IS 42. Brain stimulation in pain treatment

Abstract

Chronic epidural motor cortex stimulation (EMCS) induces significant pain relief in patients suffering from chronic neuropathic pain. Repetitive transcranial magnetic stimulation (rTMS) allowed several questions to be addressed: (i) could the analgesic effects provided by EMCS be also produced by non-invasive rTMS? (ii) Could a therapeutic application of rTMS be conceivable in patients with chronic pain? (iii) Were these effects predictive for the outcome of EMCS? (iv) Could rTMS help in understanding the mechanisms of action of EMCS? We performed various experiments based on the assessment of rTMS-induced pain relief with respect to: stimulus frequency; stimulation site; time course of the effects; influence of sensory deficit within the painful zone; combination with acute provoked pain. The assessment included clinical scoring of pain level; quantified sensory testing; cortical excitability studies. We found that pain can be transiently relieved in patients with chronic neuropathic pain by applying rTMS at 10–20 Hz over the motor cortex corresponding to the painful zone. The targeting within the precentral gyrus influenced the results, justifying the use of an image-guided navigated approach. Pain relief was associated with changes in sensory discrimination within the painful zone and with the restoration of intracortical inhibitory processes. Cortical stimulation over motor areas is able to produce analgesic effects. Regarding rTMS, the parameters of stimulation and the way of managing rTMS therapy remained to be optimized before considering this technique as a therapeutic tool. Conversely, motor cortex rTMS could be used to select good candidates for the surgical implantation of a cortical stimulator.