Characteristics of multi-channel Br(E)-MsEP waveforms for the lower extremity muscles in thoracic spine surgery: comparison based on preoperative motor status

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.

The Utility of Transcranial Stimulated Motor-Evoked Potential Alerts in Cervical Spine Surgery Varies Based on Preoperative Motor Status

STUDY DESIGN

A prospective multicenter observational study.

OBJECTIVE

The aim was to investigate the validity of transcranial motor-evoked potentials (Tc-MEP) in cervical spine surgery and identify factors associated with positive predictive value when Tc-MEP alerts are occurred.

SUMMARY OF BACKGROUND DATA

The sensitivity and specificity of Tc-MEP for detecting motor paralysis are high; however, false-positives sometimes occur.

MATERIALS AND METHODS

The authors examined Tc-MEP in 2476 cases of cervical spine surgeries and compared patient backgrounds, type of spinal disorders, preoperative motor status, surgical factors, and the types of Tc-MEP alerts. Tc-MEP alerts were defined as an amplitude reduction of more than 70% from the control waveform. Tc-MEP results were classified into two groups: false-positive and true-positive, and items that showed significant differences were extracted by univariate analysis and detected by multivariate analysis.

RESULTS

Overall sensitivity was 66% (segmental paralysis: 33% and lower limb paralysis: 95.8%) and specificity was 91.5%. Tc-MEP outcomes were 33 true-positives and 233 false-positives. Positive predictive value of general spine surgery was significantly higher in cases with a severe motor status than in a nonsevere motor status (19.5% vs . 6.7%, P =0.02), but not different in high-risk spine surgery (20.8% vs . 19.4%). However, rescue rates did not significantly differ regardless of motor status (48% vs . 50%). In a multivariate logistic analysis, a preoperative severe motor status [ P =0.041, odds ratio (OR): 2.46, 95% confidence interval (95% CI): 1.03-5.86] and Tc-MEP alerts during intradural tumor resection ( P <0.001, OR: 7.44, 95% CI: 2.64-20.96) associated with true-positives, while Tc-MEP alerts that could not be identified with surgical maneuvers ( P =0.011, OR: 0.23, 95% CI: 0.073-0.71) were associated with false-positives.

CONCLUSION

The utility of Tc-MEP in patients with a preoperative severe motor status was enhanced, even in those without high-risk spine surgery. Regardless of the motor status, appropriate interventions following Tc-MEP alerts may prevent postoperative paralysis.

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.

Efficacy of Intraoperative Neuromonitoring Using Transcranial Motor-Evoked Potentials for Degenerative Cervical Myelopathy: A Prospective Multicenter Study by the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

STUDY DESIGN

A prospective multicenter observational study.

OBJECTIVE

To elucidate the efficacy of transcranial motor-evoked potentials (Tc(E)-MEPs) in degenerative cervical myelopathy (DCM) surgery by comparing cervical spondylotic myelopathy (CSM) to cervical ossification of the posterior longitudinal ligament (OPLL) and investigate the timing of Tc(E)-MEPs alerts and types of interventions affecting surgical outcomes.

SUMMARY OF BACKGROUND DATA

Although CSM and OPLL are the most commonly encountered diseases of DCM, the benefits of Tc(E)-MEPs for DCM remain unclear and comparisons of these two diseases have not yet been conducted.

METHODS

We examined the results of Tc(E)-MEPs from 1176 DCM cases (840 CSM /336 OPLL) and compared patients background by disease, preoperative motor deficits, and the type of surgical procedure. We also assessed the efficacy of interventions based on Tc(E)-MEPs alerts. Tc(E)-MEPs alerts were defined as an amplitude reduction of more than 70% below the control waveform. Rescue cases were defined as those in which waveform recovery was achieved after interventions in response to alerts and no postoperative paralysis.

RESULTS

Overall sensitivity was 57.1%, and sensitivity was higher with OPLL (71.4%) than with CSM (42.9%). The sensitivity of acute onset segmental palsy including C5 palsy was 40% (OPLL/CSM: 66.7%/0%) whereas that of lower limb palsy was 100%. The most common timing of Tc(E)-MEPs alerts was during decompression (63.16%), followed by screw insertion (15.79%). The overall rescue rate was 57.9% (OPLL/CSM: 58.3%/57.1%).

CONCLUSION

Since Tc(E)-MEPs are excellent for detecting long tract injuries, surgeons need to consider appropriate interventions in response to alerts. The detection of acute onset segmental palsy by Tc(E)-MEPs was partially possible with OPLL, but may still be difficult with CSM. The rescue rate was higher than 50% and appropriate interventions may have prevented postoperative neurological complications.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 muscle evoked potential after epidural electrical stimulation of the spinal cord as a monitor for the corticospinal tract: studies by collision technique and double train stimulation

To study if spinal motor evoked potentials (SpMEPs), muscle responses after electrical stimulation of the spinal cord, can monitor the corticospinal tract. Study 1 comprised 10 consecutive cervical or thoracic myelopathic patients. We recorded three types of muscle responses intraoperatively: (1) transcranial motor evoked potentials (TcMEPs), (2) SpMEPs and (3) SpMEPs + TcMEPs from the abductor hallucis (AH) using train stimulation. Study 2 dealt with 5 patients, who underwent paired train stimulation to the spinal cord with intertrain interval of 50-60 ms for recording AH SpMEPs. We will also describe two illustrative cases to demonstrate the clinical value of AH SpMEPs for monitoring the motor pathway. In Study 1, SpMEPs and SpMEPs + TcMEPs recorded from AH measured nearly the same, suggesting the collision of the cranially evoked volleys with the antidromic signals induced by spinal cord stimulation via the corticospinal tracts. In Study 2, the first and second train stimuli elicited almost identical SpMEPs, indicating a quick return of transmission after 50-60 ms considered characteristic of the corticospinal tract rather than the dorsal column, which would have recovered much more slowly. Of the two patients presented, one had no post-operative neurological deteriorations as anticipated by stable SpMEPs, despite otherwise insufficient IONM, and the other developed post-operative motor deficits as predicted by simultaneous reduction of TcMEPs and SpMEPs in the face of normal SEPs. Electrical stimulation of the spinal cord primarily activates the corticospinal tract to mediate SpMEPs.

Effects of Preoperative Motor Status on Intraoperative Motor-evoked Potential Monitoring for High-risk Spinal Surgery: A Prospective Multicenter Study

STUDY DESIGN

Prospective multicenter observational study.

OBJECTIVE

To evaluate transcranial motor-evoked potentials (Tc-MEPs) baseline characteristics of lower limb muscles and to determine the accuracy of Tc-MEPs monitoring based on preoperative motor status in surgery for high-risk spinal disease.

SUMMARY OF BACKGROUND DATA

Neurological complications are potentially serious side effects in surgery for high-risk spine disease. Intraoperative spinal neuromonitoring (IONM) using Tc-MEPs waveforms can be used to identify neurologic deterioration, but cases with preoperative motor deficit tend to have poor waveform derivation.

METHODS

IONM was performed using Tc-MEPs for 949 patients in high-risk spinal surgery. A total of 4454 muscles in the lower extremities were chosen for monitoring. The baseline Tc-MEPs was recorded immediately after exposure of the spine. The derivation rate was defined as muscles detected/muscles prepared for monitoring. A preoperative neurological grade was assigned using the manual muscle test (MMT) score.

RESULTS

The 949 patients (mean age 52.5 ± 23.3 yrs, 409 males [43%]) had cervical, thoracic, thoracolumbar, and lumbar lesions at rates of 32%, 40%, 26%, and 13%, respectively. Preoperative severe motor deficit (MMT ≤3) was present in 105 patients (11%), and thoracic ossification of the posterior longitudinal ligament (OPLL) was the most common disease in these patients. There were 32 patients (3%) with no detectable waveform in any muscles, and these cases had mostly thoracic lesions. Baseline Tc-MEPs responses were obtained from 3653/4454 muscles (82%). Specificity was significantly lower in the severe motor deficit group. Distal muscles had a higher waveform derivation rate, and the abductor hallucis (AH) muscle had the highest derivation rate, including in cases with preoperative severe motor deficit.

CONCLUSION

In high-risk spinal surgery, Tc-MEPs collected with multi-channel monitoring had significantly lower specificity in cases with preoperative severe motor deficit. Distal muscles had a higher waveform derivation rate and the AH muscle had the highest rate, regardless of the severity of motor deficit preoperatively.Level of Evidence: 3.

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.

Poor derivation of Tc-MEP baseline waveforms in surgery for ventral thoracic intradural extramedullary tumor: Efficacy of use of the abductor hallucis in cases with a preoperative non-ambulatory status

Most thoracic intradural extramedullary tumors (IDEMT) are benign lesions that are treated by gross total resection and spinal cord decompression. Intraoperative transcranial-motor evoked potential (Tc-MEP) monitoring is important for reducing postoperative neurological complications. The purpose of this study is to examine the characteristics of Tc-MEP waveforms in surgery for thoracic IDEMT resection based on location of the tumor relative to the spinal cord. The subjects were 56 patients who underwent surgery for thoracic IDEMT from 2010 to 2018. The waveform derivation rate for each lower muscle was examined at baseline and intraoperatively. 56 patients had a mean age of 61.7 years, and 21 (38%) were non-ambulatory before surgery. The tumors were schwannoma (n = 28, 50%), meningioma (n = 25, 45%), and neurofibroma (n = 3, 5%); and the lesions were dorsal (n = 29, 53%) and ventral (n = 27, 47%). There was a significantly higher rate of undetectable waveforms in all lower limb muscles in the ventral group compared to the dorsal group (15% vs. 3%, p < 0.05). In non-ambulatory cases, the derivation rate at baseline was significantly lower for ventral thoracic IDMETs (47% vs. 68%, p < 0.05). The abductor hallucis (AH) had the highest waveform derivation rate of all lower limb muscles in non-ambulatory cases with a ventral thoracic IDMET. Spinal cord compression by a ventral lesion may be increased, and this may be reflected in greater waveform deterioration. Of all lower limb muscles, the AH had the highest derivation rate, even in non-ambulatory cases with a ventral IDEMT, which suggests the efficacy of multichannel monitoring including the AH.