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Disorders of the Peripheral Nervous System
A peripheral neuropathy (disorder of the nervous system) is a disorder affecting the peripheral motor, sensory, or autonomic nerves. Peripheral nerves connect the spinal cord and brain to all other organs. They transmit motor impulses from the brain and relay sensory impulses to the brain. A mononeuropathy affects a single peripheral nerve; multiple mononeuropathy or mono-neuritis multiplex indicates the involvement of multiple single peripheral nerves or their branches. Polyneuropathies are charac-terized by bilateral and symmetric disturbance of function, usually beginning in the feet and hands. (Most nutritional, metabolic, and toxic neuropathies take this form.)
The most common causes of peripheral neuropathy are dia-betes, alcoholism, and occlusive vascular disease. These disorders result in hypoxia or atrophy of the peripheral nerve. Many bac-terial and metabolic toxins and exogenous poisons also cause pe-ripheral neuropathy. Because of the growing use of chemicals in industry, agriculture, and medicine, the number of substances causing peripheral neuropathies and the incidence of peripheral neuropathies have increased. In developing countries, leprosy is a major cause of severe nerve disease because Mycobacterium leprae invade the peripheral nervous system.
The major symptoms of peripheral nerve disorders are loss of sensation, muscle atrophy, weakness, diminished reflexes, pain, and paresthesia (numbness, tingling) of the extremities. The patient frequently describes some part of the extremity as numb. Autonomic features include decreased or absent sweating, ortho-static hypotension, nocturnal diarrhea, tachycardia, impotence, and atrophic skin and nail changes.
Peripheral nerve disorders are diagnosed by history, physical examination, EMG, and somatosensory evoked potentials.
Mononeuropathy is limited to a single peripheral nerve and its branches. It arises when the trunk of the nerve is compressed or entrapped (as in carpal tunnel syndrome); traumatized, as when bruised by a blow, or overstretched, as in joint dislocation; punc-tured by a needle used to inject a drug or damaged by the drugs thus injected; or inflamed because an adjacent infectious process extends to the nerve trunk. Mononeuropathy frequently is seen in patients with diabetes.
Pain is seldom a major symptom of mononeuropathy when the condition is due to trauma, but in patients with complicating inflammatory conditions such as arthritis, pain is prominent. Pain is increased by all body movements that tend to stretch, strain, or cause pressure on the injured nerve and by sudden jarring of the body (eg, coughing and sneezing). The skin in the areas sup-plied by nerves that are injured or diseased may become reddened and glossy; the subcutaneous tissue may become edematous, and the nails and hair in this area become defective. Chemical injuries to a nerve trunk, such as those caused by drugs injected into or near it, are often permanent.
The objective of treatment of mononeuropathy is to remove the cause, if possible, such as by freeing the compressed nerve. Local corticosteroid injections may reduce inflammation and the pres-sure on the nerve. Aspirin or codeine may be used to relieve pain
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