A new criterion for the alarm point for compound muscle action potentials

Accuracy of Intraoperative Neuromonitoring in the Diagnosis of Intraoperative Neurological Decline in the Setting of Spinal Surgery-A Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVES

In an effort to prevent intraoperative neurological injury during spine surgery, the use of intraoperative neurophysiological monitoring (IONM) has increased significantly in recent years. Using IONM, spinal cord function can be evaluated intraoperatively by recording signals from specific nerve roots, motor tracts, and sensory tracts. We performed a systematic review and meta-analysis of diagnostic test accuracy (DTA) studies to evaluate the efficacy of IONM among patients undergoing spine surgery for any indication.

METHODS

The current systematic review and meta-analysis was performed using the Preferred Reporting Items for a Systematic Review and Meta-analysis statement for Diagnostic Test Accuracy Studies (PRISMA-DTA) and was registered on PROSPERO. A comprehensive search was performed using MEDLINE, EMBASE and SCOPUS for all studies assessing the diagnostic accuracy of neuromonitoring, including somatosensory evoked potential (SSEP), motor evoked potential (MEP) and electromyography (EMG), either on their own or in combination (multimodal). Studies were included if they reported raw numbers for True Positives (TP), False Negatives (FN), False Positives (FP) and True Negative (TN) either in a 2 × 2 contingency table or in text, and if they used postoperative neurologic exam as a reference standard. Pooled sensitivity and specificity were calculated to evaluate the overall efficacy of each modality type using a bivariate model adapted by Reitsma et al, for all spine surgeries and for individual disease groups and regions of spine. The risk of bias (ROB) of included studies was assessed using the quality assessment tool for diagnostic accuracy studies (QUADAS-2).

RESULTS

A total of 163 studies were included; 52 of these studies with 16,310 patients reported data for SSEP, 68 studies with 71,144 patients reported data for MEP, 16 studies with 7888 patients reported data for EMG and 69 studies with 17,968 patients reported data for multimodal monitoring. The overall sensitivity, specificity, DOR and AUC for SSEP were 71.4% (95% CI 54.8-83.7), 97.1% (95% CI 95.3-98.3), 41.9 (95% CI 24.1-73.1) and .899, respectively; for MEP, these were 90.2% (95% CI 86.2-93.1), 96% (95% CI 94.3-97.2), 103.25 (95% CI 69.98-152.34) and .927; for EMG, these were 48.3% (95% CI 31.4-65.6), 92.9% (95% CI 84.4-96.9), 11.2 (95% CI 4.84-25.97) and .773; for multimodal, these were found to be 83.5% (95% CI 81-85.7), 93.8% (95% CI 90.6-95.9), 60 (95% CI 35.6-101.3) and .895, respectively. Using the QUADAS-2 ROB analysis, of the 52 studies reporting on SSEP, 13 (25%) were high-risk, 10 (19.2%) had some concerns and 29 (55.8%) were low-risk; for MEP, 8 (11.7%) were high-risk, 21 had some concerns and 39 (57.3%) were low-risk; for EMG, 4 (25%) were high-risk, 3 (18.75%) had some concerns and 9 (56.25%) were low-risk; for multimodal, 14 (20.3%) were high-risk, 13 (18.8%) had some concerns and 42 (60.7%) were low-risk.

CONCLUSIONS

These results indicate that all neuromonitoring modalities have diagnostic utility in successfully detecting impending or incident intraoperative neurologic injuries among patients undergoing spine surgery for any condition, although it is clear that the accuracy of each modality differs.PROSPERO Registration Number: CRD42023384158.

A Novel Sensory Wave (P25) in Myelin Oligodendrocyte Glycoprotein-induced Experimental Autoimmune Encephalomyelitis Murine Model

Myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) is a murine model for multiple sclerosis. This model is characterized by chronic and progressive demyelination, leading to impairment of motor function and paralysis. While the outcomes of the disease, including impaired motor function and immunological changes, are well-characterized, little is known about the impact of EAE on the electrophysiology of the motor and sensory systems. In this study, we assessed evoked potentials as a quantitative marker for in vivo monitoring of nervous system damage. Motor-evoked potentials (MEPs) and sensory-evoked potentials (SEPs) were first standardized in naïve C57BL mice and studied thoroughly in EAE mice. The duration of MEPs and the number of connotative potentials increased significantly alongside an increase in temporal SEP amplitudes. Moreover, a new SEP wave was identified in naïve animals, which significantly increased in MOG-induced EAE animals with no or mild symptoms (clinical score 0-2, 0-5 scale). This wave occurred ∼25 milliseconds poststimulation, thus named p25. P25 was correlated with increased vocalization and was also reduced in amplitude following treatment with morphine. As the EAE score progressed (clinical score 3-4, 0-5 scale), the amplitude of MEPs and SEPs decreased drastically. Our results demonstrate that desynchronized neural motor activity, along with hypersensitivity in the early stages of EAE, leads to a complete loss of motor and sensory functions in the late stages of the disease. The findings also suggest an increase in p25 amplitude before motor deficits appear, indicating SEP as a predictive marker for disease progression. PERSPECTIVE: This article assesses p25, a new sensory electrophysiology wave that correlates with pain-related behavior in MOG-induced EAE mice and appears prior to the clinical symptoms. Motor electrophysiology correlates with traditional motor behavior scoring and histology.

Characteristics of Tc-MEP Waveforms for Different Locations of Intradural Extramedullary Tumors: A Prospective Multicenter Study of the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

Prospective multicenter study.

OBJECTIVE

To examine transcranial motor-evoked potential (Tc-MEP) waveforms in intraoperative neurophysiological monitoring in surgery for intradural extramedullary (IDEM) tumors, focused on the characteristics for cervical, thoracic, and conus lesions.

SUMMARY OF BACKGROUND DATA

IDEM tumors are normally curable after resection, but neurological deterioration may occur after surgery. Intraoperative neurophysiological monitoring using Tc-MEPs during surgery is important for timely detection of possible neurological injury.

METHODS

The subjects were 233 patients with IDEM tumors treated surgically with Tc-MEP monitoring at 9 centers. The alarm threshold was ≥70% waveform deterioration from baseline. A case with a Tc-MEP alert that normalized and had no new motor deficits postoperatively was defined as a rescue case. A deterioration of manual muscle test score ≥1 compared to the preoperative value was defined as postoperative worsening of motor status.

RESULTS

The 233 patients (92 males, 39%) had a mean age of 58.1 ± 18.1 years, and 185 (79%), 46 (20%), and 2 (1%) had schwannoma, meningioma, and neurofibroma. These lesions had cervical (C1-7), thoracic (Th1-10), and conus (Th11-L2) locations in 82 (35%), 96 (41%), and 55 (24%) cases. There were no significant differences in preoperative motor deficit among the lesion levels. Thoracic lesions had a significantly higher rate of poor baseline waveform derivation (0% cervical, 6% thoracic, 0% conus, P < 0.05) and significantly more frequent intraoperative alarms (20%, 31%, 15%, P < 0.05). Use of Tc-MEPs for predicting neurological deficits after IDEM surgery had sensitivity of 87% and specificity of 89%; however, the positive predictive value was low.

CONCLUSION

Poor derivation of waveforms, appearance of alarms, and worse final waveforms were all significantly more frequent for thoracic lesions. Thus, amplification of the waveform amplitude, using multimodal monitoring, and more appropriate interventions after an alarm may be particularly important in surgery for thoracic IDEM tumors.Level of Evidence: 3.

Characteristics of Tc-MEP Waveforms in Spine Surgery for Patients with Severe Obesity

STUDY DESIGN

Prospective multicenter study.

OBJECTIVE

The aim of this study was to evaluate transcranial motor evoked potential (Tc-MEP) waveform monitoring in spinal surgery for patients with severe obesity.

SUMMARY OF BACKGROUND DATA

Spine surgeries in obese patients are associated with increased morbidity and mortality. Intraoperative Tc-MEP monitoring can identify neurologic deterioration during surgery, but has not been examined for obese patients.

METHODS

The subjects were 3560 patients who underwent Tc-MEP monitoring during spine surgery at 16 centers. Tc-MEPs were recorded from multiple muscles via needle or disc electrodes. A decrease in Tc-MEP amplitude of ≥70% from baseline was used as an alarm during surgery. Preoperative muscle weakness with manual muscle test (MMT) grade ≤4 was defined as a motor deficit, and a reduction of one or more MMT grade postoperatively was defined as deterioration.

RESULTS

The 3560 patients (1698 males, 47.7%) had a mean age of 60.0 ± 20.3 years. Patients with body mass index >35 kg/m2 (n = 60, 1.7%) were defined as severely obese. Compared with all other patients (controls), the rates of preoperative motor deficit (41.0% vs. 29.6%, P < 0.05) and undetectable baseline waveforms in all muscles were significantly higher in the severely obese group (20.0% vs. 1.7%, P < 0.01). Postoperative motor deterioration did not differ significantly between the groups. The sensitivity and specificity of the alarm criterion for prediction of postoperative neurologic complications were 75.0% and 83.9% in severely obese patients and 76.4% and 89.6% in controls, with no significant difference between the groups.

CONCLUSION

Tc-MEPs can be used in spine surgery for severely obese cases to predict postoperative motor deficits, but the rate of undetectable waveforms is significantly higher in such cases. Use of a multichannel waveform approach or multiple modalities may facilitate safe completion of surgery. Waveforms should be carefully evaluated and an appropriate rescue procedure is required if the alarm criterion occurs.Level of Evidence: 3.

Characteristics of Cases with Poor Transcranial Motor-evoked Potentials Baseline Waveform Derivation in Spine Surgery: A Prospective Multicenter Study of the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

Prospective multicenter study.

OBJECTIVE

The purpose of the study is to examine cases with poor baseline waveform derivation for all muscles in multichannel monitoring of transcranial motor-evoked potentials (Tc-MEPs) in spine surgery.

SUMMARY OF BACKGROUND DATA

Intraoperative neuromonitoring (IONM) is useful for identifying neurologic deterioration during spinal surgery. Tc-MEPs are widely used for IONM, but some cases have poor waveform derivation, even in multichannel Tc-MEP monitoring.

METHODS

The subjects were 3625 patients (mean age 60.1 years, range 4-95; 1886 females, 1739 males) who underwent Tc-MEP monitoring during spinal surgery at 16 spine centers between April 2017 and March 2020. Baseline Tc-MEPs were recorded from the deltoid, abductor pollicis brevis, adductor longus, quadriceps femoris, hamstrings, tibialis anterior, gastrocnemius, and abductor hallucis (AH) muscles after surgical exposure of the spine.

RESULTS

The 3625 cases included cervical, thoracic, and lumbar lesions (50%, 33% and 17%, respectively) and had preoperative motor status of no motor deficit, and motor deficit with manual muscle testing (MMT) ≥3 and MMT <3 (70%, 24% and 6%, respectively). High-risk surgery was performed in 1540 cases (43%). There were 73 cases with poor baseline waveform derivation (2%), and this was significantly associated with higher body weight, body mass index, thoracic lesions, motor deficit of MMT <3, high-risk surgery (42/1540 [2.7%] vs. 31/2085 [1.5%], P < 0.05), and surgery for ossification of the posterior longitudinal ligament (OPLL). Intraoperative waveform derivation occurred in 25 poor derivation cases (34%) and the AH had the highest rate.

CONCLUSION

The rate of poor baseline waveform derivation in spine surgery was 2% in our series. This was significantly more likely in high-risk surgery for thoracic lesions and OPLL, and in cases with preoperative severe motor deficit. In such cases, it may be preferable to use multiple modalities for IONM to derive multichannel waveforms from distal limb muscles, including the AH.Level of Evidence: 3.

The Seven-Color TcMsEP Grading System: A Novel Alarm Method for Intraoperative Neurophysiological Monitoring Using Transcranial Electrical Stimulated Muscle Evoked Potentials (TcMsEPs) in Intramedullary Spinal Cord Tumor Surgeries

Introduction

Surgeons need precise information about motor deterioration risk during surgery for intramedullary spinal cord tumors (IMSCTs). However, the conventional TcMsEP alarm criterion provides limited information with a less than or a more than single alarm criterion without any grades in between, resulting in false-negative and false-positive outcomes.

Therefore, we developed a “seven-color TcMsEP grading system” for neuromonitoring to provide more graded information. This study investigates the system's efficacy.

Methods

This study included 60 patients that underwent resection surgeries for IMSCTs. TcMsEP outcomes were classified into seven grades: Grade “D-0 Green” includes a wave amplitude decrease of 0%-50% compared with the baseline amplitude. Grade “D-1 Lime” includes a 50%-70% decrease. Grade “D-2 Yellow” includes a 70%-90% decrease. Grade “D-3 Orange” includes a more than 90% decrease with a clearly visible waveform. Grade “D-4 Red” includes a minimal and abnormally shaped wave. The severest, grade “D-5 Black,” includes a wave that has completely disappeared. The additional grade “D-X Gray” includes cases in which the baseline wave is undetectable.

Postoperative motor deterioration was evaluated in the upper limbs (PUMD) and lower limbs (PLMD) individually.

Results

PLMD only occurred in cases with more than a 90% wave amplitude decrease (from D-3 to D-5) and with the undetectable baseline wave (D-X). The PLMD rate increased according to the severity of the amplitude decreases (29% in D-3, 67% in D-4, 80% in D-5). Most PUMD occurred in cases with more than a 90% decrease, but one case with grade D1 had PUMD.

Conclusions

The seven-color graded alarm criterion supports surgeons' decisions on how to treat the wave amplitude decrease during surgery. It provides motor deterioration risk in each grade without false negatives. Moreover, the corresponding colors enable quick comprehension of the risks.

Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.

Efficacy of Intraoperative Intervention Following Transcranial Motor-evoked Potentials Alert During Posterior Decompression and Fusion Surgery for Thoracic Ossification of the Posterior Longitudinal Ligament: A Prospective Multicenter Study of the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

Prospective, multicenter, observational study.

OBJECTIVE

The aim of this study was to investigate the efficacy of intervention after an alert in intraoperative neurophysiological monitoring (IONM) using transcranial motor-evoked potentials (Tc-MEPs) during surgery for thoracic ossification of the posterior longitudinal ligament (T-OPLL).

SUMMARY OF BACKGROUND DATA

T-OPLL is commonly treated with posterior decompression and fusion with instrumentation. IONM using Tc-MEPs during surgery reduces the risk of neurological complications.

METHODS

The subjects were 79 patients with a Tc-MEP alert during posterior decompression and fusion surgery for T-OPLL. Preoperative muscle strength (manual muscle testing [MMT]), waveform derivation rate at the start of surgery (baseline), intraoperative waveform changes; and postoperative motor paralysis were examined. A reduction in MMT score of ≥1 on the day after surgery was classified as worsened postoperative motor deficit. An alert was defined as a decrease in Tc-MEP waveform amplitude of ≥70% from baseline. Alerts were recorded at key times during surgery.

RESULTS

The patients (35 males, 44 females; age 54.6 years) had OPLL at T1-4 (n = 27, 34%), T5-8 (n = 50, 63%), and T9-12 (n = 16, 20%). The preoperative status included sensory deficit (n = 67, 85%), motor deficit (MMT ≤4) (n = 59, 75%), and nonambulatory (n = 26, 33%). At baseline, 76 cases (96%) had a detectable Tc-MEP waveform for at least one muscle, and the abductor hallucis had the highest rate of baseline waveform detection (n = 66, 84%). Tc-MEP alerts occurred during decompression (n = 47, 60%), exposure (n = 13, 16%), rodding (n = 5, 6%), pedicle screw insertion (n = 4, 5%), posture change (n = 4, 5%), dekyphosis (n = 2, 3%), and other procedures (n = 4, 5%). After intraoperative intervention, the rescue rate (no postoperative neurological deficit) was 57% (45/79), and rescue cases had a significantly better preoperative ambulatory status and a significantly higher baseline waveform derivation rate.

CONCLUSION

These results show the efficacy of intraoperative intervention following a Tc-MEP alert for prevention of neurological deficit postoperatively.Level of Evidence: 2.

A practical guide for anesthetic management during intraoperative motor evoked potential monitoring

Postoperative motor dysfunction can develop after spinal surgery, neurosurgery and aortic surgery, in which there is a risk of injury of motor pathway. In order to prevent such devastating complication, intraoperative monitoring of motor evoked potentials (MEP) has been conducted. However, to prevent postoperative motor dysfunction, proper understanding of MEP monitoring and proper anesthetic managements are required. Especially, a variety of anesthetics and neuromuscular blocking agent are known to attenuate MEP responses. In addition to the selection of anesthetic regime to record the baseline and control MEP, the measures to keep the level of hypnosis and muscular relaxation at constant are crucial to detect the changes of MEP responses after the surgical manipulation. Once the changes of MEP are observed based on the institutional alarm criteria, multidisciplinary team members should share the results of MEP monitoring and respond to check the status of monitoring and recover the possible motor nerve injury. Prevention of MEP-related adverse effects is also important to be considered. The Working Group of Japanese Society of Anesthesiologists (JSA) developed this practical guide aimed to help ensure safe and successful surgery through appropriate anesthetic management during intraoperative MEP monitoring.

Adverse Events Related to Transcranial Electric Stimulation for Motor-evoked Potential Monitoring in High-risk Spinal Surgery

STUDY DESIGN

Prospective multicenter study.

OBJECTIVE

The aim of this study was to study the incidence of nonneurologic adverse events related to transcranial electric stimulation (TES) for intraoperative spinal cord monitoring (IOM) with motor-evoked potentials (MEPs) (Tc(E)- MEPs) and determine the need for safety precautions.

SUMMARY OF BACKGROUND DATA

Tc(E)-MEPs monitoring requires high-voltage multipulse TES that causes widespread muscle contraction and movement. Improved awareness of TES-induced movement-related adverse events is needed.

METHODS

We analyzed data from 2643 patients who underwent high-risk spinal surgery with intraoperative Tc(E)-MEPs at 11 spinal centers from 2010 to 2016. Information about neurologic and non-neurologic postoperative complications was collected, including type of surgical procedure, operative time, estimated blood loss, and treatment for postoperative adverse events.

RESULTS

A 70% drop in Tc(E)-MEPs amplitude, which was the alarm criterion to interrupt surgery, predicted postoperative motor deficits with 93.5% sensitivity, 91.0% specificity, a false-positive rate of 8.2%, and a false-negative rate of 0.3%. Non-neurologic adverse events developed in 17 (0.64%) patients and were most commonly because of bite injuries (0.57%), including 11 cases of tongue laceration, two cases of lip laceration, and two cases of tooth breakage. Four (0.15%) tongue lacerations required surgical repair with sutures and two tooth breakages required dental treatment. One patient had hair loss corresponding to the TES site. One patient, who underwent additional IOM with transpharyngeal stimulation, had severe nasal hemorrhage following electrode placement by nasal route, which resolved spontaneously. Non-neurologic adverse events did not significantly affect the accuracy of IOM assessment. Neither operative times nor blood loss significantly influenced the occurrence of adverse events.

CONCLUSION

During TES-IOM, both the surgeon and monitoring team must consider the possibility-although rare-of non-neurologic adverse events, particularly bite injuries. Such complications can be minimized by using a soft bite-block and frequently evaluating the intraoral integrity of the anesthetized patient.

LEVEL OF EVIDENCE

4.

Alert Timing and Corresponding Intervention With Intraoperative Spinal Cord Monitoring for High-Risk Spinal Surgery

STUDY DESIGN

Prospective multicenter study.

OBJECTIVE

To analyze the incidence of intraoperative spinal neuromonitoring (IONM) alerts and neurological complications, as well as to determine which interventions are most effective at preventing postoperative neurological complications following IONM alerts in high risk spinal surgeries.

SUMMARY OF BACKGROUND DATA

IONM may play a role in identifying and preventing neural damage; however, few studies have clarified the outcomes of intervention after IONM alerts.

METHODS

We analyzed 2867 patients who underwent surgery for high risk spinal pathology using transcranial electrical motor-evoked potentials from 2010 to 2016. The high-risk spinal surgery cases consisted of 1009 spinal deformity cases, 622 cervical ossification of posterior longitudinal ligament (OPLL) cases, 249 thoracic-OPLL cases, 771 extramedullary spinal cord tumor cases, and 216 intramedullary spinal cord tumor (IMSCT) cases. We set a 70% amplitude reduction as the alarm threshold for transcranial electrical motor-evoked potentials and analyzed the outcomes of the interventions following monitoring alerts and postoperative neurological deficits.

RESULTS

The true positive, false positive, true negative, false negative, and rescue cases of IONM comprised 126, 234, 2362, 9, and 136 cases, respectively. Most alerts and interventions occurred during correction and release in deformity cases, posterior decompression and dekyphosis in OPLL cases, and tumor resection and surgery suspension with steroid injection in spinal cord tumor cases; however, individual interventions varied. The rescue rates (number of patients rescued with intervention after IONM alert/number of true positive cases plus rescue cases) for deformity, cervical-OPLL, thoracic--OPLL, extramedullary spinal cord tumor, and IMSCT cases were 61.4% (35/57), 82.1% (32/39), 40% (20/50), 52.5% (31/59), and 31.6% (18/57), respectively.

CONCLUSION

Our prospective multicenter study identified potential neural damage in 9.5% of cases and 52% rescue cases using IONM. Although the rescue ratios for t-OPLL and IMSCT were relatively low, appropriate intervention immediately after an IONM alert may prevent neural damage even in high-risk spinal surgeries.

LEVEL OF EVIDENCE

3.

A new criterion for the alarm point using a combination of waveform amplitude and onset latency in Br(E)-MsEP monitoring in spine surgery

OBJECTIVE

Monitoring of brain evoked muscle-action potentials (Br[E]-MsEPs) is a sensitive method that provides accurate periodic assessment of neurological status. However, occasionally this method gives a relatively high rate of false-positives, and thus hinders surgery. The alarm point is often defined based on a particular decrease in amplitude of a Br(E)-MsEP waveform, but waveform latency has not been widely examined. The purpose of this study was to evaluate onset latency in Br(E)-MsEP monitoring in spinal surgery and to examine the efficacy of an alarm point using a combination of amplitude and latency.

METHODS

A single-center, retrospective study was performed in 83 patients who underwent spine surgery using intraoperative Br(E)-MsEP monitoring. A total of 1726 muscles in extremities were chosen for monitoring, and acceptable baseline Br(E)-MsEP responses were obtained from 1640 (95%). Onset latency was defined as the period from stimulation until the waveform was detected. Relationships of postoperative motor deficit with onset latency alone and in combination with a decrease in amplitude of ≥ 70% from baseline were examined.

RESULTS

Nine of the 83 patients had postoperative motor deficits. The delay of onset latency compared to the control waveform differed significantly between patients with and without these deficits (1.09% ± 0.06% vs 1.31% ± 0.14%, p < 0.01). In ROC analysis, an intraoperative 15% delay in latency from baseline had a sensitivity of 78% and a specificity of 96% for prediction of postoperative motor deficit. In further ROC analysis, a combination of a decrease in amplitude of ≥ 70% and delay of onset latency of ≥ 10% from baseline had sensitivity of 100%, specificity of 93%, a false positive rate of 7%, a false negative rate of 0%, a positive predictive value of 64%, and a negative predictive value of 100% for this prediction.

CONCLUSIONS

In spinal cord monitoring with intraoperative Br(E)-MsEP, an alarm point using a decrease in amplitude of ≥ 70% and delay in onset latency of ≥ 10% from baseline has high specificity that reduces false positive results.

Evaluation of a Combination of Waveform Amplitude and Peak Latency in Intraoperative Spinal Cord Monitoring

STUDY DESIGN

Retrospective study.

OBJECTIVE

The goal of the study was to investigate the significance of a change in latency in monitoring of transcranial muscle-action potential (Tc-MsEP) waveforms.

SUMMARY OF BACKGROUND DATA

Tc-MsEP has become a common approach in spine surgery due to its sensitivity and importance in motor function. Many reports have defined the alarm point of Tc-MsEP waveform as a particular decrease in amplitude, but evaluation of the waveform latency has not attracted as much attention.

METHODS

The subjects were 70 patients who underwent spine surgery using intraoperative Tc-MsEP monitoring. The peak latency was defined as the period from stimulation until the waveform amplitude reached its peak. Relationships with postoperative paralysis were examined separately for latency delays of 5% or more and 10% or more, and in combination with a decrease in amplitude of 70% or more from baseline.

RESULTS

Acceptable baseline Tc-MsEP responses were obtained from 1225 of 1372 muscles in the extremities (89.3%). Seven of the 70 patients (10%) had postoperative paralysis. A decrease in intraoperative amplitude of 70% or more from baseline occurred in 25 cases, with sensitivity 100%, specificity 71%, false positive rate 29%, and positive predictive value (PPV) 28% for prediction of postoperative paralysis. Compared to baseline, 15 cases had a latency delay of 5% or more, which gave a sensitivity of 100%, specificity of 87%, false positive rate of 0%, and PPV 47%, and 8 cases had a delay of 10% or more, which gave a sensitivity of 86%, specificity of 97%, false positive rate of 3%, and PPV 75%. A combination of a decrease in amplitude of 70% or more from baseline and a delay in latency of 10% or more from baseline had a sensitivity of 86%, specificity of 98%, and a false positive rate of 2%, and PPV 86%.

CONCLUSION

Combined use of latency and amplitude could lead to reduction of false positives and increase of PPV in Br(E)-MsEP monitoring.

LEVEL OF EVIDENCE

3.

Efficacy of Anal Needle Electrodes for Intraoperative Spinal Cord Monitoring with Transcranial Muscle Action Potentials

Study Design

Retrospective study.

Purpose

To examine the relationship between postoperative bowel bladder disorder (BBD) and the efficacy of needle electrodes for the external anal sphincter (EAS) in intraoperative spinal cord monitoring with transcranial muscle action potentials (Tc-MsEP).

Overview of Literature

Spinal surgery for spina bifida, spinal cord tumor, and spinal tethered cord syndrome has a high rate of postoperative BBD. Monitoring of the EAS with Tc-MsEP is frequently performed during spinal surgery. We initially used plug-surface electrodes for this purpose, but have more recently switched to needle electrodes for the monitoring of the EAS. To date, there has been no comparison between the utility of these electrodes.

Methods

Waveform derivation, exacerbation of postoperative BBD, and sensitivity and specificity for prediction of BBD by 70% amplitude reduction of EAS activity using needle and plug-surface electrodes were investigated in 239 spine surgeries. The cut-off for the % drop in amplitude for BBD prediction was determined for EAS monitoring using a needle electrode.

Results

The overall rate of postoperative BBD aggravation was 7.1% (17/239 cases), with the individual rates using needle and plug-surface electrodes being 6.9% (8/116) and 7.3% (9/123), respectively. The waveform derivation rate was significantly higher using needle electrodes (91.3% [106/116] vs. 76.4% [94/123], p <0.01). In patients with baseline waveform detection, the sensitivity and specificity for postoperative BBD were similar in the two groups. With needle electrodes, a cutoff amplitude of Tc-MsEP for the EAS at the end of surgery of 25% of the baseline amplitude had a sensitivity of 89% and specificity of 82% for the prediction of postoperative BBD aggravation.

Conclusions

The significantly higher waveform derivation rate using needle electrodes suggests that these electrodes are effective for monitoring the EAS in spinal surgery in cases with preoperative BBD.

Surgical outcomes of spinal cord and cauda equina ependymoma: Postoperative motor status and recurrence for each WHO grade in a multicenter study

BACKGROUND

The goals of the study are to analyze postoperative outcomes and recurrence in cases of spinal cord and cauda equina ependymoma in each World Health Organization (WHO) Grade, and to examine the influence of extent of surgical removal on prognosis. Spinal ependymoma has a relatively high frequency among intramedullary spinal cord tumors. The tumor is classified in WHO guidelines as grades I, II, and III, but few studies have examined postoperative prognosis based on these grades.

METHODS

The records of 80 patients undergoing surgery for spinal cord and cauda equina ependymoma were examined in a multicenter study using a retrospective database. Neurological motor status, pathological type, extent of resection, and tumor recurrence were evaluated.

RESULTS

The histopathological types were grade I in 23 cases (myxopapillary: 21, subependymoma: 2), grade II in 52 cases, and grade III in 5 cases (including all anaplastic cases). Total resection was performed in 60 cases (83%), and eight cases had recurrence, including 2 in WHO grade I, 2 in grade II, and 4 in grade III. The 5-year recurrence-free survival rates were 90%, 91%, and 20% in grades I, II and III, respectively. Adjuvant radiotherapy for the local site was performed in 8 cases, including 3 in grade I and 5 in grade III; however, 4 of the 5 grade III cases (80%) had recurrence after radiotherapy. Among 59 patients with normal ambulation or independence without external assistance (McCormick Grade I or II), 53 (90%) maintained the same mobility after surgery. In cases that underwent total resection, the recurrence rate was significantly lower (p < 0.01). A good preoperative motor status also resulted in significantly better postoperative recovery of motor status (p < 0.05).

CONCLUSIONS

Total resection of spinal cord and cauda equina ependymoma leads to postoperative motor recovery and may reduce tumor recurrence. Therefore, early surgery for this tumor is recommended before aggravation of paralysis.

Can postoperative deltoid weakness after cervical laminoplasty be prevented by using intraoperative neurophysiological monitoring?

Laminoplasty, frequently performed in patients with cervical myelopathy, is safe and provides relatively good results. However, motor palsy of the upper extremities, which occurs after decompression surgery for cervical myelopathy, often reduces muscle strength of the deltoid muscle, mainly in the C5 myotome. The aim of this study was to investigate prospectively whether postoperative deltoid weakness (DW) can be predicted by performing intraoperative neurophysiological monitoring (IONM) during cervical laminoplasty and to clarify whether it is possible to prevent palsy using IONM. We evaluated the 278 consecutive patients (175 males and 103 females) who underwent French-door cervical laminoplasty for cervical myelopathy under IONM between November 2008 and December 2016 at our hospital. IONM was performed using muscle evoked potential after electrical stimulation to the brain [Br(E)-MsEP] from the deltoid muscle. Seven patients (2.5%) developed DW after surgery (2 with acute and 5 with delayed onset). In all patients, deltoid muscle strength recovered to ≥ 4 on manual muscle testing 3-6 months after surgery. Persistent IONM alerts occurred in 2 patients with acute-onset DW. To predict the acute onset of DW, Br(E)-MsEP alerts in the deltoid muscle had both a sensitivity and specificity of 100%. The PPV of persistent Br(E)-MsEP alerts had both a sensitivity and specificity of 100% for acute-onset DW. There was no change in Br(E)-MsEP in patients with delayed-onset palsy. The incidence of deltoid palsy was relatively low. Persistent Br(E)-MsEP alerts of the deltoid muscle had a 100% sensitivity and specificity for predicting a postoperative acute deficit. IONM was unable to predict delayed-onset DW. In only 1 patient were we able to prevent postoperative DW by performing a foraminotomy.

Prevention and prediction of postoperative bowel bladder disorder using an anal plug electrode with Tc-MsEP monitoring during spine surgery

A retrospective study was performed to examine the efficacy of intraoperative monitoring of the external anal sphincter (EAS) muscle-evoked potential after a transcranial muscle-action potential (Tc-MsEP) in spinal cord surgery, and to evaluate alarm points for EAS waveform deterioration related to postoperative bowel bladder disorder (BBD). BBD is caused by damage to the hypogastric, pelvic, and pudendal nerves and leads to a significant reduction in quality of life. Intraoperative Tc-MsEP monitoring using the EAS is common to prevent neurological deficit, but the relationship of BBD with intraoperative monitoring of the EAS has not been examined. Waveform derivation from the EAS using a plug-type surface electrode was investigated in 123 spine surgeries in which Tc-MsEP was recorded intraoperatively outside the anal sphincter. An acceptable baseline waveform from the EAS was detected in 105 of the 123 cases (85.3%). Preoperative BBD was present in 16 cases, postoperative BBD occurred in 8 cases, and intraoperative waveform deterioration from the EAS was detected in 25 cases. The derivation rate was significantly lower in cases with preoperative BBD compared to those without BBD (62.5% vs. 88.9%, p<0.01). Waveform deterioration from the EAS had a sensitivity of 100%, specificity of 93.0%, positive predictive value of 50%, and negative predictive value of 100% for detection of postoperative BBD. All postoperative BBD was detected with an EAS amplitude decrease to <30% of baseline. Therefore, in spine surgery, a Tc-MsEP intraoperative EAS amplitude decrease to <30% of the control waveform may be useful for prediction of postoperative BBD.

Rapid Worsening of Symptoms and High Cell Proliferative Activity in Intra- and Extramedullary Spinal Hemangioblastoma: A Need for Earlier Surgery

STUDY DESIGN

A retrospective analysis of a prospective database.

OBJECTIVE

To compare preoperative symptoms, ambulatory ability, intraoperative spinal cord monitoring, and pathologic cell proliferation activity between intramedullary only and intramedullary plus extramedullary hemangioblastomas, with the goal of determining the optimal timing for surgery.

METHODS

The subjects were 28 patients (intramedullary only in 23 cases [group I] and intramedullary plus extramedullary in 5 cases [group IE]) who underwent surgery for spinal hemangioblastoma. Preoperative symptoms, ambulatory ability on the McCormick scale, intraoperative spinal cord monitoring, and pathologic findings using Ki67 were compared between the groups.

RESULTS

In group IE, preoperative motor paralysis was significantly higher (100 versus 26%, p < 0.005), the mean period from initial symptoms to motor paralysis was significantly shorter (3.5 versus 11.9 months, p < 0.05), and intraoperative spinal cord monitoring aggravation was higher (65 versus 6%, p < 0.05). All 5 patients without total resection in group I underwent reoperation. Ki67 activity was higher in group IE (15% versus 1%, p < 0.05). Preoperative ambulatory ability was significantly poorer in group IE (p < 0.05), but all cases in this group improved after surgery, and postoperative ambulatory ability did not differ significantly between the two groups.

CONCLUSIONS

Intramedullary plus extramedullary spinal hemangioblastoma is characterized by rapid preoperative progression of symptoms over a short period, severe spinal cord damage including preoperative motor paralysis, and poor gait ability compared with an intramedullary tumor only. Earlier surgery with intraoperative spinal cord monitoring is recommended for total resection and good surgical outcome especially for an IE tumor compared with an intramedullary tumor.

Transcranial motor evoked potential waveform changes in corrective fusion for adolescent idiopathic scoliosis

OBJECTIVE Corrective surgery for spinal deformities can lead to neurological complications. Several reports have described spinal cord monitoring in surgery for spinal deformity, but only a few have included patients younger than 20 years with adolescent idiopathic scoliosis (AIS). The goal of this study was to evaluate the characteristics of cases with intraoperative transcranial motor evoked potential (Tc-MEP) waveform deterioration during posterior corrective fusion for AIS. METHODS A prospective database was reviewed, comprising 68 patients with AIS who were treated with posterior corrective fusion in a prospective database. A total of 864 muscles in the lower extremities were chosen for monitoring, and acceptable baseline responses were obtained from 819 muscles (95%). Intraoperative Tc-MEP waveform deterioration was defined as a decrease in intraoperative amplitude of ≥ 70% of the control waveform. Age, Cobb angle, flexibility, operative time, estimated blood loss (EBL), intraoperative body temperature, blood pressure, number of levels fused, and correction rate were examined in patients with and without waveform deterioration. RESULTS The patients (3 males and 65 females) had an average age of 14.4 years (range 11-19 years). The mean Cobb angles before and after surgery were 52.9° and 11.9°, respectively, giving a correction rate of 77.4%. Fourteen patients (20%) exhibited an intraoperative waveform change, and these occurred during incision (14%), after screw fixation (7%), during the rotation maneuver (64%), during placement of the second rod after the rotation maneuver (7%), and after intervertebral compression (7%). Most waveform changes recovered after decreased correction or rest. No patient had a motor deficit postoperatively. In multivariate analysis, EBL (OR 1.001, p = 0.085) and number of levels fused (OR 1.535, p = 0.045) were associated with waveform deterioration. CONCLUSIONS Waveform deterioration commonly occurred during rotation maneuvers and more frequently in patients with a larger preoperative Cobb angle. The significant relationships of EBL and number of levels fused with waveform deterioration suggest that these surgical invasions may be involved in waveform deterioration.

Intraoperative Motor-Evoked Potential Disappearance versus Amplitude-Decrement Alarm Criteria During Cervical Spinal Surgery: A Long-Term Prognosis

Background and Purpose

We studied the clinical significance of amplitude-reduction and disappearance alarm criteria for transcranial electric muscle motor-evoked potentials (MEPs) during cervical spinal surgery according to different lesion locations [intramedullary (IM) vs. nonintramedullary (NIM)] by evaluating the long-term postoperative motor status.

Methods

In total, 723 patients were retrospectively dichotomized into the IM and NIM groups. Each limb was analyzed respectively. One hundred and sixteen limbs from 30 patients with IM tumors and 2,761 limbs from 693 patients without IM tumors were enrolled. Postoperative motor deficits were assessed up to 6 months after surgery.

Results

At the end of surgery, 61 limbs (2.2%) in the NIM group and 14 limbs (12.1%) in the IM group showed MEP amplitudes that had decreased to below 50% of baseline, with 13 of the NIM limbs (21.3%) and 2 of the IM limbs (14.3%) showing MEP disappearance. Thirteen NIM limbs (0.5%) and 5 IM limbs (4.3%) showed postoperative motor deficits. The criterion for disappearance showed a lower sensitivity for the immediate motor deficit than did the criterion for amplitude decrement in both the IM and NIM groups. However, the disappearance criterion showed the same sensitivity as the 70%-decrement criterion in IM (100%) and NIM (83%) surgeries for the motor deficit at 6 months after surgery. Moreover, it has the highest specificity for the motor deficits among diverse alarm criteria, from 24 hours to 6 months after surgery, in both the IM and NIM groups.

Conclusions

The MEP disappearance alarm criterion had a high specificity in predicting the long-term prognosis after cervical spinal surgery. However, because it can have a low sensitivity in predicting an immediate postoperative deficit, combining different MEP alarm criteria according to the aim of specific instances of cervical spinal surgery is likely to be useful in practical intraoperative monitoring.

Postoperative Paralysis From Thoracic Ossification of Posterior Longitudinal Ligament Surgery Risk Factor of Neurologic Injury: Nationwide Multiinstitution Survey

STUDY DESIGN

Retrospective case-control study.

OBJECTIVE

The purpose of this study was to examine the factors of postoperative paralysis in patients who have undergone thoracic ossification of posterior longitudinal ligament (OPLL) surgery.

SUMMARY OF BACKGROUND DATA

A higher percentage of thoracic OPLL patients experience postoperative aggravation of paralysis than cervical OPLL patients, including patients that presented great difficulties in treatment. However, there were a few reports to prevent paralysis thoracic OPLL.

METHODS

The 156 patients who had received thoracic OPLL surgery were selected as the subjects of this study. The items for review were the duration of disease; the preoperative muscle strength (Muscle Manual Testing); OPLL levels (T1/2-4/5: high, T5/6-8/9: middle, and T9/10-11/12: low); the spinal canal occupancy ratio; the ratio of yellow ligament ossification as a complication; the ratio of transcranial-motor evoked potential (Tc-MEP) derivation; the preoperative/postoperative kyphotic angles in the thoracic vertebrae; the correction angle of kyphosis; the duration of surgery; and the amount of bleeding. The subjects were divided into two groups based on the absence or presence of postoperative paralysis to determine the factors of postoperative paralysis.

RESULTS

Twenty-three patients (14.7%) exhibited postoperative paralysis. Multivariate analysis identified factors associated with postoperative paralysis: the duration of disease (odds ratio, OR = 3.3); the correction angle of kyphosis (OR = 2.4); and the ratio of Tc-MEP derivation (OR = 2.2).

CONCLUSION

The risk factors of postoperative paralysis are a short duration of disease and a small correction angle of kyphosis. In addition, ratios of Tc-MEP derivation below 50% may anticipate paralysis.

LEVEL OF EVIDENCE

4.

The Efficacy of Intraoperative Neurophysiological Monitoring Using Transcranial Electrically Stimulated Muscle-evoked Potentials (TcE-MsEPs) for Predicting Postoperative Segmental Upper Extremity Motor Paresis After Cervical Laminoplasty

STUDY DESIGN

Prospective study.

OBJECTIVE

To investigate the efficacy of transcranial electrically stimulated muscle-evoked potentials (TcE-MsEPs) for predicting postoperative segmental upper extremity palsy following cervical laminoplasty.

SUMMARY OF BACKGROUND DATA

Postoperative segmental upper extremity palsy, especially in the deltoid and biceps (so-called C5 palsy), is the most common complication following cervical laminoplasty. Some papers have reported that postoperative C5 palsy cannot be predicted by TcE-MsEPs, although others have reported that it can be predicted.

METHODS

This study included 160 consecutive cases that underwent open-door laminoplasty, and TcE-MsEP monitoring was performed in the biceps brachii, triceps brachii, abductor digiti minimi, tibialis anterior, and abductor hallucis. A >50% decrease in the wave amplitude was defined as an alarm point. According to the monitoring alarm, interventions were performed, which include steroid administration, foraminotomies, etc.

RESULTS

Postoperative deltoid and biceps palsy occurred in 5 cases. Among the 155 cases without segmental upper extremity palsy, there were no monitoring alarms. Among the 5 deltoid and biceps palsy cases, 3 had significant wave amplitude decreases in the biceps during surgery, and palsy occurred when the patients awoke from anesthesia (acute type). In the other 2 cases in which the palsy occurred 2 days after the operation (delayed type), there were no significant wave decreases. In all of the cases, the palsy was completely resolved within 6 months.

DISCUSSION

The majority of C5 palsies have been reported to occur several days after surgery, but some of them have been reported to occur immediately after surgery. Our results demonstrated that TcE-MsEPs can predict the acute type, whereas the delayed type cannot be predicted.

CONCLUSIONS

A >50% wave amplitude decrease in the biceps is useful to predict acute-type segmental upper extremity palsy. Further examination about the interventions for monitoring alarm will be essential for preventing palsy.

Variety of the Wave Change in Compound Muscle Action Potential in an Animal Model

STUDY DESIGN

Animal study.

PURPOSE

To review the present warning point criteria of the compound muscle action potential (CMAP) and investigate new criteria for spinal surgery safety using an animal model.

OVERVIEW OF LITERATURE

Little is known about correlation palesis and amplitude of spinal cord monitoring.

METHODS

After laminectomy of the tenth thoracic spinal lamina, 2-140 g force was delivered to the spinal cord with a tension gage to create a bilateral contusion injury. The study morphology change of the CMAP wave and locomotor scale were evaluated for one month.

RESULTS

Four different types of wave morphology changes were observed: no change, amplitude decrease only, morphology change only, and amplitude and morphology change. Amplitude and morphology changed simultaneously and significantly as the injury force increased (p<0.05) Locomotor scale in the amplitude and morphology group worsened more than the other groups.

CONCLUSIONS

Amplitude and morphology change of the CMAP wave exists and could be the key of the alarm point in CMAP.

A new alarm point of transcranial electrical stimulation motor evoked potentials for intraoperative spinal cord monitoring: a prospective multicenter study from the Spinal Cord Monitoring Working Group of the Japanese Society for Spine Surgery and Related Research

OBJECT

Although multimodal intraoperative spinal cord monitoring provides greater accuracy, transcranial electrical stimulation motor evoked potential (TcMEP) monitoring became the gold standard for intraoperative spinal cord monitoring. However, there is no definite alarm point for TcMEPs because a multicenter study is lacking. Thus, based on their experience with 48 true-positive cases (that is, a decrease in potentials followed by a new neurological motor deficit postoperatively) encountered between 2007 and 2009, the authors set a 70% decrease in amplitude as the alarm point for TcMEPs.

METHODS

A total of 959 cases of spinal deformity, spinal cord tumor, and ossification of the posterior longitudinal ligament (OPLL) treated between 2010 and 2012 are included in this prospective multicenter study (18 institutions). These institutions are part of the Japanese Society for Spine Surgery and Related Research monitoring working group and the study group on spinal ligament ossification. The authors prospectively analyzed TcMEP variability and pre- and postoperative motor deficits. A 70% decrease in amplitude was designated as the alarm point.

RESULTS

There were only 2 false-negative cases, which occurred during surgery for intramedullary spinal cord tumors. This new alarm criterion provided high sensitivity (95%) and specificity (91%) for intraoperative spinal cord monitoring and favorable accuracy, except in cases of intramedullary spinal cord tumor.

CONCLUSIONS

This study is the first prospective multicenter study to investigate the alarm point of TcMEPs. The authors recommend the designation of an alarm point of a 70% decrease in amplitude for routine spinal cord monitoring, particularly during surgery for spinal deformity, OPLL, and extramedullary spinal cord tumor.

The cutoff amplitude of transcranial motor-evoked potentials for predicting postoperative motor deficits in thoracic spine surgery

STUDY DESIGN

Prospective clinical study of intraoperative transcranial motor-evoked potentials (TcMEP) amplitudes and postoperative motor deficits.

OBJECTIVE

To determine the cutoff amplitude during intraoperative TcMEP monitoring for predicting postoperative motor deficits after thoracic spine surgery.

SUMMARY OF BACKGROUND DATA

Several alarm points when monitoring with TcMEP have been advocated, but there have been no reports on an actual cutoff amplitude of TcMEP for predicting the occurrence of postoperative motor deficits.

METHODS

Among 80 consecutive surgical cases, 28 had a deterioration in TcMEP amplitude in at least 1 monitored muscle during surgery. We examined intraoperative electrophysiological changes and postoperative motor deficits in 270 monitorable muscles in those 28 patients. Through receiver operating characteristic curve analysis, we identified the cutoff amplitudes at the intraoperative point of deterioration and at the end of surgery for predicting postoperative motor deficits in both relative and absolute values.

RESULTS

The relative and the absolute cutoff amplitudes of TcMEP at the intraoperative point of deterioration and at the end of thoracic spine surgery were 12% of control amplitude and 1.9 μV and 25% of control amplitude and 3.6 μV, respectively. Sensitivity/specificity for those cutoff points are 88%/64%, 69%/83%, 90%/64%, and 70%/82%, respectively.

CONCLUSION

We determined the cutoff amplitude for predicting postoperative motor deficits in thoracic spine surgery. The results may help establish the alarm criteria for thoracic spine surgery.