Failure to Obtain Baseline Signals of Transcranial Motor-Evoked Potentials in Spine Surgery: Analysis of the Reasons.

Objective: Among the various intraoperative neurophysiologic monitoring (IONM) techniques, transcranial motor-evoked potential (Tc-MEP) has recently become the most widely used method to monitor motor function. However, we often find that Tc-MEP is not sufficiently detected at the start of surgery. Therefore, we aimed to analyze the reasons and risk factors for not detecting sufficient baseline signal of Tc-MEP from the beginning of spinal surgery.

Methods: We categorized IONM data from 1058 patients who underwent spine surgeries at a single institution from 2014 to 2020 and categorized them into 2 groups: 1) "poor MEP" if Tc-MEP could not be sufficiently obtained and 2) "normal MEP" if Tc-MEP could be sufficiently obtained from the surgery. We analyzed the patient's age, gender, underlying disease, operation type, level numbers, baseline motor function, existence of pathologic reflex, myelopathy, and duration from the onset and clinical diagnosis.

Results: The rate of failure to obtain sufficient baseline Tc-MEP signals in spine surgery was 21.8% (231/1058). Multivariate analysis showed significant associations of existence of diabetes mellitus, myelopathy, thoracic spine surgery, baseline motor deficit and tumor, and trauma disease with loss of meaningful and interpretable signals in baseline Tc-MEP (P < 0.05). Only 15 of 231 patients (6.4%) showed a trend of signal recovery after decompression procedures.

Conclusions: Various factors (myelopathy, diabetes mellitus, thoracic surgery, baseline motor deficit, tumor, and trauma) were closely related to not obtaining sufficient baseline signals for Tc-MEP. When operating on patients with these considerations, we need to consider the efficacy and usefulness of Tc- MEP.