[Andy U]

reflex sympathetic dystrophy

[Eddie R]

RSD occurs when the part of the sympathetic (unconscious) nervous system that controls blood flow and sweat glands in the hand and arm is disturbed and becomes overactive. Burning pain, swelling, stiffness and discolouration of the hand or other extremities develop.Infection, pressure on a nerve, heart attack, stroke or surgery may trigger RSD, but it's usually brought on by injury. Even minor injuries can be responsible, but the pain tends to be greater than would be expected from the type of injury sustained.Often, the exact reason for RSD remains unknown.Not much of an answer but it's the best I've got.

[Dizzy Devil]

For me it was caused by a injury, and than I have surgery which made it speed up the onset of the RSD. It can be any time of injury like eddie said. Here is a web page that might help you understand more.