Study design: Retrospective clinical study of intraoperative transcranial motor evoked potential (TcMEP) amplitudes and postoperative motor deficits (PMDs).
Objective: To determine the quantifiable cutoff amplitude of TcMEP for predicting transient PMDs in intramedullary spinal cord tumor (IMSCT) surgery.
Summary of background data: The "presence or absence" criterion is reliable and widely used the alarm criterion for preventing permanent PMDs in IMSCT surgery. However, we wanted to prevent PMDs even if it is transient. The cutoff amplitude for transient PMDs should be identified.
Methods: We conducted a retrospective study to identify the cutoff amplitude for predicting transient PMDs in IMSCT surgery. Thirty-seven patients were included in the study. We examined intraoperative electrophysiological changes and perioperative motor status in these patients. Receiver operating characteristic analyses were performed to identify the cutoff amplitudes for predicting transient PMDs in IMSCT surgery. The incidence of PMDs and cutoff TcMEP amplitude in cervical and thoracic lesions were compared.
Results: Thirteen cases demonstrated transient PMDs. Among 280 monitorable muscles in 37 cases, 51 muscles in 13 patients showed PMDs. Through receiver operating characteristic analysis, the relative and the absolute cutoff amplitudes at the intraoperative point of deterioration were identified to be 12% residual of baseline amplitude and 3.2 μV, respectively. Sensitivity/specificity for those cutoff points are 86%/74% and 88%/78%, respectively. The incidence of PMD was significantly higher, and the cutoff amplitude was lower in the thoracic lesions than in the cervical lesions.
Conclusion: We determined the cutoff TcMEP amplitude for predicting transient PMDs in IMSCT surgery. The cutoff amplitude for the cervical lesions was higher than that for the thoracic lesions. The results suggest the need for setting different alarm criteria in different level of spine.
Level of evidence: 3.