Peripheral neuropathy refers to any disease or dysfunction involving the peripheral nervous system. The peripheral nerves are the nerves outside the brain and spinal cord. These nerves are involved in the sensory input from the extremities and in movement of the extremities. The different types of neuropathies are often classified as sensory or motor neuropathies. Another way of classifying the neuropathies is based on the number of nerves involved. Involvement of just one nerve is called a mononeuropathy while the term polyneuropathy refers to the involvement of more than one nerve. Peripheral neuropathies affect 4-7 % of the general population but in the diabetic population this number may be as high as 30%.
Peripheral neuropathy affects both the sensory and motor fibers of the nerve. However, weakness is rarely a symptom of the neuropathy. This happens because as the muscle fibers lose their nerve connections they undergo a compensatory reinervation (reconnection) from the surrounding muscle fibers. Sensory nerve endings cannot utilize this same mechanism to stay connected to the central nervous system. This is the reason that most peripheral neuropathies initially present as burning, tingling or numbness. Weakness may become obvious only as the neuropathy markedly worsens. Most neuropathies progress slowly over months or even years. However, there is one important type of neuropathy that can rapidly progress and usually involves the motor fibers initially. This type of neuropathy is called Guillain-Barre syndrome. It often starts with weakness and numbness and rapidly progresses to paralysis and respiratory failure. If not promptly treated it can be fatal. This type of neuropathy is rare and almost always follows a respiratory or gastrointestinal viral infection. The sensory neuropathies involving the hands and feet are the most common type. They almost always present with pain often described as a tingling, burning, buzzing or prickling sensation. Patients often describe a tightness or cold/burning sensation.
There are many causes of neuropathy. Finding the underlying cause of the neuropathy is often much more difficult the making the diagnosis. Toxicity from metals such as lead, arsenic and iron overdose can cause neuropathy. Organic solvents used in the chemical industry have been shown to cause some neuropathy. Exposure history and job history are often useful in finding these causes. However, these are not extremely common causes and can be easily overlooked. Both viral and bacterial infections can cause certain types of neuropathies. Autoimmune disease and cancers have been implicated as possible causes of peripheral neuropathy. Treatments of some conditions with medication and radiation have been associated with neuropathy. However, diabetes, alcohol abuse and hypothyroidism account for well over 50% of all peripheral neuropathies. Entrapment syndromes such as carpal tunnel syndrome and cubital tunnel syndrome are other relatively common causes of neuropathy.
Diagnosis of peripheral neuropathy and its underlying cause is often very difficult. The medical history is the most useful diagnostic tool. Electrical testing of the nerves provides objective data that the history and the physical exam may not reveal. The electrical nerve tests give more precise information on the extent and distribution of involvement of the neuropathy. Laboratory testing may be useful in obtaining the exact etiology of the neuropathy. This is important because some of the identifiable causes are treatable.. Common laboratory tests useful in the evaluation of peripheral neuropathy are fasting blood sugar, vitamin B12 level, folic acid level , thyroid panel and complete blood count.
Treatment of peripheral neuropathy starts with treatment of the underlying medical condition if identified. Protection of the extremity from injury due to the numbness is very important. This includes checking the extremity daily for any signs of early injury. Proper fitting foot wear and proper treatment of any pressure points or skin breakdown is extremely important. Since peripheral neuropathy often involves pain to the extremity pain management is vitally important. Several groups of medications have shown usefulness in treating neuropathic pain. However, no one group is always successful and often finding the best treatment requires some trial and error effort. In some patients combinations have been shown to be more successful than a single agent. The anticonvulsants are the most successful group for treating the neuropathic pain. This group includes Neurontin (gabapentin), Lyrica, Tegretol and Lamictal. The antidepressants are also extremely useful in treating neuropathic pain. This group includes Elavil (amitriptyline), and Pamelor (nortriptyline). These are older types of antidepressants belonging to the tricyclic antidepressant family. This group of medications commonly cause sedation and should be cautiously in the elderly. A newer class of antidepressants called the SSRI (selective serotonin reuptake inhibitor) group is much safer but is less consistent in helping with neuropathic pain. Cymbalta is a newer dual acting agent that has recently been shown to be very effective in treating chronic pain. Some of the opioid pain meds such as Vicodin are still useful for treating the pain associated with the peripheral neuropathies. Tramadol is a safer general pain medication that has been shown to be useful in the treatment of chronic pain. Topical agents such as the Lidoderm patch and capsaicin are useful in the controlling the pain of peripheral neuropathy.
In conclusion, peripheral neuropathy is a relative common problem associated with significant pain and dysfunction. There are multiple causes but diabetes alone causes about 1/2 of the reported causes. The history usually makes the diagnosis but electrical nerve studies are extremely useful in determining severity and extent of the neuropathy. Treatment is difficult, but several medications have been shown to be useful in treating the pain associated with the neuropathy.