Last Updated: 2007-10-26 16:53:46 -0400 (Reuters Health)
NEW YORK (Reuters Health) – Fibromyalgia patients have reduced central mu-opioid receptor availability in regions of the brain known to modulate pain sensation, a study shows. The finding may explain anecdotal reports of reduced efficacy of opioids analgesics in fibromyalgia patients.
"The underlying neurophysiology of acute pain is fairly well characterized, whereas the central mechanisms operative in chronic pain states are less well understood," Dr. Richard E. Harris and colleagues at the University of Michigan, Ann Arbor and colleagues point out in a report in the September issue of The Journal of Neuroscience.
In their study, 17 fibromyalgia patients and 17 age- and sex-matched healthy controls underwent positron emission tomography using a selective mu-opioid receptor radiotracer.
Results showed that the fibromyalgia patients, compared with the healthy controls, displayed reduced mu-opioid receptor binding availability within the nucleus accumbens, the amygdala, and the anterior cingulate — regions of the brain that normally process and dampen pain signals.
The decreased availability of the mu-opioid receptor was more pronounced in patients reporting more pain and "may be due to fibromyalgia patients having fewer receptors and/or enhanced release of endogenous opioids," Dr. Harris said.
"One implication of this finding is that opiate drugs would not be very effective at reducing pain in these patients," he added.
This research is significant, Dr. Harris noted in a statement, "because it has been difficult to determine the causes of pain in patients with fibromyalgia, to the point that acceptance of the condition by medical practitioners has been slow."
J Neurosci 2007;27:10000-10006.