Radial nerve

This may be compressed as it runs through the axilla, in the

spiral groove of the humerus (Saturday night palsy), or may be

injured in fractures of the humerus. It typically causes wrist drop.

Examination sequence

• Test for weakness of brachioradialis (elbow flexor) and the

extensors of the arm (triceps), wrist and fingers.

• Look for sensory loss over the dorsum of the hand (see

Fig. 7.27B) and loss of triceps tendon jerk.

Ulnar nerve

The ulnar nerve is most often affected at the elbow by external

compression as the nerve is exposed, or by injury, as in elbow

dislocation/fracture. Compression usually occurs as the nerve

passes through the condylar groove behind the medial epicondyle

of the humerus or as it passes through the cubital tunnel.

of the face (V nerve nucleus) and contralateral body numbness

(spinothalamic tract).

Thalamic lesions may cause patchy sensory impairment on

the opposite side with unpleasant, poorly localised pain, often

of a burning quality.

Cortical parietal lobe lesions typically cause sensory inattention

but may also affect joint position sense, two-point discrimination,

stereognosis (tactile recognition) and localisation of point touch.

Two-point discrimination and touch localisation are not helpful

signs and tests are not performed routinely.

Peripheral nerves

Peripheral nerves may be damaged individually (mononeuropathy)

or multiply (peripheral neuropathy or mononeuritis multiplex).

Certain nerves (median nerve at the wrist, common peroneal

nerve at the knee) are particularly prone to compression.

Median nerve

The medial nerve may be compressed as it passes between the

flexor retinaculum and the carpal bones at the wrist (carpal tunnel

syndrome). This is the most common entrapment neuropathy

and initially produces sensory symptoms and pain in the hands,

occasionally radiating up the arm – typically at night. Carpal

tunnel syndrome occurs commonly during pregnancy (Box 7.11).

7.11 Common features of carpal tunnel syndrome

• It is more common in women

• There is unpleasant tingling in the hand

• It may not observe anatomical boundaries, radiating up the arm to

the shoulder

• Weakness is uncommon; if it does occur, it affects thumb abduction

• Symptoms are frequently present at night, waking the patient from

sleep

• The patient may hang the hand and arm out of the bed for relief

• There is thenar muscle wasting (in longstanding cases)

• It is commonly associated with pregnancy, diabetes and

hypothyroidism

Fig. 7.27 Sensory and motor deficits in nerve lesions. A Median. B Radial. C Ulnar. D Common peroneal. E Lateral cutaneous of the thigh.

Investigations • 147

7

(for example, syncope versus seizure; see Box 7.2), and also

epidemiology (sudden-onset leg weakness in a 72-year-old man

with diabetes and previous angina is unlikely to have the same

explanation as a new foot drop in a 20-year-old carpet fitter).

Draw up a differential diagnosis and then consider which (if any)

investigations are pertinent. Sometimes during the summarising

process it may become clear that there are aspects of the history

that have not been adequately addressed. Go back and resolve

these areas. Time spent reviewing the history is never wasted;

undertaking unnecessary tests, on the other hand, is more than

just a waste of time.

Do not place undue emphasis on an isolated sign that fails

to fit with the history, such as an apparently isolated extensor

plantar response in a patient with typical migraine. It is more

likely that this is a false-positive sign due to an inept examination/

interpretation of a ticklish patient rather than an indication of

underlying pathology.

Investigations

Initial investigations

Not all patients require investigation. Most patients with headache,

for example, need no tests, but some do (such as a 75-yearold man with new-onset headache and temporal tenderness

on examination, who should have urgent measurement of

the erythrocyte sedimentation rate and C-reactive protein

and a temporal artery biopsy). Unfortunately, the increasing

availability of tests means that many patients are investigated

unnecessarily, which creates new problems (such as what to

do with the unexpected, and quite incidental, finding of an

unruptured intracranial aneurysm identified in a patient with

migraine). Avoid doing tests because you can or because you

do not know what else to do. Magnetic resonance imaging

(MRI) of the brain may unearth incidental findings of no clinical

relevance in up to 20%, depending on age, and there is an

irony – usually lost on your patient – in attempting reassurance

with a scan only to identify an incidental ‘abnormality’. Sometimes

a single carefully chosen test is all that is necessary to confirm a

diagnosis. For example, a patient with chorea, whose father died

of Huntington’s disease, will almost certainly have the diagnosis

confirmed with genetic testing, without the need for imaging or

other tests.

Consider your diagnosis and start with any necessary simple

blood tests (such as exclusion of metabolic disturbance, including

diabetes); then work upwards. If imaging is required, decide

what to image using which modality (computed tomography,

MRI, ultrasound or functional imaging), and whether any special

sequences or techniques are necessary (like intravenous contrast;

Figs 7.28–7.30). Discuss the case with the radiologists if you

are unsure. For some PNS disorders, nerve conduction studies

and electromyography may be helpful. Electroencephalography

is perhaps the most misused test in neurology. Think carefully

about whether it will add anything to what you already know;

it should not be used to diagnose epilepsy. The more invasive

tests (lumbar puncture, nerve/muscle/brain biopsy) all require

careful consideration and should be guided by specialists.

Lastly, the worlds of antibody-mediated and genetic diseases

are changing rapidly, and you may need to have a discussion with

the relevant experts about which specialised test might be most

appropriate.

Examination sequence

• Examine the medial elbow, palpating the nerve in the ulnar

groove (the most common place of entrapment). Note any

scars or other signs of trauma.

• Look for wasting of the interossei (dorsal guttering).

• Test for weakness of finger abduction with the patient’s

fingers on a flat surface, and ask them to spread the

fingers against resistance from your fingers.

• Test adduction by asking them to grip a card placed

between their fingers and pulling it out using your own

fingers.

• Assess for sensory loss on the ulnar side of the hand,

splitting the ring finger (see Fig. 7.27C).

Common peroneal nerve

The nerve may be damaged by fractures as it winds around

the fibular head, or it may be compressed, particularly in thin,

immobile patients or as a result of repetitive kneeling, squatting

or sitting with the legs crossed at the knees. It typically causes

a foot drop.

Examination sequence

• Test for weakness of ankle dorsiflexion and eversion;

test for extension of the big toe (extensor hallucis

longus). Inversion and the ankle reflex will be

preserved.

• Test for sensory loss over the dorsum of the foot (see

Fig. 7.27D).

Lateral cutaneous nerve of the thigh

This purely sensory nerve may be compressed as it passes

under the inguinal ligament, producing paraesthesiae in the lateral

thigh (meralgia paraesthetica, which means burning numbness)

(see Fig. 7.27E).

Examination sequence

• Ask the patient to map out the area of disturbance.

• Test for disturbed sensation over the lateral aspect of the

thigh. Palpate the abdomen and groin for masses or

inguinal lymph nodes.

Interpretation of the findings

Having completed the history and examination, first decide

whether the symptoms are due to neurological disease, a

functional neurological disorder or non-neurological causes. Try

to localise the lesion to a single area of the nervous system if

possible (Is the lesion in the CNS or PNS?) and then localise in

more detail (for example: If the lesion is in the PNS, is it in the

root, nerves or neuromuscular junction muscle?). Some conditions,

like multiple sclerosis, may give rise to multiple symptoms and

signs because they involve several lesions; others, like migraine

or functional disorders, do not follow strict neurological and

anatomical rules.

Having localised the lesion, consider the likely underlying

pathology (What is the lesion?). This will depend on the history

148 • The nervous system

A B C

Fig. 7.28 Imaging of the head. A DaTscan showing uptake of tracer (dopamine receptors) in the basal ganglia on cross-section of the brain.

B Magnetic resonance scan showing ischaemic stroke. T2 imaging demonstrates bilateral occipital infarction and bilateral hemisphere lacunar infarction.

C Unenhanced computed tomogram showing subarachnoid blood in both Sylvian fissures (white arrows) and early hydrocephalus. The temporal horns of

the lateral ventricles are visible (black arrows).

A B C

Fig. 7.29 Imaging of the head. A Computed tomogram (CT) showing a cerebral abscess. B Magnetic resonance scan showing multiple sclerosis with

white demyelinating plaques. C CT scan showing a large meningioma arising from the olfactory groove.

A B

Fig. 7.30 T2 magnetic resonance images showing a large left paracentral L4–5 disc protrusion (arrowed) compressing the L5 nerve root.

A Sagittal section. B Axial section.

Investigations • 149

7

Specific investigations

Lumbar puncture

Lumbar puncture is a key investigation in a number of acute and

chronic neurological conditions. Always measure the CSF opening

pressure (in a lying position, not sitting), using an atraumatic (blunt)

needle. CSF is routinely examined for cells, protein content and

glucose (compared to simultaneously taken blood glucose); it is

also stained and cultured for bacteria. Other specific tests may be

carried out, such as analysis for oligoclonal bands, meningococcal

and pneumococcal antigens, polymerase chain reaction (PCR)

for certain viruses or cytology for malignant cells.

Neurophysiological tests

Electroencephalography (EEG) records spontaneous electrical

activity of the brain, using scalp electrodes. It is employed in

OSCE example 1: Headache history

Miss Bolton, 32 years old, presents acutely with a severe global headache, associated with vomiting and feeling dreadful.

Please take a history from this patient

Confirm:

• Onset – gradual or sudden.

• Site – lateralised or global.

• Severity.

• Aggravating and relieving factors, such as bright light.