Complex regional pain syndrome (CRPS) is a chronic pain condition that mainly affects the arms, legs, hands, and feet, but may involve the entire body. CRPS symptoms often begin after surgery or an injury. The main feature of CRPS is continuous, intense pain that is out of proportion to the severity of the injury. The pain gets worse over time and often spreads throughout the entire affected area. Other symptoms may include color and temperature changes of the skin over the affected area; skin sensitivity; sweating; and swelling. The underlying cause of CRPS is often not known. Two classifications of CRPS have been recognized based on causalgia. Type I (also known as reflex sympathetic dystrophy), in which there is no evidence of peripheral nerve injury and Type II, in which peripheral nerve injury is present. Treatment aims to relieve pain and often includes different interventions such as topical or oral medications; physical therapy; and/or a sympathetic nerve block.