21.10.6 Haemolytic uraemic syndrome 5027 Edwin K.S

21.10.6 Haemolytic uraemic syndrome 5027 Edwin K.S. Wong and David Kavanagh

21.10.6  Haemolytic uraemic syndrome 5027 D’Amico G (1998). Renal involvement in hepatitis C infection: cryoglobulinemic glomerulonephritis. Kidney Int, 54, 650–​71. De Vita S, et al. (2012). A randomized controlled trial of rituximab for the treatment of severe cryoglobulinemic vasculitis. Arthritis Rheum, 64, 843–​53. Saadoun D, et  al. (2006). Antiviral therapy for hepatitis C virus-​ associated mixed cryoglobulinemia vasculitis. Arthritis Rheum, 54, 3696–​706. Saadoun D, et al. (2017). Efficacy and Safety of Sofosbuvir Plus Daclatasvir for Treatment of HCV-Associated Cryoglobulinemia Vasculitis. Gastroenterology, 153, 49–52.e5. Terrier B, et  al. (2012). Management of non infectious mixed cryoglobulinaemia vasculitis: data from 242 cases included in the CryoVas survey. Blood, 119, 5996–​6004. Renal involvement in Waldenström’s macroglobulinaemia Audard V, et al. (2008). Renal lesions associated with IgM-​secreting monoclonal proliferations: revisiting the disease spectrum. Clin J Am Soc Nephrol, 3, 1339–​49. Chauvet S, et al. (2015). Kidney disorders associated with monoclonal IgM-​secreting B-​cell lymphoproliferative disorders: a case series of 35 patients. Am J Kidney Dis, 66, 756–​67. C3 glomerulopathy and monoclonal gammopathy Bridoux F, et al. (2011). Glomerulonephritis with isolated C3 deposits and monoclonal gammopathy: a fortuitous association? Clin J Am Soc Nephrol, 6, 2165–​74. Chauvet S, et al. (2017). Treatment of B-cell disorder improves renal outcome of patients with monoclonal gammopathy-associated C3 glomerulopathy. Blood, 129, 1437–447. Chauvet S, et al. (2018). Both monoclonal and polyclonal immuno- globulin contingents mediate complement activation in monoclonal gammopathy associated-C3 glomerulopathy. Front Immunol, 9, 2260. Ravindran A, et al. (2018). C3 glomerulopathy associated with mono- clonal Ig is a distinct subtype. Kidney Int, 94, 178–86. Zand L, et al. (2013). C3 glomerulonephritis associated with mono- clonal gammopathy: a case series. Am J Kidney Dis, 62, 506–​14. Renal involvement in lymphomas and leukaemias Moulin B, et al. (1992). Glomerulonephritis in chronic lymphocytic leukemia and related B-​cell lymphomas. Kidney Int, 42, 127–​35. Ronco PM (1999). Paraneoplastic glomerulopathies: new insights into an old entity. Kidney Int, 56, 355–​77. Renal involvement in POEMS syndrome Nakamoto Y, et al. (1999). A spectrum of clinicopathological features of nephropathy associated with POEMS syndrome. Nephrol Dial Transplant, 14, 2370–​8. Tumour lysis syndrome Coiffier B, et al. (2008). Guidelines for the management of pediatric and adult tumor lysis syndrome: an evidence-​based review. J Clin Oncol, 26, 2667–​78. Cairo MS, et  al. (2010). Recommendations for the evaluation of
risk and prophylaxis of tumour lysis syndrome (TLS) in adults and children with malignant diseases: an expert TLS panel consensus. Br J Haematol, 149, 578–​86. Rampello E, et al. (2006). The management of tumor lysis syndrome. Nat Clin Pract Oncol, 3, 438–​47. 21.10.6  Haemolytic uraemic syndrome Edwin K.S. Wong and David Kavanagh ESSENTIALS Haemolytic uraemic syndrome (HUS) is a thrombotic microangiopathy characterized by the triad of thrombocytopenia, microangiopathic haemolytic anaemia, and acute kidney injury. It is most often caused by Shiga toxin-​producing Escherichia coli (STEC-​HUS), and any HUS not caused by this is often termed atypical HUS (aHUS). aHUS may be caused by an underlying complement system abnormality (primary aHUS) or by a range of precipitating events, such as infections or drugs (secondary aHUS). Management of STEC-​HUS is supportive. In aHUS, plasma exchange is the initial treatment of choice until ADAMTS13 activity is available to exclude thrombotic thrombocytopenic purpura as a diagnosis. Once this has been done, eculizumab should be instigated as soon as possible. Introduction Haemolytic uraemic syndrome (HUS) is a thrombotic microangiopathy characterized by the triad of thrombocytopenia, microangiopathic haemolytic anaemia, and acute kidney injury. HUS is broadly classified according to aetiology. The most common form of HUS is secondary to Shiga toxin-​producing Escherichia coli (STEC), STEC-​HUS. The term, atypical HUS (aHUS) has been used to classify any HUS not caused by Shiga toxin. With the discovery of the role of complement gene mutations in aHUS, primary aHUS has been used to refer to those cases with documented complement dysregulation. Many precipitating events, including infections, drugs, auto- immune conditions, transplants, pregnancy, and metabolic condi- tions have been associated with aHUS. These have frequently been called secondary aHUS. It is increasingly recognized that patients with an underlying complement system abnormality often require a secondary trigger for aHUS to manifest. Classifications describing both the genetic background and aetiological trigger are beginning to be introduced. Epidemiology The incidence of STEC-​HUS is approximately 20 per million popu- lation per year, but it is more common in children. An exception to this was in the 2011 E. coli 0104:H4 outbreak in Northern Europe where more than 800 cases of STEC-​HUS were reported, predomin- antly adults. The best estimate of aHUS incidence is 0.42 per million population per year in a British population. Pathology In the acute phase of disease, glomerular capillary wall thickening is seen as a result of endothelial cell swelling and accumulation of

section 21  Disorders of the kidney and urinary tract 5028 flocculent material between the endothelium and the underlying basement membrane (Fig. 21.10.6.1). Double contouring can be seen on silver staining. Collapsed capillary loops containing frag- mented red blood cells, fibrin, and platelet thrombi give the classical bloodless glomerular appearance. Fibrinoid necrosis of the afferent arteriole associated with thrombosis is also present. Mesangiolysis and development of aneurysmal dilatation of the capillaries may be seen. Subsequently, there is mucoid intimal hyperplasia with narrowing of the vessel lumen. With time, sclerotic and membranoproliferative changes may develop. Immunofluorescence demonstrates fibrin or fibrinogen in the glomeruli and vessel walls and nonspecific depos- ition of immunoglobulin and complement may be seen. There are no pathognomonic features to allow discrimination of STEC-​HUS from aHUS on histological grounds. Pathogenesis STEC-​HUS E.  coli O157:H7 is the most common strain causing STEC-​ HUS. Other serotypes of E. coli can also produce toxin, and the largest recorded outbreak of STEC-​HUS occurred in Northern Europe in 2011 due to infection with serotype O104:H4. In developing countries, Shigella dysenteriae type 1 is a common cause of HUS. STEC strains adhere to the gut and Shiga toxin is translocated through the intestinal epithelium. It has been suggested that Shiga toxin is then taken up by circulating leucocytes and transported to the kidney. Globotriaosylceramide (Gb3) is the receptor for Shiga toxin and mediates internalization, following which it is transported to the endoplasmic reticulum. The Shiga toxin complex is then cleaved to release the enzymatically active component that inacti- vates the ribosome, leading to inhibition of protein synthesis and cell death. It can also activate signalling pathways, inducing an inflamma- tory response in affected cells Atypical HUS Complement-​mediated aHUS A series of groundbreaking studies in the late 1990s established the role of complement overactivation in the pathogenesis of aHUS (Fig. 21.10.6.2). In patients with aHUS, loss-​of-​function mutations in complement regulators, activating mutations in complement components, and autoantibodies to complement regulatory compo- nents have been reported (Table 21.10.6.1). Loss-​of-​function mutations Mutations in the complement factor H gene (CFH) are the most common genetic predisposition to disease, accounting for around 25% of aHUS. The factor H protein (FH) is the major regulator of complement in the fluid phase. It functions by competing with factor B (FB) for C3b binding, decaying the complement compo- nent 3 (C3) convertase, and by acting as a cofactor for factor I (FI)-​ mediated C3b proteolysis. There is also a recognition domain at the C-​terminal end of FH that binds to C3b and glycosaminoglycans allowing FH to bind to and regulate complement on the glomerular endothelial surface. In aHUS, many of the mutations alter this re- gion and thus impair cell surface complement regulation. FI is a serum serine protease that cleaves C3b and C4b in the pres- ence of its cofactors (FH and CD46). Mutations in the complement factor I gene (CFI) are found in around 5 to 10% of aHUS, and de- fective regulation of complement has been demonstrated in func- tional analyses. CD46 is a cell surface-​bound complement regulator that acts as a cofactor for FI. Mutations in the CD46 gene account for approximately 10% of aHUS cases, with most mutations resulting in a quantitative deficiency. Activating mutations Activating mutations have been described in the genes encoding complement factor B (CFB) and C3 (C3). These are the complement components from which the amplifying C3 convertase is comprised. C3 mutations are found in around 2 to 10% of aHUS cases, whereas CFB mutations are rare. Mutations in both result in increased C3 convertase activity and consequently greater complement-​mediated damage to glomerular endothelium. Inhibitory autoantibodies Autoantibodies against FH have been identified in aHUS. These are usually shown to block the ability of FH to bind to C3b or glycosa- minoglycans and, therefore, inhibit complement regulation at the glomerular endothelium. Penetrance of disease Penetrance of disease is age related and has been reported to be as high as 64% by the age of 70 for individuals carrying a single genetic mutation. This suggests that additional disease risk modifiers are important. Around 3% of patients have one or more mutations, with increased penetrance per extra mutation. Together, these still do not explain why some patients develop disease until later in life. This is best explained by the need for an environmental trigger such as infection, drugs, or pregnancy (Box 21.10.6.1). Fig. 21.10.6.1  A glomerulus from a patient with HUS showing severe acute changes of congestion, intraluminal thrombi, red cell fragmentation, and endothelial cell swelling (haematoxylin and eosin, magnification ×400).

21.10.6  Haemolytic uraemic syndrome 5029 Other forms of aHUS Genetic Autosomal recessive defects in methylmalonic aciduria and homocystinuria, cobalamin C (cblC) type (MMACHC) and diacylglycerol kinase-​ε (DGKE) have been shown to cause aHUS (Table 21.10.6.1). Combined methylmalonic aciduria and homocystinuria (cblC) is a disorder of cobalamin (vitamin B12) metabolism characterized by neurological, metabolic, and developmental symptoms. It is a het- erogeneous disorder and only some patients develop aHUS. The pathophysiological mechanism of HUS in the cblC defect is unclear, but the endothelial abnormalities on kidney biopsies are striking and suggest that endothelial cell dysfunction may be the precipitating event. Long-​term management of cblC disease is with cobalamin, folinic acid, and betaine. Mutations in DGKE have been reported to cause aHUS in the first year of life. DGK-​ε is part of an intracellular signalling cascade and Activation Amplification Loop C3 convertase C5 convertase C5 C5b Eculizumab MAC C5a C3b C3b C3b Bb — — Bb Ba B C3 FH FI CD46 C3b Terminal Pathway Classical Pathway Alternative Pathway Lectin Pathway Regulation Fig. 21.10.6.2  Complement cascade. Activation of the complement system occurs via one of three pathways, classical, alternative, or lectin, resulting in the cleavage of C3 into C3b. C3b then forms C3bBb, the C3 convertase of the alternative pathway, which in turn generates more C3b as part of a positive amplification loop. This then leads to the formation of C3bC3bBb, the C5 convertase, and activation of terminal pathway by cleaving C5 into C5a and C5b. C5a is an anaphylatoxin while C5b allows formation of membrane attack complex (MAC) generation and cell lysis. The regulatory proteins (FH, FI, and CD46) protect the host from complement overactivation by preventing persistent amplification of complement. Eculizumab prevents terminal pathway activation by inhibition of the cleavage of C5.

section 21  Disorders of the kidney and urinary tract 5030 although its role in the pathogenesis of aHUS has yet to be fully elu- cidated, it is not thought to participate in the complement system. In keeping with this, several individuals with mutations in DGKE have failed to respond to eculizumab. Noninherited Infection with neuraminidase-​producing Streptococcus pneumoniae accounts for approximately 5% of childhood HUS. The incidence is greatest in children younger than 2 years, most commonly in pa- tients with parapneumonic empyema. Neuraminidase cleaves sialic acid residues from the glycoproteins on the cell membrane of erythrocytes, platelets, and endothelium, exposing the normally hidden Thomsen–​Friedenreich antigen (T antigen). This then reacts with anti-​T IgM antibodies that are nor- mally present in plasma. It has been hypothesized that binding of anti-​T IgM to platelets and glomerular endothelium causes throm- botic microangiopathy by platelet aggregation and direct endo- thelial cell damage. Treatment is supportive with eradication of streptococcal infection. Many drugs have been reported to cause aHUS and this occurs by two main mechanisms:  immune-​mediated damage and direct toxicity. For example, quinine induces the development of autoanti- bodies reactive with either platelet glycoprotein Ib/​IX or IIb/​IIIa complexes, or both. In contrast, mitomycin C, an alkylating agent used to treat a variety of malignancies, is thought to cause aHUS by a direct toxic effect on endothelium. Pregnancy was historically cited as a cause of aHUS, but re- cent studies have suggested that over 80% of patients have a com- plement gene mutation and that pregnancy acts by unmasking complement-​mediated aHUS. Clinical features The diagnostic triad of acute kidney injury, microangiopathic haemolytic anaemia, and thrombocytopenia is common to both STEC-​HUS and aHUS. In cases of STEC-​HUS there is usually a prodromal phase. Around 3 days after ingestion of contaminated food, abdominal pain and bloody diarrhoea usually, although not invariably, occur. HUS de- velops in about 10% of patients after 3 to 4 days. In complement-​mediated aHUS, a triggering event is typically noted prior to presentation. Upper respiratory tract infections, fevers, pregnancy, and drugs have been suggested as potential trig- gers. Additionally, non-​STEC diarrhoea is a not uncommon trigger and clinicians should not assume diarrhoea equates to STEC-​HUS (Box 21.10.6.1). In pneumococcal-​associated aHUS, pneumonia or meningitis is usually present. Extrarenal manifestations, predominantly neurological, are re- ported in all types of HUS (Box 21.10.6.2). Laboratory investigations Once routine biochemical and haematological analyses have demonstrated a thrombotic microangiopathy, investigations are aimed at determining the underlying aetiology and excluding other differential diagnoses (Fig. 21.10.6.3). The most urgent test is an ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) assay, deficiency of which is characteristic of thrombotic thrombocytopenic purpura. Diagnosis of STEC-​HUS To confirm the diagnosis of STEC-​HUS, stool samples should be sent for STEC culture in tellurite-​enriched sorbitol–​MacConkey agar. Samples may be negative, especially if sampling is late in the course of disease. Even following cessation of diarrhoea, rectal swabs or a faecal culture should be taken. Enzyme-​linked immunosorbent assay identification of Shiga toxins should be attempted from stool and stool cultures, as should polymerase chain reaction testing of stool for Shiga toxin genes. Serology identifying IgM against the commonly occurring STEC strains should also be performed. Box 21.10.6.1  Triggers of atypical HUS • Pregnancy • Respiratory infections: Bordetella pertussis, Streptococcus pneumoniae, Haemophilus influenza • Parasites: Plasmodium falciparum • Non-​STEC diarrhoeal illnesses: norovirus, Campylobacter upsaliensis, Clostridium difficile • Drugs:  alemtuzumab, cisplatin, gemcitabine, mitomycin, clopidogrel, quinine, interferon-​α, -​β, anti-​VEGF, ciclosporin, tacrolimus, ciprofloxacin, oral contraceptives, illicit drugs • Autoimmune:  anticardiolipin, C3 nephritic factor, systemic lupus erythematosus • Vaccination • Bone marrow transplantation • Malignancy: gastric, breast, prostate, lung, colon, ovarian, pancreatic, lymphoma Box 21.10.6.2  Extrarenal manifestations of HUS • Neurological involvement • Cerebral artery thrombosis/​stenosis • Digital gangrene • Extracerebral artery stenosis • Cardiac involvement/​myocardial infarction • Ocular involvement • Pulmonary involvement • Pancreatic involvement Table 21.10.6.1  Genetic causes of atypical HUS Gene name Gene symbol OMIM number Inheritance Complement factor H CFH 235400 AD/​AR Complement factor I CFI 612923 AD CD46 CD46 612922 AD/​AR Complement
component 3 C3 612925 AD Complement factor B CFB 612924 AD Diacylglycerol kinase-​ε DGKE 615008 AR Methylmalonic aciduria and homocystinuria, cobalamin C type MMACHC 277400 AR AD, autosomal dominant; AR, autosomal recessive.

21.10.6  Haemolytic uraemic syndrome 5031 Complement analysis in aHUS Before instigation of plasma exchange, serum levels of C3, C4, FH, and FI should be measured. Low C3 concentrations are suggestive but are not diagnostic of aHUS. CD46 surface expression should be evaluated by flow cytometry. Genetic screening and testing for auto- antibodies should be performed on all suspected cases. Treatment of STEC-​HUS There are no specific interventions shown to improve the outcome in STEC-​HUS and management is supportive care. Particular atten- tion should be paid to fluid and electrolyte replacement, blood pres- sure control, anaemia, renal support, and treatment of neurological manifestations. Antimotility agents should be avoided, and antibiotics are not currently recommended in the treatment of E. coli O157:H7 infec- tion due to a lack of evidence of efficacy and the potential to increase the risk of developing HUS. Studies have suggested that treatment with antibiotics causes increased toxin production and release. In contrast, a nonrandomized assessment from the 2011 E. coli O104:H4 outbreak suggested antibiotics reduced seizures and death. Unlike the O157:H7 strain, treatment of E. coli O104:H4 with anti- biotics did not increase quantities of Shiga toxin. Antibiotic treat- ment of S. dysenteriae does not increase the risk of HUS. There is no conclusive evidence to suggest plasma exchange is beneficial in STEC-​HUS and it is not routinely administered. The complement inhibitor eculizumab did not show any benefit when retrospective analysis of the Northern European STEC-​ HUS O104:H4 outbreak was performed. As STEC-​HUS is a self-​ limiting illness, only a randomized controlled trial will delineate any benefit. Treatment of aHUS Plasma exchange remains the initial treatment of choice until the ADAMTS13 activity is available to exclude thrombotic thrombocytopenic purpura as a diagnosis. It should be initiated as soon as the diagnosis of thrombotic microangiopathy is suspected. In addition to the replacement of faulty complement regulators and removal of FH autoantibodies and hyperfunctional comple- ment components in aHUS, plasma exchange will also remove ADAMTS13 autoantibodies and replace ADAMTS13 in throm- botic thrombocytopenic purpura. It should be performed daily and the dose titrated to control haemolysis. Once haemolysis has been controlled, plasma exchange can be withdrawn slowly, although individuals with genetic defects in the complement system are fre- quently plasma dependent and require long-​term plasma therapy (weekly/​biweekly) to maintain remission. Eculizumab The complement inhibitor, eculizumab, was first reported to be ef- ficacious in aHUS in 2009. It is a recombinant humanized mono- clonal antibody directed against C5 that blocks the cleavage of C5 into its effector components (Fig. 21.10.6.2). A nonrandomized, un- controlled, prospective study demonstrated efficacy in both plasma-​ resistant and plasma-​dependent aHUS. As with plasma exchange, the earlier eculizumab is commenced, the greater the conservation of renal function, and (if its great cost does not preclude) treatment with eculizumab should be instigated as soon as ADAMTS13 defi- ciency can be excluded. The current optimal duration of therapy is unclear, although re- cent reports have suggested that eculizumab may be safely discon- tinued in selected patients with appropriate clinical monitoring. A trial of intermittent disease-​driven versus continuous eculizumab therapy is required to define the optimal treatment strategy stratified by the underlying complement defect. Eculizumab has been used safely during pregnancy in patients with paroxysmal nocturnal haemoglobinuria. The terminal pathway of complement is critical in the immune response to encapsulated organisms and therefore vaccination with both a meningococcal group A, C, W, and Y conjugated vaccine and multicomponent meningococcal group B vaccine is mandatory prior to eculizumab treatment. Long-​term prophylactic antibiotic cover is also advisable. TMA TTP HUS aHUS STEC-HUS Pneumococcal aHUS Complement- mediated aHUS Other ADAMTS13 activity <5% Culture Shiga toxin detection Serology PCR Culture Serology T-antigen C3 C4 FI FH levels CD46 FACS Genetic Screening CFH CFI CFB C3 CD46 FH autoantibodies Genetic Screening DGKE, MMACHC Plasma homocysteine Urine organic acid chromatography Autoimmune screen ANA dsDNA Antiphospholipid Anti-Scl70 ↓Hb ↓Plts ↑LDH ↓Haptoglobin Fig. 21.10.6.3  Thrombotic microangiopathy diagnostic algorithm. ADAMTS13, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13; C3, complement factor C3; C4, complement factor C4; CFB, complement factor B gene; CFH, complement factor H gene; CFI, complement factor I gene; DGKE, diacylglycerol kinase-​ε; FACS, fluorescence-​activated cell sorting; FI, factor I protein; FH, factor H protein; Hb, haemoglobin; LDH, lactate dehydrogenase; MMACHC, methylmalonic aciduria and homocystinuria, cblC type; plts, platelets; PCR, polymerase chain reaction; T-​antigen, Thomsen–​Friedenreich antigen; TMA, thrombotic microangiopathy; TTP, thrombotic thrombocytopenic purpura.