An unusual case of causalgia. Relevance to recent hypothesis on mechanism of causalgia.

Intravenous regional sympathetic block with guanethidine caused only limited improvement in a patient with longstanding causalgia. Lumbar sympathetic block with phenol also had little direct effect on the pain but completely abolished associated allodynia and vasomotor signs. Following sympathectomy the response to subsequent guanethidine blocks was enhanced. This improvement persisted even after 8 months when there was some return of the previous allodynia and vasomotor signs (to involve a smaller area than previously). The case would appear to have implications for a recently proposed hypothesis concerning the mechanism of pain in causalgia.