This medical illustration series pictures Reflex Sympathetic Dystrophy (RSD) of the upper extremity. Another term for this condition is Complex Regional Pain Syndrome, or CRPS. The cycle of pain is shown initiating from an injury to the elbow. Impulses are shown traveling to the brain and then down the sympathetic chain to the original site of injury producing inflammation, blood vessel spasm, pain and swelling. The condition is treated with a nerve block to the cervical and thoracic spine.