Editor's note: This article is from 2007. Some newer treatments may not be listed.]
sections include: single-nerve neuropathies, generalized neuropathies
The term peripheral neuropathy refers to disorders of the peripheral nerves, the wiring that connects the body to the brain and spinal cord. Older terms for the same disorders are neuritis and peripheral neuritis. The term actually covers more than 100 medically distinguishable conditions. Their symptoms are highly variable and depend on how many nerves are affected, why, and at what rate. In general, the most common symptoms are weakness, usually of the limbs (that is, motor symptoms), and numbness, frequently accompanied by unpleasant and painful sensations (sensory symptoms). The sites affected may range from the size of half of one finger or toe to almost the entire body. The rate at which a peripheral neuropathy evolves can be as rapid as a few hours, as in Guillain-Barré syndrome, or as slow as 60 or 70 years, as in some hereditary neuropathies. If this sounds confusing, it is, because the only common thread among these disorders is that some part or all of the peripheral nervous system is involved.
It is easiest to think of the peripheral nervous system as an enormously complex network that connects your brain and spinal cord (the central nervous system) to every bit of the rest of the body, which means every millimeter of your skin surface, your internal organs, your muscles, tendons, bones, ligaments, arteries, and every other organ. The system includes the nerves for your eyes and ears; the olfactory patches in your nose; the taste buds on your tongue; the lining of your sinuses, mouth, throat, esophagus, stomach, intestines, bladder, lungs, heart, liver, spleen, and pancreas; and even the sheaths of the nerve trunks themselves.
The peripheral nervous system never sleeps. There is a constant flow of nerve impulses from all the organs, particularly the skin, to the spinal cord and brain. There is also a continuous flow of nerve impulses from the central nervous system through the motor nerves to the muscles and the complicated apparatus that monitors and modifies how the muscles contract to make you move. Most of this activity is processed subconsciously to regulate bodily functions, balance, orientation in space, and the like. Certain specialized cranial nerves connect directly to the brain to convey special senses, including sight, sound, smell, taste, and feeling on the face, scalp, and tongue. All of these functions are usually coordinated seamlessly and unnoticeably—unless something goes wrong. When this connecting network between our bodies and our central nervous system does fail, we use the general term peripheral neuropathy to describe it.
In sorting out the various forms of peripheral neuropathy, one helpful distinction is between problems that involve a single nerve and those that are more general.
Carpal Tunnel Syndrome
Carpal tunnel syndrome is the most common peripheral neuropathy. The affected nerve, called the median nerve, carries the sensory fibers to the thumb, index finger, middle finger, and the adjacent side of the ring finger, plus motor connections to the muscle at the base of the thumb. The median nerve courses through the forearm and enters the hand at the wrist underneath a broad, tough band of tissue called the carpal ligament. The median nerve has to share the space beneath the carpal ligament with nine tendons. In almost all instances, carpal tunnel syndrome comes about by mechanical compression of the median nerve beneath the carpal ligament.
Repetitive hand and wrist movements may cause the median nerve to become compressed or inflamed. When this happens, symptoms appear, particularly at night. Often individuals wake up because of intense tingling and discomfort in their thumb and first two fingers and have to get up and shake the hand vigorously to soothe the symptoms a bit. Numbness in the thumb and index and middle fingers, especially in the tips, can occur, and a person may lose a strong pinch grip because of weakness of one of the muscles at the base of the thumb. A typical case is an avid gardener who overdoes it with a trowel or in repotting plants and that evening first notices the tingling, painful sensations and numbness.
Often carpal tunnel symptoms will subside with the simple use of a splint, but if they persist, particularly with numbness in the fingers and thumb, surgery on the wrist is necessary. An electrodiagnostic examination (usually referred to as an electromyogram, or EMG) of the median nerve is helpful in establishing the diagnosis and how much of the nerve is involved.
The ulnar nerve is the second most frequently affected nerve trunk. This nerve provides sensation to that part of the hand that the median nerve does not. Like the median nerve in carpal tunnel syndrome, the ulnar nerve is usually damaged mechanically, either by a blow or by chronic compression at the elbow or just an inch below the elbow, in the upper forearm. Both motor and sensory symptoms appear. The little finger and occasionally the side of the palm adjacent to it become tingly and numb. A person may feel weakness in trying to spread the fingers on that hand and sometimes in straightening the ring finger and little finger. Usually, symptoms appear slowly over weeks or several months, although a sharp blow to the elbow (“hitting the funny bone”) may cause immediate ulnar neuropathy symptoms. The first symptoms are the tingling sensations in the ring finger and little finger, but any unusual numbness or weakness in the fingers should send you to the doctor. As with carpal tunnel syndrome, the physician will probably do an EMG to determine the severity of the nerve damage. As for treatment, surgery can either decompress the ulnar nerve at or near the elbow or, if symptoms progress or persist, actually reroute it to a safer, damage-free channel. In less severe cases, simply using an elbow guard to protect against further injury is the conservative management.
Other Single-Nerve Injuries
There are three major nerve trunks in each leg and each arm. A major nerve or branch may be injured at any one of a number of sites. This will result in motor symptoms (weakness), sensory symptoms (tingling and numbness), or both, in a distinctive pattern for each nerve trunk or branch.
Generalized peripheral neuropathies are those that affect more than a single nerve. These neuropathies, which are much less frequent than carpal tunnel syndrome or ulnar neuropathy, come in two kinds:
- a patchy affliction of several individual nerve trunks, resulting in the equivalent of many single neuropathies
- a more even, symmetrical pattern, in which individual nerve fibers are affected according to their diameter, length, function (motor or sensory), or all three—the result is tingling numbness, sometimes painful, and weakness in the feet and hands; the problem is worse in the toes, soles, and fingertips
To evaluate these neuropathies, physicians determine the type and distribution of symptoms, how they began and how quickly they developed, and the degree of dysfunction. They ask about such background events as family history, toxic exposures, systemic illnesses, heavy alcohol use, as well as such factors as diabetes and medications, the latter being particularly important. Combined with these data, an EMG can distinguish most peripheral neuropathies. Doctors can then decide on more specialized tests, usually blood tests or imaging procedures, to pinpoint an exact basis for the neuropathy, if possible. Here are brief descriptions of common generalized neuropathies, also referred to as polyneuropathies.
Sensory Peripheral Neuropathy
Sensory peripheral neuropathy is a quite common disorder characterized by tingling, aching, burning, searing discomfort beginning in the toes and spreading to the soles of the feet and then to the tops of the feet, the ankles, and on occasion, the knees. The symptoms are symmetrical and even in distribution, and seem to depend on nerve length. Numbness of the feet, which is usually also painful, frequently occurs. The nerves most affected are the small-diameter fibers that carry sensations from the skin. A person’s motor strength, balance, and (usually) reflexes remain intact. Generally the problems do not rise above the knees, though some people’s fingertips and hands may also be affected. Outwardly, individuals with sensory peripheral neuropathy appear normal, and friends, relatives, and colleagues may not realize the discomfort they feel.
An electrodiagnostic study of this condition yields relatively ordinary results because it is difficult to measure abnormalities in the small diameter sensory nerve fibers. All test results for a systemic disorder usually come back normal as well. A specialized skin biopsy may pinpoint the problem but not the cause; this type of test is done only at certain academic medical centers. There is no known cause for this disorder.
The usual medications for treating sensory peripheral neuropathy are antiepileptic medications, particularly gabapentin, and tricyclic antidepressants, mainly nortriptyline and desipramine. All have selective effects on pain. Such treatment is not a cure, simply a way to reduce symptoms. In fact, there is no known cure for this common and frustrating disorder.
Diabetic Peripheral Neuropathy
The symptoms of diabetic peripheral neuropathy also begin with tingling and burning pain and then numbness in the toes and feet. In this case, however, we can link those symptoms to diabetes. Peripheral neuropathy is common in people with longstanding diabetes, usually of ten to twenty years’ duration or more. Prolonged elevation of blood sugar appears to be the important factor, but exactly how this produces nerve damage is still controversial. The only known way to stabilize and sometimes improve diabetic peripheral neuropathy is through strict control of a person’s blood sugar levels.
Peripheral Neuropathies That Develop over Months or Years
Many other chronic peripheral neuropathies also begin in the feet and spread gradually over months or years but involve motor nerve fibers. This causes weakness of the feet and ankles. A person ends up slapping his or her feet on the ground while walking. Eventually, the wasting of leg muscles may make walking or rising from a chair difficult. The person may still feel tingling, numbness, and perhaps pain alongside this weakness because of involvement of the sensory fibers. The sensory symptoms may slowly ascend from the feet to the legs and then appear in the hands and forearms if the condition continues to progress.
There are many possible causes for this motor-sensory type of peripheral neuropathy. The condition can be brought on, for instance, by prolonged exposure to such toxins as lead and arsenic. In particular, certain medications can produce this side effect: these include some of the cancer chemotherapy drugs, strong immunosuppressants used after organ transplants, amiodarone (Cordarone) for heart irregularity, and statin medications for high cholesterol. The problem can arise from excessive doses of vitamin B6 (pyridoxine), as advocated by some “nutrition experts,” and heavy alcohol use. These are all best managed by avoiding that toxin, if it can be identified.
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