UNDERSTANDING NEUROPATHY Nerve damage is a serious complication of diabetes, but severe forms are infrequent and many of the symptoms can be controlled. A common complication of diabetes is diabetic neuropathy -- damage to the nerves that run throughout the body, connecting the spinal cord to muscles, skin, blood vessels, and other organs. Diabetic neuropathy can be a painful and disabling complication. Fortunately, though, severe forms occur infrequently. And often, symptoms disappear over several months. This article explains what is known about the prevention and treatment of diabetic neuropathy. What is Neuropathy? The term diabetic neuropathy refers to a group of diseases that affect the peripheral nerves. If you think of the nervous system as the electrical circuitry in your house, then the wires that supply various lights and appliances would be the peripheral nerves, while the fuse box and main cable would be the central nervous system (the brain and spinal cord). Peripheral nerves are the nerves that extend outside the brain and spinal cord. There are three types of peripheral nerves: motor, sensory, and autonomic. Motor nerve fibers carry signals to muscles to allow motions like walking and fine finger movements. They're like the cords that supply power to appliances that do work, like a power saw or a washing machine. Sensory nerves carry information to the brain about shape, move- ment, texture, warmth, coolness, or pain from special sensors in the skin and from deep in the body. They are like the cables that supply power to instruments that sense things, like your home's thermostat. The autonomic nerve fibers are those that are not consciously controlled, like those that supply the bladder, intestinal tract, and sexual organs. Among other functions, they help to control the pace of heart beats, maintain blood pressure, and control sweating. In that way, they are like the cables in your house that supply things that are self-regulating, like the electrical cables supplying your furnace that automatically switch off and on as the house gets hotter and cooler. Some symptoms of neuropathy occur when the nerve fibers are lost, as when wires become frayed in an old electrical cord. If the loss of nerve fibers affects the motor fibers, it can cause muscular weakness. If loss of nerve fibers affects autonomic fibers, it can cause loss of functions not normally under con- scious control (like digestion). Symptoms indicating neuropathy can also arise from damaged nerves and from nerve sprouts that are regenerating because of excessive electrical discharges. Sensations like prickling, tingling, burning, aching, or sharp jabs of needle-like pain can indicate such excessive nerve activity. Loss of function such as weakness or decreased feeling and symp- toms of prickling or pain may occur together. It is common to have pain even though many fibers have degenerated. Types of Neuropathy. Though doctors use many strange-sounding terms for classifying neuropathy -- terms like "distal symmetric polyneuropathy", for example -- the classification of neuropathy boils down to a few basic questions: Are both sides or only one side of the body affected? Neuropathy that affects both sides of the body is called symmetric, while that affecting only one side is asymmetric. Which class of nerves is affected? Neuropathy can affect differ- ent nerve fibers, including the motor , sensory, and autonomic fibers. How many nerves are affected? Neuropathy in which only one nerve is affected is mononeuropathy; that involving several nerves is called polyneuropathy. What parts of the body are affected? Distal neuropathy affects the hands and feet. By contrast, in so-called proximal neuropa- thies, the thigh muscle are often affected and usually this is asymmetrical. When this type is associated with considerable pain, it is generally called "femoral neuropathy". When proximal weakness without pain occurs, it is referred to as diabetic amyotrophy (without muscle nourishment). Though different doctors classify neuropathy differently, there are a few well-known types of neuropathy: ** Distal symmetric polyneuropathy. This is the most common form of neuropathy. As the name indicates, it strikes both sides of the body. The legs and feet are usually affected, although the hands may be also. People with this form of neuropathy complain of numbness and prickling sensations or tingling. Some people feel pain in the toes or the feet. The feet can sometimes be so tender that walking on a rough surface such as pebbles is uncomfortable. When evaluated by a doctor, people with this form of neuropathy usually have a reduced ability to feel a pin-prick or a vibra- tion, as when a vibrating tuning fork is held to the toe. This type of neuropathy tends to develop only after many years of inadequate blood-glucose control. Investigators think that good blood-glucose control can prevent or improve this polyneuropathy, but proof is needed. ** Cranial neuropathy. This type of neuropathy affects the cranial nerves, the 12 pairs of nerves that are connected with the brain and control sight, eye movement, hearing, and taste. Most commonly, cranial neuropathy affects the nerves that control the eye muscles. The neuropathy begins with pain on one side of the face near the affected eye. Paralysis of the eye muscle follows the pain and causes double vision. Symptoms usually subside within two to three months. ** Autonomic neuropathy. This form affects the autonomic nerves, such as those of the bladder, intestinal tract, and genital organs. Paralysis of the bladder is a common symptom of this type of neuropathy. This symptom occurs when the nerves of the bladder lose their ability to respond normally to pressure as the bladder fills. This causes urine to be retained in the bladder, which results in subsequent urinary tract infections. Autonomic neuropathy can also lead to impotence when it affects the nerves that control erection with sexual arousal. Diarrhea can occur when the nerves that control the small intes- tine are affected by neuropathy. The diarrhea occurs most often at night. Investigators are uncertain of the precise cause and are searching for improved approaches to treatment. ** Compression mononeuropathy. This fairly common form of neuropathy occurs when a single nerve is damaged. Damage is thought to be of two kinds. In the first, nerves are compressed at places where they pass through a tight compartment or over a bony prominence. The nerves of people with diabetes are more prone to compression injury. The second kind arises when blood vessel disease caused by diabetes restricts blood flow to a part of the nerve. Possibly the most frequent mononeuropathy is called the carpal tunnel syndrome, which is a compression of the median nerve. The patient gets prickling in the fingers with or without pain when driving a car, knitting, or resting at night. Characteristical- ly, the annoyance stops in one to five minutes simply by hanging the arms by one's side. If the symptoms are severe, and after adequate evaluation, the wrist ligament can be surgically sec- tioned to give complete relief. Possibly the second most common mononeuropathy is femoral neurop- athy. This occurs especially in non-insulin-dependent (type II) diabetes. A pain may develop in the front of one thigh followed by muscle weakness and wasting of the flesh of the affected muscles. In some cases, the weakness is present on both sides of the body and no pain is present. This is called diabetic amyo- trophy. The cause is not well-understood, but vessel disease may be responsible. Irrespective of the cause, the outlook is good. Increasingly, a mononeuropathy called thoracic or lumber radicul- opathy is being recognized. It is like femoral neuropathy but affects a band of the chest (or abdominal) wall on one or both sides. It seems to occur more often in type II diabetes. Here also an improvement is expected with time. Unilateral foot drop, so that the foot can't be picked up occurs from damage to the peroneal nerve by compression or vessel dis- ease. Improvement may occur. How is Neuropathy Diagnosed? Sensitive and reliable approaches are available for the diagnosis of neuropathy. The first and most important approach is knowing the patient's history. The physician will inquire about muscle weakness (not tiredness), frequency of muscle cramps, persistent prickling numbness or pain, and symptoms of fainting, vomiting, diarrhea, state of bladder control, and sexual ability. He or she will want you to describe your symptoms so that the nature of the problem can be accurately determined. The second approach to diagnosis is a neurologic evaluation. The physician may assess muscle strength, sensation (ability to recognize pinprick and vibrating sensation), and automatic nerve function. These are simple and painless examinations. The third approach is known as an electromyographic examination. This test has two components. The first is the nerve conduction test. A physician performs this test by applying a small electric shock to nerves, for example, in the region of the knee and the ankle. The voltage is recorded with sensitive electronic ampli- fiers from a disk pasted to the skin overlying the muscle. In neuropathy, the speed of the impulse along the nerve is de- creased, indicating an abnormality. Most people do not find the shocks excessively uncomfortable. In some severe neuropathy, the physician may request that the second part of the electromyography be performed. This test is called needle electromyography. A slender needle is inserted into several muscles and the electrical discharges are recorded. From such an examination, the electromyographer can learn whether nerve fiber degeneration or regeneration has occurred. Most patients report some discomfort from the procedure but tolerate the test because it can give a firm diagnosis. In the fourth approach, standardized tests are used to measure muscle strength and the deficit in the function of sensory and autonomic nerves. What Causes Neuropathy? Researchers aren't certain yet what causes diabetic neuropathy. Many doctors believe that elevation of blood glucose is the cause of neuropathy. The frequency and severity of neuropathy appears to be related to how long a person has had diabetes and how will he or she remains in control. This suggests that the degree of glucose control does play a role. Just how isn't certain. It's possible that glucose coats pro- teins, and that these sugared or "glycosylated" proteins no longer function normally. Or it might be that high glucose levels interfere with chemical events in the nerve fibers or in the supporting cells that make an insulation material around the fiber called myelin. It is unlikely that glucose damages nerve cells directly. It may be that raised glucose levels begin a cascade of chemical events that directly affect nerve fibers of supporting cells. Alterna- tively, this cascade of chemical abnormalities may affect small blood vessels. Damaged blood vessels might leak compounds into the nerves that damage them or fail to provide the nerve with enough oxygen. Researchers are paying close attention to the caused of neuropathy. Prevention. Can neuropathy be prevented? That is another question for which there is yet no firm answer, though many physicians advocate tight control of blood-glucose levels as the best chance for prevention. Some recent, relatively small-scale studies followed a group of 74 insulin-dependent patients who at random were assigned to follow either their regular program of self-care or an intensive program. People in the intensive program used more frequent injection of insulin, received closer supervision of their diet and were taught to do home blood-glucose monitoring. After two years, function of the sensory nerves was better in the tight control group than in the conventional control group. This result has been confirmed in a second well-designed trial. What isn't known is whether all or most of the manifestations of neuropathy can be prevented or improved and what degree of blood- glucose control is needed. The final answer rests with large-scale studies conducted at many medical centers. The Diabetes Control and Complication Trials may provide an answer about the preventive potential of tight blood-glucose control. Treatment. Though there is no specific treatment as yet for neuropathy, many of its symptoms can be controlled. Good control of diabetes is a top priority. Most diabetologists and neurologists believe that reaching an ideal weight, following a regular and adequate fitness program, and controlling blood- glucose levels is the most important treatment available. Once neuropathy has begun, it is important to head off injuries and further complications. When feeling is lost in the feet and toes, for example, the foot can be injured without the person with diabetes feeling pain. Proper foot care is essential (see Advanced Information Series reprint #313, "Footcare"). Avoid using hot water bottles or heating pads to prevent serious burns. Instead, try soaking your feet in cool water to help ease discomfort. Inspect the feet daily. Foot ulcers can develop quickly in people with neuropathy, because of pressure spots or foreign objects in the shoe. When feeling in the foot is lost, ulcers can progress to a serious stage before they are noticed. Bed rest combined with antibiotic treatment usually heals foot ul- cers. It is also important to avoid urinary tract infections. These tend to recur when the bladder is involved by autonomic neuropa- thy. Alert your doctor to symptoms such as cloudy or bloody urine, painful urination, low back pain, and fever. Relieving pain is a major goal of treatment. Non-narcotic pain relievers can often help. However, they are best used on a regular basis throughout the day before pain becomes severe. Although narcotics can also relieve pain, they are used only as a last resort. Because neuropathy can persist for months, use of narcotics can lead to addiction. People with painful neuropathy often suffer form depression, anxiety, and insomnia. The depression often subsides as the neuropathy subsides. Antidepressants can relieve depression in some people. Impotence in men can be treated with a surgically implanted prosthesis. However, before considering surgery, the physician will explore psychological causes of impotence, effects of anti- hypertension drugs, and blood vessel disease. Drugs are available to treat faintness or persistent diarrhea caused by autonomic neuropathy. Finally, it is important to be aware that neuropathy in people with diabetes can be caused by diseases other that diabetes. There are at least 50 additional causes of neuropathy, including immune system disorders, infectious diseases, and nutritional deficiencies. Neuropathy is a difficult complication of diabetes. Getting the support of friends and family, and carrying on as many normal activities as possible can help prevent neuropathy from becoming the focus of life. ---------------------------------------------------------------- Author: Peter James Dyck, Professor of Neurology in the Depart- ment of Neurology at the Mayo Medical School, Mayo Clinic, in Rochester, Minn. Copyright 1986 by the American Diabetes Association, inc.