EPIDEMIOLOGY

Peripheral nerve diseases are surprisingly common. Population-based studies indicate a prevalence of symmetrical polyneuropathy of about 2.4%, more in the elderly. Carpal tunnel syndrome is present in 5% of women and 0.5% of men. While many patients with symmetrical polyneuropathy are not severely disabled, pain is common and some forms of neuropathy are progressive, disabling and ultimately fatal. Fortunately the peripheral nervous system has remarkable regenerative capacity so that peripheral nerve diseases are usually treatable and may be curable.

CLASSIFICATION

There are several patterns of peripheral nerve disease:

• mononeuropathy

• multiple mononeuropathy (better than the old-fashioned mononeuritis multiplex)

• symmetrical polyneuropathy

• plexopathy

• radiculopathy

• polyradiculoneuropathy.

The time course may be:

• acute, reaching its nadir in <4 weeks, as in Guillain-Barré syndrome (GBS)

• subacute, reaching its nadir in 4–8 weeks

• chronic, taking >8 weeks to develop.

The deficit may be:

• purely or predominantly sensory, as in diabetic distal symmetrical polyneuropathy

• purely motor, as in acute motor axonal neuropathy, a less common form of GBS in the UK

• motor and sensory, as in most cases of Charcot-Marie-Tooth (CMT) disease

• autonomic; although autonomic involvement is common in some neuropathies, pure autonomic neuropathy is rare.

The underlying pathology may be identified by nerve conduction tests as:

• axonal

• demyelinating or

• mixed.

Large and small diameter nerve fibres are usually affected together but only large fibre involvement can be detected by conventional nerve conduction tests. Some patients have pain and distal impairment of pinprick and temperature sensation due to:

• small fibre neuropathy.

DIFFERENTIAL DIAGNOSIS

The possibility of peripheral nerve disease comes into the differential diagnosis of sensory, motor or autonomic symptoms, and of loss of the tendon reflexes. If there are cognitive or visual symptoms, peripheral nerve disease cannot be the only diagnosis, although it may be present as well.

• Distal numbness and paraesthesiae are commonly caused by peripheral neuropathy but may …