Functional imaging of the brain has shown that the level of depression has little influence on the intensity of pain experienced by patients with the chronic pain syndrome fibromyalgia, researchers at the University of Michigan Health System and the University of Cologne, Germany, have found. This could be one of the reasons that an antidepressant that has no analgesic (pain-killing) properties may have little or no impact on a patient's pain.

Doctors often lump together the two conditions when they treat patients experiencing both of them. Some 30 to 54 percent of people with chronic pain also have a major depressive disorder, the article notes.

"There is an incorrect impression among many doctors that if you treat a patient’s depression, it will make their pain better. Not so," says Daniel J. Clauw, M.D., one of the authors of the paper. Clauw is director of the U-M Chronic Pain and Fatigue Research Center and professor of rheumatology at the U-M Medical School. "If someone has pain and depression, you have to treat both."

Independent Pathways

The study involved 33 women and 20 men with fibromyalgia, a type of chronic pain that affects several million people, more often in women than in men, and typically involves tenderness to the touch, stiffness and fatigue. In addition to those 53 patients, another 42 healthy companion participants were involved in the study.

The testing included a measurement of pain experienced by subjects based on their tolerance of pressure applied to their left thumbnails using a hard rubber probe. Researchers also conducted interviews and had the subjects fill out questionnaires.

Using functional MRI (fMRI) scans, researchers compared the subjects’ magnitude of pain, experimental pain sensitivity and symptoms of depression. The study was conducted at the Georgetown University Medical Center before Clauw and several colleagues moved to U-M.

Clauw and the other researchers found that in fibromyalgia patients, much less pressure was required to activate the neurons associated with acute pain in the brain’s sensory domain than among the healthy controls.

Clauw says that some other clinical research has supported the idea that pain and depression should be treated independently from one another. This, however, is the first time it has been shown using fMRI brain scans.

"We have seen that if you give antidepressants to the average patient with fibromyalgia, they'll come back a couple of months later and say, 'My pain isn’t any better, but I don’t feel so sad about it,'" Clauw says. "Our research provides further evidence that these pathways are quite independent."

Findings May Apply to Other Conditions

While this study looked at fibromyalgia patients, it is possible that the results may apply to people who have other chronic pain conditions, such as low-back pain, irritable bowel syndrome and vulvodynia, the researchers say.

The lead author of the study was Thorsten Giesecke, M.D., research fellow at the U-M Chronic Pain and Fatigue Research Center. In addition to Clauw and Giesecke, other others were Richard H. Gracely, Ph.D.; David A. Williams, Ph.D.; and Michael E. Geisser, Ph.D., all of the U-M Health System; and Frank W. Petzke, M.D., of the University of Cologne. Giesecke also is affiliated with the University of Cologne.

The research was supported by the Department of the Army and the National Institutes of Health, including a grant from the General Clinical Research Center Program of the National Center for Research Resources.

Clauw and his team at the U-M Chronic Pain and Fatigue Research Center also are working on studies of activity, exercise and pain among people with all kinds of chronic-pain conditions. They have started a registry of people who would be willing to take part in such studies, both those with chronic conditions and those without. For more information on the registry and the studies underway at U-M, visit http://www.med.umich.edu/painresearch or call 866-288-0046.