O12 RTMS therapy on M1 modifies the facial motor map in chronic neuropathic pain

Objectives Despite the poorly known mechanism of action, high-frequency rTMS targeted somatotopically to M1, is beneficial to treat therapy-resistant chronic neuropathic pain in about half of the patients. According to previous literature hand motor representation area is diminished in chronic pain. We hypothesized that face motor map is altered in chronic pain and will be restored after rTMS treatment. Another aim was to find the different patterns of plastic cortical reshaping. Methods 13 patients with severe unilateral, chronic atypical facial pain were examined before therapy (2 five-day rTMS treatment courses (2400 or 3600 pulses daily), separated by 6 weeks), and 4–5 days after the last treatment session. Motor mapping was performed at 105% rMT of the mentalis muscle using a grid (2 stimuli per square) to determine the extent of representation area on the hemisphere contralateral to painful side. Mapping was analyzed for hotspot, center-of-gravity (CoG) and representation area, calculated using spline-interpolation method. Patient scored the effect of treatment using patient global impression of change (PGIC). Results The hotspots and CoGs were located in anatomically expected areas. In group level, the rTMS did not cause any shift in mediolateral or anteroposterior axis, or affect the extent of representation areas. However, there were several patients in whom the area significantly largened or became more compact/dense after the treatment. Noteworthly, the motor map of facial muscles was surprisingly small in four patients, whereof three scored high benefit. Discussion The face motor maps in patients with chronic facial pain are variable in size. There was a trend of rTMS increasing the motor map. In some patients the face motor map was clearly diminished and mainly, these patients responded to treatment well. This may be related to enhanced cortical plasticity. Conclusion nTMS motor mapping is a feasible method to study neuronal plasticity in chronic pain and enlighten the effects of rTMS. However, larger amount of patient is needed to draw conclusions about patterns of cortical plasticity. Significance Motor map area may be a biomarker for treatment response in chronic facial pain.