Wilkinson. Essential Neurology 2005

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Myasthenia gravis

•Uncommon.

•Ocular involvement common in myasthenia gravis.

•Myasthenia should be considered in any unexplained ophthalmoplegia, even if it looks like a 4th, 6th or partial 3rd nerve palsy (see pp. 119 and 164–6).

CHAPTER 8

R L

Ptosis

Eye movement abnormality which doesn't necessarily match gaze palsy, internuclear ophthalmoplegia,

or cranial nerve palsy

Variability

Fatiguability

Normal pupils

Myopathy

•Graves’ disease is the only common myopathy to involve eye muscles.

•The patient may be hyperthyroid, euthyroid or hypothyroid.

•Inflammatory swelling of the external ocular muscles within the orbit, often leading to fibrosis, is responsible.

•Involvement of the external ocular muscles in other forms of myopathy occurs, but is exceedingly rare.

R L

Often asymmetrical Sometimes unilateral Proptosis

Lid retraction Lid lag

Ophthalmoplegia in any direction Normal pupils

Concomitant squint

•Very common.

•Caused by dissimilar visual acuity and refractive properties in the two eyes from an early age.

•Proper binocular fixation has never been established.

•Known as amblyopia.

•Fixation is by the better-seeing eye; the image from the amblyopic eye is suppressed, so there is no complaint of double vision.

Horner’s syndrome

•Uncommon.

•Caused by loss of sympathetic innervation to the eye.

•The sympathetic supply to the face and eye is derived from the hypothalamic region, descends ipsilaterally through the brainstem and cervical cord, and reaches the sympathetic chain via the motor root of T1. From the superior cervical sympathetic ganglion, the fibres pass along the outer sheath of the common carotid artery. Fibres to the eye travel via the internal carotid artery and its ophthalmic branch. Fibres to the face travel with the external carotid artery.

R L

Non-paralytic, each eye possessing a full range of movement when tested individually with the other eye covered

When one eye is covered, the other fixes. Alternate covering of each eye shows a refixation movement in each eye very clearly

R L

Minor degree of ptosis

Small pupil

Enophthalmos

Loss of sweating on the affected side of the face

CRANIAL NERVE DISORDERS

R L

Indoors

R L

After 1 min of bright sunshine

R L

After 30 min of bright sunshine

R L

Proptosis

Resistance to backward movement of the globe in the orbit

Palpable orbital mass

Globe displacement in the orbit by the mass

Distortion of the eyelid

Mechanical limitation of eye movement in the orbit

Possible impairment of vision in the affected eye

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Holmes–Adie syndrome

•Uncommon.

•Often unilateral.

•An interesting curiosity of no sinister significance.

•Very slow pupillary reaction to light, myotonic pupil (left eye in diagram).

•Absent deep tendon reflexes in the limbs is a common accompaniment, especially knee and ankle jerks.

•Site of pathology uncertain.

Orbital mass lesions

•Uncommon.

•Causes:

benign tumours;

malignant tumours, primary or secondary;

extension of inflammatory pathology from the paranasal sinuses;

non-neoplastic inflammatory infiltrate at the back of the orbit, so-called ‘pseudotumour’.

•CT scanning of the orbits is the most helpful investigation.

Trigeminal (5) nerve

Sensory loss in the face is very noticeable, as a visit to the dentist which requires a local anaesthetic will remind us. Sensory loss affecting the cornea can lead unwittingly to serious corneal damage. Pain in the face is very intrusive.

Figures 8.8 and 8.9 demonstrate the relevant clinical anatomical features of the trigeminal nerve. The following points are worth noting:

•the upper border of sensory loss in a trigeminal nerve lesion lies between the ear and the vertex, and the lower border is above the angle of the jaw. Patients with non-organic sensory loss on the face tend to have the junction of forehead and scalp as the upper border, and the angle of the jaw as the lower border;

•the corneal reflex requires corneal, not scleral, stimulation, and the response (mediated through the 7th cranial nerve) is to blink bilaterally. It can therefore be tested in the presence of an ipsilateral 7th nerve lesion;

•the jaw-jerk, like any other stretch reflex, is exaggerated in the presence of an upper motor neurone lesion. In the case of the jaw-jerk, the lesion must be above the level of the trigeminal motor nucleus in the pons. In patients with upper motor neurone signs in all four limbs, an exaggerated jaw-jerk is sometimes helpful in suggesting that the lesion is above the pons, rather than between the pons and the mid-cervical region of the spinal cord;

•pathology in the cavernous sinus affects only the ophthalmic and maxillary branches of the trigeminal nerve, as the mandibular branch has dived through the foramen ovale, behind the cavernous sinus. Similarly, orbital pathology affects only the ophthalmic branch, since the maxillary branch has

exited the skull through the foramen rotundum posterior to the orbit.

Figure 8.9 gives information about the diseases that may affect the trigeminal nerve. There are really only two common ones: trigeminal neuralgia and herpes zoster.

Trigeminal neuralgia is described in Chapter 13 (see p. 219), and is the most common disease affecting the trigeminal nerve. It can be caused by irritation of the nerve as it enters the brainstem (for example by an adjacent blood vessel) or within the brainstem itself (rarely; for example by multiple sclerosis). Presumably abnormal paroxysmal discharges within the nerve give rise to the lancinating pain.

5a

C2 + 3

5c

5b

C2 + 3

Fig. 8.8 Areas of the skin supplied by each branch of the trigeminal nerve and the 2nd and 3rd cervical dermatomes.

Fig. 8.9 Diagram to show the trigeminal nerve, and the diseases that may affect it.

Midbrain

5a Ophthalmic

Trigeminal

ganglion

Cerebellar

Pons peduncles

5b Maxillary

Medulla

5c

Mandibular, with motor branches to masseter, temporal and pterygoid muscles

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Facial (7) nerve

Figure 8.10 shows the peripheral distribution of the facial nerve. The nerve leaves the pons in the cerebellopontine angle. It provides autonomic efferent fibres to lacrimal and salivary glands, collects afferent taste fibres from the anterior two-thirds of the tongue, and provides the innervation of the stapedius muscle in the ear, before emerging from the stylomastoid foramen behind and below the ear to innervate the facial muscles as shown in Fig. 8.10.

Proximal lesions of the facial nerve produce, therefore, in addition to weakness of all the ipsilateral facial muscles, an alteration of secretion in the ipsilateral lacrimal and salivary glands, impairment of taste perception on the anterior two-thirds of the tongue, and hyperacusis (sounds heard abnormally loudly) in the ear on the side of the lesion. If the lesion has been complete, with Wallerian axonal degeneration distal to the site of the lesion, recovery is rarely complete and re-innervation is often incorrect. Axons, which used to supply the lower part of the face, may regrow along Schwann tubes which lead to the upper part of the face, and vice versa. Patients in whom this has happened are unable to contract part of their facial muscles in isolation. When they close their eyes vigorously, there is retraction of the corner of the mouth on the affected side. When they contract mouth muscles as in whistling, there is eye muscle contraction and possible closure on the side of the lesion. Sometimes, axons that used to supply the salivary glands find their way to the lacrimal glands. In such patients, tears may form excessively in the eye of the affected side at mealtimes.

Bell’s palsy

The common disease of the facial nerve is Bell’s palsy. The cause of this condition is not certain, although there is some evidence to suggest inflammation due to reactivation of herpes simplex virus within the nerve ganglion in many cases. The lesion is usually proximal enough to have effects on taste and hearing. After some aching around the ear, the facial weakness develops quite quickly within 24 hours. It affects all the facial muscles including the forehead, which distinguishes it from supranuclear facial weakness (for example due to a stroke) where the forehead is spared. The patient is usually very concerned by the facial appearance. Drainage of tears from the eye may be disturbed on the affected side because the eyelids lose close apposition with the globe of the eye, so the eye waters. The cornea may be vulnerable because of impaired eye closure. Speaking, eating and drinking may be difficult because of the weakness around the mouth.

CHAPTER 8

Cochlear

nerve

Vestibular

nerve

Semicircular

canals

Cochlea

The cortex most dedicated to auditory and vestibular function is in the superior temporal gyrus

Cochlear and vestibular nuclei in the pons, relaying input from the 8th nerve to cerebrum, cerebellum and spinal cord

External, middle and inner ear in the petrous temporal bone

Cerebrum

Cerebellum

Eighth, cochleovestibular nerve

Fig. 8.12 The main diseases affecting hearing, balance, or both.

The top section of Fig. 8.12 demonstrates that the common causes of deafness are in the external, middle or inner ear.

Acoustic neuroma is an occasional cause of slowly progressive unilateral nerve deafness. Ideally, it should be diagnosed and treated at this stage, before it has caused other evidence of a cerebellopontine space-occupying lesion (i.e. 5th and 7th cranial nerve palsy, ipsilateral cerebellar signs, and raised intracranial pressure). The tumour is a benign one, derived from the Schwann cells on the 8th nerve.

The main diseases affecting balance:

Labyrinth

Benign paroxysmal positional vertigo Acute vestibular failure (acute labyrinthitis or vestibular neuronitis

Drugs (e.g. streptomycin)

Brainstem

Vascular disease Demyelination Drugs (e.g. anticonvulsants)

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Ménière’s disease is depicted in the central section of Fig. 8.12. It is probably due to a lesion in the endolymph in both the cochlea and the labyrinth. It therefore causes auditory and vestibular symptoms. The typical patient is middle-aged with a history of unilateral deafness and tinnitus, followed by episodes of very severe vertigo, vomiting and ataxia lasting hours. It is not easy to treat.

The common diseases to affect balance without hearing loss are shown in the lower part of Fig. 8.12. It can be seen that the lesion is likely to be central in the brainstem, or peripheral in the labyrinth.

Episodes of ischaemia or infarction in the brainstem, or episodes of demyelination in patients with multiple sclerosis, are the common structural lesions in the brainstem to disturb balance. Such lesions commonly produce other neurological signs (cranial nerve, cerebellar or long tract in the limbs).

The diagnosis of benign paroxysmal positional vertigo is suggested by the occurrence of intermittent transient vertigo lasting less than 30 seconds strongly related to putting the head into a specific position. Turning over in bed, lying down in bed and looking upwards are common precipitants. No abnormalities are found on examination except for definite positional nystagmus. Spontaneous resolution of the problem occurs after a few months.

Perhaps the commonest type of severe vertigo is due to sudden vestibular failure. This denotes the sudden occurrence of rotatory vertigo, gait ataxia, vomiting and the need to stay in bed. Lateralized nystagmus and gait ataxia are the two abnormal physical signs. The incapacity lasts very severely for a few days and then gradually resolves over 4–6 weeks. Head movement aggravates the symptoms so the patient keeps still in bed in the acute stage, and walks with his head rather set on his shoulders in the convalescent stage. The underlying pathology is not certain. The problem may follow an upper respiratory infection and occasionally occurs in epidemics, hence the use of the diagnostic terms acute labyrinthitis or vestibular neuronitis.

Drugs that impair balance include:

•amino-glycoside antibiotics, such as streptomycin and gentamicin, which may permanently impair vestibular function if toxic blood levels are allowed to accumulate;

•anticonvulsants, barbiturates and alcohol which impair the function of the brainstem/cerebellum whilst blood levels are too high.

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