Peripheral neuropathy

Question 1

What are the 6 ways in which nerves may malfunction?

Answer 1

Demyelination
Axonal degeneration (e.g. due to a toxin)
Wallerian degeneration following nerve section, compression
Infarction (in arteritis)
Infiltration by inflammatory cells (e.g. sarcoid).

Question 2

What is mononeuropathy?

Answer 2

The process affecting a single nerve. This may be the result of acute compression, particularly where the nerves are exposed anatomically (common peroneal) or entrapment, particularly where the nerve runs through a relatively narrow anatomical passage (carpel tunnel).
Multiple mono-neuropathy (or mononeuritis multiplex) affects several or multiple nerves. This often indicates a systemic disorder; treatment is that of the underlying disease. Acute presentation is most commonly due to vasculitis when prompt treatment with steroids may prevent irreversible nerve damage.

Question 3

What is polyneuropathy?

Answer 3

An acute or chronic, diffuse, usually symmetrical disease. May involve motor, sensory and autonomic nerves, either alone or in combination. Sensory symptoms include numbness, tingling, ‘pins and needles’, pain in the extremities and unsteadiness on the feet. Numbness tends to affect the distal arms and legs in a ‘glove and stoking distribution’. Motor symptoms are usually those of weakness. Autonomic neuropathy causes postural hypotension, urinary retention, erectile dysfunction, diarrhoea, diminished sweating, impaired pupillary response and cardiac arrhythmias. Many varieties of neuropathy affect autonomic function to some degree, but occasionally autonomic features pre-dominate. This occurs in diabetes, amyloidosis and Guillian-Barre syndrome.

Question 4

What are the causes of neuropathy?

Answer 4

D Drugs and chemicals (Pb, phenytoin, metronidazole, amiodarone, hydralazine, vincristine, isoniazid, organic solvents, sulphonamides, nitrofurantoin, CO, OPs).

A alcohol (with or without Thiamine deficiency)

M metabolic (diabetes, hypoglycaemia, uraemia)

I infection (HIV, leprosy, lyme, diptheria, syphilis) or post infectious (GBS)

T tumour (paraneoplastic phenomenon – lung, lymphoma, myeloma)

B B12 & other vitamin deficiency states, as well as pyridoxine excess

I idiopathic and infiltrative (e.g. amyloidosis)

T toxins (botulism, ciguatera, Tetrodotoxin, Saxitoxin, BRO, tick paralysis)

C connective tissue diseases (e.g. SLE, PAN, RhA) and congenital (e.g. CMT)

H Hypothyroidism

Question 5

How does it present?

Answer 5

Often weakness, numbness and pain

Question 6

Investigations

Answer 6

First line for a patient presenting with polyneuropathy includes FBC, U&E’s, erythrocyte sedimentation rate, serum vitamin B12, blood glucose, LFTs and sometimes nerve conduction studies.