Threshold variation of transcranial motor evoked potential with threshold criterion in frontotemporal craniotomy

OBJECTIVE: Motor threshold usually varies in the intraoperative motor evoked potential (MEP) by transcranial evoked stimulation (TES). This study investigated the degree of change in the motor threshold before and after surgery in TES-MEP monitoring with threshold criterion. This study aimed to evaluate the threshold change and discuss the factors influencing the motor threshold. METHODS: We retrospectively analyzed TES-MEP monitoring during supratentorial surgery with frontotemporal craniotomy in 72 patients without pre- and postoperative motor weakness. We analyzed the percentage changes between the affected and the unaffected sides, correlating the changes on the two sides. RESULTS: The percentage change on the affected and the unaffected side was 4.4 ± 15.1% and 0.4 ± 6.5%, respectively. The percentage change on the affected side was significantly larger than that on the unaffected side. A significantly positive correlation between the percentage change on the affected and the unaffected sides was detected. CONCLUSION: The threshold for the TES-MEP varied significantly more than that on the unaffected side. SIGNIFICANCE: It is important to understand the characteristics of threshold variation for the evaluation of TES-MEP.