Complex regional pain syndrome: state of the art update.

OPINION STATEMENT: Although the pathophysiology of complex regional pain syndrome (CRPS) is not fully understood, it appears to reflect multiple interacting mechanisms. In addition to altered autonomic function, a role for inflammatory mechanisms and altered somatosensory and motor function in the brain is increasingly suggested. Several possible risk factors for development of CRPS, including genetic factors, have been identified. Few treatments have been proven effective for CRPS in well-designed clinical trials. However, recent work suggests that bisphosphonates may be useful in CRPS management and that the N-methyl-D: -aspartate receptor antagonist ketamine significantly reduces CRPS pain when administered topically or intravenously at subanesthetic dosages. Extended use of ketamine at anesthetic dosages ("ketamine coma") remains a controversial and unproven treatment for CRPS. Spinal cord stimulation may be effective for reducing pain in approximately two thirds of CRPS patients not responding to other treatments, but its efficacy appears to diminish over time.