Chronic Neuropathic Pain

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Abstract
Contrary to the conclusion drawn by Foley in the accompanying editorial (March 27 issue),1 we believe that the excellent study by Rowbotham et al.2 actually proves that central neuropathic pain is clinically unresponsive to oral opioids, even at high doses. Only 30 percent of the patients who had central pain after stroke or a focal brain lesion were able to complete the study, reporting only a 20 percent reduction in pain from base line. Other controlled studies support this assumption. In two studies of patients with central pain, morphine (18 mg given intravenously) was found to be either totally ineffective or effective in only 20.5 percent of cases.3 In patients with central pain associated with multiple sclerosis, intravenous morphine (mean dose, 41 mg) was effective in 28.5 percent of cases.4 Attal et al.5 found that the effect of morphine on central pain was not significantly different from that of placebo: only 20 percent of patients were still receiving oral morphine after one year. Even intrathecal opioids are scarcely effective for central pain.3 Central pain associated with spinal cord injury (distal, diffuse pain) also has a poor response, unlike “end-zone” pain (the root damage that accompanies spinal injury), which is peripheral neuropathic pain. This study confirms that there is a limited place for opioids in the clinical management of central neuropathic pain.