Although pain is characterized in many ways, some diagnoses are not so obvious. One such diagnosis is complex regional pain syndrome (CRPS), formerly called reflex sympathetic dystrophy (RSD). This is a disease that is characterized by varying degrees of pain and autonomic disturbances that are reflected in changes of the skin, temperature, color and swelling. Other trophic changes affecting the skin, hair and nail growth also occur beneath the skin and interfere with function of the muscles, joints and bones. While all of these may not be present at one time, their overall effect is to interfere with the recovery of function and treatment. While this disease usually develops after an injury or surgical trauma to the limbs, the name RSD was changed to reflect a better understanding of the painful disorder and to prevent inappropriate treatment directed to the sympathetic nervous system when, in many cases, this system is not involved in the disease process.
Recent evidence has led to the conclusion that Complex Regional Pain Syndrome is a multifactorial disorder with clinical features of neurogenic inflammation, nociceptive sensitisation (which causes extreme sensitivity or allodynia), vasomotor dysfunction, and maladaptive neuroplasticity, generated by an aberrant response to tissue injury. Treatment is complicated, involving drugs, physical therapy, psychologic treatments and neuromodulation and usually unsatisfactory, especially if begun late.