CRPS(Complex regional pain syndrome ) is a term used to describe a group of painful conditions. The cause of Complex regional pain syndrome (CRPS) is not well understood. CRPS is a reaction the body has after an injury, and the reaction is more severe than would be expected. This reaction happens in the limb and in the brain. The nerves and skin in the arm or leg are affected and so are the nerves in the brain. Click here for more about:- Complex Regional Pain Syndrome - Causes, Treatment and Therapies.