Reliability and Efficacy of Transcranial Motor Evoked Potential Monitoring during Spinal Surgery

Abstract

Intraoperative motor evoked potential MEP monitorings were performed during 100 spinal operations. Among these 100 operations, transcranial MEP TCMEP were performed in 98 operations including 30 cervical laminoplasties, 22 lumbar laminectomies, 12 cervical anterior fusions, 9 lumbar discectomies, 7 posterior interbody fusions, 7 vertebroplasties, 6 lumbar spinal canal fenestrations, and 4 spinal tumors. Transcranial stimulations at 300 400 V were used and applied by screw electrodes placed in the scalp and the resultant electromyographic responses were recorded with surface electrodes on the affected muscles. To exclude the effects of muscle relaxants on TCMEP, compound muscle action potential CMAP by supra maximum stimulation of the peripheral nerve immediately after transcranial stimulation was recorded in 97 operations. Among 80 patients who had had no preoperative and postoperative definitive motor palsy, the amplitudes of TCMEP compensated by CMAP after peripheral stimulation decreased less than 20 in 4 patients with cervical spondylosis, thus the false positive rate was 4.9 . A false negative finding was not recognized in one patient who had had postoperative newly progressed motor palsy. The improvement of mild motor disturbance such as reduction of grasping force or intermittent claudication could not be monitored intraoperatively by conventional TCMEP. Among 16 patients who had had preoperative severe motor palsy, TCMEP could not be recorded preoperatively in 20 limbs of 12 patients. After the decompression of the spinal cord in these 12 patients, TCMEP could be recorded in 3 limbs in 3 patients, but postoperative improvement of the motor function was recognized in only one patient. In conclusion, although TCMEP monitoring during spinal surgery might seem to be too sensitive, it should be performed to prevent most postoperative severe adverse motor function events after spinal surgery that is intended as functional surgery. Finally, the selection of the muscles for recording should be elaborately decided for the most effective TCMEP monitoring during spinal surgery.