Causalgia is a rare pain syndrome related to partial peripheral nerve injuries. The peripheral nervous system encompasses nerves that extend from the central nervous system of the brain and spinal cord to serve limbs and organs. Severe cases are called major causalgia. Minor causalgia describes less severe forms, similar to reflex sympathetic dystrophy (RSD). RSD includes muscular and joint pain symptoms, and changes in bone density. Causalgia is usually caused by brachial plexus injuries, involving nerves that run from the neck to the arm. The disruption of neural signals causes pain and increased release of the neurotransmitter norepinephrine, which causes vascular symptoms.