Clinical neurology is diverse and complex and the epidemiology of these conditions is discussed in individual sections. There s worldwide variation.

Headaches

Headache is an almost universal experience, and one of the most common symptoms in medical practice. It varies from an infrequent and trivial nuisance to a pointer to serious disease.

Mechanism

Pain receptors are located at the base of the brain in arteries and veins and throughout meninges, extracranial vessels, scalp, neck and facial muscles, paranasal sinuses, eyes and teeth. Curiously, brain substance is almost devoid of pain receptors.
Head pain is mediated by mechanical (e.g. stretching of meninges) and chemical receptors (e.g. 5-hydroxytryptamine and histamine stimulation). Nerve impulses travel centrally via fifth and ninth cranial nerves and via upper cervical sensory roots.
Most headaches are benign, but the diagnostic issue – and usual concern – is the question of serious disease. Here are some useful clinical pointers.

Chronic (benign) and recurrent headaches

Almost all recurring headaches lasting hours/days – band-like, generalized head pains, with a history for several years or months – are vaguely ascribed to muscle tension, and/or migraine. Depression is a common accompaniment.
In localized pain of short duration (minutes to hours), sinusitis, glaucoma and migrainous neuralgia should be considered. Malignant hypertension, with arterial damage and brain swelling, occasionally causes headache. Headaches are not caused by high blood pressure alone.

Eyestrain from refractive error does not cause headache, though new prescription lenses sometimes provoke pain.

Pressure headaches

Intracranial mass lesions displace and stretch meninges and basal vessels. Pain is provoked when these structures are shifted either by a mass or by changes in cerebrospinal fluid (CSF) pressure, e.g. coughing. Cerebral oedema around brain tumours causes further shift. These ‘pressure headaches’ typically become worse on lying down.
Any headache present on waking and made worse by coughing, straining or sneezing may be due to a mass lesion. Vomiting often accompanies pressure headaches. Such headaches are caused early, over days or weeks by posterior fossa masses (see hydrocephalus, but over a longer time scale – months or years – by hemisphere tumours.
A rare cause of prostrating headache with lower limb weakness is an intraventricular tumour causing intermittent hydrocephalus.

Headache of subacute onset

The onset and progression of a headache over days or weeks with or without features of a pressure headache should always raise suspicion of an intracranial mass or serious intracranial disease. Encephalitis, viral meningitis and chronic meningitis should also be considered.
Headaches with scalp tenderness
Patches of exquisite tenderness overlying superficial scalp arteries are caused by giant cell arteritis (see p. 1249), almost exclusively in patients over 50.

Headache following head injury

Subdural haematoma must be considered – the majority of post-trauma headaches lasting days, weeks or months are not caused by any serious intracranial pathology.

A single episode of severe headache

This common emergency is caused by one of the following:

- subarachnoid haemorrhage
- migraine, or other benign headaches
- meningitis (occasionally).

Particular attention should be paid to suddenness of onset (suggestive of subarachnoid haemorrhage), neck stiffness and vomiting (meningeal irritation), and to the presence of a rash and/or fever (bacterial meningitis).

Difficulty walking and falls

Change in gait is a common presenting complaint in neurology (see Table 21.2). Arthritis and muscle pain also alter gait, making walking stiff and slow (antalgia). Falls, especially in the elderly, are a common cause of morbidity. The pattern of abnormal gait is valuable diagnostically.

Spasticity

Spasticity, more pronounced in extensor muscles, with or without weakness, causes walking to be stiff and jerky. Toes of shoes become scuffed, catching level ground. Pace shortens but a narrow base is maintained. Clonus – involuntary extensor rhythmic jerking of the legs – may be noticed.
When the problem is predominantly unilateral and weakness is marked (in a hemiparesis), the stiff, weak leg drags and is circumducted.

Common neurological patterns of difficulty walking:

- Spasticity/hemiparesis
- Parkinson’s disease
- Cerebellar ataxia
- Sensory loss (joint position/loss)
- Distal weakness
- Proximal weakness
- Apraxia of gait

Parkinson’s disease

There is muscular rigidity throughout extensors and flexors. Power is preserved but walking slows. The pace shortens to a shuffle; its base remains narrow. Falls occur. A stoop and diminished arm swinging become apparent. Gait becomes festinant (hurried) in small rapid steps. There is particular difficulty initiating movement and turning quickly. Retropulsion describes small backward steps, taken involuntarily when a patient is halted.

Cerebellar ataxia

In disease of the lateral cerebellar lobes stance becomes broad-based, unstable and tremulous. Ataxia describes this imperfect control. Walking tends to veer towards the more affected cerebellar lobe.
In disease confined to cerebellar midline structures (the vermis) the trunk becomes unsteady without limb ataxia. There is a tendency to fall backwards or sideways – truncal ataxia.

Sensory ataxia

Peripheral sensory lesions (e.g. polyneuropathy) cause ataxia because there is loss of the sense of joint position – proprioception. Broad-based, high-stepping, stamping gait develops. This ataxia is made worse by removal of additional sensory input (e.g. vision) and is worse in the dark. First described in sensory ataxia of tabes dorsalis, this is the basis of Romberg’s test. Ask the patient to close the eyes while standing: observe whether the patient becomes unstable (and prevent falling).

Lower limb weakness

When weakness is distal, each leg must be lifted over obstacles. When ankle dorsiflexors are weak, such as in a common peroneal nerve palsy, each foot, returns to the ground with a visible and audible slap.
Weakness of proximal lower limb muscles (e.g. in polymyositis or muscular dystrophy) leads to difficulty in rising from sitting or squatting. 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.

Gait apraxia

With frontal lobe disease (e.g. tumour, hydrocephalus, infarction), the acquired skill of walking becomes disorganized. Leg movement is normal when sitting or lying but initiation and organization of walking fail. This is gait apraxia – a failure of the skilled act of walking. Shuffling small steps (marche à petits pas), difficulty initiating walking (gait ignition failure) or undue hesitancy may predominate. Urinary incontinence and dementia are often present with frontal lobe disease.

Falls

Falls, especially in the elderly, are a major cause of morbidity and hospital admission, e.g. following hip or upper limb fracture. Often no precise cause can be found. A multidisciplinary approach is essential, e.g. reviewing risk factors such as rugs, stairs, footwear and needs for additional home aids.

Dizziness, vertigo, blackouts, collapse and fatigue

Dizziness covers many complaints, from a vague feeling of unsteadiness to severe, acute vertigo. It is frequently used to describe light-headedness felt in panic and anxiety, during palpitations, and in syncope or chronic ill-health. The real nature of this symptom must be determined.
Vertigo – an illusion of movement – is more definite. It is a sensation of rotation, or tipping. The patient feels that the surroundings are spinning or moving. It is distinctly unpleasant and often accompanied by nausea or vomiting.

Blackout, like dizziness, is a descriptive term implying either altered consciousness, visual disturbance or falling. Epilepsy, syncope, hypoglycaemia, anaemia must be considered. However, commonly no sinister cause is found. A careful history, from an eye-witness, is essential.

Collapse is vague but often used. It is not a diagnosis. Avoid it in medical notes.
Fatigue is another common symptom of neurological disorders.

Table 21-1. Incidence rates for commoner neurological conditions/100 000/year in the UK

Headaches (GP consultations)	2200
Cerebrovascular events	205
Shingles (herpes zoster)	140
Diabetic neuropathy	54
Compressive neuropathies	49
Epilepsy	46
Parkinson’s disease	19
Post-herpetic neuralgia	11
All CNS tumours	9
Trigeminal neuralgia	8
Meningitis	7
Multiple sclerosis	7
Severe brain injury	7
Subarachnoid haemorrhage	6
Subdural haematoma	6
Presenile dementia (below 65 years)	4
Cerebral palsy	3
Guillain-Barré syndrome	3
Myasthenia gravis	3
Transient global amnesia	3
Motor neurone disease	2

The neurone and synapse

Practical Box 21.1 Five-part short neurological examination

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

The neurone is the functional unit of the nervous system. Its cell body and axon terminate in a synapse. The specificity, size and type of each group of neurones vary. A single α-motor neurone within an anterior horn of the thoracic spinal cord has an axonal length over 1 metre and innervates between several hundred and 2000 muscle fibres in one leg – a motor unit. By contrast, some spinal or intracerebral internuncial neurones have axons under 100μm long, terminating solely on one neuronal cell body.

Neurotransmitters

Synaptic transmission is mediated by neurotransmitters released by action potentials passing down an axon. Neurotransmitters then react with postsynaptic receptors and are removed by transporter proteins. The neurotransmitter-receptor reaction increases ionic permeability and propagates a further action potential. This combination of axonal electrical activity and synaptic chemical release is the basis of all neurological function.

Neurotransmitters include acetylcholine, norepinephrine (noradrenaline), epinephrine (adrenaline), 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA), opioid peptides, prostaglandins, histamine, dopamine, glutamate, nitric oxide, neuromelanin and vasoactive intestinal peptide (VIP). Of these, glutamate is the principal excitatory neurotransmitter.

The role of neurotransmitters and transporters in pathogenesis continues to be evaluated, but it is thought that a wide variety of acute and chronic neurological disease is mediated by a final common pathway of neuronal injury involving excessive stimulation of glutamate receptors.

Table 21-3. 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

Whilst it is unusual to have to recall detailed neuroanatomy, it is necessary to understand how the nervous system works and how each part is integrated. We can recognize, from symptoms and signs, the part of the nervous system that is malfunctioning – for example, the left frontal lobe, one internal capsule, or a seventh cranial (facial) nerve.

Focal lesions of the cerebral cortex, and throughout the nervous system, cause symptoms and signs by two processes:

• Suppression or destruction of neurones and surrounding structures . This is the most common process – part of the system fails to work.
• Synchronous discharge of neurones by irritative lesions , e.g. cerebral cortex lesions cause epilepsy, either partial or generalized.

This subject causes unnecessary difficulty. Work on neuronal networks, functional imaging and plasticity within the brain questions traditional views of highly specific localization of function. However, in practical neurology, it is necessary to understand the main functional roles of the cerebral cortex. The following paragraphs summarize areas of clinical importance.

The dominant hemisphere (usually left)

The concept of cerebral dominance arose with a simple observation. Right-handed stroke patients with acquired language disorders had destructive lesions within the left hemisphere. Almost all right-handed and 70% of left-handed people have language function in the left hemisphere.

Destructive lesions within the left fronto-temporo-parietal region cause various disorders of human communication:

• spoken language – aphasia, also called dysphasia
• writing – agraphia
• reading – acquired alexia.

Developmental dyslexia describes delayed and disorganized reading and writing ability in children with normal intelligence.

Aphasia

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

Broca’s aphasia (expressive aphasia, anterior aphasia)

Damage in the left frontal lobe causes reduced speech fluency with comprehension relatively preserved. The patient makes great efforts to initiate language, which becomes reduced to a few disjointed words. There is failure to construct sentences. Patients who recover from this form of aphasia say they knew what they wanted to say, but ‘could not get the words out’.

Wernicke’s aphasia (receptive aphasia, posterior aphasia)

Left temporo-parietal damage leaves language that is fluent but the words themselves are incorrect. This varies from insertion of a few incorrect or nonexistent words into fluent speech to a profuse outpouring of jargon (that is, rubbish with wholly nonexistent words). Severe jargon aphasia may be bizarre – and confused with psychotic behaviour.

Patients who have recovered from Wernicke’s aphasia say that when aphasic they found speech, both their own and others’, like a wholly unintelligible foreign language. They could neither stop themselves, nor understand themselves and others.

Nominal aphasia (anomic aphasia or amnestic aphasia)

This means difficulty naming familiar objects. Naming difficulty is an early sign in all types of aphasia. A left posterior temporal/inferior parietal lesion causes a severe, isolated form.

Global aphasia (central aphasia)

This means the combination of the expressive problems of Broca’s aphasia and the loss of comprehension of Wernicke’s. The patient can neither speak nor understand language. It is due to widespread damage to speech areas and is the commonest aphasia after a severe left hemisphere infarct. Writing and reading are also affected.

Dysarthria

Dysarthria simply means disordered articulation – slurred speech. Language is intact, cf. aphasia. Paralysis, slowing or incoordination of muscles of articulation or local discomfort causes various different patterns of dysarthria. Examples are the ‘gravelly’ speech of upper motor neurone lesions of lower cranial nerves, the jerky, ataxic speech of cerebellar lesions, the monotone of Parkinson’s disease, and speech in myasthenia that fatigues and dies away. Many aphasic patients are also somewhat dysarthric.

The non-dominant hemisphere

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

Disorders of memory follow damage to the medial surfaces of both temporal lobes and their brainstem connections – the hippocampi, fornices and mammillary bodies. Bilateral lesions are necessary to cause amnesia. It is characteristic of all organic memory disorders that more recent events are recalled poorly, in contrast to the relative preservation of distant memories.

Memory loss (the amnestic syndrome) is part of dementia, but also occurs as an isolated entity (see Table 21.4).

For clinical purposes, and particularly in general medicine, the extreme complexity of neuroanatomy must be reduced to its core elements. The following sections cover:

• cranial nerves
• three systems of motor control:
• corticospinal or pyramidal system
• extrapyramidal system
• cerebellum
• motor unit
• reflex arc
• sensory pathways and pain
• control of the bladder and sexual function.

Table 21-4. Causes of the amnestic syndrome

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 corticospinal tracts originate in neurones of the fifth cortical layer and terminate at motor nuclei of cranial nerves at the lower border of L1 in spinal cord anterior horn cells. The nerve fibre pathways of particular clinical significance congregate in the internal capsule and cross in the medulla (decussation of the pyramids), passing to the contralateral halves of the spinal 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 the anatomy and characteristic physical signs. It is used here interchangeably with the term UMN.

A small proportion of the corticospinal outflow remains uncrossed (the anterior corticospinal tracts) – this is of no relevance in practice.

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