Complex regional pain syndrome: redefining reflex sympathetic dystrophy and causalgia.

Complex regional pain syndrome (CRPS) is the new nomenclature that encompasses the older diagnostic entities of reflex sympathetic dystrophy (now CRPS 1) and causalgia (CRPS 2). CRPS arises after injuries such as sprains, strains, or fractures, but in some patients the cause is unknown. Although a perennial suspect in the pathogenesis of this entity, the sympathetic nervous system's role in CRPS remains unclear. New studies provide insight into the contribution of the sympathetic nervous system to CRPS and allow reevaluation of clinical features, diagnostic criteria, testing methods, and treatment modalities.