Fibromyalgia patients may benefit from cough remedy

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University of Florida

20.05.2005

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Fibromyalgia patients may benefit from cough remedy

Dextromethorphan, an over-the-counter medication that silences

coughs, may help fibromyalgia patients quiet over-reacting nerves

that amplify ordinary touches into agony.

A University of Florida study documents, for the first time, that

dextromethorphan temporarily reduces the intensity of fibromyalgia

" wind-up, " a snowballing pain response to minor, repetitive physical

contact. The discovery, described in the May issue of The Journal of

Pain, also enables researchers to rule out one suspected cause of the

phenomenon.

Fibromyalgia is an incurable illness that causes widespread muscle

aches, stiffness, fatigue and sleep disturbances, according to the

National Fibromyalgia Association. An estimated 10 million Americans

suffer from the condition, most of them women. Current treatment

strategies include pain medication, exercise, stretching, sleep

management and psychological support.

Though the UF study did not establish guidelines for using

dextromethorphan clinically, it suggests the drug may eventually be

an option for treating fibromyalgia and other conditions involving

heightened pain sensitivity, said rheumatology expert Roland Staud,

M.D., a UF associate professor of medicine and the study’s principal

author.

" I think it’s one piece of the mosaic, " Staud said. " We currently

have no single therapy in chronic pain that has a big effect. So 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. And in this, dextromethorphan may have a role in the future. "

Dextromethorphan is popular in cold remedies because it elevates the

threshold for the coughing reflex but does not cause physical

addiction, according to the U.S. Drug Enforcement Administration.

But fibromyalgia patients should not resort to self-medicating by

taking cough syrups for pain, Staud cautioned.

" Like every medication, dextromethorphan has side effects, " he 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, said Staud,

who is affiliated with UF’s McKnight Brain Institute.

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, he

said. A normal form of achy, lingering pain known as secondary pain

affects anyone who suffers an injury.

The UF researchers - Staud, neuroscientist Vierck, Ph.D.,

psychologist , Ph.D., and Price, Ph.D. - were

surprised to learn that dextromethorphan eased fibromyalgia patients’

wind-up pain to the same degree it soothed secondary pain induced in

healthy volunteers, Staud said. The results indicate a long-suspected

cause of wind-up may not exist.

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, Staud said.

" This has refocused much of our research now, " he said. Future UF

studies will attempt to pinpoint where the pain impulses are

originating.

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 a capsule containing 60

milligrams of dextromethorphan, 90 milligrams of dextromethorphan or

a placebo containing none of the drug, and asked them to rate the

amount of pain they experienced when the stimulation was repeated.

With the heat stimulus, 90 milligrams of dextromethorphan reduced

wind-up pain, but 60 milligrams was no more effective than the

placebo. With the pressure stimulus, 90 milligram and 60 milligram

doses were equally effective, reducing wind-up pain.

The UF study indicates the need for further research on

dextromethorphan, said fibromyalgia expert ce Bradley, Ph.D., a

professor of medicine with the University of Alabama at Birmingham’s

division of clinical rheumatology and immunology.

" This is a topic that’s actually received very little attention so

far in the literature, " Bradley said. " It would be a disservice to

start to recommend that either patients or physicians begin

experimenting right away with dextromethorphan, because I think

there’s some important questions about how to minimize the side

effects with this agent. "

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More information:

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