Cutoff Points, Sensitivities, and Specificities of Intraoperative Motor-Evoked Potential Monitoring Determined Using Receiver Operating Characteristic Analysis

Abstract

Background Although intraoperative motor-evoked potential (MEP) monitoring is widely performed during neurosurgical operations, evaluating its results is controversial. Study Aims The cutoff point of MEP monitoring should be determined not only to predict but also to prevent postoperative neurologic deficits. Material and Methods MEP monitoring was performed during 484 neurosurgical operations for patients without definitive preoperative motor palsy including 325 spinal operations, 102 cerebral aneurysmal operations, and 57 brain tumor operations, all monitored by transcranial stimulation, and 34 brain tumor operations monitored under direct cortical stimulation. To exclude the effects of muscle relaxants on MEP, the compound muscle action potential (CMAP), measured immediately after transcranial stimulation or direct cortical stimulation at supramaximal stimulation of the peripheral nerve, was used for normalization. The cutoff points, sensitivity, and specificity of MEP recorded during neurosurgery were examined by receiver operating characteristic (ROC) analyses and categorized according to the type of operation and stimulation. Results In spinal operations under transcranial stimulation, amplitude reduction of 77.9% and 80.6% as cutoff points for motor palsy with and without CMAP normalization, respectively, provided a sensitivity of 100% and specificity of 96.8% and 96.5%. In aneurysmal operations under transcranial stimulation, cutoff points of 70.7% and 69.6% offered specificities of 95.2% and 95.7% with and without CMAP normalization, respectively. The sensitivities for both were 100%. In brain tumor operations under direct stimulation, cutoff points were 83.5% and 86.3% with or without CMAP normalization, respectively, and the sensitivity and specificity for both were 100%. Conclusion An amplitude decrease of 80% in brain tumor operations, 75% in spinal operations, and 70% in aneurysmal operations should be used as the cutoff points.

Effect of Compound Muscle Action Potential After Peripheral Nerve Stimulation Normalization on Anesthetic Fade of Intraoperative Transcranial Motor-Evoked Potential

“…In our recent report, the sensitivities of tcMEP monitoring during spinal surgery and aneurysm clipping surgery were both 100%. 12 However, specificity of tcMEP monitoring was not 100%, and FIG. 3.…”

“…Compound muscle action potential normalization may not raise the sensitivity or specificity for the cutoff values of motor failure in MEP monitoring. 11,12 We reported that CMAP normalization in MEP is useful for predicting postoperative recovery after spinal cord and spinal nerve decompression surgery. 23 In the present study, we also showed that CMAP normalization corrected the decrease in synaptic transmission at the neuromuscular junction because of propofol accumulation, and its muscle-relaxant effect at the neuromuscular junction.…”

“…According to some reports, including ours, the cutoff point for nonreversible motor neuropathy in MEP monitoring was a decrease in amplitude of 70% to 80%. 11,12,24 One hundred and sixteen muscles without CMAP normalization and 196 muscles with CMAP normalization showed more than a 50% decrease in amplitude in MEP monitoring without neurologic deterioration. Both the amplitude of MEP monitoring and the CMAP amplitude after peripheral nerve stimulation increased because of a decrease in the level of muscle relaxant.…”

“…In our recent report, the sensitivities of tcMEP monitoring during spinal surgery and aneurysm clipping surgery were both 100%. 12 However, specificity of tcMEP monitoring was not 100%, and there were many false positives. Such false positives in the amplitude decrease are believed to be caused by anesthetic fade.…”

“…Compound muscle action potential normalization was performed as described in our previous articles. 9,11,12 Briefly, surface electrodes for stimulation were usually placed on the median nerve at the wrist. Compound muscle action potential, which was generated using a single, bipolar supramaximum stimulation (20-50 mA) usually on the median nerve at the wrist 2 seconds before each transcranial stimulation of the motor area, was recorded in every operation.…”