ABSTRACT
INTRODUCTION The fibromyalgia syndrome (FMS) is widespread, representing the second, most common disorder seen by rheumatologists and affecting between 2% and 4% of the U.S. adult population (1,2). Prevalence estimates vary in part because of some uncertainty in criteria used to diagnose the condition, despite the widespread acceptance of criteria promulgated by the American College of Rheumatology (ACR) almost 20 years ago (3). In part, estimates vary because FMS commonly co-occurs with other health conditions, further complicating its diagnosis (4). While there can be multiple precipitants for FMS and its mechanisms remain unclear (5), there is increasing evidence that FMS reflects a disorder of central nervous system processing, rather than abnormalities of muscle or other soft tissues (6-8). Although the specific mechanisms remain unclear, there now is a general agreement that it is a bona fide diagnostic entity, generally characterized by the ACR criteria.
