...or "CRAPS" as I like to pronounce it. This is a real, debilitating, and frustrating to treat syndrome, though it can be difficult to sort out from other chronic pain syndromes, including stuff with psychiatric overtones. I've seen a lot of it. Basically, you've got to look for a typical progression of stages (classically there are three), ranging from an "acute" form with rubor, calor, and dolor (think acute inflamation) on through a chronic stage of pallor along with skin appendage atrophy and coolness.
Various theories of the pathophysiology, but this is what I've learned clinically. Drugs and sympathetic blocks help, but the key to treating this syndrome is twofold: 1) Begin treatment as early as possible; and, 2) Physical manipulation and forced mobilization of the affected limb are needed to effect a cure. If the syndrome progresses to the chronic phase, it's very difficult to treat. Because of the pain, the patient naturally wants to guard the limb from painful movement. Guarding may be adaptive in other painful conditions, but not in this one. This is a neurological disorder where we really need to work with our colleagues in PT and OT.
Nick