This is a chronic form of pain that is uncommon and most often affects a leg or an arm. This syndrome, also known as Complex Regional Pain Syndrome, usually develops after one has had a stroke, heart attack, surgery, or injury; however, the pain is not in proportion to how severe the injury was, if there was an injury. The cause of this syndrome is not understood clearly. Those who suffer from complex regional pain syndrome seem to get the most out of treatment when treatment is started as early as possible. When this happens it can be possible to see improvement and in some cases even remission.