Complex regional pain syndrome (CRPS) is a chronic pain condition that usually affects an arm or a leg and can occur following an injury or other medical condition. CRPS typically develops after an injury, surgery, or trauma, but the exact cause is not completely understood. The condition is characterized by pain, swelling, redness, noticeable changes in temperature, and hypersensitivity, particularly to cold and touch. Symptoms may change over time and vary from person to person. Over time, the affected limb can become cold and pale, undergo skin and nail changes, as well as muscle spasms and tightening. Once these changes occur, the condition is often irreversible. CRPS occasionally may spread from its source to elsewhere in the body, such as the opposite limb.

CRPS occurs in two types, with similar signs and symptoms, but different causes. Type 1, also known as reflex sympathetic dystrophy (RSD), occurs after an illness or injury that didnt directly damage the nerves in the affected limb. About 90% of people with CRPS have type 1. Type 2, also known as causalgia, occurs after a specific nerve injury. Most CRPS illnesses are caused by damage to or improper function of the small peripheral C-fiber nerve fibers that carry pain messages to the brain. The peripheral nervous system involves nerve signaling from the brain and spinal cord to all other parts of the body. Excess nerve firing or signaling also triggers inflammation designed to promote healing and rest after injury.

There is no specific test to diagnose CRPS, and healthcare providers mainly diagnose it through a careful medical history, physical examination, and review of symptoms. Treatment for CRPS aims to relieve painful symptoms associated with the disorder and may include psychotherapy, physical therapy, and drug treatment, such as topical analgesics, narcotics, and other interventions to manage the pain[[6]](https://www.webmd.com/pain-management/complex-...