Polyneuropathy

Polyneuropathy is the simultaneous malfunction of many peripheral nerves throughout the body.

Polyneuropathy may be acute (beginning suddenly) or chronic (developing gradually, often over months or years).

Causes

Acute polyneuropathy has many causes. It may be caused by an infection involving a toxin produced by bacteria (as in diphtheria) or by an autoimmune reaction (as in Guillain-Barré syndrome). Toxic substances, including heavy metals such as lead and mercury, carbon monoxide, and some drugs can also cause acute polyneuropathy. The drugs include the anticonvulsant phenytoin, some antibiotics (such as chloramphenicol, nitrofurantoin, and sulfonamides), some chemotherapy drugs (such as vinblastine and vincristine), and some sedatives (such as barbital and hexobarbital). Cancer, such as multiple myeloma, may cause acute polyneuropathy by directly invading or compressing the nerves or by producing toxic substances.

The cause of chronic polyneuropathy is often unknown. The most common form of chronic polyneuropathy is most often due to diabetes but may be due to excessive use of alcohol. Nutritional deficiencies (such as vitamin B deficiency) are an uncommon cause of chronic polyneuropathy in the United States, except among alcoholics who are malnourished. Anemia due to vitamin B₁₂ deficiency (pernicious anemia) may also cause chronic polyneuropathy. Other causes include an underactive thyroid gland (hypothyroidism), liver failure, and kidney failure. Rare causes include certain cancers, such as lung cancer, and taking excessive amounts of vitamin B₆ (pyridoxine).

Poor control of blood sugar levels in diabetes (see Section 13, Chapter 165) causes several forms of polyneuropathy, collectively referred to as diabetic neuropathy. (Diabetes can also cause mononeuropathy or mononeuritis multiplex that leads to weakness, typically of the eye or thigh muscles.)

In some people, the cause is hereditary.

Symptoms

Acute polyneuropathy (for example, Guillain-Barré syndrome) begins suddenly in both legs and progresses upward to the arms. Symptoms include weakness and a pins-and-needles sensation or loss of sensation.

In the most common form of chronic polyneuropathy, only sensation is affected. Usually, the feet are affected first, but sometimes the hands are. A pins-and-needles sensation, numbness, burning pain, and loss of vibration sense and position sense (knowing where the arms and legs are) are prominent symptoms. Because position sense is lost, walking and even standing become unsteady. Consequently, muscles may not be used. Eventually, they may weaken and waste away.

Diabetic neuropathy commonly causes painful tingling or burning sensations in the hands and feet--a condition called distal polyneuropathy. Pain is often worse at night and may be aggravated by touch or by a change in temperature. People may lose the senses of temperature and pain, so they often burn themselves and develop open sores caused by prolonged pressure or other injuries. Without pain as a warning of too much stress, joints are susceptible to injuries; this type of injury is called Charcot's joints.

Polyneuropathy often affects the nerves of the autonomic nervous system, which controls involuntary functions in the body (such as blood pressure, heart rate, digestion, salivation, and urination). Typical symptoms are constipation, loss of bowel or bladder control (leading to fecal or urinary incontinence), sexual dysfunction, and fluctuating blood pressure--most notably a sudden fall in blood pressure when a person stands up (orthostatic hypotension). The skin may become pale and dry, and sweating may be reduced.

People who have the hereditary form may have hammer toes, high arches, and a curved spine (scoliosis). Abnormalities in sensation and muscle weakness are mild. Affected people may not notice these symptoms or may consider them unimportant.

See the sidebar No Pain: Charcot's Joints.

Diagnosis

Doctors easily recognize polyneuropathy by the symptoms. A physical examination and procedures such as electromyography and nerve conduction studies (see Section 6, Chapter 77) can provide additional information about absent or reduced sensation in the feet. After polyneuropathy is diagnosed, causes that can be treated must be identified. Blood and urine tests may detect a disorder that is causing polyneuropathy--for example, diabetes, kidney failure, or a thyroid disorder. Infrequently, a nerve biopsy is necessary.

Treatment and Prognosis

Physical therapy sometimes reduces muscle weakness.

Specific treatment depends on the cause. When taking excessive amounts of vitamin B₆ is the cause, the disorder may resolve if the vitamin is discontinued. When neuropathy is related to diabetes, careful control of blood sugar levels may slow progression of the disorder and occasionally relieves symptoms. Transplantation of cells that produce insulin (islet cells (see Section 16, Chapter 187)), located in the pancreas, sometimes results in a cure. Treatment of multiple myeloma or liver or kidney failure may result in slow recovery. When polyneuropathy is due to cancer, the cancer may have to be surgically removed to relieve compression of the nerve. When polyneuropathy is due to an underactive thyroid gland, thyroid hormone is given.

The prognosis for people with acute or chronic polyneuropathy depends on the cause.

Guillain-Barré Syndrome

Guillain-Barré syndrome (inflammatory demyelinating polyneuropathy) is a form of polyneuropathy that produces worsening muscle weakness, leading to paralysis.

The presumed cause is an autoimmune reaction: The body's immune system attacks the myelin sheath, which surrounds the axon of many nerves. In about 80% of people with this syndrome, symptoms begin about 5 days to 3 weeks after a mild infection, surgery, or an immunization.

There are two forms of Guillain-Barré syndrome. In the acute form, muscle weakness develops rapidly; in the chronic form, muscle weakness develops gradually.

Symptoms and Diagnosis

The acute form usually begins in both legs, then progresses upward to the arms. Occasionally, symptoms begin in the reverse order. Symptoms include weakness and a pins-and-needles sensation or loss of sensation. Weakness is more prominent than abnormal sensation. In 90% of people who have Guillain-Barré syndrome, weakness is most severe within 2 to 3 weeks. In 5 to 10%, the muscles that control breathing become so weak that a ventilator is needed. Because the facial and swallowing muscles become weak, about 10% of people need to be fed intravenously or through a tube placed directly through the abdominal wall into the stomach (gastrostomy tube). If the disorder is very severe, blood pressure may fluctuate, heart rhythm may become abnormal, or other functions controlled by the autonomic nervous system may be impaired.

In an unusual variant of the acute form called Miller-Fisher syndrome, only a few symptoms develop: Eye movements become paralyzed, walking becomes difficult, and normal reflexes disappear.

The chronic form produces symptoms similar to those of the acute form, but they develop more slowly, usually over a period of about 8 weeks. Symptoms also last longer and may become permanent.

The diagnosis is based on the pattern of symptoms and results of diagnostic procedures. Analysis of cerebrospinal fluid obtained by a spinal tap (lumbar puncture (see Section 6, Chapter 77)), electromyography, nerve conduction studies, and blood tests can help doctors exclude other possible causes of severe weakness, such as transverse myelitis and spinal cord injuries. A combination of high protein levels and no inflammatory cells in the cerebrospinal fluid and specific results from electromyography strongly suggest Guillain-Barré syndrome.

Treatment and Prognosis

The acute form of Guillain-Barré syndrome, which can worsen rapidly, is a medical emergency. People who develop this syndrome should be hospitalized immediately. Establishing the diagnosis is crucial because the sooner appropriate treatment is started, the better the chance of a good outcome. In the hospital, the person is closely monitored so that breathing can be assisted with a ventilator if necessary. Nurses take precautions to prevent bedsores and injuries by providing soft mattresses and by turning the person every 2 hours. Physical therapy is started immediately to help preserve joint and muscle function.

Plasmapheresis, in which toxic substances are filtered from the blood (see Section 14, Chapter 171), or infusion of immune globulin is the treatment of choice. Corticosteroids are no longer used because they have no proven benefit and may worsen the disorder.

People who have the chronic form may be given corticosteroids to help reduce weakness. These drugs may be needed for a long time. Immune globulins, plasmapheresis, and immunosuppressants (such as azathioprine) may also help.

Without treatment, most people improve slowly over several months. However, with early treatment, people can improve very quickly--in days or weeks. About 30% of adults and even more children with the disorder have residual weakness 3 years after the syndrome began. On average, less than 5% of people die during the early stage of the disease.