Despite assumptions to the contrary, people with Chronic fatigue syndrome - a mysterious illness for which there is no objective test or known cause - seem less likely than patients with other illnesses to respond to dummy “placebo” treatments, according to a research review.

Placebos are often used in clinical trials to gauge the true effectiveness of a given therapy. In such studies, a certain number of patients given the inactive treatment will nonetheless improve. It’s uncertain why this so-called placebo effect occurs, but it may in some cases arise from a patient’s expectation of a benefit.

Chronic fatigue syndrome or CFS is marked by persistent, unexplained fatigue and a range of other possible symptoms, including muscle and joint pain, headaches, problems with memory and concentration, and sleep disturbances.

Because the roots of CFS are unclear and its primary symptom of fatigue is subjective, it has been thought that it might have a strong mental component - and that patients with CFS may be particularly likely to improve after receiving a placebo.

But in the new study, an analysis of data culled from 29 studies, UK researchers found that less than 20 percent of patients with CFS responded to placebos, on average.

That compares with an estimated 30 percent of patients who have a response to placebo “treatment” for other disorders - including depression, digestive disorders, arthritis and chronic pain.

“In contrast with the conventional wisdom, the placebo response in CFS is low,” Dr. Hyong Jin Cho and colleagues at King’s College London report in the journal Psychosomatic Medicine.

The reasons for the low response, and the implications for CFS treatment, are not fully clear, according to Cho.

It may be “tempting” to say that the findings are evidence that the cause of CFS is physical rather psychological, Cho told Reuters Health, but that would go beyond the scope of the study.

“What we can say more conclusively,” Cho said, “is that the previously widely accepted idea about the placebo response in CFS doesn’t seem to be true, and CFS is indeed a complex illness.”

Perhaps most complex is the origin of CFS. Researchers do not know the extent to which physical factors, such as viral infection or immune system dysfunction, and psychological factors, such as depression, may contribute to the condition. And patients may often be at odds with their doctors about the cause and proper treatment of their symptoms.

Because CFS is difficult to treat, low patient expectations may help explain the relative lack of placebo effect across CFS studies, according to Cho’s team.

There is some evidence of this, the researchers note, in the fact that patients were more likely to show a placebo effect in trials targeting a potential physical factor - such as viral infection or immune function - than in trials that tested psychological therapies.

Many people with CFS are skeptical about psychological treatments for the illness, according to Cho’s team, and therefore may have low expectations of success going into such studies.

However, Cho pointed out, one of the two CFS therapies that have the best evidence right now is cognitive behavioral therapy, a form of psychological therapy that teaches patients to alter the thoughts and behaviors that seem to be contributing to their symptoms.

The other is graded exercise therapy, in which physical therapists help patients gradually increase their activity levels in order to boost their energy.

Improving patients’ expectations of benefit from these or other therapies, according to Cho, may make a difference in whether they find relief. Any treatment plan, the researcher noted, needs to be tailored to an individual’s symptoms, and a “collaborative therapeutic relationship” between doctors and patients may improve the odds of success.

SOURCE: Psychosomatic Medicine, March/April 2005.