Toward an integrated understanding of fibromyalgia syndrome. I. Medical and pathophysiological aspects

&NA; Fibromyalgia syndrome (FS) is a chronic pain disorder characterized by diffuse musculoskeletal soreness, stiffness, non‐restorative sleep and psychological disturbance. At present, much about the etiology, pathological mechanisms and course of FS are unknown. Indeed, standardized diagnostic criteria have only been recently agreed upon. The present paper is the first of a two‐part series which reviews the extant empirical literature concerning FS, with a view to arriving at an integrated understanding of the syndrome. The present paper describes the clinical presentation of FS and historical conceptualizations of the disorder. Available research on pathophysiological mechanisms in FS is then presented. In this section we have included literature concerning histology of muscle, sleep architecture, neurotransmitter anomalies and neuropeptide involvement in FS symptomatology.