Complex Regional Pain refers to pain in one or more limbs which occurs in a number of different situations, but especially after physical injury including burns. It can be triggered by other things including minor soft tissue problems like carpal tunnel syndrome.
Complex Regional Pain (CRPS) used to be called Reflex Sympathetic Dystrophy, but it is not called this any more because it is now know that it is not just the sympathetic nervous system that is disrupted in this condition.
CRPS type 1 occurs in the absence of any nerve injury. CRPS type 2 is defined as the same syndrome arising in a patient who has had a nerve injury
CRPS type 1 has been defined in the following way by the International Association for the Study of Pain (see below for an explanation of some of the jargon)
Some people develop pain in a limb without much in the way of swelling or colour change and there is ongoing debate about whether these patients have CRPS or not. If they don't, then they have something very similar which probably demands similar kinds of treatment
CRPS is a complicated subject hard to do justice to on this page. For a general background to the topic including a discussion of the various unresolved issues to do with complex regional pain I would suggest downloading the article above.
Some people reading this will wonder what CRPS is doing on a website for patients with functional symptoms. The reason for this is that it is
1. A disabling but genuine neurological condition which occurs in the absence of easily definable structural disease pathology
2. Many patients with CRPS have altered sensation (which can't be explained on the basis of disease and has similarities to functional sensory symptoms)
3. Patients with CRPS commonly experience weakness of their limb, often with a dissociative quality. So for example, patients might find that their limb doesn't feel as if it belongs to them as much as it should. When the limb is examined the weakness is clinically indistinugishable from that seen in functional weakness. Occasionally patients with CRPS develop a movement disorder, most commonly a fixed dystonia. Fixed dystonia is often assocaited with minor injury too.
4. In some patients one of the most important perpetuating factors in their CRPS may be immobility and avoidance of movement. This is not surprising since CRPS is an intensely painful condition. However, it may be the case that the less someone moves their limb, the more painful it gets, and the less likely they are to move it etc etc.
There is more about this on the pain page and on the physio page
There are undoubted biological changes in patients with CRPS, but then there are too in patients with other functional symptoms and they may have more in common with each other than has been thought.
There are many potential drug treatments and interventions but the mainstay seems to be increasing activity.