Fibromyalgia and the complex regional pain syndrome: similarities in pathophysiology and treatment.

Although the pain of fibromyalgia usually is not preceded by an injury to the involved tissue, whereas that of the complex regional pain syndrome usually starts at a site of prior trauma or surgery, both disorders may share a common mechanism-pathologic sensitization of brain mechanisms that integrate nociceptive signals-and both apparently respond to treatment with ketamine, an anesthetic-analgesic agent whose actions include blockade of N-methyl-D-aspartate receptors. Ketamine's widespread illegal use as a recreational agent probably precludes developing it as a general treatment of centrally mediated pain disorders; however, its efficacy suggests that related, to-be-discovered agents could be useful.