiguous   SOX9 AD Dysgenetic testis or ovotestis +/– Female or ambiguous Campomelic dysplasia DHX37 AD Dysgenetic testis +/– Female, ambiguous or male Other causes of testicular dysgenesis include: DMRT1, CBX2, MAP3K1, SOX8, ZNRF3, GATA4/ZFPM2 (congenital heart disease), DHH (neuropathy), ARX (X-linked lissencephaly), TSPYL1 (sudden infant death), MYRF (diaphragmatic hernia), ESR2/NR3A2, SAMD9 (MIRAGE syndrome), ATRX (blood), PPP1R12A (brain, gastrointestinal), MAMLD1, dupXp21, dup1p35, del9p24, del10q23, and in several other congenital syndromes Disruption of Androgen Synthesis LHCGR AR Testis – Female, ambiguous or micropenis DHCR7 AR Testis – Variable Smith-Lemli-Opitz syndrome: coarse facies, second-third toe syndactyly, failure to thrive, developmental delay, cardiac and visceral abnormalities STAR AR Testis – Female or ambiguous Congenital lipoid adrenal hyperplasia (primary adrenal insufficiency) CYP11A1 AR Testis – Female or ambiguous Primary adrenal insufficiency HSD3B2 AR Testis – Ambiguous CAH, primary adrenal insufficiency ± salt loss, partial androgenization due to ↑ DHEA CYP17A1 AR Testis – Female or ambiguous CAH, hypertension due to ↑ corticosterone and 11-deoxycorticosterone, except in isolated 17,20-lyase deficiency CYB5A AR Testis – Ambiguous Apparent isolated 17,20-lyase deficiency; methemoglobinemia POR AR Testis – Ambiguous or male Mixed features of 21-hydroxylase deficiency and 17α-hydroxylase/17,20-lyase deficiency, sometimes associated with Antley-Bixler craniosynostosis HSD17B3 AR Testis – Female or ambiguous Partial androgenization at puberty, ↑ androstenedione-to-testosterone ratio SRD5A2 AR Testis – Ambiguous or micropenis AKR1C2 (AKR1C4) AR Testis – Female or ambiguous Decreased fetal DHT production Disruption of Androgen Action Androgen receptor X Testis – Female, ambiguous, micropenis or normal male Abbreviations: AD, autosomal dominant; AKR1C2, aldo-keto reductase family 1 member 2; AR, autosomal recessive; ARX, aristaless related homeobox, X-linked; CAH, congenital adrenal hyperplasia; CBX2, chromobox homologue 2; CYB5A, cytochrome b5; CYP11A1, P450 cholesterol side-chain cleavage; CYP17A1, cytochrome P450 family 17 subfamily A member 1; DAX1, dosage sensitive sex-reversal, adrenal hypoplasia congenita on the X chromosome, gene 1; DHEA, dehydroepiandrosterone; DHCR7, sterol 7 δ reductase; DHH, desert hedgehog; DMRT1,doublesex and mab3-related transcription factor 1; GATA4, GATA binding protein 4; HSD17B3, 17β-hydroxysteroid dehydrogenase type 3; HSD3B2, 3β-hydroxysteroid dehydrogenase type 2; LHR, LH receptor; MAP3K1, mitogen-activated protein kinase kinase kinase 1; MIRAGE, myelodysplasia, infection, restriction of growth, adrenal hypoplasia, genital phenotypes, and enteropathy; MYRF, myelin regulatory factor; POR, P450 oxidoreductase; SF1, steroidogenic factor 1; SL, sex-limited; SOX8, SRY-related HMG-box gene 8; SOX9, SRY-related HMG-box gene 9; SRD5A2, 5α-reductase type 2; SRY, sex-related gene on the Y chromosome; StAR, steroidogenic acute regulatory protein; TSPYL1, testis-specific Y-encoded-like protein 1; WAGR, Wilms’ tumor, aniridia, genitourinary anomalies, and mental retardation; WNT4, wingless-type mouse mammary tumor virus integration site, 4; WT1, Wilms’ tumor–related gene 1; ZFPM2, zinc finger protein, multitype 2; ZNRF3, zinc and ring finger 3. of corticosterone and 11-deoxycorticosterone. Patients with complete loss of 17α-hydroxylase function often present as phenotypic females who do not enter puberty and are found to have inguinal testes and hypertension in adolescence. Some mutations in CYP17A1 selectively impair 17,20-lyase activity without altering 17α-hydroxylase activity, leading to underandrogenization without mineralocorticoid excess and hypertension. Disruption of the coenzyme, cytochrome b5 (CYB5A), can present similarly, and methemoglobinemia is usually present. Mutations in P450 oxidoreductase (POR) affect multiple steroidogenic enzymes, leading to reduced androgen production and a biochemical pattern of apparent combined 21-hydroxylase and 17α-hydroxylase deficiency, sometimes with skeletal abnormalities (Antley-Bixler cra­ niosynostosis). Defects in 17β-hydroxysteroid dehydrogenase type 3 (HSD17B3) and 5α-reductase type 2 (SRD5A2) interfere with the synthesis of testosterone and DHT, respectively. These conditions are characterized by minimal or absent androgenization in utero, but some

Primary adrenal failure (rare); hyposplenia (common); primary ovarian insufficiency in female (46,XX) relatives Sex Development CHAPTER 402 Testicular regression syndrome Leydig cell hypoplasia Partial androgenization at puberty, ↑ testosterone-todihydrotestosterone ratio Phenotypic spectrum from complete androgen insensitivity syndrome (female external genitalia) and partial androgen insensitivity (ambiguous) to normal male genitalia and infertility phallic development can occur during adolescence due to the action of other enzyme isoforms. Individuals with 5α-reductase type 2 defi­ ciency have normal wolffian structures and usually do not develop sig­ nificant breast tissue. At puberty, the increase in testosterone may lead to virilizing features despite DHT deficiency. DHT gel can improve prepubertal phallic growth in patients raised as male. Prevention of testosterone exposure (by gonadectomy or pubertal suppression) in adolescence and estrogen replacement at puberty can be considered in individuals who identify as female. Disruption of alternative path­ ways to fetal DHT production might also present with 46,XY DSD (AKR1C2/AKR1C4). Disruption of Androgen Action  •  ANDROGEN INSENSITIV­ ITY SYNDROME  Pathogenic variants in the androgen receptor cause resistance to androgen (testosterone, DHT) action or the androgen insensitivity syndrome (AIS). AIS is a spectrum of disorders that affects

Cholesterol LH (testis) ACTH (adrenal) StAR (Cholesterol side chain cleavage enzyme) CYP11A1 Pregnenolone (3β-hydroxysteroid dehydrogenase 2) HSD3B2 PART 12 Endocrinology and Metabolism Progesterone (17α-hydroxylase) CYP17A1 17-hydroxyprogesterone CYP17A1, (17,20-lyase), CYB5A (Cytochrome b5) CYP21A2 (21-hydroxylase) Congenital adrenal hyperplasia and 46,XX androg- enization 11-deoxycortisol Androstenedione HSD17B3 (17β-hydroxysteroid dehydrogenase 3) CYP11B1 (11-hydroxylase) Cortisol Testosterone Glucocorticoid Pathway SRD5A2 (5α-reductase) Dihydrotestosterone Androgen Pathway FIGURE 402-4  Simplified overview of glucocorticoid and androgen synthesis pathways. Defects in CYP21A2 and CYP11B1 shunt steroid precursors into the androgen pathway and cause androgenization of the 46,XX fetus. Testosterone is synthesized in the testicular Leydig cells and converted to dihydrotestosterone peripherally. Defects in enzymes involved in androgen synthesis result in underandrogenization of the 46,XY fetus. ACTH, adrenocorticotropic hormone; LH, luteinizing hormone; StAR, steroidogenic acute regulatory protein. at least 1 in 100,000 46,XY individuals. Because the androgen receptor is X-linked, only 46,XY offspring are affected. The condition is usually inherited from a mother who carries the sequence variant but can also arise de novo. XY individuals with complete AIS (formerly called tes­ ticular feminization syndrome) have a female phenotype, normal breast development (due to aromatization of testosterone), a short vagina but no uterus (because AMH/MIS production is normal), sometimes scanty pubic and axillary hair, and typically a female gender identity and sex role behavior. Gonadotropins can be variable, but testoster­ one is usually elevated and AMH/MIS levels in childhood are normal or high. CAIS sometimes presents as inguinal hernias (containing testes) in childhood or more often with primary amenorrhea in late adolescence. In the past, gonadectomy was recommended early in childhood. Increasingly, risk of tumor development is weighed against potential for endogenous hormone function. Thus gonadectomy is often delayed and gonads are left in situ until breast development is complete. Subsequently, the adolescent or young adult should be coun­ seled about the risk of malignancy and the option for gonadectomy (with estrogen replacement), especially because early detection of pre­ malignant changes by imaging or biomarkers is currently not possible. The use of graded dilators in adolescence or young adulthood is often sufficient to dilate the vagina for sexual activity. Partial AIS (Reifenstein’s syndrome) results from androgen recep­ tor mutations that maintain residual function. Patients often present in infancy with penoscrotal hypospadias and undescended testes and with gynecomastia at the time of puberty. Gender identity can be vari­ able. At puberty, testes produce testosterone with variable phenotypic development. For those who identify as male, high-dose testosterone has been given to support development if puberty does not progress,

but long-term data are limited. For those raised as female, testosterone effects at puberty can be prevented (by pubertal suppression) and femaletypical puberty induced with estrogen. They also have an increased risk of GCC, again raising the question of if and when to perform gonadec­ tomy. Azoospermia and male-factor infertility also have been described in association with mild loss-of-function mutations in the androgen receptor. Androgen resistance without AR vari­ ants is called type 2 AIS (e.g., DAAM2). Congenital adrenal hyperplasia and 46,XY underandrog- enization ■ ■OTHER DISORDERS AFFECTING 46,XY MALES Persistent müllerian duct syndrome is the pres­ ence of a uterus in an otherwise phenotypic male. This condition can result from pathogenic variants in AMH or its receptor (AMHR2). Isolated hypospadias occurs in ~1 in 250 males. Many less severe cases are idiopathic. However, evidence of penoscrotal hypospadias, poor phal­ lic development, bilateral cryptorchidism, and/ or other clinical features requires investigation for an underlying DSD (e.g., partial gonadal dysgenesis, partial defect in testosterone action, or even severe forms of 46,XX CAH) or one of many DSD/hypospadias-associated syndromes. Unilateral undescended testes (cryptorchidism) affect >3% of boys at birth. Orchidopexy should be considered if the testis has not descended by 6–9 months of age. Bilateral cryptorchidism occurs less frequently and should raise suspicion of gonadotropin deficiency or DSD. Syndromic associations and intrauterine growth retardation also occur relatively frequently in association with impaired testicular function or target tissue responsiveness, but the underlying etiology of many of these conditions is unknown except in specific syndromes (e.g., MIRAGE [myelodys­ plasia, infection, restriction of growth, adrenal hypoplasia, genital phenotypes, and enteropathy], IMAGe [intrauter­ ine growth restriction, metaphyseal dysplasia, adrenal hypoplasia congenita, and genitourinary abnormalities]). 46,XY underandrog- enization only ■ ■46,XX DSD Androgenization (virilization) of the 46,XX fetus occurs when the gonad (ovary) contains androgen-secreting testicular tissue or after increased androgen exposure, which is usually adrenal in origin (Table 402-1). 46,XX Testicular DSD  Testicular tissue can develop in 46,XX tes­ ticular DSD (46,XX males) most often following translocation of SRY. This may be diagnosed with karyotype/phenotype discordance or later in life during evaluation for hypogonadism or infertility. Individuals with this condition develop testes with normal testosterone produc­ tion, leading to external male phenotype in utero, and produce AMH/ MIS to regress müllerian structures. They have azoospermia due to lack of the AZF region of the Y chromosome. Progressive testicular regression and hypogonadism are common. Gender identity is typi­ cally male. 46,XX OTDSD  Ovotestes (or testes) can also develop in individu­ als with a 46,XX karyotype following upregulation of SOX9 or SOX3 or defects in RSPO1, NR2F2, WT1, or SF1/NR5A1 (Table 402-5). OTDSD is discussed above under “Differences of Chromosomal Sex.” Increased Androgen Exposure  •  21-HYDROXYLASE DEFICIENCY

(CONGENITAL ADRENAL HYPERPLASIA)  The classic form of 21-hydroxylase deficiency (21-OHD) is the most common cause of CAH (Chap. 398), and it is the most common cause of androgeniza­ tion in chromosomal 46,XX children (incidence around 1 in 15,000

TABLE 402-5  Selected Genetic Causes of 46,XX Differences of Sex Development (DSDs) GENE INHERITANCE GONAD UTERUS EXTERNAL GENITALIA ASSOCIATED FEATURES Testicular/Ovotesticular DSD SRY Translocation Testis or ovotestis – Male or ambiguous   SF1/NR5A1 (codon 92) AD Testis or ovotestis +/– Male or ambiguous   Other causes of testicular/ovotesticular DSD include: COUP-TF2/NR2F2 (congenital heart disease), RSPO1 (palmar plantar hyperkeratosis, squamous cell skin carcinoma), WNT4 (SERKAL syndrome), WT1 (in zinc finger 4), dysregulation/duplication of SOX3 (Xq27) and SOX9 (dup17q24) Increased Androgen Synthesis HSD3B2 AR Ovary + Clitoromegaly CAH, primary adrenal insufficiency, mild androgenization due to ↑ DHEA CYP21A2 AR Ovary + Ambiguous CAH, phenotypic spectrum from severe salt-losing forms associated with adrenal insufficiency to simple virilizing forms with compensated adrenal function, ↑ 17-hydroxyprogesterone POR AR Ovary + Ambiguous or female Mixed features of 21-hydroxylase deficiency and 17α-hydroxylase/17,20-lyase deficiency, sometimes associated with Antley-Bixler craniosynostosis CYP11B1 AR Ovary + Ambiguous CAH, hypertension due to ↑ 11-deoxycorticosterone CYP19 AR Ovary + Ambiguous Maternal virilization during pregnancy, absent breast development at puberty Abbreviations: ACTH, adrenocorticotropin; AD, autosomal dominant; AR, autosomal recessive; CAH, congenital adrenal hyperplasia; COUP-TF2, chicken ovalbumin upstream promoter transcription factor 2; CYP11B1, 11β-hydroxylase; CYP19, aromatase; CYP21A2, 21-hydroxylase; DHEA, dehydroepiandrosterone; HSD3B2, 3β-hydroxysteroid dehydrogenase type 2; POR, P450 oxidoreductase; RSPO1, R-spondin 1; SERKAL, sex reversion, kidneys, adrenal and lung dysgenesis; SF1, steroidogenic factor 1; SOX3, SRY-related HMG-box gene 3; SOX9, SRY-related HMG-box gene 9; SRY, sex-related gene on the Y chromosome; WT1, Wilms’ tumor–related gene 1. live births) (Table 402-5). Affected individuals are homozygous or compound heterozygous for severely disruptive sequence variants in the gene (CYP21A2) encoding the enzyme 21-hydroxylase. Impaired 21-hydroxylase activity prevents adrenal glucocorticoid and mineralo­ corticoid synthesis, thus shunting steroid precursors into the androgen synthesis pathway (Fig. 402-4). Increased androgen synthesis in utero causes androgenization of the 46,XX fetus in the first trimester. Atypi­ cal genitalia are usually seen at birth, with varying degrees of clitoral enlargement and labial fusion. A salt-wasting crisis usually manifests between 5 and 21 days of life and is a potentially life-threatening event that requires urgent fluid resuscitation and steroid treatment. Thus, a diagnosis of 21-OHD should be considered in any baby with atypical genitalia with bilateral nonpalpable gonads. Males (46,XY) with 21-OHD have no genital abnormalities at birth but are equally susceptible to adrenal insuf­ ficiency and salt-losing crises. Excess androgen production can cause gonadotropin-independent precocious puberty in males with 21-OHD. Nonclassic 21-OHD is discussed in Chap. 398. TREATMENT Congenital Adrenal Hyperplasia Acute salt-wasting crises require fluid resuscitation, IV hydro­ cortisone, and correction of hypoglycemia. Once the patient is stabilized, glucocorticoids must be given to correct the cortisol insufficiency and suppress adrenocorticotropic hormone (ACTH) stimulation, thereby preventing further virilization, rapid skeletal maturation, and the development of polycystic ovaries. Mineralo­ corticoid replacement may be needed. Salt supplements may be required in early life. In childhood, treatment is also titrated care­ fully to prevent impairment of linear growth. In the future, different forms of glucocorticoid replacement and multimodal therapies may improve treatment options. See Chap. 398 for detailed discussion of hormone replacement. Individuals with 46,XX CAH due to classic 21-OHD historically often underwent genitoplasty in infancy, but if and when these procedures should be performed is debated. Concerns have arisen about the importance of assent/consent by the individual for genital surgery, potential long-term side effects related to sexual function and ability to achieve orgasm, and the increased incidence of non­ female gender identity. Surgical options include vaginoplasty and clitoroplasty. When vaginoplasty is performed in infancy, surgical

Sex Development CHAPTER 402 revision or vaginal dilation may still be needed in adolescence or adulthood and, if deferred, may be necessary for menstrual flow or intercourse. Current clinical practice guidelines can vary in different countries, including supporting parents to defer sur­ gery or for individuals to have no surgery. Women with 21-OHD frequently develop polycystic ovaries and have subfertility. The latter occurs due to multiple factors including anatomic barriers, hormone imbalances, and psychological effects of the condition. Preconception genetic counseling is recommended. Due to con­ cerns about fetal neurologic development, prenatal treatment with dexamethasone to prevent androgenization of a fetus is currently not recommended unless in a study protocol that allows long-term follow-up of all children treated. The treatment of other forms of CAH (including in 46,XY indi­ viduals) includes mineralocorticoid and glucocorticoid replace­ ment for salt-losing conditions (e.g., StAR, CYP11A1, HSD3B2), suppression of ACTH drive with glucocorticoids in disorders asso­ ciated with hypertension (e.g., CYP11B1), and appropriate sex hor­ mone replacement in adolescence and adulthood, when necessary. OTHER CAUSES  Increased androgen synthesis can also occur in CAH due to defects in POR, 11β-hydroxylase (CYP11B1), and 3β-hydroxysteroid dehydrogenase type 2 (HSD3B2) and with mutations in the genes encoding aromatase (CYP19A1). Increased androgen exposure in utero can occur with maternal virilizing tumors, luteomas, and ingestion of androgenic compounds. ■ ■OTHER DISORDERS AFFECTING 46,XX FEMALES Congenital absence of the vagina occurs in association with müllerian agenesis or hypoplasia as part of the Mayer-Rokitansky-Kuster-Hauser (MRKH) syndrome. This diagnosis should be considered in otherwise phenotypic females with primary amenorrhea. Associated features include renal (agenesis) and cervical spinal abnormalities. ■ ■LONG-TERM FOLLOW-UP Whether a DSD is diagnosed during childhood or adulthood, many individuals will require ongoing care. Medical care may include hor­ mone replacement, optimization of bone health, screening related to other associated clinical features, and care for infertility or sterility. There is increasing attention to fertility preservation and investiga­ tional gonadal tissue cryopreservation in the pediatric and young adult population, which may allow for increased fertility potential in adulthood. More frequently, individuals retain gonadal tissue at

18 - 403 Disorders of the Testes and Male Reproductive System

403 Disorders of the Testes and Male Reproductive System

increased risk for germ cell cancer, requiring monitoring and potential gonadectomy. Long-term urogynecologic follow-up may be needed. Psychosocial and psychosexual evaluation and management are also important, particularly to address the reported increased rates of men­ tal health symptoms and poorer quality of life sometimes related to social relationships.

■ ■GLOBAL CONSIDERATIONS The approach to an individual with atypical genitalia or another DSD requires cultural sensitivity, as the concepts of sex and gender vary widely around the world. Rare genetic DSDs can occur more frequently in specific populations (e.g., 5α-reductase type 2 in the Dominican Republic). Different forms of CAH also show ancestral and geographic variability. In many countries, appropriate biochemical or genetic tests may not be readily available, and access to appropriate forms of treat­ ment and support may be limited. PART 12 Endocrinology and Metabolism ■ ■FURTHER READING Ahmed SF et al: Turner HE. Society for Endocrinology UK Guidance on the initial evaluation of a suspected difference or disorder of sex development (Revised 2021). Clin Endocrinol (Oxf) 95:818, 2021. Claahsen-van der Grinten HL et al: Congenital adrenal hyperplasiacurrent insights in pathophysiology, diagnostics and management. Endocr Rev 43:91, 2022. Cools M et al: Caring for individuals with a difference of sex develop­ ment (DSD): A consensus statement. Nat Rev Endocrinol 14:415, 2018. Gravholt CH et al: The changing face of Turner syndrome. Endocr Rev 12:44, 2023. Gravholt CH et al: Clinical practice guidelines for the care of girls and women with Turner syndrome. Eur J Endocrinol 190:G53, 2024. Mongan NP et al: Androgen insensitivity syndrome. Best Pract Res Clin Endocrinol Metab 29:569, 2015. Morin J et al: Gonadal malignancy in patients with differences of sex development. Transl Androl Urol 9:2408, 2020. Zitzmann M et al: European Academy of Andrology guidelines on Klinefelter syndrome: Endorsing organization: European Society of Endocrinology. Andrology 9:145, 2021. Shalender Bhasin, J. Larry Jameson

Disorders of the Testes and

Male Reproductive System The male reproductive system regulates sex differentiation, androgen­ ization, and the hormonal changes that accompany puberty, ultimately leading to spermatogenesis and fertility. Under the control of the pitu­ itary hormones—luteinizing hormone (LH) and follicle-stimulating hormone (FSH)—the Leydig cells of the testes produce testosterone and germ cells are nurtured by Sertoli cells to divide, differentiate, and mature into sperm. During embryonic development, testosterone and dihydrotestosterone (DHT) induce the wolffian duct and virilization of the external genitalia. During puberty, testosterone promotes somatic growth and the development of secondary sex characteristics. In the adult, testosterone is necessary for spermatogenesis, libido and normal sexual function, and maintenance of muscle and bone mass. This chap­ ter focuses on the physiology of the testes and disorders associated with decreased androgen production, which may be caused by gonadotropin deficiency or by primary testis dysfunction. Infertility occurs in ~5% of men and is increasingly amenable to treatment by hormone replace­ ment or by using sperm transfer techniques. For further discussion of

sexual dysfunction, disorders of the prostate, and testicular cancer, see Chaps. 409, 92, and 93, respectively. DEVELOPMENT AND STRUCTURE

OF THE TESTIS The fetal testis develops from a single bipotential progenitor cell population in the undifferentiated gonad after expression of a genetic cascade that is initiated by the gene encoding SRY (sex-related gene on the Y chromosome) (Chap. 402). SRY, whose expression is regulated by histone modification and DNA methylation, induces differentiation of Sertoli cells, which surround germ cells and, together with peritubular myoid cells, form testis cords that will later develop into seminifer­ ous tubules. Sertoli cells direct the differentiation of fetal germ cells into spermatogenic precursors. Fetal Leydig cells and endothelial cells migrate into the gonad from the adjacent mesonephros but may also arise from interstitial cells that reside between testis cords. Fetal Leydig cells atrophy after birth and do not contribute to the origin of adult Leydig cells, which originate from undifferentiated progenitor cells that appear in the testis after birth and acquire full steroidogenic function during puberty. Testosterone produced by the fetal Leydig cells sup­ ports the growth and differentiation of Wolffian duct structures that develop into the epididymis, vas deferens, and seminal vesicles. Testos­ terone is also converted to DHT (see below), which induces formation of the prostate and the external male genitalia, including the penis, urethra, and scrotum. The development of the germ cells is dependent on normally functioning Sertoli and Leydig cells and cannot occur without them; in contrast, the somatic cells can develop and function without the germ cells. Testicular descent through the inguinal canal is controlled in part by Leydig cell production of insulin-like factor 3 (INSL3), which along with testosterone, acts through their cognate receptors—relaxin/insulin-like family peptide receptor 2 (RXFP2) and androgen receptor (AR)—to guide the inguinoscrotal descent of the testes. Sertoli cells produce Müllerian inhibiting substance (MIS), which causes regression of the Müllerian structures, including the fal­ lopian tube, uterus, and upper segment of the vagina. NORMAL MALE PUBERTAL DEVELOPMENT Puberty commonly refers to the maturation of the reproductive axis, initiation of gametogenesis, rhythmic sex hormone secretion, and the development of secondary sex characteristics. In addition to reproduc­ tive hormones, it requires a coordinated response of multiple hormonal systems including metabolic signals (e.g., leptin), as well as the adrenal and growth hormone (GH, IGF-1) axes (Fig. 403-1). The development of secondary sex characteristics is initiated by adrenarche, which usu­ ally occurs between 6 and 8 years of age when the adrenal gland begins to produce greater amounts of androgens from the zona reticularis, the principal site of dehydroepiandrosterone (DHEA) production. The sex maturation process is accelerated by the activation of the hypo­ thalamic-pituitary axis and the production of gonadotropin-releasing hormone (GnRH). The GnRH pulse generator in the infundibular Height velocity Testicular volume (mL) 4–6 10–12 15–25 Genitalia

Pubic hair

Tanner stages

Age (years)

FIGURE 403-1  Pubertal events in males. Sexual maturity ratings for genitalia and pubic hair and divided into five stages.

nucleus is active during fetal life and early infancy but is restrained until the early stages of puberty by a neuroendocrine brake imposed by the inhibitory actions of glutamate and γ-aminobutyric acid (GABA) in the mediobasal hypothalamus and neuropeptide Y. Kis­ speptin 1 (kiss1), neurokinin B, dynorophin (KNDy) neurons in the arcuate nucleus and possibly other kiss1 neurons in the anteroventral periventricular nucleus (AVPV), and neurons producing neuropep­ tide Y (NPY), agouti-related protein (AgRP), pro-opiomelanocortin (POMC), and cocaine and amphetamine-regulated transcript (CART) play an important role in the control of puberty. The Kisspeptin path­ way plays a critical role in puberty. Individuals with mutations of G protein-coupled kisspeptin receptor fail to enter puberty. Infusion of the Kiss1 is sufficient to induce premature puberty in nonhuman primates. Kisspeptin signaling plays an important role in mediating the feedback action of sex steroids on gonadotropin secretion and in regulating the tempo of sexual maturation at puberty. The metabolic control of puberty is mediated via the action of leptin secreted by adipocytes, and by neurons expressing NPY and AgRP, and by POMC and CART expressing neurons that transmit the energy sensing signals communicated by leptin to the Kiss1 neurons. MKRN3, an imprinted gene encoding makorin ring finger protein 3, serves as an upstream inhibitor of GnRH secretion and plays an important role in directing the onset of puberty. Leptin plays a permissive role in the resurgence of GnRH secretion at the onset of puberty, as leptin-deficient individuals also fail to enter puberty (Chap. 413). The adipocyte hormone leptin, the gut hormone ghrelin, neuropeptide Y, AgRP, CART, and kiss 1 integrate the signals originating in energy stores and metabolic tissues and control the onset of puberty through regulation of GnRH secre­ tion. Energy deficit and excess and metabolic stress are associated with disturbed reproductive maturation and timing of puberty. The early stages of puberty are characterized by nocturnal surges of LH and FSH. Growth of the testes is usually the first clinical sign of puberty, reflecting an increase in seminiferous tubule volume. Increasing levels of testosterone deepen the voice and stimulate muscle growth. Conversion of testosterone to DHT leads to growth of the external genitalia and pubic hair. DHT also stimulates prostate and facial hair growth and initiates recession of the temporal hairline. The growth spurt occurs at a testicular volume of ~10–12 mL. GH increases early in puberty and is stimulated in part by the rise in gonadal ste­ roids. GH increases the level of insulin-like growth factor 1 (IGF-1), which enhances linear bone growth. The prolonged pubertal exposure to gonadal steroids (mainly estradiol) ultimately induces epiphyseal closure and limits further bone growth. REGULATION OF TESTICULAR FUNCTION ■ ■REGULATION OF THE HYPOTHALAMICPITUITARY-TESTIS AXIS IN ADULT MAN Pulsatile secretion of GnRH in the hypothalamus is regulated by kis­ speptin, neurokinin B (NKB), and dynorphin (DYN) (Fig. 403-2) that are co-expressed within the KNDy neurons in the arcuate nucleus and are important regulators of mammalian reproduction. Kisspeptin binds to the kisspeptin (GPR54) receptors in the cell bodies of the GnRH neurons as well as in the GnRH nerve terminals in the median eminence to induce pulsatile GnRH secretion into the portal blood. As a component of this autocrine/paracrine loop, NKB released by the KNDy neurons activates NK3R to stimulate kisspeptin release. KNDy neurons also produce dynorphin A, which inhibits basal as well as NKB-stimulated kisspeptin release through the mediation of K-type opioid receptor. Exogenous opioids suppress LH and FSH and inhibit LH pulsatility likely by mimicking the effects of DYN, an endogenous opioid peptide that acts primarily through the κ-opioid receptor (KOR). The negative feedback effects of testosterone, estradiol, and progesterone are mediated through KNDy neurons in the preoptic area by inhibition of kisspeptin release. Mutations in the genes encoding NKB, tachykinin 3 (TAC3), or its receptor (TACR3) are associated with hypogonadotrophic hypogonadism. Hypothalamic GnRH regulates the production of the pituitary gonadotropins LH and FSH (Fig. 403-2). GnRH is released in discrete

Arcuate nucleus NK3R KOR Dyn NKB Preoptic area KNDY neurons Kiss Negative feedback by sex steroids Dyn – Disorders of the Testes and Male Reproductive System CHAPTER 403 GnRH neuron GPR54 GnRH Kiss Pulsatile GnRH secretion Median eminence Anterior pituitary E2 Pulsatile LH, FSH secretion Testosterone Inhibin B + – DHT Seminiferous tubules Tunica albuginea Vas deferens LH FSH Epididymis + + Interstitial Leydig cells (testosterone) Sertoli cell (Inhibin B) Spermatid Spermatogonium FIGURE 403-2  Hypothalamic-pituitary-gonadotropin axis, structure of testis, seminiferous tubule. DHT, dihydrotestosterone; Dyn, dynorphin A; E2, 17β-estradiol; FSH, follicle-stimulation hormone; GnRH, gonadotropin-releasing hormone; KISSR, G protein–coupled receptor 54 for kisspeptin; Kiss, kisspeptin; KNDY, kisspeptin, neurokinin B, dynorphin neurons; KOR, K-type opioid receptor; LH, luteinizing hormone; NKB, neurokinin B; NK3R, neurokinin 3 receptor. pulses approximately every 2 h, resulting in corresponding pulses of LH and FSH. These dynamic hormone pulses account in part for the wide variations in LH and testosterone, even within the same individual. LH acts primarily on the Leydig cell to stimulate testosterone synthesis. The regulatory control of androgen synthesis is modulated by dynamic integration of the feedforward elements exerted on the testis by LH

and FSH and the feedback exerted by testosterone and estrogen on both the hypothalamus and the pituitary. FSH acts on the Sertoli cell to regulate spermatogenesis and the production of inhibin B, which acts to selectively suppress pituitary FSH. Despite these somewhat distinct Leydig and Sertoli cell–regulated pathways, testis function is integrated at several levels: GnRH regulates both gonadotropins; spermatogenesis requires high levels of testosterone; and numerous paracrine interac­ tions between Leydig, Sertoli, and germ cells are necessary for normal testis function.

■ ■THE LEYDIG CELL: ANDROGEN SYNTHESIS LH binds to its transmembrane G protein–coupled receptor to activate the adenylyl cyclase/cyclic AMP/protein kinase A pathway. Stimula­ tion of the LH receptor induces steroid acute regulatory (StAR) pro­ tein, along with several steroidogenic enzymes involved in androgen PART 12 Endocrinology and Metabolism

C D

A 10 B

OH

Cholesterol Cholesterol side chain cleavage enzyme CYP11A1 StAR 3β HSD 1 Pregnenolone Progesterone allopregnenolone 3β-hydroxy steroid dehydrogenase 2 17α-hydroxylase CYP17A1 17α-hydroxylase CYP17 17-hydroxyprogesterone 17 hydroxypregnenolone CYP17A1 CYB5 δ4 Androstenedione DHEA 17β-hydroxysteroid dehydrogenase 3 17β-HSD 3 Androstenediol Testosterone OH O Steroid 5α-reductase type 2 SRD5A2 CYP19 Aromatase OH O H OH 5α-dihydrotestosterone Estradiol Alternate Backdoor Pathway Classical Pathway FIGURE 403-3  The biochemical pathway in the conversion of 27-carbon sterol cholesterol to androgens and estrogens.

synthesis. LH receptor mutations cause Leydig cell hypoplasia or agenesis, underscoring the importance of this pathway for Leydig cell development and function. The rate-limiting process in testosterone synthesis is the transport of intracellular cholesterol to the inner mitochondrial membrane by a protein complex that contains the ste­ roidogenic acute regulatory (StAR) protein and a translocator protein (TSPO), previously called peripheral benzodiazepine receptor protein. Mutations of the StAR protein are associated with congenital lipoid adrenal hyperplasia, a rare form of congenital adrenal hyperplasia (CAH) characterized by very low adrenal and gonadal steroids. The major enzymatic steps involved in testosterone synthesis are sum­ marized in Fig. 403-3. After cholesterol transport into the mitochon­ drion, the formation of pregnenolone, catalyzed by CYP11A1 (side chain cleavage enzyme) and auxiliary electron transferring proteins, is a limiting enzymatic step. The 17α-hydroxylase and the 17,20-lyase AKRIC2/4 CYP17A1 CYP17A1 Steroid 5α-reductase type 1 17 hydroxydihydroprogesterone 17 hydroxy allopregnanolone SRD5AI HSD17B6 17β-hydroxysteroid dehydrogenase 6 Androsterone Androstanedione 17β hydroxy steroid dehydrogenase

17β-hydroxy steroid dehydrogenase 3 HSD17B3 AKRICI-4 HSD17B3 OH 17β hydroxy steroid dehydrogenase 6 HSD17B6 AKRIC2 Androstanediol

reactions are catalyzed by a single enzyme, CYP17A1; posttranslational modification (phosphorylation) of this enzyme and the presence of specific enzyme cofactors, such as cytochrome B, confer 17,20-lyase activity selectively in the testis and zona reticularis of the adrenal gland. Although CYP17A1 is able to catalyze the conversion of pro­ gesterone to 17α-hydroxyprogesterone, most of δ4-androstenedione in humans is derived from the conversion of 17α-hydroxypregnenolone to DHEA in the δ5 pathway and further conversion of DHEA to δ4-androstenedione. Abiraterone is a dual inhibitor of 17α-hydroxylase and 17,20-lyase activities, which play an important role in androgen synthesis in castration-resistant prostate cancers. Testosterone can be converted to the more potent DHT by a family of steroid 5α-reductase enzymes, and it is aromatized to estradiol by CYP19 (aromatase). At least two isoforms of steroid 5α-reductase, SRD5A1 and SRD5A2, have been described; most known patients with 5α-reductase defi­ ciency have had mutations in SRD5A2, the predominant form in the prostate and the skin. Finasteride predominantly inhibits SRD5A2, whereas dutasteride is a dual inhibitor of both SRD5A1 and SRD5A2. DHT can also be derived through the backdoor pathway in which 17α-hydroxyprogesterone is converted to androsterone and eventually to DHT. Recent reports of mutations in the AKR1C2/4 genes in under­ virilized 46,XY individuals suggest that the backdoor pathway for DHT formation, which was originally described in the tammar wallaby, is active in the human fetal testis. The placental progesterone serves as a substrate for the synthesis of androsterone via the backdoor pathway, which is then converted to DHT in the genital tubercle. Testosterone Transport and Metabolism  In males, 95% of circulating testosterone is derived from testicular production (3–10 mg/d). Direct secretion of testosterone by the adrenal and the peripheral conversion of androstenedione to testosterone collectively account for another 0.5 mg/d of testosterone. Only a small amount of DHT (70 μg/d) is secreted directly by the testis; most circulating DHT is derived from peripheral conversion of testosterone. Most of the daily production of estradiol (~45 μg/d) in men is derived from aromatasemediated peripheral conversion of testosterone and androstenedione. Circulating testosterone is bound predominantly to sex hormone– binding globulin (SHBG) and albumin (Fig. 403-4) and, to a lesser extent, to cortisol-binding globulin (CBG) and orosomucoid (also known as α1 acid glycoprotein). SHBG binds testosterone with much Cortisol-binding globulin Free or unbound (1–4%) Albumin (33–34%) SHBG (44–66%) Bioavailable Orosomucoid Excretion Testosterone (3–10 mg/d) Aromatase (0.3%) Steroid 5α-reductase (6–8%) Testosterone 5α-Dihydrotestosterone (DHT) Estradiol • Masculinization of external genitalia • Prostate growth • Hair growth • Bone resorption • Epiphyseal closure • Hypothalamic/ pituitary feedback • Fat mass • Some vascular and behavioral effects • Libido • Wolffian duct • Muscle mass • Bone formation • Spermatogenesis • Erythropoiesis FIGURE 403-4  Androgen metabolism and actions. SHBG, sex hormone–binding globulin.

greater affinity than albumin, CBG, and orosomucoid. The binding proteins regulate the transport and bioavailability of testosterone. SHBG circulates as a dimer, and testosterone’s binding to SHBG involves intermonomeric allostery such that neither the conformation nor the binding affinity of the two monomers is equivalent. Similarly, estradiol binding to SHBG involves bidirectional, intermonomeric allostery that changes the distribution of both monomers among various energy and conformational states. Intermonomeric allostery offers a mechanism to extend the binding range of SHBG and regulate hormone bioavailability as sex hormone concentrations vary widely during life. Albumin contains multiple, allosterically coupled binding sites for testosterone. Testosterone shares these binding sites on albu­ min with free fatty acids. Commonly used drugs such as ibuprofen and some antibiotics can displace testosterone from albumin under various physiologic states or disease conditions, affecting its bioavailability. SHBG concentrations are decreased by androgens, obesity, diabetes mellitus, hypothyroidism, nephrotic syndrome, and genetic factors. Conversely, polymorphisms in the SHBG gene, estrogen administra­ tion, hyperthyroidism, chronic inflammatory illnesses, infections such as HIV or hepatitis B and C, aging, and the use of some anticonvulsants are associated with high SHBG concentrations.

Disorders of the Testes and Male Reproductive System CHAPTER 403 Testosterone is metabolized predominantly in the liver, although some degradation occurs in peripheral tissues, particularly the prostate and the skin. In the liver, testosterone is converted by a series of enzy­ matic steps that involve 5α and 5β-reductases, 3α- and 3β-hydroxysteroid dehydrogenases, and 17β-hydroxysteroid dehydrogenase into andros­ terone, etiocholanolone, DHT, and 3α-androstanediol. These com­ pounds undergo glucuronidation or sulfation before being excreted by the kidneys. Polymorphisms of these enzymes are associated with altered testosterone metabolism and circulating testosterone levels. Mechanism of Androgen Action  Testosterone exerts its bio­ logic effects by either binding to androgen receptor (AR) directly or after its conversion to its metabolites, DHT, and 11-ketotestosterone. 11-Ketotestosterone and 11-ketoandrostenedione are 11-oxygenated steroids and potent androgens that are produced in the testes, adrenals, and some peripheral tissues by the action of CYP11B1 and CYP11B2. DHT is converted in some tissues by 3β-hydroxysteroid dehydroge­ nase to 5α-androstane-3β,17β-diol, which is a high-affinity ligand and agonist of estrogen receptor β. 5α-DHT can also be converted by 3α-hydroxysteroid dehydrogenase in some cell types to 5α-androstane3α,17β-diol, a modulator of GABAA receptors. Testosterone also is aromatized by CYP19 to 17β estradiol, a ligand for estrogen recep­ tor, that can be further converted in tissues to catechol estrogens by addition of hydroxyl groups at C2 and C4 that are inhibitors of the catecholamine methyltransferase and affect angiogenesis and cell pro­ liferation (Fig. 403-5). 16-Hydroestradiol levels have been associated with breast cancer risk in women. The actions of testosterone on the Wolffian structures, skeletal muscle, erythropoiesis, and bone in men do not require its obligatory conversion to DHT. However, the conver­ sion of testosterone to DHT is necessary for the masculinization of the urogenital sinus and genital tubercle but is not obligatory for mediat­ ing its effects on the muscle, bone, or hematopoiesis. Aromatization of testosterone to estradiol mediates additional effects of testosterone on bone resorption, epiphyseal closure, sexual desire, vascular endothe­ lium, and fat. The AR is structurally related to the nuclear receptors for estrogen, glucocorticoids, and progesterone (Chap. 389). The AR, a 919–amino acid protein with a molecular mass of ~110 kDa, is encoded by a gene on the long arm of the X chromosome. A polymorphic region in the amino terminus of the receptor, which contains a variable number of glutamine and glycine repeats, modifies the transcriptional activity of the recep­ tor. The ligand binding to the AR induces conformational changes that dissociates it from heat shock protein and allows the recruitment and assembly of tissue-specific cofactors and causes it to translocate into the nucleus, where it binds to specific androgen response elements in the DNA or other transcription factors already bound to DNA. Thus, the AR is a ligand-activated transcription factor that regulates the expres­ sion of androgen-dependent genes in a tissue-specific manner. Some

OH O Testosterone Androgen receptor OH OH PART 12 Endocrinology and Metabolism O H H O O 11-ketotestosterone 5α DHT OH H OH H OH 5α-androstanediol,3β,17β-diol 5α-androstane,3α,17β-diol ERβ receptor GABAA receptor FIGURE 403-5  Testosterone as an androgen and precursor of other steroids with diverse actions. DHT, dihydrotestosterone; ERα, estrogen receptor α; Eαβ, estrogen receptor β. androgen effects, such as those on the smooth muscle, may be mediated by nongenomic AR signal transduction pathways. The nongenomic actions of testosterone involve direct activation of kinase signaling cascades such as the Src tyrosine kinase that activates the epidermal growth factor receptor and induces the downstream mitogen-activated protein kinase cascade (RAF, MEK, and ERK), resulting in increased transcription of the cyclic AMP response element binding protein transcription factor-regulated genes. Some effects of testosterone on cell proliferation and autophagy require the mediation of GPRC6A. Tes­ tosterone and DHT improve penile blood flow and erections by rapid nongenomic endothelial-dependent (increased nitric oxide production) and endothelium-independent inhibition of l-type calcium channels and/or activation of potassium channels in the vascular smooth muscle. ■ ■THE SEMINIFEROUS TUBULES: SPERMATOGENESIS The seminiferous tubules are convoluted, closed loops that empty into the rete testis, a network of progressively larger efferent ducts that ultimately form the epididymis (Fig. 403-2). The seminiferous tubules total ~600 m in length and compose about two-thirds of testis volume. The walls of the tubules are formed by polarized Sertoli cells that are apposed to peritubular myoid cells. Tight junctions between Sertoli cells create the blood-testis barrier. Germ cells compose the majority of the seminiferous epithelium (~60%) and are intimately embedded within the cytoplasmic extensions of the Sertoli cells, which function as “nurse cells.” Germ cells progress through characteristic stages of mitotic and meiotic divisions. A pool of type A spermatogonia serve as stem cells capable of self-renewal. Primary spermatocytes are derived from type B spermatogonia and undergo meiosis before progressing to spermatids that undergo spermiogenesis (a differentiation process involving chromatin condensation, acquisition of an acrosome, elonga­ tion of cytoplasm, and formation of a tail) and are released from Sertoli

OH OH OH OH OH ERα 17β-estradiol 16 hydroxyestradiol ERβ OH OH OH OH OH OH OH 2-hydroxyestradiol 4 hydroxyestradiol Catechol estrogens cells as mature spermatozoa. The complete differentiation process into mature sperm requires 74 days. Peristaltic-type action by peritubular myoid cells transports sperm into the efferent ducts. The spermatozoa spend an additional 21 days in the epididymis, where they undergo further maturation and capacitation. The normal adult testes produce

100 million sperm per day. Naturally occurring mutations in FSHβ or in the FSH receptor confirm an important, but not essential, role for this pathway in sper­ matogenesis. Females with mutations in FSHβ or the FSH receptor are hypogonadal and infertile because ovarian follicles do not mature; males with these mutations exhibit variable degrees of reduced sper­ matogenesis, presumably because of impaired Sertoli cell function. Because Sertoli cells produce inhibin B, an inhibitor of FSH, semi­ niferous tubule damage (e.g., by radiation) causes a selective increase of FSH. Testosterone reaches very high concentrations locally in the testis and is essential for spermatogenesis. The cooperative actions of FSH and testosterone are important in the progression of meiosis and spermiation. In the prepubertal testis, testosterone alone is insufficient for completion of spermatogenesis; however, in men with postpuber­ tal onset of gonadotropin deficiency, human chorionic gonadotropin (hCG) or recombinant LH can reinitiate spermatogenesis without FSH. FSH and testosterone regulate germ cell survival via the intrinsic and extrinsic apoptotic mechanisms. FSH may also play an important role in supporting spermatogonia. Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25), a testis-specific gonadotropin/androgen-reg­ ulated RNA helicase, is present in germ cells and Leydig cells and may be an important factor in the paracrine regulation of germ cell devel­ opment. Several cytokines and growth factors are also involved in the regulation of spermatogenesis by paracrine and autocrine mechanisms. The human Y chromosome contains two pseudoautosomal regions that are located at the two tips of Y chromosome and can recombine with homologous regions of the X chromosome (Fig. 403-6). The genes

Pseudoautosomal region 1 Short arm Yp Euchromatic region of short arm Male Specific Region of y (MSY) Centromere AZFc AZFb AZFa Euchromatic region of long arm b1/b3 G1/G3 Long arm Yq Heterochromatic region of long arm Pseudoautosomal region 2 FIGURE 403-6  Structure of the Y chromosome relevant for spermatogenesis. in the pseudoautosomal regions are involved in cell signaling, tran­ scriptional regulation, and mitochondrial function. Mutations of genes in pseudoautosomal region 1 are associated with mental disorders and short stature. The euchromatic part of the Y chromosome that does not recombine with the X chromosome is referred to as the malespecific region of the Y chromosome (MSY) and contains X-transposed sequences that have 99% homology with the X chromosome, singlecopy genes or pseudogene homologues of X-linked genes, and ampli­ conic sequences that are organized in large palindromes. The MSY contains nine families of Y-specific multicopy genes; many of these Y-specific genes are testis-specific and necessary for spermatogenesis. Nonallelic homologous recombination between highly homologous repeated sequences in the MSY region renders the Y chromosome susceptible to microdeletions. Microdeletions in four major nonover­ lapping subregions of the Y chromosome—AZFa, AZFb, AZFbc, and AZFc—which contain many spermatogenic genes, are associated with oligospermia or azoospermia. Microdeletions involving the AZFc region are the most common Y microdeletions in infertile men. Several partial deletions of the AZFc region have been described including the gr/gr deletion, which is associated with infertility among Caucasian men in Europe and the Western Pacific region, whereas the b2/b3 deletion is associated with male infertility in African and Dravidian men. Approxi­ mately 6 to 15% of infertile men with nonobstructive azoospermia or severe oligozoospermia harbor a Y microdeletion. Complete deletions of the AZFa and AZFb subregions are typically associated with Sertoli cells only and azoospermia and a poor prognosis for sperm retrieval. In contrast, AZFc subregion microdeletions are typically associated with oligozoospermia and higher success rates for sperm retrieval. TREATMENT Male Factor Infertility Treatment options for male factor infertility have expanded greatly in recent years. Secondary hypogonadism is highly amenable to treatment with pulsatile GnRH or gonadotropins (see below). Assisted reproductive technologies, such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), have provided new opportunities for patients with primary testicular failure and disorders of sperm transport. Choice of initial treatment options depends on sperm concentration and motility. Expectant manage­ ment should be attempted initially in men with mild male factor infertility (sperm count of 15–20 × 106/mL and normal motility). Treatment of moderate male factor infertility (10–15 × 106/mL and 20–40% motility) should begin with intrauterine insemina­ tion alone or in combination with treatment of the female partner with clomiphene or gonadotropins, but it may require IVF with or without ICSI. For men with a severe defect (sperm count of <10 × 106/mL, 10% motility), IVF with ICSI or donor sperm has

become the treatment of choice. Yq microdeletions will be transmitted through ICSI from the affected father to his male offspring if sperm carrying the Yq microdeletion is used.

CLINICAL AND LABORATORY EVALUATION OF MALE REPRODUCTIVE FUNCTION ■ ■HISTORY AND PHYSICAL EXAMINATION The history should focus on developmental stages such as puberty and linear growth, as well as androgen-dependent events such as early morning erections, frequency and intensity of sexual thoughts, and frequency of masturbation or intercourse. Although libido and the overall frequency of sexual acts are decreased in androgen-deficient men, young hypogonadal men can achieve erections in response to visual erotic stimuli. Men with acquired androgen deficiency often report decreased energy, low mood, and less commonly hot flushes. Disorders of the Testes and Male Reproductive System CHAPTER 403 The physical examination should focus on secondary sex characteristics such as hair growth, gynecomastia, testicular volume, prostate, and height and body proportions. Eunuchoid proportions are defined as an arm span >2 cm greater than height and suggest that androgen deficiency occurred before epiphyseal fusion. Hair growth in the face, axilla, chest, and pubic regions is androgen-dependent; however, changes may not be noticeable unless androgen deficiency is severe and prolonged. Ethnicity also influences the intensity of hair growth (Chap. 406). Testicular volume is measured by using a Prader orchidometer. Testes range from 3.5 to 5.5 cm in length, which cor­ responds to a volume of 12–25 mL. Advanced age does not influence testicular size, although the consistency becomes less firm. Because of its possible role in infertility, the presence of varicocele should be sought by palpation while the patient is standing; it is more common on the left side. Patients with Klinefelter syndrome have markedly reduced testicu­ lar volumes (1–2 mL). In congenital hypogonadotropic hypogonadism, testicular volumes provide a good index of the degree of gonadotropin deficiency and the likelihood of response to gonadotropin therapy. ■ ■GONADOTROPIN AND INHIBIN MEASUREMENTS LH and FSH are measured using two-site immunoradiometric, immu­ nofluorometric, or chemiluminescent assays, which have very low crossreactivity with other pituitary glycoprotein hormones and hCG and have sufficient sensitivity to measure the low levels present in patients with hypogonadotropic hypogonadism. In men with a low testosterone level, an LH level can distinguish primary (high LH) versus secondary (low or inappropriately normal LH) hypogonadism. An elevated LH level indicates a primary defect at the testicular level, whereas a low or inappropriately normal LH level suggests a defect at the hypothalamicpituitary level. LH pulses occur about every 1–3 h in normal men. Thus, gonadotropin levels fluctuate, and samples should be pooled or repeated when results are equivocal. FSH is less pulsatile than LH because it has a longer half-life. Selective increase in FSH suggests damage to the semi­ niferous tubules. Inhibin B, a Sertoli cell product that suppresses FSH, is reduced with seminiferous tubule damage. Inhibin B is a dimer with α-βB subunits and is measured by two-site immunoassays. GnRH Stimulation Testing  The GnRH test is performed by measuring LH and FSH concentrations at baseline and at 30 and 60 min after intravenous administration of 100 μg of GnRH. A mini­ mally acceptable response is a twofold LH increase and a 50% FSH increase. In the prepubertal period or with severe GnRH deficiency, the gonadotrope may not respond to a single bolus of GnRH; in these patients, GnRH responsiveness may be restored by chronic, pulsatile GnRH administration. With the availability of sensitive and specific LH assays, GnRH stimulation testing is used rarely. ■ ■TESTOSTERONE ASSAYS Total Testosterone  Total testosterone includes both unbound and protein-bound testosterone and is measured by radioimmunoas­ says, immunometric assays, or liquid chromatography tandem mass

spectrometry (LC-MS/MS). LC-MS/MS involves extraction of serum by organic solvents, separation of testosterone from other steroids by high-performance liquid chromatography and mass spectrometry, and quantitation of unique testosterone fragments by mass spectrometry. LC-MS/MS provides accurate and precise measurements of testoster­ one levels even in the low range and has emerged as the method of choice for testosterone measurement. The use of LC-MS/MS for the measurement of testosterone in laboratories that have been certified by the Centers for Disease Control and Prevention’s (CDC) Hormone Standardization Program for Testosterone (HoST) can ensure that tes­ tosterone measurements are accurate and calibrated to an international standard. Serum testosterone levels fluctuate because of its pulsatile, diurnal, and circannual secretory rhythms. Testosterone is generally lower in the late afternoon, or after eating a meal, and is reduced by acute illness. The harmonized normal range for total testosterone, measured using LC-MS/MS in nonobese populations of European and American men aged 19–39 years, is 264–916 ng/dL. This harmonized reference range can be applied to values from laboratories that are cer­ tified by the CDC’s HoST program.

PART 12 Endocrinology and Metabolism Alterations in SHBG levels due to aging, obesity, diabetes mellitus, hyperthyroidism, some types of medications, chronic illness, or genetic factors can affect total testosterone levels. Heritable factors contribute substantially to the population-level variation in testosterone levels. Genome-wide association studies have revealed polymorphisms in the SHBG gene as well as other loci that are uniquely associated with total and bioavailable testosterone levels, but not with SHBG levels, as important contributors to variation in testosterone levels. Measurement of Unbound Testosterone Levels  Most circu­ lating testosterone is bound to SHBG and to albumin; only 2.0–4.0% of circulating testosterone is unbound, or “free.” Free testosterone should ideally be measured by equilibrium dialysis under standardized conditions using an accurate and reliable assay for total testosterone. The unbound testosterone concentration also can be calculated from total testosterone, SHBG, and albumin concentrations. Recent research has shown that testosterone binding to SHBG is a multistep process that involves complex allosteric interactions between the two binding sites within the SHBG dimer; a novel ensemble allosteric model of testosterone’s binding to SHBG dimers provides good estimates of free testosterone concentrations. The previous law-of-mass-action equa­ tions based on linear models of testosterone binding to SHBG used assumptions that have been shown to be erroneous. Tracer analogue methods are relatively inexpensive and convenient, but they are inaccu­ rate. The term bioavailable testosterone refers to unbound testosterone plus testosterone bound loosely to albumin and reflects the concept that albumin-bound testosterone can dissociate at the capillary level, especially in tissues with long transit time, such as the liver and the brain. Bioavailable testosterone can be determined by the ammonium sulfate precipitation method. However, the measurements of bioavail­ able testosterone using the ammonium sulfate precipitation are techni­ cally challenging, susceptible to imprecision, and not recommended. hCG Stimulation Test  The hCG stimulation test is performed by administering a single injection of 1500–4000 IU of hCG intramuscu­ larly and measuring testosterone levels at baseline and 24, 48, 72, and 120 h after hCG injection. An alternative regimen involves three injec­ tions of 1500 units of hCG on 3 successive days and measuring testos­ terone levels 24 h after the last dose. An acceptable response to hCG is a doubling of the testosterone concentration in adult men. In prepubertal boys, an increase in testosterone to >150 ng/dL indicates the presence of testicular tissue. No response may indicate an absence of testicular tissue or marked impairment of Leydig cell function. Measurement of Anti-Mullerian hormone, a Sertoli cell product, is also used to detect the presence of testes in prepubertal boys with cryptorchidism. ■ ■SEMEN ANALYSIS Semen analysis is the most important step in the evaluation of male infertility. Samples are collected by masturbation following absti­ nence for 2–3 days. Semen volumes and sperm concentrations vary considerably among fertile men, and several samples may be needed

before concluding that the results are abnormal. Analysis should be performed within an hour of collection. Using semen samples from

4500 men in 14 countries, whose partners had a time to pregnancy of <12 months, the World Health Organization (WHO) has generated the following one-sided reference limits for semen parameters: semen volume, 1.5 mL; total sperm number, 39 million per ejaculate; sperm concentration, 15 million per mL; vitality, 58% live; progressive motil­ ity, 32%; total (progressive + nonprogressive) motility, 40%; and mor­ phologically normal forms, 4.0%. Some men with low sperm counts are fertile. Some studies suggest that sperm counts have declined in recent decades. A variety of tests for sperm function can be performed in specialized laboratories, but these add relatively little to the treat­ ment options. ■ ■TESTICULAR BIOPSY Testicular biopsy is useful in some patients with oligospermia or azoospermia as an aid in diagnosis and in assessing the feasibility of treatment. Fine-needle aspiration biopsy is performed under local anesthesia to aspirate tissue for histology. Alternatively, open biopsies can be performed under local or general anesthesia when more tissue is required. A normal biopsy in an azoospermic man with a normal FSH level suggests obstruction of the vas deferens, which may be correct­ able surgically. Biopsies are also used to harvest sperm for ICSI and to classify disorders such as hypospermatogenesis (all stages present but in reduced numbers), germ cell arrest (usually at primary spermatocyte stage), and Sertoli cell–only syndrome (absent germ cells) or hyaliniza­ tion (sclerosis with absent cellular elements). Testing for Y Chromosome Microdeletions  Testing for Y chro­ mosome microdeletions is indicated in infertile men with nonobstruc­ tive azoospermia or severe oligozoospermia (sperm density < 5 million/ mL). Y chromosome microdeletions are detected by extracting DNA from peripheral blood leukocytes and using polymerase chain reac­ tion (PCR) analysis of a small number of sequence-tagged sites on the Y chromosome (typically sY84 and sY86 in AZFa region, sY127 and SY134 in AZFb region, and sY254 and sY255 in AZFc region). Because these Y chromosome markers account for only a small fraction of the 23 million base pairs on the Y chromosome, a negative test does not exclude microdeletions in other subregions of the Y chromosome. DISORDERS OF SEXUAL DIFFERENTIATION See Chap. 402. DISORDERS OF PUBERTY The onset and tempo of puberty vary greatly in the general popula­ tion and are affected by genetic, nutritional, and environmental fac­ tors. Although the mean age for reaching Tanner stage 2 in boys is 11.5 years, the range is much wider (9–14 years). A substantial fraction of the variance in the timing of puberty is explained by heritable fac­ tors. The timing of pubertal onset is highly correlated within families and between twins. Genome-wide association studies for age of men­ arche in girls and age of voice deepening in boys have identified nearly 400 independent loci in girls and boys. Over the past century, the age of onset of puberty has fallen by 3 years and this secular trend towards earlier onset of puberty has continued during the past decade, in part due to improved nutrition as well as increasing obesity rates in children. ■ ■PRECOCIOUS PUBERTY Precocious puberty in boys is defined by progressive testicular enlarge­ ment (>4 mL) before 9 years of age associated with acceleration of linear growth and bone age. Earlier onset of puberty is associated with increased risk of breast and endometrial cancer, cardiovascular disease, hypertension, type 2 diabetes, hair pigmentation, and shorter life span. Isosexual precocity refers to premature sexual development consis­ tent with phenotypic sex and includes features such as the develop­ ment of facial hair and phallic growth. Isosexual precocity is divided into gonadotropin-dependent and gonadotropin-independent causes of androgen excess (Table 403-1). Heterosexual precocity refers to the premature development of estrogenic features in boys, such as breast development.

TABLE 403-1  Causes of Precocious or Delayed Puberty in Boys I. Precocious puberty A. Gonadotropin-dependent

  1. Idiopathic
  2. CNS tumors such as hypothalamic hamartoma, optic glioma, arachnoid cysts, astrocytoma, ependymoma, or tunerous sclerosis
  3. Inflammatory and infectious lesions
  4. Mutations in genes that regulate GnRH secretion, such as kisspeptin (KISS1), kisspeptin receptor (KISS1R), and makorin ring finger protein 3 (MKRN3) B. Gonadotropin-independent
  5. Congenital adrenal hyperplasia
  6. hCG-secreting tumor
  7. McCune-Albright syndrome
  8. Activating LH receptor mutations (familial male-limited precocious puberty)
  9. Exogenous androgens
  10. Androgen producing tumors of the adrenal or the testis II. Delayed puberty A. Constitutional delay of growth and puberty B. Systemic disorders
  11. Chronic disease
  12. Malnutrition
  13. Eating disorders C. CNS tumors and their treatment (radiotherapy and surgery) D. Hypothalamic-pituitary causes of pubertal failure (low gonadotropins)
  14. Congenital disorders associated with GnRH or gonadotropin deficiency (Table 403-2)
  15. Acquired disorders a. Pituitary tumors b. Hyperprolactinemia c. Infiltrative disorders, such as hemochromatosis E. Gonadal causes of pubertal failure (elevated gonadotropins)
  16. Klinefelter syndrome
  17. Bilateral undescended testes
  18. Orchitis
  19. Chemotherapy or radiotherapy
  20. Anorchia F. Androgen insensitivity Abbreviations: CNS, central nervous system; GnRH, gonadotropin-releasing hormone; hCG, human chronic gonadotropin; LH, luteinizing hormone. Gonadotropin-Dependent Precocious Puberty  This disor­ der, also called central precocious puberty (CPP), is less common in boys than in girls. It is caused by premature activation of the GnRH pulse generator, sometimes because of central nervous system (CNS) lesions such as hypothalamic hamartomas, but it is often idiopathic. CPP is characterized by gonadotropin levels that are inappropri­ ately elevated for age and LH and FSH responses to GnRH typical of those seen in postpubertal boys or adults. Magnetic resonance imaging (MRI) should be performed to exclude a mass, structural defect, infection, or inflammatory process. Mutations in MKRN3, an imprinted gene encoding makorin ring finger protein 3, that serves as an upstream inhibitor of GnRH secretion and is expressed only from the paternally inherited allele, have been associated with CPP. Lossof-function mutations in MKRN3 remove the brake that restrains pulsatile GnRH secretion, resulting in precocious puberty. Additional activating mutations in kisspeptin and kisspeptin receptor and loss-offunction mutations in delta-like homolog (DLK1) have been identified in patients with CPP. Gonadotropin-Independent Precocious Puberty  In boys with gonadotropin-independent precocious puberty, circulating andro­ gens are increased but gonadotropins are low. This group of disorders includes hCG-secreting tumors; CAH; sex steroid–producing tumors of the testis, adrenal, and ovary; accidental or deliberate exogenous sex

steroid administration; hypothyroidism; and activating mutations of the LH receptor or Gsα subunit.

Familial Male-Limited Precocious Puberty  Also called testotoxicosis, familial male-limited precocious puberty is an autosomal dominant disorder caused by activating mutations in the LH receptor, leading to constitutive stimulation of the cyclic AMP pathway and testosterone production. Clinical features include premature andro­ genization in boys, linear growth acceleration in early childhood, and advanced bone age followed by premature epiphyseal fusion. Testos­ terone is elevated, and LH is suppressed. Treatment options include inhibitors of testosterone synthesis (e.g., ketoconazole, abiraterone, medroxyprogesterone acetate), AR antagonists (e.g., flutamide and bicalutamide), and aromatase inhibitors (e.g., anastrozole). Disorders of the Testes and Male Reproductive System CHAPTER 403 MCCUNE-ALBRIGHT SYNDROME  This is a sporadic disorder caused by somatic (postzygotic) activating mutations in the Gsα subunit that links G protein–coupled receptors to intracellular signaling pathways (Chap. 424). The mutations impair the guanosine triphosphatase activity of the Gsα protein, leading to ligand-independent signaling of the Gs-coupled receptor, constitutive activation of adenylyl cyclase, and stimulation of testosterone production. In addition to sexual precoc­ ity, affected individuals may have autonomy in the adrenals, pituitary, and thyroid glands. Café au lait spots are characteristic skin lesions that reflect the onset of the somatic mutations in melanocytes during embryonic development. Constitutive Gsα activation in the postnatal multipotent skeletal stem cells leads to the formation of immature woven bone and replacement of the bone marrow with fibrotic stroma (polyostotic fibrous dysplasia). Treatment is similar to that in patients with activating LH receptor mutations. Bisphosphonates have been used to treat bone lesions. CONGENITAL ADRENAL HYPERPLASIA  Boys with CAH who are not well controlled with glucocorticoid suppression of adrenocorticotropic hormone (ACTH) can develop premature virilization because of exces­ sive androgen production by the adrenal gland (Chaps. 398 and 402). LH is low, and the testes are small. Some children with CAH, who are poorly controlled with glucocorticoid treatment, may develop gonadotropin-dependent precocious puberty with early maturation of the hypothalamic-pituitary-gonadal axis, elevated gonadotropins, and testicular growth. Similar development of gonadotropin-dependent precocious puberty has been reported in children with androgensecreting tumors or other conditions associated with androgen excess, likely due to androgen-induced skeletal maturation. Adrenal rests may develop within the testis of poorly controlled patients with CAH because of chronic ACTH stimulation; adrenal rests do not require surgical removal and regress with effective glucocorticoid therapy. Heterosexual Sexual Precocity  Breast enlargement in prepuber­ tal boys can result from familial aromatase excess, estrogen-producing tumors in the adrenal gland, Sertoli cell tumors in the testis, marijuana smoking, or exogenous estrogens or androgens. Occasionally, germ cell tumors that secrete hCG can be associated with breast enlargement due to excessive stimulation of estrogen production (see “Gynecomastia,” below). APPROACH TO THE PATIENT Precocious Puberty After verification of precocious development, serum testosterone, LH, and FSH levels should be measured to determine whether gonadotropins are increased in relation to chronologic age (gonad­ otropin-dependent) or whether sex steroid secretion is occur­ ring independent of LH and FSH (gonadotropin-independent). In children with gonadotropin-dependent precocious puberty, CNS lesions should be excluded by history, neurologic examination, and MRI scan of the head. If an organic cause is not found, one is left with the diagnosis of idiopathic central precocious puberty. Patients with high testosterone but suppressed LH concentrations have gonadotropin-independent precocious puberty; in these patients,

DHEA sulfate (DHEAS) and 17α-hydroxyprogesterone should be measured. High levels of testosterone and 17α-hydroxyprogesterone suggest the possibility of CAH due to 21α-hydroxylase or 11β-hydroxylase deficiency. If testosterone and DHEAS are ele­ vated, adrenal tumors should be excluded by obtaining a computed tomography (CT) scan of the adrenal glands. Patients with elevated testosterone but without increased 17α-hydroxyprogesterone or DHEAS should undergo evaluation of the testis by palpation and ultrasound to exclude a Leydig cell neoplasm. Activating mutations of the LH receptor or Gsα subunit should be considered in chil­ dren with gonadotropin-independent precocious puberty in whom CAH, androgen abuse, and adrenal and testicular neoplasms have been excluded. PART 12 Endocrinology and Metabolism TREATMENT Precocious Puberty In patients with a known cause (e.g., a CNS lesion or a testicular tumor), therapy should be directed toward the underlying disorder. In patients with idiopathic CPP, treatment with long-acting GnRH analogues is indicated in boys showing rapid pubertal progression, who are more advanced in pubertal development (e.g., Tanner stage 3 or greater genital development) and experiencing rapid linear growth or psychological distress. GnRH analogues suppress gonad­ otropins and testosterone, halt early pubertal development, delay accelerated bone maturation, prevent early epiphyseal closure, pro­ mote final height gain, and mitigate the psychosocial consequences of early pubertal development without causing osteoporosis. The treatment is most effective for increasing final adult height if it is initiated before age 6. Puberty resumes after discontinuation of the GnRH analogue. Counseling is an important aspect of the overall treatment strategy. In children with gonadotropin-independent precocious puberty, inhibitors of steroidogenesis, such as ketoconazole or abiraterone, AR antagonists, and aromatase inhibitors have been used empiri­ cally. Long-term treatment with spironolactone (a weak androgen antagonist) and ketoconazole also has been reported to normalize growth rate and bone maturation and to improve predicted height in small, nonrandomized trials in boys with familial male-limited precocious puberty. Aromatase inhibitors, such as testolactone and letrozole, have been used as adjuncts to antiandrogen therapy for children with familial male-limited precocious puberty, CAH, and McCune-Albright syndrome. More potent novel inhibitors of testosterone synthesis, such as abiraterone, have not been systemati­ cally evaluated in boys with gonadotropin-independent precocious puberty. ■ ■DELAYED PUBERTY Puberty is considered delayed in boys if it has not ensued by age 14, an age that is 2–2.5 standard deviations above the mean for healthy children. Pubertal delay is not necessarily pathologic and may be a variant of normal pubertal development in some children. Delayed puberty has been associated with lower peak bone mass, higher risk for metabolic and cardiovascular disorders, and lower risk for breast and endometrial cancer in women. Delayed puberty is more common in boys than in girls. There are four main categories of delayed puberty: (1) self-limited delayed puberty (previously called constitutional delay of puberty) (~60% of cases); (2) functional hypogonadotropic hypogonadism caused by systemic illness, malnutrition, or eating disorders (~20% of cases); (3) hypogonadotropic hypogonadism caused by congenital or acquired defects in the hypothalamic-pituitary region (~10% of cases); and (4) hypogonadism secondary to primary gonadal failure (~15% of cases) (Table 403-1). The self-limited delayed puberty is the most common cause that accounts for nearly two-thirds of boys and one-third of girls with delayed puberty. The self-limited puberty clusters in families and

displays a complex inheritance pattern, having an autosomal domi­ nant pattern of inheritance in some families, but autosomal recessive, X-linked, or bilineal pattern in other families. Self-limited delayed puberty and congenital hypogonadotropic hypogonadism share simi­ larities in their clinical presentation but differ in their clinical course and treatment. In boys with self-limited delayed puberty, pubertal progression will occur eventually, while in those with congenital hypogonadotropin hypogonadism, hormone treatment will be needed to induce secondary sex characteristics. Genetic studies of patients with congenital hypogonadotropic hypogonadism have identified >65 genes that are involved in regulating one or more of the following: (1) development and migration of GnRH neurons (e.g., ANOS1, PROK2, PROK2R, FGFR1, FGF8, FGF17, WDR11, and CHD7); (2) regulation of GnRH secretion (KISS1, KISS1R, TAC3, and TACR3); and (3) GnRH function (e.g., GNRH1, RNRHR). The mutations in some of these genes are associated with dysmorphic features or occur as a part of a syndromic constellation that can facilitate their identification. Some of the genes associated with self-limited delayed puberty are found uniquely in kindreds of children with this disorder, while others are similar to those found in families with congenital hypogonadotropic hypogonadism. Furthermore, 10 to 20% of children with congenital hypogonadotropic hypogonadism may experience spontaneous resto­ ration of GnRH and gonadotropin secretion in adulthood. Functional hypogonadotropic hypogonadism is more common in girls than in boys. Permanent causes of congenital hypogonadotropic hypogonadism or primary testicular failure are identified in <25% of boys with delayed puberty. APPROACH TO THE PATIENT Delayed Puberty History of systemic illness, eating disorders, excessive exercise, social and psychological problems, and abnormal patterns of linear growth during childhood should be verified. Boys with pubertal delay may have accompanying emotional and physical immaturity relative to their peers, which can be a source of anxiety. Physical examination should focus on height; arm span; weight; visual fields; and secondary sex characteristics, including hair growth, testicular volume, phallic size, and scrotal reddening and thinning. Testicular size >2.5 cm generally indicates that the child has entered puberty. The main diagnostic challenge is to distinguish those with selflimited delayed puberty, who will progress through puberty at a later age, from those with congenital hypogonadotropic hypogo­ nadism as both conditions present with low testosterone and low gonadotropin levels, delayed bone age and short stature. Pituitary priming by pulsatile GnRH is required before LH and FSH are synthesized and secreted normally. Thus, blunted responses to exogenous GnRH can be seen in patients with self-limited delayed puberty, congenital hypogonadotropic hypogonadism, or pituitary disorders. On the other hand, low-normal basal gonadotropin lev­ els or a normal response to exogenous GnRH is consistent with an early stage of puberty, which is often heralded by nocturnal GnRH secretion. The presence of micropenis or history of cryptorchidism are more suggestive of congenital hypogononadotropic hypogonad­ ism. However, self-limited delayed puberty remains a diagnosis of exclusion that requires ongoing evaluation until the onset of puberty and the growth spurt. TREATMENT Delayed Puberty A major challenge in the treatment of children with delayed puberty is to determine whether and when to initiate hormonal treatment. Reassurance without hormonal treatment is appropriate for many individuals with presumed self-limited delayed puberty. However, the impact of delayed growth and pubertal progression on a child’s social relationships and school performance should be weighed.

Boys with self-limited delayed puberty are less likely to achieve their full genetic height potential and have reduced total body bone mass as adults, mainly due to narrow limb bones and vertebrae as a result of impaired periosteal expansion during puberty. Furthermore, the time of onset of puberty is negatively associated with bone mineral content and density in boys at skeletal maturity. Judicious use of testosterone therapy in carefully selected boys with self-limited delayed puberty can induce pubertal induction and progression and promote short-term growth without compromising final height, and when administered with an aromatase inhibitor, it may improve final height. If therapy is considered appropriate, it can begin with 25–50 mg of testosterone enanthate or testosterone cypionate every 2–4 weeks or by using a 2.5-mg testosterone patch or 25-mg testosterone gel. Because aromatization of testosterone to estrogen is obligatory for mediating androgen effects on epiphyseal fusion, concomi­ tant treatment with aromatase inhibitors may allow attainment of greater final adult height. Testosterone treatment should be inter­ rupted after 6 months to determine if endogenous LH and FSH secretion have ensued. Other causes of delayed puberty should be considered when there are associated clinical features or when boys do not enter puberty spontaneously after a year of observation or treatment. Boys with confirmed congenital hypogonadotropic hypogonad­ ism require an earlier institution of hormonal treatment than those with self-limited delayed puberty. Optimization of future fertility potential may require initial treatment with hCG to induce develop­ ment of secondary sex characteristics as well as spermatogenesis to enable harvesting and cryopreservation of sperm. DISORDERS OF THE MALE REPRODUCTIVE AXIS DURING ADULTHOOD ■ ■HYPOGONADOTROPIC HYPOGONADISM Because LH and FSH are trophic hormones for the testes, impaired secretion of these pituitary gonadotropins results in secondary hypo­ gonadism, which is characterized by low testosterone in the setting of low or inappropriately normal LH and FSH. Hypogonadotropic hypogonadism can be classified into congenital and acquired disorders. Congenital disorders most commonly involve GnRH deficiency, which leads to gonadotropin deficiency. Acquired disorders are more com­ mon than congenital disorders and may result from sellar mass lesions, infiltrative diseases of the hypothalamus or pituitary, drugs, nutritional or psychiatric disorders, or systemic diseases. Those with the most severe congenital gonadotropin deficiency have complete absence of pubertal development, and, in some cases, hypospadias, undescended TABLE 403-2  Causes of Congenital Hypogonadotropic Hypogonadism GENE LOCUS INHERITANCE ASSOCIATED FEATURES A. Hypogonadotropic Hypogonadism due to GnRH Deficiency A1. GnRH Deficiency Commonly Associated with Hyposmia or Anosmia ANOS1 (KAL1) Xp22 X-linked Anosmia, renal agenesis, synkinesia, cleft lip/palate, oculomotor/visuospatial defects, gut malformations NELF (NCMF) 9q34.3 AR Anosmia, hypogonadotropic hypogonadism (some may be normosmic) FGF8 10q24 AR Anosmia (some patients may be normosmic), skeletal abnormalities FGF17 8p21.3 AR Anosmia (some patients may be normosmic) FGFR1 8p11-p12 AD Anosmia, cleft lip/palate, synkinesia, syndactyly PROK2 3p21 AR Anosmia/sleep dysregulation PROKR2 20p12.3 AR Variable CHD7 8q12.1   Anosmia, other features of CHARGE syndrome FEZ1 8p22 AR Anosmia, olfactory bulb aplasia WDR11 10q26 AD Anosmia SOX10 22q13   Deafness (Wardenburg Syndrome) HS6ST1 2q14 Complex Anosmia

testes, and micropenis. Patients with congenital or prepubertal onset of partial gonadotropin deficiency have delayed or arrested sex develop­ ment. The 24-h LH secretory profiles are heterogeneous in patients with hypogonadotropic hypogonadism, reflecting variable abnormali­ ties of LH pulse frequency or amplitude. In severe cases, basal LH is low, and there are no LH pulses. A smaller subset of patients has lowamplitude LH pulses or markedly reduced pulse frequency. Occasion­ ally, only sleep-entrained LH pulses occur, reminiscent of the pattern seen in the early stages of puberty.

Congenital Disorders Associated with Gonadotropin Defi­ ciency (See Chap. 391)  Congenital hypogonadotropic hypo­ gonadism is a heterogeneous group of disorders characterized by decreased gonadotropin secretion and testicular dysfunction either due to impaired function of the GnRH pulse generator or the gonadotrope. The disorders characterized by GnRH deficiency represent a family of monogenic or oligogenic disorders whose phenotype spans a wide spectrum. Some individuals with GnRH deficiency may suffer from complete absence of pubertal development, while others may mani­ fest varying degrees of gonadotropin deficiency and pubertal delay, and a subset that carries the same mutations as their affected family members may even have normal reproductive function. In ~10% of men with congenital isolated hypogonadotropic hypogonadism (IHH), reversal of gonadotropin deficiency may occur in adult life after sex steroid therapy. Also, a small fraction of men with IHH may present with testosterone deficiency and infertility in adult life after having gone through apparently normal pubertal development. Nutritional, emotional, or metabolic stress may unmask gonadotropin deficiency and reproductive dysfunction (e.g., hypothalamic amenorrhea) in some patients who harbor mutations in the candidate genes but who previously had normal reproductive function. Oligogenicity and genegene and gene-environment interactions may contribute to variations in clinical phenotype. Disorders of the Testes and Male Reproductive System CHAPTER 403 Mutations in >60 genes involved in the development and migration of GnRH neurons (e.g., ANOS1, PROK2, PROK2R, FGFR1, FGF8, FGF17, WDR11, CHD7), GnRH secretion (KISS1, KISS1R, TAC3, TACR3), or GnRH function (e.g., GNRH1, RNRHR) have been linked to congenital IHH. The genetic defect remains elusive in nearly twothirds of cases. Familial hypogonadotropic hypogonadism can be transmitted as an X-linked (20%), autosomal recessive (30%), or auto­ somal dominant (50%) trait. Some individuals with IHH have sporadic mutations in the same genes that cause inherited forms of the disorder. The genetic defects associated with GnRH deficiency can be classi­ fied as anosmic (Kallmann syndrome) or normosmic (Table 403-2), although the occurrence of both anosmic and normosmic forms of GnRH deficiency in the same families suggests commonality of pathophysiologic mechanisms. Kallmann syndrome, the anosmic form (Continued)

PART 12 Endocrinology and Metabolism TABLE 403-2  Causes of Congenital Hypogonadotropic Hypogonadism GENE LOCUS INHERITANCE ASSOCIATED FEATURES TUBB3 Tubulin β

AR Anosmia DUSP6 12q21.33 AR Anosmia GLCE 15q23 AR Anosmia (some patients may be normosmic) FLRT3 20p12.1 AR Anosmia (some patients may be normosmic) SPRY4 5q31.3 AR Anosmia (some patients may be normosmic) IL17RD 3p14.3 AR Anosmia SEMA3A 7q21.11   Anosmia SEMA7A 15q24.1   Anosmia as well as normosmia SEMA3E 7q21.11   Anosmia PLXNA1 3q21.3   Anosmia as well as normosmia DCC 18q21.2 AR Anosmia NTN1 17p13.1 AR Anosmia KLB 4p14 AR Metabolic disorders A2. GnRH Deficiency with Normal Sense of Smell GNRHR 4q21 AR None GnRH1 8p21 AR None KISS1 1q32.1 AR None KISS1R 19p13 AR None TAC3 12q13 AR Microphallus, cryptorchidism, reversal of GnRH deficiency TAC3R 4q25 AR Microphallus, cryptorchidism, reversal of GnRH deficiency LEPR 1p31 AR Obesity LEP 7q31 AR Obesity DMXL2 15q21.2 AR Polyendocrine polyneuropathy syndrome OTUD4 4q31.21 AR Ataxia (Gordon Holmes syndrome) RNF216 7p22.1 AR Ataxia (Gordon Holmes syndrome) STUB1 16p13.3 AR Ataxia POLR3B 12q23.3 AR Ataxia (hypomyelinating leukodystrophy-8 with hypogonadotropic hypogonadism [4H] syndrome) PNPLA6 19p13.2 AR Ataxia (Laurence-Moon syndrome) NR0B1 (Dax1) Xp21.2 X-linked Primary adrenal failure CCDC141 2q31.2 AR Normosmia IGSF10 3q25.1 AR Reversible and normosmic form of hypogonadotropic hypogonadism RNF216 7p22.1 AR Atxia, dementia, and hypogonadotropic hypogonadism (Gordon Holmes syndrome) B. Hypogonadotropic Hypogonadism Not Due to GnRH Deficiency PCSK1 5q15-21 AR Obesity, diabetes mellitus, ACTH deficiency HESX1 3p21 AR Septo-optic dysplasia, CPHD LHX3 9q34 AR CPHD (ACTH spared), cervical spine rigidity PROP1 5q35 AR CPHD (ACTH usually spared) FSHb 11p13 AR ↑ LH LHb 19q13 AR ↑ FSH SF1 (NR5A1) 9p33 AD/AR Primary adrenal failure, XY sex reversal Abbreviations: ACTH, adrenocorticotropic hormone; AD, autosomal dominant; AR, autosomal recessive; CCDC141, coiled-coil domain containing 141; CHARGE syndrome, eye coloboma, heart defects, choanal atresia, growth and developmental retardation, genitourinary anomalies, ear anomalies; CPHD, combined pituitary hormone deficiency; DAX1, dosage-sensitive sex-reversal, adrenal hypoplasia congenita, X chromosome; DCC, deleted in colon cancer; DMXL2, DMX like 2; DUSP6, dual specificity phosphatase 6; FGFR1, fibroblast growth factor receptor 1; FGF17, fibroblast growth factor 17; FSHb, follicle-stimulating hormone β-subunit; FLRT3, fibronectin like domain containing leucine rich transmembrane protein 3; GH, growth hormone; GLCE, glucuronic acid epimerase; GNRHR, gonadotropin-releasing hormone receptor; GPR54, G protein– coupled receptor 54; HESX1, homeobox gene expressed in embryonic stem cells 1; IGSF10, immunoglobulin superfamily member 10; KAL1, Kallmann syndrome interval gene 1, also known as anosmin 1; KISS1, kisspeptin 1; KLB, klotho-1; LEP, leptin; LEPR, leptin receptor; LHX3, LIM homeobox gene 3; LHb, luteinizing hormone β-subunit; NELF, nasal embryonic luteinizing hormone–releasing hormone factor; NSMF, NMDA receptor synaptonuclear signaling and neuronal migration factor; NR0B1, nuclear receptor subfamily 0, group B, member 1; NTN1, netrin-1; OTUD4, OUT domain containing protein 4; PCSK1, proprotein convertase subtilisin/kexin type 1; PLXNA1, plexin A1; PNPLA6, patatin-like phospholipase domain-containing protein 6; PC1, prohormone convertase 1; PROK2, prokineticin 2; PROKR2, prokineticin 2 receptor; PROP1, prophet of pit 1; RNF216, ring finger protein 216; POLR3B, polymerase III RNA subunit B; SEMA3A, semaphorin 3A; SEMA7A, semaphorin 7A; SEMA3E, semoaphorin 3E; SF1, steroidogenic factor 1; SPRY4, sprouty RTK signaling antagonist 4; STUB1, srip 1 homologous and U box containing protein 1; TUBB3, tubulin beta 3; IL17RD, interleukin 17 receptor D. (Continued) of GnRH deficiency, can result from mutations in one or more neuro­ developmental genes associated with olfactory bulb morphogenesis or the migration of GnRH neurons from their origin in the region of the olfactory placode, along the scaffold established by the olfactory nerves, through the cribriform plate into their final location into the preoptic region of the hypothalamus. Thus, mutations in KAL1, NMDA recep­ tor synaptonuclear signaling and neuronal migration factor (NSMF), genes involved in fibroblast growth factor (FGF) signaling (FGF8, FGFR1, FGF17, IL17RD, DUSP6, SPRY4, and FLRT3), NELF, genes involved in PROK signaling (PROK2 and PROK2R), WDR11, SOX10, TUBB3 SEMA3, HS6ST1, CHD7, and FEZF1 have been described in patients with Kallmann syndrome; among these mutations in ANOS1, CHD7, FGF8, FGFR1, PRROK2, and PROLR2 are the most common. An X-linked form of IHH is caused by mutations in the ANOS1 gene,

Disorders of the Testes and Male Reproductive System CHAPTER 403 which encodes anosmin, a protein that mediates the migration of neu­ ral progenitors of the olfactory bulb and GnRH-producing neurons. These individuals have GnRH deficiency and variable combinations of anosmia or hyposmia. Proteins such as those involved in FGF and prokineticin signaling and KAL1, which account for the great majority of Kallmann syndrome cases, interact with heparin sulfate glycosami­ noglycan compounds within the extracellular matrix in supporting GnRH neuronal migration. Mutations in the FGFR1 gene cause an autosomal dominant form of hypogonadotropic hypogonadism that clinically resembles Kallmann syndrome; mutations in its putative ligand, the FGF8 gene product, have also been associated with IHH. Craniofacial tissues and olfactory ensheathing cells also play important roles in neurogenesis and migration of the GnRH neurons, and addi­ tional proteins that regulate these cell types may also be involved in the pathogenesis of Kallmann syndrome. The co-occurrence of tooth anomalies, cleft palate, craniofacial anomalies, pigmentation, and neu­ rologic defects in patients with Kallmann syndrome suggests that the syndrome may be a part of the spectrum of neurocristopathies. Other dysmorphic features associated with some forms of IHH include renal agenesis, hearing loss, synkinesia, short metacarpals, eye movement abnormalities, cerebellar ataxia, and dental agenesis. The presence of these dysmorphic features can offer clues to the underlying genetic abnormality and guide genetic testing. Normosmic GnRH deficiency results from defects in pulsatile GnRH secretion, its regulation, or its action on the gonadotrope and has been associated with mutations in GnRHR, GNRH1, KISS1R, TAC3, TACR3, NROB1 (DAX1), leptin, or leptin receptor. Some mutations, such as those in PROK2, PROKR2, NSMF, FGFR1, FGF8, SEMA3A, WDR11, and CHD7, have been associated with both anosmic and normosmic forms of IHH; it is possible that these genes are involved in GnRH neuronal migration as well in regulation of GnRH secretion. GnRHR mutations, the most frequent identifiable cause of normosmic IHH, account for ~40% of autosomal recessive and 10% of sporadic cases of hypogonadotropic hypogonadism. These patients have decreased LH response to exogenous GnRH. Some receptor mutations alter GnRH binding affinity, allowing apparently normal responses to pharmaco­ logic doses of exogenous GnRH, whereas other mutations may alter signal transduction downstream of hormone binding. Mutations of the GnRH1 gene have also been reported in patients with hypogonado­ tropic hypogonadism, although they are rare. The G protein–coupled receptor KISS1R (GPR54) and its cognate ligand, kisspeptin (KISS1), are important regulators of sexual maturation in primates. Recessive mutations in GPR54 cause gonadotropin deficiency without anosmia. The genes encoding NKB (TAC3), which is involved in preferential activation of GnRH release in early development, and its receptor (TAC3R) have been implicated in some families with normosmic IHH. The tachykinin pathway plays an important role in GnRH activation during “mini-puberty” as well as in puberty. Prokineticin 2 (PROK2) and its receptor (PROK2R) are highly expressed in the olfactory ven­ tricle and subventricular zone of the lateral ventricle and are associated with neurogenesis of the olfactory bulbs and the migration of the olfac­ tory neuronal cells. Mutations in the CHD7 gene that encodes for the chromodomain helicase DNA binding protein 7 causes CHARGE syn­ drome characterized by eye coloboma, heart anomalies, choanal atre­ sia, growth and developmental retardation, genitourinary anomalies, hypogonadism, and ear abnormalities. X-linked hypogonadotropic hypogonadism also occurs in adrenal hypoplasia congenita, a disorder caused by mutations in the DAX1 gene, which encodes a nuclear recep­ tor in the adrenal gland and reproductive axis. Adrenal hypoplasia congenita is characterized by absent development of the adult zone of the adrenal cortex, leading to neonatal adrenal insufficiency. Puberty usually does not occur or is arrested, reflecting variable degrees of gonadotropin deficiency. Although sexual differentiation is normal, some patients have testicular dysgenesis and impaired spermatogenesis despite gonadotropin replacement. Less commonly, adrenal hypoplasia congenita, sex reversal, and hypogonadotropic hypogonadism can be caused by mutations of steroidogenic factor 1 (SF1). Rarely, recessive mutations in the LHβ or FSHβ genes have been described in patients with selective deficiencies of these gonadotropins. A number of homeodomain transcription factors are involved in the development and differentiation of the specialized hormoneproducing cells within the pituitary gland (Table 403-2). Patients with mutations of PROP1 have combined pituitary hormone deficiency that includes GH, prolactin (PRL), thyroid-stimulating hormone (TSH), LH, and FSH, but not ACTH. LHX3 mutations cause combined pitu­ itary hormone deficiency in association with cervical spine rigidity. HESX1 mutations cause septo-optic dysplasia and combined pituitary hormone deficiency. Mutations of ARNT1, inherited as an autosomal recessive disorder, are associated with diabetes insipidus; ACTH, GH, LH, and FSH deficiency; anterior pituitary hypoplasia; hypoplastic frontal and temporal lobes; thin corpus callosum; prominent forehead; and retrognathia. Patients with SOX2 mutations can have gonado­ tropin deficiency, variable deficiencies of TSH and ACTH, pituitary hypoplasia, microphthalmia, and intellectual disability. Prader-Willi syndrome (PWS) is a genomic imprinting disor­ der caused by deletions of the proximal portion of the paternally derived chromosome 15q11-15q13 region, which contains a bipartite imprinting center (65–75%); uniparental disomy of the maternal alleles (20–30%); or mutations of the genes/loci involved in imprint­ ing (1–3%) (Chap. 479). The imprinting gene implicated in PWS is a ubiquitin pathway gene known as UBE3A, for which the maternal allele is normally expressed while the paternal allele is silenced. PWS is characterized by obesity, hypotonic musculature, intellectual disability, hypogonadism, short stature, and small hands and feet. Some of the major manifestations of PWS may be due to reduced expression of prohormone convertase 1. Laurence-Moon syndrome is an autosomal recessive disorder char­ acterized by obesity, hypogonadism, mental retardation, polydactyly, and retinitis pigmentosa. Recessive mutations of leptin, or its receptor, cause severe obesity and pubertal arrest, apparently because of hypo­ thalamic GnRH deficiency (Chap. 413). Acquired Hypogonadotropic Disorders  •  SEVERE ILLNESS, STRESS, MALNUTRITION, AND EXERCISE  These may cause revers­ ible gonadotropin deficiency. Although gonadotropin deficiency and reproductive dysfunction are well documented in these conditions in women, men exhibit similar but less pronounced responses. Unlike women, most male runners and other endurance athletes have normal gonadotropin and sex steroid levels, despite low body fat and frequent intensive exercise. Testosterone levels fall at the onset of illness and recover during recuperation. The magnitude of gonadotropin sup­ pression generally correlates with the severity of illness. Although hypogonadotropic hypogonadism is the most common cause of tes­ tosterone deficiency in patients with acute illness, some have elevated levels of LH and FSH, which suggests primary gonadal dysfunction. The pathophysiology of reproductive dysfunction during acute illness is unknown but likely involves the combined effects of reductive stress, inflammation, cytokines, and/or glucocorticoid effects. There is a high frequency of low testosterone levels in patients with chronic illnesses such as HIV infection, end-stage renal disease, chronic obstructive lung disease, and many types of cancer and in patients receiving glu­ cocorticoids. About 20% of HIV-infected men with low testosterone levels have elevated LH and FSH levels; these patients presumably have primary testicular dysfunction. The remaining 80% have either normal or low LH and FSH levels; these men have a central hypothalamicpituitary defect or a dual defect involving both the testis and the hypothalamic-pituitary centers. Muscle wasting is common in chronic diseases associated with hypogonadism, which also leads to debility, poor quality of life, and adverse outcome of disease. Men using opioids for relief of cancer or noncancerous pain or because of addiction often have suppressed testosterone and LH levels and high prevalence of sexual dysfunction and osteoporosis; the degree of suppression is dose-related and particularly severe with long-acting opioids such as methadone. Exogenous opioids bind to the κ-opioid receptors on the KNDy neurons, suppress GnRH secretion, and alter the sensitivity to feedback inhibition by gonadal steroids. Heavy marijuana use has been associated with reduced sperm density, motil­ ity, morphology, and capacitation, and increased risk of subfertility.

The effects of marijuana use on circulating testosterone levels have been inconsistent in humans. Gynecomastia observed in marijuana users can be caused by plant estrogens in crude preparations. Androgen deprivation therapy in men with prostate cancer has been associated with increased risk of bone fractures, diabetes mellitus, cardiovascular events, fatigue, sexual dysfunction, tender gynecomastia, and poor quality of life.

OBESITY  In men with mild to moderate obesity, SHBG levels decrease in proportion to the degree of obesity, resulting in lower total testos­ terone levels. However, free testosterone levels usually remain within the normal range. SHBG production in the liver is inhibited by hepatic lipids and by tumor necrosis factor α and interleukin 1, but it is not affected by insulin. Thus, the low SHBG levels seen in obesity and dia­ betes are likely the result of low-grade inflammation and the increased amount of hepatic lipids rather than high insulin levels. Inflamma­ tion and gliosis in the pituitary, hypothalamic leptin resistance, and increased estradiol levels because of aromatization of testosterone to estradiol in adipose tissue may impair hypothalamic-pituitary func­ tion; obesity also may directly affect testicular function. Weight gain in adult men can accelerate the rate of age-related decline in testosterone levels. Weight loss is associated with reversal of these abnormalities including an increase in total and free testosterone levels and a decrease in estradiol levels. PART 12 Endocrinology and Metabolism HYPERPROLACTINEMIA  (See also Chap. 392) Elevated PRL levels are associated with hypogonadotropic hypogonadism. PRL inhibits hypothalamic GnRH secretion either directly or through modulation of tuberoinfundibular dopaminergic pathways and also attenuates LH and FSH response to GnRH. A PRL-secreting tumor may also destroy the surrounding gonadotropes by invasion or compression of the pitu­ itary stalk. Treatment with dopamine agonists reverses gonadotropin deficiency, although there may be a delay relative to PRL suppression. SELLAR MASS LESIONS  Neoplastic and nonneoplastic lesions in the hypothalamus or pituitary can directly or indirectly affect gonadotrope function. In adults, pituitary adenomas constitute the largest category of space-occupying lesions affecting gonadotropin and other pituitary hormone production. Pituitary adenomas that extend into the supra­ sellar region can impair GnRH secretion and mildly increase PRL secretion (usually <50 μg/L) because of impaired tonic inhibition by dopaminergic pathways. These tumors that cause hyperprolactinemia by stalk compression should be distinguished from prolactinomas, which typically are associated with higher PRL levels. The presence of diabetes insipidus suggests the possibility of a craniopharyngioma, infiltrative disorder, or other hypothalamic lesions (Chap. 393). HEMOCHROMATOSIS  (See also Chap. 426) Both the pituitary and tes­ tis can be affected by excessive iron deposition. However, the pituitary defect is the predominant lesion in most patients with hemochromatosis and hypogonadism. The diagnosis of hemochromatosis is suggested by the association of characteristic skin discoloration, hepatic enlargement or dysfunction, diabetes mellitus, arthritis, cardiac conduction defects, hypogonadism, and increased serum ferritin (>300 ng/mL for men) and transferrin saturation (>45%, threshold varies in different guidelines). ■ ■PRIMARY TESTICULAR CAUSES OF HYPOGONADISM Common causes of primary testicular dysfunction include Klinefelter syndrome, uncorrected cryptorchidism, cancer chemotherapy, radia­ tion to the testes, trauma, torsion, infectious orchitis, HIV infection, anorchia syndrome, and myotonic dystrophy. Primary testicular dis­ orders may be associated with impaired spermatogenesis, decreased androgen production, or both. See Chap. 402 for disorders of testis development, androgen synthesis, and androgen action. Klinefelter Syndrome  (See also Chap. 402) Klinefelter syndrome is the most common chromosomal disorder associated with 47,XXY karyotype, testicular dysfunction, and male infertility. It occurs in about 1 in 600 live-born males. Azoospermia is the rule in men with Klinefelter syndrome who have the 47,XXY karyotype due to the pro­ gressive loss of 47,XXY spermatogonial stem cells; however, men with

mosaicism (46,XY/47,XXY) and even some with 47,XXY karyotype may have germ cells, especially at a younger age. The clinical phe­ notype of Klinefelter syndrome can be variable, possibly because of mosaicism, polymorphisms in AR gene, the parental origin of the X chromosome, X-linked copy number variations, gene-dosage effects in conjunction with X chromosome inactivation, variable testosterone levels, and variable changes in the transcriptome and methylome in various tissues. Testicular histology shows hyalinization of seminif­ erous tubules and germ cell aplasia. However, spermatogenesis can be observed in a small number of tubules from which sperm can be harvested during testicular sperm extraction for IVF. Although their function is impaired, the number of Leydig cells appears to increase. Testosterone is decreased and estradiol is increased, leading to clinical features of undervirilization and gynecomastia. Men with Klinefel­ ter syndrome are at increased risk of systemic lupus erythematosus, Sjögren’s syndrome, breast cancer, diabetes mellitus, osteoporosis, nonHodgkin’s lymphoma, and some types of lung cancers and at reduced risk of prostate cancer. Periodic mammography for breast cancer sur­ veillance is recommended for men with Klinefelter syndrome. Fertility can be achieved by intracytoplasmic injection of sperm retrieved surgi­ cally from the testes of men with Klinefelter syndrome, including some men with nonmosaic form of Klinefelter syndrome. Although sperm retrieval in adolescence for fertility preservation offers no benefit over harvesting in adulthood, fertility counseling, including the potential for sperm retrieval, should be offered prior to starting testosterone replacement therapy. The karyotypes 48,XXXY and 49,XXXXY are associated with a more severe phenotype, increased risk of congenital malformations, and lower intelligence than 47,XXY individuals. Cryptorchidism  Cryptorchidism occurs when there is incomplete descent of the testis from the abdominal cavity into the scrotum. About 1–4% of full-term and 30% of premature male infants have at least one undescended testis at birth, but descent is usually complete by the first few weeks of life. Fifty percent of undescended testes at birth will descend spontaneously within the first 6–18 months of life. Consequently, the incidence of cryptorchidism is <1% by 9 months of age. Cryptorchidism should be distinguished from retractile testes that can be pulled down into the scrotum during physical examination and require no treatment. Testosterone and insulin-like 3 (INSL3) and their cognate recep­ tors, androgen receptor and relaxin/insulin-like family peptide recep­ tor 2 (RXFP2), regulate the development and growth of the fetal gubernaculum-cremaster muscle complex and the inguinoscrotal descent of the testes. Mutations in INSL3 and RXFP2 have been found in some patients with nonsyndromic cryptorchidism. However, genome-wide association studies have not found a consistent relation of nonsyndromic cryptorchidism with any single locus, suggesting complex, multilocus genetic susceptibility. Cryptorchidism is associated with increased risk of malignancy, infertility, inguinal hernia, and torsion. Unilateral cryptorchidism, even when corrected before puberty, is associated with decreased sperm count, possibly reflecting unrecognized damage to the fully descended testis or other genetic factors. Surgical correction is usually performed between 6 and 18 months of age depending on the location of the testes, the child’s body size, and parental preference. Epidemio­ logic, clinical, and molecular evidence supports the idea that cryptor­ chidism, hypospadias, impaired spermatogenesis, and testicular cancer may be causally related to common genetic and environment perturba­ tions and are components of the testicular dysgenesis syndrome. Acquired Testicular Defects  Viral orchitis may be caused by the mumps virus, echovirus, lymphocytic choriomeningitis virus, and group B arboviruses. Orchitis occurs in as many as one-fourth of adult men with mumps; the orchitis is unilateral in about twothirds and bilateral in the remainder. Orchitis usually develops a few days after the onset of parotitis but may precede it. The testis may return to normal size and function or undergo atrophy. Semen analysis returns to normal for three-fourths of men with unilateral involvement but for only one-third of men with bilateral orchitis. Trauma, including testicular torsion, can also cause secondary

atrophy of the testes. The exposed position of the testes in the scro­ tum renders them susceptible to both thermal and physical trauma, particularly in men with hazardous occupations. The late-term adverse effects of cancer treatment on reproductive health have emerged as an important concern among cancer survivors. Many professional cancer societies have published guidelines on the fertility preservation in patients with cancer and strongly endorsed consideration of fertility preservation measures prior to initiation of cancer treatment. The testes are sensitive to radiation damage due to the direct effects of ionized radioactive particles as well as indirect effects of free radicals generated from water. Radiation doses <1.0 Gy are associated with only a transient decline in sperm density; doses between 1.0 and 2.0 Gy are associated with temporary azoospermia, and doses >2.0 Gy are generally associated with permanent azoosper­ mia. Leydig cells are relatively resistant to the effects of radiation and only doses >20 Gy are associated with Leydig cell dysfunction and increased FSH and LH levels. Permanent testosterone deficiency in adult men is uncommon after therapeutic radiation; however, most boys given direct testicular radiation therapy for acute lymphoblastic leukemia have permanently low testosterone levels. Direct testicular radiation and whole-body radiation before bone marrow transplanta­ tion pose the greatest risk of permanent testicular damage. Combination chemotherapy for acute leukemia, Hodgkin’s disease, and testicular and other cancers may impair Leydig cell function and cause infertility. The degree of gonadal dysfunction depends on the type of chemotherapeutic agent and the dose and duration of therapy. Because of the high response rates and the young age of these men, infertility and testosterone deficiency have emerged as important long-term complications of cancer chemotherapy. Cyclophosphamide, procarbazine, ifosfamide, busulfan, chlorambucil, chlormethine cispla­ tin, carboplatin, and doxorubicin are associated with moderate to high risk of infertility. Azoospermia is uncommon with cyclophosphamide equivalent doses of <4000 mg/m2, and higher doses of alkylating agents are generally associated with varying degree of damage to germ cells. The outcomes of assisted reproductive technologies in cancer survivors using cryopreserved sperm collected prior to cancer treatment are similar to those in infertile men who do not have cancer. A smaller subset of cancer survivors treated with large doses of alkylating agents may also suffer from testosterone deficiency and sexual dysfunction. Drugs interfere with testicular function by several mechanisms, including inhibition of testosterone synthesis (e.g., ketoconazole, abiraterone, GnRH agonists and antagonists), blockade of androgen action (e.g., spironolactone), increased estrogen (e.g., marijuana), and toxic effects on spermatogenesis (e.g., chemotherapy). Alcohol, when consumed in small to moderate amounts, modestly increases testosterone levels, but ingestion of large quantities decreases testosterone, independent of liver disease or malnutrition. Chronic ethanol use in large amounts lowers testosterone levels by inducing inflammation and reductive stress and by its effects on the hypothala­ mus, pituitary, and liver. The occupational and recreational history should be evaluated in all men with infertility because of the toxic effects of many chemical agents on spermatogenesis. Known environmental hazards include pes­ ticides (e.g., vinclozolin, dicofol, atrazine), sewage contaminants (e.g., ethinyl estradiol in birth control pills, surfactants such as octylphenol, nonylphenol), plasticizers (e.g., phthalates), flame retardants (e.g., polychlorinated biphenyls, polybrominated diphenol ethers), industrial pollutants (e.g., heavy metals such as cadmium and lead, dioxins, poly­ cyclic aromatic hydrocarbons), microwaves, and ultrasound. In some populations, sperm density is said to have declined by as much as 40% in the past 50 years. Environmental estrogens or antiandrogens may be partly responsible. Sperm antibodies can cause isolated male infertility. In some instances, these antibodies are secondary phenomena resulting from duct obstruction or vasectomy. Granulomatous diseases can affect the testes, and testicular atrophy occurs in 10–20% of men with leproma­ tous leprosy because of direct tissue invasion by the mycobacteria. The tubules are involved initially, followed by endarteritis and destruction of Leydig cells.

Systemic disease can cause primary testis dysfunction in addition to suppressing gonadotropin production. In cirrhosis, a combined testicular and pituitary abnormality leads to decreased testosterone production independent of the direct toxic effects of ethanol. Impaired hepatic extraction of adrenal androstenedione leads to extraglandular conversion to estrone and estradiol, which partially suppresses LH. Testicular atrophy and gynecomastia are present in approximately onehalf of men with cirrhosis. In chronic renal failure, testosterone synthe­ sis and sperm production decrease despite elevated gonadotropins. The elevated LH level is due to reduced clearance. About one-fourth of men with renal failure have hyperprolactinemia. Improvement in testoster­ one production with hemodialysis is incomplete, but successful renal transplantation may return testicular function to normal. Testicular atrophy is present in one-third of men with sickle cell anemia. The defect may be at either the testicular or the pituitary level, although hypogonadotropic hypogonadism is more common. Sperm density can decrease temporarily after acute febrile illness in the absence of a change in testosterone production. Infertility in men with celiac disease is associated with a hormonal pattern typical of androgen resistance, namely, elevated testosterone and LH levels.

Disorders of the Testes and Male Reproductive System CHAPTER 403 Neurologic diseases such as myotonic dystrophy, spinobulbar mus­ cular atrophy (Kennedy’s disease), and spinal cord injury are often associated with associated with impaired testicular function. In myo­ tonic dystrophy, small testes may be associated with impairment of both spermatogenesis and Leydig cell function. Spinobulbar muscular atrophy (Kennedy’s disease) is caused by an expansion of the glutamine repeat tract in the amino-terminal region of the AR; this expansion impairs function of the AR. Men with spinobulbar muscular atrophy often have undervirilization and infertility as a late manifestation. Spi­ nal cord injury that causes paraplegia is often associated with low tes­ tosterone levels and may cause persistent defects in spermatogenesis; some patients retain the capacity for penile erection and ejaculation. ■ ■ANDROGEN INSENSITIVITY SYNDROMES Mutations in the AR cause resistance to the action of testosterone and DHT. These X-linked mutations are associated with variable degrees of defective male phenotypic development and undervirilization (Chap. 402). Although not technically hormone-insensitivity syn­ dromes, two genetic disorders associated with mutations in the steroid 5α-reductase type 2 or the CYP19 (aromatase) gene impair testosterone conversion to active sex steroids. Mutations in the SRD5A2 gene, which encodes the steroid 5α-reductase type 2, prevent the conversion of testosterone to DHT, which is necessary for the normal development of the male external genitalia. Mutations in the CYP19 gene, which encodes aromatase, prevent testosterone conversion to estradiol. Males with CYP19 mutations have delayed epiphyseal fusion, tall stature, eunuchoid proportions, visceral adiposity, and osteoporosis, consistent with evidence from an estrogen receptor–deficient individual that these testosterone actions are mediated via estrogen. GYNECOMASTIA Gynecomastia refers to enlargement of the male breast. It is caused by excess estrogen action and is usually the result of an increased estro­ gen/androgen ratio. True gynecomastia is associated with glandular breast tissue that is >4 cm in diameter and often tender. Glandular tissue enlargement should be distinguished from excess adipose tissue: glandular tissue is firmer and contains fibrous-like cords. Gynecomas­ tia occurs as a normal physiologic phenomenon in the newborn (due to transplacental transfer of maternal and placental estrogens), during puberty (high estrogen-to-androgen ratio in early stages of puberty), and with aging (increased fat tissue and increased aromatase activity along with the age-related decline in testosterone levels), but it can also result from pathologic conditions associated with testosterone defi­ ciency or estrogen excess. The prevalence of gynecomastia increases with age and body mass index (BMI), likely because of increased aromatase activity in adipose tissue. Medications that alter androgen metabolism or action may also cause gynecomastia. The relative risk of breast cancer is increased in men with gynecomastia, although the absolute risk is relatively small.

■ ■PATHOLOGIC GYNECOMASTIA Any cause of androgen deficiency can lead to gynecomastia, reflecting an increased estrogen/androgen ratio, as estrogen synthesis still occurs by aromatization of residual adrenal and gonadal androgens. Gyneco­ mastia is a characteristic feature of Klinefelter syndrome (Chap. 402). Androgen insensitivity disorders also cause gynecomastia. Androgen deprivation therapy using GnRH analogues with and without androgen receptor blockers in men with prostate cancer is often associated with painful breast enlargement. Excess estrogen production may be caused by tumors, including Leydig cell tumors; Sertoli cell tumors in isolation or in association with Peutz-Jeghers syndrome or Carney complex; granulosa cell tumors; and adrenal tumors producing estrogen precur­ sors. Tumors that produce hCG, including some testicular germ cell tumors, stimulate Leydig cell estrogen synthesis. Increased conversion of androgens to estrogens can be a result of increased availability of substrate (androstenedione) for extraglandular estrogen formation (CAH, hyperthyroidism, and most feminizing adrenal tumors) or of diminished catabolism of androstenedione (liver disease) so that estro­ gen precursors are shunted to aromatase in peripheral sites. Obesity is associated with increased aromatization of androgen precursors to estrogens. Extraglandular aromatase activity can also be increased in tumors of the liver or adrenal gland or rarely as an inherited disorder. Several families with increased peripheral aromatase activity inher­ ited as an autosomal dominant or as an X-linked disorder have been described. In some families with this disorder, a chimeric CYP19 due to an inversion in chromosome 15q21.2-3 causes the CYP19 gene to be activated by the regulatory elements of contiguous genes (e.g., transient

PART 12 Endocrinology and Metabolism Breast enlargement True glandular enlargement Hard tissue, fixed to underlying tissue Recent onset, rapid growth Onset in neonatal or peripubertal period Known causative drugs or diseases readily apparent Longstanding, size <4 cm Glandular tissue >4 cm, cause not apparent, Clinical features of testosterone deficiency, Breast tenderness Small testes Increased E2, normal or low T, increased E2 to T ratio Low total and free T, increased E2 to T ratio T deficiency syndrome, further evaluation to determine cause of T deficiency Ultrasound of testes to locate E2 producing tumor, search for other sources of increased E2 FIGURE 403-7  Evaluation of gynecomastia. E2, 17β-estradiol; FSH, follicle-stimulating hormones; hCGβ, human chorionic gonadotropin β; LH, luteinizing hormone; T, testosterone.

receptor potential cation channel subfamily M member 7 [TRPM7], TMOD3, or FLJ14957), resulting in excessive estrogen production in the fat and other extragonadal tissues. The familial aromatase excess syndrome due to CYP19 mutation or chromosomal rearrangement is characterized by pre- or peripubertal onset of gynecomastia, advanced bone age, short adult height due to premature epiphyseal closure, and hypogonadotropic hypogonadism. Peutz-Jeghers syndrome is characterized by intestinal hamartomas, mucocutaneous pigmenta­ tion, calcifying Sertoli cell tumors, premature epiphyseal closure, and prepubertal gynecomastia due to increased aromatization. Hyperthy­ roidism is associated with elevated SHBG levels, which increase the free estradiol–to–free testosterone ratio even though total testosterone and estradiol levels are often normal. Drugs can cause gynecomastia by acting directly as estrogenic substances (e.g., oral contraceptives, phytoestrogens, digitalis) or inhibiting androgen synthesis (e.g., GnRH agonists, ketoconazole) or action (e.g., spironolactone, AR blockers such as enzalutamide); for many drugs, such as cimetidine, imatinib, or some antiretroviral drugs for HIV, the precise mechanism is unknown. Unintentional exposure to estrogenic agents in skin care products has been reported as a cause of gynecomastia in prepubertal children. Because up to two-thirds of pubertal boys and about half of hos­ pitalized men have palpable glandular tissue that is benign, detailed investigation or intervention is not indicated in all men presenting with gynecomastia (Fig. 403-7). In addition to the extent of gyneco­ mastia, recent onset, rapid growth, tender tissue, and occurrence in a lean subject should prompt more extensive evaluation. This should include a careful drug history, examination of the testes, assessment Increased adipose tissue Mammography with or without additional corroboratory imaging studies and biopsy Follow-up with serial examinations Total and free T, SHBG, LH, FSH, E2, TSH, and hCG Very high SHBG, normal or high total T, normal E2 Increased hCGβ Ultrasound of the testis, CT scan of adrenal and chest to locate an hCG producing tumor Measure free T and E2, search for a cause of high SHBG

of virilization, evaluation of liver function, and hormonal measure­ ments including testosterone, estradiol, estrone, androstenedione, LH, and hCG. Markedly elevated estradiol concentrations along with sup­ pressed LH should prompt a search for a testicular or adrenal estrogensecreting tumor. A karyotype should be obtained in men with very small testes to exclude Klinefelter syndrome. Despite extensive evalua­ tion, the etiology is established in only a small proportion of patients. TREATMENT Gynecomastia When the primary cause can be identified and corrected shortly after the onset of gynecomastia, breast enlargement usually sub­ sides over several months. However, if gynecomastia is of long duration, surgery is the most effective therapy. Indications for surgery include severe psychological distress, continued growth or tenderness, failure to respond to medical therapy, or suspected malignancy. In patients who have painful gynecomastia and in whom surgery cannot be performed, treatment with antiestrogens such as tamoxifen (20 mg/d) can reduce pain and breast tissue size in over half the patients. The estrogen receptor antagonists tamoxi­ fen and raloxifene have been reported in small trials to reduce breast size in men with pubertal gynecomastia, although complete regression of breast enlargement is unusual with the use of estrogen receptor antagonists. Aromatase inhibitors can be effective in the early proliferative phase of the disorder. However, in a randomized trial in men with established gynecomastia, anastrozole proved no more effective than placebo in reducing breast size. Tamoxifen is effective in prevention and treatment of breast enlargement and breast pain in men with prostate cancer who are receiving andro­ gen deprivation therapy. Long-standing gynecomastia is usually not responsive to drug therapy and requires mammoplasty if it is associated with pain and distress. AGING-RELATED CHANGES IN MALE REPRODUCTIVE FUNCTION A number of cross-sectional and longitudinal studies (e.g., the Balti­ more Longitudinal Study of Aging, the Framingham Heart Study, the Massachusetts Male Aging Study, and the European Male Aging Study [EMAS]) have established that testosterone concentrations decrease with advancing age. This age-related decline starts in the third decade of life and progresses slowly; the rate of decline in testosterone con­ centrations is greater in men with obesity, chronic illness, and in those taking medications. Because SHBG concentrations are higher in older men than in younger men, free or bioavailable testosterone concentra­ tions decline with aging to a greater extent than total testosterone con­ centrations. The age-related decline in testosterone is due to defects at all levels of the hypothalamic-pituitary-testicular axis: pulsatile GnRH secretion is attenuated, LH response to GnRH is reduced, and testicular response to LH is impaired. However, the gradual rise of LH with aging suggests that testis dysfunction is the main cause of declining androgen levels. The term andropause has been used to denote age-related decline in testosterone concentrations; this term is a misnomer because there is no discrete time when testosterone concentrations decline abruptly. Several epidemiologic studies, such as the Framingham Heart Study, the EMAS, and the Study of Osteoporotic Fractures in Men (MrOS), that used mass spectrometry for measuring testosterone levels have reported ~10% prevalence of low testosterone levels in middle-aged and older men; the prevalence of unequivocally low testosterone and sexual symptoms in men aged 40–70 years in the EMAS was 2.1% and increased with age from 0.1% for men aged 40–49 years of age to 5.1% for those aged 70–79 years. Low total and bioavailable testosterone concentrations have been associated with decreased sexual desire, decreased appendicular skeletal muscle mass and strength, decreased self-reported physical function, higher whole body and visceral fat mass and insulin resistance, and increased risk of type 2 diabetes, coro­ nary artery disease, and all-cause mortality. An analysis of signs and

symptoms in older men in the EMAS revealed a syndromic association of sexual symptoms with total testosterone levels <320 ng/dL and free testosterone levels <64 pg/mL in community-dwelling older men.

Two placebo-controlled randomized trials—the Testosterone Trials (TTrials) and the Testosterone Replacement Therapy for Assessment of Long-Term Vascular Events and efficacy Response in Hypogonadal Men (TRAVERSE) study—have provided important information about the efficacy and safety of testosterone replacement therapy (TRT) in middle-aged and older men with hypogonadism. In these and other randomized trials, TRT of men with hypogonadism consistently improved sexual activity and sexual desire and alleviated hypogonadal symptoms. TRT also improves mood and energy level. TRT increases hemoglobin levels and corrects anemia in a greater proportion of mid­ dle-aged and older men with hypogonadism who have unexplained anemia, compared to placebo. Testosterone treatment significantly increases vertebral as well as femoral volumetric and areal bone min­ eral density and estimated bone strength. Testosterone treatment does not improve memory or other measures of cognition in men who do not have cognitive deficits. Testosterone treatment increases lean body mass, maximal voluntary muscle strength and muscle power, and selfreported mobility, and reduces whole body and visceral fat mass. In men with hypogonadism, testosterone treatment has not been shown to prevent progression from prediabetes to diabetes or induce glycemic remission in those with diabetes. In systematic reviews of randomized controlled trials, testosterone therapy of healthy older men with low or low-normal testosterone levels was associated with greater increments in lean body mass, grip strength, and self-reported physical function than that associated with placebo. Disorders of the Testes and Male Reproductive System CHAPTER 403 Neither the testosterone trials nor a randomized trial of the effects of testosterone on atherosclerosis progression in aging men (TEAAM trial) with low or low normal testosterone levels found significant dif­ ferences between testosterone and placebo arms in the rates of change in either the coronary artery calcium scores or the common carotid artery intima-media thickness. However, in the TTrials, testoster­ one treatment was associated with a significantly greater increase in coronary artery noncalcified plaque volume, as measured by coronary artery computed tomography angiography. Neither of the trials was long enough or large enough to determine the effects of TRT on pros­ tate or major adverse cardiovascular events. The TRAVERSE trial compared the effects of TRT and placebo on major adverse cardiovascular events (MACE) in middle-aged and older men with hypogonadism and either preexisting cardiovascular disease (CVD) or increased risk of CVD. During a mean follow-up period of 33 months, the incidence of MACE did not differ between the testos­ terone and placebo groups. Testosterone treatment was associated with higher incidence of venous thromboembolism and atrial fibrillation than placebo. The incidences of high-grade prostate cancer (Gleason grade 4+3 or higher) or any prostate cancer, acute urinary retention, invasive surgical procedures for benign prostatic hyperplasia, and ini­ tiation of new pharmacologic therapy for benign prostatic hyperplasia were low and did not differ between the testosterone and placebo groups. Testosterone treatment was associated with significantly greater increase in serum prostate-specific antigen (PSA) level in the first 12 months of testosterone but the rate of change in PSA after 12 months of treatment was similar in the testosterone and placebo-treated men. Testosterone treatment did not worsen lower urinary tract symptoms. Testosterone treatment, by increasing PSA levels, could increase the risk of referral for prostate biopsy and detection of low-grade prostate cancer. Population screening of all older men for low testosterone levels is not recommended, and testing should be restricted to men who have symptoms or signs attributable to androgen deficiency. Testosterone therapy is not recommended for all older men with low testosterone levels. In older men with significant symptoms of testosterone defi­ ciency who have unequivocally low testosterone levels, testosterone treatment should be individualized based on consideration of the burden of symptoms, the presence of comorbid conditions that may increase the risk of harm from testosterone treatment, the risks versus benefits of treatment and monitoring, and clinician and patient values (see “Testosterone Replacement,” below).

PART 12 Endocrinology and Metabolism Testicular morphology, semen production, and fertility are main­ tained up to a very old age in men. Although concern has been expressed about age-related increases in germ cell mutations and impairment of DNA repair mechanisms, there is no clear evidence that the frequency of chromosomal aneuploidy is increased in the sperm of older men. However, the incidence of autosomal dominant diseases, such as achondroplasia, polyposis coli, Marfan syndrome, and Apert syndrome, increases in the offspring of men who are advanced in age, consistent with transmission of sporadic missense mutations. Advanced paternal age may be associated with increased rates of de novo mutations, which may contribute to an increased risk of neurodevelopmental diseases such as schizophrenia and autism. The somatic mutations in male germ cells that enhance the prolif­ eration of germ cells could lead to within-testis expansion of mutant clonal lines, thus favoring the propagation of germ cells carrying these pathogenic mutations and increasing the risk of mutations in the offspring of older fathers (the “selfish spermatogonial selection” hypothesis). APPROACH TO THE PATIENT Testosterone Deficiency Hypogonadism is often characterized by decreased sex drive, reduced frequency of sexual activity, inability to maintain erec­ tions, fatigue, low mood, hot flushes, reduced beard growth, loss of muscle mass, decreased testicular size, and gynecomastia. Erectile dysfunction and testosterone deficiency are two distinct clinical disorders that can coexist in middle-aged and older men. Some, but not all, patients with erectile dysfunction have testosterone deficiency. Thus, it is useful to evaluate men presenting with erec­ tile dysfunction for testosterone deficiency. Except when extreme, these clinical features of testosterone deficiency may be difficult to Ascertain signs and symptoms; exclude systemic causes, eating and body image disorders, medications, and substance use Measure fasting, early morning total T and, if indicated, free T Measure LH and FSH Low T, low or inappropriately normal LH (hypogonadotropic) Low T, high LH (hypergonadotropic) • Rule out systemic illness • Measure prolactin and ferritin • Evaluate other pituitary hormones • MRI scan of the pituitary Primary testicular dysfunction • Karyotype to exclude Klinefelter syndrome Low <200 ng/dL Borderline 200–350 ng/dL

350 ng/dL Total and/or free T low Total and free T normal Evaluate for other causes of symptoms; follow, if indicated Repeat total T and free T FIGURE 403-8  Evaluation of hypogonadism. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; T, testosterone. distinguish from changes that occur with normal aging. Moreover, testosterone deficiency may develop gradually. When symptoms or clinical features suggest possible testosterone deficiency, the labora­ tory evaluation is initiated by the measurement of total testosterone in a fasting specimen, preferably in the morning using a reliable assay, such as LC-MS/MS, that has been calibrated to an interna­ tional testosterone standard (Fig. 403-8). A consistently low total testosterone level below the lower limit of the normal male range, measured by an LC-MS/MS assay in a CDC-certified laboratory, in association with symptoms, is evidence of testosterone deficiency. An early-morning testosterone level >400 ng/dL makes the diagno­ sis of androgen deficiency unlikely. In men with testosterone levels between 200 and 400 ng/dL, the total testosterone level should be repeated, and a free testosterone level should be measured. In older men and in patients with other clinical states that are associ­ ated with alterations in SHBG levels, a direct measurement of free testosterone level by equilibrium dialysis is needed to diagnose testosterone deficiency. When testosterone deficiency has been confirmed by the consis­ tently low testosterone concentrations, LH should be measured to determine whether the patient has primary (high LH) or secondary (low or inappropriately normal LH) hypogonadism. Elevated LH and FSH levels indicate a defect at the testicular level. Common causes of primary testicular failure include Klinefelter syndrome, HIV infection, uncorrected cryptorchidism, cancer chemothera­ peutic agents, radiation, surgical orchiectomy, or prior infectious orchitis. A karyotype should be performed in men with low tes­ tosterone and elevated LH to diagnose Klinefelter syndrome. Men who have a low testosterone but “inappropriately normal” or low LH levels have secondary hypogonadism; their defect resides at the hypothalamic-pituitary level. Common causes of acquired second­ ary hypogonadism include space-occupying lesions of the sella,

hyperprolactinemia, chronic illness, hemochromatosis, excessive exercise, and the use of anabolic-androgenic steroids, opioids, marijuana, glucocorticoids, and alcohol. Measurement of PRL and MRI scan of the hypothalamic-pituitary region can help exclude the presence of a space-occupying lesion. Patients in whom known causes of hypogonadotropic hypogonadism have been excluded are classified as having IHH. It is not unusual for congenital causes of hypogonadotropic hypogonadism, such as Kallmann syndrome, to be diagnosed in young adults. TREATMENT Testosterone Deficiency GONADOTROPINS Gonadotropin therapy is used to establish or restore fertility in patients with gonadotropin deficiency of any cause. Several gonad­ otropin preparations are available. Human menopausal gonado­ tropin (hMG; purified from the urine of postmenopausal women) contains 75 IU of FSH and 75 IU of LH per vial. hCG (purified from the urine of pregnant women) has minimal FSH activity and resembles LH in its ability to stimulate testosterone production by Leydig cells. Recombinant LH is also available, but its half-life is relatively short (10 h). Treatment is usually begun with hCG alone. If hCG alone does not induce spermatogenesis, hMG is added to promote the FSH-dependent stages of spermatid development. Recombinant human FSH (hFSH) is available and is indistinguish­ able from purified urinary hFSH in its biologic activity and phar­ macokinetics in vitro and in vivo, although the mature β subunit of recombinant hFSH has seven fewer amino acids. Recombinant hFSH is available in ampoules containing 75 IU (~7.5 μg FSH), which accounts for >99% of protein content. Once spermatogen­ esis is restored using combined FSH and LH therapy, hCG alone is often sufficient to maintain spermatogenesis. Although a variety of treatment regimens are used, 1500 IU of hCG administered intramuscularly three times weekly is a reasonable starting dose. Testosterone levels should be measured 6–8  weeks later and 48–72 h after the hCG injection; the hCG dose should be adjusted to achieve testosterone levels in the mid-normal range. Sperm counts should be monitored on a monthly basis. It may take several months for spermatogenesis to be restored; therefore, it is important to forewarn patients about the potential length and expense of the treatment and to provide conservative estimates of success rates. If testosterone levels are in the mid-normal range but the sperm concentrations are low after 6 months of therapy with hCG alone, FSH should be added. This can be done by using hMG, highly purified urinary hFSH, or recombinant hFSH. A common practice is to start with the addi­ tion of 75 IU FSH three times each week in conjunction with the hCG injections. If sperm densities are still low after 3 months of combined treatment, the FSH dose should be increased to 150 IU. Occasionally, it may take ≥18–24 months for spermatogenesis to be restored. The two best predictors of the success of gonadotropin therapy in hypogonadotropic men are testicular volume at presentation and time of onset of gonadotropin deficiency. In general, men with testicular volumes >8 mL have better response rates than those who have testicular volumes <4 mL. Patients who develop gonadotropin deficiency after puberty experience higher success rates than those who have never undergone pubertal changes. Spermatogenesis can usually be reinitiated by hCG alone, with high rates of success for men with postpubertal onset of hypo­ gonadotropism. The presence of a primary testicular abnormal­ ity, such as cryptorchidism, will attenuate testicular response to gonadotropin therapy. Prior testosterone therapy does not preclude subsequent response to gonadotropin therapy, although some studies suggest that it may attenuate response to subsequent gonadotropin therapy.

TESTOSTERONE REPLACEMENT TRT is indicated to restore testosterone levels to normal and cor­ rect features of testosterone deficiency in men with hypogonad­ ism. TRT induces secondary sex characteristics; improves libido and overall sexual activity; relieves symptoms of hypogonadism; improves mood and energy level; increases skeletal muscle mass, muscle strength and power, and some measures of physical func­ tion; hemoglobin and hematocrit; and volumetric and areal bone mineral density; corrects the mild anemia associated with testos­ terone deficiency; and decreases fat mass. The benefits of TRT have only been proven in men with confirmed hypogonadism, as demonstrated by testosterone levels that are below the lower limit of normal and one or more symptoms of hypogonadism.

Disorders of the Testes and Male Reproductive System CHAPTER 403 Testosterone is available in a variety of formulations with dis­ tinct pharmacokinetics (Table 403-3). Testosterone serves as a prohormone and is converted to 17β-estradiol by aromatase and to 5α-DHT by steroid 5α-reductase. Therefore, when evaluating testosterone formulations, it is important to consider whether the formulation being used can achieve physiologic estradiol and DHT concentrations, in addition to normal testosterone concentrations. The current recommendation is to restore testosterone levels to the mid-normal range. Oral Derivatives of Testosterone  Testosterone is well absorbed after oral administration but is quickly degraded during the first pass through the liver. Therefore, it is difficult to achieve sus­ tained blood levels of testosterone after oral administration of crystalline testosterone. 17α-Alkylated derivatives of testosterone (e.g., 17α-methyl testosterone, oxandrolone, fluoxymesterone) are relatively resistant to hepatic degradation and can be administered orally; however, because of the potential for hepatotoxicity, includ­ ing cholestatic jaundice, peliosis, and hepatocellular neoplasms, these formulations should not be used for testosterone replacement. Hereditary angioedema due to C1 esterase deficiency is the only exception to this general recommendation; in this condition, oral 17α-alkylated androgens are useful because they stimulate hepatic synthesis of the C1 esterase inhibitor. Injectable Forms of Testosterone  The esterification of testosterone at the 17β-hydroxy position makes the molecule hydrophobic and extends its duration of action. The slow release of testosterone ester from an oily depot in the muscle accounts for its extended duration of action. The longer the side chain, the greater is the hydrophobic­ ity of the ester and longer the duration of action. Thus, testosterone enanthate, cypionate, and undecanoate with longer side chains have longer durations of action than testosterone propionate. Within 24 h after intramuscular administration of 200 mg testosterone enanthate or cypionate, testosterone levels rise into the high-normal or supra­ physiologic range and then gradually decline into the hypogonadal range over the next 2 weeks. A bimonthly regimen of testosterone enanthate or cypionate therefore results in peaks and troughs in tes­ tosterone levels that may be accompanied by changes in a patient’s mood, sexual desire, and energy level; weekly administration of testosterone enanthate or cypionate can reduce these variations in testosterone levels during the dosing interval. The kinetics of tes­ tosterone enanthate and cypionate are similar. Estradiol and DHT levels are normal if testosterone replacement is physiologic. A long-acting testosterone undecanoate in oil, administered at an initial priming dose of 750 mg intramuscularly followed by a sec­ ond dose of 750 mg 4 weeks later, and then at a maintenance dose of 750 mg every 10 weeks, maintains serum testosterone, estradiol, and DHT in the normal male range and corrects symptoms of tes­ tosterone deficiency in a majority of treated men. Its relative draw­ backs are the large injection volume and the risk of pulmonary oil microembolism (POME) reaction in a small proportion of patients. Testosterone Gel  Several transdermal testosterone gels, such as Androgel, Testim, Fortesta, and Axiron, and some generic ver­ sions, when applied topically to the skin in appropriate doses (Table 403-3), can maintain total and free testosterone concentra­ tions in the normal range in men with hypogonadism. The current

TABLE 403-3  Clinical Pharmacology of Some Testosterone Formulations FORMULATION REGIMEN PHARMACOKINETIC PROFILE DHT AND E2 ADVANTAGES DISADVANTAGES T enanthate or cypionate 140–200 mg IM q2wk or 70–100 mg/wk After a single IM injection, serum T levels rise into the supraphysiologic range, then decline gradually into the low-normal or the hypogonadal range by the end of the dosing interval Topical T gels Available in sachets, tubes, and pumps When used in appropriate doses, these topical formulations restore serum T and E2 levels to the physiologic male range PART 12 Endocrinology and Metabolism T pellets Several pellets implanted SC; dose and regimen vary with formulation Serum T peaks at 1 month and then is sustained in normal range for 3–4 months, depending on formulation Oral T undecanoate (TU) Two different formulations of oral testosterone are available each taken orally bid with food TU formulated in a self-emulsifying drug delivery system that includes hydrophilic and lipophilic excipients to enable the solubilization of TU and its absorption through the lymphatics after oral ingestion with a typical meal. After each administration, serum T levels rise and return to baseline by 12 h. When administered at the recommended dose, average serum T levels are maintained in the normal range in a majority of treated men Injectable longacting TU in oil U.S. regimen 750 mg IM, followed by 750 mg at 4 weeks, and 750 mg every 10 weeks When administered at the recommended dose, serum T levels are maintained in the normal range in a majority of treated men Intranasal T 2 actuations of the metered-dose pump (11 mg) applied into the nostrils 3 times daily Restores T into the normal male range Abbreviations: DHT, dihydrotestosterone; E2, estradiol; T, testosterone. recommendations are to begin with an initial U.S. Food and Drug Administration–recommended dose and adjust the dose based on testosterone and hematocrit levels. The advantages of the testoster­ one gel include the ease of application. A major concern is the poten­ tial for transfer of the gel to a sexual partner or to children who may come in close contact with the patient. The ratio of DHT to testos­ terone concentrations is higher in men treated with the testosterone gel than in healthy men. Also, there is considerable intra- and inter­ individual variation in serum testosterone levels in men treated with the transdermal gel due to variations in transdermal absorption and plasma clearance of testosterone. Therefore, monitoring of serum testosterone levels and multiple dose adjustments are required to achieve and maintain testosterone levels in the target range. Pellets of crystalline testosterone can be inserted in the subcuta­ neous tissue through a small skin incision. Testosterone is released by surface erosion of the implanted pellets and absorbed into the systemic circulation, and testosterone levels can be maintained in the normal range for 3–4 months. Potential drawbacks include the need for skin incision for insertion and removal and spontaneous extrusions and fibrosis at the insertion.

DHT and E2 levels rise in proportion to the increase in T levels; T:DHT and T:E2 ratios do not change Corrects symptoms of testosterone deficiency; relatively inexpensive if self-administered; flexibility of dosing Requires IM injection; peaks and valleys in serum T levels that are associated with fluctuations in patient’s mood, energy level, and sex drive Serum DHT levels and DHT:T ratio are higher in hypogonadal men treated with the transdermal gels than in healthy eugonadal men Corrects symptoms of testosterone deficiency, ease of application, good skin tolerability Potential of transfer to a female partner or child by direct skin-toskin contact; skin irritation in a small proportion of treated men; moderately high DHT levels; considerable interindividual and intraindividual variation in on-treatment testosterone levels T:DHT and T:E2 ratios do not change Corrects symptoms of testosterone deficiency Requires surgical incision for insertions; pellets may extrude spontaneously High DHT:T ratio Convenience of oral administration High DHT:T ratio DHT and E2 levels rise in proportion to the increase in T levels; T:DHT and T:E2 ratios do not change Corrects symptoms of testosterone deficiency; requires infrequent administration Requires IM injection of a large volume; serious pulmonary oil microembolism (POME) reactions, characterized by cough, dyspnea, throat tightening, chest pain, dizziness, and syncope, and episodes of anaphylaxis have been reported to occur during or immediately after the injection in a very small number of patients; patients should be watched for POME reaction for 30 min after each injection T:DHT and T:E2 ratio in the physiologic range   Requires 3 times daily application; nasal irritation, epistaxis, nasopharyngitis Testosterone undecanoate, formulated in a self-emulsifying drug delivery system that includes hydrophilic and lipophilic excipi­ ents to enable its solubilization in the gut, is absorbed through the lymphatics after oral ingestion with a fatty meal and is spared the first-pass degradation in the liver. After each administration, serum testosterone levels rise and return to baseline by 12 h. When administered at the recommended dose, average serum testosterone levels are maintained in the normal range in a majority of treated men, but DHT-to-testosterone ratios are higher in men with hypo­ gonadism treated with oral testosterone undecanoate, as compared to eugonadal men. An intranasal testosterone gel is available as a metered-dose pump and is administered typically at a starting dose of 11 mg testosterone in the form of two pump actuations, one in each nostril three times daily. Formulation-specific adverse effects include rhinorrhea, nasal discomfort, epistaxis, nasopharyngitis, and nasal scab. Novel Androgen Formulations  Selective AR modulators (SARMs) are a class of AR ligands that bind the AR and display tissueselective actions. A number of nonsteroidal SARMs that act as

agonists on the muscle and bone and that spare the prostate to varying degrees have advanced to phase 3 human trials. Non­ steroidal SARMs do not serve as substrates for either the steroid 5α-reductase or the CYP19 (aromatase). SARM binding to AR induces specific conformational changes in the AR protein, which then modulates protein–protein interactions between AR and its coregulators, resulting in tissue-specific regulation of gene expres­ sion. SARMs that are strong agonists for the muscle, bone, and sexual function and antagonists for the prostate may be valuable in treating men with prostate cancer who are receiving androgen deprivation therapy. 7α-Methyl-19-nortestosterone is an androgen that cannot be 5α-reduced; therefore, compared to testosterone, it has relatively greater agonist activity in muscle and gonadotropin suppression but lesser activity on the prostate. Pharmacologic Uses of Androgens  Androgens and SARMs are being evaluated as anabolic therapies for functional limitations associated with aging and chronic illness. Testosterone supplemen­ tation increases skeletal muscle mass, maximal voluntary strength, and muscle power in healthy men, hypogonadal men, older men with low testosterone levels, HIV-infected men with weight loss, and men receiving glucocorticoids. These anabolic effects of testos­ terone are related to testosterone dose and circulating concentra­ tions. Systematic reviews have confirmed that testosterone therapy of HIV-infected men with weight loss promotes improvements in body weight, lean body mass, muscle strength, and depression indices, leading to the recommendation that testosterone may be considered as an adjunctive therapy in HIV-infected men who are experiencing unexplained weight loss and who have low testoster­ one levels. It is unknown whether testosterone therapy of older men with functional limitations is safe and effective in improving physi­ cal function and reducing disability. Testosterone administration induces hypertrophy of both type 1 and 2 fibers and increases satellite cell (muscle progenitor cells) and myonuclear number. Androgens promote the differentiation of mesenchymal, multipotent progenitor cells into the myogenic lineage and inhibit their differentiation into the adipogenic lineage. Testosterone binding to AR promotes the association of liganded AR with β-catenin and its translocation into the nucleus where it binds TCF-4 and activates Wnt-target genes, including follistatin, which blocks signaling through the transforming growth factor β pathway, thereby promoting myogenic differentiation of muscle progenitor cells. Testosterone may have additional effects on satel­ lite cell replication and polyamine pathway, which may contribute to an increase in skeletal muscle mass. Other indications for androgen therapy are in selected patients with anemia due to bone marrow failure (an indication largely sup­ planted by erythropoietin) and hereditary angioedema. Recommended Regimens for Testosterone Replacement Therapy 

Testosterone esters are administered typically at doses of 70–100 mg intramuscularly every week or 140–200 mg every 2 weeks. Testos­ terone undecanoate is administered at an initial dose of 750 mg followed 4 weeks later by a second injection of 750 mg and then 750 mg every 10 weeks. Testosterone gels are typically applied over a covered area of skin at initial doses that vary with the formulation. Patients should wash their hands after gel application and keep the area of gel application covered with clothing to minimize the risk of gel transfer to another person. Oral testosterone undecanoate is taken with meals at a starting dose of 237 mg twice daily. Intranasal testosterone is administered as a spray in each nostril three times a day (33 mg/d). Evaluating Efficacy of Testosterone Replacement Therapy  The goals of TRT are to restore serum testosterone levels into the midnormal range for healthy young men, correct symptoms of hypo­ gonadism, and induce and maintain secondary sex characteristics. Testosterone should be measured 3 months after initiating therapy to assess adequacy of therapy. There is substantial interindividual variability in serum testosterone levels, especially with transdermal gels, presumably due to genetic differences in testosterone clearance

and substantial variation in transdermal absorption. In patients who are treated with testosterone enanthate or cypionate, testos­ terone levels should be 350–550 ng/dL 1 week after the injection. If testosterone levels are outside this range, adjustments should be made either in the dose or in the interval between injections. In men on transdermal testosterone patch or gel, testosterone levels should be in the mid-normal range (400–750 ng/dL) 4–12 h after application. If testosterone levels are outside this range, the dose should be adjusted. Multiple dose adjustments are often necessary to achieve testosterone levels in the desired therapeutic range.

Disorders of the Testes and Male Reproductive System CHAPTER 403 Restoration of sexual function, induction and maintenance of secondary sex characteristics, well-being, and maintenance of mus­ cle and bone health are important objectives of TRT. The patient should be asked about sexual desire and activity, the presence of early morning erections, and the ability to achieve and maintain erections adequate for sexual intercourse. The hair growth in response to androgen replacement is variable and depends on eth­ nicity. Men with prepubertal onset of testosterone deficiency who begin testosterone therapy in their late twenties or thirties may find it difficult to adjust to their newly found sexuality and may benefit from counseling. If the patient has a sexual partner, the partner should be included in counseling because of the dramatic physical and sexual changes that occur with TRT. Contraindications for Testosterone Administration  Testosterone administration is contraindicated in men with prostate or breast cancer (Table 403-4). Testosterone therapy should not be admin­ istered without further urologic evaluation to men with a palpable prostate nodule or induration, a PSA >3 ng/mL, or severe lower urinary tract symptoms (American Urological Association lower urinary tract symptom score >19). Testosterone should not be administered to men with a hypercoagulable condition, baseline hematocrit ≥50%, severe untreated obstructive sleep apnea, or uncontrolled or poorly controlled congestive heart failure, or with myocardial infarction, stroke, or acute coronary syndrome in the preceding 4 months. Monitoring Potential Adverse Experiences  The clinical effective­ ness and safety of TRT should be assessed 3–6 months after initi­ ating testosterone therapy and annually thereafter (Table 403-5). Potential adverse effects include acne, oiliness of skin, erythrocy­ tosis, venous thromboembolism, breast tenderness, leg edema, and increased risk of detection of prostate events. In addition, there may be formulation-specific adverse effects such as skin irritation with transdermal patch; risk of gel transfer to a sexual partner with testosterone gels; pain and mood fluctuation with injectable testosterone esters; cough and injection site pain with long-acting TABLE 403-4  Conditions in Which Testosterone Administration Should not be Used or Used with Increased Caution Conditions in which testosterone administration is associated with very high risk of serious adverse outcomes: Metastatic prostate cancer Some types of breast cancers Thrombophilia Conditions in which testosterone administration is associated with moderate to high risk of adverse outcomes and should be used with increased caution and only after further evaluation Undiagnosed prostate nodule or induration PSA >3 Erythrocytosis (hematocrit >50%) Severe lower urinary tract symptoms associated with benign prostatic hypertrophy as indicated by American Urological Association/International prostate symptom score >19 Uncontrolled or poorly controlled congestive heart failure Myocardial infarction, stroke, or acute coronary syndrome in the preceding 4 months Abbreviation: PSA, prostate-specific antigen.

TABLE 403-5  Monitoring Men Receiving Testosterone Therapy

  1. Evaluate the patient 3–6 months after treatment initiation and then annually to assess whether symptoms have responded to treatment and whether the patient is suffering from any adverse effects.
  2. Monitor testosterone level 3–6 months after initiation of testosterone therapy: • Therapy should aim to raise average serum testosterone level into the midnormal range (~400–750 ng/dL). • Injectable testosterone enanthate or cypionate: Measure serum testosterone level midway between injections. If testosterone is >750 ng/dL (26.2 nmol/L) or <400 ng/dL (14.0 nmol/L), adjust dose or frequency. • Transdermal gels and solution: Assess testosterone level 2–12 h after patient has been on treatment for at least 2 weeks; adjust dose to achieve serum testosterone level in the mid-normal range (400–750 ng/dL). • Testosterone pellets: Measure testosterone levels at the end of the PART 12 Endocrinology and Metabolism dosing interval. Adjust the number of pellets and/or the dosing interval to achieve serum testosterone levels in the normal range. • Oral testosterone undecanoate: Measure testosterone levels 6–8 h after an oral dose. • Injectable testosterone undecanoate: Measure serum testosterone level just prior to each subsequent injection and adjust the dosing interval to maintain serum testosterone in mid-normal range.
  3. Check hematocrit at baseline, at 3–6 months, and then annually. If hematocrit is >54%, stop therapy until hematocrit decreases to a safe level; evaluate the patient for hypoxia and sleep apnea; reinitiate therapy with a reduced dose.
  4. Measure bone mineral density of lumbar spine and/or femoral neck after 1–2 years of testosterone therapy in hypogonadal men with osteoporosis or low trauma fracture, consistent with regional standard of care.
  5. In men aged ≥55 years, perform digital rectal examination and check PSA level before initiating treatment, at 3–6 months, and then in accordance with guidelines for prostate cancer screening depending on the age and race of the patient.
  6. Obtain urologic consultation if there is: • An increase in serum PSA concentration >1.4 ng/mL within the first 12 months after starting testosterone treatment, confirmed by repeating the test. • A PSA level >4 ng/mL any time during treatment, confirmed by repeating the test. • Detection of a prostatic abnormality on digital rectal examination. • Severe lower urinary tract symptoms
  7. Evaluate formulation-specific adverse effects at each visit: • Injectable testosterone esters (enanthate, cypionate, and undecanoate): Ask about fluctuations in mood or libido, and rarely cough after injections. • Testosterone gels: Advise patients to cover the application sites with a shirt and to wash the skin with soap and water before having skin-to-skin contact because testosterone gels leave a testosterone residue on the skin that can be transferred to a woman or child who might come in close contact. Serum testosterone levels are maintained when the application site is washed 4–6 h after application of the testosterone gel. • Testosterone undecanoate injection: Observe patients for POME reaction for 30 min after each injection. • Testosterone pellets: Look for signs of infection, fibrosis, or pellet extrusion. • Intranasal testosterone: Look for signs of nasal irritation or scab. Abbreviations: AUA/IPSS, American Urological Association International Prostate Symptom Score; POME, pulmonary oil microembolism; PSA, prostate-specific antigen. testosterone undecanoate; and nasal irritation, epistaxis, and nasal scab with intranasal formulation. In the TRAVERSE trial, a ran­ domized controlled trial of TRT in middle-aged and older men with hypogonadism, TRT was associated with increased risk of atrial fibrillation, acute kidney injury, and bone fractures. Hemoglobin Levels  Administration of testosterone to men with hypogonadism is typically associated with only a small (~3%) increase in hemoglobin levels, due to direct effects of testosterone on hematopoietic progenitors in the bone marrow, stimulation of erythropoietin, suppression of hepcidin, and increased iron avail­ ability for erythropoiesis. The magnitude of hemoglobin increase during TRT is greater in older men than younger men and in men who have sleep apnea, a significant smoking history, or chronic

obstructive lung disease or who live at high altitude. The frequency of erythrocytosis is higher in men with hypogonadism treated with injectable testosterone esters than in those treated with transder­ mal formulations, presumably due to the higher testosterone dose delivered by the typical regimens of testosterone esters. Erythrocy­ tosis is a frequent adverse event reported in testosterone trials in middle-aged and older men and is also the most frequent cause of treatment discontinuation in these trials. If hematocrit rises above 54%, testosterone therapy should be stopped until hematocrit has fallen to <50%. After evaluation of the patient for hypoxia and sleep apnea, testosterone therapy may be reinitiated at a lower dose. Prostate and Serum PSA Levels  TRT increases prostate vol­ ume to the size seen in age-matched controls. In the TRAVERSE trial, the incidences of high-grade or any prostate cancer were low and did not differ between the testosterone- and placebotreated  men. The incidences of acute urinary retention, invasive surgical procedure for benign prostatic hyperplasia, prostate biopsy, or initiation of new pharmacologic therapy for benign prostatic hyperplasia also were similar in the testosterone and placebo groups. Testosterone treatment did not worsen lower urinary tract symptoms. There is no evidence that TRT causes prostate cancer. However, testosterone treatment can exacerbate preexisting meta­ static prostate cancer. Many older men harbor microscopic foci of cancer in their prostates. It is not known whether long-term TRT will induce these microscopic foci to grow into clinically significant cancers. PSA levels are lower in testosterone-deficient men and increase after initiation of TRT. An increase in PSA levels after starting TRT can lead to urologic referral, increased risk of prostate biopsy, and detection of a low-grade prostate cancer that is common among middle-aged and older men. Increments in PSA levels after testosterone supplementation in androgen-deficient men are generally <0.5 ng/mL, and increments >1.0 ng/mL over a 3- to 6-month period are unusual. The 90% confidence interval for the change in PSA values in men with benign prostatic hyperplasia, measured 3–6 months apart, is 1.4 ng/mL. Therefore, the Endo­ crine Society expert panel suggested that an increase in PSA >1.4 ng/mL in the first year after starting TRT, if confirmed, should lead to urologic evaluation. There is considerable test-retest variability in PSA measurements. Therefore, PSA elevations after starting TRT should be confirmed by repeating the PSA test no sooner than 4 weeks after the first test. PSA level >4 ng/mL at any time during treatment, if confirmed by repeat testing, requires further urologic evaluation. Because prostate biopsy has the potential for harm (infection, bleeding, and diagnosis of a low-grade prostate cancer), the institution of PSA monitoring and urologic referral for a prostate biopsy should be a shared decision of the patient and the clinician. Cardiovascular Risk  In 2015, the U.S. Food and Drug Admin­ istration (FDA), because of concerns about the cardiovascular risk of TRT, required the testosterone manufacturers to conduct a randomized controlled trial to compare the effects of TRT versus placebo on cardiovascular events. The TRAVERSE trial, a large pro­ spective randomized controlled trial, conducted in response to the FDA’s requirement, has provided strong evidence that testosterone treatment does not increase the risk of major cardiovascular events (death due to cardiovascular cause, nonfatal myocardial infarction, or nonfatal stroke) relative to placebo treatment in middle-aged and older men with hypogonadism and preexisting cardiovascular disease or increased risk of cardiovascular disease during a mean follow-up duration of 33 months. The incidence of a secondary composite cardiovascular endpoint that included death due to cardiovascular cause, nonfatal myocardial infarction, nonfatal stroke, or coronary revascularization procedure also did not differ between the testosterone and placebo groups. Testosterone-treated men experienced higher rates of venous thromboembolic events, nonfatal arrythmias clinical bone fractures, and acute kidney injury than placebo-treated men. The TRAVERSE trial also found a small

but statistically significantly greater increase in blood pressure in the testosterone than in the placebo group, similar to the findings of some other studies. Androgen Use by Athletes and Recreational Bodybuilders  The illicit use of androgenic-anabolic steroids (AAS) to enhance athletic performance first surfaced in the 1950s among powerlifters and spread rapidly to other sports, professional as well as high school athletes, and recreational bodybuilders. In the early 1980s, the use of AAS spread beyond the athletic community into the general pop­ ulation, and now, as many as 3–4 million Americans—most of them men—have likely used these compounds. Most AAS users are not athletes, but rather recreational weightlifters, almost all men, who use these drugs to look lean and more muscular. A subset of AAS users suffers from muscle dysmorphia, a form of body image dis­ order characterized by excessive preoccupation with leanness and muscularity and poor functioning in social and occupational life. A secular transformation of idealized body image toward greater muscularity and leanness has contributed to increasing prevalence of body image disorders and the use of muscle-building anabolic drugs in young men. The most commonly used AAS include testosterone esters, nandrolone, trenbolone, stanozolol, methandienone, boldenone, and methenolone. AAS users generally use large doses of multiple steroids in cycles, a practice known as stacking. AAS users may also typically use other drugs that are perceived to be muscle building or performance enhancing, such as human GH; erythropoiesisstimulating agents; insulin; stimulants such as amphetamine, clen­ buterol, cocaine, ephedrine, and thyroxine; and drugs perceived to reduce adverse effects such as hCG, aromatase inhibitors, or estrogen antagonists. Recent years have witnessed increasing use of unapproved nonsteroidal SARMs and GH secretagogues purchased from internet sites. Most of the information about the adverse effects of AAS has emerged from case reports, uncontrolled studies, or clinical trials that used replacement doses of testosterone. The adverse event data from clinical trials using physiologic replacement doses of testosterone have been extrapolated unjustifiably to AAS users, who may administer 10–100 times the replacement doses of testosterone over many years, to support the claim that AAS use is safe and manageable. The adverse events associated with AAS use may be due to AAS themselves, concomitant use of other drugs, high-risk behaviors, and host characteristics that may render these individu­ als more susceptible to AAS use or to other high-risk behaviors. Four categories of adverse events associated with AAS abuse are of particular concern: cardiovascular events, psychiatric disorders, prolonged suppression of the hypothalamic-pituitary-testicular axis, and potential neurotoxicity. The high rates of premature mortality observed in AAS users are alarming. One Finnish study reported 4.6 times the risk of death among elite powerlifters compared with age-matched men from the general population. The causes of death among powerlifters included suicides, myocardial infarction, and liver failure. A retrospective review of patient records in Sweden also reported higher standardized mortality ratios for AAS users than for nonusers and increased death rates due to suicide, homi­ cide, and accidents. High doses of AAS may induce proatherogenic dyslipidemia, accelerate atherogenesis, increase thrombosis risk via effects on clotting factors and platelets, and induce vasospasm through their effects on vascular nitric oxide. Long-term AAS use may be associated with myocardial hypertrophy and fibrosis. Myocardial tissue of powerlifters using AAS has been shown to be infiltrated with fibrous tissue and fat droplets. Current AAS users display significantly reduced left ventricular systolic and diastolic function compared to previous users and nonusers. Additionally, studies using CT angiography have reported higher coronary artery plaque volume in AAS users than in nonusers. Lifetime AAS dose is strongly associated with coronary atherosclerotic burden. Power athletes using AAS often have short QT intervals but increased QT dispersion, which may predispose them to ventricular arrhythmias.

Unlike replacement doses of testosterone, which are associated with only a small decrease in high-density lipoprotein (HDL) cholesterol and little or no effect on total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride levels, supraphysi­ ologic doses of testosterone and orally administered 17α-alkylated, nonaromatizable AAS are associated with marked reductions in HDL cholesterol and increases in LDL cholesterol.

Some AAS users develop hypomanic and manic symptoms (irri­ tability, aggressiveness, reckless behavior, and occasional psychotic symptoms, sometimes associated with violence) during AAS expo­ sure, and depression, sometimes associated with suicidality, during AAS withdrawal. Users may also be susceptible to other forms of illicit drug use. Disorders of the Testes and Male Reproductive System CHAPTER 403 Long-term AAS use suppresses LH, FSH, and testosterone levels and spermatogenesis. Men who have used AAS for more than a few months experience marked suppression of the hypothalamicpituitary-testicular (HPT) axis after stopping AAS that may be asso­ ciated with sexual dysfunction, fatigue, infertility, depressed mood, and even suicidality. In some long-term AAS users, recovery of the HPT axis may take a long time, may be incomplete, or may never occur. The symptoms of testosterone deficiency caused by AAS withdrawal may cause some men to revert back to using AAS, lead­ ing to continued use and AAS dependence. As many as 30% of AAS users develop a syndrome of AAS dependence, characterized by long-term AAS use despite adverse medical and psychiatric effects. AAS withdrawal hypogonadism has emerged as an important cause of androgen deficiency, accounting for a substantial fraction of testosterone prescriptions in many men’s health clinics; therefore, AAS use should be considered in the differential diagnosis of hypo­ gonadism in young men. Supraphysiologic doses of testosterone may also impair insulin sensitivity. Orally administered androgens also have been associ­ ated with insulin resistance and diabetes. AAS users are more likely to engage in high-risk behaviors such as unsafe injection practices and have increased rates of incarcera­ tion that may render them at increased risk of HIV and hepatitis B and C. AAS users are more likely to report high-risk unprotected anal sex than nonusers. Elevated liver enzymes, cholestatic jaundice, hepatic neoplasms, and peliosis hepatis have been reported with oral, 17α-alkylated AAS. AAS use may cause muscle hypertrophy without compensa­ tory adaptations in tendons, ligaments, and joints, thus increasing the risk of tendon, ligament, and joint injuries. Upper extremity tendon ruptures are observed predominantly among weightlift­ ers who use AAS. AAS use is associated with acne, baldness, and increased body hair. APPROACH TO THE PATIENT Androgenic-Anabolic Steroids Use The suspicion of AAS use should be raised by increased hemoglo­ bin and hematocrit levels, suppressed LH and FSH and testosterone levels, low HDL cholesterol and SHBG levels, and low testicular vol­ ume and sperm density in a person who looks highly muscular. In AAS users seeking medical attention, evaluation using the Appear­ ance and Performance Enhancing Drug Use Schedule (APEDUS), a validated semi-structured interview, is sufficient to assess the asso­ ciated body image or eating disorder, psychiatric symptoms, and the use of AAS and other substances; formal testing for AAS usually is rarely needed in clinical practice. History of AAS use should be obtained in all young men being evaluated for hypogonadism. As AAS use is often associated with the use of other substances, a urine dug screen for other substances is helpful in guiding treatment. If needed, accredited laboratories use gas chromatography–mass spec­ trometry or liquid chromatography–tandem mass spectrometry to detect anabolic steroid abuse. High-resolution mass spectrometry and tandem mass spectrometry have improved the sensitivity of

19 - 404 Disorders of the Female Reproductive System

404 Disorders of the Female Reproductive System

detecting AAS use. Illicit testosterone use is detected generally by the measurement of urinary testosterone-to-epitestosterone ratio and further confirmed by the 13C:12C ratio in testosterone using iso­ tope ratio combustion mass spectrometry. Exogenous testosterone administration increases urinary testosterone glucuronide excre­ tion and consequently the testosterone-to-epitestosterone ratio. Ratios >6 are highly suggestive of exogenous testosterone use but can also reflect genetic variation. Genetic variations in uri­ dine diphospho-glucuronyltransferase 2B17 (UGT2B17), the major enzyme for testosterone glucuronidation, affect the testosterone-toepitestosterone ratio. Synthetic testosterone has a lower 13C:12C ratio than endogenously produced testosterone, and these differences in 13C:12C ratio can be detected by isotope ratio combustion mass spectrometry, which is used to confirm exogenous testosterone use in individuals with a high testosterone-to-epitestosterone ratio. PART 12 Endocrinology and Metabolism The treatment of AAS use disorder requires a multidisciplinary team that includes an endocrinologist or an internist to treat the AAS withdrawal hypogonadism and other medical problems; a mental health expert to treat the substance use disorder and depres­ sive symptoms and to address suicide risk and body image disorder; and sometimes a social worker for care coordination. In patients who are willing to stop or who have already stopped AAS use, the initial step is to restore the hypothalamic-pituitary-gonadal axis by administering either clomiphene (or its enantiomer trans enclomi­ phene), a partial estrogen agonist, at an initial dose of 50 mg daily or hCG at a dose of 1000–2000 IU three times weekly. Some men may not respond to clomiphene and may require hCG. AAS users also need evaluation and treatment of the underlying body image disor­ der. Mirror exposure therapy in which the patient stands in front of a mirror and describes his body appearance to the mental health provider has been moderately efficacious in small, randomized trials. Body dysmorphia may require cognitive-behavioral therapy or pharmacotherapy using selective serotonin uptake inhibitors or tricyclic antidepressants. ■ ■FURTHER READING Argenta J et al: Molecular basis of normal and pathological puberty: From basic mechanisms to clinical implications. Lancet Diabetes Endocrinol 11:203, 2023. Bhasin S et al: Testosterone therapy in men with hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 103:1715, 2018. Bhasin S et al: Prostate safety events during testosterone replacement therapy in men with hypogonadism: A randomized controlled trial. JAMA Netw Open 6:e2348692, 2023. Finkelstein JS et al: Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med 369:1011, 2013. Hildebrandt T et al: Body image disturbance in 1000 male appear­ ance and performance enhancing drug users. J Psychiatr Res 44:841, 2010. Hughes JF, Page DC: The biology and evolution of mammalian Y chromosomes. Annu Rev Genet 49:507, 2015. Jasuja R et al: Estradiol binding induces bidirectional allosteric cou­ pling and repartitioning of sex hormone binding globulin monomers among various conformational states. iScience 24:102414, 2021. Krausz C et al: EAA/EMQN best practice guidelines for molecular diagnosis of Y-chromosomal microdeletions: State-of-the-art 2013. Andrology 1:5, 2014. Lincoff AM et al: Cardiovascular safety of testosterone-replacement therapy. N Engl J Med 389:107, 2023. Mäkelä JA et al: Testis development. Endocr Rev 40:857, 2019. O’Shaughnessy PJ et al: Alternative (backdoor) androgen production and masculinization in the human fetus. PLoS Biol 17:e3000002, 2019. Patel B et al: The emerging therapeutic potential of kisspeptin and neurokinin B. Endocr Rev 45:30, 2024.

Pope HG Jr et al: Adverse health consequences of performanceenhancing drugs: An Endocrine Society scientific statement. Endocr Rev 35:341, 2014. Snyder PJ et al: Effects of testosterone treatment in older men. N Engl J Med 74:611, 2016. Stamou MI et al: Kallmann syndrome: Phenotype and genotype of hypogonadotropic hypogonadism. Metabolism 86:124, 2018. Travison TG et al: Harmonized reference ranges for circulating testos­ terone levels in men of four cohort studies in the USA and Europe. J Clin Endocrinol Metab 102:1161, 2017. Zakharov MN et al: A multi-step, dynamic allosteric model of testos­ terone’s binding to sex hormone binding globulin. Mol Cell Endocri­ nol 399:190, 2015. Janet E. Hall, Anuja Dokras

Disorders of the Female Reproductive System The female reproductive system regulates the hormonal changes responsible for puberty and adult reproductive function. Normal reproductive function in women requires the dynamic integration of hormonal signals from the hypothalamus, pituitary, and ovary, result­ ing in repetitive cycles of follicle development, ovulation, and prepara­ tion of the endometrial lining of the uterus for implantation should conception occur. For further discussion of related topics, see the following chapters: amenorrhea and pelvic pain (Chap. 405), infertility and contracep­ tion (Chap. 408), menopause (Chap. 407), disorders of sex develop­ ment (Chap. 402), and disorders of the male reproductive system (Chap. 403). DEVELOPMENT OF THE OVARY AND EARLY FOLLICULAR GROWTH The ovary orchestrates the development and release of a mature oocyte and secretes hormones (e.g., estrogen, progesterone, inhibins A and B, relaxin) that play critical roles in a variety of target tissues, including breast, bone, and uterus, in addition to the hypothalamus and pitu­ itary. To achieve these functions in repeated monthly cycles, the ovary undergoes some of the most dynamic changes of any organ in the body. Primordial germ cells can be identified by the third week of gestation, and their migration to the genital ridge is complete by 6 weeks of ges­ tation. Germ cells persist within the genital ridge, are then referred to as oogonia, and are essential for induction of ovarian development. In patients with 45,X Turner syndrome, primordial germ cells proliferate and migrate to the genital ridge but do not persist because their sur­ vival requires pregranulosa cells that are dependent on the presence of both X chromosomes (Chap. 402). The germ cell population expands, and starting at ~8 weeks of gesta­ tion, oogonia begin to enter prophase of the first meiotic division and become primary oocytes. Entry into meiosis provides some degree of protection from programmed cell death. It also allows the oocyte to be surrounded by a single layer of flattened granulosa cells to form a primordial follicle. Granulosa cells are derived from mesonephric cells that migrate into the ovary early in its development, pushing the germ cells to the periphery. Although there is evidence that both oocyte-like cells and follicle-like structures can form from embryonic stem cells in culture, there is no clear evidence that this occurs in vivo, and thus, the ovary appears to contain a nonrenewable pool of germ cells. Through

7 × 106 Migratory germ cells Oogonia Primary oocytes 2 × 106 4 × 105 Menopause Menarche Birth 5 m 2 m FIGURE 404-1  Ovarian germ cell number is maximal at mid-gestation and decreases precipitously thereafter. the combined processes of mitosis, meiosis, and atresia, the popula­ tion of oogonia reaches its maximum of 6–7 million by 20 weeks in the fetus, after which there is a progressive loss of both oogonia and primordial follicles through the process of atresia. At birth, oogonia are no longer present in the ovary, and only 1–2 million germ cells remain in the form of primordial follicles (Fig. 404-1). The oocyte persists in prophase of the first meiotic division until just before ovulation, when meiosis resumes. The quiescent primordial follicles are recruited to further growth and differentiation through a highly regulated process that limits the size of the developing cohort to ensure that folliculogenesis can continue throughout the reproductive life span. Transformation of pri­ mordial follicles to form primary follicles (Fig. 404-2) is characterized by growth of the oocyte and the transition from squamous to cuboidal granulosa cells. The theca interna cells that surround the developing follicle begin to form as the primary follicle grows. Acquisition of a zona pellucida by the oocyte, and the presence of several layers of sur­ rounding cuboidal granulosa cells, further surrounded by theca cells, mark the development of secondary follicles. It is at this stage that granulosa cells develop follicle-stimulating hormone (FSH), estradiol, and androgen receptors and communicate with one another through the development of gap junctions. Bidirectional signaling between the germ cells and the somatic cells in the ovary is a necessary component underlying the maturation of the oocyte and the capacity for hormone secretion. Members of the trans­ forming growth factor beta (TGF-β) family of proteins are involved Gonadotropin-Dependent Gonadotropin-Independent Paracrine Control Endocrine Control Inhibin A Inhibin B AMH Preovulatory 20 mm Dominant 11 mm Small Antral 2–5 mm Secondary Primordial Primary Initial Recruitment Cyclic Recruitment Selection Dominance 14 Days

120 Days FIGURE 404-2  Gonadotropin-independent and gonadotropin-dependent ovarian follicle development that ultimately results in ovulation of a mature oocyte. AMH, anti-müllerian hormone. (Reproduced with permission from Donna Jeanne Corcoran.)

in this bidirectional signaling; oocyte-derived growth differentiation factor 9 (GDF-9) and bone morphogenic protein-15 (BMP-15), also known as GDF-9b, are required for migration of pregranulosa and pretheca cells to the outer surface of the developing follicle initial follicle formation. GDF-9 is also required for formation of second­ ary follicles, as are granulosa cell–derived KIT ligand (KITL) and the forkhead transcription factor (FOXL2). A significant number of genes have been identified that are required for development of the normal complement of oogonia in the ovary, initial follicle development, and resistance to follicle loss; all are candidates for premature ovarian insufficiency (POI), and mutations in >50 genes have been identified in patients with POI, with even more that have been associated with an earlier age at natural menopause.

Disorders of the Female Reproductive System CHAPTER 404 DEVELOPMENT OF A MATURE FOLLICLE The early stages of follicle growth are primarily driven by intraovarian factors. Further maturation to the preovulatory stage, including the resumption of meiosis in the oocyte, requires the combined stimu­ lus of FSH and luteinizing hormone (LH) (Figs. 404-2 and 404-3). Recruitment from the resting pool of secondary follicles, termed cyclic recruitment, requires the direct action of FSH, whereas anti-müllerian hormone (AMH) produced from small growing preantral follicles restrains this effect of FSH, controlling the number of follicles entering the actively growing pool. Accumulation of follicular fluid between the layers of granulosa cells creates an antrum that divides the granulosa cells into two functionally distinct groups: mural cells that line the folli­ cle wall and cumulus cells that surround the oocyte (Fig. 404-3). As the follicle develops into a preovulatory, or Graffian, follicle, mural granu­ losa cells in proximity to theca cells express the greatest steroidogenic activity. Cumulus cells surround the oocyte and express mammalian target of rapamycin (mTOR), which regulates cellular metabolism and increases the transfer of nutrients to the oocyte. In addition to its role in normal development of the müllerian system, the WNT signaling pathway is required for normal antral follicle development and may also play a role in ovarian steroidogenesis. Recruitment to the small antral stage generally occurs over several cycles with further growth to follicle sizes of >4–7 mm in waves during a single cycle. However, recruitment over a single cycle can occur as evidenced by a normal follicular phase length in gonadotropin-releasing hormone (GnRH)-deficient women in response to a first cycle of treatment with a physiologic regimen of pulsatile GnRH administration and normalization of FSH and LH. A single dominant follicle emerges from the growing follicle pool within the first 5–7 days after the onset of menses, while the majority of follicles Estradiol

PART 12 Endocrinology and Metabolism FIGURE 404-3  Development of ovarian follicles. The Graafian follicle is also known as a tertiary or preovulatory follicle. (Courtesy of JH Eichhorn and D Roberts, Massachusetts General Hospital; with permission.) fall off their growth trajectory and become atretic. Autocrine actions of activin and BMP-6, derived from the granulosa cells, and paracrine actions of GDF-9, BMP-15, BMP-6, and Gpr149, derived from the oocyte, are involved in granulosa cell proliferation and modulation of FSH responsiveness. Differential exposure to these factors, and to vas­ cular endothelial growth factor (VEGF), can alter vascular density and permeability, likely explaining the mechanism whereby a given follicle is selected for continued growth to the preovulatory stage. The dominant follicle can be distinguished by its size, evidence of granulosa cell pro­ liferation, large number of FSH receptors, high aromatase activity, and elevated concentrations of estradiol and inhibin A in follicular fluid. In addition, secretion of estradiol and inhibin from the dominant follicle inhibits FSH and the growth of other follicles. The dominant follicle undergoes rapid expansion during the 5–6 days prior to ovulation, reflecting granulosa cell proliferation and accumulation of follicular fluid. FSH induces LH receptors on the granulosa cells, and the preovulatory, or Graafian, follicle moves to the outer ovarian surface in preparation for ovulation. The LH surge triggers the resumption of meiosis, the suppression of granulosa cell proliferation, and the induction of cyclooxygenase 2 (COX-2), pros­ taglandins, the progesterone receptor (PR), and the epidermal growth factor–like growth factors amphiregulin, epiregulin, betacellulin, and neuroregulin 1, all of which are required for ovulation. Ovulation requires production of extracellular matrix, leading to expansion of the cumulus cell population that surrounds the oocyte and the con­ trolled expulsion of the egg and follicular fluid. Both progesterone and prostaglandins (induced by the ovulatory stimulus) are essential for this process, as are members of the matrix metalloproteinase family. After ovulation, luteinization of theca and granulosa cells is induced by LH in conjunction with the acquisition of a rich vascular network in response to VEGF and basic fibroblast growth factor (FGF). Tradi­ tional regulators of central reproductive control, GnRH and its recep­ tor (GnRHR), as well as kisspeptin, are also produced in the ovary and may be involved in corpus luteum function. REGULATION OF OVARIAN FUNCTION ■ ■HYPOTHALAMIC AND PITUITARY SECRETION GnRH neurons derive from cells in the olfactory placode and, to a lesser extent, the neural crest. They migrate into the brain across

the cribriform plate along with the olfactory neurons which then form the olfactory bulb, while the GnRH neurons continue their journey to the hypothalamus. The importance of the initial migra­ tory pathway into the brain is evidenced in patients born without a nose (bosma arhinia microphthalmia syndrome) who lack olfac­ tory foramina in the cribriform plate and are both anosmic and have hypogonadotropic hypogonadism. Studies in these and other GnRH-deficient patients who fail to undergo puberty have provided insights into genes that control the ontogeny and function of GnRH neurons (Fig. 404-4). ANOS1 (also known as KAL1), FGF8/FGFR1, Migration Function Hypothalamus KNDY Neural crest KISS1R Olfactory placode KISS1R GnRH1 Pituitary GnRHR FIGURE 404-4  Genetic studies in patients with congenital forms of hypogonadotropic hypogonadism have expanded our understanding of the development and migration of gonadotropin-releasing hormone (GnRH) neurons from the olfactory placode and possibly the neural crest to the hypothalamus as well as the upstream regulation of GnRH secretion by kisspeptin (KISS1), neurokinin B (TAC3), and dynorphin (Dyn), which are co-expressed in the KNDY neurons. GnRHR, GnRH receptor.

PROK2/PROKR2, NSMF, HS6SD1, and CDH7, among a host of others (Chap. 403), have been implicated in the migration of GnRH neurons to the hypothalamus, whereas KISS, TAC3, Dyn, and their receptors are involved in the upstream regulation of GnRH secretion. Approximately 7000 GnRH neurons, scattered throughout the medial basal hypothalamus, establish contacts with capillaries of the pitu­ itary portal system in the median eminence. GnRH is secreted into the pituitary portal system in discrete pulses to stimulate synthesis and secretion of LH and FSH from pituitary gonadotropes, which comprise ~10% of cells in the pituitary (Chap. 390). Functional con­ nections of GnRH neurons with the portal system are established by the end of the first trimester, coinciding with the production of pitu­ itary gonadotropins. Thus, like the ovary, the hypothalamic and pitu­ itary components of the reproductive system are present before birth. However, the high levels of estradiol and progesterone produced by the placenta suppress hypothalamic-pituitary stimulation of ovarian hormonal secretion in the fetus. After birth and the loss of placenta-derived steroids, gonadotropin levels rise. FSH levels are much higher in girls than in boys. The rise in FSH in girls results in circulating estradiol and inhibin B in what has been termed the mini-puberty of infancy, but without terminal follicle maturation or ovulation. Studies that have identified mutations in TAC3, which encodes neurokinin B, and its receptor, TAC3R, in patients with GnRH deficiency indicate that both are involved in con­ trol of GnRH secretion and may be particularly important at this early stage of development. By 12–20 months of age, the reproductive axis is again suppressed, and a period of relative quiescence persists until puberty (Fig. 404-5). At the onset of puberty, pulsatile GnRH secre­ tion induces pituitary gonadotropin production. In the early stages of puberty, LH and FSH secretion are apparent only during sleep, but as puberty develops, pulsatile LH secretion, a faithful marker of GnRH secretion, occurs throughout the day and night. The mechanisms responsible for the childhood quiescence and pubertal reactivation of the reproductive axis remain incompletely understood. GnRH neurons in the hypothalamus respond to both excitatory and inhibitory factors. Increased sensitivity to the inhibitory influence of gonadal steroids has long been implicated in the inhibi­ tion of GnRH secretion during childhood but has not been definitively established in the human. Metabolic signals, including adipocytederived leptin, play a permissive role in reproductive function but are not sufficient to induce puberty (Chap. 413). Studies of patients with isolated GnRH deficiency reveal that mutations in the G protein–coupled receptor 54 (GPR54) gene (now known as KISS1R) preclude the onset of puberty. Kisspeptin, the ligand for this receptor, is derived from the parent peptide, kisspeptin-1 (KISS1), and is a potent stimulant for GnRH release. The tachyki­ nin 3 gene (TAC3), which encodes neurokinin-B (NKB), stimulates GnRH secretion through kisspeptin signaling, while dynorphin (Dyn), which acts mainly through kappa opioid receptors, plays an inhibitory role in GnRH control. TAC3 and Dyn are frequently coexpressed with KISS1 in KNDy neurons of the median eminence that project to GnRH neurons. This system is intimately involved in both Plasma gonadotropins FSH 50 yr Menopause 10–14 yr Puberty reproductive years Childhood Infancy Birth−20 mo. FIGURE 404-5  Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are increased during the neonatal years but go through a period of childhood quiescence before increasing again during puberty. Gonadotropin levels are cyclic during the reproductive years and increase dramatically with the loss of negative feedback that accompanies menopause.

estrogen and progesterone negative feedback regulation of GnRH secretion as well as metabolic and stress signaling to the reproduc­ tive axis. Kisspeptin release is pulsatile, and secretion is generated by alternate stimulation and inhibition of kisspeptin by NKB and Dyn, respectively. While pulsatility is an intrinsic property of GnRH neurons, the current model suggests that pulsatile secretion of GnRH is coordinated by pulsatile kisspeptin secretion, with potential input from upstream glutaminergic neurons.

A role for kisspeptin in the onset of puberty is suggested by upregu­ lation of KISS1 and KISS1R transcripts in the hypothalamus at the time of puberty. The onset of puberty may occur via a switch from epi­ genetic repression to epigenetic activation in kisspeptin neurons. Two imprinted genes that were initially identified in families with central precocious puberty, MKRN3 and DLK1, may be involved in this switch given their known functions and their association with age at onset of menarche in a large cohort of women. Disorders of the Female Reproductive System CHAPTER 404 While short-term infusion of kisspeptin restored LH pulsatility in patients with hypothalamic amenorrhea and hyperprolactinemia, there is also evidence that tachyphylaxis occurs, potentially limiting its use as a treatment for these conditions. RFamide-related peptides (RFRPs) are the mammalian orthologues of gonadotropin inhibitory hormone (GnIH), which was initially dis­ covered in the quail. In lower animal species, these peptides decrease gonadal function and sexual motivation in addition to increasing feed­ ing behavior and mediating the inhibitory actions of stress on repro­ duction. While RFRP-1 and RFRP-3 neurons send axonal projections to GnRH neurons in humans and RFRPs are secreted into the pituitary portal system, further studies are required to determine their potential physiologic role in the human. ■ ■OVARIAN STEROIDS Ovarian steroid-producing cells do not store hormones but produce them in response to FSH and LH during the normal menstrual cycle. The sequence of steps and the enzymes involved in the synthesis of steroid hormones are similar in the ovary, adrenal, and testis. However, the enzymes required to catalyze specific steps are compartmental­ ized and may not be abundant or even present in all cell types. Within the developing ovarian follicle, estrogen synthesis from cholesterol requires close integration between theca and granulosa cells—the twocell model for steroidogenesis (Fig. 404-6). FSH receptors are confined to the granulosa cells, whereas LH receptors are restricted to the theca LH Theca cell pregnenolone Cholesterol 3βHSD progesterone 17 hydroxylase 17-OHP 17,20 lyase Androstenedione 17βHSD Testosterone LH Androstenedione Testosterone Estrone Estradiol FSH aromatase Granulosa cell FIGURE 404-6  Estrogen production in the ovary requires the cooperative function of the theca and granulosa cells under the control of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). HSD, hydroxysteroid dehydrogenase; OHP, hydroxyprogesterone.

cells until the late stages of follicular development, when they are also found on granulosa cells. The theca cells surrounding the follicle are highly vascularized and use cholesterol, derived primarily from circu­ lating lipoproteins, as the starting point for the synthesis of androstene­ dione and testosterone under the control of LH. There is some evidence that 11-oxo-androgens, which are generally thought to be produced only in the adrenal, may also be produced to some degree in the ovary. These steroid precursors cross the basal lamina to the granulosa cells, which receive no direct blood supply. The mural granulosa cells are particularly rich in aromatase and, under the control of FSH, produce estradiol, the primary steroid secreted from the follicular phase ovary and the most potent estrogen. Theca cell–produced androstenedione and, to a lesser extent, testosterone are also secreted into peripheral blood, where they can be converted to dihydrotestosterone in skin and to estrogens in adipose tissue. The hilar interstitial cells of the ovary are functionally similar to Leydig cells and are also capable of secret­ ing androgens. Stromal cells proliferate in response to androgens (as in polycystic ovary syndrome [PCOS]) but do not secrete androgens. However, high levels of androgens may be produced by luteinized theca cells within the stroma in women with hyperthecosis.

PART 12 Endocrinology and Metabolism Development of the rich capillary network following rupture of the follicle at the time of ovulation makes it possible for large molecules such as low-density lipoprotein (LDL) to reach the luteinized granulosa and theca lutein cells. As in the follicle, both cell types are required for steroidogenesis in the corpus luteum. The luteinized granulosa cells are the main source of progesterone production, whereas the smaller theca lutein cells produce 17-hydroxyprogesterone and androgenic substrates for aromatization to estradiol by the luteinized granulosa cells. Production of estrogen metabolites by the corpus luteum plays a significant role in maintenance of the vascularization required for its function. LH is critical for formation and maintenance of corpus luteum structure and function. LH and human chorionic gonado­ tropin (hCG) bind to a common receptor; thus, in conception cycles, hCG produced upon fertilization rescues the declining function of the corpus luteum, maintaining steroid and peptide secretion for the first 10 weeks of pregnancy. hCG is commonly used for luteal phase support in the treatment of infertility. Steroid Hormone Actions  Both estrogen and progesterone play critical roles in the expression of secondary sexual characteristics in women (Chap. 389). Estrogen promotes development of the ductule system in the breast, whereas progesterone is responsible for glandular development. In the reproductive tract, estrogens create a receptive environment for fertilization and support pregnancy and parturition through carefully coordinated changes in the endometrium, thicken­ ing of the vaginal mucosa, thinning of the cervical mucus, and uterine growth and contractions. Progesterone induces secretory activity in the estrogen-primed endometrium, increases the viscosity of cervical mucus, and inhibits uterine contractions. Both gonadal steroids play critical roles in negative and positive feedback of gonadotropin secre­ tion. Progesterone also increases basal body temperature, which is used clinically as a marker of ovulation. The vast majority of circulating estrogens and androgens are car­ ried in the blood bound to carrier proteins, which restrain their free diffusion into cells and prolong their clearance, serving as a reservoir. High-affinity binding proteins include sex hormone–binding globulin (SHBG), which binds androgens with somewhat greater affinity than estrogens, and corticosteroid-binding globulin (CBG), which also binds progesterone. Modulations in binding protein levels by insulin, androgens, and estrogens contribute to high bioavailable testosterone levels in PCOS and to high circulating total estrogen and progesterone levels during pregnancy. Estrogens act primarily through binding to the nuclear receptors, estrogen receptors (ER) α and β. Transcriptional coactivators and co-repressors modulate ER action (Chap. 389). Both ER subtypes are present in the hypothalamus, pituitary, ovary, and reproductive tract. Although ERα and ERβ exhibit some functional redundancy, there is also a high degree of specificity, particularly in expression within cell types. For example, ERα functions in ovarian theca cells, whereas ERβ

is critical for granulosa cell function. There is also evidence for mem­ brane-initiated signaling by estrogen. Similar signaling mechanisms pertain for progesterone with evidence of transcriptional regulation through PR-A and PR-B protein isoforms, as well as rapid membrane signaling. ■ ■OVARIAN PEPTIDES Inhibin was initially isolated from gonadal fluids based on its ability to selectively inhibit FSH secretion from pituitary cells. Inhibin is a heterodimer composed of an α subunit and a βA or βB subunit to form inhibin A or inhibin B, both of which are secreted from the ovary. Activin is a homodimer of inhibin β subunits with the capacity to stimulate the synthesis and secretion of FSH. Inhibins and activins are members of the TGF-β superfamily of growth and differentiation fac­ tors. During the purification of inhibin, follistatin, an unrelated mono­ meric protein that inhibits FSH secretion, was discovered. Within the pituitary, follistatin inhibits FSH secretion indirectly by binding and neutralizing activin. Inhibin B is constitutively secreted from the granulosa cells of small antral follicles, and its serum levels increase in conjunction with granu­ losa cell proliferation during recruitment of secondary follicles under the control of FSH (Fig. 404-2). Inhibin B is an important inhibitor of FSH, independent of estradiol, during the menstrual cycle. Inhibin A is present in both granulosa and theca cells and is secreted by the dominant follicle. Inhibin A is also present in luteinized granulosa cells and is a major secretory product of the corpus luteum. Synthesis and secretion of inhibin A are directly controlled by FSH and LH. Although activin is also secreted from the ovary, the excess of follistatin in serum, combined with its nearly irreversible binding of activin, make it unlikely that ovarian activin plays an endocrine role in FSH regulation. However, there is evidence that activin plays an autocrine/ paracrine role in the ovary in germ cell survival, follicle assembly, and inhibition of androgen production, in addition to its intrapituitary role in modulation of FSH production. AMH (also known as müllerian-inhibiting substance) is important in ovarian biology in addition to the function from which it derived its name (i.e., promotion of the degeneration of the müllerian system during embryogenesis in the male). AMH is produced by granulosa cells from small preantral and early antral follicles (Fig. 404-2) and is a marker of ovarian reserve with advantages over inhibin B because of its relative stability across the menstrual cycle. AMH inhibits FSH in the recruitment of primordial follicles into the follicle pool and counters FSH stimulation of aromatase expression. AMH levels increase dur­ ing puberty, are highest in the early twenties, and decrease markedly by menopause. AMH is increased in PCOS in conjunction with the abundance of small follicles in this disorder. Gonadotropin surge attenuating factor (GnSAF) is an ovarian fac­ tor that attenuates GnRH-induced gonadotropin secretion. Its role is not yet fully understood, but there is an inverse relationship between GnSAF and follicle size, suggesting that its primary role involves the early stages of follicle development rather than curtailing the gonado­ tropin surge as its name implies. Relaxin is produced primarily by the theca lutein cells of the corpus luteum. Both relaxin and its receptor, encoded by the gene RXFP1, are highly expressed in the uterus during the peri-implantation period and its primary role appears to be in promoting decidualization and vascularization of the endometrium prior to implantation. Relaxin was named for its ability to suppress myometrial contractility in pigs and rodents, but it does not appear to exert this activity in women. HORMONAL INTEGRATION OF THE NORMAL MENSTRUAL CYCLE The sequence of changes responsible for mature reproductive func­ tion is coordinated through a series of negative and positive feedback loops that alter pulsatile GnRH secretion, the pituitary response to GnRH, and the relative secretion of LH and FSH from gonadotropes (Fig. 404-7). The frequency and amplitude of pulsatile GnRH secretion differentially modulate the synthesis and secretion of LH and FSH. Slow GnRH pulse frequencies favor FSH synthesis, whereas increased

KNDy Neuron Hypothalamus GnRH Neuron Estradiol Progesterone GnRH Pituitary Inhibin B Inhibin A Estradiol Estradiol LH FSH Uterus Ovary FIGURE 404-7  The reproductive system in women is critically dependent on both negative feedback of gonadal steroids and inhibin to modulate follicle-stimulating hormone (FSH) secretion and on estrogen positive feedback to generate the preovulatory luteinizing hormone (LH) surge. GnRH, gonadotropin-releasing hormone. GnRH pulse frequency and amplitude favor LH synthesis. FSH syn­ thesis is also controlled by the activin-inhibin-follistatin system within the pituitary. Activin is produced in both pituitary gonadotropes and folliculostellate cells and stimulates the synthesis and secretion of FSH through autocrine-paracrine mechanisms that are modulated by follistatin, which is also produced in folliculostellate cells. Inhibins function as potent antagonists of activins through sequestration of the activin receptors. Although inhibin is expressed in the pituitary, gonadal inhibin is the principal source of feedback inhibition of FSH. For the majority of the cycle, the reproductive system functions in a classic endocrine negative feedback mode. Estradiol and progesterone inhibit GnRH secretion, acting through kisspeptin and dynorphin in the KNDy neurons, while the inhibins act at the pituitary to selectively inhibit FSH synthesis and secretion (Fig. 404-7). Estradiol also contrib­ utes to negative feedback at the pituitary with an effect that is greater for FSH than LH. This tightly regulated negative feedback control of FSH is critical for development of the single mature follicle that char­ acterizes normal reproductive cycles in women. In addition to these negative feedback controls, the menstrual cycle is uniquely dependent on estrogen-induced positive feedback to produce an LH surge that is essential for ovulation of a mature follicle. Estrogen negative feedback in women occurs primarily at the hypothalamus with a small pituitary contribution, whereas estrogen positive feedback occurs at the pitu­ itary in women with upregulation of GnRH signaling and responsive­ ness. In women, hypothalamic GnRH secretion plays a permissive role in generating the preovulatory gonadotropin surge, a mechanism that differs significantly from that in rodents and other species that rely on seasonal and circadian cues, in which a surge of GnRH also occurs. ■ ■THE FOLLICULAR PHASE The follicular phase is characterized by cyclic recruitment of a cohort of secondary follicles and the ultimate selection of a preovulatory follicle (Figs. 404-2 and 404-8). The follicular phase begins, by convention, on the first day of menses. However, follicle recruitment is initiated by the rise in FSH that begins in the late luteal phase of the previous cycle in conjunction with the loss of negative feedback of gonadal steroids and likely inhibin A. The fact that an ~20% increase in FSH is

Follicular phase Luteal phase FSH LH Dominant Ovulation Corpus luteum Corpus albicans Secondary Antral Ovarian follicles Inhibin B Disorders of the Female Reproductive System CHAPTER 404 Inhibin A E2 Prog Endo Proliferative Secretory FIGURE 404-8  Relationship between gonadotropins, follicle development, gonadal secretion, and endometrial changes during the normal menstrual cycle. E2, estradiol; Endo, endometrium; FSH, follicle-stimulating hormone; LH, luteinizing hormone; Prog, progesterone. adequate for follicular recruitment speaks to the marked sensitivity of the resting follicle pool to FSH. The resultant granulosa cell prolifera­ tion is responsible for increasing early follicular phase levels of inhibin B. Inhibin B, in conjunction with rising levels of estradiol and inhibin A, restrains FSH secretion during this critical period such that only a single follicle matures in the vast majority of cycles. The increased risk of multiple gestation associated with the higher levels of FSH char­ acteristic of advanced maternal age or with exogenous gonadotropin administration in the treatment of infertility attests to the importance of the precise negative feedback regulation of FSH that is necessary for monofollicular development. With further growth of the dominant follicle, estradiol and inhibin A increase. Increasing levels of estradiol across the follicular phase are responsible for proliferative changes in the endometrium. Acquisition of FSH-induced LH receptors on granu­ losa cells allows LH to complete the final stages of maturation of the preovulatory follicle, leading to secretion of low levels of progesterone and 17α-hydroxyprogesterone. The exponential rise in estradiol in the mid-late luteal phase results in positive feedback on the pituitary gonadotropes, leading to gen­ eration of an LH surge (and a smaller FSH surge). The low levels of progesterone secreted from the peri-ovulatory follicle are not required for the gonadotropin surge but appear to play a role in its timing. The LH surge may precede follicle rupture by 24–36 h, during which time the oocyte uncouples from the granulosa cells, and genes involved in inflammation and tissue remodeling are induced. Further alterations in steroidogenesis accompany luteinization of theca and granulosa cells. ■ ■THE LUTEAL PHASE The luteal phase begins with the formation of the corpus luteum from the ruptured follicle (Fig. 404-8). Progesterone, 17α-hydroxyprogesterone, and inhibin A are produced from the luteinized granulosa cells. The granulosa-lutein cells continue to aromatize androgen precursors derived from theca-lutein cells, producing estradiol. The combined actions of estrogen and progesterone, as well as relaxin, are respon­ sible for the secretory changes in the endometrium that are necessary for implantation. The corpus luteum is supported by LH but has a finite life span. Both the progesterone-induced decrease in LH pulse frequency and diminished postreceptor signaling are likely to con­ tribute to the demise of the corpus luteum. The progressive decline in hormonal support of the endometrium results in inflammation, local hypoxia and ischemia, and subsequent vascular changes with release of cytokines, cell death, and shedding of the endometrium. If conception occurs, hCG produced by the trophoblast binds to LH receptors on the corpus luteum, maintaining steroid hormone production and preventing involution of the corpus luteum until the luteal-placental shift in hormone production that occurs 6–10 weeks after conception.

CLINICAL ASSESSMENT OF

OVARIAN FUNCTION Menstrual bleeding should become regular within 2–4 years of men­ arche, although anovulatory and irregular cycles are common before that. For the remainder of adult reproductive life, the cycle length counted from the first day of menses to the day preceding subsequent menses is ~28 days, with a range of 25–35 days. However, cycle-tocycle variability for an individual woman is ±2 days. Luteal phase length is relatively constant between 12 and 14 days in normal cycles; thus, the major variability in cycle length is due to variations in fol­ licular phase length. The duration of menstrual bleeding in ovulatory cycles varies between 4 and 6 days. There is a gradual shortening of cycle length with age such that women aged >35 years have cycles that are shorter than during their younger reproductive years. Anovulatory cycles increase as women approach menopause, and bleeding patterns may be erratic.

PART 12 Endocrinology and Metabolism Women who report regular monthly bleeding generally have ovu­ latory cycles, but several other clinical signs can be used to assess the likelihood of ovulation. Some women experience mittelschmerz, described as midcycle pelvic discomfort that is thought to be caused by the rapid expansion of the dominant follicle at the time of ovulation. A constellation of premenstrual moliminal symptoms such as bloat­ ing, breast tenderness, mood changes, and food cravings often occur several days before menses in ovulatory cycles, but their absence can­ not be used as evidence of anovulation. Methods that can be used to determine whether ovulation occurred include a serum progesterone level >3 ng/mL ~7 days after ovulation, an increase in basal body tem­ perature of 0.24°C (>0.5°F) in the second half of the cycle due to the thermoregulatory effect of progesterone, or detection of the urinary LH surge using ovulation predictor kits, although the mere presence of an apparent LH surge does not guarantee that ovulation will occur. However, because ovulation occurs ~36 h after the LH surge, urinary LH can be helpful in timing intercourse to coincide with ovulation. Ultrasound can be used to detect the growth of the fluid-filled antrum of the developing follicle and to assess endometrial thickness in response to increasing estradiol levels in the follicular phase. It can also be used to provide evidence of ovulation by documenting collapse of the dominant follicle and/or the presence of a corpus luteum as well as the characteristic echogenicity of the secretory endometrium of the luteal phase. PUBERTY ■ ■NORMAL PUBERTAL DEVELOPMENT IN GIRLS The first menstrual period (menarche) occurs relatively late in the series of developmental milestones that characterize normal pubertal devel­ opment. Menarche is preceded by the appearance of pubic and then axillary hair (adrenarche) as a result of maturation of the zona reticu­ laris in the adrenal gland and increased adrenal androgen secretion, particularly dehydroepiandrosterone (DHEA). The triggers for adre­ narche remain unknown but may involve increases in body mass index, as well as in utero and neonatal factors. Menarche is also preceded by breast development (thelarche). The breast is exquisitely sensitive to the very low levels of estrogen that result from peripheral conversion of adrenal androgens and the low levels of estrogen secreted from the ovary early in pubertal maturation. This estrogen sensitivity also explains why infants occasionally develop breast tissue in response to endogenous or environmental estrogens. Breast development precedes the appearance of pubic and axillary hair in ~60% of girls. The interval between the onset of breast development and menarche is ~2 years. There has been a gradual decline in the age of puberty attributed to improved nutrition, however more recent changes indicate a decline in the age of thelarche but not menarche which is associated with obesity. In the United States, menarche occurs at an average age of 12.5 years. Much of the variation in the timing of puberty is due to genetic factors. Heritability estimates from twin studies range between 50 and 80%. Adrenarche and thelarche occur ~1 year earlier in black girls compared with white girls, although the difference in the timing of menarche is less pronounced. Genome-wide association studies

have identified over a hundred genes associated with pubertal tim­ ing in boys and girls, attesting to the high degree of coordination of this reproductive and growth milestone. These findings include genes involved in GnRH secretion (e.g., TACR3, and the maternally imprinted gene, MKRN3, that has been associated with familial preco­ cious puberty), pituitary development and function (e.g., POU1F1), hormone synthesis and bioactivity (e.g., STARD4, ESR1, RXRG), gonadal feedback (e.g., INHBA, ESR1), and energy homeostasis and growth, including LIN28B, a sentinel puberty gene, which is a potent regulator of microRNA processing. Other important hormonal changes also occur in conjunction with puberty. Growth hormone (GH) levels increase early in puberty, stimulated in part by the pubertal increase in estrogen secretion. GH increases insulin-like growth factor-1 (IGF-1), which enhances linear growth. The growth spurt is generally less pronounced in girls than in boys, with a peak growth velocity of ~7 cm/year. Linear growth is ultimately limited by closure of epiphyses in the long bones as a result of prolonged exposure to estrogen. Puberty is also associated with mild insulin resistance. ■ ■DISORDERS OF PUBERTY The differential diagnosis of precocious and delayed puberty is similar in boys (Chap. 403) and girls. However, there are differences in the timing of normal puberty and differences in the relative frequency of specific disorders in girls compared with boys. Precocious Puberty  Traditionally, precocious puberty has been defined as the development of secondary sexual characteristics before the age of 8 in girls based on data from Marshall and Tanner in British girls studied in the 1960s. More recent studies led to recommendations that girls be evaluated for precocious puberty if breast development or pubic hair is present at <7 years of age for white girls or <6 years for black girls; however, these guidelines have not been widely accepted in favor of careful follow-up in all girls presenting at <8 years. Precocious puberty in girls is most often centrally mediated (Table 404-1), resulting from early activation of the hypothalamicpituitary-ovarian axis. It is characterized by pulsatile LH secretion (which is initially associated with deep sleep) and an enhanced LH and FSH response to exogenous GnRH or a GnRH agonist (two- to three­ fold stimulation) (Table 404-2). True precocity is marked by advance­ ment in bone age of >2 standard deviations, a recent history of growth acceleration, and progression of secondary sexual characteristics. TABLE 404-1  Differential Diagnosis of Precocious Puberty CENTRAL (GnRH DEPENDENT) PERIPHERAL (GnRH INDEPENDENT) Idiopathic CNS tumors   Hamartomas   Astrocytomas   Adenomyomas   Gliomas   Germinomas CNS infection Genetic, i.e., KISS1, KISS1R, MKRN3, DLK1 Head trauma Iatrogenic   Radiation   Chemotherapy   Surgical CNS malformation   Arachnoid or suprasellar cysts   Septo-optic dysplasia   Hydrocephalus Congenital adrenal hyperplasia Estrogen-producing tumors   Adrenal tumors   Ovarian tumors Gonadotropin/hCG-producing tumors Exogenous exposure to estrogen or androgen or lavender or tea-tree oil McCune-Albright syndrome Aromatase excess syndrome Abbreviations: CNS, central nervous system; DLK1, delta-like 1 homolog gene; GnRH, gonadotropin-releasing hormone; hCG, human chorionic gonadotropin; KISS1, kisspeptin gene; KISS1R, kisspeptin receptor gene; MKRN3, makorin ring finger protein 3 gene.

TABLE 404-2  Evaluation of Precocious and Delayed Puberty   PRECOCIOUS DELAYED Initial Screening Tests History and physical × × Assessment of growth velocity × × Bone age × × LH, FSH × × Estradiol, testosterone × × DHEAS × × 17-Hydroxyprogesterone ×   TSH, T4 × × Complete blood count   × Sedimentation rate, C-reactive protein   × Electrolytes, renal function   × Liver enzymes   × IGF-1, IGFBP-3   × Urinalysis   × Secondary Tests     Pelvic ultrasound × × Cranial MRI × × β-hCG ×   GnRH/agonist stimulation test × × ACTH stimulation test ×   Inflammatory bowel disease panel × × Celiac disease panel   × Prolactin   × Karyotype   × Abbreviations: ACTH, adrenocorticotropic hormone; DHEAS, dehydroepiandrosterone sulfate; FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; hCG, human chorionic gonadotropin; IGF-1, insulin-like growth factor 1; IGFBP-3, IGF-binding protein 3; LH, luteinizing hormone; MRI, magnetic resonance imaging; TSH, thyroid-stimulating hormone; T4, thyroxine. In girls, centrally mediated precocious puberty (CPP) is categorized as idiopathic in ~85% of cases; however, neurogenic causes must be considered. Loss-of-function mutations in MKRN3 and DLK1, both of which are imprinted genes, have been reported in familial CPP. Activating mutations in KISS1, KISS1R, and PROKR2 have also been found in a small number of patients with CPP. However, the frequency of these mutations is insufficient to justify their use in routine clinical testing. GnRH agonists that induce pituitary desensitization are the mainstay of treatment to prevent premature epiphyseal closure and preserve adult height, as well as to manage psychosocial repercussions of precocious puberty. Peripherally mediated precocious puberty does not involve activa­ tion of the hypothalamic-pituitary-ovarian axis and is characterized by suppressed gonadotropins in the presence of elevated estradiol. Management of peripheral precocious puberty involves treating the underlying disorder (Table 404-1) and limiting the effects of gonadal steroids using aromatase inhibitors, inhibitors of steroidogenesis, and ER blockers. It is important to be aware that central precocious puberty can also develop in girls whose precocity was initially peripherally mediated, as in McCune-Albright syndrome and congenital adrenal hyperplasia. Incomplete and intermittent forms of precocious puberty may also occur. For example, premature breast development are common in girls before the age of 2 years, with no further progression and without significant advancement in bone age, estrogen production, or compro­ mised height. Premature adrenarche can also occur in the absence of progressive pubertal development, but it must be distinguished from late-onset congenital adrenal hyperplasia and androgen-secreting tumors, in which case it may be termed heterosexual precocity. Prema­ ture adrenarche may be associated with obesity, hyperinsulinemia, and the subsequent predisposition to PCOS.

Delayed Puberty  Delayed puberty (Table 404-3) is defined as the absence of secondary sexual characteristics by age 13 in girls. The diagnostic considerations are very similar to those for primary amenor­ rhea (Chap. 405). Between 25 and 40% of delayed puberty in girls is of ovarian origin, with Turner syndrome accounting for the majority of such patients. Delayed puberty may occur in the setting of systemic illnesses, including celiac disease and chronic renal disease, and endo­ crinopathies such as diabetes and hypothyroidism. In addition, girls appear to be particularly susceptible to the adverse effects of decreased energy balance resulting from exercise, dieting, and/or eating disorders, and thus, functional hypothalamic amenorrhea (HA) can present with primary amenorrhea. Together, these reversible conditions account for ~25% of delayed puberty in girls. Congenital hypogonadotropic hypo­ gonadism in girls or boys can be caused by mutations in several differ­ ent genes or combinations of genes (Fig. 404-4, Chap. 391, Table 404-3).

Disorders of the Female Reproductive System CHAPTER 404 TABLE 404-3  Differential Diagnosis of Delayed Puberty Hypergonadotropic Ovarian   Turner’s syndrome   Gonadal dysgenesis   Chemotherapy/radiation therapy   Galactosemia   Autoimmune oophoritis   Congenital lipoid hyperplasia Steroidogenic enzyme abnormalities   17α-Hydroxylase deficiency   Aromatase deficiency Gonadotropin/receptor mutations   FSHb, LHR, FSHR Androgen resistance syndrome Hypogonadotropic Genetic   Hypothalamic syndromes     Leptin/leptin receptor     HESX1 (septo-optic dysplasia)     PC1 (prohormone convertase)   IHH and Kallmann’s syndrome     KAL1, FGF8, FGFR1, NSMF, PROK2, PROKR2, SEM3A, HS6ST1, WDR11, CHD7     KISS1, KISS1R, TAC3, TAC3R, GnRH1, GnRHR, and others   Abnormalities of pituitary development/function   PROP1 CNS tumors/infiltrative disorders   Craniopharyngioma   Astrocytoma, germinoma, glioma   Prolactinomas, other pituitary tumors   Histiocytosis X Chemotherapy/radiation Functional   Chronic diseases   Malnutrition   Excessive exercise   Eating disorders Abbreviations: CHD7, chromodomain-helicase-DNA-binding protein 7; CNS, central nervous system; FGF8, fibroblast growth factor 8; FGFR1, fibroblast growth factor 1 receptor; FSHβ, follicle-stimulating hormone β chain; FSHR, FSH receptor; GNRHR, gonadotropin-releasing hormone receptor; HESX1, homeobox, embryonic stem cell expressed 1; HS6ST1, heparin sulfate 6-O sulfotransferase 1; IHH, idiopathic hypogonadotropic hypogonadism; KAL, Kallmann; KISS1, kisspeptin 1; KISSR1, KISS1 receptor; LHR, luteinizing hormone receptor; NSMF, NMDA receptor synaptonuclear signaling and neuronal migration factor; PROK2, prokineticin 2; PROKR2, prokineticin receptor 2; PROP1, prophet of Pit1, paired-like homeodomain transcription factor; SEMA3A, semaphorin-3A; WDR11, WD repeat-containing protein 11.

20 - 405 Menstrual Disorders and Pelvic Pain

405 Menstrual Disorders and Pelvic Pain

Approximately 50% of girls with congenital hypogonadotropic hypo­ gonadism, with or without anosmia, have a history of some degree of breast development, and 10% report one to two episodes of vaginal bleeding. Family studies suggest that genes identified in association with absent puberty may also cause delayed puberty, and recent reports have further suggested that a genetic susceptibility to environmental stresses such as diet and exercise may account for at least some cases of func­ tional HA, including in girls who present with primary amenorrhea. Although neuroanatomic causes of delayed puberty are considerably less common in girls than in boys, it is always important to rule these out in the setting of primary hypogonadotropic hypogonadism.

PART 12 Endocrinology and Metabolism ■ ■FURTHER READING Balasubramanian R, Crowley WF Jr: Isolated gonadotropin-releasing hormone (GnRH) deficiency. 2007 May 23 [Updated 2022 May 12], in GeneReviews [Internet]. Adam MP et al (eds). Seattle, WA, University of Washington, Seattle, 1993-2025. Available from: https://www.ncbi.nlm. nih.gov/books/NBK1334/. Brito VN et al: The congenital and acquired mechanisms implicated in the etiology of central precocious puberty. Endocr Rev 44:193, 2023. Cedars MI: Evaluation of female fertility-AMH and ovarian reserve testing. J Clin Endocrinol Metab 107:1510, 2022. Lippincott MF et al: HU206 constitutional delay of puberty and idiopathic hypogonadotropic hypogonadism: differential contri­ butions of common genetic variants. J Clin Endocrinol Metab 7:bvad114.1457, 2023. Louden ED et al: Genetics of hypogonadotropic hypogonadism: Human and mouse genes, inheritance, oligogenicity, and genetic counseling. Mol Cell Endocrinol 534:111334, 2021. Moore AM et al: KNDy neurons of the hypothalamus and their role in GnRH pulse generation: An update. Endocrinology 165:bqad194, 2023. Janet E. Hall, Anuja Dokras

Menstrual Disorders

and Pelvic Pain Menstrual dysfunction can signal an underlying abnormality that may have long-term health consequences. Although frequent or prolonged bleeding usually prompts a woman to seek medical attention, infre­ quent or absent bleeding may seem less troubling, and the patient may not bring it to the attention of the physician. Thus, a focused menstrual history is a critical part of every encounter with a female patient. Pel­ vic pain is a common complaint that may relate to an abnormality of the reproductive organs but also may be of gastrointestinal, urinary tract, or musculoskeletal origin. Depending on its cause, pelvic pain may require urgent surgical attention. Recent guidelines no longer recommend routine pelvic examination in asymptomatic, average-risk women other than periodic cervical cancer screening. However, pelvic examination is an important part of the evaluation of amenorrhea, abnormal uterine bleeding, and pelvic pain. MENSTRUAL DISORDERS ■ ■DEFINITION AND PREVALENCE Amenorrhea refers to the absence of menstrual periods and is classified as primary if menstrual bleeding has never occurred in the absence of hormonal treatment or secondary if menstrual periods cease for 3–6 months. Primary amenorrhea is a rare disorder that occurs in <1% of the female population. However, between 3 and 5% of women

experience at least 3 months of secondary amenorrhea in any specific year. There is no evidence that race or ethnicity influences the preva­ lence of amenorrhea. However, because of the importance of adequate nutrition for normal reproductive function, both the age at menarche and the prevalence of secondary amenorrhea vary significantly in dif­ ferent parts of the world. Abnormal uterine bleeding (AUB) has replaced the term dysfunc­ tional uterine bleeding and describes irregularities in the menstrual cycle involving frequency, cyclicity, duration, and volume of flow out­ side of pregnancy. A menstrual cycle typically occurs every 21–35 days, lasting between 4 and 7 days, with up to 80 mL of blood loss. Variations in any of these parameters constitutes a diagnosis of AUB, with up to one-third of women between menarche and menopause experiencing these symptoms. The acronym PALM-COEIN, which was developed to describe the etiologies for AUB, includes the structural causes (polyp, adenomyosis, leiomyoma [submucosal or other myoma], and malignancy and hyperplasia) and nonstructural causes (coagulopathy, ovulatory dysfunction, endometrial, iatrogenic, and not yet classified). Oligo- and anovulation are most frequently associated with polycystic ovary syndrome (PCOS). Primary Amenorrhea  The absence of menarche (the first men­ strual period) by age 16 has been used traditionally to define primary amenorrhea. However, other factors, such as growth, secondary sexual characteristics, and the presence of cyclic pelvic pain, also influence the age at which primary amenorrhea should be investigated. Recent studies suggest that puberty is occurring at an earlier age, particularly in obese girls. However, it is important to note that these data reflect earlier breast development alone with minimal change in the age of menarche. Thus, an evaluation for amenorrhea should be initiated by age 15 or 16 in the presence of normal growth and secondary sexual characteristics; age 13 in the absence of secondary sexual character­ istics or if height is less than the third percentile; age 12 or 13 in the presence of breast development and cyclic pelvic pain; or within 2 years of breast development if menarche has not occurred. Secondary Amenorrhea or Oligomenorrhea  Irregular cycles are relatively common for up to 3 years after menarche and for 1–2 years before the final menstrual period. In the intervening years, menstrual cycle length is ~28 days. Cycle-to-cycle variability in an individual woman who is ovulating consistently is generally +/− 2 days. Pregnancy should be excluded early in any evaluation of menstrual irregularity. However, many women occasionally miss a single period. Three months of secondary amenorrhea, or 6 months in women with previously irreg­ ular cycles, should prompt an evaluation, as should a history of inter­ menstrual intervals >35 or <21 days or bleeding that persists for >7 days. ■ ■DIAGNOSIS Pregnancy is the most common cause of amenorrhea and must be excluded in all cases, regardless of patient history. Evaluation of men­ strual dysfunction depends on understanding the interrelationships between the four critical components of the reproductive tract: (1) the hypothalamus, (2) the pituitary, (3) the ovaries, and (4) the uterus and outflow tract (Fig. 405-1; Chap. 404). This system is maintained by complex negative and positive feedback loops involving the ovar­ ian steroids (estradiol and progesterone) and peptides (inhibin B and inhibin A) and the hypothalamic (gonadotropin-releasing hormone [GnRH]) and pituitary (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) components of this system (Fig. 405-1). Disorders of menstrual function fall into two main categories: disorders of the uterus and outflow tract and disorders of ovulation. Many of the conditions that cause primary amenorrhea are congenital but go unrecognized until the time of normal puberty (e.g., genetic, chromosomal, and anatomic abnormalities). All causes of secondary amenorrhea also can cause primary amenorrhea. Disorders of the Uterus or Outflow Tract  Abnormalities of the uterus and outflow tract typically present as primary amenorrhea. In patients with normal pubertal development and a blind vagina,

– GnRH – LH FSH + Estradiol Progesterone FIGURE 405-1  Role of the hypothalamic-pituitary-gonadal axis in the etiology of amenorrhea. Gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus stimulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion from the pituitary to induce ovarian folliculogenesis and steroidogenesis. Ovarian secretion of estradiol and progesterone controls the shedding of the endometrium, resulting in menses, and, in combination with the inhibins, provides feedback regulation of the hypothalamus and pituitary to control secretion of FSH and LH. The prevalence of amenorrhea resulting from abnormalities at each level of the reproductive system (hypothalamus, pituitary, ovary, uterus, and outflow tract) varies depending on whether amenorrhea is primary or secondary. PCOS, polycystic ovarian syndrome. the differential diagnosis includes obstruction by a transverse vaginal septum or imperforate hymen; müllerian agenesis (Mayer-RokitanskyKuster-Hauser syndrome), which can be caused by mutations in the WNT4 gene, and androgen insensitivity syndrome (AIS), which is an X-linked recessive disorder that accounts for ~10% of all cases of pri­ mary amenorrhea (Chap. 403). Patients with AIS have a 46,XY karyo­ type, but because of the lack of androgen receptor responsiveness, those with complete AIS lack features of androgenization and have female external genitalia. The absence of pubic and axillary hair distinguishes them clinically from patients with müllerian agenesis, as does a testos­ terone level in the male range. The rare patient with 5α reductase type 2 enzyme deficiency has a similar presentation but undergoes viriliza­ tion at the time of puberty. Asherman’s syndrome presents as secondary amenorrhea or hypomenorrhea and results from partial or complete obliteration of the uterine cavity by adhesions that prevent normal growth and shedding of the endometrium. Curettage performed for pregnancy complications accounts for >90% of cases; genital tuberculo­ sis is an important cause in regions where it is endemic. TREATMENT Disorders of the Uterus or Outflow Tract Obstruction of the outflow tract usually presents as dysmenorrhea or lower abdominal cyclic pain with no menses. Evaluation of the patient includes a medical history, physical examination including a perineal examination, and ultrasound imaging. In many cases, a magnetic resonance imaging (MRI) scan can more accurately iden­ tify the reproductive tract anomaly prior to surgery. It is important that surgery be performed as soon as the diagnosis is made as the risk of endometriosis is increased with retrograde menstrual flow. Müllerian agenesis may require surgical intervention to allow sexual intercourse, although vaginal dilatation is adequate in some patients. In these patients, because ovarian function is normal, assisted reproductive techniques can be used with a surrogate

Primary Secondary Hypothalamus 28% 36% Menstrual Disorders and Pelvic Pain CHAPTER 405 Pituitary 2% 15% Inhibin B Inhibin A Estradiol PCOS 8% 30% Ovary 43% 12% Uterus/outflow tract 19% 7% carrier. More recently, there have been a few cases of successful uterine transplantation in women with müllerian agenesis. AIS (Chap. 402) requires gonadectomy because there is risk of gonado­ blastoma in the dysgenetic gonads, although surgery is generally delayed until after breast development and the pubertal growth spurt. Estrogen replacement is indicated after gonadectomy, and vaginal dilatation may be required to allow sexual intercourse. Disorders of Ovulation  Once uterus and outflow tract abnor­ malities have been excluded, other causes of amenorrhea involve dis­ orders of ovulation. The differential diagnosis is based on the results of initial tests, including a pregnancy test, an FSH level (to determine whether the cause is likely to be ovarian or central), and assessment of hyperandrogenism (Fig. 405-2). HYPOGONADOTROPIC HYPOGONADISM  Low estrogen levels in com­ bination with normal or low levels of LH and FSH are seen with anatomic, genetic, or functional abnormalities that interfere with hypo­ thalamic GnRH secretion or normal pituitary responsiveness to GnRH. Although relatively uncommon, tumors and infiltrative diseases should be considered in the differential diagnosis of hypogonadotropic hypo­ gonadism (Chap. 392). These disorders may present with primary or secondary amenorrhea. They may occur in association with other features suggestive of hypothalamic or pituitary dysfunction, such as short stature, diabetes insipidus, galactorrhea, and headache. Hypogo­ nadotropic hypogonadism also may be seen after cranial irradiation. In the postpartum period, amenorrhea occurs normally in association with breast feeding but may also be caused by pituitary necrosis (Shee­ han’s syndrome) or lymphocytic hypophysitis. Because reproductive dysfunction is commonly associated with hyperprolactinemia from neuroanatomic lesions or medications, prolactin should be measured in all patients with hypogonadotropic hypogonadism (Chap. 392). Isolated hypogonadotropic hypogonadism (IHH) occurs in women, although it is three times more common in men. IHH generally pres­ ents with primary amenorrhea, although 50% have some degree of

Amenorrhea uterus and outflow tract Normal Karyotype + β-hCG Pregnancy – FSH PART 12 Endocrinology and Metabolism Normal/low Normal Hyperandrogenism ↑ testosterone hirsutism, acne Pituitary causes Hypothalamic causes R/o • 21 hydroxylase deficiency • Tumor PCOS FIGURE 405-2  Algorithm for evaluation of amenorrhea. β-hCG, β-human chorionic gonadotropin; FSH, follicle-stimulating hormone; GYN, gynecologist; MRI, magnetic resonance imaging; PRL, prolactin; R/O, rule out; TSH, thyroid-stimulating hormone. breast development, and ~10% report one to two menses. IHH is asso­ ciated with anosmia in half of women (termed Kallmann’s syndrome). Genetic causes of IHH have been identified in ~50% of patients (Chaps. 403 and 404). Functional hypothalamic amenorrhea (HA) is a diagnosis of exclu­ sion of other causes of hypogonadotropic hypogonadism including chronic diseases (type 1 diabetes, celiac disease, hyperthyroidism, Cushing’s syndrome) and use of opioids, glucocorticoids, or psychotro­ pic medications that increase prolactin levels. Functional HA is most commonly associated with conditions causing a mismatch between energy expenditure and energy intake and/or significant stress leading to increased corticotropin-releasing hormone (CRH), suppression of GnRH, and decreased thyrotropin-releasing hormone (TRH) input. Variants in genes associated with IHH may increase susceptibility to these environmental inputs, accounting in part for the clinical vari­ ability in this disorder. Metabolic and stress signaling is transduced to the reproductive axis, at least in part, through leptin signaling from the periphery and via hypothalamic kisspeptin, neurokinin B, and dynorphin control of GnRH. The diagnosis of HA generally can be made on the basis of a careful history, a physical examination, and the demonstration of low levels of gonadotropins and normal prolactin levels. Eating disorders, excessive exercise, and chronic disease must be specifically excluded. An atypical history, headache, signs of other hypothalamic dysfunction, or hyperprolactinemia, even if mild, neces­ sitates cranial MRI to exclude a neuroanatomic cause. Up to 10% of women with HA may have some features of PCOS (irregular menses, increased ovarian volume with polycystic appearing ovaries, higher anti-müllerian hormone [AMH] levels, and slightly elevated androgen levels). HYPERGONADOTROPIC HYPOGONADISM  Ovarian failure is consid­ ered premature when it occurs in women <40 years old and accounts for ~10% of secondary amenorrhea. Primary ovarian insufficiency (POI) has replaced the terms premature menopause and premature ovarian failure in recognition of the continuum of impaired ovarian

Abnormal Normal Abnormal • High premature ovarian insufficiency • Turner’s syndrome • Androgen insensitivity syndrome • 5α reductase deficiency History of uterine instrumentation • Müllerian agenesis • Imperforate hymen • Transverse vaginal septum • Cervical stenosis Normal prolactin FSH negative trial of estrogen/ progesterone Asherman’s syndrome function encompassed by this disorder. Ovarian insufficiency is associ­ ated with the loss of negative feedback restraint on the hypothalamus and pituitary, resulting in increased FSH and LH levels. FSH is a better marker of ovarian failure because of loss of negative feedback effects of both estradiol and the inhibins and because its levels are less variable than those of LH. AMH levels will also be low in patients with POI. As with natural menopause, POI may wax and wane, and serial measure­ ments may be necessary to establish the diagnosis. The presentation may include irregular menses or complete cessation of menses, hot flashes, and vaginal dryness. Once the diagnosis of POI has been established, further evaluation is indicated because of other health problems that may be associated with POI. Although POI is most commonly of unknown cause, it also occurs in association with a variety of chromosomal abnormalities (most often Turner’s syndrome), autoimmune polyglandular failure syndromes, and other rare disorders. Radiotherapy and chemotherapy may reduce ovarian reserve, with effects on both the oocytes and the supporting granulosa cells. New approaches, including ovarian, oocyte, and embryo cryopreservation, should be offered to women of repro­ ductive age prior to gonadotoxic chemotherapy or pelvic radiation treatment. The recognition that early ovarian insufficiency occurs in premutation carriers of the fragile X syndrome is important because of the increased risk of severe intellectual disability in male children with FMR1 mutations. Thus, follow-up testing should include a karyotype in all POI patients, serum anti-cortical and 21-hydroxylase antibodies (specific but not sensitive for subsequent adrenal insufficiency), thy­ roid function and thyroid peroxidase antibodies, FMR1 premutation screening, and assessment of bone mineral density. Ovarian biopsy is not indicated. Although the number of genetic causes of POI is increas­ ing, routine testing for mutations other than FMR1 is currently not recommended. Hypergonadotropic hypogonadism occurs rarely in other disor­ ders, such as mutations in the FSH or LH receptors. Aromatase defi­ ciency and 17α-hydroxylase deficiency are associated with decreased estrogen and elevated gonadotropins and with hyperandrogenism and

hypertension, respectively. Gonadotropin-secreting tumors in women of reproductive age generally present with high, rather than low, estrogen levels and cause ovarian hyperstimulation or dysfunctional bleeding. TREATMENT Hypo- and Hypergonadotropic Causes of Amenorrhea Amenorrhea almost always is associated with chronically low levels of estrogen, whether it is caused by hypogonadotropic hypogonad­ ism or ovarian insufficiency. Development of secondary sexual characteristics requires gradual titration of estradiol replacement with eventual addition of progestin. Hormone replacement with either low-dose estrogen/progesterone regimens or oral contracep­ tive pills is recommended until the usual age of menopause for bone and cardiovascular protection. In women with functional HA or anorexia nervosa, hormone replacement alone may not be suf­ ficient to restore or maintain bone density. A more long-term mul­ tidisciplinary approach including behavioral health professionals is essential. Patients with hypogonadotropic hypogonadism who are interested in fertility require treatment with both exogenous FSH and LH. Patients with POI can consider oocyte donation, which has a high rate of success in this population, although its use in women with Turner’s syndrome is limited by increased cardiovascular risk in pregnancy. POLYCYSTIC OVARY SYNDROME  The diagnosis of PCOS is made in adult women using the updated Rotterdam criteria (published in the 2023 international guidelines). These include irregular menses (<8 menses per year), clinical or biochemical hyperandrogenism (elevated total or free testosterone, modified Ferriman-Gallwey score >4–6 depending on ethnicity, see Chap. 406), and polycystic-appearing ovaries on ultrasound (≥20 antral follicles or ovarian volume ≥10 cm3 in at least one ovary) or elevated AMH. The presence of two of the three criteria will confirm the diagnosis, resulting in different phe­ notypes, namely, hyperandrogenic or non-hyperandrogenic. PCOS is a diagnosis of exclusion, and other etiologies for irregular menses and hyperandrogenism should be excluded (hypothyroidism, hyper­ prolactinemia, adrenal sources for hyperandrogenism). Diagnosis in adolescents may be difficult to establish, and it is recommended to wait at least 3 years after menarche before confirming the diagnosis. In adolescents, the diagnosis is based on irregular menses and hyper­ androgenism criteria only, as the ultrasound and AMH criteria are not established for this age group. Lean oligo-ovulatory patients with PCOS generally have high LH levels in the presence of normal to low levels of FSH and estradiol, although given the pulsatility of LH secre­ tion, a random serum LH/FSH ratio is not included in the diagnostic criteria. The prevalence of obesity is high in PCOS and significantly increases the risk of comorbidities including metabolic syndrome, type 2 diabetes, dyslipidemia, hypertension, and cardiovascular disease. Frequent anovulation results in irregular menses and increased risk of endometrial hyperplasia and endometrial cancer (two- to sixfold increased risk). Abnormalities in GnRH pulsatility result in elevated LH levels resulting in increased production of ovarian androgens. Insulin resistance, especially in skeletal muscle and adipose tissue, also contributes to increased insulin-stimulated ovarian androgen production. An alternate source of androgens, namely 11-oxygenated androgens, may also be elevated in this population. Genome-wide association studies in diverse populations and PCOS phenotypes have identified several loci (~19) associated with PCOS, and cluster analyses suggest the presence of reproductive and metabolic abnor­ malities. Symptoms generally begin in adolescence and are modified by obesity and age, such that by the fourth decade of life, most women with PCOS will have regular menses and normal serum androgens. There is a high prevalence of depression and anxiety disorders, as well as disordered eating and body image distress. PCOS is also associ­ ated with an increased risk of obstructive sleep apnea and metabolic

dysfunction-associated steatotic liver disease (MDSLD), independent of body mass index (BMI).

TREATMENT Polycystic Ovary Syndrome The first-line treatment of women with PCOS not attempting preg­ nancy is combined hormonal contraceptives to regulate menstrual cycles and decrease serum androgens by increasing sex hormone– binding globulin levels. Although serum androgens decrease by 2–3 months after initiating hormonal therapy, it may take longer to observe the beneficial effects on hirsutism and acne. Patients should be prescribed hormonal contraceptives containing the lowest effective dose of estrogen, either in a cyclic or continuous manner. If there is an inadequate response to hormonal con­ traceptives after 6 months for management of hyperandrogenic symptoms, antiandrogens, such as spironolactone and flutamide, can be considered (Chap. 406). Endometrial protection can also be achieved with the use of progestins (medroxyprogesterone acetate,10 mg, or Prometrium [progesterone], 200 mg daily for 10–14 days at least every 3 months, or a levonorgestrel intrauterine device [IUD]). All women with PCOS should be screened for obesity, hypertension, glycemic control, depression, and anxiety at the time of diagnosis and then at regular intervals. Overweight and obese women should also have a fasting lipid profile at the time of diagnosis. Lifestyle management should be recommended in all women with PCOS, and metformin should be considered for prevention of cardiometabolic risk factors in those with overweight and obesity (Chap. 420). Women with PCOS are at an increased risk of early miscarriage, gestational diabe­ tes, gestational hypertension, preeclampsia, and preterm birth. Lifestyle management and prepregnancy counseling should be offered prior to attempting pregnancy (Chap. 408). Letrozole, an aromatase inhibitor, is the first-line treatment for ovulation induc­ tion followed by clomiphene citrate, a selective estrogen response modulator, with or without metformin. Injectable gonadotropins can be used judiciously by experienced practitioners to induce monofollicular growth as PCOS increases the risk of hyperstimu­ lation. Metformin can be used as an adjunct with diet and exer­ cise for obese women with PCOS or for treatment of diabetes or impaired glucose tolerance, as in non-PCOS patients. However, metformin alone is not recommended for endometrial protection or treatment of hyperandrogenic symptoms, infertility, pregnancy loss, or prevention of gestational diabetes. Menstrual Disorders and Pelvic Pain CHAPTER 405 ■ ■PELVIC PAIN The mechanisms that cause pelvic pain are similar to those that cause abdominal pain (Chap. 16) and include inflammation of the parietal peritoneum, obstruction of hollow viscera, vascular disturbances, and pain originating in the abdominal wall. Pelvic pain may reflect pelvic disease per se but also may reflect extrapelvic disorders that refer pain to the pelvis. In up to 60% of cases, pelvic pain can be attributed to gastrointestinal problems, including appendicitis, cholecystitis, infec­ tions, intestinal obstruction, diverticulitis, and inflammatory bowel disease. Urinary tract and musculoskeletal disorders are also common causes of pelvic pain. APPROACH TO THE PATIENT Pelvic Pain As with all types of abdominal pain, the first priority is to iden­ tify life-threatening conditions (shock, peritoneal signs) that may require emergent surgical management. The possibility of preg­ nancy should be identified as soon as possible by menstrual history and β-human chorionic gonadotropin (β-hCG) testing. A thorough history that includes the type, location, radiation, and recurrence can help identify the cause of acute pelvic pain. Specific associations

with vaginal bleeding, sexual activity, defecation, urination, move­ ment, or eating should be specifically sought. Determination of whether the pain is acute versus chronic and cyclic versus noncyclic will direct further investigation (Table 405-1). However, disorders that cause cyclic pain occasionally may cause noncyclic pain, and the converse is also true. ■ ■ACUTE PELVIC PAIN Pelvic inflammatory disease (PID) refers to infection of the upper geni­ tal tract and may present with a spectrum of symptoms. In the acute setting, the most common presentation is bilateral lower abdominal pain of recent onset that may be exacerbated with sexual activity. Risk factors for PID include age <25 years and history of multiple sexual partners, sexually transmitted infections (STIs), or recent uterine pro­ cedures. However, any sexually active woman can be at risk for PID. PID associated with tubo-ovarian abscess or peritonitis may present with severe pain, fever, and peritoneal signs. Abnormal uterine bleed­ ing may occur in about one-third of patients. Cervical motion tender­ ness, uterine and adnexal pain, and vaginal discharge are common findings on pelvic examination. The presence of right upper quadrant pain is suggestive of perihepatitis (Fitz-Hugh–Curtis syndrome). PART 12 Endocrinology and Metabolism The diagnosis of PID is established based on symptoms and clinical examination and can be aided by a wet mount preparation of vaginal discharge and nucleic acid amplification tests for Chlamydia trachomatis and Neisseria gonorrhoeae. Of note, a presumptive clinical diagnosis is sufficient to prescribe treatment even in the absence of positive test results, as PID can occur due to other vaginal and enteric pathogens. Pelvic imaging can be obtained based on symptoms, findings of the pelvic examination, or if there is lack of response to therapy. With public health efforts to control STIs, the incidence and severity of PID have declined in the United States and Europe; however, this is not the case in the developing world. Subclinical PID with its attendant risks of infertility and ectopic pregnancy remains a significant problem world­ wide. Public health and professional organizations recommend annual testing for C. trachomatis in all sexually active women <25 years old and both C. trachomatis and N. gonorrhoeae in all women at increased risk. Adnexal pathology can present acutely and may be due to rupture, bleeding, or torsion of ovarian cysts or, much less commonly, the fal­ lopian tubes. Rupture of an ovarian cyst may be diagnosed based on the acute presentation in a reproductive-age woman and pelvic ultrasound findings of a simple, collapsed or hemorrhagic cyst, with or without free fluid in the pelvis. Ovarian torsion typically presents as acute onset of unilateral, intermittent pain and is a diagnosis of exclusion unless absent blood flow to the ovary is demonstrated via Doppler ultrasound imaging. Neoplasms of the ovary or fallopian tube are much less com­ mon causes of acute pain. Ectopic pregnancy represents 1–2% of all pregnancies and most commonly occurs in the fallopian tubes. It may present with acute lower abdominal pain, hemodynamic instability, and peritoneal signs. The index of suspicion should be high in any reproductive-age woman TABLE 405-1  Gynecologic Causes of Pelvic Pain   ACUTE CHRONIC Cyclic pelvic pain   Mittelschmerz Dysmenorrhea Noncyclic pelvic pain Pelvic inflammatory disease Ruptured or hemorrhagic ovarian cyst, endometrioma, or ovarian torsion Ectopic pregnancy Endometritis Acute growth or degeneration of uterine myoma Threatened abortion Endometriosis Uterine fibroids Adenomyosis Pelvic adhesions Pelvic malignancy Vulvodynia Chronic pelvic inflammatory disease Tuberculous salpingitis History of sexual abuse Pelvic congestion syndrome

presenting with abdominal pain or vaginal bleeding irrespective of cur­ rent use of contraception. Risk factors for an ectopic pregnancy include history of tubal disease, pelvic infection, tubal surgery, previous ectopic pregnancy, infertility, smoking, and current use of IUD, although a large proportion may have no risk factors. Rupture of the fallopian tube remains a life-threatening emergency; the incidence depends on access to care but is ~18% in developed countries. Diagnosis of an ectopic pregnancy can be established by assessing the patient’s menstrual his­ tory and symptoms, measuring a single or serial β-hCG levels, and performing pelvic ultrasound imaging. β-hCG levels typically double every 48 h in early first trimester, and 99% of viable intrauterine preg­ nancies are associated with an increase in hCG levels of at least 53% in

2 days. The discriminatory zone refers to β-hCG values above which the landmarks of a normal intrauterine pregnancy should be seen on ultrasound (1500–3000 IU/mL). Absence of an intrauterine pregnancy and presence of an adnexal mass or free fluid increase the likelihood of an ectopic pregnancy. Threatened abortion may also present with amenorrhea, abdominal pain, and vaginal bleeding with no cervical dilation in the setting of an intrauterine pregnancy with cardiac activ­ ity in the first trimester of pregnancy. Although more common than ectopic pregnancy, it is rarely associated with systemic signs. Uterine pathology includes endometritis, and less frequently, degenerating leio­ myomas (fibroids) present with acute pain. Endometritis often is asso­ ciated with vaginal bleeding and systemic signs of infection. It occurs in the setting of STIs, uterine instrumentation, or postpartum infection. TREATMENT Acute Pelvic Pain Treatment of acute pelvic pain depends on the suspected etiology but may require surgical or medical intervention. Immediate treat­ ment of PID is indicated upon diagnosis, even if the diagnosis is presumed or the symptoms are mild, due to long-term complica­ tions resulting in increased risk of ectopic pregnancy and infertility. Treatment in patients eligible for outpatient management includes 250 mg IM ceftriaxone and a 14-day course of oral doxycycline 100 mg twice daily. If the presentation is acute with high fever, nausea, vom­ iting, severe abdominal pain, or presence of tubo-ovarian abscess, inpatient therapy is recommended (Chap. 141). Conservative man­ agement is an important consideration for ovarian cysts, if torsion is not suspected, to avoid unnecessary surgery and associated risks of reduced fertility due to cystectomy or adhesions. If surgery is performed, it is preferable to perform a cystectomy, removing the cyst wall and leaving the remaining ovary, in a reproductive-age woman. Combined hormonal contraceptives are recommended in women with a history of recurrent ovarian cyst formation. Surgi­ cal treatment may be required for ectopic pregnancies when the patient presents with acute pain, is hemodynamically unstable, or has signs of intraperitoneal bleeding. The choice of salpingectomy versus salpingostomy is based on patient’s presentation, desire for future child-bearing, and prior pelvic infections. Clinically stable women presenting with unruptured ectopic pregnancies may be appropriate for treatment with methotrexate, which is effective in ~90% of cases when multiple doses are used. Threatened abortion is managed conservatively even in the presence of a subchorionic hemorrhage. The treatment of endometritis is similar to PID. Pain from a degenerating fibroid, if visualized on pelvic sonography, can be managed with nonsteroidal anti-inflammatory drugs (NSAIDs). CHRONIC PELVIC PAIN Chronic pelvic pain is a complex condition resulting from gyneco­ logic, urologic, or gastrointestinal organs and contributes to significant frustration and burden of disease. Common gynecologic conditions contributing to chronic pain are endometriosis, fibroids, adenomyosis, and adnexal pathology. In addition to a detailed history and physical exam, the evaluation of chronic pelvic pain typically includes a pelvic ultrasound. As causes other than those related to the female reproduc­ tive system are common, referral should be made to other specialists,

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406 Hirsutism

as appropriate. Neuromuscular and psychosomatic etiologies should also be considered. Some women experience discomfort at the time of ovulation (mit­ telschmerz or ovulation pain). The pain can be quite intense but is generally of short duration. The mechanism is thought to involve rapid expansion of the dominant follicle, although it also may be caused by peritoneal irritation by follicular fluid released at the time of ovulation. Dysmenorrhea typically refers to the crampy lower abdominal mid­ line discomfort that begins with the onset of menstrual bleeding and gradually decreases over 12–72 h. It may be associated with nausea, diarrhea, fatigue, and headache and occurs in 60–93% of adolescents, beginning with the establishment of regular ovulatory cycles. Its preva­ lence decreases after pregnancy and can be treated effectively with hormonal contraceptives. Primary dysmenorrhea results, in a major­ ity of cases, from hormone-dependent prostaglandin (PG) pathway mechanisms that cause intense uterine contractions, decreased blood flow, and increased peripheral nerve hypersensitivity, resulting in pain. However, variability in response to cyclooxygenase inhibitors suggests that PG-independent pathways, such as platelet activating factor, may also mediate inflammation. Secondary dysmenorrhea refers to pain caused by underlying pelvic pathology. Endometriosis results from the presence of endometrial glands and stroma outside the uterus. These deposits of ectopic endometrium respond to hormonal stimulation and may be associated with dysmen­ orrhea, painful intercourse, and painful bowel movements. On pelvic exam, adnexal tenderness may be present or tender nodules may be palpated along the uterosacral ligaments. Pain associated with endo­ metriosis can be cyclic or continuous, and the stage/severity of endo­ metriosis, as determined by laparoscopy, does not always correlate with the extent of pain. Transvaginal pelvic ultrasound is part of the initial workup and may detect an endometrioma within the ovary. Additional sonographic techniques can be used to identify deep endometriosis including nonmobile ovaries and rectovaginal or bladder nodules. The CA-125 level may be increased, but it has low negative predictive value. Pelvic MRI has higher sensitivity and specificity for diagnosis of endometriosis. Diagnostic laparoscopy is performed when patients do not respond adequately to empiric treatment and is considered the gold standard for diagnosis. If endometriosis is detected, the severity can be staged and the endometriotic lesions ablated or excised. Large fibroids can cause chronic pelvic pain or pressure, and submu­ cosal fibroids may be associated with dysmenorrhea. Other secondary causes of dysmenorrhea include adenomyosis, a condition caused by the presence of ectopic endometrial glands and stroma within the myo­ metrium. Chronic PID may be associated with ongoing pelvic pain and is associated with tuberculosis or actinomycosis. Pelvic congestion syn­ drome is associated with pelvic varicosities with low blood flow, result­ ing in pelvic venous congestion. However, this is no clear evidence to indicate that this finding is associated with chronic pelvic pain. TREATMENT Chronic Pelvic Pain DYSMENORRHEA Local application of heat, exercise, sexual activity, a vegetarian diet, use of vitamins D, B1, B6, and E and fish oil, acupuncture, and yoga have all been suggested to be of benefit, but studies are not adequate to provide recommendations. However, NSAIDs are very effective and provide >80% sustained response rates. Ibuprofen, naproxen, ketoprofen, mefenamic acid, and nimesulide are all superior to placebo. For best response, treatment should be initiated prior to the onset of menses and continued for at least 2–3 days. Combined or progestin-only hormonal contraceptives taken cyclically or con­ tinuously effectively reduce symptoms of dysmenorrhea. ENDOMETRIOSIS Combined hormonal contraceptives or continuous progestin (either orally, implants, or a levonorgestrel IUD) is used for the treatment of endometriosis. Evidence of an endometrioma on ultrasound

imaging can be medically managed and does not require surgi­ cal removal unless it increases in size or there is persistent pain. Patients who do not respond to medical management and lapa­ roscopic resection of endometriotic lesions can be offered GnRH agonist suppression with add-back therapy or aromatase inhibitors. FIBROIDS Chronic pain and dysmenorrhea associated with fibroids can be managed medically or surgically depending on the number and location of fibroids and associated symptoms. The U.S. Food and Drug Administration (FDA) approved the first two oral treat­ ments for uterine fibroids (elagolix with estradiol/norethindrone acetate and relugolix with estradiol/norethindrone acetate), and the selective progesterone receptor modulator ulipristal acetate was withdrawn in Europe and Canada. Medical management includes oral hormonal contraceptives, tranexamic acid, NSAIDs, proges­ tins, IUDs, and GnRH agonists and antagonists. Surgical man­ agement includes myomectomy, endometrial ablation/myolysis, radiofrequency volumetric thermal ablation, laparoscopic ablation, or hysterectomy. Chronic pain and dysmenorrhea associated with adenomyosis can be managed with combined hormonal treat­ ment, levonorgestrel IUD, or hysterectomy after child-bearing is complete.

Hirsutism CHAPTER 406 ■ ■FURTHER READING Bartels CB et al: An evidence-based approach to the medical man­ agement of fibroids: A systematic review. Clin Obstet Gynecol 59:30, 2016. Bloomfield H et al: Screening pelvic examinations in asymptomatic average risk adult women. WA-ESP Project #09-009; 2013. Bouilly J et al: Identification of multiple gene mutations accounts for the new genetic architecture of ovarian insufficiency. J Clin Endocrinol Metab 101:4541, 2016. Brunham RC et al: Pelvic inflammatory disease. N Engl J Med 372:2039, 2015. Fourman LR, Fazeli PK: Neuroendocrine causes of amenorrhea—An update. J Clin Endocrinol Metab 100:812, 2015. Ju H et al: The prevalence and risk factors of dysmenorrhea. Epidem Rev 36:104, 2014. Lee IT, Barnhart KT: What is an ectopic pregnancy? JAMA 329:434, 2023. Oladosu FA et al: Nonsteroidal anti-inflammatory drug resistance in dysmenorrhea: Epidemiology, causes, and treatment. Am J Obstet Gynecol 218:390, 2018. Taylor HS et al: Endometriosis is a chronic systemic disease: Clinical challenges and novel innovations. Lancet 397:839, 2021. Teede HJ et al: International PCOS Network. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Fertil Steril 120:767, 2023. David A. Ehrmann

Hirsutism ■ ■DEFINING HIRSUTISM Body hair can be categorized as either vellus (fine, soft, and not pig­ mented) or terminal (long, coarse, and pigmented). Approximately 10% of reproductive-age women have hirsutism, defined by the presence of excessive terminal hair growth. Hirsutism is most often idiopathic or the consequence of androgen excess associated with polycystic ovary

TABLE 406-1  Causes of Hirsutism Gonadal hyperandrogenism   Ovarian hyperandrogenism   Polycystic ovary syndrome/functional ovarian hyperandrogenism   Ovarian steroidogenic blocks   Syndromes of extreme insulin resistance   Ovarian neoplasms   Hyperthecosis Adrenal hyperandrogenism   Premature adrenarche   Functional adrenal hyperandrogenism   Congenital adrenal hyperplasia (nonclassic and classic)   Abnormal cortisol action/metabolism   Adrenal neoplasms Other endocrine disorders   Cushing’s syndrome   Hyperprolactinemia   Acromegaly Peripheral androgen overproduction   Obesity   Idiopathic Pregnancy-related hyperandrogenism   Hyperreactio luteinalis   Thecoma of pregnancy Drugs   Androgens   Oral contraceptives containing androgenic progestins   Minoxidil   Phenytoin   Diazoxide   Cyclosporine   Valproic acid Ovotesticular disorders of sex development PART 12 Endocrinology and Metabolism syndrome (PCOS). Less frequently, it results from adrenal androgen overproduction as occurs in nonclassic congenital adrenal hyperplasia (CAH) (Table 406-1). Virilization refers to a condition that may the result from benign hyperplasia of ovarian theca and stroma cells (e.g., hyperthecosis); it may also be a harbinger of a serious underlying condition, such as an ovarian or adrenal neoplasm. In women with virilization, androgen levels are sufficiently high to cause deepening of the voice, breast atro­ phy, increased muscle bulk, clitoromegaly, and increased libido. Cuta­ neous manifestations commonly associated with hirsutism include acne and hair thinning or pattern hair loss (androgenic alopecia). ■ ■HAIR FOLLICLE GROWTH AND DIFFERENTIATION The number of hair follicles remains unchanged over the life span, but follicle size and the type of hair can change in response to numerous factors, particularly androgens. Androgens are necessary for terminal hair and sebaceous gland development and mediate differentiation of pilosebaceous units (PSUs) into a terminal hair follicle and/or a sebaceous gland. In the former case, androgens transform the vellus hair into a terminal hair; in the latter case, the sebaceous component proliferates and the hair remains vellus. There are three phases in the cycle of hair growth: (1) anagen (growth phase), (2) catagen (involution phase), and (3) telogen (rest phase). Depending on the body site, hormonal regulation may play an important role in the hair growth cycle. Hair growth on the face, chest, upper abdomen, and back typically requires elevated androgen concen­ trations. However, there is only a modest correlation between androgen levels and the quantity of hair growth. This is due to the fact that hair growth from the follicle also depends on local growth factors, and the variability in end-organ (PSU) sensitivity to androgens. Genetic factors

and ethnic background also influence hair growth. Androgen excess in women may result in hair thinning or loss because androgens cause scalp hairs to spend less time in the anagen phase. In general, dark-haired individuals tend to be more hirsute than blond or fair individuals. Asians and Native Americans have relatively sparse hair in regions sensitive to high androgen levels, whereas people of Mediterranean descent are more hirsute. ■ ■CLINICAL ASSESSMENT Historic elements relevant to the assessment of hirsutism include the age at onset and rate of progression of hair growth and associated symptoms or signs (e.g., menstrual irregularity and acne). Depend­ ing on the cause, excess hair growth typically is first noted during the second and third decades of life. The growth is usually slow but progressive. Sudden development and rapid progression of hirsutism suggest the possibility of an androgen-secreting neoplasm, in which case virilization may also be present. The age at onset of menstrual cycles (menarche) and the pattern of the menstrual cycle should be ascertained. Menses may be irregular in the first 2 years after menarche; oligomenorrhea (<8 cycles per calen­ dar year) thereafter is more likely to result from ovarian than adrenal androgen excess. Associated symptoms such as galactorrhea should prompt evaluation for hyperprolactinemia (Chap. 392) or possibly hypothyroidism (Chap. 394). Hypertension, striae, easy bruising, and centripetal weight gain suggest hypercortisolism (Cushing’s syndrome; Chap. 398). Rarely, patients with acromegaly present with hirsutism. Medications such as phenytoin, minoxidil, and cyclosporine may be associated with androgen-independent excess hair growth (i.e., hyper­ trichosis). A family history of infertility and/or hirsutism may indicate inherited disorders such as nonclassic CAH (Chap. 398). Physical examination should include measurement of height and weight and calculation of body mass index (BMI). A BMI >25 kg/m2 is indicative of excess weight for height, and values >30 kg/m2 are often seen in association with hirsutism, probably the result of increased conversion of androgen precursors to testosterone. Notation should be made of blood pressure, as adrenal causes may be associated with hypertension. Cutaneous signs sometimes associated with androgen excess and insulin resistance include acanthosis nigricans and skin tags. An objective clinical assessment of hair distribution and quantity is central to the evaluation in any woman presenting with concerns about excessive hair growth. This assessment permits the distinction between hirsutism and hypertrichosis and provides a baseline reference point to gauge the response to treatment. A simple and commonly used method to grade hair growth is the modified scale of Ferriman and Gallwey (Fig. 406-1), in which each of nine androgen-sensitive sites is graded from 0 (no hair growth) to 4 (hair growth typically seen in adult men). Although it is normal for most women to have some hair growth in androgen-sensitive sites, ~95% of non-Hispanic white and African American women have a score <8 on this scale. Scores >8 suggest excess androgen-mediated hair growth, a finding that should be assessed further by means of hormonal evaluation (see below). Asian and Native Ameri­ can women are less likely to manifest hirsutism, and the only cutaneous evidence of androgen excess may be pustular acne and thinning scalp hair. ■ ■HORMONAL EVALUATION Androgens are secreted by the ovaries and adrenal glands in response to their respective tropic hormones: luteinizing hormone (LH) and adrenocorticotropic hormone (ACTH). Testosterone is the principal circulating steroid involved in the etiology of hirsutism; other steroids that may contribute to the development of hirsutism include andro­ stenedione and dehydroepiandrosterone (DHEA) and its sulfated form (DHEAS). The ovaries and adrenal glands normally contribute about equally to testosterone production. Approximately half of the total tes­ tosterone originates from direct glandular secretion, and the remainder is derived from the peripheral conversion of androstenedione and DHEA (Chap. 393). Testosterone is the most important circulating androgen, but it is a precursor hormone in mediating hirsutism. Testosterone is converted to dihydrotestosterone (DHT) by the enzyme 5α-reductase, which is

Upper lip

Chin

Chest

Abdomen

Pelvis

Upper arms

Thighs

Upper back

Lower back

FIGURE 406-1  Hirsutism scoring scale of Ferriman and Gallwey. The nine body areas that have androgen-sensitive areas are graded from 0 (no terminal hair) to 4 (frankly virile) to obtain a total score. A normal hirsutism score is <8. (Modified with permission from LJ DeGroot, JL Jameson: Endocrinology, 5th ed. Philadelphia, PA: Saunders; 2006.) located in the PSU. DHT is more potent than testosterone as it has a higher affinity for, and slower dissociation from, the androgen recep­ tor. The local production of DHT allows it to serve as the primary mediator of androgen action at the level of the PSU. There are two isoenzymes of 5α-reductase: type 2 is found in the prostate gland and in hair follicles, and type 1 is found primarily in sebaceous glands.

Hirsutism CHAPTER 406

One approach to the evaluation and treatment of hirsutism is depicted in Fig. 406-2. In addition to measuring blood levels of testosterone and DHEAS, it is often important to measure the level of free (or unbound) testosterone, i.e., the fraction of testosterone that is not bound to its carrier protein, sex hormone–binding globulin (SHBG). Unbound testosterone is biologically available for conversion to DHT

Evaluation and Treatment of Hirsutism Abnormal hirsutism score or localized terminal hair growth plus clinical evidence of a hyperandrogenic disorder Localized terminal hair growth (e.g., chin) Trial of dermatologic therapy PART 12 Endocrinology and Metabolism Course stable or improving Hair growth progresses Total testosterone blood level by specialty assay Normal variant Testosterone normal Hirsutism moderate-severe and/or other clinical evidence of hyperandrogenic endocrine disorder Hirsutism mild and isolated Hyperandrogenemia Trial of dermatologic or oral contraceptive therapy Free testosterone blood level (calculated from total testosterone and SHBG or by LC/TMS) Hair growth progresses Course stable or improving Free testosterone normal Idiopathic hirsutism Re-evaluate if hirsutism progresses FIGURE 406-2  Algorithm for the evaluation and treatment of hirsutism. LC/TMS, liquid chromatography/tandem mass spectrometry; SHBG, sex hormone–binding globulin. (Reproduced with permission from KA Martin et al: Evaluation and treatment of hirsutism in premenopausal women: An endocrine society clinical practice guideline. J Clin Endocrinol Metab 103:1233, 2018.) and binding to androgen receptors. Both hyperinsulinemia and andro­ gen excess decrease hepatic production of SHBG, resulting in levels of total testosterone within the high-normal range, whereas the unbound hormone is elevated more substantially. Although there is a decline in ovarian testosterone production after menopause, ovarian estrogen production decreases to an even greater extent, and the concentration of SHBG is reduced. Consequently, there is an increase in the relative proportion of unbound testosterone, and it may exacerbate hirsutism after menopause. A baseline plasma total testosterone level >12 nmol/L (>3.5 ng/mL) usually indicates an androgen-producing tumor, whereas a level

7 nmol/L (>2 ng/mL) is suggestive of tumor but may also be observed in women with hyperthecosis. A basal DHEAS level >18.5 μmol/L (>7000 μg/L) suggests an adrenal tumor. Although DHEAS has been proposed as a “marker” of predominant adrenal androgen excess, it is not unusual to find modest elevations in DHEAS among women with PCOS. Computed tomography (CT) or magnetic resonance imaging (MRI) should be used to localize an adrenal mass, and transvaginal ultrasound usually suffices to identify an ovarian mass if clinical evalu­ ation and hormonal levels suggest these possibilities. PCOS is the most common cause of ovarian androgen excess (Chap. 404). An increased ratio of LH to follicle-stimulating hor­ mone (FSH) is characteristic in carefully studied patients with PCOS. However, because of the pulsatile nature of gonadotropin secretion, a random measurement of LH and FSH may be misleading and is not

compensatory adrenal hyperplasia and the accumulation of steroid precursors that subsequently are converted to androgen. Deficiency of 21-hydroxylase can be reliably excluded by determining a morning 17-hydroxyprogesterone level <6 nmol/L (<2 μg/L) (drawn in the follicular phase). Alternatively, 21-hydroxylase deficiency can be diag­ nosed by measurement of 17-hydroxyprogesterone 1 h after the admin­ istration of 250 μg of synthetic ACTH (cosyntropin) intravenously. TREATMENT Hirsutism Treatment of hirsutism may be accomplished pharmacologically or by mechanical means of hair removal. Nonpharmacologic treat­ ments should be considered in all patients either as the only treat­ ment or as an adjunct to drug therapy. Nonpharmacologic treatments include (1) bleaching, (2) removal of the hair from the skin surface by shaving or with chemical treat­ ments, and (3) depilatory (removal of the hair including the root) such as plucking, waxing, electrolysis, laser, and intense pulsed light (IPL). Despite perceptions to the contrary, shaving does not increase the rate or density of hair growth. Chemical depilatory treatments may be useful for mild hirsutism that affects only limited skin areas, although they can cause skin irritation. Wax treatment removes hair temporarily but is uncomfortable. Electrolysis is effec­ tive for more permanent hair removal, particularly in the hands of a skilled electrologist. Laser and IPL are used to treat large areas of pigmented, terminal hair. Light of specific wavelength, duration, and energy is absorbed by melanin in the hair shaft and follicle lead­ ing to photothermolysis. Properly delivered, this treatment delays hair regrowth and causes permanent hair removal in many patients. Pharmacologic therapy is directed at interrupting one or more of the steps in the pathway of androgen synthesis and action: (1) suppression of adrenal and/or ovarian androgen production, (2) enhancement of androgen-binding to plasma-binding proteins, particularly SHBG, (3) impairment of the peripheral conversion of androgen precursors to active androgen, and (4) inhibition of androgen action at the target tissue level. Attenuation of hair growth is typically not evident until 4–6 months after initiation of medical treatment and, in most cases, leads to only a modest reduction in hair growth. Combination estrogen-progestin therapy in the form of an oral contraceptive is usually the first-line endocrine treatment for hirsut­ ism and acne, after dermatologic management. The estrogenic com­ ponent of most oral contraceptives currently in use is either ethinyl estradiol or mestranol. The suppression of LH leads to reduced production of ovarian androgens. The reduced androgen levels also result in a dose-related increase in SHBG, thus lowering the fraction of unbound plasma testosterone. Estrogens also have a direct, dosedependent suppressive effect on sebaceous cell function. The choice of a specific oral contraceptive should be predi­ cated on the progestational component, as progestins vary in their suppressive effect on SHBG levels and in their androgenic potential. Ethynodiol diacetate has relatively low androgenic poten­ tial, whereas progestins such as norgestrel and levonorgestrel are particularly androgenic, as judged from their attenuation of the estrogen-induced increase in SHBG. Norgestimate exemplifies the newer generation of progestins that are virtually “nonandro­ genic.” Drospirenone, an analogue of spironolactone that has both antimineralocorticoid and antiandrogenic activities, is often used as a progestational agent in combination with ethinyl estradiol, although concern remains about is prothrombotic effects. Oral contraceptives are contraindicated in women with a his­ tory of thromboembolic disease and women with increased risk of breast or other estrogen-dependent cancers (Chap. 407). There is a relative contraindication to the use of oral contraceptives in smok­ ers and those with hypertension or a history of migraine headaches. Improvements in hirsutism are typically in the range of 20%, but there may be an arrest of further progression of hair growth. In

most trials, estrogen-progestin therapy alone improves the extent of acne by an average of 50%. The effect on hair growth may not be evident for 6 months, and the maximum effect may require 9–12 months owing to the length of the hair growth cycle

Because oral contraceptives are efficacious and have fewer side effects, they are recommended over glucocorticoids as first-line treatment of hirsutism in CAH. If the response to oral contracep­ tives is inadequate, glucocorticoids may be used. The lowest effec­ tive dose of glucocorticoid should be used (e.g., dexamethasone [0.2–0.5 mg] or prednisone [5–10 mg]) taken at bedtime to achieve maximal suppression by inhibiting the nocturnal surge of ACTH. Hirsutism CHAPTER 406 Cyproterone acetate is the prototypic antiandrogen. It acts mainly by competitive inhibition of the binding of testosterone and DHT to the androgen receptor. In addition, it may enhance the metabolic clearance of testosterone by inducing hepatic enzymes. Although not available for use in the United States, cyproterone acetate is widely used in Canada, Mexico, and Europe. Cyproterone (50–100 mg) is given on days 1–15, and ethinyl estradiol (50 μg) is given on days 5–26 of the menstrual cycle. Side effects include irregular uterine bleeding, nausea, headache, fatigue, weight gain, and decreased libido. Spironolactone, which usually is used as a mineralocorticoid antagonist, is also a weak antiandrogen. It is almost as effective as cyproterone acetate when used at high enough doses (100–200 mg daily). Patients should be monitored intermittently for hyperkale­ mia or hypotension, though these side effects are uncommon. Preg­ nancy should be avoided because of the risk of feminization of a male fetus. Spironolactone can also cause menstrual irregularity. It often is used in combination with an oral contraceptive, which sup­ presses ovarian androgen production and helps prevent pregnancy. Flutamide is a potent nonsteroidal antiandrogen that is effective in treating hirsutism, but concerns about the induction of hepato­ cellular dysfunction preclude its use. Finasteride is a competitive inhibitor of 5α-reductase type 2. Beneficial effects on hirsutism have been reported, but the predominance of 5α-reductase type 1 in the PSU appears to account for its limited efficacy. Finaste­ ride would also be expected to impair sexual differentiation in a male fetus, and it should not be used in women who may become pregnant. Although studies of dutasteride are limited in number, it appears that this agent may have efficacy in treating scalp hair thinning and loss as well as hirsutism. Dutasteride differs from finasteride as it targets both 5α-reductase types 1 and 2. Ultimately, the choice of any specific agent(s) must be tailored to the unique needs of the patient being treated. As noted previously, pharmacologic treatments for hirsutism should be used in conjunc­ tion with nonpharmacologic approaches. It is also helpful to review the pattern of female hair distribution in the normal population to dispel unrealistic expectations. ■ ■FURTHER READING Azarchi S et al: Androgens in women: Hormone-modulating thera­ pies for skin disease. J Am Acad Derm 80:1509, 2019. Brown DL et al: Ovarian stromal hyperthecosis: Sonographic features and histologic associations. J Ultrasound Med 28:587, 2009. Forslund M et al: Different kinds of oral contraceptive pills in poly­ cystic ovary syndrome: A systematic review and meta-analysis Eur J Endocrinol 189:S1, 2023. Haak CS et al: Hair removal in hirsute women with normal testoster­ one levels: A randomized controlled trial of long-pulsed diode laser vs. intense pulsed light. Br J Dermatol 163:1007, 2010. Martin KA et al: Evaluation and treatment of hirsutism in premeno­ pausal women: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 103:1233, 2018. McCartney CR, Marshall JC: Polycystic ovary syndrome. N Engl J Med 375:1398, 2016. Rosenfield RL, Ehrmann DA: The pathogenesis of polycystic ovary syndrome (PCOS): The hypothesis of PCOS as functional ovarian hyperandrogenism revisited. Endocr Rev 37:467, 2016.

22 - 407 Menopause and Postmenopausal Hormone Therapy

407 Menopause and Postmenopausal Hormone Therapy

JoAnn E. Manson, Shari S. Bassuk

Menopause and

Postmenopausal Hormone Therapy Menopause is the permanent cessation of menstruation due to loss of ovarian follicular function. It is diagnosed retrospectively after 12 months of amenorrhea. The average age at menopause is 51 years among U.S. women. Perimenopause refers to the time period preced­ ing menopause, when fertility wanes and menstrual cycle irregularity increases, until the first year after cessation of menses. The onset of perimenopause precedes the final menses by 2–8 years, with a mean duration of 4 years. Smoking accelerates the menopausal transition by 2 years. PART 12 Endocrinology and Metabolism Although the peri- and postmenopausal transitions share many symptoms, the physiology and clinical management of the two differ. Low-dose oral contraceptives have become a therapeutic mainstay in perimenopause, whereas postmenopausal hormone therapy (HT) has been a common method of symptom alleviation after menstruation ceases. PERIMENOPAUSE ■ ■PHYSIOLOGY Ovarian mass and fertility decline sharply after age 35 and even more precipitously during perimenopause; depletion of primary follicles, a process that begins before birth, occurs steadily until menopause (Chap. 404). In perimenopause, intermenstrual intervals shorten sig­ nificantly (typically by 3 days) as a result of an accelerated follicular phase. Follicle-stimulating hormone (FSH) levels rise because of altered folliculogenesis and reduced inhibin secretion. In contrast to the con­ sistently high FSH and low estradiol levels seen in menopause, peri­ menopause is characterized by “irregularly irregular” hormone levels. The propensity for anovulatory cycles can produce a hyperestrogenic, hypoprogestagenic environment that may account for the increased incidence of endometrial hyperplasia or carcinoma, uterine polyps, and leiomyoma observed among women of perimenopausal age. Mean serum levels of selected ovarian and pituitary hormones during the menopausal transition are shown in Fig. 407-1. With transition into menopause, estradiol levels fall markedly, whereas estrone levels are relatively preserved, a pattern reflecting peripheral aromatization of adrenal and ovarian androgens. Levels of FSH increase more than those of luteinizing hormone, presumably because of the loss of inhibin as well as estrogen feedback.

FSH (IU/L)

LH or FSH, IU/L LH (IU/L)

Estrone (pg/mL)

Estradiol (pg/mL)

–2 –4 –6

Menopause, years FIGURE 407-1  Mean serum levels of ovarian and pituitary hormones during the menopausal transition. FSH, follicle-stimulating hormone; LH, luteinizing hormone. (Data from G Rannevik et al: A longitudinal study of the perimenopausal transition: Altered profiles of steroid and pituitary hormones, SHBG and bone mineral density. Maturitas 21:103, 1995.)

■ ■DIAGNOSTIC TESTS The Stages of Reproductive Aging Workshop +10 (STRAW+10) classification provides a comprehensive framework for the clini­ cal assessment of ovarian aging. As shown in Fig. 407-2, menstrual cycle characteristics are the principal criteria for characterizing the menopausal transition, with biomarker measures as supportive cri­ teria. Because of their extreme intraindividual variability, FSH and estradiol levels are imperfect diagnostic indicators of perimenopause in menstruating women. However, a consistently low FSH level in the early follicular phase (days 2–5) of the menstrual cycle does not sup­ port a diagnosis of perimenopause, while levels >25 IU/L in a random blood sample are characteristic of the late menopause transition. FSH measurement can also aid in assessing fertility; levels of <20 IU/L, 20 to <30 IU/L, and ≥30 IU/L measured on day 3 of the cycle indicate a good, fair, and poor likelihood of achieving pregnancy, respectively. Anti-müllerian hormone and inhibin B may also be useful for assessing reproductive aging. ■ ■SYMPTOMS Determining whether symptoms that develop in midlife are due to ovarian senescence or to other age-related changes is difficult. There is strong evidence that the menopausal transition can cause hot flashes, night sweats, irregular bleeding, and vaginal dryness, and there is moderate evidence that it can cause sleep disturbances in some women. There is inconclusive or insufficient evidence that ovarian aging is a major cause of mood swings, depression, impaired memory or con­ centration, somatic symptoms, urinary incontinence, or sexual dys­ function. In one U.S. study, nearly 60% of women reported hot flashes in the 2 years before their final menses. Symptom intensity, duration, frequency, and effects on quality of life are highly variable. TREATMENT Perimenopause PERIMENOPAUSAL THERAPY For women with irregular or heavy menses or hormone-related symptoms that impair quality of life, low-dose combined oral contraceptives are a staple of therapy. Static doses of estrogen and progestin (e.g., 20 μg of ethinyl estradiol and 1 mg of norethindrone acetate daily for 21 days each month) can eliminate vasomotor symptoms and restore regular cyclicity. Oral contraceptives provide other benefits, including protection against ovarian and endome­ trial cancers and increased bone density, although it is not clear whether use during perimenopause decreases fracture risk later in life. Moreover, the contraceptive benefit is important, given that the unintentional pregnancy rate among women in their forties rivals that of adolescents. Contraindications to oral contraceptive use include cigarette smoking, liver disease, a history of thrombo­ embolism or cardiovascular disease, breast cancer, or unexplained vaginal bleeding. Progestin-only formulations (e.g., 0.35 mg of nor­ ethindrone daily) or medroxyprogesterone (Depo-Provera) injec­ tions (e.g., 150 mg IM every 3 months) may provide an alternative for the treatment of perimenopausal menorrhagia in women who smoke or have cardiovascular risk factors. Although progestins nei­ ther regularize cycles nor reduce the number of bleeding days, they reduce the volume of menstrual flow. Estradiol or estrone, pg/mL Nonhormonal strategies to reduce menstrual flow include the use of nonsteroidal anti-inflammatory agents such as mefenamic acid (an initial dose of 500 mg at the start of menses, then 250 mg qid for 2–3 days) or, when medical approaches fail, endometrial ablation. It should be noted that menorrhagia requires an evalu­ ation to rule out uterine disorders. Transvaginal ultrasound with saline enhancement is useful for detecting leiomyomata or polyps, and endometrial aspiration can identify hyperplastic changes. TRANSITION TO MENOPAUSE For sexually active women using contraceptive hormones to alle­ viate perimenopausal symptoms, the question of when and if to

Menarche FMP (0) –3a –2 –1 +2 +1a +1b +1c Terminology Stage –5 –4 –3b Reproductive Early Early Early Peak Late Late Late Perimenopause Variable Duration Principal criteria Subtle changes in flow/ length Menstrual cycle Variable to regular Regular Regular Supportive criteria Endocrine FSH AMH Inhibin B Antral follicle count Variable* Variable* Variable Stabilizes Low Low Low Low Low Low Low Low Descriptive characteristics Symptoms *Blood draw on cycle days 2–5 = elevated. **Approximate expected level based on assays using current international pituitary standard. FIGURE 407-2  The Stages of Reproductive Aging Workshop +10 (STRAW +10) staging system for reproductive aging in women. AMH, anti-müllerian hormone; FSH, folliclestimulating hormone. (Reproduced with permission from SD Harlow et al: Executive summary of the Stages of Reproductive Aging Workshop + 10: addressing the unfinished agenda of staging reproductive aging. Menopause 19:387, 2012.) switch to HT must be individualized. Doses of estrogen and proges­ togen (either synthetic progestins or natural forms of progesterone) in HT are lower than those in oral contraceptives and have not been documented to prevent pregnancy. Although a 1-year absence of spontaneous menses reliably indicates ovulation cessation, it is not possible to assess the natural menstrual pattern while a woman is taking an oral contraceptive. Women willing to switch to a barrier method of contraception should do so; if menses occur spontane­ ously, oral contraceptive use can be resumed. The average age of final menses among relatives can serve as a guide for when to initi­ ate this process, which can be repeated yearly until menopause has occurred. MENOPAUSE AND POSTMENOPAUSAL HT One of the most complex health care decisions facing women is whether to use postmenopausal HT. Once prescribed primarily to relieve vasomotor symptoms, HT has been promoted as a strategy to forestall various disorders that accelerate after menopause, including osteoporosis and cardiovascular disease. In 2000, nearly 40% of post­ menopausal women aged 50–74 in the United States had used HT. This widespread use occurred despite the paucity of conclusive data, until recently, on the health consequences of such therapy. Although many women rely on their health care providers for a definitive answer to the question of whether to use postmenopausal hormones, balancing the benefits and risks for an individual patient is challenging. Although observational studies suggest that HT prevents cardio­ vascular and other chronic diseases, the apparent benefits may result at least in part from differences between women who opt to take postmenopausal hormones and women who do not. Those choos­ ing HT tend to be healthier, have greater access to medical care, are more compliant with prescribed treatments, and maintain a more

Postmenopause Menopausal transition Variable Remaining lifespan 1–3 years 3–6 years 2 years (1+1) Menopause and Postmenopausal Hormone Therapy CHAPTER 407 Interval of amenorrhea of ≥60 days Variable Length Persistent ≥7-day difference in length of consecutive cycles

25 IU/L** Low Low Low Low Very low Very low Very low Low Low Very low Increasing symptoms of urogenital atrophy Vasomotor symptoms Most likely Vasomotor symptoms Likely health-promoting lifestyle. Randomized trials, which eliminate these confounding factors, have not consistently confirmed the benefits found in observational studies. Indeed, the largest HT trial to date, the Women’s Health Initiative (WHI), which examined >27,000 post­ menopausal women aged 50–79 (mean age, 63) for an average of 5–7 years, was stopped early because of an overall unfavorable benefitrisk ratio in the estrogen-progestin arm and an excess risk of stroke that was not offset by a reduced risk of coronary heart disease (CHD) in the estrogen-only arm. The following summary offers a decision-making guide based on a synthesis of currently available evidence. Prevention of cardiovascular disease is eliminated from the equation due to lack of evidence for such benefits in randomized clinical trials. ■ ■BENEFITS AND RISKS OF POSTMENOPAUSAL HT See Table 407-1. Definite Benefits  •  SYMPTOMS OF MENOPAUSE  Compelling evidence, including data from randomized clinical trials, indicates that estrogen therapy is highly effective for controlling vasomotor and genitourinary symptoms. Alternative approaches, including the use of antidepressants (such as paroxetine mesylate, 7.5 mg/d; venlafaxine, 37.5–75 mg/d; desvenlafaxine, 100 mg/d; fluoxetine, 20–30 mg/d; sertraline, 50–100 mg/d; citalopram, 10–30 mg/d; and escitalopram, 10–20 mg/d); the neurokinin-3 receptor antagonist fezolinetant (45 mg/d); the γ-aminobutyric acid analogue gabapentin (300 mg nightly, up to 900 mg in divided doses); and the antispasmodic anticholinergic oxy­ butynin (2.5–5 mg twice per day) may also alleviate vasomotor symp­ toms, although they are less effective than HT. Evidence is inconsistent on the efficacy of pregabalin (75–150 mg/d twice per day) and cloni­ dine (oral, 0.1–1 mg/d, or transdermal, 0.1–0.3 mg weekly). Paroxetine mesylate and fezolinetant are the only nonhormonal drugs approved

TABLE 407-1  Benefits and Risks of Postmenopausal Hormone Therapy in the Overall Study Population of Women aged 50–79 Years in the Intervention Phase of the Women’s Health Initiative (WHI) Estrogen-Progestin and Estrogen-Alone Trialsa RELATIVE BENEFIT OR RISK OUTCOME EFFECT Definite Benefits Symptoms of menopause Definite improvement ↓65–90% decreased riskc Osteoporosis Definite increase in bone mineral density and decrease in fracture risk ↓33% decreased risk for hip fracture PART 12 Endocrinology and Metabolism Definite Risksh Endometrial cancer Definite increase in risk with estrogen alone

(see below for estrogen-progestin) See below See below   4.6 excess cases (observational studies) Pulmonary embolism Definite increase in risk ↑98% increased risk 9 excess cases

(18 vs 9) Deep-vein thrombosis Definite increase in risk ↑87% increased risk 11.5 excess cases (25 vs 14) Breast cancer Definite increase in risk with long-term use

(≥5 years) of estrogen-progestin ↑24% increased risk 8.5 excess cases

(43 vs 35) Gallbladder disease Definite increase in risk ↑57% increased risk 47 excess cases

(131 vs 84) Probable or Uncertain Risks and Benefitsh Coronary heart diseased Probable increase in risk among older women and women many years past menopause; possible decrease in risk or no effect in younger or recently menopausal womene ↑18% increased risk (n.s.) Myocardial infarction Significant interaction by age group for estrogen alone, with reduced risk in younger—but not older—women (p for trend by age = .02) ↑24% increased risk (n.s.) Stroke Probable increase in risk ↑37% increased risk 9 excess cases

(33 vs 24) Ovarian cancer Probable increase in risk with long-term use

(≥5 years) ↑41% increased risk (n.s.) Endometrial cancer Probable decrease in risk with estrogenprogestin during long-term follow-up (see above for estrogen alone) ↓33% decreased riskf 3 fewer cases

(7 vs 10) Urinary incontinence Probable increase in risk ↑49% increased risk 549 excess cases (1661 vs 1112) Colorectal cancer Probable decrease in risk with estrogenprogestin; possible increase in risk in older women with estrogen alone (p for trend by age = .02 for estrogen alone) ↓38% decreased risk 6.5 fewer cases

(10 vs 17) Type 2 diabetes Probable decrease in risk ↓19% decreased risk 16 fewer cases

(72 vs 88) Dementia (age ≥65) Increase in risk in older women (but inconsistent data from observational studies and randomized trials) ↑101% increased risk 23 excess cases

(46 vs 23) Total mortality Possible increase in risk among older women and women many years past menopause; possible decrease in risk or no effect in younger or recently menopausal women (p for trend by age <.05 for both trials combined) No increase in risk No difference in risk No increase in riske No difference in riske Global indexg Probable increase in risk or no effect among older women and women many years past menopause; possible decrease in risk or no effect in younger or recently menopausal women (p for trend by age = .02 for estrogen alone) ↑12% increased risk 20.5 excess cases (189 vs 168) aThe estrogen-progestin arm of the WHI assessed 5.6 years of conjugated equine estrogens (0.625 mg/d) plus medroxyprogesterone acetate (2.5 mg/d) versus placebo. The estrogen-alone arm of the WHI assessed 7.1 years of conjugated equine estrogens (0.625 mg/d) versus placebo. bNumber of cases per 10,000 women per year. cThe WHI was not designed to assess the effect of hormone therapy (HT) on menopausal symptoms. Data from other randomized trials suggest that HT reduces risk for menopausal symptoms by 65–90%. dCoronary heart disease is defined as nonfatal myocardial infarction or coronary death. eThere was a significant interaction by age; that is, the association between HT and the specified outcome was different in younger women and older women. fThis is the risk reduction that was observed during a cumulative 13-year follow-up period (5.6 years of treatment plus 8.2 years of postintervention observation). gThe global index is a composite outcome representing the first event for each participant from among the following: coronary heart disease, stroke, pulmonary embolism, breast cancer, colorectal cancer, endometrial cancer (estrogen-progestin arm only), hip fracture, and death. Because participants can experience more than one type of event, the global index cannot be derived by a simple summing of the component events. hIncludes some outcomes where results were divergent between the estrogen-progestin arm and the estrogen-alone arm. Abbreviation: n.s., not statistically significant. Source: Data from JE Manson et al: Menopausal hormone therapy and health outcomes during the intervention and extended poststopping phases of the Women’s Health Initiative randomized trials. JAMA 310:1353, 2013.

ESTROGEN-PROGESTIN ESTROGEN ALONE ABSOLUTE BENEFIT OR RISKb RELATIVE BENEFIT OR RISK ABSOLUTE BENEFIT OR RISKb   ↓65–90% decreased riskc   6 fewer cases

(11 vs 17) of hip fracture 6 fewer cases

(13 vs 19) of hip fracture ↓33% decreased risk for hip fracture 4 excess cases

(14 vs 10) ↑35% increased risk (n.s.) ↑48% increased risk 7.5 excess cases

(23 vs 15) 7 fewer cases

(28 vs 35) ↓21% decreased risk (n.s.) ↑55% increased risk 58 excess cases

(164 vs 106) 6 excess cases

(41 vs 35) No increase in risk No difference in risk 6 excess cases

(35 vs 29) No increase in riske No difference in riske ↑35% increased risk 11 excess cases

(45 vs 34) 1 excess case

(5 vs 4) Not available Not available See above See above ↑61% increased risk 852 excess cases (2255 vs 1403) No increase or decrease in riske No difference in riske 21 fewer cases

(134 vs 155) ↓14% decreased risk 15 excess cases

(44 vs 29) ↑47% increased risk (n.s.) No increase in riske No difference in riske

by the U.S. Food and Drug Administration for treatment of vasomotor symptoms. Bazedoxifene, an estrogen agonist/antagonist, in combina­ tion with conjugated estrogens has also received approval for this use. Cognitive behavioral therapy and clinical hypnosis have been shown in randomized trials to help with vasomotor symptom management. The consumption of phytoestrogens, including soy isoflavones, may be effective in women who are able to metabolize the isoflavone daidzein to the biologically active metabolite equol. Weight loss, mindfulnessbased stress reduction, and stellate ganglion block are also promis­ ing strategies, although more trials are needed. For genitourinary syndrome of menopause, the efficacy of low-dose vaginal estrogen is similar to that of oral or transdermal estrogen; oral ospemifene and vaginal prasterone are additional options. OSTEOPOROSIS (See also Chap. 423)  Bone density  By reducing bone turnover and resorption rates, estrogen slows the aging-related bone loss experienced by most postmenopausal women. More than 50 randomized trials have demonstrated that post­ menopausal estrogen therapy, with or without a progestogen, rapidly increases bone mineral density at the spine by 4–6% and at the hip by 2–3% and that those increases are maintained during treatment. Fractures  Data from observational studies indicate a 50–80% lower risk of vertebral fracture and a 25–30% lower risk of hip, wrist, and other peripheral fractures among current estrogen users; addition of a progestogen does not appear to modify this benefit. In the WHI, 5–7 years of either combined estrogen-progestin or estrogen-only therapy was associated with a 33% reduction in hip fractures and 25–30% fewer total fractures among a population unselected for osteoporosis. Bisphos­ phonates (such as alendronate, 10 mg/d or 70 mg once per week; risedro­ nate, 5 mg/d or 35 mg once per week; ibandronate, 2.5 mg/d or 150 mg once per month or 3 mg every 3 months IV; or zoledronic acid, 5 mg once per year IV) and denosumab (60 mg twice per year SC) increase bone mass density by reducing bone resorption and have been shown in randomized trials to decrease fracture rates. Other treatment options include bazedoxifene in combination with conjugated estrogens; the selective estrogen receptor modulator (SERM) raloxifene (60 mg/d); and parathyroid hormone (teriparatide, 20 μg/d SC). Unlike estrogen, these alternative therapies do not appear to have adverse effects on the endometrium or breast. Increased weight-bearing and resistance exer­ cise; adequate calcium intake (1000–1200 mg/d through diet or supple­ ments in two or three divided doses); and adequate vitamin D intake (600–1000 IU/d) may also reduce the risk of osteoporosis-related frac­ tures. According to a 2011 report by the Institute of Medicine (now the National Academy of Medicine), 25-hydroxyvitamin D blood levels of ≥50 nmol/L are sufficient for bone-density maintenance and fracture prevention. The Fracture Risk Assessment (FRAX®) score, an algorithm that combines an individual’s bone-density score with age and other risk factors to predict her 10-year risk of hip and major osteoporotic fracture, may be of use in guiding decisions about pharmacologic treat­ ment (see www.sheffield.ac.uk/FRAX/). Definite Risks  •  ENDOMETRIAL CANCER (WITH ESTROGEN ALONE)  A combined analysis of 30 observational studies found a tripling of endometrial cancer risk among short-term users (1–5 years) of unopposed estrogen and a nearly 10-fold increased risk among longterm users (≥10 years). These findings are supported by results from the randomized Postmenopausal Estrogen/Progestin Interventions (PEPI) trial, in which 24% of women assigned to unopposed estrogen for 3 years developed atypical endometrial hyperplasia—a premalignant lesion—as opposed to only 1% of women assigned to placebo. Use of a progestogen, which opposes the effects of estrogen on the endome­ trium, eliminates these risks and may even reduce risk (see later). VENOUS THROMBOEMBOLISM  A meta-analysis of observational stud­ ies found that current oral estrogen use was associated with a 2.5-fold increase in risk of venous thromboembolism in postmenopausal women. A meta-analysis of randomized trials, including the WHI, found a 2.1-fold increase in risk. Results from the WHI indicate a nearly twofold increase in risk of pulmonary embolism and deep-vein thrombosis with estrogen-progestin and a 35–50% increase in these

risks with estrogen-only therapy. Transdermal estrogen, taken alone or with certain progestogens (micronized progesterone or pregnane derivatives), appears to be a safer alternative with respect to thrombotic risk.

BREAST CANCER (WITH ESTROGEN-PROGESTIN)  An increased risk of breast cancer has been found among current or recent estrogen users in observational studies; this risk is directly related to duration of use. In contrast to findings for endometrial cancer, combined estrogenprogestin regimens appear to increase breast cancer risk more than estrogen alone. In a 2019 meta-analysis of 58 observational studies (108,647 breast cancer cases) published between 1992 and 2017, the relative risks (RRs) for incident breast cancer with current use of estro­ gen-progestin for 1–4, 5–9, 10–14, and ≥15 years were 1.60 (95% confi­ dence interval [CI], 1.52–1.69), 1.97 (95% CI, 1.90–2.04), 2.26 (95% CI, 2.16–2.36), and 2.51 (95% CI, 2.35–2.68), respectively, compared with never use. The corresponding statistics for incident breast cancer with current use of estrogen alone were 1.17 (1.10–1.26), 1.22 (1.17–1.28), 1.43 (1.37–1.50), and 1.58 (1.51–1.66), respectively. Data from ran­ domized trials also indicate that estrogen-progestin raises breast cancer risk. In the WHI, women assigned to receive combination hormones for an average of 5.6 years were 24% more likely to develop breast cancer than women assigned to placebo, but 7.1 years of estrogenonly therapy did not increase risk. Indeed, the WHI showed a trend toward a reduction in breast cancer risk with estrogen alone, although it is unclear whether this finding would pertain to formulations of estrogen other than conjugated equine estrogens or to treatment dura­ tions of >7 years. In the Heart and Estrogen/Progestin Replacement Study (HERS), combination therapy for 4 years was associated with a 27% increase in breast cancer risk. Although the latter finding was not statistically significant, the totality of evidence strongly implicates estrogen-progestin therapy in breast carcinogenesis. Menopause and Postmenopausal Hormone Therapy CHAPTER 407 Some observational data suggest that the length of the interval between menopause onset and HT initiation may influence the asso­ ciation between such therapy and breast cancer risk, with a “gap time” of <3–5 years conferring a higher HT-associated breast cancer risk. (This pattern of findings contrasts with that for CHD, as discussed later in this chapter.) However, this association remains inconclusive and may be a spurious finding attributable to higher rates of screen­ ing mammography and thus earlier cancer detection in HT users than in nonusers, especially in early menopause. Indeed, in the WHI trial, relative risk (RRs) for HT and breast cancer risk did not differ among women 50–59, those 60–69, and those 70–79 years of age at trial entry. (There was insufficient power to examine finer age categories.) Addi­ tional research is needed to clarify the issue. GALLBLADDER DISEASE  Large observational studies report a two- to threefold increased risk of gallstones or cholecystectomy among postmenopausal women taking oral estrogen. In the WHI, women randomized to estrogen-progestin or estrogen alone were ~55% more likely to develop gallbladder disease than those assigned to placebo. Risks were also increased in HERS. Transdermal HT might be a safer alternative, but further research is needed. Probable or Uncertain Risks and Benefits  •  CORONARY HEART DISEASE/STROKE  Until recently, HT had been enthusiasti­ cally recommended as a possible cardioprotective agent. In the past three decades, multiple observational studies suggested, in the aggre­ gate, that estrogen use leads to a 35–50% reduction in CHD incidence among postmenopausal women. The biologic plausibility of such an association is supported by data from randomized trials demonstrating that exogenous estrogen lowers plasma low-density lipoprotein (LDL) cholesterol levels and raises high-density lipoprotein (HDL) cholesterol levels by 10–15%. Administration of estrogen also favorably affects lipoprotein(a) levels, LDL oxidation, endothelial vascular function, fibrinogen, and plasminogen activator inhibitor 1. However, estrogen therapy has unfavorable effects on other biomarkers of cardiovascular risk: it boosts triglyceride levels; promotes coagulation via factor VII, prothrombin fragments 1 and 2, and fibrinopeptide A elevations; and raises levels of the inflammatory marker C-reactive protein.

Randomized trials of estrogen or combined estrogen-progestin in women with preexisting cardiovascular disease have not confirmed the benefits reported in observational studies. In HERS (a secondaryprevention trial designed to test the efficacy and safety of estrogenprogestin therapy with regard to clinical cardiovascular outcomes), the 4-year incidence of coronary death and nonfatal myocardial infarction was similar in the active-treatment and placebo groups, and a 50% increase in risk of coronary events was noted during the first year among participants assigned to the active-treatment group. Although it is possible that progestin may mitigate estrogen’s benefits, the Estrogen Replacement and Atherosclerosis (ERA) trial indicated that angio­ graphically determined progression of coronary atherosclerosis was unaffected by either opposed or unopposed estrogen treatment. More­ over, no cardiovascular benefit was found in the Papworth Hormone Replacement Therapy Atherosclerosis Study, a trial of transdermal estradiol with and without norethindrone; the Women’s Estrogen for Stroke Trial (WEST), a trial of oral 17β-estradiol; or the Estrogen in the Prevention of Reinfarction Trial (ESPRIT), a trial of oral estradiol valerate. Thus, in clinical trials, HT has not proved effective for the sec­ ondary prevention of cardiovascular disease in postmenopausal women.

PART 12 Endocrinology and Metabolism Primary-prevention trials also suggest an early increase in cardio­ vascular risk and an absence of cardioprotection with postmenopausal HT. In the WHI, women assigned to 5.6 years of estrogen-progestin therapy were 18% more likely to develop CHD (defined in primary analyses as nonfatal myocardial infarction or coronary death) than those assigned to placebo, although this risk elevation was not sta­ tistically significant. However, during the trial’s first year, there was a significant 80% increase in risk, which diminished in subsequent years (p for trend by time = .03). In the estrogen-only arm of the WHI, no overall effect on CHD was observed during the 7.1 years of the trial or in any specific year of follow-up. This pattern of results was similar to that for the outcome of total myocardial infarction. However, a closer look at available data suggests that timing of initiation of HT may critically influence the association between such therapy and CHD. Estrogen may slow early stages of atherosclerosis but have adverse effects on advanced atherosclerotic lesions. It has been hypothesized that the prothrombotic and proinflammatory effects of estrogen manifest themselves predominantly among women with subclinical lesions who initiate HT well after the menopausal transi­ tion, whereas women with less arterial damage who start HT early in menopause may derive cardiovascular benefit because they have not yet developed advanced lesions. Data from experiments in nonhu­ man primates and from some randomized trials in humans support this concept. Conjugated estrogens had no effect on the extent of coronary artery plaque in cynomolgus monkeys assigned to receive estrogen alone or combined with progestin starting 2 years (~6 years in human terms) after oophorectomy and well after the establishment of atherosclerosis. However, administration of exogenous hormones immediately after oophorectomy, during the early stages of athero­ sclerosis, reduced the extent of plaque by 70%. In the Early versus Late Intervention Trial with Estradiol (ELITE), a 6-year trial among 643 healthy postmenopausal women that was designed to test whether effects of estrogen on the development and progression of atheroscle­ rosis depend on age at initiation of therapy, oral 17β-estradiol admin­ istered with or without vaginal micronized progesterone significantly slowed carotid atherosclerotic progression in women within 6 years of menopause onset (mean age, 55.4 years) but not in women >10 years past menopause onset (mean age, 65.4 years) (p for interaction = .007). On the other hand, in the Kronos Early Estrogen Prevention Study (KEEPS), a 4-year trial among 729 healthy postmenopausal women within 3 years of menopause onset at trial entry (mean age, 53 years), neither oral conjugated estrogens nor transdermal estradiol, admin­ istered with oral micronized progesterone, affected carotid athero­ sclerotic progression. However, the low prevalence of this endpoint in the overall study population may have curtailed power to detect a treatment difference. Lending further credence to the timing hypothesis are results of subgroup analyses of data from observational studies and large clini­ cal trials. For example, among women who entered the WHI trial with

a relatively favorable cholesterol profile, estrogen with or without pro­ gestin led to a 40% lower risk of incident CHD. Among women who entered with a worse cholesterol profile, therapy resulted in a 73% higher risk (p for interaction = .02). The presence or absence of the metabolic syndrome (Chap. 420) also strongly influenced the relation between HT and incident CHD. Among women with the metabolic syndrome, HT more than doubled CHD risk, whereas no associa­ tion was observed among women without the syndrome. Moreover, although there was no association between estrogen-only therapy and CHD in the WHI trial cohort as a whole, such therapy was associated with a CHD risk reduction of 40% among participants aged 50–59; in contrast, a risk reduction of only 5% was observed among those aged 60–69, and a risk increase of 9% was found among those aged 70–79 (p for trend by age = .08). For the outcome of total myocardial infarction, estrogen alone was associated with a borderline-significant 45% reduction and a nonsignificant 24% increase in risk among the youngest and oldest women, respectively (p for trend by age = .02). Estrogen was also associated with lower levels of coronary artery calcified plaque in the younger age group. Although age did not have a similar effect in the estrogen-progestin arm of the WHI, CHD risks increased with years since menopause (p for trend = .08), with a significantly elevated risk among women who were ≥20 years past menopause. For the outcome of total myocardial infarction, estrogenprogestin was associated with a 9% risk reduction among women <10 years past menopause as opposed to a 16% increase in risk among women 10–19 years past menopause and a twofold increase in risk among women >20 years past menopause (p for trend = .01). In the large observational Nurses’ Health Study, women who chose to start HT within 4 years of menopause experienced a lower risk of CHD than did nonusers, whereas those who began therapy ≥10 years after menopause appeared to receive little coronary benefit. Observational studies include a high proportion of women who begin HT within 3–4 years of menopause, whereas clinical trials include a high pro­ portion of women ≥12 years past menopause; this difference helps to reconcile some of the apparent discrepancies between the two types of studies. For the outcome of stroke, WHI participants assigned to estrogenprogestin or estrogen alone were ~35% more likely to suffer a stroke than those assigned to placebo. Whether or not age at initiation of HT influences stroke risk is not well understood. In the WHI and the Nurses’ Health Study, HT was associated with an excess risk of stroke in all age groups. Further research is needed on age, time since meno­ pause, and other individual characteristics (including biomarkers) that predict increases or decreases in cardiovascular risk associated with exogenous HT. Furthermore, it remains uncertain whether different doses, formulations, or routes of administration of HT will produce different cardiovascular effects. COLORECTAL CANCER  Observational studies have suggested that HT reduces risks of colon and rectal cancer, although the estimated magnitudes of the relative benefits have ranged from 8 to 34% in various meta-analyses. In the WHI (the sole trial to examine the issue), estrogen-progestin was associated with a significant 38% reduction in colorectal cancer over a 5.6-year period, although no benefit was seen with 7 years of estrogen-only therapy. However, a modifying effect of age was observed, with a doubling of risk with HT in women aged 70–79 but no risk elevation in younger women (p for trend by age = .02). COGNITIVE DECLINE AND DEMENTIA  A meta-analysis of 10 casecontrol and two cohort studies suggested that postmenopausal HT is associated with a 34% decreased risk of dementia. Subsequent random­ ized trials (including the WHI), however, have failed to demonstrate any benefit of estrogen or estrogen-progestin therapy on the progres­ sion of mild to moderate Alzheimer’s disease and/or have indicated a potential adverse effect of HT on the incidence of dementia, at least in women ≥65 years of age. Among women randomized to HT (as opposed to placebo) at age 50–55 in the WHI, no effect on cognition was observed during the postintervention phase. Determining whether timing of initiation of HT influences cognitive outcomes will require further study.

OVARIAN CANCER AND OTHER DISORDERS  On the basis of limited observational and randomized data, it has been hypothesized that HT increases the risk of ovarian cancer and reduces the risk of type 2 diabetes mellitus. Results from the WHI support these hypotheses. The WHI also found that HT use was associated with an increased risk of urinary incontinence and that estrogen-progestin was associated with increased rates of lung cancer mortality. ENDOMETRIAL CANCER (WITH ESTROGEN-PROGESTIN)  In the WHI, use of estrogen-progestin was associated with a nonsignificant 17% reduction in risk of endometrial cancer. A significant reduction in risk emerged during the postintervention period (see later). ALL-CAUSE MORTALITY  In the overall WHI cohort, estrogen with or without progestin was not associated with all-cause mortality. How­ ever, there was a trend toward reduced mortality in younger women, particularly with estrogen alone. For women aged 50–59, 60–69, and 70–79 years, RRs associated with estrogen-only therapy were 0.70, 1.01, and 1.21, respectively (p for trend = .04). OVERALL BENEFIT-RISK PROFILE  Estrogen-progestin was associ­ ated with an unfavorable benefit-risk profile (excluding relief from menopausal symptoms) as measured by a “global index”—a composite outcome including CHD, stroke, pulmonary embolism, breast cancer, colorectal cancer, endometrial cancer, hip fracture, and death (Table 407-1)—in the WHI cohort as a whole, and this association did not A CEE+MPA Trial

Intergroup difference in no. of events per 1000 women over 5 yr

Risks

2.5 5.0

2.5

–5 Benefits –10 –15 –20 Stroke Deep-vein thrombosis Breast cancer Colorectal cancer All cancers All fractures Death from any cause Diabetes Coronary heart disease B CEE+Alone Trial

Intergroup difference in no. of events per 1000 women over 5 yr

Risks

2.5

–0.5 –5 –5.5 Benefits –10 –15 –20 Stroke Deep-vein thrombosis Breast cancer Colorectal cancer All cancers All fractures Death from any cause Diabetes Coronary heart disease FIGURE 407-3  Benefits and risks of the two hormone therapy (HT) formulations evaluated in the Women’s Health Initiative, in women aged 50–59 years. Results are shown for the two formulations, conjugated equine estrogens (CEE) alone or in combination with medroxyprogesterone acetate (MPA). Risks and benefits are expressed as the difference in number of events (number in the HT group minus the number in the placebo group) per 1000 women over 5 years. (Reproduced with permission from JE Manson, AM Kaunitz: Menopause Management–Getting Clinical Care Back on Track. N Engl J Med 374:803, 2016.)

vary by 10-year age group. Estrogen-only therapy was associated with a neutral benefit-risk profile in the WHI cohort as a whole. However, there was a significant trend toward a more favorable benefit-risk pro­ file among younger women and a less favorable profile among older women, with RRs of 0.84, 0.99, and 1.17 for women aged 50–59, 60–69, and 70–79 years, respectively (p for trend by age = .02). The balance of benefits and risks of estrogen with and without progestin among women aged 50–59 is shown in Fig. 407-3.

CHANGES IN HEALTH STATUS AFTER DISCONTINUATION OF HT  In the WHI, many but not all risks and benefits associated with active use of HT dissipated within 5–7 years after discontinuation of therapy. For estrogen-progestin, an elevated risk of breast cancer persisted (RR = 1.28; 95% CI, 1.11–1.48) during a median cumulative 13-year followup period (5.6 years of treatment plus 8.2 years of postintervention observation), but most cardiovascular disease risks became neutral. A reduction in hip fracture risk persisted (RR = 0.81; 95% CI, 0.68–0.97), and a significant reduction in endometrial cancer risk emerged (RR = 0.67; 95% CI, 0.49–0.91). For estrogen alone, the reduction in breast cancer risk became statistically significant (RR = 0.79; 95% CI, 0.65– 0.97) during a median cumulative 13-year follow-up period (6.8 years of treatment plus 6.6 years of postintervention observation), and signif­ icant differences by age group persisted for total myocardial infarction and the global index, with more favorable results for younger women. During a median cumulative 18-year follow-up, estrogen alone was Menopause and Postmenopausal Hormone Therapy CHAPTER 407 3.0 –0.5 –0.5 –5.0 –5.5 –12.0 –2.5 –1.5 –4.0 –8.0 –5.5 –13.0

associated with a significant reduction in all-cause mortality in women aged 50–59 years (RR = 0.79; 95% CI, 0.64–0.96); the protective effect was seen primarily in those with bilateral oophorectomy (RR = 0.68; 95% CI, 0.48–0.96). During a median cumulative 20-year follow-up, estrogen-progestin was associated with a significant elevation in breast cancer risk (RR = 1.28; 95% CI, 1.13–1.45) and a suggestive elevation in breast cancer mortality (RR =1.35; 95% CI, 0.94–1.95; p = .11), whereas estrogen alone was associated with a significant reduction in breast cancer risk (RR = 0.78; 95% CI, 0.65–0.93) and breast cancer mortality (RR = 0.60; 95% CI, 0.37–0.97).

APPROACH TO THE PATIENT Postmenopausal HT PART 12 Endocrinology and Metabolism The rational use of postmenopausal HT requires balancing the potential benefits and risks. Table 407-2 provides one approach to decision-making. This approach applies to women with meno­ pausal symptoms who are age 45 years and older or to women who have had removal of both ovaries, regardless of age. Women below age 45 years or those with uncertain menopausal status may need additional clinical evaluation before determining a management plan. The clinician should first assess whether the patient has moderate to severe hot flashes and/or night sweats—the primary indication for initiation of systemic HT—that do not subside in response to behavioral/lifestyle modifications, such as lowering the thermostat, dressing in layers, avoiding warm beverages, and not smoking. Systemic HT may also be used to prevent osteoporo­ sis in women at high risk of fracture who cannot tolerate alterna­ tive osteoporosis therapies. (Vaginal estrogen or other medications may be used to treat genitourinary syndrome of menopause in the absence of vasomotor symptoms [see later].) The benefits and risks of such therapy should be reviewed with the patient, giving more emphasis to absolute than to relative measures of effect and TABLE 407-2  Approach to Initiating Menopausal Hormone Therapy for Vasomotor Symptom Management

  1. Vasomotor symptom assessment   Confirm that hot flashes and/or night sweats are adversely affecting sleep, daytime functioning, or quality of life.
  2. Risk factor assessment   Confirm that there are no absolute contraindications to menopausal hormone therapy     Breast, endometrial, or other estrogen-dependent cancer     Cardiovascular disease (heart disease, stroke, transient ischemic attack)     Active liver disease     Undiagnosed vaginal bleeding
  3. Menopausal hormone therapy initiation CONSIDER WITH CAUTION AVOID RECOMMEND Age <60 years and Menopause onset within 10 years and Low risk of breast cancera and cardiovascular diseaseb Age ≥60 years • • • • • • • OR • • • • • • • Menopause onset

10 years prior • • • • • • • OR • • • • • • • Moderate risk of breast cancera High risk of breast cancera or cardiovascular diseaseb • • • • • • • • • OR • • • • • • • • • Age ≥60 years or menopause onset >10 years prior and Moderate risk of breast cancera or cardiovascular diseaseb or cardiovascular diseasea aFor online tools to assess breast cancer risk, see AH McClintock et al: Breast cancer risk assessment: A step-wise approach for primary care providers on the front lines of shared decision making. Mayo Clin Proc 95:126, 2020. bFor online tools to assess cardiovascular disease risk, see D Lloyd-Jones et al: Use of risk assessment tools to guide decision-making in the primary prevention of atherosclerotic cardiovascular disease: A special report from the American Heart Association and American College of Cardiology. Circulation 139:e1162, 2019. Source: Adapted from JL Shifren et al: JAMA 2019; 321:2458-2459.

pointing out uncertainties in clinical knowledge where relevant. Because chronic disease rates generally increase with age, absolute risks tend to be greater in older women, even when RRs remain similar. Potential side effects—especially vaginal bleeding that may result from use of the combined estrogen-progestogen formula­ tions recommended for women with an intact uterus—should be noted. The patient’s own preference regarding therapy should be elicited and factored into the decision. Contraindications should be assessed routinely and include unexplained vaginal bleeding; liver dysfunction or disease; venous thromboembolism; known blood clotting disorder or thrombophilia (transdermal estrogen may be an option); untreated hypertension; history of endometrial cancer (except stage 1 without deep invasion), breast cancer, or other estrogen-dependent cancer; and history of CHD, stroke, or transient ischemic attack. Relative contraindications to sys­ temic HT include an elevated risk of breast cancer (e.g., women who have one or more first-degree relatives with breast cancer, susceptibility genes such as BRCA1 or BRCA2, or a personal history of cellular atypia detected by breast biopsy); hypertriglyc­ eridemia (>400 mg/dL); an elevated risk of cardiovascular disease; and active gallbladder disease (transdermal estrogen may be an option in the latter three cases because it has a less adverse effect on triglyceride levels, clotting factors, and inflammation factors than oral HT). Primary prevention of heart disease should not be viewed as an expected benefit of HT, and an increase in the risk of stroke as well as a small early increase in the risk of coronary artery disease should be considered. Nevertheless, such therapy may be appropriate if the noncoronary benefits of treatment clearly outweigh the risks. Reassess benefits and risks at least once every 6–12 months, assuming the patient’s continued preference for HT, or if the patient’s health status changes. A woman who suffers an acute coronary event or stroke while taking HT should discontinue therapy immediately. Many options for systemic HT are available. Estrogen alone is recommended for women with hysterectomy, whereas estrogen plus progestogen is recommended for women with a uterus. In the United States, the most commonly prescribed oral estrogens for systemic treatment of vasomotor symptoms are 17β-estradiol (1.0 or 0.5 mg/d or other doses) and conjugated equine estrogens (CEE; 0.625, 0.45, or 0.3 mg/d or other doses). The most commonly prescribed transdermal estrogen products are 17β-estradiol skin patches (0.035 or 0.05 mg/d or other doses). The most commonly prescribed progestogens are medroxyprogesterone acetate (MPA; 2.5, 5, or 10 mg/d) and micronized progesterone (100 or 200 mg/d). Also available are oral estrogen-progestin combinations, such as oral CEE and MPA, oral 17β-estradiol or ethinyl estradiol with norethindrone acetate, oral estradiol with progesterone, and other options. CEE/bazedoxifene may be an option for women with a uterus, especially those with concerns about breast tenderness, breast density, or uterine bleeding. Contraindications to CEE/baze­ doxifene are similar to those for systemic HT. Short-term use (<5 years for estrogen-progestogen and <7 years for estrogen alone) is appropriate for relief of menopausal symp­ toms among women without contraindications to such use. How­ ever, such therapy should be avoided by women with an elevated baseline risk of future cardiovascular events. Women who have contraindications for or are opposed to HT may derive benefit from the use of certain antidepressants (including paroxetine, mesylate, venlafaxine, fluoxetine, and others), fezolinetant, gabapentin, or oxybutynin. Long-term use (≥5 years for estrogen-progestogen and ≥7 years for estrogen alone) is more problematic because a heightened risk of breast cancer must be factored into the decision, especially for estrogen-progestogen. Reasonable candidates for such use include postmenopausal women who have persistent severe vasomotor symptoms along with an increased risk of osteoporosis (e.g., those with osteopenia, a personal or family history of nontraumatic fracture, or a weight <125 lb), who also have no personal or

23 - 408 Infertility and Contraception

408 Infertility and Contraception

family history of breast cancer in a first-degree relative or other contraindications, and who have a strong personal preference for therapy. Poor candidates are women with elevated cardiovascular risk, those at increased risk of breast cancer, and those at low risk of osteoporosis. Even for reasonable candidates, strategies to mini­ mize dose and duration of use should be employed. For example, women using HT to relieve intense vasomotor symptoms in early postmenopause should consider discontinuing therapy within

5 years, resuming it only if such symptoms persist. Because of the role of progestogens in increasing breast cancer risk, regimens that employ cyclic rather than continuous progestogen exposure as well as formulations other than MPA should be considered if treatment is extended. For prevention of osteoporosis, alternative therapies such as bisphosphonates or SERMs should be considered. Research on alternative progestogens and androgen-containing preparations has been limited, particularly with respect to long-term safety. Additional research on the effects of these agents on cardiovascular disease, glucose tolerance, and breast cancer will be of particular interest. For genitourinary symptoms such as vaginal dryness or pain with intercourse/sexual activity, intravaginal estrogen creams, tablets, or rings; prasterone (vaginal dehydroepiandrosterone); and ospemi­ fene are options. Contraindications to low-dose vaginal estrogen include unexplained vaginal bleeding or breast cancer, endometrial cancer, or other estrogen-dependent cancer. Contraindications to ospemifene and prasterone are the same as those for low-dose vaginal estrogen, and contraindications for ospemifene additionally include venous or arterial thromboembolic disease, severe liver dis­ ease, and use of estrogens or estrogen agonists-antagonists. In addition to HT, lifestyle choices such as smoking abstention, adequate physical activity, and a healthy diet can play a role in con­ trolling symptoms and preventing chronic disease. An expanding array of pharmacologic options (e.g., bisphosphonates, SERMs, and other agents for osteoporosis; cholesterol-lowering or antihyper­ tensive agents for cardiovascular disease) should also reduce the widespread reliance on hormone use. However, short-term HT may still benefit some women. ■ ■FURTHER READING Bassuk SS, Manson JE: Menopausal hormone therapy and cardiovas­ cular disease risk: Utility of biomarkers and clinical factors for risk stratification. Clin Chem 60:68, 2014. Chlebowski RT et al: Association of menopausal hormone therapy with breast cancer incidence and mortality during long-term follow-up of the Women’s Health Initiative randomized clinical trials. JAMA 324:369, 2020. Crandall CM et al: Management of menopausal symptoms: A review. JAMA 329:5, 2023. Duralde ER et al: Management of perimenopausal and menopausal symptoms. BMJ 382:e072612, 2023. Manson JE, Bassuk SS: Hot Flashes, Hormones and Your Health. New York, McGraw-Hill, 2007. Manson JE et al: Menopausal hormone therapy and health outcomes during the intervention and extended poststopping phases of the Women’s Health Initiative randomized trials. JAMA 310:1353, 2013. Manson JE et al: The Women’s Health Initiative trials of menopausal hormone therapy: Lessons learned. Menopause 27:918, 2020. North American Menopause Society: The 2020 genitourinary syndrome of menopause position statement of the North American Menopause Society. Menopause 27:976, 2020. North American Menopause Society: The 2022 hormone therapy position statement of the North American Menopause Society. Menopause 29:767, 2022. Shifren JL et al: Menopausal hormone therapy. JAMA 321:2458, 2019.

Anuja Dokras, Janet E. Hall

Infertility and

Contraception INFERTILITY The World Health Organization (WHO) categorizes infertility as a disease of the reproductive system. Infertility is the third most com­ mon disease worldwide, affecting ~48–72 million couples. It is defined as the inability to achieve a pregnancy over 12 months of unprotected intercourse. The prevalence of infertility, ~17.5% globally, has remained relatively stable over the past few decades. Primary infertility occurs in couples who have never achieved a pregnancy, whereas secondary infer­ tility refers to infertility after achieving at least one pregnancy. During the first year of attempting pregnancy, the fecundability rate, defined as the ability to achieve a pregnancy within one menstrual cycle, is highest in the first 3 months and declines over the next 9 months. Approximately 85% of couples will achieve pregnancy after 12 months, and 95% will achieve pregnancy after 24 months. Increasing trends toward later child­ bearing can have significant implications due to age-related decrease in the fecundability rate. Compared to women aged 30–31 years of age, fecundability is reduced by 14% in women aged 34–35 years, 19% in women aged 36–37 years, 53% in women aged 40–41 years, and 59% in women aged 42–44 years. Infertility and Contraception CHAPTER 408 ■ ■ETIOLOGY The causes for infertility are generally classified as female factors, male factors, and unexplained infertility (Fig. 408-1). The female causes include tubal factors (pelvic inflammatory disease, endometriosis, prior surgery, salpingitis isthmica nodosum), uterine etiology (fibroids, congenital malformations, uterine scarring), ovulatory dysfunction (polycystic ovary syndrome [PCOS], diminished ovarian reserve, pre­ mature ovarian insufficiency), and endocrine dysfunction (hypothy­ roidism, hyperprolactinemia). Although the probability of achieving a pregnancy decreases after the age of 35 in women, primarily due to chromosomal abnormalities in the oocyte during meiosis, a similar decline has not been observed in men <50 years of age. The male causes of infertility include anatomic factors in the reproductive system (vasectomy, infection, absence of the vas), endocrine factors (hypogo­ nadotropic hypogonadism, hypothyroidism, hyperprolactinemia, mor­ bid obesity, use of certain medications), sexual dysfunction (erectile or ejaculatory dysfunction, decreased libido), and genetic factors con­ tributing to primary testicular dysfunction, including defects in sper­ matogenesis (Klinefelter’s syndrome, Y chromosome microdeletions). The distribution of these causes varies significantly across the world. Overall, female factors are present in 30–40% of couples with infertility, male factors are present in 40–50%, and both male and female factors are identified in 20–30%. Unexplained infertility refers to the absence of any identified abnormality after completing the fertility workup and occurs in up to 30% of couples. As a result, a complete workup of both partners is recommended in all couples presenting with infertility. ■ ■FERTILITY EVALUATION Diagnostic evaluation for infertility is typically initiated after 1 year of unprotected intercourse because 80–85% of couples will achieve a pregnancy over this time period. Evaluation can be initiated even prior to meeting the definition of infertility, especially if one of the partners has risk factors for infertility. If the female partner’s age is

35 years, it is recommended to initiate evaluation after 6 months of attempting pregnancy. If the age of the female partner is >40 years, it is recommended to start evaluating the couple immediately. The initial evaluation should include detailed medical history, laboratory testing, radiologic evaluation, and preconception counseling for both partners. As multiple causes for infertility may be identified, it is best to perform the complete diagnostic evaluation prior to initiating treatment.

Causes of infertility 12–15% of reproductive aged women Unexplained 15–30% Male causes 40–50% Female causes 30–40% Endocrine Anatomic Testicular defects/ genetic PART 12 Endocrinology and Metabolism Uterine Other Tubal Ovulatory dysfunction Endocrine FIGURE 408-1  Causes of infertility. History and Physical Exam  A detailed history obtained from both partners is essential to identify risk factors for infertility. In the female partner, gynecologic history (menstrual frequency, menorrhagia, dys­ menorrhea, history of sexually transmitted infections, endometriosis), medical and endocrine history, exposure to pelvic radiation, abdominal or pelvic surgeries, tobacco and alcohol use, medication use including cytotoxic drugs, family history of early menopause, and prior history of pregnancy should be assessed. In addition, frequency of intercourse, timing of intercourse, use of methods to detect ovulation, and concerns regarding sexual dysfunction over the past several months should be ascertained. Physical exam in the female partner should include assess­ ment of weight and blood pressure (BP), thyroid and breast exam, assessment for signs of hyperandrogenism, and pelvic exam to assess uterine size, adnexal masses, and factors that might impact intercourse. Similarly, a detailed history should be obtained in the male partner with specific questions regarding injuries and surgery in the reproductive tract; mumps orchitis; exposure to pelvic radiation; use of androgens, cytotoxic drugs, and other medications; and fertility with any prior partner. The exam in the male partner should include body mass index (BMI), BP, and complete physical exam including testicular exam. Ultrasound  An abdominal and transvaginal pelvic ultrasound can assess uterine (myomas, adenomyosis, müllerian anomalies) and adnexal abnormalities (endometriosis, polycystic-appearing ovaries) and evalu­ ate ovarian reserve (number of antral follicles in both ovaries). Ovulation Assessment  Women who have regular menstrual cycles between 25 and 35 days will typically have ovulatory cycles. Ovulation can be assessed by using ovulation detection strips at home to detect urinary luteinizing hormone (LH) or by measuring a serum progesterone level 7 days after ovulation. Basal body temperatures can also be used to confirm ovulation when a rise in temperature is noted in the luteal phase. However, basal body temperature measurements are less reliable than the above methods. Hysterosalpingogram  An hysterosalpingogram (HSG) is per­ formed during the follicular phase to assess the patency of fallopian tubes by injecting radiopaque contrast through the cervix into the uterus and imaging the flow of contrast through one or both tubes. In addition to identifying tubal pathology, an HSG may identify intrauter­ ine abnormalities such as polyps, submucosal myomas, and adhesions. Although the negative predictive value of HSG for assessing tubal patency is high, the positive predictive value is relatively low. Interest­ ingly, pregnancy rates have been shown to be higher after an HSG test compared to no testing and higher when oil-based contrast was used compared to water-based contrast, likely related to tubal flushing of mucus plugs. Alternate options that are increasingly used include injection of agitated saline contrast through the cervix into the uterus. Tubal patency is assessed by demonstrating passage of agitated saline

Unknown contrast through the tubes or accumulation in the cul de sac as visual­ ized by ultrasonography. A saline infusion sonogram is more accurate in assessing intrauterine pathology such as polyps and intrauterine scarring compared to HSG and can be combined with ultrasound assessment of the pelvis. Ovarian Reserve Evaluation  Assessment of ovarian reserve includes measurement of serum FSH and estradiol on day 2 or 3 of the menstrual cycle and serum anti-müllerian hormone (AMH). These screening tests combined with age of the female partner and antral fol­ licle counts measured by ultrasound can identify diminished ovarian reserve and provide information on the urgency to initiate treatment. AMH and antral follicle counts are also used to determine starting doses of gonadotropins for fertility treatments. These markers of ovar­ ian reserve, however, do not predict the likelihood of pregnancy and live birth. Endocrine Tests  In women with irregular menses, serum TSH, prolactin, and androgens (total and free testosterone) should be mea­ sured to identify other causes for anovulation. Semen Analysis (see Chap. 403)  The semen sample is collected after 2–7 days of abstinence and provides an assessment of sperm count, motility, morphology, volume, and pH. None of the individual sperm parameters are predictive of fertility, but the likelihood of infertility increases with multiple abnormalities. Those with abnormal sperm parameters based on the WHO criteria (oligoasthenozoosper­ mia is defined as sperm counts <15 million/mL, motility <40%, and normal morphology <4%) should have a physical exam and endocrine evaluation (serum follicle-stimulating hormone [FSH], LH, prolactin, and thyroid-stimulating hormone [TSH]); those with azoospermia or severe oligospermia (<5 million/mL) should have genetic evalua­ tion (karyotype and Y chromosome microdeletion). Although a DNA sperm fragmentation assay is not part of the initial evaluation, it may be indicated in patients with recurrent pregnancy loss. Sperm antibody testing and scrotal ultrasound should not be routinely performed in infertile men. Genetic Screening  All couples can be offered preconception genetic screening based on ethnicity, family history, or common auto­ somal recessive conditions. Of note, diagnostic laparoscopy, postcoital test, endometrial biopsy, thrombophilia, and immunologic testing and karyotype are not indi­ cated as part of the initial workup of infertility. ■ ■COUNSELING AND TREATMENT Preconception Counseling  All patients seeking fertility care should be provided with preconception counseling to identify modifi­ able risks and optimize pregnancy outcomes. This includes counseling

about eating disorders or lifestyle modifications for weight manage­ ment as obesity in women is associated with an increase in anovulatory cycles, miscarriage rates, and maternal and fetal complications in preg­ nancy. Obesity in men is associated with abnormal sperm parameters. Preconception counseling regarding smoking cessation is important as evidence suggests that smoking cessation can reverse the detrimental impact of smoking on fecundity. Smoking decreases fertility rates by a direct impact on oocyte DNA and also increases the risk of miscar­ riage and ectopic pregnancy. In addition, smoking during pregnancy is associated with an increased risk of placental abruption and intrauter­ ine growth restriction (IUGR). Moreover, the impact of smoking on ovarian reserve has been shown to accelerate the time to menopause by 1–4 years. As high levels of caffeine consumption increase the risk of infertility and miscarriage, women should be counseled to restrict caffeine consumption to ≤2 cups while attempting pregnancy and during pregnancy. Use of testosterone products, which are widely used for the treatment of hypoandrogenism and sexual dysfunction in men, should be stopped. Inquiries should be made about possible misuse of androgens for physical appearance or performance enhancement (Chap. 411). As part of the preconception counseling, patients should be informed that the fertile window is typically 5–6 days prior to ovula­ tion, and therefore, intercourse every 1–2 days during this time period will increase the chance of pregnancy. Various methods are used by women to detect ovulation, including basal body temperature measure­ ments, assessment of changes in cervical mucus, and urinary LH kits. A rise in basal body temperatures indicates that ovulation has occurred and therefore cannot be used to time intercourse. LH kits can be used to detect the start of ovulation and subsequently time intercourse on the day of the LH surge and the following day. Physicians should coun­ sel patients that advanced maternal age (>35 years) is associated with a higher risk of aneuploidy and advanced paternal age (>40 years) is associated with adverse health outcomes in the offspring. Treatment  Treatment recommendations depend on the results of the fertility evaluation described above (Table 408-1). The success of different treatments depends on several factors including age of the female partner, assessment of ovarian reserve, history of smoking, BMI, and race. Tubal Factor Infertility  Tubal factor infertility constitutes 30–35% of cases of female infertility, and a large majority are second­ ary to tubal obstruction resulting from sexually transmitted infections. In vitro fertilization (IVF) was first developed as a treatment for tubal factor infertility as it bypasses the fallopian tubes and allows fertiliza­ tion of oocytes in the laboratory prior to transcervical transfer into the uterus. IVF offers the highest success rates for couples with tubal factor infertility. Tubal repair or reconstruction is typically not recommended in cases associated with tubal infections or hydrosalpinx, due to both TABLE 408-1  Assisted Reproductive Technologies Ovulation induction   Oral agents   Injectable hormones Clomiphene citrate (selective estrogen response modulator) Letrozole (aromatase inhibitor) FSH, LH (gonadotropins) Intrauterine insemination (IUI) Office-based procedure by which washed and concentrated ejaculated sperm is deposited in the uterine cavity via a soft catheter passed through the cervix In vitro fertilization (IVF) Oocytes are harvested transvaginally under local anesthesia or intravenous sedation and incubated with sperm to facilitate fertilization. The fertilized embryos are cultured for 3 days (cleavage stage) or 5 days (blastocyst stage) prior to transcervical placement of one or more embryos, depending on the age of the female patient, into the uterine cavity under ultrasound guidance. Intracytoplasmic sperm injection (ICSI) In cases of severe male factor infertility, a single motile morphologically normal appearing sperm is injected into the oocyte for potential fertilization. Abbreviations: FSH, follicle-stimulating hormone; LH, luteinizing hormone.

the low success rate in achieving tubal patency and increased risk of ectopic pregnancy. In fact, removal of hydrosalpinges by salpingec­ tomy will improve pregnancy rates in subsequent IVF treatments as it prevents efflux of tubal fluid into the uterine cavity. If a proximal tubal blockage is observed on HSG, radiographically guided cannulation of fallopian tubes can be attempted. In women with bilateral tubal liga­ tion, the decision between microsurgical reanastomosis versus IVF will depend on a number of factors including patient’s age, ovarian reserve, number of children desired, partner’s semen parameters, experience of the surgeon, and cost of procedure.

Infertility and Contraception CHAPTER 408 Ovulatory Dysfunction  Endocrine conditions such as hypo­ thyroidism and hyperprolactinemia should be treated prior to use of ovulation induction medications. Lifestyle modifications should be recommended in patients with low BMI or obesity. Weight loss in obese women has been shown to increase the likelihood of spontaneous or drug-induced ovulation. First-line treatment for anovulatory infertility (most common etiology is PCOS) includes use of letrozole followed by clomiphene citrate to induce ovulation (Chap. 406). A large majority of women with PCOS (60–80%) respond to these oral medications, and the addition of metformin, combined with the above medications as a second-line agent, may further increase the chance of ovulation, particularly in obese women. In women with hypothalamic amenor­ rhea, behavioral modifications such as weight gain and decreased exercise may resume ovulation. If there is no response, judicious use of low-dose injectable gonadotropins can induce monofollicular growth. In women with diminished ovarian reserve, treatment can be esca­ lated from ovulation induction with oral medications and intrauterine insemination (IUI) to IVF, as the overall live birth rates are lower. In both women with diminished ovarian reserve and women with pre­ mature ovarian insufficiency, the option of using donor oocytes can be offered. In that case, the egg donor will undergo the IVF procedure, the harvested eggs are fertilized with the male partner’s sperm, and the fertilized embryos will be transferred to the patient’s uterus. Male Infertility  Given the high prevalence of male factor infertil­ ity (40–50%), timely evaluation and treatment are recommended. Men with abnormal semen parameters have associated health risks and should have a detailed evaluation by specialists in male reproduction. In men with no sperm (azoospermia) in the ejaculate, further evaluation including a repeat semen analysis followed by physical examination, endocrine tests, and genetics studies should be performed to identify obstructive (40% prevalence) versus nonobstructive etiology. First-line treatment for mild to moderate male factor infertility includes IUI alone or IUI combined with ovulation induction, depending on the female partner’s age and other causes of infertility. In men with severe male factor infertility (sperm count <5 million/mL or motility <20%), IVF with intracytoplasmic sperm injection (ICSI) is recommended. In men with obstructive azoospermia, sperm can be procured by direct aspiration from the epididymis or testis. In men with congenital bilateral absence of the vas deferens (CBAVD), testing for CFTR muta­ tions and genetic counseling are indicated before to offering IVF with ICSI. In men with nonobstructive azoospermia, microsurgical sperm retrieval from the testes may result in successful pregnancies after IVF-ICSI; however, the use of donor sperm for IUI is an alternate option. Men with hypogonadotropic hypogonadism (e.g., Kallmann’s syndrome) can be treated with gonadotropins to initiate spermatogen­ esis followed by IUI or IVF. Treatment of male sexual dysfunction and avoidance of exogenous androgens are effective strategies for address­ ing male factor infertility. Repair of a moderate to large varicocele is recommended when associated with abnormal semen parameters or if the patient is symptomatic from the varicocele; however, it may take several months to detect an improvement in semen parameters. Unexplained Infertility  In 15–30% of couples, no clear causes of infertility are identified. In such cases, it is appropriate to initiate ovarian stimulation with oral medications to increase the number of developing oocytes combined with IUI timed to ovulation in order to increase the number of motile sperm in the reproductive tract. Depending on the age of the female partner, this approach offers

modest success rates limiting its use to 3–6 months before recommend­ ing IVF. Overall, IVF is associated with a low risk of complications; the risk of ovarian hyperstimulation syndrome is significantly decreased by judiciously monitoring stimulation and using gonadotropin-releasing hormone (GnRH) to trigger ovulation instead of human chorionic gonadotropin (hCG). Multiple pregnancy remains the highest risk associated with IVF despite improvements in cryopreservation of embryos and age-based guidelines for limiting the number of embryos to transfer. In some couples, the IVF treatment may reveal an underly­ ing cause of infertility such as lower fertilization, embryo cleavage, or blastocyst formation rates. Of note, guidelines from different medical societies around the world vary in the rapidity of offering IVF for unexplained infertility.

PART 12 Endocrinology and Metabolism Uterine Factors  Fibroids are the most common benign tumors of the reproductive tract and occur in 50–70% of reproductive-age women. It is not clear whether fibroids decrease the likelihood of pregnancy; submucosal fibroids and intramural fibroids that distort the endometrial cavity may lower pregnancy rates and increase the risk of pregnancy loss. Removal of submucosal fibroids, uterine polyps, and intrauterine adhesions hysteroscopically may improve subsequent pregnancy rates. Endometriosis  Endometriosis is a common gynecologic condition associated with pelvic pain and dysmenorrhea, and in severe cases, it is associated with tubo-ovarian infertility. Approximately 25–50% of infertile women have endometriosis, and 30–50% of women with endometriosis have infertility. Prolonged medical management to suppress endometriotic lesions and surgical treatment of stage 1 and 2 endometriosis have not been shown to improve subsequent fertility rates. Surgical removal of endometriotic lesions or endometriomas in women with stage 3 or 4 endometriosis may improve subsequent pregnancy rates. First-line treatment of infertility associated with endometriosis alone includes use of oral ovulation induction medica­ tions and IUI. ■ ■PSYCHOLOGICAL ASPECTS OF INFERTILITY It is well recognized that infertility is associated with psychological stress related not only to the diagnostic and therapeutic procedures themselves but also to repeated cycles of hope and loss associated with each new procedure or cycle of treatment that does not result in the birth of a child. These feelings are often combined with a sense of isolation from friends and family. Counseling and stress-management techniques should be offered early in the evaluation of infertility as many patients do not pursue treatments after the initial consultation. Importantly, infertility and its treatment do not appear to be associated with long-term psychological sequelae. CONTRACEPTION The desired ideal number of children per family varies around the globe and is approximately 2.6 in the United States. Couples not using any form of contraception have an 85% chance of achieving a pregnancy over 1 year. Based on these data, couples spend most of their reproductive life preventing a pregnancy and a much smaller proportion attempting to become or being pregnant. It is therefore not surprising that a majority of women who have been sexually active will have used some form of contraception to prevent a pregnancy. Unin­ tended pregnancies primarily occur due to lack of use or inconsistent use of contraceptives rather than failure of the contraceptive method used. Of the different forms of contraception used worldwide in 2022, tubal sterilization was the most common (~219 million) followed by use of male condom (208 million), intrauterine device (IUD) (161 mil­ lion), and the (birth control) pill (150 million). Contraceptive methods used by married women differ from those used by single women, and the most widely used contraceptive methods differ by world regions. The rates of female sterilization increased steadily in the last century and now show a slight decrease, likely due to the increasing use of long-acting reversible contraceptive (LARC) agents, such as IUDs and implants, which are as effective as sterilization. The convenience of use of contraceptives determines their compliance and efficacy;

TABLE 408-2  U.S. Medical Eligibility Criteria (USMEC) for Contraceptive Use USMEC Category 4 (a condition that represents an unacceptable health risk if the contraceptive method is used) Smoking: women age ≥35 years who smoke ≥15 cigarettes per day Known ischemic heart disease or multiple risk factors for cardiovascular disease (older age, smoking, diabetes, low HDL, high LDL, high triglycerides, and hypertension) Acute DVT Previous thromboembolic event; high risk of recurrent DVT Stroke or known thrombogenic mutations Complicated valvular heart disease Peripartum cardiomyopathy (<6 months, moderately to severely impaired cardiac function) Complicated solid organ transplantation Hypertension (systolic ≥160 mmHg or diastolic ≥100 mmHg, vascular disease) Systemic lupus erythematous (positive or unknown antiphospholipid antibodies) Cirrhosis, hepatocellular adenoma or hepatoma (malignant) Viral hepatitis, acute flare Pregnancy and early postpartum (<21 days) Breast-feeding <21days postpartum Breast cancer Diabetes: neuropathy/retinopathy/nephropathy Migraines with aura USMEC Category 3 (a condition for which the theoretical or proven risks outweigh the advantages for using the method) Smoking: women ≥35 years who smoke <15 cigarettes/day Previous thromboembolic event; lower risk of recurrent DVT Superficial thrombosis (acute or history of) Past history of breast cancer and no evidence for 5 years Hypertension (adequately controlled or systolic 140–159 mmHg or diastolic 90–99 mmHg) Anticonvulsant drug therapy (certain anticonvulsants (phenytoin, carbamazepine, barbiturates, primidone, topiramate, oxcarbazepine) Antimicrobial therapy: rifampin or rifabutin Antiretroviral therapy for prevention (preexposure prophylaxis) or treatment of HIV Bariatric surgery (Roux-en-Y gastric bypass or biliopancreatic diversion) Breast-feeding 21–42 days postpartum with or without risk factors for VTE Abbreviation: DVT, deep-vein thrombosis; HDL, high-density lipoprotein; LDL, lowdensity lipoprotein; VTE, venous thromboembolism. contraceptives requiring daily and coitus-related use have higher fail­ ure rates compared to long-acting reversible and permanent methods. The U.S. Medical Eligibility Criteria (USMEC) for contraceptive use are evidence-based guidelines to help health care providers recom­ mend appropriate contraceptives to women with chronic medical conditions (Table 408-2). This excellent resource is adapted from the WHO guidance and is kept up to date through continual review of published literature. ■ ■TYPES OF CONTRACEPTION These can be classified in a number of ways, such as permanent versus reversible, hormonal versus nonhormonal, or barrier versus nonbarrier (Table 408-3). Permanent Contraception  The permanent forms of contracep­ tion include tubal sterilization and vasectomy. Male sterilization has declined globally with a rate of <2% in 2022. Vasectomy is a low-risk procedure typically performed in an outpatient setting with a very low failure rate of 0.1 pregnancies per 100 women per year. It is not immediately effective, and patients should be told to use other forms of contraception for a minimum of 3 months after the procedure. Glob­ ally, tubal sterilization rates have also declined steadily and represent 23% of all methods. Tubal sterilization can be performed in the post­ partum period or as an interval procedure and has a failure rate of 0.5 pregnancies per 100 women per year. Postpartum sterilization can be

TABLE 408-3  Effectiveness of Different Forms of Contraception THEORETICAL EFFECTIVENESS (%) ACTUAL EFFECTIVENESS (%) METHOD OF CONTRACEPTION No method

34.7 Fertility awareness

1.2 Withdrawal

4.4 Barrier methods           Condoms

8.4   Diaphragm

Spermicides

Sterilization           Female 99.5 99.5

18.1   Male 99.5 99.9

5.6 Intrauterine device       10.4   Copper T 99.4 99.8

  Progestin-containing 99.8 99.8

Hormonal contraceptives           Combined and progestin only 99.7

  Transdermal patch 99.7

0.5   Vaginal ring 99.7

1.8 Implant       3.1   Depo-Provera 99.8

  Subdermal implant 99.5 99.5

Emergency contraception

Sources: Data from J Trussell et al: Contraceptive Efficacy, in Contraceptive Technology, 20th revised ed. RA Hatcher et al (eds). New York, Ardent Media, 2011; CDC. NCHS National Survey of Family Growth, 2011-2013; J Jones et al: Current contraceptive use in the United States, 2006-2010, and changes in patterns of use since 1995. Natl Health Stat Report 60:1, 2012; and NE Birgisson et al: Preventing unintended pregnancy: The contraceptive CHOICE project in review. J Womens Health (Larchmt) 24:349, 2015. Current Contraceptive Status Among Women Aged 15–49: United States, 2017–2019 NCHS Data Brief No. 388, October 2020. Available at: https://www.cdc.gov/nchs/ products/databriefs/db388.htm. performed during a cesarean section or after a vaginal delivery via minilaparotomy. Interval procedures can be performed laparoscopically or via mini-laparotomy and include partial or complete salpingectomy or occlusion of the fallopian tubes using electrocoagulation or mechanical devices such as clips. These permanent methods of contraception are highly effective as they avoid the need for user-dependent contracep­ tion. All patients should undergo preprocedure counseling regarding risk of failure, permanence of the procedure, regret, and alternatives. Hormonal Contraceptives  •  COMBINED ESTROGEN- AND PROGESTIN-CONTAINING CONTRACEPTIVES  The mechanism of action of the hormonal contraceptives involves negative feedback from continuous estrogen administration, thereby decreasing FSH secre­ tion, follicular development, and formation of a dominant follicle. The continuous progestin suppresses LH secretion and inhibits ovulation, alters endometrial receptivity, thickens the cervical mucus, and impairs tubal motility. These hormones can be delivered via oral pills to be taken daily, as a transdermal patch that is changed weekly, or a vaginal ring that is replaced monthly or annually. There are numerous pills available containing different doses of estrogen (<50 μg) and types of estrogen and progestins and varying doses within a pack (monophasic vs multiphasic); the pills can be taken in a cyclic or extended cycle schedule. The contraceptive efficacy is similar with varying doses of estrogen and progestin. Decreasing the duration of hormone-free days may decrease some side effects associated with menses, such as men­ strual migraines and dysmenorrhea. The overall failure rate for com­ bined hormonal contraceptives is 8 pregnancies per 100 women per year, although compliance with daily use of pills may be lower, affecting efficacy. The contraceptive patch and vaginal ring have higher compli­ ance compared to daily pills. Use of the contraceptive patch is associ­ ated with a low risk of skin reactions and a lower efficacy in women weighing >90 kg. The transdermal mode of delivery is associated with a higher steady state comparable to that of a 40-μg ethinyl estradiol oral contraceptive. Hormonal contraceptives offer additional benefits such as regulation of menstrual cycles; suppression of ovarian cysts; and decrease in menorrhagia, dysmenorrhea, and hyperandrogenism

CONTINUED USE AT 1 YEAR (%) USE OF CONTRACEPTIVE METHOD BY U.S. WOMEN AGE 15–49 (%) Infertility and Contraception CHAPTER 408 symptoms; in addition, they reduce the risk of both endometrial (50% reduction) and ovarian cancer (40% reduction). Common side effects include nausea, breast tenderness, bloating, and intermenstrual bleeding. There may be a mild increase in BP in some patients, and it is recommended to check BP at follow-up visits. In large studies and meta-analyses, hormonal contraceptives are not associated with sig­ nificant weight gain, mood changes, or effect on libido. Prior to admin­ istering hormonal contraceptives, a detailed patient history should be obtained to determine any absolute or relative contraindications to their use. Due to the low but slightly increased risk of deep-vein throm­ bosis (DVT) associated with estrogen-containing hormonal contracep­ tives (3–15 per 10,000 women-years), they are contraindicated in the immediate postpartum period, in smokers over the age of 35 years, and in women with a history of hereditary thrombophilias or DVT. The association between risk of DVT and different doses of estrogen (ethi­ nyl estradiol <35 μg) or different routes of administration (transdermal patch) is weak. There is, however, some association between third- and fourth-generation progestins and increased risk of DVT. Routine screening for familial thrombotic disorders is not recommended prior to prescribing hormonal contraceptives. Although obesity is associated with decreased fertility, the vast majority of women with obesity do not experience infertility. The USMEC classifies obesity alone as risk category 2, where the benefits of taking hormonal contraceptives out­ weigh any theoretical risk. PROGESTIN-ONLY HORMONAL CONTRACEPTION  Different types of progestins are used for contraception in oral pills, injectable forms, subdermal implants, and IUDs and may be an option for women who have contraindications to the use of estrogen-containing contracep­ tives (e.g., migraine with aura, DVT, stroke, breast-feeding). The failure rate with progestin-only pills is 9 pregnancies per 100 women per year, whereas the failure rate of progestin IUDs is 0.1 pregnan­ cies per 100 women per year. In addition to acting as a spermicidal, the levonorgestrel IUD also thickens the cervical mucus and thins the endometrium, thereby decreasing its receptivity. The common side effects include irregular bleeding, acne, breast tenderness, and pain,

with higher rates of expulsion when IUDs are inserted in the immedi­ ate postpartum period. Breakthrough bleeding or unscheduled bleed­ ing is commonly reported, as estrogen usually serves to stabilize the endometrial lining and prolonged exposure to progestin alone results in a thinner decidualized lining. Depending on the device used, the progestin IUD is effective for 3–7 years. The injectable form of proges­ terone (medroxyprogesterone acetate) is administered intramuscularly or subcutaneously every 3 months with a failure rate of 3 pregnancies per 100 women per year. Its side effects include weight gain, irregular menses, amenorrhea, and mood changes, and there is a slow return to ovulation and fertility after discontinuation (6–9 months). The subder­ mal implant contains etonogestrel and is placed easily over the triceps muscle in the inner arm using local anesthesia. It lasts up to 5 years and has a failure rate of 0.05 pregnancies per 100 women per year. Findings from the Contraceptive Choice research project showed that continu­ ation rates were higher for LARC (IUDs and implants) compared to short-acting methods. LARCs are the most effective reversible form of contraception with high continuation and satisfaction rates; hence, they are a good choice in adolescents and nulliparous women.

PART 12 Endocrinology and Metabolism Nonhormonal IUD  IUDs are a commonly used form of contra­ ception worldwide and are available as hormonal and nonhormonal devices. The nonhormonal copper IUD works as a spermicidal and is effective for up to 12 years with a failure rate of <1 pregnancy per 100 women per year. Patients should be counseled regarding the increased risk of heavy vaginal bleeding and dysmenorrhea resulting in higher discontinuation rates compared to the levonorgestrel-containing IUDs. IUDs can be used in adolescents and adult women and are typically inserted and removed as an office procedure with use of mild analge­ sics. They can be inserted anytime during a menstrual cycle, referred to as interval insertion, and in the immediate postpartum and postabor­ tion period. Barrier Contraception  The barrier forms of contraception include condoms (male, female) and diaphragm and cervical cap and have lower effectiveness secondary to inconsistent and incorrect use. They offer several advantages including minimal side effects, lower cost, no requirement for a prescription, and protection from sexually transmitted infections. The failure rate for male and female condoms is 17–21 pregnancies per 100 women per year. Spermicidals can be used in conjunction with barrier methods to improve effectiveness. Lactational Contraception  Lactation may serve as an effective form of contraception during the first 6 postpartum months if there is exclusive breast-feeding and menstrual cycles have not resumed. The contraceptive effect occurs due to suppression of GnRH pulsatility associated with suckling. The failure rate under these circumstances can be as low as 0.5–1.5 pregnancies per 100 women per year. Fertility Awareness  The standard days method is typically used by women with regular menstrual cycles whereby they track their cycles to avoid intercourse from cycle days 8–19. The rhythm and withdrawal method are also referred to as traditional methods of contraception. Emergency Contraception  Also known as postcoital contracep­ tion, this method is used after an unprotected or inadequately pro­ tected act of intercourse. The probability of pregnancy independent of the time of the month is 8%, but the probability varies significantly in relation to proximity to ovulation and may be as high has 30%. Many women are not aware of the availability of emergency contraception and its appropriate use. As the probability of pregnancy is highest if there has been unprotected intercourse during the 3 days prior to ovulation, the timing of administration and type of emergency contraceptive used determine the efficacy. Emergency contraception options include the copper IUD and oral medications such as ulipris­ tal acetate, levonorgestrel, and combined hormonal pills. The copper IUD prevents fertilization and implantation and is the most effective choice if inserted within 5 days of unprotected intercourse. It can be offered to obese women in whom other hormonal forms of emergency contraceptive may be less effective. Ulipristal acetate, a progesterone receptor antagonist, blocks the ability of endogenous progesterone to

act on its receptors and inhibits the LH surge, delaying or inhibiting ovulation, and may directly inhibit follicular rupture. It is administered as a 30-mg single dose up to 5 days after unprotected intercourse. Levonorgestrel administered as a single dose will prevent or delay ovu­ lation and is associated with fewer side effects compared to combined hormonal pills. Overall, the failure rate for all hormonal emergency contraception is 1–3%, with ulipristal acetate being the most effective. Side effects are mild and may include nausea, irregular vaginal bleed­ ing, and fatigue. Emergency contraception should be offered to all women who ask for it up to 5 days after unprotected intercourse and not delayed in order to obtain a pregnancy test or perform a clinical examination. Although body weight can affect the efficacy of emer­ gency hormonal contraception, treatment should not be withheld from overweight and obese women. ■ ■CONTRACEPTION COUNSELING Patients should be provided information regarding the different meth­ ods of contraception, side effects, noncontraceptive benefits, efficacy, need for strict compliance, and impact on future fertility. In order to facilitate patient-centric care, the provider should discuss plans for future pregnancy and whether childbearing is complete. A detailed patient history should be reviewed to identify potential contraindica­ tions such as migraines with aura, smoking, and hypertension. Pro­ viders should refer to the most updated USMEC or WHO Medical Eligibility Criteria for Contraceptive Use guidelines when counseling patients with associated comorbidities. As part of the shared decisionmaking approach, the patient’s choice should be the guiding factor, and the discussion should be nonjudgmental. Adolescents should be offered access to the full range of contraceptive options. In a low-risk patient, hormonal contraceptives can be prescribed from menarche to menopause; regular evaluation of side effects and assessment of changes in the patient’s medical history, however, are required. ■ ■FURTHER READING American College of Obstetricians and Gynecologists: Effec­ tiveness of birth control. Available at https://www.acog.org/womenshealth/infographics/effectiveness-of-birth-control-methods. Accessed June 30, 2024. Centers for Disease Control and Prevention: Reproduc­ tive health. Available at https://www.cdc.gov/reproductivehealth/ Infertility/#e. Accessed November 22, 2023. Curtis KM, Peipert JF: Long-acting reversible contraception. N Engl J Med 376:461, 2017. Curtis KM et al: U.S. medical eligibility criteria for contraceptive use, 2016. MMWR Recomm Rep 65:1, 2016. Infertility Workup for the Women’s Health Specialist: ACOG Committee Opinion, Number 781. Obstet Gynecol 133:e377, 2019. Reaffirmed in February 2023. Kulkarni AD et al: Fertility treatments and multiple births in the United States. N Engl J Med 369:2218, 2013. Mascarenhas MN et al. National, regional, and global trends in infertility prevalence since 1990: A systematic analysis of 277 health surveys. PLoS Med 9:e1001356, 2012. Slama R et al: Estimation of the frequency of involuntary infertility on a nation-wide basis. Hum Reprod 27:1489, 2012. Steiner AZ et al: Association between biomarkers of ovarian reserve and infertility among older women of reproductive age. JAMA 318:1367, 2017. World Family Planning 2022. Available at https://www.un.org/ development/desa/pd/sites/www.un.org.development.desa.pd/files/ files/documents/2023/Feb/undesa_pd_2022_world-family-planning. pdf. Accessed November 22, 2023. World Health Organization: Infertility. Available at https://www. who.int/news-room/fact-sheets/detail/infertility. Accessed December 23, 2020. World Health Organization: WHO Laboratory Manual for the Examination and Processing of Human Semen. 6th ed. WHO Press; Geneva, Switzerland: 2021. Available at https://www.who.int/ publications/i/item/9789240030787. Accessed December 3, 2021.

24 - 409 Sexual Dysfunction

409 Sexual Dysfunction

Kevin T. McVary

Sexual Dysfunction Male sexual dysfunction affects up to 31% of middle-aged and elderly men, whereas female sexual dysfunction, although studied less intensely, has a higher prevalence (43%) than male sexual dysfunction. Demographic changes, the popularity of newer treatments, and greater awareness of sexual dysfunction by patients and society have led to increased diagnosis and associated health care expenditures for the management of this common disorder. Sexual health and satisfaction with sex life are important aspects of quality of life for many, includ­ ing those in poor health. Because many patients are reluctant to initi­ ate discussion of their sex lives, physicians should address this topic directly to elicit a history of sexual dysfunction. Specifically addressing sexual health should be a routine part of the clinical encounter, particu­ larly in those with cardiovascular risk factors. MALE SEXUAL DYSFUNCTION ■ ■PHYSIOLOGY OF MALE SEXUAL RESPONSE An erection is a neurovascular event, and the cardiovascular system needs to be intact for sexual stimulation to successfully result in an erection. Normal male sexual function includes (1) sufficient libido, (2) the ability to achieve and maintain penile erection, (3) ejaculation, and (4) detumescence. Libido refers to sexual desire and is influenced by a variety of visual, olfactory, tactile, auditory, imaginative, and hormonal stimuli. Sex steroids, particularly testosterone, act to increase libido. Libido can be diminished by emotional context, systemic illness, hor­ monal disturbances, psychiatric disorders, and medications. Penile tumescence leading to erection depends on an increased flow of blood into the lacunar network accompanied by complete relaxation of the arteries and corporal smooth muscle. The microarchitecture of the corpora is composed of a mass of smooth muscle (trabecula) that contains a network of endothelial-lined vessels (lacunar spaces). Subse­ quent compression of the trabecular smooth muscle against the fibro­ elastic tunica albuginea causes a passive closure of the emissary veins and accumulation of blood in the corpora. In the presence of a full erection and a competent valve mechanism, the corpora become non­ compressible cylinders from which blood does not escape. This cas­ cade of relaxation and venous occlusion culminates in a rigid erection. The central nervous system (CNS) exerts an important influence by either stimulating or antagonizing spinal pathways that mediate erectile function and ejaculation. The erectile response is mediated by a combination of central (psychogenic) innervation and peripheral (reflexogenic) innervation. Sensory nerves that originate from recep­ tors in the penile skin and glans converge to form the dorsal nerve of the penis, which travels to the S2-S4 dorsal root ganglia via the puden­ dal nerve. Parasympathetic nerve fibers to the penis arise from neurons in the intermediolateral columns of the S2-S4 sacral spinal segments. Sympathetic innervation originates from the T-11 to the L-2 spinal seg­ ments and descends through the hypogastric plexus. Neural input to smooth-muscle tone is crucial to the initiation and maintenance of an erection. There is also an intricate interaction between the corporal smooth-muscle cell and its overlying endothelial cell lining (Fig. 409-1). Nitric oxide, which induces vascular relaxation, promotes erection and is opposed by endothelin 1 (ET-1) and Rho kinase, which mediate vascular contraction. Nitric oxide is synthesized from L-arginine by nitric oxide synthase (NOS) and is released from the nonadrenergic, noncholinergic (NANC) autonomic nerve supply to act postjunctionally on smooth-muscle cells. Nitric oxide increases the production of cyclic 3′,5′-guanosine monophosphate (cyclic GMP), which induces relaxation of smooth muscle (Fig. 409-2). Cyclic GMP is metabolized by phosphodiesterase type 5 (PDE-5). Inhibitors of PDE-5 such as the oral medications sildenafil, tadalafil, vardenafil, and avanafil maintain erections by reducing the breakdown of cyclic GMP. However, if nitric oxide is not produced at some level, PDE-5

inhibitors are ineffective, as these drugs facilitate, but do not initiate, the initial enzyme cascade. In addition to nitric oxide, vasoactive pros­ taglandins (PGE1, PGF2α) are synthesized within the cavernosal tissue and increase cyclic AMP levels, also leading to relaxation of cavernosal smooth-muscle cells.

Ejaculation is stimulated by the sympathetic nervous system; this results in contraction of the epididymis, vas deferens, seminal vesicles, and prostate, causing seminal fluid to enter the urethra. Seminal fluid emission is followed by rhythmic contractions of the bulbocavernosus and ischiocavernosus muscles, leading to ejaculation. This is followed by expulsion, characterized by stereotypic rhythmic contractions of the striated perineal muscles, leading to forceful expulsion of semen with the bladder neck closed. This emission and expulsion are controlled by the autonomic (parasympathetic and sympathetic) and somatic spinal centers, respectively. The synchronization between autonomic and somatic spinal centers is orchestrated by interneurons that form a spinal ejaculation generator that is present in mammals including man. Sexual Dysfunction CHAPTER 409 Premature ejaculation usually is related to anxiety or a learned behavior and is amenable to behavioral therapy or treatment with med­ ications such as selective serotonin reuptake inhibitors (SSRIs). Retro­ grade ejaculation (RE) results when the internal urethral sphincter does not close; it may occur in men with diabetes or after surgery involving the bladder neck. Anejaculation, the failure of a portion or the whole of the emission process often confused with RE, is commonly the result of selective alpha blockers used in male voiding dysfunction (e.g., tam­ sulosin, silodosin). Detumescence is mediated by norepinephrine from the sympathetic nerves, endothelin from the vascular surface, and smooth-muscle con­ traction induced by postsynaptic α-adrenergic receptors and activation of Rho kinase. These events increase venous outflow and restore the flaccid state. Venous leak can cause premature detumescence and is caused by insufficient relaxation of the corporal smooth muscle rather than a specific anatomic defect. Priapism refers to a persistent and painful erection and may be associated with sickle cell anemia, hyper­ coagulable states, spinal cord injury, or injection of vasodilator agents into the penis. ■ ■ERECTILE DYSFUNCTION Epidemiology  Erectile dysfunction (ED) is not considered a normal part of the aging process. Nonetheless, it is associated with certain physiologic and psychological changes related to age. In the Massachusetts Male Aging Study (MMAS), a community-based survey of men aged 40–70, 52% of responders reported some degree of ED. Complete ED occurred in 10% of respondents, moderate ED in 25%, and minimal ED in 17%. The incidence of moderate or severe ED more than doubled between the ages of 40 and 70. In the National Health and Social Life Survey (NHSLS), which included a sample of men and women aged 18–59, 10% of men also reported being unable to main­ tain an erection. Incidence was highest among men in the age group 50–59 (21%) and men who were poor (14%), divorced (14%), and less educated (13%). The incidence of ED is also higher among men with certain medical disorders, such as diabetes mellitus, obesity, lower urinary tract symp­ toms secondary to benign prostatic hyperplasia (LUTS/BPH), heart disease, hypertension, decreased high-density lipoprotein (HDL) lev­ els, and diseases associated with general systemic inflammation (e.g., rheumatoid arthritis). Cardiovascular disease and ED share etiologies as well as pathophysiology (e.g., endothelial dysfunction), and the degree of ED appears to correlate with the severity of cardiovascular disease. Consequently, ED represents a “sentinel symptom” in patients with occult cardiovascular and peripheral vascular disease. Smoking is also a significant risk factor in the development of ED. Medications used in treating diabetes or cardiovascular disease are additional risk factors (see below). There is a higher incidence of ED among men who have undergone radiation or surgery for prostate can­ cer and in those with a lower spinal cord injury. Psychological causes of ED include depression, anger, stress from employment or relationships, anxiety, and other stress-related causes.

Endothelial cell Parasympathetic nervous system Angiotensin II PGF2α Endothelin-1 PART 12 Endocrinology and Metabolism Tonic inhibition Rho kinase inhibitors NANC NO NO Smooth-muscle cell Adenylyl cyclase cAMP kinase cGMP kinase Guanylyl cyclase cGMP GTP Guanylyl cyclase agonists Decreased Ca2+ Decreased Ca2+ PDE5 inhibitors PDE5 5′ AMP FIGURE 409-1  Pathways that control erection and detumescence. Outflow from the parasympathetic nervous system leads to relaxation of the cavernous sinusoids in two ways, both of which increase the concentration of nitric oxide (NO) in smooth-muscle cells. First, NO is the neurotransmitter in nonadrenergic, noncholinergic (NANC) fibers; second, stimulation of endothelial nitric oxide synthase (eNOS) through cholinergic output causes increased production of NO. The NO produced in the endothelium then diffuses into the smooth-muscle cells and decreases its intracellular calcium concentration through a pathway mediated by cyclic guanosine monophosphate (cGMP), leading to relaxation. A separate mechanism that decreases the intracellular calcium level is mediated by cyclic adenosine monophosphate (cAMP). With increased cavernosal blood flow, as well as increased levels of vascular endothelial growth factor (VEGF), the endothelial release of NO is further sustained through the phosphatidylinositol 3 (PI3) kinase pathway. Active treatments (red boxes) include drugs that affect the cGMP pathway (phosphodiesterase type 5 [PDE-5] inhibitors and guanylyl cyclase agonists), the cAMP pathway (alprostadil), or both pathways (papaverine), along with neural-tone mediators (phentolamine and Rho kinase inhibitors). Agents that are being developed include guanylyl cyclase agonists (to bypass the need for endogenous NO) and Rho kinase inhibitors (to inhibit tonic contraction of smooth-muscle cells mediated through endothelin). α1, α-adrenergic receptor; GPCR, G protein–coupled receptor; GTP, guanosine triphosphate; iCa2+, intracellular calcium; NOS, nitric oxide synthase; PGE, prostaglandin E; PGF, prostaglandin F. (Reproduced with permission from KT McVary: Clinical practice. Erectile dysfunction. N Engl J Med 357:2472, 2007.) Sildenafil Vardenafil Tadalafil Avanafil L-Arginine NOS – NO PDE-5 Cyclic GMP 5’-GMP iCa2+ Smooth-muscle relaxation Erection FIGURE 409-2  Biochemical pathways modified by phosphodiesterase type 5 (PDE-5) inhibitors. Sildenafil, vardenafil, tadalafil, and avanafil enhance erectile function by inhibiting PDE-5, thereby maintaining high levels of cyclic 3′,5′-guanosine monophosphate (cyclic GMP). iCa2+, intracellular calcium; NO, nitric oxide; NOS, nitric oxide synthase.

Increased blood flow Increases sheer stress Pl3-kinase L-Arginine eNOS NO Alprostadil Sympathetic nervous system PGE Detumescence GPCR Phentolamine α1 cAMP ATP Papaverine PDE2, 3, 4 5′ AMP Relaxation Pathophysiology  ED may result from three basic mechanisms: (1) failure to initiate (psychogenic, endocrinologic, or neurogenic), (2) failure to fill (arteriogenic), and (3) failure to store adequate blood vol­ ume within the lacunar network (veno-occlusive dysfunction). These categories are not mutually exclusive, and multiple factors contribute to ED. Psychogenic factors frequently coexist with other etiologic fac­ tors and should be considered in all cases. Diabetic, atherosclerotic, and drug-related causes account for >80% of cases of ED in older men. Vasculogenic  The most common organic cause of ED is a distur­ bance of blood flow to and from the penis. Atherosclerotic or traumatic arterial disease can decrease flow to the lacunar spaces, resulting in decreased rigidity and an increased time to full erection. Excessive out­ flow through the veins despite adequate inflow also may contribute to ED. Structural alterations to the fibroelastic components of the corpora may cause a loss of compliance and inability to compress the tunical veins. This condition may result from aging, increased cross-linking of collagen fibers induced by nonenzymatic glycosylation, hypoxemia, or altered synthesis of collagen associated with hypercholesterolemia. Neurogenic  Disorders that affect the sacral spinal cord or the autonomic fibers to the penis preclude nervous system relaxation of penile smooth muscle, thus leading to ED. In patients with spinal cord injury, the degree of ED depends on the completeness and level of the lesion. Patients with incomplete lesions or injuries to the upper part of the spinal cord are more likely to retain erectile capabilities than

are those with complete lesions or injuries to the lower part. Although 75% of patients with spinal cord injuries have some erectile capability, only 25% have erections sufficient for penetration. Other neurologic disorders commonly associated with ED include multiple sclerosis and peripheral neuropathy. The latter is often due to either diabetes or alcoholism. Pelvic surgery may cause ED through disruption of the autonomic nerve supply. Endocrinologic  Androgens increase libido, but their exact role in erectile function is unclear. Individuals with castrate levels of testos­ terone can achieve erections from visual or sexual stimuli. Nonethe­ less, normal levels of testosterone appear to be important for erectile function, in which the upregulation of nitric oxide synthase and the nitric oxide cascade is optimized (Fig. 409-1A). Androgen replacement therapy can improve depressed erectile function when it is secondary to hypogonadism; however, it is not useful for ED when endogenous testosterone levels are normal and should be avoided. Increased pro­ lactin may decrease libido by suppressing gonadotropin-releasing hormone (GnRH) resulting in decreased testosterone levels. Treatment of hyperprolactinemia with dopamine agonists can restore libido and eugonadism. Diabetic  ED occurs in 35–75% of men with diabetes mellitus. Pathologic mechanisms are related primarily to diabetes-associated vascular and neurologic complications. Diabetic macrovascular com­ plications are related mainly to age, whereas microvascular complica­ tions correlate with the duration of diabetes and the degree of glycemic control (Chap. 415). Individuals with diabetes also have reduced amounts of nitric oxide synthase in both endothelial and neural tissues. Psychogenic  Two mechanisms contribute to the inhibition of erections in psychogenic ED. First, psychogenic stimuli to the sacral cord may inhibit reflexogenic responses, thereby blocking activation of vasodilator outflow to the penis. Second, excess sympathetic stimula­ tion in an anxious man may increase penile smooth-muscle tone. The most common causes of psychogenic ED are performance anxiety, depression, relationship conflict, loss of attraction, sexual inhibition, conflicts over sexual preference, sexual abuse in childhood, and fear of pregnancy or sexually transmitted disease. Almost all patients with ED, even when it has a defined organic basis, develop a psychogenic component as a reaction to ED. Medication-Related  Medication-induced ED (Table 409-1) is estimated to occur in 25% of men seen in general medical clinics. The adverse effects related to drug therapy are additive, especially in older men. In addition to the drug itself, the underlying disease being treated is likely to contribute to sexual dysfunction (e.g., hypertension). Among the antihypertensive agents, the thiazide diuretics and beta blockers have been implicated most frequently. Calcium channel blockers and angiotensin-converting enzyme inhibitors are cited less frequently. These drugs may act directly at the corporal level (e.g., calcium chan­ nel blockers) or indirectly by reducing pelvic blood pressure, which is important in the development of penile rigidity. α-Adrenergic blockers are less likely to cause ED. Estrogens, GnRH agonists, H2 antagonists, and spironolactone cause ED by suppressing gonadotropin production or by blocking androgen action. Antidepressant and antipsychotic agents—particularly neuroleptics, tricyclics, and SSRIs—are associ­ ated with erectile, ejaculatory, orgasmic, and sexual desire difficulties. Among the SSRIs, paroxetine and escitalopram have been associated with the highest risk of sexual dysfunction. Bupropion, nefazodone, and mirtazapine appear less likely to cause sexual dysfunction. A number of molecular pathways have been implicated in antidepressantinduced sexual adverse events. Serotonin has been hypothesized to inhibit normal sexual response by decreasing dopamine-enhanced libido, arousal, and erection and by increasing prolactin release. SSRIs have also been shown to be potent inhibitors of nitric oxide synthase. If there is a strong association between the institution of a drug and the onset of ED, alternative medications should be considered. Other­ wise, it is often practical to treat the ED without attempting multiple changes in medications as it may be difficult to establish a causal role for a drug.

TABLE 409-1  Drugs Associated with Erectile Dysfunction CLASSIFICATION DRUGS POSSIBLE SUBSTITUTES Diuretics Thiazides     Spironolactone   Antihypertensives Calcium channel blockers α-Adrenergic blockers Prazosin Terazosin Doxazosin ACE inhibitors Sexual Dysfunction CHAPTER 409   Methyldopa     Clonidine     Reserpine     Beta blockers     Guanethidine   Cardiac/ antihyperlipidemics Digoxin     Gemfibrozil     Clofibrate   Antidepressants Selective serotonin reuptake inhibitors Bupropion Nefazodone Mirtazapine   Tricyclic antidepressants     Lithium     Monoamine oxidase inhibitors   Tranquilizers Butyrophenones     Phenothiazines   H2 antagonists Ranitidine Proton pump inhibitors (PPI)   Omeprazole   Esomeprazole   Pantoprazole   Rabeprazole   Cimetidine   Hormones Progesterone     Estrogens     Corticosteroids     GnRH agonists     5α-Reductase inhibitors     Cyproterone acetate   Cytotoxic agents Cyclophosphamide     Methotrexate     Roferon-A   Anticholinergics Disopyramide     Anticonvulsants   Recreational Ethanol     Cocaine     Marijuana   Abbreviations: ACE, angiotensin-converting enzyme; GnRH, gonadotropin-releasing hormone. APPROACH TO THE PATIENT Erectile Dysfunction A good physician–patient relationship helps unravel the possible causes of ED, many of which require discussion of personal and sensitive topics. For this reason, a primary care provider is often ideally suited to initiate the evaluation. However, a significant percentage of men experience ED and remain undiagnosed unless specifically questioned about this issue. By far the two most com­ mon reasons for underreporting of ED are patient embarrassment and perceptions of physicians’ inattention to the disorder. Once

History: Medical, sexual, and psychosocial Physical examination Serum: Testosterone and prolactin levels Lifestyle risk management Medication review Problem resolved Problem persists Patient/partner education Goal-directed therapy planning Sex therapy Special testing PART 12 Endocrinology and Metabolism Treatment success Oral PDE-5 inhibitors Intraurethral or injection therapy Treatment success Vacuum device Implantation/ vascular surgery FIGURE 409-3  Algorithm for the evaluation and management of patients with erectile dysfunction. PDE, phosphodiesterase. the topic is initiated by the physician, patients are more willing to discuss their potency issues. A complete medical and sexual history should be taken in an effort to assess whether the cause of ED is organic, psychogenic, or multifactorial (Fig. 409-3). Both the patient and his sexual partner should be interviewed regarding sexual history. ED should be distinguished from other sexual problems, such as premature ejaculation. Lifestyle factors such as sexual orientation, the patient’s distress from ED, perfor­ mance anxiety, and details of sexual techniques should be addressed. Validated questionnaires are available to assess ED, including the International Index of Erectile Function (IIEF) and the more easily administered Sexual Health Inventory for Men (SHIM), a validated abridged version of the IIEF. These can assess the severity of ED, measure treatment effectiveness, and guide future management. The initial evaluation of ED begins with a review of the patient’s medical, surgical, sexual, and psychosocial histories. The history should note whether the patient has experienced pelvic trauma, surgery, or radiation. In light of the increasing recognition of the relationship between lower urinary tract symptoms (LUTS/BPH) and ED, it is advisable to evaluate for the presence of associated uri­ nary symptoms. Questions should focus on the onset of symptoms, the presence and duration of partial erections, and the progression of ED. A history of nocturnal or early morning erections may be useful for distinguishing physiologic ED from psychogenic ED. Nocturnal erections occur during rapid eye movement (REM) sleep and require intact neurologic and circulatory systems. Organic causes of ED generally are characterized by a gradual and persistent change in rigidity or the inability to sustain nocturnal, coital, or self-stimulated erections. It is also important to address libido, as decreased sexual drive and ED are sometimes the earliest signs of decreased testosterone levels. It is useful to ask whether the prob­ lem is confined to coitus with one partner or also involves other partners; ED not uncommonly arises with new or extramarital sexual relationships. Situational ED, as opposed to consistent ED, suggests psychogenic causes. For men with recalcitrant ED, referral to a mental health professional may promote treatment adherence, reduce performance anxiety, and integrate treatments into a sexual relationship. Ejaculation is much less commonly affected than erec­ tion, but questions should be asked about whether ejaculation is normal, premature, delayed, or absent. Relevant risk factors should be identified, such as diabetes mellitus, cardiovascular disease, and neurologic disorders. The patient’s surgical history should be explored with an emphasis on bowel, bladder, prostate, and vascular procedures. A complete drug history, including tobacco, alcohol, marijuana, and illicit drug inquiries, is also important. Social

changes that may precipitate ED are also crucial to the evaluation, including health worries, spousal death, divorce, relationship dif­ ficulties, and financial concerns. Because ED commonly involves a host of endothelial cell risk factors, men with ED report higher rates of overt and silent myocar­ dial infarction. Therefore, ED in an otherwise asymptomatic male warrants consideration of other vascular disorders, including coro­ nary disease. It is now widely recognized that ED often precedes the development of symptomatic coronary disease by several years. In addition, several studies now suggest that ED itself is an indepen­ dent risk factor for the development of CVD even after correcting for other cardiovascular risk factors. Men who suffer from ED are at high risk for concomitant LUTS from BPH and vice versa. Given that some treatments of one dis­ order will impact the other, the clinician should consider an assess­ ment of LUTS in any man with ED. The physical examination is an essential element in the assess­ ment of ED. Signs of hypertension as well as evidence of thyroid, hepatic, hematologic, cardiovascular, or renal diseases should be sought. An assessment should be made of the endocrine and vascu­ lar systems, the external genitalia, and the prostate gland. The penis should be palpated carefully along the corpora to detect fibrotic plaques. Reduced testicular size and loss of secondary sexual char­ acteristics are suggestive of hypogonadism. Neurologic examination should include assessment of anal sphincter tone, investigation of the bulbocavernosus reflex, and testing for peripheral neuropathy. Although hyperprolactinemia is uncommon, a serum prolactin level should be measured in hypogonadal men, as decreased libido and/or ED may be the presenting symptoms of a prolactinoma or another mass lesion of the sella (Chap. 392). The serum testosterone level should be measured, and if it is low, gonadotropins should be measured to determine whether hypogonadism is primary (testicu­ lar) or secondary (hypothalamic-pituitary) in origin (Chap. 403). If not performed recently, serum chemistries, hemoglobin A1c, and lipid profiles may be of value, as they can yield evidence of diabetes, hyperlipidemia, or other systemic diseases associated with ED. Additional diagnostic testing is rarely necessary in the evalua­ tion of ED. However, in selected patients, specialized testing may provide insight into pathologic mechanisms of ED and aid in the selection of treatment options. Optional specialized testing includes (1) studies of nocturnal penile tumescence and rigidity, (2) vascular testing (in-office injection of vasoactive substances, penile Dop­ pler ultrasound), (3) neurologic testing (biothesiometry-graded vibratory perception, somatosensory-evoked potentials), and (4) psychological diagnostic tests. The information potentially gained from these procedures must be balanced against their invasiveness, cost, and impact on ultimate treatment outcome. Clinicians should counsel men with ED who have comorbidities known to negatively affect erectile function that lifestyle modifica­ tions, including changes in diet and increased physical activity, improve overall health and can improve ED. TREATMENT Male Sexual Dysfunction PATIENT EDUCATION Patient and partner education is essential in the treatment of ED. In goal-directed therapy, education facilitates understanding of the disease, the results of the tests, and the selection of treatment. Discussion of treatment options helps clarify how treatment is best offered and stratify first- and second-line therapies. Patients with high-risk lifestyle issues such as obesity, smoking, alcohol abuse, and recreational drug use should be counseled on the role those factors play in the development of ED. Therapies currently employed for the treatment of ED include oral PDE-5 inhibitor (PDE-5i) therapy (most commonly used), injection therapies, testosterone therapy, penile devices, and

TABLE 409-2  PDE-5 Inhibitorsa DRUG ONSET OF ACTION T1/2 DOSE ADVERSE EFFECTS CONTRAINDICATIONS Sildenafil Tmax 30–120 min Duration 4 h High-fat meal decreases absorption Alcohol use may affect efficacy 2–5 h 25–100 mg Starting dose 50 mg Vardenafil Tmax 30–120 min Duration 4–5 h High-fat meal decreases absorption ETOH may affect efficacy 4.5 h 5–10 mg Headache, flushing, rhinitis, dyspepsia Tadalafil Tmax 30–60 min Duration 12–36 h Plasma concentration not affected by food or ETOH 17.5 h 10 or 20 mg; 2.5 or 5 mg for daily dose Avanafil Tmax 30 min Duration 2 h Plasma concentration not affected by food 3–5 h 50, 100, and 200 mg dose aSildenafil, vardenafil, tadalafil, and the newest option, avanafil, appear to be equally effective, but tadalafil has a longer duration of action and avanafil has a more rapid onset. Abbreviations: ETOH, ethanol; PDE-5, phosphodiesterase type 5. psychological therapy. In addition, limited data suggest that treat­ ments for underlying risk factors and comorbidities—for example, weight loss, exercise, stress reduction, and smoking cessation—may improve erectile function. ORAL AGENTS Sildenafil, tadalafil, vardenafil, and avanafil are the only approved and effective oral agents for the treatment of ED. These four medi­ cations have markedly improved the management of ED because they are effective for the treatment of a broad range of etiologies. They belong to a class of medications that are selective and potent inhibitors of PDE-5, the predominant phosphodiesterase isoform found in the penis. They are administered in graduated doses and enhance erections after sexual stimulation (Fig. 409-2). The onset of action is ~30–120 min, depending on the medication used and other factors, such as recent food intake. Reduced initial doses should be considered for patients who are elderly, are taking concomitant alpha blockers, have renal insufficiency, or are taking medications that inhibit the CYP3A4 metabolic pathway in the liver (e.g., erythromycin, cimetidine, ketoconazole, clarithromycin, dil­ tiazem, itraconazole, ritonavir, verapamil, grapefruit, and possibly itraconazole and mibefradil), as they may increase the serum con­ centration of the PDE-5i or promote hypotension. Initially, there were concerns about the cardiovascular safety of these drugs. It is known that these agents can act as mild vasodilators. Earlier con­ cerns that the use of PDE-5is would increase cardiovascular events have been reversed as more studies support that a general popula­ tion of men with ED who take PDE-5is have lower rates of major adverse cardiovascular events and lower overall mortality rates than men not exposed to PDE-5is, even after correcting for baseline car­ diovascular risks and concomitant medicines. These studies suggest that PDE-5is may have a significant cardiovascular protective effect and may have potential as preventive cardiology agents. Several randomized trials have demonstrated the efficacy of this class of medications. There are no compelling data to support the superiority of one PDE-5i over another. Subtle differences between agents have variable clinical relevance (Table 409-2). Patients may fail to respond to a PDE-5i for several reasons (Table 409-3). Some patients may not tolerate PDE-5i secondary to adverse events from vasodilation in nonpenile tissues expressing PDE-5 or from the inhibition of homologous nonpenile isozymes (i.e., PDE-6 found in the retina). Abnormal vision attributed to the effects of PDE-5i on retinal PDE-6 is of short duration, reported only with sildenafil, and not clinically significant. A more serious

Headache, flushing, dyspepsia, nasal congestion, altered vision Nitrates Hypotension Cardiovascular risk factors Retinitis pigmentosa Change dose with some antiretrovirals Should be on stable dose of alpha blockers Same as sildenafil May have minor prolongation of QT interval Concomitant use of class I antiarrhythmic Sexual Dysfunction CHAPTER 409 Headache, dyspepsia, backpain, nasal congestion, myalgia Same as sildenafil Headache, flushing, nasal congestion nasopharyngitis back pain Same as sildenafil concern is the possibility that PDE-5is may cause nonarteritic ante­ rior ischemic optic neuropathy (NAION); although data to support that association are limited, it is prudent to avoid the use of these agents in men with a prior history of NAION. Testosterone supplementation combined with a PDE-5i may be beneficial in improving erectile function in hypogonadal men with ED who are unresponsive to PDE-5i alone. Side effects associated with PDE-5is include headaches (19%), facial flushing (9%), dys­ pepsia (6%), and nasal congestion (4%). Approximately 7% of men using sildenafil may experience transient altered color vision (blue halo effect), and 6% of men taking tadalafil may experience loin pain. PDE-5i is contraindicated in men receiving nitrate therapy for cardiovascular disease, including agents delivered by the oral, sublingual, transnasal, and topical routes as they can potentiate its hypotensive effect. Likewise, amyl/butyl nitrate “poppers” may have a fatal synergistic effect on blood pressure. PDE-5is also should be avoided in patients with congestive heart failure and cardiomyopa­ thy because of the risk of vascular collapse. Because sexual activity leads to an increase in physiologic expenditure (5–6 metabolic equivalent tasks [METs]), physicians have been advised to exercise caution in prescribing any drug for sexual activity to those with active coronary disease, heart failure, borderline hypotension, or hypovolemia and to those on complex antihypertensive regimens. Although the various forms of PDE-5is have a common mecha­ nism of action, there are a few differences among the four agents (Table 409-2). Tadalafil is unique in its longer half-life, and avanafil appears to have the fastest onset of action. Although there are pharmacokinetic and pharmacodynamic differences among these agents, clinically relevant differences are not clear. TABLE 409-3  Issues to Consider if Patients Report Failure of Phosphodiesterase Type 5 Inhibitor (PDE-5i) to Improve Erectile Dysfunction

  1. A trial of medication on at least 6 different days at the maximal dose should be performed before declaring patient nonresponsive to PDE-5i use.
  2. Confirm that the patient did not partake in a high-fat meal prior to taking medication; pertains to sildenafil.
  3. Failure to include physical and psychic stimulation at the time of foreplay to induce endogenous NO.
  4. Took medications at an appropriate time frame prior to step 3: half-hour prior for avanafil, 1 h for sildenafil/vardenafil, or 2.5 h for tadalafil.
  5. Unrecognized hypogonadism. Abbreviation: NO, nitric oxide.

ANDROGEN THERAPY Testosterone replacement is used to treat both primary and second­ ary causes of hypogonadism (Chap. 403). Men with ED and testos­ terone deficiency (TD) who are considering ED treatment with a PDE-5i should be informed that PDE-5is may be more effective if combined with testosterone therapy. Androgen supplementation in the setting of normal testosterone is not efficacious in the treatment of ED and is discouraged secondary to additional risk for toxicity without benefit.

The increased scrutiny of testosterone caused the U.S. Food and Drug Administration (FDA) to issue a warning that there is a “weak signal” that testosterone replacement therapy increases the risk of thromboembolic events and may have addictive properties. Although testosterone therapy has known risks, such as water reten­ tion in heart failure patients and worsening sleep apnea, increasing evidence suggests that, when monitored appropriately, this therapy decreases the risk for metabolic syndrome, changes body composi­ tion by increasing lean muscle mass, and improves insulin sensi­ tivity and average hemoglobin A1c. This evidence, combined with the fact that hypogonadism is a known risk factor for metabolic syndrome and cardiovascular disease, has led to the conclusion that testosterone therapy for age-related hypogonadism in fact improves overall health and decreases the risk of cardiovascular events. It is important to note that men with secondary hypogonadism who desire fertility should not be treated directly with testosterone, but with an alternative such as the selective estrogen receptor modu­ lator (SERM) clomiphene citrate, which increases gonadotropin levels, stimulating testicular testosterone production. PART 12 Endocrinology and Metabolism Testosterone circulates in the body in two forms: free and unbound or that bound to proteins such as albumin or sex hor­ mone–binding globulin (SHBG). SHBG has a very high affinity for testosterone, and thus, testosterone bound to SHBG does not bind to the androgen receptor and is not bioavailable. Bioavailable testosterone is any testosterone that is not bound to SHBG. Unfor­ tunately, reliable assays to directly measure bioavailable testosterone or free testosterone are expensive, difficult to perform, and thus not offered by most laboratories. However, direct measurement of SHBG is inexpensive and reliable, allowing free and bioavailable testosterone to be calculated. Men who receive testosterone should be reevaluated after 3–6 months and at least annually thereafter for testosterone levels, erectile func­ tion, and adverse effects, which may include gynecomastia, sleep apnea, development or exacerbation of LUTS or BPH, prostate cancer, lowering of HDL, erythrocytosis, and elevations of liver function tests. Periodic reevaluation should include measurement of hemoglobin, liver function tests, prostate-specific antigen, and digital rectal examination. Therapy should be discontinued in patients who do not respond within 6 months without an alternate explanation (e.g., elevated estradiol). VACUUM CONSTRICTION DEVICES Vacuum constriction devices (VCDs) are a well-established non­ invasive therapy. They are a reasonable treatment alternative for select patients who cannot take PDE-5is or do not desire other interventions. VCDs draw venous blood into the penis and use a constriction ring to restrict venous return and maintain tumes­ cence. Adverse events with VCD include pain, numbness, bruising, and altered ejaculation. Additionally, many patients complain that the devices are cumbersome and that the induced erections have a nonphysiologic appearance and feel. INTRAURETHRAL ALPROSTADIL If a patient fails to respond to oral agents, a reasonable next choice is intraurethral or self-injection of vasoactive substances. Intraure­ thral prostaglandin E1 (alprostadil), in the form of a semisolid pellet (doses of 125–1000 μg), is delivered with an applicator. Approxi­ mately 65% of men receiving intraurethral alprostadil respond with an erection when tested in the office, but <50% achieve successful coitus at home.

INTRACAVERNOSAL SELF-INJECTION Injection of synthetic formulations of alprostadil is effective in 70–80% of patients with ED, but discontinuation rates are high because of the invasive nature of administration. Doses range between 1 and 40 μg. Injection therapy is contraindicated in men with a history of hypersensitivity to the drug and men at risk for priapism (hypercoagulable states, sickle cell disease). Side effects include local adverse events, prolonged erections, pain, and fibrosis with chronic use. Various combinations of alprostadil, phentol­ amine, and/or papaverine sometimes are used. SURGERY An important but less frequently used form of therapy for ED involves the surgical implantation of a semirigid or inflatable penile prosthesis. Because of the permanence of prosthetic devices, patients should first consider less invasive options for treatment. These surgical treatments are associated with a low rate of compli­ cations and are used for those who do not want the less spontaneous medical treatments, in PDE-5i–refractory ED, or in men who can­ not tolerate such medications. Despite the requirement for surgery, penile prostheses are associated with very high rates of patient and partner satisfaction. SEX THERAPY A course of sex therapy may be useful for addressing specific interpersonal factors that may affect sexual functioning. These approaches may be useful in patients who have psychogenic or social components to their ED, although data from randomized trials are inconsistent. It is preferable to include both partners in therapy if the patient is involved in an ongoing relationship. FEMALE SEXUAL DYSFUNCTION Female sexual dysfunction (FSD) includes chronic sexual conditions in the domains of desire, arousal, pain, and muted orgasm. The associ­ ated risk factors for FSD are similar to those in males: cardiovascular disease, endocrine disorders, hypertension, neurologic disorders, and smoking (Table 409-4). Women with hypertension report significantly lower sexual satisfaction (especially younger women). ■ ■EPIDEMIOLOGY Epidemiologic data are limited, but the available estimates suggest that as many as 43% of women complain of at least one sexual problem. Despite their frequency and impact, FSDs are substantially undetected by clinicians and undertreated even when recognized. Despite the recent interest in organic causes of FSD, desire and arousal phase disor­ ders (including lubrication complaints) remain the most common pre­ senting problems when surveyed in a community-based population. TABLE 409-4  Risk Factors for Female Sexual Dysfunction Neurologic disease: stroke, spinal cord injury, parkinsonism Trauma, genital surgery, radiation Endocrinopathies: diabetes, hyperprolactinemia Liver and/or renal failure Cardiovascular disease, especially hypertension Psychological factors and interpersonal relationship disorders: sexual abuse, life stressors Medications   Antiandrogens: cimetidine, spironolactone   Antidepressants, alcohol, hypnotics, sedatives   Antiestrogens or GnRH antagonists   Antihistamines, sympathomimetic amines   Antihypertensives: diuretics, calcium channel blockers   Alkylating agents   Anticholinergics Abbreviation: GnRH, gonadotropin-releasing hormone.

■ ■PHYSIOLOGY OF THE FEMALE SEXUAL RESPONSE The normal female sexual response requires the presence of estrogens. A role for androgens is also likely but less well established. In the CNS, estrogens and androgens work synergistically to enhance sexual arousal and response. A number of studies report enhanced libido in women during preovulatory phases of the menstrual cycle, suggesting that hormones involved in the ovulatory surge (e.g., estrogens) increase desire. Sexual motivation is heavily influenced by context, including the environment and partner factors. Once sufficient sexual desire is reached, sexual arousal is mediated by the central and autonomic nervous systems. Cerebral sympathetic outflow is thought to increase desire, and peripheral parasympathetic activity results in clitoral vaso­ congestion and vaginal secretion (lubrication). The neurotransmitters for clitoral corporal engorgement are similar to those in the male penile tissues, with a prominent role for neural, smooth-muscle, and endothelial released nitric oxide (NO). A fine network of vaginal nerves and arterioles promotes a vaginal transudate. The major transmitters of this complex vaginal response are not certain, but roles for NO and vasoactive intestinal polypeptide (VIP) are sup­ ported. There are doubts concerning the construct of a linear relation­ ship between initial desire, arousal, vasocongestion, lubrication, and orgasm. Caregivers should consider a paradigm of a positive emotional and physical outcome with one, many, or no orgasmic peak and release. Although there are anatomic differences as well as variation in the density of vascular and neural beds in males and females, the primary effectors of sexual response are strikingly similar. Intact sensation is important for arousal. Thus, reduced levels of sexual functioning are more common in women with peripheral neuropathies (e.g., diabetes). Vaginal lubrication is a transudate of serum that results from the increased pelvic blood flow associated with arousal. Vascular insuffi­ ciency from a variety of causes may compromise adequate lubrication and result in dyspareunia. Cavernosal and arteriole smooth-muscle relaxation occurs via increased NO synthase (NOS) activity and produces engorgement in the clitoris and the surrounding vestibule. Orgasm requires an intact sympathetic outflow tract; hence, orgasmic disorders are common in female patients with spinal cord injuries. APPROACH TO THE PATIENT Female Sexual Dysfunction Many women do not volunteer information about their sexual response. Open-ended questions in a supportive atmosphere are helpful in initiating a discussion of sexual integrity. Once a com­ plaint has been voiced, a comprehensive evaluation should be performed, including a medical history, a psychosocial history, a physical examination, and limited laboratory testing. The history should include the usual medical, surgical, obstet­ ric, psychological, gynecologic, sexual, and social information. Past experiences, intimacy, knowledge, and partner availability should also be ascertained. Medical disorders that may affect sexual health should be delineated. They include diabetes, cardiovascu­ lar disease, gynecologic conditions, obstetric history, depression, anxiety disorders, and neurologic disease. Medications should be reviewed as they may affect arousal, libido, and orgasm. The need for counseling and recognizing life stresses should be identified. The physical examination should assess the genitalia, including the clitoris. Pelvic floor examination may identify prolapse or other disorders. Laboratory studies are needed, especially if menopausal status is uncertain. Estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) are usually obtained, and dehydro­ epiandrosterone (DHEA) should be considered as it reflects adrenal androgen secretion. A complete blood count, liver function assess­ ment, and lipid studies may be useful, if not otherwise obtained. Complicated diagnostic evaluation such as clitoral Doppler ultraso­ nography and biothesiometry require expensive equipment and are of uncertain utility. It is important for the patient to identify which symptoms are most distressing.

The evaluation of FSD previously occurred exclusively in a psychosocial context. However, inconsistencies between diagnos­ tic categories based only on psychosocial considerations and the emerging recognition of organic etiologies have led to a new classification of FSD. This diagnostic scheme is based on four components that are not mutually exclusive: (1) hypoactive sexual desire—the persistent or recurrent lack of sexual thoughts and/or receptivity to sexual activity; hypoactive sexual desire may result from endocrine failure or may be associated with psychological or emotional disorders; (2) sexual interest arousal disorder—the persis­ tent or recurrent inability to attain or maintain sexual excitement; (3) orgasmic disorder—the persistent or recurrent loss of orgasmic potential after sufficient sexual stimulation and arousal; and (4) sexual pain disorder—persistent or recurrent genital pain associ­ ated with noncoital sexual stimulation. This newer classification emphasizes “personal distress” as a requirement for dysfunction and provides clinicians with an organized framework for evaluation before or in conjunction with more traditional counseling methods. Sexual Dysfunction CHAPTER 409 TREATMENT Female Sexual Dysfunction GENERAL An open discussion with the patient is important as couples may need to be educated about normal anatomy and physiologic responses, including the role of orgasm, in sexual encounters. Physiologic changes associated with aging and/or disease should be explained. Couples may need to be reminded that clitoral stimula­ tion rather than coital intromission may be more beneficial. Behavioral modification and nonpharmacologic therapies should be a first step. Patient and partner counseling may improve communication and relationship strains. Lifestyle changes involv­ ing known risk factors can be an important part of the treatment process. Emphasis on maximizing physical health and avoiding life­ styles (e.g., smoking, alcohol abuse) and medications likely to pro­ duce FSD is important (Table 409-3). The use of topical lubricants may address complaints of dyspareunia and dryness. Contributing medications such as antidepressants may need to be altered, includ­ ing the use of medications with less impact on sexual function, dose reduction, medication switching, or drug holidays. HORMONAL THERAPY In postmenopausal women, estrogen replacement therapy may be helpful in treating vaginal atrophy, decreasing coital pain, and improving clitoral sensitivity (Chap. 407). Menopause and its transition represent significant risk factors for the development of vulvovaginal atrophy–related sexual dysfunction. Available vaginal estrogen preparations include conjugated equine estrogens, estra­ diol vaginal cream, a sustained-release intravaginal estradiol ring, or a low-dose estradiol tablet. Vaginal estrogen preparations with the lowest systemic absorption rate may be preferred in women with history of breast cancer and severe vaginal atrophy. Vaginal lubricants and moisturizers applied on a regular basis have an efficacy comparable to that of local estrogen therapy and should be offered to women wishing to avoid the use of vaginal estrogens. If a hormonal supplement is chosen, then estrogen replacement in the form of local cream is the preferred method as it avoids sys­ temic side effects. Androgen levels in women decline substantially before menopause. However, low levels of testosterone or DHEA are not effective predictors of a positive therapeutic outcome with androgen therapy. The widespread use of exogenous androgens is not supported by the literature except in select circumstances (premature ovarian failure or menopausal states) and in secondary arousal disorders. Atrophic vaginitis is very common in postmenopausal women and is most commonly treated with estrogen-based treatments. However, many women are hesitant to use estrogen-based

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410 Women’s Health

treatments due to health concerns or are unable to use them due to a history of breast cancer or endometrial cancer. Hyaluronic acid vaginal gel has been found to be efficacious in treating atrophic vaginitis. ORAL AGENTS Flibanserin, originally developed as an antidepressant, is approved by the FDA as a treatment for low sexual desire in premenopausal women. Flibanserin, a postsynaptic agonist of serotonin recep­ tor 1A and antagonist of serotonin receptor 2A, increases sexual desire and reduces resultant stress in women with hyposexual desire disorder (HSDD) with few adverse effects. Flibanserin has two principal pharmacologic actions in neural microcircuits: it acts as a full agonist at postsynaptic 5-HT1A receptors and an antagonist at postsynaptic 5-HT2A receptors. Exclusive binding at these receptors differentiates flibanserin from buspirone and bupropion. This action in the prefrontal cortex causes the down­ stream release of dopamine and norepinephrine and reduction of serotonin. Flibanserin acts selectively on pyramidal neurons that excite brainstem 5-HT neurons yet also selectively on pyramidal neurons that inhibit brainstem norepinephrine and dopamine neurons.

PART 12 Endocrinology and Metabolism Flibanserin may boost sex drive in women who experience low sexual desire and who find the experience distressing. The drug should be discontinued if there is no improvement in sex drive after 8 weeks. Potentially serious side effects include low blood pressure and dizziness, particularly if it is mixed with alcohol. Other common adverse events include nausea, fatigue, sleepiness, and insomnia. Health care professionals and pharmacies dealing with flibanserin have to undergo a certification (risk evaluation and mitigation strategy [REMS]) process, and patients need to submit a written agreement to abstain from alcohol. The goal of the flibanse­ rin REMS is to inform patients about the increased risk of hypoten­ sion and syncope due to an interaction with alcohol. Bremelanotide, a melanocortin 4 receptor agonist, is also approved for HSDD. It demonstrates significant improvement in desire and a significant decrease in distress related to lack of desire. The most common adverse effects include nausea (40%), facial flushing (20%), and headache (10%). Bremelanotide’s place in ther­ apy is unclear, as the trials met statistical significance for change in sexual desire elements and distress related to sexual desire, yet the clinical benefit may only be modest. It is a subcutaneous injection given 45 min prior to sexual activity. Bremelanotide has no clini­ cally significant interactions with ethanol. Prescribing guidelines recommend no more than one dose in 24 h and no more than eight doses per month. Individuals should discontinue use after 8 weeks without benefit. There is no role for PDE-5is in FDS and should be discouraged. CLITORAL VACUUM DEVICE In patients with arousal and orgasmic difficulties, the option of using a clitoral vacuum device may be explored. This handheld battery-operated device has a small soft plastic cup that applies a vacuum over the stimulated clitoris. This causes increased caverno­ sal blood flow, engorgement, and vaginal lubrication. ■ ■FURTHER READING Burnett AL et al: Erectile dysfunction: AUA Guideline. J Urol 200:633, 2018. Geerkens MJM et al: Sexual dysfunction and bother due to erectile dysfunction in the healthy elderly male population: Prevalence from a systematic review. Eur Urol Focus 6:776, 2020. Kloner RA et al: Effect of phosphodiesterase type 5 inhibitors on major adverse cardiovascular events and overall mortality in a large nationwide cohort of men with erectile dysfunction and cardiovascular risk factors: A retrospective, observational study based on healthcare claims and national death index data. J Sex Med 20:38, 2023. McVary KT: Clinical practice. Erectile dysfunction. N Engl J Med 357:2472, 2007.

Mulhall JP et al: Evaluation and management of testosterone deficiency: AUA guideline. J Urol 200:423, 2018. Nappi RE et al: Medical treatment of female sexual dysfunction. Urol Clin North Am 49:299, 2022. Zhao B et al: Erectile dysfunction predicts cardiovascular events as an independent risk factor: A systematic review and meta-analysis. J Sex Med 16:1005, 2019. Emily Nosova, Andrea Dunaif

Women’s Health The clinical discipline of women’s health is well established. Indeed, its emphasis on greater attention to patient education and medical decision-making is a paradigm for what has become known as patientcentered health care. Moreover, the recognition of sex differences in gene expression, disease processes, and health outcomes is an impor­ tant example of precision medicine. Sex difference refers to the biologic differences conferred by sex chromosomes and hormones. In contrast, gender differences are related to psychosocial roles and cultural expec­ tations. The study of sex differences continues to grow as a scientific discipline. In 2016, the National Institutes of Health recognized its importance by implementing the expectation that sex should be con­ sidered as a biologic variable in study designs, analyses, and reporting in not only human but also vertebrate animal research. Strong scientific justification must be provided to limit research to only one sex. DISEASE RISK: REALITY AND PERCEPTION The leading causes of death are the same in women and men: (1) heart disease and (2) cancer (Fig. 410-1). In 2020, COVID-19 emerged as the third leading cause of death, representing >10% of all deaths that year. Mortality rates due to COVID-19 were slightly lower in women (9.8%) than in men (10.9%). The leading cause of cancer death, lung cancer, is the same in both sexes. Breast cancer is the second leading cause of cancer death in women. Men are more likely than women to die from suicide and accidents. Maternal mortality continues to be higher in the United States than in other industrialized nations and is associated with substantial health disparities in maternal deaths. U.S. maternal mortality rates declined for the majority of the twentieth century given improvements in maternity care and safer surgical techniques; however, the rates began to rise again in 2000. Over the past decade, the mortality rate has remained relatively stable with the exception of a slight rise in 2021–2022, followed by a decline to typical rates again in 2023. In June 2022, an historic Supreme Court decision overturned Roe v. Wade after nearly 50 years, declaring that women no longer had the constitutional right to abortion in the United States. In the year that fol­ lowed this landmark ruling, more than a dozen states banned abortion, while several enacted abortion protection laws, and at least 70 clinics ceased offering abortion-related services. These changes were projected to affect nearly 30% of women of reproductive age in the United States. A 2022 study found that maternal mortality in states that restricted abortion was 62% higher compared to that of states with more wide­ spread access (28.8 compared to 17.8 per 100,000 live births). Further longitudinal observation is needed to assess the impact of changes in abortion access on maternal and fetal mortality and outcomes. Women’s risk for many diseases increases at menopause. The median age of menopause in Caucasian women from industrialized countries is between 50 and 52 years, where women spend one-third of their lives in the postmenopausal period. Menopause occurs at earlier ages in Hispanic and African-American women as well as in women of lower socioeconomic status. Estrogen levels fall abruptly at menopause,

Septicemia, 2% Kidney Disease, 2% Influenza & Pneumonia, 2% Diabetes, 3% Accidents, 4% Stroke, 6% CLRD, 5% A Liver Disease & Cirrhosis, 1.8% Intentional Self-Harm (Suicide), 2.1% AD, 2.3% Diabetes, 3.3% COVID-19, 10.9% Accidents, 7.5% CVD, 3.9% CLRD, 4.1% B FIGURE 410-1  Percent distribution of 10 leading causes of death in (A) women compared to (B) men in the United States in 2020. In both women and men, the first, second, and third leading causes of death are the same: heart disease, cancer, and COVID-19, respectively. Causes of death then diverge by sex. Chronic lower respiratory disease (CLRD), stroke, and Alzheimer’s disease (AD) cause a larger percentage of deaths in women than in men. Suicide is among the 10 leading causes of death in men but not in women. CVD, cardiovascular disease. (Data from https://www.cdc.gov/nchs/data/nvsr/nvsr72/nvsr72-14.pdf.) inducing a variety of physiologic and metabolic responses. Rates of cardiovascular disease (CVD) increase, and bone density decreases rapidly after menopause. In the United States, women live on average 5.9 years longer than men, with a life expectancy at birth in 2021 of 79.1 years in women compared with 73.2 years in men of all races. Notably, these estimates represent a decrease in life expectancy from prior years related to the COVID-19 pandemic. Life expectancy is lower in African Americans of both sexes and higher in Hispanics of both sexes than their Cau­ casian counterparts. Accordingly, elderly women outnumber elderly men, so that age-related conditions, such as hypertension, have a female preponderance. SEX DIFFERENCES IN HEALTH AND DISEASE ■ ■ALZHEIMER’S DISEASE (See also Chap. 442) Alzheimer’s disease (AD) affects approximately twice as many women as men. Because the risk for AD increases with age, part of this sex difference is accounted for by the fact that women live longer than men. However, even in relatively younger groups (60–70 years of age), there is still a higher incidence of AD among

Women Heart Disease, 20% All Other, 26% Women’s Health CHAPTER 410 Cancer, 18% COVID-19, 10% AD, 6% Men Heart Disease, 22% All Other, 26.9% Cancer, 18.0% women. Additional factors may contribute to the increased risk for AD in women, including sex differences in brain size, structure, and func­ tional organization. Multimodal neuroimaging has demonstrated that certain biomarkers of the preclinical phase of AD, including a decline in neuronal mitochondrial function and impaired cerebral glucose metabolism, are evident earlier in women and are even distinguishable during the perimenopausal endocrine transition. There is emerging evidence for sex-specific differences in gene expression, not only for genes on the X and Y chromosomes but also for some autosomal genes. These genetic differences may translate into variable severity of AD, with women experiencing greater deficits in cognition. The ε4 allele of the apolipoprotein E gene (APOε4), a cholesterol carrier integral for lipid transport in the brain, is a major risk factor for AD. Recent studies show that the APOε4 genotype is strongly linked to develop­ ment of sporadic AD in women. Women who carry either the APOε4 homo- or heterozygous isoform have an increased risk of progressing from healthy aging patterns to cognitive impairment or AD, whereas men who carry either isoform experience marginal impact on their memory or cognition. Estrogens have pleiotropic genomic and nongenomic effects on the central nervous system, including neurotrophic actions in key areas involved in cognition and memory. Women with AD have lower

endogenous estrogen levels than do women without AD. These obser­ vations have led to the hypothesis that estrogen is neuroprotective. The Women’s Health Initiative Memory Study (WHIMS), an ancillary study in the Women’s Health Initiative (WHI) in women aged ≥65 years, found significantly increased risk for both dementia and mild cognitive impairment in women receiving estrogen alone or estrogen with pro­ gestin compared to placebo. However, the Kronos Early Estrogen Pre­ vention Study (KEEPS), a randomized clinical trial of early hormone therapy (HT) initiation after menopause that compared conjugated equine estrogen (CEE), transdermal estradiol (both estrogen arms included cyclic oral micronized progesterone), and placebo, found no adverse effect of HT on cognitive function. In summary, there is no evidence from placebo-controlled trials that HT improves cognitive function.

PART 12 Endocrinology and Metabolism While studies have shown a link between female sex and AD, other neurodegenerative disorders, including Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS), exhibit a stronger association with male sex. Men are 1.5 times more likely to develop PD than women across all age groups. A possible explanation for the male predilection may be the effect of Y-chromosome exclusive gene sex-determining region Y (SRY) on nigrostriatal dopaminergic (NSDA) neurons: the SRY upregulates neuronal numbers, synthesis of dopamine, and metabolism of neurons. ■ ■CVD AND STROKE (See also Chap. 284) There are major sex differences in CVD, the leading cause of death in developed countries. However, there are also major gender differences because of perceptions by both women and their health care providers that women are at lower risk for CVD. As a result of these misconceptions, women are less likely to seek medical help when they experience symptoms of CVD. Health care providers are less likely to suspect CVD, so women receive fewer interventions for modifiable risk factors as well as fewer acute interventions than do men. Women and their health care providers are also less aware that prodromal symptoms of cardiac disease differ in women compared to men. Women are less likely than men to present with chest pain and more likely to present with fatigue, shortness of breath, indigestion/ nausea, and anxiety. Sex steroids have major effects on the cardiovascular system and lipid metabolism. Estrogen increases high-density lipoprotein (HDL) and lowers low-density lipoprotein (LDL), whereas androgens have the opposite effect. Estrogen has direct vasodilatory effects on the vascular endothelium, enhances insulin sensitivity, and has antioxidant and anti-inflammatory properties. There is a striking increase in CVD after both natural and surgical menopause, suggesting that endogenous estrogens are cardioprotective. Women also have longer QT intervals on electrocardiograms, and this increases their susceptibility to certain arrhythmias. CVD presents differently in women, who are usually 10–15 years older than their male counterparts and are more likely to have comor­ bidities such as hypertension, congestive heart failure, and diabetes mellitus (DM). In the Framingham study, angina was the most com­ mon initial symptom of CVD in women, whereas myocardial infarc­ tion (MI) was the most common initial presentation in men. Women more often have atypical symptoms such as fatigue, anxiety, nausea, indigestion, and upper back pain. Although awareness that heart dis­ ease is the leading cause of death in women has nearly doubled over the past 15 years, women remain less aware that its symptoms are often atypical and are less likely to contact 9-1-1 when they experience such symptoms. A type of acute coronary syndrome (ACS) termed takotsubo syn­ drome, initially described in 1990 and characterized as a transient and reversible stress cardiomyopathy, disproportionately affects women. National cohort studies demonstrate that ~2% of all patients present­ ing to acute care centers with symptoms of ACS are diagnosed with takotsubo, and importantly, 80–90% are postmenopausal women. If stratified by sex, ~10% of patients with suspected ACS are ultimately diagnosed with takotsubo syndrome. Recurrence of this condition is also more common among women. Interestingly, morbidity and

mortality rates are higher in men, with cardiogenic shock, cardiac arrest, and mortality occurring more frequently than in women. The pathophysiology that leads to takotsubo is complex: potential inciting mechanisms involve microvascular dysfunction and impaired vascular reactivity, followed by reversible abnormalities in the coronary flow reserve and microvascular resistance. One potential explanation for the striking sex difference is that postmenopausal women have age- and estrogen deficiency–related coronary vasomotor dysfunction. Estrogen improves coronary blood flow through endothelium-dependent and -independent mechanisms; however, its deficiency results in increased sympathetic drive and endothelial dysfunction. An animal study suggested that estrogen supplementation may partially attenuate an excessive cardiovascular response to stress; however, this has not been studied clinically. Furthermore, hypotheses related to estrogen do not explain why takotsubo occurs in men and also appears to be associated with higher mortality rates in men. The specific mechanisms underly­ ing these sex differences in disease prevalence and outcomes remain unknown and require further study. Deaths from CVD have decreased markedly in men since 1980, whereas CVD deaths only started to decrease substantially in women beginning in 2000. After 2010, death rates from CVD among both sexes stabilized and even began to increase slightly in men. Women with MI are more likely to present with cardiac arrest or cardiogenic shock, whereas men are more likely to present with ventricular tachy­ cardia. Further, younger women with MI are more likely to die than are men of similar age. However, this mortality gap has decreased in recent years because younger women have experienced greater improvements in survival after MI than men. The improvement in survival is due largely to a reduction in comorbidities, suggesting a greater attention to modifiable risk factors in women. Sex differences account for more variable short-term outcomes observed among women with CVD who receive therapeutic interven­ tion, as compared to men. Women undergoing coronary artery bypass graft surgery have more advanced disease, a higher perioperative mortality rate, less relief of angina, and less graft patency; however, 5- and 10-year survival rates are similar. Women undergoing percu­ taneous transluminal coronary angioplasty have lower rates of initial angiographic and clinical success than men, but they also have a lower rate of re-stenosis and a better long-term outcome. Women may ben­ efit less and have more frequent serious bleeding complications from thrombolytic therapy compared with men. Factors such as older age, more comorbid conditions, smaller body size, and more severe CVD in women at the time of events or procedures account in part for the observed sex differences. Important risk factors for CVD in both men and women include elevated cholesterol levels, hypertension, smoking, obesity, low HDL cholesterol levels, DM, and lack of physical activity (Fig. 410-2). Total triglyceride levels are an independent risk factor for CVD in women but not in men. Low HDL cholesterol and DM are more important risk factors for CVD in women than in men. Several disorders conferring increased CVD risk affect women exclusively, such as pregnancyassociated hypertension, preeclampsia, gestational DM, and polycystic ovary syndrome, or predominantly, such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Cholesterol-lowering drugs are equally effective in men and women for primary and secondary prevention of CVD. In contrast to men, randomized trials showed that aspirin was not effective in the primary prevention of CVD in women; it did significantly reduce the risk of ischemic stroke. Psychosocial stressors and loneliness may also be important risk factors for the development of CVD in women. A recent cohort study of nearly 60,000 women older than 65 years showed that loneliness and social isolation were associated with a 5% and 8% higher risk of CVD, respectively, even after adjusting for health behaviors and outcomes. Women with greater loneliness and social isolation had a 13–27% higher risk of incident CVD compared with women with relatively less social isolation and less loneliness. Sex-specific factors related to reproductive and pregnancy history are now recognized as important risk-enhancing factors for CVD in women. Recent studies demonstrate that the greatest risk for CVD

FIGURE 410-2  Traditional and nontraditional risk factors for atherosclerotic cardiovascular disease (ASCVD) in women. (Reproduced with permission from M Garcia et al: Cardiovascular disease in women: Clinical perspectives. Circ Res 118:1273, 2016.) (at least twofold) was conferred by adverse pregnancy outcomes (APO), including a history of stillbirth, preterm birth, or preeclampsia, followed by a 1.5- to 1.9-fold risk with gestational diabetes and hyper­ tension, premature ovarian insufficiency, and placental abruption; the lowest risk (<1.5 fold) was associated with early menarche, early menopause, parity, and polycystic ovary syndrome. Given these strong associations, targeted counseling and increased surveillance of CVD risk factors is warranted for women in high-risk groups. Accordingly, the 2019 American Heart Association (AHA) guidelines included a recommendation to assess for pregnancy complications as a part of routine cardiovascular risk assessment for primary prevention. The sex differences in CVD prevalence, beneficial biologic effects of estrogen on the cardiovascular system, and reduced risk for CVD in observational studies led to the hypothesis that HT was cardioprotec­ tive. However, the WHI, which studied >16,000 women on CEE plus medroxyprogesterone acetate (MPA) or placebo and >10,000 women with hysterectomy on CEE alone or placebo, did not demonstrate a benefit of HT for the primary or secondary prevention of CVD. In addition, CEE plus MPA was associated with an increased risk for CVD, particularly in the first year of therapy, whereas CEE alone nei­ ther increased nor decreased CVD risk. Both HT groups were associ­ ated with an increased risk for ischemic stroke. In a subgroup analysis of the WHI estrogen-alone trial, a relatively younger age (50–59 years) combined with a history of bilateral salpingo-oophorectomy (BSO) was associated with a >30% CEE treatment–associated reduction in all-cause mortality, whereas CEE-treated older women with prior BSO did not see a significant reduction in any other outcomes, including incidence of coronary artery disease, invasive breast cancer, all-cause mortality, and a composite index of the aforementioned outcomes plus stroke, hip fracture, pulmonary embolism, and colorectal cancer. These results suggest that postmenopausal women younger than 60 with prior BSO may have mortality benefit from HT, while women older than 60 with BSO may suffer consequences associated with HT. More recent data from KEEPS indicate that even if estrogen therapy is initiated shortly after the menopausal transition, it does not reduce atherosclerotic progression or impact CVD outcomes. Additionally, HT and placebo groups have similar outcomes with respect to venous thromboembolism and breast cancer. Although HT does not slow CVD development as previously thought, findings from KEEPS sug­ gest that treated women experience significant improvements in vaso­ motor symptoms, mood, sexual function, and bone density, especially when therapy is started sooner after menopause onset. HT is discussed further in Chap. 407. ■ ■DIABETES MELLITUS (See also Chap. 415) Women are more sensitive to insulin than men. Despite this, the prevalence of type 2 DM is similar in men and women. There is a sex difference in the relationship between endogenous

Women’s Health CHAPTER 410 androgen levels and DM risk. Higher bioavailable testosterone levels are associated with increased risk in women, whereas lower bioavail­ able testosterone levels are associated with increased risk in men. This observation has been confirmed in a recent Mendelian randomization that found that genetically determined higher testosterone increases risk for DM in women but reduces risk in men. Polycystic ovary syndrome, preeclampsia, pregnancy-associated hypertension, and ges­ tational DM—common conditions in premenopausal women—are associated with a significantly increased risk for type 2 DM. Among individuals with DM, women have a greater risk for MI than do men. Women with DM have a sixfold greater risk of dying of CVD compared to women without DM. Premenopausal women with DM lose the car­ dioprotective effect of female sex and have rates of CVD identical to those in males. These women have impaired endothelial function and reduced coronary vasodilatory responses, which may predispose to cardiovascular complications. Women with DM are more likely to have left ventricular hypertrophy. Women with DM receive less aggressive treatment for modifiable CVD risk factors than men with DM. ■ ■HYPERTENSION (See also Chap. 288) After age 60, hypertension is more common in U.S. women than in men, largely because of the high prevalence of hypertension in older age groups and the longer survival of women. Isolated systolic hypertension is present in 30% of women >60 years old. Sex hormones affect blood pressure. Both normotensive and hypertensive women have higher blood pressure levels during the fol­ licular phase than during the luteal phase. In the Nurses’ Health Study, the relative risk of hypertension was 1.8 in current users of oral contra­ ceptives, but this risk is lower with the newer low-dose contraceptive preparations. Long-term data from this cohort also demonstrate that having gestational hypertension or preeclampsia during a first preg­ nancy doubled the rate of developing chronic hypertension. HT is not associated with hypertension. Among secondary causes of hyperten­ sion, there is a female preponderance of renal artery fibromuscular dysplasia. The benefits of treatment for hypertension have been dramatic in both women and men. A meta-analysis of the effects of hypertension treatment, the Individual Data Analysis of Antihypertensive Interven­ tion Trial, found a reduction of risk for stroke and major cardiovascular events in women. The effectiveness of various antihypertensive drugs appears to be comparable in women and men; however, women may experience more side effects, such as cough with angiotensin-converting enzyme inhibitors. ■ ■AUTOIMMUNE DISORDERS (See also Chap. 367) Most autoimmune disorders occur more com­ monly in women than in men; they include autoimmune thyroid and liver diseases, Hashimoto’s hypothyroidism, Graves’ disease (GD), SLE,

RA, scleroderma, multiple sclerosis (MS), and idiopathic thrombocy­ topenic purpura. However, there is no sex difference in the incidence of type 1 DM, and ankylosing spondylitis occurs more commonly in men. Sex differences in both immune responses and adverse reactions to vaccines have been reported. For example, there is a female prepon­ derance of postvaccination arthritis.

Adaptive immune responses are more robust in women than in men; this may be explained by the stimulatory actions of estrogens and the inhibitory actions of androgens on the cellular mediators of immunity. Consistent with an important role for sex hormones, there is variation in immune responses during the menstrual cycle, and the activity of certain autoimmune disorders is altered by castra­ tion or pregnancy (e.g., RA and MS may remit during pregnancy). Nevertheless, the majority of studies show that exogenous estrogens and progestins in the form of HT or oral contraceptives do not alter autoimmune disease incidence or activity. Exposure to fetal antigens, including circulating fetal cells that persist in certain tissues, has been speculated to increase the risk of autoimmune responses. There is clearly an important genetic component to autoimmunity, as indicated by the familial clustering and HLA association of many such disorders. X chromosome genes also contribute to sex differences in immunity. Indeed, nonrandom X chromosome inactivation may be a risk factor for autoimmune diseases. PART 12 Endocrinology and Metabolism ■ ■HIV INFECTION (See also Chap. 208) Women (sex assigned at birth) accounted for 18% (6600) of the ~36,100 new HIV diagnoses in the United States in 2021. This represents a similar incidence observed in recent years. Black/ African-American women accounted for 54% of new diagnoses among people assigned as female at birth, as compared to white women, who accounted for 23%, and Hispanic/Latino women, who represented about 18% of the newly diagnosed. AIDS remains an important cause of death in younger women, particularly African-American women aged 25–44 years. Heterosexual contact with an at-risk partner is the fastest-growing transmission category, and women are more suscep­ tible to HIV infection during vaginal sex than men. This increased susceptibility is accounted for in part by an increased prevalence of sexually transmitted diseases, i.e., gonorrhea and syphilis, in women. Some studies have suggested that hormonal contraceptives may increase the risk of HIV transmission. Progesterone has been shown to increase susceptibility to infection in nonhuman primate models of HIV. Women are also more likely to be infected by multiple variants of the virus than men. Women with HIV have more rapid decreases in their CD4 cell counts than do men. Compared with men, HIVinfected women more frequently develop candidiasis, but Kaposi’s sarcoma is less common than it is in men. Women have more adverse reactions, such as lipodystrophy, dyslipidemia, and rash, with antiret­ roviral therapy than do men. This observation is explained in part by sex differences in the pharmacokinetics of certain antiretroviral drugs, resulting in higher plasma concentrations in women. ■ ■OBESITY (See also Chap. 414) The prevalence of both obesity (body mass index ≥30 kg/m2) and abdominal obesity (waist circumference ≥88 cm in women) are similar in U.S. women and men. According to the most recent National Health and Nutrition Examination Survey data span­ ning 2017 until prepandemic March 2020, the age-adjusted prevalence of obesity among U.S. adults was 41.8%, and there were no significant differences observed between women and men, even across different age groups. However, some sex-specific differences were observed: the prevalence of obesity was highest among non-Hispanic black women (57.9%) as compared with non-Hispanic white (39.6%), Hispanic (45.7%), and non-Hispanic Asian women (14.5%). NonHispanic black women had a higher prevalence of obesity compared to non-Hispanic black men. There were no significant differences in prevalence between men and women among non-Hispanic white, non-Hispanic Asian, or Hispanic adults. More than 80% of patients who undergo bariatric surgery are women. Pregnancy and menopause are risk factors for obesity.

There are major sex differences in body fat distribution. Women characteristically have a gluteal and femoral or gynoid pattern of fat distribution, whereas men typically have a central or android pattern. Women have more subcutaneous fat than men. In women, endogenous androgen levels are positively associated with abdominal obesity, and androgen administration increases visceral fat. In contrast, there is an inverse relationship between endogenous androgen levels and abdominal obesity in men. Further, androgen administration decreases visceral fat in these obese men. The reasons for these sex differences in the relationship between visceral fat and androgens are unknown; however, emerging evidence suggests that there is a contribution of genetic variation. Studies in humans also suggest that sex steroids play a role in modulating food intake and energy expenditure. In men and women, abdominal obesity characterized by increased visceral fat is associated with an increased risk for CVD and DM. Obesity increases a woman’s risk for certain cancers, in particular post­ menopausal breast and endometrial cancer, in part because adipose tis­ sue provides an extragonadal source of estrogen through aromatization of circulating adrenal and ovarian androgens, especially the conversion of androstenedione to estrone. Obesity increases the risk of infertility, miscarriage, and complications of pregnancy. In addition to sex-specific epidemiologic differences in obesity, notable patterns have emerged with the advent and rising popular­ ity of the novel obesity pharmacotherapies, namely the glucagon-like 1 peptide (GLP1) receptor agonists and the combined GLP1/gastric inhibitory polypeptide (GIP) receptor agonists (Chap. 414). In the recent Semaglutide Treatment Effect in People with Obesity (STEP 1–4) studies from 2021, in which weekly semaglutide was compared to placebo for weight management, women comprised 55–80% of the study populations. Subgroup analyses evaluating the efficacy of sema­ glutide by sex have demonstrated a greater average weight reduction in women participants compared to men. Possible explanations for these findings include a lower average baseline body weight in women, potential differences in eating behavior that may be regulated by dif­ ferences in sex hormones, and differential rates of gastric emptying. Sex-related differences in gastrointestinal side effects may also play a role. A possible connection may exist at the neurologic level: a recent study in mice demonstrated sex-specific dynamics in GLP1 recep­ tor and GIP receptor expression patterns in metabolically responsive areas of the hypothalamus and the amygdala induced by exposure to a high-fat diet. It remains unclear whether mechanistic differences may explain the differential outcomes in women compared to men who use these medications. ■ ■OSTEOPOROSIS (See also Chap. 423) Osteoporosis is about five times more common in postmenopausal women than in age-matched men, and osteopo­ rotic hip fractures are a major cause of morbidity in elderly women. Men accumulate more bone mass and lose bone more slowly than do women. Sex differences in bone mass are found as early as infancy. Calcium intake, vitamin D, and estrogen all play important roles in bone formation and bone loss. Particularly during adolescence, calcium intake is an important determinant of peak bone mass. Vitamin D deficiency is surprisingly common in elderly women, occurring in

40% of women living in northern latitudes. Receptors for estrogens and androgens have been identified in bone. Estrogen deficiency is associated with increased osteoclast activity and a decreased number of bone-forming units, leading to net bone loss. The aromatase enzyme, which converts androgens to estrogens, is also present in bone. Estrogen is an important determinant of bone mass in men (derived from the aromatization of androgens) as well as in women. ■ ■PHARMACOLOGY On average, women have lower body weights, smaller organs, a higher percentage of body fat, and lower total-body water than men. There are also important sex differences in drug action and metabolism that are not accounted for by these differences in body size and composition. Sex steroids alter the binding and metabolism of a number of drugs. Further, menstrual cycle phase and pregnancy can alter drug action.

Women also take more medications than men, including over-thecounter formulations and supplements. The greater use of medications combined with these biologic differences may account for the reported higher frequency of adverse drug reactions in women than in men. Two-thirds of cases of drug-induced torsades des pointes, a rare, life-threatening ventricular arrhythmia, occur in women because they have a longer, more vulnerable QT interval. These drugs, which include certain antihistamines, antibiotics, antiarrhythmics, and antipsychot­ ics, can prolong cardiac repolarization by blocking cardiac voltagegated potassium channels. ■ ■PSYCHOLOGICAL DISORDERS (See also Chap. 463) Depression, anxiety, and affective and eating disorders (bulimia and anorexia nervosa) are more common in women than in men. Epidemiologic studies from both developed and develop­ ing nations consistently find major depression to be twice as common in women as in men, with the sex difference becoming evident in early adolescence. Depression occurs in 10% of women during pregnancy and in 10–15% of women during the postpartum period. There is a high likelihood of recurrence of postpartum depression with subse­ quent pregnancies. The incidence of major depression diminishes after the age of 45 years and does not increase with the onset of menopause. Depression in women appears to have a worse prognosis than does depression in men; episodes last longer, and there is a lower rate of spontaneous remission. Schizophrenia and bipolar disorders occur at equal rates in men and women, although there may be sex differences in symptoms. Both biologic and social factors account for the greater prevalence of depressive disorders in women. Men have higher levels of the neurotransmitter serotonin. Sex steroids also affect mood, and fluc­ tuations during the menstrual cycle have been linked to symptoms of premenstrual syndrome. Sex hormones differentially affect the hypo­ thalamic-pituitary-adrenal responses to stress. Testosterone appears to blunt cortisol responses to corticotropin-releasing hormone. Both low SARS-CoV2 SARS-CoV2 Attachment Activation Testosterone Attachment Activation TMPRSS2 ACE2 Cytosol HSP HSP AR AR Activated Virus entry Virus entry Translocation Nucleus TMPRSS2 mRNA ? TMPRSS2 ARE TMPRSS2 ARE FIGURE 410-3  Proposed sex hormone differences in TMPRSS2-mediated SARS-CoV-2 host cell entry. The virus entry point into cells is the membrane-bound angiotensin-converting enzyme 2 (ACE2) receptor. The cell-membrane protease, TMPRSS2, is also vital for host cell entry. Circulating levels of ACE2, expressed abundantly in the lung, heart, and kidney tissues, have been reported to be relatively higher in men. Upregulation of the ACE2 receptor in men may provide greater opportunity for cellular entry, viral replication, symptom development, and multiorgan involvement. (Adapted from C Gebhard et al: Impact of sex and gender on COVID-19 outcomes in Europe. Biol Sex Differ 11:29, 2020.)

and high levels of estrogen can activate the hypothalamic-pituitaryadrenal axis.

■ ■COVID-19 INFECTION (See also Chap. 205) Soon after the discovery of COVID-19, which was identified in November 2019 in Wuhan, China, as being caused by the novel coronavirus SARS-CoV-2, it was evident that there were appreciable sex differences in severity and outcomes. Indeed, observa­ tional data from the early pandemic, spanning late 2019 to early 2020, demonstrated a higher overall incidence of infectious cases, hospital­ izations, intensive care unit admissions, and case-fatality rates among men as compared to women. More pronounced sex differences were observed with advanced age, with a higher overall incidence in older male age groups. These sex differences have persisted among different racial, ethnic, and socioeconomic groups and across all continents, as SARS-CoV-2 became a global pandemic. Women’s Health CHAPTER 410 There are several potential mechanisms for these sex-specific effects of SARS-CoV-2 infection (Fig. 410-3). The virus’s entry point into cells is the membrane-bound angiotensin-converting enzyme 2 (ACE2) receptor, and it also harnesses the primer TMPRSS2, a cellular serine protease. Circulating levels of ACE2, which is expressed in a variety of tissues including the lung, heart, and kidneys, have been reported to be relatively higher in men who have diabetes and/or kidney disease, as well as in healthy men; however, not all studies have reported similar sex differences. One hypothesis is that upregulation of the ACE2 receptor in men may provide greater opportunity for cellular entry, viral replication, and development of symptoms and deleterious sequelae. ACE2 plays a critical role in bronchial transient secretory cells/type II alveolar cells as well as the renin-angiotensin-aldosterone system (RAAS). In the RAAS, ACE2 opposes angiotensin II’s vasoconstrictive actions by converting angiotensin II to the vasodilatory angiotensin 1-7 in critical tissues, including cardiac myocytes, cardiac fibroblasts, and coronary endothelial cells. Importantly, recent evidence has shown the impact of sex and sex hormones on the RAAS and ACE2: estrogen downregulates angiotensin II receptor type 1 and regulates renin activity, as well as modulates local RAAS in the atrial myocardium. Furthermore, it has been shown that ovariectomized females have increased ACE2 activity and expression in their kidney and adipose tissue and that estradiol replacement reduces ACE2 expression. On the contrary, orchiecto­ mized males have decreased ACE2 activ­ ity. Estrogen appears to reduce ACE2 expression in the heart and kidney in both rodent and human studies. SARS-CoV2 ACE2 TMPRSS2 TMPRSS2, a vital contributor to SARSCoV-2 cellular invasion, is a protein that is most abundantly expressed in prostate epithelial tissue, including high-grade prostate cancers and metastases. Accord­ ingly, the protein’s involvement in viral priming is thought to be an important reason for the higher case-fatality rate observed in men; however, the associa­ tion has not yet been proven. TMPRSS2 is also expressed in airway epithelia, where its physiologic function is not entirely clear. Transcription of the cellular protein is regulated by androgenic ligands and androgen receptor binding element; it is unknown whether estrogen plays a role in its regulation. Emerging in vitro stud­ ies have demonstrated that a TMPRSS2 inhibitor blocks viral entry into cells. These data may serve as an important foundation for sex-specific and personal­ ized therapeutic approaches in the future. TMPRSS2 mRNA

26 - 411 Men’s Health

411 Men’s Health

■ ■SUBSTANCE ABUSE AND TOBACCO (See also Chaps. 464 and 465) Substance abuse is more common in men than in women. However, nearly one-third of Americans who suf­ fer from alcoholism are women. Women are less likely to be diagnosed with alcoholism than men. A greater proportion of men than women seek help for alcohol and drug abuse. Men are more likely to go to an alcohol or drug treatment facility, whereas women tend to approach a primary care physician or mental health professional for help under the guise of a psychosocial problem. Blood alcohol levels are higher in women than in men after drinking equivalent amounts of alcohol, adjusted for body weight. This greater bioavailability of alcohol in women is due to both the smaller volume of distribution and the slower gastric metabolism of alcohol secondary to lower activity of gastric alcohol dehydrogenase than is the case in men. Women with alcohol­ ism have a higher mortality rate than do women and men without alcoholism. Women also appear to develop alcoholic liver disease and other alcohol-related diseases with shorter drinking histories and lower levels of alcohol consumption. Alcohol abuse also poses special risks to a woman, adversely affecting fertility and the health of the baby (fetal alcohol syndrome). Even moderate alcohol use increases the risk of breast cancer, hypertension, and stroke in women.

PART 12 Endocrinology and Metabolism More men than women smoke tobacco, but this sex difference continues to decrease. Women have a much larger burden of smokingrelated disease. Smoking markedly increases the risk of CVD in pre­ menopausal women and is also associated with a decrease in the age of menopause. Women who smoke are more likely to develop chronic obstructive pulmonary disease and lung cancer than men and at lower levels of tobacco exposure. Postmenopausal women who smoke have lower bone density than women who never smoked. Smoking during pregnancy increases the risk of preterm deliveries and low birth weight infants. ■ ■VIOLENCE AGAINST WOMEN Approximately 15% of women in the United States have experienced rape, physical violence, and/or stalking by an intimate partner, as compared to 4% of men with similar experiences. Adult women are much more likely to be raped by a spouse, ex-spouse, or acquaintance than by a stranger. Intimate partner violence (IPV) is a leading cause of death among young women. Rates of reported IPV in the United States increased dramatically amid stay-at-home orders during the COVID19 pandemic but have since declined again to prepandemic rates. IPV is an important risk factor for depression, substance abuse, and suicide in women. Screening instruments can identify women experiencing IPV and should be administered in settings that ensure adequate pri­ vacy and safety. SUMMARY Women’s health is now a mature discipline, and the importance of sex differences in biologic processes is well recognized. Nevertheless, ongoing misperceptions about disease risk, not only among women but also among their health care providers, result in insufficient attention to modifiable risk factors. Research into the fundamental mechanisms of sex differences will provide important biologic insights. Further, those insights will have an impact on both women’s and men’s health. ■ ■FURTHER READING Howell E: Reducing disparities in severe maternal morbidity and mortality. Clin Obstet Gynecol 61:2, 2018. Lott N et al: Sex hormones in SARS-CoV-2 susceptibility: Key play­ ers or confounders? Nat Rev Endocrinol 19:217, 2023. Rich-Edwards J et al: Sex and gender differences research design for basic, clinical, and population studies: Essentials for investigators. Endocr Rev 39:4, 2018. Rubino D et al: Effect of continued weekly subcutaneous semaglu­ tide vs placebo on weight loss maintenance in adults with over­ weight or obesity: The STEP 4 randomized clinical trial. JAMA 325:14, 2021. Singh T et al: Takotsubo syndrome: Pathophysiology, emerging con­ cepts, and clinical implications. Circulation 145:13, 2022.

Shalender Bhasin

Men’s Health The emergence of men’s health as a distinct discipline within internal medicine is founded on the wide consensus that men and women dif­ fer across their life span in their susceptibility to disease, in the clinical manifestations of the disease, and in their response to treatment. Fur­ thermore, men and women weigh the health consequences of illness differently and have different motivation for seeking care. Men and women experience different types of disparities in access to health care services and in the manner in which health care is delivered to them because of a complex array of socioeconomic and cultural factors. Attitudinal and institutional barriers to accessing care, fear and embar­ rassment due to the perception that it is not manly to seek medical help, and reticence on the part of patients and physicians in discussing issues related to sexuality, substance use, and aging have heightened the need for programs tailored to address the specific health needs of men. The sex differences in disease prevalence, susceptibility, and clinical manifestations of the disease were discussed in Chap. 410 (Women’s Health) and will not be discussed here. It is notable that the two leading causes of death in both men and women—heart disease and cancer—are the same. However, men have higher prevalence of neu­ rodevelopmental and degenerative disorders; substance use disorders, including the use of performance-enhancing drugs and alcohol use disorder; diabetes; cardiovascular disease; liver cirrhosis; and some types of cancer such as prostate, melanoma, and pancreatic cancer; and women have a higher prevalence of autoimmune disorders, depression, rheumatologic disorders, and osteoporosis. Men are substantially more likely to die from accidents, suicides, and homicides than women. Among men 15–34 years of age, unintentional injuries, homicides, and suicides account for over three-fourths of all deaths. Among men 35–64 years of age, heart disease, cancer, and unintentional injuries are the leading causes of death. Among men ≥65 years of age, heart disease, cancer, lower respiratory tract infections, and stroke are the major causes of death. From 1999 to 2010, the mortality rates in the United States decreased for men and women of all age groups, largely due to reduced death rates from heart attacks, cancer, motor vehicle injuries, and HIV infection. However, since 2010, troubling disparities in sex-specific mortality rates have emerged among middle-aged men in the United States. From 2010 to 2017, the death rates have risen and life expec­ tancy has decreased for young and middle-aged men. The increase in mortality rates among people aged 25–64 was the highest in the Ohio Valley and Appalachia, and in the New England states of New Hampshire, Maine, and Vermont. The rising mortality rates in young and middleaged men have been attributed to an increase in deaths due to drug overdose, alcohol-related liver disease, and suicide. The rising rates of “deaths of despair” among young and middle-aged men, especially white non-Hispanics, have been associated with deterioration in eco­ nomic and social well-being, reduced rates of marriage and labor force participation, and poor physical and mental health. The biologic bases of sex differences in disease susceptibility, pro­ gression, and manifestation remain incompletely understood and are likely multifactorial. Undoubtedly, sex-specific differences in the genetic architecture and circulating sex hormones influence disease phenotype; additionally, epigenetic effects of sex hormones during fetal life, infancy, and pubertal development may epigenetically imprint sexual and nonsexual behaviors, body composition, and disease sus­ ceptibility. The circulating and tissue concentrations of sex hormones differ substantially in men and women, and these hormonal differences may affect gene expression in cells of males and females in all parts of the body. The presence of only one X chromosome in men renders them more susceptible to X-linked disorders than women. Due to the X inactivation of one randomly chosen X chromosome, women’s bod­ ies contain two epigenetically different cell populations. The genes that

do not undergo X inactivation exhibit dosage differences between male and female cells. Expression of the Y chromosome genes in men may affect the function of somatic cells containing the Y chromosome. The loss of Y chromosome with aging in men is associated with increased risk of heart disease, especially heart failure, certain types of cancers, and shortened life span. The differences in the imprinting of maternally and paternally derived genes may also contribute to sex differences in the expression of disease. Reproductive load and physiologic changes during pregnancy, including profound hormonal and metabolic shifts and microchimerism (transfer of cells from the mother to the fetus and from the fetus to the mother), may affect disease susceptibility and disease severity in women. Sociocultural norms of child-rearing prac­ tices, societal expectations of gender roles, and the long-term economic impact of these practices and gender roles influence health behaviors and disease risk. Furthermore, the trajectories of age-related changes in sex hormones during the reproductive and postreproductive years vary substantially between men and women and influence the sex-specific patterns of the temporal evolution of age-related conditions such as osteoporosis, breast cancer, and autoimmune disease. In a reflection of the growing attention on issues related to men’s health, men’s health clinics have mushroomed all over the country. Although the major threats to men’s health have not changed—heart disease, cancer, and unintentional injury continue to dominate the list of major medical causes of morbidity and mortality in men—the men who attend men’s health clinics do so largely for sexual, reproductive, and urologic health concerns involving common conditions, such as testosterone deficiency syndromes, age-related decline in testos­ terone levels, sexual dysfunction, muscle dysmorphia and anabolicandrogenic steroid (AAS) use, lower urinary tract symptoms (LUTS), and medical complications of prostate cancer therapy, which are the subjects of this chapter. Additionally, we are witnessing the emergence of new categories of body image disorders in men that had not been recognized until the 1980s, such as the body dysmorphia syndrome and the use of performance-enhancing drugs to increase muscularity and lean appearance. Although menopause and women’s health have been the subject of intense investigation for more than five decades, these issues that are specific to men’s health are just beginning to gain the attention that they deserve because of their high prevalence and impact on overall health, well-being, and quality of life. AGING-RELATED CHANGES IN MALE REPRODUCTIVE FUNCTION A number of cross-sectional and longitudinal studies (e.g., the Bal­ timore Longitudinal Study of Aging, the Framingham Heart Study [FHS], the Massachusetts Male Aging Study, and the European Male Aging Study [EMAS]) have established that testosterone concentrations decrease with advancing age. This age-related decline starts in the third decade of life and progresses slowly (Fig. 411-1); the magnitude and trajectory of age-related decline in testosterone levels are affected by adiposity and weight change, comorbid conditions, and genetic factors. Because sex hormone–binding globulin (SHBG) concentrations are higher in older men than in younger men, free or bioavailable testos­ terone concentrations decline with aging to a greater extent than total testosterone concentrations. In the EMAS, 2.1% of community-dwelling men aged 40–70 years had total testosterone levels <317 ng/dL and a free testosterone level of <64 pg/mL, as well as sexual symptoms. The age-related decline in testosterone is due to defects at all levels of the hypothalamic-pituitary-testicular (HPT) axis. Pulsatile gonadotropinreleasing hormone (GnRH) secretion is attenuated, luteinizing hormone (LH) response to GnRH is reduced, and the frequency, amplitude, and area of LH pulses are reduced in older men. Leydig cell number is reduced and testicular response to LH is impaired. The gradual rise of LH with aging suggests that testis dysfunction is the main cause of declining androgen levels. In epidemiologic surveys, low total and bioavailable testosterone concentrations in middle-aged and older men are associated with decreased sexual desire, poor erections, and diminished early morning erections; lower appendicular skeletal muscle mass, muscle strength,

Total testosterone (ng/dL) vs. age (y) FHS EMAS MrOS Testosterone level (ng/dL)

Men’s Health CHAPTER 411

20–29 50–59 Age (y) 60–69 70–79 80+ 30–39 40–49 FIGURE 411-1  Age-related decline in total testosterone levels. Total testosterone levels measured using liquid chromatography–tandem mass spectrometry in men of the Framingham Heart Study (FHS), the European Male Aging Study (EMAS), and the Osteoporotic Fractures in Men Study (MrOS). (Reproduced with permission from S Bhasin et al: Reference ranges for testosterone in men generated using liquid chromatography tandem mass spectrometry in a community-based sample of healthy nonobese young men in the Framingham Heart Study and applied to three geographically distinct cohorts. J Clin Endocrinol Metab 96:2430, 2011.) and self-reported physical function; increased risk of mobility limitation and falls; higher visceral fat mass, insulin resistance, and type 2 diabetes; reduced telomere length and increased all-cause and cardiovascular mor­ tality; lower areal and volumetric bone mineral density and bone quality; and higher rates of bone fractures (Table 411-1). Middle-aged and older men with hypogonadism report a high frequency of depressive symp­ toms. However, testosterone levels have not been consistently associated with major depressive disorder. An analysis of signs and symptoms in older men in the EMAS revealed a syndromic association of sexual symp­ toms with total testosterone levels <320 ng/dL and free testosterone levels <64 pg/mL in community-dwelling older men. Men with hypogonadism or Klinefelter’s syndrome have reduced prostate cancer mortality. Mendelian randomization studies using data from the United Kingdom Biobank Study found a sexual dimorphic relation between genetically determined testosterone levels and the risk of type 2 dia­ betes; in men, lower genetically determined testosterone levels were associated with higher risk of type 2 diabetes, but in women, higher genetically determined testosterone levels were associated with higher risk of type 2 diabetes. Higher genetically determined testosterone levels were also associated with increased risk of prostate cancer in men in this study. TABLE 411-1  Association of Testosterone Levels with Outcomes in Older Men

  1. Positively associated with: • Muscle mass and muscle strength • Self-reported and performance-based measures of physical function • Sexual desire • Bone mineral density, bone geometry and quality, and volumetric bone mineral density
  2. Negatively associated with risk of: • Coronary artery disease • Type 2 diabetes mellitus • Metabolic syndrome • All-cause mortality • Falls and fracture risk • Dementia and Alzheimer’s disease • Frailty • Late-onset low-grade persistent depressive disorder (dysthymia)
  3. Not associated with: • Lower urinary tract symptoms • Erectile dysfunction • Major depressive disorder

■ ■EFFICACY OF TESTOSTERONE REPLACEMENT THERAPY IN MIDDLE-AGED AND OLDER MEN WITH HYPOGONADISM Two large, randomized trials—the Testosterone Trials (TTrials) and the Testosterone Replacement Therapy for Assessment of LongTerm Vascular Events and Efficacy Response in Hypogonadal Men (TRAVERSE) trial—have provided the most comprehensive data on the efficacy and safety of testosterone treatment in middle-aged and older men with hypogonadism. The TTrials, a set of seven coordi­ nated placebo-controlled efficacy trials of testosterone replacement therapy, enrolled 788 men, aged 65 years or older, with an average of two morning, fasting total testosterone levels <275 ng/dL and one or more of the following: low sexual desire, mobility limitation, and/or fatigue. The primary aim of the TRAVERSE trial was to compare the effects of testosterone replacement therapy and placebo treatment on major adverse cardiovascular events in middle-aged and older men, 45–80 years, with two fasting, morning testosterone concentrations <300 ng/dL, one or more symptoms of hypogonadism, and preexisting coronary artery disease (CAD) or increased risk of CAD. The eligible participants were randomized with stratification for preexisting CAD to receive either 1.62% transdermal testosterone gel or a placebo gel daily for up to 5 years. Because of its large sample size and long dura­ tion, the TRAVERSE trial has provided important data on the efficacy and long-term safety of testosterone replacement therapy. In these and other trials, testosterone treatment was associated with greater improvement in overall sexual activity, sexual desire, and hypogonadal symptoms than placebo (Table 411-2). The effects of testosterone alone on erectile function were small and inconsistent across stud­ ies. Nearly 15% of men enrolled in the TRAVERSE trial had anemia; among men with anemia, a greater proportion of testosterone-treated men than placebo-treated men experienced correction of anemia. Tes­ tosterone treatment also reduced the incidence of anemia in men who were not anemic at baseline. Fifty percent of men with hypogonadism reported significant depressive symptoms at baseline; however, only 1.5% of men in the TRAVERSE trial met the rigorous definition of latelife-onset, low-grade persistent depressive disorder (previously called dysthymia). Testosterone treatment was more efficacious in improving

PART 12 Endocrinology and Metabolism TABLE 411-2  The Potential Benefits of Testosterone Replacement Therapy in Middle-Aged and Older Men with Hypogonadism Strong Evidence of Efficacy

  1. Improves overall sexual activity and sexual desire in men with low libido
  2. Relieves hypogonadal symptoms
  3. Improves depressive symptoms in men with significant depressive symptoms
  4. Improves energy level
  5. Corrects unexplained anemia and prevents the development of anemia
  6. Increases skeletal muscle mass, reduces whole-body and abdominal fat mass
  7. Increases areal and volumetric bone mineral density and estimated bone strength Suggestive Evidence of Efficacy
  8. Modestly improves mobility in older men with mobility limitation Evidence of Lack of Efficacy
  9. Improves cognitive function in older men without cognitive deficit
  10. Improves depressive symptoms with major depressive disorder  Note: The Testosterone Trials (TTrials) and the TRAVERSE trial have provided robust evidence of efficacy of testosterone replacement therapy in middle-aged and older men with hypogonadism. The TTrials were a set of seven coordinated placebocontrolled trials whose primary aim was to determine whether testosterone treatment for 1 year of men aged 65 years or older with an average of two fasting morning testosterone levels <275 ng/dL plus one or more of low sexual desire, mobility limitation, and/or low vitality was more efficacious than placebo in improving sexual function, mobility, and/or vitality. The primary aim of the TRAVERSE trial was to compare the effect of testosterone replacement therapy with placebo on major adverse cardiovascular events in middle-aged and older men, 45–80 years of age, with at least two fasting morning testosterone level <300 ng/dL and preexisting coronary artery disease or increased risk of coronary artery disease. Because of its large sample size and longer treatment duration, the TRAVERSE trial has provided some of the most comprehensive evidence of the efficacy and safety of testosterone replacement therapy.

depressive symptoms and energy level than placebo. Testosterone treat­ ment improved volumetric as well as areal bone mineral density and estimated bone strength; the improvement in volumetric bone density in the spine was greater than in the hip and greater in the trabecular than the peripheral bone. Testosterone treatment also increased lean body mass, muscle strength, and some measures of physical function (Fig. 411-2). In the TTrials, testosterone treatment of older men with mobility limitation improved self-reported walking ability and mod­ estly improved 6-min walking distance but did not affect falls. In TRAVERSE trial participants who had prediabetes, the incidence of progression from prediabetes to diabetes was similar between testosterone- and placebo-treated groups. Testosterone treatment did not improve glycemic control in men with hypogonadism and predia­ betes or diabetes at baseline. Thus, testosterone treatment should not be used alone to improve glycemic control in men with diabetes or prediabetes. These findings of the TRAVERSE trial are in contrast to those of the Testosterone for Diabetes Mellitus (T4DM) trial in men, aged 50–74 years without hypogonadism who had a newly diagnosed type 2 diabetes or were at increased risk for type 2 diabetes. Testos­ terone treatment in conjunction with a lifestyle program for 2 years reduced the proportion of participants with type 2 diabetes more than Body composition and muscle strength Grip strength Fat mass Lean body mass –2

A Difference between change in testosterone and placebo (kg) Bone health Lumbar spine Femoral neck

Difference between testosterone and placebo change in bone mineral density (%) B Sexual function Sexual thoughts Sexual satisfaction Morning erections Intercourse Erectile function

Standardized mean difference between testosterone and placebo C FIGURE 411-2  The effects of testosterone therapy on body composition, muscle strength, bone mineral density (BMD), and sexual function in intervention trials. The point estimates and the associated 95% confidence intervals are shown. A. The effects of testosterone therapy on lean body mass, grip strength, and fat mass in a meta-analysis of randomized trials. B. The effects of testosterone therapy on lumbar and femoral BMD in a meta-analysis of randomized trials. C. The effects of testosterone therapy on measures of sexual function in men with baseline testosterone <10 nmol/L (290 ng/dL). (A. Data from S Bhasin et al: Drug insight: Testosterone and selective androgen receptor modulators as anabolic therapies for chronic illness and aging. Nat Clin Pract Endocrinol Metab 2:146, 2006. B. Data from MJ Tracz et al: Testosterone use in men and its effects on bone health. A systematic review and meta-analysis of randomized placebo-controlled trials. J Clin Endocrinol Metab 91:2011, 2006. C. Data from AM Isidori et al: Effects of testosterone on sexual function in men: results of a meta-analysis. Clin Endocrinol (Oxf) 63:381, 2005.)

TABLE 411-3  Adverse Events Associated with Testosterone Replacement Therapy in Middle-Aged and Older Men Adverse Events for Which There Is Strong Evidence     Erythrocytosis     Venous thromboembolic events     Growth of metastatic prostate cancer     Reduced sperm production and fertility     Acne     Increased risk of detection of low-grade prostate cancer Adverse Events for Which There Is Strong Evidence That Testosterone Treatment Does NOT Increase Risk     Major adverse cardiovascular events     Lower urinary tract symptoms Adverse Events for Which There Is Weak Evidence     Atrial fibrillation     Bone fractures     Acute kidney injury     Male pattern balding Adverse Events for Which There Is Insufficient Evidence to Assess Risk     Gynecomastia     Growth of breast cancer  placebo plus lifestyle program. Testosterone therapy has not been shown to improve cognitive function in men who do not have cogni­ tive dysfunction. ■ ■SAFETY OF TESTOSTERONE REPLACEMENT THERAPY IN MIDDLE-AGED AND OLDER MEN WITH HYPOGONADISM Erythrocytosis is the most frequent adverse event associated with tes­ tosterone treatment (Table 411-3). In two placebo-controlled trials, the rates of atherosclerosis progression did not differ significantly between the testosterone and placebo groups. In the Cardiovascular Trial of the TTrials, testosterone treatment was associated with a greater increase in the volume of the noncalcified plaque than placebo. In the TRA­ VERSE trial, which was designed and powered specifically to assess the cardiovascular safety of testosterone, the incidence of major adverse cardiovascular events, which included nonfatal myocardial infarction, cardiovascular death, and nonfatal stroke, was similar between the testosterone- and placebo-treated men. The incidences of high-grade prostate cancer or any prostate cancer, acute urinary retention, inva­ sive surgical procedures for benign prostatic hyperplasia, or initiation of new pharmacologic treatment for benign prostatic hyperplasia were low and did not differ significantly between the testosterone and placebo groups. Testosterone treatment did not worsen lower urinary tract symptoms but was associated with a higher incidence of venous thromboembolic events, atrial fibrillation, and acute kidney injury. The number of clinical bone fractures was greater in the testosterone group than in the placebo group; this finding was surprising because testos­ terone treatment increases areal and volumetric bone mineral density and estimated bone strength. APPROACH TO THE PATIENT Older Men with Age-Related Decline in Testosterone Population screening of all older men for low testosterone levels is not recommended; testing should be restricted to men who have symptoms or physical features suggestive of hypogonadism. Tes­ tosterone treatment of older men with hypogonadism offers some clinical benefits (e.g., improvement of sexual symptoms in men with low libido, improvements in mood and energy, correction of anemia), but also has some potential for adverse effects (e.g., increased risk of venous thromboembolism and atrial fibrillation). An expert panel of the Endocrine Society recommended against

testosterone treatment of all older men with low testosterone levels. Instead, the expert panel recommended that “testosterone therapy should be offered on an individualized basis … in men >65 years who have symptoms or conditions suggestive of testosterone defi­ ciency (e.g., low libido, significant depressive symptoms, fatigue, or unexplained anemia) and consistently low testosterone.” The decision to offer testosterone treatment to older men with hypo­ gonadism should be a shared decision, guided by an individualized assessment of potential benefits and risks and careful weighing of the burden of symptoms/conditions against the potential benefits and risks (Fig. 411-3). Evaluate whether the patient has clear evi­ dence of testosterone deficiency confirmed by two or more early morning, fasting testosterone levels below the lower limit of normal for healthy young men plus the presence of symptoms. Weigh the burden of symptoms/conditions against the known benefits and the uncertainty of long-term harm. Ascertain whether the patient has any conditions that might increase the risk of harm, such as prostate cancer, severe LUTS, erythrocytosis, or a hypercoagulable condition. Older men considering testosterone treatment should undergo baseline evaluation of prostate cancer risk. The initiation of prostate screening and monitoring should be a shared decision because prostate cancer screening has some risks. A shared decision to treat should be accompanied by a standardized monitoring plan to optimize the benefit-to-risk ratio. Men’s Health CHAPTER 411 AGE-RELATED CHANGES IN FECUNDITY Although testicular morphology, semen production, and fertility are maintained up to a very old age in men, advanced paternal age is a risk factor for reduced fertility. Compared to men aged 21–25 years, men >50 years have lower sperm motility and sperm morphology, a higher frequency of sperm tail defects, and lower fecundity. The fecundity is reduced when both parents are >40 years old. Increased workforce participation and changing career expectations of women, a higher age at reproductive union, and the availability of contraceptives that enable couples to separate their sexual and procreative lives have underpinned powerful secular trends toward postponement of child­ bearing to an older age. The median age at first childbirth has been increasing steadily across the world; postponement of childbirth to an older age increases the risk of involuntary childlessness because of the adverse effects of advanced maternal and paternal age on fecundity, increased risk of comorbidities that may indirectly affect fecundity, and the age-related changes in reproductive behaviors. Increased paternal age is associated with increased risk of germline mutations in the FGFR2, FGFR3, and RET genes and the associated autosomal dominant diseases, such as achondroplasia, Pfeiffer’s syndrome, thana­ tophoric dysplasia, Crouzon’s syndrome, Apert’s syndrome, multiple endocrine neoplasia (MEN) 2A, and MEN 2B. Advanced paternal age also increases the offspring’s risk of Klinefelter’s syndrome, trisomy 13 and 18, neurodevelopmental disorders such as schizophrenia, autism, bipolar disorders, and cardiac malformations such as ventricular septal defects, atrial septal defects, and patent ductus arteriosus. Sexual Dysfunction  Various forms of sexual dysfunction are a major motivating factor for men seeking care at men’s health clinics. The landmark descriptions of the human sexual response cycle by Masters and Johnson demonstrating that men and women display predictable physiologic responses after sexual stimulation provided the basis for rational classification of human sexual disorders. Subsequently, this model was expanded to include sexual desire, resulting in a three-stage model comprising of desire, arousal, and orgasm. Whipple and BrashMcGreer later proposed a circular model of sexual response whereby a positive sexual experience reinforces desire. The classification of sexual disorders in men has been revised in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) and the eleventh revision of the International Classification of Diseases and Related Health Problems (ICD-11). DSM-5 includes three major categories of male sexual disorders: sexual desire disorders, sexual arousal disorders, and orgasmic disorders. The DSM-5 also

The Approach to Individualized Decision-Making

  1. Establish that the patient has testosterone deficiency – consider the diagnostic imprecision.
  2. Weigh the burden of symptoms.
  3. Ascertain conditions that might increase the risk of harm.
  4. Share the burden of decision-making with the patient. Balancing the Potential for Benefits and Risks and Patient’s and Clinician’s Values The severity of testosterone deficiency and symptoms Potential benefits in context of the burden of symptoms PART 12 Endocrinology and Metabolism The strength of the evidence of testosterone deficiency Patient’s values and risk tolerance FIGURE 411-3.  An approach to individualized, shared treatment decision-making in older men with testosterone deficiency. Testosterone treatment is not indicated in all older men with testosterone deficiency. Consider the diagnostic imprecision in establishing the diagnosis, the burden of symptoms, and the presence of comorbid conditions that might increase the risk of harm. Weigh the potential benefits against the burden of symptoms, the potential of harm from treatment and monitoring in the context of other comorbid conditions, and the feasibility of alternate strategies such as weight loss, improved glycemic control, and the use of selective phosphodiesterase-5 inhibitors (PDE5Is). A shared treatment decision takes into consideration the patient’s and clinician’s values. ED, erectile dysfunction. includes an additional category of “other specified sexual dysfunction” due to causes other than those included in the above three categories. Male erectile dysfunction is now referred to as erectile disorder. Classification of the patient’s disorder into these categories is important as the etiologic factors, diagnostic tests, and therapeutic strategies vary for each class of sexual disorder. Historically, the clas­ sification and nomenclature for sexual disorders were based on the DSM, based on the erroneous belief that sexual disorders in men are largely psychogenic in origin. However, the recognition of erectile disorder as a manifestation of systemic disease and the availability of easy-to-use oral selective phosphodiesterase-5 (PDE5) inhibitors have placed sexual disorders in men within the purview of the primary care provider. These disorders have been discussed in Chap. 409 (Sexual Dysfunction). ■ ■MUSCLE DYSMORPHIA SYNDROME IN MEN—A FORM OF BODY IMAGE DISORDER Muscle dysmorphia is a form of body image disorder characterized by a pathologic preoccupation with muscularity and leanness. The men with muscle dysmorphia express a strong desire to be more muscular and lean and report dissatisfaction and embarrassment about their body size and shape, preoccupation with bodybuilding and muscular­ ity, and impairment of social and occupational functioning. Patients with muscle dysmorphia also report higher rates of mood and anxiety disorders and obsessive and compulsive behaviors than individuals without muscle dysmorphia. Patients with muscle dysmorphia syndrome—nearly all men—are almost always engaged in weightlifting and body building and are more likely to use performance-enhancing drugs, especially AASs, than men in the general population or even weightlifters without body dysmorphia. Muscle dysmorphia disorder exposes men to an increased risk of disease due to the combined interactive effects of the intensity of physical exercise, the use of performance-enhancing drugs, and other lifestyle factors associated with weightlifting and the use of performance-enhancing drugs. No randomized trials of any treatment modalities have been conducted; anecdotally, behavioral and cognitive therapies have been tried with varying degrees of success. AAS Abuse by Athletes and Recreational Bodybuilders  The illicit use of AASs to enhance athletic performance first surfaced in the 1950s among powerlifters and spread rapidly to other sports, profes­ sional as well as high school athletes, and recreational bodybuilders. In

The feasibility of alternate strategies (weight loss, glycemic control, PDE5Is for ED) The comorbid conditions that might increase the risk of adverse events Potential adverse effects of treatment and risks of monitoring Clinician’s the early 1980s, the use of AAS spread beyond the athletic community into the general population. Most AAS users are not athletes, but rather recreational weightlifters who use these drugs to look lean and more muscular. The most commonly used AASs include testosterone esters, nandro­ lone, stanozolol, methandienone, trenbolone, boldenone, and oxandro­ lone. AAS users generally use increasing doses of multiple steroids in a practice known as stacking. The adverse effects of long-term AAS abuse remain poorly under­ stood. Most of the information about the adverse effects of AAS has emerged from case reports, uncontrolled studies, or clinical trials that used replacement doses of testosterone (Table 411-4). The adverse event data from clinical trials using physiologic replacement doses of testosterone have been extrapolated unjustifiably to AAS users who may administer 10–100 times the replacement doses of testosterone over many years and to support the claim that AAS use is safe. A sub­ stantial fraction of AAS users also use other drugs that are perceived to be muscle-building or performance-enhancing, such as growth hormone; erythropoiesis-stimulating agents; insulin; stimulants such as amphetamine, clenbuterol, cocaine, ephedrine, and thyroxine; and drugs perceived to reduce adverse effects such as human chorionic gonadotropin (hCG), aromatase inhibitors, or estrogen antagonists. Men who abuse AAS are more likely to engage in other high-risk behaviors than nonusers. The adverse events associated with AAS use may be due to AAS themselves, concomitant use of other drugs, or high-risk behaviors. The high rates of mortality and morbidities observed in AAS users are alarming. One Finnish study reported 4.6 times the risk of death among elite power lifters than in age-matched men from the general population. The causes of death among power lifters included sui­ cides, myocardial infarction, hepatocellular failure, and non-Hodgkin’s lymphoma. A retrospective review of patient records in Sweden also reported higher standardized mortality ratios for AAS users than for nonusers. Studies indicate that 32% of deaths among AAS users were suicidal, 26% homicidal, and 35% accidental. The median age of death among AAS users in this study—24 years—was even lower than that for heroin or amphetamine users. Numerous reports of cardiac death among young AAS users raise concerns about the adverse cardiovascular effects of AAS. High doses of AAS may induce proatherogenic dyslipidemia, increase thrombosis risk via effects on clotting factors and platelets, induce vasospasm

TABLE 411-4  Potential Adverse Effects Associated with the Use of Anabolic-Androgenic Steroids A.  Four Major Categories of Serious Adverse Effects Associated with the Use of Anabolic-Androgenic Steroids

  1. Cardiovascular a. Hypertension b. Sudden death c. Cardiomyopathy d. Diastolic dysfunction e. Accelerated atherosclerosis f. Dyslipidemia
  2. Endocrine a. Suppression of the hypothalamic-pituitary-testicular axis i.  Anabolic steroid withdrawal hypogonadism ii.  Infertility iii.  Testicular atrophy b. Gynecomastia
  3. Neuropsychiatric a. Major mood disorders i.  Hypomania and mania during periods of high-dose anabolicandrogenic steroids use ii.  Depression and even suicidality during anabolic steroid withdrawal b. Other behavioral disorders i.  Rage reactions ii.  Aggressive responding and violence c. Dependence and addiction behaviors d. Cognitive deficits
  4. Musculoskeletal Injuries a. Tendon injuries b. Other musculoskeletal injuries B.  Other Adverse Events
  5. Hematologic a. Erythrocytosis b. Venous thromboembolic events
  6. Hepatotoxicity a. Inflammatory or cholestatic hepatic damage with the use of 17α-alkylsubstituted steroids b. Peliosis hepatis c. Hepatic adenoma d. Hepatocellular carcinoma
  7. Hair and skin a. Acne b. Scalp hair loss in genetically predisposed men c. Increased body hair d. Striae
  8. Renal a. Acute kidney injury due to rhabdomyolysis b. Focal glomerulosclerosis  through their effects on vascular nitric oxide, and induce myocardial hypertrophy and fibrosis. The supraphysiologic doses of testosterone and orally administered, 17-α-alkylated, nonaromatizable AAS are associated with marked reductions in high-density lipoprotein (HDL) cholesterol and increases in low-density lipoprotein (LDL) cholesterol. Studies using tissue Doppler and strain imaging and magnetic resonance imaging (MRI) have reported diastolic and systolic dysfunc­ tion, including lower early and late diastolic tissue velocities, reduced E/A ratio, and reduced peak systolic strain in AAS users than in nonusers. Power athletes using AAS often have short QT intervals but increased QT dispersion, which may predispose them to ventricular arrhythmias. Long-term AAS use may be associated with myocardial hypertrophy and fibrosis. Myocardial tissue of power lifters using AAS has been shown to be infiltrated with fibrous tissue and fat droplets. AAS users demonstrate higher coronary artery plaque volume than

nonusers, and lifetime AAS dose is associated with coronary athero­ sclerotic burden.

Long-term AAS use suppresses LH and follicle-stimulating hormone (FSH) secretion and inhibits endogenous testosterone production and spermatogenesis. Men who have used AAS for more than a few months experience marked suppression of the HPT axis after stopping AAS that may be associated with sexual dysfunction, fatigue, infertility, and depressive symptoms. In some long-term AAS users, HPT suppression may last more than a year, and in a few individuals, complete recovery may not occur. The symptoms of androgen deficiency during AAS withdrawal may cause some men to revert back to using AAS, leading to continued use and AAS dependence. As many as 30% of AAS users develop a syndrome of AAS dependence, characterized by long-term AAS use despite adverse medical and psychiatric effects. In some men’s health clinics, as many as 25% of young men receiving testosterone replacement therapy have anabolic steroid withdrawal hypogonadism. Men’s Health CHAPTER 411 Supraphysiologic doses of testosterone may also impair insulin sensitivity. Orally administered androgens have been associated with insulin resistance and diabetes. Unsafe injection practices, high-risk behaviors, and increased rates of incarceration render AAS users at increased risk of HIV and hepati­ tis B and C. In one survey, nearly 1 in 10 gay men had injected AAS or other substances, and AAS users were more likely to report high-risk unprotected anal sex than other men. Surveys of male prisoners find high rates of AAS use. Some AAS users develop hypomanic and manic symptoms dur­ ing AAS exposure (irritability, aggressiveness, reckless behavior, and psychotic symptoms, sometimes associated with violence) and major depression (sometimes associated with suicidality) during AAS with­ drawal. Users may also develop other forms of illicit drug use. AAS use has been associated with difficulties with spatial as well as working memory, problem solving, and attention, and structural and functional changes in many brain regions involved in inhibitory control and emotional regulation. A structural MRI study of users of high doses of AAS reported smaller cortical, gray matter, putamen, and corpus callosum volumes. Both low and high androgen levels have been associated with increased Aβ and tau-P levels and Aβ toxicity. These data have raised concern that long-term AAS use may increase the risk of Alzheimer’s disease and related dementias. Elevated liver enzymes, cholestatic jaundice, hepatic neoplasms, and peliosis hepatis have been reported with oral, 17-α-alkylated AAS. AAS use may cause muscle hypertrophy without compensatory adaptations in tendons, ligaments, and joints, thus increasing the risk of tendon and joint injuries. AAS use is associated with acne, baldness, and increased body hair. APPROACH TO THE PATIENT Detection of AAS Use AAS users generally mistrust physicians and seek medical help infrequently; when they do seek medical help, it is often for the treatment of AAS withdrawal syndrome, infertility, gynecomastia, or other medical or psychiatric complications of AAS use. The suspicion of AAS use should be raised by the increased hemoglobin and hematocrit levels; suppressed LH, FSH, SHBG and testosterone levels; low HDL cholesterol; and low testicular volume and sperm density in a person who looks highly muscular (Table 411-5). A combination of these findings along with self-report of their use by the patient—which usually can be elicited by a tactful interview— are often sufficient to establish a diagnosis in clinical practice. Accredited laboratories use gas chromatography and mass spec­ trometry or liquid chromatography and mass spectrometry to detect AAS abuse. Illicit testosterone use is detected generally by the measurement of the urinary testosterone-to-epitestosterone ratio and confirmed by the use of the 13C:12C ratio in testosterone by the use of isotope ratio combustion mass spectrometry. Exogenous testosterone administration increases urinary testosterone glucuro­ nide excretion and consequently the testosterone-to-epitestosterone

TABLE 411-5  Detection of the Use of Anabolic-Androgenic Steroids Clinical indicators that should raise suspicion of anabolic-androgenic steroid use

  1. “V” muscular phenotype
  2. Reduced testicular volume (<15 mL)
  3. Excessive concern about leanness and muscularity. Laboratory indicators
  4. Suppressed LH, FSH, and SHBG levels
  5. Increased hematocrit Detection of anabolic-androgenic steroids
  6. LC-MS/MS analysis of urine Detection of exogenous testosterone use
  7. Urinary testosterone-to-epitestosterone ratio
  8. Isotope ratio mass spectrometry analysis to detect differences in 13C:12C ratio PART 12 Endocrinology and Metabolism in exogenous and endogenous testosterone Note: In clinical settings, the use of anabolic-androgenic steroids can often be ascertained simply by direct questioning. Reduced testicular volume, suppressed LH and FSH, and increased hematocrit in an unusually muscular man should raise suspicion of anabolic-androgenic steroid use. Although rarely needed in clinical practice, recent use of anabolic-androgenic steroids can be confirmed by LC-MS/ MS analysis of urine. Exogenous testosterone use can be detected using the urinary testosterone-to-epitestosterone ratio and isotope ratio mass spectrometry analysis to detect differences in 13C:12C ratio in exogenous and endogenous testosterone. Abbreviations: FSH, follicle-stimulating hormone; LC-MS/MS, liquid chromatography–tandem mass spectrometry; LH, luteinizing hormone. ratio. Ratios >4 suggest exogenous testosterone use but can also reflect genetic variation. Genetic variations in the uridine diphos­ pho-glucuronyl transferase 2B17 (UGT2B17), the major enzyme for testosterone glucuronidation, CYP17 (the aromatase gene), SHBG, and 3’, 5’ cyclic nucleotide phosphodiesterase (PDE7B) affect the testosterone-to-epitestosterone ratio and increase the risk of a false-negative test. Synthetic testosterone has a lower 13C:12C ratio than endogenously produced testosterone, and these differences in the 13C:12C ratio can be detected by isotope ratio combustion mass spectrometry and used to confirm exogenous testosterone use in individuals with a high testosterone-to-epitestosterone ratio. TREATMENT Integrated Management of Patients with AAS Use The nonathlete weightlifters who abuse AAS frequently do not seek medical treatment and often mistrust physicians. They also do not view these drugs and the associated lifestyle as deleterious to their health. Many clinicians erroneously view AAS abuse as largely a problem of cheating in competitive sports, while, in fact, most AAS users are not athletes at all. In addition to treating the underlying body dysmorphia disorder that motivates the use of these drugs and the addiction behaviors, the treatment should be directed at the symptoms or the condi­ tion for which the patient seeks therapy, such as infertility, sexual dysfunction, gynecomastia, or depressive symptoms. Accordingly, therapy may include some combination of cognitive and behavioral therapy for muscle dysmorphia syndrome, antidepressant therapy for depression, selective PDE5 inhibitors for erectile dysfunction, and/or use of selective estrogen receptor modulators, aromatase inhibitors, or hCG to restore testosterone levels. As discussed above, AASs suppress the male hypothalamicpituitary-gonadal axis, and men with long-term AAS use may expe­ rience symptoms of profound androgen deficiency such as sexual dysfunction, fatigue, and depressive symptoms during AAS with­ drawal. Some of these patients may resume AAS use or start using other drugs to combat the distressing withdrawal symptoms. There are no randomized trials of any therapies for AAS withdrawal. Case reports and clinical experience suggest that administration of selec­ tive estrogen receptor modulators, CYP19 aromatase inhibitors, or hCG may restore circulating testosterone levels. Clomiphene

citrate, a partial estrogen receptor agonist, administered in a dose of 25–50 mg on alternate days, can increase LH and FSH levels and restore testosterone levels in a vast majority of men with AAS withdrawal syndrome. However, the recovery of sexual function during clomiphene administration is variable despite improvements in testosterone levels. Anecdotally, other aromatase inhibitors such as anastrozole have also been used. hCG, administered by intra­ muscular injections of 1500 to 2000 IU three times each week, can raise testosterone levels into the normal range. Some patients may not respond to either clomiphene or hCG therapy, raising the pos­ sibility of irreversible long-term toxic effects of AAS on Leydig cell function. Cognitive and behavioral therapy to address the body image dis­ order and addiction behaviors and antidepressants to treat depres­ sion may be needed. The opioid antagonist naltrexone blocks AAS dependence in animals. Therefore, treatments for human opioid dependence might also benefit AAS dependence. Many patients who abuse AAS suffer from body image disorder and require psy­ chiatric treatment for this underlying disorder. ■ ■LUTS IN MEN LUTS in men include storage symptoms (urgency, daytime as well as nighttime frequency, and urgency incontinence), voiding distur­ bances (slow or intermittent stream, difficulty in initiating micturi­ tion, straining to void, pain or discomfort during the passage of urine, and terminal dribbling), or postmicturition symptoms (a sense of incomplete voiding after passing urine and postmicturition dribble). The overactive bladder syndrome refers to urgency with or without urgency incontinence, usually with urinary frequency and nocturia, and is often due to detrusor muscle overactivity. A presumptive diag­ nosis of benign prostatic hyperplasia should be made only in men with LUTS, who have demonstrable evidence of prostate enlargement and obstruction based on the size of the prostate. LUTS have historically been attributed to benign prostatic hyperplasia, although it has become apparent that the pathophysiologic mechanisms of LUTS are complex and multifactorial and may include structural or functional abnormali­ ties of the bladder, bladder neck, prostate, distal sphincter mechanism, and urethra, as well as abnormalities in the neural control of the lower urinary tract and autonomic dysfunction. Diuretics, antihistamines, antidepressants, and other medications that have anticholinergic prop­ erties can cause or exacerbate LUTS in older men. The intensity of LUTS tends to fluctuate over time. LUTS is highly prevalent in older men, affecting nearly 50% of men

65 and 70% of men >80 years old. LUTS adversely affect quality of life because of their impact on sleep, ability to perform activities of daily living, and depressive symptoms. LUTS are often associated with erectile dysfunction. APPROACH TO THE PATIENT Lower Urinary Tract Symptoms Medical evaluation should include assessment of potential causes of symptoms; medications including herbal and over-the-counter products that might contribute to symptoms; the symptom severity and bother using an International Prostate Symptom Score; and in some patients, a frequency-volume chart. The impact of LUTS on sleep, activities of daily living, and quality of life should be evaluated. Evaluation should also include digital prostate exami­ nation, neurologic examination focused on perineum and lower extremities, urinalysis, fasting blood glucose, electrolytes, creati­ nine, and prostate-specific antigen (PSA). Urodynamic studies are not required in most patients but are recommended when invasive surgical therapies are being considered. A urologic referral may be appropriate if the patient has hydronephrosis, renal insufficiency, recurrent urinary tract infections, hematuria, or history of acute urinary retention.

TREATMENT Patients with LUTS Considerations of the severity of symptoms; the impact of symp­ toms on sleep, activities of daily living, and quality of life; the natural history of the disease; and potential adverse effects of the intervention should guide the decision to intervene. In men with mild to moderately severe LUTS, the symptoms typically progress slowly over many years and may remain stable or even improve in some men. The men who have mild symptoms can usually be reas­ sured and followed. Several simple steps such as reducing caffeine and alcohol intake, especially late in the day, taking the diuretic medication early in the day, avoiding excessive water intake close to bedtime, bladder training, pelvic floor exercises including bio­ feedback to promote pelvic floor relaxation, and timed voiding regimens or double voiding to ensure complete emptying of the bladder may be helpful in reducing the severity of symptoms. Men with mild to moderate bothersome LUTS can be treated effectively using α-adrenergic antagonists, steroid 5α-reductase inhibitors, PDE5 inhibitors, or anticholinergic agents alone or in combina­ tion. Selective α-adrenergic antagonists are typically the first line of therapy; their side effects include hypotension, dizziness, nasal congestion, retrograde or delayed ejaculation, and rarely floppy iris syndrome. In men with probable benign prostate obstruction with gland enlargement and LUTS, therapy with steroid 5α-reductase inhibitors, finasteride or dutasteride, improves urinary symptoms and flow rate and reduces prostatic volume. Long-term treatment with 5α-reductase inhibitors can reduce the risk of acute urinary retention and need for prostate surgery. Combined administration of a steroid 5α-reductase inhibitor and an α1-adrenergic blocker can rapidly improve urinary symptoms and reduce the relative risk of acute urinary retention and surgery. PDE5 inhibitors, when admin­ istered chronically alone or in combination with α-adrenergic blockers, are effective in improving LUTS and erectile dysfunction through their effects on nitric oxide–cyclic guanosine monophos­ phate (cGMP) in the bladder, urethra, and prostate. PDE5 inhibi­ tors do not improve uroflow parameters, and their hypotensive effect may be potentiated by α1-adrenergic blockers. Anticholiner­ gic drugs are used for the treatment of overactive bladder in men with prominent irritative symptoms, such as frequency, urgency, and incontinence, and no evidence of elevated postvoid residual urine. Containment products, such as pads, can help improve social life in men who have severe storage symptoms, including inconti­ nence. Surgery is indicated when medical therapy fails, symptoms progress despite medical therapy, or the patient develops acute urinary retention, hydronephrosis, renal insufficiency, or recurrent urinary tract infections, or if the patient has postvoid residual urine volume >25% of the urinary bladder volume. ■ ■MEDICAL COMPLICATIONS OF PROSTATE CANCER THERAPY Prostate cancer is the most common malignancy in American men. The majority of these men have low-grade, organ-confined prostate cancer; are treated with radical prostatectomy, radiation, or active sur­ veillance; and have excellent prospects of long-term survival. Substan­ tial improvement in survival in men with prostate cancer has focused attention on the high prevalence of sexual dysfunction, physical dys­ function, and low vitality in the men, which are important contribu­ tors to poor quality of life among patients treated for prostate cancer. The pathophysiology of these symptoms after radical prostatectomy or radiation therapy is multifactorial, but denervation and testosterone deficiency are important contributors to these symptoms. Testosterone deficiency is common in men with prostate cancer. Testosterone levels decline with age, and men with prostate cancer are at risk of having low testosterone levels simply by virtue of their age. However, total and free testosterone levels are even lower in men with prostate cancer who have undergone prostatectomy, when compared to noncancer age-matched controls. Testosterone deficiency in men with

prostate cancer is associated with fatigue, sexual dysfunction, mobility limitation, and decreased physical function. A majority of men treated with surgery or radiation therapy will develop sexual dysfunction and incontinence. Although there is some recovery of sexual function with passage of time, 40–50% of men undergoing radical prostatectomy find their sexual performance to be a moderate to large problem 18 months after surgery. Sexual problems are a source of psychosocial distress in men with localized prostate cancer. The men with locally advanced or metastatic prostate cancer who undergo androgen deprivation therapy (ADT) encounter even more distressing symptoms. In addition to fatigue, sexual dysfunction, and hot flushes, these men are at increased risk for diabetes, metabolic syndrome, coronary heart disease, and frailty.

Men’s Health CHAPTER 411 Testosterone Therapy in Men with a History of Prostate Cancer  A history of prostate cancer has historically been consid­ ered a contraindication for testosterone therapy. This guidance is based on observations that testosterone promotes the growth of metastatic prostate cancer and metastatic prostate cancer generally regresses after orchiectomy and ADT. Androgen receptor signaling plays a central role in maintaining growth of normal prostate and prostate cancer. The role of testosterone in prostate cancer is complex. Epidemio­ logic studies and their meta-analyses have not revealed a consistent relationship between serum testosterone or dihydrotestosterone levels and prostate cancer. However, men with hypogonadism or Klinefelter’s syndrome have lower prostate cancer mortality than the general population. In a Mendelian randomization analysis of men in the UK Biobank, higher genetically determined bioavailable testosterone levels were associated with increased risk of prostate cancer. Testosterone treatment of older men with low testosterone does not affect intra­ prostatic androgen levels or the expression of androgen-dependent prostatic genes. The suppression of circulating testosterone levels by a GnRH antagonist also does not affect intraprostatic androgen concen­ trations. Open-label trials and retrospective analyses of testosterone therapy in men with prostate cancer who have undergone radical pros­ tatectomy and have undetectable PSA levels after radical prostatectomy have found very low rates of PSA recurrence. A majority of men diagnosed with prostate cancer today have local­ ized disease that can be potentially cured by radical prostatectomy. The men with organ-confined prostate cancer (pT2, N0, M0) and Gleason score 6 or 7 (3+4) are at a very low risk of disease recurrence after radical prostatectomy, with 0.5% biochemical recurrence rate and 0.2% local recurrence rate at >10–15 years. Therefore, men with organ-confined prostate cancer (pT2), Gleason score 6 or 7 (3+4), and a preoperative PSA of <10 ng/mL, who have had undetectable PSA levels (<0.1 ng/mL) for >2 years after radical prostatectomy, have very low risk of disease recurrence (<0.5% at 10 years) and may be consid­ ered for testosterone therapy on an individualized basis. If testosterone therapy is instituted, it should be associated with careful monitoring of PSA levels and close consultation with a urologist. ■ ■MEDICAL COMPLICATIONS OF ADT In patients with prostate cancer and distant metastases, ADT improves survival. In patients with locally advanced disease, ADT in combina­ tion with external beam radiation or as an adjuvant therapy (post­ prostatectomy and pelvic lymphadenectomy) also has been shown to improve survival. However, ADT along with radiation is being increas­ ingly used as primary therapy in men with localized disease and in men encountering biochemical recurrence. The overall use of ADT in men with prostate cancer has increased in the past two decades, and its use in men with localized disease and biochemical recurrence accounts for a substantial fraction of this increase. Since most men with prostate cancer die of conditions other than their primary malignancy, recogni­ tion and management of these adverse effects are paramount. Profound hypogonadism resulting from ADT is associated with sexual dysfunction, vasomotor symptoms, gynecomastia, decreased muscle mass and strength, frailty, increased fat mass, anemia, fatigue, bone loss, loss of body hair, depressive symptoms, and reduced qual­ ity of life. Increased risk of diabetes and cardiovascular disease has

Thromboembolic Any fracture (1.54) Cardiovascular Metabolic Skeletal PART 12 Endocrinology and Metabolism Fracture requiring hospitalization (1.66) Diabetes (1.44) Myocardial infarction (1.11) Peripheral vascular disease (1.16) Coronary heart disease (1.16) Sudden death (1.16) FIGURE 411-4  Adverse cardiometabolic and skeletal effects of androgen deprivation therapy (ADT) in men receiving ADT for prostate cancer. Administration of ADT has been associated with increased risk of thromboembolic events, fractures, and diabetes. Some, but not all, studies have reported increased risk of cardiovascular events in men receiving ADT. (Data from VB Shahinian et al: N Engl J Med 352:154, 2005; NL Keating et al: J Clin Oncol 24:4448, 2006; JC Hu et al: Eur Urol 61:1119, 2012.) recently been added to the list of these complications (Fig. 411-4). Treatment with GnRH agonists in men with prostate cancer is associ­ ated with rapid induction of insulin resistance, hyperinsulinemia, and a significant increase in the risk of incident diabetes. Metabolic syn­ drome is prevalent in >50% of men undergoing long-term ADT when compared to age-matched men with prostate cancer not undergoing ADT and their age-matched eugonadal counterparts. Some but not all studies have reported an increased risk of cardiovascular events, death due to cardiovascular events, and peripheral vascular disease in men undergoing ADT. Some reports suggest that men receiving ADT are at an increased risk of thromboembolic events and cognitive dysfunction. The rates of acute kidney injury are higher in men currently receiving ADT than in men not receiving ADT; the increased risk appears to be particularly associated with the use of combined regimens of a GnRH agonist plus an antiandrogen. ADT also is associated with substantially increased risk of osteoporosis and bone fractures. APPROACH TO THE PATIENT Men Receiving ADT The benefits of ADT in treating nonmetastatic prostate cancer should be carefully weighed against the risks of ADT-induced adverse events (Table 411-6). If ADT is medically indicated, con­ sider whether intermittent ADT is a feasible option. Men being considered for ADT should undergo assessment of cardiovas­ cular, diabetes, and fracture risk; this assessment may include measurement of blood glucose, plasma lipids, and bone mineral density by dual energy x-ray absorptiometry. Institute measures to prevent bone loss, including physical activity, adequate calcium and vitamin D intake, and pharmacologic therapy in men with a previous minimal trauma fracture and those with 10-year risk of a major osteoporotic fracture >20%, unless contraindicated. Bisphos­ phonates and denosumab have been shown to reduce fracture risk in men undergoing ADT, and zoledronic acid and denosumab have been approved by the U.S. Food and Drug Administration for the prevention of metastasis-related skeletal-related events in

Shahinian et al 2005, NEJM Keating et al 2006, JCO Keating et al 2006, JCO Hu et al 2012, Eur Urol

this population. Men with prostate cancer who are receiving ADT should be monitored for weight gain and diabetes. Encourage life­ style interventions, including physical activity and exercise, and attention to weight, blood pressure, lipid profile, blood glucose, and smoking cessation to reduce the risk of cardiometabolic com­ plications. Metformin plus lifestyle intervention can prevent and improve metabolic dysregulation. In randomized trials, gabapentin, medroxyprogesterone, and the serotonin reuptake inhibitor venla­ faxine have been shown to be more efficacious than placebo in alle­ viating hot flushes. The side effects of these medications—increased appetite and weight gain with medroxyprogesterone, gynecomastia with estrogenic compounds, and dry mouth with venlafaxine— should be weighed against their relative efficacy. Acupuncture, soy products, vitamin E, herbal medicines, and transdermal estradiol have been used empirically for the treatment of vasomotor symp­ toms without clear evidence of efficacy. Gynecomastia can be TABLE 411-6  Checklist for Men Undergoing Androgen Deprivation Therapy (ADT)

  1. Weigh the risks and benefits of ADT and whether intermittent ADT is a feasible and safe option.
  2. Perform a baseline assessment including fasting glucose, plasma lipids, blood pressure, bone mineral density, and FRAX score.
  3. Optimize calcium and vitamin D intake, encourage structured physical activity and exercise, and consider pharmacologic therapy in men with a previous minimal trauma fracture and those with a 10-year risk of a major osteoporotic fracture >20%, unless contraindicated.
  4. Monitor body weight, fasting glucose, plasma lipids, blood pressure, and bone mineral density, and encourage smoking cessation and physical exercise. Consider metformin in those with metabolic disorder.
  5. In men who are receiving ADT and who experience bothersome hot flushes, as indicated by sleep disturbance or interference with work or activities of daily living, consider initial therapy with venlafaxine. If ineffective, add medroxyprogesterone acetate or gabapentin.
  6. In men who experience painful breast enlargement, consider therapy with an estrogen receptor antagonist, such as tamoxifen.

prevented by the use of an antiestrogen, an aromatase inhibitor, or local radiation therapy; these therapies are effective in alleviating pain and tenderness but are less effective in reducing established gynecomastia. For long-standing gynecomastia that persists after cessation of ADT and is bothersome, mammoplasty is an effective treatment option. Intermittent ADT can reduce the frequency of adverse effects associated with ADT, but its long-term efficacy and safety need further investigation. ■ ■PREVENTION OF SEXUALLY TRANSMITTED DISEASES Adolescent boys and young men aged 15–24 years; men who have sex with men, have multiple sex partners, have unprotected sex without condom, or have sex with sex workers; men who use illicit drugs; men who have a history of previous sexually transmitted infection (STI); and transgender men are at increased risk for STIs. STIs increase the risk of oropharyngeal and anogenital cancers, liver disease, pelvic pain, infertility, inadvertent transmission of infection to others, and emergency department visits and are a preventable cause of excess morbidity and mortality. HIV, hepatitis B and C infections, and syphilis can have additional disease-specific complications. The prevention and treatment of STIs are discussed in Chap. 141. Additionally, the Centers for Disease Control and Prevention (CDC) and U.S. Preventive Services Task Force (USPSTF) have published guidelines on the prevention, treatment, and pre- and postexposure prophylaxis of STIs. The approach to the prevention of STIs includes a structured risk assessment; counseling about safe sex practices including condom use; immunization of individuals at risk; diagnosis and treatment of infected individuals whether or not they are symptomatic; detection and treatment of sexual partners; and targeted sex education of adolescents and young men who are at high risk for STIs. The USPSTF recommends screening for HIV in all men aged 15–65 years, regardless of risk, and for hepatitis B virus and syphilis in men at increased risk. Because more than half of STIs occur in persons aged 15–24 years, the USPSTF also recommends behavioral counseling for all sexually active adolescents and adult men at increased risk of STIs to encourage condom use and other protective behaviors, including consideration of abstinence, reducing the number of sex partners, and avoidance of unsafe sex practices. Consistent and correct condom use is the most important method of preventing STIs. Effective immunizations are available against hepatitis B, human papillomavirus (HPV), and Neisseria meningitides. The CDC’s Advisory Committee on Immunization Practices (ACIP) recommends universal hepatitis B immunization for all unvaccinated adults presenting to an STI clinic, all HIV-infected adults, and health workers. Although ACIP recommends HPV vaccination in males aged 9–21 years and in men aged 9–26 if they have sex with men or have an immunocompromising condition, recent data suggest that the prevalence of HPV and its complications continue to increase until middle age, and some experts recommend extending the age limit for HPV vaccination. Meningococcal vaccination is indicated for men who have sex with men from an area of outbreak and for all HIV-infected men. Because men seeking care in men’s health clinics often do so for sexual and urogenital problems, these visits offer opportunities for counseling, screening, and treatment of STIs and institution of immunization and other preventive measures for STIs. ■ ■SEX DIFFERENCES IN COVID-19 DISEASE OUTCOMES The COVID-19 pandemic has highlighted sex differences in the susceptibility to respiratory viral infections. Men infected with SARSCoV-2 virus are more likely to have a more severe disease, require mechanical ventilation, have disease complications, and die of the disease than women. Somewhat similar sex differences in morbidity and mortality have been reported for influenza infection. In the United States, the incidence and rates of hospitalization for influenza

are higher in men than in women across all age groups. However, the sex-specific mortality rates associated with influenza vary substantially across countries and age groups. The sex differences in susceptibility to SARS-CoV-2 infection and morbidity have been attributed to behavioral factors, such as higher rates of smoking and alcohol use in men; biologic factors, such as higher rates of comorbid conditions in men than in women; sex differences in immune responses, including a poor T lymphocyte response to SARS-CoV-2 infection; and lower expression levels in men of X-linked genes that are involved in the innate detection of RNA viruses and that escape X inactivation in women, resulting in higher expression levels in women. Additionally, the expression of angiotensin-converting enzyme 2 (ACE2) and the cell surface transmembrane protease serine 2 (TMPRSS2), the two host proteins that facilitate the entry of SARS-CoV-2 into the alveolar cells, is regulated by androgens in subsets of lung epithelial cells, and it is possible that higher testosterone levels in men may contribute to increased susceptibility to the infection.

Men’s Health CHAPTER 411 ■ ■FURTHER READING Abrams P et al: Evaluation and treatment of lower urinary tract symptoms in older men. J Urol 189:S93, 2013. Ahmadi H et al: Androgen deprivation therapy: Evidence-based management of side effects. BJU Int 111:543, 2013. Baggish A et al: Cardiovascular toxicity of illicit anabolic-androgenic steroid use. Circulation 135:1991, 2017. Bhasin S et al: Testosterone therapy in men with hypogonadism: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 103:1715, 2018. Bhasin S et al: The implications of reproductive aging for the health, vitality and economic welfare of human societies. J Clin Endocrinol Metab 104:3821, 2019. Bhasin S: Testosterone replacement in aging men: An evidence-based patient-centric perspective. J Clin Invest 131:e146607, 2021. Bhasin S et al: Prostate safety events during testosterone replacement therapy in men with hypogonadism: A randomized clinical trial. JAMA Netw Open 6:e2348692, 2023. Centers for Disease Control and Prevention: National Vital Statistics System: Mortality tables. https://www.cdc.gov/nchs/nvss/ mortality_tables.htm. Accessed March 17, 2024. Lincoff AM et al: Cardiovascular safety of testosterone replacement therapy. N Engl J Med 389:107, 2023. Nelson BS et al: Anabolic-androgenic steroid use is associated with psychopathy, risk-taking anger, and physical problems. Sci Rep 12:9133, 2022. Pope HG Jr et al: Adverse health consequences of performanceenhancing drugs: An endocrine society scientific statement. Endocr Rev 35:341, 2014. Rudd RA et al: Increases in drug and opioid-involved overdose deaths—United States, 2010–2015. MMWR Morb Mortal Wkly Rep 65:1445, 2016. Ruth KS et al: Using human genetics to understand the disease impacts of testosterone in men and women. Nat Med 26:252, 2020. Snyder PJ et al: Effects of testosterone treatment in older men. N Engl J Med 374:611, 2016. U.S. Preventive Health Services Task Force. Final recommendation statement sexually transmitted infections: Behavioral counseling. https://www.uspreventiveservicestaskforce.org/Page/Document/ RecommendationStatementFinal/sexually-transmitted-infectionsbehavioral-counseling1. Accessed June 21, 2017. Wittert G et al: Testosterone treatment to prevent or revert type 2 diabetes in men enrolled in a lifestyle programme (T4DM): A randomised, double-blind, placebo-controlled, 2-year, phase 3b trial. Lancet Diabetes Endocrinol 9:32, 2021. Woolf SH, Schoomaker H: Life expectancy and mortality rates in the United States, 1959–2017. JAMA 322:1996, 2019. Workowski KA et al: Sexually transmitted infections treatment guidelines, 2021. MMWR Recomm Rep 70:1, 2021.

28 - SECTION 3 Obesity, Diabetes Mellitus, and Metabolic Syndrome

SECTION 3 Obesity, Diabetes Mellitus, and Metabolic Syndrome

Fenway Health: Glossary of LGBT terms for health care teams. February 2024. Available at https://www.lgbtqiahealtheducation.org/ publication/lgbtqia-glossary-of-terms-for-health-care-teams/. Institute of Medicine: The health of lesbian, gay, bisexual, and trans­ gender (LGBT) people: Building a foundation for better understand­ ing. 2011. Available at www.nap.edu/catalog.php?record_id=13128. Institute of Medicine: Collecting sexual orientation and gender identity data in electronic health records: Workshop summary. 2013. Available at https://www.nap.edu/catalog/18260/collecting-sexualorientation-and-gender-identity-data-in-electronic-health-records. Joint Commission: Advancing effective communication, cultural competence, patient- and family-centered care for the lesbian, gay, bisexual, and transgender community: A field guide. 2011. Available at www.jointcommission.org/lgbt. National Center for Transgender Equality: The report of the 2015 U.S. Transgender Survey. 2015. Available at https://transequality. org/sites/default/files/docs/usts/USTS-Full-Report-Dec17.pdf. Safer JD, Tangpricha V: Care of transgender persons. N Engl J Med 381:2451, 2019. Substance Abuse and Mental Health Services Administra­ tion: Top health issues for LGBT populations information & resource kit. 2012. Available at https://store.samhsa.gov/product/ top-health-issues-lgbt-populations/sma12-4684. Section 3 Obesity, Diabetes Mellitus, and Metabolic Syndrome Stephen O’Rahilly, I. Sadaf Farooqi

Pathobiology of Obesity Adipose tissue evolved as a solution to the challenge of the intermittent availability of food. At times when food is plentiful, excess calories are converted to triglycerides and efficiently stored in the unilocular lipid droplets that occupy most of the volume of fat cells. When needed, the triglyceride is rapidly broken down to free fatty acids and glycerol, which provide an energy source to other sites throughout the body. However, in environments where food is abundant and when indi­ viduals tend to be sedentary, the chronic excess of energy intake over expenditure leads to obesity. The risks of developing obesity under those circumstances and of developing the illnesses associated with obesity vary greatly between individuals, with that variation having a strong genetic basis. ■ ■DEFINITION OF OBESITY AND OVERWEIGHT Obesity is defined as a state of excess adipose tissue mass that adversely affects health. The direct measurement of fat mass is not something that is readily undertaken in routine clinical practice, so a proxy mea­ sure, the body mass index (BMI), is generally used. This is calculated as weight/height2 (in kg/m2) (Fig. 413-1). BMI-based definitions of obesity and overweight have been established based on associations with certain morbidities and excess mortality. These definitions have been based largely on studies of predominantly white, Western popula­ tions, and there is growing evidence that the relationship between BMI and adverse outcomes is different in people from other ethnic groups, usually in the direction of worse health outcomes being seen at lower levels of BMI. The World Health Organization (WHO) defines a BMI of 30 kg/m2 as the cutoff point for obesity, while individuals with values between 25 and 30 kg/m2 are classified as overweight. For individuals with a very muscular body habitus, the BMI may overestimate the

Body Mass Index (weight in kg/height in meters squared) Pathobiology of Obesity CHAPTER 413 Underweight <18.5 Normal weight 18.5–24.9 Overweight 25–29.9 Obese

30.0 FIGURE 413-1  Definitions of overweight and obesity. The World Health Organization defines obesity based on body mass index (BMI), which is calculated as weight in kilograms divided by the height in meters squared. amount of body fat. For any given BMI, women will generally have a higher percentage of body fat than men. The extent to which different adipose depots expand in response to chronic overnutrition varies markedly between people. In general, females store more fat in subcutaneous tissues, especially on buttocks, thighs, and upper arms, whereas men are more prone to store fat in intraabdominal and truncal subcutaneous sites. A simple measure of fat distribution is provided by a measurement of the waist-to-hip ratio. Independent of the degree of obesity, a waist-to-hip ratio >0.9 in women and >1.0 in men is associated with adverse health outcomes such as type 2 diabetes and dyslipidemia. ■ ■EPIDEMIOLOGY The annual National Health and Nutrition Examination Survey (NHANES) provides an ongoing record of the prevalence of obesity in the United States. In 2017–2018, 42.4% of U.S. adults aged ≥20 years old had obesity with no significant differences in prevalence by age group. Non-Hispanic black people had the highest prevalence of obesity at 49.6%, followed by Hispanic (44.8%), non-Hispanic white (42.2%), and non-Hispanic Asian (17.4%) people. In the United States, Asians repre­ sent a highly heterogeneous group encompassing both East and South Asia as well as a substantial Filipino community. The risks of obesity and its complications may differ greatly between people from different parts of Asia; in general, the prevalence of obesity is somewhat higher in women than in men, with black women having the highest preva­ lence at 56.9%. There has been a marked increase in the prevalence of obesity over time. For example, between 1976 and 1980, the NHANES survey reported a prevalence of 14.5%, indicating a near threefold increase over the past 40 years. This trend is seen globally. According to the WHO, obesity has nearly tripled worldwide since 1975. In 2016, >1.9 billion adults aged ≥18 years old were overweight. Of these, >650 million were obese; 39% of adults aged ≥18 years old were overweight in 2016, and 13% were obese. Most of the world’s population lives in countries where over­ weight and obesity kills more people than underweight. During this time, one of the most striking changes has been in the prevalence of obesity in children. In children, the relationship between BMI and body fat varies considerably with age and with pubertal maturation; however, when adjusted for age and sex, BMI is a reason­ able proxy for fat mass. Using age- and sex-specific BMI cutoffs (over­ weight ≥91st percentile; obesity ≥99th percentile), in 2019, the WHO estimated that 38 million children under the age of 5 were overweight or obese, and in 2016, they reported that 340 million children and adolescents aged 5–19 were overweight or obese. ■ ■PHYSIOLOGIC REGULATION OF ENERGY BALANCE Discussions about obesity so frequently focus on the issues of personal choice or the obesogenic environment that it can be easy to forget that

29 - 413 Pathobiology of Obesity

413 Pathobiology of Obesity

Fenway Health: Glossary of LGBT terms for health care teams. February 2024. Available at https://www.lgbtqiahealtheducation.org/ publication/lgbtqia-glossary-of-terms-for-health-care-teams/. Institute of Medicine: The health of lesbian, gay, bisexual, and trans­ gender (LGBT) people: Building a foundation for better understand­ ing. 2011. Available at www.nap.edu/catalog.php?record_id=13128. Institute of Medicine: Collecting sexual orientation and gender identity data in electronic health records: Workshop summary. 2013. Available at https://www.nap.edu/catalog/18260/collecting-sexualorientation-and-gender-identity-data-in-electronic-health-records. Joint Commission: Advancing effective communication, cultural competence, patient- and family-centered care for the lesbian, gay, bisexual, and transgender community: A field guide. 2011. Available at www.jointcommission.org/lgbt. National Center for Transgender Equality: The report of the 2015 U.S. Transgender Survey. 2015. Available at https://transequality. org/sites/default/files/docs/usts/USTS-Full-Report-Dec17.pdf. Safer JD, Tangpricha V: Care of transgender persons. N Engl J Med 381:2451, 2019. Substance Abuse and Mental Health Services Administra­ tion: Top health issues for LGBT populations information & resource kit. 2012. Available at https://store.samhsa.gov/product/ top-health-issues-lgbt-populations/sma12-4684. Section 3 Obesity, Diabetes Mellitus, and Metabolic Syndrome Stephen O’Rahilly, I. Sadaf Farooqi

Pathobiology of Obesity Adipose tissue evolved as a solution to the challenge of the intermittent availability of food. At times when food is plentiful, excess calories are converted to triglycerides and efficiently stored in the unilocular lipid droplets that occupy most of the volume of fat cells. When needed, the triglyceride is rapidly broken down to free fatty acids and glycerol, which provide an energy source to other sites throughout the body. However, in environments where food is abundant and when indi­ viduals tend to be sedentary, the chronic excess of energy intake over expenditure leads to obesity. The risks of developing obesity under those circumstances and of developing the illnesses associated with obesity vary greatly between individuals, with that variation having a strong genetic basis. ■ ■DEFINITION OF OBESITY AND OVERWEIGHT Obesity is defined as a state of excess adipose tissue mass that adversely affects health. The direct measurement of fat mass is not something that is readily undertaken in routine clinical practice, so a proxy mea­ sure, the body mass index (BMI), is generally used. This is calculated as weight/height2 (in kg/m2) (Fig. 413-1). BMI-based definitions of obesity and overweight have been established based on associations with certain morbidities and excess mortality. These definitions have been based largely on studies of predominantly white, Western popula­ tions, and there is growing evidence that the relationship between BMI and adverse outcomes is different in people from other ethnic groups, usually in the direction of worse health outcomes being seen at lower levels of BMI. The World Health Organization (WHO) defines a BMI of 30 kg/m2 as the cutoff point for obesity, while individuals with values between 25 and 30 kg/m2 are classified as overweight. For individuals with a very muscular body habitus, the BMI may overestimate the

Body Mass Index (weight in kg/height in meters squared) Pathobiology of Obesity CHAPTER 413 Underweight <18.5 Normal weight 18.5–24.9 Overweight 25–29.9 Obese

30.0 FIGURE 413-1  Definitions of overweight and obesity. The World Health Organization defines obesity based on body mass index (BMI), which is calculated as weight in kilograms divided by the height in meters squared. amount of body fat. For any given BMI, women will generally have a higher percentage of body fat than men. The extent to which different adipose depots expand in response to chronic overnutrition varies markedly between people. In general, females store more fat in subcutaneous tissues, especially on buttocks, thighs, and upper arms, whereas men are more prone to store fat in intraabdominal and truncal subcutaneous sites. A simple measure of fat distribution is provided by a measurement of the waist-to-hip ratio. Independent of the degree of obesity, a waist-to-hip ratio >0.9 in women and >1.0 in men is associated with adverse health outcomes such as type 2 diabetes and dyslipidemia. ■ ■EPIDEMIOLOGY The annual National Health and Nutrition Examination Survey (NHANES) provides an ongoing record of the prevalence of obesity in the United States. In 2017–2018, 42.4% of U.S. adults aged ≥20 years old had obesity with no significant differences in prevalence by age group. Non-Hispanic black people had the highest prevalence of obesity at 49.6%, followed by Hispanic (44.8%), non-Hispanic white (42.2%), and non-Hispanic Asian (17.4%) people. In the United States, Asians repre­ sent a highly heterogeneous group encompassing both East and South Asia as well as a substantial Filipino community. The risks of obesity and its complications may differ greatly between people from different parts of Asia; in general, the prevalence of obesity is somewhat higher in women than in men, with black women having the highest preva­ lence at 56.9%. There has been a marked increase in the prevalence of obesity over time. For example, between 1976 and 1980, the NHANES survey reported a prevalence of 14.5%, indicating a near threefold increase over the past 40 years. This trend is seen globally. According to the WHO, obesity has nearly tripled worldwide since 1975. In 2016, >1.9 billion adults aged ≥18 years old were overweight. Of these, >650 million were obese; 39% of adults aged ≥18 years old were overweight in 2016, and 13% were obese. Most of the world’s population lives in countries where over­ weight and obesity kills more people than underweight. During this time, one of the most striking changes has been in the prevalence of obesity in children. In children, the relationship between BMI and body fat varies considerably with age and with pubertal maturation; however, when adjusted for age and sex, BMI is a reason­ able proxy for fat mass. Using age- and sex-specific BMI cutoffs (over­ weight ≥91st percentile; obesity ≥99th percentile), in 2019, the WHO estimated that 38 million children under the age of 5 were overweight or obese, and in 2016, they reported that 340 million children and adolescents aged 5–19 were overweight or obese. ■ ■PHYSIOLOGIC REGULATION OF ENERGY BALANCE Discussions about obesity so frequently focus on the issues of personal choice or the obesogenic environment that it can be easy to forget that

the amount of stored energy in our bodies is subject to homeostatic control by fundamental physiologic processes essential to our survival. In the 1940s, it was demonstrated that rodents defend their level of body fat; once returned to ad libitum diets after a short period of enforced caloric restriction or excess, animals either overconsumed or underconsumed calories until they returned to their previous status. Since that time, research has progressively dissected the signals that sense nutrient stores and the contents of our diets and how this infor­ mation is integrated to control hunger, satiety, and the expenditure of energy. The key locus for the integration of these signals is the hypo­ thalamus, an area of the brain at least partially outside the blood-brain barrier that facilitates its ability to receive hormonal signals and com­ bine these with sensory, cognitive, and other neural inputs.

PART 12 Endocrinology and Metabolism The hypothalamus receives multiple hormonal signals relevant to energy balance (Fig. 413-2). The circulating concentration of leptin, a peptide hormone produced by fat cells, increases as fat stores increase and declines as fat stores are depleted. Importantly, under conditions of caloric restriction, circulating leptin levels fall faster than the dis­ appearance of fat. Humans born without functional leptin or leptin receptors, although normal weight at birth, develop severe obesity from an early age, largely as a result of an intense drive to eat (hyper­ phagia). Clearly, a reduction of leptin below normal level is a powerful stimulus to food intake and largely explains the rebound overeating and weight regain that occurs after a period of starvation or diet­ ing. The hypothalamus also receives hormonal signals that are more Hypothalamus Leptin Ghrelin Adipose tissue GLP1 CCK Insulin Amylin PYY OXM Pancreas FIGURE 413-2  The homeostatic regulation of body weight. In most people, body weight remains stable over long periods of time despite fluctuations in the amount of food we eat and the amount of activity we undertake. This homeostatic regulation of body weight is controlled by the neurons in the hypothalamus, which receive hormonal signals from adipose tissue such as leptin and neural and hormonal signals from the gut in response to meals. Glucagon-like peptide 1 (GLP1) and cholecystokinin (CCK) from enteroendocrine cells of the small intestine and peptide YY (PYY) and oxyntomodulin (OXM) from the large intestine are secreted in response to eating a meal and/or the presence of nutrients in the intestinal lumen. Their release, together with neural signals from the vagus nerve and the enteric nervous system, contributes to satiety, acting on the hypothalamus via projections from the brainstem. Insulin, produced by the pancreas in response to carbohydrate- and protein-rich meals and potentiated by the action of some of the gut hormones, also has effects on the hypothalamic neurons controlling energy balance, whereas amylin acts predominantly via the brainstem. The release of the hormone ghrelin from the stomach increases in the unfed state and induces appetite by acting on hypothalamic neurons as well as on receptors in the brainstem.

immediately related to the amount and type of food that has been ingested. Peripheral hormones such as cholecystokinin (CCK) from the stomach, glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP) from enteroendocrine cells of the small intestine, and peptide YY (PYY) and oxyntomodulin from the large intestine are secreted in response to eating a meal and/or the presence of nutrients in the intestinal lumen. Their release together with neural signals from the vagus nerve and the enteric nervous system contributes to satiety, often indirectly acting on the hypothalamus via projections from the brainstem. Insulin and amylin, produced by the pancreas in response to carbohydrate and protein-rich meals, also have effects on neurons controlling energy balance. The propeptide pro-opiomelanocortin (POMC) is expressed in a highly restricted population of hypothalamic neurons that project widely throughout the brain (Fig. 413-3). These neurons are respon­ sive to the endocrine signals described above and are critical to the regulation of energy balance. The POMC-derived peptides α- and β-melanocyte-stimulating hormone (MSH) act on the melanocortin 4 receptor (MC4R) to regulate both food intake and aspects of energy expenditure that are influenced by the sympathetic nervous system. γ-MSH, acting mostly through the MC3 receptor, appears to play more of a role in controlling linear growth and the disposition of nutrients into lean versus fat tissues. Signaling through both these melanocortin receptors is also subject to negative control by a different population of neurons, which make and release agouti-related peptide (AGRP), neu­ ropeptide Y (NPY), and the inhibitory neu­ rotransmitter γ-aminobutyric acid (GABA). AGRP actively switches off melanocortin receptors. Leptin, which suppresses food intake, simultaneously stimulates POMC neurons and inhibits NPY/AGRP neurons. Human energy balance is highly sensitive to signaling through this system as people who have a genetic defect in just one of the two copies of the MC4R gene are very prone to overeat (hyperphagia) and to gain weight. Brainstem Vagus nerve ■ ■THE PHYSIOLOGY OF NUTRIENT STORAGE IN ADIPOSE TISSUE When energy intake exceeds energy expen­ diture, a small amount of that excess energy is stored as glycogen in liver and skeletal muscle. But if the imbalance is greater, then our bodies are designed to store that excess energy in a more efficient way as triacylglyc­ erol (triglyceride). This fat is more efficient because, unlike glycogen, it does not need accompanying water, and when metabo­ lized, it generates more than twice as much energy per gram than does carbohydrate. Adipocytes (fat cells) have evolved to contain a highly specialized organelle, the unilocu­ lar fat droplet, which holds the triglycer­ ide within a single-layer of phospholipid that contains all the components needed for enzymes that make and breakdown triglyc­ erides in a manner that is rapidly responsive to metabolic requirements. No other type of cell is specifically designed to store fat safely in this manner, and many of the adverse consequences of obesity are likely caused not by having too much fat in adipocytes but by “nonprofessional” cells being forced to take up and store fat. During weight gain, the amount of lipid in each fat cell increases. Some new fat cells can also be made in adult­ hood when ~10% of our fat cell population turns over every year.

Paraventricular nucleus Ventromedial nucleus BDNF MC4R α/β-MSH AGRP Arcuate nucleus POMC AGRP Hypothalamus LEPR LEPR Hypothalamus Leptin Adipose tissue FIGURE 413-3  Hypothalamic pathways regulating body weight. Neurons in the hypothalamus regulate energy intake and expenditure in response to leptin and other hormones. In the fed state, leptin stimulates primary neurons in the arcuate nucleus of the hypothalamus that express pro-opiomelanocortin (POMC). The POMC-derived peptides α- and β-melanocyte-stimulating hormone (MSH) act on the melanocortin 4 receptor (MC4R) expressed on neurons in the paraventricular nucleus to reduce energy intake and increase energy expenditure. At the same time, leptin inhibits neurons expressing agouti-related peptide (AGRP), which switches off melanocortin receptors. When these and other key molecules, such as brain-derived neurotrophic factor (BDNF) and single minded-1 (SIM1), are disrupted by inherited mutations, affected individuals have hyperphagia and severe obesity. ■ ■THE CAUSES OF OBESITY: AN INTERACTION OF GENES AND ENVIRONMENT For a person to develop obesity, energy intake must exceed energy expenditure in a manner that is sufficiently sustained to result in the accumulation of a large excess of triglyceride in adipose tis­ sue. As obesity is a cumulative pathology, if energy intake exceeds energy expenditure by even a small amount (as little as 7 kcal/d), this is sufficient to develop obesity over a matter of years or decades. Even where obesity is common, there are many people who are not overweight. Economic and social factors are likely to play a role as there are more normal-weight people in wealthier and more socially advantaged groups, at least in Western societies. It is also true, however, that because of discrimination, people with obesity may become socially and economically disadvantaged, which complicates interpretation of that data. We can, however, state with considerable certainty that genetic factors play a major role in predisposing people to a range of adiposity. We know this from a large number of studies comparing identical and nonidentical twins. It is particularly telling that the degree of adiposity in adult life of identical twins brought up in different families is very similar between the twins but is not at all correlated with that of the adoptive siblings with whom they were raised.

■ ■THE RELATIVE ROLES OF EXCESS INTAKE AND LOWER ENERGY EXPENDITURE IN CONFERRING BIOLOGIC PREDISPOSITION Do these heritable factors influence energy intake, energy expenditure, or both? It is clear that by the time a person develops obesity the amount of energy they expend in the resting state is more, not less, than a normal weight person. However, if a person with obesity loses weight by dieting, there is some evidence that they tend to be more “energy effi­ cient” than a person who has never been obese, particularly in terms of how many calories they burn during a defined bout of activity. However, the effects are subtle. It seems very likely that there are some individuals who are predominantly pre­ disposed to develop obesity by virtue of a lower metabolic rate, but thus far, apart from severe hypothyroidism, concrete examples are scarce. In contrast, a much more consistent and compelling body of evidence supports the idea that the genetic predisposition to obesity is largely mediated through the brain’s control of food intake. When studied in controlled settings, individuals who carry genetic variants that predispose to obesity tend to eat more and be less readily satiated. This is very readily demonstrable when the mutation has a major effect on obesity predisposition, but similar data are now emerging in the case of common genetic variants with smaller effects.

Reduced food intake Increased energy expenditure Pathobiology of Obesity CHAPTER 413 SIM1 ■ ■ENVIRONMENTAL FACTORS PREDISPOSING TO OBESITY Obesity cannot exist in the absence of sufficient food to lay down and maintain excess fat stores. That fact not infre­ quently leads to the belief that the prin­ cipal cause of obesity must be either a person’s ignorance of the role of excess caloric intake or their conscious choice to prioritize the immediate pleasures of eating over the long-term health harms associated with obesity. Taken to extremes, these views can engender serious social, economic, and medical discrimination against people with obesity. It is clear that genetic factors, however important they are in an individual’s predisposition to obesity, cannot explain the marked increase in obesity prevalence that has occurred in the past few decades. We have to look to an environment that has become increas­ ingly obesogenic to explain that phenomenon. In most developed and developing countries, energy-dense and highly palatable food and beverages have been aggressively marketed, made cheaper than ever before, provided in larger portions, and made available ubiquitously and continuously. This has been combined with the reduction in physi­ cal activity in work and domestic life due to mechanization and the change in the nature of employment. Even the control of our external temperature by artificial heating and cooling has meant less energy expended on thermoregulation. Taken together, these are likely to be the major factors driving the recent increase in obesity. It is important to remember, however, that a substantial proportion of the population remains normal weight under these circumstances and a large part of that is attributable to their genetic good fortune. There is much current investigation into other environmental fac­ tors that might influence the development of obesity. Heated debates

continue about the optimal balance of macronutrients in the diet to maintain normal weight and good health. Much of this revolves around the potential benefits of reducing the relative proportion of carbohydrates in the diet (Chap. 414). There seems to be reasonable consensus that, in the short term, diets that are rich in protein and fat and lower in carbohydrates more readily result in quick weight loss. This may be because the appetite-suppressing gut hormones discussed above increase more in response to protein than to carbohydrate, thus inducing earlier satiation. However, longer-term studies to date are less compelling, and the long-term increases in protein and fat intake are not without at least theoretical risks. A growing body of evidence suggests that exposures early in life, either in utero or in early postnatal life, might “program” individuals to develop obesity and/ or cardiometabolic disease through effects that are often attributed to “epigenetics” (Chap. 497). This is an attractive idea, and if true, it would mean that time-limited and affordable interventions early in life might have lifelong benefits. Inevitably, it will take time to see if the promise of such interventions will be fulfilled. Much excitement has been generated by the increasing recognition of the diversity of our intestinal microbiome, which clearly has relevance to gastroin­ testinal health (Chap. 484). At present, it is premature to ascribe any significant role to the human microbiome in obesity or its adverse consequences.

PART 12 Endocrinology and Metabolism ■ ■WHY DOESN’T LEPTIN PREVENT OBESITY? Leptin is known to suppress food intake, and its levels rise as fat stores expand. So why does this not prevent us from developing obesity? The most plausible explanation lies in the evolutionary history of leptin and the fact that it appears to defend strongly against the loss of body fat stores, with a fall in circulating leptin below a person’s habitual level being a powerful stimulus to food intake, whereas the response to rises in leptin above the normal level is less pronounced. At higher levels of leptin, administering extra amounts of the hormone may have no discernible effect at all—a phenomenon that has come to be called leptin resistance. It is important to remember that even though a person appears to be leptin resistant, some leptin action is occurring; otherwise, the person would become as insatiably hungry and progres­ sively obese as someone with congenital leptin deficiency (see below). It also seems likely that a subgroup of people may have relatively low leptin levels, which plays a role in the etiology of their obesity. There are likely other hormonal signals produced in severe obesity that, unlike leptin, continue to exert a suppressive effect on food intake and help to ensure that the expansion of adipose tissue does not become indefinitely cumulative. ■ ■SINGLE-GENE DISORDERS LEADING TO OBESITY The assessment of severely obese children and, indeed, adults should be directed at screening for potentially treatable endocrine and neuro­ logic conditions and identifying genetic conditions so that appropriate genetic counseling and, in some cases, treatment can be started. Clini­ cally, it remains useful to categorize the genetic obesity syndromes as those with dysmorphism and/or developmental delay and those with­ out these features (Tables 413-1 and 413-2). Although individually these monogenic disorders are rare, cumulatively, up to 20% of chil­ dren with severe obesity have rare chromosomal abnormalities and/or highly penetrant genetic mutations that drive their obesity. This figure is likely to increase with wider accessibility to genetic testing and as new genes are identified. A genetic diagnosis can inform manage­ ment (many such patients find it very difficult to lose weight through diet and exercise) and can inform clinical decision-making regarding the use of bariatric surgery (feasible in some; high risk in others) (Chap. 414). There are a number of drugs in clinical trials targeted specifically at patients with genetic obesity syndromes. Specifically, setmelanotide, a MC4R agonist, has been used effectively in phase 2/3 clinical trials in children who are genetically deficient in POMC, PCSK1, and the leptin receptor. It is also being explored for the treat­ ment of other genetic obesity syndromes affecting the melanocortin pathway and in acquired hypothalamic obesity caused by tumors such as craniopharyngiomas.

TABLE 413-1  Classical Genetic Obesity Syndromes ADDITIONAL CLINICAL FEATURES SYNDROME INHERITANCE Prader-Willi Autosomal dominant Hypotonia, failure to thrive in infancy, developmental delay, short stature, hypogonadotropic hypogonadism, sleep disturbance, obsessive behavior Albright’s hereditary osteodystrophy or pseudohypoparathyroidism Autosomal dominant Short stature in some, skeletal defects, developmental delay, shortened metacarpals; hormone resistance when mutation on maternally inherited allele Bardet-Biedl Autosomal recessive Syndactyly/brachydactyly/ polydactyly, developmental delay, retinal dystrophy or pigmentary retinopathy, hypogonadism, renal abnormalities Cohen’s Autosomal recessive Facial dysmorphism, microcephaly, hypotonia, developmental delay, retinopathy Carpenter’s Autosomal recessive Acrocephaly, brachydactyly, developmental delay, congenital heart defects; growth retardation, hypogonadism Alström’s Autosomal recessive Progressive cone-rod dystrophy, sensorineural hearing loss, hyperinsulinemia, early type 2 diabetes mellitus, dilated cardiomyopathy, pulmonary, hepatic and renal fibrosis Tubby Autosomal recessive Progressive cone-rod dystrophy, hearing loss ■ ■CLASSICAL SYNDROMIC DISORDERS A number of syndromes were identified by clinicians long before their exact genetic cause was known. In these syndromes, obesity is associated with a stereotyped set of other anomalies, often neurode­ velopmental in type. The precise genetic basis for the majority of these syndromes is now known. Prader-Willi syndrome (PWS) is the most common syndromic cause of obesity, with an estimated prevalence of ~1 in 25,000. It is an autosomal dominant disorder caused by deletion of an imprinted region on the paternal chromosome 15 (Chap. 479). The characteristic clinical features are hypotonia, feeding difficulties in infancy, developmental delay, hypogonadotropic hypogonadism, hyperphagia (increased food intake), and obesity. Children with PWS are short with reduced lean body mass and increased fat mass, fea­ tures resembling those seen in growth hormone (GH) deficiency; GH treatment decreases body fat and increases linear growth and muscle mass and is now standard of care in this condition. Low levels of brain expression of the neuropeptide oxytocin and the nerve growth factor brain-derived neurotrophic factor (BDNF) in PWS patients have sug­ gested new therapeutic opportunities for these patients. Inherited or de novo (not found in either parent) mutations in another imprinted gene, GNAS1, which encodes Gsα protein, cause a syndrome known as Albright’s hereditary osteodystrophy (AHO) or pseudohypoparathyroidism (PHP) (Chap. 424). Maternal trans­ mission of GNAS1 mutations leads to short stature, obesity, and skeletal defects plus resistance to several hormones (e.g., parathyroid hormone), whereas paternal transmission leads only to the AHO phe­ notype. The clinical spectrum is very broad, and some patients may present with obesity alone. Bardet-Biedl syndrome (BBS) is a rare autosomal recessive dis­ ease characterized by obesity, developmental delay, polydactyly, reti­ nal dystrophy or pigmentary retinopathy, hypogonadism, and renal

TABLE 413-2  Obesity Syndromes due to Mutations in Genes Controlling Energy Homeostasis Pathways GENE AFFECTED INHERITANCE ADDITIONAL CLINICAL FEATURES Leptin Autosomal recessive Severe hyperphagia, frequent infections, hypogonadotropic hypogonadism, mild hypothyroidism Leptin receptor Autosomal recessive Severe hyperphagia, frequent infections, hypogonadotropic hypogonadism, mild hypothyroidism Proopiomelanocortin Autosomal recessive Hyperphagia, cholestatic jaundice or adrenal crisis due to ACTH deficiency, pale skin and red hair Prohormone convertase 1 Autosomal recessive Small-bowel enteropathy, postprandial hypoglycemia, hypothyroidism, ACTH deficiency, hypogonadism, central diabetes insipidus Carboxypeptidase E Autosomal recessive Severe insulin resistance Melanocortin 4 receptor Autosomal dominant Hyperphagia, accelerated linear growth Single-minded 1 Autosomal dominant Hyperphagia, accelerated linear growth, speech and language delay, autistic traits BDNF Autosomal dominant Hyperphagia, developmental delay, hyperactivity, behavioral problems including aggression TrkB Autosomal dominant Hyperphagia, speech and language delay, variable developmental delay, hyperactivity, behavioral problems including aggression SH2B1 Autosomal dominant Hyperphagia, disproportionate hyperinsulinemia, early type 2 diabetes mellitus, behavioral problems including aggression Abbreviations: ACTH, adrenocorticotropic hormone; BDNF, brain-derived neurotrophic factor; SH2B1, Src-homology-2 (SH2) B-adaptor protein-1 (SH2B1); TrkB, tropomyosin receptor kinase B. abnormalities. The same clinical features can arise from mutations in >26 genes, which disrupt signaling in primary cilia. Melanocortin receptor agonists may be useful in treating hyperphagia and obesity in patients with BBS. Overlapping clinical features are seen in a number of other genetic obesity syndromes (Table 413-1). ■ ■DISORDERS OF LEPTIN-MELANOCORTIN SIGNALING Homozygous mutations that disrupt the production or action of leptin are rare but result in a disorder that is treatable. Children with homo­ zygous loss-of-function leptin mutations have rapid weight gain in the first few months of life, resulting in severe obesity due to an intense drive to eat (hyperphagia) and impaired satiety with food-seeking behavior soon after the end of a meal. Congenital leptin deficiency can be treated with subcutaneous injections of recombinant leptin, which reduce hunger, increase satiety, and lead to weight loss. Similar clinical features are seen in patients with homozygous mutations in the leptin receptor gene, but they are not responsive to leptin treatment (Table 413-2). Normal pubertal development rarely occurs in adults with leptin or leptin receptor deficiency, with biochemical evidence of hypogonadotropic hypogonadism. However, there is some evidence for the delayed but spontaneous onset of menses in a small number of leptin- and leptin receptor–deficient adults. Leptin treatment per­ mits progression of pubertal development, suggesting that leptin is a permissive factor for the development of puberty. An MC4R agonist (setmelanotide) is licensed for chronic weight management in leptin receptor deficiency. Homozygous or compound heterozygous mutations in POMC lead to hyperphagia and early-onset obesity. As adrenocorticotropic hormone (ACTH) is produced in the pituitary gland by cleavage from POMC, patients also present with isolated ACTH deficiency (neonatal

hypoglycemia and cholestatic jaundice). In the skin, POMC-derived melanocortin peptides act on melanocortin 1 receptors to induce pigmentation. For this reason, the lack of POMC-derived peptides in obese patients with POMC deficiency results in hypopigmenta­ tion of skin and hair, which is more noticeable in people of Caucasian ancestry who often have red hair. Prohormone convertase 1 (PCSK1) is an enzyme involved in the cleavage of POMC into ACTH, which is then further cleaved to make α-MSH by carboxypeptidase E. Impaired processing of POMC contributes to the hyperphagic severe early-onset obesity and ACTH deficiency in people lacking PCSK1 who also have hypogonadotropic hypogonadism, postprandial hypoglycemia (due to impaired processing of proinsulin to insulin), and a neonatal enteropathy in early childhood. Heterozygous mutations that impair the function of MC4R are found in 5–6% of patients with severe earlyonset obesity and at a frequency of ~1 in 300 in the general population, making this the most common gene in which variants contribute to obesity. MC4R mutations are inherited in a co-dominant manner, with variable penetrance and expression in heterozygous carriers; homozy­ gous carriers are severely obese. Patients are often hyperphagic from early childhood and hyperinsulinemic and have increased lean mass and increased linear growth.

Pathobiology of Obesity CHAPTER 413 ■ ■GENETIC SUBTYPES OF OBESITY ASSOCIATED WITH NEUROBEHAVIORAL ABNORMALITIES Both PWS patients and patients with mutations in SIM1 (a gene that acts downstream of MC4R) exhibit a spectrum of behavioral abnor­ malities that overlap with autism-like features that could be related to reduced oxytocin signaling (Table 413-2). Mutations affecting BDNF and its receptor tropomyosin receptor kinase B (TrkB) cause speech and language delay, hyperphagia, and severe obesity, as well as hyperactivity, autistic traits, and impaired short-term memory. Interestingly, a com­ mon variant in BDNF (V66M), found in heterozygous form in ~20% of the population, is associated with a number of traits and neuropsychi­ atric disorders including anxiety and depression. Chromosomal deletion and mutations affecting Src-homology-2 (SH2) B-adaptor protein-1 (SH2B1) are associated with dominantly inherited, severe, early-onset obesity, disproportionate insulin resistance, early-onset type 2 diabetes, and behavioral problems including aggressive behavior. ■ ■OBESITY SECONDARY TO OTHER DISORDERS Endocrine Disorders  Patients with hypothyroidism may gain weight and develop obesity, although it is rarely the sole cause of severe obesity. It is nonetheless prudent always to measure thyroid function in a patient presenting with obesity. Measurement of thyroid-stimulating hormone (TSH) will detect significant primary disease of the thyroid, but for rare secondary hypothyroidism, additional measurement of free thyroxine levels is needed (Chap. 395). Weight gain can also be a presenting feature of Cushing’s syndrome. Clinically, the presence of spontaneous bruising, livid striae, myopathy, and marked centripetal distribution of body fat helps to distinguish true endogenous hyper­ cortisolism from common obesity. This condition is usually reasonably straightforward to diagnose based on tests that approximate cortisol production rates (24-h urine free cortisol) or the suppression of serum cortisol by dexamethasone (Chap. 398). Occasionally, in patients with severe obesity, effects of adiposity on glucocorticoid metabolism can make it difficult to interpret results, and more sophisticated tests, including those measuring diurnal rhythm of cortisol, may be neces­ sary to establish or exclude the diagnosis with confidence. Weight gain can also be a presenting feature of patients with insulinoma, driven largely by the need to eat more frequently than normal to avoid hypoglycemia. Hypothalamic Damage  The hypothalamic regions that control energy balance can be disrupted by tumors (such as craniopharyngio­ mas), inflammatory masses, or after a severe head injury (Chap. 391). In such cases, there is often some accompanying evidence of disruption of the hormonal functions of the anterior or posterior pituitary, although it may be subtle and the history of hyperphagia and weight gain is often short. It is worth noting that in common obesity, GH levels in response

Dementia Stroke Sleep apnea Hypertension Hypertriglyceridemia Ischemic heart disease Heart failure Gallstones Esophagitis Cancer of esophagus, colon, endometrium, pancreas, kidney Type 2 diabetes NAFLD PART 12 Endocrinology and Metabolism PCOS Arthritis Gout FIGURE 413-4  Obesity-related complications. The expanded fat mass that characterizes obesity predisposes to certain obesity-related complications (e.g., osteoarthritis of knees, reflux esophagitis, and obstructive sleep apnea) directly through its mass and/or volume. However, in the case of the metabolic, endocrine, and cardiovascular complications, the link is less clear. Further research is needed to establish whether some features of the expanded fat mass influence the development of these complications or whether other aspects of the chronically overnourished state, such as excess fat outside the fat depot, are more relevant. NAFLD, nonalcoholic fatty liver disease; PCOS, polycystic ovarian syndrome. to provocative testing may be somewhat lower than normal, but this does not necessarily suggest the presence of a structural lesion. ■ ■ADVERSE CONSEQUENCES OF OBESITY Mechanistic Considerations  Obesity is associated with a wide range of pathologies that can adversely impact morbidity and mortality (Chap. 420). Some of these consequences are related, at least in part, to the direct mechani­ cal or gravitational effects of the expanded fat mass itself (Fig. 413-4). However, the principal mechanisms behind many of the complica­ tions of obesity are less likely to be due to the expanded fat mass itself but more closely related to the chronic state of overnutrition itself and its effects on tissues throughout the body. Adipose tissue Inflammation As people develop obesity, one of the first and most prominent biochemical abnormalities that develops is the need for increased circulating concentrations of insulin to maintain glucose homeostasis. This state of insulin resistance generally worsens with a greater degree of obe­ sity, but there is a high degree of interindividual variability. It is more prominent when fat is distributed more centrally. Insulin resistance/ hyperinsulinemia is likely to play a major role in the predisposition to metabolic endocrine and cardiovascular diseases seen more frequently in obesity and may even play a role in the predispo­ sition of people with obesity to develop certain cancers. FIGURE 413-5  How does obesity cause metabolic disease? Insulin resistance is one of the earliest complications of obesity and underlies and precedes many of its adverse health consequences. The disposal and production of glucose by the most important tissues, muscle and liver, respectively, become less sensitive to insulin, and this results in a compensatory increase in insulin secretion from the pancreas. There are two main theories for the association of obesity with insulin resistance. In the first, products of macrophages and other inflammatory cells that are more abundant in obese adipose tissue can, through paracrine or endocrine routes, disturb insulin’s action in muscle and liver cells. In the second, as adipose storage deposits fill up, they become less able to take on excessive calories, which end up being stored as ectopic lipid in tissues such as muscle and liver, which are not primarily designed to store nutrients of this type. The evidence in humans is stronger for the latter hypothesis. The main sites of insulin action in the body are the liver and skeletal muscle. Thus, for insulin resistance to be discernible at the level

of the whole body, the action of insulin must be disturbed in one or both of these tissues. It seems unlikely that an expanded fat cell mass would do that directly. How then does obesity lead to a state of insulin resistance? One hypothesis suggests a leading role for the inflammation that occurs in the adipose tissue in obesity (Fig. 413-5). This undoubt­ edly happens, as there are more macrophages in obese than nonobese adipose tissues, and this is associated with higher levels of inflamma­ tory markers in the circulation of people with obesity. The majority of macrophages in obese adipose tissue are found in clusters around dead or dying adipocytes, so it appears that these cells are clearing debris after cell death. Studies in animal models provide strong support for the notion that this inflammatory state is mechanistically linked to insulin resistance, but evidence from humans for this is not as strong. An alternative hypothesis is that as individuals develop obesity they become less able to safely store nutrients in their adipose tissue and begin to redirect macronutrients to other tissues that are not designed for fat storage and may be damaged by the nutrient excess. This cer­ tainly happens to people who are born with a lack of adipose tissue (lipodystrophy) who, early in life, develop severe versions of all the metabolic complications that are seen in obesity as they have no safe depot in which to store excess nutrients. There are stronger human data from both genetic and pharmacologic studies for the existence of the latter mechanism. How ectopic fat leads to insulin resistance and other damaging effects is still a puzzle, but it is very likely a major driver of pathology associated with obesity. Metabolic Complications  •  DYSLIPIDEMIA  The insulin resis­ tance of obesity is frequently associated with dyslipidemia character­ ized by high circulating triglycerides and low high-density lipoprotein cholesterol (Chap. 419). Occasionally, the hypertriglyceridemia may be severe enough to put the patient at risk of pancreatitis. Although there is a relationship between obesity and raised circulating levels of low-density lipoprotein cholesterol (which is the major risk factor for coronary artery disease), genetic factors independent of obesity and the type of dietary fat consumed probably have an even greater impact. Chronic imbalance of energy intake > Energy expenditure Expansion of adipose tissue depots Limited fat cell capacity for continuing storage Inflammatory cytokines Storage of lipid in nonadipose tissue Defective glucose handling in liver and muscle Insulin resistance/compensatory hyperinsulinemia

30 - 414 Evaluation and Management of Obesity

414 Evaluation and Management of Obesity

FATTY LIVER DISEASE  Obesity is strongly associated with the pres­ ence of ectopic fat in hepatocytes. In a subset of patients, this can progress to nonalcoholic steatohepatitis (NASH), which can progress to fibrosis, which is a precursor to cirrhosis (Chap. 354). The reported incidence of NASH-related cirrhosis and of hepatocellular carcinoma has increased markedly in step with the increase in the prevalence of obesity in adolescents and adults. TYPE 2 DIABETES  The insulin resistance characteristic of the over­ nourished state strongly predisposes to the development of type 2 diabetes in people who, largely for genetic reasons, are less able to maintain the high levels of insulin secretion over many decades. Impaired glucose tolerance and type 2 diabetes are among the most common complications of obesity (Chap. 415). Endocrine Complications  In females, the insulin resistance/ hyperinsulinemia frequently found in obesity strongly predisposes to the development of polycystic ovaries, characterized by irregular men­ struation, anovulatory infertility, and hirsutism due to hyperandrogen­ ism. In males, obesity is more often associated with a degree of central hypogonadism, where low circulating testosterone is associated with levels of luteinizing hormone and follicle-stimulating hormone that do not rise appropriately to compensate for the testosterone-deficient state. Dermatologic Complications  Obesity can result in problems with excessive skin folds that can cause discomfort through mechanical irritation and can also become infected with fungi. Insulin resistance/ hyperinsulinemia is associated with acanthosis nigricans, where areas such as axilla, groin, and the back of neck develop velvety hyperpig­ mentation. Hidradenitis suppurativa is a potentially disabling skin con­ dition strongly associated with obesity. It is characterized by recurrent boils often with chronically draining sinus tracts affecting skin areas containing apocrine sweat glands. Cardiovascular Complications  People with obesity, even if they do not have diabetes, have increased morbidity and mortality from atherothrombotic vascular disease, including coronary artery disease and stroke. The factors that result in this are complex and involve increased prevalence of hypertension, dyslipidemia, and insulin resis­ tance/hyperinsulinemia. The rare condition of thrombotic thrombo­ cytopenic purpura, which causes microvascular platelet thrombosis, thrombocytopenia, and hemolytic anemia due to the presence of abnormally large von Willebrand factor multimers, is strongly associ­ ated with obesity. Independent of occlusive arterial disease, people with obesity are also at increased risk of heart failure, particularly characterized primar­ ily by diastolic dysfunction, and of atrial fibrillation, the most common arrhythmia. Respiratory Complications  Exertional dyspnea is common in obesity, contributed to by the increased work required to move a greater mass as well as impacts of pressure on the diaphragm and tho­ racic cage on chest wall compliance. Enlargement of soft tissue of the mouth and throat and adipose depots around the airways contribute to the high prevalence of sleep apnea, although other factors such as central nocturnal hypoventilation, also contribute in some people. Gastrointestinal Disorders  Reflux esophagitis is the most com­ mon gastrointestinal complication of obesity, particularly occurring in those with high intraabdominal pressure. Gallstones are also more common in people with obesity, bringing increased risks of biliary colic, cholecystitis, pancreatitis, and gallbladder cancer. Rheumatologic Disorders  Osteoarthritis of the knee and gout are the two most common rheumatologic conditions clearly associated with obesity. Interestingly, despite obesity being described as a proin­ flammatory state, there is no evidence for an increase in rheumatoid arthritis or the seronegative arthritides among people with obesity. Cancers  Obesity is a risk factor for a number of common cancers. Indeed, it has recently been calculated that, at least in some countries, obesity has overtaken smoking as the greatest risk factor for developing

cancer. Recent research has found that as the BMI increases by 5 kg/m2, cancer mortality increases by 10%. The largest effects are on colorec­ tal, kidney, and pancreatic cancer, adenocarcinoma of the esophagus, and, in women, endometrial carcinoma. The recent rapid increase in the prevalence of esophageal adenocarcinoma is likely related to the marked recent increase in reflux esophagitis due to the raised intraab­ dominal pressure (with or without hiatus hernia) characteristic of central obesity.

Response to Infection  The fact that obesity can influence the outcome of some infections has become very apparent with the COVID-19 pandemic. Obese patients have a substantially worse out­ come if infected by SARS-CoV-2 through mechanisms that are as yet unclear. Obese patients also appear to be more susceptible to bacterial wound infections and postoperative sepsis. Evaluation and Management of Obesity CHAPTER 414 Disorders of the Central Nervous System  There is increasing evidence that obesity is a risk factor for dementia in later life, although how that risk is mediated is not clear. Idiopathic intracranial hyperten­ sion is a rare disorder that is strongly associated with obesity. ■ ■CONCLUSION Obesity is a medical disorder that has been greatly increasing in preva­ lence due to environmental factors that are ubiquitous in developed and developing countries. However, it is important to bear in mind that it is a highly heterogeneous condition, which in some people is attrib­ utable entirely to genetic causes, and that underlying genetic variation strongly influences the risk of obesity in all people. It is a serious con­ dition leading to multiple adverse health outcomes and considerable human suffering. As our understanding of its pathogenesis increases, our duty to treat obese patients with understanding and compassion and to develop new and better options for its treatment and prevention is worthy of emphasis. ■ ■FURTHER READING Farooqi IS, O’Rahilly S: The genetics of obesity in humans, in Endo­ text. KR Feingold et al (eds). South Dartmouth, MA, 2000. Friedman JM: Leptin and the endocrine control of energy balance. Nat Metab 1:754, 2019. Hall KD et al: The energy balance model of obesity: Beyond calories in, calories out. Am J Clin Nutr 115:1243, 2022. Heymsfield SB, Wadden TA: Mechanisms, pathophysiology, and management of obesity. N Engl J Med 376:1492, 2017. Leibel RL et al: Changes in energy expenditure resulting from altered body weight. N Engl J Med 332:621, 1995. NCD Risk Factor Collaboration (NCD-RISC): Worldwide trends in body-mass index, underweight, overweight, and obesity from 1975 to 2016: A pooled analysis of 2416 population-based measurement studies in 128·9 million children, adolescents, and adults. Lancet 390:2627, 2017. O’Rahilly S: Harveian Oration 2016: Some observations on the causes and consequences of obesity. Clin Med (Lond) 16:551, 2016. Robert F. Kushner

Evaluation and

Management of Obesity More than 70% of U.S. adults are considered to be overweight or have obesity, and the prevalence of obesity is increasing rapidly in most of the industrialized world. Children and adolescents also are developing greater rates of obesity, indicating that the current trends will accelerate

over time. Obesity is associated with an increased risk of multiple health problems, including hypertension, type 2 diabetes, dyslipidemia, obstructive sleep apnea, metabolic dysfunction-associated steatotic liver disease, degenerative joint disease, and some malignancies. Thus, it is important for health care professionals to identify, evaluate, and treat patients for obesity and associated complications and comorbid conditions.

■ ■EVALUATION Health care professionals should screen all adult patients for obesity and offer intensive lifestyle counseling including behavioral interven­ tions to promote sustained weight loss. The four main steps in the evaluation of obesity, as described below, are (1) a focused obesityrelated history that includes lifestyle questions about diet, physical activity, sleep, and stress; (2) a physical examination to determine the degree and type of obesity; (3) assessment of complications and comor­ bid conditions; and (4) assessment of the patient’s readiness to engage in weight management. PART 12 Endocrinology and Metabolism The Obesity-Focused History  The first step in taking an obe­ sity-focused history is to approach the topic in a sensitive manner. The reason for this concern is that the word obesity is a highly charged, emotive term. It has a significant pejorative meaning for many patients, leaving them feeling judged and blamed when labeled as such. This is not the case when patients are told that they have other chronic dis­ eases such as diabetes or hypertension. Patients prefer that clinicians use more neutral words or terms such as weight, excess weight, body mass index (BMI), or unhealthy weight, versus more perceived stigma­ tizing terms such as obesity, morbid obesity, or fatness. Information from the history should address the following seven questions: • What factors contribute to the patient’s weight gain and obesity? • How is obesity affecting the patient’s health? • What is the patient’s level of risk from obesity? • What does the patient find difficult about managing weight? • What are the patient’s goals and expectations? • What is the patient’s motivation to begin a weight management program? • What kind of help does the patient need? Although the majority of cases of obesity are promoted by biopsy­ chosocial and behavioral factors that affect diet and physical activity patterns, the history may suggest secondary causes that merit further evaluation. Disorders to consider include polycystic ovarian syndrome, hypothyroidism, Cushing’s syndrome, and hypothalamic disease. Druginduced weight gain also should be considered. Common causes include medications for diabetes (insulin, sulfonylureas, thiazolidinediones), steroid hormones, antipsychotic agents (clozapine, olanzapine, risperi­ done), mood stabilizers (lithium), antidepressants (tricyclics, mono­ amine oxidase inhibitors, paroxetine, mirtazapine), and antiepileptic drugs (valproate, gabapentin, carbamazepine). Other medications, such as nonsteroidal anti-inflammatory drugs and calcium channel blockers, may cause peripheral edema but do not increase body fat. The patient’s current diet and physical activity patterns may reveal factors that contribute to the development of obesity and may identify behaviors to target for treatment. Physical fitness and sedentary lifestyle, in particular, are important predictors of all-cause mortality rate inde­ pendent of BMI and body composition, which highlights the importance of taking a physical activity and exercise history during examination as well as emphasizing physical activity as a treatment approach. Inquiring about sleep health that addresses regularity, duration, efficiency, and satisfaction is also important. Although the mechanisms are uncertain, sleep deprivation is associated with metabolic alterations in appetite regulation, sympathetic nervous system overactivity, insulin sensitivity, and changes in circadian rhythm. Stress may also contribute to obesity, in part due to activation of the adrenal cortical axis and elevated cortisol levels and its impact on emotional health and behav­ iors. This historic information is best obtained by the combination of a questionnaire and an interview.

TABLE 414-1  Classification of Weight Status and Disease Risk BODY MASS INDEX (kg/m2) OBESITY CLASS DISEASE RISK CLASSIFICATION Underweight <18.5 — — Healthy weight 18.5–24.9 — — Overweight 25.0–29.9 — Increased Obesity 30.0–34.9 I High Obesity 35.0–39.9 II Very high Extreme obesity ≥40 III Extremely high Source: Reproduced with permission from WHO Consultation on Obesity (1997): Geneva, Switzerland), World Health Organization; 1997. BMI and Waist Circumference  Three key anthropometric mea­ surements are important in evaluating the degree of obesity: weight, height, and waist circumference. The BMI, calculated as weight (kg)/ height (m)2 or as weight (lb)/height (in)2 × 703, is used to classify weight status and risk of disease (Table 414-1). BMI is correlated with body fat and is related to disease risk. Lower BMI thresholds for overweight and obesity have been proposed for the Asia-Pacific region since this population appears to be at risk for glucose and lipid abnor­ malities at lower body weights. The problem with BMI is that it only measures the size of an individual. It does not measure body composi­ tion, distribution of body fat, health, quality of life, or any individual characteristics. BMI has many limitations but is still useful for screen­ ing and as a population estimate of increased morbidity and mortality. Currently, direct measurement of excess body fat is not universally practical in the clinical setting. Excess abdominal fat, assessed by measurement of waist circumfer­ ence or waist-to-hip ratio, is independently associated with a higher risk for metabolic syndrome, diabetes mellitus, and cardiovascular dis­ ease. Measurement of the waist circumference is a surrogate for visceral adipose tissue and should be performed in the horizontal plane above the iliac crest in individuals with a BMI ≤35 kg/m2 (Table 414-2). Obesity-Associated Complications and Comorbid Conditions 

The evaluation of complications and comorbid conditions should be based on presentation of symptoms, risk factors, and index of suspicion. For all patients, a fasting lipid profile (total, low-density lipoprotein, and high-density lipoprotein cholesterol and triglyceride levels), chemistry panel, and glycated hemoglobin should be per­ formed, and blood pressure determined. Symptoms and diseases that are directly or indirectly related to obesity are listed in Table 414-3. TABLE 414-2  Ethnic-Specific Cutpoint Values for Waist Circumference ETHNIC GROUP WAIST CIRCUMFERENCE Europeans   Men

94 cm (>37 in)   Women 80 cm (>31.5 in) South Asians and Chinese   Men 90 cm (>35 in)   Women 80 cm (>31.5 in) Japanese   Men 85 cm (>33.5 in)   Women 90 cm (>35 in) Ethnic South and Central Americans Use South Asian recommendations until more specific data are available. Sub-Saharan Africans Use European data until more specific data are available. Eastern Mediterranean and Middle Eastern (Arab) populations Use European data until more specific data are available. Source: Reproduced with permission from KG Alberti, P Zimmet, J Shaw; IDF Epidemiology Task Force Consensus Group. The metabolic syndrome-a new worldwide definition. Lancet 366:1059, 2005.

TABLE 414-3  Obesity-Related Organ Systems Review Cardiovascular Respiratory   Hypertension   Dyspnea   Congestive heart failure   Obstructive sleep apnea   Cor pulmonale   Hypoventilation syndrome   Varicose veins   Pickwickian syndrome   Pulmonary embolism   Asthma   Coronary artery disease Gastrointestinal Endocrine   Gastroesophageal reflux disease   Metabolic syndrome   Nonalcoholic fatty liver disease   Type 2 diabetes   Cholelithiasis   Dyslipidemia   Hernias   Polycystic ovarian syndrome   Colon cancer Musculoskeletal Genitourinary   Hyperuricemia and gout   Urinary stress incontinence   Immobility   Obesity-related glomerulopathy   Osteoarthritis (knees and hips)   Hypogonadism (male)   Low back pain   Breast and uterine cancer   Carpal tunnel syndrome   Pregnancy complications Psychological Neurologic   Depression/low self-esteem   Stroke   Body image disturbance   Idiopathic intracranial hypertension   Social stigmatization   Meralgia paresthetica Integument   Dementia   Striae distensae   Stasis pigmentation of legs   Lymphedema   Cellulitis   Intertrigo, carbuncles   Acanthosis nigricans   Acrochordons (skin tags)   Hidradenitis suppurativa Stage 0 No complications BMI ≥25 BMI ≥25 BMI ≥30 BMI 25–29.9 BMI Secondary Tertiary Tertiary Prevent complications Treat complications Treat complications Treatment/ prevention Lifestyle Lifestyle Lifestyle Consider medication Plus medication consider surgery Suggested therapy • Metabolically healthy obese • No biomechanical complications Examples FIGURE 414-1  Staging the severity of obesity using the American Association of Clinical Endocrinology clinical practice guidelines. AHI, apnea-hypopnea index; BMI, body mass index; NASH, nonalcoholic steatohepatitis; OSA, obstructive sleep apnea; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index (a patientreported outcome measure for osteoarthritis registering pain, stiffness, and function). (Data from WT Garvey et al: American Association of Clinical Endocrinologists and American College of Endocrinology comprehensive clinical practice guidelines for medical care of patients with obesity. Endocr Pract 22(Suppl 3):1, 2016.)

Although individuals vary, the number and severity of organ-specific complications and comorbid conditions usually rise with increasing levels of obesity.

Identifying the High-Risk Patient  Efforts are under way to develop more practical and useful assessments to identify patients who are at high risk in addition to using BMI alone. Analogous to other staging systems commonly used for congestive heart failure or chronic kidney disease, the American Association of Clinical Endocrinology (AACE) and the American College of Endocrinology (ACE) guide­ lines advocate a simple and clinically useful obesity disease staging system that is based on ethnic-specific BMI cutoffs in conjunction with assessment for adiposity-related complications (Fig. 414-1). Stage 0 is assigned to individuals who are overweight or have obesity by BMI classification but have no complications, whereas stages 1 and 2 are defined as individuals who are overweight or have obesity by BMI classification and have one or more mild-moderate complications (stage 1) or at least one severe complication (stage 2). A different func­ tional staging system for obesity, called the Edmonton Obesity Staging System (EOSS), classifies individuals with obesity into five graded categories (0–4), based on their morbidity and health-risk profile along three domains—medical, functional, and psychological. In this system, staging occurs independent of BMI. Evaluation and Management of Obesity CHAPTER 414 Assessing the Patent’s Readiness to Change  An attempt to initiate lifestyle changes when the patient is not ready usually leads to frustration and may hamper future weight-loss efforts. Assessment includes patient motivation and support, stressful life events, psychi­ atric status, time availability and constraints, and appropriateness of goals and expectations. Readiness can be viewed as the balance of two opposing forces: (1) motivation, or the patient’s desire to change; and (2) resistance, or the patient’s barriers to change. A helpful method to begin a readiness assessment is to use the motivational interviewing technique of “anchoring” the patient’s interest and confidence to change on a numerical scale. With this technique, the patient is asked to rate—on a scale from 0 to 10, with 0 being not so important (or confident) and 10 being very important (or confident)—their level of interest in and confidence about engaging in Stage 1 Stage 2 Mild-moderate complications Severe complications • Pre-hypertension • Hepatic steatosis • OSA with AHI 5–30 and mild symptoms • Osteoarthritis with WOMAC score 1–5 • Prediabetes • Metabolic syndrome • Type 2 diabetes • NASH • Hypertension • OSA with symptoms or AHI >30 • Osteoarthritis with WOMAC score 5–10 or knee replacement surgery

weight management at this time. This exercise helps establish readiness to change and also serves as a basis for further dialogue.

TREATMENT Obesity THE GOAL OF THERAPY The primary goals of treatment are to improve obesity-related com­ plications and comorbid conditions and quality of life and reduce the risk of developing future obesity-related complications. Infor­ mation obtained from the history, physical examination, and diag­ nostic tests is used to determine risk and develop a treatment plan. The decision of how aggressively to treat the patient and which modalities to employ is determined by using shared decision-mak­ ing that includes the patient’s risk status, expectations and personal values, and available resources. Not all patients who are deemed to have obesity by BMI screening need to be treated, since BMI alone is an imperfect measurement of the disease of obesity. How­ ever, patients who present with obesity-related complications and comorbidities and who would benefit from weight-loss intervention should be managed proactively. Therapy for obesity always begins with lifestyle management and may include pharmacotherapy or bariatric surgery, depending on BMI risk category (Table 414-4). Setting an initial weight-loss goal of 8–10% over 6 months is a realistic and practical target. PART 12 Endocrinology and Metabolism LIFESTYLE MANAGEMENT Obesity care involves attention to three essential elements of life­ style: dietary habits, physical activity, and behavior modification. Because obesity is fundamentally a disease of energy imbalance, all patients must learn how and when energy is consumed (diet), how and when energy is expended (physical activity), and how to incor­ porate this information into their daily lives (behavioral therapy). Lifestyle management has been shown to result in a modest (typically 3–5 kg) weight loss when compared with no treatment or usual care. Diet Therapy  The primary focus of diet therapy is to reduce overall calorie consumption. Guidelines from the American Heart Association/American College of Cardiology/The Obesity Society (AHA/ACC/TOS) recommend initiating treatment with a calorie deficit of 500–750 kcal/d compared with the patient’s habitual diet. Alternatively, a diet of 1200–1500 kcal/d for women and 1500–1800 kcal/d for men (adjusted for the individual’s body weight) can be prescribed. This reduction is consistent with a goal of losing ~1–2 lb/week. The calorie deficit can be instituted through dietary substitutions or alternatives. Examples include choosing smaller portion sizes, eating more fruits and vegetables, consuming more whole-grain cereals, selecting leaner cuts of meat and skimmed dairy products, reducing consumption of fried foods and other foods with added fats and oils, and drinking water instead of sugar-sweetened beverages. It is important that dietary counseling remains patient centered and that the selected goals are SMART (specific, measurable, agreed upon, realistic, timely). The macronutrient composition of the diet will vary with the patient’s preference and medical condition. The 2020 U.S. Depart­ ment of Agriculture Dietary Guidelines for Americans (Chap. 343), which focus on health promotion and risk reduction, can be applied to treatment of patients who are overweight or have obesity. The TABLE 414-4  A Guide to Opting for Treatment for Obesity TREATMENT 25–26.9 27–29.9 30–34.9 35–39.9 ≥40 Diet, exercise, behavioral therapy With comorbidities With comorbidities + + + Pharmacotherapy — With comorbidities + + + Surgery — — — With comorbidities + Source: Reproduced from U.S. Department of Health and Human Services Public Health Service. National Institute of Health National Heart, Lung and Blood Institute. The Practical Guide Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. NIH Publication Number 00-4084. October 2000.

recommendations include maintaining a diet rich in whole grains, fruits, vegetables, and dietary fiber; decreasing sodium intake to <2300 mg/d; consuming fat-free or low-fat dairy products; and keeping added sugars and saturated fat intake to <10% of daily calo­ ries. Application of these guidelines to specific calorie goals can be found on the website www.choosemyplate.gov. Since portion control is one of the most difficult strategies for patients to manage, the use of preprepared products such as meal replacements is a simple and convenient suggestion. Examples include frozen entrees, protein shakes, and bars. Use of meal replacements in the diet has been shown to result in a 7–8% weight loss. Numerous randomized trials comparing diets of different mac­ ronutrient composition (e.g., low-carbohydrate, low-fat, Mediterra­ nean) have shown that weight loss depends primarily on reduction of total caloric intake and adherence to the prescribed diet, not the specific proportions of carbohydrate, fat, and protein in the diet. The macronutrient composition will ultimately be determined by the patient’s taste preferences, cooking style, and culture. However, the patient’s underlying medical problems are also important in guiding the recommended dietary composition. The dietary pre­ scription will vary according to the patient’s metabolic profile and risk factors. A consultation with a registered nutritionist for medical nutrition therapy is particularly useful in considering patient pref­ erence and treatment of comorbid diseases. Another dietary approach to consider is based on the concept of energy density, which refers to the number of calories (i.e., amount of energy) a food contains per unit of weight. People tend to ingest a constant volume of food regardless of caloric or macronutrient content. Adding water or fiber to a food decreases its energy density by increasing weight without affecting caloric content. Examples of foods with low energy density include soups, fruits, vegetables, oat­ meal, and lean meats. Dry foods and high-fat foods such as pretzels, cheese, egg yolks, potato chips, and red meat have a high energy density. Diets containing low-energy-dense foods have been shown to control hunger and thus to result in decreased caloric intake and weight loss. Occasionally, very-low-calorie diets (VLCDs) are prescribed as a form of aggressive dietary therapy. The primary purpose of a VLCD is to promote a rapid and significant (13- to 23-kg) short-term weight loss over a 3- to 6-month period. The proprietary formulas designed for this purpose typically supply ≤800 kcal, 50–80 g of pro­ tein, and 100% of the recommended daily intake for vitamins and minerals. Indications for initiating a VLCD include the involvement of well-motivated individuals who have moderate to severe obesity, have failed at more conservative approaches to weight loss, and have a medical condition that would be immediately improved with rapid weight loss. These conditions include poorly controlled type 2 diabetes, hypertriglyceridemia, obstructive sleep apnea, and symp­ tomatic peripheral edema. In the DiRECT trial of patients with type 2 diabetes and obesity, a low-energy formula diet (825–853 kcal/d) was administered for 3 months following by a structured monthly program. At 12 months, almost half of the participants achieved remission to a nondiabetic state off of all antidiabetic drugs. Use of formula diets should be prescribed by trained practitioners in a medical care setting where medical monitoring and high-intensity lifestyle intervention can be provided. Physical Activity Therapy  Although exercise alone is only moderately effective for weight loss, the combination of dietary BMI CATEGORY (kg/m2)

modification and exercise is the most effective behavioral approach for the treatment of obesity. The most important role of exercise appears to be in the maintenance of weight loss. The 2018 Physical Activity Guidelines for Americans (www.health.gov/paguidelines) recommend that adults should engage in 150 min of moderateintensity or 75 min a week of vigorous-intensity aerobic physical activity per week, preferably spread throughout the week. Focusing on simple ways to add physical activity into the normal daily rou­ tine through leisure activities, travel, and domestic work should be suggested. Examples include brisk walking, using the stairs, doing housework and yard work, and engaging in sports. Additionally, it is important to reduce sedentary behavior, which is associated with all-cause and cardiovascular disease mortality in adults. Asking the patient to use a wearable activity tracker to monitor total accumula­ tion of steps or kcal expended as part of the activities of daily living is a useful strategy. Step counts are highly correlated with activity level. Studies have demonstrated that lifestyle activities are as effec­ tive as structured exercise programs for improving cardiorespira­ tory fitness and weight loss. A high level of physical activity (>300 min of moderate-intensity activity per week) is often needed to lose weight and sustain weight loss. These exercise recommendations are daunting to most patients and need to be implemented gradu­ ally. Consultation with an exercise physiologist or personal trainer may be helpful. Behavioral Therapy  Cognitive behavioral therapy is used to help change and reinforce new dietary and physical activity behaviors. Strategies include self-monitoring techniques (e.g., journaling, weighing, and measuring food and activity); stress management; stimulus control (e.g., using smaller plates, not eating in front of the television or in the car); social support; problem solving; and cognitive restructuring to help patients develop more positive and realistic thoughts about themselves. When recommending any behavioral lifestyle change, the patient should be asked to identify what, when, where, and how the behavioral change will be per­ formed. The patient should keep a record of the anticipated behav­ ioral change so that progress can be reviewed at the next office visit. Because these techniques are time consuming to implement, their supervision is often undertaken by ancillary office staff, such as an advanced practice provider or registered nutritionist. PHARMACOTHERAPY Adjuvant pharmacologic treatments should be considered for patients with a BMI ≥30 kg/m2 or a BMI ≥27 kg/m2 who have con­ comitant obesity-related diseases and for whom dietary and physi­ cal activity therapy has not been successful. When an antiobesity medication is prescribed, patients should be actively engaged in a lifestyle program that provides the strategies and skills needed to use the drug effectively since such support increases total weight loss. Medications for obesity have traditionally fallen into two major categories: those that affect appetite and those that inhibit gastro­ intestinal fat absorption. However, since the introduction of more effective nutrient-stimulated hormone-based therapeutics in 2021, an additional designation of first- and second-generation medica­ tions has been adopted. Antiobesity medications are approved by the U.S. Food and Drug Administration (FDA) with an indication for chronic weight management, with the exception of phentermine and other sympathomimetics, which are only approved for shortterm use. The centrally active medications work biologically to suppress appetite, affecting hunger, satiety, and response to highly rewarding foods, and thus making it easier for patients to follow their dietary intentions to reduce caloric intake. In addition, one capsule that is considered a medical device was marketed in 2020. Characteristics of the currently approved antiobesity medications are shown in Table 414-5. First-Generation Centrally Acting Medications  This class of medications directly targets neurotransmitters in the hypothalamus and reward centers in the central nervous system (Chap. 413) to affect satiety (feeling of fullness after a meal), hunger (the biologic

sensation that prompts eating), and craving (intense desire for a specific food). By controlling appetite, these agents help patients reduce caloric intake without a sense of deprivation. The classic sympathomimetic adrenergic agents (benzphetamine, phendimet­ razine, diethylpropion, and phentermine) function by stimulating norepinephrine release or by blocking its reuptake. Among these agents, phentermine is the most commonly prescribed; however, there is limited long-term data on its effectiveness. A 2002 review of six randomized, placebo-controlled trials of phentermine for weight control found that patients lost 0.6–6.0 additional kg of weight over 2–24 weeks of treatment. The most common side effects of the amphetamine-derived agents are restlessness, insomnia, dry mouth, constipation, and increased blood pressure and heart rate.

Evaluation and Management of Obesity CHAPTER 414 Phentermine/topiramate (PHEN/TPM) is a combination drug that contains a catecholamine releaser (phentermine) and an anti­ convulsant (topiramate). Topiramate is approved by the FDA as an anticonvulsant for the treatment of epilepsy and for the prophylaxis of migraine headaches. Weight loss was identified as an unintended side effect of topiramate during clinical trials for epilepsy. The mechanism responsible for weight loss is uncertain but is thought to be mediated through the drug’s modulation of γ-aminobutyric acid receptors, inhibition of carbonic anhydrase, and antagonism of glutamate. PHEN/TPM has undergone two 1-year pivotal ran­ domized, placebo-controlled, double-blind trials of efficacy and safety: EQUIP and CONQUER. In a third study, SEQUEL, 78% of CONQUER participants continued to receive their blinded treatment for an additional year. All participants received diet and exercise counseling. Mean percent weight loss for participants randomized to medication and placebo are displayed in Fig. 414-2. Intention-to-treat 1-year placebo-subtracted weight loss for PHEN/ TPM was 9.3% (15-mg/92-mg dose) and 6.6% (7.5-mg/46-mg dose), respectively, in the EQUIP and CONQUER trials. Clinical and statistical dose-dependent improvements were seen in selected cardiovascular and metabolic outcome measurements that were related to the weight loss. The most common adverse events experi­ enced by the drug-randomized group were paresthesias, dry mouth, constipation, dysgeusia, and insomnia. Because of an increased risk of congenital fetal oral-cleft formation from topiramate, women of childbearing age should have a negative pregnancy test before treatment and monthly thereafter and use effective contraception consistently during medication therapy. Naltrexone SR/bupropion SR (NB) is a combination of an opioid antagonist and a dopamine and norepinephrine reuptake inhibitor, respectively. Individually, naltrexone is approved by the FDA for the treatment of alcohol dependence and for the blockade of the effects of exogenously administered opioids, whereas bupropion is approved as an antidepressant and smoking cessation aid. As a combination drug, each component works in consort: bupropion stimulates secretion of α-melanocyte-stimulating hormone (MSH) from proopiomelanocortin (POMC), whereas naltrexone blocks the feedback inhibitory effects of opioid receptors activated by the β-endorphin released in the hypothalamus, thus allowing the inhibitory effects of MSH to reduce food intake. The medication has undergone three randomized, placebocontrolled, double-blind trials for efficacy and safety. Participants were randomized to receive NB (8 mg/90 mg two tablets bid) or placebo in the three COR studies. Whereas participants received standardized nutritional and exercise counseling in COR-I and COR-II, a more intensive behavior modification program was provided in COR-BMOD (Table 414-5). Intention-to-treat 1-year placebo-subtracted weight loss was 4.8%, 5.1%, and 4.2%, respec­ tively, in the COR-I, COR-II, and COR-BMOD trials. Clinical and statistical dose-dependent improvements were seen in selected car­ diovascular and metabolic outcome measurements that were related to the weight loss. However, the medication led to slight increases or smaller decreases in blood pressure and pulse than placebo. The most common adverse events experienced by the drug-randomized groups were nausea, constipation, headache, vomiting, dizziness, diarrhea, insomnia, and dry mouth.

TABLE 414-5  Antiobesity Medications DRUG CHARACTERISTIC PHENTERMINE ORLISTAT PHEN/TPM NAL/BUP LIRAGLUTIDE SEMAGLUTIDE TIRZEPATIDE Mechanism of action Sympathomimetic, increases norepinephrine release in CNS Gastrointestinal lipase enzyme inhibitor Phen: sympathomimetic in CNS; TPM: modulates GABA receptors in the CNS Route of administration, frequency, and dose Oral, once to 3 times daily, doses of 8, 15, 30, and 37.5 mg Oral, 3 times daily, within 1 h of fatcontaining meals Oral, once daily. Start 3.75/23 mg/d × 2 weeks, then 6.5/46 mg/d; can escalate to max dose of 15/2 mg/d PART 12 Endocrinology and Metabolism Percent weight loss (placebo subtracted)a 4.4% 4.1% 8.0% 5.1% 5.4% 12.5% 17.8% Most common adverse effects Dry mouth Insomnia Constipation Headache Dizziness Steatorrhea Increased defecation Oily spotting Liquid stool Fecal urgency Paresthesia Dry mouth Constipation Headache Insomnia Dizziness Contraindications Uncontrolled hypertension, untreated hyperthyroidism, within 14 d of MAOI use Chronic malabsorption Uncontrolled hypertension, untreated hyperthyroidism, history of glaucoma, calcium oxalate nephrolithiasis, within 14 d of MAOI use aBased on maximal dose. Abbreviations: CNS, central nervous system; GABA, γ-aminobutyric acid; GIP, gastric inhibitory polypeptide; GLP-1, glucagon-like peptide 1; MAOI, monoamine oxidase inhibitor; MEN, multiple endocrine neoplasia; Nal/Bup, naltrexone/bupropion; Phen/TPM, phentermine/topiramate; POMC, proopiomelanocortin; qW, every week. Liraglutide was the first glucagon-like peptide 1 receptor agonist (GLP-1 RA) with 97% homology to human GLP-1 that introduces nutrient-stimulated, hormone-based therapy for the treatment of obesity. In addition to its effect as an incretin hormone (glucoseinduced insulin secretion), liraglutide inhibits both gastric empty­ ing and glucagon secretion and stimulates GLP-1 receptors in the arcuate nucleus of the hypothalamus, the nucleus tractus solitarius of the brainstem, and projections to other appetite-modulating relay nuclei to reduce appetite. As a result of molecular modifications of the structure, liraglutide has reduced susceptibility to DPP-4 and can be dosed once daily by subcutaneous (SC) administration with a half-life of ~11–15 h. Liraglutide was initially approved for the treatment of type 2 diabetes in the United States in 2010 at doses up to 1.8 mg once daily. It was subsequently approved for obesity treatment at doses up to 3.0 mg once daily in 2014 for adults and, in 2020, for adolescents (aged ≥12 years). Specifically targeting obesity, liraglutide has undergone five ran­ domized, double-blind, placebo-controlled trials in adults called SCALE (Satiety and Clinical Adiposity–Liraglutide Evidence) involving >5000 adult participants to evaluate its efficacy and safety for weight management. All participants received diet and physi­ cal activity counseling and were randomized to receive liraglutide (3.0 mg SC daily) or placebo with the primary outcome of change in body weight. Intention-to-treat 1-year placebo-subtracted weight loss for these trials ranged from 3.4 to 6.1%. Clinical and statistical dose-dependent improvements were seen in selected cardiovascular

Nal: blocks opioidmediated POMC autoinhibition; bup: activates POMC in the hypothalamus GLP-1 receptor agonist GLP-1 receptor agonist GLP-1/GIP dual receptor agonist Oral, 1 tablet (8 mg/90 mg) qAM × 1 week; 1 tablet in morning and evening × 1 week; 2 tablets in morning and 1 tablet in evening × 1 week; then 2 tablets in morning and 2 tablets in evening Subcutaneous, once daily; initiate at 0.6 mg/d × 1 week; increase by 0.6 mg weekly to 3 mg/d Subcutaneous, once weekly; 0.25 mg qW × 4 weeks, then 0.5 mg qW × 4 weeks, then 1 mg qW × 4 weeks, then 1.7 mg qW × 4 weeks, then 2.4 mg qW Subcutaneous, once weekly; 2.5 mg qW × 4 weeks, then 5 mg qW × 4 weeks, then 7.5 mg qW × 4 weeks, then 10 mg qW × 4 weeks, then 12.5 mg qW, then 15 mg qW Nausea Constipation Headache Vomiting Dizziness Insomnia Nausea Diarrhea Constipation Dyspepsia Vomiting Nausea Diarrhea Constipation Dyspepsia Vomiting Nausea Diarrhea Constipation Abdominal pain Uncontrolled hypertension, history of seizures, bulimia or anorexia nervosa, within 14 d of MAOI use, long-term opioid use Personal or family history of medullary thyroid cancer, MEN type 2; pancreatitis is a caution Personal or family history of medullary thyroid cancer; MEN type 2; pancreatitis is a caution Personal or family history of medullary thyroid cancer, MEN type 2; pancreatitis is a caution and metabolic outcome measurements. In SCALE TEENS, which involved adolescents with obesity (average age 14.6 years), the liraglutide-treated group demonstrated a placebo-subtracted weight loss of 5%. The most common adverse events from the SCALE tri­ als were nausea, diarrhea, constipation, and vomiting, which were reported as mild and transient. GLP-1 agonists should not be pre­ scribed in patients with a family or personal history of medullary thyroid cancer or multiple endocrine neoplasia. Setmelanotide is a melancortin-4 (MC4) receptor agonist that was FDA approved in 2020 for daily SC administration for chronic weight management in adults and pediatric patients 6 years of age and older with monogenic or syndromic obesity due to BardetBiedl syndrome (BBS) or POMC, proprotein convertase subtilisin/ kexin type 1 (PCSK1), or leptin receptor (LEPR) deficiency. The medication addresses the underlying hyperphagia and specific molecular mechanism of these rare genetic diseases. The most common side effects include injection site reactions, skin hyperpig­ mentation, nausea, and spontaneous penile erections. First-Generation Peripherally Acting Medication  Orlistat is cur­ rently the only medication in this class. It is a synthetic hydroge­ nated derivative of a naturally occurring lipase inhibitor, lipostatin, that is produced by the mold Streptomyces toxytricini. This drug is a potent, slowly reversible inhibitor of pancreatic, gastric, and carboxylester lipases and phospholipase A2, which are required for the hydrolysis of dietary fat into fatty acids and monoacylglycerols.

Orlistat Phen/TPM NB Lira Sema TZP 24.3

Percent weight loss

10.4 10.9 10.2

8.8 6.1 5.8 6.5 6.1

1.9 1.3 1.2 1.6

Davidson CONQUER COR-I COR-II COR-BMOD Sjostrom EQUIP FIGURE 414-2  One-year mean weight loss for antiobesity medications compared to placebo. Lira, liraglutide; NB, naltrexone/bupropion; Phen/TPM, phentermine/ topiramate; Sema, semaglutide; TZP, tirzepatide. Orlistat acts in the lumen of the stomach and small intestine by forming a covalent bond with the active site of these lipases. Taken at a therapeutic dose of 120 mg tid, orlistat blocks the digestion and absorption of ~30% of dietary fat. After discontinuation of the drug, fecal fat content usually returns to normal within 48–72 h. Multiple randomized, double-blind, placebo-controlled studies have shown an intention-to-treat 1-year placebo-subtracted weight loss of 2.7–4.1%. Because orlistat is minimally (<1%) absorbed from the gastrointestinal tract, it has no systemic side effects. Tolerability is related to the malabsorption of dietary fat, and this is generally diminished as patients control their dietary fat intake. Because serum concentrations of the fat-soluble vitamins D and E and β-carotene may be reduced by orlistat treatment, vitamin supple­ ments are recommended to prevent potential deficiencies. Orlistat was approved for over-the-counter use in 2007. Second-Generation Medications  Semaglutide is generally recog­ nized as the first drug in this category based on its greater weight loss efficacy and further chemical modification that allows for once-weekly SC administration with a longer half-life. Semaglutide was initially approved for the treatment of type 2 diabetes in the United States at doses up to 1.0 mg once weekly in 2017 and at 2.0 mg once weekly in 2022. It was subsequently approved at doses up to 2.4 mg once weekly for chronic weight management for adults in 2021 and for adolescents in 2022. Semaglutide has undergone multiple prospective, randomized, placebo-controlled trials in the STEP (Semaglutide Treatment Effect in People with Obesity) program that was designed to inves­ tigate the effect of semaglutide 2.4 mg SC weekly versus placebo on weight loss, safety, and tolerability in adults with obesity or over­ weight. Intention-to-treat placebo-subtracted weight loss for the STEP 1 to 4 trials ranged from 6.2 to 14.8% at 68 weeks depending on the population and study design, and loss of 12.6% occurred after 104 weeks for STEP 5. Clinical and statistical dose-dependent improvements were seen in selected cardiovascular and metabolic outcome measurements. The most common adverse effects include nausea, diarrhea, constipation, and vomiting. GLP-1 RAs should

Drug Placebo 20.9 17.4 Evaluation and Management of Obesity CHAPTER 414

11.3 9.3

5.7 5.1 4.5 3.1 2.6 2.4 SCALE MAIN SCALE STEP 1 STEP 3 STEP 4 SURMOUNT-1 SURMOUNT-3 not be prescribed in patients with a family or personal history of medullary thyroid cancer or multiple endocrine neoplasia. In the STEP TEENS trial, adolescents with overweight or obesity randomized to semaglutide 2.4 mg achieved a 16.1% reduction in BMI versus a 0.6% increase for placebo. The recent SELECT (Semaglutide Effects on Cardiovascular Outcomes in People with Overweight or Obesity) trial demonstrated a 20% reduction in major adverse cardiovascular events in patients with preexisting cardiovascular disease and overweight or obesity but without dia­ betes who were randomized to semaglutide 2.4 mg versus placebo, and the STEP-HFpEF trial observed improved heart failure–related symptoms, physical limitations, and exercise function and reduced body weight and inflammation in patients randomized to semaglu­ tide versus placebo. Tirzepatide is the first long-acting, weekly, injectable, dual GLP-1/ gastric inhibitory polypeptide (GIP) peptide analogue, engineered from the native GIP sequence with agonist activity at both the GLP-1 and GIP receptors with a half-life of ~117 h. Whereas GIP receptor agonism is equal to native GIP, the molecule’s GLP-1 recep­ tor affinity is approximately five times weaker than native GLP-1. GIP in the brain appears to act synergistically with GLP-1 recep­ tor activation to allow greater weight loss. Tirzepatide was FDA approved for type 2 diabetes in 2022 and subsequently approved for chronic weight management in adults in 2023, at 5-, 10-, and 15-mg doses. Tirzepatide has undergone multiple prospective, randomized, placebo-controlled trials in the SURMOUNT clinical development program that was designed to investigate the effect of tirzepatide 5-, 10-, and 15-mg SC weekly doses versus placebo on weight loss, safety, and tolerability in adults with obesity or overweight. Intention-to-treat placebo-subtracted weight loss for SURMOUNT 1 to 4 trials at the 15-mg dose ranged from 11.6 to 21.4% depend­ ing on the study population and design. Clinical and statistical dose-dependent improvements were seen in selected cardiovascular and metabolic outcome measurements. Similar to GLP-1 RAs, the most common adverse events are gastrointestinal (nausea, diarrhea,

constipation, and vomiting) and reported as mild and transient; tirzepatide should not be prescribed in patients with a family or personal history of medullary thyroid cancer or multiple endocrine neoplasia.

Oral Device  Gelesis100 is a nonsystemic, water-soluble gel that was approved by the FDA in 2019. In the stomach, the capsule releases the cellulose microgel, which absorbs water and forms a matrix with the consistency of food, occupying ~25% of the stomach. In the large intestine, it is broken down by enzymes and the cellulose is excreted. Gelesis100 and placebo were evaluated over 24 weeks in patients with BMI of 27 to ≤40 kg/m2 and fast­ ing plasma glucose of 90–145 mg/dL. Intention-to-treat, 24-week, placebo-subtracted weight loss was 2.1% (6.4 vs 4.4%). Gelesis100 treatment had no apparent increased safety risks. The capsules are approved for patients with a BMI of ≥25 kg/m2, with or without comorbidities. SURGERY Bariatric surgery (Fig. 414-3) can be considered for patients with severe obesity (BMI ≥40 kg/m2) or for those with moderate obesity (BMI ≥35 kg/m2) associated with a number of comorbid conditions. The clinical benefits of bariatric surgery in achieving weight loss and alleviating metabolic complications and comorbidities have been attributed largely to changes in the physiologic responses of gut hormones, bile acid metabolism, the microbiota, and adipose tissue metabolism. Metabolic effects resulting from bypassing the foregut include altered responses of ghrelin, GLP-1, peptide YY3-36, and oxyntomodulin. Additional effects on food intake and body weight control may be attributed to changes in vagal signaling. The loss of fat mass, particularly visceral fat, is associated with multiple meta­ bolic, adipokine, and inflammatory changes that include improved insulin sensitivity and glucose disposal; reduced free fatty acid flux; increased adiponectin levels; and decreased interleukin 6, tumor necrosis factor α, and high-sensitivity C-reactive protein levels. PART 12 Endocrinology and Metabolism A B x x D E C FIGURE 414-3  Bariatric surgical procedures. Examples of operative interventions used for surgical manipulation of the gastrointestinal tract. A. Laparoscopic adjustable gastric banding. B. Laparoscopic sleeve gastrectomy. C. The Roux-en-Y gastric bypass. D. Biliopancreatic diversion with duodenal switch. E. Biliopancreatic diversion.

Restrictive surgeries limit the amount of food the stomach can hold and slow the rate of gastric emptying. Laparoscopic adjustable gastric banding is the prototype of this category. The first banding device was approved for use in the United States in 2001. In con­ trast to previous devices, this band has a diameter that is adjustable by way of its connection to a reservoir that is implanted under the skin. Injection of saline into the reservoir and removal of saline from the reservoir tighten and loosen the band’s internal diameter, respectively, thus changing the size of the gastric opening. Although the mean percentage of total body weight lost at 5 years is estimated at 20–25%, longer-term follow-up has been more disappointing, leading to near abandonment of the procedure. In the laparoscopic sleeve gastrectomy, the stomach is restricted by stapling and dividing it vertically, removing ~80% of the greater curvature and leaving a slim banana-shaped remnant stomach along the lesser curvature. Weight loss after this procedure is superior to that after laparo­ scopic adjustable gastric banding. The three restrictive-malabsorptive bypass procedures combine the elements of gastric restriction and selective malabsorption: Roux-en-Y gastric bypass, biliopancreatic diversion, and biliopan­ creatic diversion with duodenal switch (Fig. 414-3). These proce­ dures are routinely performed by laparoscopy. These procedures generally produce a 28–33% average total body weight loss at 12–18 months followed by variable weight recurrence. Significant improvement in multiple obesity-related comorbid conditions, including type 2 diabetes, hypertension, dys­ lipidemia, obstructive sleep apnea, quality of life, and long-term cardiovascular events, has been reported. A meta-analysis of con­ trolled clinical trials comparing bariatric surgery versus no surgery showed that surgery was associated with a reduced odds ratio (OR) risk of global mortality (OR = 0.55), cardiovascular death (OR = 0.58), and all-cause mortality (OR = 0.70). Among the observed improvements in comorbidities, the pre­ vention and treatment of type 2 diabetes resulting from bariatric z y z 150 cm y 100 cm

32 - 416 Diabetes Mellitus- Management and Therapies

416 Diabetes Mellitus: Management and Therapies

Diabetes Mellitus:

Management and

Therapies Alvin C. Powers, Kevin D. Niswender,

Michael R. Rickels OVERALL GOALS The goals of therapy for all forms of diabetes mellitus (DM) are to (1) eliminate symptoms related to hyperglycemia, (2) reduce or eliminate the long-term microvascular and macrovascular complications of DM (Chap. 417), and (3) allow the patient to achieve as normal a lifestyle as possible. To reach these goals, the physician and health care team should identify a target level of glycemic control for each patient, pro­ vide the patient with the educational and pharmacologic resources nec­ essary to reach this target, avoid hypoglycemia, and monitor/prevent/ treat DM-related complications. Symptoms of diabetes usually resolve when the plasma glucose is <11.1 mmol/L (200 mg/dL), and thus most DM treatment focuses on achieving the second and third goals. The care of an individual with either type 1 or type 2 DM requires a multidisciplinary team. Central to the success of this team are the patient’s participation, input, and enthusiasm, all of which are essential for optimal diabetes management. Members of the health care team usually include the primary care provider and/or the endocrinologist or diabetologist, an advanced practice provider (APP), a pharmacist, a certified diabetes educator, a nutritionist, a behavioral health pro­ fessional, and possibly a social worker. In addition, when the com­ plications of DM arise, subspecialists (including ophthalmologists, neurologists, podiatrists, nephrologists, cardiologists, and cardiovascu­ lar and transplant surgeons) with experience in DM-related complica­ tions are essential. The American Diabetes Association (ADA) suggests applying the Chronic Care Model to diabetes with an emphasis on these elements: a proactive, team-based delivery and health system design that involves self-management, decision support with evidencebased guidelines for person-specific and population-based approaches, and community resources and policies that support healthy lifestyles. Space limitations do not allow a discussion of all these elements, so this chapter first reviews the ongoing treatment of diabetes in the outpa­ tient setting and then discusses the treatment of severe hyperglycemia, as well as the treatment of diabetes in hospitalized patients. ONGOING ASPECTS OF COMPREHENSIVE DIABETES CARE A number of names are sometimes applied to different approaches to diabetes care, such as intensive insulin therapy or intensive glycemic control. The current chapter, and other sources, uses the term Compre­ hensive diabetes care to emphasize the fact that optimal diabetes therapy involves much more than glucose management and medications and that individualized, patient-centered care is essential. Although glyce­ mic control is central to optimal diabetes therapy, comprehensive dia­ betes care of both type 1 and type 2 DM should also detect and modify risk factors for DM-associated disorders and manage DM-specific complications (Chap. 417). The key elements of comprehensive diabe­ tes care are summarized in Table 416-1. The morbidity and mortality of DM can be greatly reduced by timely and consistent surveillance, including the detection, prevention, and management of DM-related complications (Table 416-1 and Chap. 417). Such approaches are indi­ cated for all individuals with DM, but many individuals with diabetes do not receive these or comprehensive diabetes care. The social deter­ minants of health and family, financial, cultural, and employmentrelated issues may negatively impact diabetes care. This chapter, while recognizing that resources available for diabetes care vary widely throughout the world, provides guidance for comprehensive diabe­ tes care in health care settings with considerable societal resources.

TABLE 416-1  Guidelines for Ongoing, Comprehensive Medical Care for Individuals with Diabetes • Individualized glycemic goal and therapeutic plan with an emphasis on shared decision-making • Blood glucose measurement using continuous glucose monitoring (CGM) or capillary fingerstick device • HbA1c testing (2–4 times/year) • Lifestyle management in the care of diabetes, including: • Diabetes self-management education and support • Nutrition therapy • Physical activity • Psychosocial care, including evaluation for depression, anxiety, diabetes Diabetes Mellitus: Management and Therapies
CHAPTER 416 distress • Detection, prevention, or management of diabetes-related complications, including: • Diabetes-related eye examination (annual or biannual; Chap. 417) • Diabetes-related foot examination (1–2 times/year by provider; daily by patient; Chap. 415) • Diabetes-related neuropathy examination (annual; Chap. 415) • Diabetes-related kidney disease testing (annual; Chap. 417) • Screen for other diabetes-related complications (annual; see Table 417-1) • Assessment of fracture risk in older adults with diabetes (consider measurement of bone mineral density) • Manage or treat diabetes-relevant conditions, including: • Blood pressure (assess 2–4 times/year; Chap. 417) • Lipids (1–2 times/year; Chap. 417) • Consider screening individuals with type 2 diabetes or prediabetes for metabolic dysfunction–associated steatotic liver disease if other risk factors are present • Consider antiplatelet therapy with low-dose aspirin (Chap. 417) • Immunizations, including influenza, pneumococcal, hepatitis B, coronavirus, and respiratory syncytial virus (>60 years of age) (Chap. 6) Abbreviation: HbA1c, glycated hemoglobin A1c. Patient-oriented websites also offer important resources for patients and their caregivers. Examples of these resources include: https://www. tidepool.org/about; https://diatribe.org/understanding-diabetes/diabetestechnology; and https://pro.diabeteswise.org/en/. Lifestyle Management in Diabetes Care  The patient with type 1 or type 2 DM should receive education about nutrition, physical activity, psychosocial support, care of diabetes during illness, medications used to control the glucose, methods for glucose monitoring, and strategies to prevent diabetes-related complications. Patient education allows and encourages individuals with DM to assume greater responsibility for their care, leading to improved compliance. Diabetes Self-Management Education and Support (DSMES)  DSMES refers to ways to improve the patient’s knowl­ edge, skills, and abilities necessary for diabetes self-care and should also emphasize psychosocial issues and emotional well-being. Patient education is a continuing process with regular visits for reinforcement; it is not a process completed after one or two visits. It should receive special emphasis at the diagnosis of diabetes, annually, or at times when diabetes treatment goals are not attained, and during transitions in life or medical care. DSMES is delivered by a diabetes educator who is a health care professional (nurse, dietician, or pharmacist) with specialized patient-education skills and who is certified in diabetes education (e.g., Association of Diabetes Care and Education Specialists or Certification Board for Diabetes Care and Education). Education topics important for optimal diabetes self-care include continuous glucose monitoring (CGM) or blood glucose monitoring (BGM); urine or blood ketone monitoring (type 1 DM); insulin administra­ tion; guidelines for diabetes management during illnesses; prevention and management of hypoglycemia (Chap. 418); foot and skin care; diabetes management before, during, and after exercise; and risk factor–modifying activities. The focus is providing patient-centered, individualized education. More frequent contact between the patient

and the diabetes management team (e.g., electronic, telephone, video) improves glycemic control.

Nutrition Therapy  Medical nutrition therapy (MNT) is a term used by the ADA to describe the optimal coordination of caloric intake with other aspects of diabetes therapy (e.g., insulin, exercise, and weight loss). Some aspects of MNT are directed at preventing or delaying the onset of type 2 DM in high-risk individuals (obese or with prediabetes) by promoting weight reduction. Other measures of MNT are directed at improving glycemic control through monitoring car­ bohydrate intake, avoiding simple sugars and fructose, and managing diabetes-related complications (atherosclerotic cardiovascular disease [ASCVD], nephropathy). Medical treatment of obesity, including phar­ macologic approaches that facilitate weight loss and metabolic surgery, should be considered in some patients (Chaps. 413 and 414). PART 12 Endocrinology and Metabolism In general, the components of optimal MNT are similar for individ­ uals with type 1 or type 2 DM—high-quality, nutrient-dense foods with limits on carbohydrate intake and weight management (Table 416-2). The data are currently inconclusive about various eating patterns (e.g., intermittent fasting). Sleep deprivation and shift work are risk factors for weight gain and insulin resistance. Dietary advice should be individualized, acknowledging personal preferences, cultural, and religious traditions. Use of the glycemic index, an estimate of the post­ prandial rise in the blood glucose when a certain amount of that food is consumed, may reduce postprandial glucose excursions and improve glycemic control. The goal of MNT in type 1 DM is to coordinate and match the car­ bohydrate intake, both temporally and quantitatively, with the appro­ priate amount of insulin. MNT in type 1 DM is informed by CGM and/or BGM that should be integrated to define the optimal insulin regimen. Based on the patient’s estimate of the carbohydrate content of TABLE 416-2  Nutritional Recommendations for Adults with Diabetes or Prediabetesa General dietary guidelines • Vegetables, fruits, whole grains, legumes, low-fat dairy products and food higher in fiber and lower in glycemic content; optimal diet composition and eating pattens are not known. Fat in diet (optimal percentage of diet is not known; should be individualized) • Encourage Mediterranean-style diet rich in monounsaturated and polyunsaturated fatty acids. • Minimal or no trans fat consumption. Carbohydrate in diet (optimal percentage of diet is not known; should be individualized) • Monitor carbohydrate intake in regard to calories and set limits for meals to reduce postprandial glycemia. • Consider limiting overall carbohydrate intake in adults with diabetes as this may improve glycemia. • Avoid fructose- and sucrose-containing beverages and minimize consumption of foods with added sugar that may displace healthier, more nutrient-dense food choices and elevate postprandial glycemia. • Estimate grams of carbohydrate in diet for flexible insulin dosing (type 1 diabetes and insulin-dependent type 2 diabetes). • Consider using glycemic index to predict how consumption of a particular food may affect blood glucose. Protein in diet (optimal percentage of diet is not known; should be individualized) Other components • Reduced-calorie and nonnutritive sweeteners may be useful. • Routine supplements of vitamins, antioxidants, or trace elements not supported by evidence. • Vitamin D and calcium supplemental as recommended to promote bone health. • Sodium intake as advised for general population (<2300 mg/d). • Minimize disruption to sleep and eating patterns (chrononutrition), and note risk of hypoglycemia associated with religious fasting. aSee text for differences for patients with type 1 or type 2 diabetes. Source: Data from American Diabetes Association: Facilitating positive health behaviors and well-being to improve health outcomes: Standards of care in diabetes—2024. Diabetes Care 47:S77, 2024.

a meal, an insulin-to-carbohydrate ratio determines the bolus insulin dose for a meal or snack. MNT must be flexible enough to allow for exercise, and the insulin regimen must allow for variations in caloric intake. An important component of MNT in type 1 DM is to minimize the weight gain often associated with intensive insulin therapy and is best achieved by placing limits on carbohydrate intake. The goals of MNT in type 2 DM should focus on weight loss and address the greatly increased prevalence of cardiovascular risk factors (hypertension, dyslipidemia, obesity) and disease in this population. The majority of these individuals are obese, and weight loss is strongly encouraged. Very-low-carbohydrate diets that induce weight loss may result in rapid and dramatic glucose lowering in individuals with new-onset type 2 DM. MNT for type 2 DM should emphasize mod­ est caloric reduction, increased physical activity, and weight loss (goal of at least 5–10% loss). Weight loss and exercise each independently improve insulin sensitivity. Fasting for religious reasons, such as during Ramadan, presents a chal­ lenge for individuals with diabetes, especially those taking medications to lower the plasma glucose. Under most guidelines for fasting during Ramadan, individuals are risk-stratified based on a pre-Ramadan risk assessment for people with diabetes as those who can safely fast with medi­ cal evaluation and supervision and those in whom fasting is not advised. Thus, patient education and regular glucose monitoring are critical. Physical Activity  Exercise has multiple positive benefits, including cardiovascular risk reduction, reduced blood pressure, maintenance of muscle mass, reduction in body fat, and weight loss. For individuals with type 1 or type 2 DM, exercise is also useful for lowering plasma glucose (during and following exercise) and increasing insulin sensitivity. In patients with diabetes, the ADA recommends 150 min/week (distributed over at least 3 days) of moderate aerobic physical activity with no gaps longer than 2 days. Resistance exercise, flexibility and balance training, and reduced sedentary behavior throughout the day are also advised. Despite its benefits, exercise may present challenges for some individuals with DM because they lack the normal glucoregulatory mechanisms (normally, insulin falls and glucagon rises during exer­ cise). Skeletal muscle is a major site for metabolic fuel consumption in the resting state, and the increased muscle activity during vigorous aerobic exercise greatly increases fuel requirements. Individuals with type 1 DM are prone to either hyperglycemia or hypoglycemia during exercise, depending on the pre-exercise plasma glucose, the circulating insulin level, lactate, and the level of exercise-induced catecholamines. If the insulin level is too low, the delivery of lactate to the liver and rise in catecholamines may increase the plasma glucose excessively, promote ketone body formation, and possibly lead to ketoacidosis. Conversely, if the circulating insulin level is excessive, this relative hyperinsulinemia may reduce hepatic glucose production (decreased glycogenolysis, decreased gluconeogenesis) and increase glucose entry into muscle, leading to hypoglycemia. To avoid exercise-related hyper- or hypoglycemia, individuals with type 1 DM should (1) monitor blood glucose before, during, and after exercise (see below related to CGM and possible blood glucose dis­ cordance); (2) delay exercise if blood glucose is >14 mmol/L (250 mg/ dL) and ketones are present; (3) if the blood glucose is <5.0 mmol/L (90 mg/dL), ingest carbohydrate before exercising; (4) monitor glu­ cose during exercise and ingest carbohydrate as needed to prevent hypoglycemia; (5) decrease insulin doses (based on previous experi­ ence) before and after exercise and inject insulin into a nonexercising area; and (6) learn individual glucose responses to different types of exercise. In individuals with type 2 DM, exercise-related hypoglycemia is less common but can occur in individuals taking either insulin or insulin secretagogues. Untreated proliferative retinopathy is a relative contraindication to vigorous exercise because this may lead to vitreous hemorrhage or retinal detachment (Chap. 417). Psychosocial Care  Because the individual with DM faces chal­ lenges that affect many aspects of daily life, psychosocial assessment and support are a critical part of comprehensive diabetes care. The patient should view himself/herself/themself as an essential member of the diabetes care team and not as someone who is cared for by the

diabetes management team. Even with considerable effort, normo­ glycemia can be an elusive goal, and solutions to worsening glycemic control may not be easily identifiable. Depression, anxiety, or “diabetes distress,” defined by the ADA as “negative psychological reactions related to emotional burdens … in having to manage a chronic dis­ ease like diabetes,” should be recognized and may require the care of a mental health specialist. Emotional stress may provoke a change in behavior so that individuals no longer adhere to a dietary, exercise, or therapeutic regimen. Eating disorders, including binge eating disor­ ders, bulimia, and anorexia nervosa, appear to occur more frequently in individuals with type 1 or type 2 DM. ■ ■MONITORING THE LEVEL OF GLYCEMIC CONTROL Optimal monitoring of glycemic control involves CGM or BGM (blood collected by fingerstick) by the patient and an assessment of long-term control by providers using measurement of hemoglobin A1c (HbA1c). These measurements are complementary: the patient’s measurements provide a picture of short-term glycemic control, whereas the HbA1c reflects average glycemic control over the previous 2–3 months. By integrating glycemic measurements with diet and exercise history into comprehensive diabetes care, the diabetes management team and patient can improve glycemic control and reduce diabetes-related complications. Assessment of Short-Term Glycemic Control  All individu­ als with diabetes should be offered a device to assess their short-term patterns of glycemia. CGM technology utilizes a sensor or electrode to detect interstitial glucose, which is in equilibrium with the blood glucose but may lag when the blood glucose changes rapidly or during exercise. Glucose sensors are placed subcutaneously by the patient and replaced every 10–14 days; a different device can be placed subcutane­ ously by a minor surgical procedure and replaced every 6–12 months. Some CGMs require calibration by fingerstick blood glucose measure­ ment. CGM provides glucose data every 5 minutes, and the device’s output can be provided in an ambulatory glucose profile (AGP) that is a standardized, single page summary that includes the percentage of time in the desired glycemic range (TIR, or time in range), the per­ centage of time above the target range, the percentage of time below the target range, the glucose management indicator (GMI), which correlates with HbA1c (Table 416-3), and glucose variability. CGM in real time also allows the patient to monitor the trend of glucose change (upward or downward), with this trend being used to avoid predicted hyper- or hypoglycemia. CGM device technology is rapidly evolving with the number of available CGM devices increasing and features expanding. This chapter uses the term CGM to encompass both real-time CGM and intermit­ tently scanned CGM, with real-time CGM being more effective. Most CGMs require a provider’s prescription, but CGM devices are approved for purchase without a provider’s prescription. The selection of CGM type should consider the implications for the individual with diabetes (e.g., cost, convenience, insurance coverage), the provider (e.g., access to patient’s CGM data), and the health system (e.g., integration of patient CGM data into the electronic medical record). Selection is best optimized by the involvement of a certified diabetes educator TABLE 416-3  Relationship of HbA1c and Estimated Average Glucose (eAG) ESTIMATED AVERAGE GLUCOSE (AVERAGE, RANGE) HEMOGLOBIN A1C (%)  mmol/L mg/dL

5.4 (4.2–6.7) 97 (76–120)

7.0 (5.5–8.5) 126 (100–152)

8.6 (6.8–10.3) 154 (123–185)

10.2 (8.1–12.1) 183 (147–217)

11.8 (9.4–13.9) 212 (170–249)

13.4 (10.7–15.7) 240 (193–282)

14.9 (12.0–17.5) 269 (217–314)

16.5 (13.3–19.3) 298 (240–347) Source: Data adapted from Diabetes Care 31:1473, 2008.

knowledgeable about these technologies. Unfortunately, certified dia­ betes educators are not available in all care settings, so the individual with diabetes and the provider may need to investigate CGM options using online resources and see suggestions in the reference list. Many are vendor specific; some resources provide information on multiple vendors, technologies, and devices. The selection of a CGM device should be individualized based on patient preference and skill level, capability to collect and use the data, and ability to upload data to adjust therapy. CGM may be used in individuals whose diabetes is partially or completely managed by someone else, such as a caregiver (e.g., in a child or an individual with cognitive impairment). After the selection of a CGM device, the individual with diabetes (and/or the caregiver) should receive education and training on a regular basis.

Diabetes Mellitus: Management and Therapies
CHAPTER 416 BGM devices use a small drop of blood (<2 μL) and an enzymatic reaction to rapidly measure the capillary blood glucose. It is critical that individuals using CGM also have a capillary (fingerstick) device for times when the CGM technology is malfunctioning, CGM results are questionable, or for CGM calibration (if required or desired). Substances can interfere with the accuracy of measurements by CGM devices (e.g., hydroxyurea, acetaminophen, ascorbic acid, mannitol, and sorbitol) and BGM devices (e.g., uric acid, galactose, xylose, acet­ aminophen, L-DOPA, or ascorbic acid). Individuals with type 1 DM or individuals with type 2 DM taking insulin injections each day should monitor their blood glucose by CGM. CGM in type 1 DM, especially in those with hypoglycemia unawareness, can decrease the frequency of serious hypoglycemia (especially nocturnal hypoglycemia). The combination of an insulininfusion device (discussed below) and a CGM can automate insulin delivery with either predictive suspension of insulin delivery to avoid hypoglycemia or closed-loop control that automatically adjusts insulin delivery by a predictive algorithm (Fig. 416-1). Some CGM/insulin pump manufacturers offer the patient a way to upload glucose data into the manufacturer’s server, which can then be securely accessed by the provider’s staff. It is critical for the patient’s glycemic data to be securely accessible to the provider and uploaded into the electronic health record of the provider and health system, but approaches and systems to accomplish this need further improvement. Individuals with type 2 DM treated on oral therapy and/or only with diet/lifestyle require less intense glycemic monitoring and can use CGM or BGM to measure the glucose at a lower frequency (e.g., 3–5 times/week). Many individuals with type 1 or type 2 DM report that real-time access to glycemic information via CGM assists in lifestyle choices, diet, and activity in addition to insulin or medication manage­ ment, thereby improving control. Assessment of Long-Term Glycemic Control  Measurement of glycated hemoglobin (HbA1c) is the standard method for assess­ ing long-term glycemic control. When plasma glucose is consistently elevated, there is an increase in nonenzymatic glycation of hemo­ globin; this alteration reflects the glycemic history over the previous 2–3 months, because erythrocytes have an average life span of ∼120 days (glycemic level in the preceding month contributes about 50% to the HbA1c value). Laboratory standards for the HbA1c test should be corre­ lated to the reference assay of the Diabetes Control and Complications Trial (DCCT). Measurement of HbA1c at the “point of care” allows for more rapid feedback and may therefore assist in adjustment of therapy. As the primary predictor of long-term complications of DM, the HbA1c should mirror the short-term measurement by CGM or BGM. HbA1c should be measured in all individuals with DM during their initial evaluation and as part of their comprehensive diabetes care. In patients achieving their glycemic goal, the ADA recommends measure­ ment of the HbA1c at least twice per year. More frequent testing (every 3 months) is warranted when glycemic control is inadequate or when therapy has changed. The HbA1c correlates with the average plasma glucose value or estimated average glucose (eAG) (Table 416-3) but does not detect glycemic variability or recent intercurrent illnesses as CGM or BGM can. There is interindividual variability in the HbA1c to mean glucose relationship, likely genetically determined; there is con­ troversy and some uncertainty about the influence of race or ancestry

PART 12 Endocrinology and Metabolism A B FIGURE 416-1  Glycemic monitoring and insulin administration options for treatment of diabetes. A. Continuous glucose monitoring (CGM) profile and delivery of rapidacting insulin analogue by continuous subcutaneous insulin infusion pump involves a basal rate (light purple line) and prandial and correction boluses (purple circles) based on estimated carbohydrate intake (orange squares) and an insulin sensitivity factor. B. CGM profile with sensor-communicating insulin pump that automates insulin delivery by suspending delivery for predicted hypoglycemia and increasing basal delivery for predicted hyperglycemia (light purple curves) while still requiring user input for estimated carbohydrate intake (orange squares) to provide prandial insulin boluses (purple circles). C. CGM profile is used to generate an estimate of time-in-range with glycemic goal shown on the left side of the bar and target percent time in that glycemic range shown on the right side of the bar. D. Pharmacokinetic profile of selected insulin formulations. The duration of action of an insulin may vary among individuals. (Part C: Reproduced with permission from T Battelino et al: Clinical targets for continuous glucose monitoring data interpretation: Recommendations from the International Consensus on Time in Range. Diabetes Care 42:1593, 2019; Part D: Reproduced with permission from JJ Neumiller: Insulin Update: New and Emerging Insulins, American Diabetes Association, 2018.) on HbA1c. For example, the HbA1c in African Americans is slightly higher (~0.3%) than in non-Hispanic white or Hispanic individuals for the same mean glucose. Clinical conditions leading to abnormal red blood cell (RBC) parameters such as hemoglobinopathies, anemias, reticulocytosis, transfusions, uremia, variants in glucose-6-phosphate dehydrogenase, hemodialysis, erythropoietin therapy, and HIV treat­ ment may alter the HbA1c result. Glycemic control can also be assessed by the degree of glycation of other proteins, such as fructosamine or glycated albumin, that reflect glycemia over the prior 2–4 weeks. PHARMACOLOGIC TREATMENT OF DIABETES Comprehensive care of type 1 and type 2 DM requires an emphasis on nutrition, exercise, and monitoring of glycemic control in addition to glucose-lowering medication(s). Medications to prevent and man­ age diabetes-related complications are discussed in Chap. 417. This chapter discusses classes of such medications but does not describe all glucose-lowering agents available worldwide. The initial step is to select an individualized glycemic goal for the patient. ■ ■ESTABLISHMENT OF TARGET LEVEL OF GLYCEMIC CONTROL Because the complications of DM are related to glycemic control, nor­ moglycemia or near-normoglycemia is the desired, but often elusive, goal for most patients. Normalization or near-normalization of the plasma glucose for long periods of time had been extremely difficult, as demonstrated by the DCCT and United Kingdom Prospective Diabetes Study (UKPDS), but new technologies and medications are making this goal more feasible. Regardless of the level of hyperglycemia, improve­ ment in glycemic control will lower the risk of diabetes-related com­ plications, most notably the microvascular complications (Chap. 417). The target for glycemic control (as reflected by the HbA1c) should be individualized, and the goals of therapy should be developed in consul­ tation with the individuals with diabetes after considering a number of medical, social, and lifestyle issues (ADA terms this patient-centered care) such as age, ability to understand and implement a treatment

Type 1 & Type 2 Diabetes Target <5% <250 mg/dL (13.9 mmol/L)

180 mg/dL (10.0 mmol/L) <25% Target Range: 70–180 mg/dL (3.9–10.0 mmol/L) 70% <70 mg/dL (3.9 mmol/L) <54 mg/dL (3.0 mmol/L) C <4% <1% Rapid (aspart, lispro, glulisine, inhaled human insulin) Short (regular U-100) Mixed short/intermediate (regular U-500) Intermediate (NPH) Plasma Insulin Levels Long (U-100 glargine) Ultra-long (degludec)

10 12 14 16 18 Time (hr) 20 22 24 26 28 30 32 34 36 D regimen, presence and severity of complications of diabetes such as ASCVD, ability to recognize hypoglycemic symptoms, presence of other medical conditions or treatments that might affect survival or the response to therapy, lifestyle and occupation (e.g., possible conse­ quences of experiencing hypoglycemia on the job), and level of support available from family and friends. In general, the ADA suggests that the goal is to achieve an HbA1c as close to normal as possible without significant hypoglycemia. In most individuals, the target HbA1c should be <7% (Table 416-4) with a more stringent (≤6.5%) target for some patients. With current treatment and devices, the level of HbA1c is no longer inversely related to the frequency and severity of hypoglycemia as seen in the DCCT. A higher HbA1c target of <7.5 or 8% is appropriate for individuals with cognitive impairment, those with reduced ability to sense hypoglycemia, or those with limited life span, realizing that these factors represent a spectrum across individuals (Table 416-4). Approximately one in four individuals over the age of 65 years has diabetes. Thus, the glycemic goal in elderly individuals (>65 years) should be individualized and consider the over­ all clinical state of the individual. For example, in an elderly individual with robust cognition and few major health issues, the glycemic goal may be the same as in younger individuals (HbA1c target <7.0%), while in an individual with impaired cognition or a resident of a long-term facility, the major goal is avoidance of hypoglycemia and severe hyper­ glycemia (Table 416-4). Large clinical trials (UKPDS, Action to Control Cardiovascular Risk in Diabetes [ACCORD], Action in Diabetes and Vascular Disease: Preterax and Diamicron MR Controlled Evaluation [ADVANCE], Veterans Affairs Diabetes Trial [VADT]; DCCT/EDIC study in type 1 DM; see Chap. 417) examined glycemic control in type 2 DM in indi­ viduals with low risk of ASCVD, a high risk of ASCVD, or established ASCVD. Overall, these studies indicate that (1) improved glycemic control reduces microvascular complications of diabetes; (2) improved glycemic control in individuals early in the course of type 1 DM led to reduction in nonfatal myocardial infarction, stroke, and cardiovascular death almost two decades after the period of improved glycemic con­ trol had ended; (3) intense glycemic control is beneficial for ASCVD in

TABLE 416-4  Glycemic Goals for Adults with Diabetesa INDEX OF GLYCEMIC CONTROL ADULTS (NONPREGNANT) HbA1c <7.0% (53 mmol/mol) <7.0–7.5% (53–57 mmol/mol) <8.0% (64 mmol/mol) <8.5% (64 mmol/mol) with avoidance of hypoglycemia  

70% within 3.9–10.0 mmol/L (70–180 mg/dL)c  CGM metrics % Time within indicated rangec    Time below 3.9 mmol/L (70 mg/dL) but 54 mg/dL (>3 mmol/L) indicating level 1 or mild hypoglycemia)c  Time below <54 mg/dL (<3 mmol/L) indicating level 2 or moderate/severe hypoglycemiac  Glucose variability, % coefficient of variationd <4%           <1%         ≤36% Preprandial capillary blood glucose 4.4–7.2 mmol/L (80–130 mg/dL) Postprandial capillary blood glucosee <10.0 mmol/L (<180 mg/dL) <11.1 mmol/L (200 mg/dL)  <13.9 mmol/L (250 mg/dL)  <13.9 mmol/L (250 mg/dL)   aGlycemic goal should be individualized for each patient; elderly >65 years. Some suggest different glycemic targets such as the American Association of Clinical Endocrinology (AACE), which suggests an HbA1c goal <6.5%, and American College of Physicians (ACP), which suggests a goal of 7–8%. bMultiple chronic illnesses, impaired activities of daily living, or cognitive impairment. cOverall poor health with complex comorbidities, cognitive impairment, or limited life span or resident in skilled nursing facility or a long-term care facility. dAs determined by CGM. See Chap. 418 for hypoglycemia definitions. e1–2 h after beginning of a meal. Abbreviations: CGM, continuous glucose monitoring; HbA1c, hemoglobin A1c; N/A, not applicable to glycemia management. Source: Adapted from several sources, including Diabetes Care 47:S111, 2024, and Diabetes Care 47:S244, 2024. some populations with type 2 DM; and (4) hypoglycemia in high-risk populations with ASCVD should be avoided as it is associated with cardiovascular events and mortality. Thus, near-normal glycemia is not the goal in this population (Table 416-4). As will be discussed later, these studies were conducted before the advent of glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) and sodium-glucose cotransporter 2 (SGLT-2) inhibitors, which have greater cardiovascular benefit than agents utilized in these earlier clinical trials. ■ ■TYPE 1 DIABETES MELLITUS General Aspects  The goal is to design and implement an insulin regimen that mimics physiologic insulin secretion. Because individu­ als with type 1 DM partially or completely lack endogenous insulin production, administration of basal insulin is essential for regulat­ ing glycogen breakdown, gluconeogenesis, lipolysis, and ketogenesis (e.g., fine-tuning hepatic and adipose metabolism). Likewise, insulin replacement for meals should be appropriate for the carbohydrate intake and insulin sensitivity, promoting normal glucose utilization and storage. The continued increase in insulin costs over the past decade has been a major challenge for individuals with diabetes. Recent federal and state legislative action has begun to address this; however, the cost of insulin continues to be a major issue in diabetes care. Intensive Management of Glycemia  Intensive insulin therapy in type 1 DM seeks to achieve normal or near-normal glycemia. This goal requires the integration of multiple resources and efforts, includ­ ing thorough and continuing patient education, comprehensive record­ ing of glucose measurements and nutrition intake by the patient, and a variable insulin regimen that matches carbohydrate intake and exercise and insulin dose. Insulin is delivered subcutaneously via multiple daily injections (MDIs), continuous subcutaneous insulin infusion (CSII), a sensor-augmented system, or an automated insulin delivery system (AID). Insulin delivery by CSII requires a manual entry into the pump to alter the basal infusion rate or direct an insulin bolus. A sensor-augmented system has a pump and a CGM device, assisted by an algorithm that suspends the insulin infusion when the glucose is low or predicted to be low in 30 min based on the glucose trajec­ tory. An AID system, using a pump, CGM, and algorithm, increases or decreases the basal insulin infusion rate in real time based on CGM data. Some AID systems deliver a correction insulin bolus, but these

ELDERLY ADULTS WITH COMPLEX COMORBIDITIES, POOR HEALTH, OR IMPARIED COGNITIONc ELDERLY ADULTS WITH INTACT COGNITION AND FUNCTIONAL STATUS ELDERLY ADULTS WITH OTHER SERIOUS COMORBIDITIESb  

70% within 4.4–10.0 mmol/L (80–180 mg/dL)c     50% within 5.5–10.0 mmol/L (100–200 mg/dL)c    40% within 6.7–12.2 mmol/L (120–220 mg/dL)c  Diabetes Mellitus: Management and Therapies
CHAPTER 416 <1%           <1%         <33% 0%           0%         N/A 0%           0%         N/A 4.4–7.2 mmol/L (80–130 mg/dL) 5.0–8.3 mmol/L (90–150 mg/dL) 5.6–10.0 mmol/L (100–180 mg/dL) TABLE 416-5  Properties of Insulin Preparationsa TIME OF ACTION EFFECTIVE DURATION, h PREPARATION ONSET, h PEAK, h Rapid-acting, injected   Aspartb <0.25 0.5–1.5 3–5   Glulisine <0.25 0.5–1.5 3–5   Lisproc <0.25 0.5–1.5 3–5 Short-acting, injected         Regulard 0.5–1.0 2–3 4–8 Rapid-acting, inhaled         Inhaled human insulin <0.25 1–2

Intermediate-acting, injected         NPH 2–4 4–10 10–16 Long-acting or Ultralong-acting, injected   Degludec 1–9 —e 42f   Glargineg 2–4 —e 20–24 Examples of insulin combinationsh   75/25–75% protamine lispro, 25% lispro <0.25 Duali 10–16   70/30–70% protamine aspart, 30% aspart <0.25 Duali 15–18   50/50–50% protamine lispro, 50% lispro <0.25 Duali 10–16   70/30–70% NPH, 30% regular 0.5–1 Duali 10–16 Combination of long-acting insulin and GLP-1RA See text     aInjectable insulin preparations (with exception of inhaled formulation) available in the United States; others are available in the United Kingdom and Europe. Standard formulations are U-100 (100 units of insulin per mL solution). Insulin detemir, a long-acting insulin, will soon not be available and is not included in this table. bFormulation with niacinamide (vitamin B3) has a slightly more rapid onset and offset. cLispro-aabc formulation has a slightly more rapid onset and offset. Several forms of insulin (e.g., degludec, insulin lispro, Lispro-aabc) are also available in U-200 concentration. dFormulation also available in U-500 concentration with delayed onset and offset. eDegludec and glargine have minimal peak activity. dDuration is dose-dependent. gFormulation also available in U-300 concentration, which has longer duration. hOther insulin combinations are available. iDual: two peaks—one at 2–3 h and the second one several hours later. Abbreviations: GLP-1RA, glucagon-like peptide 1 receptor agonist; NPH, neutral protamine Hagedorn.

are not a completely closed-loop system as the patient must input carbohydrate intake data and projected activity or exercise. This is a rapidly evolving area of type 1 DM–related technology, algorithms, and artificial intelligence, with some individuals having considerable success using do-it-yourself (DIY) approaches that are based in the type 1 DM user community and not U.S. Food and Drug Administra­ tion (FDA) approved.

The benefits of intensive insulin therapy and improved glycemic control include a reduction in the acute metabolic and chronic micro­ vascular complications of DM. From a psychological standpoint, the patient experiences greater control over their diabetes and often notes an improved sense of well-being, greater flexibility in the timing and content of meals, and the capability to alter insulin dosing with exer­ cise. Intensive insulin therapy prior to and during pregnancy reduces the risk of fetal malformations and morbidity. Intensive insulin therapy is encouraged in newly diagnosed patients with type 1 DM, including the use of CGM. Although intensive management confers impressive benefits, it may not be appropriate at all times for all individuals with T1D (Table 416-4). Some individuals with diabetes prefer subcutane­ ous, intermittent insulin injections combined with a CGM to being connected continuously to an insulin infusion device, highlighting the need for individualized diabetes care. PART 12 Endocrinology and Metabolism Insulin Preparations  Insulin preparations are generated by recombinant DNA technology and consist of the amino acid sequence of human insulin or variations thereof. In the United States, most insulin is formulated as U-100 (100 units/mL); short-acting insulin formulated as U-200 (200 units/mL; lispro) and long-acting as U-300 (300 units/mL; glargine) are available in order to limit injection vol­ umes for patients with high insulin requirements. Regular insulin formulated as U-500 (500 units/mL) is sometimes used in patients with severe insulin resistance. Human insulin has been formulated with dis­ tinctive pharmacokinetics (regular and neutral protamine Hagedorn [NPH] insulin have the native insulin amino acid sequence) or geneti­ cally modified to alter insulin absorption and hence the onset and duration of insulin action. Insulins can be classified as rapid-acting, short-acting, intermediate-acting, long-acting, or ultralong-acting (Table 416-5; Fig. 416-1D). For example, one rapid-acting insulin formulation, insulin lispro, is an insulin analogue in which the 28th and 29th amino acids (lysine and proline) on the insulin B chain have been reversed. Insulin aspart and insulin glulisine are modified insulin analogues with properties similar to lispro. A biosimilar version of lis­ pro is available. These insulin analogues have full biologic activity but less tendency for self-aggregation, resulting in more rapid absorption and onset of action and a shorter duration of action. These character­ istics are particularly advantageous for allowing entrainment of insulin injection and action to the rising plasma glucose levels following meals. The shorter duration of action also appears to be associated with a decreased number of hypoglycemic episodes, primarily because the decay of insulin action corresponds to the decline in plasma glucose after a meal. Thus, insulin aspart, lispro, or glulisine is preferred over regular insulin for prandial coverage. Insulin glargine is a long-acting biosynthetic human insulin that differs from normal insulin in that asparagine is replaced by glycine at amino acid 21, and two arginine residues are added to the C terminus of the B chain, leading to the for­ mation of microprecipitates at physiologic pH in subcutaneous tissue. Compared to NPH insulin, the onset of insulin glargine action is later, the duration of action is longer (~24 h), and there is a less pronounced peak. A lower incidence of hypoglycemia, especially at night, has been reported with insulin glargine when compared to NPH insulin. A biosimilar version is available. Twice-daily injections of glargine are sometimes required to provide optimal 24-h basal insulin coverage. Because of modification and extension of the carboxy-terminus of the B chain, insulin degludec forms multihexamers in subcutaneous tissue and binds albumin, prolonging its duration of action (>42 h); it provides similar glycemic control as glargine but with less frequent nocturnal and severe hypoglycemia. Other modified insulins, such as one with a duration of action of 1 week, are in clinical trials and will likely soon be available.

Basal insulin requirements, largely fine-tuning hepatic glucose metabolism, are provided by long-acting insulin formulations (NPH insulin, insulin glargine, or insulin degludec) (Fig. 416-1D; Table 416-5). These are usually prescribed with rapid-acting insulin in an attempt to mimic physiologic insulin release with meals (prandial insulin require­ ment). In the past, NPH and short-acting insulin formulations were mixed in the same syringe, but this is not common now. The miscibil­ ity of some insulins allows for the production of combination insulins that contain 70% NPH and 30% regular (70/30), or equal mixtures of NPH and regular (50/50). By including the insulin analogue mixed with protamine, several additional combinations have a rapid-acting and long-acting profile (Table 416-5; Fig. 416-1D). Although more convenient for the patient (only two injections a day), combination insulin formulations do not allow independent adjustment of shortacting and long-acting activity and are not appropriate in type 1 DM management. Most insulin formulations are available as insulin “pens,” which are more convenient and accurate than syringes; “smart pens” can assist with insulin dose tracking. Insulin delivery by inhalation to provide mealtime insulin has a more rapid onset of action than insulin injected subcutaneously. Prior to its use, the forced expiratory volume in 1 s (FEV1) should be measured, and then monitored periodically during treatment. Inhaled insulin can cause bronchospasm and cough and should not be used by individuals with lung disease or those who smoke. Long-acting insulin/GLP-1RA combinations in fixed doses (degludec plus liraglutide or glargine plus lixisenatide) are effective and are associated with less weight gain. Insulin Regimens  There is considerable patient-to-patient varia­ tion in the peak and duration. In all regimens, long-acting insulins (NPH, glargine, or degludec) supply basal insulin, whereas regular, insulin aspart, glulisine, or lispro provide prandial insulin (Fig. 416-1D; Table 416-5). Rapid-acting insulin analogues should be injected just before (<10 min) and regular insulin 30–45 min prior to a meal. Sometimes rapid-acting insulin analogues are injected just after a meal (gastroparesis, unpredictable food intake). A consensus statement from ADA and the European Association for the Study of Diabetes provides guidance about different insulin regimens used in type 1 DM. A shortcoming of current insulin regimens is that injected insulin immediately enters the systemic circulation, whereas endogenous insu­ lin is secreted into the portal venous system. Thus, exogenous insulin administration exposes the liver to subphysiologic insulin levels, and requires achieving higher peripheral levels of insulin to restrain hepatic glucose production. No current insulin regimen reproduces the precise insulin secretory pattern of the pancreatic islet. However, the most physiologic regimens entail more frequent insulin injections, greater reliance on rapid-acting insulin, and CGM or more frequent BGM. In general, individuals with type 1 DM require 0.4–1.0 units/kg per day of insulin divided into multiple doses, with 30–50% of daily insulin given as basal insulin with the remainder as prandial insulin. All individuals with type 1 DM should have a filled glucagon prescription (Chap. 416). MDI regimens refer to the combination of basal insulin and bolus insulin (preprandial rapid-acting insulin). The timing and dose of rapid-acting, preprandial insulin are altered to accommodate the CGM or BGM results, anticipated food intake, and physical activity. Such regimens offer the patient with type 1 DM more flexibility in terms of lifestyle and the best chance for achieving near normoglycemia. Most often, basal insulin with glargine or degludec is used in conjunction with preprandial lispro, glulisine, or insulin aspart. The dose of longacting insulin is adjusted based on the fasting glucose. The insulin aspart, glulisine, or lispro dose is based on individualized algorithms that integrate the preprandial glucose and the anticipated carbohydrate intake. To determine the meal component of the preprandial insulin dose, the patient uses an insulin-to-carbohydrate ratio (a common ratio for type 1 DM is 1 unit/10–15 g of carbohydrate, but this must be determined for each individual). To this insulin dose is added the supplemental or correcting insulin based on the preprandial blood glucose (one formula uses 1 unit of insulin for every 1.6–3.3 mmol/L [30–60 mg/dL] over the preprandial glucose target; this correction factor can be estimated from 1500/[total daily insulin dose]). Such

TABLE 416-6  Agents Used for Treatment of Type 1 or Type 2 Diabetes MECHANISM OF ACTION EXAMPLESa HBA1C REDUCTION (%)b AGENT-SPECIFIC ADVANTAGES   Oral             Metformin 1–2 Weight neutral, do not cause hypoglycemia, inexpensive, extensive experience, modest

↓ CV events Biguanidesc* ↓ Hepatic glucose production, ↑ insulin sensitivity, influence gut function Sodium-glucose cotransporter 2 (SGLT-2) inhibitorsc*** Canagliflozin, dapagliflozin, empagliflozin, ertugliflozin, bexagliflozin, sotagliflozin (SGLT-1/2 inhibitor) 0.5–1.0 Renal protective,

↓ CV events, ↓ heart failure, do not cause hypoglycemia, modest ↓ weight and blood pressure ↑ Renal glucose excretion Dipeptidyl peptidase-4 inhibitorsc*** Prolong endogenous GLP-1 action;

↑ insulin, ↓ glucagon Alogliptin, linagliptin, saxagliptin, sitagliptin, vildagliptin 0.5–0.8 Well tolerated, do not cause hypoglycemia Insulin secretagogues: Sulfonylureasc* ↑ Insulin secretion Glimepiride, glipizide, gliquidone, glyburide 1–2 Short onset of action, lower postprandial glucose, inexpensive Insulin secretagogues: Nonsulfonylureasc*** ↑ Insulin secretion Nateglinide, repaglinide 0.5–1.0 Short onset of action, lower postprandial glucose Thiazolidinedionesc**** ↓ Insulin resistance,

Pioglitazone, rosiglitazone 0.5–1.4 Lower insulin requirements ↑ glucose utilization Acarbose, miglitol 0.5–0.8 Reduce postprandial glycemia α-Glucosidase inhibitorsc** ↓ GI glucose absorption Parenteral/Oral (GLP-1RA-related agents) Dulaglutide, exenatide, liraglutide, lixisenatide, semaglutide (oral formulation available) 0.5–1.0 Weight loss, do not cause hypoglycemia (unless combined with another insulin secretagogue or insulin); ↓ CV events, modest renoprotection GLP-1RAsc*** ↑ Insulin, ↓ glucagon, slow gastric emptying, satiety GLP-1/GIP receptor agonistc*** ↑ Insulin, ↓ glucagon, slow gastric emptying, satiety Tirzepatide 1.8-2.4 Weight loss, do not cause hypoglycemia (unless combined with insulin secretagogue or insulin); ↓ CV events Parenteral             Amylin agonistsc,d*** Slow gastric emptying, ↓ glucagon Pramlintide 0.25–0.5 Reduce postprandial glycemia, weight loss See text and Table 416-4 Not limited Known safety profile Injection, weight gain, hypoglycemia Insulinc,d**** ↑ Glucose utilization, ↓ hepatic glucose production, and other anabolic actions Medical nutrition therapy and physical activityc* Low-calorie, carbohydratecontrolled diet, exercise 1–3 Other health benefits Compliance difficult, long-term success of sustained weight loss low ↓ Insulin resistance, ↑ insulin secretion aExamples are approved for use in the United States; others are available in other countries. Examples may not include all agents in the class. bHbA1c reduction (absolute) depends partly on starting HbA1c. cUsed for treatment of type 2 diabetes. dUsed in conjunction with insulin for treatment of type 1 diabetes. Cost of agent in the United States: *low, **moderate, ***high, ****variable. eDegree of risk uncertain, avoid in individuals with risk factors for pancreatitis. fRisk of euglycemic DKA in patients with insulin deficiency. Note: Some agents used to treat type 2 diabetes are not included in table (see text). Abbreviations: CHF, congestive heart failure; CV, cardiovascular; DKA, diabetic ketoacidosis; GFR, glomerular filtration rate; GI, gastrointestinal; GIP, gastric inhibitory polypeptide; GLP-1, glucagon-like peptide 1; GLP-1RA, glucagon-like peptide 1 receptor agonist; HbA1c, glycated hemoglobin A1c.

AGENT-SPECIFIC DISADVANTAGES CONSIDERATIONS Diarrhea, nausea, lactic acidosis, vitamin B12 deficiency Renal insufficiency (see text for GFR <30 mL/min), CHF, radiographic contrast studies, hospitalized patients, acidosis Diabetes Mellitus: Management and Therapies
CHAPTER 416 Increased risk genital mycotic infections and necrotizing fasciitis of perineum; polyuria, dehydration; increased risk of euglycemic DKAf (see text); exacerbate tendency to hyperkalemia Moderate renal insufficiency; discontinue 3–4 days before surgery, during serious illness Angioedema/urticarial and immune-mediated dermatologic effects; rarely associated with pancreatitis Reduced dose with renal insufficiency Hypoglycemia, weight gain Renal/liver insufficiency Hypoglycemia Renal/liver insufficiency (except repaglinide) Peripheral edema, CHF, weight gain, fractures, macular edema CHF, renal/liver insufficiency GI flatulence, elevated liver function tests Renal/liver insufficiency Nausea, GI intolerance; possibly associated with pancreatitise, possibly worsen retinopathy Renal disease, agents that also slow GI motility; medullary carcinoma of thyroid, previous ileus Nausea, GI intolerance, possibly associated pancreatitise, possibly worsen retinopathy Renal disease, agents that also slow GI motility; medullary carcinoma of thyroid, pancreatic disease, history of gastroparesis Agents that also slow GI motility Injection, nausea, ↑ risk of hypoglycemia with insulin Can be combined with most other agents Other health benefits

calculations must be adjusted based on each individual’s sensitiv­ ity to insulin. CGM or BGM is essential for these types of insulin regimens.

AID is the preferred insulin delivery mechanism for most indi­ viduals with type 1 DM (Fig. 416-1), but cost and insurance coverage are critical considerations. To the basal insulin infusion, a prepran­ dial insulin (“bolus”) is delivered by the insulin infusion device based on instructions from the patient or an algorithm that incorporates the preprandial plasma glucose and anticipated carbohydrate intake. These sophisticated devices can accurately deliver small doses of insulin (microliters per hour) and have several advantages: (1) multi­ ple basal infusion rates can be programmed to accommodate noctur­ nal versus daytime basal insulin requirement; (2) basal infusion rates can be altered during periods of exercise; (3) different waveforms of insulin infusion with meal-related bolus allow better matching of insulin depending on meal composition; and (4) programmed algo­ rithms consider ongoing action of prior insulin administration and blood glucose values in calculating the insulin dose. As mentioned, the technology, algorithms, and integration of the different compo­ nents are changing rapidly, indicating the need to match these with patients’ desires, for instruction by a health professional with con­ siderable experience with insulin infusion devices, and for frequent patient interactions with the diabetes management team. Insulin infusion devices may present unique challenges, such as infection at the infusion site, unexplained hyperglycemia because the infusion set becomes obstructed, or diabetic ketoacidosis (DKA) if the insulin infusion device becomes disconnected. Because most physicians use lispro, glulisine, or insulin aspart in CSII or AID, the short half-life of these insulins quickly leads to insulin deficiency if the delivery system is interrupted. Essential to the safe use of infusion devices is thorough patient education, CGM or frequent BGM, and a backup plan for injecting long- and/or rapid-acting insulins in the event of insulin infusion device failure. CGM sensor-augmented insulin infusion devices integrate the information from the CGM to inform insulin delivery (Fig. 416-1). Currently, sensor communicating functions can interrupt basal insulin delivery during hypoglycemia (threshold suspension) or when hypoglycemia is anticipated (predic­ tive suspension), which may be particularly useful for preventing nocturnal hypoglycemia. Hybrid closed-loop systems can combine patient-directed preprandial boluses with automated adjustment of between-meal and basal insulin delivery based on CGM. Clini­ cal experience with closed-loop systems is rapidly increasing and expanding. Bihormonal infusion devices that deliver both insulin and glucagon are being tested. PART 12 Endocrinology and Metabolism Other Agents That Improve Glucose Control  The role of amylin, a 37-amino-acid peptide co-secreted with insulin from pan­ creatic beta cells in normal glucose homeostasis is uncertain. However, based on the rationale that patients who are insulin deficient are also amylin deficient, an analogue of amylin (pramlintide) was created and found to reduce postprandial glycemic excursions in individuals with type 1 or type 2 DM taking insulin. Pramlintide injected just before a meal slows gastric emptying and suppresses glucagon but does not alter insulin levels. Pramlintide is approved for insulin-treated patients with type 1 or type 2 DM. The addition of pramlintide produces a modest reduction in the HbA1c and seems to dampen meal-related glucose excursions. In type 1 DM, pramlintide is started as a 15-μg SC injec­ tion before each meal and titrated up to a maximum of 30–60 μg as tolerated. In type 2 DM, pramlintide is started as a 60-μg SC injection before each meal and may be titrated up to a maximum of 120 μg. The major side effects are nausea and vomiting, and dose escalations should be slow to limit these side effects. Because pramlintide slows gastric emptying, it may influence absorption of other medica­ tions and should not be used in combination with other drugs that slow gastrointestinal (GI) motility. The rapid-acting insulin given before the meal should initially be reduced to avoid hypoglycemia and then titrated as the effects of the pramlintide become evident. Because pramlintide suppresses glucagon, it may worsen hypoglyce­ mia recovery and should not be used in patients with hypoglycemia

Management of Type 2 Diabetes Screen for/manage complications of diabetes • Retinopathy • Nephropathy • Neuropathy • Cardiovascular disease • Other complications Treat associated conditions • Dyslipidemia • Hypertension • Obesity Individualized glycemic control • Diet/lifestyle • Exercise • Medication FIGURE 416-2  Essential elements in comprehensive care of type 2 diabetes. unawareness. GLP-1RAs and SGLT-2 inhibitors modestly improve the HbA1c in type 1 DM, but the SGLT-2 inhibitors increase the risk of DKA and in general should not be used. ■ ■TYPE 2 DIABETES MELLITUS General Aspects  The goals of glucose-directed therapy for type 2 DM are similar to those in type 1 DM and, likewise, should be individ­ ualized for each patient. Whereas glycemic control tends to dominate the management of type 1 DM, the care of individuals with type 2 DM must also include even greater attention to the treatment of conditions associated with type 2 DM (e.g., obesity, hypertension, dyslipidemia, ASCVD) and prevention/detection/management of DM-related com­ plications (Fig. 416-2; Chap. 417). Reduction in cardiovascular risk is of paramount importance because this is the leading cause of mortal­ ity in these individuals. One approach to pharmacology of glucosedirected therapies in type 2 DM is shown in Fig. 416-3. Type 2 DM management should begin with MNT (discussed above). An exercise regimen to increase insulin sensitivity and promote weight loss should also be instituted. Pharmacologic approaches to the management of type 2 DM include oral glucose-lowering agents, insulin, and other agents that improve glucose control. Any therapy that improves glycemic control reduces “glucose toxicity” to beta cells and may improve endogenous insulin secretion. However, type 2 DM is a progressive disorder and ultimately requires multiple therapeutic agents and sometimes insulin. Glucose-Lowering Agents  Advances in the therapy of type 2 DM have led to glucose-lowering agents that target different pathophysi­ ologic processes in type 2 DM. Based on their mechanisms of action, glucose-lowering agents are subdivided into agents that increase insulin secretion, reduce glucose production, increase insulin sensitivity, act as a GLP-1 receptor agonist, or promote urinary excretion of glucose (Table 416-6). Insulin is sometimes the initial glucose-lowering agent in type 2 DM if there is severe hyperglycemia or the patient is catabolic. BIGUANIDES  Metformin, representative of this class of agents, reduces hepatic glucose production and improves peripheral glucose utiliza­ tion slightly (Table 416-6) and is relatively low cost. Metformin acts in multiple tissues, but its mechanism of action remains incompletely defined. Metformin reduces fasting plasma glucose (FPG) and insulin levels, improves the lipid profile, and promotes modest weight loss. An extended-release form is available and may have fewer GI side effects (diarrhea, anorexia, nausea, metallic taste). Because of metformin’s relatively slow onset of action and GI symptoms with higher doses, the initial dose should be low and then escalated every 1–2 weeks to a maximally tolerated dose of 2000 mg daily. Metformin is effective as monotherapy and can be used in combination with other glucose lowering agents. The major toxicity of metformin, lactic acidosis, is very rare and can be prevented by careful patient selection. Vitamin B12 levels are lower during metformin treatment and should be moni­ tored. Metformin should not be used in patients with moderate renal insufficiency (glomerular filtration rate [GFR] <30 mL/min), any form of acidosis, unstable congestive heart failure (CHF), liver disease, or

severe hypoxemia. Metformin should be discontinued in hospitalized patients, in patients who can take nothing orally, and in those receiving radiographic contrast material. Insulin should be used as needed until metformin can be restarted. INSULIN SECRETAGOGUES—AGENTS THAT AFFECT THE ATP-SENSITIVE K+ CHANNEL  Insulin secretagogues stimulate insulin secretion by interacting with the ATP-sensitive potassium channel on the beta cell (Chap. 415). These drugs are most effective in individuals with type 2 DM of relatively recent onset (<5 years) who have residual endogenous insulin production. Sulfonylureas reduce both fast­ ing and postprandial glucose and should be initiated at low doses and increased at 1- to 2-week intervals based on CGM or BGM. Glimepiride and glipizide can be given in a single daily dose and are preferred over glyburide, especially in the elderly. Repaglinide and nateglinide are not sulfonylureas but also interact with the ATPsensitive potassium channel. Because of their short half-life, these glinide agents are given immediately before each meal to reduce meal-related glucose excursions. Insulin secretagogues, especially the longer-acting ones, have the potential to cause hypoglycemia, especially in elderly individuals. Hypoglycemia is usually related to delayed meals, increased physical activity, alcohol intake, or renal insufficiency. Individuals who ingest an overdose of some agents develop prolonged and serious hypogly­ cemia and should be monitored closely in the hospital (Chap. 418). Most sulfonylureas are metabolized in the liver to compounds (some of which are active, such as those of glyburide and the glinide nateg­ linide) that are cleared by the kidney. Thus, their use in individuals with significant hepatic or renal dysfunction is not advisable. For patients with chronic kidney disease the glinide repaglinide may be used with caution. Weight gain, a common side effect of sulfonylurea therapy, results from the increased insulin levels and improvement in glycemic control. Some sulfonylureas have significant drug interac­ tions with alcohol and some medications including warfarin, aspirin, ketoconazole, α-glucosidase inhibitors, and fluconazole. Sulfonylureas interact with some antibiotics such as fluoroquinolones, clarithromy­ cin, sulfamethoxazole-trimethoprim, metronidazole, and fluconazole, so the sulfonylureas should be discontinued when these antimicrobials are added to the patient’s medications. GLP-1RAS ALONE OR IN COMBINATION WITH GIP RECEPTOR AGONIST 

“Incretins” amplify glucose-stimulated insulin secretion and suppress inappropriate glucagon secretion (Chap. 415). Agents that either act as a GLP-1RA or enhance endogenous GLP-1 activity are approved for the treatment of type 2 DM and obesity (Table 416-6). Agents in this class do not cause hypoglycemia because of the glucose-dependent nature of incretin-stimulated insulin secretion (unless there is concomitant use of an agent that can lead to hypoglycemia—sulfonylureas, etc.). GLP1RAs increase glucose-stimulated insulin secretion, suppress glucagon, and slow gastric emptying, but the GLP-1 receptor is expressed in several tissues, including the brain. These agents promote weight loss (see Chaps. 413 and 414) and reduce cardiovascular events in those with type 2 DM and ASCVD (see Chap. 417 for additional discussion about the effect on diabetes-related complications). Thus, these agents are particularly advantageous in type 2 DM. Long-acting GLP-1RAs include sustained-release exenatide, dulaglutide, lixisenatide, and sema­ glutide, all administered weekly, and are the ones most commonly used. Daily oral semaglutide is available that allows gastric absorption to avoid proteolytic degradation in the small intestine. All are modified to avoid enzymatic inactivation by dipeptidyl peptidase IV (DPP-4) in the circulation. Higher doses of liraglutide and semaglutide than used for glucose-lowering effects are effective for weight-loss therapy for obesity. Liraglutide treatment has also been associated with a decrease in cardio­ vascular disease (CVD) events in patients with type 2 DM and established CVD and with lower rates of diabetic kidney disease. In similar patient populations, semaglutide treatment has been associated with fewer CVD events and reduced diabetic kidney disease, but with an increased rate of retinopathy-related complications. Dulaglutide treatment has been associated with both a reduction in CVD events and a reduc­ tion in composite microvascular retinopathy and nephropathy-related

complications primarily driven by prevention of renal events. Treatment with GLP-1RAs should start at a low dose to minimize initial side effects (nausea being the limiting one). GLP-1RAs can be used as combination therapy with metformin, sulfonylureas, and thiazolidinediones. Some patients taking insulin or an insulin secretagogue may require a reduc­ tion in those agents to prevent hypoglycemia. The major side effects are nausea and vomiting. Some formulations carry a black box warning from the FDA because of an increased risk of thyroid C-cell tumors in rodents and are contraindicated in individuals with medullary carcinoma of the thyroid or multiple endocrine neoplasia. Because GLP-1RAs slow gastric emptying, they may influence the absorption of other drugs. Whether GLP-1RAs enhance beta cell survival or promote beta cell proliferation is not known. It is not clear if these agents alter the natural history of type 2 DM.

Diabetes Mellitus: Management and Therapies
CHAPTER 416 Tirzepatide, a once-weekly subcutaneous injectable peptide engi­ neered to have dual agoniism at both the glucose-dependent insulino­ tropic polypeptide receptor (GIPR) and the GLP-1R, promotes greater weight loss than a GLP-1RA alone. Additional dual-acting and tripleacting molecules are in development and clinical trials. DPP-4 inhibitors inhibit degradation of native GLP-1 and GIP and thus enhance the incretin effect. DPP-4, which is widely expressed on the cell surface of endothelial cells and some lymphocytes, degrades a wide range of peptides (not incretin specific). DPP-4 inhibitors pro­ mote insulin secretion in the absence of hypoglycemia or weight gain and appear to have a preferential effect on postprandial blood glucose. The levels of GLP-1 action in the patient are greater with the GLP-1RAs than with DPP-4 inhibitors. DPP-4 inhibitors are used either alone or in combination with other oral agents in type 2 DM. Reduced doses should be given to patients with renal insufficiency. Allergy, including rash, hypersensitivity reactions (including anaphylaxis, angioedema, and Stevens-Johnson syndrome), and severe joint pain have been reported in association with DPP-4 inhibitors. There is evidence con­ cerning a potentially increased risk for acute pancreatitis with GLP1RAs and less so with DPP-4 inhibitors. It is prudent to avoid these agents in patients with pancreatic disease or with other significant risk factors for acute pancreatitis (e.g., heavy alcohol use, severely elevated serum triglycerides, hypercalcemia). SGLT-2 INHIBITORS  These agents (Table 416-6) lower the blood glu­ cose by selectively inhibiting this co-transporter, which is expressed almost exclusively in the proximal convoluted tubule in the kidney. This inhibits glucose reabsorption, lowers the renal threshold for glucose excretion, and leads to increased urinary glucose loss. Thus, the glucose-lowering effect is insulin independent and not related to changes in insulin sensitivity or secretion. The loss of urinary glucose may promote modest weight reduction. Since these agents also impair proximal reabsorption of sodium, their use is associated with a diuretic effect and a 3- to 6-mmHg reduction in systolic blood pressure. Due to the increased urinary glucose, urinary and genital mycotic infections are more common in both men and women, and the diuretic effect can lead to reduced intravascular volume and acutely impaired kidney function. Inhibition of SGLT-2 may lead to increased glucagon and, consequently, liver production of glucose and ketones. Euglycemic DKA may occur during illness or when ongoing glucosuria masks stress-induced requirements for insulin. Patients should be educated about this possibility, and providers should be vigilant about detec­ tion. These agents should not be prescribed for patients with type 1 DM or pancreatogenic forms of DM associated with insulin deficiency. Empagliflozin or canagliflozin reduces ASCVD events and all-cause cardiovascular mortality in patients with type 2 DM and established ASCVD. SGLT-2 inhibitors may reduce hospitalization for CHF. Empagliflozin, canagliflozin, and dapagliflozin have all been shown to reduce progression of diabetic kidney disease but should not be initi­ ated in patients with stage 3b chronic kidney disease (CKD; estimated GFR [eGFR] <45 mL/min per 1.73 m2) and should not be used in stage 4 CKD (eGFR <30 mL/min per 1.73 m2). A possible increased risk of bladder cancer has been seen with dapagliflozin. The impact of SGLT-2 inhibitors on diabetes-related complications is discussed in Chap. 417 and below.

THIAZOLIDINEDIONES  Thiazolidinediones (Table 416-6) reduce insulin resistance by binding to the peroxisome proliferator-activated receptor γ (PPAR-γ) nuclear receptor (which forms a heterodimer with the retinoid X receptor). The PPAR-γ receptor is found at highest levels in adipocytes but is expressed at lower levels in many other tissues. Agonists of this receptor regulate a large number of genes, promote adipocyte differentiation, reduce hepatic fat accumulation, and pro­ mote fatty acid storage. Thiazolidinediones promote a redistribution of fat from central to peripheral locations. Circulating insulin levels decrease with use of the thiazolidinediones, indicating a reduction in insulin resistance.

Rosiglitazone raises low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglycerides slightly. Pioglitazone raises HDL to a greater degree and LDL to a lesser degree but lowers triglycerides. The clinical significance of the lipid changes with these agents is not known. PART 12 Endocrinology and Metabolism Thiazolidinediones are associated with weight gain (2–3 kg), a small reduction in the hematocrit, and a mild increase in plasma volume. Peripheral edema and CHF are more common in individuals treated with these agents. These agents are contraindicated in patients with hepatic insufficiency or CHF (class III or IV). The FDA has issued an alert that rare patients taking these agents may experience a worsening of diabetic macular edema. An increased risk of fractures has been noted in postmenopausal women taking these agents. Thiazolidinedio­ nes have been shown to induce ovulation in premenopausal women with polycystic ovary syndrome. Women should be warned about the risk of pregnancy because the safety of thiazolidinediones in pregnancy is not established. According to an FDA review, pioglitazone may be associated with an increased risk of bladder cancer. In one study, pio­ glitazone lowered the risk for recurrent stroke or myocardial infarction in insulin-resistant individuals without diabetes who had a prior stroke or transient ischemic attack. `-GLUCOSIDASE INHIBITORS  α-Glucosidase inhibitors reduce post­ prandial hyperglycemia by delaying glucose absorption (Table 416-6). Postprandial hyperglycemia, secondary to impaired hepatic and periph­ eral glucose disposal, contributes significantly to the hyperglycemic state in type 2 DM. These drugs, taken just before each meal, reduce glucose absorption by inhibiting the enzyme that cleaves oligosaccharides into simple sugars in the intestinal lumen. Therapy should be initiated at a low dose with the evening meal and increased to a maximal dose over weeks to months. The major side effects (diarrhea, flatulence, abdominal distention) are related to increased delivery of oligosaccharides to the large bowel and can be reduced somewhat by gradual upward dose titra­ tion. α-Glucosidase inhibitors may increase levels of sulfonylureas and increase the incidence of hypoglycemia. Simultaneous treatment with bile acid resins and antacids should be avoided. These agents should not be used in individuals with inflammatory bowel disease, gastroparesis, or a serum creatinine >177 μmol/L (2 mg/dL). This class of agents is not as potent as other oral agents in lowering the HbA1c but is unique because it reduces the postprandial glucose rise. If hypoglycemia from other diabetes treatments occurs while taking these agents, the patient should consume glucose because the degradation and absorption of complex carbohydrates will be slowed. OTHER THERAPIES FOR TYPE 2 DM  •  Bile Acid–Binding Resins 

Evidence indicates that bile acids, by signaling through nuclear recep­ tors, may have a role in metabolism. Bile acid metabolism is abnormal in type 2 DM. The bile acid–binding resin colesevelam has been approved for the treatment of type 2 DM (already approved for treat­ ment of hypercholesterolemia). The role of this class of drugs in the treatment of type 2 DM is not yet defined. Bromocriptine  A formulation of the dopamine receptor agonist bro­ mocriptine (Cycloset) has been approved by the FDA for the treat­ ment of type 2 DM. However, its role in the treatment of type 2 DM is uncertain. INSULIN THERAPY IN TYPE 2 DM  Insulin should be considered for ini­ tial therapy in type 2 DM, particularly in lean individuals or those with severe weight loss, in individuals with underlying renal or hepatic dis­ ease that precludes oral glucose-lowering agents, or in individuals who

are hospitalized or acutely ill. Insulin therapy is ultimately required by a substantial number of individuals with type 2 DM because of the progressive nature of the disorder and the relative insulin deficiency that develops with long-standing diabetes. Both physician and patient reluctance often delay the initiation of insulin therapy, but glucose control and individual well-being are improved by insulin therapy in patients who have not reached their glycemic target. Because endogenous insulin secretion is capable of providing some coverage of mealtime caloric intake, insulin is usually initiated in a single dose of long-acting insulin (0.1–0.4 U/kg per day), given in the evening or just before bedtime (NPH, glargine, or degludec). Because fasting hyperglycemia and increased hepatic glucose production are prominent features of type 2 DM, bedtime insulin is more effective in clinical trials than a single dose of morning insulin. Glargine given at bedtime has less nocturnal hypoglycemia than NPH insulin. Some physicians prefer a relatively low, fixed starting dose of long-acting insulin (10–15 units) or a weight-based dose (0.1 units/kg). The insulin dose may then be adjusted in 10–20% increments as dictated by CGM or BGM results. Both morning and bedtime long-acting insulin may be used in combination with oral glucose-lowering agents. Initially, basal insulin may be sufficient, but often prandial insulin coverage with multiple insulin injections is needed as diabetes progresses (see insulin regimens used for type 1 DM). Other insulin formulations that have a combination of rapid-acting and long-acting insulin (Table 416-5) are sometimes used in patients with type 2 DM because of convenience but do not allow independent adjustment of rapid-acting and long-acting insulin dose and often do not achieve the same degree of glycemic control as basal/bolus regimens. AID in selected individuals with type 2 DM should be considered, especially in those who are insulindeficient. CGM should be used in all individuals taking insulin. CHOICE OF INITIAL GLUCOSE-LOWERING AGENT  The level of hyper­ glycemia and the patient’s individualized goal (see “Establishment of Target Level of Glycemic Control”) should influence the initial choice of therapy. Patients with mild hyperglycemia (FPG <7.0– 11.0 mmol/L [126–199 mg/dL]) often respond well to a single, oral glucose-lowering agent, while those with moderate hyperglycemia (FPG 11.1–13.9 mmol/L [200–250 mg/dL]) will usually require more than one oral agent or insulin. Patients with more severe hyperglyce­ mia (FPG >13.9 mmol/L [250 mg/dL]) may respond partially but are unlikely to achieve normoglycemia with oral therapy. Insulin can be used as initial therapy in individuals with severe hyperglycemia (FPG <13.9–16.7 mmol/L [250–300 mg/dL]) or in those who are symptom­ atic from the hyperglycemia. This approach is based on the rationale that more rapid glycemic control will reduce “glucose toxicity” to the islet cells, improve endogenous insulin secretion, and possibly allow oral glucose-lowering agents to be more effective. If this occurs, the insulin may be discontinued. Treatment algorithms by several profes­ sional societies (ADA/ European Association for the Study of Diabetes [EASD], International Diabetes Federation, American Association of Clinical Endocrinology) suggest metformin as initial therapy because of its efficacy, known side effect profile, and low cost (Fig. 416-3). Initiation of pharmacologic therapy should be accompanied by an emphasis on lifestyle modification (e.g., MNT, increased physical activ­ ity, and weight loss). Metformin’s advantages are that it promotes mild weight loss, lowers insulin levels, and improves the lipid profile slightly. Based on CGM or BGM results and the HbA1c, the dose of metformin should be increased until the glycemic target is achieved or the maxi­ mum dose is reached. GLP-1RAs and SGLT-2 inhibitors are increasing in use as evidence accumulates for CVD and CKD benefits, in addition to weight loss and glucose-lowering effects. Insulin secretagogues, biguanides, α-glucosidase inhibitors, thia­ zolidinediones, GLP-1RAs, DPP-4 inhibitors, SGLT-2 inhibitors, and insulin are approved for monotherapy of type 2 DM. Although each class of oral glucose-lowering agents has advantages and disadvantages (Table 416-6), certain generalizations apply: (1) insulin secretagogues, biguanides, GLP-1RAs, and thiazolidinediones improve glycemic con­ trol to a similar degree (1–2% reduction in HbA1c) and are more effective than α-glucosidase inhibitors, DPP-4 inhibitors, and SGLT-2

Individual with type 2 DM Develop person-centered, individualized plan • Medical nutrition therapy • Physical activity/lifestyle • Weight loss goal of 5–7% • Continue or initiate metformin Goal: Manage HbA1c + cardiorenal risk factor reduction Goal: Manage HbA1c + weight reduction or maintenance Heart failure, HFrEF, or HFpEF? CKD? ASCVD or ASCVD risk factors? GLP-1RA or SGLT-2 inhibitor SGLT-2 inhibitor SGLT-2 inhibitor HbA1c above target? HbA1c above target? • Add GLP- 1RA • Add TZD • Add SGLT-2 inhibitor or GLP-1RA HbA1c above target? • Add insulin • Combination of injectable and oral • Re-emphasize lifestyle, nutrition, physical activity FIGURE 416-3  Glycemic management of type 2 diabetes. See text for discussion of treatment of severe hyperglycemia or symptomatic hyperglycemia. In this Figure, the term glucagon-like peptide-1 receptor agonists (GLP-1RAs) refers to GLP-1 RAs and dual glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 RAs. Agents that can be combined with metformin include insulin, GLP-1RAs, sodium-glucose cotransporter 2 (SGLT-2) inhibitors, insulin secretagogues, thiazolidinediones (TZD), α-glucosidase inhibitors, and dipeptidyl peptidase-4 (DPP-4) inhibitors. Injectable refers to insulin or GLP-RA. In individuals with type 2 DM and metabolic dysfunction–associated steatotic liver disease (see Chap. 354) or metabolic dysfunction–associated steatohepatitis (see Chap. 354), a GLP-1 RA or a dual glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 RA and/or TZD (pioglitazone) should be considered. ASCVD, atherosclerotic cardiovascular disease; CKD, chronic kidney disease; DM, diabetes mellitus; HbA1c, hemoglobin A1c; HFrEF, heart failure with reduced ejection fraction; HFpEF, heart failure with preserved ejection fraction. inhibitors; (2) insulin secretagogues, GLP-1RAs, DPP-4 inhibitors, α-glucosidase inhibitors, and SGLT-2 inhibitors begin to lower the plasma glucose immediately, whereas the glucose-lowering effects of the biguanides and thiazolidinediones takes several days; (3) not all agents are effective in all individuals with type 2 DM; (4) biguanides, α-glucosidase inhibitors, GLP-1RAs, DPP-4 inhibitors, thiazolidinedio­ nes, and SGLT-2 inhibitors do not directly cause hypoglycemia; (5) most individuals will eventually require treatment with more than one class of oral glucose-lowering agents or insulin, reflecting the progressive nature of type 2 DM; and (6) durability of glycemic control is slightly less for sulfonylureas compared to metformin or thiazolidinediones. COMBINATION THERAPY WITH GLUCOSE-LOWERING AGENTS  The approach to type 2 DM has changed dramatically with the demon­ stration that GLP-1RAs and SGLT-2 inhibitors reduce cardiovascular events and slow the progression of renal disease, indicating that a GLP-1RA or an SGLT-2 inhibitor should be used in most individu­ als with type 2 DM. Therapy should be dictated by whether ASCVD, heart failure, or CKD is present or whether weight loss is a major goal (Fig. 416-3). A number of combinations of therapeutic agents are use­ ful in type 2 DM: metformin plus SGLT-2 inhibitor, metformin plus GLP-1RA, metformin plus insulin, or combinations of a long-acting insulin and a GLP-1RA. Because the mechanism of action of the first and second agents differs, the effect on glycemic control is usually additive. Recent results from the National Institutes of Health–funded Glycemia Reduction Approaches in Diabetes: A Comparative Effec­ tiveness Study (GRADE) indicated that addition of liraglutide or basal

Diabetes Mellitus: Management and Therapies
CHAPTER 416 Weight loss Glycemia • GLP-1RA • Structured medical weight loss program • Metabolic surgery • GLP-1RA • GLP-1RA and insulin • Combination oral + injectable • Sulfonylurea • TZD • DPP-4 inhibitor insulin to metformin leads to better glycemic control than glimepiride or sitagliptin (SGLT-2 inhibitors were not studied). Medication costs vary considerably (Table 416-6), and this often factors into medication choice as drugs in some categories are very expensive (e.g., SGLT-2 inhibitors, GLP-1RAs). Several fixed-dose combinations of oral agents are available, but evidence that they are superior to titration of a single agent to a maximum dose and then addition of a second agent is lack­ ing. If adequate control is not achieved with the combination of two agents (based on reassessment of the HbA1c every 3 months), a third oral agent, including basal insulin, should be considered (Fig. 416-3). Treatment approaches vary considerably from country to country. For example, α-glucosidase inhibitors are used commonly in South Asian patients (Indian) but infrequently in the United States or Europe. Whether this reflects an underlying difference in the disease or physi­ cian preference is not clear. Treatment with insulin often becomes necessary as type 2 DM enters the phase of relative insulin deficiency and is signaled by inad­ equate glycemic control with one or two oral glucose-lowering agents. Insulin alone or in combination should be used in patients who fail to reach glycemic targets. For example, a single dose of long-acting insulin at bedtime is often effective in combination with metformin. As endogenous insulin production falls further, multiple injections of long-acting insulin together with rapid-acting insulin are necessary to control postprandial glucose excursions. These insulin regimens are identical to the long-acting and rapid-acting combination regimens discussed above for type 1 DM, although usually at higher doses given

insulin resistance. Weight gain and hypoglycemia are the major adverse effects of insulin therapy. The addition of a GLP-1RA can limit this and reduce the dose of insulin needed. The daily insulin dose required can become quite large (1–2 units/kg per day) as endogenous insulin production falls and insulin resistance persists, especially in the setting of weight gain. Insulin plus a thiazolidinedione promotes weight gain and may be associated with peripheral edema. Addition of a GLP-1RA or a thiazolidinedione may necessitate a reduction in the insulin dose to avoid hypoglycemia. Patients requiring large doses of insulin (>200 units/day) can be treated with more concentrated forms of insulin to reduce the volume of injectate and improve absorption.

PART 12 Endocrinology and Metabolism ■ ■OTHER THERAPIES FOR DIABETES Metabolic (also referred to as bariatric) surgery for obese individuals with type 2 DM has shown considerable effectiveness, sometimes with dramatic resolution of diabetes or major reductions in the needed dose of glucose-lowering therapies (Chaps. 413 and 414). Several large, nonrandomized clinical trials have demonstrated a much greater efficacy of metabolic surgery compared to medical management in the treatment of type 2 DM, but these trials were conducted before the advent of recently available GLP-1RAs. The ADA clinical guide­ lines state that metabolic surgery should be considered in individuals with type 2 DM and a body mass index >30 kg/m2 if hyperglycemia is inadequately controlled despite optimal medical therapy. Metabolic surgery is ideally performed in certified centers with experience with the procedures and associated nutritional support. Short-term intense caloric restriction (very-low-calorie diet, typi­ cally 800–1000 calories/d) can dramatically improve type 2 DM, sometimes leading to resolution of the diabetes. Such an approach is more effective in recent-onset type 2 DM and should be supervised by a provider with expertise and accompanied by a long-term, weightmaintenance program. Whole-pancreas transplantation can normalize glucose control in type 1 DM and when performed simultaneously with or after kidney transplantation can prolong the life of the kidney transplant by offer­ ing protection against recurrent diabetic nephropathy. However, the number of whole-pancreas transplants is declining, likely reflecting the success with CGM and AID. Pancreatic islet transplantation is a less invasive form of beta-cell replacement therapy for type 1 DM; an islet product has received FDA approval. Despite the risks associated with chronic immunosuppression, whole-pancreas and pancreatic islet transplantation may be considered for patients with severe metabolic instability or already requiring immunosuppression in support of a kidney or other organ transplant. Patients with chronic pancreatitis and preserved islet function who require pancreatectomy for pain relief may benefit from autologous islet transplantation as this may prevent or ameliorate postsurgical DM. ■ ■EMERGING THERAPIES Recent clinical trials using transplantation of insulin-producing cells derived from human pluripotent stem cells have shown promise. Cost, durability, long-term safety, and patient selection remain to be determined. Many individuals with long-standing type 1 DM still produce very small amounts of insulin or have insulin-positive cells within the pancreas. This suggests that beta cells may slowly regen­ erate but are quickly destroyed by the autoimmune process. Efforts to suppress the autoimmune process, for example, with a monoclo­ nal antibody that targets T lymphocytes, may preserve beta cells when given at the time of new-onset hyperglycemia in type 1 DM. This agent, teplizumab, a humanized monoclonal antibody to CD3 on T cells, has been approved by the FDA to delay the onset of clinical type 1 DM (stage 3) in patients 8 years of age or older with preclinical (stage 2) disease. Agents that target thioredoxin-interacting protein (TXNIP), especially Ca2+ channel blockers, have shown promise in recent-onset type 1 DM and in rodent models of diabetes. ADVERSE EFFECTS OF THERAPY FOR DM The benefits of efforts directed toward glycemic control must be bal­ anced against the risks of treatment (Table 416-6). Side effects of inten­ sive treatment include an increased frequency of serious hypoglycemia,

weight gain, and greater demands on the individual with diabetes. The most serious complication of therapy for DM is hypoglycemia, and its prevention and treatment with oral glucose or glucagon administered intra-nasally or by injection are discussed in Chap. 418. Severe, recur­ rent, or unexplained hypoglycemia warrants reassessment of the treat­ ment regimen and glycemic goal for the individual patient and possibly deintensification of insulin therapy (see categories of individuals for this would be appropriate in Table 416-4). Weight gain occurs with most (insulin, insulin secretagogues, thiazolidinediones) but not all (metformin, α-glucosidase inhibitors, GLP-1RAs, SGLT-1 inhibitors, DPP-4 inhibitors) therapies. The weight gain is partially due to the anabolic effects of insulin and the reduction in glucosuria. ACUTE DISORDERS RELATED TO SEVERE HYPERGLYCEMIA Individuals with type 1 or type 2 DM and severe hyperglycemia should be assessed for clinical stability, including mentation and hydration. The physician should determine if the individual with diabetes is stable or if DKA or a hyperglycemic hyperosmolar state (HHS) is present. In DKA, the hyperglycemia is accompanied by increased ketone concentration in blood and metabolic acidosis. In HHS, the hyperglycemia is usually greater, leading to hyperosmolality and marked dehydration but with­ out ketosis or acidosis. Ketones bodies, an indicator of DKA, should be measured in individuals with type 1 DM when the plasma glucose is persistently >13.9 mmol/L (250 mg/dL). The possibility of DKA should always be considered in patients with type 1 DM during a concurrent illness or with symptoms such as nausea, vomiting, or abdominal pain. Measurement of β-hydroxybutyrate in the blood is preferred over urine testing with nitroprusside-based assays that measure only acetoacetate and acetone. Worldwide, the number of reported cases of DKA and HHS is increasing for unclear reasons. Both DKA and HHS are associ­ ated with potentially serious complications, including greater mortality. Most cases of DKA are in individuals with type 1 DM, while HHS occurs mostly in individuals with type 2 DM. DKA, formerly consid­ ered a hallmark of type 1 DM, can also occur at diabetes diagnosis in obese young adults, often of Hispanic or African descent, whose labo­ ratory values are similar to those seen in DKA associated with type 1 DM. However, after treatment of the DKA, these individuals recover their insulin secretory capacity, can gradually discontinue insulin treat­ ment after a few weeks or months, and remain normoglycemic with only diet or oral medication. The cause of this atypical form of diabetes is unknown; it is often termed ketosis-prone diabetes. DKA can also occur in the setting of treatment of type 2 DM with an SGLT-2 inhibi­ tor. Often the blood glucose is normal or just mildly elevated because of the glucosuria. Table 416-7 compares the features of DKA, HHS, and euglycemic DKA associated with SGLT-2 inhibitors. DKA and HHS exist along a continuum of hyperglycemia, with up to one-third of patients having features of both. ■ ■DIABETIC KETOACIDOSIS Clinical Features  The symptoms and physical signs of DKA are listed in Table 416-8 and usually develop over 24 h. DKA may be the initial symptom complex that leads to a diagnosis of type 1 DM, but more frequently, it occurs in individuals with established diabetes. Nausea and vomiting are often prominent, and their presence in an individual with diabetes warrants laboratory evaluation for DKA. Abdominal pain may be severe and can resemble acute pancreatitis or ruptured viscus. Hyperglycemia leads to glucosuria, volume depletion, and tachycardia. Hypotension can occur because of volume depletion in combination with peripheral vasodilatation. Kussmaul respirations and a fruity odor on the patient’s breath (secondary to metabolic aci­ dosis and increased acetone) are classic signs of the disorder. Lethargy and central nervous system depression may evolve into coma with severe DKA but should also prompt evaluation for other reasons for altered mental status (e.g., infection, hypoxemia). Cerebral edema, an extremely serious complication of DKA, is seen most frequently in children. Signs of infection, which may precipitate DKA, should be sought on physical examination, even in the absence of fever. Failure to augment insulin therapy during physiologic stress often compounds

TABLE 416-7  Laboratory Values in Diabetic Ketoacidosis (DKA), Hyperglycemic Hyperosmolar State (HHS), and Euglycemic DKA [Representative Ranges at Presentation; mmol/L ( mg/dL)]   DKA HHS EUGLYCEMIC DKAc Glucose,a mmol/L (mg/dL) 11.1–33.3 (250–600) 33.3–66.6 (600–1200) 5.5-13.9 (100–250)c Sodium, meq/L 125–135 135–145 Normal Potassiuma,b Normal to ↑ Normal Normal to ↑ Magnesiuma Normal Normal Normal Chloridea Normal Normal Normal Phosphatea,b Normal Normal Normal Creatinine Slightly to moderately ↑ Moderately ↑ Slightly ↑ Osmolality (mOsm/mL)

300 300 Normal Serum/urine ketonesa ++ +/– ++ Serum β-hydroxybutyrate, mmol/L 3.0 <1.0 3.0 Serum bicarbonate,a meq/L <18 18 <18 Arterial pH 6.8–7.3 7.3 <7.3 Arterial Pco2,a mmHg 20–30 Normal 20–30 Anion gapa (Na – [Cl + HCO3]) ↑ Normal to slightly ↑ ↑ aLarge changes occur during treatment of DKA; serum level may be normal initially but then require replacement. bAlthough plasma levels may be normal or high at presentation, total-body stores are usually depleted. cSometimes occurs with sodium-glucose cotransporter 2 (SGLT-2) inhibitor treatment; disproportionate glucosuria is consistent with SGLT-2 inhibitor effect. the problem. Tissue ischemia (heart, brain) can also be a precipitating factor. Omission of insulin because of an infusion pump delivery site occlusion or device malfunction, eating disorder, mental health disor­ ders, or an unstable psychosocial environment may each be a factor precipitating DKA. Complete omission or inadequate administration of insulin by the patient or health care team (in a hospitalized patient with type 1 DM) may precipitate DKA. The rising cost of insulin has been a major challenge and has contributed to individuals with diabetes omit­ ting or rationing their insulin, making them more vulnerable to DKA. Pathophysiology  DKA results from relative or absolute insulin deficiency combined with counterregulatory hormone excess (gluca­ gon, catecholamines, cortisol, and growth hormone). The decreased ratio of insulin to glucagon promotes gluconeogenesis, glycogenolysis, and ketone body formation in the liver, as well as increases in substrate delivery from fat and muscle (free fatty acids, amino acids) to the liver. Ketosis results from a marked increase in free fatty acid release from adipocytes, with a resulting shift toward ketone body synthesis in the liver. Reduced insulin levels, in combination with elevations in cate­ cholamines and growth hormone, also increase lipolysis and the release of free fatty acids. Markers of inflammation (cytokines, C-reactive protein) are elevated in both DKA and HHS. Laboratory Abnormalities and Diagnosis  The timely diag­ nosis of DKA is crucial and allows for prompt initiation of therapy. DKA is characterized by hyperglycemia (serum glucose >13.9 mmol/L [250 mg/dL], ketosis, and metabolic acidosis [serum bicarbonate <15–18 mmol/L with increased anion gap]) along with a number of TABLE 416-8  Manifestations of Diabetic Ketoacidosis Symptoms   Nausea/vomiting   Thirst/polyuria   Abdominal pain   Shortness of breath Precipitating events   Inadequate insulin administration   Infection (pneumonia/UTI/ Physical Findings   Tachycardia   Dehydration/hypotension   Tachypnea/Kussmaul respirations/ respiratory distress   Abdominal tenderness (may resemble acute pancreatitis or surgical abdomen)   Lethargy/obtundation/cerebral gastroenteritis/sepsis)   Infarction (cerebral, coronary, edema/possibly coma mesenteric, peripheral)   Pancreatitis   Drugs (cocaine)   Pregnancy Abbreviation: UTI, urinary tract infection.

Diabetes Mellitus: Management and Therapies
CHAPTER 416 secondary metabolic derangements (Table 416-7). Occasionally, the serum glucose is only minimally elevated and may even be normal (euglycemic DKA). This has been noted especially in individuals treated with SGLT-2 inhibitors. Arterial pH usually ranges between 6.8 and 7.3, depending on the severity of the acidosis. Despite a total-body potassium deficit, the serum potassium at presentation may be mildly elevated, secondary to the acidosis and volume depletion. Total-body stores of sodium, chloride, phosphorus, and magnesium are also reduced in DKA but are not accurately reflected by their levels in the serum because of hypovolemia and hyperglycemia. Elevated blood urea nitrogen (BUN) and serum creatinine levels reflect intravascular volume depletion. Leukocytosis, hypertriglyceridemia, and hyperli­ poproteinemia are commonly found as well. Hyperamylasemia may suggest a diagnosis of pancreatitis, especially when accompanied by abdominal pain. However, in DKA the amylase is usually of salivary origin and thus is not diagnostic of pancreatitis. Serum lipase should be obtained if pancreatitis is suspected. The measured serum sodium is reduced as a consequence of the hyperglycemia. An estimated correction is provided by the equa­ tion: (1.6-mmol/L [1.6-meq] reduction in serum sodium for each 5.6-mmol/L [100-mg/dL] rise in the serum glucose). A normal serum sodium in the setting of DKA indicates a more profound water deficit. In DKA, the ketone body, β-hydroxybutyrate, is synthesized at a threefold greater rate than acetoacetate; however, acetoacetate is preferentially detected by a commonly used ketosis detection reagent (nitroprusside). The nitroprusside tablet, or stick, is often used to detect urine ketones; certain medications such as captopril, penicil­ lamine, or valproic acid may cause false-positive reactions. Serum or plasma assays for β-hydroxybutyrate are preferred because they more accurately reflect the true ketone body level. The degree of acidosis and hyperglycemia do not necessarily cor­ relate closely because a variety of factors determine the level of hyper­ glycemia (oral intake, urinary glucose loss). Ketonemia is a consistent finding in DKA and distinguishes it from simple hyperglycemia. The differential diagnosis of DKA includes starvation ketosis, alcoholic ketoacidosis (bicarbonate usually >15 meq/L), and other forms of increased anion-gap acidosis (Chap. 55). TREATMENT Diabetic Ketoacidosis Based on laboratory values and clinical exam, DKA can be classified as mild (pH 7.25–7.3, serum bicarbonate 15–18 meq/L, men­ tal status normal), moderate (pH 7.0–7.25, serum bicarbonate 10–15 meq/L, mildly reduced mental status), or severe (pH <7.0,

serum bicarbonate <10–15 meq/L, reduced mental status, coma). The management of DKA is outlined in Table 416-9. After initiat­ ing IV fluid replacement and insulin therapy, the event that precipi­ tated the episode of DKA should be sought and aggressively treated. If the patient is vomiting or has altered mental status, a nasogastric tube should be inserted to prevent aspiration of gastric contents. Central to successful treatment of DKA is careful monitoring and frequent reassessment to ensure that the patient and the metabolic derangements are improving. A comprehensive flow sheet should record chronologic changes in vital signs, fluid intake and output, and laboratory values as a function of insulin administered.

After the initial bolus of normal saline or lactated Ringer’s, replacement of the sodium and free water deficit is carried out over the next 24 h (fluid deficit is often 3–5 L). When hemodynamic stability and adequate urine output are achieved, IV fluids should be switched to 0.45% saline or lactated Ringer’s, depending on the calculated volume deficit. Ringer’s lactate is associated with more rapid DKA resolution and a reduced trend toward hyperchloremia later in the course of DKA resolution. PART 12 Endocrinology and Metabolism A bolus of IV (0.1 units/kg) short-acting regular insulin is usu­ ally administered immediately (Table 416-9), and subsequent treat­ ment should provide continuous and adequate levels of circulating TABLE 416-9  Management of Diabetic Ketoacidosis (DKA)

  1. Confirm diagnosis (↑ serum glucose, ↑ serum β-hydroxybutyrate, metabolic acidosis).
  2. Admit to hospital; intensive care setting may be necessary for severe DKA (see text). Mild to moderate DKA can be treated in a step-down unit with close nursing and laboratory monitoring.
  3. Assess: Serum electrolytes (K+, Na+, Mg2+, Cl–, bicarbonate, phosphate) Acid-base status—pH, HCO3 –, PCO2, β-hydroxybutyrate Renal function (creatinine, urine output)
  4. Replace fluids: 2–3 L of 0.9% saline or lactated Ringer’s over first 1–3 h (10–20 mL/kg per hour); subsequently, 0.45% saline at 250–500 mL/h; change to 5–10% glucose and 0.45% saline or lactated Ringer’s at 150–250 mL/h when blood glucose reaches 250 mg/dL (13.9 mmol/L). For treatment of euglycemic DKA, start 5% or 10% dextrose infusion and insulin treatment when 0.9% saline is started; adjust dextrose infusion to prevent hypoglycemia.
  5. Administer short-acting regular insulin: IV (0.1 units/kg), then 0.1 units/ kg per hour by continuous IV infusion; increase two- to threefold if no response by 2–4 h. In mild to moderate DKA, subcutaneous rapid-acting insulin may be used with close monitoring (0.1 unit/kg rapid-acting insulin analogue subcutaneously and then 0.1 unit/kg every 1 h or 0.2 unit/kg every 2 h). Continue insulin treatment and 5% or 10% dextrose infusion to prevent hypoglycemia. If the initial serum potassium is <3.3 mmol/L (3.3 meq/L), do not administer insulin until the potassium is corrected.
  6. Assess patient: What precipitated the episode (noncompliance, infection, trauma, pregnancy, infarction, cocaine)? Initiate appropriate workup for precipitating event (cultures, CXR, ECG, etc.).
  7. Measure blood glucose every 1–2 h; measure electrolytes (especially K+, bicarbonate, phosphate) and anion gap every 4 h for first 24 h.
  8. Monitor blood pressure, pulse, respirations, mental status, fluid intake and output every 1–4 h.
  9. Replace K+ if ECG, urine flow, and creatinine are normal. If K+ <3.5 mmol/L, administer 10–20 mmol/L per hour until K+ >3.5 mmol/L. If K+ 3.5–5 mmol/L, administer 10–20 mmol/L in each liter of IV fluid to keep serum K+ between 4 and 5 mmol/L. If K+ >5.0 mmol/L, start insulin but hold K+. Recheck K+ every 2 h to determine when to start K+ replacement.
  10. Continue above until patient is stable, glucose goal is 8.3–11.1 mmol/L (150–200 mg/dL), normal plasma ketone and pH, and bicarbonate ≥18 mmol/L. Insulin infusion may be decreased to 0.02–0.1 unit/kg per hour. Resolution of euglycemic DKA should be based on bicarbonate, not glucose, correction; see text.
  11. Administer long-acting insulin as soon as patient is eating. Allow for a 2- to 4-h overlap in insulin infusion and SC long-acting insulin injection. Abbreviations: CXR, chest x-ray; ECG, electrocardiogram. Source: Adapted from multiple sources, including Nyenwe EA, Kitabchi AE: The evolution of diabetic ketoacidosis: An update of its etiology, pathogenesis and management. Metabolism 65:507, 2016; and Umpierrez GE et al: Hyperglycaemic crises in adults with diabetes: A consensus report. Diabetologia 67:1455, 2024.

insulin. IV administration is usually preferred (0.1 units/kg of regu­ lar insulin per h) but uncomplicated DKA can also be treated with SC short-acting insulin analogues. As the acidosis and insulin resis­ tance associated with DKA resolve, the insulin infusion rate can be decreased (to 0.02–0.1 units/kg per h). Long-acting insulin, in combination with SC short-acting insulin, should be administered as soon as the patient resumes eating, because this facilitates transi­ tion to an outpatient insulin regimen and reduces length of hospital stay. Hyperglycemia usually improves at a rate of 4.2–5.6 mmol/L (50–100 mg/dL) per h as a result of insulin-mediated glucose disposal, reduced hepatic glucose release, and rehydration. Rehy­ dration reduces catecholamines, increases urinary glucose loss, and expands the intravascular volume. The decline in the plasma glucose within the first 1–2 h may be more rapid and is mostly related to volume expansion. Ketoacidosis begins to resolve as insulin reduces lipolysis, increases peripheral ketone body use, sup­ presses hepatic ketone body formation, and promotes bicarbonate regeneration. However, the acidosis and ketosis resolve more slowly than hyperglycemia. Depending on the rise of serum chloride, the anion gap (but not bicarbonate) will normalize more quickly. A hyperchloremic acidosis (serum bicarbonate of 15–18 mmol/L [15–18 meq/L]) often follows successful treatment and gradually resolves as the kidneys regenerate bicarbonate and excrete chloride. Potassium stores are depleted in DKA (estimated deficit 3–5 mmol/kg [3–5 meq/kg]). During treatment with insulin and fluids, various factors contribute to the development of hypokale­ mia. These include insulin-mediated potassium transport into cells, resolution of the acidosis (which also promotes potassium entry into cells), and urinary loss of potassium salts of organic acids. Thus, potassium repletion should commence as soon as adequate urine output and a normal serum potassium are documented (Table 416-9). Bicarbonate replacement has not been shown to improve out­ comes. However, in the presence of severe acidosis (arterial pH <7.0), sodium bicarbonate (50 mmol [meq/L] in 200 mL of sterile water with 10 meq/L KCl per h) may be administered for the first 2 h until the pH is >7.0. Hypophosphatemia and hypomagnesemia may develop during DKA therapy, and if severe, may also require supplementation. With appropriate therapy, the mortality rate of DKA is low (<1%) and is related more to the underlying or precipitating event, such as infection ((pneumonia, SARS-Co-V2, etc.) COVID-19), pregnancy, end-stage renal disease, or myocardial infarction. Venous throm­ bosis, upper GI bleeding, and acute respiratory distress syndrome occasionally complicate DKA. The major nonmetabolic complica­ tion of DKA therapy is cerebral edema, which most often devel­ ops in children as DKA is resolving. The etiology of and optimal therapy for cerebral edema are not well established. Following treatment, the physician and patient should review the sequence of events that led to DKA to prevent future recurrences. Even a single episode of DKA is associated with a greatly increased 1-year mortality rate. Foremost is patient education about the symptoms of DKA, its precipitating factors, and the management of diabetes during a concurrent illness. In some individuals, DKA is recurrent and may indicate underlying mental health issues. The structural barriers to accessing care, insulin cost, and the social determinants of health often play a role. ■ ■HYPERGLYCEMIC HYPEROSMOLAR STATE Clinical Features  The most common presentation of HHS is an elderly individual with type 2 DM, with a several-week history of polyuria, weight loss, and diminished oral intake that culminates in mental confusion, lethargy, or coma. The physical examination reflects profound dehydration and hyperosmolality and reveals hypotension, tachycardia, and altered mental status. Notably absent are symptoms of nausea, vomiting, and abdominal pain and the Kussmaul respirations characteristic of DKA. HHS is often precipitated by a serious, concur­ rent illness such as myocardial infarction or stroke. Sepsis, pneumonia,

and other serious infections are frequent precipitants and should be sought. In addition, a debilitating condition (prior stroke or dementia) or social situation that compromises water intake usually contributes to the development of the disorder. Pathophysiology  Relative insulin deficiency and inadequate fluid intake are the underlying causes of HHS. Insulin deficiency increases hepatic glucose production (through glycogenolysis and gluconeogen­ esis) and impairs glucose utilization in skeletal muscle (see above dis­ cussion of DKA). Hyperglycemia induces an osmotic diuresis that leads to intravascular volume depletion, which is exacerbated by inadequate fluid replacement. The absence of ketosis in HHS is not understood. Presumably, the insulin deficiency is only relative and less severe than in DKA. Lower levels of counterregulatory hormones and free fatty acids have been found in HHS than in DKA in some studies. It is also possible that the liver is less capable of ketone body synthesis or that the insulin/glucagon ratio does not favor ketogenesis. Laboratory Abnormalities and Diagnosis  The laboratory fea­ tures in HHS are summarized in Table 416-7. Most notable are the marked hyperglycemia (plasma glucose may be >55.5 mmol/L [1000 mg/dL]), hyperosmolality (>300 mOsm/L), and prerenal azo­ temia. The measured serum sodium may be normal or slightly low despite the marked hyperglycemia. The corrected serum sodium is usually increased (add 1.6 meq to measured sodium for each 5.6-mmol/L [100-mg/dL] rise in the serum glucose). In contrast to DKA, acidosis and ketonemia are absent or mild. A small anion-gap metabolic acidosis may be present secondary to increased lactic acid. Moderate ketonuria, if present, is secondary to starvation. TREATMENT Hyperglycemic Hyperosmolar State Volume depletion and hyperglycemia are prominent features of both HHS and DKA. Consequently, the therapy of these disorders shares several elements (Table 416-9). In both disorders, careful monitoring of the patient’s fluid status, laboratory values, and insu­ lin infusion rate is crucial. Underlying or precipitating problems should be aggressively sought and treated. In HHS, fluid losses and dehydration are usually more pronounced than in DKA due to the longer duration of the illness. The patient with HHS is usually older, more likely to have mental status changes, and more likely to have a life-threatening precipitating event with accompanying comorbidi­ ties. Even with proper treatment, HHS has a substantially higher mortality rate than DKA (up to 15% in some clinical series). Fluid replacement should initially stabilize the hemodynamic status of the patient (1–3 L of 0.9% normal saline over the first 2–3 h). Because the fluid deficit in HHS is accumulated over a period of days to weeks, the rapidity of reversal of the hyperosmolar state must balance the need for free water repletion with the risk that too rapid a reversal may worsen neurologic function. If the serum sodium is >150 mmol/L (150 meq/L), 0.45% saline should be used. After hemodynamic stability is achieved, the IV fluid administration is directed at reversing the free water deficit using hypotonic fluids (0.45% saline initially, then 5% dextrose in water [D5W]). The calculated free water deficit (which can be as great as 9–10 L) should be reversed over the next 1–2 days (infusion rates of 200–300 mL/h of hypotonic solution). Potassium repletion is usu­ ally necessary and should be dictated by repeated measurements of the serum potassium. In patients taking diuretics, the potassium deficit can be quite large and may be accompanied by magnesium deficiency. Hypophosphatemia may occur during therapy and can be improved by using KPO4 and beginning nutrition. As in DKA, rehydration and volume expansion lower the plasma glucose initially, but insulin is also required. A reasonable regimen for HHS begins with an IV insulin bolus of 0.1 unit/kg followed by IV insulin at a constant infusion rate of 0.1 unit/kg per h. If the serum glucose does not fall, increase the insulin infusion rate by twofold. As in DKA, glucose should be added to IV fluid when the

plasma glucose falls to 11.1–13.9 mmol/L (200–250 mg/dL), and the insulin infusion rate should be decreased to 0.02–0.1 unit/kg per h. The insulin infusion should be continued until the patient has resumed eating and can be transferred to an SC insulin regi­ men. The patient should be discharged from the hospital on insulin. Some patients can later switch to oral glucose-lowering agents.

MANAGEMENT OF DIABETES IN A HOSPITAL OR FACILITY Virtually all medical and surgical subspecialties are involved in the care of hospitalized patients with diabetes or individuals with diabetes in the perioperative setting. Hyperglycemia, whether in a patient with known diabetes or in someone without known diabetes, appears to be a predictor of poor outcome in hospitalized patients. General anesthesia, surgery, infection, or concurrent illness raises the levels of counter­ regulatory hormones (cortisol, growth hormone, catecholamines, and glucagon) and cytokines that may lead to transient insulin resistance and hyperglycemia. These factors increase insulin requirements by increasing glucose production and impairing glucose utilization and thus may worsen glycemic control. The concurrent illness or surgical procedure may lead to variable insulin absorption and also prevent the patient with DM from eating normally and, thus, may promote hypoglycemia. Glycemic control should be assessed on admission using the HbA1c. Electrolytes, renal function, and intravascular volume status should be assessed as well. The high prevalence of ASCVD in individuals with DM (especially in type 2 DM) may necessitate pre­ operative cardiovascular evaluation (Chap. 417). CGM in the hospital or intensive care unit (ICU) setting is not FDA approved. Individuals using CGM and/or AID prior to admission should continue to use these devices if the provider, the nursing staff, and the patient agree that this can be safely done within the context of the patient’s current reason for hospitalization. Diabetes Mellitus: Management and Therapies
CHAPTER 416 The goals of diabetes management during hospitalization or in the perioperative periods are near-normoglycemia, avoidance of hypogly­ cemia, and transition back to the outpatient diabetes treatment regi­ men. Upon hospital admission, frequent glycemic monitoring should begin, as should planning for diabetes management after discharge. Glycemic control appears to improve clinical outcomes in a variety of settings, but optimal glycemic goals for the hospitalized patient are incompletely defined. In a number of cross-sectional studies of patients with diabetes, a greater degree of hyperglycemia was associated with worse cardiac, neurologic, and infectious outcomes. In some studies, patients who do not have preexisting diabetes but who develop modest blood glucose elevations during their hospitalization appear to benefit from achieving near-normoglycemia using insulin treatment. How­ ever, a large randomized clinical trial (Normoglycemia in Intensive Care Evaluation Survival Using Glucose Algorithm Regulation [NICESUGAR]) of individuals in the ICU (most of whom were receiving mechanical ventilation) found an increased mortality rate and a greater number of episodes of severe hypoglycemia with very strict glycemic control (target blood glucose of 4.5–6 mmol/L or 81–108 mg/dL) com­ pared to individuals with a more moderate glycemic goal (target blood glucose of <10 mmol/L or 180 mg/dL). Currently, most data suggest that very strict blood glucose control in acutely ill patients likely wors­ ens outcomes and increases the frequency of hypoglycemia. The ADA suggests the following glycemic goals for hospitalized patients: (1) in critically or non-critically ill patients, glucose of 7.8–10.0 mmol/L or 140–180 mg/dL; (2) in selected patients, glucose of 6.1–7.8 mmol/L or 110–140 mg/dL with avoidance of hypoglycemia; and (3) the target range in the perioperative period should be 80–180 mg/dL (4.4–10.0 mmol/L). Critical aspects for optimal diabetes care in the hospital include the following: (1) A hospital-wide system approach to treatment of hyper­ glycemia and prevention of hypoglycemia is needed. Inpatient diabetes management teams consisting of nurse practitioners and physicians are increasingly common. (2) Diabetes treatment plans should focus on the transition from the ICU and the transition from the inpatient to the outpatient setting. (3) Adjustment of the discharge treatment

regimen of patients whose diabetes was poorly controlled on admission (as reflected by the HbA1c) is important.

The physician caring for an individual with diabetes in the peri­ operative period, during times of infection or serious physical illness, or simply when the patient is fasting for a diagnostic procedure must monitor the plasma glucose vigilantly, adjust the diabetes treatment regimen, and provide glucose infusion as needed. Hypoglycemia is frequent in hospitalized patients, and many of these episodes are avoid­ able. Hospital systems should have a diabetes management protocol to avoid inpatient hypoglycemia. Measures to reduce or prevent hypogly­ cemia include frequent glucose monitoring, but it is also important to prevent hypoglycemia by anticipating drops in insulin requirement by factors such as decreasing renal function, decreasing glucocorticoid doses, or interruption of nutrition (parenteral or enteral or PO). PART 12 Endocrinology and Metabolism Depending on the severity of the patient’s illness and the hospital setting, the physician can use either an insulin infusion or SC insulin. Insulin infusions are preferred in the ICU or in a clinically unstable setting because the half-life of the infused insulin is quite short (minutes). The absorption of SC insulin may be variable in such situations. Insu­ lin infusions can also effectively control plasma glucose in the peri­ operative period and when the patient is unable to take anything by mouth, although for relatively short (<4 h) procedures, most patients can remain on SC insulin. Regular insulin is used rather than insulin analogues for IV insulin infusion because it is less expensive and equally effective. The physician must consider carefully the clinical setting in which an insulin infusion will be used, including whether adequate ancillary personnel are available to monitor the blood glucose frequently and whether they can adjust the insulin infusion rate to maintain the blood glucose within the optimal range. Insulin-infusion algorithms should integrate the insulin sensitivity of the patient, fre­ quent blood glucose monitoring, and the trend of changes in the blood glucose to determine the insulin-infusion rate. Insulin-infusion algo­ rithms jointly developed and implemented by nursing and physician staff are advised. Because of the short half-life of IV regular insulin, it is necessary to administer long-acting insulin prior to discontinuation of the insulin infusion (2–4 h before the infusion is stopped) to avoid a period of insulin deficiency. In patients who are not critically ill or not in the ICU, basal or “scheduled” insulin is provided by SC, long-acting insulin supple­ mented by prandial and/or “corrective” insulin using a rapid-acting insulin. “Sliding scale,” with short-acting or rapid-acting insulin alone, where no insulin is given unless the blood glucose is elevated, is inad­ equate for inpatient glucose management. The rapid-acting, prepran­ dial insulin dose should include coverage for food consumption (based on anticipated carbohydrate intake) plus corrective insulin based on the patient’s insulin sensitivity and the blood glucose. For example, if the patient is thin (and likely insulin-sensitive), an insulin correction factor might be 1 unit for each 2.7 mmol/L (50 mg/dL) over the glucose target. If the patient is obese and likely insulin-resistant, then the insu­ lin correction factor might be 2 units for each 2.7 mmol/L (50 mg/dL)

over the glucose target. It is critical to individualize the regimen and adjust the basal and prandial insulin doses frequently based on the corrective insulin required. A consistent carbohydrate-controlled diabetes meal plan for hospitalized patients provides a predictable amount of carbohydrate for a particular meal each day (but not neces­ sarily the same amount for breakfast, lunch, and supper) and avoids concentrated sweets. Individuals with type 1 DM who are undergoing general anesthesia and surgery or who are seriously ill should receive continuous insulin, through an IV insulin infusion, their insulin infu­ sion device, or by SC administration of a reduced dose of long-acting insulin. Rapid-acting insulin alone is insufficient. Prolongation of a surgical procedure or delay in the recovery room is common and may result in periods of insulin deficiency leading to DKA. Insulin infusion is the preferred method for managing patients with type 1 DM over a prolonged (several hours) perioperative period or when serious con­ current illness is present (0.5–1.0 units/h of regular insulin). If the diag­ nostic or surgical procedure is brief (<4 h), a reduced dose of SC insulin may suffice (20–50% basal reduction, with rapid-acting correctional dose insulin as needed). This approach prevents interruption of insulin

infusion device therapy or, for MDI, facilitates the transition back to basal/bolus insulin after the procedure. The blood glucose should be monitored frequently during the illness or in the perioperative period. Individuals with type 2 DM can be managed with either an insulin infusion or SC long-acting insulin (20–50% reduction depending on clinical setting) plus preprandial, rapid-acting insulin. Oral glucoselowering agents should be discontinued upon admission (or up to a week prior to planned admission for SGLT-2 inhibitors) and are not useful in regulating the plasma glucose in clinical situations where the insulin requirements and glucose intake are changing rapidly. Moreover, these oral agents may be dangerous if the patient is fasting (e.g., hypoglycemia with sulfonylureas, euglycemic DKA with SGLT-2 inhibitors) or at risk for declining kidney function due to, for example, radiographic contrast media or unstable CHF (lactic acidosis with metformin). Once clinically stable, oral glucose-lowering agents may be resumed in anticipation of discharge. Each patient should receive an individualized, structured discharge plan for diabetes management. The principles of the care of individuals with diabetes who are in a rehabilitation facility or a long-term care facility are similar to those in a hospitalized patient with the glycemic goals individualized based on the patient’s overall clinical status (outlined in Table 416-4). Often the avoidance of hypoglycemia is the major goal with less intense glycemic targets. SPECIAL CONSIDERATIONS IN DM ■ ■TOTAL PARENTERAL NUTRITION (TPN)/TOTAL ENTERAL NUTRITION (TEN) (See also Chap. 335) TPN or TEN greatly increases insulin require­ ments. In addition, individuals not previously known to have DM may become hyperglycemic during TPN or TEN and require insulin treatment. For TPN, IV insulin infusion is the preferred treatment for hyperglycemia, and rapid titration to the required insulin dose is done most efficiently using a separate insulin infusion. After the total insulin dose has been determined, a proportion of this insulin may be added directly to the TPN solution to cover the nutritional requirements for insulin and adjusted based on the need for modified dosing of rapidacting insulin. In TEN, hyperglycemia may be limited by using highprotein formulations but often requires insulin treatment. Individuals receiving enteral bolus feedings should receive SC, rapid-acting insulin prior to each bolus. As a start, 1 unit of insulin is given SC for each 10–15 g of carbohydrate in the bolus. Patients with insulin deficiency (type 1 DM and pancreatogenic DM) should also receive long-acting insulin (0.1–0.2 units/kg per day) to cover basal insulin requirements should the TPN or TEN be interrupted or cycled. ■ ■GLUCOCORTICOIDS Glucocorticoids increase insulin resistance, decrease glucose utiliza­ tion, increase hepatic glucose production, and impair insulin secretion. These changes lead to a worsening of glycemic control in individuals with DM and may precipitate hyperglycemia in other individuals. If new-onset hyperglycemia remains during chronic treatment with supraphysiologic doses of glucocorticoid (>5 mg of prednisone or equivalent), the DM may be called “steroid-induced diabetes.” The effects of glucocorticoids on glucose homeostasis are dose-related, usually reversible, most pronounced in the postprandial period, and dependent on the timing and type of glucocorticoid. If the FPG is near the normal range, oral diabetes agents (e.g., sulfonylureas, metformin) may be sufficient to reduce hyperglycemia. If the FPG is >11.1 mmol/L (200 mg/dL), oral agents are usually not sufficient, and insulin therapy is required. If steroids are administered in the morning, then shortacting insulin and/or NPH in the morning may be sufficient to control postprandial glucose excursions. ■ ■DIABETES MANAGEMENT IN OLDER ADULTS Diabetes is very common in older adults, being present in ~25% of individuals over the age of 65 years. Increasingly, individuals with many years of type 1 DM are part of this patient population. As discussed above (Table 416-4), individualized therapeutic goals and modalities in older adults should consider biologic age, other

33 - 417 Diabetes Mellitus- Complications

417 Diabetes Mellitus: Complications

comorbidities and risk factors (e.g., hypertension, CVD), neurocogni­ tive and physical functional status, living arrangements, social sup­ port, and other medications. For example, the HbA1c goal for a highly functional 80-year-old should be different from that for an individual with diabetes in long-term care (skilled nursing facilities). In the for­ mer, the HbA1c goal (<7.0–7.5%) and selected therapies may be similar to younger individuals, whereas in an individual with complex/poor health or cognitive impairment, an HbA1c goal of <8.0–8.5% would be reasonable. Critical to diabetes management in all older individu­ als is the avoidance of hypoglycemia, which can worsen underlying cognitive impairment or CVD. In choosing medications for diabetes, the adverse effects (Table 416-6) should be considered (especially heart failure, renal insufficiency, propensity for hypoglycemia, etc.). Hypertension and dyslipidemia should be treated in elderly individu­ als with diabetes because there is clear benefit of blood pressure con­ trol, with the benefit for lipid-lowering medications being less clearly demonstrated. REPRODUCTIVE ISSUES Reproductive capacity in either men or women with DM appears to be normal. Menstrual cycles may be associated with alterations in glyce­ mic control in women with DM. Pregnancy is associated with marked insulin resistance; the increased insulin requirements often precipitate DM and lead to the diagnosis of gestational diabetes mellitus (GDM). Glucose, which at high levels is a teratogen to the developing fetus, readily crosses the placenta, but insulin does not. Thus, hyperglyce­ mia from the maternal circulation may stimulate insulin secretion in the fetus. The anabolic and growth effects of insulin may result in macrosomia. GDM complicates ~7% (range 1–14%) of pregnan­ cies. The incidence of GDM is greatly increased in certain racial and ethnic groups, including Black and Hispanic, consistent with a similar increased risk of type 2 DM. Current recommendations advise screen­ ing for glucose intolerance between weeks 24 and 28 of pregnancy in women not known to have diabetes. Therapy for GDM is similar to that for individuals with pregnancy-associated diabetes and involves MNT and insulin, if hyperglycemia persists. Oral glucose-lowering agents are not approved for use during pregnancy, but studies using metformin or glyburide have shown efficacy and have not found toxicity. With current practices, the morbidity and mortality rates of the mother with GDM and the fetus are not different from those in the nondiabetic population. Individuals who develop GDM are at marked increased risk for developing type 2 DM in the future and should be screened periodically for DM (see screening recommendations in Chap. 415). Most individuals with GDM revert to normal glucose tolerance after delivery, but some will continue to have overt diabetes or impairment of glucose tolerance after delivery. In addition, children of women with GDM appear to be at risk for obesity and glucose intolerance and have an increased risk of diabetes beginning in the later stages of adolescence. Pregnancy in individuals with known DM requires meticulous plan­ ning and adherence to strict preconception treatment regimens. Inten­ sive insulin therapy and near-normalization of the HbA1c (<6.5%) are essential for individuals with existing DM who are planning pregnancy. Consideration should be given to insulin infusion (e.g., AID) and CGM devices that may help to improve glycemic control prior to con­ ception since the most crucial period of glycemic control is soon after fertilization. The risk of fetal malformations is increased 4–10 times in individuals with uncontrolled DM at the time of conception, and nor­ mal blood glucose during the preconception period and throughout the periods of organ development in the fetus should be the goal, with more frequent monitoring of HbA1c every 2 months throughout gesta­ tion. Maintenance of the HbA1c <6.0–6.5% reduces the incidence and severity of fetal macrosomia and neonatal hypoglycemia related to fetal hyperinsulinism driven by elevated maternal glucose. ■ ■FURTHER READING American Diabetes Association: Comprehensive medical evalua­ tion and assessment of comorbidities: Standards of Medical Care in Diabetes—2024. Diabetes Care 47:S52, 2024.

American Diabetes Association: Facilitating positive health behav­

iors and well-being to improve health outcomes: Diabetes—2024. Diabetes Care 44:S77, 2024. American Diabetes Association: Pharmacologic approaches to glycemic treatment: Standards of medical care in diabetes—2024. Diabetes Care 47:S158, 2024. American Diabetes Association: Obesity and weight management for the prevention and treatment of type 2 diabetes: Standards of care in diabetes—2024. Diabetes Care 47:S145, 2024. American Diabetes Association: Older adults: Standards of medi­ Diabetes Mellitus: Complications CHAPTER 417 cal care in diabetes—2024. Diabetes Care 47:S244, 2024. Chow E et al: Euglycemic diabetic ketoacidosis in the era of SGLT2 inhibitors. BMJ Open Diabetes Res Care 11:e003666, 2023. Hirsch IB et al: The evolution of insulin and how it informs therapy and treatment choices. Endocr Rev 41:733, 2020. Holt RIG et al: The management of type 1 diabetes in adults. A con­ sensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetes Care 44:2589, 2021. Kosiborod MN et al: Semaglutide in patients with obesity-related heart failure and type 2 diabetes. N Engl J Med 390:15, 2024. Mallik R et al: The future is here: An overview of technology in dia­ betes. Diabetologia 67:2019, 2024. Perkovic V et al: Effects of semaglutide on chronic kidney disease in patients with type 2 diabetes. N Engl J Med 391:2, 2024. Qaseem A et al: Newer pharmacologic treatments in adults with type 2 diabetes: A clinical guideline from the American College of Physi­ cians. Ann Intern Med 177:658, 2024. Shaltout I et al: Risk stratification in people with diabetes for fasting during Ramadan: Consensus from Arabic Association for the Study of Diabetes and Metabolism. Curr Diabetes Rev 20:e201023222409, 2024. Simmons D et al: Treatment of gestational diabetes mellitus diagnosed early in pregnancy. N Engl J Med 388:2132, 2023. Umpierrez GE et al: Hyperglycaemic crises in adults with diabetes: a consensus report. Diabetologia 67:1455, 2024. ■ ■WEBSITES Online resources for selection of diabetes technology: Diabeteswise: https://pro.diabeteswise.org/en/ Diatribe: https://diatribe.org/ Panther: https://www.pantherprogram.org/ Alvin C. Powers, John M. Stafford,

Michael R. Rickels

Diabetes Mellitus:

Complications Diabetes-related complications affect many organ systems and are responsible for most of the morbidity and mortality associated with the disease. For many years in the United States, diabetes has been a leading cause of new blindness in adults, renal failure, and non­ traumatic lower extremity amputation and is a leading contributor to coronary heart disease (CHD). Diabetes-associated microvascu­ lar complications usually do not appear until the second decade of hyperglycemia. In contrast, diabetes-associated atherosclerotic car­ diovascular disease (ASCVD) risk, related in part to insulin resistance and its resultant dyslipidemia, may develop before hyperglycemia is established. Because type 2 diabetes mellitus (DM) often has a long asymptomatic period of hyperglycemia before diagnosis, many

TABLE 417-1  Diabetes-Related Complications Microvascular   Eye disease     Retinopathy (nonproliferative/proliferative)     Macular edema   Neuropathy     Sensory and motor (mono- and polyneuropathy)     Autonomic   Nephropathy (albuminuria and declining renal function) Macrovascular PART 12 Endocrinology and Metabolism   Coronary heart disease   Peripheral arterial disease   Cerebrovascular disease Heart failure Other   Gastrointestinal (gastroparesis, diarrhea)   Genitourinary (uropathy/sexual dysfunction)   Dermatologic   Infectious   Cataracts   Glaucoma   Cheiroarthropathya   Periodontal disease   Hearing loss Other comorbid conditions associated with type 1 or type 2 diabetes (relationship to hyperglycemia is uncertain): depression, obstructive sleep apnea, fatty liver disease, hip fracture, osteoporosis, cognitive impairment or dementia, low testosterone in men aThickened skin and reduced joint mobility. individuals with type 2 DM have both glucose-related and insulin resistance–related complications at the time of diagnosis. Fortunately, many of the diabetes-related complications can be prevented or miti­ gated with aggressive glycemic, lipid, and blood pressure control, as well as efforts at early detection. Diagnosis of type 2 DM at younger age increases diabetes-related complications. One estimate indicated three to four years of reduced life expectancy for every decade of ear­ lier diabetes diagnosis. This is emphasizes the critical role of diabetes prevention or delay. Diabetes-related complications can be divided into vascular and nonvascular complications and are similar for type 1 and type 2 DM (Table 417-1). The vascular complications of DM are further subdi­ vided into microvascular (retinopathy, neuropathy, and nephropathy) and macrovascular complications (ASCVD, peripheral arterial disease [PAD], cerebrovascular disease, and heart failure). Microvascular complications are diabetes specific, whereas macrovascular complica­ tions have additional pathophysiologic features that are shared with the general population. Nonvascular complications include infections, skin changes, cheiroarthropathy, hearing loss, and increased risk of fractures, dementia, and impaired cognitive function. ■ ■GLYCEMIC CONTROL AND COMPLICATIONS The microvascular complications of both type 1 and type 2 DM result from chronic hyperglycemia (Fig. 417-1). Evidence implicating a causative role for chronic hyperglycemia in the development of mac­ rovascular complications is less conclusive with other factors such as dyslipidemia and hypertension playing more important roles. ASCVD events and mortality rate are two to four times greater in patients with type 2 DM, correlate with fasting and postprandial plasma glucose lev­ els as well as the hemoglobin A1c (HbA1c), and can be reduced by inten­ sive diabetes management as demonstrated in patients with type 1 DM. The Diabetes Control and Complications Trial (DCCT) provided definitive proof that reduction in chronic hyperglycemia can prevent many complications of type 1 DM (Fig. 417-1). This large multicenter clinical trial randomized >1400 individuals with type 1 DM to either intensive or conventional diabetes management and prospectively

Mean HbA1c = 11% 10% 9% Retinopathy progression, rate

8%

7%

Length of follow-up, years

FIGURE 417-1  Relationship of glycemic control and diabetes duration to diabetic retinopathy. The progression of retinopathy in individuals in the Diabetes Control and Complications Trial is graphed as a function of the length of follow-up with different curves for different hemoglobin A1c (HbA1c) values. (Reproduced with permission from The relationship of glycemic exposure (HbA1c) to the risk of development and progression of retinopathy in the diabetes control and complications trial. Diabetes 44:968, 1995.) evaluated the development of diabetes-related complications during a mean follow-up of 6.5 years. Individuals in the intensive diabetes management group received insulin by multiple daily injections or pump delivery along with extensive educational, psychological, and medical support, and achieved a substantially lower HbA1c (7.3%) than individuals in the conventional diabetes management group (9.1%). After the DCCT results were reported in 1993, all study par­ ticipants were offered intensive therapy and continue to be followed in the Epidemiology of Diabetes Intervention and Complications (EDIC) trial, which has completed >40 years of follow-up (DCCT + EDIC). When the DCCT phase ended at 6.5 years of follow-up, the initial separation in glycemic control disappeared with both arms maintaining a mean HbA1c of 8.0%, allowing assessment of the legacy effect of 6.5 years of near-normoglycemia on the development of longterm complications. The DCCT phase demonstrated that improvement of glycemic control reduced nonproliferative and proliferative retinopathy (47% reduction), albuminuria (39% reduction), clinical nephropathy (54% reduction), and neuropathy (60% reduction). Improved glycemic control also slowed the progression of early diabetic complications. During the DCCT phase, weight gain (4.6 kg) and severe hypoglyce­ mia (requiring assistance of another person to treat) were more com­ mon in the intensive therapy group. The benefits of an improvement in glycemic control occurred over the entire range of elevated HbA1c values (Fig. 417-1). The results of the DCCT predicted that individuals in the intensive diabetes management group would gain 7.7 additional years of vision, 5.8 additional years free from end-stage renal disease, and 5.6 years free from lower extremity amputations. If all complica­ tions of DM were combined, individuals in the intensive diabetes management group would experience >15.3 more years of life without significant microvascular complications of DM, compared to individu­ als who received standard therapy. This translates into an additional 5.1 years of life expectancy for individuals in the intensive diabetes management group. The 30-year follow-up data in the intensively treated group show a continued reduction in retinopathy, nephropathy, and cardiovascular disease. For example, individuals in the intensive therapy group had a 57% reduction in cardiovascular events (nonfatal myocardial infarction [MI], stroke, or death from a cardiovascular event) and a 33% reduction in the mortality rate, even though their subsequent glycemic control was the same as those in the conventional diabetes management group after the DCCT phase ended (year 6.5). During the EDIC phase, fewer in the intensely treated cohort became blind, lost a limb to amputation, or required dialysis. Other complica­ tions of diabetes, including autonomic neuropathy, bladder and sexual dysfunction, cardiac autonomic neuropathy, cheiroarthropathy and hearing loss, were reduced in the intensive therapy group. These results are even more impressive when one considers that initial DCCT results were reported in 1993 and diabetes therapy during the trial was quite

different in terms of insulin formulations and delivery systems. Fin­ gerstick blood glucose meters were used for glucose monitoring as this was prior to the advent of continuous glucose monitoring. The United Kingdom Prospective Diabetes Study (UKPDS) studied the course of >5000 individuals with type 2 DM for >10 years. This study used multiple treatment regimens and monitored the effect of intensive glycemic control and risk factor treatment on the develop­ ment of diabetes-related complications. Newly diagnosed individuals with type 2 DM were randomized to (1) intensive management using various combinations of insulin, a sulfonylurea, or metformin or (2) conventional therapy using dietary modification and pharmacotherapy with the goal of symptom prevention. In addition, individuals were randomly assigned to different antihypertensive regimens. Individuals in the intensive treatment arm achieved an HbA1c of 7% compared to 7.9% in the standard treatment group. The UKPDS demonstrated that each percentage point reduction in HbA1c was associated with a 35% reduction in microvascular complications. As in the DCCT, there was a continuous relationship between glycemic control and development of complications. Improved glycemic control also reduced the cardio­ vascular event rate in the follow-up period of >10 years. One of the major findings of the UKPDS was that strict blood pressure control significantly reduced both macro- and microvascular complications. In fact, the beneficial effects of blood pressure control were greater than the beneficial effects of glycemic control. Lowering blood pressure to moderate goals (144/82 mmHg) reduced the risk of DM-related death, stroke, microvascular endpoints, retinopathy, and heart failure (risk reductions between 32 and 56%). The American Diabetes Association (ADA) recommends blood pressure control <130/80 mmHg. In the UKPDS, improved glycemic control early in the course of diabetes with a sulfonylurea or insulin, or with metformin, subsequently reduced risk of death and MI. Other trials such as the Action to Control Cardiovascular Risk in Diabetes (ACCORD) and Action in Diabetes and Vascular Disease: Preterax and Diamicron MR Controlled Evaluation (ADVANCE) trials also found that improved glycemic control reduced microvascular complications. Thus, large clinical trials in type 1 and type 2 DM indicate that chronic hyperglycemia plays a causative role in the pathogenesis of diabetic micro- and macrovascular complications. In both the DCCT and the UKPDS, cardiovascular events were reduced at follow-up of

10 years, even though the improved glycemic control was not main­ tained. This legacy effect for a positive impact of a period of improved glycemic control on later diabetes complications has been termed metabolic memory, and this legacy effect was estimated to be 10 years or more. Of note, despite long-standing DM, some individuals never develop retinopathy or nephropathy, suggesting a genetic susceptibility for developing particular complications. ■ ■MECHANISMS OF COMPLICATIONS Chronic hyperglycemia is the important etiologic factor leading to complications of DM, but the mechanism(s) by which it leads to such diverse cellular and organ dysfunction is unknown. The complications are likely multifactorial with an emerging hypothesis that hypergly­ cemia leads to epigenetic changes (Chap. 479) that influence gene expression in affected cells. Chronic hyperglycemia leads to formation of advanced glycosylation end products (AGEs; e.g., pentosidine, glu­ cosepane, and carboxymethyllysine), which bind to specific cell surface receptor and/or the nonenzymatic glycosylation of intra- and extracel­ lular proteins, leading to cross-linking of proteins, glomerular dysfunc­ tion, endothelial dysfunction, altered extracellular matrix composition, and accelerated atherosclerosis. Growth factors may play an important role in some diabetesrelated microvascular complications. For example, vascular endothelial growth factor A (VEGF-A) is increased locally in diabetic prolifera­ tive retinopathy, decreases after laser photocoagulation, and is the target inhibited by intravitreous injection therapy. A possible unifying mechanism is that hyperglycemia leads to increased production of reactive oxygen species or superoxide in the mitochondria and this may activate several pathways. Although hyperglycemia serves as the initial trigger for complications of diabetes, it is still unknown whether

the same pathophysiologic processes are operative in all complications or whether some pathways predominate in certain organs.

The mechanisms of diabetes-related macrovascular complications including MI and stroke also include traditional cardiovascular risk factors (dyslipidemia, hypertension), insulin resistance, and inflamma­ tion. In T2DM, insulin resistance is present years prior to diagnosis and is associated with obesity and ectopic accumulation of lipids and fat in liver and muscle. Additionally, insulin fails to appropriately suppress lipolysis from adipose tissue, which results in increased delivery of fatty acids to liver, muscle, endothelial cells, and cardiac tissues, leading to tissue accumulation of triglycerides, diacylglycerol, and ceramides. Diabetes Mellitus: Complications CHAPTER 417 ■ ■OPHTHALMOLOGIC COMPLICATIONS OF DIABETES MELLITUS DM is the leading cause of new cases of blindness between the ages of 20 and 74 in the United States. Glaucoma and cataracts occur earlier and more frequently in individuals with diabetes. Severe vision loss is primarily the result of progressive diabetic retinopathy, which leads to significant macular edema and new blood vessel formation. Diabetic retinopathy is classified into two stages: nonproliferative and prolifera­ tive. Nonproliferative diabetic retinopathy usually appears late in the first decade or early in the second decade of hyperglycemia and is marked by retinal vascular microaneurysms, blot hemorrhages, and cotton-wool spots (Fig. 417-2). Mild nonproliferative retinopathy may progress to more extensive disease, characterized by changes in venous vessel caliber, intraretinal microvascular abnormalities, and more numerous microan­ eurysms and hemorrhages. The pathophysiologic mechanisms invoked in nonproliferative retinopathy include loss of retinal pericytes, increased retinal vascular permeability, alterations in retinal blood flow, and abnor­ mal retinal microvasculature, all of which can lead to retinal ischemia. The appearance of neovascularization in response to retinal hypox­ emia is the hallmark of proliferative diabetic retinopathy (Fig. 417-2). These newly formed vessels appear near the optic nerve and/or macula and rupture easily, leading to vitreous hemorrhage, fibrosis, and ulti­ mately retinal detachment. Not all individuals with nonproliferative ret­ inopathy go on to develop proliferative retinopathy, but the more severe the nonproliferative disease, the greater is the chance of evolution to proliferative retinopathy within 5 years. This creates an important opportunity for early detection and treatment of diabetic retinopathy. Clinically significant macular edema can occur in the context of non­ proliferative or proliferative retinopathy. Fluorescein angiography and optical coherence tomography are useful to detect macular edema, which is associated with an increased chance of moderate visual loss over the next 3 years. Duration of DM and degree of glycemic control are the best predictors of the development of retinopathy; hypertension, nephropathy, and dyslipidemia are also risk factors. Although there is genetic susceptibility for retinopathy, it confers less influence than either the duration of DM or the degree of glycemic control. FIGURE 417-2  Diabetic retinopathy results in scattered hemorrhages, yellow exudates, and neovascularization. This patient has neovascular vessels proliferating from the optic disc, requiring urgent panretinal laser photocoagulation.

TREATMENT Diabetic Retinopathy The most effective therapy for diabetic retinopathy is preven­ tion. Intensive glycemic and blood pressure control will delay the development and slow the progression of retinopathy in individu­ als with either type 1 or type 2 DM. Paradoxically, during the first 6–12 months of improved glycemic control, established diabetic retinopathy may transiently worsen. Fortunately, this progression is temporary, and in the long term, improved glycemic control is associated with less diabetic retinopathy. When associated with a marked glycemic improvement, glucagon-like peptide 1 (GLP-1) receptor agonists have been associated with an increased risk of worsening diabetic retinopathy; this should be considered when choosing agents to improve in glycemic control. Individuals with retinopathy may be candidates for prophylactic laser photocoagula­ tion when initiating intensive therapy, and especially prior to pan­ creas or islet transplantation that can rapidly normalize glycemia. Women with type 1 or type 2 DM who are planning pregnancy should be screened prior to and during pregnancy. Once advanced retinopathy is present, improved glycemic control imparts less ben­ efit. Appropriate ophthalmologic care can prevent most blindness. Lowering elevated levels of triglycerides with fenofibrate may also reduce the progression of retinopathy. PART 12 Endocrinology and Metabolism Regular, comprehensive eye examinations are essential for all individuals with DM (see Table 416-1). Most diabetic eye disease can be successfully treated if detected early. Routine, nondilated eye examinations by the primary care provider or diabetes specialist are inadequate to detect diabetic eye disease, which requires a dilated eye exam performed by an optometrist or ophthalmologist or by retinal photography with remote reading. Subsequent management should be by a retinal specialist. Treatment of severe nonprolifera­ tive or proliferative retinopathy or macular edema with panretinal laser photocoagulation therapy and/or anti-VEGF therapy (intra­ vitreous injection) usually is successful in preserving vision. Aspirin therapy does not appear to influence the natural history of diabetic retinopathy, and antiplatelet agents and anticoagulation may be continued in patients receiving intravitreal injections of anti-VEGF agents. Patients with severe proliferative retinopathy with vitreous hemorrhage and/or traction involving the macula often require surgical vitrectomy. ■ ■RENAL COMPLICATIONS OF DIABETES MELLITUS Diabetic nephropathy is the leading cause of chronic kidney dis­ ease (CKD) and stage 5 CKD (e.g., end-stage renal disease; see Chap. 322) requiring renal replacement therapy. CKD in individuals with DM is associated with an increased risk of cardiovascular disease, and the prognosis of individuals with diabetes on dialysis is poor. Individuals with type 1 DM and diabetic nephropathy commonly also have diabetic retinopathy; this association is less pronounced in type 2 DM. The presence of CKD without retinopathy in type 1 DM should prompt investigation for alternative causes of kidney disease. Approximately 20–40% of patients with diabetes develop diabetic nephropathy. Known risk factors include a family history of diabetic nephropathy with additional genetic or environmental susceptibility factors likely contributing. Smoking accelerates the decline in renal Time from onset of diabetes, years

GFR, mL/min

<10 FIGURE 417-3  Time course of development of diabetic nephropathy. The relationship of time from onset of diabetes, albuminuria (urinary albumin-to-creatinine ratio [UACR]), and the glomerular filtration rate (GFR) are shown. This figure is typical for type 1 diabetes; individuals with type 2 diabetes may present with a lower GFR at the time of diagnosis.

function. Diabetic nephropathy and stage 5 CKD (e.g., end-stage renal disease; see Chap. 322) secondary to DM develop more commonly in Black, Native American, and Hispanic individuals. Like other microvascular complications, the pathogenesis of diabetic nephropathy is related to chronic hyperglycemia. The mechanisms by which chronic hyperglycemia leads to diabetic nephropathy are incom­ pletely defined but involve the effects of soluble factors (growth factors, angiotensin II, endothelin, AGEs), epigenetic changes, hemodynamic alterations in the renal microcirculation (glomerular hyperfiltration or hyperperfusion, increased glomerular capillary pressure), structural changes in the glomerulus (increased extracellular matrix, basement membrane thickening, mesangial expansion, fibrosis), and tubular dysfunction (tubulointerstitial damage, fibrosis). See Chap. 322 for additional discussion. The natural history of diabetic nephropathy is characterized by a sequence of events that was initially defined for individuals with type 1 DM but appears similar in type 2 DM (Fig. 417-3). Glomerular hyper­ perfusion and renal hypertrophy occur in the first years after the onset of DM and are associated with an increase of the estimated glomerular filtration rate (GFR). During the first 5 years of DM, thickening of the glomerular basement membrane, glomerular hypertrophy, and mesan­ gial volume expansion occur as the GFR returns to normal. Once there is marked albuminuria and a reduction in GFR, these pathologic changes are likely irreversible. As part of comprehensive diabetes care (Chap. 416), diabetic nephropathy should be detected at an early stage when effective thera­ pies can be instituted. Because some individuals with DM may have a decline in GFR in the absence of albuminuria, assessment should include both urinary albumin-to-creatinine ratio (UACR) on a spot specimen and an estimated GFR (eGFR). The urine protein measure­ ment by routine urinalysis does not detect low levels of albumin excre­ tion. Screening for albuminuria should commence 5 years after type 1 DM onset and at the time of diagnosis of type 2 DM and be performed annually. An elevated UACR should be confirmed on two to three occasions over a 3- to 6-month period since it can be falsely elevated by strenuous exercise at a time close to its measurement, infection, fever, congestive heart failure, marked hyperglycemia, marked hypertension, or prostate disease. The ADA defines albuminuria as a persistently increased UACR

30 mg/g. Albuminuria should be quantified, with a moderate increase defined as 30–299 mg/g creatinine and severely elevated as >300 mg/g creatinine. The UACR is a continuous variable, but the greater the degree of albuminuria the more likely there is a reduced GFR. Eleva­ tions in the UACR are associated with an increased risk of cardiovas­ cular disease. Once increased, the UACR should be measured more frequently (2–4 times/year). Type IV renal tubular acidosis (hyporeninemic hypoaldosteronism) may occur in type 1 or 2 DM. These individuals develop a propensity to hyperkalemia and acidemia, which may be exacerbated by medications (especially angiotensin-converting enzyme [ACE] inhibitors, angioten­ sin receptor blockers [ARBs], and mineralocorticoid receptor antago­ nists). Patients with DM are predisposed to radiocontrast-induced nephrotoxicity. Risk factors for radiocontrast-induced nephrotoxicity are preexisting nephropathy and volume depletion. Individuals with DM undergoing radiographic procedures with iodinated contrast dye should be well hydrated before and after dye exposure, and the serum creatinine should be monitored for 24–48 h following the procedure.

Albuminuria

Metformin should be held until postintervention confirmation of pre­ served kidney function. TREATMENT Diabetic Nephropathy The optimal therapy for diabetic nephropathy is prevention by con­ trol of glycemia and blood pressure (blood pressure <130/80 mmHg) (Chap. 416 outlines glycemic goals and approaches). Renin-angio­ tensin-aldosterone system inhibitors do not prevent the develop­ ment of diabetic kidney disease if hypertension or albuminuria is not present. Interventions effective in slowing progression of albumin­ uria and the decline in kidney function include (1) improved glyce­ mic control, (2) strict blood pressure control, (3) administration of an ACE inhibitor or ARB, (4) in individuals with type 2 DM, admin­ istration of a sodium-glucose cotransporter 2 (SGLT-2) inhibitor and (5) administration of a mineralocorticoid receptor antagonist (especially finerenone). Dyslipidemia should also be treated. Improved glycemic control reduces the rate at which albumin­ uria appears and progresses in type 1 and type 2 DM. However, once there is a moderate level of albuminuria, it becomes more difficult for improved glycemic control to slow progression of renal disease, although 10 years of normoglycemia resulting from pancreas transplantation may lead to regression of mesangial glo­ merular lesions (Fig. 417-4). During the late phase of declining renal function, insulin requirements may fall as the kidney is a site of insulin degradation. As the GFR decreases with progressive nephropathy, the use and dose of glucose-lowering agents should be reevaluated (see Table 416-6). Some glucose-lowering medications (sulfonylureas and metformin) are contraindicated in advanced renal insufficiency, while others may require dose adjustment (glinides and DPP-4 inhibitors). SGLT2 inhibitors are not effective with eGFR < 20 mL/min/1.73 m2. FIGURE 417-4  Diabetic glomerular changes in a patient with type 1 diabetes are reversed by 10 years of normoglycemia as a result of pancreas transplantation. Left panel shows diabetic glomerulosclerosis (arrow) and arteriolar hyalinosis (arrowhead) on kidney biopsy. Right panel shows a near-normal glomerulus in the same patient after 10 years of normoglycemia from pancreas transplantation. (Reproduced with permission from P Fioretto et al: Reversal of lesions of diabetic nephropathy after pancreas transplantation. N Engl J Med 339:69, 1998.)

HYPERTENSION Many individuals with type 1 or type 2 DM develop hyperten­ sion. Hypertension accelerates complications of DM, particularly ASCVD, nephropathy, and retinopathy. Blood pressure should be measured at every clinic visit; individuals should also be encour­ aged to monitor their blood pressure at home. The blood pressure goal should be <130/80 mmHg in individuals with diabetes and possibly lower in individuals at increased risk for ASCVD or CKD progression. Because of the high prevalence of ASCVD disease in individuals with type 2 DM, the possibility of renovascular hyper­ tension should be considered when the blood pressure is not readily controlled.

Diabetes Mellitus: Complications CHAPTER 417 In addition to medications, therapy should include lifestyle modifications, including weight loss, exercise, stress management, sodium restriction, Dietary Approaches to Stop Hypertension (DASH)–style eating, and smoking cessation. In younger individu­ als or those with increased cardiovascular risk, the provider may recommend a lower target blood pressure. If the blood pressure is

150/90 mmHg, initial treatment should consist of two antihyper­ tensive medications. Multiple agents are often required to control blood pressure. In pregnant individuals with diabetes and chronic hypertension, blood pressure control is associated with better preg­ nancy outcomes. In the absence of kidney disease, ACE inhibitors or ARBs are effective antihypertensives but are no more effective than other antihypertensive classes such as thiazide-like diuretics and dihydro­ pyridine calcium channel blockers. There is no benefit of interven­ tion prior to onset of albuminuria or using a combination of an ACE inhibitor and an ARB. If use of either ACE inhibitors or ARBs is not possible or the blood pressure is not controlled, then diuretics, cal­ cium channel blockers (nondihydropyridine class), or beta blockers (with caution in individuals at increased risk for experiencing hypo­ glycemia) may be used. Mineralocorticoid receptor antagonists can

help reduce blood pressure and albuminuria in refractory cases but require close monitoring of the serum potassium. ALBUMINURIA OR CKD Either ACE inhibitors or ARBs should be used to reduce albu­ minuria and slow the decline in GFR in individuals with type 1 or type 2 DM. Most experts consider the two classes of drugs to be equivalent in patients with diabetes. ARBs can be used as an alter­ native in patients who develop ACE inhibitor–associated cough or angioedema. After initiation of therapy, one should increase to the maximum tolerated dose while monitoring the serum creatinine and potassium and repeating the UACR one to four times per year. A rise in the serum creatinine up to 30% is acceptable. A goal for individuals with a UACR >300 mg/g creatinine is to reduce the UACR by 30%.

PART 12 Endocrinology and Metabolism To reduce CKD progression and cardiovascular events in indi­ viduals with CKD, type 2 DM, and an eGFR >20 mL/min per 1.73 m2, the addition of an SGLT-2 inhibitor, while continuing an ACE inhibitor or ARB, is recommended with any level of albu­ minuria. A GLP-1 agonist or a nonsteroidal mineralocorticoid receptor antagonist like finerenone will also reduce cardiovascular risk in individuals with type 2 DM and CKD. The GLP-1 recep­ tor agonist semaglutide improves kidney outcomes and reduces death from cardiovascular causes in type 2 DM and CKD. SGLT-2 inhibitors are also discussed in Chap. 265, especially the use in heart failure treatment or prevention, and in Chap. 322, as related to CKD. Because of the elevated risk of euglycemic diabetic keto­ acidosis, SGLT-2 inhibitors in individuals with type 1 DM and insulin-deficient type 2 DM should be used with caution and include patient education about ketone monitoring and recogniz­ ing diabetic ketoacidosis. Nephrology consultation is indicated when the estimated GFR is <30 mL/min per 1.743 m2, albuminuria is >300 mg/g creatinine, or if there are atypical features such as hematuria or rapidly declining renal function. The ADA suggests a protein intake of 0.8 g/kg of body weight per day in individuals with diabetic kidney disease. Complications of ASCVD are the leading cause of death in diabetic individuals with nephropathy; hyperlipidemia should be treated aggressively. Preemptive (before dialysis) kidney transplantation from a living donor should be considered in those nearing stage 5 CKD (e.g., end-stage renal disease; see Chap. 333) and for those with type 1 DM or insulin deficient type 2 DM, simultaneous pancreas-kidney transplantation from a deceased donor may be an option. As compared with nondiabetic individuals, hemodialysis in patients with DM is associated with more frequent complications, such as hypotension (due to autonomic neuropathy or loss of reflex tachycardia), more difficult vascular access, accelerated progres­ sion of retinopathy, and greater mortality. ■ ■NEUROPATHY AND DIABETES MELLITUS Diabetic neuropathy, which occurs in ~50% of individuals with longstanding type 1 and type 2 DM, manifests as a diffuse neuropathy (distal symmetrical polyneuropathy and/or autonomic neuropathy), a mononeuropathy, and/or a radiculopathy/polyradiculopathy. As with other complications of DM, the development of neuropathy correlates with the duration of diabetes and glycemic control. Additional risk factors are body mass index (BMI) (the greater the BMI, the greater the risk of neuropathy) and smoking. The presence of ASCVD, ele­ vated triglycerides, and hypertension is also associated with diabetic peripheral neuropathy. Both myelinated and unmyelinated nerve fibers are lost. Because the clinical features of diabetic neuropathy are similar to those of other neuropathies, the diagnosis of diabetic neuropathy should be made only after other possible etiologies are excluded (Chap. 457). Distal Symmetric Polyneuropathy (DSPN)  DSPN, the most common form of diabetic neuropathy, most frequently presents with distal sensory loss and pain, but up to 50% of patients do not have symptoms of neuropathy. Symptoms may include a sensation

of numbness, tingling, sharpness, or burning that begins in the feet and spreads proximally. Hyperesthesia, paresthesia, and dysesthe­ sia also may occur. Pain typically involves the lower extremities, is usually present at rest, and worsens at night. Both an acute (lasting <12 months) and a chronic form of painful diabetic neuropathy may occur. The acute form is sometimes treatment-related, occurring in the context of improved glycemic control. As diabetic neuropathy progresses, the pain subsides and eventually disappears, but a sensory deficit persists, and motor defects may develop. Physical examination (Chap. 415) often reveals sensory loss (to 10-g monofilament and/ or vibration), loss of ankle deep-tendon reflexes, abnormal position sense, and muscular atrophy or foot drop. Annual screening for DSPN should begin 5 years after diagnosis of type 1 DM and at the time of diagnosis of type 2 DM and is aimed at detecting loss of protective sensation (LOPS). LOPS and DSPN are major risk factors for foot ulceration and falls due to small and large nerve fiber dysfunction and predispose to lower extremity amputation. Autonomic Neuropathy  Individuals with long-standing type 1 or 2 DM may develop signs of autonomic dysfunction involving the parasympathetic (cholinergic) and sympathetic (adrenergic) systems. DM-related autonomic neuropathy can affect multiple organ systems, including the cardiovascular, gastrointestinal (GI), genitourinary, sudomotor, and metabolic systems. Cardiovascular autonomic neurop­ athy, reflected by decreased heart rate variability, resting tachycardia, and orthostatic hypotension, is associated with an increase in ASCVD. Orthostatic hypotension, a late and unusual complication of diabetes, is sometimes seen in patients with associated DSPN and severe para­ sympathetic dysfunction. Reports of sudden death in DM have also been attributed to autonomic neuropathy affecting the cardiovascular system and predisposing to severe hypoglycemia, both of which may prolong the QTc interval. Autonomic neuropathy may reduce counter­ regulatory hormone release (especially epinephrine), and contribute to an inability to sense hypoglycemia appropriately (hypoglycemia unawareness) (Chap. 418) that increases the risk of severe hypogly­ cemia. Gastroparesis and bladder-emptying abnormalities are often caused by the autonomic neuropathy seen in DM (discussed below). Hyperhidrosis of the upper extremities and anhidrosis of the lower extremities result from sympathetic nervous system dysfunction. Anhidrosis of the feet can promote dry skin with cracking, which increases the risk of foot ulceration. Mononeuropathy and/or Radiculopathy/Polyradiculopathy 

Mononeuropathy (dysfunction of isolated cranial or peripheral nerves) is less common than polyneuropathy in DM and presents with pain and motor weakness in the distribution of a single nerve. Mononeuropathies can occur at entrapment sites such as carpal tunnel or be noncompressive. Involvement of the third cranial nerve is most common and is heralded by diplopia. Physical examination reveals ptosis and ophthalmoplegia with normal pupillary constriction to light. Sometimes other cranial nerves, such as IV, VI, or VII (Bell’s palsy), are affected. Peripheral mononeuropathies or simultaneous involve­ ment of more than one nerve (mononeuropathy multiplex) may also occur. Diabetic radiculopathy or polyradiculopathy is a syndrome characterized by severe disabling pain in the distribution of one or more nerve roots. It may be accompanied by motor weakness. Inter­ costal or truncal radiculopathy causes pain over the thorax or abdo­ men. Involvement of the lumbar plexus or femoral nerve may cause severe pain in the thigh or hip and may be associated with muscle weakness in the hip flexors or extensors (diabetic amyotrophy). Fortunately, diabetic polyradiculopathies are usually self-limited and resolve over 6–12 months. TREATMENT Diabetic Neuropathy Prevention of diabetic neuropathy is critical through improved glycemic control. Treatment of diabetic neuropathy is less than sat­ isfactory. Lifestyle modifications (exercise, diet) have some efficacy

in DSPN in type 2 DM and hypertension and hypertriglyceri­ demia should be treated. Efforts to improve glycemic control in long-standing diabetes may be limited by hypoglycemia unaware­ ness. Patients should avoid neurotoxins (including alcohol) and smoking and consider supplementation with vitamins for pos­ sible deficiencies (B12, folate; Chap. 344). Metformin may reduce intestinal absorption of vitamin B12 in type 2 DM, and pernicious anemia is more common in type 1 DM where it is associated with anti–parietal cell autoantibodies and may require sublingual or parenteral B12 replacement. Patients should be educated that loss of sensation in the foot increases the risk for ulceration and its sequelae and that prevention of such problems is paramount. Patients with symptoms or signs of neuropathy or LOPS should check their feet daily and take precautions (footwear) aimed at preventing calluses or ulcerations. If foot deformities are present, a podiatrist should be involved. Chronic, painful diabetic neuropathy is difficult to treat with only symptomatic treatment being available; evidence of the effectiveness of improved glycemic control in painful diabetic neuropathy is lacking. Sleep and mood disorders frequently accom­ pany DPSN and should be treated. Symptomatic treatment of the pain using gabapentinoids (pregabalin, gabapentin), serotoninnorepinephrine reuptake inhibitors (duloxetine, venlafaxine, and desvenlafaxine), sodium channel blockers, tricyclic antidepressants, and a capsaicin patch have some efficacy for pain related to DPSN. Tapentadol, a centrally acting opioid, is also approved by the U.S. Food and Drug Administration (FDA) but has only modest efficacy and poses addiction risk, making it and other opioids less desirable and not first-line therapy. No direct comparisons of agents are avail­ able, and it is reasonable to switch agents if there is no response or if side effects develop. Referral to a pain management center may be necessary. Therapy of orthostatic hypotension secondary to autonomic neuropathy is also difficult. Nonpharmacologic maneuvers (ade­ quate salt intake, avoidance of dehydration and diuretics, lower extremity support hose, and physical activity) may offer some ben­ efit. A variety of agents have limited success (midodrine and droxi­ dopa are approved by the FDA for orthostatic hypotension of any etiology). Patients with resting tachycardia may be considered for beta blocker therapy with caution exercised if there is hypoglycemia unawareness. Patients with type 1 DM and orthostatic hypotension should be evaluated for primary adrenal insufficiency (Addison’s disease) that may be associated with an autoimmune polyendocrine syndrome (Chap. 401). ■ ■GASTROINTESTINAL/GENITOURINARY DYSFUNCTION Long-standing type 1 and 2 DM may affect the motility and function of the GI and genitourinary systems. The most prominent GI symp­ toms are delayed gastric emptying (gastroparesis) and altered small- and large-bowel motility (constipation or diarrhea). Gastroparesis may present with symptoms of anorexia, nausea, vomiting, early satiety, and abdominal bloating. Microvascular complications (retinopathy and neuropathy) are usually present. Nuclear medicine scintigraphy after ingestion of a radiolabeled meal or digestible solids may docu­ ment delayed gastric emptying but may not correlate well with the patient’s symptoms. Although parasympathetic dysfunction secondary to chronic hyperglycemia is important in the development of gastro­ paresis, hyperglycemia itself also impairs gastric emptying. Nocturnal diarrhea, alternating with constipation, may be a feature of DM-related GI autonomic neuropathy. In type 1 DM, these symptoms should also prompt evaluation for celiac disease that is associated with anti-tissue transglutaminase autoantibodies because of its increased frequency. Diabetic autonomic neuropathy may lead to genitourinary dysfunc­ tion, including cystopathy and female sexual dysfunction (reduced sexual desire, dyspareunia, reduced vaginal lubrication). Symptoms of diabetic cystopathy begin with an inability to sense a full bladder and a failure to void completely. As bladder contractility worsens, bladder

capacity and the postvoid residual increase, leading to symptoms of urinary hesitancy, decreased voiding frequency, incontinence, and recurrent urinary tract infections.

Erectile dysfunction and retrograde ejaculation are very common in DM and may be one of the earliest signs of diabetic neuropathy (Chap. 409). Erectile dysfunction, which increases in frequency with the age of the patient and the duration of diabetes, may occur in the absence of other signs of diabetic autonomic neuropathy. TREATMENT Gastrointestinal/Genitourinary Dysfunction Diabetes Mellitus: Complications CHAPTER 417 Current treatments for these complications of DM are inadequate and nonspecific. Improved glycemic control should be a goal but has not clearly shown benefit. Smaller, more frequent meals that are easier to digest (liquid) and low in fat and fiber may minimize symptoms of gastroparesis. Medications that slow gastric empty­ ing (opioids, GLP-1 receptor agonists) should be avoided. Meto­ clopramide may be used with severe symptoms but is restricted to short-term treatment in both the United States and Europe. Symptoms of gastroesophageal reflux disease may require acidblocking therapy with a histamine-2 receptor antagonist or proton pump inhibitor. Gastric electrical stimulatory devices are available. Diabetic diarrhea in the absence of bacterial overgrowth is treated symptomatically (Chap. 336). Diabetic cystopathy should be treated with scheduled voiding or self-catheterization. Drugs that inhibit type 5 phosphodiesterase are effective for erectile dysfunction, but their efficacy in individu­ als with DM is slightly lower than in the nondiabetic population (Chap. 409). ■ ■CARDIOVASCULAR MORBIDITY AND MORTALITY ASCVD, including PAD, CHD, heart failure, and cerebrovascular disease, occurs more frequently in individuals with type 1 or type 2 DM and is the major cause of mortality for individuals with diabetes. In addition, the prognosis for individuals with diabetes who have CHD is worse than for nondiabetics. CHD is more likely to involve multiple vessels in individuals with DM. The American Heart Asso­ ciation considers DM a controllable risk factor for cardiovascular disease; in some studies, type 2 DM patients without a prior MI have a similar risk for coronary artery-related events as nondiabetic indi­ viduals who have had a prior MI. Fortunately, the outcomes related to ASCVD have improved over the last decade for those without diabetes and individuals with diabetes as a result of modification of multiple risk factors. Heart failure, which has not been recognized until recently as a dia­ betes-related complication, is twice as common in individuals with dia­ betes (type 1 or type 2). Heart failure is related to diabetes duration and hypertension and can present as heart failure with preserved ejection fraction (HFpEF), heart failure with mildly reduced ejection fraction (HFmEF), or heart failure with reduced ejection fraction (HFrEF) (see Chap 276). Some individuals with DM have reduced left ventricular function without CHD or hypertension, and this is sometimes termed “diabetic cardiomyopathy.” The pathogenesis of this and heart failure associated with DM is not clear. The prevention and management of ASCVD and heart failure in individuals with DM should focus on risk factors, including duration of diabetes, hypertension, dyslipidemia, CKD, albuminuria, obesity, and smoking. Many of these are modifiable and should prompt action by the patient and the provider. The foundation of prevention and management is the concurrent, integrated focus on four targets: gly­ cemia, blood pressure, lipids, and the incorporation of therapies with cardiovascular and kidney outcome benefits. While these results are from observations and studies in type 2 DM, these strategies are also likely relevant to type 1 DM. Cardiovascular risk assessment in type 2 DM should encompass a nuanced and individualized approach. For example, cardiovascular risk is lower and not equivalent in a younger individual with a brief

duration of type 2 DM compared to an older individual with longstanding type 2 DM. Because of the high prevalence of underlying ASCVD in individuals with diabetes (especially in type 2 DM), evi­ dence of ASCVD (e.g., cardiac stress test) should be sought in an indi­ vidual with diabetes who has symptoms, even if atypical, suggestive of cardiac ischemia or peripheral or carotid arterial disease. However, the screening of asymptomatic individuals with diabetes for CHD is not recommended or cost-effective. The absence of chest pain (“silent isch­ emia”) is common in individuals with diabetes, and a thorough cardiac evaluation should be considered prior to major surgical procedures.

TREATMENT Cardiovascular Disease PART 12 Endocrinology and Metabolism Treatment of coronary disease in individuals with DM is similar to treatment in individuals without DM (Chap. 284). Revascu­ larization procedures for CHD, including percutaneous coronary interventions (PCIs) and coronary artery bypass grafting (CABG), may be less efficacious in individuals with DM. Initial success rates of PCI in individuals with DM are similar to those in the nondia­ betic population, but higher rates of restenosis and lower long-term patency and survival rates have been reported. CABG plus optimal medical management likely has better outcomes than PCI for indi­ viduals with diabetes. Very strict glucose control has limited benefit on cardiovascular outcomes in individuals with established cardio­ vascular disease, indicating the importance of other factors such as insulin resistance, dyslipidemia, and inflammation. In individuals with type 2 DM and ASCVD, the comprehen­ sive effort to reduce cardiovascular risk (e.g., lifestyle manage­ ment, blood pressure control, lipid management) should include an SGLT-2 inhibitor or a GLP-1 receptor agonist. If diabetic CKD or heart failure is present or likely, an SGLT-2 inhibitor is preferred. In individuals with type 2 DM and ASCVD or other ASCVD risk factors, a GLP-1 receptor agonist will reduce cardiovascular events. The combination of an SGLT-2 inhibitor and a GLP-1 receptor agonist likely provides additive risk reduction. In individuals with type 2 DM and CKD with albuminuria treated with maximum ACE inhibitor or ARB, addition of either a SGLT2 inhibitor or finere­ none reduces CKD progression and improves cardiovascular out­ comes. Combining a SGLT2 inhibitor with finerenone reduces the risk of hyperkalemia. Care of individuals with type 2 DM and heart failure or cardiovascular disease should involve a cardiovascular specialist and include treatment with an ACE inhibitor or ARB and a beta blocker. If an individual is already taking metformin and has an eGFR >30 mL/min per 1.73 m2, reduced-dose metformin can be continued. Because of the elevated risk of euglycemic diabetic keto­ acidosis with SGLT-2 inhibitors, patients treated with an SGLT-2 inhibitor should be counseled about the risk and symptoms of dia­ betic ketoacidosis and educated about the importance of measuring ketones if the clinical scenario suggests this possibility. Antiplatelet therapy with aspirin (75–162 mg/d) as secondary prevention reduces cardiovascular events in individuals with DM who have ASCVD. Clopidogrel should be used in those with aspirin allergy or intolerance. The ADA recommends considering the use of aspirin for primary prevention of coronary events in individuals with diabetes with an increased cardiovascular risk (>50 years old with at least one risk factor such as hypertension, dyslipidemia, smoking, family history, or albuminuria). Aspirin is not recom­ mended for primary prevention in those with a low cardiovascular risk (<50 years old with no risk factors). Cardiovascular Risk Factors  DYSLIPIDEMIA  Individuals with DM may have several forms of dyslipidemia (Chap. 419). Because of the additive cardiovascular risk of hyperglycemia and hyperlipidemia, lipid abnormalities should be assessed and treated as part of comprehensive diabetes care (Chap. 416). The most common pattern of dyslipidemia is hypertri­ glyceridemia and reduced high-density lipoprotein (HDL) cholesterol

levels. DM itself does not increase levels of low-density lipoprotein (LDL), but the small dense LDL particles found in type 2 DM are more atherogenic because they are more easily glycated and susceptible to oxidation. Almost all treatment studies of diabetic dyslipidemia have been performed in individuals with type 2 DM because of the greater fre­ quency of dyslipidemia in this form of diabetes. Interventional studies have shown that the beneficial effects of LDL reduction with statins are similar in the diabetic and nondiabetic populations. No prospec­ tive studies have addressed similar questions in individuals with type 1 DM. Because the frequency of ASCVD is low in children and young adults with diabetes, assessment of cardiovascular risk should be incor­ porated into the guidelines discussed below. Statin usage is associated with a mild increase in the risk of developing type 2 DM. However, when appropriately indicated the cardiovascular benefits of statin use outweigh the mildly increased risk of diabetes. Based on the guidelines provided by the ADA, all individuals with diabetes should be advised about lifestyle modification, including diet, weight loss, and increased physical activity (Chap. 416). If indi­ viduals with diabetes have elevated triglyceride levels (>1.7 mmol/L [150 mg/dL]) or low HDL cholesterol (<1 mmol/L [40 mg/dL] in men and <1.3 mmol/L [50 mg/dL] in women), lifestyle modification and improved glycemic control should be further emphasized. If triglycer­ ides are >5.7 mmol/L (500 mg/dL) on a statin, icosapent or fenofibrate can be considered to reduce ASCVD risk. The addition of fenofibrate may require reduction in statin dose to minimize the risk of myopathy. In terms of pharmacologic therapy directed at LDL, the ADA rec­ ommends the following in addition to lifestyle: (1) all patients with diabetes and ASCVD should receive high-intensity statin therapy (atorvastatin 40–80 mg or rosuvastatin 20–40 mg) with a goal of >50% reduction in LDL and a cholesterol goal of <55 mg/dL. Adding ezeti­ mibe or a PCSK9 inhibitor is advised if these goals are not met; (2) in patients aged 40–75 years without ASCVD, moderate-intensity statin therapy (other statins or lower dose of atorvastatin or rosuvastatin) should be used; (3) in patients aged 40–75 years with ASCVD risk fac­ tors, use high-intensity statin therapy with a goal to reduce LDL cho­ lesterol by 50% and an LDL target of <70 mg/dL; (4) in patients aged 40–75 years with ASCVD risk factors on maximum statin therapy and a LDL ≥70 mg/dL, consider adding ezetimibe or PCSK9 inhibitor ther­ apy; (5) in patients aged >75 years on a statin, continue statin or, if not on a statin, consider starting moderate-intensity statin therapy after discussion with the patient; and (6) in patients aged 20–39 years with additional risk factors, consider moderate-intensity statin therapy. If a patient with ASCVD cannot tolerate a statin, consider PCSK9 inhibitor therapy (monoclonal antibody or inclisiran, a small interfering RNA), or bempedoic acid. Statin therapy, when combined with fibrate or nia­ cin, for reduction of LDL does not provide additional benefit. HYPERTENSION  Hypertension management is discussed above in the “Renal Complications of Diabetes Mellitus” section. ■ ■LOWER EXTREMITY COMPLICATIONS DM is the leading cause of nontraumatic lower extremity ampu­ tation in the United States. Foot ulcers and infections are also a major source of morbidity in individuals with DM. The reasons for the increased incidence of these disorders in DM involve the interaction of several pathogenic factors: neuropathy, abnormal foot biomechanics, PAD, and poor wound healing. The peripheral sen­ sory neuropathy interferes with normal protective mechanisms and allows the patient to sustain major or repeated minor trauma to the foot, often without knowledge of the injury. Disordered propriocep­ tion causes abnormal weight bearing while walking and subsequent formation of callus or ulceration. Motor and sensory neuropathy leads to abnormal foot muscle mechanics and to structural changes in the foot (hammer toe, claw toe deformity, prominent metatarsal heads, Charcot joint). Autonomic neuropathy results in anhidrosis and altered superficial blood flow in the foot, which promote dry­ ing of the skin and fissure formation. PAD and poor wound healing impede resolution of minor breaks in the skin, allowing them to enlarge and to become infected.

Some individuals with DM will develop a foot ulcer (great toe or metatarsophalangeal areas are most common), and a significant sub­ set may ultimately undergo amputation (14–24% risk with that ulcer or subsequent ulceration). Risk factors for foot ulcers or amputation include male sex, diabetes for >10 years, peripheral neuropathy, abnormal structure of foot (bony abnormalities, callus, thickened nails), PAD, smoking, history of previous ulcer or amputation, visual impairment, poor glycemic control, and diabetic nephropathy, especially dialysis. Large calluses are often precursors to or overlie ulcerations. TREATMENT Lower Extremity Complications The optimal therapy for foot ulcers and amputations is preven­ tion through identification of high-risk patients, education of the patient, and institution of measures to prevent ulceration. Highrisk patients should be identified during the routine, annual foot examination performed on all patients with DM (see “Ongoing Aspects of Comprehensive Diabetes Care” in Chap. 416). If the monofilament test or one of the other tests is abnormal, the patient is diagnosed with LOPS (Chap. 415). Providers should consider screening for asymptomatic PAD in individuals >50 years of age who have diabetes and other risk factors using ankle-brachial index testing (Chap. 292). Patient education should emphasize (1) careful selection of footwear, (2) daily inspection of the feet to detect early signs of poor-fitting footwear or minor trauma, (3) daily foot hygiene to keep the skin clean and moist, (4) avoid­ ance of self-treatment of foot abnormalities and high-risk behavior (e.g., walking barefoot), and (5) prompt consultation with a health care provider if an abnormality arises. Involvement of a podiatrist is recommended for high-risk individuals (history of foot ulcers or amputation, those on dialysis, those with PAD, and those with foot deformities). Calluses and nail deformities should be treated by a podiatrist. Interventions directed at risk factor modification include orthotic shoes and devices, callus management, nail care, and prophylactic measures to reduce increased skin pressure from abnormal bony architecture. Attention to other risk factors for vas­ cular disease (smoking, dyslipidemia, hypertension) and improved glycemic control are also important, especially LDL management as described above. Despite preventive measures, foot ulceration and infection are common and represent a serious problem. Due to the multifacto­ rial pathogenesis of lower extremity ulcers, management of these lesions is multidisciplinary and often demands expertise in ortho­ pedics, vascular surgery, endocrinology, podiatry, and infectious diseases. The plantar surface of the foot is the most common site of ulceration. Ulcers may be primarily neuropathic (no accompany­ ing infection) or may have surrounding cellulitis or osteomyelitis. Cellulitis without ulceration should be treated with antibiotics that provide appropriate empiric coverage (see below). An infected ulcer is a clinical diagnosis, because superficial culture of any ulceration will likely find multiple bacterial species of unknown significance. The infection surrounding the foot ulcer may be due to multiple organisms, with aerobic gram-positive cocci (staphylococci including methicillin-resistant Staphylococcus aureus [MRSA], group A and B streptococci) being most common and with aerobic gram-negative bacilli and/or obligate anaerobes as co-pathogens. Gas gangrene may develop in the absence of clostridial infection. Cultures should be obtained from the debrided ulcer base or from purulent drainage or aspiration of the wound. Wound depth should be determined by inspection and probing with a blunt-tipped sterile instrument. A wound that probes to the bone is highly likely to have underlying osteomyelitis. Plain radiographs of the foot should be performed to assess the possibility of osteomyelitis in chronic ulcers that have not responded to therapy. Magnetic resonance imaging (MRI) is the most specific modality, with nuclear medicine scans

(PET, CT/SPECT) and labeled white cell studies as an alternative. Surgical debridement is often necessary.

Osteomyelitis is best treated by a combination of prolonged anti­ biotics and debridement of infected bone when possible. The pos­ sible contribution of vascular insufficiency should be considered in all patients. Peripheral arterial bypass procedures are often effective in promoting wound healing and in decreasing the need for ampu­ tation of the ischemic limb (Chap. 292). Interventions with demonstrated efficacy in diabetic foot ulcers or wounds include the following: (1) off-loading (complete avoid­ ance of weight bearing on the ulcer, which removes the mechani­ cal trauma that retards wound healing), (2) surgical debridement of nonviable tissue, (3) physiologic, topical wound dressings, (4) revascularization, and (5) treatment of infections with appro­ priate use of antibiotics. Amputation should be limited initially. If a wound fails to show significant improvement after 4 weeks of wound management with these five recommendations, one should consider advanced wound therapy that may include topi­ cal growth factors, acellular matrix tissues, bioengineered cellular therapies, negative-pressure wound therapy, electrical stimula­ tion, pulsed radiofrequency, extracorporeal shockwave, hyperbaric oxygen therapy, and topical oxygen therapy. These modalities require interdisciplinary expertise and must be individualized to the patient and clinical setting. Antiseptic agents should be avoided. Topical antibiotics are of limited value. Referral for physi­ cal therapy, orthotic evaluation, and rehabilitation should occur once the infection is controlled. Diabetes Mellitus: Complications CHAPTER 417 Mild or non-limb-threatening infections can be treated with oral antibiotics directed predominantly at methicillin-susceptible staphy­ lococci and streptococci (e.g., dicloxacillin, early-generation cepha­ losporins, amoxicillin-clavulanate). However, in patients with a prior history of MRSA or in locations with a high prevalence of MRSA, treatment with trimethoprim-sulfamethoxazole, doxycycline, line­ zolid, or clindamycin is preferred, depending on local antibiogram data. Surgical debridement of necrotic tissue, local wound care, and avoidance of weight bearing over the ulcer are crucial. Optimization of glycemic control should be a goal. More severe infections may require IV antibiotics as well as offloading and local wound care. IV antibiotics should provide broad-spectrum coverage directed toward S. aureus, including MRSA, streptococci, gram-negative aerobes, and anaerobic bacteria. Initial empiric antimicrobial regimens may include vancomycin plus a β-lactam/β-lactamase inhibitor or car­ bapenem, or vancomycin plus a quinolone with metronidazole. In some cases, daptomycin, ceftaroline, or linezolid may be substituted for vancomycin in consultation with an infectious diseases expert. If the infection surrounding the ulcer is not improving with antibiot­ ics, reassessment of antibiotic coverage and reconsideration of the need for surgical debridement or revascularization are indicated. With clinical improvement, oral antibiotics and local wound care can be continued on an outpatient basis with close follow-up. ■ ■INFECTIONS Individuals with DM have a greater frequency and severity of infection. The reasons for this include incompletely defined abnormalities in cellmediated immunity and phagocyte function associated with hypergly­ cemia, as well as diminished vascularization. Hyperglycemia aids the colonization and growth of a variety of organisms (Candida and other fungal species). Many common infections are more frequent and severe in the diabetic population, whereas several rare infections are seen almost exclusively in the diabetic population. Examples of this latter category include rhinocerebral mucormycosis, emphysematous infections of the gallbladder and urinary tract, and “malignant” or invasive otitis externa. Invasive otitis externa is usually secondary to Pseudomonas aeruginosa infection in the soft tissue surrounding the external auditory canal, typically begins with pain and discharge, and may rapidly progress to osteomyelitis and meningitis. These infections should be considered, in particular, in patients presenting with severe hyperglycemia.

34 - 418 Hypoglycemia

418 Hypoglycemia

Pneumonia, urinary tract infections, and skin and soft tissue infec­ tions are all more common in the diabetic population. In general, the organisms that cause pulmonary infections are similar to those found in the nondiabetic population; however, gram-negative organ­ isms, S.  aureus, and Mycobacterium tuberculosis are more frequent pathogens. Adults with DM should receive vaccination against pneu­ mococcus, respiratory syncytial virus, annually against influenza, and the coronavirus SARS-CoV-2, which causes increased morbidity and mortality in obese individuals and patients with DM (Chap. 204). In addition to early antibiotic therapy for presumed bacterial infections, patients with DM should be considered for early intervention with antiviral agents (e.g., against influenza in flu, varicella-zoster virus in shingles) or SARS-CoV-2 in COVID. Urinary tract infections (either lower tract or pyelonephritis) are the result of common bacterial agents such as Escherichia coli, although several yeast species (e.g., Candida albicans and C. glabrata) are sometimes observed. Complications of urinary tract infections include emphysematous pyelonephritis and emphysematous cystitis. Bacteriuria occurs frequently in individuals with diabetic cystopathy and does not require antibiotic therapy except in specific circumstances such as pregnancy or a planned urologic pro­ cedure. Susceptibility to furunculosis, superficial candidal infections, and vulvovaginitis are increased. Poor glycemic control is a common denominator in individuals with these infections. Individuals with diabetes have an increased rate of colonization of S. aureus in the skinfolds and nares. Individuals with diabetes also have a greater risk of postoperative wound infections that may be mitigated by periopera­ tive protocols for insulin administration to maintain glycemic control.

PART 12 Endocrinology and Metabolism ■ ■DERMATOLOGIC MANIFESTATIONS The most common skin manifestations of DM are xerosis and pruritus and are usually relieved by skin moisturizers. Protracted wound heal­ ing and skin ulcerations are also frequent complications. Diabetic der­ mopathy, sometimes termed pigmented pretibial papules, or “diabetic skin spots,” begins as an erythematous macule or papule that evolves into an area of circular hyperpigmentation. These lesions result from minor mechanical trauma in the pretibial region and are more com­ mon in elderly men with DM. Bullous diseases, such as bullosa dia­ beticorum (shallow ulcerations or erosions in the pretibial region), are also seen. Necrobiosis lipoidica diabeticorum is an uncommon disorder, accompanying diabetes in predominantly young women. This usually begins in the pretibial region as an erythematous plaque or papules that gradually enlarge, darken, and develop irregular margins, with atrophic centers and central ulceration. They are often painful. Vitiligo and alopecia areata occur at increased frequency in individuals with type 1 DM. Acanthosis nigricans (hyperpigmented velvety plaques seen on the neck, axilla, or extensor surfaces) is sometimes a feature of severe insulin resistance and accompanying diabetes. Generalized or local­ ized granuloma annulare (erythematous plaques on the extremities or trunk), lichen planus (violaceous papules on the cutaneous surface with or without erosions in the mouth and genitalia), and scleredema (areas of skin thickening on the back or neck at the site of previous superficial infections) are more common in the diabetic population. Lipoatrophy and lipohypertrophy can occur at insulin injection sites but are now unusual with the use of human insulin and avoided by rotating injection sites. ■ ■FURTHER READING Abel ED et al: Diabetes mellitus-progress and opportunities in the evolving epidemic. Cell 187:3789, 2024. Adler AI et al: Post-trial monitoring of a randomised controlled trial of intensive glycaemic control in type 2 diabetes extended from 10 years to 24 years (UKPDS 91). Lancet 404:145, 2024. American Diabetes Association: Cardiovascular disease and risk management: Standards of Medical Care in Diabetes-2024. Diabetes Care 47:S179, 2024. American Diabetes Association: Chronic kidney disease and risk management: Standards of Care in Diabetes—2024. Diabetes Care 47:S219, 2024.

American Diabetes Association: Retinopathy, neuropathy, and foot care: Standards of Care in Diabetes—2024. Diabetes Care 2024; 47:S231, 2024. Drucker DJ: Diabetes, obesity, metabolism, and SARS-CoV-2 infec­ tion: The end of the beginning. Cell Metab 33:479, 2021. Mann JFE et al: Effects of semaglutide with and without concomitant SGLT2 inhibitor use in participants with type 2 diabetes and chronic kidney disease in the FLOW trial. Nat Med 30:2849, 2024. Naaman S, Bakris G: Diabetic nephropathy: Update on pillars of therapy slowing progression. Diabetes Care 46:1574, 2023. Nathan DM: Realising the long-term promise of insulin therapy: The DCCT/EDIC study. Diabetologia 64:1049, 2021. Perkovic V et al: Effects of semaglutide on chronic kidney disease in patients with type 2 diabetes. N Engl J Med. 391:109, 2024. Pop-Busui R et al: Heart failure: An underappreciated complication of diabetes. A consensus report of the American Diabetes Association. Diabetes Care 45:1670, 2022. Senneville É et al: IWGDF/IDSA guidelines on the diagnosis and treatment of diabetes-related foot infections. Diabetes Metab Res Rev 40:e3687, 2024. van Netten JJ et al: The International Working Group on the Diabetic Foot: Stories and numbers behind three decades of evidence-based guidelines for the management of diabetes-related foot disease. Dia­ betes Ther 15:19, 2024. Stephen N. Davis

Hypoglycemia Hypoglycemia is most commonly caused by insulin or insulin-producing drugs used to treat diabetes mellitus or by exposure to other drugs, including alcohol. However, a number of other disorders, including critical organ failure, sepsis and inanition, hormone deficiencies, nonβ-cell tumors, insulinoma, inborn errors of metabolism, and prior gastric surgery, can cause hypoglycemia (Table 418-1). Hypoglycemia may be documented by Whipple’s triad: (1) symptoms consistent with hypoglycemia, (2) a low plasma glucose concentration measured with a precise method, and (3) relief of symptoms after the plasma glucose level is raised. The lower limit of the fasting plasma glucose concentra­ tion is normally ~70 mg/dL (~3.9 mmol/L), but lower venous glucose levels occur normally, late after a meal, during pregnancy, and during prolonged fasting (>24 h). Severe hypoglycemia can cause serious morbidity and increase the risk for serious cardiovascular events and mortality during and after the initial hypoglycemic episode. It should be considered in any patient with episodes of confusion, an altered level of consciousness, or a seizure. ■ ■SYSTEMIC GLUCOSE BALANCE AND GLUCOSE COUNTERREGULATION Glucose is an obligate metabolic fuel for the brain under physiologic conditions. The brain cannot synthesize glucose or store more than a few minutes’ supply as glycogen and therefore requires a continuous supply of glucose from the arterial circulation. As the arterial plasma glucose concentration falls below the physiologic range, blood-to-brain glucose transport becomes insufficient to support brain energy metab­ olism and function. However, multiple integrated glucose counterregu­ latory mechanisms normally prevent or rapidly correct hypoglycemia. Plasma glucose concentrations are normally maintained within a relatively narrow range—roughly 70–110 mg/dL (3.9–6.1 mmol/L) in the fasting state, with transient higher excursions after a meal— despite wide variations in exogenous glucose delivery from meals and in endogenous glucose utilization by, for example, exercising muscle. Between meals and during fasting, plasma glucose levels are maintained

TABLE 418-1  Causes of Hypoglycemia Across the Life Span Ill or Medicated Individual 1.  Drugs Insulin or insulin secretagogues Alcohol Others 2.  Critical illness Hepatic, renal, or cardiac failure Sepsis Inanition 3.  Hormone deficiency Cortisol Growth hormone Glucagon and epinephrine (in insulin-deficient diabetes) 4.  Non–islet cell tumor (e.g., mesenchymal tumors) Seemingly Well Individual 5.  Endogenous hyperinsulinism Insulinoma Functional β-cell disorders (nesidioblastosis)   Noninsulinoma pancreatogenous hypoglycemia   Post–gastric bypass hypoglycemia Insulin autoimmune hypoglycemia   Antibody to insulin   Antibody to insulin receptor GLP-1 receptor agonists in combination with insulin and/or insulin secretagogues Insulin secretagogues Other 6.  Disorders of gluconeogenesis and fatty acid oxidation 7.  Exercise 8.  Accidental, surreptitious, or malicious hypoglycemia 9.  Prolonged fasting 10.  Pregnancy Source: Reproduced with permission from PE Cryer et al: Evaluation and management of adult hypoglycemic disorders: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 94:709, 2009. Arterial glucose Pancreas Brain Glucagon Sympathoadrenal outflow Pituitary Adrenal medullae Epinephrine Growth hormone Sympathetic postganglionic neurons (ACTH) Adrenal cortex Norepinephrine Acetylcholine Cortisol FIGURE 418-1  Physiology of glucose counterregulation: Mechanisms that normally prevent or rapidly correct hypoglycemia. In insulin-deficient diabetes, the key counterregulatory responses—suppression of insulin and increases in glucagon—are lost, and stimulation of sympathoadrenal outflow is attenuated. ACTH, adrenocorticotropic hormone.

by endogenous glucose production, hepatic glycogenolysis, and hepatic (and renal) gluconeogenesis (Fig. 418-1). Although hepatic glycogen stores are usually sufficient to maintain plasma glucose levels for ~8 h, this period can be shorter if glucose demand is increased by exercise or if glycogen stores are depleted by illness or starvation.

Gluconeogenesis normally requires low insulin levels and the pres­ ence of anti-insulin (counterregulatory) hormones together with a coordinated supply of precursors from muscle and adipose tissue to the liver and kidneys. Muscle provides lactate, pyruvate, alanine, gluta­ mine, and other amino acids. Triglycerides in adipose tissue are broken down into fatty acids and glycerol, which is a gluconeogenic precursor. Fatty acids provide an alternative oxidative fuel to tissues other than the brain (which requires glucose). Hypoglycemia CHAPTER 418 Systemic glucose balance, maintenance of the normal plasma glucose concentration, is accomplished by a network of hormones, neural signals, and substrate effects that regulate endogenous glucose production and glucose utilization by tissues other than the brain

(Chap. 415). Among the regulatory factors, insulin plays a dominant role (Table 418-2; Fig. 418-1). As plasma glucose levels decline within the physiologic range, pancreatic β-cell insulin secretion decreases, thereby increasing hepatic glycogenolysis and hepatic (and renal) gluconeogenesis. Low insulin levels also reduce glucose utilization in peripheral tissues, inducing lipolysis and proteolysis and consequently releasing gluconeogenic precursors. Thus, a decrease in insulin secre­ tion is the first defense against hypoglycemia. As plasma glucose levels decline just below the physiologic range, glucose counterregulatory (plasma glucose–raising) hormones are released (Table 418-2; Fig. 418-1). Among these, pancreatic α-cell glu­ cagon and adrenomedullary epinephrine play a primary role. Glucagon stimulates hepatic glycogenolysis and gluconeogenesis. Adrenomedul­ lary epinephrine also stimulates hepatic glycogenolysis and gluconeo­ genesis (and renal gluconeogenesis) but limits peripheral uptake of glucose and stimulates lipolysis with production of glycerol and fatty acids. Epinephrine becomes critical when glucagon is deficient. When hypoglycemia is prolonged beyond ~4 h, cortisol and growth hormone also support glucose production and restrict glucose utilization to a limited amount (both mechanisms are reduced by ~80% compared to epinephrine). Thus, cortisol and growth hormone play no role in defense against acute hypoglycemia. Liver Insulin Kidneys Glucose production Arterial glucose Fat Muscle Gluconeogenic precursor (lactate, amino acids, glycerol) Glucose clearance (Ingestion) Symptoms

TABLE 418-2  Physiologic Responses to Decreasing Plasma Glucose Concentrations GLYCEMIC THRESHOLD,

mmoL/L (mg/dL) PHYSIOLOGIC ↓ EFFECTS RESPONSE ↓ Insulin 4.4–4.7 (80–85) ↑ Ra (↓ Rd), increased lipolysis; ↑ FFA

↑ Glycerol ↑ Glucagon 3.6–3.9 (65–70) ↑ Ra Primary glucose counterregulatory factor/second defense against hypoglycemia ↑ Epinephrine 3.6–3.9 (65–70) ↑ Ra, ↓ Rc, increased lipolysis;

↑ FFA and glycerol 3.6–3.9 (65–70) ↑ Ra, ↓ Rc Involved in defense against prolonged hypoglycemia;

not critical ↑ Cortisol and growth hormone PART 12 Endocrinology and Metabolism Symptoms 2.8–3.1 (50–55) Recognition of hypoglycemia Prompt behavioral defense against hypoglycemia

(food ingestion) ↓ Cognition <2.8 (<50) — Compromises behavioral defense against hypoglycemia Note: Ra, rate of glucose appearance, glucose production by the liver and kidneys; Rc, rate of glucose clearance, glucose utilization relative to the ambient plasma glucose by insulin-sensitive tissues; Rd, rate of glucose disappearance, glucose utilization by insulin-sensitive tissues such as skeletal muscle. Rd by the brain is not altered by insulin, glucagon, epinephrine, cortisol, or growth hormone. Abbreviation: FFA, free fatty acids. Source: Reproduced with permission from PE Cryer, in S Melmed et al: Williams Textbook of Endocrinology, 12th ed. New York, NY: Elsevier; 2012. As plasma glucose levels fall further, symptoms prompt behavioral defense against hypoglycemia, including the ingestion of food (Table 418-2; Fig. 418-1). The normal glycemic thresholds for these responses to decreasing plasma glucose concentrations are shown in Table 418-2. However, these thresholds are dynamic. They shift to higher-thannormal glucose levels in people with poorly controlled diabetes, who can experience symptoms of hypoglycemia when their glucose levels decline toward the normal range. On the other hand, thresholds shift to lower-than-normal glucose levels in people with recurrent hypogly­ cemia; i.e., patients with intensively treated diabetes or an insulinoma have symptoms at glucose levels lower than those that cause symptoms in healthy individuals. Clinical Manifestations  Neuroglycopenic manifestations of hypoglycemia are the direct result of central nervous system glucose deprivation. These features include behavioral changes, confusion, fatigue, seizure, loss of consciousness, cardiac arrhythmias, and, if hypoglycemia is severe, death. Neurogenic (or autonomic) manifes­ tations of hypoglycemia result from the perception of physiologic changes caused by the central nervous system–mediated sympa­ thoadrenal discharge that is triggered by hypoglycemia. They include adrenergic symptoms (mediated largely by norepinephrine released from sympathetic postganglionic neurons but perhaps also by epineph­ rine released from the adrenal medullae), such as palpitations, tremor, and anxiety, as well as cholinergic symptoms (mediated by acetylcholine released from sympathetic postganglionic neurons), such as sweating, hunger, and paresthesias. Clearly, these are nonspecific symptoms. Their attribution to hypoglycemia requires that the corresponding plasma glucose concentration be low and that the symptoms resolve after the glucose level is raised (as delineated by Whipple’s triad). Common signs of hypoglycemia include diaphoresis and pallor. Heart rate and systolic blood pressure are typically increased but may not be raised in an individual who has experienced repeated, recent episodes of hypoglycemia. Neuroglycopenic manifestations are often observable. Transient focal neurologic deficits occur occasionally. Per­ manent neurologic deficits are rare. Etiology and Pathophysiology  Hypoglycemia activates proin­ flammatory, procoagulant, and proatherothrombotic responses in type 1

diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM), and nondi­ abetic individuals. These responses increase platelet aggregation, reduce fibrinolytic balance (increase plasminogen activator inhibitor-1), and increase intravascular coagulation. Hypoglycemia also reduces protec­ tive nitric oxide–mediated arterial vasodilator mechanisms in healthy, T1DM, and T2DM individuals. ■ ■HYPOGLYCEMIA IN DIABETES Impact and Frequency  Hypoglycemia is the limiting factor in the glycemic management of diabetes mellitus. First, it causes

ROLE IN PREVENTION OR CORRECTION OF HYPOGLYCEMIA (GLUCOSE COUNTERREGULATION) Primary glucose regulatory factor/first defense against hypoglycemia Third defense against hypoglycemia; critical when glucagon is deficient recurrent morbidity in most people with T1DM and in many with advanced T2DM, and it is sometimes fatal. Second, it precludes maintenance of euglycemia over a lifetime of diabetes and, thus, full realization of the well-established microvascular benefits of glycemic control. Third, it causes a vicious cycle of recurrent hypoglycemia by producing hypoglycemia-associated autonomic failure—i.e., the clinical syndromes of defective glucose counterregulation and of hypo­ glycemia unawareness. Hypoglycemia is a fact of life for people with T1DM if treated with insulin, sulfonylurea, or glinides. They suffer an average of two epi­ sodes of symptomatic hypoglycemia per week and at least one episode of severe, at least temporarily disabling hypoglycemia each year. An estimated 6–10% of people with T1DM die as a result of hypoglycemia. The incidence of hypoglycemia is lower in T2DM than in T1DM. How­ ever, its prevalence in insulin-requiring T2DM is surprisingly high. Recent studies have revealed a hypoglycemia prevalence approaching 70%. In fact, as patients with T2DM outnumber those with T1DM by 10- to 20-fold, the prevalence of hypoglycemia is now greater in T2DM. Hypoglycemia can occur at any hemoglobin A1c (HbA1c) level. Although severe hypoglycemia occurs twice as frequently at lower HbA1c levels in T1DM, it still occurs at HbA1c levels >8%. In insulinrequiring T2DM, severe hypoglycemia can occur at lower HbA1c values but also importantly at values of 8–10%. Severe hypoglycemia in T2DM carries an increased risk of severe cardiovascular and cerebrovascular morbidity and mortality for up to 1 year after the event. The risk of severe hypoglycemia and a subsequent cardiovascular adverse event is, in fact, relatively increased when trying to improve glucose control in some T2DM individuals with persistently raised HbA1c values. There­ fore, improvements in glycemic control in these individuals should be performed incrementally and carefully to avoid episodes of hypo­ glycemia. Insulin, sulfonylureas, or glinides can cause hypoglycemia in T2DM. Metformin, thiazolidinediones, α-glucosidase inhibitors, glucagon-like peptide 1 (GLP-1) receptor agonists, sodium-glucose cotransporter 2 inhibitors, and dipeptidyl peptidase IV (DPP-IV) inhibitors do not cause hypoglycemia. However, they increase the risk when combined with a sulfonylurea, glinide, or insulin. Notably, the frequency of hypoglycemia approaches that in T1DM as persons with T2DM develop absolute insulin deficiency and require more complex treatment with insulin. Conventional Risk Factors  The conventional risk factors for hypoglycemia in diabetes are identified on the basis of relative or abso­ lute insulin excess. This occurs when (1) insulin (or insulin secreta­ gogue) doses are excessive, ill-timed, or of the wrong type; (2) the influx of exogenous glucose is reduced (e.g., during an overnight fast, periods of temporary fasting, or after missed meals or snacks); (3) insulinindependent glucose utilization is increased (e.g., during exercise); (4) sensitivity to insulin is increased (e.g., with improved glycemic control,

in the middle of the night, after exercise, or with increased fitness or weight loss); (5) endogenous glucose production is reduced (e.g., after alcohol ingestion); and (6) insulin clearance is reduced (e.g., in renal failure). However, these conventional risk factors alone explain a minority of episodes; other factors are typically involved. Hypoglycemia-Associated Autonomic Failure (HAAF)  While marked insulin excess alone can cause hypoglycemia, iatrogenic hypo­ glycemia in diabetes (T1DM and/or T2DM) is typically the result of the interplay of relative or absolute therapeutic insulin excess and com­ promised physiologic and behavioral defenses against falling plasma glucose concentrations (Table 418-2; Fig. 418-2). Defective glucose counterregulation compromises physiologic defense (particularly dec­ rements in insulin and increments in glucagon and epinephrine), and hypoglycemia unawareness compromises behavioral defense (ingestion of carbohydrate). DEFECTIVE GLUCOSE COUNTERREGULATION  In the setting of abso­ lute endogenous insulin deficiency, insulin levels do not decrease as plasma glucose levels fall; thus, the first defense against hypoglycemia is lost. After a few years of disease duration in T1DM, glucagon levels do not increase as plasma glucose levels fall; a second defense against hypoglycemia is lost. Reduced glucagon responses to hypoglycemia also occur in long-duration T2DM. However, pancreatic alpha cells that produce glucagon are present in the same number and size in T1DM as compared to age-matched nondiabetic individuals. Thus, the defect that restricts glucagon release during hypoglycemia in T1DM (and presumably in long-standing T2DM) appears to be a signaling defect, as glucagon responses to other physiologic stress in T1DM (e.g., exercise) are preserved. Finally, the increase in epinephrine lev­ els, the third critical defense against acute hypoglycemia, is typically attenuated. The glycemic threshold for the sympathoadrenal (adre­ nomedullary epinephrine and sympathetic neural norepinephrine) response is shifted to lower plasma glucose concentrations. That shift is typically the result of recent antecedent iatrogenic hypoglycemia. In Early T2DM (Relative β-cell failure) Advanced T2DM and T1DM (Absolute β-cell failure) Marked absolute therapeutic hyperinsulinemia → Falling glucose levels Relative or mild-moderate absolute therapeutic hyperinsulinemia → Falling glucose levels β-cell failure → No ↓ insulin and no ↑ glucagon Isolated episodes of hypoglycemia Episodes of hypoglycemia Sleep Exercise Attenuated sympathoadrenal responses to hypoglycemia (HAAF) ↓ Adrenomedullary epinephrine responses ↓ Sympathetic neural responses Hypoglycemia unawareness Defective glucose counterregulation Recurrent hypoglycemia FIGURE 418-2  Hypoglycemia-associated autonomic failure (HAAF) in insulin-deficient diabetes. T1DM, type 1 diabetes mellitus; T2DM, type 2 diabetes mellitus. (Reprinted with permission from The American Diabetes Association. Copyright 2012 by the American Diabetes Association.)

the setting of absent decrements in insulin and of absent increments in glucagon, the attenuated increment in epinephrine causes the clinical syndrome of defective glucose counterregulation. Affected patients are at ≥25-fold greater risk of severe iatrogenic hypoglycemia during intensive glycemic therapy for their diabetes than are patients with nor­ mal epinephrine responses. This functional—and potentially revers­ ible—disorder is distinct from classic diabetic autonomic neuropathy, which also includes all of the above pathophysiologic defects, and is a structural and irreversible disorder.

HYPOGLYCEMIA UNAWARENESS  The attenuated sympathoadrenal response (largely the reduced sympathetic neural response) to hypogly­ cemia causes the clinical syndrome of hypoglycemia unawareness—i.e., loss of the warning adrenergic and cholinergic symptoms that previ­ ously allowed the patient to recognize developing hypoglycemia and therefore to abort the episode by ingesting carbohydrates. Affected patients are at a sixfold increased risk of severe iatrogenic hypoglyce­ mia during intensive glycemic therapy of their diabetes. Hypoglycemia CHAPTER 418 HAAF IN DIABETES  The concept of HAAF in diabetes posits that recent antecedent iatrogenic hypoglycemia (or sleep or prior exercise) causes both defective glucose counterregulation (by reducing the epi­ nephrine response to a given level of subsequent hypoglycemia in the setting of absent insulin and glucagon responses) and hypoglycemia unawareness (by reducing the sympathoadrenal response to a given level of subsequent hypoglycemia). These impaired responses, which can occur in individuals with either T1DM or T2DM, create a vicious cycle of recurrent iatrogenic hypoglycemia (Fig. 418-2). Hypoglycemia unawareness and, to some limited extent, the reduced epinephrine component of defective glucose counterregulation can be reversible by as little as 2–3 weeks of scrupulous avoidance of hypoglycemia in most affected patients. On the basis of this pathophysiology, additional risk factors for hypoglycemia in diabetes include (1) absolute insulin deficiency, indi­ cating that insulin levels will not decrease and glucagon levels will not increase as plasma glucose levels fall; (2) a history of severe hypoglycemia or of hypoglycemia unaware­ ness, implying recent antecedent hypoglycemia, as well as prior exercise or sleep, indicating that the sympathoadrenal response will be attenuated; (3) impaired renal function resulting in reduced clear­ ance of exogenous and endogenous insulin; (4) clas­ sical diabetic autonomic neuropathy; and (5) lower HbA1c or lower glycemic goals even at elevated HbA1c levels (8–10%), as they represent an increased prob­ ability of recent antecedent hypoglycemia. Hypoglycemia Risk Factor Reduction  Several multicenter, randomized controlled trials investigat­ ing the potential benefits of tight glucose control in either inpatient or outpatient settings have reported a high prevalence of severe hypoglycemia. In the NICESUGAR study, attempts to control in-hospital plasma glucose values toward physiologic levels resulted in increased mortality risk. The ADVANCE and ACCORD studies and the Veterans Affairs Diabetes Trial (VADT) also found a significant incidence of severe hypoglycemia among T2DM patients. Severe hypoglycemia with accompanying serious cardio­ vascular morbidity and mortality also occurred in the standard (e.g., not receiving intensified treat­ ment) control group in all of the above studies and in another large study in prediabetic and T2DM individuals (ORIGIN). Thus, as stated above, severe hypoglycemia can and does occur at HbA1c values of 8–10% in both T1DM and T2DM. Somewhat sur­ prisingly, all three studies found little or no benefit of intensive glucose control to reduce macrovascular events in T2DM. In fact, the ACCORD study was ended early because of the increased mortality rate in the intensive glucose control arm. Whether iatrogenic

hypoglycemia was the cause of the increased mortality risk is not known. In light of these findings, some new recommendations and par­ adigms have been formulated. Whereas there is little debate regarding the need to reduce hyperglycemia in the hospital, the glycemic mainte­ nance goals in critical care settings have been modified to stay between 140 and 180 mg/dL. Similar glycemic targets are also recommended in non–critically ill patients by a number of expert societies, although some recommend even more strict glucose control down to 108 mg/dL. Accordingly, the benefits of insulin therapy and reduced hyperglycemia can be obtained while the prevalence of hypoglycemia is reduced.

Similarly, evidence exists that intensive glucose control can reduce the prevalence of microvascular disease in both T1DM and T2DM. These benefits need to be weighed against the increased prevalence of hypoglycemia. Certainly, the level of glucose control (i.e., the HbA1c value, symptoms of hyper- and hypoglycemia, and home glucose val­ ues) should be evaluated for each patient. Multicenter trials have dem­ onstrated that individuals with recently diagnosed T1DM or T2DM can have better glycemic control with less hypoglycemia. In addition, there is still long-term benefit in reducing HbA1c values from higher to lower, albeit still above recommended levels. Perhaps a reasonable therapeutic goal is the lowest HbA1c level that does not cause severe hypoglycemia and that preserves awareness of hypoglycemia. PART 12 Endocrinology and Metabolism Recent studies have demonstrated the benefit of second-generation basal and prandial analogue insulins in reducing the risk of both nonsevere and severe hypoglycemia. The reduction of hypoglycemia occurred during both the day and night and was observed in T1DM and T2DM individuals. Addition of longer acting GLP-1 and dual GLP-1/gastric inhibitory polypeptide (GIP) receptor agonists to a basal insulin in the management of insulin-requiring T2DM has also resulted in lower hypoglycemic risk as compared to a basal insulin and a first-generation prandial insulin analogue. Pancreatic transplantation (both whole organ and islet cell) has been used in part as a treatment for severe hypoglycemia. Generally, rates of hypoglycemia are reduced after transplantation. This decrease appears to be due to increased physiologic insulin and glucagon responses during hypoglycemia. The use of continuous glucose monitors (CGMs), either alone or in combination with continuous subcutaneous infusion via a wearable pump, offers promise as a method of reducing hypoglycemia while improving HbA1c. Specifically, continuous glucose monitoring coupled with temporary discontinuation of subcutaneous insulin infusion when the monitor predicts a low glucose concentration is particularly promising. Studies investigating the use of CGM during inpatient care for both insulin-requiring pediatric and adult patients with diabetes are ongoing. Furthermore, progress utilizing a portable wearable closedloop automated “artificial pancreas” or sensor-augmented pump therapy incorporating continuous glucose modulation of either insulin alone or bi-hormonal delivery of both insulin and glucagon has been established. Additionally, stem cell–derived β cells also offer promise of novel therapeutic interventions to reduce hypoglycemia. Nonpharmacologic approaches of hypoglycemia risk reduction utilizing structured patient education have also been proven to be successful in T1DM and T2DM. Outpatient education consisting of adjustment of meal plans, exercise, and medications, combined with early recognition and treatment of hypoglycemia, have all been demonstrated to reduce hypoglycemic risk with even small improvements in HbA1c. Other interventions to stimulate counter­ regulatory responses, such as selective serotonin reuptake inhibitors, β-adrenergic receptor antagonists, opiate receptor antagonists, and fructose, remain experimental and have not been assessed in largescale clinical trials. Thus, intensive glycemic therapy (Chap. 416) needs to be applied along with the patient’s education and empowerment, frequent selfmonitoring of blood glucose, flexible insulin (and other drug) regimens (including the use of insulin analogues, both short- and longer-acting), individualized glycemic goals, and ongoing professional guidance, sup­ port, and consideration of both the conventional risk factors and those indicative of compromised glucose counterregulation. Given a history of hypoglycemia unawareness, a 2- to 3-week period of scrupulous avoidance of hypoglycemia is indicated.

■ ■HYPOGLYCEMIA WITHOUT DIABETES There are many causes of hypoglycemia (Table 418-1). Because hypo­ glycemia is common in insulin- or insulin secretagogue–treated diabe­ tes, it is often reasonable to assume that a clinically suspicious episode is the result of hypoglycemia. On the other hand, because hypoglyce­ mia is rare in the absence of relevant drug-treated diabetes (pregnancy and during severe episodes of morning sickness), it is reasonable to conclude that a hypoglycemic disorder is present only in patients in whom Whipple’s triad can be demonstrated. Particularly when patients are ill or medicated, the initial diag­ nostic focus should be on the possibility of drug involvement and then on critical illnesses, hormone deficiency, or non–islet cell tumor hypoglycemia. In the absence of any of these etiologic factors and in a seemingly well individual, the focus should shift to possible endog­ enous hyperinsulinism or accidental, surreptitious, or even malicious hypoglycemia. Drugs  Insulin and insulin secretagogues suppress glucose produc­ tion and stimulate glucose utilization. Ethanol blocks gluconeogenesis but not glycogenolysis. Thus, alcohol-induced hypoglycemia typically occurs after a several-day ethanol binge during which the person eats little food, with consequent glycogen depletion. Ethanol is usually measurable in blood at the time of presentation, but its levels correlate poorly with plasma glucose concentrations. Because gluconeogenesis becomes the predominant route of glucose production during pro­ longed hypoglycemia, alcohol can contribute to the progression of hypoglycemia in patients with insulin-treated diabetes. Many other drugs have been associated with hypoglycemia. These include commonly used drugs such as angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists, β-adrenergic recep­ tor antagonists, quinolone antibiotics, indomethacin, quinine, and sulfonamides. Critical Illness  Among hospitalized patients, serious illnesses such as renal, hepatic, or cardiac failure; sepsis; and inanition are second only to drugs as causes of hypoglycemia. Rapid and extensive hepatic destruction (e.g., toxic hepatitis) causes fasting hypoglycemia because the liver is the major site of endogenous glucose production. The mechanism of hypoglycemia in patients with cardiac failure is unknown. Hepatic congestion and hypoxia may be involved. Although the kidneys are a source of glucose produc­ tion, hypoglycemia in patients with renal failure is also caused by the reduced clearance of insulin (thereby inappropriately increasing insu­ lin relative to the prevailing glucose levels) and the reduced mobiliza­ tion of gluconeogenic precursors in renal failure. Sepsis is a relatively common cause of hypoglycemia. Increased glucose utilization is induced by cytokine production in macrophagerich tissues such as the liver, spleen, and lung. Hypoglycemia develops if glucose production fails to keep pace. Cytokine-induced inhibition of gluconeogenesis in the setting of nutritional glycogen depletion, in combination with hepatic and renal hypoperfusion, may also contrib­ ute to hypoglycemia. Hypoglycemia can be seen with starvation. Due to brain conversion and utilization of alternative substrates, such as lactate, pyruvate, and ketone bodies, there is only a modest counterregulatory neuroendo­ crine and autonomic nervous system response. During periods of pro­ longed starvation (fasting), plasma glucose levels are lower in women as compared to men, perhaps because of loss of whole-body fat stores and subsequent depletion of gluconeogenic precursors (e.g., amino acids), necessitating increased glucose utilization. Hormone Deficiencies  Neither cortisol nor growth hormone is critical to the prevention of hypoglycemia, at least in adults. Nonethe­ less, hypoglycemia can occur with prolonged fasting in patients with primary adrenocortical failure (Addison’s disease) or hypopituitarism. Anorexia and weight loss are typical features of chronic cortisol defi­ ciency and likely result in glycogen depletion. Cortisol deficiency is associated with impaired gluconeogenesis and low levels of gluco­ neogenic precursors; these associations suggest that substrate-limited gluconeogenesis, in the setting of glycogen depletion, is the cause of

hypoglycemia. Growth hormone deficiency can cause hypoglycemia in young children. In addition to extended fasting, high rates of glucose utilization (e.g., during exercise or in pregnancy) or low rates of glucose production (e.g., after alcohol ingestion) can precipitate hypoglycemia in adults with previously unrecognized hypopituitarism. Hypoglycemia is not a feature of the epinephrine-deficient state that results from bilateral adrenalectomy when glucocorticoid replacement is adequate, nor does it occur during pharmacologic adrenergic block­ ade when other glucoregulatory systems are intact. Combined deficien­ cies of glucagon and epinephrine play a key role in the pathogenesis of iatrogenic hypoglycemia in people with insulin-deficient diabetes, as discussed earlier. Otherwise, deficiencies of these hormones are not usually considered in the differential diagnosis of a hypoglycemic disorder. Non–β-Cell Tumors  Fasting hypoglycemia, often termed non– islet cell tumor hypoglycemia, occurs occasionally in patients with large mesenchymal or epithelial tumors (e.g., hepatomas, adrenocortical carcinomas, carcinoids). The glucose kinetic patterns resemble those of hyperinsulinism (see next), but insulin secretion is suppressed appro­ priately during hypoglycemia. In most instances, hypoglycemia is due to overproduction of an incompletely processed form of insulin-like growth factor II (“big IGF-II”) that does not complex normally with circulating binding proteins and thus more readily gains access to tar­ get tissues. The tumors are usually apparent clinically, plasma ratios of IGF-II to IGF-I are high, and free IGF-II levels (and levels of pro-IGF-II [1–21]) are elevated. Curative surgery is seldom possible, but reduction of tumor bulk may ameliorate hypoglycemia. Therapy with a gluco­ corticoid, growth hormone, or both has also been reported to alleviate hypoglycemia. Hypoglycemia attributed to ectopic IGF-I production has been reported but is rare. Endogenous Hyperinsulinism  Hypoglycemia due to endog­ enous hyperinsulinism can be caused by (1) a primary β-cell disorder— typically a β-cell tumor (insulinoma), sometimes multiple insulinomas, or a functional β-cell disorder with β-cell hypertrophy or hyperplasia; (2) an antibody to insulin or to the insulin receptor; (3) a β-cell secre­ tagogue such as a sulfonylurea; or perhaps (4) ectopic insulin secretion, among other very rare mechanisms. None of these causes are common. The fundamental pathophysiologic feature of endogenous hyperin­ sulinism caused by a primary β-cell disorder or an insulin secretagogue is the failure of insulin secretion to fall to very low levels during hypo­ glycemia. This feature is assessed by measurement of plasma insulin, C-peptide (the connecting peptide that is cleaved from proinsulin to produce insulin), proinsulin, and glucose concentrations during hypo­ glycemia. Insulin, C-peptide, and proinsulin levels need not be high rela­ tive to normal, euglycemic values; rather, they are inappropriately high in the setting of a low plasma glucose concentration. Critical diagnostic findings are a plasma insulin concentration ≥3 μU/mL (≥18 pmol/L), a plasma C-peptide concentration ≥0.6 ng/mL (≥0.2 nmol/L), and a plasma proinsulin concentration ≥5.0 pmol/L when the plasma glucose concentration is <55 mg/dL (<3.0 mmol/L) with symptoms of hypogly­ cemia. A low plasma β-hydroxybutyrate concentration (≤2.7 mmol/L) and an increment in plasma glucose level of >25 mg/dL (>1.4 mmol/L) after IV administration of glucagon (1.0 mg) indicate increased insulin (or IGF) actions. The diagnostic strategy is (1) to measure plasma glucose, insulin, C-peptide, proinsulin, and β-hydroxybutyrate concentrations and to screen for circulating oral hypoglycemic agents during an episode of hypoglycemia and (2) to assess symptoms during the episode and seek their resolution following correction of hypoglycemia by glucose (either oral or parenteral) or by IV injection of glucagon (i.e., to docu­ ment Whipple’s triad). This is straightforward if the patient is hypo­ glycemic when seen. Since endogenous hyperinsulinemic disorders usually, but not invariably, cause fasting hypoglycemia, a diagnostic episode may develop after a relatively short outpatient fast. Serial sampling during an inpatient diagnostic fast of up to 72 h or after a mixed meal is more problematic. An alternative is to give patients a detailed list of the required measurements and ask them to present to an ambulatory care center or emergency room, with the list, during a

symptomatic episode. Obviously, a normal plasma glucose concentra­ tion during a symptomatic episode indicates that the symptoms are not the result of hypoglycemia.

An insulinoma—an insulin-secreting pancreatic islet β-cell tumor— is the prototypical cause of endogenous hyperinsulinism and therefore should be sought in patients with a compatible clinical syndrome. However, insulinoma is not the only cause of endogenous hyperin­ sulinism. Some patients with fasting endogenous hyperinsulinemic hypoglycemia have diffuse islet involvement with β-cell hypertrophy and sometimes hyperplasia. This pattern is commonly referred to as nesidioblastosis, although β cells budding from ducts are not invariably found. Other patients have a similar islet pattern but with postpran­ dial hypoglycemia, a disorder termed noninsulinoma pancreatogenous hypoglycemia. Post–gastric bypass postprandial hypoglycemia, which most often follows Roux-en-Y gastric bypass, is also characterized by diffuse islet involvement and endogenous hyperinsulinism. Multiple pathophysiologic mechanisms have been suggested including exag­ gerated GLP-1 responses to meals resulting in hyperinsulinemia, hypoglucagonemia, and hypoglycemia. However, other mechanisms may be responsible for the relative hyperinsulinemia, such as reduced insulin clearance and reduced glucagon responses to hypoglycemia. The relevant pathogenesis has not been clearly established. However, if medical treatment with agents such as an α-glucosidase inhibitor, diazoxide, or octreotide fails, partial pancreatectomy may be required. Autoimmune hypoglycemias include those caused by an antibody to insulin that binds postmeal insulin and then gradually disassociates, with consequent late postprandial hypoglycemia. Alternatively, an insulin receptor antibody can function as an agonist. The presence of an insulin secretagogue, such as a sulfonylurea or a glinide, results in a clinical and biochemical pattern similar to that of an insulinoma but can be distinguished by the presence of the circulating secretagogue. Finally, there are reports of very rare phenomena such as ectopic insulin secretion, a gain-of-function insulin receptor mutation, and exercise-induced hyperinsulinemia. Hypoglycemia CHAPTER 418 Insulinomas are uncommon, with an estimated yearly incidence of 1 in 250,000. Because >90% of insulinomas are benign, they are a treat­ able cause of potentially fatal hypoglycemia. The median age at presen­ tation is 50 years in sporadic cases, but the tumor usually presents in the third decade when it is a component of multiple endocrine neopla­ sia type 1 (Chap. 400). More than 99% of insulinomas are within the substance of the pancreas, and the tumors are usually small (<2.0 cm in diameter in 90% of cases). Therefore, they come to clinical attention because of hypoglycemia rather than mass effects. Computed tomog­ raphy or magnetic resonance imaging detects ~70–80% of insulinomas. These methods detect metastases in the roughly 10% of patients with a malignant insulinoma. Transabdominal ultrasound often identifies insulinomas, and endoscopic ultrasound has a sensitivity of ~90%. Somatostatin receptor scintigraphy is thought to detect insulinomas in about half of patients. Selective pancreatic arterial calcium injec­ tions, with the endpoint of a sharp increase in hepatic venous insulin levels, regionalize insulinomas with high sensitivity, but this invasive procedure is seldom necessary except to confirm endogenous hyperin­ sulinism in the diffuse islet disorders. Intraoperative pancreatic ultra­ sonography almost invariably localizes insulinomas that are not readily palpable by the surgeon. Surgical resection of a solitary insulinoma is generally curative. Diazoxide, which inhibits insulin secretion, or the somatostatin analogue octreotide can be used to treat hypoglycemia in patients with unresectable tumors; everolimus, an mTOR (mammalian target of rapamycin) inhibitor, has also been successful in combination with the above approaches. ■ ■ACCIDENTAL, SURREPTITIOUS, OR MALICIOUS HYPOGLYCEMIA Accidental ingestion of an insulin secretagogue (e.g., as the result of a pharmacy or other medical error) or even accidental administration of insulin can occur. Factitious hypoglycemia, caused by surreptitious or even malicious administration of insulin or an insulin secretagogue, shares many clinical and laboratory features with insulinoma. It is most common among health care workers, patients with diabetes or

their relatives, and people with a history of other factitious illnesses. However, it should be considered in all patients being evaluated for hypoglycemia of obscure cause. Ingestion of an insulin secretagogue causes hypoglycemia with increased C-peptide levels, whereas exoge­ nous insulin causes hypoglycemia with low C-peptide levels, reflecting suppression of insulin secretion.

Analytical error in the measurement of plasma glucose concentra­ tions is rare. On the other hand, hand-held and continuous glucose monitors used to guide treatment of diabetes are not quantitative instruments, particularly at low glucose levels, and should not be used for the definitive diagnosis of hypoglycemia. Even with a quantitative method, low measured glucose concentrations can be artifactual—e.g., the result of continued glucose metabolism by the formed elements of the blood ex vivo, particularly in the presence of leukocytosis, eryth­ rocytosis, or thrombocytosis or with delayed separation of the serum from the formed elements (pseudohypoglycemia). PART 12 Endocrinology and Metabolism ■ ■INBORN ERRORS OF METABOLISM

CAUSING HYPOGLYCEMIA Nondiabetic hypoglycemia also results from inborn errors of metabo­ lism. Such hypoglycemia most commonly occurs in infancy but can also occur in adulthood. Cases in adults can be classified into those resulting in fasting hypoglycemia, postprandial hypoglycemia, and exercise-induced hypoglycemia. Fasting Hypoglycemia  Although rare, disorders of glycogenolysis can result in fasting hypoglycemia. These disorders include glycogen storage disease (GSD) of types 0, I, III, and IV and Fanconi-Bickel syndrome (Chap. 430). Patients with GSD types I and III characteristi­ cally have high blood lactate levels before and after meals, respectively. Both groups have hypertriglyceridemia, but ketones are high in GSD type III. Defects in fatty acid oxidation also result in fasting hypogly­ cemia. These defects can include (1) defects in the carnitine cycle;

(2) fatty-acid β-oxidation disorders; (3) electron transfer disturbances; and (4) ketogenesis disorders. Finally, defects in gluconeogenesis (fructose-1,6-biphosphatase) have been reported to result in recurrent hypoglycemia and lactic acidosis. Postprandial Hypoglycemia  Inborn errors of metabolism result­ ing in postprandial hypoglycemia are also rare. These errors include (1) glucokinase, SUR1, and Kir6.2 potassium channel mutations; (2) congenital disorders of glycosylation; and (3) inherited fructose intolerance. Exercise-Induced Hypoglycemia  Exercise-induced hypogly­ cemia, by definition, follows exercise. It results in hyperinsulinemia caused by increased activity of monocarboxylate transporter 1 in

β cells. APPROACH TO THE PATIENT Hypoglycemia In addition to the recognition and documentation of hypoglycemia as well as its treatment (often on an urgent basis), diagnosis of the hypoglycemic mechanism is critical for the selection of therapy that prevents, or at least minimizes, recurrent hypoglycemia. RECOGNITION AND DOCUMENTATION Hypoglycemia is suspected in patients with typical symptoms; in the presence of confusion, an altered level of consciousness, or a seizure; or in a clinical setting in which hypoglycemia is known to occur. Blood should be drawn, whenever possible, before the administration of glucose to allow documentation of a low plasma glucose concentration. Convincing documentation of hypoglyce­ mia requires the fulfillment of Whipple’s triad. Thus, the ideal time to measure the plasma glucose level is during a symptomatic episode. A normal glucose level excludes hypoglycemia as the cause of the symptoms. A low glucose level confirms that hypoglycemia is the cause of the symptoms, provided the latter resolve after the glucose level is raised. When the cause of the hypoglycemic

episode is obscure, additional measurements—made while the glucose level is low and before treatment—should include plasma insulin, C-peptide, proinsulin, and β-hydroxybutyrate levels; also critical are screening for circulating oral hypoglycemic agents and assessment of symptoms before and after the plasma glucose con­ centration is raised. When the history suggests prior hypoglycemia and no poten­ tial mechanism is apparent, the diagnostic strategy is to evaluate the patient as just described and assess for Whipple’s triad during and after an episode of hypoglycemia. On the other hand, while it cannot be ignored, a distinctly low plasma glucose concentration measured in a patient without corresponding symptoms raises the possibility of an artifact (pseudohypoglycemia). DIAGNOSIS OF THE HYPOGLYCEMIC MECHANISM In a patient with documented hypoglycemia, a plausible hypogly­ cemic mechanism can often be deduced from the history, physical examination, and available laboratory data (Table 418-1). Drugs, particularly alcohol or agents used to treat diabetes, should be the first consideration—even in the absence of known use of a relevant drug—given the possibility of surreptitious, accidental, or mali­ cious drug administration. Other considerations include evidence of a relevant critical illness, hormone deficiencies (less commonly), and a non-β-cell tumor that can be pursued diagnostically (rarely). Absent one of these mechanisms in an otherwise seemingly well individual, the care provider should consider endogenous hyper­ insulinism and proceed with measurements and assessment of symptoms during spontaneous hypoglycemia or under conditions that might elicit hypoglycemia. URGENT TREATMENT If the patient is able and willing, oral treatment with glucose tab­ lets or glucose-containing fluids, candy, or food is appropriate. A reasonable initial dose is 15–20 g of glucose. If the patient is unable or unwilling (because of neuroglycopenia) to take carbohydrates orally, parenteral therapy is necessary. IV administration of glucose (25 g) should be followed by a glucose infusion guided by serial plasma glucose measurements. If IV therapy is not practical, SC or IM glucagon (1.0 mg in adults) can be used, particularly in patients with T1DM. Because it acts by stimulating glycogenolysis, glucagon is ineffective in glycogen-depleted individuals (e.g., those with alcohol-induced hypoglycemia). Glucagon also stimulates insulin secretion and is therefore less useful in T2DM. The somatostatin analogue octreotide can be used to suppress insulin secretion in sulfonylurea-induced hypoglycemia. These treatments raise plasma glucose concentrations only transiently, and patients should there­ fore be urged to eat as soon as is practical to replete glycogen stores. PREVENTION OF RECURRENT HYPOGLYCEMIA Prevention of recurrent hypoglycemia requires an understand­ ing of the hypoglycemic mechanism. Offending drugs should be discontinued or their doses reduced. Hypoglycemia caused by a sulfonylurea can persist for hours or even days. Underlying critical illnesses can often be treated. Cortisol and growth hormone can be replaced if levels are deficient. Surgical, radiotherapeutic, or chemotherapeutic reduction of a non–islet cell tumor can alleviate hypoglycemia even if the tumor cannot be cured; glucocorticoid or growth hormone administration also may reduce hypoglycemic episodes in such patients. Surgical resection of an insulinoma is curative; medical therapy with diazoxide or octreotide can be used if complete resection is not possible and in patients with a nontu­ mor β-cell disorder. Partial pancreatectomy may be necessary in the latter patients. The treatment of autoimmune hypoglycemia (e.g., with glucocorticoid or immunosuppressive drugs) is problematic, but these disorders are sometimes self-limited. Failing these treat­ ments, frequent feedings and avoidance of fasting may be required. Administration of uncooked cornstarch at bedtime or even an overnight intragastric infusion of glucose may be necessary for some patients.

35 - 419 Disorders of Lipoprotein Metabolism

419 Disorders of Lipoprotein Metabolism

Acknowledgment The author acknowledges contributions of the late Phil E. Cryer to this chapter in prior editions of Harrison’s. ■ ■FURTHER READING Black JE et al: Real-world effects of second-generation versus earlier intermediate/basal insulin analogues on rates of hypoglycemia in adults with type 1 and 2 diabetes (iNPHORM, US). Diabetes Ther 14:1299, 2023. Cryer PE: Hypoglycemia in Diabetes, 3rd ed. Alexandria, VA, American Diabetes Association, 2016. Cryer PE: Hypoglycemia, in Williams Textbook of Endocrinol­ ogy, 13th ed, S Melmed et al (eds). Philadelphia, Saunders, 2016,

pp. 1582–1607. Lee AK et al: The association of severe hypoglycemia with incident cardiovascular events and mortality in adults with type 2 diabetes. Diabetes Care 41:104, 2018. Nwokolo M, Hovorka R: The artificial pancreas and type 1 diabetes. J Clin Endocrinol Metab 108:1614, 2023. Salehi M et al: Hypoglycemia after gastric bypass surgery: Current concepts and controversies. J Clin Endocrinol Metab 103:2815, 2018. Daniel J. Rader

Disorders of Lipoprotein Metabolism Lipoproteins are complexes of lipids and proteins that are essential for transport of cholesterol, triglycerides (TGs), and fat-soluble vita­ mins in the blood. Lipoproteins play essential roles in the transport of dietary cholesterol, long-chain fatty acids, and fat-soluble vitamins from the intestine to peripheral tissues and the liver; the transport of TGs, cholesterol, and fat-soluble vitamins from the liver to peripheral tissues; and the transport of cholesterol from peripheral tissues back to the liver and intestine for excretion. Disorders of lipoprotein metabo­ lism can be primary (caused by genetic conditions) or secondary (to other medical conditions or environmental exposures) and involve either a substantial increase or decrease in specific circulating lipids or lipoproteins. Lipoprotein disorders can have a number of clinical consequences, most notably atherosclerotic cardiovascular disease (ASCVD), and are therefore important to appropriately diagnose and treat. This chapter reviews the etiology and pathophysiology of TABLE 419-1  Major Apolipoproteins APOLIPOPROTEIN PRIMARY SOURCE LIPOPROTEIN ASSOCIATION FUNCTION ApoA-I Intestine, liver HDL, chylomicrons Core structural protein for HDL, promotes cellular lipid efflux via ABCA1, activates LCAT ApoA-II Liver HDL, chylomicrons Structural protein for HDL ApoA-V Liver VLDL, chylomicrons Promotes LPL-mediated triglyceride lipolysis Apo(a) Liver Lp(a) Structural protein for Lp(a) ApoB-48 Intestine Chylomicrons, chylomicron remnants Core structural protein for chylomicrons ApoB-100 Liver VLDL, IDL, LDL, Lp(a) Core structural protein for VLDL, LDL, IDL, Lp(a); ligand for binding to LDL receptor (except for Lp(a)) ApoC-II Liver Chylomicrons, VLDL, HDL Cofactor for LPL ApoC-III Liver, intestine Chylomicrons, VLDL, HDL Inhibitor of LPL activity and remnant lipoprotein binding to receptors ApoE Liver Chylomicron remnants, IDL, HDL Ligand for binding to LDL receptor and other receptors Abbreviations: HDL, high-density lipoprotein; IDL, intermediate-density lipoprotein; LCAT, lecithin-cholesterol acyltransferase; LDL, low-density lipoprotein; Lp(a), lipoprotein(a); LPL, lipoprotein lipase; VLDL, very-low-density lipoprotein.

0.95 VLDL 1.006 IDL Density, g/mL Chylomicron remnants 1.02 LDL Chylomicron CHAPTER 419 Disorders of Lipoprotein Metabolism 1.06 HDL 1.10 1.20

Diameter, nm FIGURE 419-1  The density and size distribution of the major classes of lipoprotein particles. Lipoproteins are classified by density and size, which are inversely related. HDL, high-density lipoprotein; IDL, intermediate-density lipoprotein; LDL, low-density lipoprotein; VLDL, very-low-density lipoprotein. disorders of lipoprotein metabolism and clinical approaches to their diagnosis and management. LIPOPROTEIN STRUCTURE AND METABOLISM Lipoproteins contain an “oil droplet” core of hydrophobic lipids (TGs and cholesteryl esters) surrounded by a shell of hydrophilic lipids (phospholipids, unesterified cholesterol) and proteins (called apolipo­ proteins) that interact with body fluids (Fig. 419-1). The plasma lipo­ proteins are divided into major classes based on their relative density: chylomicrons, very-low-density lipoproteins (VLDLs), intermediatedensity lipoproteins (IDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs). Each lipoprotein class comprises a family of particles that vary in density, size, and protein composi­ tion. Because lipid is less dense than water, the density of a lipoprotein particle is primarily determined by the amount of lipid per particle. Chylomicrons are the most lipid-rich and therefore least dense lipopro­ tein particles, whereas HDL have the least lipid and are therefore the most dense. Lipoprotein particles vary widely in size, with the largest particles (chylomicrons) being the most lipid-rich and the smallest particles (HDL) being the most dense. The proteins associated with lipoproteins, called apolipoproteins (Table 419-1), are required for the assembly, structure, function, metabolism, and catabolism of lipoproteins. Apolipoproteins provide a structural basis for lipoproteins, activate enzymes important in lipoprotein metabolism, and act as ligands for cell surface receptors. ApoB is the major structural protein of chylomicrons, VLDLs, IDLs, and LDLs (collectively known as apoB-containing lipoproteins). One

molecule of apoB, either apoB-48 (chylomicrons) or apoB-100 (VLDL, IDL, or LDL), is present on each lipoprotein particle. The human liver synthesizes the full-length apoB-100 (one of the largest proteins in humans), whereas the intestine makes the shorter apoB-48, which is derived from transcription of the same APOB gene after posttranscrip­ tional mRNA editing. HDLs lack apoB and have different apolipopro­ teins that define this lipoprotein class, most importantly apoA-I, which is synthesized in both the liver and intestine and is found on virtually all HDL particles. ApoA-II is the second most abundant HDL apoli­ poprotein and is on approximately two-thirds of the HDL particles. ApoC-II, apoC-III, and apoA-V regulate the metabolism of TG-rich lipoproteins. ApoE plays a critical role in the metabolism and clearance of TG-rich particles. Most apolipoproteins, other than apoB, exchange actively among lipoprotein particles in the blood. Apolipoprotein(a) [apo(a)] is a distinctive apolipoprotein that results in the formation of a lipoprotein known as lipoprotein(a) [Lp(a)], which is discussed more below.

PART 12 Endocrinology and Metabolism ■ ■TRANSPORT OF INTESTINALLY DERIVED DIETARY LIPIDS BY CHYLOMICRONS Chylomicrons play a critical role in the efficient transport of absorbed dietary lipids from the intestine to tissues that require fatty acids for energy or storage and then return of cholesterol, lipids, and fat-soluble vitamins to the liver (Fig. 419-2). Dietary lipids are hydrolyzed by lipases within the intestinal lumen and emulsified with bile acids to form micelles. Dietary cholesterol, fatty acids, and fat-soluble vitamins are absorbed in the proximal small intestine. Cholesterol and retinol are esterified (by the addition of a fatty acid) in the enterocyte to form cholesteryl esters and retinyl esters, respectively. Longer-chain fatty acids (>12 carbons) are incorporated into TGs and packaged with apoB-48, phospholipids, cholesteryl esters, retinyl esters, and α-tocopherol (vitamin E) in a process that requires the action of the microsomal TG transfer protein (MTP) to form chylomicrons. Nascent chylomicrons are secreted into the intestinal lymph and delivered via Exogenous Endogenous Dietary lipids Bile acids + cholesterol LDL LDLR Small intestines Liver HL ApoB-100 ApoE ApoB-48 ApoC’s Chylomicron VLDL IDL Chylomicron remnant Capillaries Capillaries LPL FFA LPL FFA Muscle Adipose Muscle Adipose FIGURE 419-2  The exogenous and endogenous lipoprotein metabolic pathways. The exogenous pathway transports dietary lipids to the periphery and the liver. The endogenous pathway transports hepatic lipids to the periphery. FFA, free fatty acid; HL, hepatic lipase; IDL, intermediate-density lipoprotein; LDL, low-density lipoprotein; LDLR, low-density lipoprotein receptor; LPL, lipoprotein lipase; VLDL, very-low-density lipoprotein.

the thoracic duct directly to the systemic circulation, where they are extensively processed by peripheral tissues before reaching the liver. The particles encounter lipoprotein lipase (LPL), which is transported from parenchymal cells and anchored to the luminal surface of the endothelium by the protein GPIHBP1 of capillaries in tissues, par­ ticularly adipose, heart, and skeletal muscle (Fig. 419-2). ApoC-II and apoA-V are apolipoproteins that are transferred to circulating chylomicrons from HDL in the postprandial state; apoC-II acts as a required cofactor for LPL activation, and apoA-V serves as a facilitator of LPL activity. The TGs in chylomicrons are hydrolyzed by LPL, and free fatty acids are released and taken up by adjacent myocytes or adi­ pocytes and are either oxidized to generate energy or reesterified and stored as TG. Some of the released free fatty acids bind albumin before entering cells and are transported to other tissues, especially the liver. The chylomicron particle progressively shrinks in size as the hydro­ phobic TG core is hydrolyzed and the excess hydrophilic lipids (cho­ lesterol and phospholipids) and apolipoproteins on the particle surface are transferred to HDL, ultimately creating chylomicron remnants. Chylomicron remnants contain apoB-48, which lacks the region in apoB-100 that binds to the LDL receptor. Nevertheless, they are rapidly removed from the circulation by the liver through a process that critically requires apoE as a ligand for receptors in the liver. Few, if any, chylomicrons or chylomicron remnants are generally present in the blood after a 12-h fast, except in patients with certain disorders of lipoprotein metabolism as described below. ■ ■TRANSPORT OF HEPATICALLY DERIVED LIPIDS BY VLDL AND LDL Another key role of lipoproteins is the transport of hepatic lipids from the liver to the periphery (Fig. 419-2) to provide an energy source dur­ ing fasting and to deliver fat-soluble vitamins to key tissues. During the fasting state, lipolysis of adipose TGs generates fatty acids that are transported to the liver, and the liver is also capable of synthesizing fatty acids through de novo lipogenesis. These fatty acids are esterified by the liver into TGs, which are packaged into VLDL particles along with apoB-100, phospholipids, choles­ teryl esters, and vitamin E in a process that also requires MTP. VLDL thus resemble chylomicrons in that they are “triglyceride-rich lipoproteins,” but they contain apoB100 rather than apoB-48, are smaller and less buoyant, and have a higher ratio of cholesterol to TG (~1 mg of cholesterol for every 5 mg of TG, whereas in chylomi­ crons, this ratio is closer to ~1:8). After secretion by the liver into the plasma, the circulating TGs in VLDL are hydrolyzed by LPL. After the relatively TG-depleted VLDL remnants dissociate from LPL, they are referred to as IDLs, which contain roughly similar amounts of cholesterol and TG by mass. The liver removes ~40–60% of IDL by receptor-mediated endocytosis via binding to apoE, which is acquired through transfer of this protein from HDL. The remainder of IDL is further remodeled by hepatic lipase (HL) to form LDL. During this pro­ cess, phospholipids and TGs in the particle are hydro­ lyzed, and most of the remaining apolipoproteins except apoB-100 are transferred to other lipoproteins. LDL is primarily a by-product of fatty acid energy transport by VLDL with little true physiologic role; one exception is that LDL may be partially responsible for delivery of vitamin E to the retina and brain. LDL is ultimately removed from the circulation by receptor-mediated endocytosis (primarily via the LDL receptor) in the liver, with a region of apoB-100 serving as the specific ligand for binding to the LDL receptor. It should be noted that apoB-48 does not contain the LDL receptorbinding ligand region, and therefore, clearance of apoB48-containing chylomicron remnants is dependent on apoE-mediated clearance as noted above. Some LDL particles are lipolytically processed to small dense LDL particles that are believed to be especially atherogenic. Peripheral tissues

Lp(a) is a lipoprotein similar to LDL in lipid and protein composi­ tion, but it contains an additional distinctive protein called apo(a). Apo(a) is synthesized in the liver and attached to apoB-100 by a disul­ fide linkage. The major site of clearance of Lp(a) is the liver, but the uptake pathway is not known. Lp(a) is now established as causal factor for ASCVD and aortic stenosis, and an elevated level of Lp(a) serves as an independent risk factor and merits more aggressive therapy to reduce LDL cholesterol levels (see below). ■ ■HDL METABOLISM AND REVERSE CHOLESTEROL TRANSPORT All nucleated cells synthesize cholesterol, but only hepatocytes and enterocytes can effectively excrete cholesterol from the body, into either the bile or the gut lumen, respectively. In the liver, cholesterol is secreted into the bile, either directly or after conversion to bile acids. Cholesterol in peripheral cells is transported from the plasma mem­ branes of peripheral cells to the liver and intestine by a process termed reverse cholesterol transport that is facilitated by HDL (Fig. 419-3). Nascent HDL particles are synthesized by the intestine and the liver. Newly secreted apoA-I rapidly acquires phospholipids and unesteri­ fied cholesterol from its site of synthesis (intestine or liver) via cellular efflux promoted by the membrane protein ATP-binding cassette pro­ tein A1 (ABCA1). This process results in the formation of discoidal HDL particles, which then recruit additional unesterified cholesterol from cells or circulating lipoproteins. Within the HDL particle, the cholesterol is esterified to cholesteryl ester (CE) through the addition of a fatty acid by lecithin-cholesterol acyltransferase (LCAT), a plasma enzyme associated with HDL; the hydrophobic CE forms the core of the mature HDL particle. As HDL acquires more CE, it becomes spherical, and additional apolipoproteins and lipids are transferred to the particles from the surfaces of chylomicrons and VLDLs during lipolysis. HDL cholesterol in the blood is transported to hepatocytes by two major pathways. HDL CE can be “selectively” taken up by hepatocytes via the scavenger receptor class B1 (SR-B1), a cell surface HDL receptor that mediates the selective transfer of CE from HDL with subsequent dissociation and “recycling” of the HDL particle. In addition, HDL CE can be transferred to apoB-containing lipoproteins in exchange for TG by the cholesteryl ester transfer protein (CETP). The CE esters are then removed from the circulation by LDL receptor–mediated endocytosis. HDL-derived CE taken up by the hepatocyte through these pathways is hydrolyzed, and much of the cholesterol is ultimately excreted directly into the bile or converted to bile acids with excretion to bile, providing Macrophage Free cholesterol IDL LDL VLDL CETP ApoA-I Liver ApoA-I LCAT CETP Nascent HDL Small intestines Mature HDL Chylomicrons Peripheral cells FIGURE 419-3  High-density lipoprotein (HDL) metabolism and reverse cholesterol transport. The HDL pathway transports excess cholesterol from the periphery back to the liver for excretion in the bile. The liver and the intestine produce nascent HDLs. Free cholesterol is acquired from macrophages and other peripheral cells and esterified by lecithin-cholesterol acyltransferase (LCAT), forming mature HDLs. HDL cholesterol can be selectively taken up by the liver via SR-BI (scavenger receptor class BI). Alternatively, HDL cholesteryl ester can be transferred by cholesteryl ester transfer protein (CETP) from HDLs to very-low-density lipoproteins (VLDLs) and chylomicrons, which can then be taken up by the liver. IDL, intermediate-density lipoprotein; LDL, low-density lipoprotein; LDLR, lowdensity lipoprotein receptor.

a biliary route into the intestinal lumen. There is also evidence that, under certain conditions, HDL cholesterol can be transported directly into the intestinal lumen without requiring a transhepatobiliary route, a process known as transintestinal cholesterol excretion.

HDL particles undergo extensive remodeling within the plasma compartment by a variety of lipid transfer proteins and lipases. The phospholipid transfer protein (PLTP) transfers phospholipids from other lipoproteins to HDL or among different classes of HDL par­ ticles and is a regulator of HDL metabolism. After CETP- and PLTPmediated lipid exchange, the TG-enriched HDL becomes a much better substrate for HL, which hydrolyzes the TGs and phospholipids to generate smaller HDL particles. A related enzyme called endothelial lipase (EL) hydrolyzes HDL phospholipids, generating smaller HDL particles that are catabolized faster. Remodeling of HDL influences the metabolism, function, and plasma concentrations of HDL. Disorders of Lipoprotein Metabolism CHAPTER 419 SCREENING Dyslipidemia is an important causal factor in ASCVD, and treatment has been proven to substantially reduce cardiovascular risk. Therefore, all adults (and many children) should be actively screened for plasma lipids. A lipid panel should be measured, preferably after an overnight fast. In most clinical laboratories, the total cholesterol and TGs in the plasma are measured enzymatically, and then after precipitation of apoB-containing lipoproteins, the cholesterol in the supernatant is measured to determine the HDL cholesterol (HDL-C). The LDL cho­ lesterol (LDL-C) is then estimated using the following equation (the Friedewald formula): LDL-C = total cholesterol – (TG/5) – HDL-C (The VLDL cholesterol content is estimated by dividing the plasma TG by 5, reflecting the ratio of TG to cholesterol in VLDL particles.) This formula is reasonably accurate if test results are obtained on fasting plasma and if the TG level does not exceed ~200 mg/dL; by convention, it cannot be used if the TG level is >400 mg/dL. LDL-C can be directly measured by a number of methods. The non-HDLC can be easily calculated by subtracting the HDL-C from the total cholesterol. It has the advantage of incorporating the cholesterol contained within VLDL and IDL, which in most cases is also athero­ genic and associated with increased ASCVD risk. There is increasing evidence that measurement of plasma apoB levels may provide a better assessment of cardiovascular risk than the LDL-C level, and even the non-HDL-C level, and is recommended by some experts. While this has not yet become standard clinical practice, the data supporting the use of apoB as a risk marker and guide to therapeutic intervention are quite strong. There is also increasing interest in Lp(a), an independent ASCVD risk factor that is highly heritable and may be helpful in risk stratification. In patients with evidence of dyslip­ idemia, further evaluation and treatment are based on evidence of preexisting ASCVD and clinical assessment of cardiovascular risk using risk calculators such as the American Heart Association (AHA)/American College of Cardiology (ACC) risk calculator as well as, in some cases, based on additional approaches to risk assessment such as apoB and Lp(a) (see “Approach to the Patient” for more detailed discussion). LDLR SR-BI DISORDERS ASSOCIATED WITH ELEVATED APOB-CONTAINING LIPOPROTEINS Disorders of lipoprotein metabolism that cause ele­ vated levels of apoB-containing lipoproteins are among the most common and clinically important of the dyslipoproteinemias. They are generally character­ ized by increased plasma levels of total cholesterol, accompanied by increased TGs, LDL-C, or both. Many patients with hyperlipidemia have some combination of genetic predisposition (often polygenic) and medical

or environmental contribution (medical condition, diet, lifestyle, or drug). Many, but not all, patients with hyperlipidemia are at increased risk for ASCVD, which is the primary reason for making the diagnosis, as intervention can substantially reduce this risk. In addition, patients with severe hypertriglyceridemia may be at risk for acute pancreatitis and require intervention to reduce this risk.

Although hundreds of proteins influence lipoprotein metabolism, and genetic variants in most of the genes that encode them interact with each other and the environment to produce dyslipidemia, there are a limited number of discrete “nodes” or pathways that regulate lipo­ protein metabolism and are dysfunctional in specific dyslipidemias. These include (1) lipolysis of TG-rich lipoproteins by LPL; (2) recep­ tor-mediated uptake of apoB-containing lipoproteins by the liver; (3) cellular cholesterol metabolism in the hepatocyte and the enterocyte; (4) assembly and secretion of VLDLs by the liver; and (5) neutral lipid transfer and phospholipid hydrolysis in the plasma. Primary genetic disorders of lipoprotein metabolism caused by single-gene mutations (Table 419-2) have taught us a great deal about the physiologic roles of specific proteins in these pathways in humans and are clinically impor­ tant to diagnose and treat. PART 12 Endocrinology and Metabolism ■ ■SEVERE HYPERTRIGLYCERIDEMIA Severe hypertriglyceridemia (HTG) is defined by fasting TG levels

500 mg/dL and is usually accompanied by moderately elevated total cholesterol levels and reduced levels of HDL-C, usually without impor­ tant elevation in LDL-C or apoB. It is medically important because it is associated with risk of acute pancreatitis and, in some cases, is also associated with increased risk of ASCVD. Severe HTG is usually caused by impaired lipolysis of TGs in TG-rich lipoproteins (TRLs) by the enzyme LPL. LPL is synthesized by adipocytes, skeletal myo­ cytes, and cardiomyocytes, and its posttranslational maturation and folding require the action of lipase maturation factor 1 (LMF1). After secretion, it is transported from the subendothelial to the vascular endothelial surfaces by GPIHPB1, which docks it to the endothelial surface. ApoC-II is a required cofactor for LPL, and apoA-V promotes LPL activity, and both are transported to the bound LPL on the TRLs. Single-gene Mendelian disorders that reduce LPL have been described (Table 419-3) as reviewed below; the majority of patients with severe HTG have a polygenic predisposition to secondary factors like obesity or insulin resistance. Primary (Genetic) Causes of Severe Hypertriglyceridemia  • 

FAMILIAL CHYLOMICRONEMIA SYNDROME (FCS)  LPL is required for the hydrolysis of TGs in chylomicrons and VLDLs. Genetic deficiency or inactivity of LPL results in impaired lipolysis and profound elevations in plasma TGs, mostly in chylomicrons. While chylomicronemia predomi­ nates, in fact, these patients often have elevated plasma levels of VLDL as well. The fasting plasma is turbid, and if left undisturbed for several hours, the chylomicrons float to the top and form a creamy supernatant layer. Fasting TG levels are >500 mg/dL and usually >1000 mg/dL. Because chylomicrons contain cholesterol, fasting total cholesterol levels are also elevated. There are five genes in which mutations can result in FCS (Table 419-2). FCS has an estimated frequency of ~1 in 200,000–300,000, although its true prevalence is unknown. The most common molecular cause of FCS involves mutations in the LPL gene. LPL deficiency has autosomal recessive inheritance (loss-of-function mutations in both alleles). Heterozygotes with LPL mutations often have moderate elevations in plasma TG levels and increased risk for coronary heart disease (CHD). FCS can also be caused by mutations in genes that affect LPL processing or activity. For example, apoC-II is a required cofactor for LPL. APOC2 deficiency due to loss-of-function mutations in both APOC2 alleles results in functional lack of LPL activ­ ity and severe hyperchylomicronemia that is indistinguishable from LPL deficiency. It is also recessive in inheritance pattern and much rarer than LPL deficiency. Another apolipoprotein, apoA-V, facilitates the association of TRLs with LPL and promotes hydrolysis of the TGs. Individuals harboring loss-of-function mutations in both APOA5 alleles causing APOA5 deficiency develop a form of FCS. GPIHBP1 is required for transport and tethering of LPL to the endothelial luminal

surface. Homozygosity for mutations in GPIHBP1 that interfere with its synthesis or folding causes FCS. Autoantibodies to GPIHBP1 have also been reported to cause severe hyperchylomicronemia. Finally, LMF1 is required for appropriate processing and folding of LPL, and biallelic loss-of-function mutations can cause FCS. FCS can present in childhood or adulthood with severe abdominal pain due to acute pancreatitis. In this setting, the diagnosis should be suspected if a fasting TG level is >500 mg/dL. Eruptive xanthomas, which are small, yellowish-white papules, may appear in clusters on the back, buttocks, and extensor surfaces of the arms and legs. On funduscopic examination, the retinal blood vessels may be opalescent (lipemia retinalis). Hepatosplenomegaly is sometimes noted as a result of uptake of circulating chylomicrons by reticuloendothelial cells in the liver and spleen. Premature ASCVD is not generally a feature of FCS. The diagnosis of FCS is a clinical diagnosis based on persistence and severity of HTG, with a history of acute pancreatitis or eruptive xanthomas increasing the suspicion. While LPL activity can be mea­ sured in “postheparin plasma” obtained after an IV heparin injection to release the endothelial-bound LPL, this assay is not widely available. Genetic testing of a panel of candidate FCS genes can be used to con­ firm the diagnosis but is not required for making the clinical diagnosis. Because of the risk of pancreatitis, it is important to consider the diagnosis and institute therapeutic interventions in FCS. The goal is to prevent pancreatitis by reducing fasting TG levels to <500 mg/dL. Consultation with a registered dietician familiar with this disorder is essential. Dietary fat intake should be markedly restricted (to as little as 15 g/d), often with fat-soluble vitamin supplementation. Strict adher­ ence to dietary fat restriction can be successful at controlling the chylo­ micronemia; fish oils or fibrates (such as fenofibrate) may be tried but are unlikely to be effective. Promising therapeutic approaches include the silencing of APOC3 or ANGPTL3 in the liver. In patients with APOC2 deficiency, apoC-II can be provided exogenously by infusing fresh-frozen plasma to resolve the chylomicronemia in the setting of severe acute pancreatitis. Management of patients with FCS is particu­ larly challenging during pregnancy when VLDL production is increased. FAMILIAL PARTIAL LIPODYSTROPHY (FPLD)  FPLD is a genetic con­ dition in which the generation of adipose tissue in certain fat depots is impaired and in others is excessive. FPLD is an underrecognized monogenic cause of severe HTG, which is likely due to both increased lipid synthesis and VLDL production, as well as reduced LPL-mediated clearance of TRLs. FPLD is typically a dominantly inherited disorder caused by mutations in several different genes, including lamin A/C (LMNA), PPARγ (PPARG), perilipin (PLIN1), AKT2, and ADRA2A (Table 419-2). FPLD is characterized by loss of subcutaneous fat in the extremities and buttocks, often accompanied by increased visceral fat. Because of the reduced or absent subcutaneous fat in the arms and legs, patients are often described as having a “muscular” appearance. In addition to severe HTG, FPLD patients usually have insulin resistance, often quite severe, accompanied by type 2 diabetes and hepatosteato­ sis. Pancreatitis secondary to HTG can be a complication; in addition, ASCVD risk is substantially increased in FPLD patients. The diagnosis of FPLD is a clinical diagnosis based on the constellation of metabolic findings accompanied by the distinctive distribution of adipose tissue. Genetic testing of a panel of candidate FPLD genes can be used to con­ firm the diagnosis but is not required for making the clinical diagnosis, and a negative result does not rule out the diagnosis. Because FPLD is a dominant disorder, the finding of a causal mutation should lead to family-based screening. The dyslipidemia of FPLD can be difficult to manage clinically. Patients should be treated aggressively not only to reduce TG levels but also with statins and, if necessary, additional LDL-lowering thera­ pies to reduce atherogenic lipoproteins. The insulin-resistant diabetes often requires aggressive management as well. Some patients have progression of fatty liver disease to metabolic-associated steatohepati­ tis, fibrosis, and cirrhosis. A different group of very rare patients have congenital generalized lipodystrophy, a recessive disorder caused by mutations in the AGPAT2 and BSCL2 genes. These patients have nearly complete absence of subcutaneous fat, accompanied by profound

TABLE 419-2  Primary Dyslipoproteinemias Caused by Known Single-Gene Mutations GENETIC DISORDER GENES MUTATED LIPOPROTEINS AFFECTED CLINICAL FINDINGS GENETIC TRANSMISSION ESTIMATED PREVALENCE Severe Hypertriglyceridemia Familial chylomicronemia syndrome (FCS) Biallelic LoF mutations in: LPL, APOC2, APOA5, GPIHBP1, LMF1 Elevated: Chylomicrons, VLDL Reduced: HDL Familial partial lipodystrophy (FPLD) Heterozygous LoF mutations in: LMNA, PPARG, PLIN1, AKT2, ADRA2A Elevated: Chylomicrons, VLDL, LDL Reduced: HDL Hypercholesterolemia Familial hypercholesterolemia (FH) Heterozygous LoF mutations in LDLR Elevated: LDL Tendon xanthomas, premature atherosclerotic cardiovascular disease (ASCVD) Familial defective apoB100 (FDB) Heterozygous LoF receptor binding region mutations in APOB Elevated: LDL Tendon xanthomas, premature ASCVD Autosomal dominant hypercholesterolemia (ADH), type 3 Heterozygous GoF mutations in PCSK9 Elevated: LDL Tendon xanthomas, premature ASCVD Autosomal recessive hypercholesterolemia (ARH) Biallelic LoF mutations in LDLRAP1 Elevated: LDL Tendon xanthomas, premature ASCVD Sitosterolemia Biallelic LoF mutations in ABCG5, ABCG8 Elevated: LDL Tendon xanthomas, premature ASCVD Lysosomal acid lipase deficiency Biallelic LoF mutations in LIPA Elevated: LDL Reduced: HDL   Mixed Dyslipidemia Familial dysbetalipoproteinemia (FDBL) Biallelic carriers of the APOE2 variant Elevated: Chylomicron remnants, IDL Hepatic lipase deficiency Biallelic LoF mutations in LIPC Elevated: Chylomicron remnants, IDL, HDL Familial Hypolipidemia Syndromes Abetalipoproteinemia Biallelic LoF mutations in MTTP Absent: LDL Reduced: TG, HDL Familial hypobetalipoproteinemia Heterozygous truncating mutations in APOB Reduced: LDL Fatty liver, reduced risk of ASCVD Familial PCSK9 deficiency Heterozygous LoF mutations in PCSK9 Reduced: LDL Reduced risk of ASCVD AD ~1/1,000 Familial combined hypolipidemia Heterozygous LoF mutations in ANGPTL3 Reduced: TG, LDL, HDL Reduced risk of ASCVD AD <1/1,000,000 Primary Low HDL Cholesterol Syndromes ApoA-I deletions/ mutations Heterozygous structural mutations in APOA1 Reduced: HDL Variable depending on mutation: premature ASCVD, systemic amyloidosis Tangier disease Biallelic LoF mutations in ABCA1 Nearly absent: HDL Reduced: LDL Elevated: TG Familial LCAT deficiency (FLD); fish eye disease (FED) Biallelic LoF mutations in LCAT Markedly reduced: HDL Corneal opacities (both FLD and FED), progressive chronic kidney disease (FLD only) Abbreviations: AD, autosomal dominant; apo, apolipoprotein; AR, autosomal recessive; ARH, autosomal recessive hypercholesterolemia; CHD, coronary heart disease; GoF, gain of function; HDL, high-density lipoprotein; IDL, intermediate-density lipoprotein; LCAT, lecithin-cholesterol acyltransferase; LDL, low-density lipoprotein; LoF, loss of function; LPL, lipoprotein lipase; PVD, peripheral vascular disease; TG, triglyceride; VLDL, very-low density lipoprotein. leptin deficiency, insulin resistance, severe HTG, and accumulation of TGs in multiple tissues including the liver. Patients with general­ ized lipodystrophy can be effectively treated with recombinant leptin administration, which often manages the multiple metabolic issues in these patients.

Pancreatitis, eruptive xanthomas, hepatosplenomegaly AR ~1/200,000–300,000 Insulin resistance, fatty liver disease, pancreatitis, central obesity, lack of subcutaneous adipose in extremities AD <1/1,000,000 Disorders of Lipoprotein Metabolism CHAPTER 419 AD ~1/250 AD ~1/1500 AD <1/1,000,000 AR <1/1,000,000 AR <1/1,000,000 Fatty liver disease, micronodular cirrhosis AR <1/1,000,000 Palmar and tuberoeruptive xanthomas, premature ASCVD AR ~1/10,000 Premature ASCVD AR <1/1,000,000 Spinocerebellar degeneration, retinal degeneration AR <1/1,000,000 AD <1/1,000,000 AD <1/1,000,000 Peripheral neuropathy, hepatosplenomegaly AR <1/1,000,000 AR <1/1,000,000 Multifactorial Severe Hypertriglyceridemia  Most patients with severe HTG do not have a single-gene mutation but instead have a multifactorial etiology that includes genetics and environment. The prevalence of this phenotype is ~1 in 1000. HTG often runs in families, and the term familial HTG has been employed; however, except for the

TABLE 419-3  Secondary Causes of Altered Lipid and Lipoprotein Levels   LDL-C HDL-C LP(a) ELEVATED TG ELEVATED ELEVATED REDUCED ELEVATED REDUCED   High-carbohydrate diet Alcohol Obesity Insulin resistance Type 2 diabetes Lipodystrophy Chronic kidney disease Nephrotic syndrome Viral hepatitis Sepsis Cushing’s syndrome Acromegaly Glycogen storage disease Pregnancy Drugs: estrogen, glucocorticoids, isotretinoin, bexarotene, other retinoids, beta blockers, bile acid binding resins Hypothyroidism Cholestasis Nephrotic syndrome Cushing’s syndrome Acute intermittent porphyria Drugs: corticosteroids, cyclosporin, sirolimus, carbamazepine Vegan diet Malabsorption Malnutrition Severe liver disease Gaucher’s disease Chronic infectious disease Hyperthyroidism PART 12 Endocrinology and Metabolism Abbreviations: HDL-C, high-density lipoprotein cholesterol; LAL, lysosomal acid lipase; LDL-C, low-density lipoprotein cholesterol; Lp(a), lipoprotein(a); TG, triglyceride. genes in which mutations cause FCS or FPLD, reviewed above, no other classic Mendelian causes of HTG have been identified to date. Instead, extensive human genetic studies have clearly established a polygenic basis to this phenotype that consists of two categories: (1) rare hetero­ zygous variants in the five genes discussed earlier that cause FCS in the homozygous state, and (2) a high burden of common variants that have small individual effects at raising TGs. Patients who inherit some com­ bination of rare and common TG-raising alleles often have environ­ mental factors that exacerbate their HTG. These “secondary” factors are reviewed in detail below, but the quantitatively most important fac­ tors promoting HTG include obesity, type 2 diabetes, insulin resistance, high-carbohydrate diet, and alcohol use. Multifactorial HTG is char­ acterized by elevated fasting TGs but average to below average LDL-C levels and low HDL-C levels; apoB levels are not generally elevated. This condition is not generally associated with a significantly increased risk of ASCVD. However, if the HTG is exacerbated by environmental factors, medical conditions, or drugs, the TGs can rise to a level at which acute pancreatitis is a risk. Indeed, management of patients with this condition is mostly focused on reduction of TGs to prevent pancre­ atitis. It is important to consider and rule out secondary causes of the HTG. Patients who are at high risk for ASCVD due to other risk factors should be treated with statin therapy. In patients who are otherwise not at high risk for ASCVD, lipid-lowering drug therapy can frequently be avoided with appropriate dietary and lifestyle changes. Patients with plasma TG levels >500 mg/dL after a trial of diet and exercise should be considered for drug therapy with a fibrate or fish oil to reduce TGs in order to prevent pancreatitis. These patients should also be carefully evaluated for ASCVD risk and may be candidates for statin therapy to further reduce cholesterol and cardiovascular risk. ■ ■HYPERCHOLESTEROLEMIA (ELEVATED LDL-C) Elevated LDL-C is common and is medically important because it is associated with risk of premature ASCVD. Elevated LDL-C is often caused by impaired uptake of LDL by the liver. As discussed above, the LDL receptor is the major receptor responsible for uptake of LDL, and most causes of elevated LDL-C converge on reduced expression or activity of the LDL receptor in the liver. One major environmental factor that reduces LDL receptor activity is a diet high in saturated and trans fats. Other medical conditions that reduce LDL receptor activ­ ity include hypothyroidism and estrogen deficiency. The diagnosis of familial hypercholesterolemia involving several genes that influence LDL clearance should be considered in patients with LDL-C levels

190 mg/dL (Table 419-2). However, the majority of patients with

High-fat diet Alcohol Exercise Drugs: estrogen, phenytoin Hypertriglyceridemia Vegan diet Malabsorption Malnutrition Sedentary lifestyle Smoking Obesity Gaucher’s disease LAL deficiency Drugs: anabolic steroids, testosterone, beta blockers Chronic kidney disease Nephrotic syndrome Inflammation Menopause Orchidectomy Hypothyroidism Acromegaly Drugs: growth hormone, isotretinoin elevated LDL-C have a polygenic predisposition exacerbated by sec­ ondary factors like a diet high in saturated and trans fats. Primary (Genetic) Causes of Elevated LDL-C  •  FAMILIAL HYPERCHOLESTEROLEMIA (FH)  FH is an autosomal dominant dis­ order characterized by elevated plasma levels of LDL-C usually with relatively normal TG levels. FH is caused by mutations that lead to reduced function of the LDL receptor, with the most common being mutations in the LDLR gene itself. The reduction in LDL receptor activity in the liver results in a reduced rate of clearance of LDL from the circulation. The plasma level of LDL increases to a level such that the rate of LDL production equals the rate of LDL clearance by residual LDL receptor as well as non-LDL receptor mechanisms. Individuals with two mutated LDLR alleles (homozygotes or compound hetero­ zygotes) have much higher LDL-C levels than those with one mutant allele, causing a condition known as homozygous FH. Although mutations in LDLR are the most common cause of FH (and originally the term FH was used specifically for patients with LDLR mutations), mutations in at least two other genes, APOB and PCSK9, can also cause FH. ApoB-100 is the critical structural protein in LDL and contains a domain that serves as the ligand for binding to the LDL receptor. Mutations in the LDL receptor–binding domain of apoB-100 reduce the affinity of apoB/LDL binding to the LDL receptor, such that LDL is removed from the circulation at a reduced rate. This condition has also been termed familial defective apoB (FDB). Of note, truncating mutations in APOB cause low LDL-C levels (see below). The proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that binds to the LDL receptor and targets it for lysosomal deg­ radation. Normally, after LDL binds to the LDL receptor, it is internal­ ized along with the receptor, and in the low pH of the endosome, the LDL receptor dissociates from the LDL and recycles to the cell surface. When circulating PCSK9 binds the receptor, the complex is internal­ ized and the receptor is directed to the lysosome, rather than to the cell surface, reducing the number of active LDL receptors. Gain-of-function mutations in PCSK9 that enhance the activity of PCSK9 cause a form of FH, also known as ADH type 3. Of note, loss-of-function mutations in PCSK9 reduce LDL-C levels (see below). The population frequency of heterozygous FH was originally esti­ mated to be 1 in 500 individuals, but recent data suggest it may be as high as ~1 in 250 individuals, making it one of the most common single-gene disorders in humans. FH has a much higher prevalence in certain founder populations, such as South African Afrikaners, Christian Lebanese, French Canadians, and Lancaster County Amish.

Heterozygous FH is characterized by elevated plasma levels of LDL-C (usually >190 mg/dL) and relatively normal levels of TGs. Patients with FH have hypercholesterolemia from birth, and FH diagnosis is often based on detection of hypercholesterolemia on routine lipid screen­ ing; this serves as the basis for the recommendation to screen children between the ages of 9 and 11. A family history of hypercholesterolemia or premature ASCVD should prompt targeted screening. Inheritance of FH is dominant, meaning that the condition is inherited from one parent, and ~50% of the patient’s siblings and children can be expected to have FH. For this reason, family-based “cascade screening” can be very effective in identifying additional persons with FH. Physical findings in some, but not all, patients with FH may include corneal arcus and/or tendon xanthomas, particularly involving the dorsum of the hands and the Achilles tendons. Untreated heterozygous FH is associated with a markedly increased risk of cardiovascular disease; untreated men with heterozygous FH have an ~50% chance of having a myocardial infarction before age 60 years, and women with hetero­ zygous FH are at substantially increased risk as well. The age of onset of cardiovascular disease is highly variable and depends on the specific molecular defect, the level of LDL-C, and coexisting cardiovascular risk factors. The diagnosis of FH is generally a clinical diagnosis based on hyper­ cholesterolemia with LDL-C >190 mg/dL in the absence of a secondary etiology and ideally with a family history of hypercholesterolemia and/ or premature ASCVD. Secondary causes of significant hypercholester­ olemia such as hypothyroidism, nephrotic syndrome, and obstructive liver disease should be excluded. Sequencing of an FH gene panel (LDLR, APOB, PCSK9) to confirm the diagnosis is widely available and worthy of consideration; persons with molecularly confirmed FH are at higher risk of ASCVD and therefore may benefit from more aggressive treatment, and the finding of a specific causal variant has implications for family-based cascade screening. FH patients should be actively treated to lower plasma levels of LDL-C, preferably starting in childhood. Initiation of a diet low in saturated and trans fats is recommended, but heterozygous FH patients almost always require pharmacologic therapy for effective control of their LDL-C levels. Statins are the initial drug class of choice, and usually “high-intensity” statin therapy is needed. Many FH patients cannot achieve adequate control of their LDL-C levels even with high-intensity statin therapy, and a cholesterol absorption inhibitor (ezetimibe), a PCSK9 inhibitor, an ACL inhibitor (bempe­ doic acid), and a bile acid sequestrant are other classes of drugs that can be added to statins (Table 419-4). Some patients with severe het­ erozygous FH cannot be adequately managed using existing therapies and are candidates for LDL apheresis, a physical method of purging the blood of LDL in which the LDL particles are selectively removed from the circulation. Other novel approaches for these patients are under development. Homozygous FH (HoFH) is caused by loss-of-function mutations in both alleles of the LDL receptor or double heterozygosity for mutations in two FH genes. Patients with HoFH have been classified into those with virtually no detectable LDL receptor activity (receptor negative) and patients with markedly reduced but detectable LDL receptor activ­ ity (receptor defective). Untreated LDL-C levels in patients with HoFH range from ~400 to >1000 mg/dL, with receptor-defective patients at the lower end and receptor-negative patients at the higher end of the range. TGs are usually relatively normal. Some patients with HoFH, particularly receptor-negative patients, present in childhood with cutaneous planar xanthomas on the hands, wrists, elbows, knees, heels, or buttocks. The devastating consequence of HoFH is accelerated ASCVD, which often presents in childhood or early adulthood. Ath­ erosclerosis often develops first in the aortic root, where it can cause aortic valvular or supravalvular stenosis, and typically extends into the coronary ostia, which become stenotic. Symptoms can be atypical, and sudden death is not uncommon. Untreated, receptor-negative patients with HoFH rarely survive beyond the second decade; patients with receptor-defective LDL receptor defects have a better prognosis but almost invariably develop clinically apparent atherosclerotic vascular disease by age 30 and often much sooner.

HoFH should be suspected in a child or young adult with LDL

400 mg/dL without secondary cause. Cutaneous xanthomas, evidence of ASCVD, and/or hypercholesterolemia in both parents all are sup­ portive of the diagnosis. While the diagnosis is usually made on clinical grounds, genetic testing should be performed to identify specific causal variants. Patients with HoFH must be treated aggressively to delay the onset and progression of cardiovascular disease (CVD). Although receptor-negative patients have no response to statins and PCSK9 inhibitors, receptor-defective patients can have modest responses to these medicines, and they should be tried in patients with HoFH. Two drugs that reduce the hepatic production of VLDL and thus LDL, a small-molecule inhibitor of MTP and an antisense oligonucleotide to apoB, and an antibody that inhibits ANGPLT3 are approved for the treatment of patients with HoFH and should be considered in HoFH patients. LDL apheresis should be considered in HoFH patients who have persistently elevated LDL-C levels despite drug therapy. Liver transplantation is effective in decreasing plasma LDL-C levels in this disorder and is sometimes used as a last resort. Liver-directed gene therapy is under development for HoFH, as are other new therapeutic approaches intended to address the remaining unmet medical need.

Disorders of Lipoprotein Metabolism CHAPTER 419 FH is an autosomal dominant disorder. There are a few rare con­ ditions that cause an FH-like phenotype in an autosomal recessive manner and should be considered in patients with severe hypercholes­ terolemia who do not report a family history of hypercholesterolemia or premature CHD. AUTOSOMAL RECESSIVE HYPERCHOLESTEROLEMIA (ARH)  ARH is a very rare autosomal recessive disorder that was originally reported in individuals of Sardinian descent. The disease is caused by mutations in the gene LDLRAP1 encoding the protein LDLR adaptor protein (also called the ARH protein), which is required for LDL receptor–mediated endocytosis in the liver. LDLRAP1 binds to the cytoplasmic domain of the LDL receptor and links the receptor to the endocytic machinery. In the absence of LDLRAP1, LDL binds to the extracellular domain of the LDL receptor, but the lipoprotein-receptor complex fails to be internal­ ized. ARH, like HoFH, is characterized by hypercholesterolemia, tendon xanthomas, and premature coronary artery disease (CAD). The levels of plasma LDL-C tend to be intermediate between the levels present in FH homozygotes and FH heterozygotes, and CAD is not usually symptom­ atic until the third decade. LDL receptor function in cultured fibroblasts is normal or only modestly reduced in ARH, whereas LDL receptor function in the liver is negligible. Unlike FH homozygotes, the hyper­ lipidemia responds to treatment with statins, but these patients often require additional therapy to lower plasma LDL-C to acceptable levels. SITOSTEROLEMIA  Sitosterolemia is a rare autosomal recessive disease that is caused by biallelic loss-of-function mutations in either of two members of the ATP-binding cassette (ABC) half transporter family, ABCG5 and ABCG8. These genes are expressed in both enterocytes and hepatocytes. The proteins heterodimerize to form a functional complex that transports plant sterols such as sitosterol and campes­ terol, and animal sterols, predominantly cholesterol, across the apical biliary membrane of hepatocytes into the bile and across the apical luminal membrane of enterocytes into the gut lumen, thus reduc­ ing their (re)absorption and promoting their excretion. In normal individuals, <5% of dietary plant sterols are absorbed by the proximal small intestine. The small amounts of plant sterols that enter the circu­ lation are preferentially excreted into the bile, and thus, levels of plant sterols are kept very low in tissues. In sitosterolemia, the intestinal absorption of sterols is increased and biliary and fecal excretion of the sterols is reduced, resulting in increased plasma and tissue levels of both plant sterols and cholesterol. The increase in hepatic sterol levels results in transcriptional suppression of the expression of the LDL receptor, resulting in reduced uptake of LDL and substantially increased LDL-C levels. In addition to the clinical picture of severe hypercholesterolemia, often accompanied by tendon xanthomas and premature ASCVD, these patients also have anisocytosis and poikilo­ cytosis of erythrocytes and megathrombocytes due to the incorpora­ tion of plant sterols into cell membranes. Episodes of hemolysis and splenomegaly are a distinctive clinical feature of this disease compared

TABLE 419-4  Drugs Used to Treat Dyslipidemia MAJOR INDICATIONS STARTING DOSE MAXIMAL DOSE MECHANISM ADVERSE EFFECTS DRUG LDL-Lowering Drugs           HMG-CoA reductase inhibitors (statins) Elevated LDL-C; increased CV risk     ↓ Inhibition of cholesterol synthesis → ↑ Hepatic LDL receptors   Lovastatin   20–40 mg daily 80 mg daily       Pravastatin   40–80 mg daily 80 mg daily       Simvastatin   20–40 mg daily 80 mg daily       Fluvastatin   20–40 mg daily 80 mg daily     PART 12 Endocrinology and Metabolism   Atorvastatin   20–40 mg daily 80 mg daily       Rosuvastatin   5–20 mg daily 40 mg daily       Pitavastatin   1–2 mg daily 4 mg daily     Cholesterol absorption inhibitor Elevated LDL-C     ↓ Cholesterol absorption→ ↑ LDL receptors   Ezetimibe   10 mg daily 10 mg daily     Bile acid sequestrants Elevated LDL-C     ↑ Bile acid excretion → ↑ LDL receptors   Cholestyramine   4 g daily 32 g daily       Colestipol   5 g daily 40 g daily       Colesevelam   3750 mg daily 4375 mg daily     PCSK9 inhibitors   Evolocumab (Ab)   Alirocumab (Ab) Elevated LDL-C 140 mg SC every 2 weeks 75 mg SC every 2 weeks   Inclisiran (siRNA)   300 mg SC every 6 months 300 mg SC every 6 months ↓ PCSK9 synthesis due to siRNA silencing → ↑ LDL receptors ATP citrate lyase inhibitor   Bempedoic acid Elevated LDL-C 180 mg daily 180 mg daily ↓ Inhibition of cholesterol synthesis → ↑ LDL receptors MTP inhibitor   Lomitapide HoFH 5 mg daily 60 mg daily MTP inhibition → ↓ VLDL assembly and secretion ApoB inhibitor (ASO)   Mipomersen HoFH 200 mg SC weekly 200 mg SC weekly ↓ ApoB synthesis due to ASO silencing → ↓ ApoB/VLDL secretion ANGPTL3 inhibitor (Ab)   Evinacumab HoFH 15 mg/kg IV q 4 weeks 15 mg/kg IV q 4 weeks ↓ ANGPTL3 activity due to Ab inhibition → ↑ LPL and EL activity, ↑ LDL catabolism TG-Lowering Drugs Fibric acid derivatives (fibrates)   Gemfibrozil   Fenofibrate Elevated TG 600 mg bid 40–160 mg daily

depending on product Omega-3 fatty acids   Acid ethyl esters Elevated TG 4 g daily 4 g daily ↑ TG catabolism Dyspepsia   Icosapent ethyl   4 g daily 4 g daily     Abbreviations: Ab, antibody; GI, gastrointestinal; HDL-C, high-density lipoprotein cholesterol; HoFH, homozygous familial hypercholesterolemia; LDL, low-density lipoprotein; LDL-C, LDL cholesterol; LPL, lipoprotein lipase; TG, triglyceride; VLDL, very-low-density lipoprotein. to other genetic forms of hypercholesterolemia and can be a clue to the diagnosis. Sitosterolemia should be suspected in a patient with severe hypercholesterolemia without a family history of such or who fails to respond to statin therapy. Sitosterolemia can be diagnosed by a labora­ tory finding of a substantial increase in plasma sitosterol and/or other plant sterols and should be confirmed by gene sequencing of ABCG5 and ABCG8. It is important to make the diagnosis, because diet, bile acid sequestrants, and cholesterol-absorption inhibitors are the most effective agents to reduce LDL-C and plasma plant sterol levels in these patients. Of note, heterozygosity for mutations in ABCG5 or ABCG8 is now recognized to cause a moderate form of hypercholesterolemia. LYSOSOMAL ACID LIPASE DEFICIENCY (LALD)  LALD, also known as cholesteryl ester storage disease, is an autosomal recessive disorder

Myalgias and myopathy, ↑ transaminases, ↑ diabetes risk Elevated transaminases Bloating, constipation, elevated triglycerides 420 mg SC every 1 month (HoFH) 150 mg SC every 2 weeks Injection site reactions ↓ PCSK9 activity due to Ab inhibition → ↑ LDL receptors Injection site reactions ↑ uric acid and gout ↑ cholelithiasis     Nausea, diarrhea, increased hepatic fat Injection site reactions, flu-like symptoms, increased hepatic fat Reduced HDL-C levels 600 mg bid 40–160 mg daily depending on product ↑ LPL, ↓ VLDL synthesis Dyspepsia, myalgia, cholelithiasis, elevated transaminases caused by loss-of-function variants in both alleles of the gene LIPA encoding the enzyme lysosomal acid lipase (LAL). LAL is responsible for hydrolyzing neutral lipids, particularly TGs and CEs, after delivery to the lysosome by cell surface receptors such as the LDL receptor. It is particularly important in the liver, which clears large amounts of lipoproteins from the circulation. LALD is characterized by elevated LDL-C, usually in association with low HDL-C and with variably elevated TG levels, together with progressive fatty liver ultimately lead­ ing to hepatic fibrosis. Genetic deficiency of LAL results in accumula­ tion of neutral lipid in the hepatocytes, leading to hepatosplenomegaly, microvesicular steatosis, and ultimately fibrosis and end-stage liver disease. The most severe form of this disorder, Wolman’s disease, pres­ ents in infancy and is rapidly fatal. The etiology of the elevated LDL-C levels is primarily due to impaired LDL receptor–mediated clearance

of LDL. LALD should be suspected in nonobese patients with elevated LDL-C, low HDL-C, and evidence of fatty liver in the absence of overt insulin resistance. The diagnosis can be made with a dried blood spot assay of LAL activity and confirmed by DNA genotyping for the most common mutation, followed if necessary by sequencing of the gene to find the second mutation. Liver biopsy is required to assess the degree of inflammation and fibrosis. LALD is underdiagnosed; it is criti­ cally important to suspect it and make the diagnosis because enzyme replacement therapy with sebelipase alfa is now available and is highly effective in treating this condition. The above conditions primarily cause elevations in LDL due to impaired catabolism of LDL from the blood. There are a few forms of primary dyslipidemia that impair the catabolism of “remnant” TRLs (after their processing by LPL) and therefore cause elevations in both cholesterol and TGs due to remnant accumulation. Multifactorial Hypercholesterolemia  Most patients with ele­ vated LDL-C do not have a single-gene disorder, as described above, but instead have a multifactorial etiology that includes genetics and environment. Genetic variation contributes substantially to elevated LDL-C levels in the general population. It has been estimated that at least 50% of variation in LDL-C is genetically determined. Many patients with elevated LDL-C have polygenic hypercholesterolemia due to multiple common genetic variants exerting modest LDL-raising effects. Individuals at the tail of the highest burden of polygenic risk score for LDL-C often have LDL-C levels that are similar to those with FH. In patients who are genetically predisposed to higher LDL-C levels, diet plays a key exacerbating role; indeed, increased saturated and trans fats in the diet shift the entire distribution of LDL-C levels in the popu­ lation to the right. As described in more detail below, patients with elevated LDL-C should be carefully assessed for their risk of ASCVD and managed with lifestyle modification and LDL-lowering medica­ tions as needed to reduce LDL-C and risk of ASCVD. ■ ■MIXED HYPERLIPIDEMIA (ELEVATED TG AND LDL-C) Mixed hyperlipidemia can be defined as fasting TGs >150 mg/dL and evidence of elevated cholesterol-containing lipoproteins (such as LDL-C >130 mg/dL or non-HDL-C >160 mg/dL). It is one of the most common types of lipid disorders seen in clinical practice, due both to genetic predisposition and influence of medical conditions and envi­ ronmental factors (see below). It is generally associated with elevated risk of ASCVD, and therefore, patients with mixed hyperlipidemia should be carefully evaluated and managed to reduce this risk. Primary (Genetic) Causes of Mixed Hyperlipidemia  •  FAMILIAL

DYSBETALIPOPROTEINEMIA (FDBL)  FDBL (also known as type III hyperlipoproteinemia) is a recessive disorder characterized by a mixed hyperlipidemia due to the accumulation of remnant lipoprotein par­ ticles (chylomicron remnants and VLDL remnants, or IDL). ApoE is present in multiple copies on chylomicron remnants and IDL and mediates their removal via hepatic lipoprotein receptors (Fig. 419-2). The APOE gene is polymorphic in sequence, resulting in the expression of three common isoforms: apoE3, which is the most common (~78% global allele frequency [AF]), apoE4 (~14% global AF), and apoE2 (~8% global AF). The apoE4 allele, which has an arginine instead of a cysteine at position 112, is widely known for being the major genetic risk factor for Alzheimer’s disease. It is associated with slightly higher LDL-C levels and increased ASCVD risk but is not associated with FDBL. The apoE2 allele, which has a cysteine at position 158 instead of an arginine, is the cause of FDBL when present on both alleles. ApoE2 has a lower affinity for the LDL receptor; therefore, chylomicron rem­ nants and IDL containing apoE2 are removed from plasma at a slower rate, leading to their accumulation in blood. Approximately 0.5% of the general population are apoE2/E2 homo­ zygotes, but only a small minority of these individuals actually develop hyperlipidemia characteristic of FDBL (which has a prevalence of ~1 in 10,000). Thus, an additional, sometimes identifiable, factor precipitates the development of overt dysbetalipoproteinemia in apoE2/E2 homo­ zygotes. The most common precipitating factors are a high-fat diet,

sedentary lifestyle, obesity, alcohol use, menopause, diabetes mellitus, hypothyroidism, renal disease, HIV infection, or certain drugs. Certain dominant-negative mutations in apoE can cause a dominant form of FDBL where the hyperlipidemia is fully manifest in the heterozygous state, but these mutations are very rare.

Patients with FDBL usually present in adulthood with hyperlip­ idemia, xanthomas, or premature coronary or peripheral vascular disease. In FDBL, in contrast to other disorders of elevated TGs, the plasma levels of cholesterol and TG are often elevated to a similar degree, and the level of HDL-C is usually normal. Two distinctive types of xanthomas, tuberoeruptive and palmar, are seen in FDBL patients. Tuberoeruptive xanthomas begin as clusters of small papules on the elbows, knees, or buttocks and can grow to the size of small grapes. Palmar xanthomas (alternatively called xanthomata striata palmaris) are orange-yellow discolorations of the creases in the palms and wrists. Both of these xanthoma types are virtually pathognomonic for FDBL. Subjects with FDBL have premature ASCVD and tend to have more peripheral vascular disease than is typically seen in FH. Disorders of Lipoprotein Metabolism CHAPTER 419 The definitive diagnosis of FDBL can be made either by the docu­ mentation of very high levels of remnant lipoproteins or by identifica­ tion of the apoE2/E2 genotype. A variety of methods are used to identify remnant lipoproteins in the plasma, including “β-quantification” by ultracentrifugation (ratio of directly measured VLDL cholesterol to total plasma TG >0.30), lipoprotein electrophoresis (broad β band), or nuclear magnetic resonance lipoprotein profiling. The Friedewald formula for calculation of LDL-C is not valid in FDBL because the VLDL particles are depleted in TG and enriched in cholesterol. The plasma levels of LDL-C are actually low in this disorder due to defec­ tive metabolism of VLDL to LDL. DNA-based apoE genotyping can be performed to confirm homozygosity for apoE2, which is diagnostic for FDBL. However, absence of the apoE2/E2 genotype does not strictly rule out the diagnosis of FDBL, because other mutations in apoE can (rarely) cause this condition. Because FDBL is associated with increased risk of premature ASCVD, it should be treated aggressively. Other metabolic conditions that can exacerbate the hyperlipidemia (see above) should be man­ aged. Patients with FDBL are typically diet-responsive and can respond favorably to low-cholesterol, low-fat diets and weight reduction. Alcohol intake should be curtailed. Pharmacologic therapy is often required, and statins are the first line in management. In the event of statin intolerance or insufficient control of hyperlipidemia, cholesterol absorption inhibitors, PCSK9 inhibitors, and fibrates are also effective in the treatment of FDBL. HEPATIC LIPASE DEFICIENCY  Hepatic lipase (HL; gene name LIPC) is a member of the same gene family as LPL and hydrolyzes TGs and phospholipids in remnant lipoproteins and HDL. Hydrolysis of lipids in remnant particles by HL contributes to their hepatic uptake via an apoE-mediated process. HL deficiency is a very rare autosomal reces­ sive disorder caused by biallelic loss-of-function mutations in LIPC. It is characterized by elevated plasma levels of cholesterol and TGs (mixed hyperlipidemia) due to the accumulation of lipoprotein rem­ nants, accompanied by elevated plasma level of HDL-C. The diagnosis is confirmed by confirmation of pathogenic mutations in both alleles of LIPC. Due to the small number of patients with HL deficiency, the association of this genetic defect with ASCVD is not entirely clear, although anecdotally, patients with HL deficiency who have premature CVD have been described. As with FDBL, statin therapy is recom­ mended to reduce remnant lipoproteins and cardiovascular risk. FAMILIAL COMBINED HYPERLIPIDEMIA (FCHL)  FCHL is one of the most common familial lipid disorders; it is estimated to occur in ~1 in 100–200 individuals. FCHL is characterized by elevations in plasma levels of TGs (VLDL) and LDL-C (including especially a small dense form of LDL) and reduced plasma levels of HDL-C. This disorder is an important contributor to premature CHD; ~20% of patients who develop CHD under age 60 have FCHL. FCHL can manifest in child­ hood but is usually not fully expressed until adulthood. The disease clusters in families, and affected family members typically have one of three possible phenotypes: (1) elevated plasma levels of LDL-C, (2)

elevated plasma levels of TGs due to elevation in VLDL, or (3) elevated plasma levels of both LDL-C and TG. The lipoprotein profile can switch among these three phenotypes in the same individual over time and may depend on factors such as diet, exercise, weight, and insulin sensitivity. Patients with FCHL have substantially elevated plasma lev­ els of apoB, often disproportionately high relative to the plasma LDL-C concentration, indicating the presence of small dense LDL particles, which are characteristic of this syndrome.

Individuals with this phenotype generally share the same metabolic defect, namely overproduction of VLDL and apoB by the liver. The molecular etiology of this condition remains poorly understood, and no single gene has been identified in which mutations convincingly cause this disorder in a simple Mendelian fashion. It is likely that defects in a combination of genes can cause the condition, suggesting that a more appropriate term for the disorder might be polygenic com­ bined hyperlipidemia. PART 12 Endocrinology and Metabolism The presence of a mixed dyslipidemia (plasma TG levels between 150 and 500 mg/dL and total cholesterol levels between 200 and 400 mg/dL, usually with HDL-C levels <40 mg/dL in men and <50 mg/dL in women) and a family history of mixed dyslipidemia and/or prema­ ture CHD suggests the diagnosis. Measurement of plasma apoB levels can help support the diagnosis if they are substantially elevated, partic­ ularly relative to the LDL-C level. Individuals with this disorder should be treated aggressively due to significantly increased risk of premature CHD, often disproportionate to the LDL-C level. Decreased dietary intake of simple carbohydrates, increased aerobic exercise, and weight loss can all have beneficial effects on the lipid profile. Patients with type 2 diabetes should be aggressively treated to maintain good glucose control. Virtually all patients with FCHL merit lipid-lowering drug therapy to reduce apoB-containing lipoprotein levels and lower the risk of ASCVD. High-intensity statins are first line, but many patients with FCHL require combination therapy that includes ezetimibe, a PCSK9 inhibitor, and/or bempedoic acid. ■ ■SECONDARY CONTRIBUTORS TO ELEVATED LEVELS OF APOB-CONTAINING LIPOPROTEINS There are many “secondary” factors that contribute to dyslipidemia (Table 419-3), often acting in concert with polygenic predisposition as reviewed above. Some primarily affect TGs, some primarily affect LDL-C, and some influence both, with a great deal of variability. Here the major secondary contributors are reviewed. Secondary Factors That Primarily Elevate TG Levels  •  HIGHCARBOHYDRATE DIET  Dietary carbohydrates are utilized as a sub­ strate for fatty acid synthesis in the liver. Some of the newly synthesized fatty acids are esterified, forming TGs, and secreted in VLDL. Thus, excessive intake of calories as carbohydrates, which is frequent in Western societies, leads to increased hepatic VLDL-TG secretion and elevated TG levels. Reduction in carbohydrate consumption can have a substantial effect in reducing TG levels, although replacing carbohy­ drates with saturated fat can elevate LDL-C levels. OBESITY, INSULIN RESISTANCE, AND TYPE 2 DIABETES  (See also Chaps. 413–415) Obesity, insulin resistance, and type 2 diabetes mel­ litus are the most frequent contributors to dyslipidemia, primarily by influencing TGs. The increase in adipocyte mass and accompanying decreased insulin sensitivity associated with obesity have multiple effects on lipid metabolism, with one of the major effects being exces­ sive hepatic VLDL production. More free fatty acids are delivered from the expanded and insulin-resistant adipose tissue to the liver, where they are reesterified in hepatocytes to form TGs, which are packaged into VLDLs for secretion into the circulation. In addition, the increased insulin levels promote increased fatty acid synthesis in the liver. In insulin-resistant patients who progress to type 2 diabetes mellitus, dys­ lipidemia remains common, even when the patient is under relatively good glycemic control. In addition to increased VLDL production, insulin resistance can also result in decreased LPL activity, resulting in reduced catabolism of chylomicrons and VLDLs and more severe HTG. This may be due in part to the effects of tissue insulin resistance leading to reduced transcription of LPL in skeletal muscle and adipose,

as well as to increased production of the LPL inhibitor apoC-III by the liver. This reduction in LPL activity often exacerbates the effects of increased VLDL production and contributes to the dyslipidemia seen in these patients. The dyslipidemia in this setting is almost invariably associated with low HDL-C levels as well. A cluster of metabolic risk factors are often found together, including obesity, insulin resistance, hypertension, high TGs, and low HDL-C (the so-called “metabolic syndrome,” Chap. 420). ALCOHOL CONSUMPTION  Excessive alcohol consumption inhibits hepatic oxidation of free fatty acids, thus promoting hepatic TG syn­ thesis and VLDL secretion and leading to increased plasma TG levels. Regular alcohol use also raises plasma levels of HDL-C and should be considered in patients with the relatively unusual combination of ele­ vated TGs and normal or elevated HDL-C. A careful history of alcohol use should be taken in patients with elevated TGs. Reduction in alcohol consumption can often have a substantial effect in reducing TG levels. CHRONIC KIDNEY DISEASE  (See also Chap. 322) Chronic kidney disease (CKD) is often associated with mild HTG (150–400 mg/dL) due to the accumulation of VLDLs and remnant lipoproteins in the circulation. TG lipolysis and remnant clearance are both reduced in patients with renal failure. Because the risk of ASCVD is increased in CKD, patients should usually be treated with lipid-lowering agents, particularly statins. ESTROGEN AND OTHER DRUGS  Many drugs have an impact on lipid metabolism and can result in significant alterations in the lipoprotein profile (Table 419-3). Estrogens often elevate TG levels, and TG levels can also increase during pregnancy. In women with HTG, plasma TG levels should be monitored when birth control pills or postmenopausal estrogen therapy is initiated and during pregnancy. Use of low-dose preparations of estrogen or the estrogen patch can minimize the effect of exogenous estrogen on lipids. Isotretinoin therapy for acne can cause substantial elevations in TGs, and TG levels should be checked at baseline and after initiation of therapy. Bexarotene therapy for cuta­ neous T-cell lymphoma often causes substantial increases in TGs, and patients should be monitored accordingly. Secondary Factors That Elevate LDL-C Levels  •  DIET HIGH IN SATURATED AND TRANS FATS  Dietary saturated and trans fats act to downregulate LDL receptor expression in the liver, leading to elevation in LDL-C levels and increased ASCVD risk. A careful dietary history should be taken in individuals with elevated LDL-C with a focus on sources of saturated and trans fats. Reduction in consumption of saturated and trans fats can sometimes have a substantial effect in reducing LDL-C levels and is a cornerstone of the initial nonpharma­ cologic management of hypercholesterolemia. HYPOTHYROIDISM  (See also Chap. 394) Hypothyroidism is the most important medical condition causing elevated LDL-C levels. It causes elevated plasma LDL-C levels due to downregulation of the hepatic LDL receptor, which is normally increased by the action of thyroid hormone. Because hypothyroidism is often subtle and therefore easily overlooked, all patients presenting with elevated plasma levels of LDLC, especially if there has been an unexplained increase in LDL-C, should be screened for hypothyroidism by measuring thyroid-stimulating hormone (TSH). Thyroid replacement therapy usually reduces LDL-C levels; if not, the patient probably has a primary lipoprotein disorder and may require lipid-lowering drug therapy with a statin. LIVER DISORDERS  (See also Chap. 347) Cholestasis is almost invari­ ably associated with hypercholesterolemia due to elevated LDL-C levels and, if severe, particles called Lp-X. A major pathway by which cholesterol is excreted from the body is via secretion into bile, either directly or after conversion to bile acids, and cholestasis blocks this critical excretory pathway. The increase in hepatocellular cholesterol results in downregulation of the LDL receptor, leading to increased plasma LDL-C levels. In severe cholestasis, excess free cholesterol, coupled with phospholipids, is shed into the plasma as a constituent of a lamellar particle called Lp-X. These unusual particles, which are not lipoproteins, lack apoB, and have an aqueous and not neutral lipid

core, are rich in free cholesterol, and can deposit in the skin, produc­ ing xanthomas sometimes seen in patients with cholestasis. Some liver disorders can affect plasma lipid levels in other ways. Viral hepatitis can increase TGs, and liver failure can result in reduction in plasma cholesterol and TGs. NEPHROTIC SYNDROME  (See also Chap. 322) Nephrotic syndrome is a classic cause of excessive VLDL production leading to elevation in both TGs and LDL-C. The molecular mechanism of VLDL over­ production remains poorly understood but has been attributed to the effects of hypoalbuminemia leading to increased hepatic protein synthesis. Effective treatment of the underlying renal disease may normalize the lipid profile, but many patients with chronic nephrotic syndrome require lipid-lowering drug therapy with statins and some­ times additional drugs. CUSHING’S SYNDROME  (See also Chap. 398) Endogenous glucocorti­ coid excess in Cushing’s syndrome is associated with increased VLDL synthesis and secretion leading to dyslipidemia characterized by HTG and elevated LDL-C. Treatment of the underlying cause is often suf­ ficient to manage the dyslipidemia, but sometimes lipid-lowering drug therapy is needed. IMMUNOSUPPRESSIVE THERAPY AND CORTICOSTEROIDS  Several of the immunosuppressants used after solid organ transplantation, including cyclosporin and sirolimus, can cause substantial elevation in LDL-C and TG levels. These patients can present a difficult clini­ cal management problem. Chronic corticosteroid use, whether after transplant or in other inflammatory conditions, can also result in elevations in LDL-C and TG levels, sometimes producing a substantial mixed dyslipidemia. When the immunosuppressant or steroid must be continued, which is often the case, drug therapy with statins may be indicated in certain patients, with careful attention to the potential for untoward muscle-related side effects. ■ ■DISORDERS ASSOCIATED WITH REDUCED APOBCONTAINING LIPOPROTEINS Plasma concentrations of LDL-C <60 mg/dL are unusual. Although in some cases, LDL-C levels in this range may be reflective of malnutri­ tion or serious chronic illness, LDL-C <60 mg/dL in an otherwise healthy individual suggests an inherited condition. The major inher­ ited causes of low LDL-C are reviewed here and listed in Table 419-2. Abetalipoproteinemia  The synthesis and secretion of apoB-

containing lipoproteins in the enterocytes of the proximal small bowel and in the hepatocytes of the liver involve a complex series of events that coordinate the coupling of various lipids with apoB-48 and apoB-100, respectively. Abetalipoproteinemia is a rare autosomal recessive disease caused by loss-of-function mutations in the gene encoding MTP (gene name MTTP), a protein that transfers lipids to nascent chylomicrons and VLDLs in the intestine and liver, respectively. Plasma levels of cholesterol and TG are extremely low in this disorder, and chylomi­ crons, VLDLs, LDLs, and apoB are undetectable in plasma. The parents of patients with abetalipoproteinemia (obligate heterozygotes) have normal plasma lipid and apoB levels. Abetalipoproteinemia usually presents in early childhood with diarrhea and failure to thrive due to fat malabsorption. The initial neurologic manifestations are loss of deep tendon reflexes, followed by decreased distal lower extremity vibratory and proprioceptive sense, dysmetria, ataxia, and the development of a spastic gait, often by the third or fourth decade. Patients with abetali­ poproteinemia also develop a progressive pigmented retinopathy pre­ senting with decreased night and color vision, followed by reductions in daytime visual acuity and ultimately progressing to near-blindness. The presence of spinocerebellar degeneration and pigmented retinopa­ thy in this disease has resulted in some patients with abetalipoprotein­ emia being misdiagnosed as having Friedreich’s ataxia. Most of the clinical manifestations of abetalipoproteinemia result from defects in the absorption and transport of fat-soluble vitamins. Vitamin E and retinyl esters are normally transported from enterocytes to the liver by chylomicrons, and vitamin E is dependent on VLDL for transport out of the liver and into the circulation. As a consequence

of the inability of these patients to secrete apoB-containing particles, patients with abetalipoproteinemia are markedly deficient in vitamin E and are also mildly to moderately deficient in vitamins A and K. Patients with abetalipoproteinemia should be referred to specialized centers for confirmation of the diagnosis and appropriate therapy. Treatment consists of a low-fat, high-caloric, vitamin-enriched diet accompanied by large supplemental doses of vitamin E. It is impera­ tive that treatment be initiated as soon as possible to prevent develop­ ment of neurologic sequelae, which can progress even with high-dose vitamin E therapy. New therapies for this serious, albeit rare, disease are needed. The discovery that genetic loss of MTP causes absent LDL-C led to the development of an MTP inhibitor to treat homozy­ gous FH (see below).

Disorders of Lipoprotein Metabolism CHAPTER 419 Familial Hypobetalipoproteinemia (FHBL)  FHBL generally refers to a condition of low total cholesterol, LDL-C, and apoB due to mutations in the APOB gene. Most of the mutations causing FHBL result in a truncated apoB protein, resulting in impaired assembly and secretion of chylomicrons from enterocytes and VLDL from the liver. Any secreted VLDL particles containing a truncated apoB protein are cleared from the circulation at an accelerated rate, which also contrib­ utes to the low levels of LDL-C and apoB. Individuals heterozygous for these mutations usually have LDL-C levels <60–80 mg/dL and also tend to have low levels of plasma TG. Many FHBL patients have elevated levels of hepatic fat (due to reduced VLDL export) and some­ times have increased levels of liver transaminases, although it appears that these patients infrequently develop associated hepatic inflamma­ tion and fibrosis. Truncating mutations in both apoB alleles cause homozygous FHBL, an extremely rare disorder resembling abetalipoproteinemia with nearly undetectable LDL-C and apoB. The neurologic defects in homozygous hypobetalipoproteinemia are similar to those seen in abetalipoproteinemia but tend to be less severe. Homozygous hypo­ betalipoproteinemia can be distinguished from abetalipoproteinemia by examining the inheritance pattern of the plasma LDL-C level. The levels of LDL-C and apoB are normal in the parents of patients with abetalipoproteinemia, a classic recessive condition, and low in those of patients with homozygous hypobetalipoproteinemia, a co-dominant condition. The discovery that truncating mutations in apoB reduce LDL-C led to the development of an antisense oligonucleotide to treat HoFH (see below). Familial PCSK9 Deficiency  Another inherited cause of low LDL-C results from loss-of-function mutations in PCSK9. PCSK9 is a secreted protein that binds to the extracellular domain of the LDL receptor in the liver and promotes the degradation of the receptor. Heterozygosity for nonsense mutations in PCSK9 that interfere with the synthesis of the protein are associated with increased hepatic LDL receptor activity and reduced plasma levels of LDL-C. Such mutations are more frequent in individuals of African descent. Individuals who are heterozygous for a loss-of-function mutation in PCSK9 have an ~30–40% reduction in plasma levels of LDL-C and have a substantial protection from CHD relative to those without a PCSK9 mutation, presumably due to having lower plasma cholesterol levels since birth. Homozygotes for these nonsense mutations have been reported and have extremely low LDL-C levels (<20 mg/dL) but appear otherwise healthy. A sequence variation of somewhat higher frequency (R46L) is found predominantly in individuals of European descent. This muta­ tion impairs, but does not completely destroy, PCSK9 function. As a consequence, the plasma levels of LDL-C in individuals carrying this mutation are more modestly reduced (~15–20%); individuals with these mutations have a 45% reduction in CHD risk. The discovery of this condition led to the development of therapies that antagonize or silence PCSK9, thus reducing LDL-C levels and risk of CHD (see below). Familial Combined Hypolipidemia  Nonsense mutations in both alleles of the gene angiopoietin-like 3 (ANGPTL3) lead to low plasma levels of all three major lipid fractions—TG, LDL-C, and

HDL-C—a phenotype termed familial combined hypolipidemia.

ANGPTL3 is a protein synthesized by the liver and secreted into the bloodstream. It inhibits LPL, thus delaying clearance of TRLs from the blood and increasing TRL blood concentrations. Deficiency of ANGPTL3, therefore, raises LPL activity and lowers blood TG; it also lowers LDL-C and raises HDL-C levels apparently related to the effects of ANGPTL3 on endothelial lipase. ANGPTL3 deficiency is associated with a reduced risk for CHD. The discovery of this condition led to the development of therapies that antagonize or silence ANGPTL3 to reduce LDL-C and TG levels (see below).

DISORDERS ASSOCIATED WITH REDUCED HIGH-DENSITY LIPOPROTEINS Low levels of HDL-C, generally defined as <50 mg/dL in women and <40 mg/dL in men, are very common in clinical practice. Low HDL-C is an important independent predictor of increased cardiovascular risk and has been used regularly in standardized risk calculators. As an independent risk factor, it has clinical value in the assessment of cardiovascular risk, and a patient with low HDL-C should generally be considered at higher risk of ASCVD. However, it is now consid­ ered doubtful that low HDL-C is directly causal for the development of ASCVD. Thus, while HDL-C remains an important biomarker for assessing cardiovascular risk, it is no longer considered a target for therapeutic intervention to raise HDL-C levels in order to reduce car­ diovascular risk. PART 12 Endocrinology and Metabolism HDL metabolism is strongly influenced by TG metabolism, insulin resistance, and inflammation, among other environmental and medical factors. Thus, the HDL-C measurement integrates a number of cardio­ vascular risk factors, potentially explaining its strong inverse associa­ tion with ASCVD. The majority of patients with low HDL-C have some combination of genetic predisposition and secondary factors. Variants in hundreds of genes have been shown to influence HDL-C levels. Even more important quantitatively, obesity and insulin resistance have strong suppressive effects on HDL-C, and low HDL-C in these condi­ tions is widely observed. Furthermore, the vast majority of patients with elevated TGs have reduced levels of HDL-C due to the substantial interplay between the metabolism of TRLs and HDL (see above). Most patients with low HDL-C who have been studied in detail have acceler­ ated catabolism of HDL and its associated apoA-I protein as the physi­ ologic basis for the low HDL-C. Single-gene Mendelian disorders that reduce HDL-C have been described (Table 419-2) but are rare; the vast majority of patients with low HDL-C have a polygenic predisposition with secondary factors like obesity, insulin resistance, or HTG. ■ ■PRIMARY (GENETIC) CAUSES OF LOW HDL-C Mutations in three key genes encoding proteins that play critical roles in HDL synthesis and catabolism result in hypoalphalipoproteinemia (primary low levels of HDL-C). Unlike the genetic forms of hypercho­ lesterolemia, which are invariably associated with premature coronary atherosclerosis, genetic forms of hypoalphalipoproteinemia are usually not associated with clearly increased risk of ASCVD. Nevertheless, in the clinical setting of an HDL-C level <20 mg/dL without accompany­ ing severe HTG, these rare conditions should be considered. Gene Deletions and Missense Mutations in APOA1  Com­ plete genetic deficiency of apoA-I due to a complete deletion of the APOA1 gene results in the virtual absence of circulating HDL, proving the critical role of apoA-I in HDL biogenesis. The APOA1 gene is part of a gene cluster on chromosome 11 that includes APOA5, APOC3, and APOA4. Some patients with no apoA-I have large genomic deletions that include other genes in the cluster. The rare patient lacking apoA-I may have cholesterol deposits in the cornea and in the skin, and in contrast to the other genetic disorders of low HDL-C, premature CHD has been reported. Heterozygotes for apoA-I deletions have reduced HDL-C levels but no obvious clinical sequelae. More common, but still rare, are heterozygous missense mutations in the APOA1 gene associated with low plasma levels of HDL-C. The first example reported, and still the best known, is an Arg173Cys sub­ stitution in apoA-I (so-called apoA-IMilano), found in multiple residents of a town in northern Italy. Heterozygotes for this mutation have very

low plasma levels of HDL-C (<25 mg/dL) due to impaired LCAT acti­ vation and accelerated clearance of the HDL particles containing the abnormal apoA-I. Despite having very low plasma levels of HDL-C, these individuals do not appear to have an increased risk of prema­ ture CHD (neither are they protected against CHD as was initially believed). Multiple other rare APOA1 missense mutations causing low HDL-C have been reported. A few of these mutations in APOA1 (as well as some mutations in APOA2) promote the formation of amyloid fibrils, causing systemic amyloidosis. Tangier Disease (ABCA1 Deficiency)  Tangier disease is a rare autosomal co-dominant form of extremely low plasma HDL-C levels that is caused by mutations in the ABCA1 gene encoding ABCA1, a cellular transporter that facilitates efflux of unesterified cholesterol and phospholipids from cells to apoA-I as an acceptor (Fig. 419-3). Through transporting cellular lipids, ABCA1 in the hepatocytes and intestinal enterocytes promotes the extracellular lipidation of the apoA-I secreted from the basolateral membranes of these tissues. In the genetic absence of ABCA1, the nascent, poorly lipidated apoA-I is rap­ idly cleared from the circulation. Thus, patients with Tangier disease (both ABCA1 alleles mutated) have extremely low circulating plasma levels of HDL-C (<5 mg/dL) and apoA-I (<5 mg/dL). Cholesterol accu­ mulates in the reticuloendothelial system of these patients, resulting in hepatosplenomegaly and pathognomonic enlarged, grayish yellow or orange tonsils. An intermittent peripheral neuropathy (mononeuritis multiplex) or a sphingomyelia-like neurologic disorder can also be seen in this disorder. Tangier disease may be associated with some increased risk of ASCVD, although the association is not as robust as might have been anticipated, given the extremely low levels of HDL-C in these patients. Patients with Tangier disease also have low plasma levels of LDL-C, which may attenuate the atherosclerotic risk. Heterozygotes for ABCA1 mutations have moderately reduced plasma HDL-C levels (~15–40 mg/dL), and the effect on risk of ASCVD remains uncertain. Familial LCAT Deficiency  This rare autosomal recessive dis­ order is caused by mutations in LCAT, an enzyme synthesized in the liver and secreted into the plasma, where it circulates associated with lipoproteins (Fig. 419-3). As reviewed above, the enzyme is activated by apoA-I and mediates the esterification of cholesterol to form CEs. Consequently, in familial LCAT deficiency, the proportion of free cho­ lesterol in circulating lipoproteins is greatly increased (from ~25% to

70% of total plasma cholesterol). Deficiency in this enzyme interferes with the maturation of HDL particles and results in rapid catabolism of circulating apoA-I. Two genetic forms of familial LCAT deficiency have been described in humans: complete deficiency (also called classic LCAT deficiency) and partial deficiency (also called fish eye disease). Progressive corneal opacification due to the deposition of free cholesterol in the cornea, very low plasma levels of HDL-C (usually <10 mg/dL), and variable HTG are characteristic of both disorders. In partial LCAT deficiency, there are no other known clinical sequelae. In contrast, patients with complete LCAT deficiency have hemolytic anemia and progressive renal insufficiency that eventually leads to end-stage renal disease. Remarkably, despite the extremely low plasma levels of HDL-C and apoA-I, premature ASCVD is not a consistent feature of either LCAT deficiency or fish eye disease. The diagnosis can be confirmed in a spe­ cialized laboratory by assaying plasma LCAT activity or by sequencing the LCAT gene. Primary Hypoalphalipoproteinemia  Primary hypoalphalipo­ proteinemia is defined as a plasma HDL-C level below the tenth per­ centile in the setting of relatively normal cholesterol and TG levels, no apparent secondary causes of low plasma HDL-C, and no clinical signs of LCAT deficiency or Tangier disease. A family history of low HDL-C suggests an inherited condition and may trigger an evaluation of one of the Mendelian causes of hypoalphalipoproteinemia. However, most patients with isolated low HDL do not have an identifiable single-gene disorder and likely have a polygenic etiology, possibly exacerbated by a secondary factor. The physiologic defect appears to be accelerated catabolism of HDL and its apolipoproteins. Several kindreds with

primary hypoalphalipoproteinemia and an increased incidence of premature CHD have been described, although it is not clear if the low HDL-C level is the cause of the accelerated atherosclerosis in these families. ■ ■SECONDARY FACTORS THAT

REDUCE HDL-C LEVELS Hypertriglyceridemia  Low HDL-C is very commonly found in association with elevated TG levels. The lipolysis of TRLs generates lipids that transfer to HDL, and therefore, any impairment of lipolysis (the most common cause of elevated TGs) leads to reduced HDL bio­ synthesis. In settings of elevated TGs, where the HDL-C is not reduced, alternative explanations (e.g., FDBL, alcohol, estrogens) should be con­ sidered. Conversely, an isolated low HDL-C in the presence of normal TGs should prompt consideration of a primary genetic etiology (as above) or specific secondary factors (see below). Very-Low-Fat Diet  Dietary fat is positively associated with HDL-C levels. Individuals who eat very-low-fat vegan diets or who have anorexia or severe fat malabsorption often have low levels of HDL-C that are secondary to low dietary fat. In this setting, LDL-C levels are also usually low as well. There is no known harm to low HDL-C levels in this setting and no indication for liberalizing the diet solely for the purpose of raising the HDL-C. Sedentary Lifestyle and Obesity  Physical activity is known to have a (generally modest) effect in raising HDL-C levels, and con­ versely, a sedentary lifestyle is often associated with low HDL-C levels. Concordant with that observation, obesity is frequently associated with low HDL-C levels even when overt insulin resistance or HTG is not present. Increased physical activity and weight loss usually have some effect in raising HDL-C, which is not the primary reason for recom­ mending these interventions but can have a motivating influence on the patient. ANABOLIC STEROIDS AND TESTOSTERONE  Anabolic steroids have a well-established effect on lowering HDL-C levels, sometimes quite dra­ matically. Testosterone supplementation can also reduce HDL-C levels, although not to the degree caused by anabolic steroids. In a young male patient who presents with unexplained very low HDL-C, a careful his­ tory of medication and supplement use should be taken. APPROACH TO THE PATIENT Lipoprotein Disorders The major goals in the diagnosis and clinical management of lipo­ protein disorders are (1) prevention of CVD and related cardiovas­ cular events and (2) prevention of acute pancreatitis in patients with severe HTG. Given the high prevalence of dyslipidemia and the proven clinical benefits of early diagnosis and initiation of therapy, it is essential that physicians screen lipids systematically, rule out secondary causes of dyslipidemia, suspect inherited disorders of lipoprotein metabolism where appropriate, actively promote familybased screening, carefully assess risk for ASCVD and consider addi­ tional risk stratification approaches, and be knowledgeable about the wide range of existing therapeutic options for dyslipidemia. The field of clinical lipidology has matured and is moving toward a more systematic clinical application of genomic medicine. Diagnostic DNA sequencing or genotyping in patients with suspected FCS, FPLD, FH, and FDBL has the potential to enhance molecular diag­ nosis, facilitate appropriate therapeutic interventions, and promote family-based cascade screening based on genetic diagnosis. DIAGNOSIS A critical first step in managing a lipoprotein disorder is to attempt to determine the class or classes of lipoproteins that are increased or decreased in the patient. Once the dyslipidemia is accurately classified, efforts should be directed to identify or rule out any possible second­ ary causes (Table 419-3). A careful social, medical, and family history

should be obtained. In patients with elevated TG levels (>150 mg/dL), a fasting glucose and/or hemoglobin A1c should be obtained to rule out diabetes. In patients with elevated LDL-C levels (>160 mg/dL), a TSH should be obtained to rule out hypothyroidism and consideration should be given to the possibility of liver or kidney disease. Once secondary causes have been ruled out, attempts should be made to diagnose a primary lipid disorder, because the underlying genetic defect can provide important prognostic information regarding the risk of pancreatitis in severe HTG and the risk of ASCVD in other dyslipidemias, as well as impact on the choice of drug therapy and the screening of other family members. Obtaining the correct diagnosis often requires a detailed family history, lipid analyses in family members, and sometimes specialized or genetic testing. Severe Hypertriglyceridemia  If the fasting plasma TG level is

500 mg/dL, the patient has severe HTG and may be at risk for pan­ creatitis. If the TG levels are persistently severely elevated, especially if they are >1000 mg/dL, and the total cholesterol-to-TG ratio is >8, FCS should be considered, and genetic testing of an FCS gene panel may be indicated (Table 419-2). If central obesity, insulin resistance, and/or fatty liver disease are also present, consideration should be given to the possibility of FPLD, and an FPLD gene panel may be indicated (Table 419-2). However, most individuals with severe HTG do not have a single-gene disorder but have increased poly­ genic risk for high TGs often exacerbated by secondary factors (e.g., diet, alcohol, obesity, insulin resistance, medications). Such patients are still at risk for acute pancreatitis and should be treated to reduce their TG levels and thus their risk of pancreatitis (see below). Hypercholesterolemia  If the LDL-C levels are >190 mg/dL, the patient has severe hypercholesterolemia and is at risk for premature ASCVD. In absence of secondary causes, FH should be considered, particularly if there is a family history of hypercholesterolemia and/ or premature CHD, and genetic testing of an FH gene panel may be indicated (Table 419-2). The Centers for Disease Control and Prevention has identified FH as a Tier 1 condition for implementa­ tion of public health genomics. While FH is ultimately a clinical diagnosis, a finding of a causal mutation may appropriately result in earlier and more aggressive therapy to lower LDL-C and should also promote family-based cascade screening. Recessive forms of severe hypercholesterolemia are rare, but if a patient with severe hyper­ cholesterolemia has parents with normal cholesterol levels, ARH, sitosterolemia, and LALD should be considered, and genetic test­ ing may be indicated (Table 419-2). Patients without an identified genetic variant or who have more moderate hypercholesterolemia are likely to have polygenic hypercholesterolemia but should still be considered at risk and eligible for treatment (see below). Mixed Hyperlipidemia  Patients with elevations in fasting plasma levels of both TGs (>150 mg/dL) and LDL-C (>130 mg/dL), often accompanied by reduced levels of HDL-C (<40 mg/dL in men and <50 mg/dL in women), are common and such patients are often diagnosed as having “mixed hyperlipidemia.” Most such patients are at increased risk of ASCVD and merit consideration of lifestyle and often pharmacologic interventions. Secondary factors, particu­ larly obesity, insulin resistance, and type 2 diabetes, are common in such patients, who often also have increased polygenic risk for dyslipidemia. The presence of palmar or tuberous xanthomas or an unusual lipid profile of total cholesterol and TG levels in the same range with an HDL-C that is not reduced should prompt consideration of FDBL, or type III hyperlipidemia, and can be diagnosed by advanced lipoprotein testing or genetic testing for the APOE2 genotype. FDBL patients should be managed aggressively due to substantially increased risk of ASCVD. More commonly, patients with mixed hyperlipidemia, particularly those with family histories of dyslipidemia or premature ASCVD, have familial com­ bined hyperlipidemia (FCHL). ApoB should be measured in such patients, and the finding of substantially elevated apoB levels can help identify patients with FCHL, who are at especially increased risk of ASCVD and require more aggressive treatment. Disorders of Lipoprotein Metabolism CHAPTER 419

TREATMENT Severe Hypertriglyceridemia There is a well-established observational relationship between severe HTG, particularly chylomicronemia, and acute pancreatitis; however, there has never been a clinical trial designed or powered to defini­ tively prove that intervention to reduce TGs reduces the risk of pan­ creatitis. Nevertheless, it is generally considered appropriate medical practice to intervene in patients with TGs >500 mg/dL in order to reduce the risk of pancreatitis. It remains uncertain whether chylo­ micronemia increases risk for ASCVD per se. Importantly, moder­ ate HTG (TG 150–500 mg/dL) is associated with increased ASCVD risk; management of these patients is focused on reducing risk of ASCVD and on reducing LDL-C, non-HDL-C, and apoB. PART 12 Endocrinology and Metabolism LIFESTYLE AND MODIFIABLE FACTORS In patients with severe HTG, lifestyle modification can be associ­ ated with a significant reduction in plasma TG level. Importantly, certain medications can exacerbate HTG (Table 419-3). Patients who drink alcohol should be encouraged to decrease or preferably eliminate their intake. Patients with severe HTG often benefit from a formal dietary consultation with a dietician intimately familiar with counseling patients on the dietary management of high TGs. Dietary fat intake should be restricted to reduce the formation of chylomicrons in the intestine. The excessive intake of simple car­ bohydrates should be discouraged because insulin drives TG pro­ duction in the liver. Aerobic exercise and even increase in regular physical activity can have a positive effect in reducing TG levels and should be strongly encouraged. For patients who are overweight, weight loss can help to reduce TG levels. In extreme cases, bariatric surgery has been shown to not only produce effective weight loss but also substantially reduce plasma TG levels. Many patients with diabetes have HTG, and better control of diabetes can result in lowering of TGs. GLP-1 agonists prescribed for diabetes or obesity can reduce TG levels. PHARMACOLOGIC THERAPY Despite lifestyle interventions, many patients with severe HTG require pharmacologic therapy (Table 419-4). Patients who persist in having fasting TG >500 mg/dL despite active lifestyle manage­ ment are candidates for pharmacologic therapy. The two major classes of drugs used for management of these patients are fibrates and omega-3 fatty acids (fish oils). In addition, statins can reduce plasma TG levels and also reduce ASCVD risk and should be used in patients with severe HTG who are at increased risk of ASCVD. Fibrates  Fibric acid derivatives, or fibrates, are agonists of PPARα, a nuclear receptor involved in the regulation of lipid metabolism. Fibrates stimulate LPL activity (enhancing TG hydrolysis), reduce apoC-III synthesis (enhancing lipoprotein remnant clearance), pro­ mote β-oxidation of fatty acids, and may reduce VLDL TG produc­ tion. Fibrates reduce TG levels by ~30% in individuals with severe HTG and are often used as first-line therapy. They do not reduce and sometimes modestly raise LDL-C levels. Fibrates are generally well tolerated but can cause myopathy, especially when combined with statins, can raise creatinine, and are associated with an increase in gallstones. Fibrates can potentiate the effect of warfarin and cer­ tain oral hypoglycemic agents. Omega-3 Fatty Acids (Fish Oils)  Omega-3 fatty acids, or omega-3 polyunsaturated fatty acids (n-3 PUFAs), commonly known as fish oils, are present in high concentration in fish and in flaxseed. The n-3 PUFAs used for the treatment of HTG are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). n-3 PUFAs have been concentrated into capsules and, in doses of 3–4 g/d, are effective at lowering fasting TG levels by ~30%. Fish oils can cause an increase in plasma LDL-C levels in some patients. Icosapent ethyl is an EPAonly product that has been shown to reduce cardiovascular events in patients with HTG. In general, fish oils are well tolerated, with

the major side effect being dyspepsia. They appear to be safe, at least at doses up to 3–4 g, but can be associated with a prolongation in the bleeding time. Fish oils can be first-line therapy for the treat­ ment of severe HTG or can be used in combination with fibrates. APOC3 Silencing  ApoC-III inhibits LPL and TRL uptake, and genetic variants in the APOC3 gene reduce TG levels and risk of ASCVD. Volanesorsen is an antisense oligonucleotide (ASO) targeted to the APOC3 mRNA in the liver; it significantly reduces plasma apoC-III and TG levels and is approved in Europe for patients with FCS. It has been associated with severe thrombocy­ topenia. Additional therapeutic approaches to APOC3 and other targets for TG lowering (e.g., ANGPTL3) are in development. Hypercholesterolemia (Elevated LDL-C with or without Elevated TG) There are abundant and compelling data that intervention to reduce LDL-C substantially reduces the risk of ASCVD, including myocardial infarction and stroke, as well as total mortality. Thus, it is imperative that patients with hypercholesterolemia be carefully assessed for cardiovascular risk and need for intervention. It is also worth emphasizing that patients with or at high risk for ASCVD who have plasma LDL-C levels in the “normal” or average range also benefit from intervention to reduce LDL-C levels. LIFESTYLE AND MODIFIABLE FACTORS In patients with elevated LDL-C, lifestyle modifications can be effective but are often less effective than in HTG. Patients should receive dietary counseling to reduce the content of saturated fats and trans fats in the diet. Obese patients should make an effort to lose weight. Regular aerobic exercise has relatively little impact on reducing plasma LDL-C levels, although it has cardiovascular ben­ efits independent of LDL-C lowering. Patients with hypothyroidism should be optimally controlled. Finally, certain medications can elevate LDL-C levels (Table 419-3). PHARMACOLOGIC THERAPY The decision to use LDL-lowering drug therapy (Table 419-4)— with a statin being first-line therapy—depends on the presence of ASCVD or, if absent, the level of LDL-C as well as the level of cardiovascular risk. In patients with established ASCVD, drug therapy to reduce LDL-C is well supported by clinical trial data to reduce LDL-C as long as it remains >70 mg/dL, using combination drug therapy if necessary. In the absence of ASCVD, patients with FH must be treated to reduce the very high lifetime risk of ASCVD, and treatment should be initiated as early as possible, ideally during childhood. Otherwise, the decision to initiate LDL-lowering drug therapy is generally determined by the level of cardiovascular risk. For patients >40 years old without clinical CVD, the ASCVD pooled cohort risk calculator can be used to determine the 10-year absolute risk for CVD, and current guidelines suggest that a 10-year risk

7.5% merits consideration of statin therapy regardless of plasma LDL-C level. For younger patients, the assessment of lifetime risk of CVD may help inform the decision to start a statin, as well as a care­ ful assessment of family history of ASCVD. In patients for whom the decision to start a statin is uncertain due to borderline ASCVD risk and/or borderline LDL-C levels, additional risk stratification might be considered. Blood tests that predict ASCVD risk beyond traditional risk factors include apoB, Lp(a), and high-sensitivity C-reactive protein (hs-CRP). In patients who are of a sufficient age (men >40 years and women >50 years), a coronary artery calcium (CAC) score has been shown to provide independent information about risk of future CAD. Elevated levels of one or more of these biomarkers or an elevated CAC score might be used to justify initia­ tion of statin therapy in primary prevention for patients who are in a borderline zone with regard to treatment. Finally, given the strong polygenic contribution to ASCVD, there is increasing interest in

the concept that a polygenic risk score for CAD might eventually be of clinical utility in lifetime risk assessment and decision-making regarding statin therapy in primary prevention. HMG-CoA Reductase Inhibitors (Statins)  Statins inhibit HMGCoA reductase, a key enzyme in cholesterol biosynthesis. By inhibiting cholesterol synthesis in the liver, statins lead to a coun­ terregulatory increase in the expression of the LDL receptor and thus accelerated clearance of circulating LDL, resulting in a dose-

dependent reduction in plasma levels of LDL-C. The magnitude of LDL-C lowering associated with statin treatment (~30–55%) varies by statin and among individuals, but once a patient is on a statin, the doubling of the statin dose produces a ~6% further reduction in the level of plasma LDL-C. An extensive body of randomized clinical trials has clearly established that statin therapy significantly reduces major cardiovascular events (and in some cases total mortality) in both primary and secondary prevention settings. The seven statins currently available differ in their LDL-C–reducing potency (Table 419-4). Current recommendations are to use high-intensity statin therapy in patients with ASCVD or deemed at high risk of ASCVD. Statins also modestly reduce plasma TGs in a dose-dependent fash­ ion roughly proportional to their LDL-C–lowering effects. Statins, taken in tablet form once a day, are remarkably safe and well tolerated. The most important side effect associated with statin therapy is muscle pain, or myalgia, which occurs in 3–5% of patients, some of whom are unable to tolerate any statin. Severe myopathy (associated with an increase in plasma creatine kinase [CK]) and even rhabdomyolysis can occur rarely with statin treatment. The risk of statin-associated myalgia or myopathy is increased by the presence of older age, frailty, renal insufficiency, and coadministration of drugs that interfere with the metabolism of certain statins, such as erythromycin and related antibiotics, antifungal agents, immunosuppressive drugs, and fibric acid derivatives (particularly gemfibrozil). In the event of muscle symptoms, a plasma CK level may be obtained to differentiate myopathy from myalgia. Serum CK levels need not be monitored on a routine basis in patients taking statins because an elevated CK in the absence of symptoms does not predict the development of myopathy and does not necessarily suggest the need for discontinu­ ing the drug. Statins can result in elevation in liver transaminases (alanine aminotransferase [ALT] and aspartate aminotransferase [AST]), but it is usually mild and transient and generally does not require discontinuation. Finally, meta-analyses of large random­ ized controlled clinical trials with statins indicate a slight excess in incident type 2 diabetes, an observation as yet not fully under­ stood. However, the cardiovascular benefits associated with statin therapy far outweigh the slight increase in incident diabetes. Based on their safety and extensively documented benefit with regard to cardiovascular outcomes, statins are the clear drug class of choice for LDL-C reduction and are by far the most widely used class of lipid-lowering drugs. Cholesterol Absorption Inhibitor  Cholesterol within the lumen of the small intestine is derived from the diet (about one-third) and the bile (about two-thirds) and is actively absorbed by the entero­ cyte through a process that involves the protein NPC1L1. Ezeti­ mibe (Table 419-4) is a cholesterol absorption inhibitor that binds directly to and inhibits NPC1L1 and blocks the intestinal absorp­ tion of cholesterol. Ezetimibe (10 mg taken once daily) inhibits cholesterol absorption by almost 60%, resulting in a reduction in delivery of dietary sterols in the liver and a compensatory increase in hepatic LDL receptor expression. The mean reduction in plasma LDL-C on ezetimibe (10 mg) is 18%, and the effect is additive when used in combination with a statin. Effects on TG and HDL-C levels are negligible. Ezetimibe added to a statin has been shown to sig­ nificantly reduce major cardiovascular events compared with statin alone. It is generally considered the second-line option for adding to a statin in order to achieve further LDL-C reduction. Ezetimibe

is very safe and well-tolerated. When used in combination with a statin, monitoring of liver transaminases is recommended. The only roles for ezetimibe in monotherapy are in patients who do not toler­ ate statins and in some patients with sitosterolemia.

PCSK9 Inhibitors  Circulating PCSK9 targets the LDL receptor for lysosomal degradation, thus reducing its recycling and abundance at the surface of the hepatocyte. Genetic loss of function of PCSK9 results in low levels of LDL-C and protection from CAD. Antibod­ ies to PCSK9 (Table 419-4) sequester it and functionally increase the number of LDL receptors available to remove LDL from the blood. They are highly effective in lowering LDL-C, with an ~60% reduction in LDL-C. They also reduce plasma levels of Lp(a) mod­ estly. Both PCSK9 antibodies have been shown to significantly reduce cardiovascular events when added to a statin in patients with existing CAD. These antibodies are administered subcutane­ ously every 2 weeks. They are generally well tolerated, with a side effect being injection site reactions. They are generally indicated as second-line (added to statin) or third-line (added to statin plus ezetimibe) therapy in patients with FH or ASCVD in whom LDL-C is not reduced to acceptable levels with a statin (with or without ezetimibe) alone. An alternative approach to silencing PCSK9, inclisiran, is a therapeutic siRNA molecule that targets the PCSK9 mRNA in the liver. In contrast to the antibodies, it is administered subcutaneously every 6 months. It is effective in reducing LDL-C by ~60% and appears to be well tolerated and safe; cardiovascular outcomes trials are ongoing. Disorders of Lipoprotein Metabolism CHAPTER 419 ATP Citrate Lyase Inhibitor  Bempedoic acid is a first-in-class competitive inhibitor of ATP citrate lyase (ACL), which acts on mitochondrial-derived citrate to generate production of acetylCoA, which is subsequently used for cholesterol synthesis. Thus, it reduces cholesterol synthesis through a different mechanism than statins, ultimately upregulating the hepatic LDL receptor. Bempe­ doic acid is a prodrug that requires activation by very-long-chain acyl-CoA synthetase-1 (ASCVL1), which is not expressed in skel­ etal muscle, potentially explaining why it has less association with myalgias than statins; indeed, it has been shown to be relatively well tolerated in patients with statin-induced myalgias. In phase 3 trials, bempedoic acid 180 mg daily reduced LDL-C by ~18% when added to a statin and by ~23% as monotherapy. In a large cardiovascular outcomes trial in statin-intolerant patients, bempedoic acid 180 mg daily was shown to significantly reduce (by 13%) a four-component composite of major adverse cardiovascular events. It is also available in a fixed-dose combination with ezetimibe, which reduced LDL-C by ~36%, for patients who are statin intolerant. It can be used in combination with statins but should not be used with simvastatin in a dose >20 mg. Bempedoic acid is associated with increased uric acid levels and gout as well as with increased liver enzymes and cholelithiasis. Unlike statins, it is not associated with increased incidence of diabetes. Bile Acid Sequestrants (Resins)  Bile acid sequestrants (BAS) bind bile acids in the intestine and promote their excretion rather than reabsorption in the ileum. To maintain the bile acid pool size, the liver diverts cholesterol to bile acid synthesis. The decreased hepatic intracellular cholesterol content results in upregulation of the LDL receptor and enhanced LDL clearance from the plasma. BAS, including cholestyramine, colestipol, and colesevelam (Table 419-4), primarily reduce plasma LDL-C levels but can cause an increase in plasma TGs. Therefore, patients with HTG generally should not be treated with bile acid–binding resins. Cholestyramine and colestipol are insoluble resins that must be suspended in liquids. Colesevelam is available as tablets but generally requires up to six to seven tablets per day for effective LDL-C lowering. BAS are effec­ tive in combination with statins and in combination with ezetimibe. Side effects of resins are limited to the gastrointestinal tract and include bloating and constipation. Because BAS are not systemically absorbed, they are very safe and are the cholesterol-lowering drug

36 - 420 The Metabolic Syndrome

420 The Metabolic Syndrome

of choice in children and in women who are pregnant, lactating, or actively trying to conceive. However, they are otherwise fourth- or fifth-line drugs for LDL-C reduction in other settings.

Specialized Drugs for HoFH  Three “orphan” drugs are approved specifically for the management of HoFH, a rare condition caused by biallelic mutations in the major genes causing FH in which patients respond poorly to traditional LDL-lowering medications. Lomitapide is a small-molecule inhibitor of MTP that reduces LDL-C by ~50%, and mipomersen is an antisense oligonucleotide against apoB that reduces LDL-C by ~25%. Both of these drugs reduce hepatic VLDL production and thus LDL-C levels; however, due to their mechanism of action, each drug causes an increase in hepatic fat, the long-term consequences of which are unknown. In addition, lomitapide is associated with gastrointestinal-related side effects, and mipomersen is associated with skin reactions and flulike symptoms. Finally, an antibody inhibitor of ANGPTL3, evinacumab, was approved in 2021 for the treatment of HoFH. In a phase 3 trial, an intravenous infusion every 4 weeks reduced LDL-C levels in patients with HoFH by ~50% and was well toler­ ated. One of these three drugs should be strongly considered in HoFH patients after a trial of a high-intensity statin, and possibly a PCSK9 inhibitor, is shown to be insufficient to reduce LDL-C levels. PART 12 Endocrinology and Metabolism LDL Apheresis  Patients with severe hypercholesterolemia who cannot reduce their LDL-C to acceptable levels despite optimally tolerated combination drug therapy are candidates for LDL apher­ esis. In this process, the patient’s plasma is passed over a column that selectively removes the LDL, and the LDL-depleted plasma is returned to the patient. LDL apheresis is indicated for patients on maximally tolerated combination drug therapy (including a PCSK9 inhibitor) who have CHD and a plasma LDL-C level >200 mg/dL or no CHD and a plasma LDL-C level >300 mg/dL; LDL apher­ esis could be considered in high-risk patients who have an LDL-C

160 mg/dL on maximal therapy. ■ ■FURTHER READING Cholesterol Treatment Trialists’ (CTT) Collaboration: Effects of statin therapy on diagnoses of new-onset diabetes and worsening glycaemia in large-scale randomised blinded statin trials: An indi­ vidual participant data meta-analysis. Lancet Diabetes Endocrinol 12:306, 2024. Hernandez P et al: Clinical management of hypertriglyceridemia in the prevention of cardiovascular disease and pancreatitis. Curr Ath­ eroscler Reports 23:72, 2021. Klarin D, Natarajan P: Clinical utility of polygenic risk scores for coronary artery disease. Nat Rev Cardiol 19:291, 2022. Loh WJ, Watts GF: The inherited hypercholesterolemias. Endocrinol Metab Clin North Am 51:511, 2022. Mangione CM et al: Statin use for the primary prevention of cardio­ vascular disease in adults: US Preventive Services Task Force recom­ mendation statement. JAMA 328:746, 2022. Piccirillo F et al: Novel antidiabetic agents and their effects on lipid profile: A single shot for several cardiovascular targets. Int J Mol Sci 24:10164, 2023. Sakhuja S et al: Recurrent atherosclerotic cardiovascular disease events potentially prevented with guideline-recommended choles­ terol-lowering therapy following myocardial infarction. Cardiovasc Drugs Ther 38:937, 2024. Shamsudeen I, Hegele RA: Advances in the care of lipodystrophies. Curr Opin Endocrinol Diabetes Obesity 29:152, 2022. Virani SS et al: 2023 AHA/ACC/ACCP/ASPC/NLA/PCNA guideline for the management of patients with chronic coronary disease: A report of the American Heart Association/American College of Car­ diology Joint Committee on Clinical Practice Guidelines. Circulation 148:e9, 2023. Watts GF et al: International Atherosclerosis Society guidance for implementing best practice in the care of familial hypercholesterol­ aemia. Nat Rev Cardiol 20:845, 2023.

Robert H. Eckel

The Metabolic Syndrome The metabolic syndrome (syndrome X, insulin resistance syndrome) consists of a constellation of metabolic abnormalities that confer increased risk of cardiovascular disease (CVD) and diabetes mellitus. Evolution of the criteria for the metabolic syndrome since the original definition by the World Health Organization in 1998 reflects growing clinical evidence and analysis by a variety of consensus conferences and professional organizations. The major features of metabolic syndrome include central obesity, hypertriglyceridemia, low levels of highdensity lipoprotein (HDL) cholesterol, hyperglycemia, and hyperten­ sion (Table 420-1). ■ ■GLOBAL HEALTH/EPIDEMIOLOGY The most challenging feature of the metabolic syndrome to define is waist circumference. Intraabdominal circumference (visceral adipose tissue) is most strongly related to insulin resistance and risk of diabetes and CVD, and for any given waist circumference, the distribution of adipose tissue between subcutaneous (SC) and visceral depots varies substantially. Thus, within and between populations, there is a lesser versus greater risk at the same waist circumference. These differences in populations reflect the range of waist circumferences considered to confer risk in different geographic locations (Table 420-1). The prevalence of the metabolic syndrome varies around the world, in part reflecting the age and ethnicity of the populations studied and the diagnostic criteria applied. In general, the prevalence of metabolic syndrome increases with age. The prevalence of metabolic syndrome in the U.S. adult population meeting the criteria of the National Cho­ lesterol Education Program (NCEP) and Adult Treatment Panel III (ATPIII) is ~35%. Greater global industrialization is associated with rising rates of obesity and related increase in the prevalence of the metabolic syndrome, especially as the population ages. Using National Health and Nutrition Examination Survey (NHANES) data from 1999–2018, the prevalence of metabolic syn­ drome in 28,049 adults in the United States was 33.4%. The highest prevalence was age-dependent with reduction by age 80 among all sub­ groups, i.e., from 19.5% among those aged 20–39 years to 48.6% among those aged ≥60 years. Importantly, the rising prevalence and severity of obesity among children reflect features of the metabolic syndrome in a younger population, now estimated to be 12 and 30% among obese and overweight children, respectively. The frequency distribution of different components of metabolic syndrome for the U.S. population (NHANES III) and the Guangdong Gut Microbiome Project of China is summarized in Fig. 420-1. Note the major differences in the U.S. population compared to Han Chinese. Moreover, within the United States, abdominal obesity appears equally prevalent in all U.S. races, whereas the prevalence of age-dependent other components differs as shown in Fig. 420-1. Increases in hyper­ glycemia were most evident in the 2017–2018 sample, whereas central obesity, low HDL cholesterol, and hypertension prevalence have been relatively constant, while levels of triglycerides (defined as >150 mg/dL) have progressively decreased. ■ ■RISK FACTORS Overweight/Obesity  Metabolic syndrome was first described in the early twentieth century; however, the worldwide overweight/ obesity epidemic has recently been the force driving its increasing recognition. Central adiposity is a key feature of the syndrome, and the syndrome’s prevalence reflects the strong relationship between waist circumference and increasing adiposity. However, despite the importance of obesity, patients who are of normal weight may also be insulin-resistant and may have metabolic syndrome. This phenotype is particularly evident for populations in India, Southeast Asia, and Central America.

TABLE 420-1  NCEP:ATPIIIa 2001 and Harmonizing Definition Criteria for the Metabolic Syndrome NCEP:ATPIII 2001 HARMONIZING DEFINITIONb Three or more of the following: • Central obesity: waist circumference >102 cm (males), Three of the following: Waist circumference (cm)

88 cm (females) • Hypertriglyceridemia: triglyceride level ≥150 mg/dL or Men Women Ethnicity ≥94 ≥80 Europid, sub-Saharan African, Eastern and Middle Eastern specific medication • Low HDLc cholesterol: <40 mg/dL and <50 mg/dL for ≥90 ≥80 South Asian, Chinese, and ethnic South and Central American ≥85 ≥90 Japanese men and women, respectively, or specific medication • Hypertension: blood pressure ≥130 mmHg systolic or • Fasting triglyceride level >150 mg/dL or specific medication • HDL cholesterol level <40 mg/dL and <50 mg/dL for men and women, respectively, or specific medication • Blood pressure >130 mm systolic or >85 mm diastolic or previous diagnosis or specific medication • Fasting plasma glucose level ≥100 mg/dL (alternative indication: drug treatment of elevated glucose levels) ≥85 mmHg diastolic or specific medication • Fasting plasma glucose level ≥100 mg/dL or specific medication or previously diagnosed type 2 diabetes aNational Cholesterol Education Program and Adult Treatment Panel III. bIn this analysis, the following thresholds for waist circumference were used: white men, ≥94 cm; African-American men, ≥94 cm; Mexican-American men, ≥90 cm; white women, ≥80 cm; African-American women, ≥80 cm; Mexican-American women, ≥80 cm. For participants whose designation was “other race—including multiracial,” thresholds that were once based on Europid cutoffs (≥94 cm for men and ≥80 cm for women) and on South Asian cutoffs (≥90 cm for men and ≥80 cm for women) were used. For participants who were considered “other Hispanic,” the International Diabetes Federation thresholds for ethnic South and Central Americans were used. cHigh-density lipoprotein. Sedentary Lifestyle  Physical inactivity and less cardiorespiratory fitness are predictors of CVD events and the related risk of death. Many components of the metabolic syndrome are associated with a sedentary lifestyle, including increased adipose tissue (predominantly central), reduced HDL cholesterol, and increased triglycerides, blood pressure, and glucose in genetically susceptible persons. Compared with indi­ viduals who watch television or videos or use the computer <1 h daily, those who do so for >4 h daily have a twofold increased risk of the metabolic syndrome. Genetics  No single gene explains the complex phenotype called metabolic syndrome. However, using genome-wide association and MetS Abdominal Obesity

Prevalence (%) Prevalence (%) Prevalence (%)

Age (years)

Age (years)

Age (years) Elevated BP Elevated TG Reduced HDL-C

Prevalence (%)

Age (years)

Age (years)

Age (years) Han Chinese Mexican American Non-Hispanic Black Non-Hispanic White FIGURE 420-1  The frequency distribution of the metabolic syndrome for the U.S. population (National Health and Nutrition Examination Survey [NHANES] III) and the Guangdong Gut Microbiome Project of China. The prevalence of metabolic syndrome (MetS) and its components with age across different races. Prevalence was estimated using a SWAN algorithm (shown as dots). The trajectory of the prevalence of MetS with age was fitted by cubic regressions (shown as lines). BP, blood pressure; FPG, fasting plasma glucose; HDL-C, high-density lipid cholesterol; SWAN, sliding window–based algorithm; TG, triglycerides. (Reproduced from R Zhang et al: The racial disparities in the epidemic of metabolic syndrome with increased age: A study from 28,049 Chinese and American adults. Front Public Health 9:797183, 2022.)

The Metabolic Syndrome CHAPTER 420 candidate gene approaches, several genetic variants are associated with metabolic syndrome. Although many of the loci have unknown function, many others relate to body weight and composition, insu­ lin resistance, and unfavorable disturbances in lipid and lipoprotein metabolism. In general, heritability estimates for each of the metabolic traits exceed 50%. Aging  The metabolic syndrome affects nearly 50% of the U.S. population aged >60, and at >60 years of age, women are more often affected. The age dependency of the syndrome’s prevalence is seen in most populations around the world. Elevated FPG

Prevalence (%) Prevalence (%)

Diabetes Mellitus  Diabetes mellitus can be included in both the NCEP and the Harmonizing Definitions of metabolic syndrome, but the greatest value of metabolic syndrome, and especially fast­ ing glucose, is predicting type 2 diabetes. The great majority (~75%) of patients with type 2 diabetes or impaired glucose tolerance have metabolic syndrome. The presence of metabolic syndrome in these populations relates to a higher prevalence of CVD than in patients who have type 2 diabetes or impaired glucose tolerance but do not have the syndrome.

Cardiovascular Disease  Individuals with metabolic syndrome are twice as likely to die of CVD as those who do not, and their risk of acute myocardial infarction or stroke is threefold higher. The approxi­ mate prevalence of metabolic syndrome among patients with coronary heart disease (CHD) is up to 60% in persons >75 years, with a preva­ lence of ~35% among patients with premature coronary artery disease (age ≤45) and a particularly higher prevalence among women. With appropriate cardiac rehabilitation and changes in lifestyle (e.g., nutrition, physical activity, weight reduction, and—in some cases—pharmacologic therapy), the prevalence of the syndrome can be reduced. PART 12 Endocrinology and Metabolism Lipodystrophy  Lipodystrophic disorders in general are associ­ ated with metabolic syndrome. Moreover, it is quite common for such patients to present with the metabolic syndrome. Both genetic lipodystrophy (e.g., Berardinelli-Seip congenital lipodystrophy, Dun­ nigan familial partial lipodystrophy) and acquired lipodystrophy (e.g., HIV-related lipodystrophy and in HIV patients receiving certain anti­ retroviral therapies) may give rise to severe insulin resistance and many of the components of metabolic syndrome. C-III C-II HDL cholesterol B-100 and TG Insulin Small dense LDL VLDL Glucose TNF-α IL-6 CRP FFA Fibrinogen PAI-1 Adiponectin Prothrombotic state FIGURE 420-2  Pathophysiology of the metabolic syndrome. Free fatty acids (FFAs) are released in abundance from an expanded adipose tissue mass. In the liver, FFAs result in increased production of glucose and triglycerides and secretion of very-low-density lipoproteins (VLDLs). Associated lipid/lipoprotein abnormalities include reductions in high-density lipoprotein (HDL) cholesterol and an increased low-density lipoprotein (LDL) particle number. FFAs also reduce insulin sensitivity in muscle by inhibiting insulin-mediated glucose uptake. Associated defects include a reduction in glucose partitioning to glycogen and increased lipid accumulation in triglyceride (TG). The increase in circulating glucose, and to some extent FFAs, increases pancreatic insulin secretion, resulting in hyperinsulinemia. Hyperinsulinemia may result in enhanced sodium reabsorption and increased sympathetic nervous system (SNS) activity and contribute to hypertension, as might higher levels of circulating FFAs. The proinflammatory state is superimposed and contributory to the insulin resistance produced by excessive FFAs. The enhanced secretion of interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) produced by adipocytes and monocyte-derived macrophages results in more insulin resistance and lipolysis of adipose tissue triglyceride stores to circulating FFAs. IL-6 and other cytokines also enhance hepatic glucose production, VLDL production by the liver, hypertension, and insulin resistance in muscle. Insulin resistance also contributes to increased triglyceride accumulation in the liver (nonalcoholic fatty liver disease). Cytokines and FFAs also increase hepatic production of fibrinogen and adipocyte production of plasminogen activator inhibitor 1 (PAI-1), resulting in a pro-thrombotic state. Higher levels of circulating cytokines stimulate hepatic production of C-reactive protein (CRP). Reduced production of the anti-inflammatory and insulin-sensitizing cytokine adiponectin is also associated with the metabolic syndrome. (Reproduced with permission from RH Eckel et al: The metabolic syndrome. Lancet 365:1415, 2005.)

■ ■ETIOLOGY Insulin Resistance  The most accepted and unifying hypothesis to describe the pathophysiology of metabolic syndrome is insulin resis­ tance, caused systemically by an incompletely understood defect in insulin action (Chap. 415). The onset of insulin resistance is heralded by postprandial hyperinsulinemia, which is followed by fasting hyper­ insulinemia and ultimately by hyperglycemia. An early major contributor to the development of insulin resistance is an overabundance of circulating fatty acids (Fig. 420-2). Plasma albumin-bound free fatty acids are derived predominantly from adi­ pose-tissue triglyceride stores released by intracellular lipolytic enzymes. The lipolysis of triglyceride-rich lipoproteins in tissues by lipoprotein lipase also produces free fatty acids. Insulin mediates both anti-lipolysis and the stimulation of lipoprotein lipase in adipose tissue. Of note, the inhibition of lipolysis in adipose tissue is the most sensitive pathway of insulin action. Thus, when insulin resistance develops, increased lipoly­ sis produces more fatty acids, which further decreases the anti-lipolytic effect of insulin. Excessive fatty acids enhance substrate availability and create insulin resistance by modifying downstream signaling. Fatty acids impair insulin-mediated glucose uptake and are associated with accu­ mulation of triglycerides in both skeletal and cardiac muscle, whereas increased fatty acid flux increases endogenous glucose production and triglyceride production, accumulation, and secretion in the liver. Reductions in leptin action may also be a pathophysiologic mecha­ nism to explain metabolic syndrome. Physiologically, leptin reduces appetite, promotes energy expenditure, and enhances insulin sensi­ tivity. In addition, leptin may regulate cardiac and vascular function through a nitric oxide–dependent mechanism. However, when obesity Hypertension FFA IL-6 SNS Insulin – Glycogen – CO2 FFA – Triglyceride (intramuscular droplet)

develops, hyperleptinemia ensues, with evidence of leptin resistance in the brain and other tissues resulting in insulin resistance and associ­ ated inflammation, hyperlipidemia, and a plethora of cardiovascular disorders, such as hypertension, atherosclerosis, CHD, and heart failure. Moreover, a series of adipokines relate to metabolic syndrome. Whereas adiponectin improves insulin sensitivity in adipose tissue and skeletal muscle, visfatin, fetuin-A, resistin, asprosin, and plasminogen activator inhibitor-1 contribute to insulin resistance and systemic glu­ cose intolerance. The oxidative stress hypothesis provides a unifying theory for aging and the predisposition to metabolic syndrome. In studies of insulinresistant individuals with obesity or type 2 diabetes, the offspring of persons with type 2 diabetes, and the elderly, a defect in mitochondrial oxidative phosphorylation leads to the accumulation of triglycer­ ides and related lipid molecules in muscle, liver, and other tissues, i.e., β-cells. The gut microbiome has emerged as an important contributor to the development of obesity and related metabolic disorders, includ­ ing inflammation and components of metabolic syndrome. Although the mechanisms remain uncertain, an increased ratio of Firmicutes/ Bacteroidetes species in addition to genetic predisposition, diet, and bile acid metabolism are associated with and may play an etiologic role in metabolic syndrome. Increased Waist Circumference  Waist circumference is an impor­ tant component of the most recent and frequently applied diagnostic cri­ teria for metabolic syndrome. However, measuring waist circumference does not reliably distinguish increases in SC abdominal adipose tissue from that in intra-abdominal or visceral fat; this distinction requires dual X-ray absorptiometry (DEXA), computed tomography (CT), or magnetic resonance imaging (MRI) to discriminate. With increases in visceral adipose tissue, adipose tissue–derived free fatty acids reach the liver more readily. In contrast, increases in abdominal SC fat release lipolysis products into the systemic circulation and therefore have fewer direct effects on hepatic metabolism. Relative increases in visceral versus SC adipose tissue with increasing waist circumference in Asians and Asian Indians may explain the greater prevalence of metabolic syn­ drome in those populations than in African Americans, in whom SC fat predominates. It is also possible that visceral fat is a marker for—but not the source of—excess postprandial free fatty acids in obesity. Dyslipidemia  (See also Chap. 419) In general, free fatty acid flux from adipose tissue to the liver results in increased production of apolipoprotein (apo) B–containing, triglyceride-rich, very-low-density lipoproteins (VLDLs). The direct effect of insulin on this process is complex, but hypertriglyceridemia is an excellent marker of the insulin-resistant condition. Not only is hypertriglyceridemia a feature of metabolic syndrome, but patients with metabolic syndrome have elevated levels of apoC-III carried on VLDLs and other lipoproteins. This increase in apoC-III is inhibitory to lipoprotein lipase, reducing triglyceride-rich lipoprotein remnant removal, further contributing to hypertriglyceridemia, and confers more risk for atherosclerotic cardio­ vascular disease (ASCVD). The other major lipoprotein disturbance in metabolic syndrome is a reduction in HDL cholesterol. This reduction is a consequence of changes in HDL composition and metabolism. In the presence of hypertriglyceridemia, a decrease in the cholesterol content of HDL is a consequence of reduced cholesteryl ester content of the lipoprotein core in combination with cholesteryl ester transfer protein–mediated alterations in triglycerides that make the HDL particle small and dense. This change in lipoprotein composition also results in increased clearance of HDL from the circulation. These changes in HDL have a relationship to insulin resistance that is probably indirect, occurring in concert with the changes in triglyceride-rich lipoprotein metabolism. In addition to HDLs, low-density lipoproteins (LDLs) have altera­ tions in composition in metabolic syndrome. With fasting serum triglycerides at >2.0 mM (~180 mg/dL), there is usually a predomi­ nance of small dense LDLs, which are thought to be more atherogenic, although their association with hypertriglyceridemia and low HDLs makes their independent contribution to ASCVD difficult to assess.

Individuals with hypertriglyceridemia often have increases in choles­ terol content of both VLDL1 and VLDL2 subfractions and in LDL par­ ticle number. Both lipoprotein changes may contribute to atherogenic risk in patients with metabolic syndrome. Glucose Intolerance  (See also Chap. 415) Defects in insulin action in metabolic syndrome lead to impaired suppression of endoge­ nous glucose production by the liver (and kidney) and reduced glucose uptake and metabolism in insulin-sensitive tissues—i.e., muscle and adipose tissue. There is a strong relationship between impaired fasting glucose or impaired glucose tolerance and insulin resistance in stud­ ies of humans, nonhuman primates, and rodents. To compensate for defects in insulin action, insulin secretion and/or clearance increases or decreases, respectively, so that euglycemia remains. Ultimately, this compensatory mechanism fails because of defects in insulin secretion, resulting in progression from impaired fasting glucose and/or impaired glucose tolerance to type 2 diabetes mellitus. Hypertension  The relationship between insulin resistance and hypertension is well established. Paradoxically, under normal physi­ ologic conditions, insulin-mediated increases in nitric oxide cause vaso­ dilation with secondary effects on sodium reabsorption in the kidney. However, in the setting of insulin resistance, the vasodilatory effect of insulin is lost but the renal effect on sodium reabsorption is preserved. Sodium reabsorption is increased in Caucasians with metabolic syn­ drome but not in Africans or Asians. Insulin also increases the activity of the sympathetic nervous system, an effect that is preserved in the setting of insulin resistance. Insulin resistance is also associated with pathwayspecific impairment in phosphatidylinositol-3-kinase signaling. In the endothelium, this impairment may cause an imbalance between the production of nitric oxide and the secretion of endothelin 1, with a consequent decrease in blood flow. In addition, increases in angioten­ sinogen gene expression in adipose tissue of obese subjects results in increases in circulating angiotensin II and vasoconstriction. Although these mechanisms are provocative, the inadequate evaluation of insulin action by measurement of fasting insulin levels or by homeostasis model assessment shows that insulin resistance contributes only partially to the increased prevalence of hypertension in metabolic syndrome.

The Metabolic Syndrome CHAPTER 420 Another possible mechanism underlying hypertension in metabolic syndrome is the vasoactive role of perivascular adipose tissue. Reactive oxygen species released by NADPH oxidase impair endothelial func­ tion and result in local vasoconstriction. Other paracrine effects such as leptin or other proinflammatory cytokines released from adipose tis­ sue, such as tumor necrosis factor α (TNF-α), may also be important. Hyperuricemia is another consequence of insulin resistance in metabolic syndrome. There is growing evidence not only that uric acid is associated with hypertension but also that reduction of uric acid normalizes blood pressure in hyperuricemic adolescents with hyper­ tension. The mechanism appears to be in part related to an adverse effect of uric acid on nitric oxide synthase in the macula densa of the kidney and stimulation of the renin-angiotensin-aldosterone system. Proinflammatory Cytokines  The increases in proinflammatory cytokines—including interleukins 1, 6, and 18; resistin; TNF-α; and the systemic biomarker C-reactive protein—reflect overproduction by the expanded adipose tissue mass (Fig. 420-2). Adipose tissue–derived macrophages may be the primary source of proinflammatory cytokines locally and in the systemic circulation. It remains unclear, however, how much of the insulin resistance is caused by the paracrine effects of these cytokines and how much by the endocrine effects. Adiponectin  Adiponectin is an anti-inflammatory cytokine pro­ duced exclusively by adipocytes. Adiponectin enhances insulin sensi­ tivity and inhibits many steps in the inflammatory process. In the liver, adiponectin inhibits the expression of gluconeogenic enzymes and the rate of glucose production. In muscle, adiponectin increases glucose transport and enhances fatty acid oxidation, partially through the activation of AMP kinase. Reductions in adiponectin levels are com­ mon in metabolic syndrome. The relative contributions of adiponectin deficiency and overabundance of the proinflammatory cytokines are unclear.

■ ■CLINICAL FEATURES

Symptoms and Signs  Metabolic syndrome typically is not associ­ ated with symptoms. On physical examination, waist circumference and blood pressure are often elevated. The presence of either or both signs should prompt the clinician to search for other biochemical abnormalities that may be associated with metabolic syndrome. Much less frequently, lipoatrophy or acanthosis nigricans is present on exami­ nation. Because these physical findings characteristically are associated with severe insulin resistance, other components of metabolic syn­ drome are much more common. Associated Diseases  •  CARDIOVASCULAR DISEASE  The rela­ tive risk for new-onset CVD in patients with metabolic syndrome who do not have diabetes averages 1.5- to 3-fold. However, in INTERHEART, a study of 26,903 subjects from 52 countries, the risk for acute myocardial infarction in subjects with metabolic syndrome (World Health Organization or International Diabetes Federation definition) is comparable to that conferred by some, but not all, of the component risk factors. Diabetes mellitus (odds ratio [OR], 2.72) and hypertension (OR, 2.60) are stronger than other risk factors. Although congestive heart failure and metabolic syndrome can occur together, typically this consequence is secondary to metabolic syn­ drome–related ASCVD or hypertension. Metabolic syndrome is also associated with increases in the risk for stroke, peripheral vascular disease, and Alzheimer’s disease. However, as for myocardial infarc­ tion, the risk beyond the additive role of the components of metabolic syndrome remains debatable. In the Reasons for Geographic and Racial Differences in Stroke (REGARDS) cohort, an observational study of black and white adults ≥45 years old across the United States, there were 9741 participants, and 41% had metabolic syndrome. After adjustment for multiple confounders, metabolic syndrome was asso­ ciated with increases in high-sensitivity C-reactive protein (hsCRP), and this relationship was associated with a 1.34 relative risk for allcause mortality, but <50% of deaths were from CVD. The populationattributable risk was 9.5% for metabolic syndrome alone and 14.7% for both metabolic syndrome and increased hsCRP. The relationship of metabolic syndrome and hsCRP to mortality was greater for whites than blacks. PART 12 Endocrinology and Metabolism TYPE 2 DIABETES  Overall, the risk for type 2 diabetes among patients with metabolic syndrome is increased three- to fivefold. In the Framingham Offspring Study’s 8-year follow-up of middle-aged par­ ticipants, the population-attributable risk of metabolic syndrome for developing type 2 diabetes was 62% among men and 47% among women, yet increases in fasting plasma glucose explained most, if not all, of this increased risk. Other Associated Conditions  In addition to the features specifi­ cally used to define metabolic syndrome, other metabolic alterations are secondary to or accompany insulin resistance. Those alterations include increases in apoB and apoC-III, uric acid, prothrombotic factors (fibrinogen, plasminogen activator inhibitor 1), serum viscos­ ity, asymmetric dimethylarginine, homocysteine, white blood cell count, proinflammatory cytokines, C-reactive protein, urine albumin/ creatinine ratio, metabolic-associated fatty liver disease (MAFLD) and/or nonalcoholic steatohepatitis (NASH), polycystic ovary syndrome, and obstructive sleep apnea. METABOLIC-ASSOCIATED FATTY LIVER DISEASE  MAFLD has become the most common liver disease, in part a consequence of the insulin resistance of metabolic syndrome. The mechanism relates to increases in free fatty acid flux and reductions in intrahepatic fatty acid oxidation with resultant increases in triglyceride biosynthesis and hepatocel­ lular accumulation, with variable inflammation and oxidative stress. The more serious Metabolic dysfunction-associated steatohepatitis (MASH), a consequence of MAFLD in some patients and a precursor of cirrhosis and end-stage liver disease, includes a more substantial proinflammatory contribution. MAFLD affects ~10% of the nonobese population and up to 65% of patients with metabolic syndrome; over half of these patients have metabolic dysfunction-associated

steatohepatitis (MASH). As the prevalence of overweight/obesity and metabolic syndrome increases, NASH may become one of the more common causes of end-stage liver disease and hepatocellular carci­ noma. Increasingly, studies have shown that MAFLD is related inde­ pendently to CVD, especially coronary artery disease. HYPERURICEMIA  (See also Chap. 384) Hyperuricemia reflects defects in insulin action on the renal tubular reabsorption of uric acid and may contribute to hypertension through its effect on the endothelium. An increase in asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, also relates to endothelial dysfunction. In addition, increases in the urine albumin/creatinine ratio may relate to altered endothelial pathophysiology in the insulin-resistant state. POLYCYSTIC OVARY SYNDROME  (See also Chap. 404) Polycystic ovary syndrome is highly associated with insulin resistance (50–80%) and metabolic syndrome, with a prevalence of the syndrome between 12 and 60% based on phenotypes D through A. OBSTRUCTIVE SLEEP APNEA  (See also Chap. 33) Obstructive sleep apnea is commonly associated with obesity, hypertension, increased circulating proinflammatory cytokines, impaired glucose tolerance, and insulin resistance. In fact, obstructive sleep apnea may predict metabolic syndrome, even in the absence of excess adiposity. Moreover, when biomarkers of insulin resistance are compared between patients with obstructive sleep apnea and weight-matched controls, insulin resistance is found to be more severe in those with apnea. Continu­ ous positive airway pressure treatment improves insulin sensitivity in patients with obstructive sleep apnea. ■ ■DIAGNOSIS The diagnosis of metabolic syndrome relies on fulfillment of the cri­ teria listed in Table 420-1, as assessed using tools at the bedside and in the laboratory. The medical history should include evaluation of symptoms for obstructive sleep apnea in all patients and polycystic ovary syndrome in premenopausal women. Family history will help determine the risk for CVD and diabetes mellitus. Blood pressure and waist circumference measurements provide information necessary for the diagnosis. Laboratory Tests  Measurement of fasting lipids and glucose is needed in determining whether metabolic syndrome is present. The measurement of additional biomarkers associated with insulin resistance can be individualized. Such tests might include those for apoB, hsCRP, fibrinogen, uric acid, urinary albumin/creatinine ratio, and liver function. A sleep study should be performed if symptoms of obstructive sleep apnea are present. If polycystic ovary syndrome is suspected based on clinical features and anovulation, testosterone, luteinizing hormone, and follicle-stimulating hormone should be mea­ sured. MAFLD can be further assessed by the MAFLD fibrosis score (FIB4) or elastography. TREATMENT The Metabolic Syndrome LIFESTYLE (SEE ALSO CHAP. 414) Obesity, particularly abdominal, is the driving force behind meta­ bolic syndrome. Thus, weight reduction is the primary approach to the disorder. With at least 5% and more so with 10% weight reduc­ tion, improvement in insulin sensitivity results in favorable modi­ fications in many components of metabolic syndrome. In general, recommendations for weight loss include a combination of caloric restriction, increased physical activity, and behavior modification. Caloric restriction is the most important component, whereas increases in physical activity are important for maintenance of weight loss. Some but not all evidence suggests that the addition of exercise to caloric restriction may promote greater weight loss from the visceral depot. The tendency for weight regains after successful weight reduction underscores the need for long-lasting behavioral changes.

Diet  Before prescribing a weight-loss diet, it is important to empha­ size that it has taken the patient a long time to develop an expanded fat mass; thus, the correction need not occur quickly. Given, in gen­ eral, that ~3500 kcal = 1 lb of adipose tissue, an ~500-kcal restriction daily equates to weight reduction of 1 lb per week. Diets restricted in carbohydrate typically provide a more rapid initial weight loss. However, after 1 year, the amount of weight reduction is minimally reduced or no different from that with caloric restriction alone. Thus, adherence to the diet is more important than the chosen diet. Moreover, there is concern about low-carbohydrate diets enriched in saturated fat, particularly for patients at risk for ASCVD. Therefore, a high-quality dietary pattern—i.e., a diet enriched in fruits, vegetables, whole grains, lean poultry, and fish—should be encouraged to maxi­ mize overall health benefit. Physical Activity  Before prescribing a physical activity program to patients with metabolic syndrome, it is important to ensure that the increased activity does not incur risk. Some high-risk patients should undergo formal cardiovascular evaluation before initiating an exercise program. For an inactive participant, gradual increases in physical activity should be encouraged to enhance adherence and avoid injury. Although increases in physical activity can lead to modest weight reduction, 60–90 min of moderate- to high-intensity daily activity is required to achieve this goal. Even if an overweight or obese adult is unable to undertake this level of activity, a health benefit will follow from at least 30 min of moderate-intensity activ­ ity daily. The caloric value of 30 min of a variety of activities can be found at https://www.health.harvard.edu/diet-and-weight-loss/ calories-burned-in-30-minutes-of-leisure-and-routine-activities. Of note, a variety of routine activities, such as gardening, walking, and housecleaning, require moderate caloric expenditure. Thus, physi­ cal activity should not be defined solely in terms of formal exercise such as jogging, swimming, or tennis. Behavior Modification  Behavioral treatment typically includes recommendations for dietary restriction and more physical activ­ ity that predicts sufficient weight loss that benefits metabolic health. The subsequent challenge is the duration of the program because weight regain so often follows successful weight reduction. Improved long-term outcomes often follow a variety of methods, such as a personal or group counselor, the Internet, social media, and telephone follow-up to maintain contact between providers and patients. Obesity  (See also Chap. 414) In some patients with metabolic syndrome, treatment options need to extend beyond lifestyle intervention. Weight-loss drugs come in two major classes: appe­ tite suppressants and absorption inhibitors. Appetite suppressants approved by the U.S. Food and Drug Administration (FDA) include phentermine (for short-term use [3 months] only) as well as phen­ termine/topiramate, naltrexone/bupropion, high-dose (3.0 mg) liraglutide (rather than 1.8 mg, the maximum for treatment of type 2 diabetes), and semaglutide (2.4 mg), which are approved without restrictions on the duration of therapy. In clinical trials, the phentermine/topiramate extended-release combination resulted in ~8% weight loss relative to placebo in 50% of patients. Side effects include palpitations, headache, paresthesias, constipation, and insomnia. Naltrexone/bupropion extended release reduces body weight by ≥10% in ~20% of patients; however, the drug combina­ tion is contraindicated in patients with seizure disorders or any condition that predisposes to seizures. Naltrexone/bupropion also increases pulse and blood pressure and should not be given to patients with uncontrolled hypertension. High-dose liraglutide, a glucagon-like peptide 1 (GLP-1) receptor agonist, results in ~6% weight loss relative to placebo with ~33% of patients with

10% weight loss. Common side effects are limited to the upper gastrointestinal tract, including nausea and, less frequently, emesis. Semaglutide (2.4 mg weekly) has been shown to produce an average weight loss of 14.9% over 68 weeks. Tirzepatide, a novel glucosedependent insulinotropic polypeptide (GIP) and GLP-1 receptor

agonist, has been tested for 72 weeks in participants with a mean body weight of 104.8 kg and mean body mass index (BMI) of 38.0 kg/m2, with 94.5% of patients with a BMI of ≥30 kg/m2. Participants expe­ rienced a dose-dependent reduction in weight ranging from –15.0% with 5 mg of tirzepatide weekly to 20.9% with the 15-mg dose. Benefits of GLP-1 receptor agonists on MAFLD are also notewor­ thy, but not yet FDA approved.

Orlistat inhibits fat absorption by ~30% and is moderately effec­ tive compared with placebo (~4% more weight loss). Moreover, orlistat reduced the incidence of type 2 diabetes, an effect that was especially evident among patients with impaired glucose tolerance at baseline. This drug is often difficult to take because of oily leak­ age per rectum. In general, for all weight-loss drugs, greater weight reduction leads to greater improvement in metabolic syndrome components, including the conversion from prediabetes to type 2 diabetes. The Metabolic Syndrome CHAPTER 420 Metabolic or bariatric surgery is an important option for patients with metabolic syndrome who have a BMI >40 kg/m2 or >35 kg/m2 with comorbidities. An evolving application for metabolic surgery includes patients with a BMI as low as 30 kg/m2 and type 2 diabetes. Gastric bypass or vertical sleeve gastrectomy results in dramatic weight reduction and improvement in most features of metabolic syndrome. A survival benefit with gastric bypass has also been realized. LDL CHOLESTEROL (SEE ALSO CHAP. 419) The rationale for the development of criteria for metabolic syn­ drome by NCEP was to go beyond LDL cholesterol in identifying and reducing the risk of ASCVD. The working assumption by the panel was that LDL cholesterol goals had already been achieved and that increasing evidence supports a linear reduction in ASCVD events because of progressive lowering of LDL cholesterol with statins with subsequent benefit using additional LDL cholesterol– lowering agents. The 2019 American College of Cardiology (ACC)/ American Health Association (AHA) Cholesterol Guidelines have no specific recommendations for patients with metabolic syndrome; however, they recommend that patients aged 20–75 years with LDL cholesterol levels ≥190 mg/dL should use a high-intensity statin (e.g., atorvastatin 40–80 mg or rosuvastatin 20–40 mg daily) and those with type 2 diabetes aged 40–75 years should use a moderateintensity statin and, if or when risk estimate is high, a high-intensity statin. For patients with metabolic syndrome but without diabe­ tes, the 10-year ASCVD risk estimator should be employed, and patients with a risk ≥7.5% and ≤20% or persons aged 20–59 with elevated lifetime risk should have a discussion with their provider about initiating statin therapy for primary prevention of ASCVD. A coronary calcium score may help in making this decision. Diets restricted in saturated fats (<6% of calories) and trans fats (as few as possible) should be applied aggressively. Although evidence is controversial, dietary cholesterol can also be restricted. If LDL cholesterol remains elevated, pharmacologic intervention is needed. Based on substantial evidence, treatment with statins, which lower LDL cholesterol by 15–60%, is the first-choice medi­ cation intervention. Of note, for each doubling of the statin dose, LDL cholesterol is further lowered by only ~6%. Hepatotoxicity (more than a threefold increase in hepatic aminotransferases) is rare, but myopathy occurs in ~10–20% of patients. The cholesterol absorption inhibitor ezetimibe is well tolerated and should be the second-choice medication intervention. Ezetimibe typically reduces LDL cholesterol by 15–20%. Bempedoic acid alone or in combination with ezetimibe is another option, with up to a 35% lowering of LDL cholesterol with the combination. Bempedoic acid can increase plasma uric acid. Proprotein convertase subtilisin/ kexin type 9 (PCSK9) inhibitors are potent LDL cholesterol–lowering drugs (~45–60%) but are not needed for most patients with meta­ bolic syndrome. Of course, if these patients also have familial hypercholesterolemia or insufficient LDL cholesterol lowering on statins with or without ezetimibe, a PCSK9 inhibitor should be considered. The bile acid sequestrants cholestyramine, colestipol,

and colesevelam may be more effective than ezetimibe alone, but because they can increase triglyceride levels, they must be used with caution in patients with metabolic syndrome when fasting triglycer­ ides are >300 mg/dL. Side effects include gastrointestinal symptoms (palatability, bloating, belching, constipation, anal irritation). Nico­ tinic acid has similar LDL cholesterol–lowering capabilities (<20%); however, it may be associated with multiple adverse effects. Fibrates are best employed to lower LDL cholesterol when triglycerides are not elevated. Fenofibrate may be more effective than gemfibrozil in this setting.

TRIGLYCERIDES (SEE ALSO CHAP. 419) The 2019 ACC/AHA Cholesterol Guidelines stated that fasting triglycerides >500 mg/dL should be treated to prevent more serious hypertriglyceridemia and pancreatitis. Although a fasting triglyc­ eride value of >150 mg/dL is a component of metabolic syndrome, post hoc analyses of multiple fibrate trials have not suggested a triglyceride-related reduction in the primary ASCVD outcome in patients (with or without concomitant statin therapy) with fasting triglycerides >200 mg/dL, often in the setting of reduced levels of HDL cholesterol. It remains uncertain whether triglycerides cause ASCVD or if levels are just associated with increased ASCVD risk. PART 12 Endocrinology and Metabolism A fibrate (gemfibrozil or fenofibrate) is one drug class of choice to lower fasting triglyceride levels, which are typically reduced by 30–45%. Concomitant administration with drugs metabolized by the 3A4 cytochrome P450 system (including some statins) increases the risk of myopathy. In these cases, fenofibrate may be preferable to gem­ fibrozil. In the Veterans Affairs HDL Intervention Trial, gemfibrozil was administered to men with known CHD and levels of HDL choles­ terol <40 mg/dL. A coronary disease event and mortality rate benefit was experienced predominantly among men with hyperinsulinemia and/or diabetes, many of whom were identified retrospectively as hav­ ing metabolic syndrome. Of note, the degree of triglyceride lowering in this trial or other fibrate trials did not predict benefit. Other drugs that lower triglyceride levels include statins, nico­ tinic acid, and prescription omega-3 fatty acids. For this purpose, an intermediate or high dose of the “more potent” statins (atorvas­ tatin, rosuvastatin) is needed. The effect of nicotinic acid on fasting triglycerides is dose related and ~20–35%, an effect that is less pro­ nounced than that of fibrates. In patients with metabolic syndrome and diabetes, nicotinic acid may increase fasting glucose levels, and clinical trials with nicotinic acid plus a statin have failed to reduce ASCVD events. Prescriptions of omega-3 fatty acid preparations that include high doses of eicosapentaenoic acid (EPA) with or without docosahexaenoic acid (DHA) (~1.5–4.5 g/d) lower fast­ ing triglyceride levels by ~25–40%. The two omega-3 randomized controlled trials associated with ASCVD risk reduction, JELIS and REDUCE-IT, used EPA only, whereas STRENGTH, which was ter­ minated prematurely because of futility, used EPA plus DHA. Here, no drug interactions with fibrates or statins occur, and the main side effect of their use is eructation with a fishy taste. Freezing the nutraceutical can partially block this unpleasant side effect. Impor­ tantly, lowering triglycerides with any of the pharmaceuticals has not been proven to be an independent predictor of CVD outcomes. HDL CHOLESTEROL (SEE ALSO CHAP. 419) Very few lipid-modifying compounds increase HDL cholesterol lev­ els. Statins, fibrates, and bile acid sequestrants have modest effects (5–10%), whereas ezetimibe and omega-3 fatty acids have no effect. Nicotinic acid is the only currently available drug with predictable HDL cholesterol–raising properties. The response is dose related, and nicotinic acid can increase HDL cholesterol by up to 30% above baseline. After several trials of nicotinic acid versus placebo in statin-treated patients, there is no evidence that raising HDL cholesterol with nicotinic acid beneficially affects ASCVD events in patients with or without metabolic syndrome. BLOOD PRESSURE (SEE ALSO CHAP. 288) The direct relationship between blood pressure and all-cause mor­ tality rate has been well established in studies comparing patients

with hypertension (>140/90 mmHg), patients with prehypertension (>120/80 mmHg but <140/90 mmHg), and individuals with normal blood pressure (<120/80 mmHg). In patients who have metabolic syndrome without diabetes, the best choice for the initial antihy­ pertensive medication is an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin II receptor blocker, as these two classes of drugs are effective and well tolerated. Additional agents include a diuretic, calcium channel blocker, beta blocker, and mineralocorti­ coid inhibitor, such as the recent FDA-approved mineralocorticoid receptor antagonist finerenone. In all patients with hypertension, a sodium-restricted dietary pattern enriched in fruits and vegetables, whole grains, and low-fat dairy products should be advocated. Home monitoring of blood pressure may assist in maintaining good blood pressure control. IMPAIRED FASTING GLUCOSE (SEE ALSO CHAP. 415) In patients with metabolic syndrome and type 2 diabetes, aggressive glycemic control may favorably modify fasting levels of triglyc­ erides and/or HDL cholesterol. In patients with impaired fasting glucose who do not have diabetes, a lifestyle intervention that includes weight reduction, dietary saturated fat restriction, and increased physical activity has been shown to reduce the incidence of type 2 diabetes. Metformin also reduces the incidence of dia­ betes, although the effect is less pronounced than that of lifestyle intervention. INSULIN RESISTANCE (SEE ALSO CHAP. 416) Several drug classes (biguanides, thiazolidinediones [TZDs]) increase insulin sensitivity. Because insulin resistance is the primary pathophysiologic mechanism for metabolic syndrome, representa­ tive drugs in these classes reduce its prevalence. Both metformin and TZDs enhance insulin action in the liver and suppress endog­ enous glucose production. TZDs, but not metformin, also improve insulin-mediated glucose uptake in muscle and adipose tissue. In a meta-analysis of nine trials involving 12,026 participants, the TZD pioglitazone versus placebo was associated with reduction in ASCVD events in patients with insulin resistance (metabolic syn­ drome), prediabetes, and type 2 diabetes. However, adverse effects including weight gain, bone fracture, and congestive heart failure with/or without edema were seen. Benefit of TZDs has been seen in patients with MAFLD, and with metformin in women with polycystic ovary syndrome, and both drug classes have been shown to reduce markers of inflammation. GLP-1 receptor agonists also improve insulin sensitivity, which is related to the amount of weight reduction. ■ ■FURTHER READING Alberti KG et al: Harmonizing the metabolic syndrome: A joint interim statement of the International Diabetes Federation Task Force on Epidemiology and Prevention; National Heart, Lung, and Blood Institute; American Heart Association; World Heart Federa­ tion; International Atherosclerosis Society; and International Asso­ ciation for the Study of Obesity. Circulation 120:1640, 2009. Brown AE, Walker M: Genetics of insulin resistance and the meta­ bolic syndrome. Curr Cardiol Rep 18:75, 2016. Dobrowolski P et al: Metabolic syndrome: A new definition and management guidelines. Arch Med Sci 5:1, 2022. Eckel RH et al: The metabolic syndrome. Lancet 365:1415, 2005. Fahed G et al: Metabolic syndrome: Update on pathophysiology and management in 2021. Int J Mol Sci 23: 786, 2022. Genser L et al: Obesity, type 2 diabetes, and the metabolic syndrome: Pathophysiologic relationships and guidelines for surgical interven­ tion. Surg Clin North Am 96:681, 2016. Lechner K et al: High-risk atherosclerosis and metabolic phenotype: The roles of ectopic adiposity, atherogenic dyslipidemia, and inflam­ mation. Metab Syndr Relat Disord 18:176, 2020. Neeland IJ et al: Visceral and ectopic fat, atherosclerosis, and cardio­ metabolic disease: A position statement. Lancet Diabetes Endocrinol 7:715, 2019.

37 - SECTION 4 Disorders of Bone and Mineral Metabolism

SECTION 4 Disorders of Bone and Mineral Metabolism

Section 4 Disorders of Bone and Mineral Metabolism

Bone and Mineral

Metabolism in Health

and Disease F. Richard Bringhurst, Henry M. Kronenberg,

Eva S. Liu, Marc N. Wein BONE STRUCTURE AND METABOLISM Bone is a dynamic tissue that is remodeled constantly throughout life. The arrangement of compact and cancellous bone provides strength and density suitable for both mobility and protection. Compact or cortical bone forms the roughly cylindrical shell of long bones; cancel­ lous or trabecular bone forms the plate-like meshwork that internally supports the cortical shell. In addition, bone provides a reservoir for calcium, magnesium, phosphorus, sodium, and other ions necessary for homeostatic functions. Bone also hosts and regulates hematopoiesis by providing niches for hematopoietic cell proliferation and differen­ tiation. The skeleton is highly vascular and receives ~10% of the cardiac output. Remodeling of bone is accomplished by two distinct cell types: osteoblasts produce bone matrix, and osteoclasts resorb the matrix. The activities of these cells are coordinated by osteocytes, long-lived regulatory cells embedded within bone matrix. The extracellular components of bone consist of a solid mineral phase in close association with an organic matrix, of which 90–95% is type I collagen (Chap. 425). The noncollagenous portion of the organic matrix is heterogeneous and contains serum proteins such as albumin as well as many locally produced proteins, whose functions are incompletely understood. Those proteins include cell attachment/ signaling proteins such as thrombospondin, osteopontin, and fibronectin; calcium-binding proteins such as matrix gla protein and osteocalcin; and proteoglycans such as biglycan and decorin. Some of the proteins organize collagen fibrils; others influence mineralization and binding of the mineral phase to the matrix. The mineral phase is made up of calcium and phosphate and is best characterized as a poorly crystalline hydroxyapatite. The mineral phase of bone is deposited initially in intimate relation to the collagen fibrils and is laid down in specific locations in the “holes” between the collagen fibrils. This architectural arrangement of mineral and matrix results in a two-phase material well suited to withstand mechanical stresses. The organization of collagen influences the amount and type of mineral phase formed in bone. Although the primary structures of type I collagen in skin and bone tissues are similar, there are differences in posttranslational modifications and distribution of intermolecular cross-links. The holes in the packing structure of the collagen are larger in mineralized collagen of bone and dentin than in unmineralized col­ lagens such as those in tendon. Single amino acid substitutions in the helical portion of either the α1 (COL1A1) or α2 (COL1A2) chains of type I collagen disrupt the organization of bone in the disease, osteo­ genesis imperfecta. The severe skeletal fragility associated with this group of disorders highlights the importance of the fibrillar matrix in the structure of bone (Chap. 425). Osteoblasts synthesize and secrete the organic matrix and regu­ late its mineralization. They are derived from cells of mesenchymal origin (Fig. 421-1A). Osteoblast precursors derive from the perios­ teum, the bone marrow, or the hypertrophic chondrocytes at the end of the growth plate. Active osteoblasts are found on the surface of newly forming bone. As an osteoblast secretes matrix, which then is mineralized, the cell may become an osteocyte, still connected with its nutrient supply through a series of canaliculi. Osteocytes account for the vast majority of the cells in bone. They are thought to be the

mechanosensors that communicate signals to surface osteoblasts and osteoclasts and their progenitors through the canalicular network and thereby serve as master regulators of bone formation and resorption. Osteocytes also secrete fibroblast growth factor 23 (FGF23), a major hormonal regulator of phosphate metabolism (see below). Mineraliza­ tion of the matrix, both in trabecular bone and in osteones of compact cortical bone (Haversian systems), begins soon after the matrix is secreted (primary mineralization) but is not completed for several weeks or even longer (secondary mineralization). Although this min­ eralization takes advantage of the high concentrations of calcium and phosphate, already near saturation in serum, mineralization is a care­ fully regulated process that is dependent on the activity of osteoblastderived alkaline phosphatase, which probably works by hydrolyzing inhibitors of mineralization, such as pyrophosphate.

Bone and Mineral Metabolism in Health and Disease
CHAPTER 421 Genetic studies in humans and mice have identified several key genes that control osteoblast development. Runx2 is a transcription factor expressed specifically in chondrocyte (cartilage cells) and osteo­ blast progenitors as well as in hypertrophic chondrocytes and mature osteoblasts. Runx2 regulates the expression of several important osteo­ blast proteins, including osterix (SP7) (another transcription factor needed for osteoblast maturation), osteopontin, bone sialoprotein, type I collagen, osteocalcin, and receptor-activator of nuclear factor (NF)-κB (RANK) ligand. Runx2 expression is regulated in part by bone morphogenic proteins (BMPs). Runx2-deficient mice are devoid of osteoblasts, whereas mice with a deletion of only one allele (Runx2 +/–) exhibit a delay in formation of the clavicles and some cranial bones. The latter abnormalities are similar to those in the human disorder cleidocranial dysplasia, which is also caused by heterozygous inactivat­ ing mutations in Runx2. The paracrine signaling molecule, Indian hedgehog (Ihh), also plays a critical role in osteoblast development, as evidenced by Ihh-deficient mice that lack osteoblasts in the type of bone formed on a cartilage mold (endochondral ossification). Signals originating from members of the wnt family of paracrine factors are also important for osteo­ blast proliferation and differentiation. Osteocytes regulate osteoblasts partly by secreting a potent inhibitor of wnt signaling called sclerostin. Numerous other growth-regulatory factors affect osteoblast function, including the three closely related transforming growth factor βs, fibro­ blast growth factors (FGFs) 2 and 18, platelet-derived growth factor, and insulin-like growth factors (IGFs) I and II. Hormones such as para­ thyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25(OH)2D] activate receptors expressed by osteoblasts to assure mineral homeo­ stasis and influence a variety of bone cell functions. Osteoclasts that resorb bone (see below) also regulate osteoblasts by releasing growth factors from bone matrix and by synthesizing proteins that can directly regulate osteoblastogenesis. Resorption of bone is carried out mainly by osteoclasts, multinucle­ ated cells that are formed by fusion of cells derived from the common precursor of macrophages and osteoclasts. Thus, these cells derive from the hematopoietic lineage, quite different from the mesenchymal lineage cells that become osteoblasts. Multiple factors that regulate osteoclast development have been identified (Fig. 421-1B). Factors produced by osteocytes, osteoblasts, and marrow stromal cells allow cells of the osteoblast lineage to control osteoclast development and activity. Macrophage colony-stimulating factor (M-CSF) plays a critical role during several steps in the pathway and ultimately leads to fusion of osteoclast progenitor cells to form multinucleated, active osteoclasts. RANK ligand, a member of the tumor necrosis factor (TNF) family, is expressed on the surface of osteocytes, osteoblasts, and stromal fibro­ blasts. In a process involving cell-cell interactions, RANK ligand binds to the RANK receptor on osteoclast progenitors, stimulating osteoclast differentiation and activation. Alternatively, a soluble decoy receptor, referred to as osteoprotegerin (OPG), can bind RANK ligand and inhibit osteoclast differentiation. Several growth factors and cytokines (including interleukins 1, 6, and 11; TNF; and interferon γ) modulate osteoclast differentiation and function. Most hormones that influence osteoclast function do not target these cells directly but instead target cells of the osteoblast lineage to increase production of M-CSF and RANK. Both PTH and 1,25(OH)2D increase osteoclast number and

38 - 421 Bone and Mineral Metabolism in Health and Disease

421 Bone and Mineral Metabolism in Health and Disease

Section 4 Disorders of Bone and Mineral Metabolism

Bone and Mineral

Metabolism in Health

and Disease F. Richard Bringhurst, Henry M. Kronenberg,

Eva S. Liu, Marc N. Wein BONE STRUCTURE AND METABOLISM Bone is a dynamic tissue that is remodeled constantly throughout life. The arrangement of compact and cancellous bone provides strength and density suitable for both mobility and protection. Compact or cortical bone forms the roughly cylindrical shell of long bones; cancel­ lous or trabecular bone forms the plate-like meshwork that internally supports the cortical shell. In addition, bone provides a reservoir for calcium, magnesium, phosphorus, sodium, and other ions necessary for homeostatic functions. Bone also hosts and regulates hematopoiesis by providing niches for hematopoietic cell proliferation and differen­ tiation. The skeleton is highly vascular and receives ~10% of the cardiac output. Remodeling of bone is accomplished by two distinct cell types: osteoblasts produce bone matrix, and osteoclasts resorb the matrix. The activities of these cells are coordinated by osteocytes, long-lived regulatory cells embedded within bone matrix. The extracellular components of bone consist of a solid mineral phase in close association with an organic matrix, of which 90–95% is type I collagen (Chap. 425). The noncollagenous portion of the organic matrix is heterogeneous and contains serum proteins such as albumin as well as many locally produced proteins, whose functions are incompletely understood. Those proteins include cell attachment/ signaling proteins such as thrombospondin, osteopontin, and fibronectin; calcium-binding proteins such as matrix gla protein and osteocalcin; and proteoglycans such as biglycan and decorin. Some of the proteins organize collagen fibrils; others influence mineralization and binding of the mineral phase to the matrix. The mineral phase is made up of calcium and phosphate and is best characterized as a poorly crystalline hydroxyapatite. The mineral phase of bone is deposited initially in intimate relation to the collagen fibrils and is laid down in specific locations in the “holes” between the collagen fibrils. This architectural arrangement of mineral and matrix results in a two-phase material well suited to withstand mechanical stresses. The organization of collagen influences the amount and type of mineral phase formed in bone. Although the primary structures of type I collagen in skin and bone tissues are similar, there are differences in posttranslational modifications and distribution of intermolecular cross-links. The holes in the packing structure of the collagen are larger in mineralized collagen of bone and dentin than in unmineralized col­ lagens such as those in tendon. Single amino acid substitutions in the helical portion of either the α1 (COL1A1) or α2 (COL1A2) chains of type I collagen disrupt the organization of bone in the disease, osteo­ genesis imperfecta. The severe skeletal fragility associated with this group of disorders highlights the importance of the fibrillar matrix in the structure of bone (Chap. 425). Osteoblasts synthesize and secrete the organic matrix and regu­ late its mineralization. They are derived from cells of mesenchymal origin (Fig. 421-1A). Osteoblast precursors derive from the perios­ teum, the bone marrow, or the hypertrophic chondrocytes at the end of the growth plate. Active osteoblasts are found on the surface of newly forming bone. As an osteoblast secretes matrix, which then is mineralized, the cell may become an osteocyte, still connected with its nutrient supply through a series of canaliculi. Osteocytes account for the vast majority of the cells in bone. They are thought to be the

mechanosensors that communicate signals to surface osteoblasts and osteoclasts and their progenitors through the canalicular network and thereby serve as master regulators of bone formation and resorption. Osteocytes also secrete fibroblast growth factor 23 (FGF23), a major hormonal regulator of phosphate metabolism (see below). Mineraliza­ tion of the matrix, both in trabecular bone and in osteones of compact cortical bone (Haversian systems), begins soon after the matrix is secreted (primary mineralization) but is not completed for several weeks or even longer (secondary mineralization). Although this min­ eralization takes advantage of the high concentrations of calcium and phosphate, already near saturation in serum, mineralization is a care­ fully regulated process that is dependent on the activity of osteoblastderived alkaline phosphatase, which probably works by hydrolyzing inhibitors of mineralization, such as pyrophosphate.

Bone and Mineral Metabolism in Health and Disease
CHAPTER 421 Genetic studies in humans and mice have identified several key genes that control osteoblast development. Runx2 is a transcription factor expressed specifically in chondrocyte (cartilage cells) and osteo­ blast progenitors as well as in hypertrophic chondrocytes and mature osteoblasts. Runx2 regulates the expression of several important osteo­ blast proteins, including osterix (SP7) (another transcription factor needed for osteoblast maturation), osteopontin, bone sialoprotein, type I collagen, osteocalcin, and receptor-activator of nuclear factor (NF)-κB (RANK) ligand. Runx2 expression is regulated in part by bone morphogenic proteins (BMPs). Runx2-deficient mice are devoid of osteoblasts, whereas mice with a deletion of only one allele (Runx2 +/–) exhibit a delay in formation of the clavicles and some cranial bones. The latter abnormalities are similar to those in the human disorder cleidocranial dysplasia, which is also caused by heterozygous inactivat­ ing mutations in Runx2. The paracrine signaling molecule, Indian hedgehog (Ihh), also plays a critical role in osteoblast development, as evidenced by Ihh-deficient mice that lack osteoblasts in the type of bone formed on a cartilage mold (endochondral ossification). Signals originating from members of the wnt family of paracrine factors are also important for osteo­ blast proliferation and differentiation. Osteocytes regulate osteoblasts partly by secreting a potent inhibitor of wnt signaling called sclerostin. Numerous other growth-regulatory factors affect osteoblast function, including the three closely related transforming growth factor βs, fibro­ blast growth factors (FGFs) 2 and 18, platelet-derived growth factor, and insulin-like growth factors (IGFs) I and II. Hormones such as para­ thyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25(OH)2D] activate receptors expressed by osteoblasts to assure mineral homeo­ stasis and influence a variety of bone cell functions. Osteoclasts that resorb bone (see below) also regulate osteoblasts by releasing growth factors from bone matrix and by synthesizing proteins that can directly regulate osteoblastogenesis. Resorption of bone is carried out mainly by osteoclasts, multinucle­ ated cells that are formed by fusion of cells derived from the common precursor of macrophages and osteoclasts. Thus, these cells derive from the hematopoietic lineage, quite different from the mesenchymal lineage cells that become osteoblasts. Multiple factors that regulate osteoclast development have been identified (Fig. 421-1B). Factors produced by osteocytes, osteoblasts, and marrow stromal cells allow cells of the osteoblast lineage to control osteoclast development and activity. Macrophage colony-stimulating factor (M-CSF) plays a critical role during several steps in the pathway and ultimately leads to fusion of osteoclast progenitor cells to form multinucleated, active osteoclasts. RANK ligand, a member of the tumor necrosis factor (TNF) family, is expressed on the surface of osteocytes, osteoblasts, and stromal fibro­ blasts. In a process involving cell-cell interactions, RANK ligand binds to the RANK receptor on osteoclast progenitors, stimulating osteoclast differentiation and activation. Alternatively, a soluble decoy receptor, referred to as osteoprotegerin (OPG), can bind RANK ligand and inhibit osteoclast differentiation. Several growth factors and cytokines (including interleukins 1, 6, and 11; TNF; and interferon γ) modulate osteoclast differentiation and function. Most hormones that influence osteoclast function do not target these cells directly but instead target cells of the osteoblast lineage to increase production of M-CSF and RANK. Both PTH and 1,25(OH)2D increase osteoclast number and

Osteoblast differentiation Chondrocyte Adipocyte Skeletal progenitors PART 12 Endocrinology and Metabolism Ihh, BMPs Pre-OB OB OB progenitor Osx Runx2 A Regulation of osteoclast differentiation Stromal/Osteoblast/ osteocyte 1, 25(OH)D IL6 M-CSF RANK ligand RANK Osteoclast precursor Mature osteoclasts that secrete acid and proteases”

B FIGURE 421-1  Pathways regulating development of (A) osteoblasts and (B) osteoclasts. A. Osteoblast lineage cells. Osteoblast progenitors are mesenchymal cells that are found in the perichondrium/periosteum, the bone marrow (where they also support hematopoietic stem cells and can become marrow adipocytes), and the growth plate (where late hypertrophic chondrocytes can die or become osteoblast precursors in the marrow). These progenitors can become chondrocytes early in development or in response to fracture postnatally. In response to Indian hedgehog (Ihh) and bone morphogenetic proteins (BMPs), these precursors become committed to osteoblast differentiation and are regulated by a series of transcription factors, with early essential factors, Runx2 and then osterix (SP7), shown here. On the bone surface, these cells express large amounts of collagen I and cell surface alkaline phosphatase, a crucial regulator of mineralization. Osteoblasts are relatively short-lived and subsequently either die or become osteocytes buried in bone matrix or quiescent bone-lining cells. To track the osteoblast (OB) lineage, we use CreERt mice driven by the Osx and collagen1 gene promotors. During OB differentiation, Osx is starting to be expressed early on in pre-OBs, while col1 is expressed later in OB development. It can therefore be expected that Osx- and col1-CreERt mouse lines will mark osteoblastic cells at different stages of differentiation. B. Regulation of osteoclast production. Osteoclast progenitors, derived from the hematopoietic lineage, respond to signals from cells of the osteoblast lineage to increase their number and activity. IL, interleukin; M-CSF, macrophage colony-stimulating factor; OPG, osteoprotegerin; PTH, parathyroid hormone. activity by this indirect mechanism. Calcitonin, in contrast, binds to its receptor on the basal surface of osteoclasts and directly inhibits osteo­ clast function. Estradiol has multiple cellular targets in bone, including osteoclasts, immune cells, and osteoblasts; actions on all these cells serve to decrease osteoclast number and bone resorption. Osteoclast-mediated resorption of bone takes place in scalloped spaces (Howship’s lacunae) where the osteoclasts are attached through a specific αvβ3 integrin to components of the bone matrix. The osteo­ clast forms a tight seal to the underlying matrix and secretes protons, chloride, and proteinases into a confined space that has been likened to an extracellular lysosome. The active osteoclast surface forms a ruffled border that contains a specialized proton pump ATPase that secretes acid that solubilizes the mineral phase. Carbonic anhydrase (type II isoenzyme) within the osteoclast generates the needed pro­ tons. The bone matrix is resorbed in the acid environment adjacent

Lining cell Apoptosis Mature OB Osteocyte Collagen 1 Osteocalcin R PTH RANK OPG to the ruffled border by proteases, such as cathepsin K, that act at low pH. A distinct process, called osteocytic osteolysis, also causes bone resorption. Using a molecular machinery similar to that in osteoclasts, osteocytes dissolve mineral and matrix from the bone surrounding osteocytes. PTH and its relative, parathyroid hormone–related peptide (PTHrP), stimulate osteocytic osteolysis. The relative contributions of osteoclasts and osteocytes to bone resorption is uncertain. In the embryo and the growing child, bone develops mostly by replacing previously calcified cartilage (endochondral bone forma­ tion) with subsequent remodeling or, in a few bones, is formed without a cartilage matrix (intramembranous bone formation). Dur­ ing endochondral bone formation, chondrocytes proliferate, secrete and mineralize a matrix, enlarge (hypertrophy), and then either die or differentiate into precursors of osteoblasts, lengthening bone and

Osteoclast precursor Osteoclast Active osteoclast Lining cells Resting bone surface Resorption Reversal Activation Osteocyte ~3 weeks ~3 months FIGURE 421-2  Schematic representation of bone remodeling. The cycle of bone remodeling is carried out by the basic multicellular unit (BMU), which consists of a group of osteoclasts and osteoblasts. In cortical bone, the BMUs tunnel through the tissue, whereas in cancellous bone, they move across the trabecular surface. The process of bone remodeling is initiated by the recruitment of osteoclast precursors, perhaps to sites of microdamage. These precursors fuse to form multinucleated, active osteoclasts that mediate bone resorption. Osteoclasts adhere to bone and subsequently remove it by acidification and proteolytic digestion. As the BMU advances, osteoclasts leave the resorption site, and osteoblasts, derived from marrow precursors and previously inactive bone lining cells, move in to cover the excavated area and begin the process of new bone formation by secreting osteoid, which eventually is mineralized into new bone. After osteoid mineralization, osteoblasts flatten and form a layer of lining cells over new bone, become osteocytes, or die. providing the matrix and factors that stimulate endochondral bone for­ mation. This program is regulated by both local factors, such as IGF-I and -II, Ihh, PTHrP, BMPs, and FGFs, and systemic hormones, such as growth hormone, glucocorticoids, and estrogen. New bone, whether formed in infants or in adults during repair, has a relatively high ratio of cells to matrix and is characterized by coarse fiber bundles of collagen that are interlaced and randomly dispersed (woven bone). In adults, the more mature bone is organized with fiber bundles regularly arranged in parallel or concentric sheets (lamel­ lar bone). In long bones, deposition of lamellar bone in a concentric arrangement around blood vessels forms the Haversian systems. Growth in length of bones is dependent on proliferation of cartilage cells and the endochondral sequence at the growth plate. Growth in width and thickness is accomplished by formation of bone at the peri­ osteal surface and by resorption at the endosteal surface, with the rate of formation exceeding that of resorption. In adults, after the growth plates of cartilage close through the actions of estrogen, growth in length and endochondral bone formation cease. Even in adults, how­ ever, remodeling of bone (within Haversian systems as well as along the surfaces of trabecular bone) continues throughout life. In adults, ~4% of the surface of trabecular bone (such as iliac crest) is involved in active resorption, whereas 10–15% of trabecular surfaces are covered with osteoid, unmineralized new bone formed by osteoblasts. Radioiso­ tope studies indicate that as much as 18% of the total skeletal calcium is deposited and removed each year. Thus, bone is an active metabolizing tissue that requires an intact blood supply. The cycle of bone resorption and formation is a highly orchestrated process, directed by osteocytes and carried out by the basic multicellular unit, which is composed of a group of osteoclasts and osteoblasts (Fig. 421-2). The response of bone to fractures, infection, and interruption of blood supply and to expanding lesions is relatively limited. Dead bone must be resorbed, and new bone must be formed, a process carried out in association with growth of new blood vessels into the involved area. In injuries that disrupt the organization of the tissue, such as a fracture, in which apposition of fragments is poor or when motion exists at the fracture site, progenitor stromal cells recapitulate the endochondral bone formation of early development and form carti­ lage that is replaced by bone and, variably, fibrous tissue. When there is good apposition with fixation and little motion at the fracture site, repair occurs predominantly by formation of new bone without other mediating tissue. Remodeling of bone occurs along lines of force generated by mechanical stress. The signals from these mechanical stresses are sensed by osteocytes, which transmit signals to osteoclasts and osteo­ blasts or their precursors. One such signal made by osteocytes is sclerostin, an inhibitor of wnt signaling. Mechanical forces, as well as

parathyroid hormone, suppress scleros­ tin production and thus increase bone formation by osteoblasts. Expanding lesions in bone such as tumors induce resorption at the surface in contact with the tumor by producing ligands such as PTHrP that stimulate osteoclast differen­ tiation and function. Thus, bone plastic­ ity reflects the interaction of cells with each other and with the environment.

Osteoblast precursors Bone remodeling unit Osteoblast Osteoid Cement line Bone formation Mineralization Bone and Mineral Metabolism in Health and Disease
CHAPTER 421 Measurement of the products of osteoblast and osteoclast activity can assist in the diagnosis and management of bone diseases. Osteoblast activity can be assessed by measuring serum bonespecific alkaline phosphatase. Similarly, osteocalcin, a protein secreted from osteoblasts, is made virtually only by osteoblasts. Measurement of an aminoterminal fragment of procollagen I is also an effective index of bone forma­ tion. Osteoclast activity can be assessed by measurement of products of collagen degradation. Collagen molecules are covalently linked to each other in the extracellular matrix through the formation of hydroxypyridinium cross-links (Chap. 425). After digestion by osteoclasts, these crosslinked peptides can be measured both in urine and in blood. CALCIUM METABOLISM Over 99% of the 1–2 kg of calcium present normally in the adult human body resides in the skeleton, where it provides mechanical stability and serves as a reservoir when needed to maintain extracellular fluid (ECF) calcium concentration (Fig. 421-3). Skeletal calcium accretion first becomes significant during the third trimester of fetal life, accelerates throughout childhood and adolescence, reaches a peak in early adult­ hood, and gradually declines thereafter at rates that rarely exceed 1–2% per year. These slow changes in total skeletal calcium content contrast with relatively high daily rates of closely matched fluxes of calcium into and out of bone (~250–500 mg each), a process mediated by coupled activity of osteoblasts, osteoclasts, and osteocytes. Another 0.5–1% of skeletal calcium is freely exchangeable (e.g., in chemical equilibrium) with that in the ECF. 0.4–1.5 g 1000–2000 g 0.25–0.5 g 0.25–0.5 g ECF 1–2 g 0.25–0.5 g 0.1–0.2 g 8–10 g 7.9–9.7 g Intestine Bone 0.3–1 g Kidney 0.15–.3 g FIGURE 421-3  Calcium homeostasis. Schematic illustration of calcium content of extracellular fluid (ECF) and bone as well as of diet and feces; magnitude of calcium flux per day as calculated by various methods is shown at sites of transport in intestine, kidney, and bone. Ranges of values shown are approximate and were chosen to illustrate certain points discussed in the text. In conditions of calcium balance, rates of calcium release from and uptake into bone are equal.

The concentration of ionized calcium in the ECF must be main­ tained within a narrow range because of the critical role calcium plays in a wide array of cellular functions, especially those involved in neuromuscular activity, secretion, and signal transduction. Intracel­ lular cytosolic free calcium levels are ~100 nmol/L and are 10,000-fold lower than ionized calcium concentration in the blood and ECF (1.1–1.3 mmol/L). Cytosolic calcium does not play the structural role played by extracellular calcium; instead, it serves a signaling func­ tion. The steep chemical gradient of calcium from outside to inside the cell promotes rapid calcium influx through various membrane calcium channels that can be activated by hormones, metabolites, or neurotransmitters, swiftly changing cellular function. In blood, total calcium concentration is normally 2.2–2.6 mM (8.5–10.5 mg/dL), of which ~50% is ionized. The remainder is bound ionically to negatively charged proteins (predominantly albumin and immunoglobulins) or loosely complexed with phosphate, citrate, sulfate, or other anions. Alterations in serum protein concentrations directly affect the total blood calcium concentration even if the ionized calcium concentra­ tion remains normal. An algorithm to correct for protein changes adjusts the total serum calcium (in mg/dL) upward by 0.8 times the deficit in serum albumin (g/dL) or by 0.5 times the deficit in serum immunoglobulin (in g/dL). Notably, such corrections provide only rough approximations of actual free calcium concentrations, however, and may be misleading, particularly during acute illness. Acidosis also alters ionized calcium by reducing its association with proteins. Accordingly, the best practice is to measure blood ionized calcium directly by a method that employs calcium-selective electrodes in acute settings during which calcium abnormalities might occur.

PART 12 Endocrinology and Metabolism Control of the ionized calcium concentration in the ECF ordinarily is accomplished by adjusting the rates of calcium movement across intestinal and renal epithelia and into and out of bone. These adjust­ ments are mediated mainly via changes in blood levels of the hormones PTH and 1,25(OH)2D. Acting via binding to calcium-sensing receptors (CaSRs) on the surface of parathyroid cells, blood ionized calcium sup­ presses PTH secretion by reducing levels of PTH mRNA, promoting the cleavage of PTH to inactive peptides, and suppressing release of PTH-containing granules from parathyroid cells. 1,25(OH)2D inhibits PTH production in the parathyroid by an incompletely understood mechanism of negative feedback (Chap. 422). Normal dietary calcium intake in the United States varies widely, ranging from 10 to 37 mmol/d (400–1500 mg/d). A National Academy of Medicine (formerly, Institute of Medicine) analysis recommends a daily allowance of 25–30 mmol (1000–1200 mg) for most adults. Intes­ tinal absorption of ingested calcium involves both active (transcellular) and passive (paracellular) mechanisms. Passive calcium absorption is nonsaturable and approximates 5% of daily calcium intake, whereas active absorption involves apical calcium entry via specific ion chan­ nels (TRPV5 in the kidney’s distal tubule and TRPV6 in the intestine), whose expression is controlled principally by 1,25(OH)2D. This active transport mechanism normally accounts for absorption of 20–70% of dietary calcium. Active gastrointestinal calcium transport occurs mainly in the proximal small bowel (duodenum and proximal jejunum), although some active calcium absorption occurs in most segments of the small intestine. Optimal rates of calcium absorption require gastric acid. This is especially true for weakly dissociable calcium supplements such as calcium carbonate. In fact, large boluses of calcium carbonate are poorly absorbed because of their neutralizing effect on gastric acid. In achlorhydric subjects and for those individuals taking drugs that inhibit gastric acid secretion, or with diminished acid secretion follow­ ing bariatric surgery, supplements should be taken with meals to opti­ mize their absorption. Use of calcium citrate may be preferable in these circumstances. Calcium absorption may also be blunted in disease states such as pancreatic or biliary insufficiency, in which ingested calcium remains bound to unabsorbed fatty acids or other food constituents. At high levels of calcium intake, synthesis of 1,25(OH)2D is reduced; this decreases the rate of active intestinal calcium absorption. The opposite occurs with dietary calcium restriction. Some calcium, ~2.5–5 mmol/d (100–200 mg/d), is excreted as an obligate component of intestinal secretions and is not regulated by calciotropic hormones.

The feedback-controlled hormonal regulation of intestinal absorp­ tive efficiency results in a relatively constant daily net calcium absorp­ tion of ~5–10 mmol/d (200–400 mg/d) despite large changes in daily dietary calcium intake. This daily load of absorbed calcium is excreted by the kidneys in a manner that is also tightly regulated by the con­ centration of ionized calcium in the blood. Approximately 8–10 g/d of calcium is filtered by the glomeruli, of which only 2–3% appears in the urine. Most filtered calcium (65%) is reabsorbed in the proximal tubules via a passive, paracellular route that is coupled to concomitant NaCl reabsorption and not specifically regulated. The cortical thick ascending limb of Henle’s loop (cTAL) reabsorbs roughly another 20% of filtered calcium, also via a paracellular mechanism. Calcium reabsorption in the cTAL requires a tight-junctional proteins called paracellin-1 and Claudin14 and is inhibited by increased blood con­ centrations of calcium or magnesium, acting via the CaSR, which is highly expressed on basolateral membranes in this nephron segment. Operation of the renal CaSR provides a mechanism, independent of those engaged directly by PTH or 1,25(OH)2D, by which serum ion­ ized calcium can control renal calcium reabsorption. Finally, ~10% of filtered calcium is reabsorbed in the distal convoluted tubules (DCTs) by a highly regulated transcellular mechanism. Calcium enters the luminal surface of the cell through specific apical calcium channels (TRPV5). It then moves across the cell in association with a specific calcium-binding protein (calbindin-D28k) that buffers cytosolic cal­ cium concentrations from the large mass of transported calcium. Basolateral Ca2+-ATPases and Na+/Ca2+ exchangers actively extrude calcium and thereby maintain the transcellular calcium gradient. All these processes are stimulated directly or indirectly by PTH and 1,25(OH)2D. The DCT is also the site of action of thiazide diuretics, which lower urinary calcium excretion by inducing sodium depletion and thereby augmenting proximal calcium reabsorption. Conversely, dietary sodium loads, or increased distal sodium delivery caused by loop diuretics or saline infusion, induce calciuresis. The homeostatic mechanisms that normally maintain a constant serum ionized calcium concentration may fail at extremes of calcium intake or when the hormonal systems or organs involved are compro­ mised. Thus, even with maximal activity of the vitamin D–dependent intestinal active transport system, sustained calcium intake <5 mmol/d (<200 mg/d) cannot provide enough net calcium absorption to replace obligate losses via the intestine, the kidney, sweat, and other secre­ tions. In this case, increased blood levels of PTH and 1,25(OH)2D activate osteoclastic bone resorption to obtain needed calcium from bone, which leads to progressive bone loss and negative calcium bal­ ance. Increased PTH and 1,25(OH)2D also enhance renal calcium reabsorption, and 1,25(OH)2D enhances calcium absorption in the gut. At very high calcium intakes (>100 mmol/d [>4 g/d]), passive intestinal absorption continues to deliver calcium into the ECF despite maximally downregulated intestinal active transport and renal tubular calcium reabsorption. This can cause severe hypercalciuria, nephrocal­ cinosis, progressive renal failure, and hypercalcemia (e.g., “milk-alkali syndrome”). Deficiency or excess of PTH or vitamin D, intestinal disease, and renal failure represent other commonly encountered chal­ lenges to normal calcium homeostasis (Chap. 422). PHOSPHORUS METABOLISM Although 85% of the ~600 g of body phosphorus is present in bone mineral, phosphorus is also a major intracellular constituent both as the free anion(s) and as a component of numerous organophosphate compounds, including structural proteins, enzymes, transcription fac­ tors, carbohydrate and lipid intermediates, high-energy stores (ATP [adenosine triphosphate], creatine phosphate), and nucleic acids. Unlike calcium, phosphorus exists intracellularly at concentrations close to those present in ECF (e.g., 1–2 mmol/L). In cells and in the ECF, phosphorus exists in several forms, predominantly as H2PO4 – or NaHPO4 –, with perhaps 10% as HPO4 2–. This mixture of anions will be referred to here as “phosphate.” In serum, ~12% of phosphorus is bound to proteins. Concentrations of phosphates in blood and ECF generally are expressed in terms of elemental phosphorus, with the normal range in adults being 0.75–1.45 mmol/L (2.5–4.5 mg/dL).

Because the volume of the intracellular fluid compartment is twice that of the ECF, measurements of ECF phosphate may not accurately reflect phosphate availability within cells that follows even modest shifts of phosphate from one compartment to the other. Phosphate is widely available in foods and is absorbed efficiently (65%) by the small intestine even in the absence of vitamin D. However, gut phosphate absorptive efficiency may be enhanced (to 85–90%) via active transport mechanisms that are stimulated by 1,25(OH)2D. These mechanisms involve activation of Na+/PO4 2– co-transporters, such as Npt2b, that move phosphate into intestinal cells against an unfavorable electrochemical gradient. Daily net intestinal phosphate absorption varies widely with the composition of the diet but is generally in the range of 500–1000 mg/d. Phosphate absorption can be inhibited by large doses of calcium salts or by sevelamer hydrochloride (Renagel), strategies commonly used to control levels of serum phosphate in chronic kidney disease. Aluminum hydroxide antacids also reduce phosphate absorption but are used less commonly because of the potential for aluminum toxicity. Low serum phosphate stimulates renal proximal tubular synthesis of 1,25(OH)2D, perhaps by suppressing blood levels of FGF23 (see below). Serum phosphate levels vary by as much as 50% on a normal day. This reflects the effect of food intake but also an underlying circadian rhythm that produces a nadir between 7 and 10 A.M. Carbohydrate administration, especially as IV dextrose solutions in fasting subjects, can decrease serum phosphate by >0.7 mmol/L (2 mg/dL) in common clinical settings including treatment of ketoacidosis or metabolic or respiratory alkalosis. Because of this wide variation in serum phos­ phate, it is best to perform measurements in the basal, fasting state. Control of serum phosphate is determined mainly by the rate of renal tubular reabsorption of the filtered load, which is ~4–6 g/d. Because intestinal phosphate absorption is highly efficient, urinary excretion is not constant but varies directly with dietary intake. The fractional excretion of phosphate (ratio of phosphate to creatinine clearance) is generally in the range of 10–15%. The proximal tubule is the principal site at which renal phosphate reabsorption is regulated. This is accomplished by changes in the levels of apical expression and activity of specific Na+/PO4 2– co-transporters (NaPi-2a and NaPi-2c) in the proximal tubule. Levels of these transporters at the apical surface of these cells are reduced rapidly by PTH, a major hormonal regulator of renal phosphate excretion. In addition, the circulating hormone FGF23 can inhibit phosphate reabsorption by a similar mechanism. FGF23 is synthesized by osteocytes. Activating FGF23 mutations cause the rare disorder autosomal dominant hypophosphatemic rickets (ADHR). In contrast to PTH, FGF23 reduces synthesis of 1,25(OH)2D, which may worsen the resulting hypophosphatemia by lowering intestinal phosphate absorption. Renal reabsorption of phosphate is responsive to changes in dietary intake such that experimental dietary phosphate restriction leads to a dramatic lowering of urinary phosphate within hours, preceding any decline in serum phosphate (e.g., filtered load). This physiologic renal adaptation to changes in dietary phosphate availability occurs independently of PTH and may be mediated in part by changes in levels of serum FGF23. Findings in FGF23-deficient mice suggest that FGF23 normally acts to lower blood phosphate and 1,25(OH)2D levels. In turn, elevation of blood phosphate and 1,25(OH)2D increases blood levels of FGF23. Renal phosphate reabsorption is impaired by hypocalcemia, hypo­ magnesemia, and severe hypophosphatemia. Phosphate clearance is enhanced by ECF volume expansion and impaired by dehydration. Phosphate retention is an important pathophysiologic feature of renal insufficiency (Chap. 322). ■ ■HYPOPHOSPHATEMIA Causes  Hypophosphatemia can occur by one or more of three primary mechanisms: (1) inadequate intestinal phosphate absorption, (2) excessive renal phosphate excretion, and (3) rapid redistribution of phosphate from the ECF into bone or soft tissue (Table 421-1). Because phosphate is so abundant in foods, inadequate intestinal absorption is almost never observed now that aluminum hydroxide antacids, which

TABLE 421-1  Causes of Hypophosphatemia I. Reduced renal tubular phosphate reabsorption A. PTH/PTHrP-dependent

  1. Primary hyperparathyroidism
  2. Secondary hyperparathyroidism a. Vitamin D deficiency/resistance b. Calcium starvation/malabsorption c. Bartter’s syndrome d. Autosomal recessive renal hypercalciuria with hypomagnesemia
  3. PTHrP-dependent hypercalcemia of malignancy
  4. Familial hypocalciuric hypercalcemia B. PTH/PTHrP-independent Bone and Mineral Metabolism in Health and Disease
    CHAPTER 421
  5. Excess FGF23 or other “phosphatonins” a. X-linked hypophosphatemic rickets (XLH) b. Autosomal recessive hypophosphatemia (ARHP) c. Autosomal dominant hypophosphatemic rickets (ADHR) (DMP1, ENPP1 deficiency) d. Tumor-induced osteomalacia syndrome (TIO) e. McCune-Albright syndrome (fibrous dysplasia) f. Epidermal nevus syndrome
  6. Intrinsic renal disease a. Fanconi’s syndrome(s) b. Cystinosis c. Wilson’s disease d. NaPi-2a or NaPi-2c mutations
  7. Other systemic disorders a. Poorly controlled diabetes mellitus b. Alcoholism c. Hyperaldosteronism d. Hypomagnesemia e. Amyloidosis f. Hemolytic-uremic syndrome g. Renal transplantation or partial liver resection h. Rewarming or induced hyperthermia
  8. Drugs or toxins a. Ethanol b. Acetazolamide, other diuretics c. High-dose estrogens or glucocorticoids d. Heavy metals (lead, cadmium, saccharated ferric oxide) e. Toluene, N-methyl formamide f. Cisplatin, ifosfamide, foscarnet, rapamycin II. Impaired intestinal phosphate absorption A. Aluminum-containing antacids B. Sevalamer III. Shifts of extracellular phosphate into cells A. Intravenous glucose B. Insulin therapy for prolonged hyperglycemia or diabetic ketoacidosis C. Catecholamines (epinephrine, dopamine, albuterol) D. Acute respiratory alkalosis E. Gram-negative sepsis, toxic shock syndrome F. Recovery from starvation or acidosis G. Rapid cellular proliferation
  9. Leukemic blast crisis
  10. Intensive erythropoietin, other growth factor therapy IV. Accelerated net bone formation A. After parathyroidectomy B. Treatment of vitamin D deficiency, Paget’s disease C. Osteoblastic metastases Abbreviations: PTH, parathyroid hormone; PTHrP, parathyroid hormone–related peptide.

bind phosphate in the gut, are no longer widely used. Fasting or starva­ tion, however, may result in depletion of body phosphate and predis­ pose to subsequent hypophosphatemia during refeeding, especially if this is accomplished with IV glucose alone.

Chronic hypophosphatemia usually signifies the presence of a per­ sistent renal tubular phosphate-wasting disorder. Excessive activation of PTH/PTHrP receptors in the proximal tubule, as a result of primary or secondary hyperparathyroidism or because of the PTHrP-mediated hypercalcemia syndrome in malignancy (Chap. 422), is a common cause of renal hypophosphatemia. Familial hypocalciuric hypercalce­ mia and Jansen’s metaphyseal chondrodysplasia are rare examples of genetic disorders in this category (Chap. 422). PART 12 Endocrinology and Metabolism Several genetic and acquired diseases cause PTH/PTHrP receptorindependent tubular phosphate wasting with associated rickets and osteomalacia. All these diseases manifest severe hypophosphatemia; renal phosphate wasting, sometimes accompanied by aminoaciduria; inappropriately low blood levels of 1,25(OH)2D; low-normal serum levels of calcium; and evidence of impaired cartilage or bone miner­ alization (osteomalacia). Analysis of these diseases in patients without generalized proximal tubular defects (Fanconi syndrome) led to the discovery of the hormone FGF23, which is an important physiologic regulator of phosphate metabolism. FGF23 decreases phosphate reab­ sorption in the proximal tubule and also suppresses the 1α-hydroxylase responsible for synthesis of 1,25(OH)2D. FGF23 is synthesized by cells of the osteoblast lineage, primarily osteocytes. High-phosphate diets increase FGF23 levels, and low-phosphate diets decrease them. ADHR was the first disease linked to abnormalities in FGF23. ADHR results from activating mutations in the gene that encodes FGF23. These mutations alter a cleavage site that ordinarily allows for inactivation of intact FGF23. Several other genetic disorders lead to elevated FGF23, hypophosphatemia, and osteomalacia. The most common of these is X-linked hypophosphatemic rickets (XLH), which results from inactivating mutations in an endopeptidase termed PHEX (phosphateregulating gene with homologies to endopeptidases on the X chromo­ some) that is expressed most abundantly on the surface of osteocytes and mature osteoblasts. Patients with XLH usually have high FGF23 levels, and ablation of the FGF23 gene reverses the hypophosphatemia found in the mouse version of XLH. How inactivation of PHEX leads to increased levels of FGF23 has not been determined. Two rare auto­ somal recessive hypophosphatemic syndromes associated with elevated FGF23 are due to inactivating mutations of dentin matrix protein 1 (DMP1) and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), respectively, both of which normally are highly expressed in bone and presumably regulate FGF23 production. An unusual hypophosphatemic disorder, tumor-induced osteomalacia (TIO), is an acquired disorder in which tumors, usually of mesenchymal origin, secrete FGF23. The hypophosphatemic syndrome resolves completely within hours to days after successful resection of the responsible tumor. Such tumors typically express large amounts of FGF23 mRNA, and patients with TIO usually exhibit elevations of FGF23 in their blood. Neutralizing antibodies against FGF23 can be used to treat hypophos­ phatemia in patients with XLH and TIO. Dent’s disease is an X-linked recessive disorder caused by inac­ tivating mutations in CLCN5, a chloride transporter expressed in endosomes of the proximal tubule; features include hypercalciuria, hypophosphatemia, and recurrent kidney stones. Renal phosphate wasting is common among poorly controlled diabetic patients and alcoholics, who therefore are at risk for iatrogenic hypophosphatemia when treated with insulin or IV glucose, respectively. Diuretics and certain other drugs and toxins can cause defective renal tubular phos­ phate reabsorption (Table 421-1). In hospitalized patients, hypophosphatemia is often attributable to massive redistribution of phosphate from the ECF into cells. Insulin therapy for diabetic ketoacidosis is a paradigm for this phenomenon, in which the severity of the hypophosphatemia is related to the extent of antecedent depletion of phosphate and other electrolytes (Chap. 416). The hypophosphatemia is usually greatest at a point many hours after initiation of insulin therapy and is difficult to predict from baseline measurements of serum phosphate at the time of presentation, when

prerenal azotemia can obscure significant phosphate depletion. Other factors that may contribute to such acute redistributive hypophospha­ temia include antecedent starvation or malnutrition, administration of IV glucose without other nutrients, elevated blood catecholamines (endogenous or exogenous), respiratory alkalosis, and recovery from metabolic acidosis. Hypophosphatemia also can occur transiently (over weeks to months) during the phase of accelerated net bone formation that fol­ lows parathyroidectomy for severe primary hyperparathyroidism or during treatment of vitamin D deficiency or lytic Paget’s disease. This is referred to as “hungry bone syndrome” and is most prominent in patients who preoperatively have evidence of very high bone turnover (e.g., elevated serum levels of alkaline phosphatase). Osteoblastic metastases can also lead to this syndrome. Clinical and Laboratory Findings  The clinical manifestations of severe hypophosphatemia reflect a generalized defect in cellular energy metabolism because of ATP depletion, a shift from oxidative phos­ phorylation toward glycolysis, and associated tissue or organ dysfunc­ tion. Acute, severe hypophosphatemia occurs mainly or exclusively in hospitalized patients with underlying serious medical or surgical illness and preexisting phosphate depletion due to excessive urinary losses, severe malabsorption, or malnutrition. Chronic hypophospha­ temia tends to be less severe, with a clinical presentation dominated by musculoskeletal complaints such as bone pain, osteomalacia, pseudo­ fractures, and proximal muscle weakness or, in children, rickets and short stature. Neuromuscular manifestations of severe hypophosphatemia are variable but may include muscle weakness, lethargy, confusion, dysar­ thria, dysphagia, oculomotor palsies, nystagmus, ataxia, hyporeflexia, impaired sphincter control, paresthesia, generalized or GuillainBarré–like ascending paralysis, seizures, coma, and even death. Serious sequelae such as paralysis and seizures are likely only at phosphate concentrations <0.25 mmol/L (<0.8 mg/dL). Rhabdomyolysis may develop during rapidly progressive hypophosphatemia. The diagnosis of hypophosphatemia-induced rhabdomyolysis may be overlooked, as up to 30% of patients with acute hypophosphatemia (<0.7 mM) have creatine phosphokinase elevations that peak 1–2 days after the nadir in serum phosphate, when the release of phosphate from injured myocytes may have led to a near normalization of circulating levels of phosphate. Respiratory failure and cardiac dysfunction, which are reversible with phosphate treatment, may occur at serum phosphate levels of 0.5–0.8 mmol/L (1.5–2.5 mg/dL). Renal tubular defects, including tubular acidosis, glycosuria, and impaired reabsorption of sodium and calcium, may occur. Hematologic abnormalities correlate with reduc­ tions in intracellular ATP and 2,3-diphosphoglycerate and may include erythrocyte microspherocytosis and hemolysis; impaired oxyhemo­ globin dissociation; defective leukocyte chemotaxis, phagocytosis, and bacterial killing; and platelet dysfunction. TREATMENT Hypophosphatemia Severe hypophosphatemia (<0.75 mmol/L [<2 mg/dL]), particu­ larly in the setting of underlying phosphate depletion, consti­ tutes a dangerous electrolyte abnormality that should be corrected promptly. Unfortunately, the cumulative deficit in body phosphate cannot be predicted directly from knowledge of the circulating level of phosphate, and therapy must be approached empirically. The threshold for IV phosphate therapy and consequently the dose of phosphate to be administered should reflect consideration of renal function, the likely severity and duration of the underlying phosphate depletion, and the presence and severity of symptoms consistent with those of hypophosphatemia. In adults, phosphate may be safely administered IV as neutral mixtures of sodium or potassium phosphate salts at initial doses of 0.2–0.8 mmol/kg of elemental phosphorus over 6 h (e.g., 10–50 mmol over 6 h), with doses >20 mmol/6 h reserved for those who have serum levels

TABLE 421-2  Intravenous Therapy for Hypophosphatemia CONSIDER Likely severity of underlying phosphate depletion Concurrent parenteral glucose administration Presence of neuromuscular, cardiopulmonary, or hematologic complications of hypophosphatemia Renal function (reduce dose by 50% if serum creatinine >220 μmol/L [>2.5 mg/dL]) Serum calcium level (correct hypocalcemia first; reduce dose by 50% in hypercalcemia) Guidelines RATE OF INFUSION, MMOL/H DURATION, H TOTAL ADMINISTERED, MMOL SERUM PHOSPHORUS, MM (MG/DL) <0.8 (<2.5)

<0.5 (<1.5)

<0.3 (<1)

Note: Rates shown are calculated for a 70-kg person; levels of serum calcium and phosphorus must be measured every 6–12 h during therapy; infusions can be repeated to achieve stable serum phosphorus levels >0.8 mmol/L (>2.5 mg/dL); most formulations available in the United States provide 3 mmol/mL of sodium or potassium phosphate. <0.5 mmol/L (1.5 mg/dL) and normal renal function. A suggested approach is presented in Table 421-2. Serum levels of phosphate and calcium must be monitored closely (every 6–12 h) throughout treatment. It is important to avoid a serum calcium-phosphorus product >50 mg2/dL2 to reduce the risk of heterotopic calcification. Hypocalcemia, if present, should be corrected before administer­ ing IV phosphate. Less severe hypophosphatemia, in the range of 0.5–0.8 mmol/L (1.5–2.5 mg/dL), usually can be treated with oral phosphate in divided doses of 750–2000 mg/d as elemental phos­ phorus; higher doses can cause bloating and diarrhea. Management of chronic hypophosphatemia requires knowledge of the cause(s) of the disorder. Hypophosphatemia related to the secondary hyperparathyroidism of vitamin D deficiency usually responds to treatment with vitamin D and calcium alone. XLH, ADHR, TIO, and related renal tubular disorders usually are man­ aged with divided oral doses of phosphate, often with calcium and 1,25(OH)2D supplements to bypass the block in renal 1,25(OH)2D synthesis and prevent secondary hyperparathyroidism caused by suppression of ECF calcium levels. Care must be taken to be sure that oral calcium and phosphate are not administered at the same time, to avoid precipitation before absorption. Thiazide diuretics may be used to prevent nephrocalcinosis in patients who are man­ aged this way. Complete normalization of hypophosphatemia is generally not possible in these conditions. Burosumab, a human monoclonal antibody that inhibits FGF23, has been approved for the treatment of XLH and TIO. It corrects hypophosphatemia, improves bone pain, and heals fractures in both adults and children. Optimal therapy for TIO is surgical removal of the responsible tumor, which may be localized by radiographic skeletal survey or bone scan (many are located in bone) or by radionuclide scanning using sestamibi or labeled octreotide. Successful treatment of TIOinduced hypophosphatemia with octreotide has been reported in a small number of patients. Burosumab treatment can be used to treat hypophosphatemia in patients with TIO in whom tumors cannot be localized or removed. ■ ■HYPERPHOSPHATEMIA Causes  When the filtered load of phosphate and glomerular fil­ tration rate (GFR) are normal, control of serum phosphate levels is achieved by adjusting the rate at which phosphate is reabsorbed by the proximal tubular NaPi-2 co-transporters. Hyperphosphatemia, defined in adults as a fasting serum phosphate concentration >1.8 mmol/L (5.5 mg/dL), usually results from impaired glomerular filtration, hypo­ parathyroidism, excessive delivery of phosphate into the ECF (from bone, gut, or parenteral phosphate therapy), or a combination of these

TABLE 421-3  Causes of Hyperphosphatemia I. Impaired renal phosphate excretion A. Renal insufficiency B. Hypoparathyroidism

  1. Developmental
  2. Autoimmune
  3. After neck surgery or radiation
  4. Activating mutations of the calcium-sensing receptor C. Parathyroid suppression Bone and Mineral Metabolism in Health and Disease
    CHAPTER 421
  5. Parathyroid-independent hypercalcemia a. Vitamin D or vitamin A intoxication b. Sarcoidosis, other granulomatous diseases c. Immobilization, osteolytic metastases d. Milk-alkali syndrome
  6. Severe hypermagnesemia or hypomagnesemia D. Pseudohypoparathyroidism E. Acromegaly F. Tumoral calcinosis G. Heparin therapy II. Massive extracellular fluid phosphate loads A. Rapid administration of exogenous phosphate (intravenous, oral, rectal) B. Extensive cellular injury or necrosis
  7. Crush injuries
  8. Rhabdomyolysis
  9. Hyperthermia
  10. Fulminant hepatitis
  11. Cytotoxic therapy
  12. Severe hemolytic anemia C. Transcellular phosphate shifts
  13. Metabolic acidosis
  14. Respiratory acidosis factors (Table 421-3). The upper limit of normal serum phosphate concentrations is higher in children and neonates (2.4 mmol/L [7 mg/ dL]). It is useful to distinguish hyperphosphatemia caused by impaired renal phosphate excretion from that which results from excessive deliv­ ery of phosphate into the ECF (Table 421-3). In chronic renal insufficiency, reduced GFR leads to phosphate retention. Hyperphosphatemia, and progressive loss of nephron func­ tion, in turn further impairs renal synthesis of 1,25(OH)2D, increases FGF23 levels, and stimulates PTH secretion and parathyroid gland hypertrophy both directly and indirectly (by lowering blood ionized calcium levels). Thus, hyperphosphatemia is a major cause of the secondary hyperparathyroidism of renal failure (Chaps. 322 and 422). Hypoparathyroidism leads to hyperphosphatemia via increased expression of NaPi-2 co-transporters in the proximal tubule. Hypo­ parathyroidism, or parathyroid suppression, has multiple potential causes, including autoimmune disease; developmental, surgical, or radiation-induced absence of functional parathyroid tissue; vitamin D intoxication or other causes of PTH-independent hypercalcemia; cellu­ lar PTH resistance (pseudohypoparathyroidism or hypomagnesemia); infiltrative disorders such as Wilson’s disease and hemochromatosis; and impaired PTH secretion caused by hypermagnesemia, severe hypomagnesemia, or activating mutations in the CaSR. Hypocalcemia may also contribute directly to impaired phosphate clearance, as cal­ cium infusion can induce phosphaturia in hypoparathyroid subjects. Increased tubular phosphate reabsorption also occurs in acromegaly, during heparin administration, and in tumoral calcinosis. Tumoral cal­ cinosis is caused by a rare group of genetic disorders in which FGF23 is processed in a way that leads to low levels of active FGF23 in the blood­ stream. This may result from mutations in the FGF23 sequence or via inactivating mutations in the GALNT3 gene, which encodes a galac­ tosaminyl transferase that normally adds sugar residues to FGF23 that slow its proteolysis. A similar syndrome results from FGF23 resistance due to inactivating mutations of the FGF23 co-receptor Klotho. These

abnormalities cause elevated serum 1,25(OH)2D, parathyroid suppres­ sion, increased intestinal calcium absorption, and focal hyperostosis with large, lobulated periarticular heterotopic ossifications (especially at shoulders or hips) and are accompanied by hyperphosphatemia. In some forms of tumoral calcinosis, serum phosphorus levels are normal.

When large amounts of phosphate are delivered rapidly into the ECF, hyperphosphatemia can occur despite normal renal function. Examples include overzealous IV phosphate therapy, oral or rectal administra­ tion of large amounts of phosphate-containing laxatives or enemas (especially in children), extensive soft tissue injury or necrosis (crush injuries, rhabdomyolysis, hyperthermia, fulminant hepatitis, cytotoxic chemotherapy), extensive hemolytic anemia, and transcellular phos­ phate shifts induced by severe metabolic or respiratory acidosis. PART 12 Endocrinology and Metabolism Clinical Findings  The clinical consequences of acute, severe hyperphosphatemia are due mainly to the formation of widespread calcium phosphate precipitates and resulting hypocalcemia. Thus, tetany, seizures, accelerated nephrocalcinosis (with renal failure, hyper­ kalemia, hyperuricemia, and metabolic acidosis), and pulmonary or cardiac calcifications (including development of acute heart block) may occur. The severity of these complications relates to the elevation of serum phosphate levels, which can reach concentrations as high as 7 mmol/L (20 mg/dL) in instances of massive soft tissue injury or tumor lysis syndrome. TREATMENT Hyperphosphatemia Therapeutic options for management of severe hyperphosphatemia are limited. Volume expansion may enhance renal phosphate clear­ ance. Aluminum hydroxide antacids or sevelamer may be helpful in chelating and limiting absorption of offending phosphate salts pres­ ent in the intestine. Hemodialysis is the most effective therapeutic strategy and should be considered early in the course of severe hyperphosphatemia, especially in the setting of renal failure and symptomatic hypocalcemia. MAGNESIUM METABOLISM Magnesium is the major intracellular divalent cation. Normal concen­ trations of extracellular magnesium and calcium are crucial for normal neuromuscular activity. Intracellular magnesium forms a key complex with ATP and is an important cofactor for a wide range of enzymes, transporters, and nucleic acids required for normal cellular function, replication, and energy metabolism. The concentration of magne­ sium in serum is closely regulated within the range of 0.7–1 mmol/L (1.5–2 meq/L; 1.7–2.4 mg/dL), of which 30% is protein-bound and another 15% is loosely complexed to phosphate and other anions. One-half of the 25 g (1000 mmol) of total body magnesium is located in bone, only one-half of which is insoluble in the mineral phase. Almost all extraskeletal magnesium is present within cells, where the total concentration is 5 mM, 95% of which is bound to proteins and other macromolecules. Because only 1% of body magnesium resides in the ECF, measurements of serum magnesium levels may not accurately reflect the level of total body magnesium stores. Dietary magnesium content normally ranges from 6 to 15 mmol/d (140–360 mg/d), of which 30–40% is absorbed, mainly in the jejunum and ileum. Intestinal magnesium absorptive efficiency is stimulated by 1,25(OH)2D and can reach 70% during magnesium deprivation. Urinary magnesium excretion normally matches net intestinal absorp­ tion and is ~4 mmol/d (100 mg/d). Regulation of serum magnesium concentrations is achieved mainly by control of renal magnesium reabsorption. Only 20% of filtered magnesium is reabsorbed in the proximal tubule, whereas 60% is reclaimed in the cTAL and another 5–10% in the DCT. Magnesium reabsorption in the cTAL occurs via a paracellular route that requires both a lumen-positive potential, cre­ ated by NaCl reabsorption, and tight-junction proteins encoded by members of the Claudin gene family. Magnesium reabsorption in the cTAL is increased by PTH but inhibited by hypercalcemia or hyperma­ gnesemia, both of which activate the CaSR in this nephron segment.

■ ■HYPOMAGNESEMIA Causes  Hypomagnesemia usually signifies substantial depletion of body magnesium stores (0.5–1 mmol/kg). Hypomagnesemia can result from intestinal malabsorption; protracted vomiting, diarrhea, or intestinal drainage; defective renal tubular magnesium reabsorption; or rapid shifts of magnesium from the ECF into cells, bone, or third spaces (Table 421-4). Dietary magnesium deficiency is unlikely except possibly in the setting of alcoholism. Rare genetic disorders that cause selective intestinal magnesium malabsorption have been described (primary infantile hypomagnesemia types 1 and 2). Another rare TABLE 421-4  Causes of Hypomagnesemia I. Impaired intestinal absorption A. Hypomagnesemia with secondary hypocalcemia (TRPM6 mutations) B. Malabsorption syndromes C. Vitamin D deficiency D. Proton pump inhibitors II. Increased intestinal losses A. Protracted vomiting/diarrhea B. Intestinal drainage, fistulas III. Impaired renal tubular reabsorption A. Genetic magnesium-wasting syndromes

  1. Gitelman’s syndrome
  2. Bartter’s syndrome
  3. Claudin 16 or 19 mutations
  4. Potassium channel mutations (Kv1.1, Kir4.1)
  5. Na+,K+-ATPase γ-subunit mutations (FXYD2) B. Acquired renal disease
  6. Tubulointerstitial disease
  7. Postobstruction, ATN (diuretic phase)
  8. Renal transplantation C. Drugs and toxins
  9. Ethanol
  10. Diuretics (loop, thiazide, osmotic)
  11. Cisplatin
  12. Pentamidine, foscarnet
  13. Cyclosporine
  14. Aminoglycosides, amphotericin B
  15. Cetuximab D. Other
  16. Extracellular fluid volume expansion
  17. Hyperaldosteronism
  18. SIADH
  19. Diabetes mellitus
  20. Hypercalcemia
  21. Phosphate depletion
  22. Metabolic acidosis
  23. Hyperthyroidism IV. Rapid shifts from extracellular fluid A. Intracellular redistribution
  24. Recovery from diabetic ketoacidosis
  25. Refeeding syndrome
  26. Correction of respiratory acidosis
  27. Catecholamines B. Accelerated bone formation
  28. Post-parathyroidectomy
  29. Treatment of vitamin D deficiency
  30. Osteoblastic metastases C. Other
  31. Pancreatitis, burns, excessive sweating
  32. Pregnancy (third trimester) and lactation Abbreviations: ATN, acute tubular necrosis; SIADH, syndrome of inappropriate antidiuretic hormone.

inherited disorder (hypomagnesemia with secondary hypocalcemia) is caused by mutations in the gene encoding TRPM6, a protein that, with TRPM7, forms a channel important for both intestinal and distaltubular renal transcellular magnesium transport. Malabsorptive states, often compounded by vitamin D deficiency, can critically limit magne­ sium absorption and produce hypomagnesemia despite the compensa­ tory effects of secondary hyperparathyroidism and of hypocalcemia and hypomagnesemia to enhance cTAL magnesium reabsorption. Diarrhea or surgical drainage fluid may contain ≥5 mmol/L of magne­ sium. Proton pump inhibitors (omeprazole and others) may produce hypomagnesemia by an unknown mechanism that does not involve renal wasting of magnesium. Several genetic magnesium-wasting syndromes have been described, including inactivating mutations of genes encoding the DCT NaCl co-transporter (Gitelman’s syndrome), proteins required for cTAL Na-K-2Cl transport (Bartter’s syndrome), claudin 16 or claudin 19 (autosomal recessive renal hypomagnesemia with hypercalciuria), a DCT Na+,K+-ATPase γ-subunit (autosomal dominant renal hypo­ magnesemia with hypocalciuria), DCT K+ channels (Kv1.1, Kir4.1), and a mitochondrial gene encoding a tRNA. Activating mutations of the CaSR can cause hypomagnesemia as well as hypocalcemia. ECF expansion, hypercalcemia, and severe phosphate depletion may impair magnesium reabsorption, as can various forms of renal injury, including those caused by drugs such as cisplatin, cyclosporine, ami­ noglycosides, and pentamidine as well as the epidermal growth factor (EGF) receptor inhibitory antibody cetuximab (EGF action is required for normal DCT apical expression of TRPM6) (Table 421-4). A rising blood concentration of ethanol directly impairs tubular magnesium reabsorption, and persistent glycosuria with osmotic diuresis leads to magnesium wasting and probably contributes to the high frequency of hypomagnesemia in poorly controlled diabetic patients. Magnesium depletion is aggravated by metabolic acidosis, which causes intracel­ lular losses as well. Hypomagnesemia due to rapid shifts of magnesium from ECF into the intracellular compartment can occur during recovery from diabetic ketoacidosis, starvation, or respiratory acidosis. Less acute shifts may be seen during rapid bone formation after parathyroidectomy, with treatment of vitamin D deficiency, or with osteoblastic metastases. Large amounts of magnesium may be lost with acute pancreatitis, extensive burns, or protracted and severe sweating and during preg­ nancy and lactation. Clinical and Laboratory Findings  Hypomagnesemia may cause generalized alterations in neuromuscular function, including tetany, seizures, muscle weakness, ataxia, nystagmus, vertigo, depression, irri­ tability, and psychosis. Patients are usually asymptomatic when serum magnesium concentrations are >0.5 mmol/L (1 meq/L; 1.2 mg/dL), although the severity of symptoms may not correlate well with serum magnesium levels. Cardiac arrhythmias may occur, including sinus tachycardia, other supraventricular tachycardias, and ventricular arrhythmias. Electrocardiographic abnormalities may include pro­ longed PR or QT intervals, T-wave flattening or inversion, and ST straightening. Sensitivity to digitalis toxicity may be enhanced. Other electrolyte abnormalities often seen with hypomagnesemia, including hypocalcemia (with hypocalciuria) and hypokalemia, may not be easily corrected unless magnesium is administered as well. The hypocalcemia may be a result of concurrent vitamin D defi­ ciency, although hypomagnesemia can cause impaired synthesis of 1,25(OH)2D, cellular resistance to PTH, and, at very low serum mag­ nesium (<0.4 mmol/L [<0.8 meq/L; <1 mg/dL]), defects in PTH secre­ tion; these abnormalities are reversible with therapy. TREATMENT Hypomagnesemia Mild, asymptomatic hypomagnesemia may be treated with oral magnesium salts (MgCl2, MgO, Mg[OH]2) in divided doses total­ ing 20–30 mmol/d (40–60 meq/d). Diarrhea may occur with larger doses. More severe hypomagnesemia should be treated

parenterally, preferably with IV MgCl2, which can be administered safely as a continuous infusion of 50 mmol/d (100 meq Mg2+/d) if renal function is normal. If GFR is reduced, the infusion rate should be lowered by 50–75%. Use of IM MgSO4 is discouraged; the injections are painful and provide relatively little magnesium (2 mL of 50% MgSO4 supplies only 4 mmol). MgSO4 may be given IV instead of MgCl2, although the sulfate anions may bind calcium in serum and urine and aggravate hypocalcemia. Serum magne­ sium should be monitored at intervals of 12–24 h during therapy, which may continue for several days because of impaired renal con­ servation of magnesium (only 50–70% of the daily IV magnesium dose is retained) and delayed repletion of intracellular deficits, which may be as high as 1–1.5 mmol/kg (2–3 meq/kg).

Bone and Mineral Metabolism in Health and Disease
CHAPTER 421 It is important to consider the need for calcium, potassium, and phosphate supplementation in patients with hypomagnesemia. Vitamin D deficiency frequently coexists and should be treated with oral or parenteral vitamin D or 25(OH)D (but not with 1,25(OH)2D, which may impair tubular magnesium reabsorp­ tion, possibly via PTH suppression). In severely hypomagnesemic patients with concomitant hypocalcemia and hypophosphatemia, administration of IV magnesium alone may worsen hypophos­ phatemia, provoking neuromuscular symptoms or rhabdomy­ olysis, due to rapid stimulation of previously suppressed PTH secretion. This is avoided by administering both calcium and magnesium. ■ ■HYPERMAGNESEMIA Causes  Hypermagnesemia is rarely seen in the absence of renal insufficiency as normal kidneys can excrete large amounts (250 mmol/d) of magnesium. Mild hypermagnesemia due to exces­ sive reabsorption in the cTAL occurs with CaSR mutations in familial hypocalciuric hypercalcemia and has been described in some patients with adrenal insufficiency, hypothyroidism, or hypothermia. Massive exogenous magnesium exposures, usually via the gastrointestinal tract, can overwhelm renal excretory capacity and cause life-threatening hypermagnesemia (Table 421-5). A notable example of this is pro­ longed retention of even normal amounts of magnesium-containing cathartics in patients with intestinal ileus, obstruction, or perforation. Extensive soft tissue injury or necrosis also can deliver large amounts of magnesium into the ECF in patients who have suffered trauma, shock, sepsis, cardiac arrest, or severe burns. Further, infusion of magnesium in pregnant women with eclampsia can lead to hypocalcemia. Clinical and Laboratory Findings  The most prominent clinical manifestations of hypermagnesemia are vasodilation and neuromuscu­ lar blockade, which may appear at serum magnesium concentrations

2 mmol/L (>4 meq/L; >4.8 mg/dL). Hypotension that is refractory to vasopressors or volume expansion may be an early sign. Nausea, lethargy, and weakness may progress to respiratory failure, paralysis, TABLE 421-5  Causes of Hypermagnesemia I. Excessive magnesium intake A. Cathartics, urologic irrigants B. Parenteral magnesium administration II. Rapid mobilization from soft tissues A. Trauma, shock, sepsis B. Cardiac arrest C. Burns III. Impaired magnesium excretion A. Renal failure B. Familial hypocalciuric hypercalcemia IV. Other A. Adrenal insufficiency B. Hypothyroidism C. Hypothermia

and coma, with hypoactive tendon reflexes, at serum magnesium levels

4 mmol/L. Other findings may include gastrointestinal hypomotility or ileus; facial flushing; pupillary dilation; paradoxical bradycardia; prolongation of PR, QRS, and QT intervals; heart block; and, at serum magnesium levels approaching 10 mmol/L, asystole.

Hypermagnesemia, acting via the CaSR, causes hypocalcemia and hypercalciuria due to both parathyroid suppression and impaired cTAL calcium reabsorption. TREATMENT Hypermagnesemia PART 12 Endocrinology and Metabolism Successful treatment of hypermagnesemia generally involves iden­ tifying and interrupting the source(s) of magnesium and employing measures to increase magnesium clearance from the ECF. Use of magnesium-free cathartics or enemas may be helpful in clearing ingested magnesium from the gastrointestinal tract. Vigorous IV hydration should be attempted, if appropriate. Hemodialysis is effective and may be required in patients with significant renal insufficiency. Calcium, administered IV in doses of 100–200 mg over 1–2 h, has been reported to provide temporary improvement in signs and symptoms of hypermagnesemia. VITAMIN D ■ ■SYNTHESIS AND METABOLISM 1,25-Dihydroxyvitamin D [1,25(OH)2D] is the major steroid hormone involved in regulation of mineral ion homeostasis. Vitamin D and its metabolites are hormones and hormone precursors rather than vitamins, since in the proper biologic setting, they can be synthesized endogenously (Fig. 421-4). In response to ultraviolet radiation of the skin, a photochemical cleavage results in the formation of vitamin D from 7-dehydrocholesterol. Cutaneous production of vitamin D is decreased by melanin and high solar protection factor sunblocks, which effectively impair skin penetration by ultraviolet light. The increased use of sunblocks in North America and Western Europe and a reduction in the magnitude of solar exposure of the general popula­ tion over the past several decades has led to an increased reliance on dietary sources of vitamin D. In the United States and Canada, these sources largely consist of fortified cereals and dairy products, in addi­ tion to fish oils and egg yolks. Vitamin D from plant sources is in the form of vitamin D2, whereas that from animal sources is vitamin D3. These two forms have equivalent biologic activity and are activated equally well by the vitamin D hydroxylases in humans. Vitamin D enters the circulation, whether absorbed from the intestine or synthe­ sized cutaneously, bound to vitamin D–binding protein, an α-globulin synthesized in the liver. Vitamin D is subsequently 25-hydroxylated in the liver by a cytochrome P450 oxidase in the mitochondria and microsomes. The activity of this hydroxylase is not tightly regulated, and the resultant metabolite, 25-hydroxyvitamin D [25(OH)D], is the major circulating and storage form of vitamin D. Approximately 88% of 25(OH)D circulates bound to the vitamin D–binding protein, 0.03% is free, and the rest circulates bound to albumin. The half-life of 25(OH) D is ~2–3 weeks, with that of 25(OH)D2 being shorter than that of 25(OH)D3 due to a lower affinity of vitamin D–binding protein for the former. The half-life of 25(OH)D is also greatly shortened when vita­ min D–binding protein levels are reduced, as can occur with increased urinary losses in the nephrotic syndrome. The second hydroxylation, required for the formation of the mature hormone, occurs in the kidney (Fig. 421-5). The 25-hydroxyvitamin D-1α-hydroxylase (encoded by the CYP27B1 gene) is a tightly regu­ lated cytochrome P450–like mixed-function oxidase expressed in the proximal convoluted tubule cells of the kidney. PTH and hypophospha­ temia are the major inducers of this microsomal enzyme in the kidney, whereas calcium, FGF23, and the enzyme’s product, 1,25(OH)2D, repress it. The 25-hydroxyvitamin D-1α-hydroxylase is also present in numerous other cell types, where it is not subject to hormonal

Vitamin D Skin 7-Dehydrocholesterol Gut Vitamin D Liver 25(OH)D Kidney 1,25(OH)2D FIGURE 421-4  Vitamin D synthesis and activation. Vitamin D is synthesized in the skin in response to ultraviolet radiation and also is absorbed from the diet. It is then transported to the liver, where it undergoes 25-hydroxylation. This metabolite is the major circulating form of vitamin D. The final step in hormone activation, 1α-hydroxylation, occurs in the kidney. regulation. It is expressed in epidermal keratinocytes, but keratinocyte production of 1,25(OH)2D is not thought to contribute to circulating levels of this hormone. In addition to being present in the trophoblastic layer of the placenta, the 1α-hydroxylase is produced by macrophages associated with granulomas and lymphomas. In these latter pathologic states, the activity of the enzyme is induced by interferon γ and TNF-α but is not regulated by calcium or 1,25(OH)2D; therefore, hypercalce­ mia, associated with elevated levels of 1,25(OH)2D, may be observed. Treatment of sarcoidosis-associated hypercalcemia with glucocorti­ coids, ketoconazole, or chloroquine reduces 1,25(OH)2D production and effectively lowers serum calcium. In contrast, chloroquine has not been shown to lower the elevated serum 1,25(OH)2D levels in patients with lymphoma. The major pathway for inactivation of vitamin D metabolites is an additional hydroxylation step by the vitamin D 24-hydroxylase, an enzyme that is expressed in most tissues. 1,25(OH)2D is the major inducer of this enzyme; therefore, this hormone promotes its own inactivation, thereby limiting its biologic effects. FGF23 also induces this hydroxylase, thereby reducing circulating 1,25(OH)2D levels by increasing its inactivation, as well as by impairing its synthesis. Muta­ tions of the gene encoding this enzyme (CYP24A1) can lead to infan­ tile hypercalcemia, and in those less severely affected, long-standing hypercalciuria, nephrocalcinosis, and nephrolithiasis can occur. Polar metabolites of 1,25(OH)2D are secreted into the bile and reabsorbed via the enterohepatic circulation. Impairment of this recir­ culation, which is seen with diseases of the terminal ileum, leads to accelerated losses of vitamin D metabolites.

Vitamin D3 Vitamin D-25 hydroxylase – Liver 25(OH)D3 25(OH)D-1αhydroxylase and other factors Pi – Kidney / + – /

2D H) 1,25(OH)2D3 (O

1, PTH – PTH Bone Parathyroid glands

C

a2

C Intestine H al P ci O fi

2– ca

2– O ti P on H +

a2 C Blood calcium FIGURE 421-5  Schematic representation of the hormonal control loop for vitamin D metabolism and function. A reduction in the serum calcium below ~2.2 mmol/L (8.8 mg/dL) prompts a proportional increase in the secretion of parathyroid hormone (PTH) and so mobilizes additional calcium from the bone. PTH promotes the synthesis of 1,25(OH)2D in the kidney, which in turn stimulates the mobilization of calcium from bone and intestine and regulates the synthesis of PTH by negative feedback. ■ ■ACTIONS OF 1,25(OH)2D 1,25(OH)2D mediates its biologic effects by binding to a member of the nuclear receptor superfamily, the vitamin D receptor (VDR). This receptor belongs to the subfamily that includes the thyroid hormone receptors, the retinoid receptors, and the peroxisome proliferator– activated receptors; however, in contrast to the other members of this subfamily, only one VDR isoform has been isolated. The VDR binds to target DNA sequences as a heterodimer with the retinoid X receptor, recruiting a series of coactivators that modify chromatin and approxi­ mate the VDR to the basal transcriptional apparatus, resulting in the induction of target gene expression. The mechanism of transcriptional repression by the VDR varies with different target genes but has been shown to involve either interference with the action of activating transcription factors or the recruitment of novel proteins to the VDR complex, resulting in transcriptional repression. The affinity of the VDR for 1,25(OH)2D is approximately three orders of magnitude higher than that for other vitamin D metabo­ lites. Metabolites resulting from the 24-hydroxylation of vitamin D, including 1,24,25 trihydroxyvitamin D3 (1,24,35(OH)3D3) and 24,25 dihydroxyvitamin D3 (24,25(OH)D3) have biologic effects that mimic 1,25(OH)2D. In normal physiologic circumstances, these other

metabolites are not thought to play significant roles in stimulating receptor-dependent actions. However, in states of vitamin D toxicity, the markedly elevated levels of 25(OH)D may lead to hypercalcemia by interacting directly with the VDR and by displacing 1,25(OH)2D from vitamin D–binding protein, resulting in increased bioavailability of the active hormone.

The VDR is expressed in a wide range of cells and tissues. The molecular actions of 1,25(OH)2D have been studied most extensively in tissues involved in the regulation of mineral ion homeostasis. This hormone is a major inducer of calbindin 9K, a calcium-binding pro­ tein expressed in the intestine, which is thought to play an important role in the active transport of calcium across the enterocyte. The two major calcium transporters expressed by intestinal epithelia, TRPV5 and TRPV6 (transient receptor potential vanilloid), are also vitamin D responsive. By inducing the expression of these and other genes in the small intestine, 1,25(OH)2D increases the efficiency of intes­ tinal calcium absorption, and it also has been shown to have several important actions in the skeleton. The VDR is expressed in osteoblasts and regulates the expression of several genes in this cell. These genes include the bone matrix proteins osteocalcin and osteopontin, which are upregulated by 1,25(OH)2D, in addition to type I collagen, which is transcriptionally repressed by 1,25(OH)2D. Both 1,25(OH)2D and PTH induce the expression of RANK ligand in osteoblasts, which promotes osteoclast differentiation and increases osteoclast activity, by binding to RANK on osteoclast progenitors and mature osteoclasts. This is the mechanism by which 1,25(OH)2D induces bone resorption. 1,25(OH)2D regulates phosphate homeostasis, primarily by inducing the expression of FGF23 in osteocytes. The skeletal features associated with VDR-knockout mice (rickets, osteomalacia) are largely corrected by increasing calcium and phosphorus intake, underscoring the impor­ tance of vitamin D action in the gut. Bone and Mineral Metabolism in Health and Disease
CHAPTER 421 The VDR is expressed in the parathyroid gland, and 1,25(OH)2D has been shown to have antiproliferative effects on parathyroid cells and to suppress the transcription of the parathyroid hormone gene. These effects of 1,25(OH)2D on the parathyroid gland are an important part of the rationale for current therapies directed at preventing and treating hyperparathyroidism associated with renal insufficiency and complica­ tions of chronic oral phosphate therapy. The VDR is also expressed in tissues and organs that do not play a role in mineral ion homeostasis. Notable in this respect is the obser­ vation that 1,25(OH)2D has an antiproliferative effect on several cell types, including keratinocytes, breast cancer cells, and prostate cancer cells. The effects of 1,25(OH)2D and the VDR on keratinocytes are particularly intriguing, since the VDR is primarily a transcriptional repressor in these cells. Alopecia is seen in humans and mice with mutant VDRs but is not a feature of vitamin D deficiency; thus, the effects of the VDR on the hair follicle are ligand-independent. Vitamin D action is also important for regulating the normal maturation of the bone-tendon attachment site, called the enthesis. ■ ■VITAMIN D DEFICIENCY The mounting concern about the relationship between solar exposure and the development of skin cancer has led to increased reliance on dietary sources of vitamin D. Although the prevalence of vitamin D deficiency varies, the third National Health and Nutrition Examination Survey (NHANES III) revealed that vitamin D deficiency is prevalent throughout the United States, with the prevalence being >29% in obese children. The clinical syndrome of vitamin D deficiency can be a result of deficient production of vitamin D in the skin, lack of dietary intake, accelerated losses of vitamin D, impaired vitamin D activation, or resis­ tance to the biologic effects of 1,25(OH)2D (Table 421-6). The elderly and nursing home residents are particularly at risk for vitamin D defi­ ciency, since both the efficiency of vitamin D synthesis in the skin and the absorption of vitamin D from the intestine decline with age. The presence of terminal ileal disease also results in impaired enterohepatic circulation of vitamin D metabolites. While intestinal malabsorption of dietary fats and short bowel syndrome, including that associated with intestinal bypass surgery, lead to vitamin D deficiency, the cause of vitamin D deficiency in obese individuals is poorly understood.

TABLE 421-6  Causes of Impaired Vitamin D Action Vitamin D deficiency   Impaired cutaneous production   Dietary absence   Malabsorption (short gut syndrome, Impaired 1α-hydroxylation   Hypoparathyroidism   Ketoconazole   1α-Hydroxylase mutation FGF23 excess   Oncogenic osteomalacia   Hypophosphatemic rickets   Fibrous dysplasia   Chronic kidney disease Target organ resistance   Vitamin D receptor mutation   Phenytoin Other   Obesity gastric bypass) Accelerated loss of vitamin D   Increased metabolism (barbiturates, phenytoin, rifampin)   Impaired enterohepatic circulation   Nephrotic syndrome   CYP3A4 mutation Impaired 25-hydroxylation   Liver disease, isoniazid   25-Hydroxylase mutation PART 12 Endocrinology and Metabolism In addition to intestinal diseases, accelerated inactivation of vitamin D metabolites can be seen with drugs that induce hepatic cytochrome P450 mixed-function oxidases such as barbiturates, phenytoin, and rifampin. Gain-of-function mutations in CYP3A4 accelerate the oxi­ dation and inactivation of vitamin D metabolites, thus resulting in decreased serum levels of 25OHD and 1,25(OH)2D. This form of rickets is autosomal recessive and presents during early childhood and can be treated with high doses of calcitriol or vitamin D. Impaired 25-hydrox­ ylation, associated with severe liver disease or isoniazid, is an uncom­ mon cause of vitamin D deficiency. A mutation in the gene responsible for 25-hydroxylation has been identified in a few kindreds. Increased circulating FGF23 levels impair 1α-hydroxylation, preventing the pro­ duction of 1,25(OH)2D. High levels of FGF23 are seen in those with genetic disorders associated with hypophosphatemic rickets, the most common of which is X-linked hypophosphatemia, and are prevalent in populations with profound renal dysfunction. Thus, therapeutic inter­ ventions should be considered in patients whose creatinine clearance is <0.5 mL/s (30 mL/min). Mutations in the renal 1α-hydroxylase are the basis for the genetic disorder pseudovitamin D–deficiency rickets (also called vitamin D–dependent rickets type I). This autosomal recessive disorder presents with the syndrome of vitamin D deficiency in the first year of life. Patients present with growth retardation, rickets, and hypo­ calcemic seizures. Serum 1,25(OH)2D levels are low despite normal 25(OH)D levels and elevated PTH levels. Treatment with vitamin D metabolites that do not require 1α-hydroxylation for activity results in disease remission, although lifelong therapy is required. A second autosomal recessive disorder, hereditary vitamin D–resistant rickets (also called vitamin D-dependent rickets type II), a consequence of vitamin D receptor mutations, is a greater therapeutic challenge. These patients present in a similar fashion during the first year of life, but alopecia often accompanies the disorder, demonstrating a functional role of the VDR in the keratinocyte stem cell population required for hair follicle regeneration. Serum levels of 1,25(OH)2D are dramatically elevated in these individuals both because of increased production due to stimulation of 1α-hydroxylase activity as a consequence of second­ ary hyperparathyroidism and because of impaired inactivation since induction of the 24-hydroxylase by 1,25(OH)2D requires an intact VDR. Since the receptor mutation results in hormone resistance, daily calcium and phosphate infusions may be required to bypass the defect in intestinal mineral ion absorption. Regardless of the cause, the clinical manifestations of vitamin D deficiency are largely a consequence of impaired intestinal calcium absorption. Mild to moderate vitamin D deficiency is asymptomatic, whereas long-standing vitamin D deficiency results in hypocalcemia accompanied by secondary hyperparathyroidism, impaired miner­ alization of the skeleton (osteopenia on x-ray or decreased bone mineral density), and proximal myopathy. Vitamin D deficiency also has been shown to be associated with an increase in overall mortal­ ity, including cardiovascular causes. In the absence of an intercurrent illness, the hypocalcemia associated with long-standing vitamin D deficiency rarely presents with acute symptoms of hypocalcemia such

as numbness, tingling, and seizures. However, the concurrent devel­ opment of hypomagnesemia, which impairs parathyroid function, or the administration of potent bisphosphonates, which impair bone resorption, can lead to acute symptomatic hypocalcemia in vitamin D– deficient individuals. Rickets and Osteomalacia  In children, before epiphyseal fusion, vitamin D deficiency results in growth retardation associated with an expansion of the growth plate known as rickets. Three layers of chondrocytes are present in the normal growth plate: the reserve zone, the proliferating zone, and the hypertrophic zone. Rickets associated with impaired vitamin D action is characterized by expansion of the hypertrophic chondrocyte layer. The expansion of the growth plate is a consequence of impaired apoptosis of the late hypertrophic chondro­ cytes, an event that precedes replacement of these cells by osteoblasts during endochondral bone formation. Investigations in murine models demonstrate that hypophosphatemia, which in vitamin D deficiency is a consequence of secondary hyperparathyroidism, is a key etiologic factor in the development of the rachitic growth plate. Impaired actions specific to vitamin D also contribute to the expansion of the hypertro­ phic layer in the rachitic growth plate. The hypocalcemia and hypophosphatemia that accompany vitamin D deficiency result in impaired mineralization of bone matrix proteins, a condition known as osteomalacia. Osteomalacia is also a feature of long-standing hypophosphatemia, which may result from renal phosphate wasting, or chronic use of etidronate or phosphate-binding antacids. This hypomineralized matrix is biomechanically inferior to normal bone; as a result, patients with osteomalacia are prone to bow­ ing of weight-bearing extremities and skeletal fractures. Vitamin D and calcium supplementation have been shown to decrease the incidence of hip fracture among ambulatory nursing home residents in France, suggesting that undermineralization of bone contributes significantly to morbidity in the elderly. Proximal myopathy is a striking feature of severe vitamin D deficiency both in children and in adults. Rapid reso­ lution of the myopathy is observed upon vitamin D treatment. Although vitamin D deficiency is the most common cause of rickets and osteomalacia, many disorders lead to inadequate mineralization of the growth plate and bone. Calcium deficiency without vitamin D defi­ ciency, the disorders of vitamin D metabolism previously discussed, and hypophosphatemia can all lead to inefficient mineralization. Even in the presence of normal calcium and phosphate levels, chronic aci­ dosis and drugs such as bisphosphonates can lead to osteomalacia. The inorganic calcium/phosphate mineral phase of bone cannot form at low pH. Bisphosphonates bind to and prevent hydroxyapatite crystal growth. Since alkaline phosphatase is necessary for normal mineral deposition, probably because the enzyme can hydrolyze inhibitors of mineralization such as inorganic pyrophosphate, genetic inactivation of the alkaline phosphatase gene (hereditary hypophosphatasia) also can lead to osteomalacia in the setting of normal calcium and phos­ phate levels. Diagnosis of Vitamin D Deficiency, Rickets, and Osteomalacia 

The most specific screening test for vitamin D deficiency in otherwise healthy individuals is a serum 25(OH)D level. Although the normal ranges vary, levels of 25(OH)D <37 nmol/L (<15 ng/mL) are associ­ ated with increasing PTH levels and lower bone density. The National Academy of Medicine has defined vitamin D sufficiency as a vitamin D level >50 nmol/L (>20 ng/mL), although higher levels may be required to optimize intestinal calcium absorption in the elderly and those with underlying disease states, including obesity. Vitamin D deficiency leads to impaired intestinal absorption of calcium, resulting in decreased serum total and ionized calcium values. This hypocalcemia results in secondary hyperparathyroidism, a homeostatic response that initially maintains serum calcium levels at the expense of the skeleton. Due to the PTH-induced increase in bone turnover, alkaline phosphatase levels are often increased. In addition to increasing bone resorption, PTH decreases urinary calcium excretion while promoting phos­ phaturia. This results in hypophosphatemia, which exacerbates the mineralization defect in the skeleton. With prolonged vitamin D defi­ ciency resulting in osteomalacia, calcium stores in the skeleton become

39 - 422 Disorders of the Parathyroid Gland and Calcium Homeostasis

422 Disorders of the Parathyroid Gland and Calcium Homeostasis

relatively inaccessible, since osteoclasts cannot resorb unmineralized osteoid, and frank hypocalcemia ensues. Since PTH is a major stimulus for the renal 25(OH)D 1α-hydroxylase, there is increased synthesis of the active hormone, 1,25(OH)2D. Paradoxically, levels of this hormone are often normal in severe vitamin D deficiency. Therefore, measure­ ments of 1,25(OH)2D are not accurate reflections of vitamin D stores and should not be used to diagnose vitamin D deficiency in patients with normal renal function. Radiologic features of vitamin D deficiency in children include a widened, expanded growth plate that is characteristic of rickets. These findings not only are apparent in the long bones but also are present at the costochondral junction, where the expansion of the growth plate leads to swellings known as the “rachitic rosary.” Impairment of intramembranous bone mineralization leads to delayed fusion of the calvarial sutures and a decrease in the radiopacity of cortical bone in the long bones. If vitamin D deficiency occurs after epiphyseal fusion, the main radiologic finding is a decrease in cortical thickness and relative radiolucency of the skeleton. A specific radiologic feature of osteomalacia, whether associated with phosphate wasting or vitamin D deficiency, is pseudofractures, or Looser’s zones. These are radiolucent lines that occur where large arteries are in contact with the underlying skeletal elements; it is thought that the arterial pulsations lead to the radiolucencies. As a result, these pseudofractures are usually a few mil­ limeters wide, are several centimeters long, and are seen particularly in the scapula, the pelvis, and the femoral neck. TREATMENT Vitamin D Deficiency Based on the National Academy of Medicine 2010 report, the rec­ ommended daily intake of vitamin D is 600 IU from 1 to 70 years of age, and 800 IU for those >70. Based on the observation that 800 IU of vitamin D, with calcium supplementation, decreases the risk of hip fractures in elderly women, this higher dose is thought to be an appropriate daily intake for prevention of vitamin D defi­ ciency in adults. Multiple clinical trials, including the Vitamin D and Omega-3 Trial (VITAL), revealed that supplementation of vitamin D in older community-dwelling adults (>50 years of age) with adequate vitamin D levels, at doses at or above the recom­ mended daily intake, does not further improve bone mineral density. The VITAL trial further showed that supraphysiologic doses of vitamin D in adults with normal vitamin D levels do not improve skeletal microarchitecture and do not prevent falls. Fur­ thermore, treating older adults with daily small doses of vitamin D3, such as 400 IU, can prevent fractures and falls, as compared with large intermittent bolus doses of vitamin D3, which can result in increased incidence of fractures and falls. The safety margin for vitamin D is large, and vitamin D toxicity usually is observed only in patients taking doses in the range of 40,000 IU daily. Treatment of vitamin D deficiency should be directed at the underlying dis­ order, if possible, and also should be tailored to the severity of the condition. Vitamin D should always be repleted in conjunction with calcium supplementation since most of the consequences of vitamin D deficiency are a result of impaired mineral ion homeostasis. In patients in whom 1α-hydroxylation is impaired, metabolites that do not require this activation step are the treatment of choice. They include 1,25(OH)2D3 (calcitriol [Rocaltrol], 0.25– 0.5 μg/d) and 1α-hydroxyvitamin D2 (doxercalciferol [Hectorol], 2.5–5 μg/d). Outside the United States, 1α-hydroxyvitamin D3 (alfacalcidol [One-Alpha], 0.25–1.0 μg/d) is also used. If the path­ way required for activation of vitamin D is intact, severe vitamin D deficiency can be treated with pharmacologic repletion initially (50,000 IU weekly for 3–12 weeks), followed by maintenance therapy (800 IU daily). Pharmacologic doses may be required for maintenance therapy in patients who are taking medications such as barbiturates or phenytoin that accelerate metabolism of or cause resistance to 1,25(OH)2D. Polymorphisms in the 25-hydroxylase and the 24-hydroxylase genes can also lead to different responses

to the normal recommended daily intake of vitamin D. The hepatic enzyme cytochrome P450 3A4 (CYP3A4) is a strong inducer of the catabolism of vitamin D metabolites. Polymorphisms of the CYP3A4 gene and certain drugs, such as phenytoin and rifampin, lead to strong induction of this enzyme; thus, those affected may also require higher doses of vitamin D supplementation. Calcium supplementation should include 1.5–2 g/d of elemental calcium. Normocalcemia is usually observed within 1 week of the institution of therapy, although increases in PTH and alkaline phosphatase levels may persist for 3–6 months. The most efficacious methods to monitor treatment and resolution of vitamin D deficiency are serum and urinary calcium measurements. In patients who are vitamin D replete and are taking adequate calcium supplementa­ tion, the 24-h urinary calcium excretion should be in the range of 100–250 mg/24 h. Lower levels suggest problems with adherence to the treatment regimen or with absorption of calcium or vitamin D supplements. Levels >250 mg/24 h predispose to nephrolithiasis and should lead to a reduction in vitamin D dosage and/or calcium supplementation.

Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 Acknowledgment The authors acknowledge Marie Demay (also a former author of this chapter) and Michael Mannstadt for their valuable input into this chapter. ■ ■FURTHER READING Bikle D et al: Vitamin D metabolites in captivity? Should we measure free or total 25(OH)D to assess vitamin D status? J Steroid Biochem Mol Biol 173:105, 2017. Bouillon R et al: Health effects of vitamin D supplementation: Lessons learned from randomized controlled trials and mendelian randomization studies. J Bone Miner Res 38:1391, 2023. Carpenter TO et al: Burosumab therapy in children with X-linked hypophosphatemia. N Engl J Med 378:1987, 2018. Christakos S et al: Vitamin D: Metabolism, molecular mechanism of action, and pleiotropic effects. Physiol Rev 96:365, 2016. De Baaij JH et al: Magnesium in man: Implications for health and disease. Physiol Rev 95:1, 2015. Kim JM et al: Osteoblast-osteoclast communication and bone homeo­ stasis. Cells 10:2073, 2020. Kovacs CS et al: The role of biomineralization in disorders of skeletal development and tooth formation. Nat Rev Endocrinol 17:336, 2021. Robling AG, Bonewald LF: The osteocyte: New insights. Ann Rev Physiol 82:485, 2020. Schlingmann KP, de Baaij JHF: The genetic spectrum of Gitelman (-like) syndromes. Curr Opin Nephrol Hypertens 31:508, 2022. Zofkova I: Hypercalcemia. Pathophysiological aspects. Phys Res 65:1, 2016. Michael Mannstadt, Harald Jüppner

Disorders of the

Parathyroid Gland and

Calcium Homeostasis Four parathyroid glands are located posterior to the thyroid gland. They produce parathyroid hormone (PTH), which is the primary regulator of calcium homeostasis. PTH acts directly on bone, where it induces calcium (and phosphate) release, and on the kidney, where it enhances calcium reabsorption in the distal tubules. In the proximal renal tubules, PTH increases excretion of phosphate and the synthesis of 1,25-dihydroxyvitamin D (1,25(OH)2D), a hormone that increases

gastrointestinal calcium absorption. Serum PTH levels are tightly regulated by a negative feedback loop. Calcium, acting through the calcium-sensing receptor, and vitamin D, acting through its nuclear receptor, reduce PTH release and synthesis. Additional evidence indicates that fibroblast growth factor 23 (FGF23), a phosphaturic hormone, can suppress PTH secretion. Understanding the hormonal pathways that regulate calcium and phosphate levels as well as bone metabolism is essential for effective diagnosis and management of a wide array of hyper- and hypocalcemic disorders.

Primary hyperparathyroidism, characterized by excess production of PTH, is a common cause of hypercalcemia and is usually the result of autonomously functioning adenomas or hyperplasia. Surgery for this disorder is highly effective and has been shown to reverse some of the deleterious effects of long-standing PTH excess on bone density. Humoral hypercalcemia of malignancy (HHM) is also a common cause of hypercalcemia, which is usually due to the overproduction of parathyroid hormone–related peptide (PTHrP) by cancer cells. The similarities in the biochemical characteristics of hyperparathyroidism and HHM, first noted by Albright in 1941, are now known to reflect the actions of PTH and PTHrP through the same G protein–coupled PTH/PTHrP receptor (PH1R). The converse, namely hypocalcemia, can be caused by the lack of functional PTH, i.e., hypoparathyroidism, or by reduced PTH responsiveness of the proximal renal tubules, i.e., pseudohypoparathyroidism (PHP). PART 12 Endocrinology and Metabolism The genetic basis of numerous calcium and phosphate disorders, and the molecular characterization of parathyroid cell biology, have provided new insights into the regulation of calcium and phosphate homeostasis. In addition, PTH(1-34) and possibly some of its ana­ logues are promising agents for the treatment of postmenopausal osteoporosis and as replacement therapy for hypoparathyroidism. Cal­ cimimetic agents, which activate the calcium-sensing receptor (CaSR), have provided new approaches for PTH suppression, and calcilytics, which are negative allosteric modulators of the CaSR, show promis­ ing results in early clinical trials of patients with autosomal dominant hypocalcemia type 1, a rare dominant disease that is caused by activat­ ing CaSR mutations. ■ ■PTH Structure and Physiology  PTH is an 84-amino-acid single-chain peptide. The amino-terminal portion, PTH(1–34), is highly conserved and is critical for the biologic actions of the molecule. Modified syn­ thetic fragments of the amino-terminal sequence as small as PTH(1–11) are sufficient to activate the PTH/PTHrP receptor, if provided at high enough concentrations (see below). C-terminal portions of full-length PTH(1–84) were shown to bind to a separate binding protein/receptor; however, the properties and biologic role(s), if any, of this presumed receptor for C-terminal PTH remain undefined. The primary function of PTH is to maintain ionized calcium con­ centration in the extracellular fluid (ECF) within a narrow normal range. The hormone acts directly on bone and kidney and indirectly on the intestine through its effects on synthesis of 1,25(OH)2D to increase serum calcium concentrations; in turn, PTH production is closely regulated by the concentration of serum ionized calcium. This feedback system is the critical homeostatic mechanism for mainte­ nance of ECF calcium. Any tendency toward hypocalcemia, as might be induced by calcium- or vitamin D–deficient diets, is counteracted by increased PTH secretion. This in turn (1) increases bone turnover, thereby increasing the flow of calcium (and phosphate) from bone into blood; (2) increases calcium reabsorption in the distal tubules; and (3) indirectly increases the efficiency of calcium absorption in the intes­ tine by stimulating the renal production of 1,25(OH)2D. Immediate control of blood calcium is due to PTH effects on bone and, to a lesser extent, on renal calcium clearance. Maintenance of calcium balance over a longer timescale, on the other hand, probably results from the effects of 1,25(OH)2D on intestinal calcium absorption (Chap. 421). The renal actions of PTH are exerted at multiple sites; in the proximal tubules, it increases urinary phosphate excretion, it augments calcium reabsorption in the distal tubules, and it enhances in the proximal

tubules expression of CYP27B1, the enzyme that encodes the 25(OH) D-1α-hydroxylase. Every day, up to 12 mmol (500 mg) of calcium is transferred between the ECF and bone, which is a significant amount in relation to the total ECF calcium pool, and PTH plays a crucial role in regulating this transfer. PTH has multiple actions on bone and integrates its calcemic actions (bone resorption to protect against hypocalcemia) with stimu­ lation of bone formation. PTH-mediated changes in bone calcium release can be seen within minutes. The chronic effects of PTH are to increase the number of bone cells, both osteoblasts and osteoclasts, and to increase the remodeling of bone; these effects are apparent within hours after the hormone is given and persist for hours after PTH is withdrawn. Continuous exposure to elevated PTH (as in primary hyperparathyroidism or long-term PTH infusions in animals) leads to increased osteoclast-mediated bone resorption. However, the intermit­ tent administration of relatively small amounts of PTH that elevate hormone levels minimally for 1–2 h each day lead to a net increase of bone mass rather than bone loss. Striking increases, especially in trabecular bone in the spine and hip, have been reported with the intermittent use of PTH for osteoporosis, and large clinical trials with PTH(1–34) as monotherapy revealed a highly significant increase in bone density and reduction in fracture incidence. Osteoblasts (or their stromal cell precursors), which have PTH/ PTHrP receptors, are crucial to this bone-forming effect of PTH. When PTH activates PTH/PTHrP receptors on osteocytes, release of calcium from the matrix surrounding these cells is enhanced; osteoclasts, which mediate bone breakdown, lack such receptors. PTH-mediated stimula­ tion of osteoclasts is indirect, acting in part through RANKL released from osteoblasts to activate RANK on osteoclasts; in experimental studies of bone resorption in vitro, osteoblasts must be present for PTH to activate osteoclasts to resorb bone (Chap. 421). Synthesis, Secretion, and Metabolism  •  SYNTHESIS  Para­ thyroid cells have multiple methods of adapting to increased needs for PTH production. Most rapid (within minutes) is secretion of pre­ formed hormone in response to hypocalcemia. Second, within hours, PTH mRNA expression is induced by sustained hypocalcemia. Finally, protracted challenge leads within days to cellular replication to increase parathyroid gland mass. PTH is initially synthesized as a larger molecule (preproPTH, consisting of 115 amino acids). After a first cleavage step to remove the “pre” sequence of 25 amino acid residues, a second cleavage step removes the “pro” sequence of 6 amino acid residues before secretion of the mature peptide comprising 84 residues. Homozygous or heterozy­ gous mutations in the prepro-region can cause hypoparathyroidism by interfering with hormone synthesis, transport, or secretion. Thus far, only three homozygous mutations have been identified in the secreted PTH(1–84) that reduce its biological activity and are detected in some, but not all, PTH assays (see below). Transcriptional suppression of the PTH gene by calcium is nearly maximal at physiologic calcium concentrations. Hypocalcemia increases transcriptional activity within hours. 1,25(OH)2D also strongly sup­ presses PTH gene transcription. In patients with chronic kidney dis­ ease (CKD), administration of supraphysiologic doses of 1,25(OH)2D or analogues of this active metabolite can dramatically suppress PTH overproduction and is thus used clinically to control severe secondary hyperparathyroidism. Regulation of proteolytic destruction of pre­ formed PTH (posttranslational regulation of hormone production) is an important mechanism for mediating rapid (within minutes) changes in hormone availability. High calcium increases and low calcium inhib­ its the proteolytic destruction of stored hormone. REGULATION OF PTH SECRETION  PTH secretion increases steeply to a maximum value of about five times the basal rate of secretion as the cal­ cium concentration falls from normal to 1.9–2.0 mmol/L (7.6–8.0 mg/dL; measured as total calcium). Severe intracellular magnesium deficiency impairs PTH secretion (see below). ECF calcium controls PTH secretion by interaction with a CaSR, a G protein–coupled receptor (GPCR) for which Ca2+ ions act as the primary ligand (see below). This receptor, which also has phosphate

binding sites, is a member of the class C GPCR superfamily and func­ tions as an obligate homodimer. Characterized by a large extracellular domain that effectively clamps the small-molecule ligand, the CaSR is expressed in many tissues and cell types. The CaSR can couple to all four classes of G proteins in a cell-dependent context. In the parathy­ roids, the CaSR mediates its actions by coupling to two closely related G protein alpha-subunits, namely Gαq and Gα11, as well as Gαi. Acti­ vation of the CaSR by high calcium levels negatively regulates PTH secretion in the parathyroids and reduces calcium reabsorption in the distal renal tubules. Genetic evidence further reinforced the essential role for the CaSR in maintaining calcium balance. Heterozygous loss-of-function CaSR mutations cause familial hypocalciuric hypercalcemia (FHH) type 1, a benign disease in which the blood calcium abnormality resembles that observed in hyperparathyroidism but with hypocalciuria; other more recently defined variants of FHH, namely FHH2 and FHH3, are caused either by heterozygous loss-of-function mutations in Gα11, the alphasubunit of one of the signaling proteins downstream of the CaSR, or by heterozygous mutations in the adaptor protein AP2S1, which is key in the intracellular trafficking of the CaSR. Homozygous loss-of-function mutations in the CaSR are the cause of severe neonatal hyperparathy­ roidism, a disorder that is typically lethal if not treated within the first days of life. On the other hand, heterozygous gain-of-function mutations cause a form of hypocalcemia resembling hypoparathyroidism (see below). METABOLISM  PTH undergoes intraglandular proteolysis, which is regulated by extracellular calcium, and further degradation occurs after secretion into the circulation, mainly by liver and kidney. Removal of the critically important amino-terminus (as little as the first amino acid) produces biologically inactive PTH fragments, such as PTH(7–84), which can be detected equally well as PTH(1–84) by several commonly used immunometric PTH assays that employ two antibodies directed against portions of the N- and C-terminus, respectively. Earlier assays, now used only infrequently, measure pre­ dominantly middle and carboxyl-terminal fragments that have no or incompletely defined biological activity and are cleared more slowly from blood than the secreted PTH(1–84). Although the problems inherent in PTH measurements have been largely circumvented by use of double-antibody immunometric assays, some evidence suggests that the PTH(7–84) (and probably related amino-terminally truncated fragments) can act, through yet unde­ fined mechanisms, as an inhibitor of PTH action and may therefore be of clinical significance, particularly in patients with CKD. In this group of patients, efforts to prevent secondary hyperparathyroidism by a variety of measures (vitamin D analogues, higher calcium intake, higher dialysate calcium, phosphate-lowering strategies, and calcimi­ metic drugs) can lead to oversuppression of the parathyroid glands since some amino-terminally truncated PTH fragments can react in some immunometric PTH assays, thus overestimating the levels of bio­ logically active PTH(1–84). Excessive parathyroid gland suppression in CKD can lead to adynamic bone disease (see below), which has been associated in children with further impaired growth and increased bone fracture rates in adults and can furthermore lead to significant

hPTH SER VAL SER GLU ILE GLN LEU MET HIS ASN LEU GLY LYS HIS LEU ASN SER MET GLU ARG VAL GLU TRP LEU ARG LYS LYS LEU GLN ASP hPTHrp ALA – – – HIS – – LEU – ASP LYS – – SER ILE GLN ASP LEU ARG – ARG PHE PHE – HIS HIS LEU ILE ALA GLU hPTH hPTHrP

Amino acid residues FIGURE 422-1  Schematic diagram to illustrate similarities and differences in structure of human parathyroid hormone (hPTH) and human PTH-related peptide (hPTHrP). Close structural (and functional) homology exists between the first 30 amino acids of hPTH and hPTHrP. The PTHrP sequence may be ≥139 amino acid residues in length. PTH is only 84 residues long; after residue 30, there is little structural homology between the two. Dashed lines in the PTHrP sequence indicate identity; underlined residues, although different from those of PTH, still represent conservative changes (charge or polarity preserved). Ten amino acids are identical, and a total of 20 of 30 are homologues.

hypercalcemia. The measurement of PTH with newer third-generation immunometric assays, which use detection antibodies directed against extreme amino-terminal PTH epitopes and thus detect only full-length PTH(1–84), has not yet clearly shown to be advantageous in the clini­ cal setting.

■ ■PTHRP Structure and Physiology  PTHrP is responsible for most instances of HHM (Chap. 98), a syndrome that resembles primary hyperparathyroidism but without elevated PTH levels. Most cell types normally produce PTHrP, including brain, pancreas, heart, lung, mam­ mary tissue, placenta, endothelial cells, and smooth muscle. In fetal animals, PTHrP directs transplacental calcium transfer, and high con­ centrations of PTHrP are produced in mammary tissue and secreted into milk, but the biologic significance of this peptide in breast milk is unknown. PTHrP has paracrine and autocrine functions and it plays an essential role in diverse functions such as endochondral bone forma­ tion, branching morphogenesis of the breast, and possibly in uterine contraction. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 PTH and PTHrP, although products of different genes, exhibit con­ siderable functional and structural homology (Fig. 422-1) and have evolved from a shared ancestral gene. The structure of the gene encod­ ing human PTHrP, however, is more complex than that of PTH, con­ taining multiple additional exons, which can undergo alternate splicing patterns during formation of the mature mRNA. Protein products of 139, 141, and 173 amino acids are produced, and other molecular forms may result from tissue-specific degradation at accessible internal cleavage sites. The biologic roles of these various molecular species and the nature of the circulating forms of PTHrP are unclear. In fact, it is uncertain whether PTHrP circulates at any significant level in healthy children and adults. As a paracrine factor, PTHrP may be produced, act, and be destroyed locally within tissues. In adults, PTHrP appears to have little influence on calcium homeostasis, except in disease states, when large tumors, especially of the squamous cell type as well as renal cell carcinomas, lead to massive overproduction of the hormone and hypercalcemia. Both PTH and PTHrP bind to and activate the PTH/PTHrP recep­ tor. The PTH/PTHrP receptor (also known as the PTH-1 receptor [PTH1R]) belongs to the class B GPCRs that includes the receptors for calcitonin, glucagon, secretin, vasoactive intestinal peptide, and a few other peptides. Although both ligands activate the PTH1R, the two peptides induce distinct responses by the receptor, which explains how a single receptor without isoforms can serve different biologic roles. The extracellular regions of the receptor are involved in hormone binding, and the intracellular domains, after hormone activation, bind G protein subunits to transduce hormone signaling into cellular responses through the stimulation of second messenger formation.

A second receptor that binds PTH, originally termed the PTH-2 receptor (PTH2R), is primarily expressed in brain, pancreas, and tes­ tis. Different mammalian PTH1Rs respond equivalently to PTH and PTHrP, at least when tested with traditional assays, whereas the human PTH2R responds efficiently only to PTH, but not to PTHrP. PTH2Rs from other species show little or no stimulation of second-messenger

Amino acid residues

formation in response to PTH or PTHrP. In fact, the endogenous ligand of the PTH2R was shown to be a hypothalamic peptide referred to as tubular infundibular peptide of 39 residues, TIP39, that is only distantly related to PTH and PTHrP. The PTH1R and the PTH2R can be traced backward in evolutionary time to fish, which express also a third receptor, the PTH3R, that is more closely related to the fish PTH1R than to the fish PTH2R. The evolutionary conservation of structure and function suggests important biologic roles for these receptors, even in fish, which lack discrete parathyroid glands but pro­ duce two molecules that are closely related to mammalian PTH.

Studies using the cloned PTH1R confirm that it can be coupled to more than one G protein and second-messenger pathway, thus contrib­ uting to the multiplicity of pathways stimulated by PTH. Activation of protein kinases (A and C) and calcium transport channels is associated with a variety of hormone-specific tissue responses. These responses include inhibition of phosphate and bicarbonate transport, stimulation of calcium transport, and activation of renal 1α-hydroxylase in the kidney. The responses in bone include effects on collagen synthesis, alkaline phosphatase, ornithine decarboxylase, citrate decarboxyl­ ase, and glucose-6-phosphate dehydrogenase activities; phospholipid synthesis; and calcium and phosphate transport. Ultimately, these biochemical events lead to an integrated hormonal response in bone turnover and calcium homeostasis. PTH also activates Na+/Ca2+ exchangers at renal distal tubular sites and stimulates translocation of preformed calcium transport channels, moving them from the interior to the apical surface to increase tubular uptake of calcium. PTHdependent stimulation of phosphate excretion involves reduced expres­ sion of two sodium-dependent phosphate co-transporters, NPT2a and NPT2c, at the apical membrane, thereby reducing phosphate reab­ sorption in the proximal renal tubules. Similar mechanisms may be involved in other renal tubular transporters that are influenced by PTH. PART 12 Endocrinology and Metabolism PTHrP exerts important developmental influences on fetal bone development and in adult physiology. Homozygous ablation of the gene encoding PTHrP (or disruption of the PTH1R gene) in mice causes a lethal phenotype in which animals are born with pronounced acceleration of chondrocyte maturation that resembles a human dis­ ease, Blomstrand lethal chondrodysplasia (BLC), that is caused by homozygous or compound heterozygous, inactivating PTH1R muta­ tions (Fig. 422-2). Heterozygous inactivating PTH1R mutations in humans furthermore can be a cause of delayed tooth eruption, while heterozygous inactivating PTHrP mutations lead to premature growth plate closure and reduced adult heights. Besides the lethal, biallelic PTH1R mutations that cause BLC, several homozygous mutations in this gene have now been identified in a rare recessive disease referred to as Eiken syndrome. Affected patients typically have normal min­ eral ion regulation, yet delayed growth plate maturation resulting in Many organs Parathyroids PTHrP PTH Ca2+ Growth Plate Breast Kidney Brain Smooth muscle Skin Bone Calcium Homeostasis Paracrine Actions FIGURE 422-2  Dual role for the actions of the PTH/PTHrP receptor (PTH1R). Parathyroid hormone (PTH; endocrine-calcium homeostasis) and PTH-related peptide (PTHrP; paracrine–multiple tissue actions including growth plate cartilage in developing bone) use the single receptor for their disparate functions mediated by the amino-terminal 34 residues of either peptide. Other regions of both ligands interact with other receptors (not shown).

some bone deformities, reduced growth, and delayed tooth eruption; recently, a few cases were described with symptomatic hypocalcemia and considerably elevated PTH levels. ■ ■CALCITONIN (See also Chap. 400) Calcitonin is a peptide hormone with hypocal­ cemic properties that in several mammalian species acts as an indirect antagonist to the calcemic actions of PTH. Calcitonin seems to be of limited physiologic significance in humans, at least with regard to calcium homeostasis. It is of medical significance because of its role as a tumor marker in sporadic and hereditary cases of medullary thyroid carcinoma and its medical use as an adjunctive treatment in severe hypercalcemia and in Paget’s disease of bone at pharmacologic doses. Levels can also be elevated in patients with pseudohypoparathyroidism (PHP); the significance of this observation is unclear. The hypocalcemic activity of calcitonin is accounted for primarily by inhibition of osteoclast-mediated bone resorption and secondarily by stimulation of renal calcium clearance. These effects are mediated by receptors on osteoclasts and renal tubular cells. Calcitonin exerts additional effects through receptors present in the brain, the gastro­ intestinal tract, and the immune system. The hormone, for example, exerts analgesic effects directly on cells in the hypothalamus and related structures, possibly by interacting with receptors for related peptide hormones such as calcitonin gene–related peptide (CGRP) or amylin. Both of these ligands have specific high-affinity receptors that share considerable structural similarity with the PH1R and can also bind to and activate calcitonin receptors. The calcitonin receptor shares considerable structural similarity with the PTH1R. The naturally occurring calcitonins consist of a peptide chain of 32 amino acids. There is considerable sequence variability among species. Calcitonin from salmon, which is used therapeutically, is 10–100 times more potent than mammalian forms in lowering serum calcium. The circulating level of calcitonin in humans is lower than that in many other species. In humans, even extreme variations in calcito­ nin production do not change calcium and phosphate metabolism; no definite effects are attributable to calcitonin deficiency (totally thyroidectomized patients receiving only replacement thyroxine) or excess (patients with medullary carcinoma of the thyroid, a calcitoninsecreting tumor) (Chap. 400). Calcitonin has been a useful pharmaco­ logic agent to suppress bone resorption in Paget’s disease (Chap. 424) and osteoporosis (Chap. 423) and in the treatment of hypercalcemia of malignancy (see below). However, bisphosphates are usually more effective, and the physiologic role, if any, of calcitonin in humans is uncertain. On the other hand, ablation of the calcitonin gene (com­ bined with ablation of the CGRP gene because both genes are in close proximity) in mice leads to reduced bone mineral density, suggesting that its biologic role in mammals is still not fully understood. ■ ■HYPERCALCEMIA Introduction  (See also Chap. 57) Hypercalcemia can be a mani­ festation of a serious illness such as malignancy or can be detected coincidentally by laboratory testing in a patient with no obvious illness. The number of patients recognized with asymptomatic hypercalcemia, usually primary hyperparathyroidism, increased in the late twentieth century when wider testing became readily available. Whenever hypercalcemia is confirmed, a definitive diagnosis must be established. Although hyperparathyroidism, a frequent cause of asymptomatic hypercalcemia, is a chronic disorder in which manifes­ tations, if any, may be expressed only after months or years, hypercal­ cemia can also be the earliest manifestation of malignancy, the second most common cause of hypercalcemia in the adult. The causes of hypercalcemia are numerous (Table 422-1), but hyperparathyroidism and cancer account for 90% of all cases. Before initiating a diagnostic workup, confirm the presence of true hypercalcemia, not a false-positive laboratory test from factors like hemoconcentration during blood collection or elevation in serum proteins such as albumin. Since hypercalcemia is typically chronic, it is cost-effective to obtain several serum calcium and concomitant albumin measurements, which do not require fasting.

TABLE 422-1  Classification of Causes of Hypercalcemia I.  Parathyroid-Related A.  Primary hyperparathyroidism 1.  Adenoma(s) 2.  Multiple endocrine neoplasia 3.  Parathyroid carcinoma 4.  Ectopic production of parathyroid hormone (PTH) 5.  Exogenous administration of PTH or analogues B.  Lithium therapy C.  Familial hypocalciuric hypercalcemia II.  Malignancy-Related A.  Tumors with osteolytic metastases (breast, multiple myeloma, lymphoma, etc.) B.  Solid tumor with humoral mediation of hypercalcemia (squamous cell carcinoma of the lung, kidney, breast, and others) C.  1,25(OH)2D-mediated hypercalcemia of malignancies (lymphoma, ovarian dysgerminoma, etc.) III.  Vitamin D–Related A.  Vitamin D intoxication B.  ↑ 1,25(OH)2D; sarcoidosis and other granulomatous diseases, lymphoma C.  ↑ 1,25(OH)2D; impaired 1,25(OH)2D metabolism due to biallelic 24-hydroxylase mutations or increased 1,25(OH)2D synthesis due to inactivating biallelic mutations involving the renal sodium-dependent phosphate co-transporters IV.  Associated with High Bone Turnover A.  Hyperthyroidism B.  Immobilization C.  Thiazides D.  Vitamin A intoxication E.  Fat necrosis V.  Associated with Renal Failure A.  Tertiary hyperparathyroidism B.  Aluminum intoxication and adynamic bone disease C.  Milk-alkali syndrome Clinical features are helpful in differential diagnosis. Hypercal­ cemia in an adult who is asymptomatic is usually due to primary hyperparathyroidism. In malignancy-associated hypercalcemia, the disease is usually not occult; rather, symptoms of malignancy bring the patient to the physician, and hypercalcemia is discovered during the evaluation. If asymptomatic hypercalcemia can be documented for more than a year, malignancy is unlikely. Nevertheless, differentiating primary hyperparathyroidism from occult malignancy can occa­ sionally be difficult, and careful evaluation is required, particularly when the duration of the hypercalcemia is unknown. Other causes of hypercalcemia may include excessive intake of vitamin D or activated analogues, impaired metabolism of 1,25(OH)2D, high bone turnover from any of several causes, or renal failure (Table 422-1). Immuno­ metric PTH assays serve as the principal laboratory test in establishing the diagnosis. Hypercalcemia from any cause can result in fatigue, depression, mental confusion, anorexia, nausea, vomiting, constipation, revers­ ible renal tubular defects, increased urine output, a short QT interval in the electrocardiogram, and, in some patients, cardiac arrhythmias. Generally, symptoms are more common at calcium levels >2.9–3.0 mmol/L (11.6–12.0 mg/dL), but some patients, even at this level, are asymptomatic. When the calcium level is >3.2 mmol/L (12.8 mg/dL), calcification in kidneys, skin, vessels, lungs, heart, and stomach occurs, and renal insufficiency may develop, particularly if blood phosphate levels are normal or elevated due to impaired renal excre­ tion. Severe hypercalcemia, usually defined as ≥3.7–4.5 mmol/L (14.8–18.0 mg/dL), can be a medical emergency; coma and cardiac arrest can occur. Acute management of the hypercalcemia is usually successful. The type of treatment is based on the severity of the hypercalcemia and the nature of associated symptoms, as outlined below.

■ ■PRIMARY HYPERPARATHYROIDISM

Pathophysiology  •  NATURAL HISTORY AND INCIDENCE  Primary hyperparathyroidism, which is typically a disease of postmenopausal women, results from excessive secretion of PTH that is disproportion­ ate to serum calcium levels. This typically causes hypercalcemia and hypophosphatemia. There is great variation in the manifestations. Patients may present with multiple signs and symptoms, including recurrent nephrolithiasis, peptic ulcers, mental changes, and, less fre­ quently, extensive bone resorption. However, with greater awareness of the disease and wider use of multiphasic screening tests, including measurements of blood calcium, the diagnosis is frequently made in patients who have no symptoms and minimal, if any, signs of the dis­ ease other than hypercalcemia and elevated levels of PTH. The mani­ festations may be subtle, and the disease may have a benign course for many years or a lifetime. This milder form of the disease is usually termed asymptomatic hyperparathyroidism and can present with or without end-organ involvement. Rarely, hyperparathyroidism develops or worsens abruptly and causes severe complications such as marked dehydration and coma, so-called hypercalcemic parathyroid crisis. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 The annual incidence of the disease varies globally and has changed over the decades likely reflecting changes in the usage of laboratory screening panels that include serum calcium. The current incidence in the United States is calculated to be about 50 per 100,000 person-years. ETIOLOGY  Parathyroid tumors are most often encountered as isolated monoclonal adenomas without other endocrinopathy. They may also arise in hereditary syndromes such as multiple endocrine neoplasia (MEN) syndromes. As many as 10% of patients with hyperparathyroid­ ism have a genetic basis for the disease (see below). Parathyroid tumors may also arise as secondary to underlying disease (excessive stimu­ lation in secondary hyperparathyroidism, especially chronic renal failure) or after other forms of excessive stimulation such as lithium therapy. These etiologies are discussed below. Solitary Adenomas  A single abnormal gland is the cause in ~80% of patients; the abnormality in the gland is usually a benign neoplasm or adenoma and extremely rarely a parathyroid carcinoma. More than one adenoma has been reported, and genetic causes of the disease often underlies chief cell hyperplasia of all four glands. Hereditary Syndromes and Multiple Parathyroid Tumors  Hereditary hyperpara­ thyroidism can occur without other endocrine abnormalities but is usually part of a MEN syndrome (Chap. 400). MEN 1 (Wermer’s syn­ drome) consists of hyperparathyroidism and tumors of the pituitary and pancreas, often associated with gastric hypersecretion and peptic ulcer disease (Zollinger-Ellison syndrome). MEN 2A is characterized by pheochromocytoma and medullary carcinoma of the thyroid, as well as hyperparathyroidism; MEN 2B has additional associated fea­ tures such as multiple neuromas but usually lacks hyperparathyroid­ ism. MEN4, caused by mutations in the p27 cyclin-dependent kinase inhibitor (encoded for by CDKN1B), has similar clinical manifestations as MEN 1. Mutations in the MAX gene are associated with familial forms of pheochromocytoma/paraganglioma, and a few family mem­ bers have also been reported to have primary hyperparathyroidism. Each of these MEN syndromes is transmitted in an apparent autosomal dominant manner. The hyperparathyroidism jaw tumor (HPT-JT) syndrome occurs in families with parathyroid tumors (sometimes carcinomas) in asso­ ciation with benign jaw tumors. This disorder is caused by mutations in CDC73 (HRPT2), and mutations in this gene are also observed in sporadic parathyroid cancers. Some kindreds exhibit hereditary hyperparathyroidism without other endocrinopathies, which has been referred to as nonsyndromic familial isolated hyperparathyroidism (FIHP). In some of these familial cases, the disease co-segregated with heterozygous mutations in GCM2. Inactivating or dominant-negative mutations in this parathyroid-specific transcription factor had initially been identified in familial forms of hypoparathyroidism. However, GCM2 variants that are predicted to cause a gain-of-function of GCM2 have been reported in a subset of patients with FIHP. Because the prevalence of these GCM2 variants is much higher than the prevalence

of primary hyperparathyroidism, they might be a risk factor for devel­ oping the disease. Furthermore, there is speculation that some FIHP cases may be examples of variable expression of the other syndromes such as MEN 1, MEN 2, or the HPT-JT syndrome, but they may also have distinctive, still unidentified genetic causes.

Genetic Defects Associated with Hyperparathyroidism  As in many other types of neoplasia, two fundamental types of genetic defects have been identified in parathyroid gland tumors: (1) overac­ tivity of protooncogenes and (2) loss of function of tumor-suppressor genes. The former, by definition, can lead to uncontrolled cellular growth and function by activation (gain-of-function mutation) of a single allele of the responsible gene, whereas the latter requires loss of function of both allelic copies. Biallelic loss of function of a tumorsuppressor gene is usually characterized by a germline defect (all cells) of one allele (autosomal-dominant mode of inheritance) and an additional somatic deletion/mutation in the second allele of the tumor (Fig. 422-3). PART 12 Endocrinology and Metabolism Mutations in the MEN1 gene, which encodes the tumor suppressor MENIN, on chromosome 11q13 are responsible for causing MEN 1. Inheritance of one mutated allele in this hereditary syndrome, followed by loss of the other allele via somatic cell mutation, leads to monoclo­ nal expansion and tumor development. Also, in ~15–20% of sporadic parathyroid adenomas, both alleles of the MEN1 locus on chromosome 11 are somatically deleted, implying that the same defect responsible for MEN 1 can also cause the sporadic disease (Fig. 422-3A). Con­ sistent with the Knudson hypothesis for two-step neoplasia in certain inherited cancer syndromes (Chap. 76), the earlier onset of hyperpara­ thyroidism in the hereditary syndromes reflects the need for only one mutational event to trigger the monoclonal outgrowth. In sporadic adenomas, typically occurring later in life, two different somatic events must occur before the MEN1 gene is silenced. MEN 2 is an example for a mutation in a protooncogene and is asso­ ciated with gain-of-function mutations in the Ret oncogene. Chromosome 11 Somatic deletion/mutation of remaining normal allele Normal copy Mutant copy Clonal progenitor cell lacks functional gene product Mutant copy of putative tumor suppressor gene on 11q13 is inherited in MEN1 and present in all parathyroid cells Mutation of one allele of same gene may occur somatically in other patients, present in specific parathyroid cell(s) Chromosome 1 Somatic deletion/mutation of remaining normal allele Normal copy Mutant copy Clonal progenitor cell lacks functional HRPT2 gene product Somatic mutation of one copy of the HRPT2 tumor suppressor gene on 1q21–31 no adverse consequences to parathyroid cell A B FIGURE 422-3  A. Schematic diagram indicating molecular events in tumor susceptibility. The patient with the hereditary abnormality (multiple endocrine neoplasia [MEN]) is envisioned as having one defective gene inherited from the affected parent on chromosome 11, but one copy of the normal gene is present from the other parent. In the monoclonal tumor (benign tumor), a somatic event, here partial chromosomal deletion, removes the remaining normal gene from a cell. In nonhereditary tumors, two successive somatic mutations must occur, a process that takes a longer time. By either pathway, the cell, deprived of growth-regulating influence from this gene, has unregulated growth and becomes a tumor. A different genetic locus also involving loss of a tumor-suppressor gene termed HRPT2 is involved in the pathogenesis of parathyroid carcinoma. (Reproduced with permission from A Arnold: Genetic basis of endocrine disease 5. Molecular genetics of parathyroid gland neoplasia. J Clin Endocrinol Metab 77:1108, 1993.) B. Schematic illustration of the mechanism and consequences of gene rearrangement and overexpression of the PRAD1 protooncogene (pericentromeric inversion of chromosome 11) in parathyroid adenomas. The excessive expression of PRAD1 (a cell cycle control protein, cyclin D1) by the highly active PTH gene promoter in the parathyroid cell contributes to excess cellular proliferation. (Reproduced with permission from J Habener, in L DeGroot, JL Jameson (eds): Endocrinology, 4th ed. Philadelphia, PA: Saunders; 2001.)

A more complex pattern, still incompletely resolved, arises with genetic defects and carcinoma of the parathyroids. This appears to be due to biallelic loss of a functioning copy of a gene, CDC73 (or HRPT2), originally identified as the cause of the HPT-JT syndrome. Several inactivating mutations have been identified in CDC73 (located on chromosome 1q21-31), which encodes a 531-amino-acid protein called parafibromin. The discovery of the genetic mutations that lead to multiple endo­ crine neoplasias allows genetic testing of suspected probands and fam­ ily members. Benefits of genetic testing include the ability to verify the clinical diagnosis, identify affected family members, and rule out the genetic variant in family members, who seem to be unaffected. An important contribution from studies on the genetic origin of parathyroid carcinoma has been the realization that the mutations involve a different pathway than that involved with the benign gland enlargements. Unlike the pathogenesis of genetic alterations seen in colon cancer, where lesions evolve from benign adenomas to malignant disease by progressive genetic changes, the alterations commonly seen in most parathyroid cancers (HRPT2 mutations) are infrequently seen in sporadic parathyroid adenomas. Study of the parathyroid cancers found in some patients with the HPT-JT syndrome has led to identification of a much larger role for HRPT2 mutations in most parathyroid carcinomas, including those that arise sporadically, without apparent association with the HPT-JT syndrome. Mutations in the coding region have been identified in 75–80% of all parathyroid cancers analyzed, leading to the conclusion that, with addition of presumed mutations in the noncoding regions, this genetic defect may be seen in essentially all parathyroid carcino­ mas. Of special importance was the discovery that, in some sporadic parathyroid cancers, germline mutations have been found; this, in turn, has led to careful investigation of the families of these patients and a new clinical indication for genetic testing in this setting. Abnormalities at the Rb gene were the first to be noted in para­ thyroid cancer. The Rb gene, a tumor-suppressor gene located on Benign tumor PTH  Coding PTH   Coding PTH 5'   Regulatory Break Centromere PTH 5'   Regulatory Break PRAD1 PRAD1 Inverted Normal Parathyroid carcinoma

chromosome 13q14, was initially associated with retinoblastoma but has since been implicated in other neoplasias, including parathyroid carcinoma. Early studies implicated allelic deletions of the Rb gene in many parathyroid carcinomas and decreased or absent expression of the Rb protein. However, because there are often large deletions in chromosome 13 that include many genes in addition to the Rb locus (with similar findings in some pituitary carcinomas), it remains pos­ sible that other tumor-suppressor genes on chromosome 13 may be playing a role in parathyroid carcinoma. Overall, it seems there are multiple factors in parathyroid cancer, in addition to the HRPT2 and Rb gene, although the HRPT2 gene muta­ tion is the most invariant abnormality. RET encodes a tyrosine kinase type receptor; specific inherited germline mutations lead to a constitu­ tive activation of the receptor, thereby explaining the autosomal domi­ nant mode of transmission and the relatively early onset of neoplasia. In the MEN 2 syndrome, the RET protooncogene may be responsible for the earliest disorder detected, the polyclonal disorder C-cell hyper­ plasia, which then is transformed into a clonal outgrowth—a medul­ lary carcinoma with the participation of other, still uncharacterized genetic defects. In some parathyroid adenomas, activation of a protooncogene occurs (Fig. 422-3B). A reciprocal translocation involving chromo­ some 11 was identified as a somatic event that juxtaposes the PTH gene promoter upstream of CCND1, which encodes a cyclin D protein that plays a key role in normal cell division. This translocation plus other mechanisms that cause an equivalent overexpression of cyclin D1 are found in 20–40% of parathyroid adenomas. Mouse models have confirmed the role of several of the major iden­ tified genetic defects in parathyroid disease and the MEN syndromes. Loss of the MEN1 gene locus and overexpression of the CCND1 pro­ tooncogene or the mutated RET protooncogene have been analyzed by genetic manipulation in mice, with the expected onset of parathyroid tumors or medullary thyroid carcinoma, respectively. Pathology  Adenomas are most often located in the inferior para­ thyroid glands, but in 6–10% of patients, parathyroid adenomas may be located in the thymus, the thyroid, the pericardium, or behind the esophagus. Adenomas are usually 0.5–5 g in size but may be as large as 10–20 g (normal glands weigh 25 mg on average). Chief cells are pre­ dominant in both hyperplasia and adenoma. With chief cell hyperpla­ sia, the enlargement may be so asymmetric that some involved glands appear grossly normal. If generalized hyperplasia is present, however, histologic examination reveals a uniform pattern of chief cells and disappearance of fat even in the absence of an increase in gland weight. Thus, microscopic examination of biopsy specimens of several glands is essential to interpret findings at surgery. Parathyroid carcinoma is often not aggressive. Long-term survival without recurrence is common if at initial surgery the entire gland is removed without rupture of the capsule. Recurrent parathyroid carcinoma is usually slow growing with local spread in the neck, and surgical correction of recurrent disease may be feasible. Occasion­ ally, however, parathyroid carcinoma is more aggressive, with distant metastases (lung, liver, and bone) found at the time of initial operation. It may be difficult to appreciate initially that a primary tumor is carci­ noma; increased numbers of mitotic figures and increased fibrosis of the gland stroma may precede invasion. The diagnosis of carcinoma is often made in retrospect when metastasis occur. Hyperparathyroidism from a parathyroid carcinoma may be indistinguishable from other forms of primary hyperparathyroidism but is usually more severe clinically. A potential clue to the diagnosis is offered by the degree of calcium elevation. Calcium values of 3.5–3.7 mmol/L (14–15 mg/dL) are frequent with carcinoma and may alert the surgeon to remove the abnormal gland with care to avoid capsular rupture. Recent findings concerning the genetic basis of some patients with parathyroid carci­ noma (distinct from that of benign adenomas) indicate the need, in these kindreds, for family screening (see below). Signs and Symptoms  Many patients with primary hyperpara­ thyroidism are asymptomatic. Manifestations of hyperparathyroid­ ism involve primarily the kidneys and the skeletal system. Kidney

involvement, due either to deposition of calcium in the renal paren­ chyma or to recurrent nephrolithiasis, was present in 60–70% of patients prior to 1970. With earlier detection, renal complications occur in <20% of patients in many large series. Renal stones are usually composed of either calcium oxalate or calcium phosphate. In occa­ sional patients, repeated episodes of nephrolithiasis or the formation of large calculi may lead to urinary tract obstruction, infection, and loss of renal function. Nephrocalcinosis may also cause decreased renal function and phosphate retention.

The distinctive bone manifestation of hyperparathyroidism is osteitis fibrosa cystica, which occurred in 10–25% of patients in series reported 50 years ago. Histologically, the pathognomonic features are an increase in the giant multinucleated osteoclasts in scalloped areas on the surface of the bone (Howship’s lacunae) and a replacement of the normal cellular and marrow elements by fibrous tissue. Radiographic changes include resorption of the phalangeal tufts and replacement of the usually sharp cortical outline of the bone in the digits by an irregu­ lar outline (subperiosteal resorption). In recent years, osteitis fibrosa cystica is very rare in primary hyperparathyroidism, probably due to the earlier detection and therefore milder form of the disease. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 Dual-energy x-ray absorptiometry of the spine provides reproduc­ ible quantitative estimates (within a few percent) of spinal bone density. Similarly, bone density in the extremities can be quantified by densi­ tometry of the hip or of the distal radius at a site chosen to be primarily cortical. Computed tomography (CT) is a very sensitive technique for estimating spinal bone density, but reproducibility of standard CT is no better than 5%. Newer CT techniques (spiral, “extreme” CT) are more reproducible but are currently available in a limited number of medical centers and used for research purposes. Cortical bone density is reduced, while cancellous bone density, especially in the spine, is relatively preserved. In symptomatic patients, dysfunctions of the central nervous system (CNS), peripheral nerve and muscle, gastrointestinal tract, and joints also occur. It has been reported that severe neuropsychiatric manifesta­ tions may be reversed by parathyroidectomy. When present in symp­ tomatic patients, neuromuscular manifestations may include proximal muscle weakness, easy fatigability, and atrophy of muscles and may be so striking as to suggest a primary neuromuscular disorder. The distin­ guishing feature is the complete regression of neuromuscular disease after surgical correction of the hyperparathyroidism. Gastrointestinal manifestations are sometimes subtle and include vague abdominal complaints and disorders of the stomach and pan­ creas. Again, cause and effect are unclear. In MEN 1 patients with hyperparathyroidism, duodenal ulcer may be the result of associ­ ated pancreatic tumors that secrete excessive quantities of gastrin (Zollinger-Ellison syndrome). Pancreatitis has been reported in associ­ ation with hyperparathyroidism, but the incidence and the mechanism are not established. Much attention has been paid in recent years to the manifestations of and optimum management strategies for asymptomatic hyperpara­ thyroidism. This is now the most prevalent form of the disease. Asymp­ tomatic primary hyperparathyroidism is defined as biochemically confirmed hyperparathyroidism (elevated or inappropriately normal PTH levels despite hypercalcemia) with the absence of symptoms typi­ cally associated with more severe hyperparathyroidism and can occur with or without target organ involvement such as renal or bone disease. Five conferences on the topic have been held in the United States over the past two decades, with the most recent in 2022. The published proceedings provide guidelines for diagnosis and treatment of primary hyperparathyroidism. Issues of concern include the potential for cardiovascular dete­ rioration, the presence of subtle neuropsychiatric symptoms, and the longer-term status of skeletal integrity in patients not treated surgically. The current consensus is that medical monitoring rather than surgical correction of hyperparathyroidism may be justified in certain patients. The current recommendation is that patients who show mild disease, as defined by the meeting guidelines (Table 422-2), can be safely fol­ lowed under management guidelines (Table 422-3). There is, however, growing uncertainty about subtle disease manifestations and whether

TABLE 422-2  Guidelines for Surgery in Asymptomatic Primary Hyperparathyroidism PARAMETER GUIDELINE Serum calcium

1 mg/dL above normal Renal Creatinine clearance <60 mL/min 24-h urine for calcium >300 mg/d in men or >250 mg/d in women and increased stone risk by biochemical stone risk analysis Presence of nephrolithiasis or nephrocalcinosis by x-ray, ultrasound, or other imaging modalities Skeletal BMD by DXA: T score <–2.5 at any site Vertebral fracture by x-ray or VFA PART 12 Endocrinology and Metabolism Age <50 Abbreviations: BMD, bone mineral density; DXA, dual-energy x-ray absorptiometry; VFA, vertebral fracture assessment. Source: Data from JP Bilezikian et al: Evaluation and management of primary hyperparathyroidism: Summary statement and guidelines from the Fifth International Workshop. JBMR 37:2293, 2022. surgery is therefore indicated in most patients. Among the issues is the evidence of eventual (>8 years) deterioration in bone mineral density after a decade of relative stability. There is concern that this late-onset deterioration in bone density in nonoperated patients could contribute significantly to the well-known age-dependent fracture risk (osteopo­ rosis). Significant and sustained improvements in bone mineral density are seen after successful parathyroidectomy, and there is some evidence for reduction in fractures. Cardiovascular disease, including left ventricular hypertrophy, car­ diac functional defects, and endothelial dysfunction, has been reported as reversible in European patients with more severe symptomatic dis­ ease after surgery, leading to numerous studies of these cardiovascular features in those with milder disease. There are reports of endothelial dysfunction in patients with mild asymptomatic hyperparathyroidism, but the expert panels concluded that more observation is needed, espe­ cially regarding whether there is reversibility with surgery. A topic of considerable interest and some debate is assessment of neuropsychiatric status and health-related quality of life status in hyperparathyroid patients both before surgery and in response to parathyroidectomy. Several observational studies have suggested improvements in symptom score after surgery. Randomized studies of surgery versus observation, however, have yielded inconclusive results, especially regarding benefits of surgery. Many studies report that hyperparathyroidism is associated with increased neuropsychiatric symptoms, but it is not possible at present to determine which patients might improve after surgery. Diagnosis  The diagnosis is typically made by detecting an elevated or inappropriately normal immunoreactive PTH level in a patient with asymptomatic hypercalcemia (Fig. 422-4) (see “Differential Diagnosis: TABLE 422-3  Guidelines for Monitoring in Patients with Primary Hyperparathyroidism Who Do Not Undergo Parathyroidectomy PARAMETER GUIDELINE Serum calcium and 25OHD Annually Renal eGFR, annually; serum creatinine, annually. Abdominal imaging (x-ray, ultrasound, or CT), if clinically indicated. 24-h urine for calcium, if indicated Creatinine clearance Annually Skeletal DXA every 1–2 years (3 sites) (unless BMD is normal). X-ray or VFA of spine if clinically indicated (e.g., height loss, back pain) Abbreviations: BMD, bone mineral density; CT, computed tomography; DXA, dualenergy x-ray absorptiometry; eGFR, estimated glomerular filtration rate; VFA, vertebral fracture assessment. Source: Data from JP Bilezikian et al: Evaluation and management of primary hyperparathyroidism: Summary statement and guidelines from the Fifth International Workshop. JBMR 37:2293, 2022.

Hyperparathyroidism Hypercalcemia of malignancy Hypoparathyroidism

Parathyroid hormone 1–84 (pg/mL)

0 6

Calcium (mg/dL) FIGURE 422-4  Levels of immunoreactive parathyroid hormone (PTH) detected in patients with primary hyperparathyroidism, hypercalcemia of malignancy, and hypoparathyroidism. Boxed area represents the upper and normal limits of blood calcium and/or immunoreactive PTH. (Reproduced with permission from SR Nussbaum et al (eds): Endocrinology, 4th ed. Philadelphia, PA: Saunders; 2001.) Special Tests,” below). Serum phosphate is usually low but may be nor­ mal, especially if renal failure has developed. Several modifications in PTH assays have been introduced in efforts to improve their utility in light of information about metabolism of PTH (as discussed above). First-generation assays were based on dis­ placement of radiolabeled PTH from anti-PTH antibodies that often reacted with PTH fragments. Second-generation, double-antibody, or immunometric assays (one antibody that is usually directed against the carboxyl-terminal portion of intact PTH to capture the hormone and a second enzyme-labeled antibody that is usually directed against the amino-terminal portion of intact PTH) greatly improved the diagnostic discrimination of the tests by eliminating interference from circulating biologically inactive fragments, detected by the original first-generation assays. Third-generation assays, which detect even fewer inactive fragments, may be useful for clinical research studies as in management of chronic renal disease but have not replaced secondgeneration assays, which reliably help make the diagnosis of hypo- and hyperparathyroidism and differentiate this disease from other condi­ tions of hypo- and hypercalcemia TREATMENT Primary Hyperparathyroidism Surgical excision of the abnormal parathyroid tissue is the defini­ tive therapy for this disease. As noted above, medical surveillance without operation for patients with mild, asymptomatic disease is, however, still preferred by some physicians and patients, par­ ticularly when the patients are more elderly. Evidence favoring surgery, if medically feasible, is growing because of concerns about skeletal, cardiovascular, and neuropsychiatric disease, even in mild hyperparathyroidism. Two surgical approaches are generally practiced. The conven­ tional parathyroidectomy procedure is neck exploration with general anesthesia; however, an outpatient procedure with local anesthesia,

termed minimally invasive parathyroidectomy, is gaining traction though it has not yet replaced the traditional surgical approach. Parathyroid exploration is challenging and should be undertaken by a surgeon experienced in this procedure. Certain features, like multiple abnormal glands in familial cases along with presurgical identification of one enlarged gland using several different imaging methods, can assist in determining the surgical approach. However, some critical decisions regarding management can be made only during the operation. Preoperative imaging, such as neck ultrasounds, 99mTc sestamibi scans with single-photon emission CT (SPECT), C(11) choline PET/CT, and four-dimensional (4D) CT are used to predict the location of an abnormal gland. Intraoperative monitoring of PTH levels by rapid PTH immunoassays may be useful in guiding the surgery and a rapid fall (>50%) to normal levels of PTH is used in many centers to predict successful removal of the culprit gland(s). Multiple-gland hyperplasia, as predicted in familial cases, and reoperation pose more difficult questions of surgical management and increase the risk of developing permanent hypoparathyroid­ ism. Immediate transplantation of a portion of a removed, minced parathyroid gland into the muscles of the forearm is sometimes performed, with the view that surgical excision is easier from the ectopic site in the arm if there is recurrent hyperfunction. In a minority of cases, if no abnormal parathyroid glands are found in the neck, the issue of further exploration must be decided. There are documented cases of five or six parathyroid glands and of unusual locations for adenomas such as in the mediastinum. A decline in serum calcium often occurs within 24 h after suc­ cessful surgery; usually, blood calcium falls to low-normal values for 3–5 days until the remaining parathyroid tissue resumes full hormone secretion. Risk factors for acute postoperative hypocalce­ mia is undermineralized bone matrix leading to “hungry bone” and vitamin D deficiency. With unexpected hypocalcemia, coexistent hypomagnesemia should be considered, as it interferes with PTH secretion and impairs response to PTH (Chap. 421). Transient hypoparathyroidism can occur but typically resolves within days; protracted recovery over several months can occur. Patients are unlikely to develop permanent hypoparathyroidism (often defined as hypoparathyroidism that persists 12 months after surgery) if their PTH levels tested within 12–24 h after surgery are

15 pg/mL. Signs of hypocalcemia include symptoms such as muscle twitch­ ing, a general sense of anxiety, and positive Chvostek’s and Trous­ seau’s signs coupled with hypocalcemia. Therapy with oral calcium and sometimes low-dose calcitriol is often sufficient. Parenteral calcium therapy should be instituted when severe hypocalcemia is present. The rate and duration of IV therapy are determined by the severity of the symptoms and the response of the serum calcium to treatment. An infusion of 0.5–2 mg/kg per hour or 30–100 mL/h of a 1-mg/mL solution usually suffices to relieve symptoms. Usu­ ally, parenteral therapy is required for only a few days. If symptoms worsen or if parenteral calcium is needed for >2–3 days, therapy with a vitamin D analogue and/or oral calcium (2–4 g/d) should be started (see below). It is cost-effective to use calcitriol (doses of 0.5–1 μg/d) because of the rapidity of onset of effect and prompt cessation of action when stopped, in comparison to other forms of vitamin D. A rise in blood calcium after several months of treat­ ment with calcium and calcitriol may indicate restoration of para­ thyroid function to normal. It is also appropriate to monitor serum PTH serially to estimate gland function in such patients. If magnesium deficiency is present, it can complicate the postop­ erative course since significant magnesium deficiency impairs the secretion of PTH. Hypomagnesemia should be corrected whenever detected, typically with oral magnesium replacement, but paren­ teral repletion may be necessary. MEDICAL MANAGEMENT Medical monitoring rather than corrective surgery is still accept­ able, but it is clear that surgical intervention is the more frequently

There is no long-term experience regarding specific clinical outcomes such as fracture prevention, but it has been established that bisphosphonates increase bone mineral density significantly without changing serum calcium. Calcimimetics reduce PTH secre­ tion and thus lower serum calcium but do not affect bone mineral density (BMD). A Scandinavian randomized clinical trial of para­ thyroidectomy versus observation in patients with mild primary hyperparathyroidism revealed no differences in morbidity or mor­ tality after 10 years. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 ■ ■OTHER PARATHYROID CAUSES

OF HYPERCALCEMIA Lithium Therapy  Lithium, used in the management of bipolar depression and other psychiatric disorders, causes hypercalcemia in ~10% of treated patients. The hypercalcemia is dependent on con­ tinued lithium treatment, remitting and recurring when lithium is stopped and restarted. The parathyroid adenomas reported in some hypercalcemic patients with lithium therapy may reflect the presence of an independently occurring parathyroid tumor; a permanent effect of lithium on parathyroid gland growth need not be implicated as most patients have complete reversal of hypercalcemia when lithium is stopped. However, long-standing stimulation of parathyroid cell replication by lithium may predispose to development of adenomas (as is documented in secondary hyperparathyroidism and renal failure). At the levels achieved in blood in treated patients, lithium can be shown in vitro to shift the PTH secretion curve to the right in response to calcium; i.e., higher calcium levels are required to lower PTH secre­ tion, probably acting at the calcium sensor (see below). This effect can cause elevated PTH levels and consequent hypercalcemia in otherwise normal individuals. Cinacalcet has been used successfully in these patients. Fortunately, there are usually alternative medications for the underlying psychiatric illness. Parathyroid surgery should not be rec­ ommended unless hypercalcemia and elevated PTH levels persist after lithium is discontinued. ■ ■GENETIC DISORDERS CAUSING HYPERPARATHYROIDISM-LIKE SYNDROMES Familial Hypocalciuric Hypercalcemia  FHH (also called famil­ ial benign hypercalcemia) is inherited as an autosomal dominant trait. Affected individuals are discovered because of asymptomatic hypercal­ cemia. Most cases of FHH are caused by an inactivating heterozygous CaSR mutations; this disorder, designated as FHH type 1, leads to inappropriately normal or even increased PTH secretion. Other forms of FHH are caused either by heterozygous loss-of-function mutations in GNA11 (encoding Gα11), one of the signaling proteins at the CaSR (FHH2), or by heterozygous mutations in AP2S1 (FHH3). In FHH1, the primary defect is abnormal sensing of the blood cal­ cium by the parathyroid gland and renal tubule, causing inappropriate secretion of PTH and excessive reabsorption of calcium in the distal renal tubules. Many different inactivating CaSR mutations have been identified in patients with FHH1. These mutations lower the capacity of the sensor to bind calcium and the mutant receptors function as though blood calcium levels were low; thus, inappropriate secretion of PTH occurs from an otherwise normal gland. Approximately twothirds of patients with FHH have mutations within the protein-coding region of the CaSR gene (FHH1). Others have mutations in GNA11, the gene encoding the alpha-subunit of G11, a G-protein through which the CaSR signals (FHH2). These loss-of-function mutations have simi­ lar consequences to the loss-of-function mutations in the CaSR. FHH3 is caused by heterozygous mutations of the adaptor protein-2d subunit (AP2S1), which is a component of clathrin-coated vesicles, and critical in clathrin-mediated endocytosis. Since FHH is a life-long disease that cannot be cured by parathy­ roidectomy, it is critical to distinguish this rare disease from the more common primary hyperparathyroidism. One striking exception to the

FHH1, NSHPT Blomstrand’s lethal chondrodysplasia Jansen’s metaphyseal chondrodysplasia ADH1 Pseudohypoparathyroidism CaSR Ca2+ McCune-Albright syndrome PLC Gq/11 PART 12 Endocrinology and Metabolism PIP2 IP3
Gs PDE G ATP PTH/PTHrP receptor Proto-oncogenes and tumor-supressor genes PTH Transcription factors, e.g. GATA3, GCM2, FAM111A Gq/11 PTHrP Brachydactyly short stature PARATHYROID CELL FIGURE 422-5  Illustration of some genetic mutations that alter calcium metabolism by effects on the parathyroid cell or target cells of parathyroid hormone (PTH) action. Alterations in PTH production by the parathyroid cell can be caused by changes in the response to extracellular fluid calcium (Ca2+) that are detected by the calcium-sensing receptor (CaSR). Furthermore, PTH (or PTH-related peptide [PTHrP]) can show altered efficacy in target cells such as in proximal tubular cells, by altered function of its receptor (PTH/PTHrP receptor) or the signal transduction proteins, G proteins such as Gsα that is linked to adenylate cyclase (AC), the enzyme responsible for producing cyclic AMP (cAMP) (also illustrated are Gαq/Gα11, which activate an alternate pathway of receptor signal transmission involving the generation of inositol triphosphate [IP3] or diacylglycerol [DAG]). Heterozygous loss-of-function mutations in the CaSR cause familial benign hypocalciuric hypercalcemia (FBHH) and homozygous mutations (both alleles mutated) and neonatal severe hyperparathyroidism (NSHPT); heterozygous gain-of-function causes autosomal dominant hypercalciuric hypocalcemia (ADH1). Other defects in parathyroid cell function that occur at the level of gene regulation (oncogenes or tumor-suppressor genes) or transcription factors are discussed in the text. Blomstrand’s lethal chondrodysplasia is due to homozygous or compound heterozygous loss-of-function mutations in the PTH/PTHrP receptor, a neonatally lethal disorder, while pseudohypoparathyroidism involves inactivation at the level of the G proteins, specifically mutations that eliminate or reduce Gsα activity in the kidney (see text for details). Acrodysostosis can occur with (mutant regulatory subunit of PKA) or without hormonal resistance (mutant PDE4D or PDE3A). Jansen’s metaphyseal chondrodysplasia and McCune-Albright syndrome represent gain-of-function mutations in the PTH/PTHrP receptor and Gsα protein, respectively. rule against parathyroid surgery in this syndrome is the occurrence, usually in consanguineous marriages (due to the rarity of the gene mutation), of a homozygous or compound heterozygote state, result­ ing in severe impairment of CaSR function. In this condition, neonatal severe hypercalcemia, total parathyroidectomy is mandatory, but calci­ mimetics have been used as a temporary measure. Patients with FHH have lifelong hypercalcemia, which is typi­ cally mild and about 11 mg/dL. PTH values are often within normal laboratory range (which is inappropriate for hypercalcemia) or mildly elevated. Family history is often positive but can be negative because the patient has a de novo mutation or the penetrance of the disease is not 100%. Patients with primary hyperparathyroidism have <99% renal calcium reabsorption, whereas most patients with FHH have

99% reabsorption. The calcium–to–creatine clearance ratio (CCCR), determined on spot or 24-hour urine, can be used to help differentiate the two disorders, with the CCCR typically <0.01 in FHH and >0.02 in primary hyperparathyroidism. This distinction is far from perfect, and genetic testing is helpful in establishing the diagnosis. Panel testing for hypercalcemic disorders allows the simultaneous sequencing of all genes known to be implicated in hypercalcemia, including the genes causing FHH. Rare but well-documented cases of acquired hypocalciuric hypercal­ cemia are reported due to antibodies against the CaSR. They appear to be a complication of an underlying autoimmune disorder and respond to therapies directed against the underlying disorder. Jansen’s Disease  Activating mutations in the PTH/PTHrP recep­ tor (PTH1R) have been identified as the cause of this rare autosomal dominant syndrome. Because the mutations lead to constitutive activa­ tion of receptor function, one abnormal copy of the mutant receptor is sufficient to cause the disease, thereby accounting for its dominant mode of transmission. Besides often severe hypercalcemia, patients affected by Jansen’s disease have short-limbed dwarfism due to abnor­ mal regulation of chondrocyte maturation in the growth plates of the

cAMP AMP Acrodysostosis (with or without hormonal resistance) AC Catalytic subunit Regulatory subunit (PRKAR1A) Active PKA cAMP Cellular events, including HDAC4 activation C R R C C R R C Inactive PKA PIP2 IP3 + DAG Acrodysostosis with hormonal resistance PLC TARGET CELL (e.g. kidney, bone, or cartilage) bone that are formed through the endochondral process. In adult life, there are numerous abnormalities in bone, including multiple cystic resorptive areas resembling those seen in severe hyperparathyroidism. Hypercalcemia and hypophosphatemia with undetectable or low PTH levels are typically observed. The pathogenesis of the growth plate abnormalities in Jansen’s disease has been confirmed by transgenic experiments in which targeted expression of the mutant PTH/PTHrP receptor to the proliferating chondrocyte layer of growth plate emu­ lated several features of the human disorder. Other genetic mutations in the parathyroid gland or PTH target cells that affect Ca2+ metabolism are illustrated in Fig. 422-5. ■ ■MALIGNANCY-RELATED HYPERCALCEMIA Clinical Syndromes and Mechanisms of Hypercalcemia 

Hypercalcemia due to malignancy is common (occurring in as many as 20% of cancer patients, especially with certain types of tumors such as lung carcinoma), often severe and difficult to manage, and, typically easy to distinguish from primary hyperparathyroidism by a suppressed PTH. Although malignancy is usually clinically obvious or readily detectable by medical history, hypercalcemia can occasionally be due to an occult tumor. Three main mechanisms of hypercalcemia are operative in cancer hypercalcemia. Humoral hypercalcemia of malignancy (HHM) is caused by tumors producing and secreting PTHrP that causes a clinical picture similar to primary hyperparathyroidism with increased bone resorption and hypercalcemia. However, PTH is suppressed. Patients with HHM may have low to normal levels of 1,25(OH)2D, instead of elevated levels as in true hyperparathyroidism probably reflecting sub­ tle differences in the activation of the PTH1R by PTHrP versus PTH. Squamous cell carcinomas and renal, bladder, and colorectal cancer are examples of tumors that can cause HHM. Several different assays (single- or double-antibody, different epitopes) have been developed to detect PTHrP and do not cross-react with PTH. Most data indicate that

circulating PTHrP levels are undetectable or low in normal individuals except in pregnancy (high in human milk) and elevated in most cancer patients with the humoral syndrome. Alternatively, local osteolysis leading to release of cytokines (e.g., interleukin 1 and tumor necrosis factor) that activate osteoclasts occurs with hematologic malignancies such as leukemia, lymphoma, and mul­ tiple myeloma, but also with breast cancer. A third mechanism leading to malignancy-associated hypercalcemia is an increased production and blood level of 1,25(OH)2D, produced by abnormal lymphocytes or adjacent macrophages in lymphoma but also in ovarian dysgerminomas. The etiologic mechanisms in cancer hypercalcemia may be multiple, even in the same patient. For example, in breast carcinoma (metastatic to bone) and in a distinctive type of T-cell lymphoma/leukemia initi­ ated by human T-cell lymphotropic virus 1, hypercalcemia is caused by direct local lysis of bone as well as by a humoral mechanism involving excess production of PTHrP. Hyperparathyroidism has been reported to coexist with the humoral cancer syndrome, and rarely, ectopic hyperparathyroidism due to tumor elaboration of true PTH is reported. TREATMENT Malignancy-Related Hypercalcemia Treatment of the hypercalcemia of malignancy is first directed to control of tumor; reduction of tumor mass usually corrects hypercalcemia. If a patient has severe hypercalcemia yet has a good chance for effective tumor therapy, treatment of the hypercalcemia should be vigorous while awaiting the results of definitive therapy (see “General Approach to Hypercalcemic States” below). If hyper­ calcemia occurs in the late stages of a tumor that is resistant to antitumor therapy, the treatment of the hypercalcemia should be judicious as high calcium levels can have a mild sedating effect. Standard therapies for hypercalcemia (discussed below) are appli­ cable to patients with malignancy. ■ ■VITAMIN D–RELATED HYPERCALCEMIA Vitamin D–mediated hypercalcemia can be due to excessive inges­ tion of vitamin D analogues or abnormal metabolism of the vitamin. Abnormal metabolism of the vitamin is usually acquired in association with a widespread granulomatous disorder. Vitamin D metabolism is carefully regulated, particularly the activity of renal 1α-hydroxylase, the enzyme responsible for the production of 1,25(OH)2D

(Chap. 421). The regulation of 1α-hydroxylase in sites other than the renal tubule differs and lacks the negative feedback regulations; these phenomena may explain the occurrence of hypercalcemia secondary to excessive 1,25(OH)2D production in patients with sarcoidosis or lymphoma. Vitamin D Intoxication  Chronic ingestion of >10 times the normal physiologic requirement of vitamin D (amounts >10,000 U/d) is usually required to produce significant hypercalcemia in otherwise healthy individuals. The stated upper limit of safe dietary intake is 2000 U/d (50 μg/d) in adults because of concerns about potential toxic effects of cumulative supraphysiologic doses. These recommendations are now regarded as too restrictive, since some estimates are that, in elderly individuals in northern latitudes, ≥2000 U/d may be necessary to avoid vitamin D insufficiency. Hypercalcemia in vitamin D intoxication is due to an excessive bio­ logic action of the vitamin, perhaps the consequence of increased levels of 25(OH)D rather than merely increased levels of the active metabo­ lite 1,25(OH)2D (the latter may not be frankly elevated in vitamin D intoxication). These actions lead to both increased intestinal absorp­ tion of calcium and increased release of calcium from bone. 25(OH) D has definite, if low, biologic activity in the intestine and bone. The production of 25(OH)D is less tightly regulated than is the production of 1,25(OH)2D. Hence, concentrations of 25(OH)D can be elevated severalfold in patients with excess vitamin D intake.

The diagnosis is substantiated by documenting elevated levels of 25(OH)D >100 ng/mL. Hypercalcemia is usually controlled by restric­ tion of dietary calcium intake and appropriate attention to hydration. These measures, plus discontinuation of vitamin D, usually lead to resolution of hypercalcemia. However, because of the increased bone resorption caused by high levels of vitamin D, simple cessation of cal­ cium intake is often insufficient therapy. Further, 25(OH)D stores in fat may be substantial, and vitamin D intoxication may persist for weeks after vitamin D ingestion is terminated. Such patients are responsive to glucocorticoids, which in doses of 40–100 mg/d of prednisone or its equivalent, usually return serum calcium levels to normal over several days; severe intoxication may require intensive therapy.

Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 Sarcoidosis and Other Granulomatous Diseases  In patients with sarcoidosis and other granulomatous diseases, such as tuberculo­ sis and fungal infections, excess 1,25(OH)2D is synthesized in macro­ phages or other cells in the granulomas. Indeed, increased 1,25(OH)2D levels have been reported in anephric patients with sarcoidosis and hypercalcemia. Macrophages obtained from granulomatous tissue convert 25(OH)D to 1,25(OH)2D at an increased rate. There is a posi­ tive correlation in patients with sarcoidosis between 25(OH)D levels (reflecting vitamin D intake) and the circulating concentrations of 1,25(OH)2D, whereas normally, there is no increase in 1,25(OH)2D with increasing 25(OH)D levels due to multiple feedback controls on renal 1α-hydroxylase (Chap. 421). The usual regulation of active metabolite production by calcium and phosphate or by PTH does not operate in these patients. Instead, macrophages increase their produc­ tion of the vitamin D receptor and of the 1α-hydroxylase in response to tumor necrosis factor and other inflammatory stimuli. PTH levels are usually low and 1,25(OH)2D levels are elevated, but primary hyper­ parathyroidism and sarcoidosis may coexist in some patients. Management of the hypercalcemia can often be accomplished by avoiding excessive sunlight exposure and limiting vitamin D and cal­ cium intake. Presumably, however, the abnormal sensitivity to vitamin D and abnormal regulation of 1,25(OH)2D synthesis will persist as long as the disease is active. Alternatively, glucocorticoids in the equivalent of 100 mg/d of hydrocortisone or equivalent doses of glucocorticoids may help control hypercalcemia. Glucocorticoids appear to act by blocking excessive production of 1,25(OH)2D, as well as the response to it in target organs. Hypercalcemia of Infancy  Several variants of this rare abnor­ mality of calcium homeostasis are now known. For example, Williams’ syndrome is an autosomal dominant disorder characterized by multiple congenital development defects, including supravalvular aortic steno­ sis, intellectual disability, and an elfin facies, in association with hyper­ calcemia due to abnormal sensitivity to vitamin D. The hypercalcemia associated with the syndrome was first recognized in England, where it was thought, incorrectly, to be caused by the fortification of milk with vitamin D. The cardiac and developmental abnormalities were independently described, but the connection between these defects and hypercalcemia was not described until later. Levels of 1,25(OH)2D can be elevated, ranging from 46 to 120 nmol/L (150–500 pg/mL). The mechanism of the abnormal sensitivity to vitamin D and of the increased circulating levels of 1,25(OH)2D is still unclear. Studies suggest that genetic mutations involving microdeletions at the elastin locus and perhaps other genes on chromosome 7 may play a role in the pathogenesis. Another genetic cause of hypercalcemia that starts in infancy is 24-hydroxylase deficiency that impairs catabolism of 1,25(OH)2D caused by biallelic inactivating mutations in CYP24A1. Another rare cause of hypercalcemia involves mutation in the renal sodiumdependent phosphate transporters that lead to increased production of 1,25(OH)2D leading to hypercalcemia (NPT2a mutations lead to more severe hypercalcemia than NPT2c mutations). ■ ■HIGH-BONE-TURNOVER STATES Hyperthyroidism  As many as 20% of hyperthyroid patients have high-normal or mildly elevated serum calcium concentrations;

hypercalciuria is even more common. The hypercalcemia is due to increased bone turnover, with bone resorption exceeding bone forma­ tion. Usually, the diagnosis is obvious, but signs of hyperthyroidism may occasionally be occult, particularly in the elderly (Chap. 396). Hypercalcemia is managed by treatment of the hyperthyroidism.

Immobilization  Immobilization is a rare cause of hypercalcemia in adults in the absence of an associated disease but may cause hyper­ calcemia in children and adolescents, particularly after spinal cord injury and paraplegia or quadriplegia. With resumption of ambulation, the hypercalcemia in children usually returns to normal. The mechanism appears to involve a disproportion between bone formation and bone resorption; the former decreased and the latter increased. Hypercalciuria and increased mobilization of skeletal cal­ cium can develop in normal volunteers subjected to extensive bed rest, although hypercalcemia is unusual. Immobilization of an adult with a disease associated with high bone turnover, however, such as Paget’s disease, may cause hypercalcemia. PART 12 Endocrinology and Metabolism Thiazides  Administration of thiazides can cause hypercalcemia in patients with high rates of bone turnover. Commonly, thiazides are associated with aggravation of hypercalcemia in primary hyperparathy­ roidism, but this effect can be seen in other high-bone-turnover states as well. The mechanism of thiazide action is complex. Chronic thiazide administration leads to reduction in urinary calcium; the hypocalciuric effect appears to reflect the enhancement of proximal tubular resorp­ tion of sodium and calcium in response to sodium depletion. Some of this renal effect is due to augmentation of PTH action and is more pronounced in individuals with intact PTH secretion. However, thia­ zides cause hypocalciuria in hypoparathyroid patients if sodium intake is restricted. This finding is the rationale for the use of thiazides as an adjunct to therapy in hypoparathyroid patients, as discussed below. Thi­ azide administration to normal individuals causes a transient increase in blood calcium (usually within the high-normal range) that reverts to preexisting levels after a week or more of continued administration. If hormonal function and calcium and bone metabolism are normal, homeostatic controls are reset to counteract the mild calcium-elevating effect of the thiazides. In the presence of hyperparathyroidism or increased bone turnover from another cause, homeostatic mechanisms are ineffective. The abnormal effects of the thiazide on calcium metabo­ lism disappear within days of cessation of the drug. Vitamin A Intoxication  Vitamin A intoxication is a rare cause of hypercalcemia and is most commonly a side effect of dietary faddism (Chap. 344). Calcium levels can be elevated into the 3- to 3.5-mmol/L (12–14 mg/dL) range after the ingestion of 50,000–100,000 units of vitamin A daily (10–20 times the minimum daily requirement). Typi­ cal features of severe hypercalcemia include fatigue, anorexia, and, in some, severe muscle and bone pain. Excess vitamin A intake is pre­ sumed to increase bone resorption. The diagnosis can be established by history and by measurement of vitamin A levels in serum. Diagnostic challenges may arise in CKD where mildly elevated vitamin A levels are often seen with no asso­ ciation to hypercalcemia. Occasionally, skeletal x-rays reveal periosteal calcifications, particularly in the hands. Withdrawal of the vitamin is usually associated with prompt disappearance of the hypercalcemia and reversal of the skeletal changes. As in vitamin D intoxication, administration of 100 mg/d hydrocortisone or its equivalent leads to a rapid return of the serum calcium to normal. ■ ■HYPERCALCEMIA ASSOCIATED WITH

CHRONIC KIDNEY DISEASE The pathogenesis of secondary hyperparathyroidism in CKD is mul­ tifactorial and includes resistance to PTH and an increase in FGF23, which, in turn, inhibits the renal 1a-hydroxylase, thus reducing 1,25(OH)2D levels and leading to further increases of PTH. Occasional patients develop severe manifestations of secondary hyperparathyroidism, including hypercalcemia, pruritus, extraskeletal calcifications, and painful bones, despite aggressive medical efforts to suppress the hyperparathyroidism. It is now recognized that a

true clonal outgrowth (irreversible) can arise in long-standing, inad­ equately treated CKD. PTH hypersecretion no longer responsive to medical therapy, a state of severe hyperparathyroidism in patients with CKD that requires surgery, has been referred to as tertiary hyperparathyroidism. TREATMENT Hypercalcemia in Tertiary Hyperparathyroidism Medical therapy to reverse secondary hyperparathyroidism in CKD includes reduction of excessive blood phosphate by restriction of dietary phosphate, the use of nonabsorbable phosphate binders, and careful, selective addition of calcitriol (0.25–2 μg/d) or related analogues. Calcium carbonate became preferred over aluminumcontaining antacids to prevent aluminum-induced bone disease. However, synthetic gels that also bind phosphate (such as sevelamer; Chap. 322) are now widely used, with the advantage of avoiding not only aluminum retention but also excess calcium loading, which may contribute to cardiovascular calcifications. Intravenous cal­ citriol (or related analogues), administered as several pulses each week, helps control secondary hyperparathyroidism. Aggressive but carefully administered medical therapy can often, but not always, reverse hyperparathyroidism and its symptoms and manifestations. Parathyroid surgery is necessary to control tertiary hyperpara­ thyroidism. Based on genetic evidence from examination of tumor samples in these patients, the emergence of autonomous parathy­ roid function is due to a monoclonal outgrowth of one or more previously hyperplastic parathyroid glands. The adaptive response has become an independent contributor to disease; this finding seems to emphasize the importance of optimal medical manage­ ment to reduce the proliferative response of the parathyroid cells that enables the irreversible genetic change. ■ ■OTHER CAUSES OF HYPERCALCEMIA Aluminum Intoxication  Aluminum intoxication (and often hypercalcemia as a complication of medical treatment) in the past occurred in patients on chronic dialysis; manifestations included acute dementia and unresponsive and severe osteomalacia. Bone pain, multiple nonhealing fractures, particularly of the ribs and pelvis, and a proximal myopathy occur. Hypercalcemia develops when these patients are treated with vitamin D or calcitriol because of impaired skeletal responsiveness. Aluminum is present at the site of osteoid min­ eralization, osteoblastic activity is minimal, and calcium incorporation into the skeleton is impaired. The disorder is now rare because of the avoidance of aluminum-containing antacids or aluminum excess in the dialysis regimen. Milk-Alkali Syndrome  The milk-alkali syndrome is due to exces­ sive ingestion of calcium and absorbable antacids such as milk or cal­ cium carbonate. It is much less frequent since proton pump inhibitors and other treatments became available for peptic ulcer disease. For a time, the increased use of calcium carbonate in the management of secondary hyperparathyroidism led to reappearance of the syndrome. Several clinical presentations—acute, subacute, and chronic—have been described, all of which feature hypercalcemia, alkalosis, and renal failure. The chronic form of the disease, termed Burnett’s syndrome, is associated with irreversible renal damage. The acute syndromes reverse if the excess calcium and absorbable alkali are stopped. Individual susceptibility is important in the pathogenesis, as some patients are treated with calcium carbonate and alkali regimens with­ out developing the syndrome. One variable is the fractional calcium absorption as a function of calcium intake. Some individuals absorb a high fraction of calcium, even with intakes ≥2 g of elemental calcium per day, instead of reducing calcium absorption with high intake, as occurs in most normal individuals. Resultant mild hypercalcemia after meals in such patients is postulated to contribute to the generation of alkalosis. Development of hypercalcemia causes increased sodium excretion and some depletion of total-body water. These phenomena

and perhaps some suppression of endogenous PTH secretion due to mild hypercalcemia lead to increased bicarbonate resorption and to alkalosis in the face of continued calcium carbonate ingestion. Alkalo­ sis per se selectively enhances calcium resorption in the distal nephron, thus aggravating the hypercalcemia. The cycle of mild hypercalcemia → bicarbonate retention → alkalosis → renal calcium retention → severe hypercalcemia perpetuates and aggravates hypercalcemia and alkalosis as long as calcium and absorbable alkali are ingested. ■ ■DIFFERENTIAL DIAGNOSIS OF HYPERCALCEMIA Differential diagnosis of hypercalcemia is best achieved by using clinical criteria, but immunometric assays to measure PTH are especially useful in distinguishing among major causes (Fig. 422-6). The clinical features that deserve emphasis are the presence or absence of symptoms or signs of disease and evidence of chronicity. If one discounts fatigue or depression, >90% of patients with primary hyperparathyroidism have asymptomatic hypercalcemia; symptoms of malignancy are usually present in cancer-associated hypercalcemia. Disorders other than hyperparathyroidism and malignancy cause <10% of cases of hypercalcemia, and some of the nonparathyroid causes are associated with clear-cut manifestations such as renal failure. Hyperparathyroidism is the likely diagnosis in patients with chronic hypercalcemia. If hypercalcemia has been manifesting for >1 year, malignancy as the underlying cause is very unlikely. A striking feature of malignancy-associated hypercalcemia is the rapidity of the course, whereby signs and symptoms of the underlying malignancy are evident within months of the detection of hypercalcemia. Although clinical considerations are helpful in arriving at the correct diagnosis of the cause of hypercalcemia, appropriate laboratory testing is essential for definitive diagnosis. The immunoassay for PTH usually separates primary hyperparathyroidism from all other causes of hypercalce­ mia (exceptions are very rare reports of ectopic production of excess PTH by nonparathyroid tumors). Patients with hyperparathyroidism have elevated (or nonsuppressed) PTH levels despite hypercalcemia, whereas patients with malignancy and the other causes of hyper­ calcemia (except for disorders mediated by PTH such as lithiuminduced hypercalcemia) have very low or undetectable levels. Intact PTH assays, based on the double-antibody method for PTH, exhibit very high sensitivity (especially if serum calcium is simultaneously Hypercalcemia Acute (or unknown) duration Chronic duration (months) PTH high PTH high PTH low PTH low 1˚ Hyperpara- thyroidism Consider MEN syndromes Consider malignancy PTHrP assay Clinical evaluation FIGURE 422-6  Algorithm for the evaluation of patients with hypercalcemia. PTH levels (high or low) should be interpreted in the context of serum calcium levels, as they may be inappropriately high or low for the level of serum calcium. See text for details. FHH, familial hypocalciuric hypercalcemia; MEN, multiple endocrine neoplasia; PTH, parathyroid hormone; PTHrP, parathyroid hormone–related peptide; Vit, vitamin.

evaluated) and specificity for the diagnosis of primary hyperparathy­ roidism (Fig. 422-4).

In summary, PTH values are elevated in >90% of parathyroid-related causes of hypercalcemia, undetectable or low in malignancy-related, vitamin D–related and high-bone-turnover causes of hypercalcemia. In view of the specificity of the PTH immunoassay and the high frequency of hyperparathyroidism in hypercalcemic patients, it is cost-effective to measure the PTH level in all hypercalcemic patients unless malignancy or a specific nonparathyroid disease is obvious. False-positive PTH assay results are rare but can be due to heterotopic antibodies. Immunoassays for PTHrP are helpful in diagnosing cer­ tain types of malignancy-associated hypercalcemia. Although FHH is parathyroid-related, the disease should be managed distinctively from primary hyperparathyroidism. Clinical features, family history, and the low urinary calcium excretion can help make the distinction, and genetic testing confirms the diagnosis. Because the incidence of malignancy and hyperparathyroidism both increase with age, they can coexist as two independent causes of hypercalcemia. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 1,25(OH)2D levels are in the upper range of normal or frankly ele­ vated in many (but not all) patients with primary hyperparathyroidism. In other disorders associated with hypercalcemia, concentrations of 1,25(OH)2D are low or, at the most, normal. However, this test is of low specificity and is not cost-effective, as not all patients with hyperpara­ thyroidism have elevated 1,25(OH)2D levels and not all nonparathyroid hypercalcemic patients have suppressed 1,25(OH)2D. Measurement of 1,25(OH)2D is, however, critically valuable in establishing the cause of hypercalcemia in sarcoidosis and certain lymphomas. A useful general approach is outlined in Fig. 422-6. If the patient is asymptomatic and there is evidence of chronicity to the hypercalcemia, hyperparathyroidism is likely the cause and FHH needs to be excluded. If PTH levels (usually measured at least twice) are elevated, the clinical impression is confirmed, and little additional diagnostic evaluation is necessary. If there is only a short history or no data as to the duration of the hypercalcemia, occult malignancy must be considered; if the PTH levels are suppressed then a thorough workup must be undertaken for malignancy, which may include chest x-ray, CT of chest and abdomen, and bone scan. Immunoassays for PTHrP may be especially useful in such situations. Attention should also be paid to clues for underlying hematologic disorders such as anemia, increased plasma globulin, and abnormal serum immunoelectrophoresis; bone scans can be negative Key historical considerations • Confirm if ↑Ca2+ chronic • Clues from history and physical findings Screen negative Other causes Granulomatous disease FHH Milk-alkali syndrome Medications (lithium, thiazides) Immobilization Vit D or Vit A intoxication Adrenal insufficiency Hyperthyroidism Hyperpara- thyroidism or MEN syndromes (consider FHH)

in some patients with metastases such as in multiple myeloma. Finally, if a patient with chronic hypercalcemia is asymptomatic and malig­ nancy therefore seems unlikely on clinical grounds, but PTH values are not elevated, it is useful to search for other chronic causes of hypercalcemia such as occult sarcoidosis. A careful history of dietary supplements and drug use may suggest intoxication with vitamin D or vitamin A or the use of thiazides.

TREATMENT General Approach to Hypercalcemic States PART 12 Endocrinology and Metabolism The approach to medical treatment of hypercalcemia varies with its severity. Mild hypercalcemia, <3 mmol/L (12 mg/dL), can usually be managed by hydration. More severe hypercalcemia (levels of 3.2–3.7 mmol/L [13–15 mg/dL]) must be managed more aggres­ sively; above that level, hypercalcemia can be life-threatening and requires emergency measures (Table 422-4). By using a combina­ tion of approaches in severe hypercalcemia, the serum calcium concentration can be decreased within 24–48 h in most patients, enough to relieve acute symptoms, prevent death from hypercalce­ mic crisis, and permit diagnostic evaluation. Therapy can then be directed at the underlying disorder—the second priority. Hypercalcemia develops because of excessive skeletal calcium release, increased intestinal calcium absorption, or inadequate renal calcium excretion. Understanding the particular pathogen­ esis helps guide therapy. For example, hypercalcemia in patients with malignancy is primarily due to excessive skeletal calcium release and is, therefore, minimally improved by restriction of dietary calcium. On the other hand, patients with vitamin D hypersensitivity or vitamin D intoxication have excessive intestinal calcium absorption, and restriction of dietary calcium is beneficial. Decreased renal function or ECF depletion decreases urinary cal­ cium excretion. In such situations, rehydration may rapidly reduce or reverse the hypercalcemia, even though increased bone resorp­ tion persists. As outlined below, the more severe the hypercalcemia, the greater the need for a combination of therapies. Rapid-acting (hours) approaches—rehydration, forced diuresis, and calcitonin— can be used with the most effective antiresorptive agents such TABLE 422-4  Therapies for Severe Hypercalcemia ONSET OF ACTION DURATION OF ACTION ADVANTAGES DISADVANTAGES TREATMENT Most Useful Therapies IV hydration with normal saline Hours During infusion Rehydration invariably needed Volume overload Forced diuresis; normal saline plus loop diuretic Hours During treatment Rapid action Volume overload, cardiac decompensation, intensive monitoring, electrolyte disturbance, inconvenience Pamidronate 1–2 days 10–14 days to weeks High potency; intermediate onset of action Zoledronate 1–2 days

3 weeks Same as for pamidronate (lasts longer) Denosumab 1–2 days 3 weeks Strongest antiresorptive Occasional severe hypocalcemia, rarely jaw necrosis, skin infections Special Use Therapies     Calcitonin Hours 1–2 days Rapid onset of action; useful as adjunct in severe hypercalcemia Phosphate oral 24 h During use Chronic management (with hypophosphatemia); low toxicity if P <4 mg/dL Glucocorticoids Days Days, weeks Oral therapy, antitumor agent Active only in certain malignancies, vitamin D excess, and sarcoidosis; glucocorticoid side effects Dialysis Hours During use and 24–48 h afterward Source: Data from JP Bilezikian et al: Evaluation and management of primary hyperparathyroidism: Summary statement and guidelines from the Fifth International Workshop. JBMR 37:2293, 2022.

as bisphosphonates (since severe hypercalcemia usually involves excessive bone resorption). HYDRATION, INCREASED SALT INTAKE, AND MILD

AND FORCED DIURESIS The first principle of treatment is to restore normal hydration. Many hypercalcemic patients are dehydrated because of vomiting, inanition, and/or hypercalcemia-induced defects in urinary con­ centrating ability. The resultant drop in glomerular filtration rate is accompanied by an additional decrease in renal tubular sodium and calcium clearance. Restoring a normal ECF volume corrects these abnormalities and increases urine calcium excretion by 2.5–7.5 mmol/d (100–300 mg/d). Increasing urinary sodium excretion to 400–500 mmol/d increases urinary calcium excretion even further than simple rehydration. After rehydration has been achieved, saline can be administered, or furosemide or ethacrynic acid can be given to depress the tubular reabsorptive mechanism for cal­ cium (care must be taken to prevent dehydration). The combined use of these therapies can increase urinary calcium excretion to

≥12.5 mmol/d (500 mg/d) in most hypercalcemic patients. Since this is a substantial percentage of the exchangeable calcium pool, the serum calcium concentration usually falls 0.25–0.75 mmol/L (1–3 mg/dL) within 24 h. Precautions should be taken to prevent potassium and magnesium depletion; calcium-containing renal calculi are a potential complication. Under life-threatening circumstances, the preceding approach can be pursued more aggressively, but the availability of effective agents to block bone resorption (such as bisphosphonates) has reduced the need for extreme diuresis regimens (Table 422-4). Depletion of potassium and magnesium is inevitable unless replace­ ments are given; pulmonary edema can be precipitated. The poten­ tial complications can be reduced by careful monitoring of central venous pressure and plasma or urine electrolytes; catheterization of the bladder may be necessary. Dialysis treatment may be needed when renal function is compromised. BISPHOSPHONATES The bisphosphonates are analogues of pyrophosphate, with high affinity for bone, especially in areas of increased bone turnover, Fever in 20%, hypophosphatemia, hypocalcemia, hypomagnesemia, rarely jaw necrosis Same as pamidronate above Rapid tachyphylaxis Limited use except as adjuvant or chronic therapy Useful in renal failure; onset of effect in hours; can immediately reverse life-threatening hypercalcemia Complex procedure, reserved for extreme or special circumstances

where they are powerful inhibitors of bone resorption. These boneseeking compounds are stable in vivo because phosphatase enzymes cannot hydrolyze the central carbon-phosphorus-carbon bond. The bisphosphonates are concentrated in areas of high bone turnover and are taken up by and inhibit osteoclast action; the mechanism of action is complex. The bisphosphonate molecules that contain amino groups in the side chain structure (see below) interfere with prenylation of proteins and can lead to cellular apoptosis. The highly active non-amino-group–containing bisphosphonates are also metabolized to cytotoxic products. A number of second- or third-generation compounds have become the mainstays of antiresorptive therapy for treatment of hypercalcemia and osteoporosis. The newer bisphosphonates have a highly favorable ratio of blocking resorption versus inhibiting bone formation; they inhibit osteoclast-mediated skeletal resorption yet do not cause mineralization defects at ordinary doses. Though the bisphosphonates have similar structures, the routes of administra­ tion, efficacy, toxicity, and side effects vary. Compounds commonly used are pamidronate, alendronate, and zoledronate. The IV use of pamidronate and zoledronate is approved for the treatment of hypercalcemia; between 30 and 90 mg pamidronate, given as a single IV dose over a few hours, returns serum calcium to normal within 24–48 h with an effect that lasts for weeks in 80–100% of patients. Zoledronate given as an infusion in doses of 5 mg has a more rapid and more sustained effect that lasts longer than pami­ dronate in direct comparison. These drugs are used extensively in cancer patients. Absolute survival improvements are noted with pamidronate and zoledronate in multiple myeloma, for example. However, though rare, osteone­ crosis of the jaw, especially after dental surgery, mainly in cancer patients treated with multiple doses of the more potent bisphospho­ nates, and atypical femoral fractures are potential side effects. DENOSUMAB Denosumab is the most recent antiresorptive therapy to be approved for the treatment of hypercalcemia, a monoclonal antibody that binds to RANK ligand (RANKL) and prevents it from binding to the receptor RANK on osteoclast precursors and mature osteo­ clasts. The inhibition of differentiation, activation, and function of osteoclasts leads to a reduction in bone resorption. It has a pro­ found suppressive effect on biochemical markers of bone resorption and is the most powerful antiresorptive agent currently available. Repeated doses of denosumab, 120 mg given subcutaneously, may be effective in patients with hypercalcemia of malignancy who are not controlled by bisphosphonates. There are currently uncertain­ ties how to manage rebound effects (fractures, hypercalcemia) after stopping denosumab, but antiresorptives such as alendronate and zoledronic acid can mitigate these effects. OTHER THERAPIES Calcitonin acts within a few hours of its administration, princi­ pally through receptors on osteoclasts, to block bone resorption. Calcitonin, after 24–48 h of use, is no longer effective in lowering calcium. Tachyphylaxis, a known phenomenon with this drug, seems to explain the results since the drug is initially often effective. Therefore, in life-threatening hypercalcemia, calcitonin can be used effectively within the first 24–48 h in combination with rehydra­ tion and saline diuresis while waiting for more sustained effects from simultaneously administered antiresorptives. Usual doses of calcitonin are 2–8 U/kg of body weight IV, SC, or IM every 6–12 h. Glucocorticoids have utility, especially in hypercalcemia compli­ cating certain malignancies. They increase urinary calcium excre­ tion and decrease intestinal calcium absorption when given in pharmacologic doses, but they also cause negative skeletal calcium balance. In normal individuals and in patients with primary hyper­ parathyroidism, glucocorticoids neither increase nor decrease the serum calcium concentration. In patients with hypercalcemia due to certain osteolytic malignancies, however, glucocorticoids may be effective as a result of antitumor effects. The malignancies in

which hypercalcemia responds to glucocorticoids include mul­ tiple myeloma, leukemia, Hodgkin’s disease, other lymphomas, and carcinoma of the breast, at least early in the course of the disease. Glucocorticoids are also effective in treating hypercalcemia due to vitamin D intoxication and sarcoidosis. Glucocorticoids are also useful in the rare form of hypercalcemia, now recognized in certain autoimmune disorders in which inactivating antibodies against the receptor imitate FHH. Elevated PTH and calcium levels are effec­ tively lowered by the glucocorticoids. In all the preceding situations, the hypocalcemic effect develops over several days, and the usual glucocorticoid dosage is 40–100 mg prednisone (or its equivalent) daily in divided doses. The side effects of chronic glucocorticoid therapy may be acceptable in some circumstances.

Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 For patients with hypercalcemia due to CYP24A1 mutations, avoidance of sun, vitamin D intake, and reducing calcium intake are recommended. Fluconazole and ketoconazole, inhibitors of CYP27B1, and rifampin (an inducer of CYP3A4) have been reported to be beneficial; particular attention should be given to potential side effects of each of these medications. Dialysis is often the treatment of choice for severe hypercalcemia complicated by renal failure, which is difficult to manage medi­ cally. Peritoneal dialysis with calcium-free dialysis fluid can remove 5–12.5 mmol (200–500 mg) of calcium in 24–48 h and lower the serum calcium concentration by 0.7–2.2 mmol/L (3–9 mg/dL). Large quantities of phosphate are lost during dialysis, and serum inorganic phosphate concentration usually falls, potentially aggra­ vating hypercalcemia. Therefore, the serum inorganic phosphate concentration should be measured after dialysis, and phosphate sup­ plements should be added to the diet or to dialysis fluids if necessary. Phosphate therapy, PO or IV, has a limited role in certain cir­ cumstances (Chap. 421). Correcting hypophosphatemia lowers the serum calcium concentration by several mechanisms, includ­ ing bone/calcium exchange. The usual oral treatment is 1–1.5 g phosphorus per day for several days, given in divided doses. It is generally believed, but not established, that toxicity does not occur if therapy is limited to restoring serum inorganic phosphate con­ centrations to normal. Raising the serum inorganic phosphate concentration above nor­ mal decreases serum calcium levels, sometimes strikingly. Intrave­ nous phosphate is one of the most dramatically effective treatments available for severe hypercalcemia but is toxic and even dangerous (fatal hypocalcemia). For these reasons, it is used rarely and only in severely hypercalcemic patients with cardiac or renal failure where dialysis, the preferable alternative, is not feasible or is unavailable. SUMMARY The various therapies for hypercalcemia are listed in Table 422-4. The choice depends on the underlying disease, the severity of the hypercalcemia, the serum inorganic phosphate level, and the renal, hepatic, and bone marrow function. Mild hypercalcemia (≤3 mmol/L [12 mg/dL]) can usually be managed by hydration. Severe hyper­ calcemia (≥3.7 mmol/L [15 mg/dL]) requires rapid correction. IV pamidronate or zoledronate or subcutaneous denosumab should be administered. In addition, for the first 24–48 h, aggressive sodium-calcium diuresis with IV saline should be given. Following rehydration, furosemide or ethacrynic acid can be added, but only if appropriate monitoring is available and cardiac and renal function are adequate. For intermediate degrees of hypercalcemia between 3 and 3.7 mmol/L (12 and 15 mg/dL), vigorous hydration is recom­ mended. Depending on symptoms and underlying causes, this may be combined with antiresorptives and other previously mentioned treatments. ■ ■HYPOCALCEMIA (See also Chap. 57). Pathophysiology  Chronic hypocalcemia is less common than hyper­ calcemia; causes include CKD, hereditary and acquired hypoparathy­ roidism, vitamin D deficiency, PTH resistance, and hypomagnesemia.

Acute rather than chronic hypocalcemia is seen in critically ill patients or as a consequence of certain medications and often does not require specific treatment. Transient hypocalcemia is seen with severe sepsis, burns, acute kidney injury, and extensive transfusions with citrated blood. Although as many as one-half of patients in an intensive care setting are reported to have calcium concentrations of <2.1 mmol/L (8.5 mg/dL), most do not have a reduction in ionized calcium. Patients with severe sepsis may have a decrease in ionized calcium (true hypocalcemia), but in other severely ill individuals, hypoalbuminemia is the primary cause of the reduced total calcium concentration. Alkalosis increases calcium binding to proteins.

Medications such as protamine, heparin, and glucagon may cause transient hypocalcemia. These forms of hypocalcemia are usually not associated with tetany and resolve with improvement in the overall medical condition. The hypocalcemia after repeated transfusions of citrated blood usually resolves quickly. PART 12 Endocrinology and Metabolism Patients with acute pancreatitis have hypocalcemia that persists dur­ ing the acute inflammation and varies in degree with disease severity. The cause of hypocalcemia remains unclear but may include saponifi­ cation and systemic inflammation. PTH values are reported to be low, normal, or elevated, and both resistance to PTH and impaired PTH secretion have been postulated. Chronic hypocalcemia, however, is usually symptomatic and requires treatment. Neuromuscular and neurologic manifestations of chronic hypocalcemia include tingling, muscle spasms, carpopedal spasm, and, in extreme cases, laryngeal spasm and convulsions. Increased intracranial pressure occurs in some patients with longstanding hypocalcemia, often in association with papilledema. Mental changes include irritability, depression, and psychosis. The QT interval on the electrocardiogram is prolonged, in contrast to its shortening with hypercalcemia. Arrhythmias occur, and digitalis effectiveness may be reduced. Intestinal cramps and chronic malabsorption may occur. Chvostek’s or Trousseau’s sign can be used to confirm latent tetany; the latter is more specific and sensitive for hypocalcemia. Classification of Hypocalcemia  The classification of hypocalce­ mia shown in Table 422-5 is based on an organizationally useful prem­ ise that hypocalcemia may be primarily due to one of the two main calcium-regulating hormones, PTH and vitamin D, or other causes. PTH-related  Hereditary or acquired forms of hypoparathyroidism have a number of common components. The disease is rare with esti­ mates from all causes to be ~25–35 patients/100,000 of the population (based on U.S. and Danish estimates). Symptoms of untreated hypo­ calcemia are shared by both types of hypoparathyroidism, although the onset of hereditary hypoparathyroidism can be more gradual and associated with other developmental defects. Basal ganglia calcification and extrapyramidal syndromes are more common and earlier in onset in hereditary hypoparathyroidism. Acquired hypoparathyroidism sec­ ondary to surgery in the neck is the most common cause of hypopara­ thyroidism, but the frequency of surgically induced parathyroid failure has diminished as a result of improved surgical techniques that spare the parathyroid glands and increased use of nonsurgical therapy for hyperthyroidism. PHP, an example of resistance to PTH action rather than a failure of production by the parathyroid gland, may share several features with hypoparathyroidism, including extraosseous calcification and extrapyramidal manifestations such as choreoathetotic movements and dystonia but circulating PTH is increased rather than decreased in the other conditions. Papilledema, raised intracranial pressure, and lenticular cataracts may occur in both hereditary and acquired hypoparathyroidism, as do chronic changes in fingernails and hair, the latter usually reversible with treatment of hypocalcemia. Certain skin manifestations, includ­ ing alopecia and candidiasis, are characteristic of hereditary hypo­ parathyroidism associated with autoimmune polyglandular failure

(Chap. 401). Hypocalcemia associated with hypomagnesemia is associated with both deficient PTH release and impaired responsiveness to the hor­ mone and is reversible with normalization of serum magnesium. Patients with hypocalcemia secondary to hypomagnesemia have low

TABLE 422-5  Functional Classification of Hypocalcemia (Excluding Neonatal Conditions) 1.  PTH-Related a.  Absence of parathyroid glands or inactive PTH i.  Congenital: 22q11 deletion syndrome (DS), isolated hypoparathyroidism, PTH mutations, mutations in specific transcription factors (GCM2, GATA3) ii.  Destruction of glands: postsurgical, APECED, infiltrative disorders b.  Impaired secretion i.  Congenital: autosomal-dominant hypocalcemia ii.  Functional: hypomagnesemia, hypermagnesemia c.  Target organ resistance i.  Pseudohypoparathyroidism ii.  Hypomagnesemia 2.  Vitamin D–related a.  Vitamin D deficiency: nutritional deficiency, impaired cutaneous production, malabsorption b.  Accelerated loss: impaired enterohepatic recirculation; increased metabolism due to anticonvulsants or antituberculosis therapy (e.g., rifampin) c.  Impaired 25-hydroxylation: severe liver disease, CYP2R1 mutations d.  Impaired 1a-hydroxylation: renal insufficiency, azole antifungal medications that inhibit CYP27B1 (e.g., ketoconazole), genetic 1α hydroxylase deficiency, FGF23-related (TIO, XLH, CKD) e.  Target organ resistance: VDR mutations 3.  Others a.  Impaired bone resorption: denosumab, antiresorptives b.  Excessive deposition into the skeleton: hungry bone syndrome (e.g., after parathyroidectomy for primary hyperparathyroidism), osteoblastic malignancies c.  Chelation: infusion of citrated blood products or EDTA, phosphate infusion d.  Critical illness: pancreatitis, ICU patients Abbreviations: 22q11DS, 22q11 deletion syndrome; APECED, autoimmune polyendocrinopathy candidiasis ectodermal dystrophy; CKD, chronic kidney disease; EDTA, ethylenediaminetetraacetic acid; FGF23, fibroblast growth factor 23; ICU, intensive care unit; PTH, parathyroid hormone; TIO, tumor-induced osteomalacia; VDR, vitamin D receptor; XLH, X-linked hypophosphatemic rickets. levels of circulating PTH, indicative of diminished hormone release despite a maximum physiologic stimulus by hypocalcemia. Hyperma­ gnesemia, which can be iatrogenic, may inhibit PTH release leading to hypocalcemia. GENETIC CAUSES  Hereditary hypoparathyroidism can occur as an isolated entity without other endocrine or dermatologic manifestations or in association with other abnormalities. Hypoparathyroidism Associated with Other Abnormalities  Hypoparathyroidism associated with defective development of both the thymus and the parathyroid glands is termed DiGeorge syndrome, velocardiofacial syn­ drome, or 22q11 deletion syndrome. Congenital cardiovascular, facial, and other developmental defects are present, and patients may die in early childhood with severe infections, hypocalcemia and seizures, or cardiovascular complications. Patients can survive into adulthood, and milder, incomplete forms may become manifest in childhood or adolescence. Most cases are sporadic, but autosomal dominant forms involving microdeletions of chromosome 22q11.2 or point mutations in the transcription factor TBX1 within that chromosomal region exist. Another autosomal dominant developmental defect with hypoparathy­ roidism, deafness, and renal dysplasia (HDR) is caused by mutations in the transcription factor GATA3 (chromosome 10p14), which is important in embryonic development and is expressed in develop­ ing kidney, ear structures, and the parathyroids. Autosomal recessive disorders comprising hypoparathyroidism include Kenney-Caffey syn­ drome type 1, which also features short stature, osteosclerosis, and thick cortical bones, and the related Sanjad-Sakati syndrome, which also exhibits growth failure and other dysmorphic features. Both syndromes involve mutations in a chaperone protein called TBCE (chromosome 1q42-q43), which is relevant to tubulin function. FAM111A defects (chromosome 11q12.1) were identified as the cause of Kenney-Caffey syndrome type 2.

Hypoparathyroidism that can occur in association with a mono­ genetic autoimmune syndrome involving failure of the adrenals, the ovaries, the immune system, and the parathyroids in association with recurrent mucocutaneous candidiasis, alopecia, vitiligo, and pernicious anemia is commonly referred to as polyglandular autoimmune type 1 deficiency or autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) (Chap. 401). This disorder is caused by muta­ tions in the AIRE gene (chromosome 21q22.3). A stop codon mutation occurs in many Finnish families with the disorder, while another muta­ tion (Y85C) is typically observed in Jews of Iraqi and Iranian descent. Hypoparathyroidism is also seen in two disorders associated with mitochondrial dysfunction and myopathy, one termed Kearns-Sayre syndrome (KSS), with ophthalmoplegia and pigmentary retinopathy, and the other termed MELAS syndrome (mitochondrial encephalopa­ thy, lactic acidosis, and stroke-like episodes). Mutations or deletions in mitochondrial genes have been identified. Isolated Hypoparathyroidism  Several forms of hypoparathyroidism, each rare in frequency, are seen as isolated defects; the genetic mechanisms are varied. The inheritance includes autosomal dominant, autosomal recessive, and X-linked modes. PTH Mutations  Several autosomal defects involving the preproPTH sequence or the mature PTH have been recognized. The dominant forms are caused by point mutations in a critical region involved in intracellular transport of the hormone precursor. For example, an Arg for Cys mutation interferes with processing of the precursor and is believed to trigger an apoptotic cellular response, hence acting as a dominant negative. Recessive forms require both PTH alleles encoding the prepro sequence to be mutated. Only three homozygous mutations affecting the mature PTH have been described that lead to an autoso­ mal recessive form of hypoparathyroidism. The defect for an X-linked recessive form of hypoparathyroidism has been localized to chromo­ some Xq26-q27, perhaps involving the SOX3 gene. CaSR Mutations  Different gain-of-function mutations in the CaSR gene have been found in one form of hypocalcemia termed autosomal dominant hypocalcemia (ADH) type 1. The mutant receptor senses the ambient calcium level as excessive and suppresses PTH secretion, lead­ ing to hypocalcemia. The hypocalcemia is aggravated by constitutive receptor activity in the renal tubule causing excretion of inappropri­ ate amounts of calcium. Recognition of the syndrome is important because efforts to treat the hypocalcemia with vitamin D analogues and increased oral calcium exacerbate the already excessive urinary calcium excretion leading to irreversible renal damage from stones and ectopic calcification. The orally available negative allosteric modulator (NAM) on the CaSR encaleret has been shown to normalize serum and urine calcium, as well as serum phosphate and magnesium in a phase 2 trial in patients with ADH1. Other Causes of Isolated Hypoparathyroidism  These include homozygous, inac­ tivating mutations in the parathyroid-specific transcription factor GCM2 or heterozygous point mutations in this protein, which have a dominant-negative effect on the wild-type protein and thus lead to an autosomal dominant form of hypoparathyroidism. Furthermore, heterozygous mutations in Gα11, one of the two signaling proteins downstream of the CaSR, have been identified as a cause of autoso­ mal dominant hypocalcemia, now referred to as ADH type 2. The Bartter syndrome is a group of disorders associated with disturbances in electrolyte and acid-base balance, sometimes with nephrocalcino­ sis and other features. Several types of ion channels or transporters are involved. Curiously, Bartter syndrome type V has electrolyte and pH disturbances but is caused by a gain-of-function mutation in the CaSR. The defect may be more severe than in ADH1 and explains the additional features seen beyond hypocalcemia and hypercalciuria. As with autoimmune disorders that block the CaSR (discussed above under hypercalcemic conditions), there are autoantibodies that at least transiently activate the CaSR, leading to suppressed PTH secretion and hypocalcemia. Acquired chronic hypoparathyroidism is usually the result of inad­ vertent surgical removal of or damage to all the parathyroid glands; in some instances, not all the tissue is removed, but the remainder

undergoes vascular supply compromise secondary to fibrotic changes in the neck after surgery. In the past, the most frequent cause of acquired hypoparathyroidism was surgery for hyperthyroidism. Hypo­ parathyroidism can also occur after surgery for hyperparathyroidism when the surgeon, facing the dilemma of removing too little tissue and thus not curing the hyperparathyroidism, removes too much. Parathy­ roid function may not be totally absent in all patients with postopera­ tive hypoparathyroidism.

Very rare causes of acquired chronic hypoparathyroidism include radiation-induced damage subsequent to radioiodine therapy of hyper­ thyroidism and glandular damage in patients with hemochromatosis or hemosiderosis after repeated blood transfusions. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 Transient hypoparathyroidism is frequent following surgery for hyperparathyroidism. After a variable period of hypoparathyroidism, normal parathyroid function may return due to hyperplasia or recov­ ery of remaining tissue. Occasionally, recovery occurs months after surgery. TREATMENT Acquired and Hereditary Hypoparathyroidism Conventional treatment has involved increasing serum calcium by administration of active vitamin D (calcitriol) combined with oral calcium supplementation. In many patients, blood calcium and phosphate levels are maintained satisfactorily, but some patients show a tendency to alternate between hypocalcemia and hyper­ calcemia, thus requiring close monitoring. Treatment with active vitamin D (calcitriol or alpha-calcidol) is preferred over high-dose plain vitamin D, which was standard in the past, particularly since calcitriol is cleared much more rapidly from the circulation than vitamin D. PTH analogues are being incorporated into the range of treatment options for this disease (see below). Oral calcium and vitamin D increase serum calcium but do not address other functions of PTH. This current standard of care treatment exacerbates hypercalciuria, does not normalize hyper­ phosphatemia, and does not normalize the low bone turnover of hypoparathyroidism. Because of the hypercalciuria, blood calcium levels should be maintained at the lower end of the normal range or just below normal in these patients to avoid excessive urinary calcium excretion; otherwise, nephrocalcinosis and kidney stones can develop, and the risk of CKD is increased. Thiazide diuretics lower urine calcium by as much as 100 mg/d in hypoparathyroid patients on calcium and vitamin D, provided they are maintained on a low-sodium diet. Until recently, hypoparathyroidism was the only endocrine dis­ order not being treated with the missing hormone. After the ini­ tial experimental use of PTH(1–34), the synthetic PTH fragment used in treatment of osteoporosis, showed promise, full-length PTH(1–84) has been shown to be effective and was approved by the U.S. Food and Drug Administration for therapy of hypopara­ thyroidism. The effective half-life of these PTH analogues is not long enough to achieve effective PTH effects over 24 h with one injection. Moreover, they are not approved or no longer available in the United States. Long-acting PTH molecules have been developed and are in clinical trials. Palopegteriparatide, an inactive prodrug that is given as an SC injection once daily and releases PTH(1–34) from an inert carrier in a sustained manner, showed normaliza­ tion of blood and urine calcium in a phase 3 clinical trial and is approved in the US and Europe. Eneboparatide, a biased peptide agonist to the PTH receptor with a prolonged intracellular signal­ ing, showed normalization of blood and urine calcium in patients with hypoparathyroidism in a phase 2 clinical trial and is currently undergoing a phase 3 trial. HYPOMAGNESEMIA  Severe hypomagnesemia (<0.4 mmol/L; <0.8 meq/L) is associated with hypocalcemia (see above). Restoration of the total-body magnesium deficit leads to rapid reversal of hypo­ calcemia. There are at least two causes of the hypocalcemia in severe

hypomagnesemia—impaired PTH secretion and reduced responsive­ ness to PTH. For further discussion of causes and treatment of hypomagnesemia, see Chap. 421.

PTH levels are undetectable or inappropriately low in severe hypo­ magnesemia despite the stimulus of severe hypocalcemia, and acute repletion of magnesium leads to a rapid increase in PTH level. Serum phosphate levels are often not elevated, in contrast to the situation with acquired or idiopathic hypoparathyroidism, probably because phosphate deficiency is often seen in hypomagnesemia. In addition to diminished PTH secretion, some patients with low calcium and mag­ nesium levels show a blunted peripheral response to exogenous PTH as documented by subnormal response in urinary phosphorus and urinary cyclic AMP excretion. PART 12 Endocrinology and Metabolism TREATMENT Hypomagnesemia Repletion of magnesium cures the condition. Repletion should be parenteral. Attention must be given to restoring the intracellular deficit, which may be considerable. After IV magnesium admin­ istration, serum magnesium may return transiently to the normal range, but unless replacement therapy is adequate, serum magne­ sium will again fall. If the cause of the hypomagnesemia is renal magnesium wasting, magnesium may have to be given long-term to prevent recurrence (Chap. 421). PTH TARGET ORGAN RESISTANCE  PHP refers to a group of distinct inherited disorders that resemble hypoparathyroidism (in which PTH synthesis is deficient) and is manifested by hypocalcemia and hyper­ phosphatemia yet elevated PTH levels. Patients affected by PHP type Ia (PHP1A) develop symptoms and signs of hypocalcemia in association with distinctive skeletal and devel­ opmental defects, referred to as Albright’s hereditary osteodystrophy (AHO). The hypocalcemia is due to a deficient PTH response in the proximal renal tubules, probably leading to insufficient 1,25(OH)2D production and thus impaired intestinal calcium absorption. Further­ more, PTH resistance in this portion of the kidney impairs urinary phosphate excretion, thus leading to elevated serum phosphate levels. Patients affected by PHP type Ib (PHP1B) also present with hypocal­ cemia and hyperphosphatemia but less frequently with obvious AHO features. In response to the hypocalcemia observed in either disorder, PTH levels increase, leading to parathyroid hyperplasia and, in some cases, to autonomous PTH secretion. Studies, both clinical and basic, have clarified some aspects of these disorders, including the variable clinical spectrum, the pathophysiology, the genetic defects, and their mode of inheritance. A working classification of the various PHP forms is given in

Table 422-6. The classification scheme is based on the signs of ineffec­ tive PTH action (low calcium and high phosphate), low or normal uri­ nary cyclic AMP response to exogenous PTH, the presence or absence of AHO, and assays to measure the concentration of the Gsα subunit. TABLE 422-6  Classification of Pseudohypoparathyroidism (PHP) and Pseudopseudohypoparathyroidism (PPHP) HYPOCALCEMIA, HYPERPHOSPHATEMIA RESPONSE OF URINARY cAMP TO PTH SERUM PTH TYPE PHP1A Yes ↓ ↑ Yes Yes Yes PPHP No Normal Normal Yes Yes No PHP1B Yes ↓ ↑ No Yes (less frequently and usually less severe) PHP2 Yes Normal (but ↓ phosphaturic response) Acrodysostosis due to PRKAR1A mutations with hormonal resistance Yes Normal (but ↓ phosphaturic response) Abbreviations: ↓, decreased; ↑, increased; AHO, Albright’s hereditary osteodystrophy; cAMP, cyclic adenosine monophosphate; PTH, parathyroid hormone.

Using these criteria, there are four types: PHP types Ia and Ib (PHP1A and PHP1B); pseudopseudohypoparathyroidism (PPHP), and PHP type II (PHP2). Another classification has been proposed recently, which is being debated. PHP1A and PHP1B  Individuals with PHP type I (PHP1), the most com­ mon of the disorders, show deficient urinary cyclic AMP excretion in response to administration of exogenous PTH. Patients with PHP1 are divided into PHP1A and PHP1B. Most patients with PHP1A show evidence for AHO and reduced amounts of Gsα protein/activity, as previously determined in readily accessible tissues such as erythro­ cytes, lymphocytes, or fibroblasts. Only some PHP1B patients show typical AHO features, but they usually have normal Gsα activity. PHP1C, sometimes listed as a third form of PHP1, is really a variant of PHP1A, although the mutant Gsα shows normal activity in certain in vitro assays. Most patients who have PHP1A reveal characteristic features of AHO, which consist of short stature, early-onset obesity, round face, obesity, skeletal anomalies (brachydactyly), intellectual impairment, and/or heterotopic calcifications. Patients have low calcium and high phosphate levels, as with true hypoparathyroidism. PTH levels, how­ ever, are elevated, reflecting resistance to hormone action. In addition, hormonal resistance is observed at other Gsα-coupled receptors, par­ ticularly at the TSH receptor, leading to elevated levels of this hormone. Calcium and phosphate deposits are frequently found in the basal ganglia. The typical shortening of metacarpal and metatarsal bones is caused by premature closing of the epiphyses and is probably a particu­ larly sensitive sign of overall advanced skeletal maturation resulting in adult short stature. INHERITANCE AND GENETIC DEFECTS  Multiple defects at the GNAS locus have now been identified in PHP1A, PHP1B, and PPHP patients. This gene, which is located on chromosome 20q13.3, encodes the α-subunit of the stimulatory G protein (Gsα), among other products (see below). Mutations involving the GNAS exons encoding Gsα, which are the cause of PHP1A and PPHP, include abnormalities at splice junc­ tions, point mutations, insertions, and/or deletions that all result in a Gsα protein with defective function, resulting in a 50% reduction of in vitro Gsα activity in erythrocytes or other cells. While PHP1A is caused by inactivating Gsα mutations on the maternal allele, PPHP is caused by the same or similar mutations on the paternal GNAS allele (Fig. 422-7). The Gsα transcript is biallelically expressed in most tissues; however, expression from paternal allele is silenced through as-of-yet-unknown mechanisms in some tissues, including proximal renal tubules, thyroid, and pituitary. Consequently, inheritance of a molecular defect involv­ ing the paternal exons encoding Gsα has no implications with regard to hormone function, while inactivating Gsα mutations involving the maternal GNAS allele lead to little or no Gsα protein in these tissues (Chap. 479). Thus, females affected by either PHP1A or PPHP will have offspring with PHP1A, if these children inherit the allele carrying the GNAS mutation; in contrast, if the mutant allele is inherited from a male affected by either disorder, the offspring will exhibit PPHP. How­ ever, patients affected by both disease subtypes develop some but not Gs` SUBUNIT DEFICIENCY AHO RESISTANCE TO HORMONES OTHER THAN PTH Yes (in some patients) ↑ No No No ↑ No Yes Yes

PTH PHP-Ia (+ AHO) Urinary cyclic AMP/ phosphate PTH PPHP (+ AHO) FIGURE 422-7  Paternal imprinting of renal parathyroid hormone (PTH) resistance (GNAS gene for Gs` subunit) in pseudohypoparathyroidism (PHP1A and PHP1B). An impaired excretion of urinary cyclic AMP and phosphate is observed in patients with PHP type I. In the renal cortex, there is selective silencing of paternal Gsα expression; consequently, mutations involving the maternal GNAS exons encoding Gsα or loss of methylation at GNAS exon A/B leads to reduced or completely absent Gsα protein in this portion of the kidney. The disease becomes manifest only in patients who inherit the defective gene from an obligate female carrier (left). If a genetic defect involving GNAS exons encoding Gsα is inherited from an obligate male carrier of the mutation (PHP1A or PPHP patient), no biochemical abnormality is encountered, and the administration of PTH causes an appropriate increase in the urinary cyclic AMP and phosphate concentration (pseudoPHP [PPHP]; right). Both patterns of inheritance lead to some but not all features of Albright’s hereditary osteodystrophy (AHO), most likely because of haploinsufficiency; for example, Gsα protein derived from both parental GNAS alleles must be active for normal bone development. Maternal inheritance of a mutation (deletion, duplication, or inversion within or upstream of the GNAS locus) causes AD-PHP1B, while paternal inheritance does not lead to any detectable abnormality. all AHO features, making it likely that Gsα haploinsufficiency becomes apparent during embryonic or postnatal development. The complex mechanisms that control the GNAS gene contributed particularly to challenges involved in unraveling the pathogenesis of PHP1B. Analysis of families in which multiple members are affected by PHP1B, as well as studies of the complex parent-specific methylation of four regions within the complex GNAS locus, revealed that the autoso­ mal dominant forms of PHP1B (AD-PHP1B) are caused by microdele­ tions, duplications, retrotransposon insertions, or inversions within or upstream of the GNAS locus. These genetic mutations are associated with a loss of DNA methylation at one or several loci on the maternal GNAS allele (Table 422-6). These abnormalities in methylation silence maternal Gsα expression, thus leading in the proximal renal tubules— where Gsα appears to be expressed predominantly from the maternal allele—to PTH resistance. While most cases of AD-PHP1B are by now resolved at the molecular level, the genetic defect responsible for the sporadic variant of PHP1B (sporPHP1B), the most frequent form of PHP1B, remains to be defined, except for those sporPHP1B cases that are caused by paternal uniparental isodisomy/heterodisomy of chro­ mosome 20q (patUPD20q). PHP1B patients, who rarely develop an AHO phenotype as severe as in PHP1A, develop hypocalcemia and hyperphosphate­ mia caused by PTH resistance and thus elevated PTH levels. The previously used Ellsworth-Howard test to assess the presence or absence of hormone resistance is used much less frequently, largely because of routinely available sensitive PTH assays (Table 422-6). As for PHP1A, these endocrine abnormalities become apparent only if disease-causing mutations are inherited maternally. Bone responsiveness may be excessive rather than blunted in PHP1B (and in PHP1A) patients, based on case reports that have empha­ sized an osteitis fibrosa–like pattern in several PHP1B patients. Some patients present with PTH resistance in the absence of AHO features and without GNAS methylation changes; it remains unclear

why this PHP variant readily resolves upon treatment with vitamin D supplements.

PHP2 refers to patients with hypocalcemia and hyperphosphate­ mia, who have normal urinary cyclic AMP excretion, but an impaired urinary phosphaturic response to PTH. In one PHP2 variant, referred to as acrodysostosis with hormonal resistance, patients have a het­ erozygous defect in the regulatory subunit of PKA (PRKAR1A) that mediates the response to PTH distal to cyclic AMP production. Acrodysostosis without or with only mild hormonal resistance can be caused by heterozygous mutations in the cyclic AMP–selective phos­ phodiesterase 4D. Patients with one variant of acrodysostosis that is associated with hypertension, were shown to have heterozygous phos­ phodiesterase 3A mutations. Disorders of the Parathyroid Gland and Calcium Homeostasis
CHAPTER 422 The diagnosis of these hormone-resistant states can usually be made when there is a positive family history for signs and symptoms of hypocalcemia with or without AHO features. In both categories— PHP1A and PHP1B—serum PTH levels are elevated, particularly when patients start to experience hypocalcemia during childhood. In PHP1A and PHP1B, the response of urinary cyclic AMP to the administration of exogenous PTH is blunted. The diagnosis of PHP2, in the absence of acrodysostosis, is more complex, and vitamin D deficiency must be excluded before such a diagnosis can be entertained. TREATMENT Pseudohypoparathyroidism Treatment of PHP is similar to that of hypoparathyroidism, except that calcium and activated vitamin D analogues are usually given at higher doses to maintain blood calcium levels within the nor­ mal range and PTH levels in the upper end of normal or slightly elevated. Patients with PHP1 show no PTH resistance in the distal tubules—hence, urinary calcium clearance is typically not elevated, and these individuals are not at risk of developing nephrocalcino­ sis, as are patients with hypoparathyroidism, unless overtreatment occurs, for example, after the completion of pubertal development and skeletal mutation, when calcium and 1,25(OH)2D treatment should be reduced. Variability in response makes it necessary to establish the optimal regimen for each patient. Vitamin D Related  •  VITAMIN D DEFICIENCY DUE TO INADEQUATE

DIET AND/OR SUNLIGHT  Vitamin D deficiency due to inadequate intake of dairy products enriched with vitamin D, lack of vitamin supplementation, and reduced sunlight exposure in the elderly, par­ ticularly during winter in northern latitudes, is more common in the United States than previously recognized. Biopsies of bone in elderly patients with hip fracture (documenting osteomalacia) and abnor­ mal levels of vitamin D metabolites, PTH, calcium, and phosphate indicate that vitamin D deficiency may occur in as many as 25% of elderly patients, particularly in northern latitudes in the United States. Concentrations of 25(OH)D are low or low-normal in these patients. Quantitative histomorphometric analysis of bone biopsy specimens from such individuals reveals widened osteoid seams consistent with osteomalacia (Chap. 421). PTH hypersecretion compensates for the tendency for the blood calcium to fall but also increases renal phos­ phate excretion and thus causes osteomalacia. Treatment involves adequate replacement with vitamin D and cal­ cium until the deficiencies are corrected. Severe hypocalcemia rarely occurs in moderately severe vitamin D deficiency of the elderly, but vitamin D deficiency must be considered in the differential diagnosis of mild hypocalcemia. Mild hypocalcemia, secondary hyperparathyroidism, severe hypo­ phosphatemia, and a variety of nutritional deficiencies occur with gastrointestinal diseases. Hepatocellular dysfunction can lead to reduc­ tion in 25(OH)D levels, as in portal or biliary cirrhosis of the liver, and malabsorption of vitamin D and its metabolites, including 1,25(OH)2D, may occur in a variety of bowel diseases, hereditary or acquired. Depending on the disorder, vitamin D or its metabolites can be given parenterally, guaranteeing adequate blood levels of active metabolites.

DEFECTIVE VITAMIN D METABOLISM  •  Anticonvulsant Therapy  Anticonvul­ sant therapy with any of several agents induces acquired vitamin D deficiency by increasing the conversion of vitamin D to inactive com­ pounds and/or causing resistance to its action. The more marginal the vitamin D intake in the diet, the more likely that anticonvulsant therapy will lead to abnormal mineral and bone metabolism.

Vitamin D–Dependent Rickets Type I  Vitamin D–dependent rickets type I, pre­ viously termed pseudo-vitamin D–resistant rickets, is caused by homo­ zygous or compound heterozygous mutations in the gene CYP27B1 encoding 25(OH)D-1α-hydroxylase. It differs from true vitamin D–resistant rickets (vitamin D–dependent rickets type II, see below) in that it is typically less severe and the biochemical and radiographic abnormalities can be readily reversed with physiologic doses of the vitamin’s active metabolite, 1,25(OH)2D (Chap. 421). Clinical features include hypocalcemia, often with tetany or convulsions; hypophospha­ temia due to secondary hyperparathyroidism; and thus, osteomalacia and increased levels of alkaline phosphatase. PART 12 Endocrinology and Metabolism Vitamin D–Dependent Rickets Type II  Vitamin D–dependent rickets type II results from end-organ resistance to the active metabolite 1,25(OH)2D. The clinical features resemble those of the type I disorder and include hypocalcemia, hypophosphatemia, secondary hyperparathy­ roidism, and rickets but also partial or total alopecia. Plasma levels of 1,25(OH)2D are elevated, in keeping with the refractoriness of the end organs. This disorder is caused by homozygous or compound heterozygous mutations in the gene encoding the vitamin D receptor; treatment requires regular, usually nocturnal calcium infusions, which normalize PTH levels, thus reducing urinary phosphate excretion and thereby improving rickets and thus growth, but do not restore hair growth (Chap. 421). CKD  Improved medical management of CKD allows many patients to survive for decades and, hence, provides time enough to develop features of renal osteodystrophy, which must be controlled to avoid additional morbidity. Impaired production of 1,25(OH)2D is a principal factor that causes calcium deficiency, secondary hyperparathyroidism, and bone disease; hyperphosphatemia, which lowers further blood calcium lev­ els, typically occurs only in the later stages of the disease. Low levels of 1,25(OH)2D due to increased FGF23 production in bone (and possibly other tissues) are critical in the development of hypocalcemia. It is nota­ ble that FGF23 levels are often dramatically elevated in end-stage kidney disease (ESKD). The uremic state also causes impairment of intestinal absorption by mechanisms other than defects in vitamin D metabolism. Nonetheless, treatment with supraphysiologic amounts of vitamin D or calcitriol can correct impaired calcium absorption. Increased FGF23 lev­ els are seen already during the early CKD stages and have been reported to correlate with kidney disease progression, increased mortality, and left ventricular hypertrophy. Strategies involving different oral phos­ phate binders have therefore been pursued to lower intestinal phosphate absorption early during the course of kidney disease and to thereby lower FGF23 levels. However, these approaches have been largely disappoint­ ing. Furthermore, there is concern as to whether supplementation with activated vitamin D analogues increases further the circulating FGF23 levels and their “off-target” effects in CKD patients. TREATMENT Chronic Kidney Disease Therapy of CKD (Chap. 322) involves appropriate management of patients prior to dialysis and adjustment of regimens once dialysis is initiated. Attention should be paid to restriction of phosphate in the diet; avoidance of aluminum-containing phosphate-binding antacids; provision of an adequate calcium intake by mouth, usually around 1 g/d; and supplementation with 0.25–1 μg/d calcitriol or other activated forms of vitamin D. The aim of therapy is to restore normal calcium balance to prevent osteomalacia and severe second­ ary hyperparathyroidism (it is usually recommended to maintain PTH levels between 100 and 300 pg/mL) and, in light of evidence of genetic changes and monoclonal outgrowths of parathyroid glands

in CKD patients, to prevent secondary hyperparathyroidism from becoming autonomous hyperparathyroidism. Reduction of hyper­ phosphatemia and restoration of normal intestinal calcium absorp­ tion by calcitriol can improve blood calcium levels and reduce the manifestations of secondary hyperparathyroidism. Since adynamic bone disease can occur in association with low PTH levels, it is important to avoid excessive suppression of the parathyroid glands while recognizing the beneficial effects of controlling the secondary hyperparathyroidism. These patients should be closely monitored with intact PTH assays. Oral phosphate-binding agents such as sevelamer lower blood phosphate levels in ESKD, but their use in earlier CKD stages does not seem to be beneficial in lowering blood phosphate levels and to prevent the rise in FGF23. Other Causes  Treatment of patients using antiresorptives, such as bisphosphonates and denosumab, my result in hypocalcemia. Risk factors for this condition include vitamin D deficiency, low calcium intake, or advanced chronic kidney disease. Increased enteric loss of 25-hydroxyvitamin D and 1,25(OH)2D due to intestinal disease and increased metabolism due to anticonvulsants or antituberculosis therapy can also lead to hypocalcemia. Impaired 25-hydroxylation due to severe liver disease or mutations in CYP2R1, the 25-hydroxylase, are rare causes of hypocalcemia. Impaired 1a-hydroxylation is not uncommon and occurs in renal insufficiency, certain antifungals, and FGF23-related disorders. Occasionally, loss of calcium from the ECF is so severe that PTH cannot compensate. Such situations include acute pancreatitis and severe, acute hyperphosphatemia, often in association with renal failure, conditions in which there is rapid efflux of calcium from the ECF. Severe hypocalcemia can occur quickly; PTH rises in response to hypocalcemia but does not return blood calcium to normal. SEVERE, ACUTE HYPERPHOSPHATEMIA  Severe hyperphosphate­ mia is associated with extensive tissue damage or cell destruction

(Chap. 421). The combination of increased release of phosphate from muscle and impaired ability to excrete phosphorus because of renal failure causes moderate to severe hyperphosphatemia, the latter caus­ ing calcium loss from the blood and mild to moderate hypocalcemia. Hypocalcemia is usually reversed with tissue repair and restoration of renal function as phosphorus and creatinine values return to normal. There may even be a mild hypercalcemic period in the oliguric phase of renal function recovery. This sequence, severe hypocalcemia followed by mild hypercalcemia, reflects widespread deposition of calcium in muscle and subsequent redistribution of some of the calcium to the ECF after phosphate levels return to normal. Other causes of hyperphosphatemia include hypothermia, mas­ sive hepatic failure, and hematologic malignancies, either because of high cell turnover of malignancy or because of cell destruction by chemotherapy. TREATMENT Severe, Acute Hyperphosphatemia Treatment is directed toward lowering of blood phosphate by the administration of phosphate-binding antacids or dialysis. Although calcium replacement may be necessary if hypocalcemia is severe and symptomatic, calcium administration during the hyperphos­ phatemic period tends to increase extraosseous calcium deposition and aggravate tissue damage. The levels of 1,25(OH)2D may be low during the hyperphosphatemic phase and return to normal during the oliguric phase of recovery. OSTEITIS FIBROSA AFTER PARATHYROIDECTOMY  Severe hypocalce­ mia after parathyroid surgery is rare now that osteitis fibrosa cystica is an infrequent manifestation of hyperparathyroidism. When osteitis fibrosa cystica is severe, however, bone mineral deficits can be large. After parathyroidectomy, hypocalcemia can persist for days if cal­ cium replacement is inadequate. Treatment may require parenteral administration of calcium; addition of calcitriol and oral calcium

40 - 423 Osteoporosis

423 Osteoporosis

supplementation is sometimes needed for weeks to a month or two until bone defects are filled (which, of course, is of therapeutic benefit in the skeleton), making it possible to discontinue parenteral calcium and/or reduce the amount. Differential Diagnosis  Care must be taken to ensure that true hypocalcemia is present; in addition, acute transient hypocalcemia can be a manifestation of a variety of severe, acute illnesses, as discussed above. Chronic hypocalcemia, however, can usually be ascribed to a few disorders associated with absent or ineffective PTH. Important clinical criteria include the duration of the illness, signs or symptoms of asso­ ciated disorders, and the presence of features that suggest a hereditary abnormality. A nutritional history can be helpful in recognizing a low intake of vitamin D and calcium in the elderly, and a history of exces­ sive alcohol intake may suggest magnesium deficiency. Differential Diagnosis  Inherited hypoparathyroidism and PHP are lifelong illnesses, usually (but not always) appearing by adolescence; hence, a recent onset of hypocalcemia in an adult is more likely due to nutritional deficiencies, CKD, or intestinal disorders that result in defi­ cient or ineffective vitamin D. Neck surgery, even long past, however, can be associated with a delayed onset of postoperative hypoparathy­ roidism. A history of seizure disorder raises the issue of anticonvulsive medication. Developmental defects may point to the diagnosis of PHP1A. Rickets and a variety of neuromuscular syndromes and defor­ mities may indicate ineffective vitamin D action, either due to defects in vitamin D metabolism or to vitamin D deficiency. A pattern of low calcium with high phosphorus in the absence of renal failure or massive tissue destruction almost invariably means hypoparathyroidism or PHP. A low calcium and low phosphorus pat­ tern points to absent or ineffective vitamin D, thereby impairing the action of PTH on calcium metabolism (but not phosphate clear­ ance). The relative ineffectiveness of PTH in calcium homeostasis in

vitamin D deficiency, anticonvulsant therapy, gastrointestinal disor­ ders, and hereditary defects in vitamin D metabolism leads to second­ ary hyperparathyroidism as a compensation. The excess PTH on renal tubule phosphate transport accounts for renal phosphate wasting and hypophosphatemia. Acknowledgment The authors are grateful to John T. Potts, Jr., for his contributions to this chapter over many previous editions of Harrison’s. ■ ■FURTHER READING Bastepe M, Jüppner H: Pseudohypoparathyroidism, Albright’s heredi­ tary osteodystrophy, and progressive osseous heteroplasia: Disorders caused by inactivating GNAS mutations, in Endocrinology, 8th ed, in Endocrinology, JL Jameson, LJ DeGroot (eds). Philadelphia, W.B. Saunders Company, 2023; pp 974–991. Bilezikian JP et al: Evaluation and management of primary hyper­ parathyroidism: Summary statement and guidelines from the Fifth International Workshop. J Bone Miner Res 37:2293, 2022. Thakker RV et al: Regulation of calcium homeostasis and Genetic disorders that affect calcium metabolism, in DeGroot’s Endocrinology, 8th ed, RP Robertson (eds). Philadelphia, Elsevier 2023. Peter R. Ebeling

Osteoporosis Osteoporosis, a condition characterized by decreased bone strength and fragility fractures, is most common among postmenopausal women, but 30% of fragility fractures occur in men. Other underlying diseases can result in secondary osteoporosis. The clinical manifestations of

osteoporosis are primarily vertebral, nonvertebral, and hip fractures. Osteoporosis affects >10 million individuals in the United States, but only a minority are currently diagnosed and treated.

DEFINITION Osteoporosis is defined as a reduction in the strength of bone that leads to skeletal fragility and fractures. Despite bone mineral density being used to define osteoporosis, other important factors such as micro­ architectural deterioration and misalignment of bone components also contribute. Thus, relying solely on the measure of bone mineral density may underestimate bone fragility. The World Health Organiza­ tion (WHO) operationally defined osteoporosis as a bone density that falls 2.5 standard deviations (SDs) or more below the mean for young healthy adults (age 30 years) of the same sex and race—also referred to as a T-score of –2.5. Postmenopausal women in the lower end of the young normal range (a T-score <–1.0 to –2.5) are defined as having low bone density or osteopenia, a risk factor for developing osteoporosis. Despite a lower fracture risk in this group, >50% of fractures among postmenopausal women, including hip fractures, occur in individu­ als with osteopenia because the size of that population is much larger than the group defined as having osteoporosis by bone density T-score. This has led to a greater emphasis on absolute fracture risk, incorpo­ rating age, sex, and other major clinical risk factors with or without bone mineral density (BMD) to calculate the 10-year risk of hip or major osteoporotic fractures. The calculation of absolute fracture risk with tools such as FRAX® or the Garvan Fracture Risk Calculator has allowed the development of intervention thresholds for osteoporosis treatment that may be country specific and may differ from diagnostic thresholds (e.g., T-score <–2.5). Osteoporosis CHAPTER 423 Fragility fractures are defined as fractures in adults occurring fol­ lowing a fall from standing height or less, but exclude finger, toes, face, and skull fractures. However, recent studies also indicate traumatic fractures should also be regarded as indicative of underlying skeletal fragility and require further evaluation. EPIDEMIOLOGY In the United States, as many as 10.8 million women and 2.5 million men have osteoporosis (BMD T-score <–2.5 at lumbar spine, total hip, or femoral neck). This does not include additional people who pres­ ent with an osteoporosis-related fracture but with osteopenia (T-score <–1.0 to –2.5). It is estimated that 2 million osteoporosis-related fractures occur each year in the United States at a cost of $19 billion, a problem that will increase as the population ages. Globally, hip fractures are increasing and are associated with high costs. The fail­ ure to identify the first fragility fracture and intervene is estimated to cost $6 billion to Medicare alone for secondary fractures. Another 40 million Americans have osteopenia that potentially puts them at increased of fracture and of developing osteoporosis. Although osteo­ porosis is mostly age-related, some individuals appear more at risk. In women, the rapid loss of ovarian function during the perimenopause (on average around age 50 years) precipitates rapid bone loss over the next 5–7 years such that most women will have osteoporosis by age 70–80 years. As the population is aging, the number of individuals with osteoporosis and fractures is rising. As many fragility fractures due to osteoporosis occur in individuals with osteopenia, identification of those individuals with a high absolute fracture risk and their evaluation and treatment are important. Most fractures, especially those of the hip and vertebrae, show exponential increases with advancing age (Fig. 423-1). Lifetime osteo­ porotic fracture risk for a Caucasian woman who reaches the age of

50 years is ~50%, while the corresponding risk for a 50-year-old man is ~25%. Recent data suggest that fractures, including hip fractures, are increasing despite age-related fracture rates decreasing. This may be related to the aging of the population globally or to failure to evaluate and treat patients with a high absolute fracture risk. About 300,000 hip fractures occur each year in the United States, almost all requiring hospital admission and surgical intervention. The lifetime probability that a 50-year-old white individual will have a hip fracture is 14% for women and 5% for men; the risk for African

Women

Hip Incidence/100,000 person-year Vertebrae

PART 12 Endocrinology and Metabolism

Colles’ 35–39 Age group, year FIGURE 423-1  Epidemiology of vertebral, hip, and Colles’ fractures with age. (Reproduced with permission from C Cooper, LJ Melton 3rd: Epidemiology of osteoporosis. Trends Endocrinol Metab 3:224, 1992.) Americans is about half of those rates, and the risk for Asians and non­ black Hispanics appears to be like that for Caucasians. Hip fractures are associated with a high incidence of mortality and morbidity, with 20–25% of patients dying in the year following the injury, with higher mortality rates among males and African Americans. Hip fracture rates and mortality also demonstrate high global variability. About 30% of survivors require long-term care (at least temporarily), and many never regain the independence that they had prior to the fracture. This sequela is the one most feared by patients. There are ~500,000 symptomatic vertebral fractures per year in the United States, but >1,000,000 vertebral fractures may occur annually since only one-third are recognized clinically. The vast majority are clinically “silent” vertebral fractures identified incidentally during spinal radiography (Fig. 423-2) or may be suggested by significant height loss (>4 cm). However, even asymptomatic vertebral fractures are a major sign of skeletal fragility and increase the risk for subse­ quent fracture. Vertebral fractures, like other fragility fractures, are also associated with long-term morbidity and an increase in mortality. The occurrence of the first fracture greatly increases the risk of further fractures, especially in the first year. The consequence is height loss, FIGURE 423-2  Lateral spine x-ray showing severe osteopenia and a severe wedgetype deformity (severe anterior compression).

Other risk factors Menopause Aging Increased bone loss Low peak bone mass Low bone density Propensity to fall Poor bone quality Fractures FIGURE 423-3  Factors leading to osteoporotic fractures. kyphosis, and secondary pain and discomfort related to altered spinal biomechanics. Thoracic fractures can be associated with restrictive lung disease, whereas lumbar fractures are associated with abdominal symptoms including distention, early satiety, and constipation. ≥85 Approximately 400,000 wrist fractures occur in the United States each year. Fractures of other bones (including ~150,000 pelvic frac­ tures and >100,000 proximal humerus fractures) also occur due to osteoporosis. The threshold for fracture is reduced in osteoporotic bone (Fig. 423-3) due to increased skeletal fragility. Traumatic frac­ tures are also increased in patients at risk of osteoporosis. Fewer than 20% of patients with a fracture are currently either investigated for osteoporosis or started on treatment within 6 months. A number of clinical risk factors for fracture exist; the common ones are sum­ marized in Table 423-1. Prior fragility fractures, a family history of hip fracture, low body mass index, cigarette smoking, and exces­ sive alcohol consumption are all independent predictors. Chronic inflammatory diseases, such as rheumatoid arthritis, increase the risk of osteoporosis, as do diseases associated with malabsorption (e.g., celiac disease) and male hypogonadism. Chronic diseases that increase the risk of falling or frailty, including dementia, Parkinson’s disease, and multiple sclerosis, also increase fracture risk (Table 423-1). Many other risk factors for osteoporosis have been described including glucocorticoids, aromatase inhibitors, androgen deprivation therapy, air pollution, triclosan, bariatric surgery, diabetes mellitus, cerebrovascular accidents, dementia (including Alzheimer’s), the death of a spouse, depression and its treatment with selective serotonin reup­ take inhibitors (SSRIs), and proton pump inhibitors, to name a few. Increasing frailty with age is a potent risk factor for fracture, as is sensory inattention (e.g., walking while looking at mobile phone). Globally, fragility fractures are more common among women than men, presumably due to a lower peak bone mass as well as rapid post­ menopausal bone loss in women. However, this sex difference in bone density and hip fracture incidence is not apparent in all countries, pos­ sibly due to genetics, physical activity levels, or diet. Fragility fractures increase the risk for future fractures (Table 423-1). Vertebral fractures increase the risk of other vertebral fractures as well TABLE 423-1  Risk Factors for Osteoporosis Fracture NONMODIFIABLE POTENTIALLY MODIFIABLE Personal history of fracture as an adult History of fracture in first-degree relative Female gender Advanced age White race Dementia Current cigarette smoking Estrogen deficiency   Early menopause (<45 years) or bilateral ovariectomy   Prolonged premenstrual amenorrhea (>1 year) Poor nutrition especially low calcium and vitamin D intake Alcoholism Impaired eyesight despite adequate correction Recurrent falls Inadequate physical activity Poor health/frailty

as fractures of the peripheral skeleton such as the hip and wrist. Wrist fractures also increase the risk of vertebral and hip fractures. Among individuals aged >50 years, any fracture (except those of the fingers, toes, face, and skull) should be considered as fragility fractures. Any fracture in a woman aged >50 years or a man aged >60 years should trigger investigations for osteoporosis. However, this does not occur in the majority as postfracture care is fragmented. Recent attempts to coordinate care using fracture liaison services to guide patients with fragility fractures through health care systems and ensure their investigation and initiate treatment for osteoporosis have been shown to improve outcomes but may be difficult to implement in countries without single-payor systems or closed health care systems. The risk for future fracture after a first fracture is exponentially increased in the first 12–24 months, leading to the concept of immi­ nent fracture risk. A recent large Medicare database study indicated that almost 20% of women will have a second fracture within 2 years after the first. Risk diminishes to less than half of that rate in the sub­ sequent 3 years but remains persistently elevated after a vertebral or hip fracture. PATHOPHYSIOLOGY ■ ■BONE REMODELING A low peak bone mass may underlie the development of osteoporo­ sis due to hormonal, genetic, or nutritional influences. Age-related changes in bone remodeling as well as extrinsic and intrinsic factors may then be superimposed. Consequently, an appreciation of bone remodeling is fundamental to developing an understanding of both the pathophysiology of bone loss (Chap. 421) and mechanisms of phar­ macologic intervention. During growth, the skeleton increases in size by linear growth and by apposition of new bone tissue on the cortical periosteum (Fig. 423-4). The latter process is called modeling, a process that also allows the long bones to adapt in shape to the stresses placed on them. Increased sex hormone production at puberty is required for skeletal maturation, with peak bone mass being achieved by early adulthood. Recent data suggest delayed puberty may be associated with low bone peak mass that persists into adulthood in both sexes. Sexual dimorphism in skeletal size occurs after puberty with larger bones in males, although true bone mineral density remains similar in both sexes. Nutrition and exercise also play an important role in growth, although genetic factors primarily determine peak bone mass. Numerous genes control skeletal growth, peak bone mass, and body size, as well as skeletal structure and density. Heritability estimates of 50–80% for bone mineral density and size have been derived from twin studies. Though peak bone mass is often lower among individuals with a family history of osteoporosis, association studies of candidate genes (vitamin D receptors; type I collagen, estrogen receptors [ERs], and interleukin 6 [IL-6]; and insulin-like growth factor I [IGF-I]) and bone mass, bone turnover, and fracture prevalence have been inconsistent. There is no panel of genetic markers that can be used to diagnose osteo­ porosis. Linkage studies suggest that a genetic locus on chromosome 11 is associated with high bone mass. Families with high bone mass and lacking age-related bone loss have been shown to have an activating mutation in LRP5, low-density lipoprotein receptor–related protein 5. Conversely, an inactivating mutation results in osteoporosis-pseudogli­ oma syndrome, and LRP5 signaling is important in controlling bone for­ mation. Genome-wide scans for low bone mass suggest multiple genes are involved, many of which are also implicated in control of body size. In adults, bone remodeling, not modeling, is the principal metabolic skeletal process. Bone remodeling has two critical functions: (1) to repair bone microdamage to maintain skeletal strength and (2) to supply calcium from the skeleton when required to maintain serum calcium. Remodeling may be activated by bone microdamage due to excessive or accumulated mechanical stress. Acute demands for calcium involve osteoclast-mediated resorption as well as calcium transport by osteocytes. Chronic demands for calcium can result in secondary hyperparathyroidism, increased bone remodeling, and bone loss. Bone remodeling occurs through the well-coordinated activity of osteocytes, osteoblasts, and osteoclasts. Osteocytes are the terminal-differentiated

Preosteoclast BMU A Preosteoblast Osteoporosis CHAPTER 423 Osteoclast B Osteoblasts Osteoid C D E F FIGURE 423-4  Mechanism of bone remodeling. The basic molecular unit (BMU) moves along the trabecular surface at a rate of ~10 μm/d. The figure depicts remodeling over ~120 days. A. Origination of BMU-lining cells contracts to expose collagen and attract preosteoclasts. B. Osteoclasts fuse into multinucleated cells that resorb a cavity. Mononuclear cells continue resorption, and preosteoblasts are stimulated to proliferate. C. Osteoblasts align at bottom of cavity and start forming osteoid (black). D. Osteoblasts continue formation and mineralization. Previous osteoid starts to mineralize (horizontal lines). E. Osteoblasts begin to flatten.

F. Osteoblasts turn into lining cells; bone remodeling at initial surface (left of drawing) is now complete, but BMU is still advancing (to the right). (Reproduced with permission from SM Ott, in JP Bilezikian, LG Raisz, GA Rodan: Principles of Bone Biology, vol. 18. San Diego, CA: Academic Press; 1996.) cells derived from osteoblasts after incorporation into newly formed bone tissue. Osteoblasts derive from mesenchymal cell lineage and osteoclasts from monocyte/macrophage lineage. Remodeling sites are discrete units with osteoclasts initiating the process by removal of dam­ aged bone tissue and osteoblasts synthesizing new organic bone that becomes gradually mineralized. Bone remodeling is regulated by multiple hormones, including estrogens (in both sexes), androgens, vitamin D, and parathyroid hor­ mone (PTH), as well as locally produced bone-derived growth factors, such as IGF-I, transforming growth factor β (TGF-β), PTH-related peptide (PTHrP), interleukins (ILs), prostaglandins, and members of the tumor necrosis factor (TNF) superfamily. These factors primar­ ily modulate the rate at which new remodeling sites are activated, a process that results initially in bone resorption by osteoclasts, followed by a period of repair during which new bone tissue is synthesized by osteoblasts (Chap. 421). The cytokine responsible for communication

CFU-GM OPG Activated T lymphocytes Activated synovial fibroblasts RANKL RANK M-CSF Preosteoclast Activated dendritic cells PART 12 Endocrinology and Metabolism T Multinucleated osteoclast Bone Osteoblasts or bone marrow stromal cells Activated osteoclast Proresorptive and calciotropic factors 1,25(OH)2 vitamin D3. PTH, PTHrP, PGE2, IL-1, IL-6, TNF, prolactin, corticosteroids, oncostatin M, LIF A FIGURE 423-5  Hormonal control of bone resorption. A. Proresorptive and calciotropic factors. B. Anabolic and antiosteoclastic factors. RANKL expression is induced in osteoblasts, activated T cells, synovial fibroblasts, and bone marrow stromal cells. It binds to membrane-bound receptor RANK to promote osteoclast differentiation, activation, and survival. Conversely, osteoprotegerin (OPG) expression is induced by factors that block bone catabolism and promote anabolic effects. OPG binds and neutralizes RANKL, leading to a block in osteoclastogenesis and decreased survival of preexisting osteoclasts. CFU-GM, colony-forming units, granulocyte macrophage; IL, interleukin; LIF, leukemia inhibitory factor; M-CSF, macrophage colony-stimulating factor; OPG-L, osteoprotegerin ligand; PDGF, platelet-derived growth factor; PGE2, prostaglandin E2; PTH, parathyroid hormone; RANKL, receptor activator of nuclear factor-κB; TGF-β, transforming growth factor β; TNF, tumor necrosis factor; TPO, thrombospondin. (Reproduced with permission from WJ Boyle et al: Osteoclast differentiation and activation. Nature 423:337, 2003.) between the osteoblasts, other marrow cells, and osteoclasts is recep­ tor activator of nuclear factor-κB (RANK) ligand (RANKL). RANKL, a member of the TNF family, is secreted by osteocytes, osteoblasts, and certain immune cells. The osteoclast receptor for this protein is referred to as RANK. Activation of RANK by RANKL is a final common path in osteoclast development and activation. A humoral decoy for RANKL, also secreted by osteoblasts, is referred to as osteoprotegerin (Fig. 423-5). Modulation of osteoclast recruitment and activity appears to be related to the interplay among these three factors (RANKL, RANK, and osteoprotegerin). Additional influences include nutrition (particularly calcium intake) and physical activity level. RANKL production is in part regulated by the canonical Wnt signaling pathway. Wnt activation through mechanical loading or by hormonal or cytokine factors stimulates bone formation by increasing formation and activity of osteoblasts and decreases RANKL secretion, which inhibits osteoclast formation and activity. Sclerostin, also an osteocyte protein, is a major inhibitor of Wnt activation and bone formation. Its secretion is inhibited by weight-bearing physical activity and PTH. Both the RANKL and Wnt pathways have become major targets for osteoporosis treatment (see below). In young adults, bone remodeling is balanced with resorbed bone being replaced by an equal amount of new bone. Thus, the mass of the skeleton remains constant after peak bone mass is achieved. However, after age 30–45 years, bone resorption exceeds formation, resulting in bone loss. This imbalance may begin at different ages, varies at differ­ ent skeletal sites, and becomes exaggerated in women due to estrogen deficiency. Bone loss can be due to an increase in osteoclastic activity and/or a decrease in osteoblastic activity. In addition, an increase in remodeling activation frequency, and thus the number of remodeling sites, can magnify small imbalances seen at the individual remodeling unit. Increased bone remodeling can result in permanent bone loss and disrupted skeletal microarchitecture, with an imbalance between resorption and formation within each cycle. In trabecular bone, if the osteoclasts penetrate trabeculae, rapid bone loss ensues and cancel­ lous connectivity is reduced. A higher number of remodeling sites

M-CSF T Apoptotic osteoclast Anabolic or antiresorptive factors Estrogens, calcitonin, BMP 2/4, TGF-β, TPO, IL-17, PDGF, calcium B increases the likelihood of this event. In cortical bone, increased activation of bone remodeling creates more porous bone. The effect of this increased cortical porosity on cortical bone strength may be modest if the overall diameter of the bone is not changed. However, decreased apposition of new bone on the periosteal surface coupled with increased endocortical resorption of bone decreases the biome­ chanical strength of long bones. Even a slight exaggeration in normal bone loss increases the risk of osteoporosis-related fractures because of microarchitectural changes, and osteoporosis is largely a disease of dis­ ordered skeletal microarchitecture. Currently the predominant clinical tool (dual-energy x-ray absorptiometry [DXA]) measures bone mass rather than bone microarchitecture. Several additional tools are avail­ able to estimate bone microarchitecture (including the trabecular bone score [TBS], a noninvasive addition to spinal DXA measurements, and high-resolution peripheral quantitative computerized tomography [HR-pQCT], which has limited availability). ■ ■CALCIUM NUTRITION Peak bone mass may be impaired by inadequate dietary calcium intake during growth among other nutritional factors (calories, protein, and other minerals), leading to increased risk of osteoporosis later in life. During the adult phase of life, insufficient calcium intake contributes to secondary hyperparathyroidism and an increase in bone remodel­ ing rate. PTH stimulates the 1-alpha hydroxylation of vitamin D in the kidney, leading to increased levels of 1,25-dihydroxyvitamin D [1,25(OH)2D] and enhanced gastrointestinal calcium absorption. PTH also reduces renal calcium loss. Although these are appropriate com­ pensatory homeostatic responses for improving calcium economy, the long-term effects are detrimental to the skeleton because the increased remodeling rates and the ongoing imbalance between resorption and formation at remodeling sites combine to accelerate bone loss. Total daily calcium intakes <400 mg are detrimental to the skeleton, and intakes in the range of 600–800 mg, which is about the average intake among adults in the United States, are also probably suboptimal. The recommended daily required intake of 1000–1200 mg for adults

accommodates population heterogeneity in controlling calcium bal­ ance. Such intakes should preferentially come from dietary sources, with supplements used only when dietary intakes fall short and cannot be modified easily. The supplement should be enough to bring total intake to ~1200 mg/d. Recent studies have suggested that there may be differences in safety based on calcium source so that increasing dietary calcium is preferred; higher intakes from supplement sources appear to result in a greater risk of renal stones and perhaps cardiovascular events (although the literature is inconsistent and controversial); how­ ever, supplement doses below about 700 mg/d have not been associated with cardiovascular events. Increasing calcium intake above this level does not have any benefit. Increasing calcium intake by itself will not prevent bone loss due to other factors (e.g., postmenopausal status) ■ ■VITAMIN D (See also Chap. 421) Severe vitamin D deficiency causes rickets in children and osteomalacia in adults. However, vitamin D insufficiency (circulating levels of 25-hydroxyvitamin D [25(OH)D] that may be inadequate [<75 nmol/L or 30 ng/mL] but above the level that results in rickets) may be more prevalent than previously thought, particularly among individuals at increased risk such as the elderly; those living in northern or southern latitudes; and individuals with poor nutrition, obesity, malabsorption, or chronic liver or renal disease. Dark-skinned individuals are also at high risk of vitamin D in the insufficiency range or lower, but African Americans have a low risk of osteoporosis, with better calcium homeostasis than Caucasians. Although there is considerable controversy about overall optimal health targets for serum 25(OH)D, there is evidence that for optimal skeletal health, serum 25(OH)D should be >75 nmol/L (30 ng/mL). To achieve this level for most adults requires limited skin exposure to sunlight (estimated to be exposure of face and arms for at least one-half hour each day) or an intake of at least 800–1000 units/d, or even higher in individuals with risk factors (as above), particularly obesity. Vitamin D insufficiency leads to compensatory secondary hyper­ parathyroidism and is an important risk factor for osteoporosis and fractures. Some studies have shown that >50% of inpatients on a general medical service exhibit biochemical features of vitamin D defi­ ciency, including increased levels of PTH and alkaline phosphatase and lower levels of ionized calcium. Among those living in northern and southern latitudes, vitamin D levels decline during the winter months without supplementation due to insufficient ultraviolet B radiation. This is associated with seasonal bone loss, reflecting increased bone turnover. Even among healthy ambulatory individuals, mild vitamin D deficiency is increasing in prevalence. In part, this is due to decreased exposure to sunlight. Treatment with vitamin D can return levels to normal (>75 nmol/L [30 ng/mL]) and prevent the associated increase in bone remodeling, bone loss, and fractures. Reduced falls and frac­ ture rates also have been documented among individuals in northern latitudes who have greater vitamin D intake and have higher 25(OH)D levels (though one study suggested an increased fall risk with 25[OH] D levels >70 ng/mL or >175 nmol/L). Although vitamin D levels are suspected to affect risk and/or severity of other diseases, including can­ cers (colorectal, prostate, and breast), autoimmune diseases, multiple sclerosis, and cardiovascular disease, most controlled clinical trials have not confirmed these effects. However, vitamin D does prevent progression of prediabetes to diabetes in those with vitamin D defi­ ciency (25[OH]D levels <12 ng/mL or <30 nmol/L). Treating vitamin D–sufficient individuals with vitamin D does not reduce fractures. For most adults, supplements of 1000–2000 IU/d are adequate and safe. ■ ■ESTROGEN STATUS Estrogen deficiency causes bone loss by two distinct but interrelated mechanisms: (1) activation of new bone remodeling sites and (2) ini­ tiation or exacerbation of an imbalance between bone formation and resorption, in favor of the latter. The change in activation frequency causes a transient bone loss until a new steady state between resorp­ tion and formation is achieved. This commences in the perimenopause prior to cessation of periods. This remodeling imbalance results in a permanent decrement in mass. In addition, the increase in remodeling

sites in the skeleton alone increases the probability of trabecular per­ foration, eliminating the template on which new bone can be formed and accelerating bone loss. The consequence is degraded skeletal microarchitecture, particularly affecting trabecular bone, so that at any given bone density, the risk of a fracture is greater in those who have experienced rapid bone loss than in those who have not. The addition of the TBS to spinal DXA measurements is an attempt to indirectly capture these microarchitectural changes, while HR-pQCT scans mea­ sure these directly.

The most common cause of estrogen deficiency is the menopause, which occurs on average at age 51 years (Chap. 407). Thus, with cur­ rent life expectancy, an average woman will spend ~35 years without an ovarian estrogen supply. Breast cancer treatment with either bilateral ovariectomies and/or aromatase inhibitors is an increasingly common cause of even more severe estrogen deficiency. The mechanism by which estrogen deficiency causes bone loss is summarized in Fig. 423-5. Bone marrow cells (macrophages, monocytes, osteoclast precursors, mast cells) as well as bone cells (osteoblasts, osteocytes, osteoclasts) express both ERs (α and β). Loss of estrogen increases RANKL production but also reduces osteoprotegerin production, increasing osteoclast forma­ tion and recruitment. Estrogen also may play a role in determining the life span of bone cells by controlling their rate of apoptosis. Thus, in situations of estrogen deprivation, the life span of osteoblasts may be decreased, whereas the longevity and activity of osteoclasts are increased. The rate and duration of bone loss after menopause are het­ erogeneous and unpredictable. Once surfaces are lost from trabecular bone, the rate of bone loss declines. In cortical bone, loss is slower but may continue for longer. Osteoporosis CHAPTER 423 Since remodeling is initiated at the surface of bone, it follows that trabecular bone—which has a considerably larger surface area (80% of the total) than cortical bone—will be affected preferentially by estro­ gen deficiency. Fractures occur earliest at sites where trabecular bone contributes most to bone strength; consequently, vertebral fractures are the most common early skeletal consequence of estrogen deficiency. In males, estrogen may have an important role in regulation of bone remodeling. In an experiment in which males were rendered estrogen and androgen deficient, restoring estrogen supply reduced remodeling rate more than restoring androgen. ■ ■PHYSICAL ACTIVITY Inactivity, such as prolonged bed rest or paralysis, results in significant bone loss. Concordantly, athletes have higher bone mass than non­ athletes. These increases in skeletal mass are most marked when the stimulus begins during growth in the years before puberty at the time of skeletal modeling and can result in a higher peak bone mass in both sexes. Adults are less able to increase bone mass after restoration of physical activity. Epidemiologic data support the beneficial effects on the skeleton of chronic high levels of physical activity. Fracture risk is lower in rural communities and in countries where physical activity is maintained into old age. However, when exercise is initiated during adult life, the effects of progressive resistance training on the skeleton are modest, with increases in spine and hip bone mass of 2–4% in short-term randomized trials of <2 years’ duration. Muscle strength is also increased, while balance and functional exercises combined also reduce falls by about 25%. A Cochrane review showed balance and functional exercises reduced the number of people who experienced one or more fall-related fractures. Continuing physical activity into the later years may also slow cognitive decline, another major reason for including exercise programs for the aging population. ■ ■CHRONIC DISEASES Various genetic and acquired diseases are associated with an increase in the risk of osteoporosis (Table 423-2). Mechanisms that contribute to bone loss are unique for each disease and typically result from mul­ tiple factors, including nutrition, reduced physical activity levels, and factors that affect rates of bone remodeling or bone quality. In most, but not all circumstances, the primary diagnosis is made before osteo­ porosis presents clinically. Both type 1 and type 2 diabetes mellitus are associated with an increased fracture risk, with increased risk at higher

TABLE 423-2  Diseases Associated with an Increased Risk of Generalized Osteoporosis in Adults Hypogonadal states Turner’s syndrome Klinefelter’s syndrome Anorexia nervosa Hypothalamic amenorrhea Hyperprolactinemia Other primary or secondary hypogonadal states Endocrine disorders Cushing’s syndrome Hyperparathyroidism Thyrotoxicosis Diabetes mellitus (both type 1 and 2) Acromegaly Adrenal insufficiency Nutritional and gastrointestinal disorders Malnutrition Parenteral nutrition Malabsorption syndromes Gastrectomy Severe liver disease, especially biliary cirrhosis Pernicious anemia Rheumatologic disorders Rheumatoid arthritis Ankylosing spondylitis Hematologic disorders/malignancy Multiple myeloma Lymphoma and leukemia Malignancy-associated parathyroid hormone–related peptide (PTHrP) production Mastocytosis Hemophilia Thalassemia Selected inherited disorders Osteogenesis imperfecta Marfan’s syndrome Hemochromatosis Hypophosphatasia Glycogen storage diseases Homocystinuria Ehlers-Danlos syndrome Porphyria Menkes’ syndrome Epidermolysis bullosa Other disorders Immobilization Chronic obstructive pulmonary disease Pregnancy and lactation Scoliosis Multiple sclerosis Sarcoidosis Amyloidosis PART 12 Endocrinology and Metabolism bone density than in the nondiabetic population. This is due to differ­ ences in collagen cross-linking in bone tissue due to accumulation of advanced glycation end products, making it more brittle than normal, a predilection for conversion of precursors to adipose cells rather than osteoblasts, and the sequelae of diabetes that increase the risk of falls and injury. Severe bone loss occurs in quadriplegic and paraplegic individuals below the level of the injury. The combination of loss of muscle func­ tion and innervation of both muscle and bone contributes to failure to recover mobility, which leads to a high fracture risk in those attempting to pursue athletic activities despite their primary diagnosis (e.g., wheel­ chair athletes). Bone loss also follows a stroke and is again dependent on the severity of the paralysis. The risk of fracture can be predicted by the FRAX (Fracture Risk Assessment) score and seems highest in the first year after stroke. The increasing prevalence of transgender and gender nonconforming individuals has prompted a guideline for evalu­ ation of bone density in that population by the International Society of Clinical Densitometry published in 2019. ■ ■MEDICATIONS Many medications used in clinical practice have potentially detrimen­ tal effects on the skeleton (Table 423-3). Glucocorticoids are the most TABLE 423-3  Drugs Associated with an Increased Risk of Generalized Osteoporosis in Adults Glucocorticoids Excessive thyroxine Cyclosporine Aluminum Cytotoxic drugs Gonadotropin-releasing hormone agonists Anticonvulsants Heparin Aromatase inhibitors Selective serotonin reuptake inhibitors Lithium Protein pump inhibitors Thiazolidinediones Androgen deprivation therapies

common cause of medication-induced osteoporosis. It is often not possible to determine the extent to which osteoporosis is related to glucocorticoid treatment or to other factors, as the effects of medica­ tion are superimposed on the effects of the primary disease, which may be associated with bone loss (e.g., rheumatoid arthritis). Excessive doses of thyroid hormone can accelerate bone remodeling and result in bone loss. Other medications have less detrimental effects on the skeleton than pharmacologic doses of glucocorticoids. Anticonvulsants are thought to increase the risk of osteoporosis, although many affected individuals have concomitant insufficiency of 1,25(OH)2D, as some anticonvul­ sants induce the cytochrome P450 system and vitamin D metabolism. Patients undergoing transplantation are at high risk for rapid bone loss and fracture not only from glucocorticoids but also from treatment with other immunosuppressants such as cyclosporine and tacrolimus (FK506). In addition, these patients often have preexisting metabolic abnormalities such as hepatic or renal failure predisposing to bone loss. Long-term use of proton pump inhibitors and selective serotonin reuptake inhibitors has been shown to be associated with a higher risk of fracture in observational studies. Given their frequent long-term use, their skeletal effects are important from a public health perspective and for individual fracture risk. Aromatase inhibitors, which potently block the aromatase enzyme that converts androgens and other adrenal precursors to estrogen, reduce circulating postmenopausal estrogen levels severely. These agents, used to treat breast cancer, also cause declines in bone density and rapidly increase fracture risk. Androgen deprivation therapy, used to treat men with prostate cancer, also results in rapid bone loss and increased fracture risk. The diabetes medications, thiazolidinediones and insulin, also increase the risk of fracture; however, metformin and glucagon-like peptide-1 receptor agonists decrease risk. It is difficult in some cases to separate the risk accrued by the underlying disease from that attributable to the medication. For example, both depression and diabetes are risk factors for fracture by themselves. ■ ■SMOKING Smoking produces detrimental effects on bone mass mediated directly by toxic effects on osteoblasts or indirectly by modifying estrogen metabolism. On average, cigarette smokers reach menopause 1–2 years earlier than the general population. Cigarette smoking also results in intercurrent respiratory and other illnesses, frailty, decreased exercise, poor nutrition, and the need for additional medications (e.g., glucocor­ ticoids for lung disease) that can all increase fracture risk. ■ ■OTHER POTENTIAL FACTORS In the past few years, many potential risk factors for fracture have been identified. These include excessive alcohol intake and other drugs of abuse, pollution, use of triclosan, chronic obstructive pulmonary disease, excess vitamin B, and hormonal therapies utilized among the transgender population. DIAGNOSIS ■ ■MEASUREMENT OF BONE MASS Several noninvasive techniques are available for estimating skeletal mass or BMD. They include DXA, quantitative computed tomography (QCT), peripheral QCT, HR-pQCT, and ultrasound. DXA is a highly accurate x-ray technique that has become the standard for measuring bone density. Though it can be used for measurement in any skeletal site, clinical determinations usually are made of the lumbar spine and hip. DXA also can be used to measure the radius, total body bone mass, and body composition (lean mass, fat mass). Two x-ray ener­ gies are used to estimate mineralized tissue, allowing for correction for attenuation through soft tissue. The mineral content is divided by bone area, which partially corrects for body and bone size. However, this correction is only partial since DXA is a two-dimensional scan­ ning technique and cannot estimate the depth of the bone. Thus, small slim people tend to have lower than average BMD, a feature that is important in interpreting BMD measurements. Bone spurs, which are common in osteoarthritis (spinal spondylosis), tend to falsely increase

Z- and T-scores

BMD score

–1 –2 T-Score = –2.5 –3 Z-Score = –1

Age FIGURE 423-6  Relationship between Z-scores and T-scores in a 60-year-old woman. BMD, bone mineral density; SD, standard deviation. bone density, mostly of the spine, which is a particular problem in mea­ suring spine BMD in older individuals. Because DXA measurement devices are provided by different manufacturers, the output varies in absolute terms. Absolute bone density results are related to “normal” values by using T-scores (a T-score of 1 equals 1 SD), which compare individual results to those in a young adult population (age 30 years) matched for race and sex. The mean value is given a score of zero and the range is +2.5 to –2.5 (i.e., 2.5 SDs above or below the mean). Z-scores (also SDs) compare individual results to those of an age- and sex-matched reference population. Thus, a 60-year-old woman with a Z-score of –1 (1 SD below mean for age) has a T-score of –2.5 (2.5 SDs below mean for a young adult population) (Fig. 423-6). A T-score ≤–2.5 in the lumbar spine, femoral neck, or total hip has been defined as osteoporosis, whereas a T-score of –1.0 to –2.5 has been defined as low bone density or osteopenia. Although the outputs from different instruments and, more importantly, different manufacturers correlate well, different machines used over time may show changes in BMD that may be attributed to biological changes or simply the result of differences between machines. This is particularly true with measure­ ments of the femoral neck. Consequently, it is recommended that serial measurements be performed on the same machine and preferably by the same technician. As noted above, since >50% of fractures occur in individuals with osteopenia (e.g., a T-score between –1.0 and –2.5), it is important to consider absolute fracture risk in addition to BMD. The most com­ monly used absolute fracture risk assessment tool is FRAX, which includes age, sex, height, weight, fracture history, hip fracture in a parent, glucocorticoid use, rheumatoid arthritis, and other secondary causes, with or without bone density of the femoral neck. The pro­ gram calculates the estimated risk over a 10-year time frame for major osteoporosis-related fractures (clinical spine, hip, wrist, and proximal humerus) and for hip fracture. Computed tomography (CT) can also be used to measure the spine and hip but is rarely used clinically, in part because the radiation exposure and cost are both much higher than with DXA. HR-pQCT measures cortical and trabecular bone variables in the forearm or tibia and provides information on skeletal microarchitecture noninvasively. Magnetic resonance imaging (MRI) can also be used to obtain some architectural information on the forearm and perhaps the hip but is primarily a research tool. Ultrasound can be used to measure bone mass by calculating the attenuation of the signal as it passes through bone or the speed with which it traverses the bone. Although the ultrasound technique was purported to assess properties of bone other than mass (e.g., quality), this has not been confirmed. Because of its relatively low cost and mobility, ultrasound bone density measurement is amenable for use as a screening tool. All these techniques for measuring BMD have been approved by the U.S. Food and Drug Administration (FDA) based on their capacity to predict fracture risk. The total hip is the preferred site of measure­ ment, since it allows the best prediction of hip fracture risk. When hip measurements are performed by DXA, the spine is usually measured at the same time. In younger individuals such as perimenopausal or early

TABLE 423-4  Indications for Bone Mineral Density Testing • Women aged ≥65 and men aged ≥70; regardless of clinical risk factors • Younger postmenopausal women, women in the menopausal transition, and men aged from 50 to 69 with clinical risk factors for fracture • Adults who have a fracture at or after age 50 • Adults with a condition (e.g., rheumatoid arthritis) or taking a medication (e.g., glucocorticoids at a daily dose >5 mg prednisone or equivalent for >3 months associated with low bone mass or bone loss +1 SD –1 SD

Osteoporosis CHAPTER 423 postmenopausal women, spine measurements may be more sensitive. When the spine or hip is not measurable due to severe degenerative spine disease or scoliosis, or prior spine or hip surgery, wrist BMD is often measured. ■ ■INDICATIONS FOR BONE MASS MEASUREMENT Several clinical guidelines have been developed for the use of bone den­ sitometry in clinical practice (Table 423-4). The National Osteoporosis Foundation (NOF) guidelines recommend bone mass measurements in postmenopausal women who have one or more risk factors for osteo­ porosis in addition to age, sex, and estrogen deficiency. The guidelines further recommend that bone mass measurement be considered in all women by age 65, a position ratified by the U.S. Preventive Health Services Task Force. In males, the use of bone density determination is not recommended until the age of 70 years in the absence of multiple risk factors or the occurrence of a fragility fracture. The FRAX score incorporates clinical risk factors (age, prior frac­ ture, family history of hip fracture, low body weight, tobacco use, excessive alcohol use, glucocorticoid use, and rheumatoid arthritis) with or without BMD to assess the 10-year fracture probabilities for major osteoporotic (hip, clinical spine, wrist, or humerus) and hip fractures. Fracture risk probability calculators are available as part of the report from all DXA machines and available online (https://www

.sheffield.ac.uk/FRAX/) (Fig. 423-7). In the United States, cost-effective treatment thresholds occur if the 10-year major osteoporotic fracture risk from FRAX is ≥20% and/or the 10-year risk of hip fracture is ≥3%. FRAX is an imperfect tool, as it does not include any assessment of fall risk, and secondary causes are excluded when BMD is entered. It also does not account for glucocorticoid dose or diabetes. Most importantly, it does not increase the absolute fracture risk conferred by a recent fracture versus the lesser risk conferred by a more remote fracture. Moreover, there is no mandate for vertebral fracture diagnosis and no additional fracture probability estimated for patients who have had multiple fragility fractures. Many of these deficiencies are likely to be corrected in the next version of FRAX (FRAX Plus and FRAX 2.0). ■ ■VERTEBRAL IMAGING DXA equipment can also be used to obtain lateral images of the tho­ racic and lumbar spine, a technique called vertebral fracture assess­ ment (VFA). While not as definitive as a radiograph, it is an excellent screening tool for vertebral abnormality in both women and men. It is an important assessment as the majority of vertebral fractures are asymptomatic (70%). Furthermore, VFA can detect vertebral abnor­ malities causing height loss or back pain that may be indicative of an undiagnosed vertebral fracture. Because most vertebral fractures are asymptomatic, the diagnosis of vertebral fracture is rarely made when they first occur. However, ver­ tebral fractures, whether symptomatic or asymptomatic, are associated with the same clinical sequelae, so it is critical they are identified. Ver­ tebral fracture prevalence in the United States based on the National Health and Nutrition Evaluation Studies (NHANES) population appears to be 20% in the 1980s, when the strictest criteria for diagnosis are utilized. It is recommended that women aged 65 years or older and men aged 70 years or older undergo vertebral imaging if there is a T-score is ≤–1.5 at the spine, hip, or femoral neck. Vertebral imaging is also recommended for women by the age of 70 years and men by the age of 80 years if a T-score is <–1.0. For younger individuals, vertebral imaging is recommended for those with a fragility fracture, height loss, or glucocorticoid use. (See Table 423-5.)

PART 12 Endocrinology and Metabolism FIGURE 423-7  FRAX calculation tool. When the answers to the indicated questions are filled in, the calculator can be used to assess the 10-year probability of fracture.

The calculator (available online at http://www.shef.ac.uk/FRAX/tool.jsp?locationValue=9) also can risk adjust for various ethnic groups. APPROACH TO THE PATIENT Osteoporosis The development of osteoporosis is a gradual process occurring under a variety of genetic and environmental influences throughout life. Just prior to and at the time of puberty are important times to affect accrual of peak bone mass while the perimenopause and menopause in women are important times to reduce bone loss. Rec­ ognition of these influences allows intervention at several points, although the type of intervention depends on a careful evaluation of each individual patient. TABLE 423-5  Indications for Vertebral Testing Consider vertebral imaging tests for the following individualsa • All women aged ≥70 and all men aged ≥80 if bone mineral density (BMD) T-score at the spine, total hip, or femoral neck is <1.0 • Women aged from 65 to 69 and men aged from 70 to 79 if BMD T-score at the spine, total hip, or femoral neck is <1.5 • Postmenopausal women and men aged ≥50 with specific risk factors: • Low-trauma fracture during adulthood (aged ≥50) • Historical height loss of ≥1.5 in. (4 cm)b • Prospective height loss of ≥0.8 in. (2 cm)c • Recent or ongoing long-term glucocorticoid treatment aIf bone density testing is not available, vertebral imaging may be considered based on age alone. bCurrent height compared to peak height during childhood. cCumulative height loss measured during interval medical assessment.

The menopausal transition affects all women by their late 50s and represents an opportunity to initiate a discussion about bone loss, the role of estrogen loss, and other clinical risk factors. Assessment of fracture risk with FRAX (with or without bone density) provides a 10-year estimate of hip and major osteoporosis-related fracture risk and opens the discussion about preventive steps including, if required, the use of medication. If risk is low, then nutrition and resistance training exercise are the focus. If menopausal symp­ toms are prominent and estrogen intervention is needed, then the added protection against bone loss and fragility fractures should be emphasized. Among older women with a fracture, an evaluation of skeletal status including bone density testing should proceed. In this case, any fracture, whether traumatic or not, should trigger this assess­ ment. Although osteoporosis is associated with a risk of fragility fracture, individuals with osteoporosis are also more likely to experience traumatic fractures, and such individuals should not be excluded from osteoporosis evaluation simply because of the level of trauma. This concept, while obvious and evidence-based, still needs emphasis with individual patients, physicians, and payors. Patients who present with hip or spine fractures by definition have osteoporosis and will require treatment for both the fracture itself and the underlying skeletal disorder. Other long bone frac­ tures (e.g., distal radius) are triggers for evaluation of the skeleton upon which treatment decisions can be based. In all individuals presenting with a fracture as a result of a fall, fall prevention strategies including balance exercises are an impor­ tant adjunct to other lifestyle and nutritional interventions.

ROUTINE LABORATORY EVALUATION There is no established algorithm for the evaluation of women or men who present with osteoporosis. A general evaluation that includes complete blood count, serum and 24-h urine calcium, and renal and liver function tests is useful for identifying selected secondary causes of low bone mass, particularly for those with frac­ tures or unexpectedly low Z-scores. An elevated serum calcium level suggests hyperparathyroidism or malignancy, whereas a reduced serum calcium level may reflect malnutrition or a malabsorption disease, such as celiac disease. In the presence of hypercalcemia, a serum PTH level differentiates between hyperparathyroidism (PTH↑) and malignancy (PTH↓), and a high PTHrP level can help document the presence of humoral hypercalcemia of malignancy (Chap. 422). A low urine calcium (<50 mg/24 h) suggests malnutri­ tion, or malabsorption; a high urine calcium (>300 mg/24 h) during normal calcium intake (excluding calcium supplements for at least a week before the urine collection) is indicative of hypercalciuria. Hypercalciuria occurs primarily in three situations: (1) a renal cal­ cium leak; more common in males with osteoporosis; (2) absorptive hypercalciuria, which can be idiopathic or associated with increased 1,25(OH)2D in granulomatous disease; or (3) hematologic malig­ nancies or conditions associated with excessive bone turnover such as Paget’s disease, hyperparathyroidism, hyperthyroidism, and iron chelation therapy (desferoxamine) for thalassemia. Renal hypercal­ ciuria is treated with thiazide diuretics, which lower urine calcium and help improve calcium economy. In this setting, thiazides alone can improve bone mass and possibly reduce risk of fracture. They might also reduce renal stone risk. Individuals who have fragility fractures or bone density in the osteoporotic range should have a measurement of serum 25(OH) D level since serum 25(OH)D levels <30 ng/mL (vitamin D insuf­ ficiency) are common, particularly in older adults. Hyperthy­ roidism should be evaluated by measuring thyroid-stimulating hormone (TSH). When there is clinical suspicion of Cushing’s syndrome, 24-h urinary free cortisol levels or a fasting serum cortisol should be measured after taking 1 mg dexamethasone at midnight. When bowel disease, malabsorption, or malnutrition is suspected, serum albumin, cholesterol, and a complete blood count should be checked. Asymptomatic malabsorption may be heralded by anemia (macrocytic—vitamin B12 or folate deficiency; microcytic—iron deficiency) or low serum cholesterol or urinary calcium levels. If these or other features suggest malabsorption, further evaluation is required. Asymptomatic celiac disease with selective malabsorp­ tion is being found with increasing frequency; the diagnosis can be made by testing for transglutaminase IgA antibodies but may require confirmation by endoscopic biopsy. A trial of a gluten-free diet can also be confirmatory (Chap. 336). When osteoporosis is found associated with symptoms of rash, multiple allergies, diar­ rhea, or flushing, mastocytosis should be considered and excluded by using 24-h urine histamine collection or serum tryptase. Myeloma can masquerade as generalized osteoporosis, although it more commonly presents with bone pain and characteristic “punched-out” lesions on radiography. Serum and urine electro­ phoresis and/or evaluation for serum free light chains in serum are required to exclude this diagnosis. More commonly, a monoclo­ nal gammopathy of undetermined significance (MGUS) is found, and the patient is subsequently monitored to ensure that this is not an incipient myeloma. MGUS itself may be associated with an increased risk of osteoporosis. A bone marrow biopsy may be required to rule out myeloma (in patients with equivocal electro­ phoretic results) and can be used to exclude mastocytosis, leukemia, and other marrow infiltrative disorders, such as Gaucher’s disease. Testosterone levels should be checked in men with osteoporosis. An important cause of fracture among the aging population is diabetes, both type 1 and type 2. Patients with diabetes appear, at any given bone density, to be at higher risk of fracture than non­ diabetics. The reasons include the effects on muscle and nerve that

increase the risk of falls, but it can also be due to an underlying skeletal fragility as part of the metabolic consequences of diabetes with deposition of advanced glycation end products in bone. BONE BIOPSY Double tetracycline labeling of the skeleton allows determination of the rate of remodeling as well as evaluation for other metabolic bone diseases. However, the current use of BMD, in combina­ tion with hormonal evaluation and biochemical markers of bone remodeling, has largely replaced the clinical use of bone biopsy, although it remains an important tool in the diagnosis of chronic kidney disease–mineral bone disease (CKD-MBD), in evaluating the mechanism of action of osteoporosis pharmacology and in clinical research. Osteoporosis CHAPTER 423 BIOCHEMICAL MARKERS Several biochemical tests are available that provide an index of the overall rate of bone remodeling (Table 423-6). Biochemical mark­ ers usually are characterized as those related primarily to bone formation or bone resorption. These tests measure the overall state of bone remodeling at a single point in time. Clinical use of these tests has been hampered by biologic variability (in part related to circadian rhythm and food consumption) as well as analytic vari­ ability, although the latter has improved. For the most part, remodeling markers do not predict rates of bone loss well enough in individuals to make accurate assessment of potential future changes in bone density. However, they do provide adjunct information that assists in both evaluation of the patient and in assessment of treatment response. Markers of bone resorption may help in the prediction of fracture risk, indepen­ dently of bone density, particularly in older individuals. In women ≥65 years, when bone density results are greater than the usual treatment thresholds noted above, a high level of bone resorption should prompt consideration of treatment. However, the primary use of biochemical markers is for monitoring treatment response. With the introduction of antiresorptive drugs, bone remodeling declines rapidly, with the fall in resorption occurring earlier than the fall in formation. Inhibition of bone resorption is maximal within 3 months or so. Thus, measurement of bone resorption (serum C-terminal telopeptide measured in a fasting specimen at 9 A.M. is the preferred marker) before initiating therapy and 3–6 months after starting therapy provides an earlier estimate of patient response than does bone densitometry. A decline in bone resorption markers can be ascertained after treatment with bisphos­ phonates, denosumab, or estrogen; this effect is less marked after treatment with weaker agents such as raloxifene or calcitonin. Bone turnover markers are also useful in monitoring the effects of ana­ bolic drugs [hPTH(1–34) or teriparatide or romosozumab], which both rapidly increases bone formation (P1NP is the most sensi­ tive, but osteocalcin is also a very good bone remodeling marker), while teriparatide increases bone resorption and romosozumab decreases bone resorption. The recent suggestion of “drug holi­ days” (see below) has opened another use for biochemical markers, allowing evaluation of the offset of effect of drugs such as oral and intravenous bisphosphonates. Drug holidays should be avoided for denosumab or anabolic drugs because of a more rapid offset effect observed with these drugs. TABLE 423-6  Biochemical Markers of Bone Metabolism in Clinical Use Bone formation   Serum bone-specific alkaline phosphatase   Serum osteocalcin   Serum propeptide of type I procollagen Bone resorption   Urine and serum cross-linked N-telopeptide   Urine and serum cross-linked C-telopeptide

TREATMENT Osteoporosis MANAGEMENT OF PATIENTS WITH FRACTURES Treatment of a patient with osteoporosis frequently involves man­ agement of acute fractures as well as treatment of the underly­ ing disease. Hip fractures almost always require surgical repair. Depending on the location and severity of the fracture, condition of the neighboring joint, and general status of the patient, procedures may include open reduction and internal fixation with pins and plates, hemiarthroplasties, and total arthroplasties. These surgical procedures are followed by intense rehabilitation to return patients to their prefracture functional level. Long bone fractures often require either external or internal fixation. Other fractures (e.g., vertebral, rib, and pelvic fractures) can often be managed with sup­ portive care, requiring no specific orthopedic treatment. PART 12 Endocrinology and Metabolism Only ~30% of vertebral compression fractures present with sudden-onset back pain. For acutely symptomatic fractures, treat­ ment with analgesics is required, including nonsteroidal antiinflammatory agents and/or acetaminophen, sometimes with the addition of a narcotic agent. (A few small, randomized clinical trials suggest that calcitonin may reduce pain related to acute vertebral compression fracture). Vertebral augmentation with the percutane­ ous injection of artificial cement (polymethylmethacrylate) into the vertebral body (vertebroplasty or kyphoplasty) may offer significant pain relief in a subset of patients with continuing pain; however, systematic reviews of controlled trials of both procedures have provided doubt about their efficacy. Furthermore, risks include acute extravasation of cement outside of the vertebral body with neurologic impairment and possibly an increased risk of vertebral fracture in adjacent vertebrae due to increased rigidity of the treated vertebral body. Short periods of bed rest may be helpful for pain management, but in general, early mobilization is recommended as it helps prevent further bone loss associated with immobilization. Occasionally, use of a soft elastic-style back brace may facilitate earlier mobilization. Muscle spasms often occur with acute com­ pression fractures and can be treated with muscle relaxants and heat treatments. Severe pain usually resolves within 6–10 weeks. More chronic severe pain might suggest the possibility of multiple myeloma or other underlying bone conditions. Vertebral fractures cause height loss because of the loss of verte­ bral body height during compression of the vertebral body. These fractures can produce a kyphosis, particularly when wedge shaped, or just loss of thoracic height. Chronic pain following vertebral fracture is probably not bony in origin; instead, it is related to abnormal strain on muscles, ligaments, and tendons and to second­ ary facet-joint arthritis associated with alterations in thoracic and/ or abdominal shape. Chronic pain may also be the result of ribs sitting right on top of the iliac crest bones, particularly in patients who have had multiple vertebral compression fractures. Chronic pain is difficult to treat effectively and may require analgesics, sometimes including narcotic analgesics with the attendant risk of addiction. Frequent intermittent rest in a supine or semireclin­ ing position is often required to allow the soft tissues, which are under tension, to relax. Back and core-strengthening exercises may be beneficial. Heat treatments help relax muscles and reduce the muscular component of discomfort. Various physical modalities, such as ultrasound and transcutaneous nerve stimulation, may be beneficial in some patients. Pain also occurs in the neck region, not as a result of compression fractures (which almost never occur in the cervical spine as a result of osteoporosis) but because of chronic strain associated with trying to elevate the head in a person with a significant thoracic kyphosis. Multiple vertebral fractures often are associated with often neglected psychological symptoms. Changes in body configuration and back pain can lead to marked loss of self-image and a secondary depression. Altered balance, precipitated by the kyphosis and the anterior movement of the body’s center of gravity, leads to a fear of

falling, a consequent tendency to remain indoors, and the onset of social isolation. These symptoms sometimes can be alleviated by family support and/or psychotherapy. Medication may be necessary when depressive features are present. A MISSED OPPORTUNITY Multiple studies show most patients presenting with fractures after age 50 years (even fractures traditionally linked to osteoporosis) are not screened or treated for osteoporosis. Only <25% of fracture patients receive follow-up care. Recently, several studies have dem­ onstrated the effectiveness of a relatively simple and inexpensive program that reduces the risk of subsequent fractures. In the Kaiser system, it is estimated that a 20% decline in hip fracture occurrence was seen with the introduction of a fracture liaison service. This approach has also been successful in other non-U.S. health systems, including the United Kingdom and New Zealand. This involves a health care professional (usually a nurse or physician’s assistant) whose job is to educate patients and coordinate evaluation and osteoporosis treatment as patients move through the emergency room, inpatient care in an acute care hospital, rehabilitation hos­ pital care, and/or orthopedic practice to outpatient management. If the Kaiser experience can be repeated, there would not only be significant savings of health care dollars but also a dramatic drop in hip fracture incidence and a marked improvement in morbidity and mortality among the aging population. Initiatives to obtain Medicare funding for fracture liaison services in the United States are continuing but have not yet been successful. MANAGEMENT OF THE UNDERLYING DISEASE Risk Factor Reduction  After risk assessment, patients should be thoroughly educated to reduce the impact of modifiable risk fac­ tors associated with bone loss and falling. Medications should be reviewed to ensure that all are necessary and taken at the lowest required dose. Glucocorticoid medication, if present, should be evaluated to determine that it is truly indicated and is being given in doses as low as possible. For those on thyroid hormone replace­ ment, TSH testing should be performed to determine that an excessive dose is not being used, as iatrogenic thyrotoxicosis can be associated with increased bone loss. In patients who smoke, efforts should be made to facilitate smoking cessation. Reducing risk fac­ tors for falling also includes alcohol abuse treatment and a review of the medical regimen for any drugs that might be associated with orthostatic hypotension and/or sedation, including hypnotics, anti­ psychotics, and anxiolytics. If nocturia occurs, the frequency should be reduced, if possible (e.g., by decreasing or modifying diuretic use), as arising in the middle of sleep is a common precipitant of a fall. Patients should be instructed about environmental safety, such as eliminating exposed wires, curtain strings, slippery rugs, and mobile tables. Avoiding stocking feet on wood floors, checking carpet condition (particularly on stairs), and providing good light in paths to bathrooms and outside the home are important preven­ tive measures. Treatment for impaired vision is recommended, particularly a problem with depth perception, which is specifically associated with increased falling risk. Patients with neurologic impairment (e.g., stroke, Parkinson’s disease, Alzheimer’s disease, multiple sclerosis) are particularly at risk of falling and require specialized supervision and care. In patients with risk factors for falls, especially those who live alone or spend significant time alone, medical alert systems should be prescribed. Nutritional Recommendations  •  Calcium  A large body of data indicates that less than optimal calcium intake results in bone loss. Consequently, an adequate intake suppresses bone turnover. Recom­ mended intakes from an Institute of Medicine report are shown in Table 423-7. The NHANES have consistently documented that aver­ age calcium intakes fall considerably short of these recommendations. The preferred source of calcium is diet, but many patients require calcium supplementation to bring intake to ~1000 mg/d. Calcium supplement doses of ≤600 mg/d are likely to be safe. Best sources of

TABLE 423-7  Adequate Calcium Intake ESTIMATED ADEQUATE DAILY CALCIUM INTAKE, mg/d LIFE STAGE GROUP Young children (1–3 years)

Older children (4–8 years)

Adolescents and young adults (9–18 years)

Men and women (19–50 years)

Men and women (51 years and older)

Note: Pregnancy and lactation needs are the same as for nonpregnant women (e.g., 1300 mg/d for adolescents/young adults and 1000 mg/d for those ≥19 years old). Source: Data from Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: The National Academies Press; 1997. calcium include dairy products (milk, yogurt, and cheese), nondairy milks (almond, rice, soy), nuts, and fortified foods such as certain cereals, waffles, snacks, juices, and crackers. Some of these fortified foods contain as much calcium per serving as milk. Various veg­ etables and fruits, such as kale, broccoli, and dried figs, contain rea­ sonably high calcium content, although some of it may not be fully bioavailable. Calcium intake calculators are available at NOF.org or NYSOPEP.org and will give a rough idea of total calcium intake. If calcium supplements are required, they should be taken in doses sufficient to bring total intake to the required level (~1000 mg/d). Doses of supplements should be ≤600 mg per single dose, as the calcium absorption fraction decreases at higher doses. Calcium supplements should be calculated on the basis of the elemental calcium content of the supplement, not the weight of the calcium salt (Table 423-8). Calcium supplements contain­ ing carbonate are best taken with food since they require acid for solubility. Calcium citrate supplements can be taken at any time, although taking calcium supplements in the evening may reduce nocturnal increases in PTH. Several controlled clinical trials of calcium, mostly with accom­ panying vitamin D, have confirmed reductions in clinical fractures, including fractures of the hip (~20–30% risk reduction), particu­ larly in elderly individuals who are likely to be dietarily deficient. The majority of recent studies of pharmacologic agents have been conducted in the context of calcium replacement (± vitamin D). Thus, it is standard practice to ensure an adequate calcium and vitamin D intake in patients with osteoporosis whether they are receiving additional pharmacologic therapy or not. A systematic review confirmed a greater BMD response to antiresorptive therapy when calcium intake was adequate. Although side effects from supplemental calcium are minimal (eructation and constipation mostly with carbonate salts), indi­ viduals with a history of kidney stones should have a 24-h urine calcium determination before starting increased calcium to avoid exacerbating hypercalciuria. A recent analysis of published data has suggested that high intakes of calcium from supplements are associated with an increase in the risk of renal stones, calcification in arteries, and potentially an increased risk of heart disease and stroke. This is controversial, with recent meta-analyses showing no TABLE 423-8  Elemental Calcium Content of Various Oral

Calcium Preparations CALCIUM PREPARATION ELEMENTAL CALCIUM CONTENT Calcium citrate 60 mg/300 mg Calcium lactate 80 mg/600 mg Calcium gluconate 40 mg/500 mg Calcium carbonate 400 mg/g Calcium carbonate + 5 μg vitamin D2 (OsCal 250) 250 mg/tablet Calcium carbonate (Tums 500) 500 mg/tablet Source: Adapted from SM Krane, MF Holick, in Harrison’s Principles of Internal Medicine, 14th ed. New York, NY: McGraw Hill; 1998.

effect of calcium supplements on cardiovascular events. Daily doses of <700 mg appear safe. However, since high calcium intakes also increase the risk of renal stones and confer no extra benefit to the skeleton, the recommendation that total intakes should be between 1000 and 1500 mg/d seems reasonable.

Vitamin D  Diet alone is inadequate to maintain vitamin D suf­ ficiency (serum 25[OH]D consistently >75 μmol/L [30 ng/mL]). Vitamin D is synthesized from a precursor in the skin under the influence of heat and ultraviolet light (Chap. 421). Production is blocked by sunscreen and sun avoidance. However, large segments of the population do not obtain sufficient vitamin D from either skin production or dietary sources. Since vitamin D supplemen­ tation at doses that would achieve these serum levels is safe and inexpensive, the National Academy of Medicine recommends daily intakes of 200 IU for adults <50 years of age, 400 IU for those 50–70 years, and 600 IU for those >70 years (based on obtaining a serum level of 20 ng/mL, lower than the level recommended by most other guidelines). Multivitamin tablets usually contain 400 IU, and many calcium supplements also contain vitamin D. Some data suggest that higher doses (≥1000 IU) may be required, particularly in the obese, elderly, and chronically ill. A daily intake of up to 4000 IU/d is safe. For those with osteoporosis or those at risk, 1000–2000 IU/d can usually maintain serum 25(OH)D above 30 ng/mL. Recent large randomized controlled trials show vitamin D supplementation by itself at doses equivalent to 2000 IU/d does not appear to reduce fracture risk in older individuals with normal baseline vitamin D levels. However, the combination of adequate calcium intake and vitamin D does decrease fracture risk in those with vitamin D deficiency, particularly the institutionalized elderly population. Although low vitamin D levels appear associated with more serious outcomes in response to COVID-19, trials of vitamin D supplementation have been inconsistent and largely negative. Osteoporosis CHAPTER 423 Other Nutrients  Other nutrients such as salt, high animal protein intakes, and caffeine may have modest effects on calcium excretion or absorption. Adequate vitamin K status is required for optimal carboxylation of osteocalcin. States in which vitamin K nutrition or metabolism is impaired, such as with long-term war­ farin therapy, have been associated with reduced bone mass. How­ ever, a recent trial showed no benefit of vitamin K2 on BMD when added to calcium and vitamin D supplementation. Research concerning cola-based soda beverage intake is controversial but suggests a possible link to reduced bone mass through factors that appear independent of caffeine. Magnesium is abundant in foods, and magnesium deficiency is quite rare in the absence of a serious chronic disease. Magnesium supplementation may be warranted in patients with inflammatory bowel disease, celiac disease, chemotherapy, severe diarrhea, mal­ nutrition, or alcoholism. Dietary phytoestrogens, which are derived primarily from soy products and legumes (e.g., garbanzo beans [chickpeas] and lentils), exert some estrogenic activity but are insuf­ ficiently potent to justify their use in place of a pharmacologic agent in the treatment of osteoporosis. Patients with hip fractures are often frail and relatively malnour­ ished. Some data suggest an improved outcome in such patients when they are provided calorie and protein supplementation. Excessive protein intake can increase renal calcium excretion, but this can be corrected by an adequate calcium intake. Exercise  Exercise in young individuals prior to and at the time of puberty increases the likelihood that they will attain the maximal genetically determined peak bone mass. Meta-analyses of studies performed in postmenopausal women indicate that progressive high-intensity resistance training results in small gains in bone mass of 3–4%. However, this beneficial effect wanes if exercise is discon­ tinued. Most of the studies are relatively short term, and a more substantial effect on bone mass is likely if exercise is continued over a long period. Exercise also has beneficial effects on neuromuscu­ lar function, and it improves coordination, balance, and strength,

thereby reducing the risk of falling. A walking program is a practical way to start. Other activities such as dancing, racquet sports, crosscountry skiing, and progressive high-intensity resistance training are also recommended, depending on the patient’s personal prefer­ ence and general condition. Even women who cannot walk benefit from swimming or water exercises, not so much for the effects on bone, which are quite minimal, but because of effects on muscle. Exercise habits should be consistent, optimally at least three times a week. For most patients, participation in exercise regimens that the patient enjoys is recommended in order to improve adherence. We also emphasize the importance of making exercise a social activity, again to improve adherence. Many individuals experience a fear of falling that can lead to social isolation and depression. Group exer­ cise can help to alleviate this problem by providing a sense of social connectivity among participants.

PART 12 Endocrinology and Metabolism Tai chi is a traditional Chinese martial art that utilizes a series of gentle, flowing movements to promote and maintain flexibil­ ity, balance, endurance, proprioception, and strength. It involves constant movement through all three spatial dimensions. As a three-dimensional exercise, tai chi may be incorporated as part of balance training program for individuals with osteoporosis. Tai chi is generally considered a safe activity. The evidence for fall preven­ tion in tai chi has been evaluated in randomized controlled trials, and systematic reviews indicate tai chi can significantly reduce the risk of falls in older adults, particularly when it is practiced with increased frequency. It is recommended that individuals with osteoporosis or osteo­ porotic vertebral fractures participate in exercise programs that involve both high-intensity progressive resistance and balance training. Slow, controlled movements are recommended in order to avoid injuries. Exercise modifications and avoidance of certain postures (such as spinal flexion) may be advised. Caution should be taken to avoid activities that can lead to potential fractures, such as performing activities on slippery surfaces, or twisting or bending the spine quickly while transitioning between different positions. Precautions should be taken to avoid injury when exercising with loads and performing exercises that challenge balance. For individ­ uals with osteoporosis who have a high risk for fracture, vertebral fractures, sedentary lifestyle, or comorbid conditions that impact exercise tolerance, consultation with physical therapists to learn safe exercise programs is recommended. PHARMACOLOGIC TREATMENT OF OSTEOPOROSIS Several international osteoporosis management guidelines have been published. They recommend patients with fractures of the hip and spine should be evaluated for treatment. Patients with minimal trauma fractures in the setting of a BMD in the osteopenia or osteo­ porosis range should be treated with pharmacologic agents. Most guidelines also suggest that patients be considered for treatment when BMD T-score is ≤–2.5, a level consistent with the diagnosis of osteoporosis. Treatment should also be considered in postmeno­ pausal women with a minimal trauma fracture or multiple risk factors even if BMD is not in the osteoporosis range. Treatment thresholds depend on cost-effectiveness analyses but, in the United States, are a >20% 10-year major fracture probability and >3% 10-year hip fracture probability. It must be emphasized, however, that as with other diseases, risk assessment is an inexact science when applied to the individual. As a result, patients often accept fracture risks that are higher than the physician might like out of concern for the usually considerably lower but better publicized risks of adverse events of drugs. Pharmacologic therapies for osteoporosis are either antiresorp­ tive or anabolic. The antiresorptive agents include medications that have broad effects such as hormone/estrogen therapy and selective estrogen receptor modulators (SERMS) as well as specific agents for osteoporosis treatment (bisphosphonates, denosumab, and cal­ citonin). The anabolic agents are teriparatide, abaloparatide, and romosozumab. Denosumab allows bone formation to continue, and thus, there is an increase in bone density beyond that occurring

with agents that inhibit resorption directly leading to a reduction in bone formation like bisphosphonates. Antiresorptive Agents  •  Estrogens  A large body of clinical trial data indicates that various types of estrogens (conjugated equine estrogens, estradiol, estrone, esterified estrogens, ethinyl estradiol, and mestranol) reduce bone turnover, prevent bone loss, and induce small increases in bone mass of the spine, hip, and total body. The effects of estrogen are seen in women with natural or surgical menopause and in late postmenopausal women with or without established osteoporosis. Estrogens are efficacious when administered orally, transdermally, or by subcutaneous implant. For both oral and transdermal routes of administration, combined estrogen/progestin preparations are now available in many coun­ tries, obviating the problem of taking two tablets or using a patch and oral progestin. For oral estrogens, the standard recommended doses have been 0.3 mg/d for esterified estrogens, 0.625 mg/d for conjugated equine estrogens, and 5 μg/d for ethinyl estradiol. For transdermal estro­ gen, the commonly used dose supplies 50 μg of estradiol per day, but a lower dose may be appropriate for some individuals. Doseresponse data for conjugated equine estrogens indicate that lower doses (0.3 and 0.45 mg/d) are also effective. Doses even lower have also been shown to slow bone loss. Fracture Data  Epidemiologic databases indicate that women who take estrogen replacement have a 50% reduction, on average, of osteoporosis-related fractures, including hip fractures. The ben­ eficial effect of estrogen is greatest among those who start replace­ ment early and continue the treatment; the benefit declines after discontinuation to the extent that there is no residual protective effect against fracture by 10 years after discontinuation. The first clinical trial evaluating fractures as secondary outcomes, the Heart and Estrogen-Progestin Replacement Study (HERS) trial, showed no effect of hormone therapy on hip or other clinical fractures in women with established coronary artery disease. These data made the results of the Women’s Health Initiative (WHI) exceedingly important (Chap. 395). The estrogen-progestin arm of the WHI in

16,000 postmenopausal healthy women not selected based on low bone mass indicated that hormone therapy reduces the risk of hip and clinical spine fracture by 34% and that of all clinical fractures by 24%. A few smaller clinical trials have evaluated spine fracture occur­ rence as an outcome with estrogen therapy. They have consistently shown that estrogen treatment reduces vertebral fracture incidence. The WHI has provided a vast amount of data on the multisys­ temic effects of hormone therapy. Although earlier observational studies suggested that estrogen replacement might reduce heart disease, the WHI showed that combined estrogen-progestin treat­ ment increased risk of fatal and nonfatal myocardial infarction by ~29%, confirming data from the HERS study. Other important relative risks included a 40% increase in stroke, a 100% increase in venous thromboembolic disease, and a 26% increase in risk of breast cancer. Subsequent analyses have confirmed the increased risk of stroke and, in a substudy, showed a twofold increase in dementia. Benefits other than the fracture reductions noted above included a 37% reduction in the risk of colon cancer. These relative risks must be interpreted in light of absolute risk (Fig. 423-8). For example, out of 10,000 women treated with estrogen-progestin for 1 year, there will be 8 excess heart attacks, 8 excess breast cancers, 18 excess venous thromboembolic events, 5 fewer hip fractures, 44 fewer clinical fractures, and 6 fewer colorectal cancers. These numbers must be multiplied by the number of years of hormone treatment. There was no effect of combined hormone treatment on the risk of uterine cancer or total mortality. It is important to note that these WHI findings apply specifically to hormone treatment in the form of conjugated equine estrogen plus medroxyprogesterone acetate. The relative benefits and risks of unopposed estrogen in women who had hysterectomies vary somewhat. They still show benefits against fracture occurrence

Risks Benefits Neutral

Additional events

in 10,000 women/year

Number of cases

Reduced events

CHD Stroke Deaths Breast cancer VTE Hip fracture Endometrial cancer Colorectal cancer FIGURE 423-8  Effects of hormone therapy on event rates: green, placebo; purple, estrogen and progestin. CHD, coronary heart disease; VTE, venous thromboembolic events. (Adapted from Women’s Health Initiative. WHI HRT Update.) and increased risk of venous thrombosis and stroke, similar in magnitude to the risks for combined hormone therapy. In contrast, though, the estrogen-only arm of WHI indicated no increased risk of heart attack and a decreased risk of breast cancer. The data suggest that at least some of the detrimental effects of combined therapy are related to the progestin component. In addition, there is the possibility, suggested by primate data, that the risk accrues mainly to women who have some years of estrogen deficiency before initiating treatment. Therefore, the benefit/risk ratio of hormone therapy is improved if it is commenced before the age of

60 years or within 10 years of menopause. Nonetheless, there has been marked reluctance among women for estrogen therapy/ hormone therapy, and the U.S. Preventive Services Task Force has specifically suggested that estrogen therapy/hormone therapy not be used for disease prevention. Mode of Action  Two subtypes of ERs, α and β, have been identified in bone and other tissues. Cells of monocyte lineage express both ERα and ERβ, as do osteoblasts. Estrogen-mediated effects vary with the receptor type. Using ER knockout mouse models, elimination of ERα produces a modest reduction in bone mass, whereas mutation of ERβ has less of an effect on bone. A man with a homozygous mutation of ERα had markedly decreased bone density as well as abnormalities in epiphyseal closure, con­ firming the important role of ERα in bone biology. The mecha­ nism of estrogen action in bone is an area of active investigation

(Fig. 423-5). Although data are conflicting, estrogens may inhibit osteoclasts directly. However, most estrogen (and androgen) effects on bone resorption are mediated indirectly through paracrine fac­ tors produced by osteoblasts. These actions include (1) increasing the inhibitor of RANK-L, osteoprotegerin, production by osteo­ blasts, (2) increasing IGF-I and TGF-β, and (3) suppressing IL-1 (α and β), IL-6, TNF-α, and osteocalcin synthesis. These indirect estrogen actions primarily decrease bone resorption. Progestins  In women with a uterus, daily progestin or cyclical progestins at least 12 days per month are prescribed in combination with estrogens to reduce the risk of uterine cancer. Medroxypro­ gesterone acetate and norethindrone acetate blunt the high-density lipoprotein response to estrogen, but micronized progesterone does not. Neither medroxyprogesterone acetate nor micronized pro­ gesterone appears to have an independent effect on bone; at lower doses of estrogen, norethindrone acetate may have an additive ben­ efit. In breast tissue, progestins may account for the increased risk of breast cancer with combination treatment. SERMs  Two SERMs are used currently in postmenopausal women: raloxifene, which is approved by the FDA for the preven­ tion and treatment of osteoporosis as well as the prevention of breast cancer, and tamoxifen, which is approved for the prevention and treatment of breast cancer. A third SERM, bazedoxifene, is marketed in combination with conjugated estrogen for treatment of

menopausal symptoms and prevention of bone loss. Bazedoxifene protects the uterus and breast from effects of estrogen and makes the use of progestin unnecessary.

Tamoxifen reduces bone turnover and bone loss in postmeno­ pausal women compared with placebo groups. These findings support the concept that tamoxifen acts as an estrogenic agent in bone. There are limited data on the effect of tamoxifen on fracture risk, but the Breast Cancer Prevention study indicated a possible reduction in clinical vertebral, hip, and Colles’ fractures. Tamoxifen is not FDA approved for prevention or treatment of osteoporosis. The major benefit of tamoxifen is on breast cancer occurrence and recurrence in women with ER-positive tumors. The breast can­ cer prevention trial indicated that tamoxifen administration over 4–5 years reduced the incidence of new invasive and noninvasive breast cancer by ~45% in women at increased risk of breast cancer. The incidence of ER-positive breast cancers was reduced by 65%. Tamoxifen increases the risk of uterine cancer in postmenopausal women, limiting its use for breast cancer prevention in women at low or moderate risk. Osteoporosis CHAPTER 423 Raloxifene (60 mg/d) has effects on bone turnover and bone mass that are very similar to those of tamoxifen, indicating that this agent is also estrogenic on the skeleton. The effect of raloxifene on bone density (+1.4–2.8% vs. placebo in the spine, hip, and total body) is somewhat less than that seen with standard doses of estrogens. Raloxifene reduces the occurrence of vertebral fracture by 30–50%, depending on the population; however, there are no data confirm­ ing that raloxifene can reduce the risk of nonvertebral fractures after 8 years of observation. Raloxifene, like tamoxifen and estrogen, has effects on other organ systems. The most beneficial effect appears to be a reduction in invasive breast cancer (mainly decreased ER-positive) occurrence of ~65% in women who take raloxifene compared with placebo. In a head-to-head study, raloxifene was as effective as tamoxifen in preventing breast cancer in high-risk women, and raloxifene is FDA approved for this indication. In a further study, raloxifene had no effect on heart disease in women with increased risk for this outcome. In contrast to tamoxifen, raloxifene is not associated with an increase in the risk of uterine cancer or benign uterine disease. Raloxifene increases the occurrence of hot flashes but reduces serum total and low-density lipoprotein cholesterol, lipoprotein(a), and fibrinogen. Raloxifene, with its positive effects on breast cancer and vertebral fractures, has become a useful agent for the treatment of the younger asymptomatic postmenopausal woman. In some women, a recurrence of menopausal symptoms may occur. Usually this is evanescent but occasionally is sufficiently impactful on daily life and sleep that the drug must be withdrawn. Raloxifene increases the risk of deep-vein thrombosis and may increase the risk of death from stroke among older women. Consequently, it is not usually recommended for women over age 70 years. MODE OF ACTION OF SERMS All SERMs bind to the ER, but each agent produces a unique recep­ tor-drug conformation. As a result, specific coactivator proteins or co-repressor proteins are bound to the receptor (Chap. 389), result­ ing in differential effects on gene transcription that vary depending on other transcription factors present in the cell. Another aspect of selectivity is the affinity of each SERM for the different ERα and ERβ subtypes, which are expressed differentially in various tissues. These tissue-selective effects of SERMs offer the possibility of tailoring estrogen therapy to best meet the needs and risk factor profile of an individual patient. Bisphosphonates  Bisphosphonates have become the mainstay of osteoporosis treatment globally, in part related to cost as they have become generic. Alendronate, risedronate, ibandronate, and zole­ dronic acid are approved for the prevention and treatment of post­ menopausal osteoporosis. Alendronate, risedronate, and zoledronic acid are also approved for the treatment of glucocorticoid-induced osteoporosis, and risedronate and zoledronic acid are approved for prevention of glucocorticoid-induced osteoporosis. Alendronate,

risedronate, and zoledronic acid are also approved for treatment of osteoporosis in men.

Alendronate decreases bone turnover and increases bone mass by up to 8 and 6% versus placebo in the spine and hip, respectively. Multiple trials have evaluated its effect on fracture occurrence. The Fracture Intervention Trial provided evidence in >2000 women with prevalent vertebral fractures that daily alendronate treatment (5 mg/d for 2 years and 10 mg/d for 9 months afterward) reduces vertebral fracture risk by ~50%, multiple vertebral fractures by up to 90%, and hip fractures by up to 50%. Several subsequent trials have confirmed these findings (Fig. 423-9). For example, in a study of >1900 women with low bone mass treated with alendronate

(10 mg/d) versus placebo, the incidence of all nonvertebral fractures was reduced by ~47% after only 1 year. In the United States, the 70-mg weekly dose is approved for treatment of osteoporosis and the dose of 35 mg per week is approved for prevention, with those doses showing equivalence to daily dosing based on bone turnover and bone mass response. PART 12 Endocrinology and Metabolism Consequently, once-weekly therapy generally is preferred because of lower incidence of gastrointestinal side effects, ease of adminis­ tration, and improved persistence with therapy. Alendronate should be taken with a full glass of water before breakfast after an over­ night fast, as bisphosphonates are poorly absorbed. Because of the potential for esophageal irritation, alendronate is contraindicated in patients who have stricture, achalasia, or inadequate emptying of the esophagus. It is recommended that patients remain upright (standing or sitting) for at least 30 min after taking the medication to avoid esophageal irritation and that food and fluids (other than water) be avoided for the same duration. In clinical trials, overall gastrointestinal symptomatology was no different with alendronate than with placebo, but in practice, all oral bisphosphonates have been associated with esophageal irritation and inflammation. Risedronate also reduces bone turnover and increases bone mass. Controlled clinical trials have demonstrated 40–50% reduction in vertebral fracture risk over 3 years, accompanied by a 40% reduc­ tion in clinical nonspine fractures. The only clinical trial specifically designed to evaluate hip fracture outcome (HIP) indicated that risedronate reduced hip fracture risk in women in their seventies with confirmed osteoporosis by 40%. In contrast, risedronate was not effective at reducing hip fracture occurrence in older women (80+ years) without proven osteoporosis. Studies have shown that 35 mg of risedronate administered once weekly is therapeutically equivalent to 5 mg/d. The instructions for oral administration noted for alendronate apply to all three oral bisphosphonates. There is also a preparation of risedronate with an enteric coating (35 mg) that can be taken after breakfast. Risedronate is the only bisphos­ phonate that has this dosing flexibility. Ibandronate is the third amino-bisphosphonate approved in the United States. Ibandronate (2.5 mg/d) has been shown in clinical trials to reduce vertebral fracture risk by ~40% but with no overall effect on nonvertebral fractures. In a post hoc analysis of subjects with a femoral neck T-score of ≤–3, ibandronate reduced the risk of nonvertebral fractures by ~60%. In clinical trials, ibandronate doses of 150 mg per month PO or 3 mg every 3 months IV had greater effects on turnover and bone mass than did 2.5 mg/d. Patients should take oral ibandronate in the same way as other bisphospho­ nates but with 1 h elapsing before other food or drink (other than plain water). Zoledronic acid is a potent bisphosphonate with a unique admin­ istration regimen (5 mg by 30-min IV infusion at most annually). Zoledronic acid data confirm that it is highly effective in fracture risk reduction. In a study of >7000 women followed for 3 years, zoledronic acid (5 mg IV annually) reduced the risk of vertebral fractures by 70%, nonvertebral fractures by 25%, and hip fractures by 40%. These results were associated with less height loss and disability. In the treated population, there was an increased risk of almost 25% of an acute phase response (APR) in patients with no prior bisphosphonate exposure (fever, myalgias, headache, malaise), but effects were short-lived (2–3 days). A recent study shows the

APR can be eliminated by the administration of dexamethasone

(4 mg) for 3 days commencing 90 min before the infusion. Although there was also an increased risk of atrial fibrillation in this trial, detailed evaluation of all bisphosphonates has failed to confirm a risk of atrial fibrillation. Zoledronic acid has also been studied in a placebo-controlled trial of older women and men within 3 months of an acute hip fracture. The risk of recurrent fracture was reduced by 35%, and there was a 28% reduction in mortality that was asso­ ciated with a reduction in infections and cardiovascular events. In older postmenopausal women with osteopenia, the risk of non­ vertebral, vertebral, or clinical fragility fractures was significantly lower in women with osteopenia who received zoledronate every 18 months for 6 years than in women who received placebo. In an extension study of the women who had received zoledronic acid infusions for 6 years, the risk of nonvertebral fractures remained low for up to 3.5 years after the last dose but increased after that time. This suggests less frequent dosing may be required after an initial course of three or four zoledronic acid infusions. Common Bisphosphonate Adverse Events  All bisphospho­ nates have been associated with some musculoskeletal and joint pains of unclear etiology, which are occasionally severe. There is poten­ tial for renal toxicity, particularly in women with stage 3 chronic kidney disease (CKD), and bisphosphonates are contraindicated in those with an estimated glomerular filtration rate <30–35 mL/min.

Hypocalcemia can occur. Two potential side effects have been associated with bisphospho­ nate use. The first is medication-related osteonecrosis of the jaw (MRONJ). MRONJ usually follows a dental procedure in which bone is exposed (dental extractions and implants). It is presumed that the exposed bone becomes infected and dies. MRONJ is more common among cancer patients receiving high doses of bisphos­ phonates for skeletal metastases. It is rare among persons with osteoporosis on usual doses of bisphosphonates. Additional risk factors for MRONJ are poor dental hygiene, diabetes, and gluco­ corticoids. Oral antibiotic rinses and oral systemic antibiotics may be useful to prevent this rare adverse event if risk is perceived to be particularly high. In addition, any invasive dental procedures should be performed prior to commencement of bisphosphonate therapy. Because bisphosphonates have a long skeletal half-life, it is unlikely that withholding therapy prior to an invasive procedure will reduce MRONJ risk; however, this is often recommended by dentists and faciomaxillary surgeons. Teriparatide treatment for 2 months has been shown to reduce bone lesions associated with MRONJ versus placebo. The second side effect is called atypical femoral fracture. These are stress fractures occurring in the subtrochanteric femoral region or across the femoral shaft distal to the lesser trochanter. They are often preceded by pain in the lateral thigh or groin that can be present for weeks, months, or even years before the fracture. The fractures occur following either no or trivial trauma, are predomi­ nantly horizontal with a medial beak, and are noncomminuted. An American Society for Bone and Mineral Research Task Force described the major and minor criteria for these fractures, which are related to duration of bisphosphonate therapy and increase after 5–7 years of treatment, but only after 3 years of exposure in Asian patients. The overall risk appears quite low, especially when compared with the number of hip fractures prevented by these therapies, but they often require surgical fixation and show delayed healing. The risk is also increased with Asian ethnicity, rheumatoid arthritis, glucocorticoids, proton pump inhibitors, and SSRIs. In some cases (10–30%), there is no bisphosphonate exposure, and in some of these cases, there may be an underlying rare monogenetic bone disease such as osteogenesis imperfecta, hypophosphatasia, X-linked hypophosphatemic rickets, X-linked osteoporosis, or pyc­ nodysostosis. Other genetic risk factors for atypical femur fractures have been identified in families with bisphosphonate-associated atypical femur fractures. If the fractures are found early, when there is evidence of periosteal stress reaction or stress fracture, prior to the occurrence of overt fracture, surgical intervention may be

Risedronate pooled, post hoc Alendronate pooled, post hoc

PLB PLB ALN RIS

Percent of patients 45%↓*

A Months Months Months Months Alendronate pooled, post hoc Risedronate pooled, post hoc

PLB ALN 27%↓* Percent of patients

Months B Months Cumulative incidence of hip fractures over 3 years

Cumulative incidence (%)

Placebo (n = 3861) Zolendronate (n = 3875)

Time to first hip fracture (months) C FIGURE 423-9  Effects of various bisphosphonates on fracturs. A. Clinical vertebral fractures. B. Nonvertebral fractures. C. Hip fractures. Plb, placebo; RRR, relative risk reduction. (Data from DM Black et al: J Clin Endocrinol Metab 85:4238, 2000; C Roux et al: Curr Med Res Opin 4:433, 2004; CH Chesnut et al: J Bone Miner Res 19: 1241, 2004; DM Black et al: N Engl J Med 356:1809, 2007; JT Harrington et al: Calcif Tissue Int 74:129, 2003.)

Vertebral fractures Ibandronate preplanned Zoledronate preplanned

PLB IBAN PLB ZOL

49↓* Osteoporosis CHAPTER 423 77%↓*

69%↓* ?

Nonvertebral fractures Zoledronate preplanned

PLB PLB RIS ZOL

25%↓* 59%↓* ?

Months Hip fractures RRR 41%

required. The evidence that teriparatide can help heal the fracture and preclude the need for surgical repair from case series is mixed, and published trial data are not available. When patients initiate bisphosphonates, they should be informed that if they develop thigh or groin pain, they should inform their health care profes­ sional. Routine x-rays will sometimes detect cortical thickening or even a stress fracture, but MRI or technetium bone scans are more sensitive. The presence of an abnormality requires, at minimum, a period of modified weight-bearing and may need prophylactic rodding of the femur. It is important to realize that these may often be bilateral (~50% of the time), and when an abnormality is found, the other femur should be checked. It is unknown whether patients who have these atypical femur fractures can ever receive antiresorp­ tive therapies again in the future, but it seems prudent to avoid their use for most of these individuals.

PART 12 Endocrinology and Metabolism Mode of Action  Bisphosphonates are structurally related to pyrophosphates, compounds that are incorporated into bone matrix. Bisphosphonates are taken up at sites of active bone remodeling and specifically impair osteoclast function and reduce osteoclast number, in part by inducing apoptosis. Recent evidence suggests that the nitrogen-containing bisphosphonates also inhibit protein prenyl­ ation, one of the end products in the mevalonic acid pathway, by inhibiting the enzyme farnesyl pyrophosphate synthase. This effect disrupts intracellular protein trafficking and ultimately may lead to apoptosis. Some bisphosphonates have very long retention in the skeleton and may exert long-term effects via recirculation of bisphos­ phonates retained in bone when bone remodeling recurs at that site. Calcitonin  Calcitonin is a polypeptide hormone produced in the thyroid gland (Chap. 422). Its physiologic role is unclear as no skeletal disease has been described in association with calcitonin deficiency or excess. Calcitonin preparations are approved by the FDA for Paget’s disease, hypercalcemia, and osteoporosis in women

5 years past menopause. Injectable calcitonin produces small increments in bone mass of the lumbar spine. However, difficulty of administration and frequent reactions, including nausea and facial flushing, make gen­ eral use limited. A nasal spray containing calcitonin (200 IU/d) is available for treatment of osteoporosis in postmenopausal women. One study suggests that nasal calcitonin produces small increments in bone mass and a small reduction in new vertebral fractures in calcitonin-treated patients (at one dose) versus those on calcium alone. There has been no proven effectiveness against nonvertebral fractures. Calcitonin is not indicated for prevention of osteoporosis and is not sufficiently potent to prevent bone loss in early post­ menopausal women. Calcitonin might have an analgesic effect on bone pain, both in the subcutaneous and possibly in the nasal form. Concerns have been raised about an increase in the incidence of cancer associated with calcitonin use. Initially, the cancer noted was of the prostate, but an analysis of all data suggested a more general increase in cancer risk. In Europe, the European Medicines Agency has removed the osteoporosis indication, and an FDA Advisory Committee has voted for a similar change in the United States. Mode of Action  Calcitonin suppresses osteoclast activity by direct action on the osteoclast calcitonin receptor. Osteoclasts exposed to calcitonin cannot maintain their active ruffled border, which normally maintains close contact with underlying bone. Denosumab  Denosumab is a human monoclonal antibody that inhibits RANKL, a potent stimulus of osteoclast activity. It is administered twice yearly by subcutaneous injection. In a random­ ized controlled trial in postmenopausal women with osteoporosis, it has been shown to increase BMD at the spine, hip, and forearm and reduce vertebral, hip, and nonvertebral fractures over a 3-year period by 68, 40, and 20%, respectively (Fig. 423-10). Unlike bisphosphonates in which BMD plateaus after 4–5 years of treat­ ment, bone density continues to increase as long as denosumab treatment is continued. In a long-term extension of the pivotal fracture trial, BMD increased by 21.7 and 9.2% at the spine and

A New vertebral fracture Placebo Denosumab RR, 0.32 p <0.001 RR, 0.39 p <0.001 RR, 0.22 p <0.001 RR, 0.35 p <0.001

Crude incidence (%)

0–36 0–12

12–24 12–36 Month B Time to first nonvertebral fracture

Placebo

Cumulative incidence (%) Cumulative incidence (%)

Denosumab

Month

No. at risk Placebo Denosumab

C Time to first hip fracture 1.4 Placebo 1.2 1.0 0.8 0.6 Denosumab 0.4 0.2 0.0

Month

No. at risk Placebo Denosumab

FIGURE 423-10  Effects of denosumab on the following: A. new vertebral fractures; and B. and C. times to nonvertebral and hip fracture. RR, relative risk. (From SR Cummings et al: Denosumab for prevention of fractures in postmenopausal women with osteoporosis. N Engl J Med 361:756, 2009. Copyright © 2009 Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society.) hip, respectively, after 10 years of denosumab treatment. Over the 10 years, fracture rates also remained at least as low as those seen with denosumab during the active placebo-controlled portion of the trial. Other clinical trials indicate ability to increase bone mass in postmenopausal women with osteopenia and in postmenopausal women with breast cancer treated with aromatase inhibitors. In the oncology literature, denosumab reduces the risk of fractures in women on aromatase inhibitors. In a study of men with prostate cancer treated with androgen deprivation therapy, denosumab increased bone mass and reduced vertebral fracture incidence over 3 years. An analysis of five placebo-controlled studies has also

suggested reduced risk of falls in patients with osteoporosis treated with denosumab. Denosumab was approved by the FDA in 2010 for the treatment of postmenopausal women who have a high risk for osteoporotic fractures, including those with a history of fracture or multiple risk factors for fracture, and those who have failed or are intolerant to other osteoporosis therapy. Denosumab is also approved for the treatment of osteoporosis in men at high risk for fracture, women with breast cancer on aromatase inhibitors, and men with prostate cancer on androgen deprivation treatment. Denosumab may increase the risk of MRONJ and atypical femur fractures similarly to bisphosphonates. Estimated incidence is 5/10,000 patient-years for MRONJ and 1/10,000 patient-years for atypical femur fractures. Denosumab can cause hypersensitivity reactions, hypocalcemia, and skin reactions including dermatitis, rash, and eczema. Early concerns about an imbalance in infections with denosumab have largely been allayed. Severe hypocalcemia may occur in patients with CKD and an estimated glomerular filtration rate <30 mL/min, particularly in those on hemodialysis. Serum calcium levels should be monitored if denosumab is used in such patients, and active vitamin D analogues and calcium may be required for its treatment. Unlike bisphosphonates, when denosumab is discontinued, there is a rebound increase in bone turnover and an acceleration of bone loss. This likely reflects the maturation of accumulated osteoclast precursors (osteomorphs) in bone marrow when the drug was administered that then coalesce to become mature bone resorbing cells once denosumab is withdrawn. Other mechanisms involv­ ing reduced osteoprotegerin levels and osteocytes may also be involved. The consequences of this rebound increase in remodelingassociated bone loss are trabecular perforation and a rapid increase in the risk of fracture, particularly vertebral fracture, with a specific increase in multiple vertebral fractures. In patients who need to stop denosumab or in patients in whom BMD and fracture risk reduc­ tion goals have been met, temporary use of bisphosphonate treat­ ment may prevent the rebound increase in remodeling and rapid bone loss. In clinical practice, a single infusion of zoledronic acid at the time of the missed denosumab dose seems to maintain BMD for 1–2 years but may need to be repeated after 3 months, or more often, if bone turnover markers remain elevated. Oral bisphospho­ nates can also be used for 12–24 months to maintain bone density. In both cases, the required duration of bisphosphonate use to eliminate the rebound effect is not clear and may vary considerably among patients so bone density should continue to be monitored. Mode of Action  Denosumab is a fully human monoclonal anti­ body to RANKL, the final common effector of osteoclast formation, activity, and survival. Denosumab binds to RANKL, inhibiting its ability to initiate formation of mature osteoclasts from osteoclast precursors and to bring mature osteoclasts to the bone surface and initiate bone resorption. Denosumab also plays a role in reducing osteoclast survival. Through these actions on the osteoclast, deno­ sumab induces a potent and rapid antiresorptive action, as assessed biochemically and histomorphometrically. Anabolic Agents  •  Parathyroid Hormone  Endogenous PTH is an 84-amino-acid peptide that is largely responsible for calcium homeostasis (Chap. 422). Although chronic elevation of PTH, as occurs in hyperparathyroidism, is associated with bone loss (par­ ticularly at cortical bone sites such as the femoral neck and radius), PTH also can exert anabolic effects on bone if administered inter­ mittently. Consistent with this, some observational studies have indicated that mild endogenous hyperparathyroidism is associated with maintenance of trabecular bone mass but loss of cortical bone. Based on these findings, early small-scale observational stud­ ies showed that PTH analogues could augment trabecular BMD. Subsequent controlled clinical trials have confirmed that PTH can increase bone mass and reduce fracture incidence. The first random­ ized controlled trial in postmenopausal women showed that PTH (1–34) (teriparatide), when superimposed on ongoing estrogen

therapy, produced substantial increments in bone mass (13% over a 3-year period compared with estrogen alone) and reduced the risk of vertebral compression fractures. In the pivotal study (median,

19 months’ duration), 20 μg PTH (1–34) daily by subcutaneous injection (with no additional therapy) reduced vertebral fractures by 65% and nonvertebral fractures by 53% (Fig. 423-11). Teriparatide produces rapid and robust increases in bone formation and then bone remodeling overall, resulting in substantial increases in bone mass and improvements in microarchitecture, including cancel­ lous connectivity and cortical width. The BMD effects, particularly in the hip, are lower when patients switch from bisphosphonates to teriparatide, possibly in proportion to the potency of the anti­ resorptive agent. The hip BMD effect is particularly impaired and may result in transient bone loss, when patients switch from

Osteoporosis CHAPTER 423 Effect of teriparatide on the risk of new vertebral fractures

more new vertebral fractures Number of women with 1 or

Risk reduction

Relative: 65% Absolute: 9.3% Relative: 69% Absolute: 9.9% % of women

Placebo (n = 448) TPTD20 (n = 444) TPTD40 (n = 434) A Effect of teriparatide on the risk of nonvertebral fragility fractures

nonvertebral fragility fractures Risk reduction

Number of women with Relative: 53% Absolute: 2.9% Relative: 54% Absolute: 3.0%

% of women

Placebo (n = 544) TPTD20 (n = 541) TPTD40 (n = 552) B Effect of teriparatide on the risk of nonvertebral fragility fractures (time to first fracture)

% of women** *p <0.05 vs. placebo Placebo

TPTD20 TPTD40 * *

C Months since randomization FIGURE 423-11  Effects of teriparatide (TPT) on the following: A. new vertebral fractures; and B. and C. nonvertebral fragility fractures. (A and B are data from RM Neer et al: Effect of parathyroid hormone (1–34) on fractures and bone mineral density in postmenopausal women with osteoporosis. N Engl J Med May 344:1434, 2001. C From New England Journal of Medicine RM Neer et al: Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis, 344:1434-1441. Copyright © 2001 Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society.)

denosumab to teriparatide. In patients on denosumab who need teriparatide treatment, there may be a role for combination therapy. In previously untreated women, teriparatide is administered as monotherapy and followed by a potent antiresorptive agent such as denosumab or an oral or intravenous bisphosphonate. Combi­ nation therapy is generally avoided because of cost and potential inhibition of the anabolic activity of teriparatide. Comparison with Antiresorptive Therapy  In women with painful acute osteoporotic vertebral fractures, teriparatide reduced subsequent vertebral fractures by ~50% compared with risedronate. There was no difference in nonvertebral fracture outcome between the two medications. A study comparing teriparatide with risedro­ nate in patients with prevalent vertebral fractures showed significant benefit for teriparatide against vertebral fractures (Fig. 423-12) and clinical fractures with a trend for a benefit of teriparatide against nonvertebral fractures.

PART 12 Endocrinology and Metabolism Side effects of teriparatide are generally mild and can include muscle pain, weakness, dizziness, headache, and nausea. These tend to remit with continuing treatment but may be mitigated by giving injections at night. Rodents given prolonged treatment with PTH in high doses (3–60 times the human dose) developed osteogenic sarcomas after ~18 months of treatment. Rare cases of osteosarcoma have been described in patients treated with teriparatide consistent with the background incidence of osteosarcoma in adults. Long-term surveillance studies of a high proportion of patients diagnosed with osteosarcoma as adults in both the United States and Scandinavia reveal no prior exposure to teriparatide in any of the cases. Teriparatide use may be limited by cost and its mode of admin­ istration (daily subcutaneous injection). Alternative modes of delivery have been investigated, but none have proven successful. Because of the rodent osteosarcoma data and the maximum dura­ tion of teriparatide in the pivotal trial of 2 years, the FDA previously limited teriparatide treatment to 2 years in a lifetime. However, registry data confirming no increased risk of osteogenic sarcoma in humans treated with teriparatide have allowed the FDA to drop this restriction on duration of use. As a result, consideration may be given to using intermittent courses of teriparatide therapy. In many other countries, however, teriparatide use is still restricted to 2 years in a lifetime. Mode of Action  Exogenously administered PTH appears to have direct actions on osteoblast activity, with biochemical and his­ tomorphometric evidence of de novo bone formation within a week or two in response to teriparatide. There is subsequently resorption. Incidence of new vertebral fractures First clinical fracture

64/533 Relative risk: 0.44 (95% Cl: 0.29–0.68) p<0.0001 Hazard ratio: 0.48 (95% Cl: 0.32–0.74) p=0.0009 Teriparatide Risedronate Patients with new vertebral fractures (%)

Relative risk: 0.52 (95% Cl: 0.30–0.91) p=0.019

35/585 28/516

18/574

A FIGURE 423-12  Effect of parathyroid hormone (PTH) treatment on vertebral fracture incidence at 12 and 24 months (A) and clinical fractures (B) compared with risedronate. (Reproduced with permission from D Kendler et al: Effects of teriparatide and risedronate on new fractures in post-menopausal women with severe osteoporosis (VERO):

A multicentre, double-blind, double-dummy, randomised controlled trial. Lancet 391:230, 2018.)

A B FIGURE 423-13  Effect of parathyroid hormone (PTH) treatment on bone microarchitecture. Paired biopsy specimens from a 64-year-old woman before (A) and after (B) treatment with PTH. (Reproduced with permission from DW Dempster et al: Effects of daily treatment with parathyroid hormone on bone microarchitecture and turnover in patients with osteoporosis: A paired biopsy study. J Bone Miner Res 16:1846, 2001.) Subsequently, teriparatide primarily activates remodeling-based bone formation, favoring bone formation over bone resorption. Teriparatide given by daily injection stimulates osteoblast recruit­ ment and activity through activation of Wnt signaling. Teriparatide produces a true increase in bone tissue and an apparent restoration of bone microarchitecture (Fig. 423-13). Abaloparatide  Abaloparatide is a synthetic analogue of human PTHrP, which has significant homology to PTH and binds the PTH type 1 receptor. Abaloparatide and teriparatide exert different bind­ ing affinities to the two different receptor conformations, R0 and RG. Compared with teriparatide, abaloparatide binds with similar high affinity to the RG conformation but with much lesser affinity to the R0 conformation. These differences appear to result in a simi­ lar bone formation stimulus but lesser bone resorption stimulus, and abaloparatide was specifically chosen for development among many PTH and PTHrP analogues for what appeared to be an opti­ mized anabolic profile. In the phase 3 Abaloparatide Comparator Trial in Vertebral Endpoints (ACTIVE) study, 2463 postmenopausal women with osteoporosis were randomized to blinded daily subcutaneous aba­ loparatide versus placebo or open-label teriparatide. At 18 months, spine BMD increase was similar with abaloparatide and teriparatide (11.2% with abaloparatide and 10.5% with teriparatide); in the total hip, BMD increments were slightly larger with abaloparatide

Risedronate

Cumulative incidence (%)

Teriparatide

Number at risk Teriparatide Risedronate

B

Osteoporosis CHAPTER 423 (4.2 vs 3.3%). New vertebral fracture incidence was reduced by 86% with abaloparatide and 80% with teriparatide compared with placebo (both p <.001). The hazard ratio for abaloparatide versus teriparatide was not quoted. Nonvertebral fractures were reduced by 43% with abaloparatide (p = .05) and by 28% with teriparatide (not significant; p = .22). The ACTIVE study was extended, with 92% of eligible participants from the abaloparatide and placebo arms transitioned to open-label alendronate for a total treatment period of 24 months of alendronate. Both vertebral and nonvertebral fractures were less common in the group who transitioned from abaloparatide to alendronate, suggesting that the fracture benefit of abaloparatide can be maintained with antiresorptive treatment. Romosozumab  Romosozumab is a humanized antibody that blocks the osteocyte production of sclerostin, resulting in a unique action, with an increase in bone formation and decrease in bone resorption. In the pivotal trial (FRAME), 7180 postmenopausal women with osteoporosis were randomized to receive blinded monthly subcutaneous romosozumab (210 mg) or placebo for 1 year followed by transition to open-label subcutaneous deno­ sumab (60 mg) every 6 months for an additional year. BMD increased by over 13% in the spine and almost 7% in the hip in 1 year with romosozumab. At 1 year, the incidence of new vertebral fractures in the romosozumab group was significantly reduced by 73% compared with placebo. Clinical fracture risk (nonvertebral fractures and clinical vertebral fractures combined) was signifi­ cantly reduced by 36%. Nonvertebral fractures were also reduced, but the difference just missed statistical significance perhaps due to geographical differences; in the high-enrolling Latin American region, there was no significant reduction in nonvertebral fractures, probably due to a very low background incidence in that region. In the rest of the world, nonvertebral fractures were significantly reduced by >40%. During the second year of the FRAME study, both groups transitioned to denosumab. Over 24 months, women who had received romosozumab during the first 12 months and then denosumab had 75% fewer new vertebral fractures than those who had received placebo for a year followed by denosumab. There were also nearly significant trends toward reduced clinical and nonvertebral fractures in the romosozumab/denosumab group. Compared with baseline, BMD increased by 17.6% in the spine and 8.8% in the total hip in the romosozumab/denosumab group. Safety and tolerability of the two drugs were similar, with a slightly higher incidence of injection site reactions in the denosumab group. There was no increase of cardiovascular events in patients treated with romosozumab. The FRAME extension study where all participants received continued denosumab for an additional year (2 years in total) showed significant decreases in vertebral, clinical, and non­ vertebral fractures with a trend for hip fracture reduction. Comparison with Antiresorptive Therapy  The ARCH trial of very-high-risk patients, all of whom have prevalent vertebral fractures, compared romosozumab with alendronate for 1 year, followed by transition to, or continuation of, alendronate for at least 2 additional years. This study showed increases in bone den­ sity that were comparable with the FRAME study and significant reductions in vertebral, nonvertebral, clinical, and hip fractures compared with alendronate (Fig. 423-14). In this study, there was an increase in cardiovascular adverse events in patients treated with romosozumab, prompting a warning on the label and avoidance of this medication in patients with a past history of acute myocardial infarction or stroke. Comparison with Other Anabolic Therapy  No studies have compared romosozumab with other anabolic drugs with frac­ tures as the primary outcome. One study compared the effects of romosozumab with teriparatide in postmenopausal women with osteoporosis who had been previously treated with bisphospho­ nates, including 12 months of alendronate immediately prior to the study. Effects of both anabolic drugs on BMD were attenuated by prior bisphosphonate therapy, but the increases in spine, total hip, and femoral neck BMD were greater with romosozumab than with teriparatide. Increases in cortical bone mineral content and bone strength at the hip were also greater with romosozumab than with teriparatide. Sequence of Therapy  Because teriparatide and romosozumab have greater efficacy at reducing vertebral and clinical fractures, and vertebral, clinical, nonvertebral, and hip fractures, respectively, compared with bisphosphonates, they are now being considered as first-line therapy for patients with severe osteoporosis. Increases in BMD also occur more rapidly and to a greater extent with ana­ bolic drugs than with antiresorptive drugs, although the relative risk reduction for vertebral fractures is similar for zoledronic acid, denosumab, teriparatide, and romosozumab at about 70%. When their use is second-line following antiresorptive drugs, improve­ ments in BMD are attenuated, particularly following denosumab therapy. In response to these clinical data, initiatives have been made to identify patients at very high risk for fracture who would derive the most benefit from these greater improvements in BMD and more rapid reductions in fracture risk. Both U.S. and inter­ national guidelines have therefore focused on defining a group of individuals at very high fracture risk who could be selected for ana­ bolic therapy as first-line treatment. The definitions vary between these guidelines, but the criteria showing the most agreement are a recent fracture within the last 12–24 months, multiple fragility fractures (two or more), fractures while on antiresorptive therapy, or high absolute fracture risk (FRAX-derived 10-year risks of >4.5% or >30% for hip and major osteoporotic fractures, respectively). There has also been a focus on a goal-directed approach to long-term management of fracture risk. This helps ensure the most appropriate initial treatment and treatment sequence is selected for individual patients. Importantly, the selection of initial treatment should focus on reducing fracture risk rapidly for patients at very high and/or imminent risk, such as in those with recent fractures. Initial treatment selection should also consider the likelihood that a BMD treatment target can be attained relatively rapidly and needs to consider differences in fracture risk reduction and BMD increases with anabolic versus antiresorptive therapy. In conclusion, for those patients with a very high and/or imminent fracture risk, the ideal treatment sequence would be anabolic followed by anti­ resorptive therapy. However, reimbursement considerations may limit the implementation of this approach. OTHER PHARMACOLOGIC AGENTS NOT APPROVED IN THE UNITED STATES Testosterone has been used to treat osteoporosis associated with low testosterone levels in men. There are data that indicate that testos­ terone can increase bone density, but there are no data indicating reductions in fractures. In fact, a recent large study showed fracture incidence was numerically higher among men who received tes­ tosterone than among those who received placebo. Since there are many other effects of testosterone, especially in older men (includ­ ing prostate hypertrophy), decisions to use it for treatment of osteoporosis must take these multisystemic effects into account. In hypogonadal men with a high or very high fracture risk, anti-osteo­ porosis therapy should be used in addition to testosterone therapy. Sodium fluoride was tested in two large parallel clinical trials in the late 1980s. Although BMD increased substantially, the increase was in part due to fluoride incorporation in the hydroxyapatite crystal. Fracture risk was not reduced and, in fact, was increased in nonvertebral sites. Therefore, fluoride is no longer considered a viable option for osteoporosis treatment. Several small studies of growth hormone, alone or in combina­ tion with other agents, have not shown consistent or substantial positive effects on bone mass. NONPHARMACOLOGIC APPROACHES Protective pads worn around the outer thigh, which cover the trochanteric region of the hip, can prevent hip fractures in elderly residents in nursing homes. They are only effective when worn, and their use is limited largely by issues of compliance and comfort, but

Incidence of new vertebral fracture 12 Months

Patients (%) Risk ratio, 0.63 P=0.003 6.3 (128/2047) 4.0 (82/2046)

PART 12 Endocrinology and Metabolism

Alendronate Romosozumab A First clinical fracture in time-to-event analysis

P<0.001 Cumulative incidence (%) Alendronate→ Alendronate

Romosozumab→ Alendronate Alendronate

Romosozumab

Month

No. at Risk Alendronate 2047 1868 1743 Romosozumab 2046 1865 1770 Alendronate→ 1645 1564 1066 680 325 108 alendronate Romosozumab→ 1683 1615 1103 705 347 109 alendronate B C FIGURE 423-14  Effect of romosozumab versus alendronate for 12 months followed by alendronate on vertebral, clinical, and nonvertebral fracture incidence. (From The New England Journal of Medicine, Romosozumab or Alendronate for Fracture Prevention in Women with Osteoporosis, KG Saag et al: 377:1417. Copyright @2017 Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society.) new devices are being developed that may circumvent these problems and provide adjunctive treatments. Kyphoplasty and vertebroplasty are nonpharmacologic approaches for the treatment of painful vertebral fractures. The overall data do not support routine surgical intervention for painful vertebral fractures since, while this can reduce pain, there is concern about long-term vertebral fracture risk. Vertebral augmentation should be avoided in patients with vertebral fractures associated with denosumab discontinuation as it can increase the risk of adjacent vertebral fractures in this setting. TREATMENT MONITORING There are currently no well-accepted guidelines for monitoring treatment of osteoporosis. Because most osteoporosis treatments produce small or moderate bone mass increments on average, it is reasonable to consider BMD as a monitoring tool. Changes must exceed ~3% in the spine and 6% in the hip to be considered significant in any individual. The total hip is the preferred site due to larger surface area and greater reproducibility. Medication-induced increments may require several years to produce changes of this magnitude. Consequently, it can be argued that BMD should be repeated at intervals of every 2 years. Only significant BMD reductions (>~3% or ~6% at the spine and or hip, respectively) should prompt a change in therapy, as it is expected that some individuals will not show responses greater than the detection limits of the current measurement techniques.

24 Months Risk ratio, 0.52 P<0.001

11.9 (243/2047)

6.2 (127/2046)

Alendronate→ Alendronate Romosozumab→ Alendronate First nonvertebral fracture in time-to-event analysis

P=0.04 Cumulative incidence (%) Alendronate→ Alendronate

Romosozumab→ Alendronate Alendronate

Romosozumab

Month

No. at Risk Alendronate 2047 1873 1755 Romosozumab 2046 1867 1776 Alendronate→ 1661 1590 1097 697 330 110 alendronate Romosozumab→ 1693 1627 1114 714 350 109 alendronate Biochemical markers of bone turnover can help in treatment monitoring, with significant changes seen within 3 months of initiating treatment with approved medications and the possible benefit of improving adherence. It remains unclear which endpoint is most useful. If bone turnover markers are used, a determination should be made before therapy is started and repeated ≥3–4 months after therapy is initiated. In general, a change in bone turnover markers must be 30–40% lower than the baseline, or in the lower part of the standardized premenopausal range, to be significant because of the biologic and analytic variability in these tests. Because markers change more rapidly than bone density, they are often early signs of treatment effect. Currently collagen C-telopeptide (CTX) measured on a fasting serum sample in the morning is the preferred marker of bone resorption, and the propeptide of type 1 collagen (P1NP) is the preferred marker for bone formation. GLUCOCORTICOID-INDUCED OSTEOPOROSIS Osteoporotic fractures are a well-characterized consequence of the hypercortisolism associated with Cushing’s syndrome. However, the therapeutic use of glucocorticoids is by far the most common form of glucocorticoid-induced osteoporosis (GCIOP). Glucocorticoids are used widely in the treatment of a variety of disorders, including chronic lung disorders, rheumatoid arthritis and other connective tissue diseases, and inflammatory bowel disease, and after transplantation.

41 - 424 Paget’s Disease and Other Dysplasias of Bone

424 Paget’s Disease and Other Dysplasias of Bone

Osteoporosis and related fractures are serious side effects of chronic glucocorticoid therapy. Because the effects of glucocorticoids on the skeleton are often superimposed on the consequences of aging and menopause, it is not surprising that postmenopausal women and older men are most frequently affected. The skeletal response to glucocorti­ coids is remarkably heterogeneous, however, and even young, growing individuals treated with glucocorticoids can present with fractures. The risk of fractures depends on the dose and duration of gluco­ corticoid therapy, although recent data suggest that there may be no completely safe dose. Bone loss is more rapid during the early months of treatment, and trabecular bone is affected more severely than corti­ cal bone. As a result, fractures have been shown to increase within 3 months of glucocorticoid treatment. There is an increase in fracture risk in both the axial skeleton and the appendicular skeleton, including risk of hip fracture. Bone loss can occur with any route of glucocorti­ coid administration, including high-dose inhaled glucocorticoids and intra-articular injections. Alternate-day delivery does not appear to ameliorate the skeletal effects of glucocorticoids. ■ ■PATHOPHYSIOLOGY Glucocorticoids increase bone loss by multiple mechanisms, includ­ ing (1) inhibition of osteoblast function and an increase in osteoblast apoptosis, resulting in impaired synthesis of new bone; (2) stimula­ tion of bone resorption, probably as a secondary effect; (3) impair­ ment of the absorption of calcium across the intestine, probably by a vitamin D–independent effect; (4) increase of urinary calcium loss and perhaps induction of some degree of secondary hyperparathyroidism; (5) reduction of adrenal androgens and suppression of ovarian and testicular secretion of estrogens and androgens; and (6) induction of glucocorticoid myopathy, which may exacerbate effects on skeletal and calcium homeostasis as well as increase the risk of falls. ■ ■EVALUATION OF THE PATIENT Because of the high prevalence of GCIOP, it is important to evaluate the status of the skeleton in all patients starting or already receiving long-term glucocorticoid therapy. Modifiable risk factors should be identified, including those for falls. Examination should include testing of height and muscle strength. Laboratory evaluation should include an assessment of 24-h urinary calcium. All patients on long-term

(>3 months) glucocorticoids should have measurement of bone mass at both the spine and the hip using DXA. If only one skeletal site can be measured, it is best to assess the spine in individuals <60 years and the hip in those >60 years. ■ ■PREVENTION Bone loss caused by glucocorticoids can be prevented, and the risk of fractures significantly reduced. Strategies must include using the lowest dose of glucocorticoid for disease management. Topical and inhaled routes of administration are preferred, where appropriate. Risk factor reduction is important, including smoking cessation, limitation of alcohol consumption, and participation in weight-bearing and resis­ tance exercise, when appropriate. All patients should receive an ade­ quate calcium and vitamin D intake from the diet or from supplements. TREATMENT Glucocorticoid-Induced Osteoporosis Several bisphosphonates (alendronate, risedronate, and zoledronic acid) have been demonstrated in large clinical trials to reduce the risk of fractures in patients being treated with glucocorticoids and are FDA approved for the treatment of GCIOP. Teriparatide is also approved for treatment of GCIOP. In one trial comparing teripara­ tide with alendronate, BMD increases were much greater and verte­ bral fracture risk reduction was greater with teriparatide compared with alendronate. A study of denosumab indicates greater efficacy of denosumab compared with risedronate for treatment of GCIOP. There are no data for romosozumab in GCIOP. The American Col­ lege of Rheumatology has published guidelines for the management of GCIOP.

Acknowledgment The author gratefully acknowledges the foundational contributions of Drs. Robert Lindsay, Felicia Cosman, and Blossom Samuels to this chap­ ter in previous editions of Harrison’s.

■ ■FURTHER READING Black DM et al: Atypical femur fracture risk versus fragility fracture prevention with bisphosphonates. N Engl J Med 383:743, 2020. Compston J: Glucocorticoid-induced osteoporosis: An update. Endo­ crine 61:7, 2018. Cosman F et al: Spine fracture prevalence in a nationally representa­ Paget’s Disease and Other Dysplasias of Bone CHAPTER 424 tive sample of US women and men aged >/=40 years: results from the National Health and Nutrition Examination Survey (NHANES) 2013–2014. Osteoporos Int 28:2319, 2017. Cosman F et al: Treatment sequence for osteoporosis. Endocr Pract S1530, 2024. Kendler DL et al: Effects of teriparatide and risedronate on new frac­ tures in post-menopausal women with severe osteoporosis (VERO): A multicentre, double-blind, double-dummy, randomised controlled trial. Lancet 391:230, 2018. Khosla S, Hofbauer LC: Osteoporosis treatment: Recent develop­ ments and ongoing challenges. Lancet Diabetes Endocrinol 5:898, 2017. Reid IR, Billington EO: Drug therapy for osteoporosis in older adults. Lancet 399:1080, 2022. Reid IR et al: Fracture prevention with zoledronate in older women with osteopenia. N Engl J Med 379:2407, 2018. Roux C, Briot K: Imminent fracture risk. Osteoporos Int 28:1765, 2017. Saag KG et al: Romosozumab or alendronate for fracture prevention in women with osteoporosis. N Engl J Med 377:1417, 2017. Sing CW et al: Global epidemiology of hip fractures: Secular trends in incidence rate, post-fracture treatment, and all-cause mortality.

J Bone Miner Res 38:1064, 2023. Snyder PJ et al: Testosterone treatment and fractures in men with hypogonadism. N Engl J Med 390:203, 2024. Rajesh K. Jain, Tamara J. Vokes

Paget’s Disease and

Other Dysplasias of Bone PAGET’S DISEASE OF BONE Paget’s disease is a localized bone-remodeling disorder that affects widespread, noncontiguous areas of the skeleton. The pathologic pro­ cess is initiated by overactive osteoclastic bone resorption followed by a compensatory increase in osteoblastic new bone formation, resulting in a structurally disorganized mosaic of woven and lamellar bone. Pagetic bone is expanded, less compact, and more vascular; thus, it is more susceptible to deformities and fractures. Although most patients are asymptomatic, symptoms resulting directly from bony involvement (bone pain, secondary arthritis, fractures) or secondarily from the expansion of bone causing compression of surrounding neural tissue are not uncommon. Epidemiology  There is a marked geographic variation in the frequency of Paget’s disease, with high prevalence in Western Europe (Great Britain, France, and Germany, but not Switzerland or Scandinavia) and among those who have immigrated to Australia, New Zealand, South Africa, and North and South America. The disease is rare in native populations of the Americas, Africa, Asia, and the Middle East; when it does occur, the affected subjects usually have evidence of

European ancestry, supporting the migration theory. For unclear rea­ sons, the prevalence and severity of Paget’s disease are decreasing, and the age of diagnosis is increasing.

The prevalence is greater in males and increases with age. Autopsy series reveal Paget’s disease in ~3% of those over age 40. Prevalence of positive skeletal radiographs in patients aged >55 years is 2.5% for men and 1.6% for women. Elevated alkaline phosphatase (ALP) levels in asymptomatic patients have an age-adjusted incidence of 12.7 and 7 per 100,000 person-years in men and women, respectively. Etiology  The etiology of Paget’s disease of bone remains unknown, but evidence supports both genetic and viral etiologies. A positive family history is found in 15–25% of patients and, when present, raises the prevalence of the disease seven- to tenfold among first-degree relatives. PART 12 Endocrinology and Metabolism A clear genetic basis has been established for several rare familial bone disorders that clinically and radiographically resemble Paget’s disease but have more severe presentation and earlier onset. A homo­ zygous deletion of the TNFRSF11B gene, which encodes osteoprotegrin (Fig. 424-1), causes juvenile Paget’s disease, also known as familial idiopathic hyperphosphatasia, a disorder characterized by uncontrolled osteoclastic differentiation and resorption. Familial patterns of disease in several large kindred are consistent with an autosomal dominant pattern of inheritance with variable penetrance. Familial expansile osteolysis, expansile skeletal hyperphosphatasia, and early-onset Paget’s disease are associated with mutations in the TNFRSF11A gene, which encodes RANK (receptor activator of nuclear factor-κB), a member of the tumor necrosis factor superfamily critical for osteoclast differentia­ tion (Fig. 424-1). A mutation in profilin 1, a small actin protein that acts as a tumor suppressor, also causes early-onset Paget’s disease with a predisposition for the development of osteosarcoma. Finally, muta­ tions in the gene for valosin-containing protein cause a rare syndrome with autosomal dominant inheritance and variable penetrance known as inclusion body myopathy with Paget’s disease and frontotemporal Mesenchymal cell M-CSF c-fms OPG + RANK L Osteoclast precursor IL-1, IL-6 IGF-1 IGF-2 RANK Osteoblasts Osteoblasts Collagen osteocalcin Osteoclast FIGURE 424-1  Diagram illustrating factors that promote differentiation and function of osteoclasts and osteoblasts and the role of the RANK pathway. Stromal bone marrow (mesenchymal) cells and differentiated osteoblasts produce multiple growth factors and cytokines, including macrophage colony-stimulating factor (M-CSF), to modulate osteoclastogenesis. RANKL (receptor activator of nuclear factor-κB [NF-κB] ligand) is produced by osteoblast progenitors and mature osteoblasts and can bind to a soluble decoy receptor known as osteoprotegerin (OPG) to inhibit RANKL action. Alternatively, a cell-cell interaction between osteoblast and osteoclast progenitors allows RANKL to bind to its membranebound receptor, RANK, thereby stimulating osteoclast differentiation and function. RANK binds intracellular proteins called tumor necrosis factor receptor–associated factors (TRAFs) that mediate receptor signaling through transcription factors such as NF-κB. M-CSF binds to its receptor, c-fms, which is the cellular homologue of the fms oncogene. See text for the potential role of these pathways in disorders of osteoclast function such as Paget’s disease and osteopetrosis. IGF, insulin-like growth factor; IL, interleukin.

dementia (IBMPFD). The role of genetic factors is less clear in the more common form of late-onset Paget’s disease. The most common mutations identified in familial and sporadic cases of Paget’s disease have been in the SQSTM1 gene (sequestasome-1 or p62 protein) in the C-terminal ubiquitin-binding domain. The other candidate genes include CSF1 (1p13), which encodes macrophage colony-stimulating factor (M-CSF), a cytokine that is required for osteoclast differentia­ tion; RIN3 (14q32), which encodes a guanine exchange factor called Rab and Ras interactor 3; OPTN (10p13), which is involved in regu­ lating nuclear factor (NF)-κB; TNFRSF11A, mentioned earlier; and TM7SF4, which encodes dendritic cell–specific transmembrane protein (DC-STAMP), a molecule that is essential for fusion of the osteoclast. The phenotypic variability in patients with SQSTM1 mutations sug­ gests that additional factors, such as other genetic influences or viral infection, may influence clinical expression of the disease. Several lines of evidence suggest that a viral infection may contrib­ ute to the clinical manifestations of Paget’s disease, including (1) the presence of cytoplasmic and nuclear inclusions resembling paramyxo­ viruses (measles, respiratory syncytial virus, canine distemper virus) in pagetic osteoclasts and (2) viral mRNA in precursor and mature osteoclasts. The viral etiology is further supported by conversion of osteoclast precursors to pagetic-like osteoclasts by vectors containing the measles virus nucleocapsid or matrix genes. The decline in the incidence of Paget’s disease coincides with the widespread vaccination against measles, also consistent with the potential role of virus in the development of the disease. However, the viral etiology has been ques­ tioned by the inability to culture a live virus from pagetic bone and by failure to clone the full-length viral genes from material obtained from patients with Paget’s disease. Furthermore, patients with Paget’s disease do not have higher antibody levels against paramyxoviruses or measles as compared to controls, nor do antibody levels correlate with disease severity in those with Paget’s disease. Pathophysiology  The principal abnormality in Paget’s disease is the increased number and activity of osteoclasts. Pagetic osteoclasts are large, increased 10- to 100-fold in number, and have a greater number of nuclei (as many as 100 compared to 3–5 nuclei in the normal osteoclast). The overactive osteoclasts may create a sevenfold increase in resorptive surfaces and an erosion rate of 9 μg/d (normal is 1 μg/d). Several causes for the increased number and activity of pagetic osteoclasts have been identified: (1) osteoclastic precursors are hyper­ sensitive to 1,25(OH)2D3; (2) osteoclasts are hyperresponsive to RANK ligand (RANKL), the osteoclast stimulatory factor that mediates the effects of most osteotropic factors on osteoclast formation; (3) marrow stromal cells from pagetic lesions have increased RANKL expression; (4) osteoclast precursor recruitment is increased by interleukin (IL) 6, which is increased in the blood of patients with active Paget’s disease and is overexpressed in pagetic osteoclasts; (5) expression of the proto­ oncogene c-fos, which increases osteoclastic activity, is increased; and (6) the antiapoptotic oncogene Bcl-2 in pagetic bone is overexpressed. Numerous osteoblasts are recruited to active resorption sites and pro­ duce large amounts of new bone matrix. As a result, bone turnover is high, and bone mass is normal or increased, not reduced, unless there is concomitant deficiency of calcium and/or vitamin D. The characteristic feature of Paget’s disease is increased bone resorp­ tion accompanied by accelerated bone formation. An initial osteolytic phase involves prominent bone resorption and marked hypervascular­ ization. Radiographically, this manifests as an advancing lytic wedge, or “blade of grass” lesion. The second phase is a period of very active bone formation and resorption that replaces normal lamellar bone with haphazard (woven) bone. Fibrous connective tissue may replace nor­ mal bone marrow. In the final sclerotic phase, bone resorption declines progressively and leads to a hard, dense, less vascular pagetic or mosaic bone, which represents the so-called burned-out phase of Paget’s disease. All three phases may be present at the same time at different skeletal sites. Clinical Manifestations  Diagnosis is often made in asymptom­ atic patients because they have elevated ALP levels on routine blood chemistry testing or an abnormality on a skeletal radiograph obtained

for another indication. The skeletal sites most commonly involved are the pelvis, vertebral bodies, skull, femur, and tibia. Familial cases with an early presentation often have numerous active sites of skeletal involvement. The most common presenting symptom is pain, which may result from increased bony vascularity, expanding lytic lesions, fractures, bowing, or other deformities. Bowing of the femur or tibia causes gait abnormalities and abnormal mechanical stresses with secondary osteoarthritis of the hip or knee joints. Long bone bowing also causes extremity pain by stretching the muscles attached to the bone softened by the pagetic process. Back pain results from enlarged pagetic ver­ tebrae, vertebral compression fractures, spinal stenosis, degenerative changes of the joints, and altered body mechanics with kyphosis and forward tilt of the upper back. Rarely, spinal cord compression may result from bone enlargement or from the vascular steal syndrome. Skull involvement may cause headaches, symmetric or asymmetric enlargement of the parietal or frontal bones (frontal bossing), and increased head size. Cranial expansion may narrow cranial foramens and cause neurologic complications including hearing loss from cochlear nerve damage from temporal bone involvement, cranial nerve palsies, and softening of the base of the skull (platybasia) with the risk of brainstem compression. Pagetic involvement of the facial bones may cause facial deformity; loss of teeth and other dental conditions; and, rarely, airway compression. Fractures are serious complications of Paget’s disease and usually occur in long bones at areas of active or advancing lytic lesions. Com­ mon fracture sites are the femoral shaft and subtrochanteric regions. Neoplasms arising from pagetic bone are rare (<0.5%). The incidence of sarcoma appears to be decreasing, possibly because of earlier, more effective treatment with potent antiresorptive agents. The majority of tumors are osteosarcomas, which usually present with new pain in a long-standing pagetic lesion. Osteoclast-rich benign giant cell tumors may arise in areas adjacent to pagetic bone, and they respond to glu­ cocorticoid therapy. Cardiovascular complications may occur in patients with involve­ ment of large (15–35%) portions of the skeleton and a high degree of disease activity (e.g., ALP four times above normal). The extensive arteriovenous shunting and marked increases in blood flow through the vascular pagetic bone lead to a high-output state and cardiac enlargement. However, high-output heart failure is relatively rare and usually develops in patients with concomitant cardiac pathology. In addition, calcific aortic stenosis and diffuse vascular calcifications have been associated with Paget’s disease. Diagnosis  The diagnosis may be suggested on clinical examination by the presence of an enlarged skull with frontal bossing, bowing of an extremity, or short stature with simian posturing. An extremity with an FIGURE 424-2  A 48-year-old woman with Paget’s disease of the skull. Left. Lateral radiograph showing areas of both bone resorption and sclerosis. Right. 99mTc hydroxymethylene diphosphonate (HDP) bone scan with anterior, posterior, and lateral views of the skull showing diffuse isotope uptake by the frontal, parietal, occipital, and petrous bones.

area of warmth and tenderness to palpation may suggest an underlying pagetic lesion. Other findings include bony deformity of the pelvis, skull, spine, and extremities; arthritic involvement of the joints adja­ cent to lesions; and leg-length discrepancy resulting from deformities of the long bones.

Paget’s disease is usually diagnosed from radiologic and biochemical abnormalities. Radiographic findings typical of Paget’s disease include enlargement or expansion of an entire bone or area of a long bone, cortical thickening, coarsening of trabecular markings, and typical lytic and sclerotic changes. Skull radiographs (Fig. 424-2) reveal regions of “cotton wool,” or osteoporosis circumscripta, thickening of diploic areas, and enlargement and sclerosis of a portion or all of one or more skull bones. Vertebral cortical thickening of the superior and infe­ rior end plates creates a “picture frame” vertebra. Diffuse radiodense enlargement of a vertebra is referred to as “ivory vertebra.” Pelvic radiographs may demonstrate disruption or fusion of the sacroiliac joints; porotic and radiodense lesions of the ilium with whorls of coarse trabeculation; thickened and sclerotic iliopectineal line (brim sign); and softening with protrusio acetabuli, with axial migration of the hips and functional flexion contracture. Radiographs of long bones reveal bowing deformity and typical pagetic changes of cortical thickening and expansion and areas of lucency and sclerosis (Fig. 424-3). Radio­ nuclide 99mTc bone scans are less specific but are more sensitive than standard radiographs for identifying sites of active skeletal lesions. Although computed tomography (CT) and magnetic resonance imag­ ing (MRI) studies are not necessary in most cases, CT may be useful for the assessment of possible fracture, and MRI is necessary to assess the possibility of sarcoma, giant cell tumor, or metastatic disease in pagetic bone. Definitive diagnosis of malignancy often requires bone biopsy. Paget’s Disease and Other Dysplasias of Bone CHAPTER 424 Biochemical evaluation is useful in the diagnosis and management of Paget’s disease. The marked increase in bone turnover can be moni­ tored using biochemical markers of bone formation and resorption. The parallel rise in markers of bone formation and resorption confirms the coupling of bone formation and resorption in Paget’s disease. The degree of bone marker elevation reflects the extent and severity of the disease. For most patients, serum total ALP remains the test of choice both for diagnosis and assessing response to therapy. Occasionally, a symptomatic patient with evidence of progression at a single site may have a normal total ALP level but increased bone-specific ALP. For unclear reasons, serum osteocalcin, another marker of bone formation, is not always elevated and is not recommended for use in diagnosis or management of Paget’s disease. In contrast, bone formation marker P1NP does reflect the activity of the disease and can be used instead of total ALP. Bone resorption markers (serum or urine N-telopeptide or C-telopeptide measured in the blood or urine) are also elevated in active Paget’s disease and decrease more rapidly in response to therapy than does ALP.

PART 12 Endocrinology and Metabolism FIGURE 424-3  Radiograph of a 73-year-old man with Paget’s disease of the right proximal femur. Note the coarsening of the trabecular pattern with marked cortical thickening and narrowing of the joint space consistent with osteoarthritis secondary to pagetic deformity of the right femur. Serum calcium and phosphate levels are normal in Paget’s disease. Immobilization of a patient with active Paget’s disease may rarely cause hypercalcemia and hypercalciuria and increase the risk for nephrolithiasis. However, the discovery of hypercalcemia, even in the presence of immobilization, should prompt a search for another cause of hypercalcemia. In contrast, hypocalcemia or mild secondary hyper­ parathyroidism may develop in Paget’s patients with very active bone formation and insufficient calcium and vitamin D intake, particularly during bisphosphonate therapy when bone resorption is rapidly sup­ pressed and active bone formation continues. Therefore, adequate calcium and vitamin D intake should be instituted prior to administration of bisphosphonates. TREATMENT Paget’s Disease of Bone The development of effective and potent pharmacologic agents (Table 424-1) has changed the treatment philosophy from treating only symptomatic patients to treating asymptomatic patients who are at risk for complications. According to the Endocrine Society Clinical Practice Guidelines published in 2014, pharmacologic therapy is indicated for most patients with active Paget’s disease who are at risk of complications. Treatment may be initiated to control symptoms caused by metabolically active Paget’s disease such as bone pain, fracture, headache, pain from pagetic radicu­ lopathy or arthropathy, or neurologic complications; to decrease local blood flow and minimize operative blood loss in patients TABLE 424-1  Pharmacologic Agents Approved for Treatment of Paget’s Disease NORMALIZATION OF ALKALINE PHOSPHATASE (ALP) DOSE AND MODE OF DELIVERY NAME Zoledronic acid 5 mg IV over 15 min 90% of patients at 6 mo Pamidronate 30 mg/d IV over 4 h on 3 days ~50% of patients Risedronate 30 mg/d PO for 2 mo 73% of patients Alendronate 40 mg/d PO for 6 mo 63% of patients Tiludronate 800 mg/d PO for 3 mo 35% of patients Etidronate 200–400 mg/d PO × 6 mo 15% of patients Calcitonin (Miacalcin) 100 U SC daily for 6–18 mo (may reduce to 50 U 3× per week) (Reduction of ALP by up to 50%)

who need surgery at an active pagetic site; to reduce hypercalciuria that may occur during immobilization; and to decrease the risk of complications when disease activity is high (elevated ALP) and when the site of involvement involves weight-bearing bones, areas adjacent to major joints, vertebral bodies, and the skull. Whether or not early therapy prevents late complications remains to be deter­ mined. Randomized studies from the United Kingdom showed no difference in bone pain, fracture rates, quality of life, and hearing loss between patients who received pharmacologic therapy to con­ trol symptoms (bone pain) and those receiving bisphosphonates to normalize serum ALP. However, the conclusions of these studies are debatable since the majority of subjects had already received bisphosphonate therapy in the past, perhaps limiting generalizabil­ ity, and because the bone deformities that occur with Paget’s disease may take many years to manifest. It seems likely that the restoration of normal bone architecture following suppression of pagetic activ­ ity will prevent further deformities and complications. Agents approved for treatment of Paget’s disease suppress the very high rates of bone resorption and secondarily decrease the high rates of bone formation (Table 424-1). As a result of decreas­ ing bone turnover, pagetic structural patterns, including areas of poorly mineralized woven bone, are replaced by more nor­ mal cancellous or lamellar bone. Reduced bone turnover can be documented by a decline in serum formation markers (ALP and P1NP) and urine or serum resorption markers (N-telopeptide, C-telopeptide). Bisphosphonates are the mainstay of pharmacologic therapy of Paget’s disease. Among them, zoledronic acid is currently recom­ mended as the first choice, particularly for those who have severe disease or need rapid normalization of bone turnover (neurologic symptoms, severe bone pain due to a lytic lesion, risk of an impend­ ing fracture, or pretreatment prior to elective surgery in an area of active disease). Zoledronic acid normalized bone turnover faster and in a high proportion of patients (>90%) than oral bisphos­ phonates with the therapeutic effect persisting for months or even years. It is given at a dose of 5 mg as an intravenous infusion over 20 min, although slower rates of infusion are recommended for elderly or those with mild impairment of renal function. More sig­ nificant renal impairment (glomerular filtration rate <35 mL/min) is a contraindication for use of zoledronic acid due to higher risk of further deterioration of renal function. About 20–25% of patients experience a flulike syndrome after the first infusion, which can be partly ameliorated by pretreatment with acetaminophen, non­ steroidal anti-inflammatory drugs (NSAIDs), or glucocorticoids. Oral bisphosphonates, alendronate and risedronate, can be used in subjects who have mild disease or some degree of renal impairment. Oral bisphosphonates should be taken first thing in the morning on an empty stomach, followed by maintenance of upright posture with no food, drink, or other medications for 30–60 min. The efficacy of different agents, based on their ability to normalize or decrease ALP levels, is summarized in Table 424-1, although the response rates are not comparable because they are obtained from different studies. The subcutaneous injectable form of salmon calcitonin is approved for the treatment of Paget’s disease but is rarely used due to its low potency and should be reserved for patients who either do not tolerate bisphosphonates or have a contraindication to their use. For patients with contraindication to bisphosphonates, another alternative is denosumab, an antibody to RANKL, which has been reported to result in reduction in ALP. However, it has not been approved for this indication and has less complete and less durable effects than bisphosphonates. SCLEROSING BONE DISORDERS ■ ■OSTEOPETROSIS Osteopetrosis refers to a group of disorders caused by severe impair­ ment of osteoclast-mediated bone resorption. Other terms that are often used include marble bone disease, which captures the solid x-ray

appearance of the involved skeleton, and Albers-Schonberg disease, which refers to the milder, adult form of osteopetrosis also known as autosomal dominant osteopetrosis type II. The major types of osteope­ trosis include malignant (severe, infantile, autosomal recessive) osteo­ petrosis and benign (adult, autosomal dominant) osteopetrosis types I and II. A rare autosomal recessive intermediate form has a more benign prognosis. Autosomal recessive carbonic anhydrase (CA) II deficiency produces osteopetrosis of intermediate severity associated with renal tubular acidosis and cerebral calcification. Etiology and Genetics  Naturally occurring and gene-knockout animal models with phenotypes similar to those of the human dis­ orders have been used to explore the genetic basis of osteopetrosis. The primary defect in osteopetrosis is the loss of osteoclastic bone resorption and preservation of normal osteoblastic bone forma­ tion. Osteoprotegerin (OPG) is a soluble decoy receptor that binds osteoblast-derived RANK ligand, which mediates osteoclast differ­ entiation and activation (Fig. 424-1). Transgenic mice that overex­ press OPG develop osteopetrosis, presumably by blocking RANK ligand. Mice deficient in RANK lack osteoclasts and develop severe osteopetrosis. Recessive mutations of CA II prevent osteoclasts from generat­ ing an acid environment in the clear zone between its ruffled bor­ der and the adjacent mineral surface. Absence of CA II, therefore, impairs osteoclastic bone resorption. Other forms of human disease have less clear genetic defects. About one-half of the patients with malignant infantile osteopetrosis have a mutation in the TCIRG1 gene encoding the osteoclast-specific subunit of the vacuolar proton pump, which mediates the acidification of the interface between bone mineral and the osteoclast ruffled border. Mutations in the CLCN7 chloride channel gene cause autosomal dominant osteopetrosis type II. A drug-induced version of osteopetrosis has been reported in children with osteogenesis imperfecta who receive repeated doses of bisphosphonates. Clinical Presentation  The incidence of autosomal recessive severe (malignant) osteopetrosis ranges from 1 in 200,000 to 1 in 500,000 live births. As bone and cartilage fail to undergo modeling, paralysis of one or more cranial nerves may occur due to narrowing of the cranial foramens. Failure of skeletal modeling also results in inadequate mar­ row space, leading to extramedullary hematopoiesis with hypersplen­ ism and pancytopenia. Hypocalcemia due to lack of osteoclastic bone resorption may occur in infants and young children. The untreated infantile disease is fatal, often before age 5. Adult (benign) osteopetrosis is an autosomal dominant disease that is usually diagnosed by the discovery of typical skeletal changes in young adults who undergo radiologic evaluation of a fracture. The prevalence is 1 in 100,000 to 1 in 500,000 adults. The course is not always benign, because fractures may be accompanied by loss of vision, deafness, psychomotor delay, mandibular osteomyelitis, and other complications usually associated with the juvenile form. In some kindred, nonpenetrance results in skip generations, while in other families, severely affected children are born into families with benign disease. The milder form of the disease does not usually require treatment. Radiography  Typically, there are generalized symmetric increases in bone mass with thickening of both cortical and trabecular bone. Diaphyses and metaphyses are broadened, and alternating sclerotic and lucent bands may be seen in the iliac crests, at the ends of long bones, and in vertebral bodies. The cranium is usually thickened, particularly at the base of the skull, and the paranasal and mastoid sinuses are underpneumatized. Laboratory Findings  The only significant laboratory findings are elevated serum levels of osteoclast-derived tartrate-resistant acid phosphatase (TRAP) and the brain isoenzyme of creatine kinase. Serum calcium may be low in severe disease, and parathyroid hormone and 1,25-dihydroxyvitamin D levels may be elevated in response to hypocalcemia.

TREATMENT Osteopetrosis Allogeneic human leukocyte antigen (HLA)–identical bone mar­ row transplantation has been successful in some children. Fol­ lowing transplantation, the marrow contains progenitor cells and normally functioning osteoclasts. With long-term follow-up after transplantation, radiographic improvements, such as improvements in Erlenmeyer flask deformities, are seen, although there is not complete normalization. A cure is most likely when children are transplanted before age 4. Marrow transplantation from nonidenti­ cal HLA-matched donors has a much higher failure rate. Limited studies in small numbers of patients have suggested variable benefits following treatment with interferon γ-1β, 1,25-dihydroxyvitamin D (which stimulates osteoclasts directly), methylprednisolone, and a low-calcium/high-phosphate diet. Paget’s Disease and Other Dysplasias of Bone CHAPTER 424 Surgical intervention is indicated to decompress optic or audi­ tory nerve compression. Orthopedic management is required for the surgical treatment of fractures and their complications, includ­ ing malunion and postfracture deformity. ■ ■PYKNODYSOSTOSIS This is an autosomal recessive form of osteosclerosis that is believed to have affected the French impressionist painter Henri de ToulouseLautrec. The molecular basis involves mutations in the gene that encodes cathepsin K, a lysosomal metalloproteinase highly expressed in osteoclasts and important for bone-matrix degradation. Osteoclasts are present but do not function normally. Pyknodysostosis is a form of short-limb dwarfism that presents with frequent fractures but usually a normal life span. Clinical features include short stature; kyphosco­ liosis and deformities of the chest; high arched palate; proptosis; blue sclerae; dysmorphic features including small face and chin, frontooccipital prominence, pointed beaked nose, large cranium, and obtuse mandibular angle; and small, square hands with hypoplastic nails. Radiographs demonstrate a generalized increase in bone density, but in contrast to osteopetrosis, the long bones are normally shaped. Sepa­ rated cranial sutures, including the persistent patency of the anterior fontanel, are characteristic of the disorder. There may also be hypopla­ sia of the sinuses, mandible, distal clavicles, and terminal phalanges. Persistence of deciduous teeth and sclerosis of the calvarium and base of the skull are also common. Histologic evaluation shows normal cortical bone architecture with decreased osteoblastic and osteoclastic activities. Serum chemistries are normal, and unlike osteopetrosis, there is no anemia. There is no known treatment for this condition, and there are no reports of attempted bone marrow transplant. ■ ■PROGRESSIVE DIAPHYSEAL DYSPLASIA Also known as Camurati-Engelmann disease, progressive diaphyseal dysplasia is an autosomal dominant disorder that is characterized radio­ graphically by diaphyseal hyperostosis and a symmetric thickening and increased diameter of the endosteal and periosteal surfaces of the diaphyses of the long bones, particularly the femur and tibia, and, less often, the fibula, radius, and ulna. The genetic defect responsible for the disease has been localized to the area of chromosome 19q13.2 encoding transforming growth factor (TGF)-β1. The mutation promotes activa­ tion of TGF-β1. The clinical severity is variable. The most common pre­ senting symptoms are pain and tenderness of the involved areas, fatigue, muscle wasting, and gait disturbance. The weakness may be mistaken for muscular dystrophy. Characteristic body habitus includes thin limbs with little muscle mass yet prominent and palpable bones and, when the skull is involved, large head with prominent forehead and proptosis. Patients may also display signs of cranial nerve palsies, hydrocephalus, central hypogonadism, and Raynaud’s phenomenon. Radiographi­ cally, patchy progressive endosteal and periosteal new bone formation is observed along the diaphyses of the long bones. Bone scintigraphy shows increased radiotracer uptake in involved areas. Treatment with low-dose glucocorticoids relieves bone pain and may reverse the abnormal bone formation. Intermittent bisphosphonate

therapy has produced clinical improvement in a limited number of patients. Disease activity may also attenuate as patients enter adulthood.

■ ■HYPEROSTOSIS CORTICALIS GENERALISATA This is also known as van Buchem’s disease; it is an autosomal recessive disorder characterized by endosteal hyperostosis in which osteosclero­ sis involves the skull, mandible, clavicles, and ribs. The major manifes­ tations are due to narrowed cranial foramens with neural compressions that may result in optic atrophy, facial paralysis, and deafness. Adults may have an enlarged mandible. Serum ALP levels may be elevated, which reflect the uncoupled bone remodeling with high osteoblastic formation rates and low osteoclastic resorption. As a result, there is increased accumulation of normal bone. Endosteal hyperostosis with syndactyly, known as sclerosteosis, is a more severe form. The genetic defects for both sclerosteosis and van Buchem’s disease have been asso­ ciated with mutations in the SOST gene. PART 12 Endocrinology and Metabolism ■ ■MELORHEOSTOSIS Melorheostosis (Greek, “flowing hyperostosis”) may occur sporadically or follow a pattern consistent with an autosomal recessive disorder. The major manifestation is progressive linear hyperostosis in one or more bones of one limb, usually a lower extremity. The name comes from the radiographic appearance of the involved bone, which resembles melted wax that has dripped down a candle. Symptoms appear during childhood as pain or stiffness in the area of sclerotic bone. There may be associated ectopic soft tissue masses, composed of cartilage or osse­ ous tissue, and skin changes overlying the involved bone, consisting of scleroderma-like areas and hypertrichosis. The disease does not prog­ ress in adults, but pain and stiffness may persist. Laboratory tests are unremarkable. Somatic mutations in MAP2K1, which increases MEK1 activity downstream of the RAS pathway, and SMAD3, which upregu­ lates the TGF-β/SMAD pathway, have been identified in affected bone in patients with melorheostosis. There is no specific treatment. Surgical interventions to correct contractures are often unsuccessful. ■ ■OSTEOPOIKILOSIS The literal translation of osteopoikilosis is “spotted bones”; it is a benign autosomal dominant condition in which numerous small, vari­ ably shaped (usually round or oval) foci of bony sclerosis are seen in the epiphyses and adjacent metaphyses. The lesions may involve any bone except the skull, ribs, and vertebrae. They may be misidentified as metastatic lesions. The main differentiating points are that bony lesions of osteopoikilosis are stable over time and do not accumulate radionucleotide on bone scanning. In some kindred, osteopoikilosis is associated with connective tissue nevi known as dermatofibrosis lenticularis disseminata, also known as Buschke-Ollendorff syndrome. Most cases are caused by mutations in LEMD3, which is involved with bone morphogenetic protein (BMP) signaling. Histologic inspection reveals thickened but otherwise normal trabeculae and islands of nor­ mal cortical bone. No treatment is indicated. ■ ■HEPATITIS C–ASSOCIATED OSTEOSCLEROSIS Hepatitis C–associated osteosclerosis (HCAO) is a rare acquired dif­ fuse osteosclerosis in adults with prior hepatitis C infection. After a latent period of several years, patients develop diffuse appendicular bone pain and a generalized increase in bone mass with elevated serum ALP. Bone biopsy and histomorphometry reveal increased rates of bone formation, decreased bone resorption with a marked decrease in osteoclasts, and dense lamellar bone. One patient had increased serum OPG levels, and bone biopsy showed large numbers of osteoblasts positive for OPG and reduced osteoclast number. Empirical therapy includes pain control, and there may be beneficial response to bisphos­ phonate. Long-term antiviral therapy may reverse the bone disease. DISORDERS ASSOCIATED WITH DEFECTIVE MINERALIZATION ■ ■HYPOPHOSPHATASIA This is a rare inherited disorder that presents as rickets in infants and children or osteomalacia in adults with paradoxically low serum levels of ALP. The frequency of the severe neonatal and infantile forms is

about 1 in 100,000 live births in Canada, where the disease is most common because of its high prevalence among Mennonites and Hut­ terites. It is rare in African Americans. The severity of the disease is remarkably variable, ranging from intrauterine death associated with profound skeletal hypomineralization at one extreme to premature tooth loss as the only manifestation in some adults. Severe cases are inherited in an autosomal recessive manner, but the genetic patterns are less clear for the milder forms. The disease is caused by a deficiency of tissue nonspecific (bone/liver/kidney) ALP (TNSALP), which, although ubiquitous, results only in bone abnormalities. Protein levels and functions of the other ALP isozymes (germ cell, intestinal, pla­ cental) are normal. Defective ALP permits accumulation of its major naturally occurring substrates including phosphoethanolamine (PEA), inorganic pyrophosphate (PPi), and pyridoxal 5′-phosphate (PLP). The accumulation of PPi interferes with mineralization through its action as a potent inhibitor of hydroxyapatite crystal growth. Perinatal hypophosphatasia becomes manifest during pregnancy and is often complicated by polyhydramnios and intrauterine death. The infantile form becomes clinically apparent before the age of 6 months with failure to thrive, rachitic deformities, functional craniosynostosis despite widely open fontanels (which are actually hypomineralized areas of the calvarium), raised intracranial pressure, and flail chest with predisposition to pneumonia. Hypercalcemia and hypercalciuria are common. This form has a mortality rate of ~50%. Prognosis seems to improve for the children who survive infancy. Childhood hypophos­ phatasia has variable clinical presentation. Premature loss of decidu­ ous teeth (before age 5) is the hallmark of the disease. Rickets causes delayed walking with waddling gait, short stature, and dolichocephalic skull with frontal bossing. The disease often improves during puberty but may recur in adult life. Adult hypophosphatasia presents during middle age with painful, poorly healing metatarsal stress fractures or thigh pain due to femoral pseudofractures. Presentation may be subtle with muscle pain or recurring headaches as the predominant symp­ toms. It is important to recognize hypophosphatasia in adults because treatment with bisphosphonates can result in increased rather than decreased bone fragility. Laboratory investigation reveals low ALP levels and normal or elevated levels of serum calcium and phosphorus despite clinical and radiologic evidence of rickets or osteomalacia. Serum parathyroid hormone, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D levels are normal. The elevation of PLP is specific for the disease and may even be present in asymptomatic parents of severely affected children. Because vitamin B6 increases PLP levels, vitamin B6 supplements should be discontinued 1 week before testing. Clinical testing is avail­ able to detect loss-of-function mutation(s) within the ALPL gene that encodes TNSALP. In contrast to other forms of rickets and osteomalacia, calcium and vitamin D supplementation should be avoided because they may aggra­ vate hypercalcemia and hypercalciuria. A low-calcium diet, glucocor­ ticoids, and calcitonin have been used in a small number of patients with variable responses. Because fracture healing is poor, placement of intramedullary rods is best for acute fracture repair and for pro­ phylactic prevention of fractures. In 2015, asfotase alfa, a TNSALP, was approved as enzyme replacement therapy for the perinatal/ infantile- and juvenile-onset forms. With 7 years of therapy, children with perinatal/infantile forms showed sustained improvements in mineralization, along with improvements in other features, such as respiratory function and growth. In adolescents and adults, 5 years of therapy demonstrated improved functional abilities, such as increases in 6-min walk time. ■ ■AXIAL OSTEOMALACIA This is a rare disorder characterized by defective skeletal mineraliza­ tion despite normal serum calcium and phosphate levels. Clinically, the disorder presents in middle-aged or elderly men with chronic axial skeletal discomfort. Cervical spine pain may also be present. Radio­ graphic findings are mainly osteosclerosis due to coarsened trabecu­ lar patterns typical of osteomalacia. Spine, pelvis, and ribs are most commonly affected. Histologic changes show defective mineralization

and flat, inactive osteoblasts. The primary defect appears to be an acquired defect in osteoblast function. The course is benign, and there is no established treatment. Calcium and vitamin D therapies are not effective. ■ ■FIBROGENESIS IMPERFECTA OSSIUM This is a rare condition of unknown etiology. It presents in both sexes; in middle age or later; and with progressive, intractable skeletal pain and fractures; worsening immobilization; and a debilitating course. The only biochemical abnormality is elevated ALP. Radiographic evaluation reveals generalized osteomalacia, osteopenia, and occa­ sional pseudofractures. Histologic features include a tangled pattern of collagen fibrils with abundant osteoblasts and osteoclasts. Use of growth hormone led to substantial short-term clinical improvement in two adult patients, but long-term outcomes are unknown. No other effective treatment is known. Spontaneous remission has been reported in a small number of patients. FIBROUS DYSPLASIA AND

MCCUNE-ALBRIGHT SYNDROME Fibrous dysplasia is a sporadic disorder characterized by the presence of one (monostotic) or more (polyostotic) expanding fibrous skeletal lesions composed of bone-forming mesenchyme. The association of the polyostotic form with café au lait spots and hyperfunction of an endocrine system such as pseudoprecocious puberty of ovarian origin is known as McCune-Albright syndrome (MAS). A spectrum of the phenotypes is caused by activating mutations in the GNAS1 gene, which encodes the α subunit of the stimulatory G protein (Gsα). As the postzygotic mutations occur at different stages of early development, the extent and type of tissue affected are variable and explain the mosaic pattern of skin and bone changes. GTP binding activates the Gsα regu­ latory protein and mutations in regions of Gsα that selectively inhibit GTPase activity, which results in constitutive stimulation of the cyclic AMP–protein kinase A signal transduction pathway. Such mutations of the Gsα protein–coupled receptor may cause autonomous function in bone (parathyroid hormone receptor); skin (melanocyte-stimulating hormone receptor); and various endocrine glands including ovary (follicle-stimulating hormone receptor), thyroid (thyroid-stimulating hormone receptor), adrenal (adrenocorticotropic hormone receptor), and pituitary (growth hormone–releasing hormone receptor). The skeletal lesions are composed largely of mesenchymal cells that do not differentiate into osteoblasts, resulting in the formation of imperfect bone. In some areas of bone, fibroblast-like cells develop features of osteoblasts in that they produce extracellular matrix that organizes into woven bone. Calcification may occur in some areas. In other areas, cells have features of chondrocytes and produce cartilage-like extracellular matrix. Clinical Presentation  Fibrous dysplasia occurs with equal fre­ quency in both sexes, whereas MAS with precocious puberty is more common (10:1) in girls. The monostotic form is the most common and is usually diagnosed in patients between 20 and 30 years of age without associated skin lesions. The polyostotic form typically mani­ fests in children <10 years old and may progress with age. Early-onset disease is generally more severe. Lesions may become quiescent in puberty and progress during pregnancy or with estrogen therapy. In polyostotic fibrous dysplasia, the lesions most commonly involve the maxilla and other craniofacial bones, ribs, and metaphyseal or diaphyseal portions of the proximal femur or tibia. Expanding bone lesions may cause pain, deformity, fractures, and nerve entrapment. Sarcomatous degeneration involving the facial bones or femur is infrequent (<1%). The risk of malignant transformation is increased by radiation, which has proven to be ineffective treatment. In rare patients with widespread lesions, renal phosphate wasting and hypo­ phosphatemia may cause rickets or osteomalacia. Hypophosphatemia may be due to production of a phosphaturic factor by the abnormal fibrous tissue. MAS patients may have café au lait spots, which are flat, hyper­ pigmented skin lesions that have rough borders (“coast of Maine”)

Paget’s Disease and Other Dysplasias of Bone CHAPTER 424 FIGURE 424-4  Radiograph of a 16-year-old male with fibrous dysplasia of the right proximal femur. Note the multiple cystic lesions, including the large lucent lesion in the proximal midshaft with scalloping of the interior surface. The femoral neck contains two lucent cystic lesions. in contrast to the café au lait lesions of neurofibromatosis that have smooth borders (“coast of California”). The most common endocri­ nopathy is isosexual pseudoprecocious puberty in girls. Other less common endocrine disorders include thyrotoxicosis, Cushing’s syn­ drome, acromegaly, hyperparathyroidism, hyperprolactinemia, and pseudoprecocious puberty in boys. Radiographic Findings  In long bones, the fibrous dysplastic lesions are typically well-defined, radiolucent areas with thin cortices and a ground-glass appearance. Lesions may be lobulated with trabecu­ lated areas of radiolucency (Fig. 424-4). Involvement of facial bones usually presents as radiodense lesions, which may create a leonine appearance (leontiasis osea). Expansile cranial lesions may narrow foramens and cause optic lesions, reduce hearing, and create other manifestations of cranial nerve compression. Laboratory Results  Serum ALP is occasionally elevated, but calcium, parathyroid hormone, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D levels are normal. Patients with extensive polyostotic lesions may have hypophosphatemia, hyperphosphaturia, and osteomalacia. The hypophosphatemia and phosphaturia are directly related to the levels of fibroblast growth factor 23 (FGF23). Biochemical markers of bone turnover may be elevated. TREATMENT Fibrous Dysplasia and MAS Spontaneous healing of the lesions does not occur, and there is no established effective treatment. Improvement in bone pain and partial or complete resolution of radiographic lesions have been reported after IV bisphosphonate therapy. Deno­ sumab given monthly or every 3 months is effective in reducing bone turnover markers and leads to some clinical improvement, though subsequent discontinuation of denosumab occasionally results in hypercalcemia. Surgical stabilization is used to pre­ vent pathologic fracture or destruction of a major joint space and to relieve nerve root or cranial nerve compression or sinus obstruction.

OTHER DYSPLASIAS OF BONE

AND CARTILAGE

■ ■PACHYDERMOPERIOSTOSIS Pachydermoperiostosis, or hypertrophic osteoarthropathy (primary or idiopathic), is an autosomal dominant disorder characterized by periosteal new bone formation that involves the distal extremities. The lesions present as clubbing of the digits and hyperhidrosis and thickening of the skin, primarily of the face and forehead. The changes usually appear during adolescence, progress over the next decade, and then become quiescent. During the active phase, progressive enlarge­ ment of the hands and feet produces a paw-like appearance, which may be mistaken for acromegaly. Arthralgias, pseudogout, and limited mobility may also occur. The disorder must be differentiated from secondary hypertrophic osteopathy that develops during the course of serious pulmonary disorders. The two conditions can be differentiated by standard radiography of the digits in which secondary pachydermo­ periostosis has exuberant periosteal new bone formation and a smooth and undulating surface. In contrast, primary hypertrophic osteopathy has an irregular periosteal surface. PART 12 Endocrinology and Metabolism The disease is genetically heterogeneous and is related to increases in prostaglandin E2. Synovial fluid does not have an inflammatory profile. There is no specific therapy, although a limited experience with colchicine suggests some benefit in controlling the arthralgias. ■ ■OSTEOCHONDRODYSPLASIAS These include several hundred heritable disorders of connective tissue. These primary abnormalities of cartilage manifest as disturbances in cartilage and bone growth. Selected growth-plate chondrodysplasias are described here. For discussion of chondrodysplasias, see Chap. 425. Achondrodysplasia  This is a relatively common form of shortlimb dwarfism that occurs in 1 in 15,000 to 1 in 40,000 live births. The disease is caused by a mutation of the fibroblast growth factor receptor 3 (FGFR3) gene that results in a gain-of-function state. Most cases are sporadic mutations. However, when the disorder appears in families, the inheritance pattern is consistent with an autosomal dominant disorder. The primary defect is abnormal chondrocyte proliferation at the growth plate that causes development of short, but proportionately thick, long bones. Other regions of the long bones may be relatively unaffected. The disorder is manifest by the presence of short limbs (particularly the proximal portions), normal trunk, large head, saddle nose, and an exaggerated lumbar lordosis. Severe spinal deformity may lead to cord compression. The homozygous disorder is more serious than the sporadic form and may cause neonatal death. Vosoritide, an analog of C-type natriuretic peptide, increased growth among children in phase 3 clinical trials and was approved in 2021. Treatment is controversial among patient support communities. Infigratinib, a selective FGFR1-3 tyrosine kinase inhibitor, is in clinical trials. Pseudoachondroplasia clinically resembles achondrodysplasia but has no skull abnormalities. Enchondromatosis  This is also called dyschondroplasia or Ollier’s disease; it is also a disorder of the growth plate in which the primary cartilage is not resorbed. Cartilage ossification proceeds normally, but it is not resorbed normally, leading to cartilage accumulation. The changes are most marked at the ends of long bones, where the highest growth rates occur. Chondrosarcoma develops infrequently. The asso­ ciation of enchondromatosis and cavernous hemangiomas of the skin and soft tissues is known as Maffucci’s syndrome. Both Ollier’s disease and Maffucci’s syndrome are associated with various malignancies, including granulosa cell tumor of the ovary and cerebral glioma. Multiple Osteochondromas  This is also called multiple exostoses or diaphyseal aclasis; it is a genetic disorder that follows an autosomal dominant pattern of inheritance. In this condition, areas of growth plates become displaced, presumably by growing through a defect in the perichondrium. The lesion begins with vascular invasion of the growth-plate cartilage, resulting in a characteristic radiographic finding of a mass that is in direct communication with the marrow cavity of the parent bone. The underlying cortex is resorbed. The disease is caused

by inactivating mutations of the EXT1 and EXT2 genes, whose prod­ ucts normally synthesize heparan sulfate chains. The resulting heparan sulfate deficiency impacts signaling pathways and leads to ectopic chon­ drogenesis. Solitary or multiple lesions are located in the metaphyses of long bones. Although usually asymptomatic, the lesions may interfere with joint or tendon function or compress peripheral nerves. The lesions stop growing when growth ceases but may recur during pregnancy. There is a small risk for malignant transformation into chondrosarcoma. Palovarotene, a retinoic acid receptor agonist, is in clinical trials. EXTRASKELETAL (ECTOPIC) CALCIFICATION AND OSSIFICATION Deposition of calcium phosphate crystals (calcification) or formation of true bone (ossification) in nonosseous soft tissue may occur by one of three mechanisms: (1) metastatic calcification due to a supranormal calcium × phosphate concentration product in extracellular fluid; (2) dystrophic calcification due to mineral deposition into metaboli­ cally impaired or dead tissue despite normal serum levels of calcium and phosphate; and (3) ectopic ossification, or true bone formation. Disorders that may cause extraskeletal calcification or ossification are listed in Table 424-2. ■ ■METASTATIC CALCIFICATION Soft tissue calcification may complicate diseases associated with significant hypercalcemia, hyperphosphatemia, or both. In addition, vitamin D and phosphate treatments or calcium administration in the presence of mild hyperphosphatemia, such as during hemodialysis, may induce ectopic calcification. Calcium phosphate precipitation may complicate any disorder when the serum calcium × phosphate concentration product is >75. The initial calcium phosphate deposition is in the form of small, poorly organized crystals, which subsequently organize into hydroxyapatite crystals. Calcifications that occur in hypercalcemic states with normal or low phosphate have a predilection for kidney, lungs, and gastric mucosa. Hyperphosphatemia with nor­ mal or low serum calcium may promote soft tissue calcification with predilection for the kidney and arteries. The disturbances of calcium and phosphate in renal failure and hemodialysis are common causes of soft tissue (metastatic) calcification. ■ ■TUMORAL CALCINOSIS This is a rare genetic disorder characterized by masses of metastatic calcifications in soft tissues around major joints, most often shoulders, hips, and ankles. Tumoral calcinosis differs from other disorders in that the periarticular masses contain hydroxyapatite crystals or amorphous calcium phosphate complexes, whereas in fibrodysplasia ossificans pro­ gressiva (below), true bone is formed in soft tissues. About one-third of tumoral calcinosis cases are familial, with both autosomal recessive and autosomal dominant modes of inheritance reported. The disease is also associated with a variably expressed abnormality of dentition marked TABLE 424-2  Diseases and Conditions Associated with Ectopic Calcification and Ossification Metastatic calcification   Hypercalcemic states     Primary hyperparathyroidism     Sarcoidosis     Vitamin D intoxication     Milk-alkali syndrome     Renal failure   Hyperphosphatemia     Tumoral calcinosis     Secondary hyperparathyroidism     Pseudohypoparathyroidism     Renal failure     Hemodialysis     Cell lysis following chemotherapy     Therapy with vitamin D and Dystrophic calcification   Inflammatory disorders     Scleroderma     Dermatomyositis     Systemic lupus erythematosus   Trauma-induced Ectopic ossification   Myositis ossificans     Postsurgery     Burns     Neurologic injury     Other trauma   Fibrodysplasia ossificans progressiva phosphate

42 - SECTION 5 Disorders of Intermediary Metabolism

SECTION 5 Disorders of Intermediary Metabolism

by short bulbous roots, pulp calcification, and radicular dentin depos­ ited in swirls. The disorder is caused by gene mutations in GALNT3, FGF23, or α-Klotho, leading to FGF23 deficiency or resistance. The reduced activity of FGF23 leads to increased renal tubular reabsorption of phosphate, elevated serum phosphate, and spontaneous soft tissue calcification from elevated calcium-phosphate concentration product. The disease usually presents in childhood and continues throughout the patient’s life. The calcific masses are typically painless and grow at variable rates, sometimes becoming large and bulky. The masses are often located near major joints but remain extracapsular. Joint range of motion is not usually restricted unless the tumors are very large. Com­ plications include compression of neural structures and ulceration of the overlying skin with drainage of chalky fluid and risk of secondary infection. Small deposits not detected by standard radiographs may be detected by 99mTc bone scanning. The most common laboratory findings are hyperphosphatemia and elevated serum 1,25-dihydroxyvitamin D levels. Serum calcium, parathyroid hormone, and ALP levels are usually nor­ mal. Renal function is also usually normal. Urine calcium and phosphate excretions are low, and calcium and phosphate balances are positive. An acquired form of the disease may occur with other causes of hyperphosphatemia, such as secondary hyperparathyroidism associ­ ated with hemodialysis, hypoparathyroidism, pseudohypoparathyroid­ ism, and massive cell lysis following chemotherapy for leukemia. Tissue trauma from joint movement may contribute to the periarticular cal­ cifications. Metastatic calcifications are also seen in conditions associ­ ated with hypercalcemia, such as in sarcoidosis, vitamin D intoxication, milk-alkali syndrome, and primary hyperparathyroidism. In these con­ ditions, however, mineral deposits are more likely to occur in protontransporting organs such as kidney, lungs, and gastric mucosa in which an alkaline milieu is generated by the proton pumps. TREATMENT Tumoral Calcinosis Therapeutic successes have been achieved with surgical removal of subcutaneous calcified masses, which tend not to recur if all calci­ fication is removed from the site. Reduction of serum phosphate by chronic phosphorus restriction may be accomplished using low dietary phosphorus intake alone or in combination with oral phos­ phate binders. The addition of the phosphaturic agent acetazol­ amide may be useful. Limited experience using the phosphaturic action of calcitonin deserves further testing. ■ ■DYSTROPHIC CALCIFICATION Posttraumatic calcification may occur with normal serum calcium and phosphate levels and normal ion-solubility product. The depos­ ited mineral is either in the form of amorphous calcium phosphate or hydroxyapatite crystals. Soft tissue calcification complicating con­ nective tissue disorders such as scleroderma, dermatomyositis, and systemic lupus erythematosus may involve localized areas of the skin or deeper subcutaneous tissue and is referred to as calcinosis circum­ scripta. Mineral deposition at sites of deeper tissue injury including periarticular sites is called calcinosis universalis. ■ ■ECTOPIC OSSIFICATION True extraskeletal bone formation that begins in areas of fasciitis following surgery, trauma, burns, or neurologic injury is referred to as myositis ossificans. The bone formed is organized as lamellar or trabecular, with normal osteoblasts and osteoclasts conducting active remodeling. Well-developed haversian systems and marrow elements may be present. A second cause of ectopic bone formation occurs in an inherited disorder, fibrodysplasia ossificans progressiva. ■ ■FIBRODYSPLASIA OSSIFICANS PROGRESSIVA This is also called myositis ossificans progressiva; it is a rare autosomal dominant disorder characterized by congenital deformities of the hands and feet and episodic soft tissue swellings that ossify. The disor­ der is caused by an activating mutation in activin receptor A type 1. Ectopic bone formation occurs in fascia, tendons, ligaments, and connective

tissue within voluntary muscles. Tender, rubbery induration, some­ times precipitated by trauma, develops in the soft tissue and gradually calcifies. Eventually, heterotopic bone forms at these sites of soft tissue trauma. Morbidity results from heterotopic bone interfering with nor­ mal movement and function of muscle and other soft tissues. Mortality is usually related to restrictive lung disease caused by an inability of the chest to expand. Laboratory tests are unremarkable.

Until recently, there was no effective approved medical therapy. Bisphosphonates, glucocorticoids, and a low-calcium diet have largely been ineffective in halting progression of the ossification. Palovaro­ tene has been shown to reduce new heterotopic ossification by 60% versus historical controls but increased premature epiphyseal closure in children. In 2023, the therapy was approved in the United States for females over age 8 and males over age 10. Another potential therapeu­ tic option, REGN2477 (also known as garetosmab), an anti–activin A antibody, is in clinical trials. Surgical removal of ectopic bone is not recommended because the trauma of surgery may precipitate forma­ tion of new areas of heterotopic bone. Dental complications, including frozen jaw, may occur following injection of local anesthetics. Heritable Disorders of Connective Tissue CHAPTER 425 Acknowledgment The authors acknowledge the contribution of Dr. Murray J. Favus to this chapter in previous editions of Harrison’s. ■ ■FURTHER READING Boyce AM, Collins MT: Fibrous dysplasia/McCune-Albright syn­ drome: A rare, mosaic disease of Gαs activation. Endocr Rev 41:345, 2020. De Castro LF et al: Safety and efficacy of denosumab for fibrous dys­ plasia of bone. N Eng J Med 388:8, 2023. Pognolo RJ et al: Reduction of new heterotopic ossification (HO) in the open-label, phase 3 MOVE trial of palovarotene for fibrodysplasia ossificans progressive (FOP). J Bone Miner Res 38:3, 2022. Ralston SH et al: Diagnosis and management of Paget’s disease of bone in adults: A clinical guideline. J Bone Miner Res 34:579, 2019. Shapiro JR, Lewiecki EM: Hypophosphatasia in adults: Clinical assessment and treatment considerations. J Bone Miner Res 32:1977, 2017. Singer FR et al: Paget’s disease of bone: An endocrine society clinical practice guideline. J Clin Endocrinol Metab 99:4408, 2014. Tan A et al: Long-term randomized trial of intensive versus symptom­ atic management in Paget’s disease of the bone: The PRISM-EZ Study. J Bone Miner Res 32:1165, 2017. Wu CC et al: Diagnosis and management of osteopetrosis: Consensus guidelines from the osteopetrosis working group. J Clin Endocrinol Metab 102:3111, 2017. Section 5 Disorders of Intermediary Metabolism Joan C. Marini, Fransiska Malfait

Heritable Disorders of Connective Tissue CLASSIFICATION OF CONNECTIVE

TISSUE DISORDERS Some of the most common conditions that are transmitted genetically in families are disorders that produce clinically obvious changes in the bone, cartilage, skin, or relatively acellular tissues such as tendons

43 - 425 Heritable Disorders of Connective Tissue

425 Heritable Disorders of Connective Tissue

by short bulbous roots, pulp calcification, and radicular dentin depos­ ited in swirls. The disorder is caused by gene mutations in GALNT3, FGF23, or α-Klotho, leading to FGF23 deficiency or resistance. The reduced activity of FGF23 leads to increased renal tubular reabsorption of phosphate, elevated serum phosphate, and spontaneous soft tissue calcification from elevated calcium-phosphate concentration product. The disease usually presents in childhood and continues throughout the patient’s life. The calcific masses are typically painless and grow at variable rates, sometimes becoming large and bulky. The masses are often located near major joints but remain extracapsular. Joint range of motion is not usually restricted unless the tumors are very large. Com­ plications include compression of neural structures and ulceration of the overlying skin with drainage of chalky fluid and risk of secondary infection. Small deposits not detected by standard radiographs may be detected by 99mTc bone scanning. The most common laboratory findings are hyperphosphatemia and elevated serum 1,25-dihydroxyvitamin D levels. Serum calcium, parathyroid hormone, and ALP levels are usually nor­ mal. Renal function is also usually normal. Urine calcium and phosphate excretions are low, and calcium and phosphate balances are positive. An acquired form of the disease may occur with other causes of hyperphosphatemia, such as secondary hyperparathyroidism associ­ ated with hemodialysis, hypoparathyroidism, pseudohypoparathyroid­ ism, and massive cell lysis following chemotherapy for leukemia. Tissue trauma from joint movement may contribute to the periarticular cal­ cifications. Metastatic calcifications are also seen in conditions associ­ ated with hypercalcemia, such as in sarcoidosis, vitamin D intoxication, milk-alkali syndrome, and primary hyperparathyroidism. In these con­ ditions, however, mineral deposits are more likely to occur in protontransporting organs such as kidney, lungs, and gastric mucosa in which an alkaline milieu is generated by the proton pumps. TREATMENT Tumoral Calcinosis Therapeutic successes have been achieved with surgical removal of subcutaneous calcified masses, which tend not to recur if all calci­ fication is removed from the site. Reduction of serum phosphate by chronic phosphorus restriction may be accomplished using low dietary phosphorus intake alone or in combination with oral phos­ phate binders. The addition of the phosphaturic agent acetazol­ amide may be useful. Limited experience using the phosphaturic action of calcitonin deserves further testing. ■ ■DYSTROPHIC CALCIFICATION Posttraumatic calcification may occur with normal serum calcium and phosphate levels and normal ion-solubility product. The depos­ ited mineral is either in the form of amorphous calcium phosphate or hydroxyapatite crystals. Soft tissue calcification complicating con­ nective tissue disorders such as scleroderma, dermatomyositis, and systemic lupus erythematosus may involve localized areas of the skin or deeper subcutaneous tissue and is referred to as calcinosis circum­ scripta. Mineral deposition at sites of deeper tissue injury including periarticular sites is called calcinosis universalis. ■ ■ECTOPIC OSSIFICATION True extraskeletal bone formation that begins in areas of fasciitis following surgery, trauma, burns, or neurologic injury is referred to as myositis ossificans. The bone formed is organized as lamellar or trabecular, with normal osteoblasts and osteoclasts conducting active remodeling. Well-developed haversian systems and marrow elements may be present. A second cause of ectopic bone formation occurs in an inherited disorder, fibrodysplasia ossificans progressiva. ■ ■FIBRODYSPLASIA OSSIFICANS PROGRESSIVA This is also called myositis ossificans progressiva; it is a rare autosomal dominant disorder characterized by congenital deformities of the hands and feet and episodic soft tissue swellings that ossify. The disor­ der is caused by an activating mutation in activin receptor A type 1. Ectopic bone formation occurs in fascia, tendons, ligaments, and connective

tissue within voluntary muscles. Tender, rubbery induration, some­ times precipitated by trauma, develops in the soft tissue and gradually calcifies. Eventually, heterotopic bone forms at these sites of soft tissue trauma. Morbidity results from heterotopic bone interfering with nor­ mal movement and function of muscle and other soft tissues. Mortality is usually related to restrictive lung disease caused by an inability of the chest to expand. Laboratory tests are unremarkable.

Until recently, there was no effective approved medical therapy. Bisphosphonates, glucocorticoids, and a low-calcium diet have largely been ineffective in halting progression of the ossification. Palovaro­ tene has been shown to reduce new heterotopic ossification by 60% versus historical controls but increased premature epiphyseal closure in children. In 2023, the therapy was approved in the United States for females over age 8 and males over age 10. Another potential therapeu­ tic option, REGN2477 (also known as garetosmab), an anti–activin A antibody, is in clinical trials. Surgical removal of ectopic bone is not recommended because the trauma of surgery may precipitate forma­ tion of new areas of heterotopic bone. Dental complications, including frozen jaw, may occur following injection of local anesthetics. Heritable Disorders of Connective Tissue CHAPTER 425 Acknowledgment The authors acknowledge the contribution of Dr. Murray J. Favus to this chapter in previous editions of Harrison’s. ■ ■FURTHER READING Boyce AM, Collins MT: Fibrous dysplasia/McCune-Albright syn­ drome: A rare, mosaic disease of Gαs activation. Endocr Rev 41:345, 2020. De Castro LF et al: Safety and efficacy of denosumab for fibrous dys­ plasia of bone. N Eng J Med 388:8, 2023. Pognolo RJ et al: Reduction of new heterotopic ossification (HO) in the open-label, phase 3 MOVE trial of palovarotene for fibrodysplasia ossificans progressive (FOP). J Bone Miner Res 38:3, 2022. Ralston SH et al: Diagnosis and management of Paget’s disease of bone in adults: A clinical guideline. J Bone Miner Res 34:579, 2019. Shapiro JR, Lewiecki EM: Hypophosphatasia in adults: Clinical assessment and treatment considerations. J Bone Miner Res 32:1977, 2017. Singer FR et al: Paget’s disease of bone: An endocrine society clinical practice guideline. J Clin Endocrinol Metab 99:4408, 2014. Tan A et al: Long-term randomized trial of intensive versus symptom­ atic management in Paget’s disease of the bone: The PRISM-EZ Study. J Bone Miner Res 32:1165, 2017. Wu CC et al: Diagnosis and management of osteopetrosis: Consensus guidelines from the osteopetrosis working group. J Clin Endocrinol Metab 102:3111, 2017. Section 5 Disorders of Intermediary Metabolism Joan C. Marini, Fransiska Malfait

Heritable Disorders of Connective Tissue CLASSIFICATION OF CONNECTIVE

TISSUE DISORDERS Some of the most common conditions that are transmitted genetically in families are disorders that produce clinically obvious changes in the bone, cartilage, skin, or relatively acellular tissues such as tendons

that have been loosely defined as connective tissues. Because of their heritability, some of the disorders were recognized as potentially traceable to mutated genes soon after the principles of genetics were introduced into medicine by Garrod and others. About half a century later, McKusick emphasized the specificity of many of the diseases for selective connective tissues and suggested that they were probably caused by mutations in genes coding for the major proteins found in those tissues. In the past several decades, mutations in several hundred different genes expressed in connective tissues have been identified as the cause of many connective tissue disorders. However, classifying the disorders on the basis of either their clinical presentations or the mutations causing them continues to present a challenge for both the clinician and the molecular biologist.

PART 12 Endocrinology and Metabolism Information on the disorders has continued to develop on two levels. The initial clinical classifications suggested by McKusick and many others had to be refined as more patients were examined. For example, some patients had skin changes similar to those commonly seen in Ehlers-Danlos syndrome (EDS), but this feature was overshad­ owed by other features such as extreme hypotonia or sudden rupture of large blood vessels. To account for the full spectrum of presentations in patients and families, many of the disorders have been reclassified several times, dividing each into a series of subtypes. The identification of mutations causing the diseases has developed on a parallel track. The first genes cloned for connective tissues were the two genes coding for type I collagen (COL1A1 and COL1A2), the most abundant protein in bones, skin, tendons, and several other tis­ sues. This facilitated early studies in patients with osteogenesis imper­ fecta (OI) that revealed mutations in type I collagen genes. Biochemical data, developed primarily with cultures of skin fibroblasts from affected individuals, demonstrated that the mutations dramatically altered the synthesis of collagen α-chains or the structure of collagen fibers. The results stimulated efforts to identify additional mutations in genes cod­ ing for structural proteins. Genes for collagens provided an attractive paradigm to search for mutations, since a series of different types of collagens were found in different connective tissues and the collagen genes were readily isolated by their unique signature sequences. Also, the collagen genes were vulnerable to a large number of different muta­ tions because of unusual structural requirements of the protein. The search for mutations in collagen genes proved fruitful in that mutations were found in most patients with OI, in many patients with hyperex­ tensible skin and hypermobile joints, in some patients with dwarfism, and in patients with other disorders, including some such as Alport syndrome (AS) that were not initially classified as disorders of con­ nective tissue. Also, mutations in collagen genes were found in subset of patients presenting with osteoarthritis (OA) or osteoporosis, likely representing the mildest end of the syndromic spectrum. However, the search for mutations quickly expanded to hundreds of other genes that included genes for other structural proteins, for the posttranslational modification and processing of the structural proteins, for chaperones, and for growth factors and their receptors and other genes whose func­ tions are still not fully understood. In many instances, the mutations helped to define the clinical sub­ type of the disorder, while in others, they revealed the genetic hetero­ geneity of the same clinical presentations. Conversely, some patients with different manifestations were found to have mutations in the same genes. In noncollagenous genes, it was sometimes difficult to establish whether a change in the structure of a gene caused the phenotypic changes in the patients or was simply a neutral polymorphism. There­ fore, there has been a continuing debate as to whether the disorders should be classified by their clinical presentations or by the causative genes. As an illustration of the problems, mutations in 552 genes have now been found associated with 771 defined disorders of the skeleton. The latest (2023) nosology for the disorders, which adopted a dyadic naming system, systematically associating a phenotypic entity with the gene it arises from, remains “hybrid” in nature in the sense that the classification is not always based on the same criteria. Some dis­ eases are grouped based on the causal gene, others are listed together, because they share common radiographic features, and still others are brought together because of a similar clinical course (lethality) or

involvement of similar parts of the skeleton. A simpler system of clas­ sification proved feasible for one rare heritable disorder of skin, epider­ molysis bullosa. The disorder was first defined clinically into subtypes based on the layers of the skin that were cleaved in friction-induced blisters. Most patients in each subtype were subsequently shown to have mutations in genes expressed in the corresponding layer of skin. Even with these patients, the strength of the genotype-phenotype cor­ relation varies and mutations have not yet been found in every patient. The best pathway through this maze of information is probably to begin by matching the signs and symptoms in a patient with the pre­ sentations that define each clinical classification. A major focus should be on the most common disorders, recognizing that the signs and symptoms may vary among different individuals and family members with the same diagnosis. Then, attempt to reach a decision, in consul­ tation with the patient, parents, and specialist, as to whether a DNA analysis for the probable mutation is indicated. Among the consider­ ations are the cost, the rigor with which the clinical classification has been linked to mutated genes, the reassurance the diagnosis can bring to patients and their families, the use of the genetic information for prenatal diagnosis, and the possibility that mutation-specific therapies may be developed in the future. For individuals affected with these dis­ orders, consulting a specialist in the disease is highly recommended to determine a multidisciplinary program for management and therapy. Patient support groups have formed for many of the diseases and are an important source of information. Patients with the most common forms of the disorders have muta­ tions in a limited number of genes. This chapter will focus primarily on these. Also, it will provide a brief summary of biosynthesis and structure of connective tissues that may help guide the physician from the nature of the mutations to their clinical presentations. ■ ■COMPOSITION OF CONNECTIVE TISSUES Connective tissues such as skin, bone, cartilage, ligaments, and ten­ dons are the critical structural frameworks of the body. They consist of a complex interacting extracellular matrix network of collagens, proteoglycans, and a large number of noncollagenous glycoproteins and proteins. While these precise combinations of up to ~500 potential extracellular matrix building blocks, collectively called “the matri­ some,” provide tissue-specific function, there are many overarching similarities in composition such as the role of composite collagen fibrils in providing strength and form, elastin fibrils and proteoglycans and other interacting proteins, and glycoproteins that fine-tune function (Table 425-1). The most abundant components of many connective tissues are three similar fibrillar collagens (types I, II, and III). They have a similar tensile strength that is comparable to that of steel wires. The three fibrillar collagens are distributed in a tissue-specific manner: type I collagen accounts for most of the protein of dermis, ligaments, tendons, and demineralized bone; type I and type III are the most abundant proteins of large blood vessels; and type II is the most abun­ dant protein of cartilage. ■ ■BIOSYNTHESIS AND TURNOVER OF

CONNECTIVE TISSUES Connective tissues are among the most stable components in living organisms, but they are not inert. During embryonic development, connective tissue membranes appear as early as the four-cell blastocyst to provide a structural scaffold for the developing embryo. With the development of blood vessels and skeleton, there is a rapid increase in the synthesis, degradation, and resynthesis of connective tissues. The turnover continues at a slower, but still rapid pace throughout postnatal development and then spikes during the growth spurt of puberty. During adulthood, the metabolic turnover of most connective tissues is slow, but it continues at a moderate pace in bone. With age, malnutrition, physical inactivity, and low gravitational stress, the rate of degradation of most connective tissues, especially in bone and skin, begins to exceed the rate of synthesis and the tissues shrink. In starva­ tion, a large fraction of the collagen in skin and other connective tissues is degraded and provides amino acids for gluconeogenesis (Chap. 345). In both OA and rheumatoid arthritis, there is extensive degradation of

TABLE 425-1  Constituents of Connective Tissues and Their Associated Heritable Conditions PROTEIN TISSUE DISTRIBUTION DISEASE KEY MANIFESTATIONS Collagen I Bone, cornea, dermis, tendon Osteogenesis imperfecta Bone fragility with fractures and deformity; blue sclerae; dentinogenesis imperfecta; hearing loss EDS (various rare types) Joint hypermobility; skin hyperextensibility; skin fragility; soft connective tissue fragility Caffey disease Subperiosteal new bone formation; soft tissue swelling; fever and irritability Collagen II Cartilage, vitreous Various chondrodysplasias Skeletal dysplasia; ocular manifestations; hearing loss; orofacial findings Collagen III Dermis, aorta, uterus, intestine Vascular EDS Arterial, intestinal, and uterine fragility; thin translucent skin; easy bruising Collagen IV Basement membranes Alport syndrome (COL4A3/A4/A5) Hematuria; hearing loss; ocular abnormalities Brain small-vessel disease (COL4A1/A2) Porencephaly; intracerebral hemorrhage; retinal arterial tortuosity; (congenital) cataract; Axenfeld-Rieger anomaly; hematuria; renal cysts; muscle cramps Collagen V Placental tissue, bone, dermis, cornea Classic EDS Joint hypermobility; skin hyperextensibility; atrophic scarring Collagen VI Uterus, dermis, cornea, cartilage Bethlem myopathy and Ullrich congenital muscular dystrophy Collagen VII Skin, amniotic membrane, mucosal epithelium Dystrophic epidermolysis bullosa Skin blistering; oral and esophageal blistering; corneal erosions Collagen VIII Descemet’s membrane, endothelial cells Corneal dystrophy Corneal endothelial dystrophy; stromal edema Collagen IX Cartilage, vitreous Stickler syndrome Spondyloepiphyseal dysplasia; early-onset osteoarthritis; high myopia; vitreoretinal abnormalities; hearing loss; cleft palate; midfacial hypoplasia Collagen X Calcifying cartilage Multiple epiphyseal dysplasia Epiphyseal dysplasia; early-onset osteoarthritis Collagen XI Cartilage, intervertebral disk Various chondrodysplasias Skeletal dysplasia; ocular manifestations; hearing loss; orofacial findings Collagen XII Dermis, tendon, cartilage Myopathic EDS Joint hypermobility; congenital muscle hypotonia and/or atrophy; proximal joint contractures Collagen XVII Corneal epithelial cells Junctional epidermolysis bullosa Blistering of the skin and mucosae (mild to severe) Collagen XVIII Pia, blood vessels of the developing human cerebral cortex Knobloch syndrome Early-onset severe myopia; vitreoretinal degeneration with retinal detachment; hydrocephalus; structural brain defects; epilepsy; cognitive dysfunction Collagen XXVII Chondrocytes, epithelial cell layers in developing tissues, including stomach, lung, gonad, skin, cochlea, and tooth Steel syndrome Osteochondrodysplasia with hip dislocations; dislocations of radial heads; carpal coalition; short stature; facial dysmorphism; scoliosis Cartilage oligomeric matrix protein (COMP) Cartilage, tendon, ligament, bone Pseudoachondroplasia Short-limb dwarfism; early-onset osteoarthritis Multiple epiphyseal dysplasia Mildly short stature; early-onset osteoarthritis Elastin Dermis, arterial wall, lung Cutis laxa Wrinkled, redundant, sagging inelastic skin Williams syndrome Cardiovascular disease (especially supravalvular aortic stenosis); orofacial features; intellectual deficit; connective tissue abnormalities; endocrine abnormalities Fibrillin 1 Dermis, arterial wall, lung Marfan syndrome Aortic root aneurysm or dissection; ectopia lentis; marfanoid habitus Weill-Marchesani-syndrome Short stature; joint stiffness; lens abnormalities; cardiovascular features Stiff skin syndrome Progressive rock-hard skin; flexion contractures; hypertrichosis Geleophysic dysplasia Short stature; joint stiffness; thickened skin; progressive cardiac valvular disease; orofacial features Fibrillin 2 Bruch membrane Congenital contractural arachnodactyly (CCA) or Beals-Hecht syndrome Acromelic dysplasia Relative short stature; brachydactyly; toe walking; early onset carpal tunnel syndrome; short palpebral fissures Fibronectin Dermis, tendons, ligaments Glomerulopathy with fibronectin deposits Glomerulopathy with fibronectin deposits Spondylometaphyseal dysplasia, corner fracture type

Heritable Disorders of Connective Tissue CHAPTER 425 Muscle weakness; joint contractures; joint hypermobility Tall stature; arachnodactyly; (kypho)scoliosis; pectus deformities; contractures; muscle hypoplasia; mild cardiovascular involvement; long, narrow face, highly arched palate, micrognathia, crumpled external ears Spondylometaphyseal dysplasia characterized by flake-like, triangular, or curvilinear ossification centers at the edges of irregular metaphyses that simulate fractures; short stature (Continued)

TABLE 425-1  Constituents of Connective Tissues and Their Associated Heritable Conditions PROTEIN TISSUE DISTRIBUTION DISEASE KEY MANIFESTATIONS Aggrecan Cartilage Spondyloepiphyseal dysplasia, Kimberley type Short stature; advanced bone age, with or without early-onset osteoarthritis and/or osteochondritis dissecans Spondyloepimetaphyseal dysplasia, aggrecan type Decorin Dermis, tendons, ligaments, cornea Congenital stromal corneal dystrophy Corneal stromal opacification; visual loss; increased corneal thickness PART 12 Endocrinology and Metabolism Biglycan Bone, cartilage, tendons Meester-Loeys syndrome Aortic aneurysm or dissection; orofacial features; joint hypermobility; ventricular dilatation on brain imaging; relative macrocephaly; hip dislocation; platyspondyly; phalangeal dysplasia; dysplastic epiphyses of the long bones X-linked spondyloepimetaphyseal dysplasia Abbreviation: EDS, Ehlers-Danlos syndromes. articular cartilage collagen. Glucocorticoids weaken most tissues by decreasing collagen synthesis. In some pathologic states, however, col­ lagen is deposited in excess. With most injuries to tissues, inflamma­ tory and immune responses stimulate the deposition of collagen fibrils in the form of fibrotic scars. In humans, as distinct from many other species, the deposition of the fibrils is largely irreversible and prevents regeneration of normal tissues in diseases such as hepatic cirrhosis, pulmonary fibrosis, atherosclerosis, and nephrosclerosis. Structure and Biosynthesis of Fibrillar Collagens  The tensile strength of collagen fibers derives primarily from the self-assembly of protein monomers into large fibril structures in a process that resem­ bles crystallization. The self-assembly requires monomers of highly uniform and relatively rigid structure. It also requires a complex series of posttranslational processing steps that maintain the solubility of the monomers until they are transported to the appropriate extracellular sites for fibril assembly. Because of the stringent requirements for cor­ rect self-assembly, it is not surprising that mutations in genes for fibril­ lar collagens cause many of the heritable diseases of connective tissues. The monomers of the three fibrillar collagens are formed from three polypeptide chains, called α chains, that are wrapped around each other into a rope-like triple-helical conformation. The triple helix is a unique structure among proteins, and it provides rigidity to the molecule. It also orients the side chains of amino acids in an “inside out” manner relative to most other proteins so that the charged and hydrophobic residues on the surface can direct self-assembly of the monomers into fibrils. The triple-helical conformation of the monomer is generated because each of the α chains has a repetitive amino acid sequence in which glycine (Gly) appears as every third amino acid. Each α chain contains ~1000 amino acids. Therefore, the sequence of each α chain can be designated as (-Gly-X-Y-)n, where X and Y represent amino acids other than glycine and n is >338. The presence of glycine, the smallest amino acid, in every third position in the sequence is critical because this residue must fit into a sterically restricted space in the interior of the helix where the three chains come together. The requirement for a glycine residue at every third position explains the significant clinical effects of mutations that convert a glycine residue to an amino acid with a bulkier side chain (see below). Many of the X- and Y-position amino acids are proline and hydroxyproline, which, because of their ring structures, provide additional rigidity to the triple helix. Other X- and Y-positions are occupied by charged or hydrophobic amino acids that precisely direct lateral and longitudinal assembly of the monomers into highly ordered fibrils. Mutations that substitute amino acids in some X- and Y-positions, particularly arginine-to-cysteine substitutions, can also produce genetic diseases. The fibers formed by the three fibrillar collagens differ in thick­ ness and length, but they have a similar fine structure. As viewed by electron microscopy, they all have a characteristic pattern of crossstriations that are about one-quarter the length of the monomers and

(Continued) Short stature; habitus; progressive osteoarthropathy; spondyloepiphyseal dysplasia Short stature and advanced bone age, with or without early-onset osteoarthritis and/or osteochondritis dissecans Severe short stature; spondyloepimetaphyseal dysplasia Severe short-trunked dwarfism; brachydactyly; spondyloepimetaphyseal dysplasia reflect the precise packing into fibrils. The three fibrillar collagens, however, differ in sequences found in the X- and Y-positions of the α chains and therefore in some of their physical properties. Type I col­ lagen is a heterotrimer, composed of two identical α1(I) chains and a third α2(I) chain that differs slightly in its amino acid sequence. Types II and III collagen are homotrimers, each composed of three identical α chains distinct to that type of collagen. To deliver a monomer of the correct structure to the appropriate site of fibril assembly, the biosynthesis of fibrillar collagens involves a large number of unique processing steps (Fig. 425-1). The monomer, first synthesized as a soluble precursor called procollagen, contains an additional globular domain at each end. As the pre-proα chains of pro­ collagen are synthesized on ribosomes, the free N-terminal ends move into the cisternae of the rough endoplasmic reticulum (ER). Signal peptides at the N-termini are cleaved, and additional posttranslational reactions begin. Proline and lysine residues in the Y-position of the Gly-X-Y repeating triplet are hydroxylated along the length of the helix by the enzymes prolyl 4-hydroxylase (P4H1) and lysyl hydroxylase (LH1), respectively. Hydroxyproline residues are essential for the three α chains of the monomer to fold into a triple helix at body tempera­ ture. P4H1 requires ascorbic acid as an essential cofactor, an observa­ tion that explains why wounds fail to heal in scurvy (Chap. 344). In scurvy, some of the underhydroxylated and unfolded protein accumu­ lates in the cisternae of the rough ER and is degraded. Many hydroxy­ lysine residues are glycosylated with galactose or with galactose and glucose. Also, a large mannose-rich oligosaccharide is assembled on the C-terminal propeptide of each chain. The proα chains are assembled by interactions among these C-terminal propeptides that control the selection of the appropriate partner chains to form hetero- or homotrimers and provide the correct chain registration required for subsequent formation of the collagen triple helix. After the C-terminal propeptides assemble the three proα chains, a nucleus of triple helix is formed near the C-terminus, and the helical conformation is propa­ gated toward the N-terminus in a zipper-like manner that resembles crystallization. The folding into the triple helix is spontaneous in solu­ tion, but as discussed below, identification of rare mutations causing OI demonstrated that the folding in cellulo is assisted by a number of ancillary proteins that also prevent collagen fibril formation within the ER. The fully folded procollagen is then transported to the Golgi via a specific COPII vesicle process. After further modifications in the Golgi stack, the procollagen is secreted into the pericellular space where distinct proteases remove the N- and C-propeptides at specific cleavage sites. The release of the propeptides decreases the solubility of the resulting collagen ~1000-fold. The entropic energy that is released drives the self-assembly of the collagen into fibrils. Self-assembled collagen fibers have considerable tensile strength, but their strength is increased further by cross-linking reactions that form covalent bonds between α chains in one molecule and α chains in adjacent molecules.

Endoplasmic reticulum Late transport vesicles and extracellular matrix Polypeptide synthesis OH OH OH OH Collagen prolyl 4-hydroxylase Lysyl hydroxylase Prolyl 3-hydroxylase Collagen gal-transferase and glc-transferase OH OH OH OH O-Gal OH OH OH OH OH OH OH OH OH O-Gal-Glc -Gal-Glc OH Glc Gal O OH N glycosylated residue (Man)n GlcNAc SH OH OH OH Assembly of three procollagen chains OH OH OH SH SH OH OH SH O Gal Glc Gal O OH (Man)n GlcNAc OH OH OH S OH OH OH S S Protein disulfide isomerase OH OH S O Gal Assembly of triple helix Secretion of procollagen in transport vesicles FIGURE 425-1  Schematic summary of biosynthesis of fibrillar collagens. (Reproduced with permission from J Myllyharju, KI Kivirikko: Collagens, modifying enzymes and their mutations in humans, flies and worms. Trends Genet 20:33, 2004.) The resulting fibers, composed of hundreds or thousands of triplehelical monomers, have some of the properties of a crystal but have innate imperfections that make them highly flexible. Although the assembly of collagen monomers into fibers is largely a spontaneous reaction, the process in tissues is modulated by the pres­ ence of less abundant collagens (type V with type I, and type XI with type II) and by other components such as a series of small leucine-rich proteins (SLRPs). Some of the less abundant components alter the rate of fibril assembly, whereas others change the morphology of the fibers or their interactions with cells and other molecules. The presence of these other components is one explanation for why, in some tissues, the fibers are further assembled into large tendons; in others, into sheets; and in still others, into complex structures such as the hexago­ nal array of fibers that provide both the strength and transparency of the cornea. Collagen fibers are resistant to most proteases, but during degrada­ tion of connective tissues, they are cleaved by specific matrix metal­ loproteinases (collagenases) that cause partial unfolding of the triple helices into gelatin-like structures that are further degraded by less specific proteinases. ■ ■OTHER COLLAGENS AND RELATED MOLECULES The unique properties of the triple helix are used to define a family of at least 28 collagens that contain repetitive -Gly-X-Y- sequences and form triple helices of varying length and complexity. The proteins are heterogeneous both in structure and function, and many are the sites of mutations causing genetic diseases. For example, the type IV col­ lagen found in basement membranes is composed of three α chains synthesized from any of six different genes. Mutations in the COL4A3, COL4A4, or COL4A5 genes cause AS, while mutations in COL4A1 and rarely COL4A2 are associated with a spectrum of phenotypes including small-vessel brain disease of varying severity including porencephaly, variably associated with eye defects (retinal arterial tortuosity, Axen­ feld-Rieger anomaly, cataract) and systemic findings (kidney involve­ ment, muscle cramps, cerebral aneurysms, Raynaud phenomenon, cardiac arrhythmia, and hemolytic anemia).

N and C proteinases Heritable Disorders of Connective Tissue CHAPTER 425 Cleavage of propeptides Assembly into collagen fibrils Lysyl oxidase Formation of covalent cross-links Fibrillin Aggregates and Elastin  In addition to tensile strength, many tissues such as the lung, large blood vessels, and ligaments require elasticity. The elasticity was originally ascribed to an amor­ phous rubber-like protein named elastin. Subsequent analyses, largely sparked by discoveries of mutations causing the Marfan syndrome (MFS), demonstrated that the elasticity resided in thin fibrils com­ posed primarily of large glycoproteins named fibrillins. The fibrillins contain large numbers of epidermal growth factor–like domains inter­ spersed with characteristic cysteine-rich domains that are also found in latent transforming growth factor β (TGF-β) binding proteins. The fibrillins assemble into long beadlike strands that also contain numer­ ous other components including small and variable amounts of elas­ tin, bone morphogenic proteins (BMPs), and microfibril-associated glycoproteins (MAGPs). Besides contributing to extracellular matrix structure, a major role for fibrillins in TGF-β signaling was empha­ sized by the discovery of mutations in genes coding for proteins involved in canonical TGF-β signaling in patients with Marfan-like manifestations, including thoracic aortic aneurysm. Proteoglycans  The resiliency to compression of connective tis­ sues such as cartilage or the aorta is largely explained by the presence of proteoglycans. Proteoglycans are composed of a core protein to which are attached a large series of negatively charged polymers of disaccharides (largely chondroitin sulfates). At least 30 proteoglycans have been identified. They vary in their binding to collagens and other components of matrix, but specific functions have not been assigned to most. The major proteoglycan of cartilage, called aggrecan, has a core protein of 2000 amino acids that is decorated with ~100 side chains of chondroitin sulfate and keratin sulfate. The core protein, in turn, binds to long chains of the polymeric disaccharide hyaluronan to form proteoglycan aggregates, one of the largest soluble macromo­ lecular structures in nature. Because of its highly negative charge and extended structure, the proteoglycan aggregate binds large amounts of water and small ions to distend the three-dimensional arcade of col­ lagen fibers found in the same tissues. It thereby makes the cartilage resilient to pressure.

SPECIFIC DISORDERS

■ ■OSTEOGENESIS IMPERFECTA OI is a phenotypically and genetically heterogeneous generalized con­ nective tissue disorder. The hallmark features of OI are increased sus­ ceptibility to skeletal fractures, bone deformity, and growth deficiency. Bone fragility is based on decreased bone mass and increased bone brittleness due to defective mineralization. Secondary features of OI are highly variable even within a type and include blue sclerae, den­ tinogenesis imperfecta, hearing loss, basilar invagination, pulmonary function impairment, cardiac valve abnormalities, and ligamentous laxity. Most patients have defects in the structure or quantity of type I collagen. PART 12 Endocrinology and Metabolism Classification  OI was originally classified into congenita and tarda subtypes depending on the age of symptom onset. Sillence proposed the classification that bears his name for four types based on clinical and radiologic findings and mode of inheritance. The extension of the Sillence classification was first based on distinctive bone histol­ ogy (types V and VI OI) and subsequently on the discovery of new recessive genes (types VII–XXII). The debate between classification by phenotypic severity or gene defects has resulted in clinical and genetic classifications. The clinical classification can be useful for management but results in different type assignments in the same family or even in the same individual over their lifetime. The genetic classification (Table 425-2) groups patients by the causative gene. Because related causative genes were discovered close in time to each other, the genetic classification consequently groups types by overall mechanism and features OI as a collagen-related disorder. Types I–IV OI are due to quantitative or structural defects in type I collagen itself. Type I is the mildest subtype, with reduced quantity of structurally normal collagen, and can produce mild or inapparent skeletal deformities. Most patients have distinctly blue sclerae. Types II, III, and IV are all caused by structural defects in one of the type I col­ lagen α chains. Type II produces bone so brittle that infants have in utero fractures of ribs and long bones and die in the perinatal period. Type III is progressively deforming with moderate to severe bone deformity, and type IV has mild to moderate bone fragility and second­ ary features. Subsequent rare recessive OI types are all collagen-related. Types V and VI (ITITM5 and SERPINF1) particularly compromise matrix mineralization. Types VII, VIII, and IX (CRTAP, P3H1, and PPIB) represent defects in the components of the procollagen prolyl 3-hydroxylation complex that modifies collagen posttranslationally. Types X–XII and XXI (SERPINH1, FKBP10, BMP1, and KDELR1) have compromised procollagen processing and cross-linking. The final grouping of types XIII–XVIII (SP7, TMEM38B, WNT1, CREBL1, SPARC, MBTPS2, TEMTSA, MESD, CCDS134) alter osteoblast differ­ entiation and impair collagen matrix quality. The clinical heterogeneity of affected individuals within a particu­ lar OI type and even with the same mutation is not understood, with unknown modifying factors presumably involved. Among adults with OI, women are prone to fracture during pregnancy and after meno­ pause. Some variants of mild OI are first detected perimenopausally and must be distinguished from postmenopausal osteoporosis. Incidence  In North America and Europe, the estimated incidence of OI is 1 per 10,000–15,000 births, based on a combination of cases recognized at birth and population surveys for milder cases. In popu­ lations with a high level of consanguinity or a founder mutation, the incidence of the rare recessive forms of OI is a significant addition to the prevalence of dominant collagen defects. Effects on Tissue Systems  The phenotypic features of OI are highly variable, even within the types caused by defects in type I colla­ gen. The following section generally focuses on dominant forms com­ prising the majority of cases, except as specified, but the descriptions can be generalized to a large extent. Musculoskeletal Effects  Bone in OI is both weak and brittle. At the mildest end of the spectrum (type I OI), individuals may have only several childhood fractures and be limited only from contact sports.

More severe forms of OI require bone to be partially unloaded with assistive devices such as walkers or canes; many severe patients use electric chairs for both the weight bearing and the normal speed of mobility. In dominant OI, fragility fractures often decrease sharply after adequate bone mass is gained at puberty. Radiographs generally show osteopenia in all types, with disordered matrix organization detected most easily in lower long bones in moderate and severe forms. In lethal OI, radiographs show continuous beading of ribs from healing fractures and crumpled and undertubulated long bones. Lateral skull radiographs may show islands of Wormian bones, even in mild forms. The appearance of “popcorn” at the metaphyses of long bones occurs in many type III and IV children and coincides with increased growth deficiency. Often these bones are so soft that normal muscle pull can produce severe deformities. Kyphoscoliosis is associated with vertebral compressions but is not prevented by bisphosphonates, suggesting a contribution from ligamentous laxity. OI bone is weak, in that it fractures with a lower load than normal, and brittle, in that it does not tolerate postyield displacement and snaps like chalk. The brittleness results from the paradoxical increased min­ eralization of OI bone. While dual-energy x-ray absorptiometry (DXA) bone density measurements uniformly return a reduced value for OI bone, it is performed with a phantom and detects mineral crystals that are in proper alignment. In contrast, quantitative backscattered electron imaging or three-dimensional (3D) computed tomography (CT), which detect all mineral in 3D, reveals that both dominant and recessive (except types XIV and XV) OI bone is hypermineralized. On histomorphometry, dominant OI bone has proper formation of lamel­ lae but increased turnover, causing decreased bone volume. Type V OI has mesh-like bone lamellae, as well as a dislocated radial head, and may have hyperplastic callus formation, while type VI OI has distinc­ tive fish scale lamellae on polarized light microscopy. Many OI patients across the severity spectrum have increased ligamentous laxity. Patients with defects in processing the N-terminal propeptide of type I procollagen have large and small joint hypermobil­ ity similar to EDS. Muscle weakness of unknown etiology also occurs in OI, and the weakness and ligamentous laxity contribute to delayed motor development. Pulmonary  The leading cause of death in OI is pulmonary disease. Young children with severe OI often have repeated pneumonia; restric­ tive or obstructive disease develops in most older children and adults. Pulmonary function is impaired by marked scoliosis and chest wall deformity but also arises from intrinsic defects of lung parenchyma containing type I collagen, as shown by declining pulmonary function over time in children without scoliosis. More recent studies have rein­ forced the significant role of intrinsic lung abnormalities in OI, dem­ onstrating reduced gas exchange, reduced airflow in small airways, and atelectasis in most individuals with collagen structural abnormalities. Bronchial thickening at the level of subsegmental bronchi in almost all patients further indicates the critical role of small airways. Mice with null CRTAP mutations (type VII OI) have abnormal alveolar develop­ ment, and patients with recessive forms also have pulmonary complica­ tions. Evaluation of even asymptomatic moderate to severe OI patients by spirometry should initiate standard pulmonary interventions. Cardiovascular  Cardiovascular effects of OI manifest predomi­ nantly in adults. With type I collagen as a major component of matrix in cardiac valves and aortic wall, the most frequent manifestations are valvular, especially mitral regurgitation and aortic root dilatation. Impaired mechanical properties occasionally lead to aortic dissection. Echocardiography is appropriate with heart murmurs or cardiac symp­ toms and every 3–5 years in asymptomatic patients. Dentinogenesis Imperfecta  Dentinogenesis imperfecta (DI) is associated with types III and IV OI and recessive types with collagen processing defects. Tooth agenesis, especially of premolars, is also found in types III/IV OI. Teeth with disturbed formation of dentin dur­ ing development may be translucent gray or have yellowish or brown­ ish discoloration. Defects are manifest predominantly in primary teeth; detection in secondary teeth may require radiographs to identify

defects V AD IFITM5 BRIL (BRIL5’ MALEP)

11p15.5 Yes Calcification of interosseous membrane, dense metaphyseal band, hyperplastic Atypical VI AD IFITM5 BRIL (BRIL Ser40Leu) 610967 11p15.5 Yes Increased osteoid, fish scale pattern in lamellar bone, increased ALP levels in modification VII AR CRTAP CRTAP

3q22.3 Yes Absent procollagen prolyl 3-hydroxylation; full OM, rhizomelia, white sclerae scoliosis; overlaps AD defects in type I collagen C-propeptide cleavage site VIII AR LERPE1 P3H1

1p34.2 Yes Absent procollagen prolyl 3-hydroxylation; full OM, rhizomelia, “popcorn” XII AR BMP1 BMP1

8p21.3 Yes Deficiency of C-propeptidase; skeletal deformity severe plus rhizomelia, VI AR SERPINF1 PEDF

17p13.3 Yes PEDF deficiency, increased osteoid, fish scale pattern in lamellar bone, 7q21.3 Yes Defects in 90 residues at N-terminus of collagen helix that decrease HBM AD COL1A1, COL1A2 Collagen α1 or α2 NA 17q21.33 Yes Defects in C-propeptide cleavage site, DXA normal to increased increased ALP levels in childhood, onset after age 1 year 7q21.3 Yes Structural defects in collagen helix or C-propeptides I AD COL1A1 Collagen α1

17q21.33 Yes Loss of function of one of the COL1A1 alleles callus, mesh-like pattern in lamellar bone childhood, symptom onset at birth GENE PROTEIN OMIM LOCUS HYPERMINERALIZATION DISTINGUISHING FEATURES pN-processing 259420, 166220 17q21.33, processing defects OI/EDS AD COL1A1, COL1A2 Procollagen α1 or α2 NA 17q21.33, II–IV AD COL1A1, COL1A2 Collagen α1 or α2 166210, TABLE 425-2  Different Types of Osteogenesis Imperfecta (OI)   OI TYPE INHERITANCE DEFECTIVE Bone mineralization Defects in collagen Defects in collagen structure and Procollagen processing

MESD

15q25.1 ND Progressive deforming OI; severe to lethal; survivors have dental disorganization XVI AR CREB3L1 OASIS

11p11.2 Yes Defect in RIP pathway; Oasis substrate of S1P/S2P; severe skeletal fragility and Abbreviations: AD, autosomal dominant; ALP, alkaline phosphatase; AR, autosomal recessive; BMP, bone morphogenetic protein; DI, dentinogenesis imperfect; DXA, dual-energy x-ray absorptiometry; EDS, Ehlers-Danlos syndrome; HBM, X AR SERPINH1 HSP47

11q13.5 ND Severe skeletal deformity, blue sclerae, DI, skin abnormalities, inguinal hernias disorders XIX AR TEMT5A FAM46A

6q14.1 ND Defect in BMP/TGF-β signaling pathway; poly-adenylates transcripts of type I

7p22.1 ND Short stature, progressive skeletal deformation; dysmorphic facies, failure to XIV AR TMEM38B TRIC-B

9q31.2 No Decreased modification of collagen helix; Bedouin founder mutation; normal collagen, SERPINF1, and SPARC; severe to lethal OI; hyperlaxity, motor delay IX AR PPIB CyPB

15q22.31 Yes Absent procollagen prolyl 3-hydroxylation; helix modification varies, without

22q13.2 ND Severe OI with pseudoarthrosis; could also be classified with MAPK/ERK XVIII XR MBTPS2 S2P

Xp22.12 Yes X-linked OI, defect in RIP pathway; moderate to severe fragility, bowing; and intellectual disability; also classified with LRP5/6-related disorders XV AD/AR WNT1 WNT1

12q13.12 No AR cases have severe progressive OI; may have neurologic defects and differentiation XIII AR SP7 OSTERIX

12q13.13 ND Severe skeletal deformity, delayed tooth eruption, facial hypoplasia XVII AR SPARC SPARC

5q33.1 Yes Progressive severe bone fragility; hypotonia, joint laxity Heritable Disorders of Connective Tissue CHAPTER 425 thrive, hypotonia, joint hypermobility XI AR FKBP10 FKBP65

17q21.2 Yes May have congenital contractures high bone mass; NA, not applicable; ND, not determined; OI, osteogenesis imperfecta; OM, overmodification; OMIM, Online Mendelian Inheritance in Man; TGF, transforming growth factor. NA AR PLOD2 LH2

3q24 Yes Progressive joint contractures metaphyses; white sclerae rhizomelia, white sclerae skeletal dysplasias teeth, hearing rhizomelia deformity interacts with HSP47 XXII AR CCDC134 Coiled-coil domainretention receptor; containing protein XXI AR KDELR2 KDEL ER protein XX AR MESD LRP chaperone

Osteoblast function Defects in collagen Unclassified cross-linking folding and

characteristic narrow or obliterated pulp chambers. Crumbling at the dentin-enamel junction may require capping of teeth. Hypoplastic maxilla and relative mandibular prognathism in moderate to severe OI can result in type III malocclusion and impair normal chewing, requir­ ing surgical correction.

Hearing Loss  About half of patients with types I, III, and IV OI develop hearing loss, but its incidence in recessive types is unknown. Hearing loss usually begins in the second decade and progresses. The initial conductive loss, based on changes in the inner ear leading to stapes footplate fixation, can evolve into a mixed conductive and senso­ rineural loss. Regular screening allows referral for hearing aids, stapes surgery, or cochlear implants, as appropriate. PART 12 Endocrinology and Metabolism Other Features  A variable intensity of blue or grayish sclerae is a well-known feature of OI. The color is most striking with collagen defects, especially types I and II OI and defects that affect N-terminal procollagen processing. Blue sclerae often occur in other connective tissue disorders such as EDS or MFS and may occur in individu­ als without connective tissue defects. Severe neonatal OI with white sclerae should prompt consideration of recessive forms, especially prolyl 3-hydroxylation defects. Abnormalities of the skull base, such as platybasia and basilar invagination, sometimes progress to clini­ cally devasting basilar impression. Patients with height Z-scores of <–3 should be CT scanned at 3- to 5-year intervals. Significant growth deficiency is a cardinal feature of OI, ranging from minimally shorter than siblings in mild forms to greater extents in some severe cases, with adults shorter than 5-year-old children. There is both end-organ resis­ tance to growth hormone (GH) and defective transition to bone at the growth plate. Types I and IV OI are often responsive to recombinant GH therapy. Molecular Defects  The great majority (80–85%) of cases of OI are caused by heterozygous mutations in either of the genes coding for the chains of type I procollagen, COL1A1 or COL1A2 (Table 425-2). Although thousands of unique mutations have been identified in type I collagen, they fall into several structural types. Null mutations in collagen chains are less detrimental than structural defects. Null mutations in COL1A1 result in about half the normal level of collagen synthesis, but the collagen in matrix is structurally normal. These patients have mild type I OI. Null COL1A2 mutations are rare, leading to an EDS-like condition with progressive cardiac-valvular defects when present in homozygous state. Mutations that produce structural changes in type I collagen α chains cause types II, III, and IV OI. The most common of these are mutations resulting in substitutions for glycine residues required at every third residue along the helix. In effect, any of the 338 glycine residues in the helical domain of either the proα1 or proα2 chain of type I procollagen is a potential site for a disease-producing muta­ tion. Other mutations affect the splicing of the exons encoding the α chains. Because each collagen exon encodes a discrete set of Gly-X-Y triplets, the abnormal splice products are most often in-frame and cause severe structural abnormalities. Use of alternative splice sites may lead to premature termination, mimicking null mutations, and a milder phenotype. Structural abnormalities in the procollagen helical region delay collagen folding and expose chains to posttranslational hydroxylation/glycosylation for a longer time. The abnormal procolla­ gen triggers a cascade of intracellular and extracellular events including delayed collagen folding, ER stress, abnormal interaction with noncol­ lagenous molecules, impaired osteoblast development and cross-talk with osteoclasts, and abnormal mineralization. There are some special sets of procollagen structural mutations with distinct mechanisms within types II, III, and IV. Mutations in the C-propeptide significantly delay chain assembly, and resulting procollagen is mislocalized to the ER lumen. Some of this procollagen is targeted for degradation by the ER-associated proteosomal pathway, while the secreted molecules delay pericellular processing of the C-propeptide. Mutations in the C-propeptide cleavage site itself prevent processing of the propeptide, leaving pC-collagen to be incorporated into matrix. This affects matrix mineralization, resulting in an unusual high bone mass form of OI that

falls at the milder end of the type IV OI phenotype. Not surprisingly, null mutations in the C-propeptidase enzyme, BMP1, cause recessive type XII OI. Type XII OI is a severe condition because BMP1 is the cleavase for types I, II, and III procollagens and the glycoprotein deco­ rin, which is a regulator of fibrillogenesis. Processing defects of the N-propeptide occur in the cleavage site itself or the 90 helix residues at the amino end. The persistence of the N-propeptide on a fraction of the molecules interferes with the self-assembly of normal collagen so that thin and irregular collagen fibrils are formed. They cause extreme laxity of large and small joints, intensely blue sclerae, and an OI sever­ ity comparable to type III/IV. Rare substitutions of charged amino acids (Asp, Arg) or a branched amino acid (Val) in X- or Y-positions produce lethal phenotypes, apparently because they are located at sites for lateral assembly of the monomers or binding of other components of the matrix. Starting in 2006, a series of noncollagenous genes have been identi­ fied that cause (mostly) recessive OI. Importantly, all the genes have encoded proteins or cellular processes related to collagen, shifting the OI paradigm to dominant OI caused by collagen defects or IFITM5 and recessive OI caused by proteins related to collagen modification, processing, folding, and cross-linking and osteoblast differentiation. The largest group of patients with OI not caused by collagen gene mutations have types V and VI OI, affecting bone mineralization. Type V OI, with dominant inheritance, is unusual in that all patients have the same recurrent mutation at the 5′-end of IFITM5, which generates a novel start codon in the transmembrane protein BRIL. The gain-of-function mutation causes distinctive radiologic (ossifi­ cation of interosseus membrane and dense metaphyseal band) and phenotypic findings (hypertrophic callus). Osteoblasts with type V OI have increased mineralization and differentiation in culture. Type VI OI is a recessive form caused by null mutations in PEDF, a collageninteracting molecule with a known antiangiogenic effect. A connection between types V and VI OI has been revealed by a set of patients with a BRIL p.S42L substitution who have clinical, histologic, serum marker, and phenotypic features of type VI OI. Both type VI OI osteoblasts and BRIL p.S42L osteoblasts have decreased cellular mineralization and SERPINF1 expression, while classic type V OI osteoblasts have the opposite findings. All three types decrease collagen production. Types VII, VIII, and IX OI are severe recessive forms caused by deficiency of one of the components of the procollagen prolyl 3-hydroxylation complex, P3H1, CRTAP, or cyclophilin B (PPIB/ CyPB). This complex 3-hydroxylates one proline residue per α chain, most critically α1(I)P986, in contrast to the proline 4-hydroxylation of multiple helical residues by P4H1. In murine models, loss of complex function results in a severe phenotype, while mutation of the P986 residue impairs collagen cross-linking and fine-tuning of collagen alignment in fibrils. The phenotype of these patients is distinctive for white sclerae, rhizomelia, and lack of relative macrocephaly; they share the bone fragility, high bone turnover, and elevated bone mineraliza­ tion of classical OI. Some recessive OI types that impair osteoblast function are caused by mutation in genes not previously understood to affect bone. Regu­ latory intramembrane proteolysis (RIP) is well known for its role in cholesterol synthesis, in which cells transport regulatory proteins from the ER membrane to the Golgi membrane in times of cell stress, where S1P and S2P Golgi proteases sequentially cleave the transcription fac­ tors, activating them to enter the nucleus. X-linked type XVIII OI with defective MBTPS2/S2P and type XVI OI with deficiency of an RIP sub­ strate Oasis, a member of the ATF6 family of stress sensors, indicate the importance of RIP for bone formation (Table 425-2). For more recently identified OI types, the relationship of the causative gene to collagen has extended the spectrum of matrix abnormality. FAM46A (type XIX OI) polyadenylates collagen transcripts; defects lead to collagen defi­ ciency approaching a null COL1A1 allele that does not fully explain the severe disorganization of collagen in bone matrix. Since FAM46A also polyadenylates the transcripts of other OI-causative genes, SERPINF1 and SPARC, the matrix defect may be multifactorial. For type XX OI, MESD is a direct cytosolic chaperone of pro-alpha1(I) chains, but several bone features that are not typical of OI, such as oligodontia and

cartilage remnants, may reflect MESD’s role as a chaperone for LRP5. KDELR2 defects (OI type XXI) have impaired retrograde transport of ER resident proteins, such as HSP47, because KDELR2 is a compo­ nent of CopI vesicles. Collagen quantity in matrix is lower because of reduced collagen expression, but the impaired collagen fibrillogenesis may be caused by increased interaction of HSP47 with collagen mono­ mers in the extracellular space. The causative gene for type XXII OI, CCDC134, is involved in the MAPK signaling pathway. The osteoblasts of affected individuals have increased ERK1/2 phosphorylation as well as reduced COL1A1 and osteopontin expression. Inheritance and Mosaicism in Germline Cells and Somatic Cells  Types I–V OI are inherited as autosomal dominant traits, while the rare forms are mostly recessive. Many patients with mild dominant OI represent familial traits, while sporadic new mutations are often responsible for dominant severe or lethal cases. Germline mosaicism in one parent may be the etiology of a severe dominant mutation in the child; in this circumstance, a second child may be affected with the same dominant mutation from unaffected parents. Recessive mutations in genes causing the rare forms of OI lead to more severe clinical outcomes; many of these offspring do not survive child­ hood, but moderately to severely affected young adults show us that these conditions must also be considered. Diagnosis  OI is usually diagnosed on the basis of clinical and radiographic criteria. The presence of fractures together with blue sclerae, DI, or family history of the disease is usually sufficient to make the diagnosis. X-rays reveal a decrease in bone density that can be veri­ fied by DXA bone densitometry, as well as characteristic deformities of long bones, thorax, and cranium. The differential diagnosis varies with age, including battered child syndrome, nutritional deficiencies, malignancies, and other inherited disorders such as chondrodysplasias and hypophosphatasia that can have overlapping presentations. A molecular diagnosis is now routinely obtained using targeted candidate gene sequencing, sometimes beginning with the dominant collagen and IFITM5 panel. Skeletal disorder gene panels and whole-exome sequencing may be financially advantageous and pick up additional skeletal gene variants as well as the OI-causative gene. Although almost all cases can be diagnosed by sequencing, some may require bone his­ tology and exome sequencing. TREATMENT Osteogenesis Imperfecta Therapy should be directed toward maximizing the function of each individual, which includes decreasing fractures and deformity that interfere with function. Physical and occupational therapy are critical modalities. They are most commonly utilized after severe fractures or major surgery and should also be engaged consistently throughout the life span for maximizing mobility, functions of daily living, and the extent of physical conditioning possible. Water ther­ apy is particularly useful at all ages. Diet should include adequate intake of calcium and vitamin D. Many patients are underweight for height as young children but overweight as adults, and nutritional management may be useful. Orthopedic procedures are required for deformities of long bone that interfere with standing or walking or when a bone has sustained repeated fractures. Intramedullary rods are often inserted when children are ready to stand and as needed thereafter to keep bone segments in good alignment and provide partial unloading of weight from bones. If scoliosis progresses, sta­ bilization of the spine may be needed to maintain the curve at <60°. Medical management should also include presymptomatic screen­ ing for hearing loss, cardiac valve dysfunction, pulmonary function, and, in severe individuals, basilar invagination. Drugs that have been developed for the therapy of postmeno­ pausal osteoporosis are beneficial for some patients. Bisphospho­ nates, antiresorptive drugs that inhibit osteoclasts, increase DXA bone density and relieve vertebral compressions in most patients. They are regarded as a mainstay of care in many pediatric centers.

However, several Cochran reports have not supported a clear reduction in fracture rate or bone pain from their use, and the dos­ ing and duration of use are controversial. Currently, drugs with a bone-forming mechanism are in trials for OI, especially monoclo­ nal antibodies to sclerostin that relieve its inhibition of osteoblast Wnt/β-catenin signaling, TGF-β inhibitors, and a PTH analogue that stimulates osteoblasts and is most beneficial for adults with milder OI. Potential therapies under investigation in animal models include chemical chaperones and mesenchymal stem cell therapy, and, currently in murine models, correction of specific defects in collagen by CRISPR. Heritable Disorders of Connective Tissue CHAPTER 425 ■ ■EHLERS-DANLOS SYNDROMES The Ehlers-Danlos syndromes (EDS) comprise a genetically heteroge­ neous group of heritable conditions that share several characteristics such as soft and hyperextensible skin, abnormal wound healing, easy bruising, and joint hypermobility. Additional clinical features that dif­ fer among the EDS types include fragility of soft tissues, blood vessels, and hollow organs and involvement of the musculoskeletal system and the eye. Mutations in genes coding for fibrillar collagens (type I, III, or V) are found in many patients, but other genes are affected in rare forms. Classification  Several types of EDS have been defined, based on clinical characteristics, mode of inheritance, and molecular defects (Table 425-3), and the classification of these types has been a dynamic process. The current classification defines 13 clinical EDS types that are caused by alterations in 19 different genes, but a recent study described another genetically distinct EDS type, bringing the total number of EDS-associated genes to 20. The EDS classification guides the clinical diagnosis, molecular confirmation, and genetic counseling of affected individuals and their family members. Incidence  An incidence of about 1 in 5000 individuals for all forms of EDS was proposed, with no apparent ethnic predisposition. The diagnosis of hypermobile EDS is more common in females than in males, but whether this is due to an increased incidence or more severe manifestation is unknown. The incidence for other types of EDS is similar in males and females. With incidences of 1 in 20,000 and 1 in 50,000–200,000 respectively, classic and vascular EDS are the most common genetically elucidated types of EDS. For the other types of EDS for which causative variants have been identified, there are no incidence estimates, but the numbers of people who have been reported worldwide with these disorders range between ~5 and ~100 individuals per EDS type. Patients with milder forms frequently do not seek medical attention. Skin  One of the principal features of EDS is skin hyperextensibility, that is, the skin stretches easily but snaps back after release. The skin often has a smooth, soft, or velvety feel to it and can be thin and trans­ lucent. It is fragile and tears easily, even after minor trauma, and heals slowly. Widened and thin atrophic scars are frequently observed in different types of EDS. Especially in classic EDS, atrophic scarring may be widespread, especially over pressure points and exposed areas such as the forehead, elbows, knees, and shins, with marked widening of the scars, which are covered by a very thin inelastic skin (papyraceous scars). Individuals with vascular EDS usually do not have a velvety hyperextensible skin, but skin can be thin and translucent with visible superficial veins. Easy bruising is common to most types of EDS and may manifest itself as spontaneous or recurring hematomas. These may cause discoloration of the skin due to deposition of hemosiderin, often referred to as “hemosiderotic” scars, especially in classic, vascular, and periodontic EDS. Ligament and Joint Changes  Joint hypermobility, another cardi­ nal sign, is variable in severity and usually, but not always, generalized. While often an “asset” in childhood, it can become a serious burden over time, often complicated by repetitive subluxations, dislocations, sprains, and chronic joint pain that is difficult to treat. Other observed musculoskeletal features include congenital bilateral hip dislocation,

Spontaneous sigmoid colon perforation in the absence of known colon Severe generalized joint hypermobility with multiple dislocations Carotid-cavernous sinus fistula (in the absence of trauma) Progressively redundant, lax skin with excessive skinfolds Dermatosparactic EDS (dEDS) AR

5q35.3 ADAMTS2 ADAMTS2 Extreme skin fragility with congenital or postnatal tears Uterine rupture during third trimester of pregnancy Proα2(V) Skin hyperextensibility with atrophic scarring Classic EDS (cEDS) AD / 17q21.33 COL1A1 Proα1(I) p.Arg312Cys Skin hyperextensibility with atrophic scarring PART 12 Endocrinology and Metabolism Proα2(I) Congenital bilateral hip dislocation Generalized joint hypermobility Generalized joint hypermobility Arterial rupture at young age Vascular EDS (vEDS) AD

2q32.2 COL3A1 Proα1(III) Arterial rupture at young age Increased palmar wrinkling   EDS TYPE INHERITANCE OMIM LOCUS GENE PROTEIN KEY MANIFESTATIONS Skin hyperextensibility Craniofacial features Severe bruisability Umbilical hernia disease COL5A2 Proα1(V) COL1A2 Proα1(I) 2q32.2 COL5A1 7q21.3 COL1A1

17q21.33

9q34.3 Classic EDS (cEDS) AD

Arthrochalasia EDS (aEDS) AD

TABLE 425-3  Different Types of Ehlers-Danlos Syndrome (EDS) Defects in collagen primary structure and collagen processing

Classic-like EDS type 1 (clEDS1) AR

6p21.33-p21.32 TNXB Tenascin XB Skin hyperextensibility with velvety skin texture and absence of atrophic Myopathic EDS (mEDS) AD/AR

6q13-q14 COL12A1 Proα1(XII) Congenital muscle hypotonia and/or muscle atrophy Generalized joint hypermobility with (sub)luxations Cardiac-valvular EDS (cvEDS) AR

7q21.3 COL1A2 proα2(I) Severe progressive cardiac-valvular insufficiency Perinatal complications related to tissue fragility Easily bruisable skin/spontaneous ecchymoses Postnatal growth retardation with short limbs Congenital or early-onset kyphoscoliosis Generalized joint hypermobility FKBP22 Congenital muscle hypotonia Joint hypermobility Joint hypermobility Joint contractures Skin involvement scarring FKBP14 Lysylhydroxylase 1 7p14.3 PLOD1

1p36.22 AR

AR collagen cross-linking Kyphoscoliotic EDS (kEDS-PLOD1) Kyphoscoliotic EDS (kEDS-FKBP14) Defects in collagen folding and interface between muscle and function of myomatrix, the Defects in structure and ECM

sulfotransferase-1 Congenital multiple contractures (typically adduction/flexion contractures Skin hyperextensibility, easy bruising, skin fragility with atrophic scars Muscle hypotonia (ranging from severe congenital to mild later-onset) Muscle hypotonia (ranging from severe congenital to mild later-onset) C1s Severe and intractable early-onset periodontitis β4GalT7 Short stature (progressive in childhood) (spEDS-SLC39A13) AR

11p11.2 SLC39A13 ZIP13 Short stature (progressive in childhood) Increased palmar wrinkling and talipes equinovarus) Lack of attached gingiva Craniofacial features Skeletal dysplasia Skeletal dysplasia Pretibial plaques Bowing of limbs Bowing of limbs (spEDS-B3GALT6) AR

1p36.33 B3GALT6 Galactosyltransferase II (spEDS-B4GALT7) AR

5q35.3 B4GALT7 Galactosyltransferase I (mcEDS-DSE) AR

6q22.1 DSE Dermatan sulfate epimerase-1 (mcEDS-CHST14) AR

15q15.1 CHST14 Dermatan-4 β3GalT6 C1S C1r pathways Periodontal EDS (pEDS) AD

12p13.31 C1R Musculocontractural EDS Musculocontractural EDS biosynthesis Spondylodysplastic EDS Spondylodysplastic EDS processes Spondylodysplastic EDS Defects in glycosaminoglycan Defects in complement Defects in intracellular

Exclusion of other EDS types and other joint hypermobility-associated Systemic manifestations of generalized connective tissue fragility Early-onset progressive keratoconus and/or keratoglobus Unclassified Classic-like EDS type 2 (clEDS2) AR

7p13 AEBP1 AEBP1 (ACLP) Skin hyperextensibility with atrophic scarring Heritable Disorders of Connective Tissue CHAPTER 425 PRDM5 Thin cornea with/without rupture Generalized joint hypermobility Unknown Hypermobile EDS (hEDS) ? (AD)

? ? ? Generalized joint hypermobility Musculoskeletal complaints Early-onset osteopenia Positive family history Foot deformities Blue sclerae conditions PRDM5 ZNF469 Abbreviations: AD, autosomal dominant; AR, autosomal recessive; ECM, extracellular matrix; OMIM, Online Mendelian Inheritance in Man. 4q27 ZNF469

16q24 Brittle cornea syndrome (BCS) AR

spine deformities (scoliosis, kyphosis), pectus deformities (pectus carinatum, pectus excavatum), club feet and other contractures, and in some rare types, a (mild) skeletal dysplasia. Muscle hypotonia is observed in a number of EDS types and, in combination with joint lax­ ity, may cause floppy infant syndrome or a delay in motor development.

Other Features  Signs of more generalized connective tissue weak­ ness and fragility can be observed in varying degrees and may help to distinguish between the different EDS types. Rupture of medium and large-sized arteries is typical of vascular EDS but has been reported in a few other types as well, i.e., classic and kyphoscoliotic type. Vascular EDS patients are also at increased risk for rupture of the gastrointes­ tinal tract, especially the sigmoid colon, the gravid uterus, and, more rarely, other internal organs such as liver or spleen. Valvular defects and aortic root dilatation are rare and are also restricted to some of the rarer types of EDS. Obstetrical and pelvic complications such as cervi­ cal insufficiency, premature rupture of membranes, vaginal lacerations, and organ prolapses (uterus, bladder, rectum) may occur. Sclerae may be blue, and more severe ophthalmologic complications, including keratoconus, keratoglobus, and scleral or corneal rupture, may be observed in some rare types. PART 12 Endocrinology and Metabolism Molecular Defects  Subsets of patients with different types of EDS have mutations in the structural genes for fibrillar collagen types I, III, and V (Table 425-3). About 90% of classic EDS patients harbor a heterozygous mutation in COL5A1 or COL5A2 cod­ ing for type V collagen, a minor collagen found in association with type I collagen. Heterozygous mutations in the COL3A1 gene for type III collagen, which is abundant in the blood vessel wall, are responsible for vascular EDS. Arthrochalasia EDS is caused by hetero­ zygous mutations in either COL1A1 or COL1A2 that make type I pro­ collagen resistant to cleavage by the procollagen N-proteinase ADAMTS2, whereas dermatosparaxis EDS is caused by biallelic muta­ tions in the gene that codes for the ADAMTS2 itself, thereby reducing its enzyme activity. The persistence of the N-propeptide causes the formation of collagen fibrils that are thin and irregular. Other specific mutations in either COL1A1 or COL1A2 give rise to a few rare types of EDS. These include the cardiac-valvular type, which is caused by bial­ lelic COL1A2 mutations, leading to a complete absence of α2(I) chains. Patients with this condition are at risk for severe, progressive cardiacvalvular disease necessitating valve replacement. A specific arginineto-cysteine substitution in the type I collagen α chain (p.Arg312Cys) is associated with an EDS phenotype that resembles that of classic EDS, but patients appear at increased risk for vascular rupture of mediumsized arteries. A few patients with a phenotype that couples EDS with signs of moderate to severe myopathy harbor heterozygous or homozy­ gous mutations in COL12A1, coding for type XII collagen, a fibrilassociated collagen with interrupted triple helices. Kyphoscoliotic EDS is caused by biallelic mutations either in the PLOD1 gene, which encodes procollagen-lysine 5-dioxygenase (lysyl hydroxylase 1), an enzyme required for formation of stable cross-links in collagen fibers, or in the FKBP14 gene, which encodes FKBP22, an endoplasmic resi­ dent molecular chaperone that acts as a quality control on the folded triple helix of type III collagen. Some patients with clinical character­ istics that resemble those of classic EDS harbor biallelic mutations in either TNXB, encoding tenascin X, an extracellular matrix glycoprotein that appears to regulate the assembly of collagen fibers, or in AEBP1, which encodes the extracellular matrix–associated adipocyte enhancer-binding protein (AEBP1), which assists in collagen polymer­ ization. Spondylodysplastic EDS is caused by biallelic mutations in B3GALT7, coding for galactosyltransferase I, or in B3GALT6, coding for galactosyltransferase II, both key enzymes in the biosynthesis of the linker region of glycosaminoglycans. Musculocontractural EDS results from mutations in genes coding enzymes responsible for dermatan biosynthesis: CHST14, dermatan 4-O-sulfotransferase 1, and DSE, der­ matan sulfate epimerase. A rare spondylodysplastic type of EDS is caused by biallelic mutations in SLC39A13, encoding the intracellular zinc transporter ZIP13. Brittle cornea syndrome is caused by biallelic mutations in either ZNF469 or PRDM5, both (putative) transcriptional

regulators. Finally, periodontal EDS is caused by heterozygous muta­ tions in C1R or C1S, coding for the complement pathway components C1q and C1s, respectively. Diagnosis  Diagnostic workup comprises clinical examination and should be followed by genetic testing in individuals who are suspected to have an EDS type. Genetic testing can include targeted mutation analysis in those with a family history of EDS caused by a known genetic variant or, more frequently, next-generation sequencing using multigene panels. Genetic diagnosis should lead to family testing. Of note, the genetic cause of hypermobile EDS has not been determined, and therefore, diagnosis of this condition is based on the presence of clinical manifestations and the exclusion of other types of EDS or other conditions associated with joint hypermobility. Correlations between genotype and phenotype are challenging and only starting to emerge, and as with other heritable diseases of connective tissue, there is a large degree of variability among members of the same family carrying the same mutation. TREATMENT Ehlers-Danlos Syndrome All patients with EDS should receive multidisciplinary care and, if available, be part of a patient advocacy community. The precise treatment depends on the type of EDS and the clinical manifesta­ tions. Physiotherapy is essential for patients with musculoskeletal problems. Helmets and/or skin protections or joint protections, braces, or splints can be used to reduce the risk of injury in patients with skin fragility or joint hypermobility. Low-resistance exercises (such as walking or swimming) can improve joint stability, although exercises that place considerable strain on the joints (such as gym­ nastics or weightlifting) should be avoided. Monitoring for cardio­ vascular alterations using noninvasive procedures is recommended in patients at risk of adverse cardiovascular events only. Given the rarity of vascular EDS, referral to a center with EDS expertise is of vital importance. A clear protocol for emergency room evalua­ tion in the case of major complications should be established, and patients should carry documentation of their genetic diagnosis, such as a MedicAlert. The psychosocial impact of a vascular EDS diagnosis often requires psychological care. ■ ■CHONDRODYSPLASIAS (See also Chap. 424) Chondrodysplasias (CDs), also referred to as skeletal dysplasias or osteochondrodysplasias, encompass a heteroge­ neous group of disorders characterized by intrinsic abnormalities of cartilage and bone and are generally characterized by dwarfism and abnormal body proportions (disproportionate short stature). Many affected individuals develop degenerative joint changes, and mild CD in adults may be difficult to differentiate from primary generalized OA. Classification  The Nosology and Classification of Genetic Skeletal Disorders comprises 771 distinct disorders based on clinical, radio­ graphic, and/or molecular phenotypes. Pathogenic variants have cur­ rently been found in 551 different genes. The conditions are divided into 41 groups based on gene/protein families (e.g., the type II collagen group), phenotypic presentation (e.g., spondylometaphyseal dysplasia), and pathophysiology (i.e., lysosomal storage disorders). One gene may be responsible for more than one condition (e.g., COL2A1 mutations may cause a number of CDs including achondrogenesis, hypochondro­ genesis, spondyloepiphyseal dysplasia congenita, Kniest and Stickler syndromes), or a condition may be due to mutations in more than one gene (e.g., geleophysic dysplasia can be caused by mutations in ADAMTSL2, FBN1, and LTBP3). Incidence  The overall incidence of all forms of CD ranges from 1 per 2500 to 1 per 4000 births. Data on the frequency of individual CDs are incomplete. The most common form of inherited disproportionate short stature is achondroplasia, with an estimated incidence of 1 per 26,000 to 1 per 28,000 live births.

Molecular Defects  Mutations in the COL2A1 gene, coding for the α chain of type II collagen of cartilage, are found in a group of patients with both mild and severe CDs. For example, a mutation in COL2A1 substituting a cysteine residue for an arginine was found in a few unrelated families with spondyloepiphyseal dysplasia (SED) and precocious generalized OA. Mutations in the gene were also found in some lethal CDs characterized by gross deformities of bones and cartilage, such as those found in SED congenita, spondyloepime­ taphyseal dysplasia congenita, hypochondrogenesis/achondrogenesis type II, and Kniest syndrome. The highest incidence of COL2A1 muta­ tions, however, occurs in patients with the distinctive features of the Stickler syndrome, which is characterized by skeletal changes, orofacial abnormalities, and ophthalmologic and auditory abnormalities. Most of the mutations in COL2A1 are premature stop codons that produce haploinsufficiency. In addition, some of the patients with Stickler syn­ drome or a closely related syndrome have mutations in two genes specific for type XI collagen (COL11A1 and COL11A2), which is an unusual heterotrimer formed from α chains encoded by COL2A1, COL11A1, and COL11A2. Mutations in the COL11A1 gene are also found in patients with Marshall syndrome, which is similar to classic Stickler syndrome, but with more severe hearing loss and dysmorphic features, such as a flat or retracted midface with a flat nasal bridge, short nose, anteverted nos­ trils, long philtrum, and large-appearing eyes. CDs are also caused by mutations in the less abundant collagens found in cartilage. For example, patients with Schmid metaphyseal CD have mutations in the gene for type X collagen, a short, networkforming collagen found in the hypertrophic zone of endochondral cartilage. The syndrome is characterized by short stature, coxa vara, flaring metaphyses, and waddling gait. As with other collagen genes, the most common mutations are of two types: nonsense mutations that lead to haploinsufficiency and structural mutations that compromise collagen assembly. Some patients have mutations in genes for proteins that interact with collagens. Patients with pseudoachondroplasia or autosomal dominant multiple epiphyseal dysplasia have mutations in the gene for the carti­ lage oligomeric matrix protein (COMP), a protein that interacts with both collagens and proteoglycans in cartilage. However, some families with multiple epiphyseal dysplasia have a defect in one of the three genes for type IX collagen (COL9A1, COL9A2, and COL9A3) or in matrilin-3, another extracellular protein found in cartilage. Some CDs are caused by mutations in genes that affect early development of cartilage and related structures. Achondroplasia is caused by mutations in the gene for a receptor for a fibroblastic growth factor (FGFR3). The mutations in the FGFR3 gene causing achondroplasia are unusual in several respects. More than 99% of individuals with achondroplasia have one of two pathogenic variants (c.1138G> or c.1138G>C) in FGFR3, both resulting in the amino acid change p.Gly380Arg. Most patients harbor a sporadic new (de novo) mutation, and therefore, this nucleotide change is one of the most common recurring mutations in the human genome. The muta­ tion causes unregulated signal transduction through the receptor and inappropriate development of cartilage. Mutations that alter other domains of FGFR3 have been found in patients with the more severe disorders of hypochondroplasia and thanatophoric dysplasia and in a few families with a variant of craniosynostosis. However, most patients with craniosynostosis appear to have mutations in the related FGFR2 gene. The similarities between the phenotypes produced by mutations in genes for fibroblast growth factor (FGF) receptors and mutations in structural proteins of cartilage are probably explained by the observa­ tion that the activity of FGFs is regulated in part by binding of FGFs to proteins sequestered in the extracellular matrix. Therefore, the situ­ ation parallels the interactions between transforming growth factors (TGFs) and fibrillin in MFS (see below). Other mutations involve the proteoglycans of cartilage, aggrecan (AGC1) and perlecan (HSPG2), and in the proteoglycan posttransla­ tional sulphation pathway (DTDST, PAPSS2, and CHST3). Diagnosis  The diagnosis of CDs is made on the basis of the physi­ cal appearance, slit-lamp eye examinations, x-ray findings, histologic

changes, and clinical course. Targeted gene and exome sequencing or more global sequencing strategies are used for molecular diagnosis. Given the wide spectrum of CD phenotypes, these genetic tests are becoming critical diagnostic tools. For Stickler syndrome, more precise diagnostic criteria have made it possible to identify type I variants with mutations in the COL2A1 gene with a high degree of accuracy. It has been suggested that the type II variant with mutations in the COL11A1 gene can be identified on the basis of a “beaded” vitreous phenotype and that the type III variant with mutations in the COL11A2 gene can be identified on the basis of the characteristic systemic features without the ocular involvement. Prenatal diagnosis based on analysis of DNA obtained from chorionic villus or amniotic fluid is possible.

Heritable Disorders of Connective Tissue CHAPTER 425 TREATMENT Chondrodysplasias The treatment of CDs is symptomatic and is directed to secondary features such as degenerative arthritis. Many patients require joint replacement surgery and corrective surgery for cleft palate. The eyes should be monitored carefully for the development of cataracts and the need for laser therapy to prevent retinal detachment. In general, patients should be advised to avoid obesity and contact sports. Counseling for the psychological problems of short stature is critical. A randomized, double-blind, phase 3, placebo-controlled, multicenter trial with vosoritide, a biologic analogue of C-type natriuretic peptide, which is a potent stimulator of endochondral ossification, in children with achondroplasia showed that this is an effective and safe treatment to increase growth in children with achondroplasia. ■ ■HERITABLE THORACIC AORTIC

ANEURYSM DISEASE Heritable thoracic aortic aneurysm disease (HTAD) encompasses conditions in which aortic disease has a familial occurrence, due to an underlying genetic defect. HTAD is classified as syndromic or nonsyn­ dromic. Syndromic HTAD may be associated with ocular, craniofacial, musculoskeletal, and skin features, with a recognizable, yet sometime subtle, phenotype. They are caused by mutations in genes that code for extracellular matrix proteins. Besides syndromic HTAD, there are several nonsyndromic forms of HTAD; patients with these conditions do not display an outward recognizable phenotype and are classified as having familial thoracic aortic aneurysm (FTAA). More extensive genetic screening in cohorts of patients with thoracic aortic aneurysm is, however, slowly revealing that there is no strict boundary between syndromic and nonsyndromic HTAD entities (Table 425-4) (Chap. 291). Classification  The most common form of syndromic HTAD is MFS, caused by mutations in the gene for fibrillin-1 (FBN1). MFS was initially characterized by a triad of features: (1) skeletal changes that include long, thin extremities, frequently associated with loose joints; (2) reduced vision as the result of dislocations of the lenses (ectopia lentis); and (3) aortic aneurysms. An international panel has developed a series of revised Ghent criteria that are useful in clas­ sifying patients. Other major syndromic HTADs include the different genetic variants of Loeys-Dietz syndrome (LDS) (TGFBR1, TGFBR2, TGFB2, TGFB3, SMAD2, and SMAD3). Rare forms of syndromic HTAD include Shprintzen-Goldberg syndrome (SKI), Meester-Loeys syndrome (BGN), and arterial tortuosity syndrome (ATS) (SLC2A10). Incidence and Inheritance  The incidence of MFS is among the highest of any heritable disorder: ~1 in 3000–5000 births in most racial and ethnic groups. The related syndromes are less common. Muta­ tions are generally inherited as autosomal dominant traits, but about one-fourth of patients have sporadic new mutations. The LDSs are less common, but their exact incidence is currently unknown. Skeletal Effects  Patients with MFS typically display a marfanoid habitus with tall stature and long limbs. The ratio of the upper segment (top of the head to the top of the pubic ramus) to the lower segment

TABLE 425-4  Heritable Thoracic Aortic Disease and Associated Genes and Proteins   GENE PROTEIN CONDITION OMIM LOCUS Extracellular matrix proteins COL3A1 α1(III) collagen chain Vascular EDS

2q32 FBN1 Fibrillin 1 Marfan syndrome

15q21.1 MFAP5 Microfibrillar associated protein 5 Familial thoracic aortic aneurysm 9

12p13.31 LOX Lysyl oxidase Familial thoracic aortic aneurysm 10

5q23.1 TGF-β signaling TGFBR1 Transforming growth factor receptor 1 Loeys-Dietz syndrome 1

9q22.33 TGFBR2 Transforming growth factor receptor 2 Loeys-Dietz syndrome 2

3p24.1 SMAD3 Mothers against decapentaplegic drosophila homolog 3 Loeys-Dietz syndrome 3

15q22.33 TGFB2 Transforming growth factor β2 Loeys-Dietz syndrome 4

1q41 PART 12 Endocrinology and Metabolism TGFB3 Transforming growth factor β3 Loeys-Dietz syndrome 5

14q23.3 SMAD2 Mothers against decapentaplegic drosophila homolog 2 Arterial aneurysms and dissections / 18q21.1 ACTA2 Smooth muscle actin α2 Familial thoracic aortic aneurysm 6

10q23.31 Smooth muscle contraction MYH11 Smooth muscle myosin heavy chain 11 Familial thoracic aortic aneurysm 4

16p13.11 MYLK Myosin light chain kinase Familial thoracic aortic aneurysm 7

3q21.1 PRKG1 Protein kinase cGMP-dependent type 1 Familial thoracic aortic aneurysm 8

10q11.2-q21.1 Abbreviations: EDS, Ehlers-Danlos syndromes; OMIM, Online Mendelian Inheritance in Man; TGF, transforming growth factor. (top of the pubic ramus to the floor) is usually 2 standard deviations below mean for age, race, and sex. The fingers and hands are long and slender and have a spider-like appearance (arachnodactyly). Overlap­ ping features in MFS and LDS include scoliosis or kyphoscoliosis; anterior chest deformities, including pectus excavatum, pectus carina­ tum, or asymmetry; pes planus; pneumothorax; and dural ectasia. A few patients have severe joint hypermobility similar to EDS. Clubfeet, joint contractures, and cervical spine instability are more frequently observed in LDS. Patients with SMAD3 mutations are particularly prone to premature OA. Cardiovascular Features  Cardiovascular abnormalities are the major source of morbidity and mortality both in MFS and LDS (Chap. 291). Patients with MFS often have mitral valve prolapse that develops early in life and that progresses to mitral valve regurgitation of increasing severity in about one-quarter of patients. Dilation of the root of the aorta and the sinuses of Valsalva are characteristic and omi­ nous features of MFS that can develop at any age. The rate of dilation is unpredictable, but it can lead to aortic regurgitation, dissection of the aorta, and rupture. Dilation is probably accelerated by physical and emo­ tional stress as well as by pregnancy. Cardiovascular features of LDS also include dilatation of the aortic root at the level of the sinus of Valsalva, which can progress to dissection or rupture when left untreated. LDS is also known for its involvement of aneurysms affecting arterial branches of head, neck, thoracic and abdominal aorta, lung, and lower extremities and for the presence or tortuosity of these vessels. In contrast to MFS, congenital heart malformations are often noted. Ocular Features  Myopia is the most common ocular feature of MFS and often presents in early childhood. Displacement of the lens from the center of the pupil (ectopia lentis) occurs in ~60% of MFS patients. The ocular globe is frequently elongated. Retinal detachment, early cataract formation, and glaucoma can occur. Ectopia lentis does not usually occur in LDS, but other ocular features may be present, such as blue sclerae, strabismus, amblyopia, and myopia. Other Features  MFS patients typically have a high arched palate. Patients with LDS characteristically display hypertelorism (widely spaced eyes) and cleft palate or bifid (split) uvula. They may also have craniosynostosis. Shared mucocutaneous features include striae, typi­ cally over the shoulders and buttocks, and inguinal and incisional her­ nias. Patients with LDS may display more EDS-like skin features, such as thin translucent skin and widened scars. Molecular Defects  Approximately 95% of MFS patients are explained by FBN1 defects, and so far, over 2000 different FBN1 mutations have been described. Mutations in the same gene are found in a few patients who do not meet the Ghent criteria. Most FBN1 gene mutations are unique and are scattered throughout its 65 coding

exons. Approximately 10% are recurrent mutations that are largely located in CpG sequences known to be “hot spots.” About one-third of the mutations introduce premature termination codons, and about two-thirds are missense mutations that alter calcium-binding domains in the repetitive epidermal growth factor–like domains of the protein. Rarer mutations alter the processing of the protein. As in many genetic diseases, the severity of the phenotype cannot be predicted from the nature of the mutation. In LDS, components of the TGF-β signaling pathway are mutated, including the cytokines (TGFβ2, TGFβ3), the receptors (TGFBR1, TGFBR2), and the downstream effectors (SMAD2, SMAD3). The discovery that various conditions with pronounced clinical overlap with MFS were caused by mutations in genes coding for direct effectors and/or regulators of TGFβ signaling, including LDS, revealed that FBN1 mutations not only lead to weakening of the extracellular matrix structure, but also influence the bioavailability of TGFβ. As a result, some of the manifestations of MFS have been shown to arise from alterations in binding sites that modulate TGFβ bioavailability during development of the skeleton and other tissues. In aortic tis­ sues, reduced or altered forms of fibrillin-1 can stimulate the release of sequestered TGFβ and increase its activity. This results in altered transcription of target genes, including connective tissue growth factor and matrix metalloproteinases MMP2 and MMP9. The aortic pheno­ type is therefore caused by vascular remodeling due to a combination of structural microfibril changes, excess TGFβ, and overexpression of MMP-2 and MMP-9. The role of TGFβ in the pathophysiology of MFS has been further solidified by therapeutic use of angiotensin 2 recep­ tor blockers (ARBs), proven to decrease TGFβ activity, to reduce the progression of aortic dilation. However, clinical trials with ARBs did not provide evidence of a dramatic decrease or prevention of aortic growth with ARBs. Diagnosis  When HTAD is present, genetic testing can confirm the diagnosis and allow identification of at-risk individuals. Referral to a specialty genetics service is critically important, and genetic counsel­ ing before testing is recommended. In view of phenotypic overlap between the syndromic HTAD, a multigene panel (usually including genes for syndromic and nonsyndromic HTAD) is recommended. All patients with a suspected diagnosis of MFS should have a slit-lamp examination and an echocardiogram. Also, homocystinuria should be ruled out by amino acid analysis of plasma (Chap. 431). The diagnosis of MFS according to the international Ghent standards places empha­ sis on two cardinal features, dilation of the ascending aorta with or without dissection and ectopia lentis. Other cardiovascular and ocular manifestations and findings in other organ systems such as the skel­ eton, dura, skin, and lungs contribute to a systemic score that guides diagnosis when aortic disease is present but ectopia lentis is not.

44 - 426 Hemochromatosis

426 Hemochromatosis

TREATMENT Marfan and Loeys-Dietz Syndromes Patients should be advised that vascular risks are increased by severe physical exertion, smoking, emotional stress, and pregnancy. Low-level moderate aerobic exercise and limits on isometric exer­ cise are recommended. Prophylactic beta blocker and/or angio­ tensin II receptor blocker therapy are prescribed in normotensive individuals, and blood pressure control is important for those with hypertension. Surgical correction of the aorta, aortic valve, and mitral valve has been successful in many patients, but tissues are frequently friable. The scoliosis tends to be progressive, and surgi­ cal stabilization may be required. Dislocated lenses rarely require surgical removal, but patients should be followed closely for retinal detachment. Acknowledgment Darwin J. Prockop and John F. Bateman contributed to this chapter in the 20th edition and some material from that chapter has been retained here. ■ ■FURTHER READING Besio R et al: Bone biology: Insights from osteogenesis imperfecta and related rare fragility syndrome. FEBS J 286:3033, 2019. De Backer J et al: Genetic testing for aortopathies: Primer for the nongeneticist. Curr Opin Cardiol 34:585, 2019. Jovanovic M et al: Osteogenesis imperfecta: Mechanisms and signal­ ing pathways connecting classical and rare OI types. Endocr Rev 12:61, 2022. Loeys BL et al: The revised Ghent nosology for the Marfan syndrome. J Med Genet 47:476, 2010. Malfait F et al: The Ehlers-Danlos syndromes. Nat Rev Dis Primers 6:64, 2020. Marini JC et al: Osteogenesis imperfecta. Nat Rev Dis Primers 3:17052, 2017. Marzin P, Cormier-Daire V: New perspectives on the treatment of skeletal dysplasia. Ther Adv Endocrinol Metab 11:2042018820904016, 2020. Unger S et al: Nosology and classification of genetic skeletal disorders: 2023 revision. Am J Med Genet A 191:1164, 2023. Darrell H. G. Crawford, David M. Frazer

Hemochromatosis ■ ■DEFINITION Hemochromatosis is a relatively common inherited disorder of iron metabolism more prevalent in European populations. It is now known to be an iron-storage disorder with underlying genetic heterogeneity that, in nearly all cases, causes inappropriately high cellular release of iron from iron exporting cells such as enterocytes and macrophages. The increase in intestinal iron absorption results in the deposition of excess iron in parenchymal cells with eventual cellular injury, tissue fibrosis, and organ failure. Cirrhosis of the liver, diabetes mellitus, arthritis, cardiomyopathy, and hypogonadotropic hypogonadism are the most important clinical consequences. The term hemochromatosis describes the unique genetic clinicalpathologic condition with features of increased serum transferrin saturation, iron overload in the liver but not the spleen, prevalent involvement of periportal hepatocytes with iron sparing of Kupffer

cells, and/or signs and symptoms of iron overload. These characteris­ tics should occur in the absence of a primary/predominant red blood cell disorder to distinguish hemochromatosis from other iron overload conditions, which are also often genetic in origin.

The condition is most often caused by a mutation in the homeostatic iron regulator (HFE) gene, which is tightly linked to the HLA-A locus on chromosome 6p. Persons who are homozygous for the mutation are at increased risk of iron overload and account for 80–90% of hemo­ chromatosis in persons of northern European descent. In such subjects, the presence of hepatic fibrosis, cirrhosis, arthropathy, or hepatocel­ lular carcinoma constitutes iron overload–related disease. Rarer forms of non-HFE hemochromatosis are caused by mutations in other genes involved in iron metabolism (Table 426-1). The disease is now often diagnosed during its early stages when iron overload and organ dam­ age are minimal. Hemochromatosis CHAPTER 426 Secondary iron overload occurs as a result of an iron-loading anemia, such as thalassemia or sideroblastic anemia, in which erythropoiesis is ineffective and causes increased intestinal iron absorption. In the acquired iron-loading disorders, massive iron deposits in parenchy­ mal tissues can lead to the same clinical and pathologic features as in hemochromatosis. ■ ■PREVALENCE The prevalence of HFE-associated hemochromatosis mutations varies among different ethnic groups. It is most common in populations of northern European extraction in whom ~1 in 10 persons are hetero­ zygous carriers and 0.3–0.5% are homozygotes, with even higher per­ centages in some Celtic populations such as those residing in Ireland and Brittany. The expression of the disease is variable and modified by several factors, especially alcohol consumption, dietary iron intake, blood loss associated with menstruation and pregnancy, and blood donation. Recent population studies indicate that ~40% of homozy­ gous men develop iron overload–related complications and about 6% develop hepatic cirrhosis. For women, iron overload–related complica­ tions occur in ~10%. In addition, there are as yet unidentified modify­ ing genes responsible for variable disease expression. Nearly 70% of untreated patients develop the first symptoms between ages 40 and 60. The disease is rarely evident before age 20, although with family screening (see “Screening for Hemochromatosis,” below) and periodic TABLE 426-1  Classification of Iron Overload States Hereditary Hemochromatosis Hemochromatosis, HFE-related (type 1)   C282Y homozygosity   C282Y/H63D compound heterozygosity Hemochromatosis, non-HFE-related   Juvenile hemochromatosis (type 2A) (hemojuvelin mutations)   Juvenile hemochromatosis (type 2B) (hepcidin mutation)   Mutated transferrin receptor 2, TFR2 (type 3)   Mutated ferroportin 1 gene, SLC40A1 (type 4) Acquired Iron Overload Iron-loading anemias   Thalassemia major   Sideroblastic anemia   Chronic hemolytic anemias   Transfusional and parenteral iron Chronic liver disease   Hepatitis C   Alcoholic cirrhosis, especially when advanced   Nonalcoholic steatohepatitis   Porphyria cutanea tarda   Dysmetabolic iron overload syndrome   Post-portacaval shunting overload   Dietary iron overload Miscellaneous Iron overload in sub-Saharan Africa Neonatal iron overload Aceruloplasminemia Congenital atransferrinemia

health examinations, asymptomatic subjects with iron overload can be identified, including young menstruating women.

Mutations in other genes involved in iron metabolism are respon­ sible for non-HFE-associated hemochromatosis. In contrast to HFEassociated hemochromatosis, the non-HFE-associated forms of hemochromatosis (Table 426-1) are rare, but they affect all populations and may affect young people (juvenile hemochromatosis). These con­ ditions result from mutations in one or more of the genes encoding proteins in the hepcidin pathway (Fig. 426-1), including hepcidin, hemojuvelin, and transferrin receptor 2 (TFR2). The resultant clinical disease is very similar to HFE-related disease because they all lead to hepcidin deficiency via a final common pathway (Fig. 426-1). PART 12 Endocrinology and Metabolism A rare autosomal dominant form of hemochromatosis results from two types of mutations in the gene for the iron transporter ferroportin. Loss-of-function mutations decrease the cell surface localization of ferroportin in certain tissues, thereby reducing its ability to export iron (“ferroportin disease”) and causing cellular iron retention, particularly DCYTB DMT1 Liver FPN Heph TMPRSS6 Villus HFE/TFR1 TFR2 Crypt Hepcidin Duodenum FIGURE 426-1  Pathways of normal iron homeostasis. Dietary inorganic iron traverses the brush border membrane of duodenal enterocytes via divalent metal-ion transporter 1 (DMT1) after reduction of ferric (Fe3+) iron to the ferrous (Fe2+) state by intestinal ferrireductases such as duodenal cytochrome B (DCYTB). Iron then moves from the enterocyte to the circulation via a process requiring the basolateral iron exporter ferroportin (FPN) and the iron oxidase hephaestin (Heph). In the circulation, iron binds to plasma transferrin and is thereby distributed to sites of iron utilization and storage. Much of the diferric transferrin supplies iron to immature erythrocyte cells in the bone marrow for hemoglobin synthesis. At the end of their life, senescent red blood cells (RBCs) are phagocytosed by macrophages, and iron is returned to the circulation after export through ferroportin. The liver-derived peptide hepcidin represses basolateral iron transport in the gut as well as iron released from macrophages and other cells and serves as a central regulator of body-iron traffic. At least two separate signals regulate hepcidin production in response to changes in body-iron requirements. The first involves the detection of circulating diferric transferrin by HFE and TFR2. A second relies on hepatic iron stores activating the hemojuvelin (HJV)-dependent bone morphogenetic protein (BMP)/SMAD pathway. This pathway is modified by erythroferrone released from erythroid precursor cells, which binds to BMP6 and inhibits its function. TMPRSS6 is a protease that regulates hepcidin production, possibly by modulating HJV activity. Heme is metabolized by heme oxygenase within the enterocytes, and the released iron then follows the same pathway. Mutations in the genes encoding HFE, TFR2, HJV, and hepcidin all lead to decreased hepcidin release and increased iron absorption, resulting in hemochromatosis (Table 426-1).

in macrophages. A second mutation abolishes the hepcidin-induced ferroportin internalization and degradation resulting in a “gain of func­ tion.” Here the tissue iron distribution is similar to that in HFE-related disease (e.g., in parenchymal cells). ■ ■GENETIC BASIS The most common mutation in the HFE gene is a homozygous G to A transition that leads to a cysteine to tyrosine substitution at position 282 (C282Y) of the HFE protein. It has been identified in 85–90% of patients with hereditary hemochromatosis in populations of northern European descent but is found in only 60% of cases from Medi­ terranean populations. A second, relatively common HFE variant (H63D) results in a substitution of aspartic acid for histidine at residue 63 of the HFE protein. Homozygosity for H63D is not associated with clinically significant iron overload. Some compound heterozygotes (i.e., one copy each of C282Y and H63D) have mild to moderately increased body-iron stores but develop clinical disease only in association with Plasma Transferrin Bone marrow Erythroferrone RBC FPN BMP6 HJV BMPR Macrophage Hepcidin P ? SMAD P P Hepcidin

cofactors such as heavy alcohol intake or hepatic steatosis. HFEassociated hemochromatosis is inherited as an autosomal recessive trait, and heterozygotes have no, or minimal, increase in iron stores. However, this slight increase in hepatic iron can act as a cofactor that may modify the expression of other diseases such as porphyria cutanea tarda (PCT) or metabolic dysfunction associated steatohepatitis (MASH). ■ ■PATHOPHYSIOLOGY AND THE

ROLE OF HEPCIDIN Normally, the body-iron content of 3–4 g is maintained as a result of intestinal mucosal absorption of iron being equal to iron loss. This amount is ~1 mg/d in men and 1.5 mg/d in menstruating women. In hemochromatosis, intestinal iron absorption is greater than body requirements and amounts to ≥4 mg/d. The progressive accumulation of iron increases plasma iron concentration and saturation of transfer­ rin and results in a progressive increase of plasma ferritin (Fig. 426-2). Hepcidin is a key regulatory hormone that allows the bone marrow and other tissues to communicate their iron requirements. It was called hepcidin based upon its antibacterial activity (“HEPatic bacterioCIDal proteIN”). This liver-derived peptide represses basolateral iron export from intestinal enterocytes and iron release from macro­ phages and other cells by binding to ferroportin. Hepcidin, in turn, responds to signals in the liver mediated by HFE, TFR2, and hemo­ juvelin (Fig. 426-1). The development of hepcidin agonists represents a promising new therapeutic approach for iron overload disorders caused by low hepcidin levels. The HFE gene encodes a 343-amino-acid protein that is structurally related to MHC class I proteins. The basic defect in HFE-associated hemochromatosis is a lack of cell surface expression of HFE (due to the C282Y mutation). The normal (wild-type) HFE protein forms a complex with β2-microglobulin and transferrin receptor 1 (TFR1), and the C282Y mutation completely abrogates this interaction. As a result, the mutant HFE protein remains trapped intracellularly. Although the precise function of HFE at the cell surface is not known, mutations in this protein reduce hepcidin production leading to increased dietary iron absorption (Fig. 426-1). In advanced disease, the body may con­ tain 20 g or more of iron, which is deposited mainly in parenchymal cells of the liver, pancreas, and heart. Iron deposition in the pituitary

Serum ferritin concentration (µg/L)

Age (yrs.)

Cirrhosis, organ failure Progressive tissue injury Increased total body iron Increased hepatic iron Increased serum iron Increased iron absorption FIGURE 426-2  Sequence of events in genetic hemochromatosis and their correlation with the serum ferritin concentration. Increased iron absorption is present throughout life. Overt, symptomatic disease usually develops between ages 40 and 60, but latent disease can be detected long before this.

causes hypogonadotropic hypogonadism in both men and women. Tissue injury results from disruption of iron-laden lysosomes, lipid peroxidation of subcellular organelles by excess iron, and stimulation of collagen synthesis by activated hepatic stellate cells.

Secondary iron overload with iron deposition in parenchymal cells occurs in chronic disorders of erythropoiesis, particularly in those with defects in hemoglobin synthesis and ineffective erythro­ poiesis such as sideroblastic anemia and thalassemia (Chap. 103). In these disorders, iron absorption is increased. Moreover, these patients require blood transfusions and are frequently treated inap­ propriately with iron. PCT, a disorder characterized by a defect in porphyrin biosynthesis (Chap. 428), can also be associated with excessive parenchymal iron deposits. The magnitude of the iron load in PCT is usually insufficient to produce tissue damage. However, some patients with PCT also have mutations in the HFE gene, and some have associated hepatitis C virus (HCV) infection. Although the relationship between these disorders remains to be clarified, iron overload accentuates the inherited enzyme deficiency in PCT and should be avoided along with other agents (alcohol, estrogens, halo­ aromatic compounds) that may exacerbate PCT. Another cause of hepatic parenchymal iron overload is hereditary aceruloplasminemia. In this disorder, impairment of iron mobilization due to deficiency of ceruloplasmin (a ferroxidase) causes iron overload in hepatocytes and a range of other cell types. Hemochromatosis CHAPTER 426 Excessive iron ingestion over many years rarely results in hemochro­ matosis. An important exception has been reported in South Africa among groups who brew fermented beverages in vessels made of iron. Hemochromatosis has been described in apparently normal persons who have taken medicinal iron over many years, but such individuals probably had genetic disorders. The common denominator in all patients with hemochromatosis is excessive amounts of iron in parenchymal tissues. Parenteral adminis­ tration of iron in the form of blood transfusions or iron preparations results predominantly in reticuloendothelial cell iron overload. This appears to lead to less tissue damage than iron loading of parenchymal cells. In the liver, parenchymal iron is in the form of ferritin and hemo­ siderin. In the early stages, these deposits are seen in the periportal parenchymal cells, especially within lysosomes in the pericanalicular cytoplasm of the hepatocytes. This stage progresses to perilobular fibrosis and the formation of fibrous septa due to activation of hepatic stellate cells. In the advanced stage, a macronodular or mixed macro- and micronodular cirrhosis develops. The underlying hepatic iron con­ centration is an important determinant of the risk of the development of hepatic fibrosis and cirrhosis. Histologically, iron is increased in many organs, particularly in the liver, heart, and pancreas, and, to a lesser extent, in the endocrine glands. The epidermis of the skin is thin, and melanin is increased in the cells of the basal layer and dermis. Deposits of iron are present around the synovial lining cells of the joints. ■ ■CLINICAL MANIFESTATIONS C282Y homozygotes can be characterized by their stage in the pro­ gression of disease as follows: (1) a genetic predisposition without biochemical or clinical abnormalities; (2) iron overload without symp­ toms; (3) iron overload with symptoms (e.g., arthritis and fatigue); and (4) iron overload with organ damage—in particular, cirrhosis. Many subjects with significant iron overload are asymptomatic. For example, in a study of 672 asymptomatic C282Y homozygous subjects (identi­ fied by either family screening or routine health examinations), there was hepatic iron overload (grades 2–4) in 56% and 34.5% of male and female subjects, respectively, hepatic fibrosis (stages 2–4) in 18.4% and 5.4%, respectively, and cirrhosis in 5.6% and 1.9%, respectively. Normal range Initial symptoms of hemochromatosis are often nonspecific and include lethargy, arthralgia, skin pigmentation, loss of libido, and features of diabetes mellitus. Hepatomegaly, increased pigmentation, spider angiomas, splenomegaly, arthropathy, ascites, cardiac arrhyth­ mias, congestive heart failure, loss of body hair, testicular atrophy, and jaundice are prominent in advanced disease.

Hepatocellular carcinoma develops in ~30% of patients with cirrho­ sis, and it is the most common cause of death in treated patients with cirrhosis—hence the importance of early diagnosis and therapy. The incidence increases with age, it is more common in men, and it occurs almost exclusively in cirrhotic patients.

Excessive skin pigmentation is present in patients with advanced disease. The characteristic metallic or slate-gray hue is sometimes referred to as bronzing and results from increased melanin and iron in the dermis. Pigmentation usually is diffuse and generalized. Diabetes mellitus occurs in ~65% of patients with advanced disease and is more likely to develop in those with a family history of diabetes, suggesting that direct damage to the pancreatic islets by iron deposi­ tion occurs in combination with other risk factors. The management is similar to that of other forms of diabetes. PART 12 Endocrinology and Metabolism Arthropathy develops in 25–50% of symptomatic patients. It usu­ ally occurs after age 50 but may occur as a first manifestation or long after therapy. The joints of the hands, especially the second and third metacarpophalangeal joints, are usually the first joints involved, a feature that helps to distinguish the chondrocalcinosis associated with hemochromatosis from the idiopathic form (Chap. 384). A progres­ sive polyarthritis involving the wrists, hips, ankles, and knees may also ensue. Acute attacks of synovitis may be associated with deposition of calcium pyrophosphate (chondrocalcinosis or pseudogout), mainly in the knees. Radiologic manifestations include cystic changes of the subchondral bones, loss of articular cartilage with narrowing of the joint space, diffuse demineralization, hypertrophic bone proliferation, and calcification of the synovium. The arthropathy tends to progress despite removal of iron by phlebotomy. Although the relation of these abnormalities to iron metabolism is not known, the fact that similar changes occur in other forms of iron overload suggests that iron is directly involved. Cardiac involvement is the presenting manifestation in ~15% of symptomatic patients. The most common manifestation is congestive heart failure, which occurs in ~10% of young adults with the disease, especially those with juvenile hemochromatosis. Symptoms of conges­ tive heart failure may develop suddenly, with rapid progression to death if untreated. The heart is diffusely enlarged. This may be misdi­ agnosed as idiopathic cardiomyopathy if other overt manifestations are absent. Cardiac arrhythmias include premature supraventricular beats, paroxysmal tachyarrhythmias, atrial flutter, atrial fibrillation, and vary­ ing degrees of atrioventricular block. Hypogonadism occurs in both sexes and may antedate other clinical features. Manifestations include loss of libido, impotence, amenorrhea, testicular atrophy, gynecomastia, and sparse body hair. These changes are primarily the result of decreased production of gonadotropins due to impairment of hypothalamic-pituitary function by iron deposition. ■ ■DIAGNOSIS The association of (1) hepatomegaly, (2) skin pigmentation, (3) dia­ betes mellitus, (4) heart disease, (5) arthritis, and (6) hypogonadism should suggest the diagnosis. However, as stated above, significant iron overload may exist with none or only some of these manifestations. Therefore, a high index of suspicion is needed to make the diagnosis TABLE 426-2  Representative Iron Values in Normal Subjects, Patients with Hemochromatosis, and Patients with Alcoholic Liver Disease SYMPTOMATIC HEMOCHROMATOSIS DETERMINATION NORMAL Plasma iron, μmol/L (μg/dL) 9–27 (50–150) 32–54 (180–300) Usually elevated Elevated or normal Often elevated Total iron-binding capacity, μmol/L (μg/dL) 45–66 (250–370) 36–54 (200–300) 36–54 (200–300) Normal 45–66 (250–370) Transferrin saturation, % 22–45 50–100 50–100 Normal or elevated 27–60 Serum ferritin, μg/L   1000–6000 200–500 Usually <500 10–500   Men 20–250           Women 15–150         Liver iron, μg/g dry wt 300–1400 6000–18,000 2000–4000 300–3000 300–2000 Hepatic iron index <1.0

2 1.5–2 <2 <2

early. Treatment before permanent organ damage occurs can reverse the iron toxicity and restore life expectancy to normal. The history should be particularly detailed in regard to disease in other family members and should include information on alcohol ingestion; iron intake; and ingestion of large doses of ascorbic acid, which promotes iron absorption (Chap. 344). Appropriate tests should be performed to exclude iron deposition due to hematologic disease. The presence of liver, pancreatic, cardiac, and joint disease should be confirmed by physical examination, radiography, and standard func­ tion tests of these organs. The degree of increase in total body iron stores can be assessed by (1) measurement of serum iron and the percent saturation of trans­ ferrin (or the unsaturated iron-binding capacity), (2) measurement of serum ferritin concentration, (3) liver biopsy with measurement of the iron concentration (Table 426-2), and (4) magnetic resonance imaging (MRI) of the liver to quantify hepatic iron stores. In addi­ tion, a retrospective assessment of body-iron storage is also provided by performing weekly phlebotomy and calculating the amount of iron removed before iron stores are exhausted (1 mL blood = ~0.5 mg iron). Each of these methods for assessing iron stores has advantages and limitations. The serum iron level and percent saturation of transferrin are elevated early in the course, but their specificity is reduced by sig­ nificant false-positive and false-negative rates. For example, serum iron concentration may be increased in patients with alcoholic liver disease without iron overload (Table 426-2). In otherwise healthy persons, a fasting serum transferrin saturation >45% is abnormal and suggests homozygosity for hemochromatosis. The serum ferritin concentration is used as an index of body-iron stores, whether decreased or increased. In fact, an increase of 1 μg/L in serum ferritin level reflects an increase of ~8–10 mg in body stores. In most untreated patients with hemochromatosis, the serum ferritin level is significantly increased (Fig. 426-2 and Table 426-2), and a serum ferritin level >1000 μg/L is a strong predictor of cirrhosis among individuals homozygous for the C282Y mutation. However, in patients with hepatic necroinflammatory conditions such as alcoholic liver dis­ ease and metabolic dysfunction–associated steatotic liver disease, acute hepatocellular necrosis, or systemic inflammatory conditions, serum ferritin levels may be elevated out of proportion to body iron stores due to increased release from tissues. Therefore, a repeat determination of serum ferritin should be carried out after acute hepatocellular damage has subsided (e.g., in alcoholic liver disease). Ordinarily, the combined measurements of the percent transferrin saturation and serum ferritin level provide a simple and reliable screening test for hemochromatosis, including the precirrhotic phase of the disease. If either of these tests is abnormal, genetic testing for hemochromatosis should be performed (Fig. 426-3). The role of liver biopsy in the diagnosis and management of hemochromatosis has been reassessed as a result of the widespread availability of genetic testing for the C282Y mutation. The absence of severe fibrosis can be accurately predicted in most patients using clini­ cal and biochemical variables. Thus, there is virtually no risk of severe fibrosis in a C282Y homozygous subject with (1) serum ferritin level HOMOZYGOTES WITH EARLY, ASYMPTOMATIC HEMOCHROMATOSIS HETEROZYGOTES ALCOHOLIC LIVER DISEASE

Subjects with unexplained liver disease Adult first-degree relative of patient with HH Individual with suggestive symptoms (see text) Reassure, possibly retest later Transferrin saturation and serum ferritin* TS <45% SF <300 TS ≥45% and/or SF >300 µgL Normal Counsel and consider non-HFE hemochromatosis HFE genotype C282Y Homozygote C282Y/H63D (compound heterozygote) Serum ferritin –300–1000 µg/L LFT normal Serum ferritin

1000 µg/L and/or LFT abnormal Serum ferritin <300 µg/L LFT normal Observe, retest in 1–2 years No iron overload Investigate and treat as appropriate Liver biopsy Confirmed iron overload Phlebotomy *For convenience both genotype and phenotype (iron tests) can be performed together at a single visit in first-degree relatives. FIGURE 426-3  Algorithm for screening for HFE-associated hemochromatosis. HH, hereditary hemochromatosis, homozygous subject (C282Y +/+); LFT, liver function test; SF, serum ferritin concentration; TS, transferrin saturation. <1000 μg/L, (2) normal serum alanine aminotransferase values, (3) no hepatomegaly, and (4) no excess alcohol intake. However, it should be emphasized that liver biopsy is the most reliable method for establish­ ing or excluding the presence of hepatic cirrhosis, which is the critical factor determining prognosis and the risk of developing hepatocellular carcinoma. Biopsy also permits histochemical estimation of tissue iron and measurement of hepatic iron concentration. Serum tests for liver fibrosis and transient elastography can guide decisions about the need for liver biopsy in affected patients. Increased density of the liver due to iron deposition can be demonstrated by computed tomography (CT) or MRI, and with improved technology, MRI can accurately determine hepatic iron concentration. ■ ■SCREENING FOR HEMOCHROMATOSIS When the diagnosis of hemochromatosis is established, it is important to counsel and screen other family members (Chap. 480). Asymptom­ atic and symptomatic family members with the disease usually have an increased saturation of transferrin and an increased serum ferritin concentration. These changes occur even before iron stores are greatly increased (Fig. 426-2). All adult first-degree relatives of patients with hemochromatosis should be tested for the C282Y and H63D mutations and counseled appropriately (Fig. 426-3). In affected individuals, it is important to confirm or exclude the presence of cirrhosis and begin therapy as early as possible. For children of an identified proband, testing for HFE mutations in the other parent is helpful because if normal, the child is an obligate heterozygote and at no risk. Otherwise, for practical purposes, children need not be checked before they are 18 years old. The role of population screening for hemochromatosis is controver­ sial. Recent studies indicate that it is highly effective for primary care physicians to screen subjects using transferrin saturation and serum ferritin levels. Such screening also detects iron deficiency. Genetic screening of the normal population is feasible but remains controver­ sial in terms of cost-effectiveness.

TREATMENT Hemochromatosis The therapy of hemochromatosis involves removal of the excess body iron and supportive treatment of damaged organs. Iron removal is best accomplished by weekly or, with gross iron loading, twice-weekly phlebotomy of 500 mL. Although there is an initial modest decline in the volume of packed red blood cells to about 35 mL/dL, the level stabilizes after several weeks. The plasma trans­ ferrin saturation remains increased until the available iron stores are depleted. In contrast, the plasma ferritin concentration falls progres­ sively, reflecting the gradual decrease in body-iron stores. One 500mL unit of blood contains 200–250 mg of iron, and ≥25 g of iron may have to be removed. Therefore, in patients with advanced disease, weekly phlebotomy may be required for 1–2 years, and it should be continued until the serum ferritin level is ≤100 μg/L. Thereafter, phlebotomies are performed at appropriate intervals to maintain ferritin levels at ≤100 μg/L. The transferrin saturation fluctuates and may still be elevated but should not dictate further therapy unless it is persistently at 100% when free unbound iron may circulate. Usually, one phlebotomy every 3 months will suffice. It is important, however, not to overtreat and render the patient iron deficient. Hemochromatosis CHAPTER 426 Chelating agents such as deferoxamine, when given parenter­ ally, remove 10–20 mg of iron per day, which is much less than that mobilized by once-weekly phlebotomy. Phlebotomy is also less expensive, more convenient, and safer for most patients. However, chelating agents may be indicated when anemia or hypoprotein­ emia is severe enough to preclude phlebotomy. Effective oral iron chelating agents, deferasirox (Exjade) and deferiprone, are now available. These agents are effective in thalas­ semia and secondary iron overload but are expensive and carry the risk of significant side effects. Alcohol consumption should be severely curtailed or eliminated because it increases the risk of cirrhosis in hereditary hemochroma­ tosis nearly tenfold. Dietary adjustments are unnecessary, although vitamin C and iron supplements should be avoided. The manage­ ment of hepatic failure, cardiac failure, and diabetes mellitus is similar to conventional therapy for these conditions. Loss of libido and change in secondary sex characteristics are managed with tes­ tosterone replacement or gonadotropin therapy (Chap. 403). End-stage liver disease may be an indication for liver trans­ plantation, although results are improved if the excess iron can be removed beforehand. The available evidence indicates that the fun­ damental metabolic abnormality in hemochromatosis is reversed by successful liver transplantation. ■ ■PROGNOSIS The principal causes of death are cardiac failure, hepatocellular failure, or portal hypertension and hepatocellular carcinoma. Life expectancy is improved by removal of excessive iron stores and maintenance of these stores at near-normal levels. The 5-year survival rate with therapy increases from 33 to 89%. With repeated phlebotomy, the liver decreases in size, liver function improves, pigmentation of skin decreases, and cardiac failure may be reversed. Diabetes improves in ~40% of patients, but removal of excess iron has little effect on hypogo­ nadism or arthropathy. Hepatic fibrosis may decrease, and cirrhosis may regress with adequate phlebotomy therapy. Hepatocellular carcinoma occurs as a late sequela in patients who are cirrhotic at presentation. The apparent increase in its incidence in treated patients is probably related to their increased life span. Hepatocellular carcinoma rarely develops if the disease is treated in the precirrhotic stage. Indeed, the life expectancy of homozygotes treated before the development of cirrhosis is normal. The importance of family screening and early diagnosis and treat­ ment cannot be overemphasized. Asymptomatic individuals detected by family studies should have phlebotomy therapy if iron stores are moderately to severely increased. Assessment of iron stores at appro­ priate intervals is also important. With this management approach, most manifestations of the disease can be prevented.

45 - 427 Wilson’s Disease

427 Wilson’s Disease

■ ■ROLE OF HFE MUTATIONS IN OTHER

LIVER DISEASES

There is considerable interest in the role of HFE mutations and hepatic iron in several other liver diseases. Several studies have shown an increased prevalence of HFE mutations in PCT patients. Iron accentuates the inherited enzyme deficiency in PCT and clinical manifestations of PCT. The situation in metabolic dysfunction– associated steatohepatitis is less clear, but some studies have shown an increased prevalence of HFE mutations. Available evidence does not support a role for phlebotomy therapy unless there is a proven increase in hepatic iron stores. HFE mutations are not increased in frequency in alcoholic liver disease. However, alcohol does reduce hepcidin expression, which accounts for increased iron absorption and hepatic iron sometimes seen in alcoholic liver disease. Hemochromatosis in a heavy drinker can be distinguished from alcoholic liver disease by the presence of the C282Y mutation. PART 12 Endocrinology and Metabolism End-stage liver disease may also be associated with iron overload of the degree seen in hemochromatosis. The mechanism is uncertain, although studies have shown reduced hepcidin and intestinal iron transporter expression. Hemolysis also plays a role. HFE mutations are uncommon. ■ ■GLOBAL CONSIDERATIONS The HFE mutation is of northern European origin (Celtic or Nordic) with a heterozygous carrier rate of ~1 in 10 (1 in 8 in Ireland). Thus, HFEassociated hemochromatosis is quite rare in non-European populations, e.g., Asia. However, non-HFE-associated hemochromatosis resulting from mutations in other genes involved in iron metabolism (Fig. 426-1) is ubiquitous and should be considered when one encounters iron overload. African iron overload occurs primarily in sub-Saharan Africa and was previously thought to be due to the consumption of an iron-rich fermented maize beverage. However, recent evidence suggests that it is primarily the result of a non-HFE-related genetic trait that is exacer­ bated by dietary iron loading. A similar form of iron overload has been described in African Americans. Acknowledgment The authors extend their gratitude to the late Professor Lawrie W. Powell and recognize his outstanding contributions to previous versions of this chapter. ■ ■FURTHER READING Adams PC et al: Haemochromatosis. Lancet 401:1811, 2023. Anderson GJ, Bardou-Jacquet E: Revisiting hemochromatosis: Genetic vs. phenotypic manifestations. Ann Transl Med 9:731, 2021. Girelli D et al: Hemochromatosis classification: Update and recom­ mendations by the BIOIRON Society. Blood 139:3018, 2022. Olynyk JK, Ramm GA: Hemochromatosis. N Engl J Med 387:2159, 2022. Powell LW et al: Haemochromatosis. Lancet 388:706, 2016. Stephen G. Kaler

Wilson’s Disease Wilson’s disease is an autosomal recessive inherited disorder of cop­ per transport that primarily impacts the liver and brain. This reflects the critical need for homeostatic mechanisms to properly utilize this trace metal, both systemically and in the central nervous system. Since the initial detailed clinical description in 1912, Wilson’s disease has emerged as arguably one of the best-characterized and most effectively managed human inborn errors of metabolism. The condition results

from variants in ATP7B, a highly evolutionarily conserved P-type ion-motive ATPase that normally mediates copper removal from the liver via biliary excretion and prevents brain copper accumulation. Prompt diagnosis in the presymptomatic or early symptomatic phase of the illness and lifelong treatment are needed to prevent premature mortality in affected individuals. HISTORY OF WILSON’S DISEASE Wilson’s disease (hepatolenticular degeneration) was first described in 1912 by neurologist S.A.K. Wilson, who recognized the heritable aspect of the condition. In 1948, the pathologist J.N. Cumings pro­ posed an etiologic connection with copper overload. Several years later, a metal chelator developed to counteract an arsenic-based chem­ ical warfare agent (lewisite) was used to successfully treat advanced Wilson’s disease. In 1956, copper chelation by d-penicillamine was introduced and found preferable to anti-lewisite with respect to route of administration and side effect profile. In the early 1970s, an alternative copper chelator, triethylene tetramine, became the second U.S. Food and Drug Administration (FDA)–approved treatment for Wilson’s disease. Also in the early 1970s, the first liver transplants were performed for Wilson’s disease, with resultant correction of both hepatic failure and crippling neurologic impairments in patients unresponsive to medical therapies. The treatment potential of zinc salts to reduce gastrointestinal copper absorption in Wilson’s dis­ ease was recognized in the early 1960s, eventually leading to FDA approval for this indication. Tetrathiomolybdate, which forms a tripartite complex with copper and albumin, and a bacterial peptide, methanobactin, which traverses mitochondrial membranes, are more recently proposed copper chelators with potential for treatment of Wilson’s disease. In 1993, the gene for Wilson’s disease was identified and found to encode a copper-transporting ATPase, ATP7B, expressed primarily in liver and kidney. In addition to providing a molecular basis for diagnosis and genotype-phenotype correlations, the finding presents current opportunities for viral gene therapy that could impact future management of this illness. PHENOTYPES ■ ■CLINICAL Presenting clinical features of Wilson’s disease include nonspecific liver disease, neurologic abnormalities, psychiatric illness, hemolytic anemia, renal tubular Fanconi syndrome, and various skeletal abnor­ malities. Age influences the specific presentation in Wilson’s disease. Nearly all individuals who present with liver disease are <30 years of age, whereas those presenting with neurologic or psychiatric signs may range in age from the first to the fifth decade. This reflects the sequence of events in the pathogenesis of the illness. However, regard­ less of clinical presentation, some degree of liver disease is invariably present. Hepatic Presentation  With hepatic presentations, signs and symptoms include jaundice, hepatomegaly, edema, or ascites. Viral hepatitis and cirrhosis are often initial diagnostic considerations in individuals who, in fact, have Wilson’s disease. Neurologic Presentation  In patients with neurologic presenta­ tions, abnormalities include distinctive speech difficulties (dysar­ thria), dystonia, rigidity, tremor (e.g., wing-beating) or choreiform movements, abnormal gait, and uncoordinated handwriting. Wilson’s disease can properly be classified as a movement disorder. The neu­ rologic signs and symptoms reflect the predilection for basal ganglia (e.g., caudate, putamen) involvement in the brains of affected persons. Wilson’s disease may be mistakenly diagnosed as Parkinson disease or other movement disorders. Psychiatric Presentation  In psychiatric presentations, changes in personality (irritability, anger, poor self-control) or school perfor­ mance, depression, and anxiety are common symptoms. Typically, patients presenting in this fashion are in their late teens or early

FIGURE 427-1  Kayser-Fleischer ring in Wilson’s disease, representing copper deposition in Descemet membrane of the cornea. (Image courtesy of Tjaard U. Hoogenraad MD, PhD, Department of Neurology, University Medical Centre Utrecht, Utrecht, The Netherlands.) twenties, a period during which substance abuse is also a diagnostic consideration. Wilson’s disease should be formally excluded in all teen­ agers and young adults with new-onset psychiatric signs. Ocular Manifestations  The eye is a primary site of copper deposition in Wilson’s disease, producing a pathognomonic sign, the Kayser-Fleischer ring (Fig. 427-1), a golden to greenish-brown band in the peripheral cornea. This important diagnostic sign first appears as a superior crescent, then develops inferiorly, and ultimately becomes circumferential. Slit-lamp or optical coherent tomography examina­ tions are required to detect rings in their early stage of formation. Copper can also accumulate in the lens and produce “sunflower” cata­ racts. Approximately 95% of Wilson’s disease patients with neurologic signs manifest the Kayser-Fleischer ring compared to two-thirds of those with hepatic presentations. Copper chelation therapy causes fad­ ing and eventual disappearance of corneal copper. Other Clinical Manifestations  Secondary endocrine effects of Wilson-associated liver disease may include delayed puberty or amen­ orrhea. Renal tubular dysfunction in Wilson’s disease leads to abnormal losses of amino acids, electrolytes, calcium, phosphorus, and glucose. Presumably, this effect is related to renal copper toxicity; high copper levels have been noted previously in the kidneys of patients with Wilson’s disease. Treatment with copper chelation often improves the renal disturbances. There also can be skeletal effects of Wilson’s disease, including osteoporosis and rickets, which may be attributable to renal losses of calcium and phosphorus. Osteoarthritis, primarily affecting the knees and wrists, may involve excess copper deposition in the bone and cartilage. Hemolytic anemia due to the direct toxic effects of copper on red blood cell membranes is usually associated with release of massive quantities of hepatic copper into the circulation, a phenomenon that can be sudden and catastrophic. ■ ■BIOCHEMICAL Laboratory findings that support the diagnosis of Wilson’s disease include low levels of serum copper and serum ceruloplasmin, elevated hepatic transaminase levels, aminoaciduria, and hemolytic anemia. Incorporation of radiolabeled 64Cu into serum ceruloplasmin, mea­ sured as the appearance of copper in the serum after an oral load, is a highly specific diagnostic test; patients with Wilson’s disease incorpo­ rate very little 64Cu into ceruloplasmin. Increased urinary excretion of copper (>100 μg/24 h) is an easily per­ formed and important diagnostic test for Wilson’s disease. Acid-washed (copper-free) collection containers should be used. The penicillamine

challenge is a variation using serial urine copper measurements in which 500 mg of penicillamine are administered orally after collecting a baseline 24-h urine. The penicillamine dose is repeated after 12 h, the midpoint of the second 24-h urine collection. A several-fold increase in copper excretion in the second collection suggests the diagnosis.

Although invasive, percutaneous needle liver biopsy for mea­ surement of hepatic copper remains a gold standard technique for biochemical diagnosis of Wilson’s disease. Hepatic copper values

200 μg per gram of dry weight (normal 20–50 μg) are characteristic of Wilson’s disease. Inductively coupled plasma mass spectrometry and atomic absorption spectrometry are preferred quantitative meth­ ods; histochemical staining for copper in liver biopsy specimens is considered less reliable. Wilson’s Disease CHAPTER 427 ■ ■MOLECULAR Wilson’s disease is caused by loss-of-function variants in ATP7B. Despite similar genomic structures, large deletions are much less common in ATP7B than in ATP7A, the closely related X-linked gene responsible for Menkes disease. Several ATP7B missense variants are common (H1069Q, M645R, and R778L), with various allelic frequen­ cies reflecting geographic, racial, and/or ethnic differences. Major ATP7B databases list >650 pathogenic or likely pathogenic variants. Population-based and genomic-based estimates of prevalence range from 1 in 7000 to 1 in 30,000, with genome-based ascertainments sup­ porting the higher prevalence. This disparity may reflect incomplete penetrance, although there is little doubt that some affected individuals unfortunately escape medical attention. Advances in the application of whole genome sequencing (and/or measurement of ATP7B peptides) from newborn dried blood spots may transform presymptomatic diag­ nostic screening for Wilson disease in the future. DIAGNOSIS Currently, a formal diagnosis of Wilson’s disease relies on a combina­ tion of clinical, biochemical, and molecular features (Table 427-1). A scoring system (Leipzig) that weights and collates various signs and symptoms was produced by an international expert group in 2001 and remains a valuable guide to diagnosis that is endorsed by the European Association for the Study of the Liver (EASL). TABLE 427-1  Main Diagnostic Features of Wilson’s Disease CLINICAL SIGNS AND SYMPTOMS BIOCHEMICAL FINDINGS MOLECULAR FINDINGS Hepatic:   Jaundice   Anorexia   Vomiting   Ascites and/or edema   Splenomegaly Neurologic:   Dysarthria   Facial grimace (risus sardonicus)   Drooling   Dysphagia   Dysgraphia   Dystonia   Tremor (“wing-beating”)   Ataxia   Seizures (rare) Ocular:   Kayser-Fleischer ring   Sunflower cataract (rare) Psychiatric:   Decline in school performance   Personality change   Mood disorder   Schizophrenia Low serum copper Low serum ceruloplasmin Increased urinary copper excretion Elevated liver enzymes Hypoalbuminemia Increased liver copper Fatty liver Cirrhotic liver Hemolytic anemia Renal Fanconi syndrome Variants in ATP7B on both chromosomes Variants or polymorphisms in other genes (e.g., CAT, SOD2, MTHFR) may influence clinical expression of Wilson’s disease in some individuals

46 - 428 The Porphyrias

428 The Porphyrias

TREATMENT Wilson’s Disease COPPER CHELATION The era of successful treatment of Wilson’s disease began with the use of British anti-lewisite (BAL) by a defined regimen of intramuscular injections. An orally administered alternative was d-penicillamine (Cuprimine), a free thiol that binds copper. This chelating drug does not formally correct the basic defect of impaired copper excre­ tion in the bile. However, it greatly enhances urinary excretion of copper and thereby corrects and prevents copper overload and its effects. Pyridoxine (vitamin B6) is usually prescribed concomitantly to counter the tendency for deficiency of this vitamin to develop during chronic penicillamine administration. PART 12 Endocrinology and Metabolism Certain individuals are intolerant of penicillamine, however, encountering significant side effects that include nephrotoxicity, hematologic abnormalities, and a distinctive rash, elastosis perforans serpiginosa (usually involving the neck and axillae). Furthermore, in some Wilson’s disease patients with neurologic presentations, peni­ cillamine treatment induces paradoxical worsening of neurologic status. Triethylenetetramine dihydrochloride (trientine hydrochloride [Syprine]) is a suitable alternative chelating agent with a somewhat better side effect profile. Tetrathiomolybdate (TM) is another molecule in the Wilson’s disease therapeutic armamentarium. TM forms stable tripartite complexes among albumin, copper, and itself. This drug functions both to decrease copper absorption and to reduce circulating free copper. It is fast-acting and can restore normal copper balance within several weeks compared to the several months required with other copper chelators or with zinc. Copper Chelation Treatment During Pregnancy  The rate of spon­ taneous miscarriage is increased in pregnant women with untreated Wilson’s disease. From a benefit/risk perspective, it is important to maintain copper chelation treatment during pregnancy to prevent hepatic or neurologic relapse, as well as to lower risk of pregnancy loss. Some academic centers favor reduction of copper chelator dose during pregnancy, although if zinc monotherapy (see below) is in place at the time of conception, evidence suggests it is safe to maintain the usual daily dose. Since all anticopper medications enter breast milk, breastfeeding is not recommended for mothers with Wilson’s disease. REDUCTION OF COPPER ABSORPTION Zinc acetate (Galzin) has proven highly effective for treatment of

Wilson’s disease. The mechanism involves induction of metallothionein synthesis in intestinal epithelial cells; increased metallothionein synthe­ sis results in greater binding of dietary copper and thus decreased absorption. Zinc therapy has particular value in (1) young, presymp­ tomatic patients; (2) patients who are pregnant given the possible fetal teratogenic effects of other compounds; and (3) as maintenance therapy for patients after their initial “de-coppering” is accomplished. Zinc acetate has minimal side effects. The sole drawback is the rela­ tively long time (4–6 months) needed for restoration of proper copper balance when used as monotherapy in the initial stages of treatment. LIVER TRANSPLANTATION Liver transplantation is a consideration for Wilson’s disease in advanced stages and/or when the condition is unresponsive to med­ ical therapy. This is generally necessary only in cases where delayed diagnosis or poor medication compliance results in irreversible hepatic damage. A recently proposed alternative for this circum­ stance is methanobactin, a bacterial peptide that binds copper avidly and dramatically improves mitochondrial copper overload and restores normal mitochondrial morphology in a preclinical (rat) model of advanced Wilson’s disease. GENE THERAPY In a preclinical (mouse) model of Wilson’s disease, adeno-associated virus-mediated ATP7B introduction into hepatocytes was shown to

be effective. Transduction of only 20% of hepatocytes was suffi­ cient to normalize copper homeostasis in the animal model. Those results potentially pave the way for viral gene therapy in Wilson’s disease patients, and clinical trials to evaluate this approach are underway. FUTURE OUTLOOK Wilson’s disease is arguably one of the best-characterized human inborn errors of metabolism from combined clinical, biochemical, and molecular perspectives, related to the detailed attention devoted to this condition. As noted, novel copper chelators are still being evalu­ ated, and generic formulations of established drugs are contributing to increased affordability for patients and their families. Viral gene therapy to provide working versions of ATP7B to the liver, kidney, and brain or that delivers gene-editing molecules to correct specific mutant alleles is now an emerging prospect. In addition, advances in newborn screening technology may eventually enable wider population-based screening for Wilson’s disease, which would help address lingering questions about clinical penetrance. Such future progress in newborn screening would also avert the tragedy that missed diagnoses of this eminently treatable disorder of copper transport represent. ■ ■FURTHER READING Bandmann O et al: Wilson’s disease and other neurological copper disorders. Lancet Neurol 14:103, 2015. Dev S et al: Wilson disease: Update on pathophysiology and treatment. Front Cell Dev Biol 10:871877, 2022. Gao J et al: The global prevalence of Wilson disease from nextgeneration sequencing data. Genet Med 21:1155, 2019. Kumar M et al: WilsonGen: A comprehensive clinically annotated genomic variant resource for Wilson’s disease. Sci Rep 10:9037, 2020. Lichtmannegger J et al: Methanobactin reverses acute liver failure in a rat model of Wilson disease. J Clin Invest 126:2721, 2016. Murillo O et al: Liver expression of a MiniATP7B gene results in long-term restoration of copper homeostasis in a Wilson disease model in mice. Hepatology 70:108, 2019. Sandahl TD et al: The prevalence of Wilson’s disease: An update. Hepatology 71:722, 2020. Wallace DF, Dooley JS: ATP7B variant penetrance explains differ­ ences between genetic and clinical prevalence estimates for Wilson disease. Hum Genet 139:1065, 2020. Robert J. Desnick, Manisha Balwani

The Porphyrias The porphyrias are metabolic disorders, each resulting from the deficiency or increased activity of a specific enzyme in the heme biosynthetic pathway (Fig. 428-1 and Table 428-1). These enzyme disorders are inherited as autosomal dominant, autosomal recessive, or X-linked traits, with the exception of porphyria cutanea tarda (PCT), which is usually sporadic (Table 428-1). The porphyrias are classified as either hepatic or erythropoietic, depending on the primary site of overproduction and accumulation of their respective porphyrin pre­ cursors or porphyrins (Tables 428-1 and 428-2), although some have overlapping features. For example, PCT is hepatic and presents with blistering cutaneous photosensitivity, which is typically characteristic of the erythropoietic porphyrias. The major manifestations of the acute hepatic porphyrias are neurologic, including neuropathic abdominal pain, peripheral motor neuropathy, and mental disturbances, with attacks often precipitated by dieting, certain porphyrinogenic drugs, and hormonal changes. While hepatic porphyrias are symptomatic primarily in adults, rare homozygous variants of the autosomal dominant hepatic porphyrias

X-linked protoporphyria (XLP) X-linked sideroblastic anemia (XSLA) ALA-dehydratase Deficiency porphyria (ADP) Acute intermittent porphyria (AIP) Congenital erythropoietic porphyria (CEP) Uroporphyrinogen III synthase Uroporphyrinogen III Uroporphyrinogen I — Uroporphyrin I Porphyria cutanea tarda (PCT) Hepatoerythropoietic porphyria (HEP) Uroporphyrinogen decarboxylase Coproporphyrinogen III Hereditary coproporphyria (HCP) Coproporphyrinogen oxidase Protoporphyrinogen IX Variegate porphyria (VP) Protoporphyrinogen oxidase Protoporphyrin IX Erythropoietic protoporphyria (EPP) Ferrochelatase HEME FIGURE 428-1  The human heme biosynthetic pathway indicating in linked boxes the enzyme that, when deficient or overexpressed, causes the respective porphyria. Hepatic porphyrias are shown in yellow boxes and erythropoietic porphyrias in pink boxes. usually manifest clinically prior to puberty. In contrast, the erythro­ poietic porphyrias usually present at birth or in early childhood with cutaneous photosensitivity or, in the case of congenital erythropoietic porphyria (CEP), even in utero as nonimmune hydrops fetalis. Cutane­ ous sensitivity to sunlight results from excitation of excess porphyrins in the skin by long-wave ultraviolet light, leading to cell damage, TABLE 428-1  Human Porphyrias: Major Clinical and Laboratory Features PRINCIPAL SYMPTOMS: NV OR CP+ DEFICIENT ENZYME INHERITANCE PORPHYRIA Hepatic Porphyrias 5-ALA-dehydratasedeficient porphyria (ADP) ALAdehydratase AR NV ~5 Zn-protoporphyrin ALA, coproporphyrin III — Acute intermittent porphyria (AIP) HMB-synthase AD NV ~50 — ALA, PBG, uroporphyrin — Porphyria cutanea tarda (PCT) UROdecarboxylase AD CP ~20 — Uroporphyrin, 7-carboxylate porphyrin Hereditary coproporphyria (HCP) COPRO-oxidase AD NV and CP ~50 — ALA, PBG, coproporphyrin III Coproporphyrin III Variegate porphyria (VP) PROTO-oxidase AD NV and CP ~50 — ALA, PBG, coproporphyrin III Coproporphyrin III, protoporphyrin Erythropoietic Porphyrias Congenital erythropoietic porphyria (CEP) URO-synthase AR CP 1–5 Uroporphyrin I Coproporphyrin I Erythropoietic protoporphyria (EPP) Ferrochelatase AR CP ~20–30 Protoporphyrin — Protoporphyrin X-linked protoporphyria (XLP) ALA-synthase 2 XL CP

100b Protoporphyrin — Protoporphyrin aType I isomers. bIncreased activity due to gain-of-function mutations in ALAS2 exon 11. Abbreviations: AD, autosomal dominant; ALA, 5-aminolevulinic acid; AR, autosomal recessive; COPRO, coproporphyrin; CP, cutaneous photosensitivity; NV, neurovisceral; PBG, porphobilinogen; PROTO, protoporphyrin; URO, uroporphyrin; XL, X-linked.

Succinyl CoA Glycine ALA-synthase Negative feedback δ-Aminolevulinic acid ALA-dehydratase Porphobilinogen Hydroxymethylbilane synthase The Porphyrias CHAPTER 428 Hydroxymethylbilane Non-enzymatic Coproporphyrinogen I — Coproporphyrin I Negative feedback scarring, and disfigurement. Thus, the porphyrias are metabolic disor­ ders in which environmental, physiologic, and genetic factors interact to cause disease. Because many symptoms of the porphyrias are nonspecific, diag­ nosis is often delayed. Laboratory measurement of porphyrin precur­ sors (5′-aminolevulinic acid [ALA] and porphobilinogen [PBG]) in ENZYME ACTIVITY % OF NORMAL INCREASED PORPHYRIN PRECURSORS AND/OR PORPHYRINS ERYTHROCYTES URINE STOOL Isocoproporphyrin Uroporphyrin Ia Coproporphyrin Ia Coproporphyrin I

TABLE 428-2  Human HEME Biosynthetic Enzymes and Genes THREEDIMENSIONAL STRUCTUREc SIZE (KB) EXONSa GENE SYMBOL CHROMOSOMAL LOCATION CDNA (bp) ENZYME ALA-synthase                     Housekeeping ALAS1 3p21.1

M —     Erythroid-specific ALAS2 Xp11.2

M

30 — ALA-dehydratase                     Housekeeping ALAD 9q32

15.9 12 (1A + 2 – 12)

C

Y   Erythroid-specific ALAD 9q32

15.9 12 (1B + 2 – 12)

C —   PART 12 Endocrinology and Metabolism HMB-synthase                     Housekeeping HMBS 11q23.3

15 (1 + 3 – 15)

C

E   Erythroid-specific HMBS 11q23.3

15 (2 – 15)

C

URO-synthase                     Housekeeping UROS 10q26.2

10 (1 + 2B – 10)

C

H   Erythroid-specific UROS 10q26.2

10 (2A + 2B – 10)

C

URO-decarboxylase UROD 1p34.1

C

H COPRO-oxidase CPOX 3q12.1

M

H PROTO-oxidase PPOX 1q23.3

5.5

M

— Ferrochelatase FECH 18q21.31

M

B aNumber of exons and those encoding separate housekeeping and erythroid-specific forms indicated in parentheses. bNumber of known mutations from the Human Gene Mutation Database (www.hgmd.org). cCrystallized from human (H), murine (M), Escherichia coli (E), Bacillus subtilis (B), or yeast (Y) purified enzyme; references in Protein Data Bank (www.rcsb.org). Abbreviations: ALA, 5-aminolevulinic acid; C, cytoplasm; COPRO, coproporphyrin; HMB, hydroxymethylbilane; M, mitochondria; PROTO, protoporphyrin; URO, uroporphyrin. Source: Reproduced with permission from KE Anderson et al: Disorders of heme biosynthesis: X-linked sideroblastic anemia and the porphyrias, in CR Scriver: The Metabolic and Molecular Bases of Inherited Diseases. New York, NY: McGraw-Hill; 2001. the urine or porphyrins in the urine, plasma, erythrocytes, or feces is required to confirm or exclude the various types of porphyria (see below). However, a definite diagnosis requires demonstration of the specific gene defect (Table 428-3). The genes encoding all the heme biosynthetic enzymes have been characterized, permitting identifica­ tion of the mutations causing each porphyria (Table 428-2). Molecular genetic analyses now make it possible to provide precise heterozygote or homozygote identification and prenatal diagnoses in families with known mutations. In addition to recent reviews of the porphyrias, informative and upto-date websites are sponsored by the United Porphyrias Association (www.porphyria.org) and the European Porphyria Network (https:// porphyria.eu/). An extensive list of unsafe and safe drugs for individu­ als with acute porphyrias is provided at the Drug Database for Acute Porphyrias (www.drugs-porphyria.org). GLOBAL CONSIDERATIONS The porphyrias are panethnic metabolic diseases that affect individuals globally. The acute hepatic porphyrias—acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP)—are autosomal dominant disorders. The frequency of AIP, the most common acute hepatic porphyria, is ~1 in 20,000 among Caucasian individuals of Western European ancestry, and it is particularly frequent in Scandinavians, where the frequency in Sweden is ~1 in 10,000. VP is particularly frequent in South Africa, and its high prevalence (>10,000 affected patients) is in part due to a genetic “founder effect.” The auto­ somal recessive acute hepatic porphyria, ALA-dehydratase-deficient porphyria (ADP), is extremely rare, and <20 patients have been identi­ fied worldwide. The erythropoeitic protoporphyrias—CEP, erythropoietic protopor­ phyria (EPP), and X-linked protoporphyria (XLP)—also are panethnic. EPP is likely the most common porphyria, while CEP is very rare with about 200 reported cases worldwide. The frequency of EPP varies globally since most patients have the common low expression FECH allele, which ranges in frequency in different populations. This allele rarely occurs in Africans, is present in ~10% of the Caucasians, and is frequent (~30%) in the Japanese. The autosomal recessive porphyrias, ADP, CEP, EPP, and hepato­ erythropoietic porphyria (HEP), are more frequent in regions with

GENE PROTEIN (aa) SUBCELLULAR LOCATION KNOWN MUTATIONSb high rates of consanguineous marriages. PCT, which is typically sporadic, occurs more frequently in countries in which its predispos­ ing risk factors such as hepatitis C and HIV are more prevalent. The reported prevalence of EPP in the Caucasian population ranges from 1 in ~75,000 to 1 in ~150,000. ■ ■HEME BIOSYNTHESIS Heme biosynthesis involves eight enzymatic steps in the conversion of glycine and succinyl-CoA to heme (Fig. 428-2 and Table 428-2). These eight enzymes are encoded by nine genes, as the first enzyme in the pathway, ALA-synthase, has two genes that encode unique housekeep­ ing (ALAS1) and erythroid-specific (ALAS2) isozymes. The first and last three enzymes in the pathway are located in the mitochondria, whereas the other four are in the cytosol. Heme is required for a variety of hemoproteins such as hemoglobin, myoglobin, respiratory cytochromes, and the cytochrome P450 (CYP) enzymes. Hemoglobin synthesis in erythroid precursor cells accounts for ~85% of daily heme synthesis in humans. Hepatocytes account for most of the rest, primar­ ily for the synthesis of CYPs, which are especially abundant in the liver endoplasmic reticulum, and turn over more rapidly than many other hemoproteins, such as the mitochondrial respiratory cytochromes. As shown in Fig. 428-2, the pathway intermediates are the porphyrin pre­ cursors, ALA and PBG, and porphyrins (mostly in their reduced forms, known as porphyrinogens). At least in humans, these intermediates do not accumulate in significant amounts under normal conditions or have important physiologic functions. The first enzyme, ALA-synthase, catalyzes the condensation of gly­ cine, activated by pyridoxal phosphate and succinyl-coenzyme A, to form ALA. In the liver, this rate-limiting enzyme can be induced by a variety of drugs, steroids, and other chemicals. Distinct nonerythroid (e.g., housekeeping) and erythroid-specific forms of ALA-synthase are encoded by separate genes located on chromosome 3p21.1 (ALAS1) and Xp11.2 (ALAS2), respectively. Defects in the erythroid gene ALAS2 that decrease its activity cause an X-linked sideroblastic anemia (XLSA). Gain-of-function mutations in the last exon (11) of ALAS2 that increase its activity cause an X-linked form of EPP, known as XLP. The second enzyme, ALA-dehydratase, catalyzes the condensa­ tion of two molecules of ALA to form PBG. Hydroxymethylbilane synthase (HMB-synthase; also known as PBG-deaminase) catalyzes

TABLE 428-3  Diagnosis of Acute and Cutaneous Porphyrias SECOND-LINE TESTING IF FIRST-LINE TESTING IS POSITIVE: TO INCLUDE: URINE (U), PLASMA (P), AND FECAL (F) PORPHYRINS; FOR ACUTE PORPHYRIAS, ADD RED BLOOD CELL (RBC) HMB-SYNTHASE; FOR BLISTERING SKIN LESIONS, ADD P AND RBC PORPHYRINS FIRST-LINE TEST: ABNORMALITY POSSIBLE PORPHYRIA SYMPTOMS Neurovisceral Spot U: ↑↑ALA and normal PBG ADP U porphyrins: ↑↑, mostly COPRO III P and F porphyrins: normal or slightly ↑ RBC HMB-synthase: normal Spot U: ↑↑PBG AIP U porphyrins: ↑↑, mostly URO and COPRO P and F porphyrins: normal or slightly ↑ RBC HMB-synthase: usually ↓ “ HCP U porphyrins: ↑↑, mostly COPRO III P porphyrins: normal or slightly ↑ (↑ if skin lesions present) F porphyrins: ↑↑, mostly COPRO III “ VP U porphyrins: ↑↑, mostly COPRO III P porphyrins: ↑↑ (characteristic fluorescence peak at neutral pH) F porphyrins: ↑↑, mostly COPRO and PROTO Blistering skin lesions P: ↑ porphyrins PCT and HEP U porphyrins: ↑↑, mostly URO and heptacarboxylate porphyrin P porphyrins: ↑↑ F porphyrins: ↑↑, including increased isocoproporphyrin RBC porphyrins: ↑↑ zinc PROTO in HEPa “ HCP and VP See HCP and VP above. Also, U ALA and PBG: may be ↑   “ CEP RBC and U porphyrins: ↑↑, mostly URO I and COPRO I F porphyrins: ↑↑; mostly COPRO I Nonblistering photosensitivity P: porphyrins usually ↑ EPP RBC porphyrins: ↓↓, mostly free PROTO U porphyrins: normal F porphyrins: normal or ↓, mostly PROTO P: porphyrins usually ↑ XLP RBC porphyrins: ↑↑, approximately equal free and zinc PROTO U porphyrins: normal F porphyrins: normal or ↑, mostly PROTO aNonspecific increases in zinc protoporphyrins are common in other porphyrias. Abbreviations: ADP, 5-ALA-dehydratase-deficient porphyria; AIP, acute intermittent porphyria; ALA, 5-aminolevulinic acid; CEP, congenital erythropoietic porphyria; COPRO I, coproporphyrin I; COPRO III, coproporphyrin III; EPP, erythropoietic protoporphyria; F, fecal; HCP, hereditary coporphyria; HEP, hepatoerythropoietic porphyria; ISOCOPRO, isocoproporphyrin; P, plasma; PBG, porphobilinogen; PCT, porphyria cutanea tarda; PROTO, protoporphyrin IX; RBC, erythrocytes; U, urine; URO I, uroporphyrin I; URO III, uroporphyrin III; VP, variegate porphyria; XLP, X-linked protoporphyria. Source: Data from KE Anderson et al: Recommendations for the diagnosis and treatment of the acute porphyrias. Ann Intern Med 142:439, 2005. the head-to-tail condensation of four PBG molecules by a series of deaminations to form the linear tetrapyrrole, HMB. Uroporphyrinogen III synthase (URO-synthase) catalyzes the rearrangement and rapid cyclization of HMB to form the asymmetric, physiologic, octacarboxyl­ ate porphyrinogen, uroporphyrinogen (URO’gen) III. The fifth enzyme in the pathway, uroporphyrinogen decarboxylase (URO-decarboxylase), catalyzes the sequential removal of the four car­ boxyl groups from the acetic acid side chains of URO’gen III to form coproporphyrinogen (COPRO’gen) III, a tetracarboxylate porphy­ rinogen. This compound then enters the mitochondrion via a specific transporter, where COPRO-oxidase, the sixth enzyme, catalyzes the decarboxylation of two of the four propionic acid groups to form the two vinyl groups of protoporphyrinogen (PROTO’gen) IX, a decarbox­ ylate porphyrinogen. Next, PROTO-oxidase oxidizes PROTO’gen to protoporphyrin IX by the removal of six hydrogen atoms. The product of the reaction is a porphyrin (oxidized form), in contrast to the pre­ ceding tetrapyrrole intermediates, which are porphyrinogens (reduced forms). Finally, ferrous iron is inserted into protoporphyrin IX to form heme, a reaction catalyzed by the eighth enzyme in the pathway, FECH (also known as heme synthase or protoheme ferrolyase). ■ ■REGULATION OF HEME BIOSYNTHESIS Regulation of heme synthesis differs in the two major heme-forming tissues, the liver and erythron. In the liver, the concentration of “free” heme regulates the synthesis and mitochondrial translocation of the

CONFIRMATORY TEST: ENZYME ASSAY AND/OR MUTATION ANALYSIS Rule out other causes of elevated ALA; ↓↓RBC ALA-dehydratase activity (<10%); ALA-dehydratase mutation analysis HMB-synthase mutation analysis The Porphyrias CHAPTER 428 Measure RBC HMB-synthase: normal activity COPRO-oxidase mutation analysis Measure RBC HMB-synthase: normal activity PROTO-oxidase mutation analysis RBC URO-decarboxylase activity: half-normal in familial PCT (~20% of all PCT cases); substantially deficient in HEP URO-decarboxylase mutation analysis: mutation(s) present in familial PCT (heterozygous) and HEP (homozygous) ↓↓ RBC URO-synthase activity (<15%) URO-synthase mutation analysis FECH mutation analysis ALAS2 mutation analysis housekeeping form of ALA-synthase 1. Heme represses the synthesis of the ALA-synthase 1 messenger RNA (mRNA) and interferes with the transport of the enzyme from the cytosol into mitochondria. Hepatic ALA-synthase 1 is increased by many of the same chemicals that induce the CYP enzymes in the endoplasmic reticulum of the liver. Because most of the heme in the liver is used for the synthesis of CYP enzymes, hepatic ALA-synthase 1 and the CYPs are regulated in a coordinated fashion, and many drugs that induce hepatic ALAsynthase 1 also induce CYP gene expression. The other hepatic heme biosynthetic enzymes are presumably expressed at constant levels, although their relative activities and kinetic properties differ. For example, normal individuals have high activities of ALA-dehydratase but low activities of HMB-synthase, the latter being the second ratelimiting step in the pathway. In the erythron, novel regulatory mechanisms allow for the produc­ tion of the very large amounts of heme needed for hemoglobin synthe­ sis. The response to stimuli for hemoglobin synthesis occurs during cell differentiation, leading to an increase in cell number. In contrast, the erythroid-specific ALA-synthase 2 is expressed at higher levels than the housekeeping enzyme, and erythroid-specific control mechanisms regulate other pathway enzymes as well as iron transport into erythroid cells. Separate erythroid-specific and nonerythroid or “housekeeping” transcripts are known for the first four enzymes in the pathway. As noted above, housekeeping- and erythroid-specific ALA-synthases are encoded by genes on different chromosomes, but for each of the

Cytoplasm Mitochondria SUCCINYL COA COO CH CH2 C CoAS O ALA-synthase COO CH2 CH2 C=O H-C-NH H δ-Aminolevulinic acid B6 CoASH CO2 H H-C-NH2 COO PART 12 Endocrinology and Metabolism Glycine Feedback repression Vi CH3 CH3 Vi N N Fe N N CH3 CH3 Pr Pr Heme 2H Ferrochelatase Fe2+ CH3 Vi Vi CH3 N N H H N N CH3 CH Pr Pr Protoporphyrin IX 6H PROTO-oxidase Vi CH Vi CH3 N N COPRO-oxidase H H H H 2CO2 2H N N CH3 CH Coproporphyrinogen III Protoporphyrinogen IX Pr Pr FIGURE 428-2  The heme biosynthetic pathway showing the eight enzymes and their substrates and products. Four of the enzymes are localized in the mitochondria and four in the cytosol. next three genes in the pathway, both erythroid and nonerythroid transcripts are transcribed by alternative promoters from their single respective genes (Table 428-2). ■ ■CLASSIFICATION OF THE PORPHYRIAS As mentioned above, the porphyrias can be classified as either hepatic or erythropoietic, depending on whether the heme biosynthetic inter­ mediates that accumulate arise initially from the liver or developing erythrocytes, or as acute or cutaneous, based on their clinical mani­ festations. Table 428-1 lists the porphyrias, their principal symptoms, and major biochemical abnormalities. Three of the five hepatic porphyrias—AIP, HCP, and VP—usually present during adult life with acute attacks of neurologic manifestations and elevated levels of one or

COO– COO CH2 CH2 CH2 ALA-dehydratase H NH2 — CH2 N H2O H Porphobilinogen HMBsythase 4NH3 Ac Pr Pr Ac N N H H H H H N N Ac Pr Pr Ac Hydroxymethylbilane H2O UROsynthase Pr Ac Pr Ac N N H H H H N N Ac Ac Pr Pr Uroporphyrinogen III UROdecarboxylase 4H 4CO2 Pr CH3 Pr CH3 N N H H H H N N CH3 CH3 Pr Pr both of the porphyrin precursors, ALA and PBG, and are thus classi­ fied as acute hepatic porphyrias. Patients with ADP have presented in infancy and adolescence and typically have elevated ALA with normal or slightly elevated PBG levels. The fifth hepatic disorder, PCT, pres­ ents with blistering skin lesions. HCP and VP also may have cutaneous manifestations similar to PCT. The erythropoietic porphyrias—CEP, EPP, and XLP—are charac­ terized by elevations of porphyrins in bone marrow and erythrocytes and present with cutaneous photosensitivity. The skin lesions in CEP resemble PCT but are usually much more severe, whereas EPP and XLP cause a more immediate, severe, painful, and nonblistering type of photosensitivity. EPP is the most common porphyria to cause symptoms before puberty. About 20% of EPP patients develop minor

abnormalities of liver function, with up to ~5% developing hepatic complications that can lead to liver failure requiring liver transplanta­ tion. XLP has a clinical presentation similar to EPP causing photosen­ sitivity and liver disease. ■ ■DIAGNOSIS OF PORPHYRIA A few specific and sensitive first-line laboratory tests should be used whenever symptoms or signs suggest the diagnosis of porphyria (Table 428-3). If a first-line test is significantly abnormal, more com­ prehensive testing should follow to establish the type of porphyria, including the specific causative gene mutation. Acute Hepatic Porphyrias  An acute hepatic porphyria should be suspected in patients with neurovisceral symptoms after puberty. Symptoms include acute abdominal pain, nausea, vomiting, tachy­ cardia, hypertension, and motor neuropathy. As these symptoms are common, other causes should be ruled out. The diagnosis is made by measuring urinary porphyrin precursors (ALA and PBG) in a spot sample of urine (Fig. 428-2). Urinary PBG is always increased during acute attacks of AIP, HCP, and VP and is not substantially increased in any other medical condition. Therefore, this measurement is both sensitive and specific. Results from spot (single-void) urine specimens are highly informative because very substantial increases in PBG are expected during acute attacks of porphyria. A 24-h collection is unnec­ essary. The same spot urine specimen should be saved for quantitative determination of ALA, PBG, and creatinine, in order to confirm the qualitative PBG result and also to detect patients with ADP. Urinary porphyrins may remain increased longer than porphyrin precursors in HCP and VP. Therefore, it is useful to measure total urinary por­ phyrins in the same sample, keeping in mind that urinary porphyrin increases are often nonspecific. Measurement of urinary porphyrins alone should be avoided for screening, because these may be increased in disorders other than porphyrias, such as chronic liver disease, and misdiagnoses of porphyria can result from minimal increases in uri­ nary porphyrins that have no diagnostic significance. Measurement of erythrocyte HMB-synthase is not useful as a first-line test. Moreover, the enzyme activity is not decreased in all AIP patients, a borderline low normal value is not diagnostic, and the enzyme is not deficient in other acute porphyrias. More extensive testing is justified when an initial test is positive. A substantial increase in PBG may be due to AIP, HCP, or VP. These acute porphyrias can be distinguished by measuring urinary porphy­ rins (using the same spot urine sample), fecal porphyrins, and plasma porphyrins. Assays for COPRO-oxidase or PROTO-oxidase are not available for clinical testing. More specifically, mutation analysis by sequencing the genes encoding HMB-synthase, COPRO-oxidase, and PROTO-oxidase will detect almost all disease-causing mutations and is diagnostic even when the levels of urinary ALA and PBG have returned to normal or near normal. Cutaneous Porphyrias  Blistering skin lesions due to porphyria are virtually always accompanied by increases in total plasma por­ phyrins. A fluorometric method is preferred, because the plasma porphyrins in VP are mostly covalently linked to plasma proteins and may be less readily detected by high-performance liquid chromatog­ raphy (HPLC). The normal range for plasma porphyrins is somewhat increased in patients with end-stage renal disease. Although a total plasma porphyrin determination will usually detect EPP and XLP, an erythrocyte protoporphyrin determination is more sensitive. Increases in erythrocyte protoporphyrin occur in many other conditions. Therefore, the diagnosis of EPP must be confirmed by showing a predominant increase in free protoporphyrin rather than zinc protoporphyrin. In XLP, both free and zinc protoporphyrin are markedly increased. Interpretation of laboratory reports can be difficult, because the term free erythrocyte protoporphyrin sometimes actually represents zinc protoporphyrin. The various porphyrias that cause blistering skin lesions can be differ­ entiated by measuring porphyrins in urine, feces, and plasma. The por­ phyrias should be confirmed by genetic testing and the demonstration of the causative pathogenic variant. It is often difficult to diagnose or “rule

out” porphyria in patients who have had suggestive symptoms months or years in the past and in relatives of patients with acute porphyrias, because porphyrin precursors and porphyrins may be normal. In those situations, detection of the specific gene mutation in the index case can make the diagnosis and facilitate the diagnosis and genetic counseling of at-risk relatives. With the increased access and accuracy of genetic testing, this often precedes secondary biochemical testing in clinical practice. Consultation with a specialist laboratory and physician will assist in selecting the heme biosynthetic gene or genes to be sequenced.

THE HEPATIC PORPHYRIAS Markedly elevated plasma and urinary concentrations of the porphyrin precursors, ALA and/or PBG, which originate from the liver, are espe­ cially evident during attacks of neurologic manifestations of the four acute porphyrias—ADP, AIP, HCP, and VP. In PCT, excess porphyrins also accumulate initially in the liver and cause chronic blistering of sun-exposed areas of the skin. The Porphyrias CHAPTER 428 ■ ■ALA-DEHYDRATASE-DEFICIENT PORPHYRIA ADP is a rare, autosomal recessive, acute hepatic porphyria caused by a severe deficiency of ALA-dehydratase activity. To date, there are only a dozen documented cases, some in children or young adults, in which specific gene mutations have been identified. These affected homozy­ gotes had <10% of normal ALA-dehydratase activity in erythrocytes, but their clinically asymptomatic parents and heterozygous relatives had about half-normal levels of activity and did not excrete increased levels of ALA. The frequency of ADP is unknown, but the frequency of heterozygous individuals with <50% normal ALA-dehydratase activity was ~2% in a screening study in Sweden. Because there are multiple causes for deficient ALA-dehydratase activity, it is important to con­ firm the diagnosis of ADP by mutation analysis. Clinical Features  The clinical presentation depends on the amount of residual ALA-dehydratase activity. Four of the documented patients were male adolescents with symptoms resembling those of AIP, including abdominal pain and neuropathy. One patient was an infant with more severe disease, including failure to thrive beginning at birth. The earlier age of onset and more severe manifestations in this patient reflect a more significant deficiency of ALA-dehydratase activity. Another patient developed an acute motor polyneuropathy at age 63 that was associated with a myeloproliferative disorder. He was heterozygous for an δ-aminolevulinic acid dehydratase (ALAD) mutation that presumably was present in erythroblasts that underwent clonal expansion due to the bone marrow malignancy. Diagnosis  All patients had significantly elevated levels of plasma and urinary ALA and urinary coproporphyrin (COPRO) III; ALAD activities in erythrocytes were <10% of normal. Hereditary tyrosinemia type 1 (fumarylacetoacetase deficiency) and lead intoxica­ tion should be considered in the differential diagnosis because either succinylacetone (which accumulates in hereditary tyrosinemia and is structurally similar to ALA) or lead can inhibit ALA-dehydratase, increase urinary excretion of ALA and COPRO III, and cause manifes­ tations that resemble those of the acute porphyrias. Heterozygotes are clinically asymptomatic and do not excrete increased levels of ALA but can be detected by demonstration of intermediate levels of erythrocyte ALA-dehydratase activity or a specific mutation in the ALAD gene. To date, molecular studies of ADP patients have identified 12 pathogenic mutations, including missense mutations, splice-site mutations, and a two-base deletion in the ALAD gene (Human Gene Mutation Data­ base; www.hgmd.org). The parents in each case were not consanguine­ ous, and the index cases had inherited a different ALAD mutation from each parent. Prenatal diagnosis of this disorder is possible by determi­ nation of ALA-dehydratase activity and/or gene mutations in cultured chorionic villi or amniocytes. Treatment  The treatment of ADP acute attacks is similar to that of AIP (see below). The severely affected infant referred to above was sup­ ported by hyperalimentation and periodic blood transfusions but did not respond to intravenous hemin and died after liver transplantation.

■ ■ACUTE INTERMITTENT PORPHYRIA This hepatic porphyria is an autosomal dominant condition resulting from the half-normal level of HMB-synthase activity. The disease is widespread but is especially common in Scandinavia and Great Britain. Clinical expression is highly variable, and activation of the disease is often related to environmental or hormonal factors, such as drugs, diet, and steroid hormones. Attacks can be prevented by avoiding known precipitating factors. Rare homozygous dominant AIP also has been described in children (see below).

Clinical Features  Induction and increased expression of the ratelimiting hepatic gene ALAS1 in heterozygotes who have half-normal HMB-synthase activity is thought to underlie the acute attacks in AIP. The disorder remains latent (or asymptomatic) in the great majority of those who are heterozygous for pathogenic HMBS mutations, and this is almost always the case prior to puberty. In patients with no history of acute symptoms, porphyrin precursor excretion is usually normal, suggesting that half-normal hepatic HMB-synthase activity is sufficient and that hepatic ALA-synthase activity is not increased. However, under conditions where heme synthesis is increased in the liver, half-normal HMB-synthase activity may become limiting, and ALA, PBG, and other heme pathway intermediates may accumulate and be excreted in the urine. Common precipitating factors include endogenous and exogenous steroids, porphyrinogenic drugs, alcohol ingestion, and low-calorie diets, usually instituted for weight loss. PART 12 Endocrinology and Metabolism The fact that AIP is almost always latent before puberty suggests that adult levels of steroid hormones are important for clinical expression. Symptoms are more common in women, suggesting a role for estrogens or progestins. Premenstrual attacks are probably due to increasing endogenous progesterone during the luteal phase of the menstrual cycle. Acute porphyrias are sometimes exacerbated by exogenous steroids, including oral contraceptive preparations containing proges­ tins. Surprisingly, pregnancy is usually well tolerated, suggesting that beneficial metabolic changes may ameliorate the effects of high levels of progesterone. Extensive lists of unsafe and safe drugs are available on websites sponsored by the United Porphyria Association (www

.porphyria.org) and the European Porphyria Network (https://por­ phyria.eu/), and at the Drug Database for Acute Porphyrias website (www.drugs-porphyria.org). Reduced intake of calories and carbohy­ drate, as may occur with illness or attempts to lose weight, can also increase porphyrin precursor excretion and induce attacks of porphyria. Studies in a knockout AIP mouse model indicate that the hepatic ALAS1 gene is regulated, in part, by the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). Hepatic PGC-1α is induced by fasting, which in turn activates ALAS1 transcription, resulting in increased heme biosynthesis. This finding suggests an important link between nutritional status and the attacks in acute porphyrias. Attacks also can be provoked by infections, surgery, and ethanol. Because the neurovisceral symptoms rarely occur before puberty and are often nonspecific, a high index of suspicion is required to make the diagnosis. The disease can be disabling but is rarely fatal. Abdomi­ nal pain, the most common symptom, is poorly localized but may be associated with cramping, ileus, abdominal distention, and decreased bowel sounds. However, increased bowel sounds and diarrhea may occur. Abdominal tenderness, fever, and leukocytosis are usually absent or mild because the symptoms are neurologic rather than inflammatory. Nausea; vomiting; constipation; tachycardia; hyperten­ sion; mental symptoms; pain in the limbs, head, neck, or chest; muscle weakness; sensory loss; dysuria; and urinary retention are characteris­ tic. Tachycardia, hypertension, restlessness, tremors, and excess sweat­ ing are due to sympathetic overactivity. The peripheral neuropathy is due to axonal degeneration (rather than demyelinization) and primarily affects motor neurons. Significant neuropathy does not occur with all acute attacks; abdominal symptoms are usually more prominent. Motor neuropathy affects the proximal muscles initially, more often in the shoulders and arms. The course and degree of involvement are variable and sometimes may be focal and involve cranial nerves. Deep tendon reflexes initially may be nor­ mal or hyperactive but become decreased or absent as the neuropathy

advances. Sensory changes such as paresthesia and loss of sensation are less prominent. Progression to respiratory and bulbar paralysis and death occurs especially when the diagnosis and treatment are delayed. Sudden death may result from sympathetic overactivity and cardiac arrhythmia. Mental symptoms such as anxiety, insomnia, depression, disorienta­ tion, hallucinations, and paranoia can occur in acute attacks. Seizures can be due to neurologic effects or to hyponatremia. Treatment of seizures is difficult because most antiseizure drugs can exacerbate AIP (clon­ azepam may be safer than phenytoin or barbiturates). Hyponatremia results from hypothalamic involvement and inappropriate vasopressin secretion or from electrolyte depletion due to vomiting, diarrhea, poor intake, or excess renal sodium loss. When an attack resolves, abdominal pain may disappear within hours, and paresis begins to improve within days and may continue to improve over several years. Homozygous dominant AIP (HD-AIP) is a rare form of AIP in which patients inherit HMBS mutations from each of their heterozy­ gous parents and, therefore, have very low (<2%) enzyme activity. The disease has been described in a Dutch girl, two young British siblings, and a Spanish boy. In these homozygous affected patients, the disease presented in infancy with failure to thrive, developmental delay, bilat­ eral cataracts, and/or hepatosplenomegaly. Urinary ALA and PBG concentrations were markedly elevated. All of these patients’ HMBS mutations (R167W, R167Q, and R172Q) were in exon 10 within five bases of each other. Studies of the brain magnetic resonance images (MRIs) of children with homozygous AIP have suggested damage primarily in white matter that was myelinated postnatally, while tracks that myelinated prenatally were normal. Most children with homozygous AIP die at an early age. Recently, later-onset HD-AIP was described in an adult with leukoencephalopathy. Diagnosis  ALA and PBG levels are substantially increased in plasma and urine, especially during acute attacks. For example, urinary PBG excretion during an attack is usually 50–200 mg/24 h (220–880 μmol/

24 h) (normal, 0–4 mg/24 h [0–18 μmol/24 h]), and urinary ALA excre­ tion is 20–100 mg/24 h (150–760 μmol/24 h) (normal, 1–7 mg/24 h

[8–53 μmol/24 h]). Because levels often remain high after symptoms resolve, the diagnosis of an acute attack in a patient with biochemically proven AIP is based primarily on clinical features. Excretion of ALA and PBG decreases over a few days after intravenous hemin adminis­ tration or in a day after subcutaneous givosiran (see below). A normal urinary PBG level before hemin effectively excludes AIP as a cause for current symptoms. Fecal porphyrins are usually normal or minimally increased in AIP, in contrast to HCP and VP. Most AIP heterozygotes with no history of symptoms have normal urinary excretion of ALA and PBG and are classified as “latent” or “asymptomatic heterozy­ gotes.” Patients can also have high levels of urinary PBG and ALA with no clinical symptoms. These patients may have a previous history of an acute attack and are classified as asymptomatic high excretors (ASHE) or chronic high excretors (CHE). Therefore, the detection of the family’s HMBS mutation will diagnose heterozygous asymptomatic family members. A urinary ALA and PBG will diagnosis CHE patients who may have a higher risk of an attack if they experience a precipitat­ ing factor such as administration of a porphyrinogenic drug. Patients with HMBS mutations in the initiation of translation codon in exon 1 and in the intron 15′-splice donor site have normal enzyme levels in erythrocytes and deficient activity only in nonerythroid tis­ sues. This occurs because the erythroid and housekeeping forms of HMB-synthase are encoded by a single gene, which has two promot­ ers. Thus, the enzyme assay may not be diagnostic, and genetic testing should be used to confirm the diagnosis. More than 550 HMBS mutations have been identified in AIP, including missense, nonsense, AND splicing lesions, insertions, and deletions, with most mutations found in only one or a few families (Human Gene Mutation Database, www.hgmd.org). The prenatal diag­ nosis of a fetus at risk can be made by analysis of the familial mutation in cultured amniotic cells or chorionic villi. However, this is seldom done because the prognosis of individuals with HMBS mutations is generally favorable.

TREATMENT Acute Intermittent Porphyria During acute attacks, narcotic analgesics may be required for abdominal pain, and phenothiazines are useful for nausea, vom­ iting, anxiety, and restlessness. Chloral hydrate can be given for insomnia, and benzodiazepines are probably safe in low doses if a minor tranquilizer is required. Carbohydrate loading, usually with intravenous glucose (at least 300 g daily), may be effective in milder acute attacks of porphyria (without paresis, hyponatremia, etc.) if hemin or givosiran (see below) is not available. Intravenous hemin was approved by the U.S. Food and Drug Administration (FDA) in 1984 to treat acute attacks and has been used effectively as a firstline therapy for acute attacks. The standard regimen is 3–4 mg/kg per d of heme, in the form of lyophilized hematin (Panhematin, Recordati Rare Diseases), heme albumin (hematin reconstituted with human albumin), or heme arginate (Orphan Europe), infused daily for 4 days or longer to reduce the pain. Heme arginate and heme albumin are chemically stable and are less likely than hematin to produce phlebitis or an anticoagulant effect. Recovery depends on the degree of neuronal damage and usually occurs in days, if therapy is started early. Recovery from severe motor neuropathy may require months or years. Identification and avoidance of incit­ ing factors can hasten recovery from an attack and prevent future attacks. Inciting factors are usually multiple, and removal of one or more hastens recovery and helps prevent future attacks. Frequent attacks that occur during the luteal phase of the menstrual cycle may be prevented with a gonadotropin-releasing hormone ana­ logue, which prevents ovulation and progesterone production, or by prophylactic hematin or givosiran administration. In 2019, a hepatocyte-targeted RNA interference (RNAi) therapy, givosiran (Givlarri, Alnylam Pharmaceuticals), was approved by the FDA and the European Medicines Agency (EMA) for the treatment of the acute hepatic porphyrias. Givosiran, a monthly subcutane­ ous injection of 2.5 mg/kg, is designed to silence the expression of hepatic ALAS1 mRNA and was initially shown in clinical trials to markedly reduce ALA and PBG levels in CHE patients and in patients with recurrent attacks. In a phase 3 trial in acute hepatic porphyria patients with recurrent attacks, the RNAi therapy sig­ nificantly reduced the frequency of acute attacks, decreased hemin utilization, and improved daily pain scores. The long-term risk of hypertension and chronic renal disease is increased in AIP; a number of patients have undergone suc­ cessful renal transplantation. Studies have shown that up to 59% of symptomatic AIP patients will develop chronic kidney disease. The PEPT2 receptor polymorphic genotype affects the severity and prognosis of porphyria-associated kidney disease with the high affinity polymorphic PEPT2 *1 allele and the PEPT2 genotypes 11 and, to a lesser degree, 12 associated with decreasing kidney function. Chronic, low-grade abnormalities in liver function tests are common, and the risk of hepatocellular carcinoma is increased. Hepatic imaging is recommended at least every 6 months for early detection of these tumors. Other long-term complications include neuropathy, fatigue, chronic pain, nausea, depression, and/ or anxiety. Orthotopic liver transplantation (OLT) has been effective in patients with severe, disabling, intractable attacks that are refrac­ tory to hemin therapy. Reports from both the United Kingdom and the United States show a marked improvement with no subsequent attacks, an improvement in the neuropathic manifestations, and normalization of the urinary PBG and ALA levels after liver trans­ plantation. OLT is associated with morbidity and mortality and should be considered a treatment of last resort in these patients. In addition, patients who already have advanced neuropathy are considered poor risks for transplantation. Of note, the effectiveness of givosiran in such patients has not been described. Some patients with both recurrent attacks and end-stage renal disease have ben­ efitted from combined liver and kidney transplantation.

Liver-directed gene therapy has proven successful in the pre­ vention of drug-induced biochemical attacks in a murine model of human AIP, and clinical trials of adeno-associated virus vector (AAV)-HMBS gene transfer were carried out over a decade ago. Although the therapy was safe, there was essentially no biochemi­ cal evidence of its effectiveness, nor did it prevent recurrent attacks in the treated patients. Recent advances have led to FDA-approved gene-editing/gene therapies for genetic disorders and may lead to future treatments and/or cures for the acute hepatic and erythro­ poietic porphyrias.

The Porphyrias CHAPTER 428 ■ ■PORPHYRIA CUTANEA TARDA PCT, the most common of the porphyrias, can be either sporadic (type 1) or familial (type 2) and can also develop after exposure to halogenated aromatic hydrocarbons. Hepatic URO-decarboxylase is deficient in all types of PCT, and for clinical symptoms to manifest, this enzyme deficiency must be substantial (~20% of normal activity or less). Its deficiency is currently attributed to generation of an URO-decarbox­ ylase inhibitor in the liver, which forms a uroporphomethene in the presence of iron and under conditions of oxidative stress. The majority of PCT patients (~80%) have no UROD mutations and are said to have sporadic (type 1) disease. PCT patients heterozygous for UROD muta­ tions have the familial (type 2) PCT. In these patients, inheritance of a UROD mutation from one parent results in half-normal enzymatic activity in liver and all other tissues, which is a significant predispos­ ing factor, but is insufficient by itself to cause symptomatic PCT. As discussed below, other genetic and environmental factors contribute to susceptibility for both types of PCT. Because penetrance of the genetic trait is low, many patients with familial (type 2) PCT have no family history of the disease. HEP is an autosomal recessive form of porphyria due to the inheritance of two pathogenic UROD mutations resulting in the marked systemic deficiency of URO-decarboxylase activity with clinical symptoms in childhood. Clinical Features  Blistering skin lesions that appear most commonly on the backs of the hands are the major clinical feature (Fig. 428-3). These rupture and crust over, leaving areas of atrophy and scarring. Lesions may also occur on the forearms, face, legs, and feet. Skin friability and small white papules termed milia are common, especially on the backs of the hands and fingers. Hypertrichosis and hyperpigmentation, especially of the face, are especially troublesome in women. Occasion­ ally, the skin over sun-exposed areas becomes severely thickened, with scarring and calcification that resembles systemic sclerosis. Neurologic features are absent. A number of susceptibility factors, in addition to inherited UROD mutations in type 2 PCT, are recognized clinically and can affect management. These include hepatitis C, HIV, excess alcohol, elevated FIGURE 428-3  Typical cutaneous lesions in a patient with porphyria cutanea tarda. Chronic, crusted lesions resulting from blistering due to photosensitivity on the dorsum of the hand of a patient with porphyria cutanea tarda. (Used with permission from Dr. Karl E. Anderson.)

iron levels, and estrogens. The importance of excess hepatic iron as a precipitating factor is underscored by the finding that the incidence of the common hemochromatosis-causing mutations, hemochroma­ tosis gene (HFE) mutations p.C282Y and p.H63D, are increased in patients with types 1 and 2 PCT (Chap. 426). Excess alcohol is a longrecognized contributor, as is estrogen use in women. HIV is probably an independent but less common risk factor that, like hepatitis C, does not cause PCT in isolation. Multiple susceptibility factors that appear to act synergistically can be identified in individual patients. PCT patients characteristically have chronic liver disease and some­ times cirrhosis and are at risk for hepatocellular carcinoma. Various chemicals can also induce PCT; an epidemic of PCT occurred in eastern Turkey in the 1950s as a consequence of wheat contami­ nated with the fungicide hexachlorobenzene. PCT also occurs after exposure to other chemicals, including di- and trichlorophenols and 2,3,7,8-tetrachlorodibenzo-(p)-dioxin (TCDD, dioxin).

PART 12 Endocrinology and Metabolism Diagnosis  Porphyrins are increased in the liver, plasma, urine, and stool. The urinary ALA level may be slightly increased, but the PBG level is normal. Urinary porphyrins consist mostly of uro­ porphyrins and heptacarboxylate porphyrin, with lesser amounts of coproporphyrin and hexa- and pentacarboxylate porphyrins. Plasma porphyrins are also increased, and fluorometric scanning of diluted plasma at neutral pH can rapidly distinguish VP and PCT (Table 428-3). Isocoproporphyrins, which are increased in feces and sometimes in plasma and urine, are diagnostic for hepatic UROdecarboxylase deficiency. Type 2 PCT and HEP can be distinguished from type 1 by finding decreased URO-decarboxylase in erythrocytes. URO-decarboxylase activity in liver, erythrocytes, and cultured skin fibroblasts in type 2 PCT is ~50% of normal in affected individuals and in asymptomatic heterozygous family members. In HEP, the URO-decarboxylase activity is markedly deficient, with typical levels of 3–10% of normal. Over 150 mutations have been identified in the UROD gene (Human Gene Muta­ tion Database; www.hgmd.org). Of the mutations listed in the database, ~65% are missense or nonsense, and ~8% are splice-site mutations. Many UROD mutations have been identified in only one or two families. TREATMENT Porphyria Cutanea Tarda Alcohol, estrogens, iron supplements, and, if possible, any drugs that may exacerbate the disease should be discontinued, but this step does not always lead to improvement. A complete response can almost always be achieved by the standard therapy, repeated phlebotomy, to reduce hepatic iron. A unit (450 mL) of blood can be removed every 1–2 weeks. The aim is to gradually reduce excess hepatic iron until the serum ferritin level reaches the lower limits of normal. Because iron overload is not marked in most cases, remission may occur after only five or six phlebotomies; however, PCT patients with hemochromatosis may require more treatments to bring their iron levels down to the normal range. To document improvement in PCT, it is most convenient to follow the total plasma porphyrin concentration, which becomes normal some­ time after the target ferritin level is reached. Hemoglobin levels or hematocrits and serum ferritin should be followed closely to prevent development of iron deficiency and anemia. After remis­ sion, continued phlebotomy may not be needed. Plasma porphyrin levels are followed at 6- to 12-month intervals for early detection of recurrences, which are treated by additional phlebotomy. An alternative when phlebotomy is contraindicated or poorly tolerated is a low-dose regimen of chloroquine or hydroxychlo­ roquine, both of which complex with the excess porphyrins and promote their excretion. Small doses (e.g., 125 mg chloroquine phosphate twice weekly) should be given, because standard doses can induce transient, sometimes marked increases in photosensi­ tivity and hepatocellular damage. Studies indicate that low-dose hydroxychloroquine is as safe and effective as phlebotomy in PCT.

Hepatic imaging can diagnose or exclude complicating hepatocel­ lular carcinoma. Treatment of PCT in patients with end-stage renal disease is facilitated by administration of erythropoietin. Because hepatitis C virus (HCV) is a common precipitating factor causing PCT, the recent development of oral direct-acting antivirals for HCV has proven effective as a first primary treatment in HCV-infected PCT patients. ■ ■HEREDITARY COPROPORPHYRIA HCP is an autosomal dominant hepatic porphyria that results from the half-normal activity of COPRO-oxidase. The disease presents with acute attacks, as in AIP. Cutaneous photosensitivity also may occur, but much less commonly than in VP. HCP patients may have acute attacks and cutaneous photosensitivity together or separately. HCP is less common than AIP and VP. Homozygous dominant HCP and har­ deroporphyria, a biochemically distinguishable variant of HCP, present with clinical symptoms in children (see below). Clinical Features  HCP is influenced by the same factors that cause attacks in AIP. The disease is latent before puberty, and symptoms, which are virtually identical to those of AIP, are more common in women. HCP is generally less severe than AIP. Blistering skin lesions are identical to PCT and VP and begin in childhood in rare homozygous cases. Diagnosis  COPRO III is markedly increased in the urine and feces in symptomatic patients and often persists, especially in feces, when there are no symptoms. Urinary ALA and PBG levels are increased (but less than in AIP) during acute attacks but may revert to normal more quickly than in AIP when symptoms resolve. Plasma porphyrins are usually normal or only slightly increased, but they may be higher in cases with skin lesions. The diagnosis of HCP is readily confirmed by increased fecal porphyrins consisting almost entirely of COPRO III, which distinguishes it from other porphyrias. Although the diagnosis can be confirmed by measuring COPROoxidase activity, the assays for this mitochondrial enzyme are not avail­ able and require cells other than erythrocytes. To date, >95 mutations have been identified in the CPOX gene, ~70% of which are missense or nonsense (Human Gene Mutation Database; www.hgmd.org). Detec­ tion of a CPOX mutation in a symptomatic individual permits the identification of asymptomatic family members. TREATMENT Hereditary Coproporphyria Neurologic symptoms are treated as in AIP (see above). Phlebotomy and chloroquine are not effective for the cutaneous lesions. ■ ■VARIEGATE PORPHYRIA VP is an autosomal dominant hepatic porphyria that results from the deficient activity of PROTO-oxidase, the seventh enzyme in the heme biosynthetic pathway, and can present with neurologic symptoms, photosensitivity, or both. VP is particularly common in South Africa, where 3 of every 1000 whites have the disorder. Most are descendants of a couple who emigrated from the Netherlands to South Africa in 1688. In other countries, VP is less common than AIP. Rare cases of homozygous dominant VP, presenting in childhood with cutaneous symptoms, also have been reported. Clinical Features  VP can present with skin photosensitivity, acute neurovisceral crises, or both. In two large studies of VP patients, ~60% had only skin lesions, 20% had only acute attacks, and ~20% had both. Acute attacks are identical to those in AIP and are precipitated by the same factors as AIP (see above). Blistering skin manifestations are similar to those in PCT but are more difficult to treat and usually are of longer duration. Homozygous VP is associated with photosensitiv­ ity, neurologic symptoms, and developmental disturbances, including growth retardation, in infancy or childhood; all cases had increased

erythrocyte levels of zinc protoporphyrin, a characteristic finding in all homozygous porphyrias so far described. Diagnosis  Urinary ALA and PBG levels are increased during acute attacks but may return to normal more quickly than in AIP. Increases in fecal protoporphyrin and COPRO III and in urinary COPRO III are more persistent. Plasma porphyrin levels also are increased, particu­ larly when there are cutaneous lesions. VP can be distinguished rapidly from all other porphyrias by examining the fluorescence emission spectrum of porphyrins in plasma since VP has a unique fluorescence peak at neutral pH. Assays of PROTO-oxidase activity in cultured fibroblasts or lym­ phocytes are not widely available. Over 215 mutations have been identified in the PPOX gene from unrelated VP patients (Human Gene Mutation Database; www.hgmd.org). The missense mutation encoding p.R59W is the common mutation in most South Africans with VP of Dutch descent. Five missense mutations were common in English and French VP patients; however, most mutations have been found in only one or a few families. TREATMENT Variegate Porphyria Acute attacks are treated as in AIP, and hemin should be started early in most cases. Givosiran has proven effective in clinical tri­ als for patients with recurrent attacks. Other than avoiding sun exposure, there are few effective measures for treating the skin lesions. β-Carotene, phlebotomy, and chloroquine are not helpful. THE ERYTHROPOIETIC PORPHYRIAS In the erythropoietic porphyrias, excess porphyrins from bone marrow erythrocyte precursors are transported via the plasma to the skin and lead to cutaneous photosensitivity. ■ ■X-LINKED SIDEROBLASTIC ANEMIA XLSA results from the deficient activity of the erythroid form of ALAsynthase (ALA-synthase 2) and is associated with ineffective erythro­ poiesis, weakness, and pallor. Clinical Features  Typically, males with XLSA develop refractory hemolytic anemia, pallor, and weakness during infancy. They have secondary hypersplenism, become iron overloaded, and can develop hemosiderosis. The severity depends on the level of residual erythroid ALA-synthase activity and on the responsiveness of the specific muta­ tion to pyridoxal 5′-phosphate supplementation (see below). Peripheral blood smears reveal a hypochromic, microcytic anemia with striking anisocytosis, poikilocytosis, and polychromasia; the leukocytes and platelets appear normal. Hemoglobin content is reduced, and the mean corpuscular volume and mean corpuscular hemoglobin concentra­ tion are decreased. Patients with milder, later-onset disease have been reported recently. Diagnosis  Bone marrow examination reveals hypercellularity with a left shift and megaloblastic erythropoiesis with an abnormal matura­ tion. A variety of Prussian blue–staining sideroblasts are observed. Levels of urinary porphyrin precursors and of both urinary and fecal porphyrins are normal. The activity of erythroid ALA-synthase 2 is decreased in bone marrow, but this enzyme is difficult to measure in the presence of the normal ALA-synthase 1 housekeeping enzyme. Definitive diagnosis requires the demonstration of loss-of-function mutations in the erythroid ALAS2 gene, of which >120 have been identified. Treatment  The severe anemia may respond to pyridoxine supple­ mentation. This cofactor is essential for ALA-synthase activity, and mutations in the pyridoxine binding site of the enzyme have been found in several responsive patients. Cofactor supplementation may make it possible to eliminate or reduce the frequency of transfusions.

Unresponsive patients may be transfusion dependent and require che­ lation therapy.

■ ■CONGENITAL ERYTHROPOIETIC PORPHYRIA CEP, also known as Günther’s disease, is an autosomal recessive dis­ order. It is due to the markedly deficient, but not absent, activity of URO-synthase and the resultant accumulation of URO I and COPRO I isomers. CEP is associated with hemolytic anemia and cutaneous lesions. Clinical Features  Severe cutaneous photosensitivity typically begins from birth. The skin over light-exposed areas is friable, and bullae and vesicles are prone to rupture and infection. Skin thickening, focal hypo- and hyperpigmentation, and hypertrichosis of the face and extremities are characteristic. Secondary infection of the cutaneous lesions can lead to disfigurement of the face and hands. Porphyrins are deposited in teeth and in bones. As a result, the teeth are brownish and fluoresce on exposure to long-wave ultraviolet light. Hemolysis is due to the marked increase in erythrocyte porphyrins and leads to spleno­ megaly. Adults with a milder later-onset form of the disease also have been described, including late-onset patients with myelodysplasias. The Porphyrias CHAPTER 428 Diagnosis  URO and COPRO (mostly type I isomers) accumulate in the bone marrow, erythrocytes, plasma, urine, and feces. The pre­ dominant porphyrin in feces is COPRO I. The diagnosis of CEP can be confirmed by demonstration of markedly deficient URO-synthase activity and/or by the identification of specific mutations in the UROS gene. The disease can be detected in utero by measuring porphyrins in amniotic fluid and URO-synthase activity in cultured amniotic cells or chorionic villi or by the detection of the family’s specific gene mutations. Molecular analyses of the mutant alleles from unrelated patients have revealed the presence of >65 mutations in the UROS gene, including six in the erythroid-specific promoter of the UROS gene. Genotype/phenotype correlations can predict the severity of the disease. The CEP phenotype may be increased by the presence of exon 10 variants in the erythroid-specific ALA-synthase 2, mutations that typically cause XLP. One mutation (p.Arg216Trp) in GATA1, encod­ ing the X-linked erythroid-specific transcription factor GATA binding protein 1 (GATA1), has been identified in two individuals with CEP who both also had other hematologic abnormalities. TREATMENT Congenital Erythropoietic Porphyria Transfusion-dependent patients require periodic transfusions for anemia. Chronic transfusions of sufficient fresh packed erythro­ cytes to suppress erythropoiesis are effective in reducing porphyrin production but result in iron overload. Oral iron chelation is recom­ mended. Splenectomy may reduce hemolysis and decrease transfu­ sion requirements. Protection from sunlight and from minor skin trauma is essential to avoid/minimize cutaneous blistering. Com­ plicating bacterial infections should be treated promptly. Recently, non-transfusion-dependent patients have been treated by periodic phlebotomies to decrease iron levels, thereby decreasing erythro­ poiesis and porphyrin accumulation. This approach has not been evaluated in clinical trials to date. Bone marrow and hematopoi­ etic stem cell transplantation has proven curative in transfusiondependent children, providing the rationale for future stem cell gene therapy. ■ ■ERYTHROPOIETIC PROTOPORPHYRIA EPP is an autosomal recessive disorder resulting from the deficient activity of FECH, the last enzyme in the heme biosynthetic pathway. As noted above, EPP is likely the most common porphyria with onset typically in early childhood. EPP patients have FECH activities as low as 15–30% of normal in lymphocytes and cultured fibroblasts. Proto­ porphyrin IX accumulated in bone marrow reticulocytes and circulat­ ing erythrocytes is released into the plasma and then is taken up in the

liver where it is excreted in the bile and feces. Plasma protoporphyrin IX taken up by the vascular cells in the skin is photoactivated on exposure to sunlight causing phototoxic cellular damage and excru­ ciatingly painful nonblistering phototoxicity. In most symptomatic patients (>95%) with this disorder, a deleterious mutation in one FECH allele was inherited with the relatively common (~10% of Caucasians) intronic 3 (IVS3) variant (IVS3–48T>C) on the other allele; together, they result in the low expression of the normal enzyme. In ~2% of EPP families, two FECH deleterious mutations have been found.

XLP is a less common condition with the same phenotype in affected males, including increased erythrocyte protoporphyrin IX levels resulting from gain-of-function mutations in the last exon of the erythroid-specific form of 5-aminolevulinate-synthase 2 (ALAS2). These mutations delete or alter the ALAS2 C-terminal amino acids, resulting in its increased activity and the subsequent accumulation of protoporphyrin IX. Manifestations in female heterozygotes with XLP can range from asymptomatic to as severe as their affected male relatives. The variation in the presence and severity of manifestations in XLP heterozygotes results primarily from random X-chromosomal inactivation. XLP accounts for ~2–10% of cases with the EPP pheno­ type in Europe and North America. Rare patients with EPP symptoms and elevated erythrocyte protoporphyrin IX levels do not have muta­ tions in FECH or ALAS2 on genetic testing. In an affected family with EPP symptoms and accumulation of protoporphyrin IX, an autosomal dominant mutation was found in human CLPX, a modulator of heme biosynthesis. PART 12 Endocrinology and Metabolism Clinical Features  In EPP and male XLP patients, skin photosen­ sitivity, which differs from that in other cutaneous porphyrias, usually begins in early childhood. The initial symptoms on sun exposure consist of tingling, stinging, itching, or heat/burning sensations on the exposed skin occurring within <10 to 30 min of exposure in >60% of patients; most will have these prodromal symptoms within an hour of sun exposure. The prodromal symptoms are the “warning signal” to get out of the sun, thereby avoiding a severe incapacitating painful attack that can last from 2–5 days. Photosensitivity is associated with substantial elevations in erythrocyte protoporphyrin IX and occurs only in patients with genotypes that result in FECH activities below ~35% of normal. Vesicular lesions are uncommon. Redness and swell­ ing develop after prolonged sun exposure and resemble angioedema (Fig. 428-4). Pain symptoms may seem out of proportion to the visible FIGURE 428-4  Erythema and edema of the hands due to acute photosensitivity in a 10-year-old boy with erythropoietic protoporphyria. (Reproduced with permission from P Poblete-Gutiérrez et al: The porphyrias: clinical presentation, diagnosis and treatment. Eur J Dermatol 16:230, 2006.)

skin involvement. Chronic skin changes may include lichenification, leathery pseudovesicles, labial grooving, and nail changes. Severe scar­ ring is rare, as are pigment changes, friability, and hirsutism. Unless hepatic or other complications develop, protoporphyrin IX levels and symptoms of photosensitivity tend to remain remarkably stable over many years in most patients. Factors that exacerbate the hepatic por­ phyrias play no role in EPP or XLP. The primary source of excess protoporphyrin is the bone marrow ery­ throid cells. In EPP patients, erythrocyte protoporphyrin IX is free (not complexed with zinc) and is mostly bound to hemoglobin. In plasma, protoporphyrin IX is bound to albumin. Hemolysis and anemia are absent or usually mild. Although EPP is an erythropoietic porphyria, up to 27% of EPP patients may have minor abnormalities of liver function, and in ~2–5% of these patients, the accumulation of protoporphyrins causes chronic liver disease that can progress to liver failure requiring transplantation. Protoporphyrin IX is insoluble, and excess amounts form crystalline structures in liver cells (Fig. 428-4) and can decrease hepatic bile flow. Studies in the mouse model of EPP have shown that the bile duct epi­ thelium may be damaged by toxic bile, leading to biliary fibrosis. Thus, rapidly progressive liver disease appears to be related to the cholestatic effects of protoporphyrins and is associated with increasing hepatic protoporphyrin IX levels due to impaired hepatobiliary excretion and increased photosensitivity. The hepatic complications also are often characterized by increasing levels of protoporphyrins in erythrocytes and plasma as well as severe abdominal and back pains, especially in the right upper quadrant. Gallstones composed at least in part of pro­ toporphyrin IX occur in some patients. Hepatic complications appear to be higher in EPP due to two pathogenic FECH mutations and in males with XLP. Diagnosis  A substantial increase in erythrocyte protoporphyrin IX, which is predominantly free and not complexed with zinc, is the hallmark of EPP. Protoporphyrin levels also are variably increased in bone marrow, plasma, bile, and feces. Erythrocyte protoporphyrin IX concentrations are increased in other conditions such as lead poison­ ing, iron deficiency, various hemolytic disorders, all homozygous forms of other porphyrias, and sometimes even in acute porphyrias. In all these conditions, however, in contrast to EPP, protoporphyrin IX is complexed with zinc. Therefore, after an increase in erythrocyte protoporphyrin IX is found in a suspected EPP patient, it is impor­ tant to confirm the diagnosis by an assay that distinguishes free and zinc-complexed protoporphyrin. Erythrocytes in EPP also exhibit red fluorescence under fluorescence microscopy at 620 nm. Urinary levels of porphyrins and porphyrin precursors are normal. FECH activity in cultured lymphocytes or fibroblasts is decreased (<30% of normal mean). DNA diagnosis by mutation analysis is recommended to detect the causative FECH mutation(s) and/or the presence of the IVS3–48T>C low expression allele. To date, >235 mutations have been identified in the FECH gene, many of which result in an unstable or absent enzyme protein (null alleles) (Human Gene Mutation Database; www.hgmd.org). In XLP, the erythrocyte protoporphyrin levels appear to be higher than in EPP, and the proportions of free and zinc protoporphyrin IX may reach 50%. XLP accounts for ~2% of patients with the EPP phenotype in Western Europe. Recent studies show that ~10% of North American patients with the EPP phenotype have XLP. TREATMENT Erythropoietic Protoporphyria Avoiding sunlight exposure and wearing clothing designed to provide protection for conditions with chronic phototoxicity are essential. Various other treatments, including oral β-carotene and cimetidine, have proven of little benefit. Afamelanotide, an α-melanocyte-stimulating hormone (MSH) analogue that

47 - 429 Lysosomal Storage Diseases

429 Lysosomal Storage Diseases

stimulates tanning, is administered subcutaneously every 2 months and has been approved for the treatment of EPP and XLP by the EMA and the FDA. Dersimelagon, an orally administered, smallmolecule, selective melanocortin-1 receptor (MC1R) agonist that increases skin melanin without sun exposure, is currently in phase 3 clinical trials for EPP and XLP. Bitopertin, an orally administered glycine reuptake inhibitor, recently was shown to reduce blood pro­ toporphyrin IX levels in clinical studies and is currently in phase 3 clinical trials. Treatment of hepatic complications, which may be accompa­ nied by motor neuropathy, is difficult. Cholestyramine and other porphyrin absorbents such as activated charcoal may interrupt the enterohepatic circulation of protoporphyrin and promote its fecal excretion, leading to some improvement. Plasmapheresis and intra­ venous hemin are sometimes beneficial. Liver transplantation has been carried out in some EPP and XLP patients with severe liver complications and is often successful in the short term. However, the disease often recurs in the trans­ planted liver due to continued bone marrow production of excess protoporphyrin. In a retrospective study of 17 liver-transplanted EPP patients, 11 (65%) had recurrent EPP liver disease. Posttrans­ plantation treatment with hematin and plasmapheresis should be considered to prevent the recurrence of liver disease. However, bone marrow transplantation, which has been successful in human EPP and which prevented liver disease in a mouse model, should be considered after liver transplantation, if a suitable donor can be found. Acknowledgment The authors thank Dr. Karl E. Anderson for his review of the manuscript and helpful comments and suggestions. This work is supported in part by the Porphyrias Consortium (U54 DK083909), a part of the National Institutes of Health (NIH) Rare Disease Clinical Research Network (RDCRN), supported through collaboration between the NIH Office of Rare Diseases Research (ORDR) at the National Center for Advancing Translational Science (NCATS) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. ■ ■FURTHER READING Balwani M et al: Clinical, biochemical, and genetic characterization of North American patients with erythropoietic protoporphyria and X-linked protoporphyria. JAMA Dermatol 153:789, 2017. Balwani M et al: Phase 3 trial of RNAi therapeutic givosiran for acute intermittent porphyria. N Engl J Med 382:2289, 2020. Bonkovsky HL et al: Ledipasvir/sofosbuvir is effective as sole treat­ ment of porphyria cuteanea tarda with chronic hepatitis C. Dig Dis Sci 68:2738,2023. Chen B et al: Acute intermittent porphyria: Predicted pathogenicity of HMBS variants indicates extremely low penetrance of the autoso­ mal dominant disease. Hum Mutat 37:1215, 2016. Kazamel M et al: Pain in acute hepatic porphyrias: Update on patho­ physiology and management. Front Neurol 13:1004125, 2022. Levy C et al: Evidence-based consensus guidelines for the diagnosis and management of protoporphyria-related liver dysfunction in erythropoietic protoporphyria and X-linked protoporphyria. Hepa­ tology 79:731, 2024. Tchernitchko D et al: A variant of peptide transporter 2 predicts the severity of porphyria-associated kidney disease. J Am Soc Nephrol 28:1924, 2017. Wang B et al: AGA clinical practice update on diagnosis and manage­ ment of acute hepatic porphyrias: Expert review. Gastroenterology 164:481, 2023. Yasuda M et al: Liver transplantation for acute intermittent porphyria: Biochemical and pathologic studies of the explanted liver. Mol Med 21:487, 2015.

Robert J. Hopkin, Gregory A. Grabowski

Lysosomal Storage

Diseases Lysosomes are heterogeneous subcellular organelles containing specific hydrolases that allow selective processing or degradation of proteins, nucleic acids, carbohydrates, and lipids. There are >50 different lysosomal storage diseases, now termed lysosomal system diseases (LSDs), classified according to the nature of the major accumulated materials (Table 429-1). Although all are rare diseases, an overview of several are provided here: Tay-Sachs disease, Fabry disease, Gaucher disease, Niemann-Pick disease, the mucopolysaccharidoses, Pompe disease, lysosomal acid lipase deficiency (LALD), Krabbe disease, CLN2-related Batten disease, and α-mannosidosis. LSDs should be considered in the differential diagnosis of patients with neurologic, renal, or muscular degeneration and/or unexplained hepatomegaly, splenomegaly, cardiomyopathy, or skeletal dysplasias and deforma­ tions. Physical findings are disease specific, and enzyme assays or genetic testing can be used to make a definitive diagnosis. Although the nosology of LSDs segregates the variants into distinct phenotypes, these are heuristic; in the clinic, each disease exhibits—to varying degrees—a spectrum of manifestations, from severe to attenuated variants. PATHOGENESIS Lysosomal biogenesis involves ongoing synthesis of lysosomal hydrolases, membrane constitutive proteins, and new membranes. Lysosomes originate from the fusion of trans-Golgi network vesicles with late endosomes. Progressive acidification accompanies the matu­ ration of these vesicles; this gradient facilitates the pH-dependent dissociation of receptors and ligands and also activates lysosomal hydrolases. Lysosomes are components of the lysosome/autophagy/ mitophagy system that are regulated by the mTORC1 modulation, via phosphorylation, of the transcription factors TFEB/TFE3 and the resultant control of the balance between anabolic and catabolic path­ ways. This regulation is disrupted to varying degrees in specific tissues affected by individual LSDs. Lysosomal Storage Diseases CHAPTER 429 Abnormalities at any biosynthetic step can impair lysosomal enzyme function and lead to an LSD. After leader sequence clipping from the primary protein, remodeling of complex oligosaccharides (including the lysosomal targeting ligand mannose-6-phosphate as well as highmannose oligosaccharide chains of many soluble lysosomal hydrolases) occurs during transit through the Golgi. Lysosomal integral or associ­ ated membrane proteins are sorted to the membrane or interior of the lysosome by several different peptide signals. Phosphorylation, sulfa­ tion, additional proteolytic processing, and macromolecular assembly of heteromers occur concurrently. Such posttranslational modifica­ tions are critical to enzyme function, and defects in these processes can result in multiple enzyme/protein deficiencies. The final common pathway for LSDs is the accumulation of specific macromolecules within selected tissues and cells that normally have a high flux of these substrates. The majority of lysosomal enzyme deficiencies result from point mutations or genetic rearrangements at a locus that encodes a single lysosomal hydrolase or protein subunit. However, some mutations cause deficiencies of several different lyso­ somal hydrolases by alteration of the enzymes/proteins involved in targeting, active site modifications, macromolecular association, or trafficking. Nearly all LSDs are inherited as autosomal recessive disor­ ders, except for Hunter (mucopolysaccharidosis type II), Danon, and Fabry diseases that are X-linked, and two autosomal dominant condi­ tions causing Parry type neuronal ceroid lipofuscinosis (CLN) due to mutations in DNAJC5 or frontotemporal dementia and CLN11 due to GRN (progranulin) mutations. Substrate accumulations lead to lyso­ somal distortions/dysfunctions that have significant pathophysiologic

stiffness; distinctive DYSPLASIA OPHTHALMOLOGIC HEMATOLOGIC UNIQUE FEATURES pebbly skin lesions lymphocytes Mild coarse facies lymphocytes Mild coarse facies involvement; joint involvement; joint cardiovascular cardiovascular lymphocytes Coarse facies; lymphocytes Coarse facies; stiffness degeneration           MPS I S, Scheie         None           degeneration +++ ++++ Corneal clouding Vacuolated Granulated degeneration + + None Granulated degeneration + + None Granulated PART 12 Endocrinology and Metabolism degeneration, no corneal clouding       CLINICAL FEATURES +++ ++++ Retinal ENLARGEMENT SKELETAL (ONSET) INHERITANCE NEUROLOGIC LIVER, SPLEEN degeneration, less (SGSH) Heparan sulfate Late infantile AR Severe cognitive Heparan sulfate Late infantile AR Severe cognitive in mild form Intermediate AR Cognitive Scheie     Childhood/adult   Cognitive Mild juvenile X-linked Cognitive TABLE 429-1  Selected Lysosomal System Diseases (also known as Lysosomal Storage Diseases) MATERIALS CLINICAL TYPES Heparan sulfate Severe infantile Heparan sulfate Infantile [ET, HSCT] Dermatan sulfate (IDS) [ET] Dermatan sulfate ACCUMULATED PRIMARY MPS I H, Hurler α-L-Iduronidase (IDUA) ENZYME DEFICIENCY

MPS III A, Sanfilippo A Heparan-N-sulfatase MPS II, Hunter Iduronate sulfatase (GENE) [SPECIFIC glucosaminidase MPS III B, Sanfilippo B N-Acetyl-αTHERAPY] Mucopolysaccharidoses (MPS) (NGALU) MPS I H/S, Hurler/ DISORDERa

hypoplasia; aortic valve neutrophils Coarse facies; vascular hyperacusis in infantile Coarse facies; valvular fetalis in neonatal form involvement; hydrops deformity; odontoid neutrophils Distinctive skeletal lymphocytes Mild coarse facies lymphocytes Mild coarse facies infantile form None Macrocephaly; ++ ± Cherry red spot None Macrocephaly; heart disease hyperacusis disease form MPS IV B, Morquio β-Galactosidase (GLB1)   Childhood AR None ± ++++       neutrophils and lymphocytes degeneration + + None Granulated degeneration + + None Granulated Chondroitin-6 sulfate Childhood AR None + ++++ Corneal clouding Granulated [ET, HSCT] Dermatan sulfate Late infantile AR None ++ ++++ Corneal clouding Granulated +++ +++ Corneal clouding Granulated None None Cherry red spot in Heparan sulfate Late infantile AR Severe cognitive 6-sulfate sulfatase (GNS) Heparan sulfate Late infantile AR Severe cognitive absent in some seizures; later degeneration, degeneration; degeneration; juvenile form AR Cognitive Juvenile AR Cognitive and B (HEXB) GM2 gangliosides Infantile AR Cognitive seizures adults Heparan sulfate Neonatal Infantile (HEXA) GM2 gangliosides Infantile Adult [ET] Dermatan sulfate Keratan sulfate MPS IV A, Morquio A N-AcetylgalactosamineSly β-Glucuronidase (GUS) Maroteaux-Lamy Arylsulfatase B (ARSB) MPS III D, Sanfilippo D N-Acetylglucosamine-

Sandhoff disease β-Hexosaminidases A Tay-Sachs disease β-Hexosaminidase A N-acetyltransferase 6-sulfate sulfatase α-glucosaminide (GALNS) [ET] MPS III C, Sanfilippo C Acetyl-CoA: (HGSNAT) GM2 Gangliosidoses MPS VI, MPS VII

Coarse facies; enlarged bone marrow Pulmonary infiltrates Types 1 and 3 highly angiokeratomas in angiokeratomas; Angiokeratomas Coarse facies; hypohydrosis juvenile form Lung failure vascular lesions None Cutaneous variable tongue Gaucher cells in bone marrow; lymphocytes; lymphocytes, lymphocytes, degeneration Foam cells in degeneration ++ ++ None Vacuolated clouding Vacuolated degeneration   ++ None Vacuolated granulated neutrophils cytopenias foam cells Supranuclear gaze acroparesthesias None None Corneal dystrophy, degeneration +++ +++ Cataracts, corneal Strabismus Osteoporosis Macular None palsy ++++ None ++++ ++++ + ++++ ++++ +++ (MANBA) Oligosaccharides   AR Seizures; cognitive degeneration; AR Cognitive Juvenile AR Cognitive Milder variant AR Cognitive seizures [ET, Chaperone] Globotriaosylceramide Childhood X-linked Painful –/+++ AR None ++++ Nonneuronopathic, (SMPD1) [ET] Sphingomyelin Neuronopathic, oligosaccharides Infantile (MAN2B1) [ET] Oligosaccharides Infantile type A type B Glucosylsphingosine Type 1 Type 2 Type 3 Glucosylceramide, Fucosidosis α-Fucosidase (FUCA1) Glycopeptides; Fabry disease α-Galactosidase A (GLA) A and B Acid sphingomyelinase Gaucher disease Acid β-glucosidase (GBA, a.k.a. GBA1)

α-Mannosidosis α-Mannosidase β-Mannosidosis β-Mannosidase [ET, SRT] Neutral Glycosphingolipidoses Niemann-Pick disease Glycoproteinoses

(Continued) mucopolysacchariduria;

Coarse facies; stiffness of hands and shoulders None None None None White matter globoid None None Optic atrophy None Gait abnormalities in gingival hypoplasia lymphocytes MPS phenotype in late infantile form Coarse facies; Coarse facies absence of type II cells and granulated lymphocytes, degeneration ± ++ None Vacuolated type I Cherry red spot Vacuolated degeneration + ++++ Corneal clouding Vacuolated neutrophils foam cells foam cells Lysosomal Storage Diseases CHAPTER 429 degeneration None +++ Corneal clouding, mild retinopathy, astigmatism hyperopic ++, less in type I ++, less in psychosis in adult dysmyelination glycolipids Late infantile AR Mild cognitive degeneration, degeneration; degeneration AR Myoclonus; CNS, PNS dementia; glycopeptides Young adult AR Cognitive glycolipids Infantile AR Cognitive Infantile AR Cognitive AR Cognitive cognitive Sialidosis Neuraminidase (NEU1) Sialyloligosaccharides Type I, congenital Type II, infantile and juvenile Juvenile leukodystrophy Arylsulfatase A (ARSA) Cerebroside sulfate Infantile Adult Galactosylsphingosine, (AGA) Aspartylglucosamine; (GALC) [BMT/HSCT] Galactosylceramide a.k.a., psychosine Glycoprotein; Glycoprotein; Aspartylglucosaminuria Aspartylglucosaminidase Krabbe disease Galactosylceramidase 1-phosphotransferase 1-phosphotransferase Acetylglucosamine-

Acetylglucosamine-

(GNPTAB) (GNPTAB) ML-II, I-cell disease UDP-Npolydystrophy UDP-NMucolipidoses (ML) ML-III, pseudo-Hurler Leukodystrophies Metachromatic

None Rare fatal neonatal liver known cellular sulfatases

subcutaneous nodules granulated cells Absent activity of all DYSPLASIA OPHTHALMOLOGIC HEMATOLOGIC UNIQUE FEATURES (LIPA) [ET] Cholesteryl esters Childhood AR None Hepatomegaly None None None Fatty liver disease; disease, cirrhosis triglycerides Infantile AR None +++ None None None Adrenal cortical (GAA) [ET] Glycogen Infantile, late onset AR Neuromuscular ± None None None Myocardiopathy degeneration None Arthropathy, calcification cirrhosis degeneration Vacuolated and PART 12 Endocrinology and Metabolism ophthalmoplegia supranuclear       CLINICAL FEATURES ± None Macular hepatosplenomegaly None Vertical degeneration + ++ Retinal ENLARGEMENT SKELETAL (ONSET) INHERITANCE NEUROLOGIC LIVER, SPLEEN degeneration Variable adulthood AR Progressive CNS degeneration Juvenile AR Occasional mucopolysaccharides Late infantile AR Cognitive cognitive TABLE 429-1  Selected Lysosomal System Diseases (also known as Lysosomal Storage Diseases) (Continued) MATERIALS CLINICAL TYPES Cholesterol Childhood to (ASAH1) Ceramide Infantile (LIPA) [ET, HSCT] Cholesteryl esters; ACCUMULATED enzyme, a.k.a. FGE (SUMF1) Sulfatides; PRIMARY deficiency Formylglycine-generating Infantile-onset LALD Lysosomal acid lipase ENZYME DEFICIENCY

LALD Acid lysosomal lipase Pompe disease Acid α-glucosidase (GENE) [SPECIFIC Farber disease Acid ceramidase THERAPY] (NPC1) (NPC2) C1 and C2 NPC1 NPC2 Disorders of Neutral Lipids Disorders of Glycogen Niemann-Pick disease Childhood/adult-onset Multiple sulfatase DISORDERa

neuromuscular disease None None None None Myocardial vacuolar loss None Symmetric retinal Abbreviations: AR, autosomal recessive; BMT/HSCT, bone marrow or hematopoietic stem cell transplantation; ET, enzyme therapy; ICV ET, intracerebroventricular enzyme therapy; LALD, lysosomal acid lipase deficiency; SRT, substrate degeneration by insufficiency; degeneration aComprehensive reviews of these lysosomal storage diseases can be found in DL Valle et al: The Online Metabolic and Molecular Bases of Inherited Disease, New York, McGraw-Hill, https://ommbid.mhmedical.com/book.aspx?boo progressive to adulthood AR Neuromuscular None None None None Respiratory 4–6 years None None Progressive vision Ceroid lipofuscin Early childhood AR Neurodegenerative Wheelchair bound Loss of motor skills (?Dominant) Cardiomyopathy by adolescence Neuromuscular Cognitive loss Loss of vision degeneration Inconsistent Myoclonus cognitive to adulthood X-linked Glycogen Variable: childhood (GAA) [ET] Glycogen Variable: juvenile synthesis inhibition therapy (a.k.a., substrate reduction therapy). associated membrane peptidase 1) (TPP1) Danon disease LAMP-2 (lysosomal deficiency Acid α-glucosidase protein-2) (LAMP2) CLN2 (a.k.a. NCL2) TPP1 (tripeptidyl Neuronal Ceroid Lipofuscinoses [ICV ET] kID=2709#225069419. Late-onset GAA

consequences. In addition, abnormal amounts of metabolites may also have pharmacologic effects important to disease pathophysiology and propagation, particularly activation of the innate immune responses. For many LSDs, the accumulated substrates are synthesized within particular tissue sites of pathology. Other diseases have greater exog­ enous substrate supplies. For example, substrates are delivered by lowdensity lipoprotein receptor–mediated uptake in Fabry and LALD or by phagocytosis in Gaucher disease type 1. The threshold hypothesis refers to a level of enzyme activity below which disease develops. Small changes in enzyme activity near that threshold can lead to or modify disease. A critical element of this model is that enzymatic activity can be challenged by changes in substrate flux based on genetic back­ ground, cell turnover, recycling, or metabolic demands. Thus, a set level of residual enzyme may be adequate for substrate in some tissues or cells but not in others. In addition, several variants of each LSD exist at the clinical level. These disorders therefore represent a spectrum of manifestations that are not easily dissociated into discrete entities. The molecular/genetic bases for such variations have not been elucidated in any detail. Treatments approved by the European Medicines Agency (EMA) and U.S. Food and Drug Administration (FDA) are available for several LSDs. The first was enzyme replacement therapy (ET) for Gaucher disease; this has been followed by additional ETs, but subsequent devel­ opments have included modified enzyme infusion, substrate synthesis inhibition, hematopoietic stem cell transplant (HSCT), pharmacologic chaperone therapy (which use small molecules to stabilize or enhance enzyme function resulting from the mutated gene), intrathecal enzyme delivery, Trojan-horse strategies for blood-brain barrier penetration for central nervous system (CNS) delivery, and gene therapy. The technical ability to intervene for most LSDs now exists but with highly variable impact, i.e., therapeutic outcome, particularly in bones and the CNS. Significant additional research is needed to reach the goals of longterm survival with good function and quality of life. SELECTED DISORDERS ■ ■TAY-SACHS DISEASE About 1 in 30 Ashkenazi Jews is a carrier for Tay-Sachs disease (total hexosaminidase A [Hex A] deficiency), resulting from α-chain gene mutations. The infantile form is a neurodegenerative disease that results in death in infancy. It is characterized by macrocephaly, loss of motor skills, increased startle reaction, and a macular cherry red spot. The juvenile-onset form presents as ataxia and dementia, with death by age 10–15 years. The adult-onset disorder is characterized by clumsiness in childhood; progressive motor weakness in adolescence; and additional spinocerebellar and lower-motor-neuron signs and dysarthria in adulthood; intelligence declines slowly, and psychiatric disorders are common. Screening for Tay-Sachs disease carriers is recommended in the Ashkenazi Jewish population. Sandhoff disease, due to a deficiency in both Hex A and Hex B resulting from defective β-chains, is phenotypically similar to Tay-Sachs disease with the addi­ tion of hepatosplenomegaly and bony dysplasias. ■ ■FABRY DISEASE Fabry disease, an X-linked disorder and likely the most prevalent LSD, results from mutations in GLA, which encodes α-galactosidase A. The estimated prevalence of hemizygous males ranges from 1 in 40,000 to 1 in 3500 in selected populations. Females have a higher prevalence of mutations, but more variable manifestations due to Lyonization effects. The disease manifests with angiokeratomas (telangiectatic skin lesions), hypohidrosis, corneal and lenticular opacities, acroparesthesia, and progressive disease of the kidney, heart, and brain vascular systems. Abdominal pain, recurrent diarrhea, and acroparesthesias (debilitating episodic burning pain of the hands and feet) may appear in childhood. In females, the overall manifestations vary greatly. Angiokeratomas are punctate, dark red to blue-black, and flat or slightly raised skin lesions; they do not blanch with pressure. They can be easily overlooked. They usually are most dense between the umbilicus and the knees—the “bathing suit area”—but may occur anywhere. Angiokeratomas also

occur in several other very rare LSDs. Corneal and lenticular lesions, detectable on slit-lamp examination, may help in establishing a diag­ nosis of Fabry disease. Acroparesthesia can last from minutes to days and can be precipitated by changes in temperature, exercise, fatigue, or fever. Abdominal pain can resemble appendicitis or renal colic. Proteinuria, isosthenuria, and progressive renal dysfunction occur in the second to fourth decades; ~5% of male patients with “idiopathic renal failure” have GLA mutations. Hypertension, left ventricular hypertrophy, anginal chest pain, and congestive heart failure can occur in the third to fourth decades. About 1–3% of patients with “idiopathic hypertrophic myocardiopathy” have Fabry disease. Similarly, ~2–5% of patients with “idiopathic stroke” at 35–50 years of age have GLA mutations. Leg lymphedema occurs without hypoproteinemia. Death is due to cardiovascular, renal, or cerebrovascular disease. Variants with residual α-galactosidase A activity may have late-onset manifestations that are most prominent in the cardiovascular system and resemble hypertrophic cardiomyopathy. Cases with predominant cardiac, renal, or CNS manifestations have been reported. Up to 70% of heterozygous females exhibit clinical manifestations. However, in females, heart dis­ ease is the most common life-threatening manifestation. In males, it is renal disease followed by cardiovascular disease. Lysosomal Storage Diseases CHAPTER 429 Gabapentin and carbamazepine diminish chronic and episodic acroparesthesias. Chronic hemodialysis or kidney transplantation can be lifesaving in patients with renal failure. Intravenous ET clears stored lipids from a variety of cells. More recently a chaperone therapy (migalastat) that stabilizes the residual enzyme made by the patient’s body has allowed oral therapy for some patients with amenable muta­ tions. Renal insufficiency, cardiac fibrosis, and stroke are irreversible; therefore, early institution of therapy provides the best opportunity to prevent or slow the progression of life-threatening complications. ■ ■GAUCHER DISEASE Gaucher disease, a panethnic autosomal recessive disorder, results from defective activity of acid β-glucosidase; ~600 GBA, a.k.a. GBA1, mutations have been described in such patients. Clinically, disease variants are classified by the absence or presence and progression of primary CNS involvement. Gaucher disease type 1 is a nonneuronopathic disease (i.e., absence of early-onset or progressive CNS disease) presenting in child­ hood to adulthood as slowly to rapidly progressive visceral disease. About 55–60% of patients are diagnosed at <20 years of age in white populations and at even younger ages in other groups. This pattern of presentation is distinctly bimodal, with peaks at <10–15 years and at ~25 years. Younger patients tend to have greater degrees of hepato­ splenomegaly and accompanying blood cytopenias. In contrast, older patients have a greater tendency for chronic bone disease. Hepato­ splenomegaly occurs in virtually all clinically identified patients and can be minor or massive. Accompanying anemia and thrombocytope­ nia are variable and are not directly related to liver or spleen volumes. Severe liver dysfunction is unusual, but progressive cirrhosis can occur. Splenic infarctions can resemble an acute abdomen. Pulmonary hypertension and alveolar Gaucher cell accumulation are uncommon but life-threatening and can occur at any age; this is more common in females who have been splenectomized. GBA1 mutations in the hetero­ zygous or homozygous states lead to a significantly increased lifetime risk for developing Parkinson disease. The complex mechanisms for this major risk require elucidation. All patients with Gaucher disease have nonuniform infiltration of bone marrow by lipid-laden macrophages, termed Gaucher cells. This phenomenon can lead to marrow packing with subsequent infarc­ tion, ischemia, necrosis, and cortical bone destruction. Bone marrow involvement spreads from proximal to distal in the limbs and can involve the axial skeleton extensively, causing vertebral collapse. In addition to bone marrow involvement, bone remodeling is defective, with loss of total bone calcium leading to osteopenia, osteonecrosis, avascular infarction, and vertebral compression fractures with spinal cord involvement. Aseptic necrosis of the femoral head is common, as is fracture of the femoral neck. The mechanism by which diseased bone marrow macrophages interact with osteoclasts and/or osteoblasts

to cause bone disease is not well understood. Chronic, ill-defined bone pain can be debilitating and poorly correlated with radiographic findings. “Bone crises” are associated with localized excruciating pain and, on occasion, local erythema, fever, and leukocytosis. These crises represent acute infarctions of bone, as evidenced in nuclear scans by localized absent uptake of pyrophosphate agents. Decreased acid β-glucosidase activity (0–20% of normal) in nucleated cells establishes the diagnosis. The enzyme is not normally present in bodily fluids. The sensitivity of enzyme testing is poor for heterozygote detection; molecular testing by whole GBA1 sequencing is the standard. The disease frequency varies from ~1 in 1000 among Ashkenazi Jews to <1 in 100,000 in other populations; ~1 in 12–15 Ashkenazi Jews carries a Gaucher disease allele. Four common mutations account for ~85% of the mutations in that population of affected patients: p.N370S (a.k.a. p.N409S), 84GG (a G insertion at cDNA position 84), p.L444P (also known as p.L483P), and IVS-2+1 (an intron 2 splice junction mutation).

PART 12 Endocrinology and Metabolism Genotype/phenotype studies indicate a significant, though not absolute, correlation between disease type and severity and the GBA1 genotype. The most common mutation in the Ashkenazi Jewish popu­ lation (p.N370S) shares, either homozygously or heteroallelically, a 100% association with nonneuronopathic or type 1 Gaucher disease. The N370S/N370S and N370S/other mutant allele genotypes are asso­ ciated with later-onset/less severe disease and with earlier-onset/severe disease, respectively. As many as 40% of individuals with the N370S/ N370S genotype do not present clinically. Other alleles include L444P (very low activity), 84GG (null), or IVS-2 (null) and rare/private or uncharacterized alleles. The L444P/L444P patients frequently have lifethreatening to very severe/early-onset disease, and many, though not all, develop CNS involvement in the first two decades of life. Symptom-based treatment of blood cytopenias and joint replace­ ment surgeries continue to have important roles in management. However, regular intravenous ET has been the first-line treatment for significantly affected patients and is highly efficacious and safe in diminishing hepatosplenomegaly and improving hematologic values. An oral substrate reduction therapy (SRT; eliglustat tartrate), which inhibits glucosylceramide synthesis, is approved as a first-line therapy for adults. Bone disease is decreased and can be prevented, but irre­ versible damage cannot be reversed, by ET. Adult patients may benefit from adjunctive treatment with bisphosphonates or other interventions to improve bone density. Adults who cannot be treated with enzyme, either because it is not effective or because they have developed an allergy or other hypersensitivities to the enzyme, may receive SRT with either eliglustat tartrate or miglustat; the latter is approved as a secondline oral therapy. Gaucher disease type 2 is a rare, severe, progressive CNS disease that leads to death by 2 years of age, depending on supportive care. Gaucher disease type 3 has highly variable manifestations in the CNS and viscera. It can present in early childhood with rapidly progressive, massive visceral disease and slowly progress to static CNS involvement that may not be evident by standard IQ evaluations; in adolescence with dementia; or in early adulthood with rapidly progressive, uncon­ trollable myoclonic seizures and mild visceral disease. Visceral disease in type 3 is nearly identical to that in type 1 but is generally more severe. Early CNS findings may be limited to defects in lateral gaze tracking (supranuclear lateral gaze palsy), which may remain static for decades. Cognitive degeneration can be slowly progressive or static. Type 3 is much more frequent among individuals of non–Western world descent. Visceral—but not CNS—involvement responds to ET. ■ ■NIEMANN-PICK DISEASES Niemann-Pick diseases (acid sphingomyelinase deficiency [ASMD]) are autosomal recessive disorders that result from defects in acid sphingomyelinase (ASM). Types A and B are distinguished by the early age of onset and progressive CNS disease in type A. Type A typically has its onset in the first 6 months of life, with rapidly progressive CNS deterioration, spasticity, failure to thrive, and massive hepatospleno­ megaly. Type B has a later, more variable onset and is characterized by a progression of hepatosplenomegaly, with eventual development of cir­ rhosis and hepatic parenchymal and Kupffer cell replacement by foam

cells filled with sphingomyelin. Affected patients develop potentially lethal progressive pulmonary disease with dyspnea, hypoxemia, and a reticular infiltrative pattern on chest x-ray. Foam cells are present in alveoli, lymphatic vessels, and pulmonary arteries. Progressive hepatic or lung disease can lead to death in adolescence or early adulthood. The “type B” phenotype includes some patients with slowly progressive CNS involvement, termed A/B variant. The diagnosis is established by markedly decreased (1–10% of normal) ASM activity in nucleated cells. Intravenous ET improves nonneurologic manifestations, including pulmonary disease. The efficacies of hepatic transplant (HT) or bone marrow transplantation (BMT/HSCT) are not established. More complications than expected have occurred with these interventions due to either (1) recurrence of hepatic disease in the transplant following HT due to repopulation of bone marrow–derived ASM-deficient myeloid cells or (2) lack of clearance of sphingomyelin in hepatocytes by ASM cross-correction following the BMT/HSCT of ASM-normal bone marrow stem cells. Niemann-Pick C diseases are progressive CNS diseases due to muta­ tions in either of the genes encoding NPC1 or NPC2, lysosomal pro­ teins involved in free cholesterol and selected sphingolipid transport out of the lysosome. They can present with liver or splenic disease, but their major manifestations are progressive CNS disease over one to two decades. Treatment with substrate inhibition agents (e.g., miglustat) has shown minor CNS effects, and substrate depletion with cyclodex­ trin is in clinical trials for NPC1 disease. ■ ■MUCOPOLYSACCHARIDOSES Mucopolysaccharidosis type I (MPS I) is an autosomal recessive dis­ order caused by deficiency of α-L-iduronidase (IDU). The spectrum of involvement traditionally has been divided into three categories: (1) Hurler disease (MPS I H) for severe deficiency with neurodegen­ eration, (2) Scheie disease (MPS I S) for later-onset disease without neurologic involvement and with relatively less severe disease in other organ systems, and (3) Hurler-Scheie syndrome (MPS I H/S) for patients intermediate between these extremes. MPS I H/S is character­ ized by severe somatic disease, usually without major overt neurologic deterioration. MPS I often presents in infancy or early childhood as chronic rhinitis, clouding of the corneas, hepatosplenomegaly, and progressive dysmorphia. As the disease progresses, nearly every organ system can be affected. In the more severe forms, cardiac and respira­ tory diseases become life threatening in childhood. Skeletal disease can be severe, resulting in very limited mobility. There are two current treatments for the MPS I diseases. HSCT is the standard treatment for patients presenting at <2 years of age who appear to have or are at risk for neurologic degeneration. Because early diagnosis and intervention are essential, MPS I has been added to the recommended newborn screen (NBS). HSCT results in stabilization of CNS disease, reverses hepatosplenomegaly, and improves cardiac and respiratory disease. HSCT does not eliminate corneal disease or result in the resolution of progressive skeletal disease. ET effectively addresses hepatospleno­ megaly and alleviates cardiac and respiratory disease. The enzyme does not penetrate the blood-brain barrier and does not directly affect CNS disease. ET and HSCT appear to have similar effects on visceral signs and symptoms. ET poses a lower risk of life-threatening complications and may therefore be advantageous for patients without CNS disease. A combination of ET and HSCT has been used, with ET initiated prior to transplantation in an attempt to reduce the disease burden. The experience with this approach is not well documented, but it appears to have advantages over HSCT alone. It is clear that HSCT has benefited patients. However, late cardiac and respiratory complications of MPS I are being reported including obstructive breathing requiring pressure support, cardiomyopathy, and/or valve disease. Regular follow-up for patients with MPS I is required throughout their lives even after suc­ cessful HSCT. Hunter disease (MPS II) is an X-linked disorder due to deficiency in iduronate sulfate sulfatase (IDS) and has manifestations similar to those of MPS I, including some variants with neurologic degeneration. There is no corneal clouding or other eye disease. Like MPS I, MPS II is clinically variable, with CNS and non-CNS variants. HSCT has not

been successful in treating CNS disease associated with MPS II. The FDA and EMA have approved ET for the visceral manifestations of MPS II. MPS IV or Morquio syndrome is a rare autosomal recessive condi­ tion (1 in 200,000–300,000) and is different than the other mucopoly­ saccharidoses in presenting as a spondyloepiphyseal skeletal dysplasia and hyperextensibility of all joints. There are also major heart and respi­ ratory complications. This disorder often presents in childhood, but the age of onset and rate of progression are quite variable. Two variants, type A and type B, are caused by deficiencies in N-acetyl-galactosamine6-sulfatase (GALNS) and an acid β-galactosidase, respectively. A recom­ binant human GALNS ET (elosulfase alfa) is approved for the treatment of MPS IVA, making it essential to confirm the specific enzyme diag­ nosis. Treatment has been shown to improve ambulatory mobility and decrease pain. There is no current specific treatment for MPS IVB. ET for Maroteaux-Lamy disease (MPS VI), arylsulfatase B (ARSB) deficiency, has received FDA approval as well as approval by similar agencies in other countries. This very rare autosomal recessive disorder is characterized by hepatosplenomegaly, bone disease, heart disease, and respiratory compromise. Short stature is also an important mani­ festation. Visceral signs and symptoms are similar to those in MPS I; however, MPS VI is not associated with neurologic degeneration. MPS VII, Sly syndrome, is due to mutations in GUSB, which encodes β-glucuronidase. Severe deficiency in this enzyme may pres­ ent with fetal hydrops, which can lead to stillbirth or perinatal demise. Other patients with MPS VII may present later with short stature, coarse facial features, and hepatosplenomegaly. There is ET for this disorder (vestronidase alfa-vjbk). ■ ■POMPE DISEASE Acid maltase (acid α-glucosidase deficiency) due to GAA mutations, also called Pompe disease, is the only LSD leading to primary glyco­ gen storage. The classic severe infantile form presents with hypotonia, myocardiopathy, and hepatosplenomegaly, as well as total deficiency of the enzyme. This variant is rapidly progressive and generally results in death in the first year of life. However, as with other LSDs, there are early- and late-onset forms of this disorder. The late-onset variants may be as common as 1 in 40,000; patients typically present with a slowly progressive myopathy that may resemble limb-girdle muscular dystrophy. Respiratory insufficiency may be the presenting sign or may develop with advancing disease. In late stages of the disease, patients may require mechanical ventilation, report swal­ lowing difficulties, and experience loss of bowel and bladder control. Myocardiopathy is not usually present in late-onset variants of Pompe disease. The FDA, EMA, and similar agencies have approved ETs for Pompe disease patients of all ages. This treatment clearly prolongs life in the infantile form, consistently resulting in improved cardiac function. Respiratory function is also improved in most treated infants if insti­ tuted before age 6 months. Some infants demonstrate marked improve­ ment in motor functions, while others have minor changes in muscle tone or strength. Many states have instituted NBS for Pompe disease. In addition, newer protocols for treatment with methotrexate and ritux­ imab have greatly decreased antidrug antibody reactions, particularly in the enzyme-absent infantile variants. The combination of NBS and immunomodulation preceding ET has greatly improved therapeutic response and long-term survival. Prevention of deterioration has been shown with GAA ET in the late-onset forms. Early intervention with acid a-glucosidase ET in such patients may limit or prevent dete­ rioration, but very advanced disease will have significant irreversible components. ■ ■LYSOSOMAL ACID LIPASE DEFICIENCY Wolman syndrome (now infantile-onset LALD) and cholesterol ester storage disease (now childhood/adult-onset LALD) are caused by defi­ ciency of lysosomal acid lipase (LAL) due to autosomal recessive muta­ tions in LIPA. The diagnosis is established by enzyme or gene analyses of LAL or LIPA in serum/plasma or nucleated cells, respectively. LAL hydrolyzes cholesterol esters (CEs) and triglycerides (TGs)

delivered to the lysosome via the LDLR pathway. Accumulation of these in the tissues leads to progressive organ dysfunction includ­ ing liver disease, intestinal malabsorption, heart dysfunction, and other manifestations. The most severe form presents in early infancy as a medical emergency with severe failure to thrive, vomiting, and hepatosplenomegaly. The infantile-onset LALD patients die without specific treatment by age 1 year (median age of death, 3.7 months) from tissue accumulations of CEs and TGs and near total absence of LAL. Childhood/adult-onset LALD can have a variable age of initial presentation with nonspecific signs but often involves elevated liver enzymes, microvesicular fatty liver disease, cryptogenic cirrhosis, and varying severities of hepato-/splenomegaly, due to massive accumula­ tions of CEs secondary to the LAL substrate preference for TGs by the low LAL levels. Importantly, neither clinical variant manifests primary CNS disease. Without treatment, disease progresses throughout life and may result in early (adolescence, mean ~13 years) liver cirrhosis and (early adulthood) atherosclerosis or early death. Importantly, statins can decrease the hypercholesterolemia but do not alter the basic progressive tissue (e.g., liver) pathology. The majority of the later onset patients are evaluated by hepatology or lipidology physicians. ET for LALD has major effects in reversing disease manifestations and is approved for patients at all ages by the EMA, FDA, and several other country agencies.

Lysosomal Storage Diseases CHAPTER 429 ■ ■KRABBE DISEASE Deficiency in β-galactocerebrosidase (GALC) causes Krabbe disease, an autosomal recessive neurodegenerative disorder due to mutations in GALC. Krabbe disease is panethnic but quite rare. The early infantile form presents at an average age of 4 months and progresses rapidly, with death at an average age of 18 months. Later onset forms also exist and have onsets and survival that are highly variable. The early-onset form presents with hyperirritability, feeding problems, fever, seizures, and neurodegeneration. Blindness, hypotonia, and loss of voluntary movement develop over time. Later onset forms present with spasticity, ataxia, vision loss, and behavioral problems and progress to dementia and early death. There is no FDA-approved treatment, but early, i.e., first or second month after birth, presymptomatic HSCT has been used. This results in improved survival, but neurologic problems are still common and slowly progressive in the CNS and more severe in the peripheral nervous system. More recently, studies in mouse and dog models have used gene therapy with dramatic improvement in both neurologic function and survival. Human studies are in clinical trials. ■ ■NEURONAL CEROID LIPOFUSCINOSIS TYPE 2 (NCL2 OR CLN2) There are at least 13 mutant genes that have been associated with storage of neuronal ceroid lipofuscin. CLN2 is due to mutations in TPP1 and deficiency in tripeptidyl peptidase 1. This autosomal reces­ sive neurodegenerative disorder typically presents between age 2 and 4 years, most commonly with seizures, ataxia, myoclonus, and vision loss. Motor skill losses include sitting, walking, speech, and feeding and lead to severe disability and eventually death at an average age of 12 years. Intellectual disability and behavioral problems also become increasingly severe with age. Most affected children are wheelchair bound in late childhood, and survival beyond adolescence is rare. There are also later onset patients, and there is significant clinical over­ lap between CLN2 and other CLNs; confirmation of the diagnosis by gene sequencing is essential. FDA/EMA-approved treatment of CLN2 is with cerliponase alfa, an ET that is administered by intracerebroven­ tricular infusions over several hours every 2 weeks. Administration of cerliponase alfa is facilitated by placement of an indwelling intracere­ broventricular port to allow reliable access. Currently, this is the only approved ET that is intrathecally administered. CLN2 is the only neu­ ronal ceroid lipofuscinosis that has a specific treatment. Several others are in preclinical development. ■ ■ALPHA MANNOSIDOSIS Alpha mannosidosis is a very rare disorder caused by deficiency in α-d-mannosidase due to biallelic loss of function of MAN2B1. This leads to buildup of mannose-rich oligosaccharides in the cells, blood,

49 - 431 Inherited Disorders of Amino Acid Metabolism in Adults

431 Inherited Disorders of Amino Acid Metabolism in Adults

ethnic populations, but clinical symptoms are remarkably similar, and treatment guidelines apply to all. Symptomatic treatment is available for these disorders, and today, advances in the field includ­ ing newborn screening have resulted in more definitive diagnosis and better treatment approaches. There are many promising thera­ pies on the horizon with several ongoing clinical trials, including those investigating the use of ERT, mRNA therapy, gene replace­ ment therapy, gene editing, and substrate reduction therapy. In the past, prognosis for many disorders of carbohydrate metabolism was guarded, but with early diagnosis and better management, survival rates have improved and many affected children are surviving into adulthood. ■ ■FURTHER READING Fernandes SA et al: Benign or not benign? Deep phenotyping of liver glycogen storage disease IX. Mol Genet Metab 131:299, 2020. Heinemann JB et al: Features and outcome of galactokinase defi­ ciency in children diagnosed by newborn screening. J Inherit Metab Dis 34:399, 2011. Hong KN et al: International consensus on differential diagnosis and management of patients with Danon disease: JACC state-of-the-art review. J Am Coll Cardiol 82:1628, 2023. Grünert SC et al: Improved inflammatory bowel disease, wound healing and normal oxidative burst under treatment with empa­ gliflozin in glycogen storage disease type Ib. Orphanet J Rare Dis 15:218, 2020. Hannah WB et al: Glycogen storage diseases. Nat Rev Dis Primers 9:46, 2023. Hedberg-Oldfors C et al: Cardiomyopathy as presenting sign of glycogenin-1 deficiency—report of three cases and review of the literature. J Inherit Metab Dis 40:139, 2017. Herbert M et al: Role of continuous glucose monitoring in the man­ agement of glycogen storage disorders. J Inherit Metab Dis 41:917, 2018. Katler QS et al: A multinational study of acute and long-term out­ comes of Type 1 galactosemia patients who carry the S135L (c.404C

 T) variant of GALT. J Inherit Metab Dis 45:1106, 2022. Kiely et al: A novel approach to characterize phenotypic variation in GSD IV: Reconceptualizing the clinical continuum. Front Genet 13:992406, 2022. Koch RL et al: Natural history study of hepatic glycogen storage disease type IV and comparison to Gbe1ys/ys model. JCI Insight 9:e177722, 2024. Kronn DF et al: Management of confirmed newborn-screened patients with Pompe disease across the disease spectrum. Pediatrics 40:S24, 2017. Li N et al: Clinical and molecular characterization of patients with fructose 1,6-bisphosphatase deficiency. Int J Mol Sci 18:857, 2017. Musumeci O et al: Recurrent rhabdomyolysis due to muscle β-enolase deficiency: Very rare or underestimated? J Neurol 261:2424, 2014. Papadopoulos C et al: Aldolase A deficiency: Report of new cases and literature review. Mol Genet Metab Rep 23:100730, 2021. Porto AG et al: Clinical spectrum of PRKAG2 syndrome. Circ Arrhythm Electrophysiol 9:e003121, 2016. Quinlivan R et al: Pharmacological and nutritional treatment for McArdle disease (glycogen storage disease type V). Cochrane Data­ base Syst Rev 2014:CD003458, 2014. Rubio-Gozalbo ME et al: The natural history of classic galactosemia: Lessons from the GalNet registry. Orphanet J Rare Dis 14:86, 2019. Steinmann B et al: Disorders of fructose metabolism. The Online Metabolic and Molecular Bases of Inherited Disease. New York, McGraw-Hill, 2013. Timson DJ: The structural and molecular biology of type III galacto­ semia. IUBMB Life 58:83, 2006. Welling L et al: International clinical guideline for the management of classical galactosemia: Diagnosis, treatment, and follow-up. J Inherit Metab Dis 40:171, 2017.

Nicola Longo

Inherited Disorders

of Amino Acid Metabolism

in Adults Amino acids are the building blocks of proteins and serve as neurotransmitters (glycine, glutamate, γ-aminobutyric acid) or as pre­ cursors of hormones, coenzymes, pigments, purines, or pyrimidines. Eight amino acids, referred to as essential (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine), cannot be synthesized by humans and must be obtained from dietary sources. The others can be formed endogenously. Each amino acid has a unique degradative pathway by which its nitrogen and carbon com­ ponents are used for the synthesis of other amino acids, carbohydrates, and lipids. Disorders of amino acid metabolism and transport (Chap. 432) are individually rare—the incidences range from 1 in 10,000 for cystinuria or phenylketonuria to 1 in 200,000 for homocys­ tinuria or alkaptonuria—but collectively, they affect perhaps 1 in 4000 newborns. Almost all are transmitted as autosomal recessive traits. Inherited Disorders of Amino Acid Metabolism in Adults CHAPTER 431 The features of inherited disorders of amino acid catabolism are summarized in Table 431-1. In general, these disorders are named for the compound that accumulates to highest concentration in blood (-emias) or urine (-urias). In the aminoacidopathies, the parent amino acid is found in excess, whereas products in the catabolic pathway accumulate in organic acidemias. Which compound(s) accumulates depends on the site of the enzymatic block, the reversibility of the reactions proximal to the lesion, and the availability of alternative path­ ways of metabolic “runoff.” Biochemical and genetic heterogeneity are common. Six distinct forms of hyperphenylalaninemia and nine forms of homocystinuria (with or without methylmalonic acidemia) are recognized. Such heterogeneity reflects the complexity of amino acid metabolism requiring multiple enzymes (gene products) for proper functioning. The manifestations of these conditions differ widely (Table 431-1). Some, such as sarcosinemia, produce no clinical consequences. At the other extreme, complete deficiency of ornithine transcarbamylase is lethal in the untreated neonate. Central nervous system (CNS) dys­ function, in the form of delays in development/intellectual disability, seizures, or behavioral disturbances, is present in more than half the disorders. Protein-induced vomiting, neurologic dysfunction, and hyperammonemia occur in many disorders of the urea cycle. Metabolic ketoacidosis, often accompanied by hyperammonemia, is frequent in organic acidemias. Some disorders produce focal tissue or organ involvement such as liver disease, renal failure, cutaneous abnormali­ ties, or ocular lesions. Defects in the synthesis of nonessential amino acids (asparagine, glutamine, proline, serine) involve predominantly the brain with neu­ rologic symptoms, with other organs occasionally affected. Dominant mutations in at least one of these genes can cause tremor or spastic paraplegia in adults. The analysis of plasma amino acids (by ion-exchange chromatog­ raphy or liquid chromatography/tandem mass spectrometry), urine organic acids (by gas chromatography/mass spectrometry), and plasma acylcarnitine profile (by tandem mass spectrometry) is commonly used to diagnose and monitor most of these disorders. The diagnosis is confirmed by enzyme assay on cells or tissues from the patients or, more commonly, by DNA testing. The clinical manifestations in many of these conditions can be prevented or mitigated if a diagno­ sis is achieved early and appropriate treatment (e.g., dietary protein or amino acid restriction or vitamin supplementation) is instituted promptly. For this reason, newborn screening programs seek to iden­ tify several of these disorders. Infants with a positive screening test need additional metabolic testing (usually suggested by the newborn screening program) to confirm or exclude the diagnosis. Confirmed

TABLE 431-1  Inherited Disorders of Amino Acid Metabolism AMINO ACID(S) CONDITION ENZYME DEFECT CLINICAL FINDINGS INHERITANCE Phenylalanine Phenylketonuria Phenylalanine hydroxylase Intellectual disability, microcephaly, hypopigmented skin and hairs, eczema, “mousy” odor DHPR deficiency Dihydropteridine reductase Intellectual disability, hypotonia, spasticity, myoclonus AR PTPS deficiency 6-Pyruvoyl-tetrahydropterin synthase Dystonia, neurologic deterioration, seizures, intellectual disability GTP cyclohydrolase 1 deficiency GTP cyclohydrolase 1 Intellectual disability, seizures, dystonia, temperature instability Carbinolamine dehydratase deficiency Pterin-4α-carbinolamine dehydratase Transient hyperphenylalaninemia (benign) AR PART 12 Endocrinology and Metabolism DNAJC12 deficiency Hydroxylase co-chaperone Dystonia, parkinsonism, intellectual disability AR Tyrosine Tyrosinemia type 1 (hepatorenal) Fumarylacetoacetate hydrolase Liver failure, cirrhosis, rickets, failure to thrive, peripheral neuropathy, “boiled cabbage” odor Tyrosinemia type 2 (oculocutaneous) Tyrosine transaminase Palmoplantar keratosis, painful corneal erosions with photophobia, learning disability Tyrosinemia type 3 4-Hydroxyphenylpyruvate dioxygenase Hypertyrosinemia with normal liver function, occasional mental delay Hawkinsinuria 4-Hydroxyphenylpyruvate dioxygenase Transient failure to thrive, metabolic acidosis in infancy AD Alkaptonuria Homogentisic acid oxidase Ochronosis, arthritis, cardiac valve involvement, coronary artery calcification Maleylacetoacetate isomerase deficiency Maleylacetoacetate isomerase No clinical symptoms, elevated succinylacetone in blood and urine Albinism (oculocutaneous) Tyrosinase Hypopigmentation of hair, skin, and optic fundus; visual loss; photophobia Albinism (ocular) Different enzymes or transporters Hypopigmentation of optic fundus, visual loss AR, XL DOPA-responsive dystonia Tyrosine hydroxylase Rigidity, truncal hypotonia, tremor, intellectual disability AR GABA 4-Hydroxybutyric aciduria Succinic semialdehyde dehydrogenase Seizures, intellectual disability, hypotonia AR ABAT deficiency GABA transaminase Seizures, intellectual disability, hypotonia AR Tryptophan Hydroxykynureninuria Kynureninase Intellectual disability, spasticity AR Histidine Histidinemia Histidine-ammonia lyase Benign AR Urocanic aciduria Urocanase Occasional intellectual disability AR Formiminoglutamic aciduria Formiminotransferase Occasional intellectual disability AR Glycine Glycine encephalopathy Glycine cleavage (4 enzymes) Infantile seizures, lethargy, apnea, profound intellectual disability Sarcosinemia Sarcosine dehydrogenase Benign AR Hyperoxaluria type I Alanine:glyoxylate aminotransferase Calcium oxalate nephrolithiasis, renal failure AR Hyperoxaluria type II D-Glyceric acid dehydrogenase/ glyoxylate reductase Serine 3-PGDH deficiency Phosphoglycerate dehydrogenase Seizures, microcephaly, intellectual disability AR PSAT1 deficiency Phosphoserine aminotransferase Seizures, microcephaly, intellectual disability AR PSP deficiency Phosphoserine phosphatase Seizures, microcephaly, intellectual disability AR Proline Hyperprolinemia type 1 Proline oxidase Benign AR Hyperprolinemia type 2 Δ1-Pyrroline-5-carboxylate dehydrogenase Hyperhydroxyprolinemia Hydroxyproline oxidase Benign AR Prolidase deficiency Prolidase Mild intellectual disability, chronic dermatitis, autoimmunity AR PYCR1 deficiency Pyrroline-5-carboxylate reductase 1 Wrinkly skin, joint laxity, typical facial features, intellectual disability, osteopenia, intrauterine growth retardation, hypotonia PYCR2 deficiency Pyrroline-5-carboxylate reductase 2 Microcephaly, hypomyelination, and reduced cerebral white matter volume, failure to thrive, intellectual disability, movement disorders, seizures Proline (ornithine, arginine, citrulline) Δ1-Pyrroline-5-carboxylate synthase deficiency Δ1-Pyrroline-5-carboxylate synthase Hypotonia, seizures, neurodegeneration, peripheral neuropathy, joint laxity, skin hyperelasticity, subcapsular cataracts, hyperammonemia, adult spastic paraparesis (AD) Methionine Hypermethioninemia Methionine adenosyltransferase Usually benign AR S-Adenosylhomocysteine hydrolase deficiency S-Adenosylhomocysteine hydrolase Hypotonia, intellectual disability, absent tendon reflexes, delayed myelination Glycine N-methyltransferase deficiency Glycine N-methyltransferase Elevated liver transaminases AR Adenosine kinase deficiency Adenosine kinase Intellectual disability, seizures, liver dysfunction AR

AR AR AR AR AR AR AR AR AR AR Calcium oxalate nephrolithiasis, renal failure AR Febrile seizures, intellectual disability AR AR AR AR, AD AR (Continued)

TABLE 431-1  Inherited Disorders of Amino Acid Metabolism (Continued) AMINO ACID(S) CONDITION ENZYME DEFECT CLINICAL FINDINGS INHERITANCE Homocysteine Homocystinuria Cystathionine β-synthase Lens dislocation, thrombotic vascular disease, intellectual disability, osteoporosis Homocystinuria 5,10-Methylenetetrahydrofolate reductase Homocystinuria Methionine synthase and Methionine synthase reductase (cblE, G) Homocystinuria and methylmalonic acidemia Vitamin B12 lysosomal efflux and metabolism (cblC, -epiC, -D, -F, -J, -X) Cystathionine Cystathioninuria β-Cystathioninase Benign AR Cysteine Sulfocystinuria Sulfite oxidase or molybdenum cofactor deficiency Lysine Hyperlysinemia, saccharopinuria α-Aminoadipic semialdehyde synthase Benign AR Pyridoxine-dependent seizures L-Δ1-Piperideine-6-carboxilate dehydrogenase Lysine, tryptophan α-Ketoadipic acidemia α-Ketoadipic acid dehydrogenase DHTKD1 Lysine, tryptophan Glutaric acidemia type 1 Glutaryl-CoA dehydrogenase Progressive severe dystonia and athetosis, motor delays AR Ornithine Gyrate atrophy of the choroid and retina Ornithine-Δ-aminotransferase Myopia, night blindness, loss of peripheral vision, cataracts, chorioretinal degeneration Urea cycle Carbamoylphosphate synthase-1 deficiency Carbamoylphosphate synthase-1 Lethargy progressing to coma, protein aversion, intellectual disability, hyperammonemia N-Acetylglutamate synthase deficiency N-Acetylglutamate synthase Lethargy progressing to coma, protein aversion, intellectual disability, hyperammonemia Ornithine transcarbamylase deficiency Ornithine transcarbamylase Lethargy progressing to coma, protein aversion, intellectual disability, hyperammonemia Citrullinemia type 1 Argininosuccinate synthase Lethargy progressing to coma, protein aversion, intellectual disability, hyperammonemia, liver failure Argininosuccinic acidemia Argininosuccinate lyase Lethargy progressing to coma, protein aversion, intellectual disability, hyperammonemia, trichorrhexis nodosa, liver failure Arginase deficiency Arginase Spastic tetraparesis, microcephaly, intellectual disability, mild hyperammonemia Hyperornithinemia, hyperammonemia, homocitrullinuria Mitochondrial ornithine carrier ORNT1 Vomiting, lethargy, failure to thrive, intellectual disability, episodic confusion, hyperammonemia, protein intolerance Citrullinemia type 2 Mitochondrial aspartate/glutamate carrier CTLN2 Glutamine Glutamine synthetase deficiency Glutamine synthase Brain malformations, pachygyria, seizures, hypotonia, intellectual disability, dysmorphic features, low glutamine Glutaminase deficiency Glutaminase Epileptic encephalopathy, intellectual disability, ataxia, elevated glutamine Asparagine Asparagine synthetase deficiency Asparagine synthase Epileptic encephalopathy, seizures, microcephaly, simplified gyration pattern, hypotonia, tetraplegia, intellectual disability Valine Isobutyryl-CoA dehydrogenase deficiency Isobutyryl-CoA dehydrogenase Benign AR Isoleucine, leucine, valine Maple syrup urine disease Branched chain ketoacid dehydrogenase (E1α, E1β, E2,

E3 deficiency) Isoleucine, leucine, valine Hypervalinemia Branched-chain amino acid transferase 2 (BCAT2) Isoleucine, leucine, valine Branched-chain amino acid deficiency Branched chain ketoacid dehydrogenase kinase (BCHDK) Leucine Isovaleric acidemia Isovaleryl-CoA dehydrogenase Acidosis, ketosis, vomiting, coma, hyperammonemia, “sweaty feet” odor, protein intolerance 3-Methylcrotonyl

glycinuria 3-Methylcrotonyl-CoA carboxylase Stress-induced metabolic acidosis, hypotonia, hypoglycemia, “cat’s urine” odor 3-Methylglutaconic aciduria type I 3-Methylglutaconyl-CoA hydratase deficiency 3-Hydroxy-3-methylglutaric aciduria 3-Hydroxy-3-methylglutaryl-CoA lyase Stress-induced hypoketotic hypoglycemia and acidosis, encephalopathy, hyperammonemia

AR Intellectual disability, gait and psychiatric abnormalities, recurrent strokes AR Intellectual disability, hypotonia, seizures, megaloblastic anemia AR Intellectual disability, lethargy, failure to thrive, hypotonia, seizures, megaloblastic anemia AR, XL Inherited Disorders of Amino Acid Metabolism in Adults
CHAPTER 431 Seizures, intellectual disability, dislocated lenses AR Seizures, intellectual disability AR Benign AR AR AR AR XL AR AR AR AR Neonatal intrahepatic cholestasis, adult presentation with sudden behavioral changes and stupor, coma, hyperammonemia, liver failure AR AR AR   Lethargy, vomiting, encephalopathy, seizures, intellectual disability, “maple syrup” odor, protein intolerance AR Autism, headaches, intellectual disability AR Autism, epilepsy, intellectual disability, microcephaly   AR AR Stress-induced acidosis, leukodystrophy, hypotonia, hepatomegaly AR AR (Continued)

TABLE 431-1  Inherited Disorders of Amino Acid Metabolism (Continued) AMINO ACID(S) CONDITION ENZYME DEFECT CLINICAL FINDINGS INHERITANCE Isoleucine 2-Methylbutyryl-glycinuria 2-Methylbutyryl-CoA dehydrogenase Benign AR 2-Methyl-3-hydroxybutyrylCoA dehydrogenase deficiency 2-Methyl-3-hydroxybutyryl-CoA dehydrogenase 3-Oxothiolase deficiency 3-Oxothiolase Fasting-induced acidosis and ketosis, vomiting, lethargy AR Isoleucine, methionine, threonine, valine Propionic acidemia (pccA, -B) Propionyl-CoA carboxylase Metabolic ketoacidosis, hyperammonemia, hypotonia, lethargy, coma, protein intolerance, intellectual disability, hyperglycinemia Multiple carboxylase/ biotinidase deficiency Holocarboxylase synthase or biotinidase PART 12 Endocrinology and Metabolism Methylmalonic acidemia (mutase, cblA, B, racemase) Methylmalonyl-CoA mutase/ racemase or cobalamin reductase/ adenosyltransferase Abbreviations: AD, autosomal dominant; AR, autosomal recessive; Cbl, cobalamin; DOPA, dihydroxyphenylalanine; GABA, γ-aminobutyric acid; GTP, guanosine 5′-triphosphate; XL, X-linked. cases should be referred to a metabolic center for initiation of therapy. The parents need to be counseled about the natural history of the disease and its recurrence risk in future pregnancies. In some cases, parents need testing because they might have a disorder themselves (such as glutaric acidemia type 1, methylcrotonyl coenzyme A carbox­ ylase deficiency, primary carnitine deficiency, or fatty acid oxidation defects) since mothers with these conditions can sometimes be identi­ fied by abnormal newborn screening results in their offspring. Some metabolic disorders can remain asymptomatic until adult age, present­ ing only when fasting or severe stress requires full activity of affected metabolic pathways to provide energy. Selected disorders that illustrate the principles, properties, and problems presented by the disorders of amino acid metabolism are discussed in this chapter. THE HYPERPHENYLALANINEMIAS The hyperphenylalaninemias (Table 431-1) result from impaired conversion of phenylalanine to tyrosine. The most common and clinically important is phenylketonuria (frequency 1:16,500), which is an autosomal recessive disorder characterized by an increased con­ centration of phenylalanine and its by-products in body fluids and by severe intellectual disability if untreated in infancy. It results from reduced activity of phenylalanine hydroxylase. The accumulation of phenylalanine inhibits the transport of other amino acids required for protein or neurotransmitter synthesis, reduces synthesis and increases degradation of myelin, and leads to inadequate formation of norepi­ nephrine and serotonin. Phenylalanine is a competitive inhibitor of tyrosinase, a key enzyme in the pathway of melanin synthesis, resulting in hypopigmentation of hair and skin. Untreated children with classic phenylketonuria are normal at birth but fail to attain early develop­ mental milestones, develop microcephaly, and demonstrate progressive impairment of cerebral function. Hyperactivity, seizures, and severe intellectual disability are major clinical problems later in life. Elec­ troencephalographic abnormalities; “mousy” odor of skin, hair, and urine (due to phenylacetate accumulation); and a tendency to develop hypopigmentation (compared to the family background) and eczema complete the devastating clinical picture. In contrast, affected children who are detected and treated at birth show none of these abnormalities. TREATMENT Phenylketonuria To prevent intellectual disability, diagnosis and initiation of dietary treatment of classic phenylketonuria must occur before the child is 2 weeks of age. For this reason, newborns in North America, Australia, and Europe are screened by determinations of blood phe­ nylalanine levels. Abnormal values are confirmed using quantitative analysis of plasma amino acids. Dietary phenylalanine restriction is usually instituted if blood phenylalanine levels are >360 μmol/L. Treatment consists of a special diet low in phenylalanine and

Developmental regression, seizures, and rigidity sometimes triggered by illnesses XL AR Metabolic ketoacidosis, diffuse rash, alopecia, seizures, intellectual disability AR Metabolic ketoacidosis, hyperammonemia, hypertonia, lethargy, coma, protein intolerance, intellectual disability, hyperglycinemia AR supplemented with tyrosine since tyrosine becomes an essential amino acid in phenylalanine hydroxylase deficiency. With ther­ apy, plasma phenylalanine concentrations should be maintained between 120 and 360 μmol/L for life. Compliance with the strict diet is often difficult as patients become older; increased levels of phenylalanine in adults can cause deficits in executive function or psychiatric symptoms. Oral tetrahydrobiopterin (5–20 mg/kg per d), an essential cofactor of phenylalanine hydroxylase, can reduce phenylalanine levels in some patients with phenylketonuria in conjunction with a low-protein diet. Pegvaliase is a pegylated form of phenylalanine ammonia lyase, a bacterial enzyme that converts phenylalanine to trans-cinnamic acid and ammonia. This inject­ able drug can substantially reduce phenylalanine levels, allowing a normal diet. The bacterial origin of pegvaliase can cause immune reactions that limit its use in some patients with phenylketonuria. Women with phenylketonuria can become pregnant. If mater­ nal phenylalanine levels are not strictly controlled before and dur­ ing pregnancy, their offspring are at increased risk for congenital defects and microcephaly (maternal phenylketonuria). After birth, these children have severe intellectual disability and growth retar­ dation. Pregnancy risks can be minimized by continuing lifelong phenylalanine-restricted diets and assuring strict phenylalanine restriction 2 months prior to conception and throughout gestation. ■ ■THE HOMOCYSTINURIAS (HYPERHOMOCYSTEINEMIAS) The homocystinurias include 10 biochemically and clinically distinct disorders (Table 431-1) characterized by increased concentration of the sulfur-containing amino acid homocysteine in blood and urine. Classic homocystinuria, the most common (frequency 1:450,000), results from reduced activity of cystathionine β-synthase (Fig. 431-1), the pyridoxal phosphate–dependent enzyme that condenses homocys­ teine with serine to form cystathionine. Most patients present between 3 and 5 years of age with dislocated optic lenses and intellectual disabil­ ity (in about half of cases). Some patients develop a marfanoid habitus and radiologic evidence of osteoporosis. Life-threatening vascular complications (affecting coronary, renal, and cerebral arteries) can occur during the first decade of life and are the major cause of morbidity and mortality. Classic homocystin­ uria can be diagnosed with analysis of plasma amino acids, showing elevated methionine and presence of free homocystine. Total plasma homocysteine is also extremely elevated (usually >100 μM). Elevated levels of methionine can be also detected by neonatal screening, but milder variants can be missed by this approach. Treatment consists of a special diet restricted in protein and methionine. In approximately half of patients, oral pyridoxine (25–500 mg/d) produces a fall in plasma methionine and homocysteine concentration in body fluids. Folate and vitamin B12 deficiency should be prevented by adequate supplementa­ tion. Betaine is also effective in reducing homocysteine levels by favor­ ing its remethylation to methionine.

Re-methylation Methionine Synthase Reductase (cblE) CH3-S-(CH2)2-CH-COOH Glycine Serine Methionine Synthase (cblG) Methionine TetraHydro Folate (THF) Cobalamin (B12) cbl C, D, F, J, X, epi-cblC Dimethylglycine Betaine Homocysteine Methyltransferase Methyl-Cobalamin 5,10-Methylene THF N5-Methyl THF Methylene Tetrahydro Folate Reductase (MTHFR) Cystathionine b Synthase (B6) Cystathionase (B6) `-Ketobutyrate Cysteine FIGURE 431-1  Pathways, enzymes, and coenzymes involved in the homocystinurias. Methionine transfers a methyl group during its conversion to homocysteine. Defects in methyl transfer or in the subsequent metabolism of homocysteine by the pyridoxal phosphate (vitamin B6)-dependent cystathionine β-synthase increase plasma methionine levels. Homocysteine is transformed into methionine via remethylation. This occurs through methionine synthase, a reaction requiring methylcobalamin and folic acid. Deficiencies in these enzymes or lack of cofactors is associated with decreased or normal methionine levels. In an alternative pathway, homocysteine can be remethylated by betaine:homocysteine methyl transferase. The other forms of homocystinuria are the result of impaired remethylation of homocysteine to methionine. This can be caused by defective methionine synthase or reduced availability of two essential cofactors, 5-methyltetrahydrofolate and methylcobalamin (methylvitamin B12). In contrast to cystathionine β-synthase, elevated levels of free homocysteine are associated with low levels of methionine in the plasma amino acid profile in remethylation defects. Most of these conditions present with delays in development and some with megaloblastic anemia (methionine synthase-cblG and methio­ nine synthase reductase-cblE deficiency, in addition to combined methylmalonic acidemia-homocystinuria- cblC, cblD, cblF, cblJ, see Chap. 104). Therapy in these cases requires administration of meth­ ylfolate, hydroxycobalamin (an activated form of vitamin B12), and betaine. Hyperhomocysteinemia refers to increased total plasma concentra­ tion of homocysteine with or without an increase in free homocys­ teine (disulfide form). Hyperhomocysteinemia, in the absence of significant homocystinuria, is found in some heterozygotes for the genetic defects noted above or in homozygotes for milder variants. Changes of homocysteine levels are also observed with deficiency of pyridoxine, folic acid, or vitamin B12; with increasing age; with smoking; in postmenopausal women; in patients with renal failure, hypothyroidism, leukemias, autoinflammatory disorders; and during therapy with drugs such as methotrexate, nitrous oxide, givosiran, isoniazid, and some antiepileptic agents. Elevated homocysteine pro­ duces endothelial dysfunction, acting as an atherogenic and thrombo­ philic agent. Increased total plasma homocysteine has been associated with an increased risk for coronary, cerebrovascular, and peripheral arterial disease as well as for deep-vein thrombosis. In addition, hyperhomocysteinemia and folate and vitamin B12 deficiencies have been associated with an increased risk of neural tube defects in preg­ nant women and dementia (Alzheimer’s type), as well as Parkinson’s disease in the general population. Vitamin B12, folic acids, and pyri­ doxine supplements can reduce total plasma homocysteine levels in these cases, with reduction of the risk of stroke when levels are more severely increased (>30 μM).

Methyl transfer NH2 ATP Methionine Adenosyl Transferase (MAT) N-Methylglycine (Sarcosine) S-Adenosyl Methionine Inherited Disorders of Amino Acid Metabolism in Adults
CHAPTER 431 Glycine N-Methyltransferase Methyltransferases CH3 S-Adenosyl Homocysteine Glycine Betaine S-Adenosyl Homocysteine Hydrolase Creatine Guanidinoacetate Methyltransferase Homocysteine Adenosine Serine Guanidinoacetate Cystathionine Trans-sulfuration ALKAPTONURIA Alkaptonuria is a rare (frequency 1:250,000) disorder of tyrosine catabolism in which deficiency of homogentisate 1,2-dioxygenase (also known as homogentisic acid oxidase) leads to excretion of large amounts of homogentisic acid in urine and accumulation of oxidized homogentisic acid pigment in connective tissues (ochronosis). Alkap­ tonuria may go unrecognized until middle life, when degenerative joint disease develops. Prior to this time, about half of patients might be diagnosed for the presence of urine that becomes dark with stand­ ing or addition of alkali. Foci of gray-brown scleral pigment and gen­ eralized darkening of the concha, antihelix, and, finally, helix of the ear usually develop after age 30. Low back pain usually starts between 30 and 40 years of age. Ochronotic arthritis is heralded by pain, stiff­ ness, and some limitation of motion of the hips, knees, and shoulders. Acute arthritis may resemble rheumatoid arthritis, but small joints are usually spared. Pigmentation of heart valves, larynx, tympanic membranes, and skin occurs, and occasional patients develop pig­ mented renal or prostatic calculi. Pigment deposition in the heart and blood vessels leads to aortic stenosis necessitating valve replacement, especially after 60 years of age. The diagnosis should be suspected in a patient whose urine darkens to blackness. Homogentisic acid in urine is identified by urine organic acid analysis. Ochronotic arthritis is treated symptomatically with pain medications, spinal surgery, and arthroplasty (Chap. 383). Nitisinone (2-[2-nitro4-trifluoromethylbenzoyl]-1,3-cyclohexanedione), a drug used in tyrosinemia type 1, at low dose (10 mg/d) reduces urinary excre­ tion of homogentisic acid, delays progression, and improves clini­ cal signs of alkaptonuria. UREA CYCLE DEFECTS Excess ammonia generated from protein nitrogen is removed by the urea cycle, a process mediated by several enzymes and transporters (Fig. 431-2, Table 431-1). Complete absence of any of these enzymes usually causes severe hyperammonemia in newborns, while milder variants can be seen in adults. The accumulation of ammonia and glu­ tamine leads to direct neuronal toxicity and brain edema. Deficiencies

Acetyl-CoA+Glutamate NAG Synthase N-acetyl-Glutamate CO2+H2O CPS-1 CA5A H2CO3+NH3+2ATP Carbamylphosphate + Ornithine Mitochondrion PART 12 Endocrinology and Metabolism Aspartate Cytosol Citrin ORNT1 Aspartate + ASA Synthase Argininosuccinic Acid Arginine FIGURE 431-2  The urea cycle. This cycle, which is fully expressed only in the liver, forms urea starting from ammonia (NH3) derived from the nitrogen group of all amino acids. It requires many enzymes and mitochondrial transporters, any of which can be defective and may impair the function of the urea cycle. Ammonia escaping the urea cycle in periportal hepatocytes is conjugated with glutamate by glutamine synthase in perivenous hepatocytes to generate glutamine. ARG, arginase; ASA, argininosuccinic acid; ASL, argininosuccinate lyase; ASS, argininosuccinate synthase; CA5A, carbonic anhydrase 5a; citrin (SLC25A13), aspartate/glutamate exchanger; CP, carbamylphosphate; CPS-1, carbamylphosphate synthase 1; CTP, cytidine triphosphate; HHH, hyperammonemia, hyperornithinemia, homocitrullinuria syndrome; NAG, N-acetylglutamate; NAGS, N-acetylglutamate synthase; ORNT1 (SLC25A15), ornithine/citrulline mitochondrial transporter; OTC, ornithine transcarbamylase; UTP, uridine triphosphate. in urea cycle enzymes are individually rare, but as a group, they affect ~1:35,000 individuals. They are all transmitted as autosomal recessive traits, with the exception of ornithine transcarbamylase deficiency, which is X-linked and the most frequent urea cycle defect. Hepatocytes of females with ornithine transcarbamylase deficiency express either the normal or the mutant allele due to random X-inactivation and may be unable to remove excess ammonia if mutant cells are predominant. Infants with classic urea cycle defects present at 1–4 days of life with refusal to eat and lethargy progressing to coma and death. Milder enzyme deficiencies present with protein avoidance, recurrent vomiting, migraine, mood swings, chronic fatigue, irritability, and disorientation that can progress to coma. Some cases have presented with acute or chronic hepatic dysfunction. Females with ornithine transcarbamylase deficiency can present at time of childbirth due to the combination of involuntary fasting and stress that favors catabo­ lism. Administration of systemic corticosteroids or chemotherapy can precipitate hyperammonemia and can be fatal in previously asymp­ tomatic individuals of any age. These patients may be misdiagnosed as having gastrointestinal disorders, food allergies, behavioral prob­ lems, or nonspecific hepatitis. The diagnosis requires measurement of plasma ammonia, plasma amino acids, and urine orotic acid, useful for differentiating ornithine transcarbamylase deficiency from carba­ myl phosphate synthase-1 and N-acetylglutamate synthase deficiency. Increased plasma glutamine is seen with all urea cycle defects since ammonia not removed by the urea cycle in periportal hepatocytes is conjugated to glutamate by glutamine synthase in perivenous hepa­ tocytes. Citrulline is low or undetectable in proximal defects of the urea cycle (N-acetylglutamate synthase, carbamylphosphate synthase 1, and ornithine transcarbamylase deficiency), with urine orotic acid being increased only in ornithine transcarbamylase deficiency. Plasma citrulline is markedly increased in argininosuccinic acid synthase deficiency (citrullinemia type 1), with a milder elevation in arginino­ succinic acid lyase deficiency in the presence of argininosuccinic acid (argininosuccinic aciduria). Arginine levels are usually normal to low in these conditions and become markedly elevated only in patients with arginase deficiency. In addition to urea cycle defects, hyperammonemia can also be caused by liver disease from any cause and several organic acidemias and fatty acid oxidation defects (the latter two excluded by the analysis of urine organic acids and plasma acylcarnitine profile).

Urea Cycle UTP CTP Orotic Acid NAGS Carbamyl Phosphate Ornithine OTC ORNT1 (HHH) Citrulline Urea Arginase ARG Citrulline ASS ASA Lyase ASL Fumarate TREATMENT Urea Cycle Defects Therapy is aimed at stopping catabolism and ammonia produc­ tion by providing adequate calories (as IV glucose and lipids in the comatose patient) and, if needed, insulin. Excess nitrogen is removed by IV phenylacetate and benzoate (0.25 g/kg for the prim­ ing dose and subsequently as an infusion over 24 h) that conjugate with glutamine and glycine, respectively, to form phenylacetyl­ glutamine and hippuric acid, water-soluble molecules efficiently excreted in urine. Arginine (200 mg/kg per d) becomes an essential amino acid (except in arginase deficiency) and should be provided intravenously to resume protein synthesis. If these measures fail to reduce ammonia, hemodialysis should be initiated promptly. Chronic therapy consists of a protein-restricted diet, phenylbutyr­ ate, glycerol phenylbutyrate (a liquid drug better tolerated by most patients), arginine, or citrulline supplements, depending on the specific diagnosis. Oral carglumic acid can restore a functional urea cycle in patients with N-acetylglutamate synthase deficiency and renders other therapies unnecessary. Liver transplantation should be considered in patients with severe urea cycle defects that are dif­ ficult to control medically. Hyperammonemia due to a functional deficiency of glutamine synthase can occur in patients receiving chemotherapy for differ­ ent malignancies or undergoing solid organ transplants. It can also be seen with hepatic cirrhosis. Several of these patients have been successfully rescued from hyperammonemia using the protocol described above for urea cycle defects. ■ ■FURTHER READING Guéant JL et al: Hyperhomocysteinemia in cardiovascular diseases: Revisiting observational studies and clinical trials. Thromb Haemost 123:270, 2023. Ranganath LR et al: Efficacy and safety of once-daily nitisinone for patients with alkaptonuria (SONIA 2): An international, multicentre, open-label, randomised controlled trial. Lancet Diabetes Endocrinol 8:762, 2020. Van Spronsen FJ et al: Phenylketonuria. Nat Rev Dis Primers 7:36, 2021.

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432 Inherited Defects of Membrane Transport

Nicola Longo

Inherited Defects of

Membrane Transport Membrane transporters mediate the passage of amino acids, oligopeptides, sugars, cations, anions, vitamins, water, and other molecules across cellular membranes and are encoded by members of the solute-carrier gene (SLC) superfamily. These transporters are located on the plasma membrane or intracellular organelles, and their cellular and tissue distribution in addi­ tion to the presence (or absence) of redundant transporters explains organ involvement and possible metabolic disturbances. Transport processes are essential for the normal function of every organ, but especially the brain and sensory organs (Table 432-1). Inherited defects impairing the transport of selected amino acids that can present in adults are discussed here as examples of the abnormalities encountered; others are considered elsewhere in this text. ■ ■CYSTINURIA Cystinuria (worldwide frequency of 1 in 7000) is an autosomal reces­ sive disorder caused by defective transporters in the apical brush border of proximal renal tubule and small intestinal cells. It is char­ acterized by impaired reabsorption and excessive urinary excretion of the amino acids lysine, arginine, ornithine, and cystine that are dibasic in the physiologically acidic pH of urine. Because cystine is poorly soluble, its excess predisposes to the formation of renal, ureteral, and bladder stones. Such stones are responsible for the signs and symptoms of the disorder. There are two variants of cystinuria. Homozygotes for both variants have high urinary excretion of cystine, lysine, arginine, and ornithine. Type A heterozygotes usually have normal urinary amino acid excre­ tion, whereas most type B heterozygotes have moderately increased urinary excretion of cystine that, in some circumstances, can result in the formation of kidney stones. The gene for type A cystinuria (SLC3A1, chromosome 2p16.3) encodes a membrane glycoprotein. Type B cystinuria is caused by mutations in SLC7A9 (chromosome 19q13) that encodes the b0,+ amino acid transporter. The glycoprotein encoded by SLC3A1 favors the correct processing of the b0,+ membrane transporter and explains why mutations in two different genes cause a similar disease. Cystine stones account for 1–2% of all urinary tract calculi and for ~4–5% of stones in children. Cystinuria homozygotes regularly excrete 2400–7200 μmol (600–1800 mg) of cystine daily. Since the maximum solubility of cystine in the physiologic urinary pH range of 4.5–7.0 is ~1200 μmol/L (300 mg/L), cystine needs to be diluted to 2.5–7 L of water to prevent crystalluria. Stone formation usually manifests in the second or third decade but may occur in the first year of life. Symptoms and signs are those typical of urolithiasis: hematuria, flank pain, renal colic, obstructive uropathy, and infection (Chap. 330). Recurrent uro­ lithiasis may lead to progressive renal insufficiency. Cystinuria is suspected after observing typical hexagonal crystals in the sediment of acidified, concentrated, chilled urine or after per­ forming a urinary nitroprusside test. Quantitative urine amino acid analysis shows selective overexcretion of cystine, lysine, arginine, and ornithine. Quantitative measurements are important for differentiating heterozygotes from homozygotes and for following free cystine excre­ tion during therapy. Management is aimed at preventing cystine crystal formation by increasing urinary volume and by maintaining an alkaline urine pH. Fluid ingestion in excess of 4 L/d is essential, and 5–7 L/d is optimal. Urinary cystine concentration should be <1000 μmol/L (250 mg/L). The daily fluid ingestion necessary to maintain this dilution of excreted cystine should be spaced over 24 h, with one-third of the total vol­ ume ingested between bedtime and 3 a.m. Cystine solubility rises sharply above pH 7.5, and urinary alkalinization (with potassium citrate) can be therapeutic. Penicillamine (1–3 g/d) and tiopronin

(α-mercaptopropionylglycine, 800–1200 mg/d in four divided doses) undergo sulfhydryl-disulfide exchange with cystine to form mixed disulfides. Because these disulfides are much more soluble than cys­ tine, pharmacologic therapy can prevent and promote dissolution of calculi. Penicillamine can have significant side effects and should be reserved for patients who fail to respond to hydration alone or who are in a high-risk category (e.g., one remaining kidney, renal insuf­ ficiency). When medical management fails, shock wave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy are effective for most stones. Open urologic surgery is considered only for complex staghorn stones or when the patient has concomitant renal or ureteral abnormalities. Occasional patients progress to renal failure and require kidney transplantation.

Inherited Defects of Membrane Transport CHAPTER 432 ■ ■LYSINURIC PROTEIN INTOLERANCE Lysinuric protein intolerance is characterized by a defect in renal tubular reabsorption and intestinal transport of the three dibasic amino acids lysine, arginine, and ornithine but not cystine. It is most common in Finland (1 in 60,000), southern Italy, and Japan, but is rare elsewhere. The transport defect affects basolateral rather than luminal membrane transport and causes secondary impairment of the urea cycle. The defective gene (SLC7A7, chromosome 14q11.2) encodes the y+LAT membrane transporter, which associates with the cell-surface glycoprotein 4F2 heavy chain to form the complete sodium-independent transporter y+L. Manifestations are related to impairment of the urea cycle and to immune dysfunction likely attributable to nitric oxide overproduc­ tion secondary to arginine intracellular trapping within white blood cells. Affected patients present in childhood with hepatosplenomegaly, protein intolerance, and episodic ammonia intoxication. Adults may present with severe osteoporosis, pancreatitis, impaired renal function, pulmonary alveolar proteinosis, various autoimmune disorders, and an incompletely characterized immune deficiency. Plasma concentra­ tions of lysine, arginine, and ornithine are reduced, whereas urinary excretion of lysine, arginine, ornithine, and orotic acid is increased. Hyperammonemia may develop after the ingestion of protein loads or with infections, probably because of insufficient amounts of ornithine to maintain proper function of the urea cycle. Diagnosis is confirmed by sequencing of the SLC7A7 gene that is included in most hyper­ ammonemia panels. Therapy consists of dietary protein restriction, supplementation of citrulline (2–8 g/d), a neutral amino acid that fuels the urea cycle when metabolized to arginine and ornithine, and nitrogen scavengers (phenylbutyrate, benzoate) in case of persistent hyperammonemia. Pulmonary disease can respond to glucocorticoids or recombinant human granulocyte-macrophage colony-stimulating factor but might require broncho-alveolar or whole lung lavage in some patients. Women with lysinuric protein intolerance who become preg­ nant have an increased risk of anemia, toxemia, and bleeding complica­ tions during delivery. These can be minimized by aggressive nutritional therapy and control of blood pressure. Their infants can have intrauter­ ine growth restriction but have normal neurologic function. ■ ■CITRULLINEMIA TYPE 2 (CITRIN DEFICIENCY) Citrullinemia type 2 is a recessive condition caused by deficiency of the mitochondrial aspartate-glutamate carrier AGC2 (citrin). A defect in this transporter reduces the availability of cytoplasmic aspartate to combine with citrulline to form argininosuccinate (see Fig. 431-2), impairing the urea cycle and decreasing the transfer of reducing equivalents from the cytosol to the mitochondria through the malateaspartate NADH shuttle. Mutations in the SLC25A13 gene on chromo­ some 7q21.3 that encodes for this transporter are rare in Caucasians but affect ~1:20,000 people with ancestry from Japan, China, and Southeast Asia with variable penetrance. The disease can present in children with neonatal intrahepatic cho­ lestasis, failure to thrive, and dyslipidemia but usually presents with sudden onset between 20 and 50 years of age with recurring episodes of hyperammonemia with associated neuropsychiatric symptoms such as altered mental status, irritability, seizures, or coma-resembling hepatic encephalopathy. Some patients might come to medical attention for

TABLE 432-1  Genetic Disorders of Amino Acid Transport TISSUES MANIFESTING TRANSPORT DEFECT MOLECULAR DEFECT MAJOR CLINICAL MANIFESTATIONS INHERITANCE DISORDER SUBSTRATES Cystinuria Cystine, lysine, arginine, ornithine Proximal renal tubule, jejunal mucosa Lysinuric protein intolerance Lysine, arginine, ornithine Proximal renal tubule, jejunal mucosa Hartnup disease Neutral amino acids Proximal renal tubule, jejunal mucosa Histidinuria Histidine Proximal renal tubule, jejunal mucosa PART 12 Endocrinology and Metabolism Iminoglycinuria Glycine, proline, hydroxyproline Proximal renal tubule, jejunal mucosa Dicarboxylic aminoaciduria Glutamic acid, aspartic acid Proximal renal tubule, jejunal mucosa Hyperargininemia Arginine, lysine, ornithine Ubiquitous CAT2 cationic amino acid transporter SLC7A2 Brain branched-chain amino acid deficiency Leucine, isoleucine, valine Plasma membrane of blood-brain barrier Citrullinemia type 2 Aspartate, glutamate, malate Inner mitochondrial membrane Hyperornithinemia, hyperammonemia, homocitrullinuria Ornithine, citrulline Inner mitochondrial membrane Epileptic encephalopathy Aspartate, glutamate, malate Inner mitochondrial membrane Epileptic encephalopathy Glutamate Inner mitochondrial membrane Epileptic encephalopathy Glutamic acid, aspartic acid Presynaptic glutamatergic nerve endings Episodic ataxia Glutamic acid, aspartic acid Presynaptic glutamatergic nerve endings Brain serine deficiency Alanine, serine, cysteine, threonine Neuronal cells ASCT neutral amino acid transporter SLC1A4 Glycine encephalopathy with normal serum glycine Glycine Astrocytes and neuronal cells Hyperekplexia-3 Glycine Neuronal cells GLYT2 Presynaptic glycine transporter SLC6A5 Intellectual disability Proline, glycine, leucine, and alanine, glutamine Neuronal cells synaptic vesicles Deafness Glutamic acid Neuronal cortical synaptic vesicles Foveal hypoplasia Glutamine Retinal photoreceptors SLC38A8 Foveal hypoplasia, optic nerve decussation defects, anterior segment dysgenesis Retinitis pigmentosa Arginine, lysine, ornithine Retinal photoreceptors Cationic amino acid transporter SLC7A14 Early retinal degeneration Taurine Retinal cells TAUT taurine transporter SLC6A6 Cystinosis Cystine Lysosomal membranes Lysosomal cystine transporter Abbreviations: AD, autosomal dominant; AR, autosomal recessive. hypertriglyceridemia, pancreatitis, hepatoma, or fatty liver histo­ logically similar to nonalcoholic steatohepatitis. Without therapy, most symptomatic patients die with cerebral edema within a few years. Epi­ sodes are usually triggered by medications (such as acetaminophen), surgery, alcohol, or high sugar intake, with the latter conditions causing NADH production in the cytoplasm. NADH is not generated by the metabolism of proteins or fats, and individuals with citrullinemia type 2 spontaneously prefer foods such as meat, eggs, and fish and avoid carbohydrates.

Shared dibasic-cystine transporter SLC3A1, SLC7A9 Cystine nephrolithiasis AR Dibasic transporter SLC7A7 Protein intolerance, hyperammonemia, intellectual disability AR Neutral amino acid transporter SLC6A19 Constant neutral aminoaciduria, intermittent symptoms of pellagra AR Histidine transporter Intellectual disability AR Shared glycine–amino acid transporter SLC6A20, SLC6A18, SLC36A2 None AR Shared dicarboxylic amino acid transporter SLC1A1 None AR Hyperargininemia, Hyperammonemia (?) AR Branched-chain amino acid transporter SLC7A5 Microcephaly, intellectual disability, seizures, autism AR Mitochondrial aspartate/ glutamate carrier 2 SLC25A13 Sudden behavioral changes with stupor, coma, hyperammonemia AR Mitochondrial ornithine carrier SLC25A15 Lethargy, failure to thrive, intellectual disability, episodic confusion, hyperammonemia, protein intolerance AR Mitochondrial aspartate/ glutamate carrier 1 SLC25A12 Intellectual disability, epilepsy, hypotonia, cerebral atrophy, and hypomyelination AR Mitochondrial glutamate carrier SLC25A22 Intellectual disability, epilepsy AR EEAT2 Neuronal dicarboxylic amino acid transporter SLC1A2 Developmental and Epileptic Encephalopathy AD EEAT1 Neuronal dicarboxylic amino acid transporter SLC1A3 Episodic ataxia AD Progressive microcephaly, intellectual disability, spasticity AR GLYT1 astrocyte glycine transporter SLC6A9 Arthrogryposis, apnea, axial hypotonia, spasticity, intellectual disability AR Exaggerated startle response, hypertonia, apnea AR NTT4 synaptic vesicle neutral amino acid transporter SLC6A17 Intellectual disability, tremor AR VGLUT3 vesicular glutamate transporter SLC17A8 Deafness AD AR Retinitis pigmentosa, blindness AR Nystagmus, vision loss, retinal degeneration AR Renal failure, hypothyroidism, blindness AR Laboratory studies during an acute attack can show elevated ammo­ nia, citrulline, and arginine with low or normal levels of glutamine (the latter is usually increased in classic urea cycle defects). Levels of galactose1-phosphate in red blood cells are also increased, reflecting defective transfer of reducing equivalents from the cytosol to mitochondria. The diagnosis is confirmed by demonstrating pathogenic variants in the SLC25A13 gene. Liver transplantation prevents progression of the disease and normalizes biochemical parameters. A ketogenic diet high in fats and proteins and low in carbohydrates with supplements of

medium-chain triglycerides, arginine, and pyruvate is also effective in preventing or delaying disease progression. ■ ■HARTNUP DISEASE Hartnup disease (frequency 1 in 24,000) is an autosomal recessive dis­ order characterized by pellagra-like skin lesions, variable neurologic manifestations, and neutral and aromatic aminoaciduria. Alanine, serine, threonine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, glutamine, asparagine, and histidine are excreted in urine in quantities 5–10 times greater than normal, and intestinal transport of these same amino acids is defective. The defective neutral amino acid transporter, B°AT1 encoded by the SLC6A19 gene on chro­ mosome 5p15, requires either collectrin or angiotensin-converting enzyme 2 (one of the binding sites for SARS-CoV-2) for surface expres­ sion in the kidney and intestine, respectively. The clinical manifestations result from nutritional deficiency of the essential amino acid tryptophan, caused by its intestinal and renal malabsorption, and of niacin, which derives in part from tryptophan metabolism. Only a small fraction of patients with Hartnup disease develop symptoms, implying that manifestations depend on other factors in addition to the transport defect. The diagnosis of Hartnup disease should be suspected in any patient with clinical features of pel­ lagra, recurrent diarrhea, and/or neurologic symptoms who does not have a history of dietary niacin deficiency (Chap. 345). The neurologic and psychiatric manifestations range from attacks of spastic paraplegia to cerebellar ataxia to mild emotional lability to frank delirium, and they are usually accompanied by exacerbations of the erythematous, eczematoid skin rash. Fever, sunlight, stress, and sulfonamide therapy provoke clinical relapses. Diagnosis is made by detection of the neutral aminoaciduria (which does not occur in dietary niacin deficiency) and is confirmed by genetic testing of the SLC6A19 or the CTLRN gene (coding for collectrin), whose deficiency produces a biochemical phe­ nocopy. Treatment includes a high-protein diet and daily nicotinamide supplementation (50–250 mg). ■ ■CYSTINOSIS Cystinosis (frequency 1 in 100,000–200,000) is an autosomal reces­ sive disorder caused by mutations in the CTNS gene encoding the lysosomal cystine/proton transporter (cystinosin). In this condition, cystine derived from protein degradation accumulates inside lyso­ somes and forms crystals due to its poor solubility. Depending on the degree of impairment of transporter function, three clinical forms are recognized. The most severe form, classic nephropathic cystinosis, causes renal Fanconi syndrome with rickets during the first year of life and, without treatment, evolves to renal failure usually by 10 years of

age. Juvenile nephropathic cystinosis presents with proteinuria slowly leading to kidney failure, whereas photophobia, caused by deposition of cystine crystals in the cornea, is the only manifestation of ocular nonnephropathic cystinosis. Cystinosis is suspected by the identifica­ tion of cystine crystals in the cornea by slit lamp examination and diagnosed by measuring cystine content in white blood cells and/or DNA testing (including deletion analysis) of the CTNS gene. Therapy consists in the administration of extended release cysteamine bitartrate that enters lysosomes and forms a mixed disulfide with cysteine that is exported from the lysosome using a cationic amino acid transporter. This drug is given orally and should be slowly increased to the main­ tenance dose of 1.3 g/m2 divided into two daily administrations while monitoring white blood cell (WBC) cystine levels for efficacy. This therapy delays renal failure and is more effective if started early in the course of the disease. Cysteamine eye drops can relieve photophobia. Renal replacement therapy with salts, alkali, and activated vitamin D is necessary for renal Fanconi syndrome. Cystine accumulation occurs in all organs and tissues, causing additional complications such as hypothyroidism, hypohydrosis, diabetes, and delayed puberty in both males and females with primary hypogonadism in males. Growth hormone replacement, l-thyroxine for hypothyroidism, insulin for diabetes mellitus, and testosterone for hypogonadism in males may be necessary. Despite therapy, many patients with cystinosis progress to end-stage renal failure and require kidney transplantation. Late-onset complications include hepatomegaly and splenomegaly that occur in approximately one-third of subjects and a vacuolar myopathy caus­ ing weakness (initially involving the distal extremities), swallowing difficulties, gastrointestinal dysmotility, and pulmonary insufficiency. Before the availability of cystine-depleting therapy and renal trans­ plantation, the life span in nephropathic cystinosis was <10 years. With current therapies, affected individuals can survive into the late forties with satisfactory quality of life.

Inherited Defects of Membrane Transport CHAPTER 432 ■ ■FURTHER READING Bölsterli BK et al: Ketogenic diet treatment of defects in the mito­ chondrial malate aspartate shuttle and pyruvate carrier. Nutrients 14:3605, 2022. Levtchenko E et al: Expert guidance on the multidisciplinary man­ agement of cystinosis in adolescent and adult patients. Clin Kidney J 15:1675, 2022. Servais A et al: Cystinuria: Clinical practice recommendation. Kidney Int 99:48, 2021. Yahyaoui R, Pérez-frías J: Amino acid transport defects in human inherited metabolic disorders. Int J Mol Sci 21:119, 2019.

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