Researchers may have discovered why powerful opioid based pain medications seem to have little effect in fibromyalgia patients.
Fibromyalgia is an extremely dibilitating condition in which patients experience pain and tenderness in soft tissues all over their bodies, particularly in specific areas known as 'tender points'. The reasons for this pain have been hard to pin down which has led to a certain amount of scepticism about the condition, even amongst doctors.
New research may now have identified a mechanism behind the pain that also explains the widely accepted observation that opioid pain killing drugs don't work for fibromyalgia pain.Researchers from the University of Michigan Health System discovered that in patients with fibromyalgia, receptors that bind with opioids in the brain are less able to do so than in healthy individuals. As a result of this opioid drugs such as morphine, codeine, Vicodin, and Oxycontin, which are normally very powerful pain killers, have a much reduced effect in fibromyalgia patients.
The researchers used various techniques to uncover this important finding. The study included conducting positron emission tomography (PET) scans of the brains of patients with fibromyalgia, and of an equal number healthy control subject who were matched for age and gender. Results of these scans showed that the fibromyalgia patients had reduced mu-opioid receptor (MOR) availability within specific regions of the brain that are involved with processing and dampening pain signals -- specifically, the nucleus accumbens, the anterior cingulate and the amygdala.
Fibromyalgia patients have frequently reported that opioid medications don't seem to work for them and this is something that doctors have come to accept. Opioid medications were notably absent from the recent fibromyalgia treatment recommendations published by The European League Against Rheumatism (EULAR). EULAR is an organization representing patients, healthcare professionals, and scientific bodies concerned with rheumatic conditions throughout Europe. This is the first research however that offers and explanation for this.
"When the painkillers cannot bind to the receptors, they cannot alleviate the patient's pain as effectively, Harris says. The reduced availability of the receptors could result from a reduced number of opioid receptors, enhanced release of endogenous opioids (opioids, such as endorphins, that are produced naturally by the body), or both" said Richard E. Harris, Ph.D. Harris, from the Division of Rheumatology at the U-M Medical School's Department of Internal Medicine and a researcher at the U-M Chronic Pain and Fatigue Research Center, was lead researcher on the study.
As well as an explanation for the failure of certain drugs in fibromyalgia patients, these findings may help to explain the pain of fibromyalgia itself. The pain being experienced could be due to this dysregulation of the mu-opioid receptor. Further research will be needed to determine what exactly is going on however.
Source: The Journal of Neuroscience, Sept. 12, 2007, 27(37):10000-10006
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