Complex regional pain syndrome (CRPS) comprises two subtypes, depending on whether or not primary nerve injury is the main provocative component. Complex regional pain syndrome (CRPS) type 1, also known as reflex sympathetic dystrophy, is an uncommon syndrome of unknown etiology. It is characterized by symptoms of spontaneous and evoked neuropathic pain, with varied qualities such as burning, stabbing, and throbbing, as well as pain in response to nonpainful stimuli (allodynia) and pain out of proportion to stimulus (hyperalgesia). It is almost always accompanied by at least one of the following: tenderness, swelling, changes in skin color and temperature of a body part / extremity, abnormal sudomotor activity, limb hair changes, atrophy, or focal osteoporosis. There is a close association with sympathetic abnormalities, and this is often referred to as sympathetically maintained pain (SMP). There is usually a history of prior injury or surgery. CRPS type 1 is without clear nerve injury.

CRPS type 2, formerly called causalgia, has similar symptoms but with peripheral nerve injury as a major part of initiating the syndrome.