Peripheral neuropathy occurs when the nerves connecting your spinal cord and brain to other parts of your body (peripheral nerves) become damaged Figure 01. Damage to the peripheral nerves causes symptoms such as tingling and numbness, lack of sensation, pain, and muscle weakness that begins in the hands or feet and may spread through the limbs.There are several types of peripheral neuropathy. Mononeuropathy is damage to a single nerve; multiple mononeuropathy is damage to two or more nerves; polyneuropathy is damage to many nerves throughout the body. The symptoms of these three types of neuropathy are similar. Your physician will determine which type is responsible for your symptoms.
Figure 01. Peripheral nerves
The nerve damage of peripheral neuropathy most commonly appears as a complication of another disorder such as diabetes or AIDS, or as a reaction to drugs or chemicals. Nerve damage can result from viral and bacterial infections, rheumatoid arthritis, lupus, cancer, vitamin deficiencies, kidney disease, liver disease, or inherited conditions. Other causes of peripheral neuropathy include trauma, penetrating injuries, bruises, fractures, and dislocated bones. Nerve damage can also result from extended exposure to cold or heat, radiation therapy for cancer, excessive vomiting (which may occur during early pregnancy), and various other causes. Sometimes the cause of peripheral neuropathy remains a mystery.
When peripheral nerves are damaged, communication between your central nervous system and the rest of your body is disrupted. The type of damage to the nerves influences the types of symptoms that will occur. For example, if the sensory nerve fibers are damaged, you will likely experience changes in sensation such as numbness or pain. However, if the motor fibers are damaged, your muscles will be affected, causing changes in your ability to move.
Peripheral neuropathy usually starts with numbness and tingling in the feet or hands Table 01. Most of the time symptoms appear over a period of months or years. However, neuropathy sometimes develops and worsens in a matter of days or weeks, particularly if it was caused by an injury, or by Guillain-Barré syndrome. Symptoms usually begin in the extremities (for example in the toes) and then spread up towards the trunk. If the symptoms first appear in the fingers, a sensation of numbness, prickling, or tingling may then spread through the hands and arms. Symptoms usually occur in a symmetrical fashion; for example, both hands or both feet would be affected.
You may experience burning, freezing, shooting pain that may be worse at night, gradual muscular weakening, skin that is extremely sensitive to touch, and loss of balance or coordination. In extreme cases, you may lose the ability to stand, walk, or hold objects in your hand.
Peripheral neuropathy can also affect the nerves that control automatic functions such as heartbeat, bladder control, or bowel function. You may experience diarrhea or constipation, incontinence, sexual impotence, and high or low blood pressure. Your skin may become dry and pale, and you may sweat excessively. You may also develop blurred vision, dizziness or fainting spells, or stomach and intestinal problems.
The nerve damage and numbness of peripheral neuropathy can lead to injuries and infections. Because sensation is limited with neuropathy, you may be unaware of an injury such as a burn or a cut. The untreated wound may then become infected. This is especially common in diabetic patients who develop neuropathy in their feet, and then develop painless cuts which can become infected.
Table 1. Symptoms of Peripheral Neuropathy
Numbness Tingling or prickling Sharp pain Burning or freezing sensations Decreased sensation Lack of sensation Extreme sensitivity to touch Muscle weakness Lack of muscle control Loss of balance or coordination
Peripheral neuropathy affects men and women equally. Older adults (those 55 to 60 or over) are most likely to develop peripheral neuropathy. However, a mononeuropathy such as carpal tunnel syndrome may affect younger adults who use computers extensively, or who work in situations requiring repetitive motions. Some inherited conditions that cause nerve damage can strike during childhood.
Nerve damage is a frequent complication of diabetes mellitus. Peripheral neuropathy occurs in 5% to10% of patients newly diagnosed with diabetes, and may affect more than 50% of patients who have had diabetes for more than 25 years. If you develop neuropathy, the numbness and diminished sensation in your feet and legs may prevent you from noticing an injury or infection until it becomes a bedsore. Diabetic neuropathy can also cause weakness of the eye, face, and thigh muscles.
Diabetic neuropathy is more likely to develop in patients with poor blood glucose control.
Neuropathy is commonly associated with HIV and AIDS. An estimated one-third of AIDS patients experience the typical symptoms of neuropathy, such as loss of feeling in the feet or hands, and other sensations, including prickling or burning. The type of neuropathy that occurs typically varies with the stage of the disease. The most common condition is a type of polyneuropathy that develops during the late stages of HIV infection.
In patients with HIV, peripheral neuropathy can be caused by the viral infection itself, can develop as a side effect of drugs taken to fight the infection, or can be related to vitamin deficiencies or diabetes. AIDS drugs associated with peripheral neuropathy include stavudine, didanosine, and zalcitabine. Although neuropathy can affect anyone with HIV, it is more likely to occur if you are taking one or more of these drugs. Your symptoms may improve if you stop taking the medication. Your doctor may be able to prescribe another drug that relieves your symptoms without causing neuropathy.
Alcoholism is a leading cause of neuropathy. The symptoms of alcoholic neuropathy (numbness, abnormal or painful sensations, muscular weakness) are caused by the effect of alcohol on nerve tissue. Habitual, heavy drinking or a history of alcoholism seems to increase your risk for developing this disorder.
Guillain-Barré syndrome, rheumatoid arthritis, lupus, scleroderma, atherosclerosis, sarcoidosis, leprosy, and polyarteritis nodosa are also associated with peripheral neuropathy. Guillain-Barré Syndrome, rheumatoid arthritis, and lupus are examples of autoimmune diseases—diseases in which the body's immune system attacks organs, organ systems, or tissues instead of protecting them. In Guillain-Barré syndrome, for example, the immune system attacks the peripheral nervous system. This rare form of polyneuropathy is marked by rapidly developing muscular weakness that sometimes leads to paralysis. In the vast majority of cases, the weakness reaches its peak within two to three weeks. Most patients recover, although some degree of weakness may persist.
Exposure to toxic chemicals can cause neuropathy. Toxic chemicals that can cause neuropathy include industrial agents such as solvents; heavy metals such as lead, arsenic, and mercury; pesticides; and nitrous oxide. Sniffing glue or other toxic compounds can also cause peripheral neuropathy.
Nutritional deficiencies can cause peripheral neuropathy. A deficiency in vitamin B
12 or another vitamin can cause polyneuropathy. However, a poor diet is rarely the cause of peripheral neuropathy in the U.S.
Many drugs can cause neuropathy. Certain medications can damage the nerves and cause changes in sensation characteristic of peripheral neuropathy. Some of the drugs that may cause neuropathy include:
- Heart or blood pressure medications such as amiodarone and hydralazine
- Cancer drugs such as vincristine and other vinca alkaloids, cisplatin, suramin, and paclitaxel
- Drugs that fight infection, such as metronidazole, nitrofurantoin, thalidomide, isoniazid, emetine, chlorobutanol, and sulfonamides
- Drugs that treat skin conditions, such as dapsone
- The anticonvulsant phenytoin
- The antialcohol drug disulfiram
- Sedatives such as hexobarbital and barbital
Peripheral neuropathy can be associated with inherited diseases. The most common heritable disease to be associated with peripheral neuropathy in both adults and children is Charcot-Marie-Tooth disease. People with this condition have progressive muscular degeneration and a mild loss of limb sensation. A condition known as Friedreich's ataxia or spinocerebellar degeneration can also cause damage to multiple nerves.
Prevention and Screening
Since peripheral neuropathy can be caused by so many factors, prevention is difficult. However, you can reduce your risk for neuropoathy by avoiding some of the known causes of the disorder. For example, you can avoid contact with solvents or pesticides, and follow a balanced diet to prevent vitamin deficiencies. If you are a heavy drinker, you may be able to reduce your risk of developing neuropathy by drinking less, or by abstaining from alcohol. If you have diabetes, make sure you follow your doctor's advice for proper management of your condition. Strict control of blood sugar decreases the risk of developing diabetic neuropathy over time. If you are taking a drug that may affect your nervous system, be sure that you discuss your concerns with your doctor and promptly report any possible symptoms of peripheral neuropathy.
Using keyboards increases your chances of developing carpal tunnel syndrome, a form of neuropathy Figure 02. Carpal tunnel syndrome is caused when the median nerve that extends from the forearm to the hand (going through a “tunnel” in the wrist formed by a series of bones) becomes compressed. When the nerve becomes compressed, it can cause numbness, tingling, and pain in the hands. You may experience decreased feeling in your thumb, index finger, and middle finger. The pain can also extend to the arm and shoulder.
Figure 02. Carpal tunnel syndrome (animation)
If you work at a computer, there are precautionary measures you can take to decrease your risk of getting carpal tunnel syndrome. For example, you can learn correct keyboard techniques, take frequent breaks from keyboard use, and practice stretching and strengthening exercises for the hand, fingers, and wrist. You can also use a wrist protector pad when typing or using a mouse.
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