While the separate treatment of concurrent depression and chronic pain is not new, evidence for a treatment regimen has been based largely on clinical research. Now American and German researchers have used brain imaging to confirm that when depression and chronic pain occur together, they should be treated independently because sensory pain and affective pain are processed along parallel, virtually independent pain-processing networks.

This is believed to be the first proof of the independence of pain and depression shown by brain scans and may explain why medications used to treat depression might not help in the management of pain. It is estimated that some 30 percent to 54 percent of people with chronic pain also have a major depressive disorder.

Using functional magnetic resonance imaging (fMRI) of the brain, researchers at the University of Michigan Health System and the University of Cologne in Germany found that the presence or severity of depression in patients who also have fibromyalgia does not appear to be related to the intensity of pain they experience from fibromyalgia. However, the depression does appear to be associated with the extent to which two brain regions involved in emotional responses are activated—the anterior insula and the amygdala. As depression becomes more severe, there are substantial increases in blood flow in areas of the brain that code for the" affective" and "cognitive" aspects of pain.

While the researchers studied only fibromyalgia patients, they reported in the May Arthritis and Rheumatism that the findings may apply to people who have other chronic pain conditions, such as low-back pain, irritable bowel syndrome, and vulvodynia.

"There is an incorrect impression among many doctors that if you treat a patient's depression, it will make their pain better. Not so," Daniel Clauw, M.D., one of the study's researchers, told Psychiatric News. Clauw is director of the University of Michigan Chronic Pain and Fatigue Research Center and a professor of rheumatology at the University of Michigan Medical School. "If someone is diagnosed with pain and depression, you have to treat both," he added.

The study involved 33 women and 20 men with fibromyalgia, a chronic pain that affects several million people. It afflicts more women than men and typically involves tenderness to the touch, stiffness, and fatigue. There were 42 healthy control subjects 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. Subjects were interviewed and filled out a questionnaire that assessed depression symptoms. Functional MRI scans were used to compare the subjects' magnitude of pain, experimental pain sensitivity, and symptoms of depression.

The main finding was that fibromyalgia patients needed much less pressure to activate neurons associated with acute pain in the brain's sensory domain than the healthy controls.

"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 said.

The lead author of the study was Thorsten Giesecke, M.D., a research fellow at the University of Michigan Chronic Pain and Fatigue Research Center.

The research was funded 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.

Clauw and his team at the 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 willing to take part in such studies, both those with chronic conditions and those without.

An abstract of "The Relationship Between Depression, Clinical Pain, and Experimental Pain in a Chronic Pain Cohort" is posted online at<www3.interscience.wiley.com/cgi-bin/abstract/110489315/ABSTRACT>. More information about the registry and the studies at Michigan are posted online at<www.med.umich.edu/painresearch> or available by phone at (866) 288-0046. ▪