Family doctor

What is it?

Peripheral neuropathy is a group of conditions affecting the nerves outside the brain and spinal cord, interfering with their function. The term generally excludes single nerve lesions (mononeuropathy) due to entrapment of the nerve or trauma. The nerves at the extremities (e.g. hands and feet) are most commonly involved.

The nerves affected may be sensory (touch), motor (activating the muscles) or autonomic (feeding organs and controlling sweating and blood pressure), or a combination of these types.

Thus the patient may suffer symptoms of burning, numbness or pins and needles in the hands or feet, weakness of muscles, or disturbance in sweating, blood pressure (dizzy turns), and gut function. As the condition progresses the symptoms may extend closer to the trunk. The numbness may spread in a "glove and stocking" distribution.

Causes:

There are very many causes. The most important are listed here:

Hereditary:

• Hereditary motor and sensory neuropathy type 1 and 2 (Charcot-Marie-Tooth disease)
• Hereditary sensory neuropathy
• Hereditary dysautonomia
• Porphyria
• Leucodystrophy

Metabolic:

• Diabetes
• Renal failure
• Thyroid disease

Vitamin deficiencies:

• Vitamin B12
• Vitamin B1

Drugs:

• A large number may cause peripheral neuropathy. Important ones are: steroids, colchicine, lithium, phenytoin, isoniazid, indomethacin, perhexiline, nitrofurantoin, colchicine, amiodarone, some cytotoxic drugs.

Toxins:

• Cyanide
• Toluene
• Arsenic
• Solvents
• Alcohol

Infections:

• Tetanus
• Leprosy
• Diptheria
• HIV infection
• Guilain-Barre syndrome (acute polyneuropathy)

Cancers:

• Lung cancer ("paraneoplastic syndrome")
• Myeloma
• Lymphoma

Collagen disorders:

• SLE (lupus)
• Rheumatoid arthritis

Vascular:

• Peripheral vascular disease

The most common cause is diabetes, followed by alcohol excess, renal (kidney) failure, disease of the arteries (usually smoking related) and drugs. Different causes affect different nerves e.g. alcohol causes a mostly sensory nerve damage, and diphtheria affects mostly motor nerves. In a large number of cases, the cause cannot be identified ("idiopathic").

The diagnosis is made with a history and neurological examination, and blood tests may help identify the cause. Nerve conduction tests, electrical tests of the nerves themselves may be needed. Frequently these show more widespread and severe abnormalities than are evident to the patient. X-rays, such as a chest x-ray may be needed, and occasionally other radiological tests are needed. Sometimes a biopsy of the nerve is useful, so it can be examined under the microscope.

Assessment is best done by a suitable doctor with a knowledge of these underlying conditions, such as a neurologist.

What can be done about it?

The precise cause needs to be established, if possible, as the treatment is of the cause. Thus, in diabetes it is important to control the diabetes well. Treatment of an underlying cancer may improve the peripheral neuropathy symptoms. Withdrawal of causative drugs is important, if possible.

Where motor nerves are affected, physiotherapy and exercises may help.

Numb skin needs to be protected from injury; this is extremely important as small knocks and bumps may not be felt by the patient and can rapidly turn into ulcers which are slow to heal.

Irritated nerves can cause pain, often burning and unpleasant. Drugs which reduce nerve pulses and pain sensitivity, such as phenytoin, carbamazapine and tricyclic antidepressants may be useful. Nerve stimulation therapies can also help.

Useful contacts:

New Zealand Neurological Foundation, 27 Edinburgh St, Newton. Ph 09 3798470.