Corticobulbar Motor Evoked Potentials: A Systematic Review of Technical Variations

Corticobulbar motor evoked potentials (coMEPs) were introduced in 2005 as an alternative to direct stimulation and free running electromyography for continuous monitoring of the facial nerve during skull base surgery. The technique has been expanded for monitoring of multiple cranial nerves (CNs) and adapted across diverse pathologies. Nonetheless, broad adoption has lagged. This study aimed to understand the basis of this disparity by systematically mapping current practices and characterizing the variations in technical implementation and reporting of coMEPs.

We conducted a Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 adherent systematic review of all articles reporting coMEP neuromonitoring published through December 6, 2023. Multiple reviewers screened publications for inclusion. Data were extracted using a standardized template to enable quantitative and qualitative data synthesis. Aggregate data were analyzed to address incidence, reporting variability, and sensitivity/specificity of the method.

We identified 2711 unique cases using coMEPs, reported across 72 studies (2005-2023). Significant heterogeneity was observed in the technique of coMEPs, including stimulation montages and measurements of accuracy. Overall, 81.9% (59/72) of studies reported clinical outcomes, whereas the remainder were technically focused. coMEPs were often used alongside other neuromonitoring modalities (87.5% of studies, 63/72), but performance was directly compared only 25% of the time (18/72). The facial nerve was the most common single target analyzed (n = 41 publications), followed by the vagus (n = 9). Twenty-two percent of studies analyzed multiple CNs (n = 16). Less than 50% of facial nerve studies, and no vagal nerve study, reported sensitivity or specificity of coMEPs.

coMEPs are an evolving technique in intraoperative neuromonitoring, powerful for their continuous monitoring of the entire motor pathways involving a CN. Comparison of the sensitivity and specificity of coMEPs to other modalities was limited by inconsistent reporting, highlighting the need for further investigation and prospective studies. Standardization of technique may facilitate broader adoption and acceptance of coMEPs.