Primary motor cortex stimulation within the central sulcus for treating deafferentation pain

Nine patients with post-stroke pain, six with brachial plexus injuries, two with phantom limb pain, one with spinal cord injury, and one with brain stem injury were treated with a modified motor cortex stimulation (MCS) protocol. Preoperative pharmacological tests were performed with phentolamine, lidocaine, ketamine, thiopental, morphine, and placebo. We placed a grid electrode in the subdural space to decide upon the best stimulation point for pain relief over a few weeks with the purpose of determining the placement of a Resume electrode. In five patients, Resumes were implanted in the interhemispheric fissure to reduce lower extremity pain. In five other patients, Resumes were placed within the central sulcus to stimulate area 4 and area 3b. In addition, electrodes were also placed on the surface of the precentral gyrus. Fourteen of the 19 patients showed pain reduction (6 excellent, 3 good, and 5 fair) using the MCS with our results indicating area 4 within the central sulcus to be the optimal stimulation point for pain relief. We speculate that conventional method may sometimes fail to stimulate area 4 and that focal stimulation of the primary motor cortex within the central sulcus may improve the efficacy of this treatment. Our pharmacological tests show that patients with ketamine sensitivity seem to be good candidates for MCS. Test stimulation with a subdural multi-grid electrode and Resumes in the cetral sulcus were helpful in locating the best stimulation point for pain relief.