When you sprain an ankle, first you feel a sharp electric pain, and then you feel a burning pain. The sharp pain comes from the fast sensory pain fiber, and the slow onset, longer lasting burning pain is transmitted by the sympathetic nerve fiber. Normally, the burning pain stops over time. If it does not, you may have something referred to as reflex sympathetic dystrophy (RSD)-also called chronic regional pain syndrome (CRPS).
What is RSD?
RSD is a chronic pain syndrome of the sympathetic nervous system. It usually follows an identifiable event, such as a fracture, torn ligament or crush injury. There are different levels of sympathetic pain and RSD/CRPS is classically reserved for the most severe forms but both erms are used loosely to help describe a wide array of cold or weather sensitive pain syndromes.