Motor cortex rTMS reduces acute pain provoked by laser stimulation in patients with chronic neuropathic pain.

OBJECTIVE

To assess the modulation of acute provoked pain by repetitive transcranial magnetic stimulation (rTMS) of the motor cortex in patients with chronic neuropathic pain.

METHODS

In 32 patients with chronic neuropathic pain affecting one upper limb, laser-evoked potentials (LEPs) (N2 and P2 components) were recorded in response to laser stimulation of the painful or painless hand, before and after active or sham rTMS applied at 10Hz over the motor cortex corresponding to the painful hand. Laser-induced pain was scored on a visual analogue scale.

RESULTS

Both active and sham rTMS reduced N2-P2 amplitude of the LEPs in response to painful or painless hand stimulation, likely due to the decline of attention during the sessions. However, active rTMS, but not sham rTMS, specifically reduced N2 amplitude and N2/P2 amplitude ratio of the painful hand LEPs. Painful hand LEP attenuation correlated with the magnitude of pain relief produced by active rTMS.

CONCLUSION

Motor cortex rTMS delivered at high frequency (10Hz) was able to reduce LEP amplitude in parallel with laser-induced pain scores in patients with chronic neuropathic pain. The preferential change in the N2 component suggested a modulation of the sensori-discriminative aspect of laser-induced pain.

SIGNIFICANCE: Previous studies have shown that rTMS delivered to various cortical targets by different protocols could modulate experimental pain, primarily in healthy subjects. The present results demonstrate the ability of motor cortex rTMS to interfere with the processing of acute provoked pain, even if there is an underlying chronic neuropathic pain.