Peripheral neuropathy is the degeneration of peripheral nerves that supply mainly the distal muscles of the extremities.
This syndrome is associated with non-inflammatory degeneration of the axon and myelin sheaths. Although peripheral neuropathy can occur at any age, incidence is highest in men between ages 30 and 50. Onset is usually insidious, and patients may compensate by overusing unaffected muscles.
The peripheral nervous system is the network of nerves used for all movements (motor nerves) and sensations (sensory nerves). This network of nerves is connected to the central nervous system at the brainstem and at many points along the spinal cord. It reaches to the remote parts of the body. The peripheral nerves provide communication between the brain and the organs, blood vessels, muscles, and skin. The brain’s commands are conveyed by motor nerves, and information is delivered back to the brain by the sensory nerves.
Damage to a peripheral nerve can interfere with communication between the area it serves and the brain. This can impair the ability to move muscles or to feel normal sensations. It can produce a painful sensation along the involved peripheral nerve.
Peripheral neuropathy is the term used to describe damage to the peripheral nerves that does not affect the brain and spinal cord. With minor damage, there may be acute burning pain, whereas major damage can result in imbalance or muscle weakness and even paralysis. There may be damage to a single nerve, as is the case in carpal tunnel syndrome, or damage to many nerves at the same time, as in Guillain-Barre syndrome.
The causes of peripheral neuropathy are numerous. A partial list includes immediate injury, continuing pressure on a nerve and nerve destruction from disease or poisoning. The most common causes of peripheral neuropathies are diabetes mellitus, vitamin deficiency, alcoholism associated with poor nutrition and inherited disorders.
Pressure on a nerve can be due to a tumor, abnormal bone growth, use of a cast or crutches, or prolonged periods in cramped postures. Rheumatoid arthritis, excessive vibration from power tools, bleeding into a nerve, herniated discs, exposure to cold or radiation and various forms of cancer can also cause pressure on nerves.
A common peripheral neuropathy, meralgia paresthetica, is characterized by burning sensations, numbness, and sensitivity of the front of the thighs. Microorganisms can attack the nerves directly and result in peripheral nerve damage. The cause can also be toxic substances, including heavy metals (lead, mercury, arsenic), carbon monoxide and solvents.
The symptoms usually begin gradually over many months. A tingling sensation usually begins in the toes or the balls of the feet and spreads upwards. Occasionally, it begins in the hands and extends up the arms. Then numbness may proceed in the same way. The skin can become sensitive, and even the lightest touch can be painful. In severe forms, a gradual weakness in the muscles may occur. A special risk is that a numbed part of the body can sustain an injury without the patient’s awareness until it becomes infected or ulcerated.
With diabetes mellitus, symptoms of a peripheral neuropathy may not appear until 15 or 20 years after onset. A severe form of vitamin B12 deficiency, known as pernicious anemia, occurs when the body cannot absorb vitamin B12 as it should. Specific symptoms before the onset of peripheral neuropathy include paleness, weakness, fatigue, faintness, or breathlessness. The skin may turn yellow, and the mouth and tongue may be sore.
Diagnosis is usually based upon a history compatible with the disease coupled with a clinical exam showing diminished function of the peripheral nerves.
Specific therapy will be directed at the cause of the peripheral neuropathy. This may mean closer control of the underlying disease, such as regular injections of vitamin B12 for pernicious anemia, returning the blood glucose level to normal if the patient has diabetes mellitus, or avoidance of alcohol. Multivitamin therapy may be appropriate.
In severe cases with permanent impairment, physical therapy may be needed to maintain as much muscle strength as possible and to avoid muscle cramping and spasms. Mechanical devices may be needed for mobility. The skin should be checked regularly and any bruises or open sores reported to the physician.