Complex Regional Pain Syndrome (CRPS) refers to chronic pain in a limb following an injury to it. Arms, hands, legs, and feet are most affected by this disorder, and it is believed to be caused by injury to one of two nervous systems. The systems in question are the peripheral and central nervous systems. The central nervous system directly controls the body’s brain and spine. The peripheral system sends “messages” to the rest of the body from the central nervous system. Both systems can be adversely affected by disease in addition to mechanical injury.