Concepts of illness in populations as applied to fibromyalgia syndromes.

Fibromyalgia syndromes are common noninflammatory, painful musculoskeletal disorders that vary in the extent and intensity of involvement. The biologic gradient of musculoskeletal pain varies from no or few symptoms and tender points in the majority of persons to generalized fibromyalgia with multiple tender points. Standardized criteria are needed in order to categorize different strata of the biologic gradient of fibromyalgia syndromes and differentiate them from other conditions. Both the sensitivity and specificity of criteria should be high. The course and prognosis of fibromyalgia syndromes are not yet known. Limited clinical data suggest three basic patterns: remitting-intermittent; fluctuating-continuing; and progressive. However, course patterns need to be derived scientifically. Multiple host and environmental factors seem to contribute to the onset and course of fibromyalgia syndromes, and these require definition. Generalized fibromyalgia syndromes share many constitutional manifestations with other common functional disorders, e.g., irritable bowel syndrome and tension headache syndrome, which suggest common underlying psychoneurophysiologic mechanisms in a subset of patients. Progress made in fibromyalgia research will find application in many dysfunctional syndromes without obvious organ pathology.