Somatotopic organization of the analgesic effects of motor cortex rTMS in neuropathic pain

Background: Motor cortex repetitive transcranial magnetic stimulation (rTMS) was found to relieve chronic neuropathic pain, but the optimal parameters of stimulation remain to be determined, including the site of stimulation. Objective: To determine the relationship between cortical stimulation site and pain site regarding the analgesic efficacy of rTMS of motor cortex in chronic neuropathic pain. Methods: Thirty-six patients with unilateral chronic neuropathic pain located at the face or the hand were enrolled. Motor cortex rTMS was applied at 10 Hz over the area corresponding to the face, hand, or arm of the painful side, whatever pain location. Analgesic effects were daily assessed on visual analogue scale for the week that followed each rTMS session. Results: All types of rTMS session, whatever the target, significantly relieved pain, compared with baseline. However, analgesic effects were significantly better after hand than face area stimulation in patients with facial pain and after face than hand or arm area stimulation in patients with hand pain. Conclusion: Repetitive transcranial magnetic stimulation was more effective for pain relief when the stimulation was applied to an area adjacent to the cortical representation of the painful zone rather than to the motor cortical area corresponding to the painful zone itself. This result contradicts the somatotopic efficacy observed for chronic epidural motor cortex stimulation with surgically implanted electrodes.