• Ridzky Firmansyah Hardian, Tetsuya Goto, Kohei Kanaya, Yosuke Hara, Yu Fujii, Yoshiki Hanaoka, Tetsuyoshi Horiuchi, and Kazuhiro Hongo.
• Department of Neurosurgery, Shinshu University School of Medicine, Matsumoto, Nagano, Japan.
• World Neurosurg. 2021 Feb 1; 146: e1126-e1133.

BackgroundStimulating electrodes for lower extremity motor-evoked potential (LE-MEP) monitoring with transcortical stimulation are usually placed on the medial side of motor cortex convexity, which is not lower extremity but lumbar motor area. Lumbar MEP may be elicited with lower stimulation intensity than LE-MEP through this location, and it is useful to monitor lower extremity motor function intraoperatively.MethodsIntraoperative lumbar and LE-MEP monitoring with transcortical stimulation during surgery of 12 patients with lesions involving the motor cortex from January 2012 to February 2019 at Shinshu University Hospital were reviewed retrospectively. Stimulations were delivered by a train of 5 pulses of anodal constant current stimulation. Stimulating electrode position was determined by motor cortex mapping. Recording needle electrodes were placed on bilateral lumbar muscles and contralateral leg muscles. The threshold-level stimulation method was used for MEP monitoring. The thresholds, monitoring result, and postoperative motor function of lumbar and lower extremities were compared.ResultsThe mean baseline thresholds were 19.9 ± 8.9 mA for lumbar MEP and 26.5 ± 11.5 mA for LE-MEP (P = 0.02). Patterns of intraoperative monitoring changes were the same between lumbar and LE-MEP monitoring.ConclusionsLumbar MEP was stimulated with lower stimulation intensity than the LE-MEP with the same intraoperative pattern of waveform changes in 12 patients. Lumbar MEP monitoring may be useful for preserving the corticospinal tract of lower extremities intraoperatively.Copyright © 2020 Elsevier Inc. All rights reserved.

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