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DIET AND EXERCISE RELIEVE NEUROPATHIC PAIN

SAN FRANCISCO, CA — Diet and exercise can help to relieve neuropathic pain in patients with impaired glucose tolerance and neuropathy (IGTN), a prospective analysis shows.

In the study of 25 patients with IGTN, those who lost weight on a structured diet and exercise program were rewarded with an improvement in pain, according to J. Robinson Singleton, MD, Associate Professor of Neurology at the University of Utah in Salt Lake City. Those who did not lose weight reported more pain at the end of the six-month study, he reported here at the AAN Annual Meeting.

The analysis, part of a larger study designed to evaluate the natural history of peripheral neuropathy, builds on earlier findings that many patients diagnosed with idiopathic peripheral neuropathy suffer from impaired glucose tolerance (IGT), Dr. Singleton said. Those with IGT have blood glucose levels that are higher than normal – measured at 140 mg/dL to 199 mg/dL two hours after the start of an oral glucose tolerance test – but they are not high enough for a diagnosis of diabetes. Most people with IGT, which is also called pre-diabetes, are at increased risk for developing type 2 diabetes.

IMPAIRED GLUCOSE TOLERANCE

Overall, about 7 percent of the population suffers from peripheral neuropathy, and about half of these cases have known diabetes, Dr. Singleton told Neurology Today (Neurology 1995;45:1832–1836). “While many of the remainder have been classified as ‘idiopathic’ neuropathy with no identifiable cause, evidence suggests that one-third to one-half of these people have impaired glucose tolerance,” (Muscle Nerve 2001;24:1225–1228).

In 2002, an NIH-funded Diabetes Prevention Program study of more than 3,000 patients with IGT was terminated early because there was unequivocal evidence of benefit from diet and exercise over pharmacologic treatment in preventing diabetes. Consequently, Dr. Singleton said his group felt obligated to offer a program of diet and exercise to all their IGTN patients.

In the Diabetes Prevention Program, patients were randomized to treatment with the glucose-lowering agent metformin, placebo, or intensive diet and exercise counseling, and monitored for the development of diabetes or evidence of cardiovascular disease and its risk factors.

“Our study wasn't powered to see if diet and exercise have an effect on the progression of peripheral neuropathy,” he said. “But we did find that it affected pain.”

STUDY PROTOCOLS

The analysis included 25 patients with IGTN, all of whom suffered neuropathic pain, with a mean score of about 41 mm on a 100-mm visual analog scale (VAS), where 0 corresponded to no pain and 100 mm to the worst pain possible. At baseline, all the patients were overweight, with an average weight of 215 pounds, and indolent, performing an average of only 15 minutes of exercise each week. All the patients were put on individually tailored diet and exercise plans that called for losing at least 7 percent of body weight and exercising 30 minutes, five times a week. They met with an exercise physiologist and nutritionist every three months.

Over the first six months of follow-up, patients lost an average of three pounds and increased exercise time to 84 minutes a week. More important, those who lost weight experienced improvement in neuropathic pain, with their average VAS score dropping by nearly 15 mm, Dr. Singleton reported. In contrast, those whose weight remained the same experienced an average 14-mm increase in their VAS score over the first six months – a statistically significant difference.

Similarly, statistically significant changes in neuropathic pain were found after stratifying subjects for minutes of exercise and overall compliance score, Dr. Singleton said. Based on the results, Dr. Singleton recommended that all patients with peripheral neuropathy associated with pre-diabetes be put on a structured diet and exercise program. But, he stressed, both neurologists and their patients need to be committed to get results. “Just seeing a nutritionist once won't help,” he said.

Researchers still do not know why diet and exercise relieves pain, he added. “It's possible that it simply represents an improvement in patients' mood,” Dr. Singleton said. “Losing weight and exercising can improve depression and make pain better. But regardless of why diet and exercise helps neuropathic pain, it is clear it does.”

EXPERTS COMMENT

Commenting on the study, P. James B. Dyck, MD, a consultant in neurology at the Mayo Clinic in Rochester, MN, said that the finding of improved pain scales in patients with glucose impairment and peripheral neuropathy after exercise and improved diet is “intriguing.”

However, there are still many unanswered questions, he said, such as whether the reduction in pain is due to an improvement in the neuropathy or if the exercise and altered diet themselves led to fewer symptoms. “Would patients without glucose impairment have experienced a similar improvement if they had been put on a special exercise program and diet?” he asked.

Part of the problem in understanding the link between neuropathic pain and diet and exercise is that the association between peripheral neuropathy and glucose impairment itself still is not clear, he said.

Given the epidemic of obesity in the Western world, “we don't even know what normal blood sugar is in the elderly,” he said. And without knowing that, one doesn't know what percentage of elderly people has glucose impairment, he explained.

“If by current standards, 50 percent of ‘normal’ 70-year-olds have glucose impairment, an association between peripheral neuropathy and glucose impairment may be meaningless,” Dr. Dyck said. “We have to decide if the association means anything before we decide whether to do anything about it.”

That said, he stressed that the connection between peripheral neuropathy and glucose impairment “is potentially exciting” and the work is “important.” But, Dr. Dyck said, “In my mind, it is still preliminary data. We need a population-based epidemiological study with good controls.”

Figure

Dr. P. James B. Dyck: “If by current standards, 50 percent of ‘normal’ 70-year-olds have glucose impairment, an association between peripheral neuropathy and glucose impairment may be meaningless. We have to decide if the association means anything before we decide whether to do anything about it.”

ARTICLE IN BRIEF

✓ A prospective analysis of data from the NIH-sponsored Diabetes Prevention Program reported that patients with impaired glucose tolerance and peripheral neuropathy experienced less pain after participating in a diet and exercise program.