Repetition suppression of motor cortex may predict responsiveness to high-frequency rTMS in chronic pain

BackgroundHigh-frequency repetitive transcranial magnetic stimulation (rTMS) has been reported to yield promising, albeit variable, outcomes in chronic pain therapy and management. A factor contributing to the treatment success is individual neuroplastic capacity. Neuroplasticity can be assessed in various ways with TMS, e.g. through neural repetition suppression (RS) based on habituation. The present study aimed to evaluate the TMS-induced RS in patients with chronic pain, undergoing conventional rTMS treatment, and observing whether RS is indicative of the experienced analgesic effects. MethodsTwenty-one patients received standard 10-Hz rTMS treatment in five or ten daily sessions. Twenty RS trials, each consisting of four TMS pulses given 1 s apart, were given and assessed for motor evoked potentials (MEPs) before the first rTMS therapy session. For analysis purpose, the RS paradigm was evaluated through two states: 1) "dynamic" state (spontaneous excitability), first to second pulse, and 2) "stable" state (suppressed excitability), suppressed responses induced by second to fourth pulse. Analgesic effect from rTMS was assessed using Brief Pain Inventory (BPI), and painDETECT screening questionnaire, both conducted before and after the rTMS treatment. ResultsBoth the dynamic and the stable state RS exhibited good accuracy (0.789 - 0.944) in identifying patients showing analgesic effect in response to rTMS. Also, significantly greater suppression of MEPs (p<0.05) were observed in the RS between those who benefitted from rTMS and those who did not. ConclusionsThese indicative findings provide support for the potential of RS to set a premise for improved individualized neuromodulation treatments.