Influence of Pre-Operative Motor Power and Patient Comorbidity on Transcranial Motor-Evoked Potential Acquisition in Intracranial Surgery

Introduction: Intraoperative neuromonitoring (IONM) plays a pivotal role in modern neurosurgery, aiding in real-time assessment of eloquent neural structures to mitigate iatrogenic neural injury. This study represents the largest retrospective series to date in monitoring corticospinal tract integrity during intracranial surgery with transcranial motor-evoked potentials (TCMEPs), focusing on the influence of demographic factors, comorbidities, and preoperative motor deficits on the reliability of intraoperative neurophysiological monitoring. While the impact of patient-specific factors affecting TCMEP monitoring in spine surgery are well-documented, similar insights for intracranial surgery are lacking.

Methods: 420 craniotomy patients were retrospectively analyzed from electronic medical records from December 2017 to February 2023, excluding patients without pre-operative MRC scores or medical histories. Using intrinsic hand muscles as a robust dataset, 840 hand TCMEPs acquired during intracranial surgery were assessed. Demographic and clinical factors, including preoperative motor scores, were analyzed to identify associations with TCMEP acquisition and amplitude. Non-parametric statistics and multivariate regression analysis were employed.

Results: TCMEPs were successfully acquired in 737 (87.8%) patient hands, even in the presence of preoperative motor deficits in 12.3% of patients. Preoperative motor scores did not predict the ability to acquire baseline TCMEPs (p = 0.6). Notably, older age (p < 0.001) and hypertension (p=0.01) were independent predictors of lower TCMEP acquisition rates. Preoperative motor scores significantly influenced TCMEP amplitudes, with higher scores correlating with higher amplitudes (1771[SD=1550] eve vs. 882 [SD=856] μV, p< 0.0001). Older age (p < 0.001) and chronic kidney disease (p=0.04) were also associated with reduced TCMEP amplitudes.

Conclusion : Our investigation into TCMEPs during intracranial surgery demonstrated a notably high acquisition rate in hand muscles, irrespective of preoperative motor deficits. Preoperative motor scores reliably correlated with TCMEP amplitudes in a linear fashion, while advanced age and renal disease emerged as independent predictors of lower TCMEP amplitudes.