Opioid Resistance in Fibromyalgia Explained by Receptor Function

ANN ARBOR, Mich., Sept. 27 -- The reason that opioids seem to fizzle for fibromyalgia may be because of reduced receptor activity in regions of the brain that process and dampen pain signals, researchers here found.

Reduced -opioid receptor-binding potential in fibromyalgia patients was also significantly correlated with depression and emotional components of pain, reported Richard E. Harris, Ph.D., of the University of Michigan, and colleagues, in the Sept. 12 issue of the Journal of Neuroscience.

"Because these receptors are the target of opiate drugs," they wrote, "a profound reduction in the concentration or function of these receptors is consistent with a poor response of fibromyalgia patients to this class of analgesics, observed anecdotally in clinical settings."

The researchers used PET with a selective -opioid receptor radiotracer to assess receptor availability differences between fibromyalgia patients and healthy pain-free individuals.

Their study included 17 right-handed women with fibromyalgia (mean age 44.8, mean diagnosis duration 8.4 years) and 17 age- and sex-matched healthy controls who were part of an ongoing study of acupuncture treatment. The analysis was done on PET scans and other data collected at baseline.

No participants were taking opioids or had a history of their use. Of the 17 fibromyalgia patients, 10 were taking antidepressant medication, either serotonin reuptake inhibitors or dual serotonin/norepinephrine reuptake inhibitors.

The women reported "sensory" and "affective" characteristics of their pain on the Short Form of the McGill Pain Questionnaire immediately prior to undergoing the PET scan.

Depressive symptoms were self-reported on the Center for Epidemiological Studies-Depression Scale, which is used to detect major or clinical depression.

The PET scans showed significantly less opioid receptor-binding potential overall in fibromyalgia patients than in controls (P

The relative amount of emotional versus sensory pain varied between patients in correlation with differences in opioid receptor binding in the dorsal anterior cingulate (P