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Neuropathy is one of the three most common complications of diabetes (along with retinopathy and kidney disease). As its name implies, neuropathy affects the nervous system. It can result in pain and/or a dangerous lack of sensation.
When neuropathy manifests itself, the red blood cells tend to be brittle and unable to bend freely. Consequently, cells cannot fit into the small capillary vessels to deliver oxygen. If these vessels in the nerves cannot receive oxygen, then nerve cells die.
There are two major types of neuropathy: one affects the autonomic nervous system and the other targets the sensory nervous system.
The autonomic nervous system is like an electric generator. It controls the automatic functions, those unconcious bodily functions like breathing and circulating the blood. Autonomic neuropathy leads to such problems as gastroparesis (delayed digestion), incontinence, cardiovascular irregularity and sexual disfunction in both men and women. Impotence is the most common manifestation of autonomic neuropathy, affecting more than half of all men with diabetes.
The sensory nervous system is responsible for sensation and can be likened to household electrical wiring since it loops through the entire body. Sensory neuropathy may cause numbness and tingling in the extremities, slowed reflexes and episodes of pain. The nerves of the fingers and toes are affected most often. The tingling and numbness associated with this type of neuropathy may be worse at night and do not tend to fluctuate in response to changing blood sugar levels.
Taking Care of the Pain
Pain management for neuropathy is a complex issue. Many treatments are available, but the complete elimination of discomfort due to neuropathy has remained elusive.
In a study conducted by the Diabetes Research and Treatment Center at Southern Illinois University and School of Medicine, and the Diabetes Center of Excellence at Humana Hospital in Lexington, Ky., three distinct types of neuropathic pain were identified: superficial pain, characterized by burning and tingling; deeper pain experienced as "pins and needles;" and muscle pain, characterized by cramping, aching and muscle tenderness (Diabetes Care, August 1993).
Large nerve fibers in the body carry impulses for voluntary actions or muscle reaction, while small nerve fibers carry impulses for pain. These allow us to sense hot and cold, according to Dr. Rup Tanden, associate professor in the department of neurology at the University of Vermont College of Medicine.
"Often a patient having problems with large nerve fibers will come in with complaints like 'When I play tennis and try to hit the ball down the line, I'm swinging all over the place,'" says neuropathy expert Aaron Vinik, MD, PhD, professor at the Diabetes Research Institute at Eastern Virginia Medical School. These patients complain of being unstable on their feet, and there is weakness in their hands and feet. Hammertoe deformities often are present. Feet are hot, rather than cold.
Most neuropathies involve damage to both large and small nerve fibers, resulting in numbness and loss of sensory detection. In cases where only small nerve fibers are damaged, however, the regeneration of those nerves causes hyper-excitability. These abnormally excitable regenerating nerve fibers correspond to the superficial pain described above.
Anyone who has had nearly frostbitten ears will understand this phenomenon. As the affected ears begin to warm up, the intensity of pain increases. In such cases, physicians often wait before prescribing pain killers since the discomfort often disappears on its own.
However, it is important to distinguish between numbness and the disappearance of pain. The spontaneous disappearance of neuropathic pain may actually be the result of a damaged nerve, which transmits pain while it is dying but ceases to transmit pain once it is completely dead.
According to Vinik, "The disappearance of pain may reflect improvement of nerve function or, alternately, indicate that neural function has deteriorated to the extent that it is no longer sufficient to transmit pain." In other words, the end of nerve pain does not necessarily indicate the healing of neuropathy, but may instead indicate the transition to a more serious, though less painful, condition.
One of the primary dangers of numbness due to advanced peripheral sensory neuropathy is the increased risk of undetected trauma to the area of numbness. The feet are especially at risk, since they are prone to injuries and diabetic ulcers. For this reason, proper attention and care of the feet is extremely important for people with neuropathy in order to reduce or prevent the incidence of gangrene and amputation. It is beneficial to test the feet regularly for loss of sensation.
In the study described above (Diabetes Care, August 1993), each of the three types of pain were treated differently, based on the understanding of its cause. Superficial pain, attributed to the hyper-excitability of regenerating nerve fibers was treated with capsaicin (Zostrix - a topical cream). Deep, electric pain, which is thought to result from some form of nerve cell body or nerve root dysfunction, was treated systematically, using a combination of imipramine, an antidepressant and mexiletine, a heartbeat regulator. And muscle pain, thought to be caused by a feedback loop (in which nerve stimuli creates a muscle spasm, which causes more nerve stimuli, which creates more muscle spasm and so forth), was treated with a combination of stretching exercises and metaxalone, a muscle relaxant.
The results of the study demonstrated dramatic pain improvement for all three categories of pain, suggesting that proper diagnosis is a key to successful treatment. Vinik warns practitioners that this may be difficult. "The trap that we may fall into is that we may not ask the right questions in order to specifically diagnose neuropathy," he says.
The Earlier, the Better
Early detection is of critical importance. It has been found that if impotence due to autonomic neuropathy is treated early (before nerve fibers have deteriorated to the point where there is no function at all), there is a chance that the damaged nerves can regenerate, and the impotence can be reversed by treatments such as direct drug injections (intracavernosal therapy).
However, if the neuropathy remains untreated for six months or more, there is little hope of reversal. Normalization of blood glucose levels in newly-diagnosed patients prevents deterioration of nerve conduction. Improvement in later stages of the disease does not return nerve function to normal levels, but may prevent future damage and alleviate symptoms (Clinical Diabetes, March-April 1993).
Causes of Neuropathy
Vinik describes neuropathy as a complex disease with multiple causes including: metabolic dysfunction, involving both hyperglycemia and essential fatty acid deficiency; autoimmune response involving antibodies discovered in the nerve tissue of people with diabetes which actually destroys the nerve tissue itself; and hypoxia (a lack of sufficient oxygen leading to nerve damage). (Diabetes Review 3:139-157, 1995).
Vinik argues that both genetic and environmental causes, such as tobacco and alcohol use, play a more primary role than hypoxia in the development of neuropathy. Newer studies also implicate autoimmune self-destruct mechanisms in nerve damage for certain people.
Constant Care is Best
Neuropathy is a multi-faceted condition and treatment requires a clear understanding of the specific type of nerve damage involved. The most effective kinds of treatment are those aimed toward the specific type of neuropathy involved and those which address the causes of the neuropathy, rather than its symptoms. See "The Varied Treatments for Neuropathy" (page 1) for more information on specific treatments.
No matter what treatment is used, Vinik stresses that proper attention and care of the feet is vitally important. Patients should check their feet and shoes daily (or have someone check them for you). Foot care kits for health care providers and educational materials for patients can be ordered from the National Institutes of Diabetes and Digestive and Kidney Diseases at (800) 438-5383.
Awareness Is Key
For how serious and damaging this disorder is, public awareness still remains low. "When Ella Fitzgerald's leg was amputated," Vinik says "she was asked 'Why do you think your leg was amputated?' She responded with 'I guess it's because I wore pointy shoes all those years.'" Ella had short fiber neuropathy.
Don't make the same mistake as Ella. Neuropathy can be controlled and prevented, but it must be respected. Being aware of the prevalence and destructive power of neuropathy and taking all the preventative measures you can are vitally important.
Mar 1, 1998
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