Peripheral neuropathies

Disorders of the peripheral nerves, the nerves that branch from the brain and spinal cord to the rest of the body, are called neuropathies. Depending on the nerves affected, peripheral neuropathies may affect sensation, movement, or automatic functions, such as bladder control. Rarely, a peripheral neuropathy may be life-threatening.

What are the causes?

In developed countries, the most common cause of damage to the peripheral nerves is diabetes mellitus. Vitamin B complex deficiencies and some nutritional disorders may also result in nerve damage. In the developed world, nutritional neuropathy is often the result of a poor diet in people who abuse alcohol. Drinking too much alcohol may also damage peripheral nerves directly.

Damage to a single nerve may occur as a result of an injury or because of compression. For example, in carpal tunnel syndrome, the median nerve, which supplies that part of the hand, is compressed at the wrist.

Neuropathy may also be associated with an infection, such as Hansen’s disease or HIV infection. Guilain-Barre syndrome, a neuropathy that is rapidly progressive, is caused by an abnormal immune response that sometimes occurs after an infection.

Autoimmune disorders such as systemic lupus erythematosus, in which the immune system attacks the body’s tissues, may cause nerve damage occasionally, a disorder such as polyarteritis nodosamay damage nerves by causing inflammation of the blood vessels that supply them. Neuropathy may also result from certain cancers, particularly primary lung cancer and lymphoma. Occasionally, neuropathy is caused by amyloidosis, in which an abnormal protein is deposited in the body.

Some drugs, such as isoniazid, may cause nerve damage, as may exposure to certain toxic substances, such as lead. In some cases, the cause is unknown.

A painless ulcer developing under the big toe joint due to peripheral neuropathy

What are the types?

Peripheral neuropathies may affect the nerves that transmit sensory information (sensory nerves), the nerves that stimulate the muscles (motornerves), and/or the nerves that control automatic functions (autonomic nerves).

Sensory nerve neuropathies: these neuropathies first affect the hands and feet and the spread towards the centre of the body. The symptoms may include tingling, pain, and numbness in the affected area. If the fingertips are numb, everyday tasks may become difficult. This type of neuropathy is most often caused by nutritional disorders or drugs.

Motor nerve neuropathies: if the motor nerves are damaged, the muscles they supply become weak, and wasting occurs eventually. In severe cases, mobility may become restricted, and very rarely, breathing may have to be assisted by mechanical ventilation. Lead poisoning may result in a neuropathy that affects the motor nerves only.

Autonomic nerve neuropathies: a neuropathy that is affecting one or more autonomic nerves may result in constipation, fainting due to low blood pressure, diarrhoea, urinary in continence, or impotence. This type of neuropathy is often caused by long-standing diabetes mellitus.

What might be done?

Your doctor may be able to tell which nerves are affected from your symptoms and an examination. If the cause of your neuropathy is not clear, he or she will probably arrange for blood tests to look for evidence of an underlying disorder, such as nutritional deficiencies or an autoimmune disorder. If Mere is evidence of compression of a nerve, you may also have CT scanning or MRI to assess the severity and extent of nerve damage. Special tests to assess the function of the nerves may also be carried out.

The treatment of a peripheral neuropathy depends on the cause and the type of nerve affected. For example, careful control of diabetes mellitus may keep diabetic neuropathy from worsening, and vitamin B complex injections may help a nutritional neuropathy. If motor nerves are affected, you may have physiotherapy to help to maintain muscle tone. Wearing a foot splint may assist walking. Sometimes, the underlying cause can be treated, but long-standing nerve damage may be irreversible.


TEST NERVE AND MUSLCE ELECTRICAL TESTS

Nerve and muscle electrical test consist of nerve conduction studies and electromyography (EMG). Nerve conduction studies are used to assess how well a nerve is conducting electrical impulses. They are often followed by EMG to see whether symptoms, such as weakness, are due to a disorder of the muscle or the nerve supplying it. Both tests are usually done on an outpatient basis. Each takes about 15 minutes and may cause discomfort.

Nerve conduction studies

Nerve conduction studies are carried out to assess nerve damage in disorders such as peripheral neuropathies. A nerve is stimulated by an electrical impulse, and the response to the stimulus and the speed at which this response travels along the nerve indicates whether the nerve is damaged and the nature and extent of the damage.

Electromyography

EMG is used to differentiate between nerve and muscle disorders and to diagnose disorders such as muscular dystrophy. A fine needle is used to record the electrical activity of a muscle at rest and when contracting. The results are recorded on a trace.