Neuromonitoring in Cervical Spine Surgery: When Is a Signal Drop Clinically Significant?

Abstract

To identify the clinical significance of different patterns of intraoperative neuromonitoring (IONM) signal alerts. Overview of Literature: IONM is a long-established valuable adjunct to complex spine surgeries. IONM for cervical spine surgery is in the form of somatosensory evoked potential (SSEP) and motor evoked potential (MEP). The efficacy of both modalities (individually or in combination) to detect clinically significant neurological compromise is constantly being debated and requires conclusive suggestions. Methods: Clinical and neuromonitoring data of 207 consecutive adult patients who underwent cervical spine surgeries at multiple surgical centers using bimodal IONM were analyzed. Signal changes were divided into three groups. Group 0 had transient signal changes in either MEPs or SSEPs, group 1 had sustained unimodal changes, and group 2 had sustained changes in both MEPs and SSEPs. The incidences of true neurological deficits in each group were recorded. Results: A total of 25% (52/207) had IONM signal alerts. Out of these signal drops, 96% (50/52) were considered to be false positives. Groups 0 and 1 had no incidence of neurological deficits, while group 2 had a 29% (2/7) rate of true neurological deficits. The sensitivities of both MEP and SSEP were 100%. SSEP had a specificity of 96.6%, while MEP had a lower specificity at 76.6%. C5 palsy rate was 6%, and there was no correlation with IONM signal alerts (p=0.73). Conclusions: This study shows that we can better predict its clinical significance by dividing IONM signal drops into three groups. A sustained, bimodal (MEP and SSEP) signal drop had the highest risk of true neurological deficits and warrants a high level of caution. There were no clear risk factors for false-positive alerts but there was a trend toward patients with cervical myelopathy.

Surgical Causes of Significant Intraoperative Neuromonitoring Signal Changes in Three-Column Spinal Surgery

“…A reduction of more than 50% in MEP baseline amplitude elicited by direct cortical stimulation was considered a significant change. Relevant EMG activities reported to the surgeon included spikes, bursts, and trains [2,5,[15][16][17]. Abnormal monitoring results were reported immediately by the electroneurophysiologist to allow the surgeon to suspend the surgery and investigate the cause in real-time.…”

“…To improve neurologic safety, intraoperative neurophysiological monitoring (IONM) is used to detect and give a chance to reverse the related causes of neurologic complications during spinal surgery [9][10][11][12][13]. Many studies provide alarm criteria of the IONM signal change and confirm its reliability in detecting neurologic complications [14][15][16][17]. However, few of these studies reported a specific surgical procedure related to a significant IONM signal change during surgery.…”

The Use of Intraoperative Neuromonitoring for Cervical Spine Surgery: Indications, Challenges, and Advances

“…A retrospective cohort study of 207 patients undergoing cervical spine surgery divided the cases based on their signal changes, with one group experiencing transient changes in SSEP or MEP, another group with sustained changes in either modality, or the last group with sustained changes in both modalities. While fifty-two patients (25%) were initially considered to have experienced signal drops, fifty of these fifty-two cases (96%) were eventually recognized as false positives [8]. This argues for the need to standardize signal loss thresholds representative of true damage.…”

“…Moreover, varying patterns in signal detection for various types of nervous system disturbances have resulted in falsepositive or false-negative results. Several studies have investigated these pitfalls in cervical spine procedures, and current solutions center around the use of multiple modalities to provide as much of a comprehensive picture as possible [8].…”

Efficacy of Intraoperative Neuromonitoring during the Treatment of Cervical Myelopathy

“…There has been increasing use of intraoperative neuromonitoring (IONM) for intraoperative evaluation of surgical correction as well as prediction of postoperative neurological changes. [1][2][3][4][5][6][7][8][9][10] One study showed 296% increase in the use of IONM between 2008 (n ¼ 31,762) and 2014 (n ¼ 124,835), along with substantial heterogeneity in clinical application. 11 Multimodality IONM (involving somatosensory evoked potentials [SSEPs], transcranial motor evoked potentials [tcMEPs], and electromyography [EMG]) is now used as a surgical adjuvant to help reduce neurological deficits by detecting neurologic injury while still reversible.…”