<b>The mechanism of high-frequency rTMS </b><b>for intractable pain, a TMS study </b>

Abstract

We have previously reported the efficacy of navigation-guided 5-Hz repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex in relief of intractable neuropathic pain. The objective of this study was to assess changes of cortical excitability induced by rTMS which might give an insight to the mechanism of pain relief with rTMS. In 14 patients with neuropathic pain in a hand and five healthy controls, the cortical excitability and visual analogue scale (VAS) were evaluated before and after 5Hz-rTMS of the primary motor cortex corresponding to the painful hand. Resting motor threshold, amplitude of motor evoked potential, cortical silent period, intracortical inhibition and intracortical facilitation (ICF) were measured as parameters of cortical excitability with single- or paired-pulse TMS method. The patients who showed ≥ 30% pain reduction in VAS after rTMS were classified as “good responders", the others were as “poor responders". Five of 14 patients were good responders,in whom ICF was significantly lower than that in controls at baseline (p=0.039). ICF increase induced by rTMS was significantly higher in good responders than in poor responders (p=0.046). There were no significant differences and changes in the other parameters. Our findings suggested that restoration of the abnormal cortical excitability was one of the mechanism underling the pain relief with rTMS in neuropathic pain.