Motor cortex stimulation for deafferentation pain.

The authors tested a modified motor cortex stimulation (MCS) protocol for the treatment of deafferentation pain in 15 patients: eight patients with poststroke pain, four with brachial plexus injury, two with phantom limb pain, and one with spinal cord injury. Preoperative pharmacological tests were performed with phentolamine, lidocaine, ketamine, thiopental, morphine, and a placebo. In 12 patients we placed a 20- or 40-grid electrode in the subdural space to determine the best stimulation point for pain relief over a few weeks and therefore the optimum position for a permanent internal device. In four patients, the MCS devices were implanted in the interhemispheric fissure to reduce lower-extremity pain. In one patient, the MCS device was placed within the central sulcus, and a 20-grid electrode was placed on the brain surface. In two patients with pain extending from the upper extremity to the hyperbody, dual-electrode devices were implanted to drive two electrodes. In 10 of the 15 patients MCS-induced pain reduction was achieved (four with excellent, two with good, and four with fair alleviation of pain). The result of pharmacological testing indicated that patients with ketamine sensitivity seem to be good candidates for MCS. Test stimulation with a subdural multigrid electrode was helpful in locating the best stimulation point for pain relief.