27th June 2023

Causes of polyneuropathy

Polyneuropathy is the damage to multiple peripheral nerves and is commonly called peripheral neuropathy. This has a wide aetiology, the most common causes being diabetes and alcohol abuse. The presentation is usually symmetrical and, depending on the cause, may present with predominantly sensory, motor, or autonomic symptoms. Causes of predominantly sensory neuropathies include diabetes, alcohol, vitamin B12 or B1 deficiency, vasculitis, uraemia, and drugs such as isoniazid and vincristine. Causes of predominantly motor neuropathies include Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, Charcot-Marie-Tooth, porphyria, botulism, and lead toxicity.

Causes of peripheral neuropathies can also be classified by demyelinating or axonal causes depending on the part of the nerve affected. This can be determined by nerve conduction studies; demyelinating neuropathies classically show a reduction in conduction velocity, whereas axonal neuropathies show a reduction in amplitude.

Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is the most common cause of acute, acquired weakness, often provoked by an infection (commonly respiratory or gastrointestinal). Campylobacter jejuni is a common cause and is associated with slower recovery and residual disability. The pathogenesis involves cross-reaction of antibodies with gangliosides in the peripheral nervous system. There is an ascending progressive symmetrical muscle weakness and eventually paralysis within 2 weeks. There may also be a loss of the deep tendon reflexes. Investigations include lumbar puncture, which will show high protein C and normal white cell count in the cerebral spinal fluid. EMG will show slow nerve conduction velocity. Treatment is with plasma exchange and IV immunoglobulins.

Miller-Fisher syndrome

This is a variant of Guillain-Barré syndrome. It is associated with areflexia, ataxia, ophthalmoplegia, but the paralysis is descending rather than ascending. Anti-GQ1b antibodies can be found in many cases.

Autonomic neuropathies

These are neuropathies which may present with some autonomic symptoms such as postural hypotension, sweating, diarrhoea or constipation, urinary incontinence, and impotence. The main causes include diabetes, amyloidosis, Guillain-Barré Syndrome, renal failure, and chronic hepatic failure.