The Interpretation of Muscle Motor Evoked Potentials for Spinal Cord Monitoring

Intramedullary spinal cord cavernous malformations-association between intraoperative neurophysiological monitoring changes and neurological outcome

BACKGROUND

Microsurgical resection of spinal cord cavernous malformations can be assisted by intraoperative neurophysiological monitoring (IONM). While the clinical outcome after surgical resection has been discussed in several case series, the association of intraoperative IONM changes and detailed neurological outcome, however, has not been analyzed so far.

METHODS

Seventeen patients with spinal cavernomas underwent surgery between 02/2004 and 06/2020. Detailed neurological and clinical outcome as well as IONM data including motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring were retrospectively analyzed. Intraoperative IONM changes were compared to outcome at 3-month and 1-year follow-up in order to identify surrogate parameters for an impending neurological deficit.

RESULTS

Compared to the preoperative state, McCormick score at 1-year follow-up remained unchanged in 12 and improved in five patients, none worsened, while detailed neurological examination revealed a new or worsened sensorimotor deficit in 4 patients. The permanent 80% amplitude reduction of MEP and 50% amplitude reduction of SSEP showed the best diagnostic accuracy with a sensitivity of 100% and 67% respectively and a specificity of 73% and 93% respectively. The relative risk for a new neurological deficit at 1-year follow-up, when reversible IONM-deterioration was registered compared to irreversible IONM deterioration, was 0.56 (0.23-1.37) for MEP deterioration and 0.4 (0.18-0.89) for SSEP deterioration.

CONCLUSIONS

Reversible IONM changes were associated with a better neurological outcome at follow-up compared to irreversible IONM deterioration during SCCM surgery. Our study favors the permanent 80% amplitude reduction criterion for MEP and 50% amplitude reduction criterion for SSEP for further prospective evaluation of IONM significance and the effectiveness of corrective maneuvers during SCCM surgeries.

Surgeon-Directed Neuromonitoring in Adolescent Spinal Deformity Surgery Safely Assesses Neurological Function

Background

Spinal deformity correction is associated with the risk of intra-operative neurological injury. Surgeon-directed monitoring (SDM) of transcranial motor-evoked potentials (TcMEP) is an option to monitor intra-operative spinal cord function. We report a retrospective analysis of a prospective database to assess the safety of this technique in spinal deformity correction in adolescent patients.

Methods

Surgeon-directed neuro-monitoring was utilised in 142 consecutive deformity correction surgeries (2012-2017). Surgeons were responsible for electrode placement, intra-operative stimulation, and interpretation of TcMEP data. If waveform disappearance occurred in the lower limb (LL), the surgeon would re-stimulate after excluding technical or anaesthetic factors. Failure to return normal waveforms led to maneuver reversal and reducing distractive force and ensuring subsequent return to baseline. Wake up test and ankle clonus followed by staging surgery was considered if the LL waveforms failed to return indicating potential motor injury.

Results

Of 142 patients, three cases (2.11%) had a complete visual loss of LL signals that did not resolve with anaesthetic stabilisation, leading to reversed surgical manoeuvre and staged surgery. No cases with permanent neurological dysfunction were recorded. This outcome supports surgeon-directed monitoring as a safe monitoring option, as an alternative to neurophysiologist-led monitoring. It also provides evidence in support of the waveform disappearance criteria as a safe TcMEP warning criterion with a 100% negative predictive value.

Conclusions

Where there is a lack of availability of trained neurophysiologists, surgeon-directed neuro-monitoring is a safe and reliable method of preventing intra-operative neurological injury amongst adolescent patients undergoing deformity correction.

Transcranial Electrical Motor Evoked Potential in Predicting Positive Functional Outcome of Patients after Decompressive Spine Surgery: Review on Challenges and Recommendations towards Objective Interpretation

Spine surgeries impose risk to the spine's surrounding anatomical and physiological structures especially the spinal cord and the nerve roots. Intraoperative neuromonitoring (IONM) is a technology developed to monitor the integrity of the spinal cord and the nerve roots via the surgery. Transcranial motor evoked potential (TcMEP) (one of the IONM modalities) is adopted to monitor the integrity of the motor pathway of the spinal cord and the motor nerve roots. Recent research suggested that the IONM is conducive as a prognostic tool towards the patient's functional outcome. This paper summarizes the researches of IONM being adopted as a prognostic tool. In addition, this paper highlights the problems associated with the signal parameters as the improvement criteria in the previous researches. Lastly, we review the challenges of TcMEP to achieve a prognostic tool focusing on the factors that could interfere with the generation of a stable TcMEP response. The final section will discuss recommendations for IONM technology to achieve an objective prognostic tool.

The surgical challenge of ossified ventrolateral spinal meningiomas: tricks and pearls for managing large ossified meningiomas of the thoracic spine

The authors present an illustrative technical note on microsurgical resection of ventrolateral completely ossified spinal meningiomas (OSMs) and a literature review of the surgical management of calcified spinal meningiomas or OSMs. These tumors are surgically demanding due to their solid consistency, especially when in a ventrolateral location with dislocation of the spinal cord. A challenging case with significant thoracic cord compression and displacement is described. Due to the firm consistency and the ventrolateral localization of the meningioma, a piecemeal resection was necessary. This could have resulted in a free-floating tumor remnant adherent to the spinal cord, impeding safe tumor resection. To avoid such a remnant, an anchoring burr hole was drilled at the border between the spinal cord and the adamantine tumor mass. Then, a microdissector was placed within the anchoring burr hole and the tumor was gently pulled laterally while drilling away the medial parts of the ossified tumor. This procedure was repeated until separation of the tumor from the spinal cord was possible and a gross-total resection (Simpson grade II) was manageable. Throughout the procedure, continuous intraoperative neurophysiological monitoring was performed.

[Quantitative characterization of risk of iatrogenic damage to pyramidal tracts based on data of intraoperative neuromonitoring during surgical correction of spinal deformities]

OBJECTIVE

Development of a quantitative indicator for the risk level of intraoperative iatrogenic motor disorders in the process of surgical correction of spinal deformity based on current neurophysiological monitoring data.

MATERIAL AND METHODS

288 patients 12.6±0.35 y.o. underwent surgical correction of spinal deformities under the control of intraoperative neuromonitoring. The nature of changes in motor evoked potentials was assessed according to the earlier proposed ranking scale. The incidence of different variants of changes in the rank values of the state of the pyramidal system during the operation and the resulting postoperative motor disturbances was calculated.

RESULTS

By comparing probabilities of various changes in the conduction properties of pyramidal tracts during surgery with the incidence of the observed motor deficiencies we quantitatively assessed the possible correlation between these phenomena. We propose a method for calculating the risk index for postoperative motor disorders depending on the maximum rank of the pyramidal system's response to surgical aggression.

CONCLUSION

The developed system of ranking evaluation of changes in motor evoked potentials during surgical correction of spinal deformity makes it possible to quantify the risk of postoperative motor disorders and, accordingly, to monitor the level of anxiety for a neurosurgeon during individual stages of surgical intervention.

Monopolar 250-500 Hz language mapping: Results of 41 patients

•

Monopolar mapping is effective for cortical and subcortical language areas.

•

250–500 Hz stimulation parameters are adequate and safe for speech testing.

•

It may improve resection rate of infiltrating tumor areas involving the speech area.

Objectives

To determine whether high-frequency 250–500 Hz monopolar stimulation is effective for mapping cortical and subcortical language structures during brain tumor resection.

Methods

Using high-frequency monopolar stimulation, we mapped the speech areas of 41 awake patients undergoing brain tumor resection in the dominant hemisphere, subject to risk of lesions in the cortical and subcortical speech tracts. Patients were tested for object naming, semantic and other language tasks.

Results

Mapping was positive in 22 out of 41 patients. Nine patients presented clinical worsening immediately after surgery. Only one patient did not recover after the 30-day follow-up. Nineteen patients showed negative mapping for language tracts, none of whom exhibited worsening of symptoms at the final evaluation. The applied method showed 89% sensitivity and 56% specificity rates.

Conclusions

The applied method was effective in identifying cortical and subcortical speech areas during the surgical resection of brain tumors.

Significance

Determining whether monopolar high-frequency stimulation is effective for language mapping is important, since it may be very effective in infiltrating tumor areas and nearby edema region.

A new criterion for detection of radiculopathy based on motor evoked potentials and intraoperative nerve root monitoring

OBJECTIVE

Our objective is to use the area of the motor evoked potential (MEP) as a diagnostic tool for intraoperative radicular injury.

METHODS

We analyzed the intraoperative neurophysiological monitoring data and clinical outcomes of 203 patients treated for dorsolumbar spine deformity. The decrease in amplitude was compared with the reduction in the MEP area.

RESULTS

In 11 cases, new intraoperative injuries occurred, nine of them were lumbar radiculopathies. Our new criteria, a decrease MEP area of 70%, yielded a sensitivity and specificity of 1, since it detected all the radicular injuries, with no false positive cases. Using a 70% amplitude decrease criteria, we obtained a sensitivity of 0,89 and a specificity of 0,99. A lower threshold (65% amplitude reduction) yielded a higher number of false positives, whereas a higher threshold (75 and 80%) gave rise to a higher number of false negatives.

CONCLUSIONS

The measurement of the MEP area gave evidence to be more reliable and accurate than the measurement of the amplitude reduction in order to assess and detect intraoperative radicular injuries.

SIGNIFICANCE

The criterion of decrease of the MEP area has a higher reliability and accuracy in the detection of intraoperative radicular lesions than the amplitude reduction.

Transcranial Motor Evoked Potential Alarm Criteria to Predict Foot Drop Injury During Lumbosacral Surgery

STUDY DESIGN

A retrospective cohort analysis.

OBJECTIVE

This study aims to investigate whether waveform alterations in transcranial motor evoked potentials (TCMEPs) can reliably predict postoperative foot drop.

SUMMARY OF BACKGROUND DATA

Nerve injury leading to foot drop is a potential complication of lumbosacral surgery. Very limited data exist on the use of intraoperative TCMEPs to identify iatrogenic foot drop.

METHODS

We retrospectively reviewed neuromonitoring data from 130 consecutive spine surgeries with instrumentation involving L4-S1. TCMEP waveform analysis included amplitude (A), area under the curve (AUC), latency (L), and duration (D). Patient outcomes were correlated with neuromonitoring results. Intraoperative alert criteria were established on the basis of observed intraoperative changes.

RESULTS

Three patients developed severe foot drop with a muscle weakness functional grade ranging from 0/5 to 3/5. Two patients developed a mild foot drop with functional grade 4/5. Twenty-three patients had preoperative weakness in an L5 distribution. One-hundred two patients who had neither preoperative nor postoperative neurological complications served as a control group. Amplitude significantly decreased in patients with a severe postoperative deficit (P = 0.005) as did AUC and duration (P < 0.05). Intraoperative alert criteria defined as a >65% decrease in AUC resulted in a sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 100%, 91.4%, 12%, and 100%, respectively. When defining an alert criteria as a >50% decrease in amplitude, sensitivity, specificity, PPV, and NPV were 100%, 87.9%, 8.8%, and 100%, respectively.

CONCLUSION

Reduction of TCMEP waveform associated with postoperative severe foot drop can be detected during lumbar surgery. Other waveform parameters such as AUC may predict foot drop better than the amplitude. Additional examinations in larger samples of foot drops are needed to validate these alert threshold findings.

LEVEL OF EVIDENCE

4.

Short-term Efficacy of Hand-Arm Bimanual Intensive Training on Upper Arm Function in Acute Stroke Patients: A Randomized Controlled Trial

Background

Rehabilitation training during the acute phase of stroke (<48 h) markedly improves impaired upper-limb movement. Hand-arm bimanual intensive training (HABIT) represents an intervention that promotes improvements in upper extremity function in children with cerebral palsy. This study repurposed HABIT in acute stroke patients and assessed recovery of upper extremity function when compared with a conventional rehabilitation program (CRP).

Methods

In a randomized trial, 128 patients with acute stroke were assigned to the HABIT or the CRP groups. The primary endpoint was clinical motor functional assessment that was guided by the Fugl-Meyer motor assessment (FMA) and outcomes of the action research arm test (ARAT). The secondary endpoint was an improved neurophysiological evaluation according to the motor-evoked potential amplitude (AMP), resting motion threshold (RMT), and central motor conduction time (CMCT) scores over the 2-week course of therapy. In both groups, scores were evaluated at baseline, 1 week from commencing therapy, and post-therapy.

Results

After 2 weeks, the HABIT group showed improved scores as compared the CRP group for FMA (51.7 ± 6.44 vs. 43.5 ± 5.6, P < 0.001), ARAT (34.5 ± 6.2 vs. 33.3 ± 6.3, P = 0.022), and AMP (1.1 ± 0.1 vs. 1.0 ± 0.1, P < 0.001). However, CMCT (8.6 ± 1.0 vs. 9.1 ± 0.6, P = 0.054) and RMT (55.3 ± 4.2 vs. 57.5 ± 4.1, P = 0.088) were similar when comparing between groups.

Conclusion

HABIT significantly improved motor functional and neuro-physiological outcomes in patients with acute stroke, which suggested that HABIT might represent an improved therapeutic strategy as compared CRP.