Why painkillers may not work in fibromyalgia

NEW YORK (Reuters Health) - People who suffer from a common chronic pain condition called fibromyalgia often report that they don't respond to the types of medications that relieve other people's pain. Results of a new study suggest why that may be.

According to the study published in the Journal of Neuroscience, patients with fibromyalgia have reduced binding ability of a type of receptor in the brain that is the target for opioid painkiller drugs such as codeine. When the painkillers cannot bind to the receptors, they cannot alleviate the patient's pain as effectively.

This research is significant, Dr. Richard E. Harris of University of Michigan, Ann Arbor, noted in a written 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."

In the study, Harris and colleagues performed positron emission tomography scans on 17 fibromyalgia patients and 17 age- and sex-matched healthy pain-free controls.

Results showed that the fibromyalgia patients, relative to healthy controls, displayed reduced binding availability of the mu-opioid receptor within 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," Harris said.

"One implication of this finding is that opiate drugs would not be very effective at reducing pain in these patients," he added.

SOURCE: Journal of Neuroscience, September 2007.