Knowledge Grows About Puzzling Disorder

It has only been two decades since fibromyalgia—a baffling mix of chronic pain throughout the body variously coupled with anxiety, depression, fatigue, insomnia, and difficulty thinking clearly—was officially recognized as an illness by the American College of Rheumatology (ACR).

The ACR developed research classification criteria for fibromyalgia that required not only a history of chronic widespread pain, but the physical finding of widespread pain points in the body.

Since then, scientists have made considerable progress toward understanding fibromyalgia and finding treatments for it.

"It is a familial disorder, so we do believe that there is a genetic component to it," Lesley Arnold, M.D., a professor of psychiatry at the University of Cincinnati who treats and researches fibromyalgia, said in an interview. "In addition, there are environmental influences, and studies suggest they are varied. It could be a viral infection, physical trauma, even emotional distress. Research is supporting a strong central nervous system component that largely becomes independent of more peripheral pain inputs.... It's as if a volume-control setting for pain is abnormally high in fibromyalgia."

Or to put it another way, such patients have an abnormally low pain threshold, I. Jon Russell, M.D., Ph.D., a San Antonio rheumatologist and fibromyalgia expert, told Psychiatric News. For example, if a subject with fibromyalgia and a healthy subject are exposed to a painful stimulus, neuroimaging shows that the same brain areas are activated in both subjects. But it takes much less of a painful stimulus to produce such activation in the subject with fibromyalgia than in the healthy subject.

The basic central nervous system mechanisms of fibromyalgia also include some neurochemical abnormalities, Russell continued. Whereas the metabolite levels of two neurotransmitters—serotonin and norepinephrine—are abnormally low in the spinal fluid of such patients, the level of substance P in their spinal fluid is abnormally high—about three times higher than in healthy individuals.

"Since substance P is a known amplifier of pain messaging, there is suspicion that elevated levels of it may be responsible for the patients' low pain threshold," he said. Moreover, "this elevation seems to be unique to people with fibromyalgia, because patients with some other painful conditions have been examined, and they don't exhibit such high levels."