Intra-operative neurophysiological monitoring in patients with pre-operative neurological deficit: its feasibility and high-risk factors for failed monitoring

Abstract

Objective. To analyze the performance of intra-operative neurophysiological monitoring (IONM) including somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) in patients with pre-operative neurological deficit and to identify the high-risk factors for failed IONM. Methods. Patients with pre-operative neurological deficit undergoing spinal surgery between October 2010 and August 2019 were retrospectively reviewed. The presence or absence of SEP and MEP of target muscles were separately recorded and the high-risk factors for failed IONM results were investigated. Results. A total of 136 patients (86 males, 50 females) with an average age of 43.0±17.7 years were included. The muscle strength of recorded muscles in 272 lower extremities included grade 1 in 25 muscles, grade 2 in 15, grade 3 in 41, grade 4 in 134 and grade 5 in 57. The SEP records were available in 177 (65.1%) lower extremities while MEP records were available in 199 (73.2%) lower extremities. Significantly higher success rates of SEP and MEP were obtained in lower extremities with muscle strength of grade 4-5 than those of grade 1-3 (P<0.001). Patients with spinal trauma and cervical spinal stenosis were associated with more prevalent failed IONM results. Conclusions. The overall success rates of SEP and MEP were 65.1% and 73.2%, respectively. The high-risk indicators for failed IONM results included muscle strength lower than grade 4, spinal trauma and cervical spinal stenosis.