Weight-loss surgery for severe obesity may carry the risk of damage to the network of nerves that runs throughout the body, researchers reported Thursday.

The investigators found that of the 435 obesity-surgery patients whose records they reviewed, 16 percent developed peripheral neuropathy. That contrasted with 3 percent in a group of obese gallbladder-surgery patients who were studied for comparison.

Peripheral neuropathy refers to damage to the nerves that relay information to and from the brain and spinal cord to the rest of the body.

In this study, many peripheral neuropathy sufferers had symptoms in the hands and feet, such as tingling, numbness and weakness. Others had damage to a single nerve, including 31 who had carpal tunnel syndrome. A few had more severe, painful nerve damage.

The investigators believe that the nerve damage is largely explained by the nutritional deficiencies that can result from obesity surgery, which alters the digestive tract in order to limit the amount of calories a person can consume and absorb.

This can be viewed as good news because it suggests that many cases of post-surgery neuropathy are preventable, according to Dr. P. James B. Dyck, the study’s senior author.

Dyck, a neurologist at the Mayo Clinic in Rochester, Minnesota, explained in an interview that many of the patients in the study who developed peripheral neuropathy showed signs of malnourishment.

Risk factors for the condition included very rapid weight loss, prolonged symptoms of nausea, vomiting and diarrhea, and failure to take enough vitamin and calcium supplements.

Ensuring that obesity-surgery patients get proper nutritional counseling and follow-up care may prevent long-term nerve damage, Dyck said.

He spoke about the findings Thursday at an American Medical Association conference in Washington, D.C. The study will be published in the October 26th issue of the journal Neurology.

The report comes on the heels of a study released this week that concluded that the various forms of surgery used to treat morbid obesity are effective, and in most cases can improve co-existing conditions like diabetes and high blood pressure.

Referring to that study, Dyck said he does not dispute that with the right medical care, patients who have these procedures often do well.

However, he added, they should be aware that they are having a “major, life-changing procedure,” and that their medical care does not end with the surgery. Nutritional counseling and other follow-up care are crucial to long-term health, according to Dyck.

Several forms of surgery are available for treating people who are 100 pounds or more overweight and considered morbidly obese. Some are known as malabsorptive procedures because they restrict the amount of calories and nutrients a person can absorb after they eat.

For instance, in Roux-en-Y gastric bypass, staples are used to create a pouch in the stomach that can hold only a small amount of food at a time; then, a portion of the small intestine is attached to the pouch so that food bypasses the rest of the stomach and part of the small intestine.

Because nutrient absorption is diminished in such procedures, patients must learn to eat a balanced diet and take supplements in order to prevent vitamin and mineral deficiencies.

Dyck noted that patients in the study who did not have their surgery at the Mayo Clinic were at greater risk of peripheral neuropathy. The likely reason, he said, is that obesity surgery patients at his center attend a nutritional clinic. In general, his team found, patients who went to such clinics had fewer cases of nerve damage.

SOURCE: Neurology, October 26, 2004.