Intraoperative Motor Evoked Potential Improvement in Cervical Spondylotic Myelopathy: Comparison of Cortical Stimulation Parameters

BACKGROUND AND PURPOSE: Intraoperative monitoring of the motor pathways is a routine procedure for ensuring the integrity of descending motor tracts during spinal surgery. Intraoperative motor evoked potential improvement (MEPI) may be associated with a better postsurgical outcome in cervical spondylotic myelopathy (CSM). To compare the efficacy of two cortical stimulation parameters in eliciting MEPI intraoperatively during CSM surgery. METHODS: We studied 69 patients who underwent decompression surgery for CSM over a 9-month period using either 5 (Group 1) or 9 (Group 2) stimuli. MEPI was defined as the increase in the amplitude of MEPs from baseline at the end of CSM surgery just prior to skin closure. RESULTS: An MEPI of 100% from baseline was observed in 10 patients (53%) in Group 1 and 36 patients (72%) in Group 2. Comparisons of the baseline mean MEP amplitudes of muscles bilaterally between Groups 1 and 2 did not reveal any significant differences. Supramaximal stimulation showed that a significantly higher mean intensity was required for Group 1 than for Group 2. CONCLUSIONS: MEPI is observed in a much larger proportion of cervical decompression surgery cases than previously thought. Intraoperative MEPI with longer-train cortical stimulation may reflect adequacy of decompression and provide additional guidance for the surgical procedure.