Dextromethorphan, an antitussive used to relieve a nonproductive cough caused by a cold, the flu, or other conditions, may help fibromyalgia patients.

Researchers at University of Florida showed, for the first time, that Dextromethorphan temporarily reduces the intensity of fibromyalgia " wind-up.”

Fibromyalgia is an incurable illness that causes widespread muscle aches, stiffness, fatigue and sleep disturbances.
An estimated 10 million Americans suffer from the condition, most of them women.

Dextromethorphan is popular in cold remedies because it elevates the threshold for the coughing reflex but does not cause physical addiction.

" Like every medication, Dextromethorphan has side effects," Roland Staud, of University of Florida, said. " At high doses, patients can have problems related to memory and confusion. "

The underlying cause of fibromyalgia remains unknown, but in the past 25 years substantial progress has been made toward understanding the mechanisms behind specific features of fibromyalgia, Staud said.
One is central sensitization, a feature of many chronic pain conditions in which the central nervous system - the brain and spinal cord - somehow magnifies pain signals to abnormally high levels.
Central sensitization is associated with wind-up, a phenomenon in which repeated touches - even handshakes or pats on the back - generate lingering pain that increases with each new contact.

Previous studies at other institutions had shown that Dextromethorphan blocks the action of a chemical messenger called N-methyl-D-aspartate, or NMDA, which relays pain impulses in the spinal cord.
Many fibromyalgia researchers have theorized that wind-up is caused by abnormalities in the spinal-cord structures that process NMDA.

The UF results suggest those structures function normally but that pain impulses are more amplified in fibromyalgia than in healthy participants.

In the current study, researchers worked with 14 women with fibromyalgia and 10 women who did not have the disease, using mechanical devices that tapped the participants' hands repeatedly.
One part of the study involved contact with a heated probe, the other used a small rubber-tipped peg.
The intensity of the heat or pressure of the stimulation was individually adjusted so that all participants reported feeling the same degree of pain.

Researchers then gave each participant 60 mg of Dextromethorphan, 90 mg of Dextromethorphan or placebo, and asked them to rate the amount of pain they experienced when the stimulation was repeated.

With the heat stimulus, 90 mg of Dextromethorphan reduced wind-up pain, but 60 mg was no more effective than the placebo.
With the pressure stimulus, 90 mg and 60 mg doses were equally effective, reducing wind-up pain.

Source: Journal of Pain, 2005


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