The use of repetitive transcranial magnetic stimulation (rTMS) in chronic neuropathic pain

Chronic motor cortex stimulation using implanted epidural stimulation was proposed to treat chronic, drug-resistant neuropathic pain. Various studies showed that repetitive transcranial magnetic stimulation (rTMS) applied over the motor cortex could also relieve neuropathic pain, at least partially and transiently. Controlled rTMS studies with other cortical targets, such as the dorsolateral prefrontal cortex, are in waiting. The mechanisms of action of rTMS on chronic pain are mostly unknown. The changes induced by rTMS in neural activities may occur at the stimulated cortical site as well as in remote structures along functional anatomical connections. Compared to chronic implanted procedure, the main limitation of rTMS application is the short duration of clinical effects. Repeated daily rTMS sessions have proved some efficacy to induce long-lasting pain relief that could have therapeutic potential. However, rTMS-induced analgesia varies with the site and parameters of stimulation, in particular the stimulus rate. The efficacious rTMS parameters could differ from those used in chronic epidural stimulation. Differences in the pattern of the current fields respectively induced in the brain by these two techniques might explain this finding. Actually, stimulation parameters remain to be optimised and clinical efficacy to be confirmed by multicentre randomised trials, before considering rTMS as therapeutic tool for patients with chronic pain in neurological practice.