Neurological disease

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Chapter 22 Neurological disease

The impact of neurological disease

Neurology is a large and diverse subject which covers many conditions that require long-term coordinated care and have serious effects on the daily lives of patients and their families. Neurology includes conditions as diverse as cognitive disorders involving higher level mental functioning through to disorders of peripheral nerve and skeletal muscle. It is a specialty requiring good clinical skills and examination technique which cannot be replaced with investigations or imaging techniques alone (Table 22.1).

Table 22.1 UK incidence of common neurological conditions

Conditions Events per 100 000/year

Cerebrovascular events

210

Shingles (herpes zoster) and postherpetic neuralgia

150

Diabetic and other neuropathies

105

Epilepsy

46

Parkinson’s disease

19

Severe brain injury and subdural haematoma

13

All CNS tumours

9

Trigeminal neuralgia

8

Meningitis

7

Multiple sclerosis

7

Presenile dementia (below 65 years)

4

Myasthenia, all muscle and motor neurone disease

5

Common symptoms and signs

Pattern recognition in neurology – interpretation of history, symptoms and examination – is very reliable. Practical experience is vital. There are three critical questions in formulating a clinical diagnosis:

Difficulty walking and falls

Change in walking pattern is a common complaint (Box 22.1). Arthritis and muscle pain make walking painful and slow (antalgic gait). The pattern of gait is valuable diagnostically.

Spasticity and hemiparesis

Spasticity (p. 1082), more pronounced in extensor muscles, with or without weakness, causes stiff and jerky walking. Toes of shoes become scuffed, catching level ground. Pace shortens; a narrow base is maintained. Clonus – involuntary extensor rhythmic leg jerking – may occur.

In a hemiparesis when spasticity is unilateral and weakness marked, the stiff, weak leg is circumducted and drags.

Parkinson’s disease: shuffling gait

There is muscular rigidity (p. 1118) throughout extensors and flexors. Power is preserved; the pace shortens, and slows to a shuffle; its base remains narrow. A stoop and diminished arm swinging become apparent. Gait becomes festinant (hurried) with short rapid steps. There is difficulty turning quickly and initiating movement, sometimes with falls. Retropulsion means small backward steps, taken involuntarily when a patient is halted.

Cerebellar ataxia: broad-based gait

In lateral cerebellar lobe disease (p. 1083) stance becomes broad-based, unstable and tremulous. Ataxia describes this incoordination. When walking, the person tends to veer to the side of the affected cerebellar lobe.

In disease of midline structures (cerebellar vermis), the trunk becomes unsteady without limb ataxia, with a tendency to fall backwards or sideways – truncal ataxia.

Sensory ataxia: stamping gait

Peripheral sensory lesions (e.g. polyneuropathy, p. 1145) cause ataxia because of loss of proprioception (position sense). Broad-based, high-stepping, stamping gait develops. This form of ataxia is exacerbated by removal of sensory input (e.g. vision) and worse in the dark. Romberg’s test, first described in sensory ataxia of tabes dorsalis (p. 1129), becomes positive.

Examination and formulation

Following a short or detailed examination, relevant findings are summarized in a brief formulation – the basis for investigation, transfer of information and management (Practical Boxes 22.1, 22.2 and Table 22.2).

Table 22.2 Six grades of muscle power

Grade Definition

5

Normal power

4

Active movement against gravity and resistance

3

Active movement against gravity

2

Active movement with gravity eliminated

1

Flicker of contraction

0

No contraction

Functional neuroanatomy

Localization within the cerebral cortex

This subject causes unnecessary difficulty. Work on neuronal networks, functional imaging and plasticity questions the traditional views of highly specific localization of cortical function. The following paragraphs summarize areas of clinical relevance.

Aphasia

Aphasia is loss of or defective language from damage to the speech centres within the left hemisphere. Numerous varieties have been described.

Cranial nerves (Table 22.3)

I: Olfactory nerve

This sensory nerve arises from olfactory (smell) receptors within nasal mucosa. Branches pierce the cribriform plate and synapse in the olfactory bulb. The olfactory tract passes to the olfactory cortex.

Table 22.3 Cranial nerves

Number Name Main clinical action

I

Olfactory

Smell

II

Optic

Vision, fields, afferent light reflex

III

Oculomotor

Eyelid elevation, eye elevation, ADduction, depression in ABduction, efferent (pupil)

IV

Trochlear

Eye intorsion, depression in ADduction

V

Trigeminal

Facial (and corneal) sensation, mastication muscles

VI

Abducens

Eye ABduction

VII

Facial

Facial movement, taste fibres

VIII

Vestibular
Cochlear

Balance and hearing

 

Cochlear

 

IX

Glossopharyngeal

Sensation – soft palate, taste fibres

X

Vagus

Cough, palatal and vocal cord movements

XI

Accessory

Head turning, shoulder shrugging

XII

Hypoglossal

Tongue movement

Anosmia (loss of sense of smell) is caused by head injury (shearing of olfactory neurones as they pass through the cribriform plate at the skull base) or tumours of the olfactory groove (e.g. meningioma). Olfaction is temporarily (occasionally permanently) lost or diminished after upper respiratory infections and with local disorders of the nose. Many patients with gradual onset anosmia over many years may be unaware of the deficit, e.g. in Parkinson’s disease where anosmia precedes motor symptoms by many years but is often not noticed by the patient.

Detailed smell testing is difficult in routine clinical practice and rarely performed. Adequate testing requires use of commercially available kits such as scratch and sniff cards or odour filled pens with forced multiple choice identification.

II: Optic nerve and visual system (Fig. 22.4)

Light regulated by the pupillary aperture is converted into action potentials by retinal rod, cone and ganglion cells (see page 1055). The lens, under control of the ciliary muscle, produces the image (inverted) on the retina. Axons in the optic nerve (1) decussate at the optic chiasm (2), fibres from the nasal retina cross and join with uncrossed fibres originating in the temporal retina to form the optic tract (3). Each optic tract thus carries information from the contralateral visual hemifield.

From the lateral geniculate body, fibres pass in the optic radiation through the parietal and temporal lobes (4 and 5) to reach the visual cortex of the occipital lobe (6 and 7), which is somatotopically organized with macular vision located at the occipital pole (see Fig. 22.4).

Beyond the visual cortex visual information is further processed by neighbouring visual association areas to detect lines, orientation, shapes, movement, colour and depth; there is even a distinct area responsible for face recognition.

Visual field defects

Visual fields are assessed at the bedside by confrontation – comparing the examiner’s and patient’s fields, one eye at a time and quadrant by quadrant. Patience and good technique are required to get reliable results. White and red targets (traditionally hatpins) are used to assess peripheral and central fields respectively although in practice a fingertip is often substituted as a cruder screening test. More detailed quantification of fields may be obtained using Goldmann (manual) or Humphrey (automated) perimetry testing.

Field defects are described as hemianopic when half the field is affected and quadrantanopic when a quadrant is affected. Lesions posterior to the optic chiasm produce homonymous field defects, indicating involvement of the same part of the visual field in both eyes as information from the two visual hemifields is separated beyond this point. Lesions damaging decussating nasal fibres at the optic chiasm cause bitemporal defects.

Optic nerve lesions

Unilateral visual loss, commencing with a central or paracentral (off-centre) scotoma, is the hallmark of an optic nerve lesion. Because most fibres in the optic nerve subserve macular vision, lesions within the nerve disproportionately affect central vision and colour vision. A total optic nerve lesion causes unilateral blindness with loss of pupillary light reflex. Examination findings in optic neuropathy:

Causes are listed in Box 22.3.

Papilloedema

Papilloedema means swelling of the optic disc. Causes are shown in Box 22.4. The earliest signs of swelling are disc pinkness, with blurring and heaping up of disc margins, nasal first. There is loss of spontaneous pulsation of retinal veins within the disc. The physiological cup becomes obliterated, the disc engorged with dilated vessels. Small haemorrhages often surround the disc.

Various conditions simulate true disc swelling. Marked hypermetropic (long-sighted) refractive errors make a disc appear pink, distant and ill-defined. Myelinated nerve fibres at disc margins and hyaline bodies (drusen, p. 1064) can be mistaken for disc swelling.

Disc infiltration also causes a swollen disc with raised margins (e.g. in leukaemia).

When there is doubt about disc oedema, i.v. fluorescein angiography is diagnostic; retinal leakage is seen with papilloedema.

Papilloedema produces few if any visual symptoms other than momentary visual obscurations with changes in posture. The underlying disease is the source of the patient’s symptoms. The blind spot is enlarged but this is not noticed by the patient. However, over time progressive and permanent constriction of visual fields occurs, ultimately culminating in optic atrophy.

The pupils

A slight difference between the size of each pupil (up to 1 mm) is common (physiological anisocoria) and does not vary with differing light levels. The pupil tends to become smaller and irregular in old age (senile miosis); anisocoria is more pronounced. Convergence becomes sluggish with ageing.

Pupillary reactions to light and accommodation may be tested (Fig. 22.5). A bright torch (not an ophthalmoscope light!) should be used to test the pupillary light reaction.

Afferent pupillary defect. A complete optic nerve lesion causes a dilated pupil and an afferent pupillary defect (APD). For a left APD:

Relative afferent pupillary defect (RAPD). This occurs with incomplete damage to one optic nerve relative to the other. An RAPD is a sensitive sign of optic nerve pathology and can provide evidence of an optic nerve lesion even after recovery of vision. For a left RAPD:

III, IV, VI: Oculomotor, trochlear and abducens nerves

These cranial nerves supply the extraocular muscles and disorders commonly result in abnormal eye movements and diplopia (double vision) due to breakdown of conjugate (yoked) eye movements. Diplopia may also occur with local orbital lesions or myasthenia gravis.

Abnormalities of conjugate lateral gaze

A destructive lesion on one side allows the eyes to be driven by the intact opposite pathway. A left frontal destructive lesion (e.g. an infarct) leads to failure of conjugate lateral gaze to the right. In an acute lesion the eyes are often deviated to the side of the lesion, past the midline and therefore look towards the left (normal) limbs; there is usually a contralateral (i.e. right) hemiparesis.

In the brainstem a unilateral destructive lesion involving the PPRF leads to failure of conjugate lateral gaze towards that side. There is usually a contralateral hemiparesis and lateral gaze is deviated towards the side of the paralysed limbs.

Nystagmus

Nystagmus is rhythmic oscillation of eye movement, and a sign of disease of the retina, cerebellum and/or vestibular systems and their connections. Nystagmus is either jerk or pendular. Nystagmus must be sustained within binocular gaze to be of diagnostic value – a few beats at the extremes of gaze are normal.

V: Trigeminal nerve

The largest cranial nerve; mainly sensory with a motor component to the muscles of mastication.

Sensory fibres (Fig. 22.7; see also Figs 22.11 and 22.12) of the three divisions – ophthalmic (V1), maxillary (V2) and mandibular (V3) – pass to the trigeminal (Gasserian) ganglion at the apex of the petrous temporal bone. Ascending fibres transmitting light touch enter the Vth nucleus in the pons. Descending central fibres carrying pain and temperature form the spinal tract of V, to end in the spinal Vth nucleus that extends from the medulla into the cervical cord.

VII: Facial nerve

The VIIth nerve is largely motor, supplying muscles of facial expression. VII carries sensory taste fibres from the anterior two-thirds of the tongue via the chorda tympani and supplies motor fibres to the stapedius muscle. The VIIth nerve (Fig. 22.7) arises from its nucleus in the pons and leaves the skull through the stylomastoid foramen. Neurones in each VIIth nucleus supplying the upper face (principally frontalis) receive bilateral supranuclear innervation.

Unilateral facial weakness

Upper motor neurone (UMN lesions) cause weakness of the lower part of the face on the opposite side. Frontalis is spared: normal furrowing of the brow is preserved; eye closure and blinking are largely unaffected. The earliest sign is slowing of one side of the face, e.g. on baring teeth. There is sometimes relative preservation of spontaneous emotional movement (e.g. smiling) compared with voluntary movement.

Lower motor neurone (LMN) lesions. A complete unilateral LMN VIIth lesion causes weakness (ipsilateral) of all facial expression muscles. The angle of the mouth falls; unilateral dribbling develops. Frowning (frontalis) and eye closure are weak. Corneal exposure and ulceration occur if the eye does not close during sleep. Taste sensation is frequently also impaired.

Causes of facial weakness

The commonest cause of a UMN lesion is hemispheric stroke with hemiparesis on the opposite side. At lower levels, lesion sites are recognized by LMN weakness with additional signs.

Pons. Here the VIIth nerve loops around the VIth (abducens) nucleus (Fig. 22.7), leading to a lateral rectus palsy (see p. 1076) with unilateral LMN facial weakness. When the neighbouring PPRF and corticospinal tract are involved, there is the combination of:

Causes include pontine tumours (e.g. glioma), MS and infarction.

Cerebellopontine angle (CPA). The neighbouring Vth, VIth and VIIIth nerves are compressed with VII in the CPA, e.g. by acoustic neuroma, meningioma or metastasis.

Petrous temporal bone. The nerve may be damaged within the bony facial canal, within which lies the sensory geniculate ganglion (receiving taste fibres from the anterior two-thirds of the tongue via the chorda tympani). As well as LMN facial weakness, lesions in this region cause:

Causes include:

Skull base, parotid gland and within the face. The facial nerve can be compressed by skull base tumours and in Paget’s disease of bone. Branches of VII may be damaged by parotid gland tumours as the nerve traverses the parotid, sarcoidosis (p. 845) and trauma.

Bell’s palsy

This common (1 per 5000 incidence), acute facial palsy is thought to be due to viral infection (often herpes simplex) causing swelling of nerve within the tight petrous bone facial canal. There is unilateral LMN facial weakness developing over 24–48 hours, sometimes with lost or altered taste on the tongue, and hyperacusis. Pain behind the ear is common at onset. Patients often suspect a stroke and may be very distressed. Vague altered facial sensation is often reported although examination of facial sensation is normal.

Diagnosis is made on clinical grounds and tests are usually not required. The ear (and palate) should be examined for vesicles (see Ramsay Hunt syndrome below), hearing loss or evidence of local pathology such as cholesteatoma or malignant otitis externa and parotid tumours should be excluded. Involvement of other cranial nerves means facial weakness is not due to Bell’s palsy. Lyme disease may account for one-quarter of cases of facial palsy in endemic areas and HIV seroconversion is the commonest cause in parts of Africa.

(Bell’s phenomenon is the upward conjugate eye movement that occurs when the eyes are closed.)

Hemifacial spasm (HFS)

This is an irregular, painless unilateral spasm of facial muscles, usually occurring after middle age. It starts in the orbicularis oculi and usually progresses gradually over the years to involve other facial muscles on the same side. It varies from a mild to a severe, disfiguring spasm.

HFS is usually caused by compression of the root entry zone of the facial nerve, generally by vascular structures such as the vertebral or basilar arteries or their branches (a mechanism similar to that of trigeminal neuralgia see p. 1110). Other mass lesions in the cerebellopontine angle, including tumours, are the cause in approximately 1% of cases.

Occasionally HFS may occur with ipsilateral trigeminal neuralgia, one symptom usually preceding the other, a combination called tic convulsif. The paroxysms of pain and spasm occur independently. A compressive cause such as a vascular loop or other structural lesion is usually identified.

VIII: Vestibulo-cochlear nerve; cochlear nerve

Auditory fibres from the spiral organ of Corti within the cochlea pass to the cochlear nuclei in the pons. Fibres from these nuclei cross the midline and pass upwards via the medial lemnisci to the medial geniculate bodies and then to the temporal cortex.

Symptoms of a cochlear nerve lesion are deafness and tinnitus (p. 1050). Sensorineural and conductive deafness can be distinguished with tuning fork tests, e.g. Rinne’s and Weber’s (256 Hz, not 128 Hz tuning fork) (p. 1048).

Basic investigations of cochlear lesions

Causes of deafness are listed in Table 22.4 and Table 21.1 (see p. 1048).

Table 22.4 Some causes of vertigo and hearing loss

Conditions Symptom(s)

Benign paroxysmal positional vertigo

V

Vestibular neuritis

V

Ménière’s disease

V, D

Alcohol, antiepileptic drug intoxication

V

Cerebellar lesions

V

Partial (temporal lobe) seizures

V

Migraine

V+ phonophobia

Brainstem ischaemia

V, occasionally D

Multiple sclerosis

V, occasionally D

Mumps, intrauterine rubella and congenital syphilis (D)

D

Advancing age (presbyacusis) and otosclerosis (D)

D

Acoustic trauma (D)

D

Congenital, e.g. Pendred’s syndrome

D

Gentamicin, furosemide

V, D

Middle and external ear disease

V, D

Cerebellopontine angle lesions, e.g. acoustic neuroma

V, D

Carcinomatous meningitis, sarcoid and tuberculous meningitis

V, D

V, vertigo; D, hearing loss.

Vertigo and the vestibular system

The vestibular system of the inner ear detects head movements and has three primary functions:

Nerve impulses generated by movement of hair cells within the three semicircular canals detect head motion in the three planes (yaw/pitch/roll). Balance is maintained by integrating information from:

The main symptoms of vestibular lesions are vertigo and loss of balance.

Vestibular disorders

Vestibular disorders are fully discussed elsewhere (p. 1049). Attack duration and frequency and trigger factors help the clinician distinguish on history between different pathological causes. The ability to perform a Hallpike test, head impulse test and Epley particle repositioning manoeuvre are invaluable skills for all clinicians (p. 1049; see Fig. 22.8 and Fig. 21.3).

The most commonly encountered vestibular disorders presenting with vertigo are:

Lower cranial nerves IX, X, XI, XII

The glossopharyngeal (IX), vagus (X) and accessory (XI) nerves arise in the medulla and leave the skull through the jugular foramen. The hypoglossal (XII) arises in the medulla, to leave the skull base via the hypoglossal foramen. Outside the skull, the four cranial nerves lie together, close to the carotid artery and sympathetic trunk.

IXth and Xth nerve lesions

Principal causes of IXth, Xth, XIth and XIIth nerve lesions are listed in Box 22.7.

Isolated lesions of IXth and Xth nerves are unusual, since disease at the jugular foramen affects both nerves and sometimes XI.

A unilateral IXth nerve lesion causes diminished sensation on the same side of the pharynx, and is hard to recognize in isolation. A Xth nerve palsy produces ipsilateral failure of voluntary and reflex elevation of the soft palate (which is drawn to the opposite side) and ipsilateral vocal cords.

Bilateral lesions of IXth and Xth nerves cause palatal weakness, reduced palatal sensation, an absent gag reflex, dysphonia and choking with nasal regurgitation. Bulbar palsy is a general term describing palatal, pharyngeal and tongue weakness of LMN or muscle origin.

Recurrent laryngeal nerve lesions. Paralysis of this branch of each vagus causes hoarseness (dysphonia) and failure of the forceful, explosive part of coughing (‘bovine cough’). There is no visible palatal weakness; vocal cord paralysis is seen endoscopically. Bilateral acute lesions (e.g. postoperatively) cause respiratory obstruction – an emergency.

The left recurrent laryngeal nerve (looping beneath the aorta) is damaged more commonly than the right.

Causes of recurrent laryngeal nerve lesions include:

Corticospinal (pyramidal) system

The corticospinal tracts originate in neurones of the cortex and terminate at motor nuclei of cranial nerves and spinal cord anterior horn cells. The pathways of particular clinical significance (Fig. 22.9) congregate in the internal capsule and cross in the medulla (decussation of the pyramids), passing to the contralateral cord as the lateral corticospinal tracts. This is the pyramidal system, disease of which causes upper motor neurone (UMN) lesions. ‘Pyramidal’ is simply a descriptive term that draws together anatomy and characteristic physical signs, and is used interchangeably with the term UMN.

A proportion of the corticospinal outflow is uncrossed (anterior corticospinal tracts). This is of no relevance in practice.

Characteristics of pyramidal lesions (Box 22.8)

Signs of an early pyramidal lesion may be minimal. Weakness, spasticity or changes in superficial reflexes can predominate, or be present in isolation.

Patterns of UMN disorders

There are three main patterns:

Hemiplegia, paraplegia and tetraplegia indicate (strictly) total paralysis, but are often used to describe severe weakness.

Spastic paraparesis

Paraparesis indicates bilateral damage to corticospinal pathways causing weakness and spasticity (or flaccid weakness in the initial phase of spinal shock after an acute cord insult). Cord compression (p. 1135) or cord diseases are the usual causes; cerebral lesions occasionally produce paraparesis. Paraparesis is a feature of many neurological conditions; finding the cause is crucial (p. 1135).

Extrapyramidal system

The extrapyramidal system is a general term for basal ganglia motor systems, i.e. corpus striatum (caudate nucleus + globus pallidus + putamen), subthalamic nucleus, substantia nigra and parts of the thalamus. In basal ganglia/extrapyramidal disorders, two features (either or both) become apparent, in limbs and axial muscles:

Extrapyramidal disorders are classified broadly into akinetic-rigid syndromes (p. 1130) where poverty of movement predominates, and dyskinesias where there are involuntary movements (p. 1121).

The most common extrapyramidal disorder is Parkinson’s disease.

Function and dysfunction

Overall function of this system is modulation of cortical motor activity by a series of servo loops between cortex and basal ganglia (Fig. 22.10). In involuntary movement disorders there are specific changes in neurotransmitters (Table 22.5) rather than focal lesions seen on imaging or at autopsy.

Table 22.5 Changes in neurotransmitters in Parkinson’s and Huntington’s diseases

Condition Site Neurotransmitter

Parkinson’s

Putamen

Substantia nigra

Cerebral cortex

Dopamine ↓ 90%Norepinephrine (noradrenaline) ↓ 60%5-HT ↓ 60%Dopamine ↓ 90%GAD + GABA ↓↓GAD + GABA ↓↓

Huntington’s

Corpus striatum

Acetylcholine ↓↓GABA ↓↓Dopamine: normalGAD + GABA ↓↓

GABA, γ-aminobutyric acid; GAD, glutamic acid decarboxylase, the enzyme responsible for synthesizing GABA; 5-HT, 5-hydroxytryptamine.

Proposed model of principal pathways

The model helps explain how basal ganglia disease can either reduce excitatory thalamo-cortical activity at synapse H, i.e. movement – causing bradykinesia, or increase it, causing dyskinesias.

Parkinson’s disease (PD). This is characterized by slowness, stiffness and rest tremor (p. 1118). Degeneration in SNc causes loss of dopamine activity in the striatum. Dopamine is excitatory for synapse A and inhibitory for synapse B. Through the direct pathway there is reduced activity at synapse F, leading to increased inhibitory output (G) and decreased cortical activity (H).

Also in PD, in the indirect pathway, dopamine deficiency results in disinhibition of neurones synapsing at C. This leads to reduced activity at D, and to increased activity of neurones in the subthalamic nucleus. There is excess stimulation at synapse E, enhancing further inhibitory output of GPm-SNr.

The net effect via both pathways is to inhibit the ventral anterior (VA) and ventrolateral (VL) nuclei of the thalamus at synapse G. Cortical (motor) activity at H is thus reduced.

Levodopa helps slowness and tremor in PD (p. 1119) but induces unwanted dyskinesias by increasing dopamine activity at synapses A and B, it is thought by reversing sequences in both direct and indirect pathways.

Hemiballismus (p. 1121). Wild, flinging (ballistic) limb movements are caused by a lesion in the subthalamic nucleus, typically an infarct. This reduces excitatory activity at synapse E, reduces inhibition at G, with increased thalamo-cortical neuronal activity, and increases activity at H.

Cerebellum

The third system of motor control modulates coordination and learned movement patterns, rather than speed. Ataxia, i.e. unsteadiness, is characteristic.

The cerebellum receives afferents from:

Efferents pass from the cerebellum to:

Each lateral cerebellar lobe coordinates movement of the ipsilateral limbs. The vermis (a midline structure) is concerned with maintenance of axial (midline) posture and balance.

Cerebellar lesions (Box 22.9)

Expanding lesions obstruct the aqueduct to cause hydrocephalus, with severe pressure headaches, vomiting and papilloedema. Coning of the cerebellar tonsils (p. 1133) through the foramen magnum leads to respiratory arrest, sometimes within minutes/hours. Rarely, tonic seizures (attacks of limb stiffness) occur.

Sensory pathways and pain

Lesions of the sensory pathways

Altered sensation (paraesthesia), tingling, clumsiness, numbness and pain are the principal symptoms of sensory lesions. The pattern and distribution point to the site of pathology (Fig. 22.14).

Peripheral nerve lesions

Symptoms are felt within the distribution of a peripheral nerve (p. 1143). Section of a sensory nerve is followed by complete sensory loss. Nerve entrapment (p. 1144) causes numbness, pain and tingling. Tapping the site of compression sometimes causes a sharp, electric-shock-like pain in the distribution of the nerve, known as Tinel’s sign, e.g. in carpal tunnel syndrome (p. 1144).

Spinal cord lesions

Parietal cortex lesions

Sensory loss, neglect of one side, apraxia (p. 1068) and subtle disorders of sensation occur. Pain is not a feature of destructive cortical lesions. Irritative phenomena (e.g. partial sensory seizures from a parietal cortex glioma) cause tingling sensations in a limb, or elsewhere.

Pain

Pain is an unpleasant, unique physical and psychological experience. Acute pain serves a biological purpose (e.g. withdrawal) and is typically self-limiting, ceasing as healing ensues. Some forms of chronic pain (e.g. causalgia) outlast the period required for healing, and may be permanent.

Essential physiology of pain

Pain perception is mediated by free nerve endings, terminations of finely myelinated A-delta and of non-myelinated C fibres. Chemicals released following injury produce pain either by direct stimulation or by sensitizing nerve endings. A-delta fibres give rise to perception of sharp, immediate pain, then slower-onset, more diffuse and prolonged pain is mediated by slower-conducting C fibres.

Sensory impulses enter the cord via dorsal spinal roots. Impulses ascend either in each dorsal (posterior) column or in each spinothalamic tract. Grey matter neurones in the cord are arranged in laminae labelled I–X (dorsal to ventral). A fibres terminate in laminae I and V and excite second-order neurones that project to the contralateral side via the anterior commissure and via the anterolateral column of the direct spinothalamic tract. C fibres mostly terminate in the substantia gelatinosa (laminae II and III); axons then pass through the anterior commissure to the contralateral side and rostrally, up the spino-reticulo-thalamic tract.

The spinothalamic tracts carry impulses that localize pain. Thalamic pathways to and from the cortex mediate emotional components. Sympathetic activity increases pain, e.g. hyperaemia in a painful limb.

Management of chronic pain

Chronic pain is gravely disabling, distressing, and taxing to treat (p. 509). Multidisciplinary pain-relief clinics provide specific and supportive therapy.

Management plans for intractable pain have seven components:

Psychological

Chronic pain influences quality of life. Depression (p. 1170) is commonly associated with pain when the pathology is benign; antidepressants can help. Of patients suffering pain from secondary cancer about one-third are clinically depressed.

Bladder control and sexual dysfunction

Changes in micturition and failure of normal sexual activity due to neurological conditions are seen in sacral, spinal cord and cortical disease.

Neurological tests

Neuro-imaging

Lumbar puncture and CSF examination

See Table 22.8 and Practical Box 22.3.

Table 22.8 The normal CSF

Appearance Crystal clear, colourless

Pressure

60–150 mm of CSF, recumbent

Cell count

<5/mm3No polymorphsMononuclear cells only

Protein

0.2–0.4 g/L

Glucose

imageimage of blood glucose

IgG

<15% of total CSF protein

Oligoclonal bands

Absent

image Practical Box 22.3

Lumbar puncture

The procedure should be explained to the patient, and consent obtained. LP should not be performed in the presence of raised intracranial pressure or when an intracranial mass lesion is a possibility.

Indications for lumbar puncture (LP):

Meticulous attention should focus on microbiology in suspected CNS infection. Close liaison between clinician and microbiologist is essential. Specific techniques (e.g. polymerase chain reaction to identify bacteria) are invaluable. Repeated CSF examination is often necessary in chronic infection such as tuberculosis. Post-LP headaches, worse on standing, are a common complaint for several days (or more). Prolonged headaches can be treated by an ‘autologous intrathecal blood patch’ – injection of 20 mL of the patient’s venous blood into the CSF.

Routine tests

See Table 22.9.

Table 22.9 Value of routine investigations neurology

Test Yield Condition

Urinalysis

Glycosuria

Polyneuropathy

Ketones

Coma

Bence Jones protein

Cord compression

Blood picture

↑ T MCV↑↑ T T ESR

B12 deficiencyGiant cell arteritis

Blood glucose

HypoglycaemiaHyperglycaemia

ComaComa

Serum electrolytes

Hyponatraemia

Coma

Hypokalaemia

Weakness

Serum calcium

Hypocalcaemia

Tetany, spasms

Serum CPK

Raised

Muscle disease

Chest X-ray

Lytic bone or mass lesion

Bronchial cancer, thymoma

Unconsciousness and coma

Consciousness is dependent on the functioning of two separate anatomical and physiological systems:

Impaired functioning of either anatomical system may cause coma.

Disturbed consciousness: definitions

Table 22.10 Glasgow Coma Scale

  Score

Eye opening (E)

 

 Spontaneous To speech To pain No response

4321

Motor response (M)

 Obeys Localizes Withdraws Flexion Extension No response

654321

Verbal response (V)

 Orientated Confused conversation Inappropriate words Incomprehensible sounds No response

54321

Glasgow Coma Scale = E + M + V (GCS minimum = 3; maximum = 15).

Mechanisms and causes of coma (Box 22.11)

Altered consciousness is produced by four mechanisms affecting the ARAS in the brainstem or thalamus, and/or widespread impairment of cortical function (Fig. 22.18).

image

Figure 22.18 Anatomy of vegetative state, locked-in syndrome and brainstem death.

(Adapted from Bates D. Coma and brainstem death. Medicine 2004; 32, with permission of Elsevier.)

A single focal hemisphere (or cerebellar) lesion does not produce coma unless it compresses the brainstem. Cerebral oedema frequently surrounds masses, increasing their pressure effects.

The commonest causes of coma are:

The unconscious patient

General and neurological examination

Neurological examination

Neurological examination aims to determine:

Brainstem function

Diagnosis and investigations in coma

Often, the cause is evident (e.g. head injury, metabolic disorder, overdose). Where lateralizing signs or brainstem pathology are found on examination, a mass lesion or infarction/haemorrhage is likely (note hypoglycaemia may also cause focal signs). If no cause is evident after clinical assessment, further investigations are essential.

Prognosis in coma and the vegetative state

Prognosis depends on the cause of coma and the extent of brain damage sustained. Metabolic and toxic causes of coma have the best prognosis when the underlying problem can be corrected. Following hypoxic-ischaemic brain injury, e.g. after cardiac arrest, only 11% make a good recovery and following stroke the prognosis is worse still with only 7% recovering. Of those patients who do not recover consciousness, a substantial proportion will remain in a vegetative or minimally responsive state.

Distinction between these states is essential before addressing issues of prognosis and cessation of supportive care.