The Nerve Damage of Diabetes

What Is Diabetic Neuropathy?

Diabetic neuropathy is a nerve disorder caused by diabetes. Symptoms of neuropathy include numbness and sometimes pain in the hands, feet, or legs. Nerve damage caused by diabetes can also lead to problems with internal organs such as the digestive tract, heart, and sexual organs, causing indigestion, diarrhea or constipation, dizziness, bladder infections, and impotence. In some cases, neuropathy can flare up suddenly, causing weakness and weight loss. Depression may follow. While some treatments are available, a great deal of research is still needed to understand how diabetes affects the nerves and to find more effective treatments for this complication.

DCCT: Can Diabetic Neuropathy Be Prevented?

A 10-year clinical study that involved 1,441 volunteers with insulin-dependent diabetes (IDDM) was recently completed by the National Institute of Diabetes and Digestive and Kidney Diseases. The study proved that keeping blood sugar levels as close to the normal range as possible slows the onset and progression of nerve disease caused by diabetes. The Diabetes Control and Complications Trial (DCCT) studied two groups of volunteers: those who followed a standard diabetes management routine and those who intensively managed their diabetes. Persons in the intensive management group took multiple injections of insulin daily or used an insulin pump and monitored their blood glucose at least four times a day to try to lower their blood glucose levels to the normal range. After 5 years, tests of neurological function showed that the risk of nerve damage was reduced by 60 percent in the intensively managed group. People in the standard treatment group, whose average blood glucose levels were higher, had higher rates of neuropathy. Although the DCCT included only patients with IDDM, researchers believe that people with noninsulin-dependent diabetes would also benefit from maintaining lower levels of blood glucose.

How Common Is Diabetic Neuropathy?

People with diabetes can develop nerve problems at any time. Significant clinical neuropathy can develop within the first 10 years after diagnosis of diabetes and the risk of developing neuropathy increases the longer a person has diabetes. Some recent studies have reported that:

• 60 percent of patients with diabetes have some form of neuropathy, but in most cases (30 to 40 percent), there are no symptoms.
• 30 to 40 percent of patients with diabetes have symptoms suggesting neuropathy, compared with 10 percent of people without diabetes.
• Diabetic neuropathy appears to be more common in smokers, people over 40 years of age, and those who have had problems controlling their blood glucose levels.

What Causes Diabetic Neuropathy?

Scientists do not know what causes diabetic neuropathy, but several factors are likely to contribute to the disorder. High blood glucose, a condition associated with diabetes, causes chemical changes in nerves. These changes impair the nerves' ability to transmit signals. High blood glucose also damages blood vessels that carry oxygen and nutrients to the nerves. In addition, inherited factors probably unrelated to diabetes may make some people more susceptible to nerve disease than others.