NEW YORK (Reuters Health) - Brain scans of people with fibromyalgia offer the first hard evidence of what patients already know: Their pain is real and their threshold for tolerating it is substantially lower than that of most individuals.

"When patients with fibromyalgia tell us that they're tender, that they're experiencing pain at a much lower level than people without the condition, they are in fact experiencing that pain," said Dr. Daniel Clauw, a professor of medicine at the University of Michigan Medical Center in Ann Arbor.

"This is the first neurobiological evidence of the veracity of their pain," he told Reuters Health.

Fibromyalgia affects an estimated 2% to 4% of the population, mostly women. Patients commonly report feeling tenderness, stiffness and sometimes unbearable pain in various areas of the body. They also may suffer from fatigue, depression and gastrointestinal problems. Some doctors without expertise in fibromyalgia have dismissed patients' complaints because there have been no documented physical signs of the disorder.

"I hope this study helps convince physicians that this is a real condition," Clauw said.

In the new report, published in a recent issue of Arthritis & Rheumatism, Clauw and colleagues studied 16 people who had been diagnosed with fibromyalgia and 16 healthy people who had not (the "control" group). All underwent a type of detailed brain scan known as functional magnetic resonance imaging (fMRI) while an instrument intermittently applied different levels of pressure to their left thumbnail.

When all study participants received the same level of mild pressure, blood flow increased much more in the brains of patients with fibromyalgia than among those in the control group. The increased blood flow--which is a "surrogate measure" for nerve activity--occurred in areas of the brain known to be associated with pain, Clauw noted.

In addition, when study participants were subjected to different levels of pressure, fibromyalgia patients reported pain at half the level of pressure that caused the same feelings of pain among the healthy controls, results showed.

Clauw said the findings suggest that something is awry with the way the central nervous system processes painful stimuli in fibromyalgia patients. Future research should be aimed at identifying the problem and working to develop better treatments, he added.

SOURCE: Arthritis & Rheumatism 2002;46:1333-1343.

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