Complex Regional Pain Syndrome (CRPS) is a chronic pain condition that typically affects a limb after an injury or surgery. It is characterized by severe pain, swelling, and changes in skin color and temperature. The pain is often disproportionate to the initial injury and can spread to other areas of the body. The exact cause of CRPS is not fully understood, but it is believed to involve abnormal responses of the nervous system and immune system. Treatment options may include physical therapy, medications, and sometimes nerve blocks to help manage symptoms and improve function.