What's missing from the review itself, he and others noted, is the “consistent” evidence of altered neuroendocrine function in patients with FM.
Dr. Robert Bennett, who has led studies in this area, said that FM also appears to be a manifestation of an abnormal acute stress response involving abnormalities in levels of cortisol and growth hormone, an imbalance in sympathetic and vagal tone, and other phenomena–a notion that puts FM at least partly in the same camp, for underlying mechanisms, as chronic fatigue syndrome.
“The major things we know now [about FM] relate to the pain system,” said Dr. Bennett, professor of medicine at Oregon Health and Science University, Portland. “The neuroendocrine abnormalities–the manifestations of the acute stress response–have still, I think, been underinvestigated.”
Dr. Klimas, director of the University of Miami's chronic fatigue syndrome research center, said that more than 60% of her patients with the syndrome meet the case definition of FM as well, which reflects at least in part the fact that the FM definition is looser and more inclusive while the chronic fatigue syndrome definition has many exclusionary criteria.
Dr. Bradley added that a number of recent studies have also shown a familial aggregation of pain sensitivity. The studies show that first-degree relatives of patients with FM tend to have the “same sorts of unusual sensitivities to pain and abnormal pain responses,” even though this isn't always manifested as FM.