Intraoperative neuromonitoring as real-time diagnostic for cerebral ischemia in endovascular treatment of ruptured brain aneurysms.

OBJECTIVE: To evaluate the diagnostic accuracy of intraoperative neurophysiological monitoring (IONM) during endovascular treatment (EVT) of ruptured intracranial aneurysms (rIA). METHODS: IONM and clinical data from 323 patients who underwent EVT for rIA from 2014-2019 were retrospectively reviewed. Significant IONM changes and outcomes were evaluated based on visual review of data and clinical documentation. RESULTS: Of the 323 patients undergoing EVT, significant IONM changes were noted in 30 patients (9.29%) and 46 (14.24%) experienced postprocedural neurological deficits (PPND). 22 out of 30 (73.33%) patients who had significant IONM changes experienced PPND. Univariable analysis showed changes in somatosensory evoked potential (SSEP) and electroencephalogram (EEG) were associated with PPND (p-values: <0.001 and <0.001, retrospectively). Multivariable analysis showed that IONM changes were significantly associated with PPND (Odd ratio (OR) 20.18 (95%CI:7.40-55.03, p-value: <0.001)). Simultaneous changes in both IONM modalities had specificity of 98.9% (95% CI: 97.1%-99.7%). While sensitivity when either modality had a change was 47.8% (95% CI: 33.9%-62.0%) to predict PPND. CONCLUSIONS: Significant IONM changes during EVT for rIA are associated with an increased risk of PPND. SIGNIFICANCE: IONM can be used confidently as a real time neurophysiological diagnostic guide for impending neurological deficits during EVT treatment of rIA.

Intraoperative Neurophysiological Monitoring in Corrective Surgery of Scoliosis - Experience at a Tertiary Care Hospital.

OBJECTIVE: To evaluate the role of intraoperative neurophysiological monitoring (IONM) in reducing the postoperative neurologic deficit following corrective surgery of scoliosis. STUDY DESIGN: Observational Study. Place and Duration of the Study: Spine Surgery Department, Combined Military Hospital, Rawalpindi, from December 2022 to May 2023. METHODOLOGY: The study included 170 cases of scoliosis operated under multimodal IONM. Decreased amplitude of ≥50% in SSEP or 70-80% in MEPs were considered warning signs. Cases were divided into two groups: Group 1 (signal drop) and Group 2 (no signal drop). Group 1 was subdivided into Group 1a (true positive), Group 1b (false positive) and Group 1c (intermediate positive). Group 2 was subdivided into Group 2a (true negative) and Group 2b (false negative). RESULTS: Evoked potential changes were observed in 27 (15.9%) cases. This includes transient drop of signals in 16 (9.4%) and sustained drop of signals in 11 (6.5%) cases. Among sustained signal drop, 9 (5.29%) cases had exhibited postoperative neurological deficit whereas 2 (1.17%) cases did not show postoperative neurological deficit (false positive). Multimodal IONM in the current study shows sensitivity of 100%, specificity of 98.6%, positive predictive value of 92.6%, and negative predictive value of 100%. CONCLUSION: Multimodal IONM reduces the incidence of postoperative neurological deficit in corrective surgery of scoliosis by effectively detecting neurologic injury during surgery. Monitoring events alert surgical team to exercise immediate corrective measures which likely results in recovery of lost signals and predict the favorable outcome. KEY WORDS: Intraoperative monitoring, Motor evoked potentials, Neurological deficit, Scoliosis, Somatosensory evoked potentials.

Intraoperative High-Resolution Color-Coded Ultrasound to Identify the Posterior Median Sulcus for Midline Myelotomy in Intramedullary Spinal Cord Surgery.

A 14-year-old boy presented with a 2-year history of slowly increasing weakness and atrophy in the right forearm and leg. Magnetic resonance imaging (MRI) revealed an intramedullary diffusely infiltrating lateralized tumor at C3-7. An extended biopsy was planned. After laminotomy and durotomy, the swollen spinal cord was noted to be rotated by 45° with the right dorsal root entry zone being in the midline. A 15 MHz linear ultrasound probe was used to identify the midline by visualizing the dorsal median sulcal vein within the midline raphe. A myelotomy was made in that zone without deterioration of somatosensory evoked potentials (SEPs) and an extended biopsy was performed. Histological examination revealed a pilocytic astrocytoma. Modern intraoperative high-resolution color-coded ultrasound enables the identification of the midline in intramedullary spinal cord lesions even when the spinal cord anatomy is distorted.

Intraoperative Neurophysiologic Monitoring and Mapping During Surgery on Intramedullary Spinal Cord Tumors in Children and Adolescents.

SUMMARY: Surgical resection of intramedullary spinal cord tumors carries significant risks of neurologic deficits, especially in cases of infiltrative tumors. In pediatric patients, this type of surgery may be associated with a high risk of poor neurologic outcome. Intraoperative neurophysiologic monitoring has been adopted as part of the clinical routine by many centers as a useful adjunct for intraoperative assessment of neurologic integrity. To what extent intraoperative neurophysiologic mapping strategies may further support intraoperative decision-making is still a matter of debate. Here, we report on a small cohort of five pediatric patients in whom mapping with the double-train paradigm was used to identify the dorsal column and corticospinal tract and to guide the surgical resection. We also discuss the possible benefits and challenges regarding the available literature.

Intraoperative Monitoring of Scoliosis Surgery in Young Patients.

SUMMARY: Intraoperative neurophysiologic monitoring has added substantially to the safety of spinal deformity surgery correction since its introduction over four decades ago. Monitoring routinely includes both somatosensory evoked potentials and motor evoked potentials. Either modality alone will detect almost all instances of spinal cord injury during deformity correction. The combined use of the two modalities provides complementary information, can permit more rapidly identification of problems, and enhances safety though parallel redundancy should one modality fail. Both techniques are well established and continue to be refined. Although there is room for provider preference, proper monitoring requires attention to technical detail, understanding of the underlying physiology, and familiarity with effects of commonly used anesthetic agents.

Diagnostic utility of different types of somatosensory evoked potential changes in pediatric idiopathic scoliosis correction surgery.

PURPOSE: To evaluate the diagnostic accuracy of intraoperative somatosensory evoked potential (SSEP) monitoring and types of SSEP changes in predicting the risk of postoperative neurological outcomes during correction surgery for idiopathic scoliosis (IS) in the pediatric age group (≤ 21 years). METHODS: Database review was performed to identify literature on pediatric patients with IS who underwent correction with intraoperative neuromonitoring. The sensitivity, specificity, and diagnostic odds ratio (DOR) of transient and persistent SSEP changes and complete SSEP loss in predicting postoperative neurological deficits were calculated. RESULTS: Final analysis included 3778 patients. SSEP changes had a sensitivity of 72.9%, specificity of 96.8%, and DOR of 102.3, while SSEP loss had a sensitivity of 41.8%, specificity of 99.3%, and DOR of 133.2 for predicting new neurologic deficits. Transient and persistent SSEP changes had specificities of 96.8% and 99.1%, and DORs of 16.6 and 59, respectively. CONCLUSION: Intraoperative SSEP monitoring can predict perioperative neurological injury and improve surgical outcomes in pediatric scoliosis fusion surgery. LEVEL OF EVIDENCE: Level 2. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Cost-benefit analysis of intraoperative neuromonitoring for cardiac surgery.

BACKGROUND: Intraoperative neuromonitoring (IONM) can detect large vessel occlusion (LVO) in real-time during surgery. The aim of this study was to conduct a cost-benefit analysis of utilizing IONM among patients undergoing cardiac surgery. METHODS: A decision-analysis tree with terminal Markov nodes was constructed to model functional outcome, as measured via the modified Rankin Scale (mRS), among 65-year-old patients undergoing cardiac surgery. Our cost-benefit analysis compares the use of IONM (electroencephalography and somatosensory evoked potential) against no IONM in preventing neurological complications from perioperative LVO during cardiac surgery. The study was performed over a lifetime horizon from a societal perspective in the United States. Base case and one-way probabilistic sensitivity analyses were performed. RESULTS: At a baseline LVO rate of 0.31%, the mean attributable lifetime expenditure for IONM-monitored cardiac surgeries relative to unmonitored cardiac surgeries was $1047.41 (95% CI, $742.12 - $1445.10). At a critical LVO rate of approximately 3.67%, the costs of both monitored and unmonitored cardiac surgeries were the same. Above this critical rate, implementing IONM became cost-saving. On one-way sensitivity analysis, variation in LVO rate from 0% - 10% caused lifetime costs attributable to receiving IONM to range from $1150.47 - $29404.61; variations in IONM cost, percentage of intervenable LVOs, IONM sensitivity, and mechanical thrombectomy cost exerted comparably minimal influence over lifetime costs. DISCUSSION: We find considerable cost savings favoring the use of IONM under certain parameters corresponding to high-risk patients. This study will provide financial perspective to policymakers, clinicians, and patients alike on the appropriate use of IONM during cardiac surgery.

Descending Neurogenic Evoked Potentials Monitoring Is an Effective Alternative in Spinal Deformity Surgery Under Inhaled Anesthesia.

BACKGROUND: To evaluate the reliability of descending neurogenic evoked potentials (DNEP) monitoring in spinal deformity surgery under inhaled anesthesia. METHODS: A total of 180 consecutive patients who underwent spinal deformity surgery in our scoliosis center from July 2014 to August 2016 were reviewed. Intraoperative monitoring including somatosensory evoked potentials (SEP), motor evoked potentials (MEP), and DNEP was conducted routinely throughout operation. Patients were divided into 2 groups according to anesthesia methods: group A (n = 72, inhaled anesthesia, SEP/DNEP) and group B (n = 108, total intravenous anesthesia, SEP/MEP/DNEP). Intraoperative monitoring data were collected and analyzed. RESULTS: Positive alerts were observed in 26 patients (14.5%), of whom 18 (10%) were confirmed as true-positive events in the study population. No false-negative events were recorded. In group A, the sensitivity and specificity of SEP and DNEP were 100% and 93.8% and 100% and 98.5%, respectively. For group B, the sensitivity and specificity of SEP/MEP and DNEP were 100% and 95.9% and 100% and 98%, respectively. CONCLUSIONS: DNEP monitoring seemed to be effective for the detection and prevention of iatrogenic neurologic deficits during spinal deformity surgery. This study indicates that DNEP was an effective alternative in spinal deformity surgery under inhaled anesthesia.

Effectiveness of MEP and SSEP Monitoring in the Diagnosis of Neurological Dysfunction Immediately After Craniotomy Aneurysm Clipping.

OBJECTIVE: To explore the diagnostic accuracy of motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring in predicting immediate neurological dysfunction after craniotomy aneurysm clipping. METHODS: A total of 184 patients with neurosurgery aneurysms in the Affiliated Hospital of Qingdao University from April 2019 to December 2021 were retrospectively included. All patients underwent craniotomy aneurysm clipping, and MEP and SSEP were used to monitor during the operation. Receiver operating characteristic (ROC) curve analysis was used to determine the optimal cutoff value for early warning of MEP and SSEP amplitude decline and to evaluate the effectiveness of MEP and SSEP changes in predicting immediate postoperative neurological dysfunction. RESULTS: Among the 184 patients with intracranial aneurysms, the incidences of immediate postoperative neurological dysfunction were 44.4% (12/27) and 3.2% (5/157) in patients with intraoperative MEP changes and without changes, respectively. For SSEP, The incidence rates were 52.6% (10/19) and 4.2% (7/165), respectively, and the differences were statistically significant ( P <0.001). Significant changes in intraoperative MEP and SSEP were significantly associated with the development of immediate postoperative neurological deficits ( P <0.05). The critical values for early warning of MEP and SSEP amplitude decrease were: 61.6% ( P < 0.001, area under the curve 0.803) for MEP amplitude decrease and 54.6% ( P <0.001, area under the curve 0.770) for SSEP amplitude decrease. The sensitivity and specificity of MEP amplitude change in predicting immediate postoperative neurological dysfunction were 70.6% and 91.0%, respectively. For SSEP amplitude changes, the sensitivity and specificity were 58.8% and 95.8%, respectively. CONCLUSIONS: Motor-evoked potential and SSEP monitoring have moderate sensitivity and high specificity for immediate postoperative neurological dysfunction after craniotomy aneurysm clipping. Motor-evoked potential is more accurate than SSEP. Patients with changes in MEP and SSEP are at greatly increased risk of immediate postoperative neurologic deficits.

Changes in motor evoked potentials after erector spinae block in scoliosis surgery-when to take pre-incision baseline recordings?

Multimodal intraoperative neurophysiological monitoring (IONM) is highly valuable in scoliosis surgeries for monitoring spinal cord function, particularly during instrumentation. Accurate timing of baseline recordings of TcMEP and SSEP is crucial, as any changes observed during surgery and instrumentation are compared to these baseline recordings. However, the impact of ultrasound-guided erector spinae block (USG-ESPB) on SSEP and TcMEP is not well-studied in scoliosis surgery. In this report, we present two cases of scoliosis surgery where bilateral two-level USG-ESPB using different concentrations of ropivacaine (0.375% and 0.2%) resulted in a transient and significant deterioration of TcMEP, occurring 3 minutes after the block and lasting for 20 minutes. Remarkably, SSEPs remained unchanged during this period. These findings suggest that USG-ESPB may produce TcMEP changes, highlighting the importance of carefully considering the timing of baseline TcMEP acquisition in scoliosis surgery.

Role of Intraoperative Neuromonitoring to Predict Postoperative Delirium in Cardiovascular Surgery.

OBJECTIVE: Postoperative delirium (POD) can occur in up to 50% of older patients undergoing cardiovascular surgery, resulting in hospitalization and significant morbidity and mortality. This study aimed to determine whether intraoperative neurophysiologic monitoring (IONM) modalities can be used to predict delirium in patients undergoing cardiovascular surgery. DESIGN: Adult patients undergoing cardiovascular surgery with IONM between 2019 and 2021 were reviewed retrospectively. Delirium was assessed multiple times using the Intensive Care Delirium Screening Checklist (ICDSC). Patients with an ICDSC score ≥4 were considered to have POD. Significant IONM changes were evaluated based on a visual review of electroencephalography (EEG) and somatosensory evoked potentials data and documentation of significant changes during surgery. SETTING: University of Pittsburgh Medical Center hospitals. PARTICIPANTS: Patients 18 years old and older undergoing cardiovascular surgery with IONM monitoring. MEASUREMENTS AND MAIN RESULTS: Of the 578 patients undergoing cardiovascular surgery with IONM, 126 had POD (21.8%). Significant IONM changes were noted in 134 patients, of whom 49 patients had delirium (36.6%). In contrast, 444 patients had no IONM changes during surgery, of whom 77 (17.3%) patients had POD. Upon multivariate analysis, IONM changes were associated with POD (odds ratio 2.12; 95% CI 1.31-3.44; p < 0.001). Additionally, baseline EEG abnormalities were associated with POD (p = 0.002). CONCLUSION: Significant IONM changes are associated with an increased risk of POD in patients undergoing cardiovascular surgery. These findings offer a basis for future research and analysis of EEG and somatosensory evoked potential monitoring to predict, detect, and prevent POD.

Validity of evoked potential as biomarker for predicting early neural function changes after thoracic spinal decompression surgery in patients with neurological deficits.

OBJECTIVE: To evaluate the validity of intraoperative evoked potential (EP) including motor evoked potential (MEP) and somatosensory evoked potentials (SEP) as a biomarker for predicting neural function changes after thoracic spinal decompression (TSD) surgery. METHOD: A consecutive series of 336 TSD surgeries were reviewed between 2010 and 2021 from four spine center. All patients with TSD were divided into 3 groups according to different intraoperative EP results: group 1, EP alerts; group 2, no obvious EP deterioration; group 3, EP improvement compared with baselines. The lower limb Japanese Orthopedic Association (JOA) scores (as well as early and long-term JOA recovery rate) were utilized to quantitatively assess pre- and postoperative neural function change. RESULTS: Among the 3 subgroups according to the different EP changes, the early JOA recovery rate (RR%) in the EP improvement group was significantly better than the other two groups (51.3 ± 58.6* vs. 27.5 ± 31.2 and 33.3 ± 43.1; p < 0.01) after 3-month follow-up. The mean MEP and SEP amplitude were from 116 ± 57 µV to 347 ± 71 µV (p < 0.01) and from 1.86 ± 0.24 µV to 2.65 ± 0.29 µV (p < 0.01) between spinal cord pre-decompression and post-decompression. Moreover, multivariate logistic regression analysis revealed that risk factors of EP improvement were duration of symptom (p < 0.001, OR 10.9) and Preop. neurologic deficit degree (p = 0.013, OR 7.46). CONCLUSION: The intraoperative EP can predict postoperative neural function changes as a biomarker during TSD. Patient with EP improvement probably has better prognosis for early neural function recovery. The duration of symptom and preoperative neurologic deficit degree may be related to intraoperative EP improvement.

The effects of dexmedetomidine on intraoperative neurophysiologic monitoring modalities during corrective scoliosis surgery in pediatric patients: A systematic review.

BACKGROUND: During scoliosis surgery, motor evoked potentials (MEP), and somatosensory evoked potentials (SSEP) have been reported to be affected by the use of higher doses of anesthetic agents. Dexmedetomidine, a sympatholytic agent, an alpha-2 receptor agonist, has been used as an adjunctive agent to lower anesthetic dose. However, there is conflicting evidence regarding the effects of dexmedetomidine on the intraoperative neurophysiological monitoring of MEP and SSEP during surgery, particularly among pediatric patients. OBJECTIVES: This systematic review aimed to determine whether, during spinal fusion surgery in pediatric patients with scoliosis, dexmedetomidine alters MEP amplitude or SSEP latency and amplitude and, if so, whether different doses of dexmedetomidine display different effects (PROSPERO registration number CRD42022300562). METHODS: We searched PubMed, Scopus, and Cochrane Library on January 1, 2022 and included randomized controlled trials, observational cohort and case-control studies and case series investigating dexmedetomidine in the population of interest and comparing against a standardized anesthesia regimen without dexmedetomidine or comparing multiple doses of dexmedetomidine. Animal and in vitro studies and conference abstracts were excluded. RESULTS: We found substantial heterogeneity in the risk of bias (per Cochrane-preferred tools) of the included articles (n = 5); results are summarized without meta-analysis. Articles with the lowest risk of bias indicated that dexmedetomidine was associated with MEP loss and that higher doses of dexmedetomidine increased risk. In contrast, articles reporting no association between dexmedetomidine and MEP loss suffered from higher risk of bias, including suspected or confirmed problems with confounding, outcome measurement, participant selection, results reporting, and lack of statistical transparency and power. CONCLUSION: Given the limitations of the studies available in the literature, it would be advisable to conduct rigorous randomized controlled trials with larger sample sizes to assess the effects of dexmedetomidine use of in scoliosis surgery in pediatric patients.

Intraoperative neural monitoring during head and neck surgery in patients with concern for cervical spine instability.

Cervical and craniocervical instability are associated with catastrophic procedural outcomes. We discuss three individuals who required otolaryngologic surgical intervention: two with symptomatic spinal instability and one in whom spinal stability was unable to be assessed. Two cases were managed with procedural positioning precautions and evoked potential monitoring, and the other with procedural positioning precautions alone. Methods of monitoring and triggers for repositioning are discussed. This series is intended to discuss the approach and potential added value of evoked potential monitoring for risk mitigation in pediatric patients with concern for cervical spine instability.

Somatosensory pathway dysfunction in patients with amyotrophic lateral sclerosis in a completely locked-in state.

OBJECTIVE: To investigate somatosensory pathway function in patients with amyotrophic lateral sclerosis (ALS) dependent on invasive ventilation and in a completely locked-in state (CLIS). METHODS: We examined median nerve somatosensory evoked potentials (SEPs) in 17 ALS patients in a CLIS, including 11 patients with sporadic ALS, one with familial ALS with genes not examined, four with a Cu/Zn superoxide-dismutase-1 (SOD1) gene variant (Val118Leu, Gly93Ser, Cys146Arg), and one with a fused-in-sarcoma gene variant (P525L). We evaluated N9, N13, N20 and P25, and central conduction time (CCT); the data were compared with those of 73 healthy controls. RESULTS: N20 and N13 were abolished in 12 and 10 patients, and their latencies was prolonged in four and three patients, respectively. The CCT was prolonged in five patients with measurable N13 and N20. Two patients with SOD1 gene mutations had absent or slightly visible N9. Compared to the CCT and latencies and amplitudes of N13 and N20 in the controls, those in the patient cohort were significantly abnormal. CONCLUSIONS: The central somatosensory pathway is severely involved in patients with ALS in a CLIS. SIGNIFICANCE: Our findings suggest that median nerve SEP cannot be utilized for communication in patients with ALS in a CLIS.

Value of multi-channel somatosensory evoked potentials recording in patients undergoing scoliosis correction surgery.

PURPOSE: We aimed to investigate the value of intraoperative multi-channel recording of somatosensory evoked potentials (SSEPs) in patients undergoing posterior instrumentation surgery with fusion. METHODS: This study included 176 patients with scoliosis who underwent posterior correction surgery from January 2019 to June 2020. Among them, 88 patients underwent routine SSEPs monitoring via single-channel (Cz'-Fpz) cortical recording (control group), while the remaining 88 patients underwent multi-channel (Cz'-Fpz and C3'-C4') SSEPs monitoring in the cortex. Chi-square and Fisher's exact tests were used to analyze the influence of age, spinal deformity classification, and Cobb angle on waveform differentiation and the success rate of SSEPs monitoring. RESULTS: Univariate analysis revealed that age, type of scoliosis, and Cobb angle exerted significant effects on the success rate of intraoperative SSEPs monitoring, and the SSEPs waveform differentiation rate was poorest among patients with congenital scoliosis. Intraoperative monitoring results indicated that the success rate of single-channel SSEPs monitoring was 90.9%, while that of multi-channel monitoring was 98.9% (P < 0.05). Among the intraoperative alarm cases, the incidence of adverse events after single-channel SSEPs monitoring was 66.7%, while the incidence of adverse events after multi-channel SSEPs monitoring was only 28.6%. CONCLUSION: Multi-channel cortical SSEPs monitoring can effectively and accurately evaluate the function of the posterior column of the spinal cord. Use of multi-channel SSEP monitoring may help to improve the success rate of monitoring and reduce the incidence of postoperative adverse events in patients with congenital scoliosis.

Intraoperative neurophysiological monitoring in scoliosis surgery: literature review of the last 10 years.

INTRODUCTION: Patients with spinal deformities undergoing corrective surgery are at risk for iatrogenic spinal cord injury (SCI) and subsequent neurological deficit. Intraoperative neurophysiological monitoring (IONM) allows early detection of SCI which enables early intervention resulting in a better prognosis. The primary aim of this literature review was to search if there are threshold values of TcMEP and SSEP in the literature that are widely accepted as alert during IONM. The secondary aim was to update knowledge concerning IONM during scoliosis surgery. METHOD: PubMed/MEDLINE and Cochrane library electronic databases were used to search publication from 2012 to 2022. The following keywords were used: evoked potential, scoliosis, surgery, intraoperative monitoring and neurophysiological. We included all studies dealing with SSEP and TcMEP monitoring during scoliosis surgery. Two authors reviewed all titles and abstracts to identify studies that met the inclusion criteria. RESULTS: We included 43 papers. Rates of IONM alert and neurological deficit varied from 0.56 to 64% and from 0.15 to 8.3%, respectively. Threshold values varied from a loss of 50 to 90% for TcMEP amplitude, whereas it seems that a loss of 50% in amplitude and/or an increase of 10% of latency is widely accepted for SSEP. Causes of IONM changes most frequently reported were surgical maneuver. CONCLUSION: Concerning SSEP, a loss of 50% in amplitude and/or an increase of 10% of latency is widely accepted as an alert. For TcMEP, it seems that the use of highest threshold values can avoid unnecessary surgical procedure for the patient without increasing risk of neurological deficit.

Feasibility of multimodal intraoperative neurophysiological monitoring for extramedullary spinal cord tumor surgery in elderly patients.

BACKGROUND/PURPOSE: Extramedullary spinal cord tumors (EMSCTs) are mostly benign tumors which are increasingly diagnosed and operatively treated in the elderly. While there are hints that multimodal intraoperative neurophysiological monitoring (IONM) could be influenced by age and age-related comorbidities, no study has ever systematically evaluated its feasibility and value for EMSCT surgery in elderly patients. METHODS: We retrospectively evaluated all patients with microsurgical EMSCT resection under continuous multimodal IONM with SSEPs, MEPs and electromyography between 2016 and 2020. Epidemiological, clinical, imaging and operative/IONM records as well as detailed individual outcomes were analyzed and compared for the cohort < / ≥ 65 years. RESULTS: Mean age was 45 years in cohort < 65 years (n = 109) and 76 years in cohort ≥ 65 years (n = 64), while baseline/operative characteristics did not significantly differ. Mean baseline SSEPs' latencies (left-right average) were significantly higher in the cohort ≥ 65 years for both median (20.9 ms vs. 22.1 ms; p < 0.01) and tibial nerve (42.9 ms vs. 46.1 ms; p < 0.01) without significant differences for SSEPs' amplitudes. Stimulation intensity to elicit intraoperative MEPs was significantly higher in the cohort ≥ 65 years (surrogate-marker: left-right-averaged quotient ID1-muscle/abductor-hallucis-muscle; 1.6 vs. 2.1; p < 0.001). Intraoperatively, SSEP and MEP monitoring were feasible in 99%/100% and 99%/98% for the cohort < / ≥ 65 years without significant differences in rates for significant IONM changes during surgery or postoperatively new sensorimotor deficits. Sensitivity of IONM was 29%/43%, specificity 99%/98%, positive and negative predictive values 67%/75% and 95%/93% for the cohort < / ≥ 65 years. Overall, age was no risk factor for IONM feasibility or rate of significant IONM changes. DISCUSSION: Multimodal IONM is feasible/reliable for EMSCT surgery in elderly patients. An age-related prolongation of SSEPs' latencies and demand for higher stimulation intensities for MEPs' elicitation has to be considered.

Technical note: pre-positioning lower limb SSEP during semi-sitting positioning in posterior fossa surgery- does it matter?

Intra-operative monitoring has been a crucial tool in modern neurosurgery as it allows to optimize surgical outcome whilst reducing neurological deficits. Somatosensory evoked potentials are routinely monitored in most spinal and brain surgeries due to providing invaluable information regarding the functional integrity of sensory pathways. The use of this neurophysiological technique is particular useful when positioning patients in semi-sitting position during posterior fossa surgery. However, there is general agreement within the intra-operative neuromonitoring community that either upper or lower limb SSEPs monitoring typically suffice. Nonetheless, we report a case study of a patient in whom lower limb SSEPs were independently affected from upper limb SSEPs during positioning. In this respect, we suggest that both upper and lower limb SSEPs monitoring should be considered during semi-sitting positioning in patients undergoing posterior fossa surgery.

Single-trial neuromagnetic analysis reveals somatosensory dysfunction in chronic Minamata disease.

Methylmercury pollution is a global problem, and Minamata disease (MD) is a stark reminder that exposure to methylmercury can cause irreversible neurological damage. A "glove and stocking type" sensory disturbance due to injured primary sensory cortex (SI) (central somatosensory disturbance) is the most common neurologic sign in MD. As this sign is also prevalent in those with polyneuropathy, we aimed to develop an objective assessment for detecting central somatosensory disturbances in cases of chronic MD. We selected 289 healthy volunteers and 42 patients with MD. We recorded the sensory nerve action potentials (SNAPs) and somatosensory evoked magnetic fields (SEFs) to median nerve stimulation with magnetoencephalography. Single-trial epochs were classified into three categories (N20m, non-response, and P20m epochs) based on the cross-correlation between averaged sensor SEFs and individual epochs. We assessed SI responses (the appearance rate of P20m [P20m rate] and non-response epochs [non-response rate]) and early somatosensory cortical processing (N20m amplitude, reproducibility of N20m in single-trial responses [cross-correlation value], and induced gamma-band oscillations of the SI [gamma response] of single epochs excluding non-response epochs). Receiver operating characteristic curve analyses were used to examine the diagnostic accuracy of each parameter. We found that SNAPs exerted a marginal effect on the N20m. The N20m amplitude, cross-correlation value, and gamma response were significantly reduced in the MD group on either side (p < 0.0001), suggestive of altered early somatosensory cortical processing. Interestingly, the P20m rate and non-response rate were significantly increased in the MD group on either side (p < 0.0001), thereby suggesting impaired SI responses. Notably, P20m and absent N20m peaks were observed in 6 and 11 patients with MD, respectively, which may be attributed to increased numbers of P20m epochs. The cross-correlation value exhibited the highest correlation with the P20m rate or non-response rate. Thus, reduced reproducibility of N20m may play an important role in chronic MD. The cross-correlation value exhibited the highest correlation with the gamma response for both SI parameters in early somatosensory cortical processing. The area under the curve was > 0.77 (range: 0.77-0.79) for all parameters. Their confidence intervals overlapped with each other; thus, each SEF parameter likely had an approximately equivalent discrimination ability. In conclusion, chronic MD is characterized by impaired SI responses and alterations in early somatosensory cortical processing. Thus, single-trial neuromagnetic analysis of somatosensory function may be useful for detecting central somatosensory disturbance and elucidating the relevant pathophysiological mechanisms even in the context of chronic MD.