a chronic progressive nerve condition, characterized by burning pain, swelling, stiffness, and discoloration of the affected extremity. If affects both men and women, usually around 40-60 and occurs weeks to months after a nerve inury. involves a complex interaction of sensory, motor, and autonomic nerves, as well as the immune system. Nerve injury may modify the usual pain pathway causing a neuropathic windup or short circuit mechanism. KEY FEATURE: typically innocuous stimulus can create a sever, intense painful response.