Recording Of Somatosensory Evoked Potentials Research Articles

Evaluation of the Relationship between Pain Exposure and Somatosensory Evoked Potentials in Preterm Infants: A Prospective Cohort Study.

First, to compare somatosensory evoked potentials (SEPs) in preterm newborns without major brain injury studied at term equivalent age (TEA) with a term historical control group. Second, to investigate the impact of pain exposure during the first 28 days after birth on SEPs. Third, to evaluate the association between SEPs and Bayley-III at 2 years corrected age (CA). Infants born at <32 weeks' gestational age (GA) were studied with continuous-SEPs. First, SEP differences between preterm and term infants were analyzed. Second, regression analyses were conducted to explore the association between SEPs and painful procedures, and then between SEPs and neurodevelopment. 86 preterm infants were prospectively enrolled. Preterm infants exhibited prolonged N1 latencies, central conduction times (CCTs), lower N1-P1 amplitudes, and more recurrently abnormal SEPs compared to term infants. Higher pain exposure predicted longer N1 latency and slower CCT (all p < 0.005), adjusting for clinical risk factors. Younger GA and postmenstrual age (PMA) at SEP recording were associated with longer N1 latency and lower N1-P1 amplitude (all p < 0.005). A normal SEP at TEA positively predicted cognitive outcome at 2 years CA (p < 0.005). Pain exposure and prematurity were risk factors for altered SEP parameters at TEA. SEPs predicted cognitive outcome.

A Novel Technique for Intraoperative Mapping of the Somatosensory Cortex

Intraoperative mapping of the nervous system is used to identify "eloquent" cortical areas. In this technical report, we describe a novel way of mapping the somatosensory cortex so that injury to those critical pathways can be avoided. An 8-year-old female with drug resistant epilepsy presented for resection of a right posterior parietal focal cortical dysplasia. Left median nerve stimulation was used to record somatosensory evoked potentials (SEPs) directly from the somatosensory cortex with a strip electrode. A handheld monopolar electrode was also used to record both the median and tibial SEP. Total intravenous anesthesia with propofol and remifentanil was used. SEP recordings were obtained from a 4-contact strip electrode placed across the central sulcus. A phase reversal was identified and the most likely post central gyrus was noted. With the strip electrode left in place, a monopolar handheld electrode was used to record the median nerve SEPs from different locations on the postcentral gyrus. The tibial nerve was also stimulated to record where the highest amplitude tibial nerve SEP was present. This map was used delineate functionally "eloquent" areas to avoid during surgery. During resection, the median nerve SEP was recorded from the strip electrode continuously. No significant change in the SEP was noted, and the patient awoke without any sensory deficits. Sensory mapping of the cortex is possible with a handheld monopolar electrode. This technique is easy to perform and can help reduce neurological morbidity.

Somatosensory evoked potentials recorded from DBS electrodes: the origin of subcortical N18.

The different peaks of somatosensory-evoked potentials (SEP) originate from a variety of anatomical sites in the central nervous system. The origin of the median nerve subcortical N18 SEP has been studied under various conditions, but the exact site of its generation is still unclear. While it has been claimed to be located in the thalamic region, other studies indicated its possible origin below the pontomedullary junction. Here, we scrutinized and compared SEP recordings from median nerve stimulation through deep brain stimulation (DBS) electrodes implanted in various subcortical targets. We studied 24 patients with dystonia, Parkinson's disease, and chronic pain who underwent quadripolar electrode implantation for chronic DBS and recorded median nerve SEPs from globus pallidus internus (GPi), subthalamic nucleus (STN), thalamic ventral intermediate nucleus (Vim), and ventral posterolateral nucleus (VPL) and the centromedian-parafascicular complex (CM-Pf). The largest amplitude of the triphasic potential of the N18 complex was recorded in Vim. Bipolar recordings confirmed the origin to be close to Vim electrodes (and VPL/CM-Pf) and less close to STN electrodes. GPi recorded only far-field potentials in unipolar derivation. Recordings from DBS electrodes located in different subcortical areas allow determining the origin of certain subcortical SEP waves more precisely. The subcortical N18 of the median nerve SEP-to its largest extent-is generated ventral to the Vim in the region of the prelemniscal radiation/ zona incerta.

Increased Perirolandic Cortical Excitability May Facilitate Sensory Motor Mapping in Children (P13-1.003)

<h3>Objective:</h3> We are hereby describing a case of refractory pediatric epilepsy where resection of perirolandic seizure foci was performed successfully under neurophysiologic guidance. <h3>Background:</h3> Pediatric neurophysiologic sensory-motor mapping is frequently unsuccessful, due to inability to localize central sulcus (CS) and primary motor cortex (M1). These shortcomings result from poor somatosensory evoked potentials (SSEP) and high M1 depolarization thresholds respectively, both reflections of the immaturity of the central nervous system. <h3>Design/Methods:</h3> Case report <h3>Results:</h3> An 8-year-old boy with developmental delay, debilitating focal epilepsy and epileptic encephalopathy underwent phase 2 video EEG monitoring. The recordings showed seizures with early involvement of several depth electrodes located within the right parieto-frontal regions, and an early motor semiology involving the left arm. The patient underwent neurophysiologically guided resection of the seizure foci under general anesthesia. Pre-resection electrocorticography (ECoG) via a 64 contact grid showed abundant perirolandic epileptiform discharges (ED), maximal postcentrally. Cortical recordings of high amplitude median SSEP and a low depolarization threshold led to successful CS localization and identification of M1, respectively. A subdural strip electrode placed over the precentral gyrus and secured in position, allowed simultaneous ECoG and motor monitoring during the resection of the postcentral foci. Initially, ECoG showed near continuous runs of ED, unchanged by cortical electrical stimulation. Under steady state anesthesia, at a constant propofol infusion rate, this activity decreased in frequency and stopped altogether towards the end stages of the resection, as the M1 threshold increased by 7 mA. Post-resection fronto-parietal ECoG recordings were quiet. Post-operatively, the patient became seizure free, showed cognitive improvement and no motor deficits. <h3>Conclusions:</h3> Increased cortical excitability may lead to successful functional mapping in children. Under steady anesthetic conditions, increases in the M1 threshold during resection of nearby epileptic foci may be an early sign of decrease in the abnormal regional cortical excitability. <b>Disclosure:</b> Dr. Alzahrany has nothing to disclose. Dr. Simon has received personal compensation in the range of $500-$4,999 for serving as an Expert Witness for Risk Management Foundation of the Harvard Institutions Incorporated. Dr. Simon has received personal compensation in the range of $5,000-$9,999 for serving as an Expert Witness for MCIC Vermont. Dr. Simon has received personal compensation in the range of $5,000-$9,999 for serving as an Expert Witness for Aaronson, Rappaport, Feinstein&amp; Deutch. Dr. Simon has received publishing royalties from a publication relating to health care. Dr. Simon has received personal compensation in the range of $0-$499 for serving as a Speaker with American Clinical Neurophysiology Society . Dr. Simon has a non-compensated relationship as a Speaker with International Society of Intraoperative Neurophysiology that is relevant to AAN interests or activities. Dr. Simon has a non-compensated relationship as a Speaker with Brazilian Congress of Neurology that is relevant to AAN interests or activities.

Magnetoneurography to investigate the mechanisms underlying the P9 far-field potential

ObjectiveThe mechanism underlying the generation of P9 far-field somatosensory evoked potentials (SEPs) is unresolved. Accordingly, we used magnetoneurography to visualize the current distribution in the body at the P9 peak latency and elucidate the origin of P9 generation. MethodsWe studied five healthy male volunteers without neurological abnormalities. We recorded far-field SEPs after median nerve stimulation at the wrist to identify the P9 peak latency. Using magnetoneurography, we recorded the evoked magnetic fields in the whole body under the same stimulus conditions as the SEP recording. We analyzed the reconstructed current distribution at the P9 peak latency. ResultsAt the P9 peak latency, we observed the reconstructed current distribution dividing the thorax into two parts, upper and lower. Anatomically, the depolarization site at the P9 peak latency was distal to the interclavicular space and at the level of the second intercostal space. ConclusionsBy visualizing the current distribution, we proved that P9 peak latency originates in the change in volume conductor size between the upper and lower thorax. SignificanceWe clarified that magnetoneurography analysis is affected by the current distribution due to the junction potential.

A Novel Approach to Screen for Somatosensory Evoked Potentials in Critical Care.

Somatosensory evoked potentials (SSEPs) help prognostication, particularly in patients with diffuse brain injury. However, use of SSEP is limited in critical care. We propose a novel, low-cost approach allowing acquisition of screening SSEP using widely available intensive care unit (ICU) equipment, specifically a peripheral "train-of-four" stimulator and standard electroencephalograph. The median nerve was stimulated using a train-of-four stimulator, and a standard 21-channel electroencephalograph was recorded to generate the screening SSEP. Generation of the SSEP was supported by visual inspection, univariate event-related potentials statistics, and a multivariate support vector machine (SVM) decoding algorithm. This approach was validated in 15 healthy volunteers and validated against standard SSEPs in 10 ICU patients. The ability of this approach to predict poor neurological outcome, defined as death, vegetative state, or severe disability at 6months, was tested in an additional set of 39 ICU patients. In each of the healthy volunteers, both the univariate and the SVM methods reliably detected SSEP responses. In patients, when compared against the standard SSEP method, the univariate event-related potentials method matched in nine of ten patients (sensitivity = 94%, specificity = 100%), and the SVM had 100% sensitivity and specificity when compared with the standard method. For the 49 ICU patients, we performed both the univariate and the SVM methods: a bilateral absence of short latency responses (n = 8) predicted poor neurological outcome with 0% FPR (sensitivity = 21%, specificity = 100%). Somatosensory evoked potentials can reliably be recorded using the proposed approach. Given the very good but slightly lower sensitivity of absent SSEPs in the proposed screening approach, confirmation of absent SSEP responses using standard SSEP recordings is advised.

Optimization of signal-to-noise ratio in short-duration SEP recordings by variation of stimulation rate

ObjectiveThe intraoperative averaging of the somatosensory evoked potential (SEP) requires reliable recordings within the shortest possible duration. We here systematically optimized the repetition rate of stimulus presentation. MethodsWe recorded medianus and tibial nerve SEP during 22 surgeries and varied the rate of stimulus presentation between 2.7 Hz and 28.7 Hz. We randomly sampled a number of sweeps corresponding to recording durations up to 20 s and calculated the signal-to-noise ratio (SNR). ResultsFor the medianus nerve at 5 s recording duration, SEP stimulation rate at 12.7 Hz obtained the highest median SNR = 22.9 for the N20, which was higher than for rate 4.7 Hz (p = 1.5e-4). When increasing the stimulation rate, latency increased and amplitude decayed for cortical but not for peripheral recording sites. For the tibial nerve, the rate 4.7 Hz achieved the highest SNR for all durations. ConclusionsWe determined the time-dependence of SNR for N20 and elucidated the underlying physiology. For short recordings, rapid reduction of noise through averaging at high stimulation rate outweighs the disadvantage of smaller amplitude. SignificanceFor a short duration of medianus nerve SEP recording only, it may be advantageous to stimulate with a repetition rate of 12.7 Hz.

Recording of motor and somatosensory evoked potential in an anaesthetised Wistar rat using digital polyrite system

Objectives: The aim of this article is to explain the detailed methodology to record Motor evoked potential (MEP) and somatosensory evoked potential (SSEP) in adult albino Wistar rat, male (200–250 g) which has not been defined previously. Materials and Methods: We have standardised recording of both MEP and SSEP in these rats under anaesthesia on ADI digital polyrite system. Results: Evoked potentials have been widely studied in spinal cord injured patients to estimate the degree of injury and to establish a predictive measure of functional recovery. MEPs and SSEPs, arising from the motor cortex or peripheral nerve and generated either by direct electrical stimulation or by transcranial magnetic stimulation, have been advocated as a reliable indicator of descending and ascending pathway integrity. In the rat brain, there is a physical overlap between the motor and somatosensory cortex. Hence, our objective was to identify the exact area for stimulation in the cortex where we could record maximum response with the application of minimum electrical stimulation. Conclusion: The recording of MEP and SSEP together provides a powerful neurological technique to monitor the tracts of the spinal cord.

Direct brainstem somatosensory evoked potentials for cavernous malformations.

Brainstem cavernous malformations (CMs) often require resection due to their aggressive natural history causing hemorrhage and progressive neurological deficits. The authors report a novel intraoperative neuromonitoring technique of direct brainstem somatosensory evoked potentials (SSEPs) for functional mapping intended to help guide surgery and subsequently prevent and minimize postoperative sensory deficits. Between 2013 and 2019 at the Stanford University Hospital, intraoperative direct brainstem stimulation of primary somatosensory pathways was attempted in 11 patients with CMs. Stimulation identified nucleus fasciculus, nucleus cuneatus, medial lemniscus, or safe corridors for incisions. SSEPs were recorded from standard scalp subdermal electrodes. Stimulation intensities required to evoke potentials ranged from 0.3 to 3.0 mA or V. There were a total of 1 midbrain, 6 pontine, and 4 medullary CMs-all with surrounding hemorrhage. In 7/11 cases, brainstem SSEPs were recorded and reproducible. In cases 1 and 11, peripheral median nerve and posterior tibial nerve stimulations did not produce reliable SSEPs but direct brainstem stimulation did. In 4/11 cases, stimulation around the areas of hemosiderin did not evoke reliable SSEPs. The direct brainstem SSEP technique allowed the surgeon to find safe corridors to incise the brainstem and resect the lesions. Direct stimulation of brainstem sensory structures with successful recording of scalp SSEPs is feasible at low stimulation intensities. This innovative technique can help the neurosurgeon clarify distorted anatomy, identify safer incision sites from which to evacuate clots and CMs, and may help reduce postoperative neurological deficits. The technique needs further refinement, but could potentially be useful to map other brainstem lesions.

Feasibility of non-invasive recording of somatosensory evoked potential in pigs

BackgroundNon-invasive measurement of somatosensory-evoked potentials (SEP) in a large animal model is important to translational cognitive research. We sought to develop a methodology for neurophysiological recording via a transcranial electroencephalography (EEG) cap under an effective sedative regimen with dexmedetomidine, midazolam, and butorphanol that will produce sedation instead of anesthesia while not compromising data quality.ResultsPigs received intramuscular dexmedetomidine, midazolam, and butorphanol for SEP assessment with peroneal nerve stimulation. Semi-quantitative sedation assessment was performed after the animal was sufficiently sedated and 30 min later, during the transcranial SEP recording. SEP data were analyzed with commercial software. Binary qualitative analysis of the recording was categorized by an experienced neurophysiologist. All four animals had adequate surface SEP recordings. Animals received 43 [21–47] mcg/kg of dexmedetomidine, 0.3 [0.2–0.3] mg/kg of midazolam, and 0.3 [0.3–0.3] mg/kg of butorphanol IM. All treatments resulted in moderate to deep sedation (Baseline median sedation score 11.5 [11–12]; median score at 30 min: 11.5 [10.5–12]). Heart rate (median [range]) (55 [49–71] beats per minute), respiratory rate (24 [21–30] breaths per minute), and hemoglobin oxygen saturation (99 [98–100]%) and body temperature (37.7 [37.4–37.9] °C) remained within clinically acceptable ranges. There were no undesirable recovery incidents.ConclusionsIn this pilot study, we demonstrate the feasibility of SEP recording via a transcranial EEG cap under an effective sedative regimen in pigs. Our approach will expand the use of a large animal model in neurotranslational research.

SSEP N20 and P25 amplitudes predict poor and good neurologic outcomes after cardiac arrest

BackgroundTo assess in comatose patients after cardiac arrest (CA) if amplitudes of two somatosensory evoked potentials (SSEP) responses, namely, N20-baseline (N20-b) and N20–P25, are predictive of neurological outcome.MethodsMonocentric prospective study in a tertiary cardiac center between Nov 2019 and July-2021. All patients comatose at 72 h after CA with at least one SSEP recorded were included. The N20-b and N20–P25 amplitudes were automatically measured in microvolts (µV), along with other recommended prognostic markers (status myoclonus, neuron-specific enolase levels at 2 and 3 days, and EEG pattern). We assessed the predictive value of SSEP for neurologic outcome using the best Cerebral Performance Categories (CPC1 or 2 as good outcome) at 3 months (main endpoint) and 6 months (secondary endpoint). Specificity and sensitivity of different thresholds of SSEP amplitudes, alone or in combination with other prognostic markers, were calculated.ResultsAmong 82 patients, a poor outcome (CPC 3–5) was observed in 78% of patients at 3 months. The median time to SSEP recording was 3(2–4) days after CA, with a pattern “bilaterally absent” in 19 patients, “unilaterally present” in 4, and “bilaterally present” in 59 patients. The median N20-b amplitudes were different between patients with poor and good outcomes, i.e., 0.93 [0–2.05]µV vs. 1.56 [1.24–2.75]µV, respectively (p < 0.0001), as the median N20–P25 amplitudes (0.57 [0–1.43]µV in poor outcome vs. 2.64 [1.39–3.80]µV in good outcome patients p < 0.0001). An N20-b > 2 µV predicted good outcome with a specificity of 73% and a moderate sensitivity of 39%, although an N20–P25 > 3.2 µV was 93% specific and only 30% sensitive. A low voltage N20-b < 0.88 µV and N20–P25 < 1 µV predicted poor outcome with a high specificity (sp = 94% and 93%, respectively) and a moderate sensitivity (se = 50% and 66%). Association of “bilaterally absent or low voltage SSEP” patterns increased the sensitivity significantly as compared to “bilaterally absent” SSEP alone (se = 58 vs. 30%, p = 0.002) for prediction of poor outcome.ConclusionIn comatose patient after CA, both N20-b and N20–P25 amplitudes could predict both good and poor outcomes with high specificity but low to moderate sensitivity. Our results suggest that caution is needed regarding SSEP amplitudes in clinical routine, and that these indicators should be used in a multimodal approach for prognostication after cardiac arrest.

Dermatomal somatosensory evoked potentials and cortical somatosensory evoked potentials assessment in congenital scoliosis

BackgroundThe aim of this study was to assess the value of dermatomal somatosensory evoked potentials (DSEPs) and cortical somatosensory evoked potentials (SSEPs) in monitoring spinal cord function for patients with congenital scoliosis (CS).MethodsThis retrospective study reviewed the medical records of patients (n = 102) who underwent DSEP (T2-S1 dermatome), of whom 60 were normal subjects and 62 with congenital scoliosis. The study analyzed the latencies and peaks of N1-L, N1-R, P1-L and P1-R recorded by DSEPs of patients’ thoracolumbar dermatomes. To observe the incidence of abnormal DSEPs and SSEPs in CS patients and to analyze the difference in sensitivity and reliability between the two in the examination of scoliosis patients. SPSS 22.0 statistical software package was used to analyze the data, and χ2 test and correlation analysis were used to indicate that the difference was statistically significant, p < 0.05.ResultsSixty two patients with CS were evaluated with total spine magnetic resonance imaging (MRI). Only 23 patients (37.09%) showed spinal cord malformations in the MRI findings. The DSEP recordings showed a relatively high sensitivity (97.8%) compared to the abnormality rate of SSEPs recordings, and the rates of waveform, latency and amplitude abnormalities were much higher in DSEPs recordings (36.6, 36.3, 24.8%) than in SSEPs recordings (3.2, 22.5, 14.5%). The abnormality rate of DSEP records with and without neurological symptoms was higher than the abnormality rate of SSEP records (100% vs 20, 96.2% vs 44.2%, p<0.05). And in 62 patients with CS, the rate of positive MRI (37.1%) was lower than that recorded by DSEP (79.6% / 57.9%). p < 0.05.ConclusionDSEPs are more sensitive to microscopic posterior column dysfunction in patients with CS that cannot be detected by either radiology or routine clinical examination. Preoperative DSEPs assessment is recommended as a baseline examination for intraoperative monitoring and comparison with the postoperative situation. DSEPs recording complements the information obtained from routine clinical and radiological evaluation.

Abstract WMP93: Somatosensory Evoked Potentials Monitoring In Acute Ischemic Stroke (Promise) Study: A Biomarker Of Functional Recovery Prior To Mechanical Thrombectomy (clinicaltrials.gov: NCT04099615)

Hypothesis: Somatosensory evoked potentials (SEPs), as surrogate of cerebral blood flow, may give substantial additional predictive value to that provided by clinical and imaging factors and optimize the selection of patients benefiting from mechanical thrombectomy (MT) Methods: Bilateral median nerve SEPs were recorded before and continuously during MT in consecutive patients with AIS and anterior LVO. N20 response ipsilateral to the ischemic hemisphere was measured. The adjusted predictive value of the N20 on functional Independence (modified Rankin Scale score ≤2) after MT was analyzed by binary logistic regression and its predictive value on the full range of disability by ordinal logistic regression. We constructed different regression models with other clinical and imaging predictors at the pre- and in- hospital setting to determine the independent predictive power of N20 for a potential treatment decision-making Results: A total of 223 patients were recruited. A blinded reading of SEPs recordings identified presence of N20 in 110 (49.3%), absence in 58 (26%) and not assessable in 55 patients due to radiofrequency interferences. Prior to MT, N20 had positive predictive value (PPV) of 93% (95%CI, 0.8 to 0.98) and increased 10 fold the likelihood of good functional outcome at 7 days (adjusted OR, 9.9; 95%CI, 3.1-44.6). Receiver operating curves showed that N20 had a higher capacity to predict good functional outcome (AUC 0.82) than models constructed with pre-hospital (age, sex, serum glucose, median blood pressure, NIHSS; AUC 0.75) or in-hospital (NIHSS, ASPECTS; AUC 0.72) factors. During MT, N20 had PPV of 100% (95% CI, 0.85-1) and was the unique independent factor associated with functional independence (adjusted OR, 2.74; 95%CI, 1.90-4.29). Perfusion CT or MR was available in a subgroup of 116 patients. Baseline N20 showed a higher capacity to predict good functional outcome (n=168, AUC 0.71) compared with ischemic core (n=127, AUC 0.66), ischemic penumbra (Tmax&gt;6) (n=116, AUC 0.54) and collateral status (n=191, AUC 0.61) Conclusions: SEPs monitoring is a fast and bedside technique that could complement current clinical factors in terms of increasing the eligibility of AIS patients for MT and improving prognosis.

Habituation of Somatosensory Evoked Potentials in Patients with Alzheimer's Disease and Those with Vascular Dementia.

Background and Objectives: The most prevalent dementia are Alzheimer’s disease and vascular dementia. There is evidence that cortical synaptic function may differ in these two conditions. Habituation of cortical responses to repeated stimuli is a well-preserved phenomenon in a normal brain cortex, related to an underlying mechanism of synaptic efficacy regulation. Lack of habituation represents a marker of synaptic dysfunction. The purpose of this study was to assess the habituation of somatosensory evoked potentials (SEPs) in 29 patients affected by mild-to-moderate Alzheimer’s disease (AD-type) or vascular (VD-type) dementia. Materials and Methods: All patients underwent a clinical history interview, neuropsychological evaluation, and neuroimaging examination. SEPs were elicited by electrical stimulation of the right median nerve at the wrist. Six-hundred stimuli were delivered, and cortical responses divided in three blocks of 200. Habituation was calculated by measuring changes of N20 amplitude from block 1 to block 3. SEP variables recorded in patients were compared with those recorded in 15 age- and gender-matched healthy volunteers. Results: SEP recordings showed similar N20 amplitudes in AD-type and VD-type patients in block 1, that were higher than those recorded in controls. N20 amplitude decreased from block 1 to block 3 (habituation) in normal subjects and in VD-type patients, whereas in AD-type patients it remained unchanged (lack of habituation). Conclusions: The findings suggest that neurophysiologic mechanisms of synaptic efficacy that underneath habituation are impaired in patients with AD-type dementia but not in patients with VD-type dementia. SEPs habituation may contribute to early distinction of Alzheimer’s disease vs. vascular dementia.

Intraoperative Monitoring (IOM) P-IM002. Somatosensory evoked potentials in cervical and cerebellopontine angle Neurosurgical procedures: Experience from a tertiary care center in india

Introduction . The role of Intraoperative neuromonitoring (IONM) as a guiding technique in neurosurgical procedures is well established. Somato-Sensory Evoked Potentials (SSEPs) are an important modality in IONM. We report our experience with SSEPs in surgeries of Cervical Spine, Cranio-Vertebral junctions and Cerebellopontine angle at our centre. Methods . Sixty two patients underwent surgery in the cervical region and cerebellopontine angle under IONM guidance at the Department of Neurosurgery from May 2018 and September 2018. Out of which SSEPs were not performed in 22 patients and SSEPs could not be recorded in 20 patients due to technical reasons, therefore 20 patients were included in the study. SSEPs were recorded during the surgical procedures to provide information about neural integrity. Median nerves in both the limbs were stimulated at the level of the wrist using sterile transdermal needle electrodes. SSEP recordings were obtained using corkscrew needle electrodes placed at the scalp in Cp3, Cp4 and Fz, according to the 10-20 recording system. Signals were acquired using Medtronics NimEclipse© and Natus Protektor© system. The cortical recordings were taken from Cp3-Fz and Cp3-Cp4 montage for right sided SSEP and Cp4-Fz and Cp4-Cp3 montage for left sided SSEP. Results . The stimulation intensity was decided on a case-to-case basis. Range of stimulation varied from 10 - 23 mA with frequency of 4.70 Hz and stimulation duration of 0.2 ms. Real time averaging of 1000 waveforms was done. N20 and P22 latencies were checked pre-operatively just after induction, intra-operatively and post-operatively just before closure. In all the 20 patients, intra-operative period was uneventful. All cases showed normal recovery in the post- operative period. Conclusion . SSEP monitoring is a very useful tool for intraoperative sensory tract monitoring in the patients undergoing Cervical and Cerebellopontine region surgery. Change in the latency or amplitude in the cortical SSEP recordings can predict injury to the vital structures which can be reversed by surgeons if early warning is raised by Neurophysiologists.

Proximal Upper Limb Sensorimotor Integration in Response to Novel Motor Skill Acquisition.

Previous studies have shown significant changes in cortical and subcortical evoked potential activity levels in response to motor training with the distal upper-limb muscles. However, no studies to date have assessed the neurological processing changes in somatosensory evoked potentials (SEPs) associated with motor training whole-arm movements utilizing proximal upper-limb muscles. The proximal upper-limb muscles are a common source of work-related injuries, due to repetitive glenohumeral movements. Measuring neurophysiological changes following performance of a proximal motor task provide insight into potential neurophysiological changes associated with occupational postures and movements involving proximal upper limb muscles. This study sought to assess the impact of a novel motor skill acquisition task on neural processing of the proximal upper-limb muscle groups, through the measurement of short-latency median nerve SEPs. One group of 12 participants completed a novel motor training task, consisting of tracing a sinusoidal waveform varying in amplitude and frequency. Baseline SEP measurements were recorded from each participant, followed by a mental recitation control task. Pre-test SEP measurements were then recorded, followed by the motor training task, and post-test SEP recordings. The participants completed the tracing with their right thumb, using glenohumeral rotation only to move their hand. Significant improvements in task accuracy were demonstrated, indicating that motor acquisition had occurred. Significant changes were also seen in the N11, N13, N20, N24, P25, and the N30 SEP peaks were seen following the motor training task. Conclusion: Early SEPs appear to be a sensitive measure of changes in sensorimotor integration in response to novel motor skill acquisition within the proximal upper-limb muscles.

Is there inter-observer variation in the interpretation of SSEPs in comatose cardiac arrest survivors? Further considerations following the Italian multicenter ProNeCa study

BackgroundBilateral absence of N20 peak in median nerve Somatosensory Evoked Potentials (SSEPs) is considered the most valid predictor of poor outcome in comatose survivors after cardiopulmonary resuscitation. We investigated the consistency in interpreting SSEP recordings in a multicentre study. Methods44 SSEP recordings randomly extracted from 600 recordings of 392 patients included in the “Prognostication of Neurological outcome after Cardiac Arrest (ProNeCa) study” were blindly read by three expert neurophysiologists. Agreement between raters, and individual agreement of each rater vs. reference standard (RS), were calculated using Kappa Coefficients. Inter-rater reliability was calculated with Intra-class Correlation Coefficient (ICC). ResultsWhen raters had to evaluate the presence of N20 with normal amplitude, the inter-rater agreement was very high (Kappa = 0.84). In the case of N20 absence the agreement was good (Kappa = 0.66), but when N20 amplitude was low, the agreement decreased to moderate (Kappa = 0.579) becoming even weaker when it was “Non Assessable” (Kappa = 0.107). The agreement of each rater with the RS had a range from moderate to very good; rater1 Kappa = 0.589 (95%CI 0.397–0.781; p < 0.001), rater2 Kappa = 0.644 (95%CI 0.460–0.828; p < 0.001), rater3 Kappa = 0.859 (95%CI 0.698–1.000; p < 0.001). The ICC was barely good, 0.682 (95%CI 0.539−0.798; p = 0.0075). ConclusionDifferent health professionals, using different equipment in a multicentre study, had very good inter-rater agreement in interpreting SSEP records. The interpretation of “Non Assessable” SEPPs, mainly in relation to noise level, is still a crucial issue because it increases rater uncertainty. For this reason, it is important to focus on improving recording quality and interpretation of records.

Prognostic value of somatosensory evoked potential in cardiac arrest patients without withdrawal of life-sustaining therapy

BackgroundThe reliability of somatosensory evoked potential (SSEP) to predict a poor outcome of cardiac arrest patients after targeted temperature management (TTM) has been questioned due to self-fulfilling prophecy. MethodsThis was a multicentre, prospective, registry-based study. Data were collected from the Korean Hypothermia Network (KORHN)-pro registry between November 2015 and December 2018. We excluded cases with possible bias (inappropriate SSEP recordings and patients who decided on the withdrawal of life-sustaining therapy [WLST]) and calculated the sensitivities and false positive rates (FPRs) for an absent N20 and an absent brainstem reflex. A poor outcome was defined as a cerebral performance category score of 3–5 after 6 months. ResultsA total of 262 patients were analysed: 83 in the good outcome group and 179 in the poor outcome group. A bilaterally absent N20 was found in 127 patients and predicted a poor outcome with a sensitivity of 71.0% (95% confidence interval [CI], 63.7–77.5) and an FPR of 0.0% (95% CI, 0.0–4.3). Among the patients with absent brainstem reflexes (n = 103), 3 had a good outcome, with an FPR of 4.3% (95% CI, 0.9–12.2). The absence of one or both N20 and brainstem reflex had a sensitivity of 84.2% (95% CI, 77.4–89.6) and an FPR of 4.3% (95% CI, 0.9–12.2). ConclusionsOur results provide further evidence that SSEP exactly predicts poor neurological outcome in these patients and suggest that caution be taken when the brainstem reflex is used as a single test to make decisions regarding WLST.

Central Sulcus Misfolding: Polarity Reversal of SSEP N20 Potential in “Layered” Polymicrogyria

ABSTRACTParadoxical cortical potential polarity of the upper extremity somatosensory evoked potential (SSEP) has been reported in cases of polymicrogyria (PMG) syndrome. To date, the pathophysiological basis of this electrophysiological aberration remains under investigation. Here we present a case of mild PMG that showed “layered” microgyri in the left frontoparietal cortices affecting both hand and foot sensorimotor areas. The SSEP recordings revealed an isolated polarity reversal of N20 from the dysplastic cortex. We postulate a central sulcus misfolding theory to explain the “positive” N20 potential recorded in the PMG cortex.

Abstracts from The 37th Annual National Neurotrauma Symposium June 29–July 3, 2019 Pittsburgh, Pennsylvania

Abstracts from The 37^th Annual National Neurotrauma Symposium June 29–July 3, 2019 Pittsburgh, Pennsylvania