Complex regional pain syndrome (CRPS) is a chronic condition characterized by severe burning pain, pathological changes in bone and skin, excessive sweating, tissue swelling, and extreme sensitivity to touch. The syndrome is a nerve disorder that occurs at the site of an injury (most often to the arms or legs). It occurs especially after injuries from high-velocity impacts such as those from bullets or shrapnel. However, it may occur without apparent injury. One visible sign of CRPS near the site of injury is warm, shiny red skin that later becomes cool and bluish.The pain that patients report is out of proportion to the severity of the injury and gets worse, rather than better, over time. Eventually the joints become stiff from disuse, and the skin, muscles, and bone atrophy.