Approach to challenges in a case of cervical spine neuromonitoring - One case many learnings: Case report and review of literature

Abstract

Introduction: Intraoperative monitoring (IONM) during spine surgery can be fraught with challenges at various stages. Mal-occluded teeth can impede transcranial motor evoked potential (TcMEP) monitoring. Prone positioning may further compromise existing myelopathy. Tibial somatosensory evoked potentials (SSEP) may be absent at baseline due to the myelopathy. Certain total intravenous anesthesia (TIVA) can enhance the SSEPs. Here, a case is reported with such challenges that required customizing the IONM along with systematic interpretation of IONM signals, leading to a good outcome.

Case presentation: A 73-year-old male with severe cervical myelopathy underwent C3-7 decompression with fixation under IONM. He had a deep bite, which was covered with 3 soft bite blocks made of gauze placed between the molars and incisors. Preposition baseline bilateral Median SSEPs were well elicited, but bilateral baseline Tibial SSEPs were absent. Hence, Ulnar SSEPs were recorded to increase the yield of SSEP monitoring. Postposition TcMEPs were absent from the foot muscles and attenuated significantly in the other muscles. Reducing the neck extension restored the signals. The patient was given bolus etomidate prior to closure. A significant augmentation of SSEP amplitudes was noted. Etomidate can augment the amplitude of cortical SSEP recordings. The surgery was completed uneventfully, and the patient did not have any postoperative neurologic deficits.

Conclusion: This case highlights the importance of tailoring IONM methodology, like creating the soft bite block, so that TcMEP could be monitored, employing Ulnar SSEPs when Tibial SSEPs were unrecordable because it was below the level of the lesion, prompt recognition and correction of position-related signal alerts, and awareness of specific effects of anesthetic agents to avoid misinterpretation