A new study by researchers at the University of Michigan Health System sheds some light on one group of people that seems to experience the "placebo effect." The researchers found that people with one type of chronic pain who have greater swings in their pain fluctuations tend to be more likely to respond to placebos.
The study of people with fibromyalgia - a type of chronic pain affecting several million people that typically involves tenderness, stiffness and fatigue - appears in the current edition of the journal Arthritis & Rheumatism.
"There is substantial evidence that the placebo effect has strong biological underpinnings, and that some individuals are more likely than others to demonstrate this effect," says Daniel J. Clauw, M.D., director of the U-M Chronic Pain and Fatigue Research Center and professor of rheumatology at the U-M Medical School.
"This study suggests that individuals with greater hour-to-hour and day-to-day variability in their pain may be more likely to be placebo responders," says Clauw, senior author of the paper. "When such individuals are placed in clinical trials of new interventions, the strong placebo effect they experience can make it difficult to determine if there is a superimposed effect of the treatment being tested."
"This finding is important because so far, nobody has been able to fingerprint placebo responders," adds Richard A. Harris, Ph.D., lead author of the paper, research investigator in the Division of Rheumatology at the U-M Medical School's Department of Internal Medicine and a researcher at the Chronic Pain and Fatigue Research Center. "The research is helping us gain a better understanding of who responds to placebos. That's especially important to the research community as we design clinical trials."
It is not clear if these findings are only present in fibromyalgia, or may also be seen in other chronic pain conditions, the researchers said.
Each of the 125 participants in the study carried a Palm-based electronic diary and was prompted at random intervals to record his or her pain level. Participants were prompted on average about three and a half times per day.
The patients who were enrolled in a multicenter drug trial of the anti-depressant milnacipran versus a placebo. Some of the participants experienced a large range of pain variability, while others experienced pain at fairly constant levels.
Those whose pain levels varied widely were more likely to respond to the placebo. They were not, the researchers found, necessarily more likely to respond to milnacipran, which suggests that high pain variability may be a predictor of a placebo response.
"These results have direct implications for drug trials in fibromyalgia and perhaps broader implications for other pain syndromes," the researchers note.
The researchers also found that the electronic recording of pain levels was much more accurate than earlier pencil-and-paper recordings. The electronic system contained a time stamp when the participants recorded the data, removing some of the uncertainty and inaccuracy that often accompanied pencil-and-paper diaries.
Fibromyalgia is a common condition that affects 2 to 4 percent of the U.S. population and is more commonly diagnosed in women. Clauw and his colleagues at the Chronic Pain and Fatigue Research Center are conducting extensive research into the causes and treatments of fibromyalgia.
For more about the U-M Chronic Pain and Fatigue Research Center, go to www.med.umich.edu/painresearch. For more about other recent research at U-M related to pain and the placebo effect, go to www.med.umich.edu/opm/newspage/2005/placebo.htm.
In addition to Clauw and Harris, other authors of the study were David A. Williams, Ph.D., associate professor of psychiatry at the U-M Medical School, director of research development within the Center for the Advancement of Clinical Research at U-M and co-director of the Chronic Pain and Fatigue Research Center; Samuel A. McLean, M.D., lecturer in the Department of Emergency Medicine at the U-M Medical School; Ananda Sen, Ph.D., associate research scientist at the U-M Center for Statistical Consultation and Research; Richard H. Gracely, Ph.D., professor of internal medicine and neurology at the U-M Medical School and co-director of the Chronic Pain and Fatigue Research Center; Michael Hufford, Ph.D., of Amylin Pharmaceuticals, San Diego, Calif.; and R. Michael Gendreau, M.D., of Cypress Bioscience, San Diego, Calif.
The research was supported by Cypress Bioscience. Grants from the National Institutes of Health supported Harris's and McLean's work.
Hufford has received consulting fees or honoraria of more than $10,000 a year from invivodata and owns stock in invivodata, creator of the Palm-based electronic diary. Clauw is chairman of the FMS Scientific Advisory Board at Cypress.
Citation: Arthritis & Rheumatism, Vol. 52, No. 11, Nov. 2005, pages 3670-3674.