Nervous system

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14 Nervous system

Rodney W.H. Walker

Introduction

In recent years there have been impressive advances throughout the whole spectrum of neurological and muscle diseases; in delineating disease entities and understanding their aetiology and pathogenesis; in diagnostic methods, particularly imaging and genetic testing; and in treatment and management. However, advances in investigations have not rendered careful clinical assessment redundant.

The fundamental importance of the clinical history and examination cannot be overemphasized. In the diagnosis of neurological disease, it is the history that is paramount, so it is even more important for this to be comprehensive than the examination. History taking has not changed significantly, but clinical neurological examination continues to evolve. Significant contributions have come from clinical assessment scales, some of which have been so successful as to have become internationally institutionalized, for example the Glasgow Coma Scale and the Mini-Mental State Examination.

A thorough neurological examination does involve doing more than is the case for other systems. Some basic neuroanatomical knowledge is necessary, but most clinical neurology need not be daunting. In new patients presenting for diagnosis, a sensible formulation of the nature of the problem on the basis of the history and examination is critical in order to request appropriate investigations, should they be necessary. Modern imaging undoubtedly has been the biggest revolution in clinical neurology in recent years, but injudicious use of imaging frequently leads to confusion, delay in diagnosis and sometimes harm. Similar considerations apply to the other major investigational modalities.

This chapter will discuss some aspects of neurological history, concentrate on neurological examination and the formulation of the nature of the neurological diagnosis and include some remarks on neurological investigations. Not covered in this chapter are coma, delirium and dementia.

The neurological history

The essentials of history taking have been covered elsewhere, but there are some points particularly salient to neurological conditions. The repertoire of neurological symptoms is actually quite limited, though perhaps larger than that of other specialties. Box 14.1 lists the usual ones, and each should be specifically enquired about in taking a neurological history.

Box 14.1 Neurological symptoms

image Cognitive symptoms, especially memory impairment

image Headache

image Loss of awareness

image Loss of consciousness

image Alteration of perception, including déjà vu

image Dizziness, vertigo

image Loss of balance

image Falls

image Loss of sense of smell

image Loss of taste

image Loss of vision

image ‘Positive’ visual symptoms, including components of migraine auras, unformed and formed hallucinations

image Double vision

image More than double vision (polyopia, palinopsia)

image Oscillopsia (a visual sensation of stationary objects swaying back and forth)

image Deafness

image Tinnitus

image Difficulty with speech

image Difficulty swallowing

image Weakness

image Abnormal movements of muscles (including cramp, fasciculations)

image Abnormal movements of parts of the body (including tremor, dystonia, myoclonus)

image Clumsiness

image Impairment of control of limbs

image Altered sensation

image Loss of sensation

image Pain

image Symptoms of postural hypotension

image Impairment of sexual function

image Impairment of bladder control

image Impairment of bowel control

The time course of evolution and sometimes resolution of neurological symptoms very frequently indicates the nature of the problem, and so this needs to be clarified as precisely as possible. Thus, sensory or motor symptoms which start abruptly and are at their most marked at, or very soon after, their onset strongly suggest a vascular causation (transient ischaemia or ischaemic or haemorrhagic stroke). In contrast, similar symptoms evolving over a few days, reaching a plateau in severity and then slowly receding typify inflammatory central nervous system (CNS) demyelination (a first episode or a relapse of multiple sclerosis). Subacute (developing over weeks to months), progressive symptoms can be caused by many kinds of pathology, but neoplasia is always a prime concern.

These statements are true enough to be clinically useful, although there are exceptions. For example, one of the reasons for requesting cranial imaging in all stroke patients is to exclude a benign or malignant tumour or other pathology which has caused a stroke-like presentation. Neurodegenerative conditions always develop insidiously with gradual progression, but occasionally patients present acutely. For example, motor neurone disease can present acutely with ventilatory failure. Alzheimer’s disease commonly becomes evident after an episode of acute delirium caused by an intercurrent illness.

Two common neurological presentations require a history not only from the patient but also, if at all possible, from others: attacks of loss of consciousness and memory impairment.

The three most common causes of attacks of reduced consciousness or awareness that lead to neurological consultations are: neurocardiogenic syncope, epilepsy and psychogenic non-epileptic attacks. It is far more informative to hear a description from a witness than to request potentially misleading and inappropriate investigations. In the setting of the emergency department, obtaining the witness’s account may involve contact by telephone; this is time well invested. Table 14.1 summarizes some points which help to distinguish syncope from seizures.

Table 14.1 Points which help to distinguish syncope from seizures involving loss of consciousness. Minor injury, incontinence and sleepiness after the event do not distinguish well

Syncope Seizure

In neurocardiogenic syncope, characteristic prodromal features include: tinnitus, muffled hearing, dimming of vision, loss of vision while still conscious, widespread altered sensation, dizziness (may be described as spinning), lightheadedness, feeling of impending faint, weakness

Marked pallor

Sweating (but not in those with autonomic failure)

Any convulsion is brief (seconds)

Rapid recovery of lucidity and memory (registration and recall)

Patient comes round on the ground where he fell

A second attack immediately on being sat up after the first attack is very suggestive of neurocardiogenic syncope

Neurocardiogenic syncope is commonly set off by pain, squeamishness, gastrointestinal illness, public places indoors (clubs, restaurants, trains), prolonged standing

The symptoms of focal seizure activity which precede a secondarily generalized attack may or may not be remembered after the attack is over

Usually little or no pallor

Vocalization at onset of generalized convulsion (GC)

Apnoea

Cyanosis associated with GC

Stertorous breathing

Tongue biting

Postictal amnesia – paramedical staff present when patient ‘comes round’, or patient ‘comes round’ in hospital (although he walked to the ambulance)

Patients frequently complain of memory impairment. Distinguishing between the worried well and those with real impairment is greatly facilitated by information provided by close family or other informants. In general, if a patient is brought along to a doctor by a relative who complains that the patient has memory impairment, then there is an organic disorder, usually dementia. In contrast, many, but not all, patients who come to a doctor by themselves with the same complaint have good cognitive function. Furthermore, it is the relative who can report on changes in personality, behaviour, self-care and capacity which may be crucial to the diagnosis.

The most frequent symptom leading to neurological referral is headache. It is also a common reason for attending an emergency department. The vast majority of headaches are not caused by life-threatening disorders such as aneurysmal subarachnoid haemorrhage, meningitis or brain tumour, but are caused by common primary headache syndromes, particularly migraine. Table 14.2 outlines some of the features which may help to distinguish headaches of different sorts.

Table 14.2 Headaches: points to consider in the history

Aspect of history Feature Diagnosis
Region/location Focal, retro-orbital Cluster headache
Migraine
Retro-orbital lesion
Focal, frontal Sinus pathology
Unilateral Migraine
Chronic paroxysmal hemicrania (CPH)
Hemicrania continua
Generalized Migraine
Tension-type headache
Temporal aspects >50% of days Chronic daily headache (chronic migraine; tension-type headache)
Attacks of hours/days Migraine
Attacks of up to 1 hour Cluster headache
Many attacks, lasting minutes CPH
Attacks of seconds Trigeminal neuralgia
Worse on waking Raised intracranial pressure
Sleep apnoea
New, acute/subacute onset Meningitis
Abscess
Encephalitis
Explosive onset, severe Subarachnoid haemorrhage (SAH)
Character and severity Tight band around head, bland, featureless, not very severe Tension-type headache
Throbbing, moderately severe Migraine
Extremely severe, constant Cluster headache
Severe, stabbing, lancinating Trigeminal neuralgia
Provoking/relieving factors Provoked by alcohol Migraine
Cluster headache
Occur at night, start in sleep Migraine
Cluster headache
Hypnic headache
Relieved by sleep Migraine
Triggered by touching or moving the face Trigeminal neuralgia
Caused by cough Chiari malformation
Idiopathic cough headache
Exertion Exacerbates migraine
Benign exertional headache
Orgasm Benign coital headache (SAH has to be excluded in a severe single attack)
Associated symptoms Nausea, vomiting, photophobia, phonophobia Migraine
Migraine aura (visual, sensory, etc.) Migraine
Neck stiffness, photophobia, vomiting, symptoms of fever Meningitis
Tear production ipsilateral to a unilateral headache Migraine
Cluster headache
SUNCT*
Ipsilateral conjunctival injection Cluster headache
SUNCT*
Visual obscurations Raised intracranial pressure with papilloedema
Persistent focal neurological symptoms Intracranial lesion
General health Indications of systemic neoplasia Metastasis
Polymyalgia and weight loss Giant cell arteritis

* SUNCT, short-lasting, unilateral, neuralgiform headache attacks with conjunctival injection and tearing (a rare disorder).

Vertigo (a hallucination of movement) is an important symptom and requires careful characterization. It indicates a disorder of one or both labyrinths, vestibular nerves, vestibular nuclei in the brainstem or, rarely, the cerebrum. A clear-cut description of a spinning feeling usually signifies true vertigo. Patients are more likely to complain of dizziness or giddiness than vertigo, and both dizziness and giddiness mean different things to different patients, including vertigo, oscillopsia (a visual sensation that stationary objects are swaying back and forth), lightheadedness, loss of balance or even sometimes headache. It is always important to establish whether a patient with vertigo has positional vertigo. Enquiring whether the patient’s symptom is provoked by sitting from a lying position or standing from a sitting position will not distinguish vertigo from postural hypotension or ataxia, as all give rise to symptoms on rising. Symptoms brought on by lying down or turning over in bed or looking up at a high shelf or the sky more certainly signify real positional vertigo. It is not uncommon for patients with loss of balance to complain of dizziness; such patients will spontaneously comment that they feel secure sitting in a chair but dizzy as soon as they stand up and move around.

Focal weakness is self-explanatory. Many patients complain of feeling generally weak when they have no loss of muscle strength at all. Some patients become weak without realizing it. Thus, patients with unilateral or bilateral quadriceps weakness may present with falls rather than complain of weakness. Patients with bilateral ankle dorsiflexion weakness may complain of being off balance or of tripping rather than weakness. Exertional weakness or worsening of weakness is characteristic of neuromuscular junction disorders, but also occurs in cauda equina compression (spinal canal stenosis), spinal cord compression (cervical spondylotic myelopathy) and in multiple sclerosis and sometimes other disorders, so it is not specific but can be diagnostically helpful and so should be asked about.

Sensory symptoms may be negative (a reduction or absence of normal sensation) or positive (an abnormal sensation which is felt, e.g. buzzing, tingling, ‘pins and needles’, pain). In ordinary usage, the word numb would seem to be unambiguous, but some patients who are weak without sensory loss refer to numbness (particularly in Bell’s palsy) and, conversely, patients with sensory migraine auras may be misdiagnosed as having hemiplegic migraine because of their impression of paralysis even though they can move the affected limbs. Patients who seem imprecise have some justification; the Shorter Oxford Dictionary defines numb as ‘deprived of feeling, or of the power of movement’ so it is important to clarify exactly what the patient is describing.

As a rule, transient ischaemic attacks which involve the parietal cortex give rise to brief negative sensory symptoms. Conversely, focal sensory seizures are characterized by positive sensory symptoms.

Most organic neurological disorders which give rise to sensory symptoms involve structural or functional damage to nerves somewhere, whether it be in peripheral nerves, nerve roots, spinal cord or brain. Hypersensitivity (hyperaesthesia) to all modalities of sensation is therefore improbable or impossible. Patients who appear to have very sensitive skin as a result of a lesion (e.g. herpes zoster radiculitis) have combinations of paraesthesia, hypoaesthesia, dysaesthesia, allodynia, hyperalgesia and hyperpathia. Some of these terms are not without their ambiguities. Table 14.3 provides a definition for each.

Table 14.3 Nomenclature of cutaneous sensory symptoms

Hypoaesthesia Reduced cutaneous sensation of any modality
Paraesthesia Spontaneous abnormal sensation including, tingling, pins and needles and pain
Neuralgia Pain in the distribution of a nerve or nerve root
Dysaesthesia An abnormal perception of a sensory stimulus, e.g. touch causes tingling or pain
Allodynia Pain caused by a stimulus that does not normally cause pain
Hyperalgesia An abnormally intense perception of a mildly painful stimulus
Hyperpathia Perseveration, augmentation and, on occasion, spread of pain
The pain threshold is normal or sometimes high
In this, the threshold for perceiving pain may be raised and there may be delay in perceiving a painful stimulus, but once perceived, the pain is severe and prolonged and may spread
Hyperaesthesia An ambiguous term, best avoided

Neurological examination is poor at identifying and characterizing disorders of the autonomic nervous system, making it particularly important that autonomic function (including bladder and bowel control and sexual function) is addressed in the history.

The neurological examination

Aspects of neurological examination can start from the moment the patient is first encountered, before and during the taking of the history, such as noting an abnormality of gait, difficulties with speech, parkinsonism or a hyperkinetic movement disorder. There is no such thing as a comprehensive neurological examination – it would take hours or days. However, too many patients without neurological symptoms have no neurological examination at all, which on occasions proves regrettable. Consider, for instance, the case of a man who develops areflexic weakness some days after a hernia operation. How helpful would it be to know that the reflexes had been normal at the time of preoperative clinical clerking? A suggested minimal neurological examination for non-neurological patients would be: assessments of the binocular visual fields, the eye movements, the biceps, triceps, knee and ankle reflexes, the plantar reflexes and funduscopy. Most patients attending for a neurological consultation (with problems such as headache or epilepsy) have no neurological signs. A minimal routine neurological examination for such patients should include assessments of vision, the cranial nerves, motor and sensory examination and examination of gait. Bear in mind that many patients with early cognitive impairment are adept at concealing it, so that without probing, it can be missed.

For most patients, it is best to be systematic with regard to neurological examination, adhering to a routine well rehearsed by the examiner and familiar to those with whom the examiner will communicate. Thus, even if the patient’s problem is foot drop, it is entirely valid to start with examination of cranial nerves, but sensible to explain to the patient that you are going to start at the top and work down. Certain situations require flexibility; patients with any degree of impairment of consciousness need assessment of their delirium or coma from the outset. In patients with cognitive impairment, it is best to start the examination with cognitive assessment. It is important in all neurological patients to pay attention to and document mobility, and in patients presenting with a gait disorder it is appropriate to examine the gait first. For most other patients, an appropriate order of examination is: cranial nerves, speech if necessary, motor system, sensory system and gait, followed by cognitive testing if relevant.

Cranial nerve examination

Examination of the twelve cranial nerves actually involves an assessment of much more than just the nerves and nuclei, particularly in respect of the sensory visual system and eye movements. The naming and numbering of cranial nerves and their nuclei is in some measure idiosyncratic and confusing; for example, there is no olfactory nerve as such and the eighth cranial nerve is actually two nerves, as is the seventh. Within the brainstem, trigeminal sensory nuclei receive fibres not just from the fifth cranial nerve but also from the seventh, ninth and tenth nerves.

The olfactory (I) nerves

Olfactory receptor cells are bipolar sensory neurones situated under the nasal epithelium. Their central axons project in numerous bundles, not a discrete nerve, up through the cribriform plate of the skull into the olfactory bulb on the inferior surface of the frontal lobe. These project via the olfactory tract to parts of the temporal lobe and frontal lobe.

Examination of the olfactory nerves

For ordinary clinical purposes, olfaction is tested using a small number of bottles containing either a fragrant or pungent smelling substance such as lemon, clove or asafoetida. Each nostril should be tested separately. A necessary precondition is that a rhinological disorder does not preclude the test. Ideally the patient should identify the smell rather than just report that it can be smelt. There is little value in routinely testing olfaction; it is uncommon to detect an abnormality and even less common for an abnormality to contribute to a diagnosis. A subfrontal tumour such as a meningioma may cause unilateral anosmia, but other features of the history and examination will mandate the imaging which should establish that diagnosis. Subfrontal meningiomas can cause bilateral anosmia, so imaging is indicated in a patient presenting just with anosmia, unless another cause is clearly evident. Olfactory nerve fibres passing through the cribriform plate are not uncommonly sheared as a result of head injury, frequently leading to permanent bilateral anosmia. Anosmia is commonly neurodegenerative, occurring particularly in Lewy body disease, so its presence in a patient with parkinsonism increases the likelihood that the patient has idiopathic (Lewy body) Parkinson’s disease. Endocrinologists test olfaction when Kallman’s syndrome is suspected.

The optic (II) nerves

The optic nerve runs from the back of the globe of the eye to the apex of the orbit and into the skull through the optic canal to the optic chiasm, where it is joined by the optic nerve from the other eye. Directly above the optic chiasm is the hypothalamus. Directly below is the pituitary gland. The pituitary stalk runs from the hypothalamus to the pituitary gland just behind the optic chiasm, between the optic tracts. Sensory afferents from all points of the retina run in the nerve-fibre layer on the inner surface of the retina to enter the optic nerve at the optic disc. Fibres from the temporal retina (nasal visual half-field) are placed laterally while those from the nasal retina (temporal visual half-field) are medial. Fibres from the upper half of the retina run in the upper half of the optic nerve. At the optic chiasm, fibres from the nasal half of the retina (temporal visual half-field) cross (decussate) to the contralateral optic tract, while the fibres from the temporal half of the retina do not cross but proceed posteriorly into the ipsilateral optic tract (Fig. 14.1). Starting within the chiasm and continuing further posteriorly within the optic tract, fibres which convey matching information from each eye (i.e. homonymous fibres, representing equivalent parts in the temporal retina for one eye, nasal retina for the other eye) become aligned with each other. Thus, each optic nerve conveys information from its respective eye, but every part of the sensory visual system behind the optic chiasm on each side deals with vision for the contralateral binocular visual half-field.

image

Figure 14.1 A diagram of the sensory visual pathways. Sites of lesions and the visual field defects they produce are shown.

1: Optic nerve lesion.

2: Optic chiasm lesion (bitemporal hemianopia).

3a or 3b: Uniocular nasal hemianopia (rare).

3a plus 3b: Binasal hemianopia (very rare).

4: Optic tract lesion (incongruous homonymous hemianopia).

5: Visual radiation (homonymous quadrantanopia or hemianopia).

6a: Occipital cortex lesion sparing the occipital pole (homonymous hemianopia with macular sparing).

6b: Occipital pole lesion (homonymous paracentral hemiscotoma).

7: A bilateral occipital cortex lesion (homonymous altitudinal hemianopia).

The majority of optic tract fibres pass, via the lateral geniculate nucleus, to the occipital cortex. The lower part of the visual radiation transmits visual information from the inferior temporal retina of the ipsilateral eye and inferior nasal retina of the other eye. A few optic tract fibres pass via the superior colliculus to the midbrain to mediate the afferent limb of the pupillary light reflex via connections to the Edinger-Westphal nuclei.

Visual acuity and colour vision

Visual acuity is of neurological as well as ophthalmological importance, since optic nerve disease may lead to any degree of loss of acuity. For ordinary clinical neurological purposes, the acuities measured by the Snellen chart are adequate. Severe loss of acuity (less than 6/60, the top letter on the Snellen chart) is documented as ability to count fingers at 1 metre, ability to perceive hand movements, perception of light only and no perception of light.

Acquired unilateral loss of colour vision is a characteristic feature of optic neuropathy, and loss of colour vision can occur when visual acuity is well preserved. Thus, testing colour vision using Ishihara plates may be a sensitive bedside test for mild optic neuropathy.

Visual fields

Assessment of the visual fields is a key part of the neurological examination, and need not take very long to perform. Field defects of importance are commonly missed because they have not been looked for adequately. Increasingly, opticians measure visual fields, but it cannot always be assumed that a recent ophthalmological assessment will have included the visual fields.

Visual field defects in one eye indicate a retinal or optic nerve disorder. They may affect any part of the field of the affected eye or nerve. Lesions at the optic chiasm or lesions behind the chiasm in the optic tracts, visual radiations or occipital cortex give rise to visual field defects affecting both eyes. Unilateral retrochiasmal lesions give rise to field defects affecting the contralateral binocular half-field, and the defects are homonymous (i.e. they affect equivalent parts of the temporal half-field of one eye and the nasal half-field of the other). Congruity refers to the extent to which the defects in the two half-fields match each other exactly. A congruous homonymous hemianopia indicates a lesion in the occipital cortex, while a non-congruous homonymous hemianopia is more likely to occur with an optic tract lesion.

When ophthalmologists do visual field testing, they tend to do Goldman perimetry or to obtain automated Humphrey field, and the results of these tests are very useful, but in the clinic or on the ward, neurologists and general physicians test visual fields by simple confrontation field testing, comparing the patient’s fields with their own, assuming their own to be normal.

Examination of the visual fields

It is best to start by testing the binocular visual fields (i.e. the patient and examiner both have both eyes open). Start by asking the patient to look at your face. Ensure that he avoids the common temptation to look to either side. Hold your hands up one on each side at face level, with your hands about 1 m apart and ask the patient whether he can see both hands. This simple test will detect a dense homonymous hemianopia. Next ask the patient to look into your eyes. Switch from hands held up to index fingers held up and move them up so that they are situated in the right and left superior quadrants of vision. Instruct the patient to point at the finger which wiggles. Getting the patient to point is better than asking him to say whether it is the right or left finger which is moving – very many muddle left and right in this situation. First wiggle one finger, then the other, to check the integrity of the superior quadrants. Failure of the patient to see one of the fingers wiggling suggests a homonymous quadrantanopia. If that happens, carry on wiggling the finger which has not been registered by the patient and move it first across the midline to make sure that it becomes visible at the midline and then go back and do the same, this time moving the finger down into the inferior quadrant, where the finger will be visible if the patient has a quadrantanopia, or remain unseen if the patient has a homonymous hemianopia. If the patient sees each finger wiggling consecutively in each of the upper quadrants, then wiggle both fingers simultaneously and ask the patient what is happening. If the patient only sees the wiggling of the finger on one side consistently, then he has visual inattention – an occipitotemporal or occipitoparietal disorder. Having tested the superior quadrants, move down to the inferior quadrants to test them in the same way. With a cooperative patient, all of this takes only a matter of seconds to do. The technique described will not detect a bitemporal hemianopia, optic nerve lesions or retinal disorders; these require testing of the field for each eye separately.

The best way to test the monocular visual fields at the bedside is to use a pin with a bright red pinhead of about 5-8 mm diameter. The patient needs to be positioned such that light is not shining from behind the examiner into the patient’s eyes, so as to interfere with his ability to see the colour of the pinhead. The margin of the field is defined by the points at which perception of the colour of the pinhead changes from black to red. Ask the patient to cover one eye with the palm of his hand (or cover the eye with your own hand) and then to look with his open eye straight into your own confronting eye (his left into your right and vice versa). First, put the pinhead into the middle of the visual field and check that the patient sees it as bright red. Swap to the other eye and compare the perceived brightness of red reported by the patient for his two eyes. Loss of perceived redness in one eye (red desaturation) raises the possibility of a mild optic neuropathy. A patient who is already known to have poor acuity in one eye may have a central scotoma, in which case the pinhead will either not be seen in the centre of the field or will be perceived black. A small central scotoma can be defined by moving the pinhead outwards in four different directions until the patient sees its redness. Next, put the pinhead into each of the four quadrants of vision close to the centre and check that the patient sees it as bright red. This may detect a paracentral scotoma, and is also a good way of detecting temporal field defects due to optic chiasm lesions such as pituitary tumours. Then finally, while ensuring that the patient maintains fixation into your eye, compare the periphery of his field with your own by moving the pin from outside the field in towards the centre at various points around the periphery, with the pin midway between you and the patient. The patient has to report not when he first sees the pin or your hand, but when the pinhead colour changes from black to red.

The pupils

Examination of the pupils and their responses to light and accommodation provides information not only about specific neurological syndromes which affect the pupils, such as Adie’s syndrome, but also information about the integrity of the anterior visual pathways (particularly the optic nerves), the brainstem and the efferent parasympathetic and sympathetic pathways to the pupillary sphincter and dilator muscles, respectively.

Pupil constriction is a parasympathetic function. The first-order neurones are in the Edinger-Westphal nucleus adjacent to the oculomotor nucleus in the midbrain. Axons travel in the oculomotor nerve to the ciliary ganglion in the orbit. Second-order neurones innervate the pupillary sphincter. Lesions of the Edinger-Westphal nucleus or the pupilloconstrictor nerve fibres in the third cranial nerve or in the orbit lead to dilatation of the pupil (mydriasis) unless there is simultaneously a lesion of the sympathetic innervation of the pupil. In either case, there is a failure of constriction of the pupil to light. In general, compression of the third cranial nerve (classically by a posterior communicating artery aneurysm) affects the pupilloconstrictor fibres. A microvascular ischaemic lesion of the third nerve may spare the pupilloconstrictor fibres, giving rise to a pupil-sparing third nerve lesion. Microvascular lesions of the oculomotor nucleus may spare the Edinger–Westphal nucleus with the same result. A mid-sized unreactive pupil due to a lesion of both parasympathetic and sympathetic supplies is seen in aneurysms of the internal carotid artery within the cavernous sinus, along with other features of a cavernous sinus syndrome.

Pupil dilatation is achieved by sympathetic innervation of pupillodilator muscle fibres. The first-order neurones are in the hypothalamus. They project down through the brainstem and cervical spinal cord to the ciliospinal centre in the lower cervical and upper thoracic spinal cord, from where second-order neurones project via the T1 nerve root and sympathetic chain to the superior cervical ganglion. Third-order axons run up the internal carotid artery as far as the cavernous sinus and from there through the orbit to the pupil. There is also sympathetic innervation of the levator palpebrae superioris muscle by the same route. A lesion of the sympathetic supply to the pupil at any point between the hypothalamus and the orbit will give rise to the two main features of Horner’s syndrome: constriction of the pupil (which will still react to light by further constricting) and ptosis (drooping of the upper eyelid).

Examination of the pupils

First, in normal illumination, establish whether the pupils are of equal size. If they are not, bear in mind that there are two possibilities: either one is smaller than it should be, or the other is bigger. Avoid jumping to the wrong conclusion.

Ideally, the reactions of the pupils to light should be tested in moderately low illumination. Use a bright torch, not an ophthalmoscope. Shine the light into one eye and observe the response of the pupil (the direct response), the normal response being constriction of the pupil which is sustained until the light is removed. Repeat the test, this time looking at the contralateral pupil, which will normally constrict (the consensual response). Then test the other eye. Next, test accommodation (constriction of the pupils when focusing on a near object). Ask the patient to look into the distance, then at your finger held at a distance and to keep looking as you advance your finger to a distance of about 20 cm from the patient’s face. Advancing your finger in a wavy line allows you to check that the patient is looking at the finger. Observe the adduction of the eyes and the constriction of the pupils. Then ask the patient to look into the distance again.

Afferent pupillary defect

A patient with a severe lesion of the anterior visual system in one eye (an ophthalmological disorder or an optic nerve disorder such as severe optic neuritis or an ischaemic optic neuropathy) will have an afferent pupillary defect (i.e. a failure of constriction of either pupil to light shone into the affected eye). If the visual system on the other side is unaffected, light shone into the normal eye will lead to a normal direct pupillary response and there will also be a consensual response in the visually impaired eye, assuming the efferent pathway is intact.

Relative afferent pupillary defect

A patient with a mild lesion of the anterior visual apparatus on one side will exhibit a direct pupillary response to light, but it will be less vigorous than the consensual response to light shone into the other eye. In this situation, the swinging torch test may reveal a relative afferent pupillary defect. If a patient has a mild optic nerve lesion in the left eye, then acuity and colour vision may be only mildly impaired and the field normal. Shine the torch into the affected left eye and note the seemingly normal response. After 2 seconds, move the torch briskly to shine into the normal right eye. The right pupil will already be constricted as a result of the consensual response. It will stay constricted and, if anything, will constrict a little further. After 2 seconds, move the torch briskly back to the left eye. Because of the subtle afferent defect, the signal strength of the input to the midbrain pupilloconstrictor (Edinger-Westphal) nuclei will be reduced, resulting in an apparently paradoxical dilatation of the left pupil in spite of light being shone into it. If you keep swinging the torch back and forth from one eye to the other, the relative afferent pupillary defect will continue to be observed, though the defect is best seen within the first few goes.

Afferent and relative afferent pupillary defects are important because they are objective. A person who gives the impression of having functional visual impairment in one eye, but who has an afferent pupillary defect, must have an organic problem. In contrast, a person who reports uniocular blindness and has normal pupillary responses to light will not be blind.

Efferent pupillary defect (part of a third cranial nerve lesion)

A lesion of the pupilloconstrictor nerve fibres in the oculomotor nerve will lead to dilatation of the ipsilateral pupil (due to the unrestrained effect of the intact sympathetic supply). Further, there will be failure of constriction of the pupil to light, although the consensual response in the other eye will be preserved. Light shone into the contralateral eye will elicit a normal direct response but no consensual response.

Other common pupillary abnormalities of neurological relevance

image Simple (physiological) anisocoria (inequality of pupil size): this is common. The pupillary inequality is not marked and the reactions to light and accommodation are normal.

image Tonic pupil: this is seen in Holmes Adie syndrome, a relatively benign polyneuropathy comprising a lesion of the ciliary ganglion and a degree of loss of tendon reflexes. An acute Adie pupil is enlarged, does not react to light and there is a slow constriction to accommodation. Redilatation of the pupil after accommodation is delayed such that, temporarily, the normal pupil may be larger than the affected one.

image Argyll Robertson pupils: these are small, irregular, unequal pupils which do not react to light but do to accommodation. They were seen in advanced syphilis. Without the irregularity but with the other features, diabetic small vessel disease is currently the most common cause.

image The pupils in coma: this is important but covered elsewhere (Ch. 8).

Funduscopy

This technique is described in Chapter 19. The neurological examination focuses on papilloedema, optic atrophy or pigmentary retinal degeneration and vascular disease.

The oculomotor (III), trochlear (IV) and abducens (VI) nerves – eye movements

Abnormalities of eye movements may result from disorders of the cerebral hemispheres, brainstem, cerebellum, cranial nerves III, IV and VI, the neuromuscular junctions between oculomotor nerves and eye muscles, the eye muscles themselves and from lesions affecting the structure and contents of the orbits. Their importance in neurological and general physical examination is therefore evident.

The nucleus for the third cranial nerve is in the midbrain (Fig. 14.2) and emerges ventrally (anteriorly), medial to the cerebral peduncle, passing forward through the cavernous sinus to the superior orbital fissure. In the orbit, the superior ramus supplies superior rectus and levator palpebrae superioris. The inferior ramus supplies inferior rectus, inferior oblique and medial rectus and parasympathetic fibres from the inferior ramus pass to the ciliary ganglion and thence to the ciliary muscle and the pupil sphincter.

image

Figure 14.2 A diagram of the midbrain. Note the dorsally positioned third nerve nuclei. Vascular territories are shown on the left.

The fourth nerve nucleus lies just caudal to the third nerve nucleus in the brainstem. The nerve fibres of the fourth nerve decussate. The nerve starts on the dorsal aspect of the brainstem and passes around the brainstem through the cavernous sinus and superior orbital fissure to the superior oblique muscle. Consequent upon the decussation of fibres, the right trochlear nucleus innervates the left superior oblique and vice versa.

The sixth nerve nucleus is beneath the floor of the fourth ventricle in the pons (Fig. 14.3). Nerve fibres run forward (ventrally) through the pons emerging at its lower border, then up the skull base and forward through the cavernous sinus to the superior orbital fissure and into the orbit to supply the lateral rectus muscle. The nerve is long, thin and very susceptible to dysfunction, most notably in the setting of raised intracranial pressure of any aetiology, which may give rise to either unilateral or bilateral sixth nerve lesions. This is referred to as a ‘false localizing sign’, since a focal mass lesion causing raised intracranial pressure may be remote from the sixth nerves and their nuclei or there may be no focal cause of the raised pressure at all (e.g. idiopathic intracranial hypertension).

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Figure 14.3 A diagram of the fifth, sixth and seventh nerve nuclei in the pons. Note how the nerve fibres of VII loop round the nucleus of VI.

Table 14.4 and Figure 14.4 outline the actions of each eye muscle.

Table 14.4 Actions of the eye muscles

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Figure 14.4 A diagram showing which muscles elevate and depress the abducted and adducted eye.

Terminology in eye movements

Horizontal movement of the eye outwards (laterally) is termed abduction and inwards (medially) is termed adduction. Vertical movement upwards is termed elevation and downwards is depression. The eye is also capable of diagonal movements (version) at any intermediate angle. Rotary movements are those in which the eye twists on its anterior–posterior axis. Convergence refers to adduction of both eyes to fixate on a near object. Lateral rotation of the head causes replex rotation of the eyes in the opposite direction (internal rotation of one eye, external rotation of the other). A squint (the eyes point in different directions) is described as convergent or divergent strabismus, depending on whether the eyes point towards or away from each other. Saccades are abrupt, rapid small movements of both eyes, such as those needed to shift fixation from one object to another. Nystagmus denotes rhythmic oscillations of one or (more usually) both eyes. In pendular nystagmus, the movement is slow in both directions. In jerk nystagmus, there is a slow phase in one direction and a fast phase in the opposite direction. By convention, the direction of nystagmus is the direction of the fast phase, but the defect is in fact the slow phase and is either an abnormal deviation of the eyes or a failure of the eyes to maintain position, and the fast phase is a compensatory saccade aimed at restoring the correct position of the eyes. Some types of nystagmus are outlined below.

Examination of eye movements

As with every other component of examination, the detail in which the eye movements are examined depends on whether there are relevant symptoms and whether abnormal signs are likely to be present. Ask the patient to keep his head still (assist him by putting your left hand on his head to steady it) and then to look at your right index finger held directly in front of his eyes at about half a metre distance. In the primary position of gaze, look for any visible abnormality of the alignment of the two eyes (an affected patient may or may not complain of double vision) and any pendular or vestibular nystagmus (see below). Now move your finger to the right, left, up and down in a large ‘H’ pattern. The pursuit eye movements which are elicited should precisely follow your finger at the appropriate constant velocity. Eye movements which are ‘broken up’ into a series of short saccades indicate a brainstem or cerebellar lesion affecting eye movement control. Patients with diplopia will experience their diplopia at some point (or at all times) during this simple test. Gaze-evoked and vestibular nystagmus will be observable (see below). When looking for nystagmus, it is important not to get the patient to look too far in any direction since, at the extremes of gaze, nystagmus can be normal as the patient struggles to deviate his eyes beyond what is possible. Look for nystagmus at about 30° away from the primary position of gaze.

Diplopia testing

If a patient complains of double vision, first establish that it is true diplopia and not monocular diplopia. In patients who have obvious, easily visible paresis of movement of one or both eyes, the reason for diplopia is self-evident (Fig. 14.5).

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Figure 14.5 Right third nerve palsy. The patient had a complete ptosis. The eyelid is lifted to reveal a dilated pupil with external strabismus.

(Reproduced with permission from Mir 2003 Atlas of Clinical Diagnosis, 2nd edn, Saunders, Edinburgh.)

Diplopia develops with even very subtle misalignment of the eyes, which cannot be seen on simple inspection. In this situation, if the ophthalmoparesis affects just one eye, it is possible to work out which eye muscles are underactive by diplopia testing. The true image is that generated by the eye with normal movements. The false image is that generated by the eye with the paretic muscle or muscles. For example, if a patient develops double vision on looking to the right, with horizontal separation of the images, the false image will be the one further out to the right. This is true whether it is the right eye which does not abduct adequately (right lateral rectus weakness) or if it is the left eye which does not adduct adequately (left medial rectus weakness). If this does not seem immediately clear, consider the extreme case: one eye moves, the other does not. An image (an examiner’s finger or a white pinhead) moves to the patient’s right. The image remains in the middle of the field of the eye which moves, but moves progressively to the right of the field of the eye which does not. The same rule applies in all directions of gaze. Diplopia is always maximal in the direction in which the weak muscle has its purest action (see Table 14.4).

The severity of the diplopia should be assessed in eight positions: looking to left and right, up and down, and obliquely up and down to the left and obliquely up and down to the right. To work out which muscle is underactive, where the diplopia is maximal, cover each eye in turn and get the patient to tell you which of the two images disappears. Inconsistent answers are common, however, and the assistance of an ophthalmologist or optometrist is frequently desirable. The features of lesions of the third, fourth and sixth cranial nerves are summarized in Table 14.5.

Table 14.5 The effects of lesions of the oculomotor (III), trochlear (IV) and abducens (VI) nerves

Affected nerve Signs Comment
Oculomotor Paresis of adduction (medial rectus) The eye becomes abducted because of unopposed action of lateral rectus, and slightly depressed because of action of superior oblique
Paresis of elevation (superior rectus and inferior oblique) The pure depressor action of superior oblique cannot be tested because the eye cannot be adducted
Intorsion of the eye on attempted down gaze indicates intact trochlear nerve and superior oblique function
Paresis of depression (inferior rectus)  
Ptosis due to paresis of levator palpebrae superioris With complete ptosis, there is of course no diplopia
Dilated, unreactive pupil This feature is not present in pupil-sparing lesions (microvascular lesions of nucleus or nerve)
Trochlear Paresis of superior oblique Extorsion of the eye due to unopposed action of inferior oblique leads to diplopia such that a vertical line looks V-shaped
The patient compensates with a head tilt to the side opposite the lesion, intact intorsion on that side tending to correct the diplopia
Abducens Paresis of lateral rectus Horizontal diplopia

In assessing patients who have double vision, it is best first to establish which muscles appear to be weak, and then try to decide what the nature of the problem is likely to be, taking into consideration all the physical signs. Thus, impairment of eye movements in one eye in combination with proptosis of that eye may occur because of mechanical restriction of eye movements by an intraorbital lesion. Weakness of muscles in both eyes with different patterns of involvement of the muscles in the two eyes is likely to be due to a disorder of the muscles themselves (orbital myositis, thyroid eye disease) or due to ocular or generalized myasthenia. The pupils will not be involved. Bilateral, asymmetrical combinations of cranial nerve lesions are relatively uncommon (neoplastic infiltration, cranial polyneuritis). Bilateral sixth cranial nerve lesions are common, usually but not exclusively as a feature of raised intracranial pressure. Multiple oculomotor neuropathies in one eye direct attention to the superior orbital fissure and the cavernous sinus (see Box 14.2).

Box 14.2 Cranial nerve involvement in lesions of the cavernous sinus and superior orbital fissure

1 Lesion of the cavernous sinus (e.g. internal carotid aneurysm; internal carotid artery dissection; meningioma):

– potential involvement of cranial nerves III, IV, VI, V1 (ophthalmic division), V2 (maxillary division) and sympathetic pupillodilator nerve fibres
– cavernous sinus thrombosis combines the above with proptosis, chemosis, papilloedema and visual failure

2 Lesion of the superior orbital fissure (e.g. Tolosa Hunt syndrome):

– potential involvement of III, IV, VI and V1 (ophthalmic division)
– extension into the orbit may lead to involvement of the optic nerve

Horizontal gaze paresis; internuclear ophthalmoparesis

Neural control of voluntary lateral gaze to the right starts in the left cerebral hemisphere, such that a large left cerebral hemisphere lesion may be associated with failure of right gaze and a tendency for the eyes to deviate to the left (the side of the lesion). Output runs to the right paramedian pontine reticular formation (PPRF); hence,a right-sided pontine lesion may involve a right gaze paresis. Output from the right PPRF goes to the right sixth nerve nucleus, resulting in right eye abduction, and across, via the left medial longitudinal fasciculus (MLF), to the left third nerve nucleus, resulting in simultaneous left eye adduction. Attempted right gaze in the setting of a left MLF lesion results in abduction of the right eye, but failure of adduction of the left eye – an internuclear ophthalmoparesis (INO) (see Fig. 14.6). Bilateral MLF lesions give rise to bilateral INO, in which case, with lateral gaze in either direction, only the abducting eye moves normally. Commonly, nystagmus is seen in the abducting eye. The pathway for adducting both eyes for near vision is separate, and sometimes in bilateral INO preservation of adduction of the eyes for near vision can be demonstrated, proving that the problem is not bilateral medial rectus weakness.

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Figure 14.6 (A) A right internuclear ophthalmoparesis. (B) A diagram of the pathways for horizontal gaze. The command for left gaze originates in the right cerebral hemisphere. Descending nerve fibres decussate to reach the left pons. Lesion 1 produces a left horizontal gaze paresis. Lesion 2 produces a right internuclear ophthalmoparesis. Lesion 3 produces the ‘one and a half’ syndrome: a left gaze paresis and left internuclear ophthalmoparesis (failure of adduction of the left eye on right gaze) – only abduction of the right eye on right gaze remains. NPH, nucleus prepositus hypoglossi; MLF, medial longitudinal fasciculus; PPRF, paramedian pontine reticular formation.

Vertical gaze pareses

The neural control of upgaze and downgaze is complex. Ultimately, output for upgaze is via components of the third nerve nucleus mainly to the superior rectus and inferior oblique muscles bilaterally. The output for downgaze is from the third and fourth nerve nuclei to the inferior rectus and superior oblique muscles, respectively. In general, defects of upgaze or downgage localize rather poorly, but lesions such as pineal tumours which compress the midbrain and bilateral descending connections from the hemispheres often cause upgaze paresis.

Non-paralytic strabismus

Neurologists need to be able to recognize non-paralytic strabismus. Decompensation of a longstanding squint may be a cause of acquired diplopia, but this is an ophthalmological problem and it is covered in Chapter 19.

Testing saccadic eye movements

Getting a patient to follow a moving finger tests pursuit eye movements. It takes very little time to test saccadic eye movements and useful signs may be detected. First, simply ask the patient to keep his head still and look to the left, to the right, up and down. Then hold your hands up in front of the patient, one in the primary position of gaze, the other to the side, with palms facing the patient, fists closed. Ask the patient to keep his head still. Open the fist of the hand in front of the patient and ask him to look at it. Then close that fist and open the other and ask the patient to switch his gaze to the hand at the side. By alternating which hand is open you can get the patient to refixate briskly to and fro. Then check the other side. These manouevers test saccadic movements; in disease, saccades may be slowed or interrupted. They are also the best way of detecting a mild internuclear ophthalmoparesis.

Supranuclear gaze pareses

Reflex eye movements related to head movements are generated and organized by vestibular, cerebellar and brainstem systems, whereas voluntary gaze is initiated in the cerebral hemispheres. A patient’s gaze paresis is therefore supranuclear if reflex eye movements are intact. Take a patient with selective paresis of downgaze. If brisk backward rotation of the head (extension of the neck) produced reflex depression of both eyes, a supranuclear lesion would be inferred. In practice, this is often not easily achieved since the relatively common disorder giving supranuclear downgaze paresis is progressive supranuclear palsy, a condition in which there is also axial rigidity affecting neck movements.

Peripheral vestibular nystagmus

This occurs in lesions of the labyrinth or vestibular nerve. Normally there is tonic input to the brainstem vestibular nuclei from the periphery. Loss of this tonic input leads to deviation of the eyes towards the affected side (slow phase) with fast-phase nystagmus directed to the opposite side. In mild lesions, the nystagmus is only seen when the eyes look in the direction of the fast phase. In more severe lesions, the nystagmus is seen with the eyes in the primary position of gaze or even when looking away from the direction of the fast phase. Usually the nystagmus is of high frequency and relatively low amplitude.

Gaze paretic nystagmus

This is a gaze-evoked nystagmus in which the eyes are not able to maintain a position away from their primary position, so the slow phase is a drift back to the primary position while the fast phase is in the direction of gaze. In the primary position, the eyes are still. The nystagmus may be of large amplitude and low frequency. Drug-induced nystagmus (alcohol, benzodiazepines, antiepileptic medication) is of this sort and is seen in all directions of gaze. Structural brainstem or cerebellar lesions may cause asymmetric gaze paretic nystagmus. In cerebellar hemisphere lesions, the nystagmus may be unidirectional with the fast phase towards the side of the lesion.

Upbeat nystagmus (fast phase upwards) may occur with lesions at various locations in the brainstem and with cerebellar vermis lesions. Downbeat nystagmus is characteristic of cervicomedullary junction lesions such as Chiari malformations, but can also be seen with cerebellar degenerations.

Congenital nystagmus

The rule here is that the nystagmus is horizontal, even when the patient looks up or down. On left gaze, it is left beating, and on right gaze, it is right beating. There may be a null point at which the nystagmus is least conspicuous, but it is not necessarily in the primary position, and the eyes may not be completely still. Congenital nystagmus is damped by convergence.

Pendular nystagmus

This may be seen as a complication of congenital or acquired very poor vision. It is also seen in pontine lesions (e.g. multiple sclerosis).

The trigeminal (V) nerve

This is a mixed motor and sensory nerve. The nerve trunk emerges from the pons as sensory and motor roots.

Sensory component of the trigeminal nerve

The primary sensory neurones are in the trigeminal ganglion, just behind the cavernous sinus at the apex of the petrous bone. Central projections run in the trigeminal nerve into the pons. Figure 14.7 shows the cutaneous distribution of the three divisions of the trigeminal nerve: ophthalmic (V1), maxillary (V2) and mandibular (V3). These nerves also mediate general sensation inside the mouth and nose and proprioception. The ophthalmic nerve passes through the cavernous sinus and superior orbital fissure. The maxillary nerve also passes through the cavernous sinus, but leaves the inside of the skull through the foramen rotundum. The mandibular nerve passes through the foramen ovale.

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Figure 14.7 Areas of cutaneous innervation of the head and neck by the three divisions of the trigeminal nerve and the upper cervical nerve roots.

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