Pain relief by rTMS:: Differential effect of current flow but no specific action on pain subtypes

Objectives: To assess, against placebo, the pain-relieving effects of high-rate repetitive transcranial magnetic stimulation (rTMS) on neuropathic pain. Methods: Double-blind, randomized, cross-over study of high-rate rTMS against placebo in 28 patients. The effect of a change in coil orientation (posteroanterior vs lateromedial) on different subtypes of neuropathic pain was further tested in a subset of 16 patients. Pain relief was evaluated daily during 1 week. Results: High-frequency, posteroanterior rTMS decreased pain scores significantly more than placebo. Posteroanterior rTMS also outmatched placebo in a score combining subjective (pain relief, quality of life) and objective (rescue drug intake) criteria of treatment benefit. Changing the orientation of the coil from posteroanterior to lateromedial did not yield any significant pain relief. The analgesic effects of posteroanterior rTMS lasted for approximately 1 week. The pain-relieving effects were observed exclusively on global scores reflecting the most distressing type of pain in each patient. Conversely, rTMS did not modify specifically any of the pain subscores that were separately tested (ongoing, paroxysmal, stimulus-evoked, or disesthesic pain). Conclusions: Posteroanterior repetitive transcranial magnetic stimulation (rTMS) was more effective than both placebo and lateromedial rTMS. When obtained, pain relief was not specific of any particular submodality, but rather reduced the global pain sensation whatever its type. This is in accord with recent models of motor cortex neurostimulation, postulating that its analgesic effects may derive in part from modulation of the affective appraisal of pain, rather than a decrease of its sensory components.