Treatment of chronic neuropathic pain by motor cortex stimulation: results of a bicentric controlled crossover trial.

BACKGROUND Chronic motor cortex stimulation (MCS) with surgically implanted epidural electrodes has been proposed as a treatment for neuropathic pain refractory compared with medical treatment. However, no prospective controlled trial has been published to provide convincing evidence of MCS analgesic efficacy. OBJECTIVE To compare MCS analgesic efficacy between "ON"- and "OFF"-stimulation conditions in a double-blinded crossover trial. METHODS Ten patients with chronic neuropathic pain of either peripheral or central origin underwent MCS implantation in two centers (Créteil, France, and Mexico City, Mexico). At the end of the second postoperative month, patients were randomly assigned into two groups. In the first group, the stimulator was switched "OFF" for two weeks and then was switched "ON" for the next 2 weeks. The opposite sequence was applied in the second group. Preoperative and postoperative assessment (until 1 year after surgery) was performed using visual analogue scale (VAS), verbal scale (VS), Wisconsin brief pain questionnaire (WBPQ), McGill pain questionnaire (MPQ), McGill quality of life scale, and medication quantification scale. RESULTS During the crossover trial, VAS, VS, WBPQ, and MPQ scores were significantly reduced in the"ON"- compared with the "OFF"-stimulation condition. One year after surgery, all clinical scores were significantly reduced compared with preoperative values. In particular, MCS decreased the affective MPQ subscore relative to the sensory MPQ subscore. Six of the 10 patients clearly benefited from MCS treatment. CONCLUSIONS These results were in favor of real analgesic effects produced by MCS with no loss of benefit over time. The differential changes in MPQ subscores suggested that MCS relieved pain by acting predominantly on its affective aspect. The decrease in pain intensity was associated with improved daily living activities and quality of life and reduced consumption of analgesic medication.