Polyneuropathy
By Gary Cordingley, Thu Dec 8th

The peripheral nerves are bundles containing many individualnerve-fibers, and are similar to telephone cables carrying manyindividual wires. There are two basic types ofnerve-fibers--motor and sensory. The motor fibers carryelectrical impulses outward from the spinal cord to the muscles,causing them to contract. The sensory fibers carry electricalimpulses inward from the skin, joints and other structures tothe spinal cord, providing the nervous system with inputs, amongothers, concerning the senses of touch, pain and temperature.

Peripheral nerves can be pinched or injured in specificlocations. When this occurs, the problem is called a"mononeuropathy," meaning that a single peripheral nerve isaffected. Examples of mononeuropathy include carpal tunnelsyndrome in which the median nerve is pinched at the wrist, andperoneal neuropathy in which the peroneal nerve is injured nearthe knee. Because the median and peroneal nerves contain bothmotor and sensory fibers, people with these conditions canexperience both weakness and numbness.

In carpal tunnel syndrome, certain muscles of the thumb canbecome weak, while numbness affects the thumb, index finger,middle finger and part of the ring finger--but not the littlefinger. In peroneal neuropathy muscles that lift the front andouter edges of the foot can become weak, while numbness affectsthe outer surface of the calf and the top of the foot--but notits bottom. In cases of mononeuropathy only the structuresconnected to that one nerve's fibers are affected.

In contrast, "polyneuropathy" produces a pattern of weakness andnumbness completely different from that seen inmononeuropathies. Instead of affecting the fibers of just asingle peripheral nerve, polyneuropathy simultaneously impactsfibers traveling in numerous peripheral nerves.

In usual cases of polyneuropathy it is the longest nerve-fibersthat are most at risk, while the shorter nerve-fibers are lessaffected. In brief, polyneuropathy is a "length-dependent"neuropathy. Because the longest nerve-fibers in the body arethose that run from the lower back to the feet, in typical casesof polyneuropathy the first part of the body to become weak ornumb is the feet.

In polyneuropathy muscles ordinarily served by more than oneperipheral nerve can become weak, and the numbness extendsbeyond the territory of any single nerve. If a person withpolyneuropathy pulled on stockings, he or she could cover theparts of the legs affected by weakness and numbness. Thus, theweakness and numbness affecting the legs are described asshowing a "stocking" pattern of loss.

When the medical condition responsible for the polyneuropathycauses worsening damage to the peripheral nerves, the stockingsclimb ever higher as the next-longest nerve-fibers becomeinvolved. By the time a person's stockings climb as high theknees, he or she might also notice symptoms in the fingers. Thisis because the nerve-fibers running from the neck to the fingersare about as long as those running from the lower back to theknees.

If a person with polyneuropathy affecting the hands and armspulled on gloves, he or she could cover the parts of the armsaffected by weakness and numbness. Thus, the weakness andnumbness affecting the arms are described as showing a "glove"pattern of loss, and when legs and arms are simultaneouslyimpacted, it is called a "stocking-glove" pattern.

Medical doctors are usually able to detect polyneuropathy frompatients' histories of symptoms and their physical examinations,but tests of muscle

and nerve electricity--calledelectromyography and nerve conduction studies--are often helpfulin characterizing the extent and pattern of nerve impairment.

Polyneuropathy is more of a category of nerve impairment than afinal diagnosis, and numerous diseases can produce the sameend-result of stocking-glove loss.

Diabetes is the most common cause of polyneuropathy in both theU.S. and the rest of the world. Blood sugars are elevated inpeople with diabetes, but the extent of polyneuropathy is notstrictly related to how bad the blood sugars are, or for howlong they have been elevated. For example, one person withsevere, long-term elevations of blood sugars might have verylittle polyneuropathy, while another person might havepolyneuropathy as the very first symptom of their diabetes. Atpresent there is no good treatment for the polyneuropathy ofdiabetes apart from best-achievable control of blood sugars, butwhen annoying sensations like burning or tingling are present,these can be managed with topical or oral medications.

Ingestion of toxic chemicals can also produce polyneuropathy,and alcohol is the chemical most frequently involved. And whilepeople with heavy and prolonged use of alcohol are more likelythan light drinkers to develop this complication, here, too,some people seem more susceptible to this problem than others.Abstinence can keep the polyneuropathy from worsening, but thealready damaged nerve-fibers might not fully recover. Becausepeople with alcoholic polyneuropathy often lack sufficientquantities of thiamine, a vitamin important to the nerves,supplementing well-rounded, nutritious meals with this vitaminis usually helpful.

Inherited polyneuropathy can be transmitted in families ineither a dominant or recessive form. In families with dominanttransmission a bad gene from just one parent is sufficient toproduce the disease in a child. In families with recessivetransmission defective genes from both parents are required inorder to produce the disease.

As a final illustration of the range of disease processes thatcan cause polyneuropathy let's consider Guillain-Barré(pronounced GEE-on bah-RAY) syndrome, also known by the morecumbersome term of acute inflammatory demyelinatingpolyradiculoneuropathy. In contrast to the diabetic, alcoholicand genetic forms of polyneuropathy that typically worsen at apace measured in months or years, Guillain-Barré develops in amatter of days. The affected patient usually notices weaknessabout the ankles, followed rapidly by weakness about the knees,hips, arms and even of the muscles controlling breathing.Symptoms usually peak within two weeks during which time apatient should be monitored in a hospital in case a ventilatoris needed to support breathing. Subsequent recovery of strengthoccurs over a course of weeks to months.

Guillain-Barré syndrome involves inflammation of nerves andnerve-roots (spinal cord connections) caused by an overactiveimmune system. This is a so-called auto-immune disease in whicha person's immune system attacks a tissue within their ownbodies, in this case the nerves. Certain treatments thattemporarily suppress the action of the immune system have beenshown by randomized, controlled trials--the gold-standard ofmedical proof--to improve outcome in this condition.

(C) 2005 by Gary Cordingley

About the author:Gary Cordingley, MD, PhD, is a clinical neurologist, teacher andresearcher who works in Athens, Ohio. For more health-relatedarticles see his websites at: http://www.cordingleyneurology.com and http://www.neurologyarticles.com