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Successful Motor Evoked Potential Monitoring in Cervical Myelopathy : Related Factors and the Effect of Increased Stimulation Intensity

Journal of Korean Neurosurgical Society 2021년 64권 1호 p.78 ~ 87
심혁기, 이재민, 김동환, 남경협, 최병관, 한인호,
소속 상세정보
심혁기 ( Shim Hyok-Ki ) - Pusan National University School of Medicine Pusan National University Hospital Department of Neurosurgery
이재민 ( Lee Jae-Meen ) - Pusan National University School of Medicine Pusan National University Hospital Department of Neurosurgery
김동환 ( Kim Dong-Hwan ) - Pusan National University School of Medicine Pusan National University Hospital Department of Neurosurgery
남경협 ( Nam Kyoung-Hyup ) - Pusan National University School of Medicine Pusan National University Hospital Department of Neurosurgery
최병관 ( Choi Byung-Kwan ) - Pusan National University School of Medicine Pusan National University Hospital Department of Neurosurgery
한인호 ( Han In-Ho ) - Pusan National University School of Medicine Pusan National University Hospital Department of Neurosurgery

Abstract


Objective : Intraoperative neurophysiological monitoring (IONM) has been widely used during spine surgery to reduce or prevent neurologic deficits, however, its application to the surgical management for cervical myelopathy remains controversial. This study aimed to assess the success rate of IONM in patients with cervical myelopathy and to investigate the factors associated with successful baseline monitoring and the effect of increasing the stimulation intensity by focusing on motor evoked potentials (MEPs).

Methods : The data of 88 patients who underwent surgery for cervical myelopathy with IONM between January 2016 and June 2018 were retrospectively reviewed. The success rate of baseline MEP monitoring at the initial stimulation of 400 V was investigated. In unmonitorable cases, the stimulation intensity was increased to 999 V, and the success rate final MEP monitoring was reinvestigated. In addition, factors related to the success rate of baseline MEP monitoring were investigated using independent t-test, Wilcoxon rank-sum test, chi-squared test, and Fisher’s exact probability test for statistical analysis. The factors included age, sex, body mass index, diabetes mellitus, smoking history, symptom duration, Torg-Pavlov ratio, space available for the cord (SAC), cord compression ratio (CCR), intramedullary increased signal intensity (SI) on magnetic resonance imaging, SI length, SI ratio, the Medical Research Council (MRC) grade, the preoperative modified Nurick grade and Japanese Orthopedic Association (JOA) score.

Results : The overall success rate for reliable MEP response was 52.3% after increasing the stimulation intensity. No complications were observed to be associated with increased intensity. The factors related to the success rate of final MEP monitoring were found to be SAC (p<0.001), CCR (p<0.001), MRC grade (p<0.001), preoperative modified Nurick grade (p<0.001), and JOA score (p<0.001). The cut-off score for successful MEP monitoring was 5.67 mm for SAC, 47.33% for the CCR, 3 points for MRC grade, 2 points for the modified Nurick grade, and 12 points for the JOA score.

Conclusion : Increasing the stimulation intensity could significantly improve the success rate of baseline MEP monitoring for unmonitorable cases at the initial stimulation in cervical myelopathy. In particular, the SAC, CCR, MRC grade, preoperative Nurick grade and JOA score may be considered as the more important related factors associated with the success rate of MEP monitoring. Therefore, the degree of preoperative neurological functional deficits and the presence of spinal cord compression on imaging could be used as new detailed criteria for the application of IONM in patients with cervical myelopathy.

키워드

Cervical myelopathy; Evoked potentials, Motor; Success rate; Stimulation intensity

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