Polyneuropathy

Acute polyneuropathy has many causes:

• Infections involving a toxin produced by bacteria, as occurs in diphtheria

• An autoimmune reaction (when the body attacks its own tissues), as occurs in Guillain-Barré syndrome

• Certain toxins, such as triorthocresyl phosphate (TOCP) and thallium

The cause of chronic polyneuropathy is often unknown. Known causes include the following:

• Diabetes mellitus (the most common)

• Excessive use of alcohol

• Infections (such as hepatitis C, HIV infection, Lyme disease, shingles)

• Hereditary neuropathies (such as Charcot-Marie-Tooth disease)

• Autoimmune disorders (such as chronic inflammatory demyelinating polyneuropathy, vasculitis, and systemic lupus erythematosus)

• Vitamin B12 deficiency, which also causes subacute combined degeneration of the spinal cord and often pernicious anemia

• Other nutritional deficiencies (such as thiamin deficiency), an uncommon cause in the United States, except among people with alcohol use disorder who are malnourished

• An underactive thyroid gland (hypothyroidism)

• Toxic substances, including heavy metals such as arsenic, lead and mercury

• Kidney failure

• Cancer (such as multiple myeloma), which damages nerves by directly invading or putting pressure on them

• Rarely, vitamin B6

The most common form of chronic polyneuropathy usually results from poor control of blood sugar levels in people with diabetes 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 the following:

• Motor nerves (which control muscle movement)

• Sensory nerves (which transmit sensory information)

• Cranial nerves (which connect the head, face, eyes, nose, certain muscles, and ears to the brain)

• Autonomic nerves (which control involuntary functions such as blood pressure and heart rate)

• A combination of the above

Polyneuropathy may result from damage to any of the following:

• Myelin sheath (the membranes that surround the axon and that enable nerve impulses to travel quickly), as occurs in Guillain-Barré syndrome

• The blood supply to the nerve, as can occur in vasculitis (inflammation of blood vessels)

• Axon (the long branch of the nerve that sends messages), as can occur in diabetes or kidney failure

Symptoms of polyneuropathy may appear suddenly (acute, occurring over a few days to a couple of weeks) or develop slowly and occur over a period of time (chronic, occurring over months to years) depending on the cause.

Acute polyneuropathies (as occurs in Guillain-Barré syndrome or with toxins) often begin 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.

Many chronic polyneuropathies affect sensation primarily. 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 joint injury is called 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, 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. Much less often, control of bowel movements or urination is lost, leading to fecal or urinary incontinence.

People who have a hereditary polyneuropathy (such as Charcot-Marie-Tooth disease) may have hammer toes, high arches, and a curved spine (scoliosis). Abnormalities in sensation and muscle weakness may be mild. Affected people with mild symptoms may not notice the symptoms or may consider them unimportant. Other people are severely affected.

How completely people recover depends on the cause of polyneuropathy.

• A doctor's evaluation

• Electromyography and nerve conduction studies

• Blood and urine tests to determine the cause

Doctors usually recognize polyneuropathy by the symptoms. A physical examination can help doctors diagnose polyneuropathy and identify the cause.

Electromyography and nerve conduction studies are usually done, particularly in the legs and feet. These tests may be used to do the following:

• Confirm that polyneuropathy is present

• Determine how severe it is

• Determine whether motor nerves, sensory nerves, or a combination are involved

• Determine what type of damage is causing the problem—for example, whether the myelin sheath around nerves is damaged (called demyelination)

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. This information may suggest possible causes.

Blood and urine tests may detect a disorder that is causing polyneuropathy, such as diabetes, kidney failure, or an underactive thyroid gland.

Sometimes a nerve or muscle 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.

If weakness is widespread and rapidly worsening, doctors do other tests:

• A spinal tap (lumbar puncture) is done to obtain a sample of cerebrospinal fluid, which surrounds the brain and spinal cord. If the protein level in the fluid is high and few or no white blood cells are present, the cause may be an autoimmune disorder that causes demyelination, such as Guillain-Barré syndrome.

• Spirometry is done to determine whether the muscles that control breathing are affected. Spirometry is used to measure how much air the lungs can hold as well as how much and how quickly air can be exhaled.

• Treatment of the cause

• Relief of pain

• Sometimes physical and occupational therapy

Specific treatment of polyneuropathy depends on the cause, as for the following:

• Diabetes: Careful control of blood sugar levels may slow progression of the disorder and occasionally relieves symptoms. Transplantation of islet cells (cells that produce insulin), located in the pancreas, is sometimes done and may cure the diabetes and lessen the neuropathy.

• Multiple myeloma, liver failure, or kidney failure: Treatment of these disorders may result in slow recovery.

• Cancer: Surgically removing the cancer may lessen the neuropathy

• An underactive thyroid gland: Thyroid hormone is given.

• Autoimmune disorders: Treatments include corticosteroids, medications that inhibit the immune system (immunosuppressants), plasma exchange (filtering of toxic substances, including abnormal antibodies, from the blood), and immune globulin (a solution containing many different antibodies collected from a group of donors) given by vein (intravenously).

• Medications and toxins: Stopping the medication or avoiding exposure to the toxin can sometimes reverse the polyneuropathy. Antidotes are available for certain medications and toxins and can reverse some toxic effects.

• Excessive amounts of vitamin B6: If the vitamin is stopped, polyneuropathy may resolve.

If the cause cannot be corrected, treatment focuses on relieving pain and problems related to muscle weakness. Physical therapy sometimes reduces muscle stiffness and can prevent muscles from shortening and becoming stiff. Physical and occupational therapists can recommend useful assistive devices.

Some medications that are usually not considered pain relievers can lessen pain due to nerve damage