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).
Acute polyneuropathy has many causes:
The cause of chronic polyneuropathy is often unknown. Known causes include the following:
The most common form of chronic polyneuropathy usually results from poor control of blood sugar levels in people with diabetes (see Diabetes Mellitus (DM)) but may result from excessive use of alcohol.
Diabetic neuropathy refers to the several forms of polyneuropathy that diabetes can cause. (Diabetes can also cause mononeuropathy or multiple mononeuropathy, which leads to weakness, typically of the eye or thigh muscles.)
Some people have a hereditary form of polyneuropathy.
Depending on the cause, polyneuropathies may affect motor nerves (which control muscle movement), sensory nerves (which transmit sensory information), cranial nerves (which connect the head, face, eyes, nose, muscles, and ears to the brain), or a combination.
Acute polyneuropathy (as occurs in Guillain-Barré syndrome) begins suddenly in both legs and progresses rapidly upward to the arms. Symptoms include weakness and a pins-and-needles sensation or loss of sensation. The muscles that control breathing may be affected, resulting in respiratory failure.
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. Then, muscles may become stiff and permanently shortened (called contractures).
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 may have 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 joints (see Neurogenic Arthropathy (Charcot 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 a hereditary form may have hammer toes, high arches, and a curved spine (scoliosis). Abnormalities in sensation and muscle weakness may be mild. Affected people may not notice these symptoms or may consider them unimportant.
How completely people recover depends on the cause of polyneuropathy.
Doctors usually recognize polyneuropathy by the symptoms. A physical examination and tests such as electromyography and nerve conduction studies (see Electromyography and Nerve Conduction Studies) can provide additional information about absent or reduced sensation in the feet.
After polyneuropathy is diagnosed, its cause, which may be treatable, must be identified. Doctors ask whether other symptoms are present and how quickly the symptoms developed. Blood and urine tests may detect a disorder that is causing polyneuropathy, such as diabetes, kidney failure, or an underactive thyroid gland. Infrequently, a nerve biopsy is necessary.
Sometimes polyneuropathy affecting the hands and feet is the first indication that people have diabetes. Sometimes, when extensive testing detects no obvious cause, the cause is a hereditary neuropathy that affects other family members so mildly that the disorder was never suspected.
Specific treatment depends on the cause, as for the following: