Category Archives: Neurological Diseases and Diseases of Voluntary Muscle

The trigeminal nerve is mainly sensory but contains some motor fibres.

Sensory fibres

from the three divisions-ophthalmic (VI)’ maxillary (V2) and mandibular (V,) – pass to the trigeminal ganglion at the apex of the petro us temporal bone. From here central fibres enter the brain stem. Ascending fibres transmitting the sensation of light touch enter the nucleus in the pons. Descending fibres carrying pain and temperature sensation form the spinal tract of the fifth nerve and end in the spinal nucleus in the medulla and upper cervical cord.
Motor fibres arise in the upper pons and join the mandibular branch to supply the muscles of mastication. Signs of a trigeminal nerve lesion Diminution of the corneal reflex is often the first sign of a fifth nerve lesion.
A complete fifth nerve lesion causes unilateral sensory loss on the face, tongue and buccal mucosa. The jaw deviates to the side of the lesion when the mouth is opened. Central (brain stem) lesions of the lower trigeminal nuclei (e.g. in syringobulbia,) produce a characteristic circumoral sensory loss.
When the spinal tract (or spinal nucleus) alone is involved, the sensory loss is restricted to pain and temperature sensation, i.e. ‘dissociated’.

Causes of trigeminal nerve lesions

BRAIN STEM. Lesions at this site involve the nuclei and central connections, and include:
• Brain stem glioma
• MS
• Infarction
• Syringobulbia
CEREBELLOPONTINE ANGLE. Here the nerve is compressed by:
• Acoustic neuroma
• Meningioma
• Secondary neoplasm
APEX OF THE PETROUS TEMPORAL BONE. Infection from chronic middle-ear disease involves the nerve at this site. The combination of this with pain and a sixth nerve lesion is called Gradenigo’s syndrome.
CAVERNOUS SINUS. Here the trigeminal ganglion is compressed by:
• Aneurysm of internal carotid artery
• Extension of a pituitary neoplasm
• Cavernous sinus thrombosis
• Secondary neoplasm
The trigeminal ganglion is infected in ophthalmic herpes zoster, the commonest lesion of the ganglion.

PERIPHERAL BRANCHES OF THE TRIGEMINAL

NERVE. These are affected by neoplastic infiltration of the skull base.

Trigeminal neuralgia

Trigeminal neuralgia (‘tic douloureux’) is a condition of unknown cause, seen most commonly in old age. It is almost always unilateral.

SYMPTOMS

Severe paroxysms of knife-like or electric-shock-like pain, lasting seconds, occur in the distribution of the fifth nerve. The pain tends to commence in the mandibular division (V,) and spreads to the maxillary (V2) and (rarely) to the ophthalmic division (VI)’ It occurs many times a day.
Each paroxysm is stereotyped, brought on by stimulation of a specific ‘trigger zone’ in the face. Washing, shaving, a cold wind or eating are examples of the trivial stimuli that may provoke the pain. The face may be screwed up in agony (hence ‘tic’ -an involuntary movement).
The pain characteristically does not occur at night. Spontaneous remissions last for months or years before recurrence.

SIGNS

There are no signs of trigeminal nerve dysfunction. The corneal reflex is preserved. Diagnosis is on clinical grounds alone.

TREATMENT

The anticonvulsant carbamazepine 600-1200 mg daily suppresses attacks in the majority of patients. Phenytoin and clonazepam are also used, but are less effective. If drug therapy fails, surgical procedures (radio frequency extirpation of the ganglion, nerve decompression or sectioning of the sensory root) are useful in difficult cases. Alcohol injection into the trigeminal ganglion or peripheral fifth nerve branches can also be carried out.

‘Secondary’ trigeminal neuralgia

Trigeminal neuralgia also occurs in MS, with lesions of the cerebellopontine angle (see below) and with tumours of the fifth nerve (e.g. neuroma). These lesions are usually accompanied by physical signs (e.g. a depressed corneal reflex).

Idiopathic trigeminal neuropathy

A chronic and isolated fifth nerve lesion may sometimes develop without any apparent cause. When sensory loss is severe, trophic changes (facial scarring and corneal ulceration) occur.

Postherpetic neuralgia

This may occur in the distribution of one division of the trigeminal nerve, commonly the first.

Sympathetic impulses from fibres in the nasociliary nerve stimulate the dilator muscle of the pupil (dilator pupillae).
Preganglionic sympathetic fibres to the eye (and face) {yiginate in the hypothalamus, pass uncrossed through re midbrain and lateral medulla and emerge finally from the spinal cord at Tl (close to the lung apex). Postganglionic fibres begin in the superior cervical ganglion. These pass to the pupil in the nasociliary nerve from a plexus surrounding the internal carotid artery. Those fibres to the face (sweating and pilo-erection) form a plexus surrounding the external carotid artery. This arrangement is of clinical importance in Horner’s syndrome. Parasympathetic impulses from the ciliary ganglion in the short ciliary nerves to the sphincter muscle of the pupil (sphincter pupillae) cause the pupil to constrict. An outline of the arrangement of parasympathetic fibres to the pupils and the mechanism of the light reflex is shown.

The light reflex

Afferent fibres in each optic nerve (some crossing in the chiasm, see Fig. 18.5) pass to both lateral geniculate bodies and relay to the Edinger-Westphal nuclei via the pretectal nucleus. Efferent (parasympathetic) fibres from each Edinger- Westphal nucleus pass via the third nerve to the ciliary ganglion and thence to the pupil.
Light constricts the pupil of the eye being tested (direct reflex) and the contralateral pupil (consensual reflex).

The convergence reflex

Fixation on a near object requires convergence of the ocular axes and is accompanied by pupillary constriction. The afferent fibres in each optic nerve, which pass through both lateral geniculate bodies, also relay to the convergence centre. This centre receives la spindle afferent fibres from the extraocular muscles-principally the medial recti, which are innervated by the third nerve. The efferent route is from the convergence centre to the Edinger-Westphal nucleus, ciliary ganglion and pupils. Voluntary or reflex fixation on a near object is thus accompanied by appropriate convergence and pupillary constriction.

Clinical abnormalities of the pupils

DEGENERATIVE CHANGES.IN OLD AGE. The pupil tends to become small (3-3.5 mrn) in old age (senile miosis) and may be irregular; a bright light is necessary to demonstrate constriction and the convergence reflex is sluggish. A slight difference between the size of the pupils is common (physiological anisocoria) but the changes may cause confusion with the Argyll Robertson pupil.
THE ARGYLL ROBERTSON PUPIL. This is a small, irregular (3 mm or less) pupil that is fixed to light, but constricts on convergence. The lesion is believed to be in the area surrounding the aqueduct. The Argyll Robertson pupil is (almost) diagnostic of neurosyphilis. Similar changes are occasionally seen in diabetes mellitus.
THE MYOTONIC PUPIL (HOLMEs-ADIE PUPIL). This is a dilated pupil seen most commonly in young women. It is usually unilateral. There is no reaction (or a very slow reaction) to a bright light and also an incomplete constriction to convergence. The condition is due to denervation in the ciliary ganglion. The myotonic pupil is of no pathological significance but is often associated with diminished or absent tendon reflexes.
HORNER’S SYNDROME. This syndrome is due to interruption of sympathetic fibres to one eye. It presents as unilateral pupillary constriction with slight relative ptosis and enophthalmos. The conjunctival vessels may be injected. There is loss of sweating of the same side of the face or body; the extent depends upon the level of the lesion. The syndrome indicates a lesion of the sympathetic pathway on the same side. Causes of Horner’s syndrome.
The level of the lesion is indicated by the distribution of the loss of sweating:
CENTRAL LESIONS affect sweating over the entire half of the head, arm and upper trunk.
LESIONS OF THE NECK PROXIMAL TO THE SUPERIOR CERVICAL GANGLION cause diminished sweating on
the face.
LESIONS DISTAL TO THE SUPERIOR CERVICAL GANGLION do not affect sweating at all. Pharmacological tests may indicate the level of the lesion. For example, a lesion distal to the superior cervical ganglion causes denervation hypersensitivity of the pupil, which dilates when 1 : 1000 adrenaline is instilled. This dose has little effect on the normal pupil or a proximal lesion. In clinical practice the test is of limited value. Other abnormalities of the pupils seen in coma are discussed.

Hemisphere and brain stem lesions
Massive cerebral infarction
Pontine glioma
Lateral medullary syndrome
‘Coning’ of the temporal lobe
Cervical cord lesions
Syringomyelia
Cord tumours
T1 root lesions
Bronchial neoplasm (apical)
Apical tuberculosis
Cervical rib
Brachial plexus trauma
Sympathetic chain in the neck
Following thyroid/laryngeal surgery
Carotid artery occlusion
Neoplastic infiltration
Cervical sympathectomy
Miscellaneous
Congenital
Migrainous neuralgia (usually transient)

THE OCULAR MOVEMENTS AND, THIRD, FOURTH AND SIXTH CRANIAL NERVES

The control of eye movement can be divided into:
1 The central upper motor neurone mechanisms, which drive the normal yoked parallel movements of the eyes (conjugate gaze)
2 The oculomotor, abducens and trochlear nerves and the muscles they supply

Conjugate gaze

Fast voluntary and reflex eye movements originate in each. frontal lobe. Fibres pass in the anterior limb of the internal capsule and cross in the pons to end in the centre for lateral gaze (paramedian pontine reticular formation (PPRF)) (Fig. 18.6a), which is close to each sixth nerve nucleus. It also receives fibres from:
THE IPSILATERAL OCCIPITAL CORTEX. These pathways are concerned with movements to track or pursueobjects within the visual fields.
BOTH VESTIBULAR NUCLEI. These pathways are concerned with the relationship between eye movements and the position of the head and neck.
Lateral eye movements are coordinated from the centre of lateral gaze through the medial longitudinal fasciculus (MLF) (Fig. 18.6b). Fibres from the centre pass to both the ipsilateral sixth nerve nucleus and, having crossed the midline, the opposite third nerve nucleus via the MLF. Each sixth nerve nucleus (supplying the lateral rectus) and the opposite third nerve nucleus (supplying the medial rectus and others) are thus linked. The eyes move with parallel axes and at the same velocity.

Abnormalities of conjugate lateral gaze

A destructive lesion of one side of the brain allows the eyes to be driven laterally by the intact opposite pathway. A destructive frontal-lobe lesion (e.g. an infarct) causes failure of conjugate lateral gaze to the side opposite to the lesion. In an acute lesion the eyes are often deviated past the midline to the side of the lesion and therefore look towards the normal limbs. There is usually a contralateral hemiparesis.
An irritative frontal-lobe lesion (e.g. an epileptic focus), by stimulating the opposite lateral gaze centre, drives the eyes away from the side of the lesion. A unilateral destructive brain stem lesion involving the centre causes failure of horizontal conjugate gaze towards  the side of the lesion. There is usually a hemiparesis and the eyes are deviated towards the paralysed limbs.

Doll’s head reflexes and skew deviation

These are of diagnostic value in coma. Internuclear ophthalmoplegia Internuclear ophthalmoplegia (INO) is one of the commoner complex brain stem signs that involve the oculomotor system. It is due to a lesion within the MLF. It is a common sign in MS. When present bilaterally it is almost pathognomonic of MS. Unilateral lesions are also caused by small brain stem infarcts. In a right INO there is a lesion of the right MLF. On attempted left lateral gaze the right eye fails to adduct. The left eye develops coarse nystagmus in abduction.

The side of the lesion is on the side of impaired adduction, not on the side of the nystagmus.

Abnormalities of vertical gaze

A failure of up-gaze is caused by an upper brain stem lesion, such as a supratentorial mass pressing from above, or a tumour of the brain stem (e.g. a pinealoma). When the pupillary convergence reflex fails, this combination is called Parinaud’s syndrome. Defective up-gaze also occurs in certain degenerative disorders (e.g. progressive supranuclear palsy). Impairment of up-gaze also occurs as part of normal ageing.

Weakness of the extraocular muscles (diplopia)

Diplopia (double vision) implies that there is weakness of one or more of the extraocular muscles. The cause is usually a lesion of the third, fourth or sixth cranial nerves (or a combination of these) or their nuclei, or disease of the neuromuscular junction (myasthenia gravis) or the ocular muscles.

Squint (strabismus)

This is the appearance of the eyes when the visual axes fail to meet at the fixation point.
PARALYTIC SQUINT. Paralytic or ‘incornitant’ squint occurs when there is an acquired defect of the movement of an eye. There is a squint (and hence diplopia) maximal in the direction of action of the weak muscle.

NON-PARALYTIC SQUINT. Non-paralytic or ‘concomitant’ squint describes a squint beginning in childhood in which the angle between the visual axes does not vary when the eyes are moved, i.e. the squint remains the same in all directions of gaze. Diplopia is almost never a symptom. The deviating eye (the one that does not fixate) usually has defective vision; this is called ‘amblyopia ex anopsia’.
Non-paralytic squint may be latent, i.e. only visible at certain times, such as when the patient is tired. The cover test is used to assess squint and to recognize latent squint. The patient is asked to fix on an object. The eye that is apparently fixing the object centrally is covered. If the uncovered eye makes any movement to take up fixation, then a squint must have been present. The test is repeated with the opposite eye-the fixing eye will not move when the other, squinting, eye is covered or uncovered.

The oculomotor nerve (third cranial nerve)

The nucleus of the third nerve lies ventral to the aqueduct in the midbrain. Efferent fibres to four external ocular muscles (the superior, inferior and medial recti, and the inferior oblique), the levator palpebrae superioris and the sphincter pupillae (parasympathetic) enter the orbit through the superior orbital fissure.
The common causes of an oculomotor nerve lesion are given. Signs of such a lesion are:
• Unilateral complete ptosis
• The eye facing ‘down and out’
• Fixed and dilated pupil
‘Sparing of the pupil’ means that the parasympathetic fibres which run in a discrete bundle on the superior surface of the nerve are undamaged by the lesion and the pupil reacts normally.
In diabetes, infarction of the nerve usually spares the pupil. In a third nerve palsy the eye can still abduct (sixth nerve) and ‘intort’ (fourth nerve). When a patient with a right third nerve lesion attempts to converge and look downwards, the conjunctival vessels of the right eye can be seen to twist clockwise; this is ‘intortion’ and indicates that the trochlear nerve is intact.

Aneurysm of the posterior communicating artery ‘Coning’ of the temporal lobe.
Infarction of the nerve
In diabetes mellitus
Atheroma
Midbrain infarction
Midbrain tumour

The trochlear nerve (fourth cranial nerve)

The trochlear nerve supplies the superior oblique muscle. An isolated fourth nerve lesion is a rarity. The head is tilted away from the side of the lesion. The patient complains of diplopia when attempting to look down and away from the affected side. The abducens nerve (sixth cranial nerve).
The abducens nerve supplies the lateral rectus muscle. In a sixth nerve lesion there is a convergent squint with diplopia maximal on looking to the side of the lesion. The eye cannot be abducted beyond the midline. There are many causes of a sixth nerve lesion. The nerve may be involved in the brain stem, e.g. MS. In raised intracranial pressure it is compressed against the tip of the petrous temporal bone. The nerve sheath may be infiltrated by tumours, particularly nasopharyngeal carcinoma. An isolated sixth nerve palsy due to infarction may occur in diabetes mellitus. A sixth nerve lesion is a common sequel of head injury.

THE OLFACTORY NERVE (FIRST CRANIAL NERVE)

This sensory nerve arises from olfactory (smell) receptors in the nasal mucosa. Branches pierce the cribriform plate and synapse in the olfactory bulb. The olfactory tract then passes to the olfactory cortex in the anteromedial surface of the temporal lobe.
Loss of the sense of smell (anosmia) occurs with head injury andtumours of the olfactory groove (e.g. meningioma, frontal glioma).
The sense of smell is often lost, sometimes permanently, after upper respiratory viral infections. It is diminished in nasal obstruction.

THE OPTIC NERVE (SECOND CRANIAL NERVE) AND THE VISUAL SYSTEM

The optic nerve carries axons from the ganglion cells of the retina to the lateral geniculate bodies. The visual pathway is shown in Fig. 18.4. It should be noted that the lens causes the image on the retina to be inverted. Thus, an object in the lower part of the visual field is projected to the upper retina and an object in the temporal half of the visual field is projected to the nasal half of the retina. At the optic chiasm, fibres travelling in the nasal portions of the optic nerves cross to the opposite sides, where they join uncrossed temporal fibres from the lateral portion of each optic nerve. One optic tract thus carries fibres from the temporal side of the ipsilateral retina and the nasal side of the contralateral retina.
From the lateral geniculate body, fibres pass in the optic radiation to the visual cortex of the occipital lobe. The visual field projected to each optic tract, radiation and cortex is called ‘homonymous’, to indicate the different (i.e. bilateral) origins of each pathway. (A homonym is the same word used to denote different things.) Field defects are ‘hemianopic’ when half the field is affected, and ‘quadrantanopic’ when a quadrant is affected. ‘Congruous’ denotes symmetry and ‘incongruous’ lack of symmetry.

Visual acuity

This should be tested with a Snellen test chart and corrected for refractive errors with lenses or a pinhole. The corrected visual acuity should be recorded. The normal acuity should be 6/6 to 6/9 in both eyes. Blindness can be due to:
• Ocular causes, e.g. glaucoma, macular degeneration or diabetes
• Central (neurological) causes, e.g. optic nerve lesions, chiasmal compression

Visual field defects

These should be charted by confrontation with white and red headed pins and, if abnormal or in doubt, recorded in detail with a Goldmann (or similar) screen. The common defects.

Retinal and local eye lesions

Lesions of the retina produce either scotomata (small areas of visual loss) or peripheral visual loss (tunnel vision). Common causes are diabetic retinal vascular disease, glaucoma and retinitis pigmentosa.
Local lesions of the eye (e.g. cataract) can also cause visual loss.

Optic nerve lesions

Unilateral visual loss, commencing as a central or paracentral scotoma, is characteristic of optic nerve lesions. Complete lesions of the optic nerve produce total unilateral visual loss with loss of pupillary light reflex (direct and consensual) when the blind eye is illuminated. The causes of optic nerve lesions. The principal pathological appearances of the visible part of the nerve (the disc) seen on fundoscopy are:
• Disc swelling (papilloedema)
• Pallor (optic atrophy)
PAPILLOEDEMA (TABLE 18.10). This means swelling of the papilla-the optic disc. The earliest ophthalmoscopic signs are redness of the disc followed by blurring and heaping up of its margins (the nasal margin first). There is loss of the normal, visible, spontaneous pulsation of the retinal veins. The physiological cup becomes obliterated and the disc engorged, with dilatation of its vessels and the retinal veins. Small haemorrhages surround the disc.
True disc oedema should be distinguished from various conditions that simulate it. Marked hypermetropic (longsighted) refractive errors make the disc appear pink, distant and ill-defined. Opaque (myelinated) nerve fibres near the disc and hyaline bodies (drusen) can be mistaken for disc swelling.
In difficult cases fluorescein angiography is diagnostic . In papilloedema, fluorescein injected intravenously leaks from the disc capillaries and may be seen and photographed. Early papilloedema from causes other than optic neuritis (see below) often produces few visual symptoms, the  patient’s complaints being those of the underlying disease.
As disc oedema develops there is enlargement of the blind spot and blurring of the vision. As the disc becomes engorged its arterial blood flow is reduced and, in severe papilloedema, infarction of the nerve occurs, often suddenly, with resulting blindness.
OPT IC NEURITI s. Optic neuritis is swelling of the optic disc due to inflammation of the optic nerve. The commonest cause is demyelination (e.g. multiple sclerosis). Disc swelling due to optic neuritis is distinguished from other causes of disc oedema by the occurrence of early  and severe visual loss.
The term retrobulbar neuritis implies that the inflammatory process is ‘behind the bulb’ (i.e. the eye), so that no abnormality may be seen with the ophthalmoscope in spite of visual impairment. OPTIC ATROPHY. Disc pallor (optic atrophy) may fol- Iowa variety of pathological processes, including infarction of the nerve, demyelinating optic neuritis (in MS), optic nerve compression, syphilis, vitamin BI2 deficiency and toxins (e.g. quinine and methyl alcohol). Optic atrophy is described as consecutive or secondary when it follows papilloedema. The degree of visual loss depends upon the underlying pathology.

Lesions of the optic chiasm

Bi-temporal hemianopic field defects occur when a lesion compresses the central part of the chiasm. Common causes are:
• Pituitary neoplasm
• Craniopharyngioma
• Secondary neoplasm

Lesions of the optic tract and optic radiation. Homonymous hemianopia or quadrantanopia are the typical field defects caused by unilateral compression or infarction of these structures. Optic tract lesions are rare. Temporal lobe lesions (due to tumour or infarction) cause upper quadrantanopic defects; parietal lobe lesions cause lower quadrantanopic defects. Lesions of the occipital cortex. Homonymous hemianopic defects are caused by unilateral posterior cerebral artery infarction. The macular region (at the occipital pole) is spared because it has a separate blood supply from the middle cerebral artery. Damage to one occipital pole causes a small, congruous, scotomatous, homonymous hemianopia (site 8). Widespread bilateral occipital lobe damage by tumour, trauma or infarction causes the syndrome of ‘cortical blindness’ (Anton’s syndrome). The patient is blind but characteristically lacks insight into the degree of visual loss and may deny it. The pupillary responses are normal .

Optic and retrobulbar neuritis

Optic nerve compression (e.g. tumour or aneurysm) Toxic optic neuropathy (e.g. tobacco, ethambutol, methyl alcohol, quinine)

Syphilis

Ischaemic optic neuropathy (e.g. in giant-cell arteritis) Hereditary optic neuropathies.

Severe anaemia

Vitamin B’2 deficiency
Trauma
tnfective=spread of paranasal sinus infection or orbital cellulitis
Causes of papilloedema

Intracranial mass lesions

Brain oedema, e.g. encephalitis, trauma Subarachnoid haemorrhage
Benign intracranial hypertension Metabolic causes, e.g. CO2 retention, chronic anoxia, hypocalcaemia.

Accelerated hypertension
Optic neuritis
Disc infiltration, e.g. leukaemia
Ischaemic optic neuropathy
Retinal venous obstruction (thrombosis, orbital lesions

CEREBRAL LOCALIZATION

This subject causes everyone considerable difficulty. The following paragraphs summarize the areas of principal clinical importance in general medicine .

The dominant hemisphere

The concept of cerebral dominance arose with the observation that right-handed stroke (and other) patients with acquired language disorders had destructive lesions within the left hemisphere. Almost all right-handed people have language function in the left hemisphere; so do over 70% of those who are apparently left-handed. Destructive lesions within the left frontotemporoparietal region cause disorders of:
SPOKEN LANGUAGE-knOwn as aphasia or dysphasia WRITING-knOwn as agraphia
READING-knOwn as alexia (or acquired dyslexia) Developmental dyslexia describes children who have delayed and disorganized reading and writing ability with normal intelligence.

The non-dominant hemisphere

Disorders in right-handed patients with right hemisphere lesions are more difficult to define but comprise abnormalities of perception of internal and external space. Examples of this are losing the way in familiar surroundings, failing to put on clothing correctly (‘dressing apraxia’) or failure to draw simple shapes (‘constructional apraxia’).

APHASIA AND DYSARTHRIA

Aphasia (or dysphasia) is a loss or defect in language and is caused by left frontotemporoparietal lesions. Dysarthria is simply disordered articulation. Any lesion that produces paralysis, slowing or incoordination of the muscles of articulation or local discomfort will cause dysarthria. Examples are upper and lower motor lesions of the lower cranial nerves, cerebellar lesions, Parkinson’s disease and local lesions of the mouth, larynx, pharynx and tongue. Many aphasic patients are also somewhat dysarthric.

Some varieties of aphasia

Broca’s aphasia (expressive aphasia, anterior aphasia). A lesion in the left frontal lobe causes reduced fluency of speech with comprehension relatively preserved. The patient makes great efforts to initiate speech. Language is reduced to a few disjointed words and there is failure to construct sentences.
Patients who recover from this form of aphasia say that they knew what they wanted to say. but ‘could not get he words out’.
Wernicke’s aphasia (receptive aphasia, posterior aphasia) A left temporoparietal lesion leaves language that is fluent but the words themselves are incorrect. This varies from the insertion of a few incorrect or non-existent words into fluent speech (when it may be difficult to recognize aphasia) to a profuse outpouring of jargon, i.e. rubbish with wholly non-existent words. This may be so bizarre as to be confused with psychotic behaviour. Patients who have recovered from Wernicke’s aphasia say that when aphasic they found the speech of others like a wholly unintelligible foreign language, and though they knew they were speaking could neither stop themselves nor understand what they said.

Nominal aphasia (anomie aphasia or amnestic aphasia)

This describes difficulty naming familiar objects. When it occurs in a severe and isolated form it is caused by a left posterior temporal/inferior parietal lesion. Naming difficulty is, however, an early sign in all types of aphasia. Global aphasia (central aphasia) This is the expressive disturbance characteristic of Broca’s aphasia and the loss of comprehension of Wernicke’s. It is due to widespread damage to the areas concerned with speech and is the commonest form of aphasia after a severe left hemisphere infarct. Writing and reading are also affected.

CLINICAL FEATURES OF LOCAL

CEREBRAL LESIONS

Focal lesions of the cerebral cortex cause symptoms and signs by three processes:
1 Destruction or suppression of function of cortical neurones and surrounding structures.
2 Synchronous discharge of neurones by irritative lesions which cause partial (focal) seizures that may become generalized seizures.
3 Displacement of the intracranial contents and surrounding cerebral oedema.

MEMORY AND ITS DISORDERS

Disorders of memory follow damage to the medial surface of the temporal lobe and its brain stem connections, including the hippocampi, fornices and mammillary bodies. Bilateral lesions are usually necessary to cause amnesia.

Effects of an irritative lesion of the cortex.

It is characteristic of all organic disorders of memory that more recent events are recalled poorly in contrast to the relative preservation of distant memories. Memory loss is a part of dementia of any cause and occurs in a wide variety of clinical situations.

Alcohol (Wernicke-Korsakoff syndrome)

Head injury (severe)
Anoxia
Posterior cerebral artery occlusion (bilateral)
Herpes simplex encephalitis
Chronic sedative and solvent abuse
Bilateral invasive tumours
Arsenic poisoning
Following hypoglycaemia

The functional unit of the nervous system is the neurone, with its cell body and axon, which terminates at a synapse. The specificity, size and type of each group of neurones varies greatly. For example, an ex motor neurone of the anterior horn cell of the lumbar spinal cord has an axonal length of over 1 m and innervates several hundred to 2000 muscle fibres-to form the motor unit. By contrast, a spinal or intracerebral internuncial neurone may have an axon under 100 /-Lm in length and terminate solely on one or other neuronal cell body. It is now generally agreed that transmission at most if not all synapses is mediated by chemical neurotransmitters.
These transmitters are released by action potentials passing down the axon. They then react with the receptors on the postsynaptic cell body, increasing its ionic permeability and propagating a further action potential within it.
This combination of electrical activity in the axon and chemical release at the synapse is the basis of all neurological function.
Important neurotransmitter substances are:
• Acetylcholine
• Noradrenaline
• Adrenaline
• 5-Hydroxytryptamine
• y-Aminobutyric acid (GABA)
• Opioid pep tides
• Prostaglandins
• Histamine
• Dopamine
• Glutamate
The exact role of these neurotransmitters in pathogenesis is being evaluated, but it is now thought that a wide variety of acute and chronic neurological disease may be mediated, at least in part, by a final common pathway of neuronal injury involving excessive stimulation of glutamate receptors. Effective glutamate antagonists are being used in clinical trials.

The history and examination remain most valuable ‘tests’ in neurology, but computed tomography (CT), magnetic resonance imaging (MRI), and other non-invasive tests have revolutionized the management of patients.

look at the patient:
General demeanour
Speech
Gait
Arm swinging
Examine head:
Fundi
Pupils
Eye movements
Facial movements
Tongue
Examine upper limbs:
Posture of outstretched arms
Wasting, fasciculation
Power, tone
Coordination
Reflexes
Examine lower limbs:
Power (hip flexion, ankle dorsiflexion), tone
Reflexes
Plantar responses
Assess sensation:
Ask the patient

PRELIMINARY INVESTIGATION
Examples of helpful routine investigations.

SPECIALIZED TESTS
Skull X-rays

Plain X-rays should not be done unnecessarily. Examples of diagnostically important changes are:

FRACTURES AND LESIONS OF THE VAULT OR BASE OF SKULL (e.g. metastases)
ENLARGEMENT OR DESTRUCTION OF THE SELLA TURCICA (e.g. intrasellar tumour, raised intracranial pressure)
INTRACRANIAL CALCIFICATION (e.g. tuberculoma, oligodendroglioma, wall of an aneurysm, cysticercosis) PINEAL CALCIFICATION (to show midline shift)

Spinal X-rays

These show fractures and degenerative, destructive and congenital bone lesions.

Computed tomography

Method

This technique uses a collimated X-ray beam moving synchronously with detectors across a slice of brain between 2 mm and l3 mm thick. The transmitted Xirradiation from an element, or pixel of that slice « 1 mm”) is processed by computer and a numerical value (the Hounsfield number) is assigned to its density (air = -1000 units; water = 0; bone = +1000 units). The difference in X-ray attenuation between bone, brain and CSF makes it possible to distinguish normal and infarcted tissue, tumour, extravasated blood and oedema. Examples of normal CT scans.
The image can be enhanced with intravenous contrast media to show areas of increased blood supply and oedema more clearly. Additional information about the subarachnoid space and the cerebral ventricles is obtained by  scanning after the intrathecal injection of water-soluble contrast media (e.g. metrizamide) or air. In general, lesions greater than 1 ern in diameter can be visualized on CT scans.
The method is safe (apart from occasional systemic reactions to contrast); the irradiation involved is small.

Uses

CT scanning is used for the diagnosis of:
• Cerebral tumours
• Intracerebral haemorrhage and infarction
• Subdural and extradural haematoma
• Subarachnoid haemorrhage
• Lateral shift of midline structures and displacement of the ventricular system
• Cerebral atrophy
• Pituitary lesions
• Spinal lesions (with CT myelography)
The CT scan can also be used to show that a brain is anatomically normal with a high degree of accuracy. Limitations
LESIONS UNDER 1 CM IN DIAMETER may be missed. LESIONS WITH ATTENUATION CLOSE TO THAT OF BONE may be missed if they are near the skull.
LESIONS WITH ATTENUATION SIMILAR TO THAT OF BRAIN may be difficult to diagnose (e.g. ‘isodense’ subdural haematoma).
THE RESULTS ARE POOR WHEN THE PATIENT CANNOT COOPERATE-a general anaesthetic may occasionally be necessary.
Magnetic resonance imaging
This technique makes use of the properties of protons aligned in a strong magnetic field. The protons are bombarded with radio frequency waves at right angles to generate images. The equipment is expensive and still restricted to specialized units. MRI scanning can distinguish between white matter and grey matter (Fig. 18.2) in the brain. Brain tumours, syringomyelia, the lesions of multiple sclerosis (MS) and lesions in the posterior fossa and at the foramen magnum are demonstrated well. In the spinal cord the technique can visualize tumours, cord compression and vascular malformations and is replacing myelography. Cerebral angiography and digital

imaging

This demonstrates the cerebral arterial and venous systems. Contrast is injected intra-arterially or intravenously. Carotid and vertebral arteriography is used for the demonstration of aneurysms, arteriovenous malformations and venous occlusion. Films of the aortic arch and the carotid and vertebral arteries demonstrate occlusion, stenoses and atheromatous plaques. Spinal angiography is used to investigate arteriovenous malformations of the cord.
Conventional arteriography is invasive and requires a general anaesthetic; it should rarely be performed outside a specialist centre. It carries a mortality of around 1%  and a 1% risk of stroke.
Digital subtraction angiography (DSA), using a computerized subtraction technique is superseding traditional angiography. Contrast is injected intravenously or intraarterially.

No anaesthetic is necessary.

Myelography

A water-soluble radiopaque dye is injected into the lumbar (or rarely cervical) subarachnoid space and viewed by conventional X-rays or CT. This is used in the diagnosis of tumours of the spinal cord and other causes of cord compression.
Radiculography is an examination confined to the lumbar region to show the anatomy of nerve roots. Isotope brain and bone scanning A radioisotope, usually [99ffiTc]pertechnate is injected intravenously to detect:
• Vascular tumours
• Arteriovenous malformations
• Cerebral infarcts
• Subdural haematoma
Isotope brain scanning is safe, non-invasive and cheap but has largely been overtaken by CT scanning because of the high incidence of false-negative isotope scans. Isotope bone scanning is useful for detecting vertebral lesions (e.g. metastases).

Electroencephalography

The electroencephalogram (EEG) is recorded from scalp electrodes on 16 channels simultaneously for 10-30 min The main value of the EEG is in the diagnosis of epilepsy and diffuse brain diseases.
Epilepsy Spikes, or spike and wave abnormalities occur, but it should be emphasized that patients with epilepsy may have a normal EEG between fits.

Diffuse brain disorders

Slow-wave EEG abnormalities are seen in encephalitis, dementia and metabolic states (e.g. hypoglycaemia and hepatic coma).

Brain deat

The EEG is isoelectric (i.e. flat). An EEG is no longer necessary to confirm the diagnosis of brain death in the UK.
Fig. 18.2 Multiple areas of high signal on T2 weighted images in the peri-ventricular white matter in a patient with multiple sclerosis.
Electromyography and nerve conduction studies.

Electromyography

A concentric needle electrode is inserted into voluntarymuscle. The amplified recording is viewed on an oscilloscope  and heard through a speaker. The following can0 be demonstrated:
• Normal interference pattern
• Denervation and reinnervation
• Myopathic, myotonic or myasthenic changes

Peripheral nerve conduction

Four measurements are of principal value in the diagnosis of neuropathies and nerve entrapment:
1 Mean conduction velocity (motor and sensory)
2 Distal motor latency
3 Sensory action potentials
4 Muscle action potentials

Cerebral-evoked potentials

Visual-evoked potentials record the time taken for the response to a retinal stimulus to travel to the occipital cortex. Their value is chiefly in documenting previous retrobulbar neuritis, which causes a permanent delay in the latency despite clinical recovery of vision.

Similar techniques exist for the measurement of auditory and somatosensory potentials (from an arm or leg). Lumbar puncture Examination of the CSF The indications for lumbar puncture are: DIAGNOSIS OF MENINGITIS AND ENCEPHALITIS DIAGNOSIS OF MS AND NEUROSYPHILIS INTRATHECAL INJECTION OF CONTRAST MEDIA AND DRUGS
DIAGNOSIS OF SUSPECTED SUBARACHNOID HAEMORRHAGE
MEASUREMENT OF CSF PRESSURE (e.g. in benign intracranial hypertension
REMOVAL OF CSF THERAPEUTICALLY (e.g. in benign intracranial hypertension)
DIAGNOSIS OF MISCELLANEOUS CONDITIONS (e.g. certain polyneuropathies, sarcoidosis, intrathecal neoplastic involvement)

Biopsy

Muscle

Biopsy is useful in the diagnosis of inflammatory and dystrophic disorders of muscle.

Peripheral nerve

Biopsy, usually of the sural nerve, is carried out to aid diagnosis in certain polyneuropathies, e.g. due to vasculitides.

Brain

Brain biopsy (e.g. of a non-dominant frontal lobe) is undertaken to diagnose inflammatory and degenerative brain diseases. CT -guided stereotactic biopsy of intracranial mass lesions is being used increasingly. It is less traumatic and more accurate than conventional biopsy through a skull burr hole or craniotomy.
Psychometric assessment Formal psychometric testing is used to assess intellectual function. Preservation of the verbal IQ (a measure of past attainments) in the presence of deterioration of the performance IQ (a measure of present abilities) is a useful indicator of dementia. Low subtest scores (e.g. for block design, speech or constructional skills) indicate impaired function of specific regions of the brain. The main limitation of these techniques is that depression and lack of concentration can also impair scores.

Miscellaneous tests

Certain specialized tests are employed in the diagnosis of individual (and often rare) neurological diseases. Examples are:
SERUM ENZYMES LIBERATED FROM MuscLE-greatly raised in many primary muscle diseases.
Creatine phosphokinase is the enzyme usually assayed in most laboratories.
SERUM COPPER AND CAERULOPLASMIN in Wilson’s disease .
ANTIBODIES TO ACETYLCHOLINE RECEPTOR PROTEIN in myasthenia gravis.

Lumbar puncture should not be performed in the presence of raised intracranial pressure or when an intracranial mass lesion is a possibility.

Technique

The patient is placed on the edge of the bed in the left lateral position with the knees and chin as close together as possible
The third and fourth lumbar spines are marked. The fourth lumbar spine usually lies on a line joining the iliac crests Using sterile precautions, 2% lignocaine is injected into the dermis by raising a bleb in either the third or fourth lumbar interspace
The special lumbar puncture needle is pushed through the skin in the midline. It is pressed steadily forwards and slightly towards the head When the needle is felt to penetrate the dura mater, the stylet is withdrawn and a few drops of (SF are allowed to escape The (SF pressure can now be measured by connecting a manometer to the needle. The patient’S head must be on the same level as the sacrum. Normal (SF pressure is 60-150 mmH20. It rises and falls with respiration and the heart beat Specimens of (SF are collected in three sterilized test tubes and sent to the laboratory. An additional sample in which the sugar level can be measured, together with a simultaneous blood sample for blood sugar measurement, should be taken when relevant (e.g. in meningitis). Patients are usually asked to lie flat after the procedure to avoid a headache that may develop but this is probably of little value.

Analgesics may be required

Contraindications for lumbar puncture

Suspicion of a mass lesion in the brain or spinal cord. Caudal herniation of the cerebellar tonsils (‘coning’) may occur if an intracranial massis present and the pressure below is reduced by removal of (SF. This is extremely dangerous.

Any cause of raised intracranial pressure

Local infection near the site of puncture

Congenital lesions in the lumbosacral region (e.g. meningomyelocele). Platelet count below 40 x 10’/litre and other clotting abnormalities, including anticoagulant drugs Unconscious patients and those with papilloedema must have a (T scan before lumbar puncture These contraindications are relative, i.e. there are circumstances when lumbar puncture is carried out in spite of them.
The composition of the normal.

 

The following headings summarize the essential elements of the clinical examination:
1 State of consciousness, arousal
2 Appearance, attitude, insight
3 Mental state
4 Orientation in time and place
5 Recall of recent and distant events/memory
6 Level of intellect
7 Language and speech/cerebral dominance
8 Disorders of higher function (e.g. apraxia)
9 Gait
10 Romberg’s test
11 The skull-shape, circumference, bruits
12 The neck-stiffness, palpation and auscultation of carotid arteries
l3 The cranial nerves-see individual nerves
14 The motor system
(a) Upper limbs:
(i) Wasting and fasciculation
(ii) Posture of the outstretched arms-drift, rebound, tremor
(iii) Tone-if increased, is it spasticity or ‘extrapyramidal’ rigidity?
(iv) Power-weakness may be graded roughly into ‘slight’, ‘moderate’ or ‘severe’ or numerically (0-5)
(v) Tendon reflexes: + or ++, normal; +++, increased; 0, absent even with reinforcement
(b) Thorax and abdomen:
(i) Respiration
(ii) Abdominal reflexes and muscles
(c) The lower limbs:
(i) Wasting and fasciculation
(ii) Tone, power and tendon reflexes
(iii) Plantar responses
15 Coordination and fine movements
16 The sensory system. First, the patient is asked whether or not the feeling in the limbs, face and trunk is entirely normal .
(a) Posterior columns:
(i) Light touch
(ii) Vibration (using a 128 Hz tuning fork)
(iii) Joint position
(iv) Two-point discrimination (normal: 0.5 cm on fingertips, 2 cm on soles)
(b) Spinothalamic tracts:
(i) Pain (pin prick) – using a split orangestick
(ii) Temperature
Chart areas of abnormal sensation Short neurological examination A detailed neurological examination is time-consuming and is not necessary in all patients, particularly those without symptoms suggestive of neurological disease. A short examination will detect the majority of defects.

There are two essential questions in any neurological diagnosis:
1 What is/are the site(s) of the lesion(s)?
2 What is the likely pathology?
Most of the diagnoses in neurology are made on a detailed history alone. The method of recording the details is beyond the scope of this chapter, but an important point is that the history should read chronologically and portray the story of the disease. A summary should conclude the history.

HEADACHE

Headache at some time is an almost universal experience. It varies from an infrequent and trivial nuisance to a symptom of serious disease.

Mechanism of headache

Pain receptors are found in the vessels at the base of the brain (both arterial and venous) and in the meninges . These receptors are also present in extracranial vessels, the muscles of the scalp, neck and face, the paranasal sinuses, the eyes and the teeth. The brain substance itself is almost devoid of pain receptors.
The pain of headache is mediated by mechanical and chemical (e.g. 5-hydroxytryptamine, histamine) stimulation of receptors: nerve impulses are carried centrally via the fifth and ninth cranial nerves and via the upper cervical sensory roots.

Pressure headaches

Intracranial mass lesions displace the meninges and the basal vessels. When these structures are physically moved by changes in cerebrospinal fluid (CSF) pressure (e.g. coughing), pain is exacerbated. Cerebral oedema, which accumulates around mass lesions, causes further shift. Headache is typically worse after lying down for some hours (as cerebral oedema increases). Any headache, however mild, that is present on waking and which is made worse by coughing, straining or sneezing may well be due to displacement or dilatation of the intracranial vessels and may be due to a mass lesion. These are often called ‘the headaches of raised intracranial pressure’. Vomiting often accompanies them.

Headache of subacute onset

The onset and progression of a headache over days or weeks with or without the features of ‘pressure headaches’ should always raise the suspicion of an intracranial mass lesion or serious intracranial disease. Encephalitis and viral meningitis should be considered. Giant-cell arteritis causes headache, with scalp tenderness, particularly over the age of 60 years.

The single episode of severe headache

This common emergency is caused principally by:
• Subarachnoid haemorrhage
• Migraine and, occasionally,
• Meningitis
Particular attention should be paid to the suddenness of onset (suggestive of a subarachnoid haemorrhage), neck stiffness and vomiting (meningeal irritation) and rashes and fever (meningitis).

Recurrent headaches

Migraine and tension headache are the commonest causes of recurrent pain. Sinusitis, glaucoma and migrainous neuralgia should also be considered. Hangover headache is usually obvious! Malignant hypertension occasionally causes a patient to seek medical advice because of headache. Headaches are not caused by essential hypertension.
Intermittent hydrocephalus due to an intraventricular tumour is a rare cause of recurrent prostrating headache with weakness of the lower limbs. ‘Eyestrain’ from refractive error is an unusual cause of headache. Headache following head injury Subdural haematoma should be considered, whether or not the headaches are suggestive of a mass lesion. The vast majority of post-traumatic headaches , which last days, weeks or months are not, however, associated with any serious intracranial cause.

Chronic headaches

Almost all recurring headaches with a history going back for several years or more are due to muscle tension and/or migraine. Depression usually accompanies them.

DIZZINESS, VERTIGO AND BLACKOUTS

‘Dizziness’ is a word patients use for a wide variety ofcomplaints ranging from a vague feeling of unsteadiness  to severe, acute vertigo. It is also frequently used to describe the light-headedness that is felt in anxiety and ‘panic attacks’, during palpitations, and in syncope or chronic ill-health. Therefore, the site of this symptom must be determined, i.e. whether it is perceived in the limbs, the chest or the head.
Vertigo (an illusion of movement) is a more definite symptom. It is usually a sensation of rotation in which the patient feels that their surroundings are spinning or moving. Vertigo indicates disease of the labyrinth, vestibular pathways or their central connections.
Like dizziness, ‘blackouts’ is a vague, descriptive term implying either altered consciousness, visual disturbance or falling. Epilepsy, syncope, hypoglycaemia and other conditions must be considered (see p.916). However, commonly no sinister cause is found. A careful history, particularly from an eye-witness, is essential.

Spasticity
Parkinson’s disease
Cerebellar ataxia
Sensory loss (ioint position)
Distal weakness
Proximal weakness
Apraxia of gait

DIFFICULTY WALKING

This is a common presenting complaint in neurological disease; the main causes are given. Arthritis and muscle pain also alter the gait, making it stiff and slow. The recognition of an abnormal gait is important in diagnosis.

Spasticity

Spasticity with or without pyramidal weakness causes stiffness and jerkiness of gait, which is maintained on a narrow base. The toes catch level ground, causing wearing down and scuffing of the toes of the shoes. The pace shortens. Clonus may be noticed as involuntary extensor jerking of the legs. When the problem is predominantly unilateral and weakness is marked (in a hemiparesis), the weaker leg drags stiffly and is circumducted.

Parkinson’s disease

Here there is muscular rigidity in both the extensors and the flexors of the limbs. Power remains normal. The gait slows; the pace shortens to a shuffle. The base remains narrow. Falls occur. A stoop is apparent and swinging of the arms is diminished. The gait is ‘festinant’, i.e. hurried, as small rapid steps are taken. There is particular difficulty in initiating movement and in turning quickly. Sometimes when the patient stops or is halted, a few rapid, small and unsteady backward steps are taken; this is known as retropulsion.

Cerebellar ataxia

In disease of the lateral lobes of the cerebellum the stance becomes broad-based, unstable and tremulous. The gait tends to veer towards the side of the more affected cerebellar lobe.
In disease of the cerebellar vermis (a midline structure), the trunk becomes unsteady and there is a tendency to fall backwards (truncal ataxia).

Sensory ataxia

The ataxia of peripheral sensory lesions (e.g. polyneuropathy, is due to diminution of the sense of proprioception (joint position). The patient cannot perceive accurately the position of the legs. The gait becomes broad-based and high-stepping or ‘stamping’. The ataxia is made worse by removal of additional sensory input, e.g. in the dark or when the eyes are closed. This is the basis of a positive Romberg’s test, which was first described in the sensory ataxia of tabes dorsalis.

Weakness of the lower limbs

With distal weakness the affected leg is lifted overobstacles. When the dorsiflexors of the foot are weak,  such as in a common peroneal nerve palsy, the foot, having been lifted, returns to the ground with a visible and audible ‘slap’. Weakness of proximal lower limb muscles (e.g. polymyositis, muscular dystrophy) leads to difficulty in rising from the sitting position. Once upright, the patient walks with a waddling gait, the pelvis being ill-supported by each lower limb as it carries the full weight of the body.

Apraxia of gait

In frontal-lobe disease (e.g. tumours, hydrocephalus, infarction) the central organization of walking is disturbed. The patient is able to move the legs normally while sitting or lying but cannot walk in an organized way. This is known as ‘apraxia of gait’ -a failure of the skilled movement of walking. Urinary incontinence and a degree of dementia are often present.

Introduction

The wide range of neurological conditions seen in the UK is summarized in Table 18.1. The pattern of practice has changed much in the last 40 years with the disappearance of poliomyelitis, and (almost) of neurosyphilis, the treatment for Parkinson’s disease, the use of newer anticonvulsants and now, the emergence of AIDS. Despite clinical neurology being primarily concerned with the organic conditions, ‘neurological’ symptoms may be the presenting features of common psychological illness (e.g. depression or anxiety) which require sympathy, interpretation and therapy.

Neurology in developing countries

Low standards of nutrition, hygiene and education, with widespread economic hardship, contribute to different patterns of disease. Common neurological conditions of the Indian subcontinent, South East Asia and Africa include:
• Leprosy
• Tuberculosis (meningitis, tuberculoma)
• Meningococcal meningitis
• Tetanus
• Rabies
• Cerebral malaria
• Multiple vitamin deficiencies
• Cysticercosis
• Neurological complications of AIDS (Africa and South East Asia)
Of these, only tuberculosis and meningococcal infection are seen commonly in Europe. AIDS, however, is increasing.
Prevalence rates often differ widely from annual incidence rates; these will be mentioned under the individual diseases.