Short-Interval Intracortical Facilitation Improves Efficacy in nTMS Motor Mapping of Lower Extremity Muscle Representations in Patients with Supra-Tentorial Brain Tumors

SIMPLE SUMMARY: Presurgical motor mapping of cortical muscle representations by single-pulse navigated transcranial magnetic stimulation (sp-nTMS) is used to localize and enclose motor function in patients harboring motor-eloquent lesions. This study investigates paired-pulse nTMS (pp-nTMS) with biphasic pulses for motor mapping of lower extremity (lE) muscle representations, showing that significantly lower stimulation intensities are needed while reliable motor maps can be achieved even in the most demanding patient cases in whom conventionally used sp-nTMS fails. Thus, novel pp-nTMS with biphasic pulses may have potential to considerably facilitate improvements of currently used nTMS-based mapping procedures in the preoperative workup of neurooncological patients. ABSTRACT: Navigated transcranial magnetic stimulation (nTMS) is increasingly used for mapping of motor function prior to surgery in patients harboring motor-eloquent brain lesions. To date, single-pulse nTMS (sp-nTMS) has been predominantly used for this purpose, but novel paired-pulse nTMS (pp-nTMS) with biphasic pulse application has been made available recently. The purpose of this study was to systematically evaluate pp-nTMS with biphasic pulses in comparison to conventionally used sp-nTMS for preoperative motor mapping of lower extremity (lE) muscle representations. Thirty-nine patients (mean age: 56.3 ± 13.5 years, 69.2% males) harboring motor-eloquent brain lesions of different entity underwent motor mapping of lE muscle representations in lesion-affected hemispheres and nTMS-based tractography of the corticospinal tract (CST) using data from sp-nTMS and pp-nTMS with biphasic pulses, respectively. Compared to sp-nTMS, pp-nTMS enabled motor mapping with lower stimulation intensities (61.8 ± 13.8% versus 50.7 ± 11.6% of maximum stimulator output, p < 0.0001), and it provided reliable motor maps even in the most demanding cases where sp-nTMS failed (pp-nTMS was able to provide a motor map in five patients in whom sp-nTMS did not provide any motor-positive points, and pp-nTMS was the only modality to provide a motor map in one patient who also did not show motor-positive points during intraoperative stimulation). Fiber volumes of the tracked CST were slightly higher when motor maps of pp-nTMS were used, and CST tracking using pp-nTMS data was also possible in the five patients in whom sp-nTMS failed. In conclusion, application of pp-nTMS with biphasic pulses enables preoperative motor mapping of lE muscle representations even in the most challenging patients in whom the motor system is at high risk due to lesion location or resection.