Complex regional pain syndrome (CRPS) is a syndrome that has been around for many years but has not always been recognized or diagnosed properly. It has been found as far back as the American Civil War but it was only in 1993 that the umbrella term, CRPS, was decided upon for consistent use.
CRPS is not understood yet. It occurs usually after a trauma to a limb, but it doesn't have to be severe, it can be just a sprain or a strain. Symptoms of CRPS are pain, skin temperature changes at the site, change in skin color, and abnormal muscle weakness.