Cough suppressant may ease fibromyalgia pain

A medication normally used to quiet a stubborn cough may also help ease the chronic pain of fibromyalgia, a small study suggests.

Researchers found that the cough suppressant, dextromethorphan, temporarily diminished pain perception in both fibromyalgia patients and healthy adults. The benefit appears to stem from the fact that dextromethorphan blocks the action of a chemical messenger known as NMDA, which helps relay pain signals to the brain.But that doesn't mean people with fibromyalgia should start downing over-the-counter cough syrup, the researchers caution. "Like every medication, dextromethorphan has side effects," Dr. Roland Staud, the study's lead author, said in a statement. "At high doses, patients can have problems related to memory and confusion."Instead, the findings open the door to evaluating the effects of dextromethorphan on fibromyalgia and other conditions marked by heightened pain sensitivity, according to Staud, an associate professor of medicine at the University of Florida in Gainesville.They also cast doubt on one theory about the roots of fibromyalgia pain, Staud and his colleagues report in the Journal of Pain.Fibromyalgia is a disorder marked by widespread muscle pain and tenderness, fatigue and sleep problems. To be diagnosed with the condition, a person must have pain or tenderness in a number of specific "tender points" on the body.The cause of fibromyalgia is unknown, but researchers generally believe that people with the condition have "amplified" pain signals due to abnormal sensory processing in the central nervous system.One theory has held that fibromyalgia "wind-up" pain -- in which repeated touches create pain that intensifies with each new contact -- is caused by an abnormality in the spinal cord structures that process NMDA.But in the new study, dextromethorphan was as effective at easing pain in the 14 women with fibromyalgia as it was for 10 women without the condition.Since dextromethorphan acts on NMDA receptors, the findings suggest that people with fibromyalgia do not have a "radically altered" NMDA system, according to Staud's team.For the study, the women underwent two tests, in which either a heated probe or a rubber-tipped peg repeatedly tapped their hands until they said they felt a certain degree of pain. As expected, women with fibromyalgia had a lower threshold for pain. A single dose of dextromethorphan, however, reduced the women's pain response to the tests -- with women with fibromyalgia benefiting as much as those without the condition.According to Staud, dextromethorphan could eventually find a place in the repertoire of treatments for chronic pain."What this really means for chronic pain patients is that they need to use a whole host of different interventions to decrease the pain they have," he said. "And in this, dextromethorphan may have a role in the future."(Source: Journal of Pain: Reuters Health: June 2005.)