Also called CPRS and previously referred to variously as causalgia, reflex sympathetic dystrophy, Sudeck's atrophy or shoulder-hand syndrome, this is a disorder involving constant burning pain within a region of the body not defined by the usual distribution of a particular nerve, so not attributable to a lesion of that nerve root. It is usually associated with abnormal sensation, motor strength or function, autonomic changes (such as sweating or skin colour) and trophic changes (such as abnormal hair or nail growth or thinning of the skin). It is generally provoked by an injury but the pain seems disproportionate to the severity or nature of the injury. Some patients recover (in one series 30 per cent within 5 years) but others have persisting problems, with many unable to resume work. There is little evidence for any particular treatment option being effective with both psychological assistance and drug therapy being used.