FMRI shows evidence of fibromyalgia patients' pain
Faulty central nervous system functions, not musculoskeletal problems, may be the root of fibromyalgia pain, according to a new imaging study.
Functional MR images suggest that the brains in fibromyalgia patients show activation associated with high pain levels in response to stimulus that most would regard as a light touch. The study was performed at Georgetown University Medical Center and the National Institutes of Health.
"We wanted to determine whether the pain in fibromyalgia was more of a perceptual problem, or whether there was neurobiological evidence of abnormal pain processing in the central nervous system in these patients," said researcher Dr. Daniel J. Clauw, director of the Chronic Pain and Fatigue Research Center at the University of Michigan. "We found the latter to be true."
Along with 16 control patients, the study assessed 16 nondepressed, right-handed patients who met the 1990 American College of Rheumatology fibromyalgia criteria. They stopped taking analgesics 12 hours before psychophysical and fMRI evaluation. Patients receiving opioid medications were excluded.
The study was designed to determine if the pattern of brain activation in fibromyalgia patients matched either that produced by low-stimulus physical pressures or that produced by significantly greater -- and more painful -- pressures in the control group.
FMRI following low-stimulus pressure showed higher activation in 13 areas of the brain in fibromyalgia patients compared with controls. In contrast, stimulus pressures resulted in higher activation in only one region of the controls' brains, located in the ipsilateral medial frontal gyrus.
Functional imaging confirmed that in fibromyalgia patients, mild pressure produced subjective pain reports and cerebral responses that were qualitatively and quantitatively similar to many of the effects produced by application of at least twice the pressure in control subjects. The study was sponsored by the National Fibromyalgia Research Association, the U.S. Army, and the NIH. It was published in the May issue of Arthritis and Rheumatism.
Many chronic pain states characterized as musculoskeletal conditions, by virtue of the fact that pain is felt in peripheral tissues, may be caused in part by an abnormality in the way the central nervous system processes the pain, according to Clauw. The results of the study may shed a different light on fibromyalgia, which has traditionally been characterized as a musculoskeletal condition. The mechanisms working in the brain and the nervous system that cause the pain remain unknown.
Functional imaging is useful only as a research tool, not to diagnose individual patients, and it does not have direct implications for treatment of fibromyalgia, Clauw said.
"Perhaps it adds further evidence that this is a central nervous system problem and that treatments that act upon the central nervous system are most likely to be effective," he said.
