Complex regional pain syndrome (CRPS) and reflex sympathetic dystrophy (RSD) are the same thing. RSD is the old term used for the problem. It's been updated now to CRPS based on research in the last 10 years. The change came about in naming this condition when researchers were able to identify the problem a little more clearly.
Dr. S. W. Mitchell first reported CRPS in 1872. Back then it was called causalgia from burning pain in wounded soldiers. Symptoms of intense pain, swelling, and skin changes were common. Less involved injuries got the label reflex sympathetic dystrophy.
A similar problem called shoulder-hand syndrome was identified after heart attacks. Years ago anyone who had a heart attack was treated by six weeks of bed rest. There is a known connection between the heart and shoulder. The enforced immobility fired up those connections resulting in shoulder pain, loss of motion, and symptoms in the arm and hand.
New efforts are being made to understand this complex syndrome. Finding out what causes it will be a big step toward finding better ways to treat it and perhaps even prevent it from happening.