Factors Associated With Unexpected Movement During Transcranial Electrical Stimulation–Motor Evoked Potential Monitoring for Neurosurgical and Neuroendovascular Procedures: A Propensity-weighted Study

INTRODUCTION: Transcranial electrical stimulation-motor evoked potential (TES-MEP) is used during neurosurgical procedures to assess motor pathway integrity. TES-MEP-associated unexpected movement may compromise surgical precision and anesthetic management. This study aimed to evaluate the incidence of unexpected movements and compare neuroendovascular procedures (NE) versus conventional neurosurgery (CV). METHODS: We conducted a retrospective observational study of patients undergoing TES-MEP monitoring. The primary outcome was the occurrence of TES-MEP-associated unexpected movements. Inverse probability of treatment weighting (IPTW) was applied to adjust for baseline differences. Multivariable logistic regression was used to identify factors associated with unexpected movements. Sensitivity and bootstrap analyses were performed to confirm the stability of findings. RESULTS: A total of 252 patients (NE: 63, 25.0%; CV: 189, 75.0%) were included. Overall, unexpected movements occurred in 20 patients (7.9%), with a higher incidence in the NE group (n = 11, 17.5%) compared with the CV group (n = 9, 4.8%). After IPTW adjustment, covariate balance was achieved between the two groups, and NE remained associated with higher odds of movements (weighted OR: 3.78, 95% CI: 1.23 to 11.64). Multivariable analysis showed that earlier MEP initiation and higher total charge per stimulation were independently associated with increased odds of unexpected movements (OR: 0.96 per minute delay, 95% CI: 0.93 to 0.99; OR: 1.04 per µC/phase, 95% CI: 1.03 to 1.06), respectively. CONCLUSION: TES-MEP-associated unexpected movements were more frequent during NE procedures. Procedural timing and total stimulation charge, rather than patient baseline characteristics, were associated with the odds of movement. Future studies should investigate potential interventions to reduce unexpected movements, such as the optimization of MEP stimulation parameters and initiation timing, to enhance intraoperative safety.