Reflex sympathetic dystrophy (RSD) is a condition of severe localized pain. We have known about this syndrome since the 19th century when it was called causalgia. Over the years this syndrome has changed names. RSD is also known as Complex Regional Pain Syndrome Type 1.
A person with CRPS often has had a major stressful event like trauma, infection, sprain, emotional stress, surgery or a similar event which is very hard on the body. The body's nervous system reacts by causing the body to keep sending pain signals to the brain. Your brain then interprets these signals as ongoing pain which triggers a pain cycle. Most people have pain in their arms or legs but almost any body part can be affected.