Complex regional pain syndrome (CRPS), also known as reflex sympathetic dystrophy (RSD), describes an array of painful conditions that are characterized by a continuing (spontaneous and/or evoked) regional pain that is seemingly disproportionate in time or degree to the usual course of any known trauma or other lesion. Usually starting in a limb, it manifests as extreme pain, swelling, limited range of motion, and changes to the skin and bones. [Source: Wikipedia ]