Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

Simple Summary Motor evoked potential (MEP) alarm criteria may have an important impact on the preservation of motor function in supratentorial neurosurgical procedures. However, no consensus exists regarding the optimal cut-off values and interpretation of MEP signal changes. In addition, their performance as diagnostic and surrogate biomarkers has not been adequately investigated. The existing clinical studies that utilized alarm criteria are heterogeneous, rendering quantitative evidence synthesis problematic. In this study, we sought to summarize the pertinent literature using an emerging synthesis methodology, namely a scoping review. The objective was to assess the extent and range of available evidence, identifying research gaps, clarifying concepts, and providing insights for further research. Due to the heterogeneity of studies, we applied a descriptive approach, in particular by visualizing instead of pooling the data. A comprehensive overview of MEP warning criteria has not been provided yet, and therefore, our study should pave the way for future research. During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.