24.12 Disorders of cranial nerves 6120 Robert D.M.

24.12 Disorders of cranial nerves 6120 Robert D.M. Hadden

ESSENTIALS The 12 cranial nerves are peripheral nerves except for the olfactory and optic nerves which are central nervous system tracts. Disorders of particular note include the following: olfactory (I) nerve—​anosmia is most commonly encountered as a sequel to head injury. Eye movements—​third, fourth, and sixth cranial nerves—​complete lesions lead to the following deficits (a) third nerve—​a dilated and un- reactive pupil, complete ptosis, and loss of upward, downward and medial movement of the eye; (b) fourth nerve—​extorsion of the eye when the patient looks outwards, with diplopia when gaze is directed downwards and medially; (c)  sixth nerve—​convergent strabismus, with inability to abduct the affected eye and diplopia maximal on lateral gaze to the affected side. The third, fourth, and sixth nerves may be affected singly or in combination: in older patients the most common cause is vascular disease of the nerves themselves or their nuclei in the brainstem. Other causes of lesions include (a) false lo- calizing signs—​third or sixth nerve palsies related to displacement of the brainstem produced by supratentorial space-​occupying lesions; (b)  intracavernous aneurysm of the internal carotid artery—​third, fourth, and sixth nerve lesions. Lesions of these nerves can be mim- icked by myasthenia gravis or myopathies. Pupillary abnormalities—​these include (a)  constriction (miosis)—​ due to paralysis of the sympathetic innervation (Horner’s syndrome); (b) dilatation—​due to lesions of the third nerve. Trigeminal nerve—​pathology causes numbness and tingling of the side of the face and scalp back to the vertex, loss of the corneal re- flex and deviation of the jaw to the affected side. May be affected by intramedullary lesions, during the intracranial part of its course, and extracranially. Trigeminal neuralgia is usually due to compression of the nerve by aberrant vessels in the posterior fossa. It is characterized by paroxysms of intense pain strictly confined to the nerve’s distribu- tion and often responsive to carbamazepine. Facial nerve—​in upper (but not lower) motor neuron lesions there is relative preservation of power in the upper facial muscles. In Bell’s palsy, onset is rapid and frequently heralded or accompanied by aching pain in or around the ear: treatment with prednisolone with an antiviral agent improves the prognosis. Hemifacial spasm is characterized by irregular clonic or simultaneous twitching move- ments of the facial muscles, usually of insidious onset; injections of botulinum toxin may be helpful. Glossopharyngeal nerve—​rarely affected in isolation, when it is very difficult to detect any neurological deficit; usually affected in combination with the vagus nerve. Vagus nerve—​important symptoms of damage relate to pharyn- geal and laryngeal innervation producing a bulbar palsy with dys- phonia, dysarthria, and dysphagia. Causes include brainstem stroke, motor neuron disease, malignant infiltration anywhere along the course of the nerve and cranial polyneuropathy. Spinal accessory nerve—​may be affected by lesions, often neo- plastic, in the region of the jugular foramen, but more commonly by injuries to the neck or by operations for the removal of cervical lymph nodes. Hypoglossal nerve—​may be affected by tumours in the region of the anterior condyloid foramen, or by tumours or penetrating in- juries in the neck. The most common cause of bilateral lesions is the progressive bulbar palsy variant of motor neuron disease. Multiple cranial neuropathies (cranial polyneuropathy) might be due to inflammatory conditions (such as Guillain–​Barré syndrome, (Miller) Fisher syndrome, vasculitis, granulomatosis with polyangiitis (Wegener’s), sarcoidosis); infections (basal meningitis such as tu- berculosis, Lyme borreliosis, fungi); diabetes mellitus; meningeal carcinomatosis or lymphomatosis; or might be mimicked by my- asthenia gravis, motor neuron disease, botulism, or myopathies. Cranial MRI (with contrast) and cerebrospinal fluid analysis are the key investigations. Bulbar palsy is the syndrome of abnormality of cranial nerves arising from the medulla oblongata (nerves IX, X, XI, and XII). Tongue wasting and fasciculations, absent jaw jerk, absent gag reflex (unreliable unless unilateral), and flaccid dysarthria with nasal regurgitation distinguish this lower motor neuron syndrome from pseudobulbar palsy which is an upper motor neuron lesion of the medulla. A unilateral lesion of nerves V, VII, and VIII sug- gests pathology in the cerebellopontine angle such as vestibular schwannoma. 24.12 Disorders of cranial nerves Robert D.M. Hadden1 1  This chapter is adapted from earlier editions written by Professors P. K. Thomas (deceased) and Richard Hughes.

24.12  Disorders of cranial nerves 6121 The olfactory nerve (I) Loss of the sense of smell (anosmia) is most commonly encoun- tered as a sequel to head injury and is probably related to sever- ance of the central processes of the olfactory neurons as they pass through the cribriform plate to the olfactory bulb. It is usually per- manent. Distortion of olfaction (parosmia) may occur and can be persistent. The sense of smell is occasionally congenitally absent or may be acutely and permanently lost after a coryzal infection. Bilateral anosmia is frequently accompanied by impairment of taste related to reduced detection of the volatile substances that impart flavours to foods. Unilateral anosmia may occur in olfactory groove meningiomas or other subfrontal tumours. This is usually not de- tected by the patient. The central connections of the olfactory pathways are complex and include projections to the temporal lobes, hypothalamus, septal region, and amygdaloid nuclei. Olfactory hallucinations occur as a manifestation of temporal lobe epilepsy. Identification of odours may be impaired after bilateral medial temporal lesions and may be defective in multiple sclerosis, possibly as the result of demye- lination in the olfactory tracts. Reduced sense of smell occurs as an early symptom of some neurodegenerative disorders, including Alzheimer’s disease and idiopathic Parkinson’s disease. Complaints of hypersensitivity of the sense of smell commonly have a psycho- neurotic or migrainous basis and persistent olfactory hallucinations may be reported by psychotic patients. Persistent parosmia is some- times produced by lesions of the temporal lobe. Third, fourth, and sixth cranial nerves The third, or oculomotor, nerve supplies all the external ocular muscles with the exception of the superior oblique and lateral rectus. It also carries the parasympathetic innervation of the preganglionic pupilloconstrictor fibres of the iris. A complete third nerve lesion produces a dilated and unreactive pupil, complete ptosis, and loss of upward, downward, and medial movement of the eye. The eye becomes deviated laterally and slightly downwards. Diplopia is only experienced when the lid is lifted. The fourth or trochlear nerve supplies the superior oblique muscle. Following a lesion of this nerve, there is extorsion of the eye when the patient looks outwards. When the patient looks down- wards and medially, diplopia is experienced. This is particularly disturbing because looking downwards is important for walking and especially when descending stairs. The patient may compensate for this by tilting the head to the opposite side. The sixth or abducent nerve supplies the lateral rectus. A lesion of this nerve causes convergent strabismus, inability to abduct the affected eye, and diplopia which is maximal on lateral gaze to the affected side. The third, fourth, and sixth nerves may be affected singly or in combination, and the paralysis may be complete or partial. In some instances, the lesion is within the brainstem, where it may affect ei- ther the nuclei or the intramedullary portions of the nerve fibres. In older patients, the most common cause of single nerve lesions is microvascular ischaemia which typically spontaneously recovers in a few months. Extramedullary lesions of the third, fourth, and sixth nerves may occur at any point along their course, either intracranially or within the orbit. A third nerve palsy may develop in the region of the tentorial hiatus as a false localizing sign related to displacement of the brainstem produced by supratentorial space-​occupying lesions. Unilateral or bilateral sixth nerve palsies may also arise as a con- sequence of raised intracranial pressure, probably caused by trac- tion, again secondary to brainstem displacement. These nerves can be involved singly or together in conditions such as chronic basal meningitis or carcinoma of the skull base. Gradenigo’s syndrome comprises a sixth nerve palsy and pain of trigeminal distribution. It is produced by a lesion at the apex of the petrous temporal bone. As this syndrome was most commonly infective in origin and related to chronic middle ear disease, it is now much less frequent. The third, fourth, and sixth nerves traverse the cavernous sinus, as do the first and second divisions of the trigeminal nerve. In this situation, they are most commonly damaged by an intracavernous aneurysm of the internal carotid artery. The third nerve is affected more often than the fourth or sixth. The consequent internal and external ophthalmoplegia is frequently accompanied by pain, and sometimes sensory loss and paraesthesiae in the corresponding frontal region related to compression of the first division of the tri- geminal nerve. Sometimes pain occurs in the cheek from damage to the maxillary division. In the superior orbital fissure syndrome, caused for example by a tumour invading the fissure, a total oph- thalmoplegia may result, associated with pain and sensory loss in the distribution of the first division of the trigeminal nerve. The eye is often proptosed because of obstruction of the ophthalmic vein. The Tolosa–​Hunt syndrome consists of a painful external ophthal- moplegia related to a granulomatous angiitis. Within the orbit, the third, fourth, and sixth nerves may be affected by conditions such as tumours and granulomas. They may be damaged as a result of trauma at any point along their course and may be affected singly or as part of multiple cranial neuropathies, of which diabetes, the (Miller) Fisher syndrome, Lyme disease, vasculitis, and sarcoidosis are the most important causes. Internal and external ophthalmoplegias are common and this list of nerve lesions causing the syndrome is by no means exhaustive. Complex external ophthalmoplegia may also be caused by myasthenia or myopathy. Pupillary abnormalities Constriction of the pupil (miosis) occurs as a result of paralysis of the sympathetic innervation of the pupillodilator fibres of the iris and may be accompanied by the other features of Horner’s syn- drome; mild ptosis and vasodilatation and anhidrosis of the face on the same side. The ocular manifestations may be encountered alone if the damage is restricted to the intracranial portion of the sympa- thetic plexus around the carotid artery such as in carotid dissection. Raeder’s syndrome consists of these components of Horner’s syn- drome together with involvement of the first division of the trigem- inal nerve. It may be caused by tumours of the skull base. Miosis may also be produced by the local action of cholinergic drugs and by morphine and related compounds. Pupillary dilatation may be caused by lesions of the third nerve. The isolated third nerve palsies of presumed microvascular origin that can occur in diabetes mellitus characteristically spare the pupil.

section 24  Neurological disorders 6122 In contradistinction, compressive lesions of the nerve, for instance by an aneurysm or transtentorial brain herniation, involve the pupil prominently and early. Anticholinergic drugs, such as atropine and related substances, and cocaine also cause pupillary dilatation. The Argyll–​Robertson pupil is small, fails to react to light, but constricts on ocular convergence, and, if bilateral, the pupils are fre- quently unequal in size (anisocoria). The pupil may be irregular in outline and does not dilate fully in response to mydriatics. Argyll–​ Robertson pupils are often related to neurosyphilis but somewhat similar pupils are occasionally encountered in diabetic neuropathy, in some hereditary neuropathies, and following the use of atropine-​ like eyedrops. The Adie’s tonic pupil reacts abnormally slowly both to light and on convergence, but particularly so for the response to illumination. A very bright light may be required to demonstrate any slow pu- pillary constriction. If the patient remains in a dark room for some minutes, the pupil slowly dilates. The condition may be unilateral or bilateral and is commoner in women than men. It causes minimal symptoms and requires no treatment. Tonic pupils may be associ- ated with absence or depression of the tendon reflexes (Holmes–​ Adie syndrome) and occasionally with anhidrosis in the limbs. Trigeminal nerve (V) The fifth cranial nerve is predominantly sensory in function, but also innervates the muscles of mastication. It emerges from the pons and runs forwards to the Gasserian (trigeminal) ganglion which is situated in Meckel’s cave near the apex of the petrous tem- poral bone. The three sensory divisions of the nerve run anteriorly from the ganglion. The first or frontal division passes through the cavernous sinus and the superior orbital fissure. Its branches supply sensation to the anterior part of the scalp, the forehead, and the eye, including the conjunctiva and cornea. The second or maxillary division leaves the skull through the foramen rotundum, traverses the infraorbital canal, and supplies the cheek. The mandibular div- ision emerges from the skull through the foramen ovale to reach the infratemporal fossa with the motor root with which it unites to form a single trunk. It is distributed to the lower lip, chin, and the lower part of the cheek, and its auriculotemporal branch sup- plies the tragus of the ear and temple. It also supplies the inner aspect of the cheek and the anterior two-​thirds of the tongue, and its lingual branch carries taste fibres from the anterior two-​thirds of the tongue which leave it in the chorda tympani to join the fa- cial nerve. The skin over the angle of the jaw is supplied from the second cervical nerve root, not the trigeminal nerve, which may be useful in distinguishing non​organic loss of sensation on the face, which usually follows the angle of the jaw. The motor root innerv- ates temporalis, masseter, pterygoids, mylohyoid, the anterior belly of the digastric and tensor tympani, and tensor palati muscles. With unilateral paralysis of the masticatory muscles, the jaw is pushed towards the affected side on opening by the unopposed external pterygoid on the unaffected side. The trigeminal nerve may be affected by intramedullary lesions. It may also be damaged during the intracranial part of its course. Its branches may be compromised extracranially. A  vestibular schwannoma or other space-​occupying lesion in the cerebellopontine angle may compress the nerve in the posterior fossa or the nucleus of its descending root in the brainstem. Loss of corneal sensation (tested by the corneal reflex) is usually the earliest feature. Reference has already been made to involvement of the nerve in association with damage to the sixth nerve at the apex of the petrous temporal bone (Gradenigo’s syndrome), as has involvement of the first and second divisions in the cavernous sinus, or the first division in the superior orbital fissure. Fluctuating facial numbness is a common functional symptom, typically sparing inside the mouth, not conforming to anatomical boundaries, and without objective sensory loss on examination. Fluctuating facial pain or dysaesthesia is commonly due to a variant of migraine, typically around one eye, often changing sides over time. Bilateral numbness around the mouth may be of brainstem origin. Isolated trigeminal neuropathy Rarely, a slowly progressive, isolated unilateral or bilateral affection of the trigeminal nerve causing numbness and/​or pain may occur as a manifestation of Sjögren’s syndrome, connective tissue disease, progressive systemic sclerosis, or amyloidosis. Most cases are idio- pathic. It may start in the chin as ‘mental numbness’. Trigeminal neuralgia Symptoms This condition is characterized by brief paroxysms of intense pain strictly confined to the distribution of the trigeminal nerve. It is generally encountered in individuals over the age of 50 years. It is commonly caused by the impingement of a vascular loop on the tri- geminal nerve root entry zone in the posterior fossa, though vascular loops are often asymptomatic. It may be idiopathic, or symptom- atic of underlying pathology such as multiple sclerosis, especially in younger patients, or compression/​infiltration of the nerve, for ex- ample by tumours in the cerebellopontine angle, to which a clue may be sensory loss. The pain is usually unilateral (never switching sides) and is felt either within the territory of one division of the nerve only, or may involve two adjacent divisions or affect the whole territory of the nerve. The distribution is usually in the second or third divisions of the nerve or both. The first division is rarely affected primarily, but pain may spread into it from the second division. Pain often starts in a tooth and fails to improve after dental extraction. Less commonly, it is bilateral. The pain occurs in brief searing paroxysms, each attack lasting only seconds, but repeated many times per day. The pain is often described as piercing, knife-​like, or electrical. Its intense quality may cause the patient to screw up their face in agony, hence the use of the term ‘tic doloureux’. The paroxysms may be spontaneous or pro- voked by movements of the face and jaw, by touching the skin, or by draughts of cold air on the face. Eating and speaking may become extremely difficult. ‘Trigger spots’ on the skin of the face may be present, the touching of which provokes the paroxysms. The attacks may be followed by less severe pain of a dull, boring character, and by tenderness of the skin in the affected area. The attacks usually cease at night.

24.12  Disorders of cranial nerves 6123 The timing and triggering of the pain is characteristic, and when trigeminal neuralgia is present the diagnosis is not usually missed. The usual mistake is to regard as trigeminal neuralgia pain that which is due to some other cause. Pain of continuous character is not trigeminal neuralgia. Absence of provocation by touching or moving the face or mouth also makes the diagnosis unlikely. Other causes of facial pain include migraine (often giving pain in, behind, or around one eye), cluster headache, atypical facial pain, or trigem- inal neuropathy. In the early stages, remissions lasting for months or years are usual, but in older patients’ remissions, if they occur, are likely to be brief. In all cases the remissions tend to become shorter as time goes on, and without treatment the condition persists for the rest of the patient’s life. Treatment The introduction of carbamazepine revolutionized treatment of this distressing condition. In most patients, pain a can be abolished or reduced. It is best to start with a low dose of 100 mg once or twice a day and increase by 100 mg every 2–​7 days until control is achieved (usually at 300–​800 mg per day, sometimes higher). Slow release preparations are preferred. The rate of increase and maximum dose may be titrated to minimize adverse effects of ataxia and drowsi- ness. In a pain crisis, the dose may be increased as fast as the pa- tient can tolerate; dosing three or four times daily gives more stable serum levels. Reduce the dose again when pain improves. Patients should be warned to stop the drug if an allergic rash occurs, because of the danger of exfoliative dermatitis. Hyponatraemia is common but usually mild and asymptomatic. Bone marrow suppression is very rare. Oxcarbazepine, a metabolite of carbamazepine, is an alternative first line treatment: it is probably equally effective and may have fewer adverse effects, but has a shorter serum half-​life. If these are not effective or not tolerated, baclofen, lamotrigine, pregabalin, gabapentin, or topiramate, may be tried, although the evidence base is weaker. In an acute pain crisis, small case series suggest short term benefit from topical lidocaine, intravenous phenytoin loading, or subcutaneous sumatriptan. If medical treatment is inadequate, the patient should be re- ferred for a neurosurgical opinion. Microvascular decompression of a vessel, shown on MRI to be impinging on the nerve, requires open craniotomy but usually gives a good long-​term outcome and is often curative. Patients unsuitable for this often benefit from destructive procedures of the trigeminal ganglion (gamma knife radiosurgery or percutaneous lesioning by heat, balloon compres- sion or chemical injection) which are less invasive procedures but have a lower chance of long-​term benefit, and a risk of persistent analgesia and sometimes painful dysaesthesiae, called ‘anaes- thesia dolorosa’, which may be more troublesome than the original condition. Ophthalmic herpes zoster The fifth nerve is prone to involvement in herpes zoster, usually in elderly individuals. The first division is most vulnerable, giving rise to the distressing condition of ophthalmic herpes. The clinical fea- tures and treatment of herpes zoster are considered elsewhere (see Chapter 8.5.2). An unfortunate sequel may be visual impairment from residual corneal scarring. Postherpetic neuralgia may give rise to persistent and unre- mitting spontaneous pain associated with cutaneous hyperaes- thesia in the affected area. Treatment of neuralgia should start with standard medication for neuropathic pain (tricyclic antidepres- sants, gabapentin or pregabalin) or perhaps the topical lidocaine 5% patch (but not ideal in this location). Alternatives could include duloxetine, carbamazepine, opioids, or tramadol. Facial nerve (VII) The seventh cranial nerve is largely motor. The nerve traverses the facial canal in the petrous temporal bone in close relationship to the middle ear and emerges at the stylomastoid foramen. Its branches pass forwards through the parotid gland to be distributed to the muscles of the face and the platysma. Within the petrous bone, a branch is given to the stapedius muscle. The chorda tympani, carrying the taste fibres from the anterior two-​thirds of the tongue, joins the nerve within the facial canal and a small branch supplies cutaneous sensation to the external auditory meatus. (The symptom of loss of taste is more commonly due to abnormality of the sense of smell.) The nerve also carries preganglionic parasympathetic fibres destined for the lacrimal gland. The distinction between upper and lower motor neuron lesions of the facial muscles is usually easy. In general, with upper motor neuron lesions (such as a stroke) there is relative preservation of power in the upper facial muscles, because these have a represen- tation in both cerebral hemispheres. There is no loss of tone with upper motor neuron lesions, so that the sagging of the face that is an unsightly feature of lower motor neuron palsy does not occur. In common with the trigeminal nerve, the facial nerve may be affected by tumours in the cerebellopontine angle. In the past, it was often involved in middle ear infections. It may be involved in meningeal carcinomatosis, fractures, and tumours of the skull base, in a variety of cranial neuropathies, and cephalic herpes zoster, but the most common lesion by far is Bell’s palsy. More peripherally, the nerve may be compromised in tumours of the parotid gland. Bell’s (idiopathic facial) palsy This is usually unilateral facial paralysis of rapid onset due to in- flammation of the nerve within the facial canal. Taste may also be affected. It has an annual incidence of 20–​32 per 100 000 and may develop at any age, most commonly between 20 and 50 years, and affects both sexes equally. There is some, but inconclusive, evidence that it is a manifestation of herpes simplex infection. In the acute stage, the nerve is swollen and compression within the facial canal may contribute to the damage to the nerve fibres. The onset is rapid and is frequently heralded or accompanied by aching pain below the ear or in the mastoid region. This clears within a few days and is not present in every case. The paralysis usually reaches its maximum severity after 1 or 2 days. Complete paralysis may occur. This may cause a mild dysarthria and some difficulty in eating because of food collecting between the gums and the inner sides of the cheek and the escape of fluid when drinking. The face sags, and the mouth may be drawn across to the unaffected side (which may give the false impression of tongue deviation). Paralysis of orbicularis oculi may render voluntary eye

section 24  Neurological disorders 6124 closure impossible and, particularly in the older subject, ectropion develops. This can result in conjunctival injury from foreign bodies or drying (‘exposure keratitis’). The patient may complain of facial numbness due to altered movement, although objective sensory examination is normal and the trigeminal nerve is not involved. In more severe cases, loss of taste over the anterior two-​thirds of the tongue may be present, and paralysis of the stapedius muscle may result in a lack of tolerance for high-​pitched or loud sounds, called hyperacusis. Diagnostic tests are not usually required in typical cases, but in atypical cases the following may be considered. Selective lesions of the facial nerve within the brainstem do not affect taste, but almost always cause fifth or sixth nerves palsies and long tract symptoms or signs as well. With respect to peripheral lesions, middle ear disease requires exclusion. Facial paralysis may also be caused by herpes zoster as described next. A lesion of the facial nerve may be part of a more generalized disorder of which diabetes, Lyme disease, and sarcoidosis are the most important. Bell’s palsy is rarely bilateral and bilateral facial paralysis would raise the possibility of another dis- order, such as sarcoidosis, a Guillain–​Barré syndrome variant (‘fa- cial diplegia with paraesthesiae’), or Lyme. In approximately 85% of patients with Bell’s palsy, especially those with mild weakness, the paralysis is the result of a local conduction block within the facial canal without axonal degeneration. The con- duction block is presumably the consequence of segmental demye- lination. Provided that such cases do not progress to more severe weakness, remyelination is rapid, and most recover fully within a few weeks. In cases where there is total paralysis, axonal degeneration is likely to have occurred so that recovery has to take place by axonal re- generation, which is slow and incomplete. Evidence of reinnervation does not appear in under 3 months and the ultimate recovery is often incomplete or may fail to occur altogether. After reinnervation the regenerated axons may form inappropriate connections, causing synkinesis and ‘crocodile tears’. In synkinesis, blinking results in a simultaneous twitch of the angle of the mouth. ‘Crocodile tears’ are caused by aberrant parasympathetic reinnervation so that food elicits weeping instead of salivation. Axons remain excitable distal to the lesion for 3 or 4 days after interruption. It is, therefore, not possible to be certain from electrodiagnostic tests whether axonal degeneration has taken place until later. After that stage, electrical stimulation of the facial nerve at the stylomastoid foramen will still elicit a muscle contraction if the paralysis is due to conduction block, whereas none will be obtained if axonal degeneration has taken place. Treatment Oral corticosteroids and antivirals should be started as soon as possible, preferably within 3  days from onset. In a large high-​ quality trial, the percentage of patients with complete recovery after 9 months was significantly increased from 82% without to 94% with prednisolone, 25 mg twice daily for 10 days. Another trial obtained similar results with prednisolone 60 mg daily for 5 days and then a reducing dose for the next 5 days. In the Cochrane review of seven trials, the proportion of patients with incomplete recovery after six months was reduced by corticosteroids from 33% to 23%, and there was reduction in motor synkinesis but surprisingly not in cos- metically disabling sequelae after six months. Antiviral medication (acyclovir or valaciclovir) provides additional benefit. Hyperbaric oxygen was beneficial in an unblinded study. Patients with se- vere palsy, with inability to close the eye, should use moisturizing eye ointment and eye protection to protect the eye from exposure keratitis (some may require stitching of the lateral parts of the eye- lids, lateral tarsorrhaphy). Tailored facial exercises may help to im- prove facial function in people with moderate chronic weakness and perhaps in acute cases. Stretching exercises of the ipsilateral upper eyelid and contralateral mouth help to prevent contractures. Electrical stimulation of the paralysed facial muscles does not help long-​term outcome. If regeneration is inadequate after waiting at least a year, cosmetic operations may be considered to counteract the facial deformity. The angle of the mouth may be elevated by a fascial sling attached to the temporalis fascia, but the result is never highly satisfactory. Restoration of facial tone may be achieved by anastomosis of the hypoglossal to the facial nerve, but at the expense of denervation of the tongue on that side. Facial paralysis related to ‘geniculate’ herpes zoster
(Ramsay–​Hunt syndrome) Very rarely facial palsy is due to zoster infection. If typical vesicles are detected in the ear and ulceration in the fauces, or anywhere on the head, then it is reasonable to give antiviral agents as well as corticosteroids, although evidence is lacking. Occasionally there is concomitant vertigo, tinnitus, and deafness due to involvement of the eighth nerve. Hemifacial spasm This consists of a unilateral disturbance affecting the facial muscles, producing irregular twitching movements of the facial muscles, usually of insidious onset. All affected parts of the face twitch syn- chronously. It most commonly occurs in middle-​aged women. Facial power is usually normal or there may be mild facial weakness. Usually no underlying cause is demonstrable. The condition select- ively affects the facial nerve, within the brainstem or in the posterior fossa. Hemifacial spasm is painless. If it is associated with pain, there may be a lesion in the cerebellopontine angle compressing both the trigeminal and facial nerves. It begins with intermittent twitching of the facial muscles such as around the eye, in the cheek, or at the angle of the mouth. These movements gradually become more frequent and extend to involve the rest of the facial muscles, over the course of some years. If they become severe, the face is contorted by irregular clonic spasms which may keep the eye closed for prolonged periods. The facial dis- tortion is often a considerable embarrassment to the patient, who finds that the spasms tend to be aggravated by emotional stress. It does not switch sides and is only rarely bilateral. Injections of botulinum toxin are usually helpful, but have to be repeated every 3 months. Neurosurgical intervention to relieve com- pression of the facial nerve by aberrant vessels in the posterior fossa may help selected cases. Clonazapam may help. The condition must be distinguished from the very common be- nign fasciculations of the face, usually periorbital, related to fatigue or emotional tension, and from facial myokymia that is occasionally encountered as a manifestation of multiple sclerosis. The latter con- sists of a persisting irregular rippling movement of the facial muscles that usually subsides after a week or two. These conditions can be distinguished by electromyography (see Chapter 24.3.2).

24.12  Disorders of cranial nerves 6125 Glossopharyngeal nerve (IX) The ninth cranial nerve leaves the skull through the jugular foramen, closely related to the tenth nerve. It supplies the stylopharyngeus muscle and the constrictor muscles of the pharynx. Parasympathetic fibres are supplied to the parotid gland. Sensory fibres are carried from the posterior third of the tongue, the ear, the fauces, and the nasopharynx, and chemoreceptor and baroreceptor afferents from the carotid sinus. The glossopharyngeal nerve is rarely affected in isolation. If it is affected alone, it is very difficult to detect the deficits expected from its anatomical distribution. Lesions usually occur in conjunc- tion with involvement of the vagus and give rise to some dysphagia, impaired pharyngeal sensation, and loss of taste over the posterior third of the tongue. It may be affected in the jugular foramen syn- drome, along with the tenth and eleventh nerves, of which glomus tumours or metastatic carcinomas are the commonest causes. The nerve may also be involved in diphtheritic neuropathy, Fisher syn- drome, and in cranial polyneuropathy. Glossopharyngeal neuralgia is rare and resembles trigeminal neuralgia but with symptoms in the distribution of the glossopha- ryngeal nerve. As with trigeminal neuralgia, it is most often en- countered in elderly subjects, and the pain may initially be confined to individual branches. Thus, it may be felt deep in the ear, related to the tympanic branch, or in the throat, related to the pharyngeal branches. It usually responds to treatment with carbamazepine. If that and other antiepileptic drugs fail, surgical treatment, usually section of the nerve, may be required. Vagus nerve (X) The tenth cranial nerve is structurally complex. Within the skull it is joined by the cranial portion of the eleventh nerve. It leaves the skull through the jugular foramen. Motor fibres supply the striated musculature of the palate and pharynx and, through the internal, external, and recurrent laryngeal nerves, the muscles of the larynx. Cutaneous sensory fibres are carried from the external ear and vis- ceral afferent fibres are carried from the pharynx, larynx, trachea, oe- sophagus, and the thoracic and abdominal viscera. Parasympathetic fibres innervate the parotid gland (through the glossopharyngeal nerve), the heart, and the abdominal viscera. Neurostimulation of the vagus nerve is a treatment for refractory epilepsy mediated by autonomic afferent fibres. The important symptoms of damage to the vagus nerve are those relating to pharyngeal and laryngeal innervation, causing dysphonia and dysarthria; a weak or bovine cough is probably the earliest sign of a mild lesion. The cells of origin in the nucleus ambiguus of the medulla may be damaged in the lateral medullary syndrome, motor neuron disease, and acute bulbar poliomyelitis, leading to dysphagia and dysphonia. Involvement along with the glossopharyngeal nerve in the jugular foramen syndrome has already been mentioned. The recurrent laryngeal nerve may be damaged during operations on the thyroid gland or by tumours within the neck, or within the thorax, usually due to carcinoma of the bronchus. The nerve on the left is vulnerable to damage by an aneurysm of the aortic arch. Isolated and unexplained lesions of the recurrent laryngeal nerve are not uncommon. Nuclear or high vagal lesions, as well as involving the larynx, cause palatal and pharyngeal paralysis. If unilateral, there are few symp- toms from palatopharyngeal paralysis. The uvula is pulled up to the opposite side on phonation and pharyngeal sensation is impaired on the affected side. The gag reflex is a reliable indicator if asym- metric, but is bilaterally absent in some normal people. With bilat- eral paralysis, the palate is paretic leading to nasality of the voice and nasal regurgitation of liquids on attempts at swallowing. Bilateral palatopharyngeal paralysis may be encountered in motor neuron disease, bulbar poliomyelitis, diphtheritic neuropathy, and cranial polyneuropathy. Intrinsic laryngeal paralysis from lesions of the recurrent laryn- geal nerve, if unilateral, may be asymptomatic or give rise to hoarse- ness of the voice. If the superior laryngeal nerve is also involved leading to paralysis of the cricothyroid muscle, the affected cord lies in a paramedian or cadaveric position. The effects of bilateral lesions of the recurrent laryngeal nerves depend upon the degree of approximation of the vocal cords. Lesions of insidious onset give rise to dysphonia and also to stridor on exertion. In partial lesions, close approximation of the cords may result from selective paralysis of the abductor muscles, giving rise to limitation of the airway and sometimes necessitating tracheostomy. With bilateral lesions involving both the recurrent and superior laryngeal nerves, both cords are paralysed and in the cadaveric position. Phonation is impossible. Spinal accessory nerve (XI) The spinal accessory portion of the eleventh cranial nerve arises from the upper cervical cord and the lower medulla. The nerve enters the foramen magnum and briefly joins the cranial portion (functionally part of the vagus nerve) before emerging from the skull through the jugular foramen. The spinal accessory nerve then separates and supplies the sternomastoid and trapezius muscles, the latter also receiving an innervation from the cervical plexus. The nerve may be affected by lesions, often neoplastic, in the region of the jugular foramen, but more commonly it is damaged by injuries to the neck or by operations for the removal of cervical lymph nodes, particularly as it crosses the posterior triangle of the neck. Isolated and unexplained lesions of the nerve are occasion- ally encountered. Unilateral paralysis of the sternomastoid usually passes un- noticed by the patient. The muscle does not stand out when the head is turned to the opposite side. Paralysis of the trapezius, on the other hand, causes difficulty in lifting the arm above the horizontal, in shrugging the shoulder, and in approximating the scapula to the midline and therefore also in carrying the extended arm backwards. The shoulder droops when the arm is hanging at the side and there is moderate winging of the scapula which is accentuated when the patient attempts to elevate the arm laterally. Hypoglossal nerve (XII) The twelfth cranial nerve supplies all the muscles of the tongue, both intrinsic and extrinsic. It leaves the skull through the anterior

section 24  Neurological disorders 6126 condyloid foramen. A unilateral lesion of the hypoglossal nerve causes weakness, wasting, and fasciculations of the tongue on the affected side. The protruded tongue may deviate to the affected side if weakness is severe, but this is often misdiagnosed when not truly present. Articulation is unaffected. The nerve may be affected by tumours in the region of the anterior condyloid foramen, or by tumours or penetrating injuries in the neck, or by complications of carotid endarterectomy. If damage is the result of a unilateral lower brainstem lesion, it is usually combined with a contralateral hemiplegia. Bilateral lesions give rise to generalized wasting of the tongue. Wasting of the tongue is usually accompanied by fasciculation which is best detected with the tongue at rest. Protrusion becomes impossible and articulation is disturbed. The most common cause is the progressive bulbar palsy variant of motor neuron disease. Many normal people have irregular involuntary twitching or writhing movements of the tongue at rest, but the lack of wasting helps to distinguish this from pathological fasciculations. FURTHER READING Asbury AK, et  al. (1970). Oculomotor palsy in diabetic mellitus:  a clinicopathological study. Brain, 93, 555–​66. Brodal A (1965). The cranial nerves, 2nd edition. Blackwell Scientific, Oxford. Dyck PJ, Thomas PK (2005). Peripheral neuropathy, 4th edition. Elsevier Saunders, Philadelphia, PA. Gagyor I, et al. (2015). Antiviral treatment for Bell’s palsy (idiopathic facial paralysis). Cochrane Database Syst Rev, 11, CD001869. Kennard C (2007). How to examine eye movements. Practical Neurol, 7, 326–​30. Leigh JR, Zee DS (2006). The neurology of eye movements. Oxford University Press, New York, NY. Sullivan F, et al. (2007). Early treatment with prednisolone or acyclovir in Bell’s palsy. N Engl J Med, 357, 1598–​607. Younge BR (1966). Paralysis of cranial nerves III, IV and VI: causes and prognosis of 1000 cases. Arch Ophthalmol, 99, 76–​89.