Reflex sympathetic dystrophy syndrome (RSD) is a disorder that causes lasting pain, usually in an arm or leg, and it shows up after an injury, stroke, or even heart attack. But the severity of pain is typically worse than the original injury itself. Doctors don’t know exactly what causes it, but they are able to treat many cases.

The term reflex sympathetic dystrophy syndrome is actually not a name that doctors use anymore. It’s an older term used to describe one form of Complex Regional Pain Syndrome (CRPS). RSD is sometimes called Type I CRPS, and it’s caused by injury to tissue with no related nerve damage.