Transcranial electrical motor-evoked potential monitoring during surgery for spinal deformity -: A study of 145 patients

Study Design. A descriptive historic cohort study was conducted. Objectives. To determine intraoperative response amplitude criteria for transcranial electrical motor-evoked potential monitoring that warn of neurologic damage, and to determine the additional value of monitoring six instead of two muscle sites. Summary of Background Data. Transcranial electrical motor-evoked potential monitoring provides immediate and reliable information about the integrity of the motor pathways during spine surgery. Although this monitoring technique is more frequently used, criteria for interpretation of the amplitude responses have not been defined. Methods. The intraoperative monitoring outcomes were compared with the patient's clinical outcomes. The sensitivity, specificity, positive predictive value, and negative predictive value were determined for four different monitoring criteria. Results. Transcranial electrical motor-evoked potential monitoring was possible 142 of 145 patients undergoing corrective surgery. In this study, 16 patients had a neurologic event, and 11 patients showed recovery of response amplitude after a second surgical maneuver, whereas the remaining 5 patients had permanent partial neurologic damage. The criterion that at least one of six recordings must show an amplitude decrease of more than 80% was sufficiently strict to achieve a sensitivity of 1.0 and a specificity of 0.91. Less strict criteria, including recording at two instead of six sites, resulted in lower sensitivity, with the lower bound of the 95% confidence interval at 0.62. Conclusions. Transcranial electrical motor-evoked potential monitoring allowed successful intraoperative monitoring. The criterion of one recording showing a response amplitude decrease of more than 80% during a surgical action can be considered a valuable warning criterion for neurologic damage. The authors also consider that monitoring at six instead of two muscles improves the value of neuromonitoring.