Peripheral neuropathy is a condition involving the nerves of the peripheral portion of the nervous system. Neurobiologists describe the peripheral nervous system as any part of that system found in the arms or legs. The nerves that traverse the arms and legs occur in fibrous groups identified from the vascular system by their whitish color. These nerve tracts, or bundles of similar type nerve cell fibers, exit the brain and spinal cord from the intervertebral spaces in the spinal column to the rest of the body. The majority of the peripheral nerves are responsible for sensations such as touch, pain, and temperature. There is a greater concentration of particular types of nerve cells located in both the hands and feet. This concentration is a result of the need for sensory integration with the numerous small muscles and intricacy of movement in these regions of the body.
When certain traumatic conditions exist in the peripheral nerves, some people experience a highly uncomfortable condition in which they describe sensations as burning, tingling, shooting pain, overall persistent pain, and a wide variety of additional discomforting sensations. When this condition this persistent, it is called peripheral neuropathy. Peripheral neuropathy is also known as somatic neuropathy or distal sensory polyneuropathy.
This disorder is primarily recorded in persons with diabetes, compromised immune systems, or those who have suffered some sort of injury to these nerves. The traumas can range from overexposure to certain chemical toxins, penetration injury, fractures, staying in one position too long, severe impact, or even prolonged compression, as in the wearing of inappropriate footwear. Athletes who use their feet in sports such as tennis, basketball, soccer, or any running exercise are at moderate-to-severe risk. Among those with diabetes and HIV the risk is highest. As a result of high computer usage, the incidence of carpal tunnel syndrome, a type of peripheral neuropathy, is rising.
Many researchers assume the condition itself is caused by the loss of myelin (a waxy type substance) along the axon of the nerve cell. The role of myelin will be discussed later in the description of the nerves themselves. As a result of this loss of myelin, patients describe a variety of symptoms such as those previously described. A variety of initial complaint descriptions like aching, throbbing, the feeling of cold such as frostbite or even heat sensation so severe some patients compare it to "walking on a bed of coals," are the first clues to the possibility of advancing neuropathy.
Because the initial symptoms are similar to many other disorders, doctors are sometimes hesitant to diagnose peripheral neuropathy until the disease has reached a more advanced stage. By that time rehabilitation and treatment may take longer and be less effective.
Description
Many persons with peripheral neuropathy in the legs experience an inability to walk properly. The incidence of injuries from falling increase, and affected persons may eventually develop a shuffling-type gait. In the hands, many people with this disorder must wear a brace or some sort of support. They lack their previous dexterity and fingers become numb. Manual tasks become difficult or almost impossible.
This disease may affect the nerves in several ways. If a single nerve is involved, the condition is called mononeuropathy. This condition is considered rare as it is unusual to find a condition in which only a single nerve maybe involved. Trauma is likely to involve multiple neurons and toxins or diabetes will most likely produce a global reaction.
Another condition likely to exist is one in which two or more nerves in separate areas of the body are affected. This case is described as multiple mononeuropathy. While this is still a less frequent scenario it is more common that the disease will occur in the same areas of either side of the body. This situation is more common when the cause is systemic rather than a physical injury.
Most often many nerves in the same vicinity are simultaneously involved, which is known as polyneuropathy. This is the most common expression of the disorder. Damage to nerve fibers may eventually result in loss of motor function or a reduction in proprioceptive or sensation types of responses. This type of neuropathy causes the greatest distress among patients. Treatment is difficult and often the nerve damage is irreversible. A halt to the advancement of the disease is one of the most promising types of relief a patient can expect.
Demographics
Statistics on the occurrence of this disorder are not always reliable. Because peripheral neuropathy can accompany a great number of other disorders, many cases go undiagnosed. Carpal tunnel syndrome, which is on the increase, is just one form of peripheral neuropathy and affects millions of people worldwide. There is evidence that some forms of this disease are inherited. Those neuropathies that are inherited are called either sensorimotor neuropathies or sensory neuropathies.
Race has not been found as a contributing factor in the onset of peripheral neuropathy. In fact, the only risk factors aside from inheritance are those that result from traumas, reaction to toxic substances, and malnutrition. While malnutrition has been erroneously paired with certain social demographics this does not necessarily mean that those who suffer from inadequate nutritional intake are more susceptible. Trauma and associated diseases, such as diabetes and HIV, are the major factors associated with this neuropathy. The occurrence of peripheral neuropathy is about 2,400 cases per 100,000 population (2.4%). However with continued aging the rates increase to about 8,000 per 100,000 people (8%).
Causes and symptoms
One of the more prevalent and reasonable descriptions of how the disease is caused lies in the declining myelination of the actual nerve cells and fibers. In order to illustrate this condition, a discussion of one of the more common and most often discussed type of nerve cell will aid in the understanding of this type of neuropathy. The motor neuron, which is responsible for the initiation of movement, is a large nerve cell with a body and a long extension called the axon. The cell terminates at the end of the axon into a branched formation from which neurotransmitters are released to stimulate other motor neurons. The axon is the region of the cell along which electrical signals are passed. These electrical impulses are generated in the cell body and travel at high speeds to the ends of the neuron. The branched ends, called the synaptic end bulbs release acetylcholine which, in turn, activates the next cell body to produce an electrical signal and on down the fiber of a new nerve cell in the tract.
A waxy lipid is generated inside a specialized cell, the Schwann cell, that wraps around the axon of the nerve cell. Many Schwann cells grow along the axon and act as a kind of insulation for the nerve cell. The Schwann cells assure that the electric charge goes where the central nervous system (CNS) intends it to go. In diseases such as multiple sclerosis, the degeneration and death of these Schwann cells cause CNS electrical signals to go in random directions, preventing the muscles from responding properly.
It is assumed that in peripheral neuropathy the same sort of condition may occur. Whether due to trauma or a reaction to toxins, the myelin appears to start disappearing in many nerve cells and the otherwise contained electrical signals spread throughout the affected region. In turn, the neighboring neurons receive an overstimulation of random impulses and movement is impaired.
Muscle weakness is one of the first symptoms of peripheral neuropathy and is maximized soon after the beginning of the disease or about three to four weeks after onset. Sensory nerve cells, especially those that transmit pain are overstimulated and can cause severe aching and shooting pains, including the feeling of extreme cold or heat. Misdirected signals can cause cramping in advanced stages.
Diagnosis
Once a physician suspects a patient may be affected with from peripheral neuropathy, the diagnosis can be confirmed by a series of tests. An EMG (a recording of electrical activity in the muscles) allows the physician to see how much of a small electrical current passing through a suspected nerve region is lost due to damage in the nerves. The difference in electrical charge from its origin to its endpoint provides a measure of potential damage.
Nerve conduction tests are performed by having a machine determine the speed at which a nerve impulse passes through a nerve region. The slower the passage, the greater the neuropathy. This may relate to the loss of myelin around the nerve axons and fibers or actual physical damage. Nerve biopsies are performed in the more serious conditions. The biopsy will permit the physician to see the actual condition of the nerve and rule out other causes for the pain the patient experiences.
Finally, a simple blood test can be administered. Toxins that may damage nerves are screened for. Vitamin levels are observed since nutrition may be a causative factor. Vitamin B6 has been demonstrated in some studies to be toxic for some patients with peripheral neuropathy. A diabetic condition is examined for presence or absence or degree of severity.
For persons with HIV, certain drugs such as didanosine (ddI, Videx), zalcitabine (ddC, Hivid), and stavudine (d4T, Zerit) are common culprits in the occurrence of peripheral neuropathy. Not everyone taking these drugs will acquire peripheral neuropathy, but those with the disease appear to have had a damaging response to these chemicals. Additionally, in some cases, alcohol consumption may be a contributing factor.
Treatment team
The family physician and a neurologist are the traditional specialists in recognizing and treating peripheral neuropathy. Alternative therapists include nutritionists and acupuncturists, who also have found a place among those seeking treatment for peripheral neuropathy. One thing agreed upon is that peripheral neuropathy is often treatable. Better results occur with those patients who receive an early diagnosis and are younger, although physical therapists working with patients in all stages of the disease have reported improvement over time.
Treatment
A variety of treatments are available to patients with peripheral neuropathy. Some report a significant degree of improvement after taking higher doses of vitamin B12. Physical therapies and exercise influence the nerves to respond to correct stimuli and decrease the loss of myelin. Treatment is aimed at two goals. The first is to try and alleviate or eliminate the cause of the underlying disease. The second is to relieve its symptoms. Painkillers are often prescribed (including morphine) for the most severe cases. Prosthetic devices can be used when muscle weakness has reduced a person's ability to walk.
Managing diabetes is extremely important in those patients who have developed peripheral neuropathy as a symptom of the disease. Good nutrition, exercise, and avoiding alcohol are highly recommended. Those with HIV may experiment with alternate therapies and, again, focus on good nutrition and exercise.
Recovery and rehabilitation
The recovery from peripheral neuropathy varies. Those who are diagnosed early stand a better chance of a full recovery than those who are diagnosed after the disease has progressed over a long period. While not all cases are reversible, many patients have made a full recovery with proper treatment. For many, a halt in the progression of the disease is highly possible and often achieved. No quick cures have been found, however, and those who do improve do so after a great deal of work and commitment to recovery.
One of the aspects of the disease not often discussed is the emotional and psychological impact this disease has on its sufferers. Many find the constant pain an unbearable condition and are left to live a life dependent on pain-killing drugs. Others are distraught at the loss of movement and weakness that accompany the disorder. For these patients, there are support groups and websites devoted to the sharing of ideas and promising new therapies. Relatives and friends can be very supportive in recognizing that this is a real and diagnosable disease with proven treatments. Peripheral neuropathy is not an imaginary condition and it is not only possible to find cessation from advancing symptoms, but a partial if not total recovery.
Clinical trials
Many clinical trials are underway to search for treatments and prevention methods for peripheral neuropathy. A clinical trial is a research study designed to test or target a specific aspect of a research topic. They are designed to ask and attempt to answer very specific questions about the causation and new therapies for medical or other research types of questions. Many new vaccines or new ways of using known treatments for a specific pathology have been discovered in clinical trials. They are often the source of new drug therapies or alternate types of treatment. Often, the criteria for entering a clinical trial is very specific, but the results can prove to be enormously helpful.
Some of the current clinical trials for peripheral neuropathy include the following: The University of Chicago is undertaking two separate clinical trials for the study of a particular drug's effectiveness in relieving the pain of diabetic peripheral neuropathy, as well as slowing the rate of progression. Washington University of St. Louis School of Medicine is sponsoring a trial to study treatments for those with peripheral neuropathy resulting from HIV infection. Information on these studies and other ongoing clinical trials can be found at the National Institutes of Health website for clinical trials at <http://www.clinicaltrials.gov>.
Prognosis
Prognosis varies for persons with peripheral neuropathy. Quick identification and diagnosis is critical to beginning therapies in the early phases of the disease. Age is also a contributing factor, as younger persons fare better than older patients when they follow a multi-disciplinary approach to the disease. However, most patients can find a degree of relief from symptoms and the advancement of the disease.
Special concerns
While there are many cases in which peripheral neuropathy is unavoidable, most podiatrists recommend good foot hygiene. Recommendations include using appropriate and supportive footwear. Support measures such as arch and wrist braces may help in prevention of some types of peripheral neuropathy. If a person finds that one of the conditions of their employment is repetitive motion of the hand, as in typing, newer more ergonomic types of keyboards may reduce pressure on the nerves associated with carpal tunnel syndrome.
Senneff, John A. Numb Toes and Aching Soles: Coping with Peripheral Neuropathy. San Antonio, TX: Medpress, 1999.
Stewart, John D. and M. M. Stewart. Focal Peripheral Neuropathies, 3rd ed. New York: Lippincott Williams & Wilkins Publishers, 2000.
OTHER
National Institute of Diabetes and Digestive and Kidney Diseases. " Diabetic Neuropathies: The Nerve Damage of Diabetes." January 4, 2004 (June 1, 2004). <http://diabetes.niddk.nih.gov/>. "
