CHICAGO (AP) - Research on chronic fatigue syndrome indicates that behavior-based therapies, including exercise, may be among the most effective treatments, but data are deficient and scarce, a review suggests.

While evidence on medications is less conclusive than behavioral approaches, research into treatments has been hampered by a lack of consensus on what causes the disease and even who is afflicted with it, according to the review.

The review, which evaluated 44 studies from 1986 through last year, appears in Wednesday's Journal of the American Medical Association.

A JAMA editorial said the review may be interpreted as confirming the bias that chronic fatigue syndrome is psychological in nature.

But Dr. Anthony Komaroff, a professor of medicine at Harvard University medical school, noted that behavioral therapy also has been used to treat physical illnesses such as heart disease and multiple sclerosis.

"It helps people cope with the illness, but it's not curative," said Komaroff, who was not involved in the review. "In order to come up with really good treatments, you need to understand more about the causes."

Once given the misnomer "yuppie flu," chronic fatigue syndrome is a complex, hard-to-diagnose illness. It involves persistent, debilitating fatigue that renders many patients bedridden. Any variety of other symptoms are also usually present, including memory problems, depression and flu-like signs such as fever, chills and joint pain.

About 800,000 U.S. adults are believed to have CFS; women, Hispanics and blacks are disproportionately affected.

Abnormalities in the body's disease-fighting immune system have been found in many patients, and some researchers think viruses or defects in the body's ability to regulate blood pressure can trigger the disease. The diagnosis is generally made by excluding other illnesses.

The studies in the JAMA review generally showed mixed results, and most treatments have been evaluated in only one or two studies, said lead author Penny Whiting of the University of York in England and colleagues.

What is called cognitive behavioral therapy - counseling in coping strategies such as stress management - and a program of gradually increasing exercise showed the most promising results.

Whiting said more limited benefits were found with drugs designed to stimulate the immune system and steroids such as hydrocortisone, used to treat deficiencies in production of cortisol, a hormone involved in immune system function.

The editorial author, Dr. Simon Wessely of Guy's King and St. Thomas's School of Medicine and Institute of Psychiatry in London, said the review underscores the need for better research and more coordination among researchers.

Kim Kenney, president of the Chronic Fatigue and Immune Dysfunction Syndrome Association advocacy group, said the variability of the symptoms "makes it a difficult field to attract" researchers to, and makes it hard to standardize research methods.

The review should help "in terms of pointing to some of the things that might make future studies more sound," Kenney said.

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