Median Somatosensory Evoked Potentials Research Articles

Central sensitization mechanisms in chronic migraine with medication overuse headache: a study of thalamocortical activation and lateral cortical inhibition.

It is unclear whether cortical hyperexcitability in chronic migraine with medication overuse headache (CM-MOH) is due to increased thalamocortical drive or aberrant cortical inhibitory mechanisms. Somatosensory evoked potentials (SSEP) were performed by electrical stimulation of the median nerve (M), ulnar nerve (U) and simultaneous stimulation of both nerves (MU) in 27 patients with CM-MOH and, for comparison, in 23 healthy volunteers (HVs) of a comparable age distribution. We calculated the degree of cortical lateral inhibition using the formula: 100 - [MU/(M + U) × 100] and the level of thalamocortical activation by analyzing the high frequency oscillations (HFOs) embedded in parietal N20 median SSEPs. Compared to HV, CM-MOH patients showed higher lateral inhibition (CM-MOH 52.2% ± 15.4 vs. HV 40.4% ± 13.3; p = 0.005), which positively correlated with monthly headache days, and greater amplitude of pre-synaptic HFOs (p = 0.010) but normal post-synaptic HFOs (p = 0.122). Our findings suggest that central neuronal circuits are highly sensitized in CM-MOH patients, at both thalamocortical and cortical levels. The observed changes could be due to the combination of dysfunctional central pain control mechanisms, hypersensitivity and hyperresponsiveness directly linked to the chronic intake of acute migraine drugs.

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.

척추 수술 수술중신경계감시 중 자세의 중요성: 증례 보고

Intraoperative neurophysiological monitoring (IONM) has been widely used to detect iatrogenic neural damage to minimize postoperative neurological deterioration. In this case, a damage was prevented by early detection of the improper position and by a correction of marked drops in blood pressure through IONM. A 72-year-old man underwent surgery due to cervical myelopathy. The somatosensory evoked potentials (SEPs) in bilateral median nerves showed prolongation of latency and reduction of amplitude. It was suspected that the cervical spine was excessively flexed by traction, and all tractions were released. In addition, the mean blood pressure was lowered to 53 mmHg, and it was confirmed that the infusion line and the SEP electrode were compressed in the right wrist. After decompression, bilateral median SEPs were recovered, and there was no postoperative neurological deterioration. Thus, IONM is useful in identifying early evidence of neural insult which may be caused by improper positioning during surgery.

Unexpected median SEPs fluctuations during brain cavernous malformation resection with no post-operative deficit.

Median nerve somatosensory evoked potentials (SEPs) may present changes during cavernous malformation (CM) resection unrelated to new post-operative sensory deficits. We performed intraoperative neurophysiological monitoring of median SEPs (m-SEPs) in three patients who underwent CM resection (surgery) near the sensory-motor cortex. The only preoperative clinical manifestations in all patients were seizures. All patients presented m-SEPs alterations on the side of the lesion during the procedure. Two patients presented permanent changes in the cortical potentials. In the third patient, the cortical and subcortical components suffered temporal fluctuations to return to baselines at the end of the surgery. None of these patients developed new post-operative clinical deficits. During brain cavernous malformation resection, significant fluctuations in the amplitude of different components of m-SEPs may occur. These changes may be due to excitability variations on m-SEP generators and do not translate into new post-operative neurological deficits.

Intraoperative neurophysiological monitoring during urgent surgical extracranial internal carotid artery recanalization

ObjectiveThe clinical outcome of surgical extracranial internal carotid artery (eICA) recanalization may be adversely affected by intraoperative ischemia. Median nerve somatosensory evoked potential (SEP) amplitude correlates well with cerebral blood flow.Our study presents the value of intraoperative SEP and selective shunting in the prevention of intraoperative ischemia development during urgent eICA recanalization. MethodsProspective recruitment of patients with acute unilateral eICA occlusion. All underwent surgical recanalization with intraoperative monitoring of scalp median SEPs. Preoperative clinical findings, cerebral collaterals, and 3 month functional outcome were evaluated. ResultsThe cohort consisted of 33 patients. Intraoperative SEP amplitude decreased significantly in 6 (18.2%). An intraluminal shunt was inserted twice (6.1%), surgical complications occurred in 6 (18.2%), intracerebral hemorrhage was not found.Favorable outcome 3 months after surgery according to the modified Rankin scale (mRS 0–2) was achieved in 28 (84.8%), 3 patients died (9.1%). ConclusionsIntraoperative SEP during urgent eICA recanalization seems to be beneficial.Thanks to the effective measure based on the intraoperative SEP changes, the clinical outcome in four(12.1%) could be positively affected. SignificanceThe results suggest that selective shunting based on intraoperative median SEPs may prevent intraoperative ischemia and may improve overall outcome of urgent eICA recanalization.

Neurophysiologic Mapping of Thalamocortical Tract in Asleep Craniotomies: Promising Results From an Early Experience.

Subcortical mapping of the corticospinal tract has been extensively used during craniotomies under general anesthesia to achieve maximal resection while avoiding postoperative motor deficits. To our knowledge, similar methods to map the thalamocortical tract (TCT) have not yet been developed. To describe a neurophysiologic technique for TCT identification in 2 patients who underwent resection of frontoparietal lesions. The central sulcus (CS) was identified using the somatosensory evoked potentials (SSEP) phase reversal technique. Furthermore, monitoring of the cortical postcentral N20 and precentral P22 potentials was performed during resection. Subcortical electrical stimulation in the resection cavity was done using the multipulse train (case #1) and Penfield (case #2) techniques. Subcortical stimulation within the postcentral gyrus (case #1) and in depth of the CS (case #2), resulted in a sudden drop in amplitudes in N20 (case #1) and P22 (case #2), respectively. In both patients, the potentials promptly recovered once the stimulation was stopped. These results led to redirection of the surgical plane with avoidance of damage of thalamocortical input to the primary somatosensory (case #1) and motor regions (case #2). At the end of the resection, there were no significant changes in the median SSEP. Both patients had no new long-term postoperative sensory or motor deficit. This method allows identification of TCT in craniotomies under general anesthesia. Such input is essential not only for preservation of sensory function but also for feedback modulation of motor activity.

Multimodal Evoked Potential Profiles in Woodhouse-Sakati Syndrome.

Woodhouse-Sakati syndrome is a rare autosomal recessive syndrome caused by homozygous mutations in the DCAF17 gene, characterized by marked neurologic and endocrine manifestations in the setting of brain iron accumulation and white matter lesions on neuroimaging. Here, we report electrophysiologic profiles in Woodhouse-Sakati syndrome and their possible value in understanding disease pathophysiology and phenotypic variability. Thirteen genetically confirmed Woodhouse-Sakati syndrome patients were evaluated via different evoked potential (EP) modalities, including brainstem auditory EPs, pattern reversal visual EPs, and somatosensory EPs to tibial and/or median nerves. All EP modalities showed variable abnormalities. Pattern reversal visual EPs were recorded in all patients, with nine patients exhibiting abnormal results. From those, seven patients showed prolonged P100 latencies after stimulation of right and left eyes for each in turn. Two patients showed P100 latency abnormality after single eye stimulation recorded from midoccipital electrode. Median somatosensory EPs were recorded in 10 patients, with 6 patients having a prolonged cortical N19 response. Tibial somatosensory EP was performed for 11 patients, and 8 patients showed abnormal results where P37 cortical response was absent or prolonged, whereas peripheral potentials at the popliteal fossa were normal. Brainstem auditory EPs were abnormal only in two patients, with prolonged wave III and V latencies. Five patients with hearing impairment presented with normal brainstem auditory EP results. Multiple EP abnormalities are observed in Woodhouse-Sakati syndrome patients, mainly in pattern reversal visual EPs and somatosensory EPs. These findings indicate potential myelin dysfunction that has a role in the underlying pathophysiology, disease course, and phenotypic variability.

Median somatosensory evoked potential as a predictor of clinical outcome after urgent surgical extracranial internal carotid artery recanalization

ObjectiveChanges in the N20/P25 amplitude of somatosensory evoked potentials (SEP) of the median nerve have been found to correlate with those in cortical regional cerebral blood flow (rCBF). Our study presents the use of median nerve SEP amplitude in predicting the clinical outcome of urgent surgical internal carotid artery (ICA) recanalization. MethodsA total of 27 patients suffering an acute ischemic stroke (AIS) with extracranial ICA occlusion within 24 h were prospectively recruited. The primary preoperative endpoints included the SEP amplitude absolute value (SEP-amp) and the SEP amplitude side-to-side ratio (SEP-ratio).Clinical outcome at 3 months postoperatively was assessed using the modified Rankin scale (mRS-3M). ResultsThe positive predictive values (PPVs) for SEP-amp and SEP-ratio were 95.5% and 100%, respectively, with the negative predictive values (NPVs) being 60.0% and 100%, respectively. The SEP-ratio correlated fully with mRS-3M. ConclusionThe median SEP side-to-side N20/P25 amplitude ratio seems to be a very strong positive and negative predictor of the clinical outcome of urgent recanalization of an extracranial ICA occlusion. SignificanceThe results suggest that cortical evoked activity may help in selection patient for surgical recanalization and predict clinical recovery after an acute ischemic stroke.

227. MR Diffusion Tensor Imaging fiber tractography of thalamocortical and optical radiation tracts: Comparison between probabilistic fiber tracking and evoked potential recorded in epileptic patients

Purpose The purpose of this study was to evaluate the accuracy of the probabilistic tracking method of diffusion tensor imaging fiber tractography (DTI-FT), compared to imaging-represented electrophysiology data in epileptic patients who underwent stereoelectroncephalography (SEEG) for neurosurgical planning. Methods We identified 17 epileptic patients (mean age 26 ± 11) who underwent DTI acquisition on a 1.5T Philips Achieva scanner by using echo planar imaging and a Receive Coil Head SENSE 8 channels. Sequence details include: 64 non collinear diffusion gradient directions, b-value = 1000 s/mm2, TR/TE = 6522/86 ms, FA = 90°, SENSE factor = 2 and voxel-size = 2 × 2 × 2.6 mm. In addition, a three-dimensional T1-weighted Fast Field Echo (FFE) image was acquired with a TR/TE = 7.22/3.24 ms and FA = 8° and voxel size = 0.46 × 0.46 × 0.90 mm. These data were obtained with other brain MR sequences, used for SEEG planning. Depending on electrodes location, we recorded tibial and median somatosensory-evoked potentials (SEP) in 11 patients and flash-visual evoked potential (VEP) in 12. The thalamocortical (THC) and optical radiation (OR) tracts were blindly reconstructed using a probabilistic algorithm implemented in FSL 5.0.6, using two ROIs corresponding to the sensory thalamus and white matter (WM) lying underneath the somatosensory cortex for the THC, and the lateral geniculate body and WM lying next to the calcarine cortex for the OR. The 3D tractographies were then compared to the position of SEEG electrodes contacts, on which evoked potentials (EPs) were recorded. Results Comparison between DTI-FT and EPs shown that a superposition of the neurophysiological recording contacts and the tracts resulted in 15 out of 17 patients (88%). In particular, we obtained correspondence in the reconstruction of 9 out of 11 THC and 8 out of 12 OR. Conclusions This study is a preliminary one, suggesting that EPs recorded during SEEG monitoring can be considered as a valuable tool to validate the probabilistic tracking method in the reconstruction of THC and OR tracts.

OA261] Validation of probabilistic tracking method in the reconstruction of thalamocortical and optical radiation tracts: Comparison between reconstructed tracts and evoked potential recorded in epiletic patients

Purpose The aim of this study is to evaluate the accuracy of the probabilistic tracking method of diffusion tensor imaging fiber tractography (DTI-FT), comparing to imaging-represented electrophysiology data in epileptic patients who underwent stereoelectroncephalography (SEEG). Methods Fourteen epileptic patients (mean age 28 ± 9), who underwent DTI acquisition and other brain MR sequences used for SEEG plannig, were selected from “Claudio Munari” Epilepsy Surgery Center database. DTI sequences were collected using a 1.5T Philips Achieva scanner by using echo planar imaging and a receive coil head SENSE 8 channels. According to the implanted electrodes position, we recorded intracerebral tibial and median somatosensory-evoked potentials (SEP) in 7 patients and flash-visual evoked potential (VEP) in 8. The thalamocortical (THC) (separately considered as median and tibial THC) and optical radiation (OR) tracts were blindly reconstructed using a probabilistic algorithm implemented in FSL 5.0.6. The tracts’ reconstruction was obtained using two ROIs corresponding to a seed-point and to a way-point. The seed-point represents the starting region of the reconstructed tract, while the way-point is a region that is crossed by the reconstructed tract. In the reconstruction of THC bundle, we used the sensory thalamus as seed-point and the white matter (WM) lying underneath the somatosensory cortex as way-point. In the OR’s reconstruction we used the lateral geniculate body as seed-point and the WM lying next to the calcarine cortex as way-point. The 3D tractographies were then compared to the position of SEEG electrodes contacts, on which evoked potentials (EPs) were recorded. Results Comparison between DTI-FT and EPs showed a satisfactory superimposition of the neurophysiological recording contacts and the reconstructed tracts. We obtained full superimposition in all median thalamocortical tracts. We observed a correspondence in 81% of tibial THC and in 81% of OR, considering a maximum distance of 3mm from the tract and the neurophysiological contact. In particular, we had full correspondence in 52% of tibial THC and 70% of OR. Conclusions This study is a preliminary one, suggesting that EPs recorded during SEEG monitoring can be considered as a valuable tool to validate the probabilistic tracking method in the reconstruction of THC and OR tracts.

F71. Preoperative median SEP amplitude and paresis in emergent recanalization of internal carotid artery – Outcome prediction

Introduction Median somatosensory evoked potentials (SEP) are considered to be reliable marker of cortical ischemia in rolandic area. Intraoperative SEPs monitoring during carotid endarterectomy (CEA) is well established. Emergent neurosurgical internal carotid artery (ICA) desobliteration after ischaemic stroke is not yet recommended treatment because of uncertain efficacy. There is subgroup of patients that recover after early ICA recanalization despite severe paresis in admission. Preoperative SEPs might be helpful in selection in such subgroup. Prognostic value of preoperative median SEPs on 3 month clinical outcome and its comparison to admission upper extremity paresis. Methods During the period 05/2013–7/2017, were prospectively enrolled 33 patients after acute ischaemic stroke (AIS) that underwent emergent neurosurgical ICA recanalization. Intravenous thrombolysis preceded the surgery in 14 cases (42.4%). Patient file included 29 men (87.9%) and 4 women (12.1%) aged from 52 to 88 years (average 71). ICA occlusion and pseudoocclusion was: 21 (63.6%), 90–95% stenosis: 7 (21.2%), 70–95% stenosis 5 (15.2%). Median SEPs were performed before and monitored during the surgery in all cases. Preoperative N20/P25 amplitude decrease on symptomatic side was measured as “asymptomatic/symptomatic side ratio”. SEP ratio > 0.8 was evaluated as normal; 0.5–0.8: mild decrease; Results Clinical finding in admission: Average MRC was 2.4 and 3.1 on upper (UE) and lower extremity (LE) respectively, speech disorder was present in 20 (60.1%). 3 months after CEA: Average MRC was 3.9 and 4.2 on UE and LE respectively, speech disorder was present in 9 (27.2%). Functional outcome: mRS 0–2: 27 (81.2%); mRS 3–5: 5 (15.1%); died: 2 (6.1%). Outcome predictors: 3 month clinical outcome (mRS) was reanalysed according to admission UE muscle strength (UE-MRC) and preoperative SEP ratio. UE-MRC 0–1: in 12 (36.4%): mRS 0–2: 6 (50%), mRS 3–5: 4 (33.3%), died: 2 (16.7%). UE-MRC 2–3: in 8 (24.2%): mRS 0–2: 7 (87.5%), mRS 4: 1 (12.5%). UE-MRC 4–5: in 13 (39.4%): mRS 0–2: 13 (100%). SEP ratio 0.8: in 19 (57.6%): mRS 0–2: 18 (94.7%), mRS 5: 1 (5.3%). Conclusion Significant SEP amplitude decrease (ratio

O135 Sensory evoked potentials and central motor conduction times in children with dystonia help predict outcomes from Deep Brain Stimulation (DBS)

Objectives Deep Brain Stimulation (DBS) of the Globus Pallidus Internus produces dramatic benefits in primary dystonia. Improvements in patients with secondary dystonia are smaller and vary markedly between individuals. Predictive markers are lacking. This study tests the hypothesis that Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) may predict outcome from DBS in childhood dystonia. Methods Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary assessment for DBS (mean age 10 years; range 2.5–19). CMCT to each limb was obtained using Transcranial Magnetic Stimulation and the F-wave method. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Technically unsatisfactory data were excluded. Structural abnormalities were assessed with cranial MRI. Outcome from DBS at 1 year was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). Results Satisfactory CMCT data were obtained from 146 children, of whom 28 (19%) had an abnormal CMCT to at least one limb. Satisfactory cortical SEP data were obtained from 100 children, of whom 47 had at least one abnormal cortical potential. Abnormal CMCTs and SEPs were both observed more frequently in secondary than primary/primary plus dystonia (CMCT abnormal in 22% secondary versus 9% primary patients; SEP abnormal in 53% secondary vs 24% primary patients). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney test p = 0.002) and was also greater in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney test p = 0.001). On sub-group analysis, the relationships between CMCT/SEPs and BFMDRS-m scores were independent of aetiology (primary versus secondary) and MRI findings (normal versus abnormal). Discussion/Conclusion CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome. These markers may therefore contribute to patient selection and counselling of families about potential benefit from neuromodulation. Significance We identify neurophysiological markers that can guide the selection of patients for DBS.

Utility of somatosensory evoked potentials in the assessment of response to IVIG in a long-lasting case of chronic immune sensory polyradiculopathy

BackgroundChronic immune sensory polyradiculopathy (CISP) identifies a progressive acquired peripheral dysimmune neuropathy recognized as a chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) variant. We describe a young woman with a thirteen-year history of CISP with a belated variable response to intravenous immunoglobulin (IVIG) and an almost erratic anticipation of symptoms between IVIG cycles. The association of IVIG and corticosteroids, immunosuppressants, plasmapheresis, did not lead to clinical improvement and was characterized by significant side effects. We evaluated a combined clinical and somatosensory evoked potentials (SSEPs) approach aimed to identify possible predictive parameters concerning the effect and duration of each IVIG administration. Neurologic disability was evaluated using INCAT - Overall Disability Sum Score (INCAT-ODSS).Case presentationA 30-year-old woman presented on 2004 for the subacute onset of asymmetric paresthesias in the lower limbs over the previous six months. The symptoms had been relapsing-remitting during the first four months, followed by a slow progression, resulting in limbs ataxia and a progressive gait disturbance requiring Canadian crutches. Motor and sensory nerve conduction studies and electromyographic evaluation were into normal limits. Median SSEPs were normal, while tibial SSEPs were characterised by the bilateral absence of both lumbar and cortical responses. Cerebrospinal fluid detected an increased protein concentration, while spinal MRI showed a pronounced thickening of the sacral nerve roots, together with a tube-shaped enlargement. These findings led to the diagnosis of CISP and the patient was treated with IVIG reaching a stable remission over the following 9 years. In early 2014, the patient began to show a variable response to treatment with erratic anticipation of sensory disturbances, and a more pronounced walking disability: corticosteroids, plasmapheresis, mycophenolate mofetil and cyclophosphamide were uneffective and burdened by relevant side effects. To better assess the response to IVIG in terms of time-effect, consistency and duration, we have combined a scheduled clinical and SSEPs evaluation during and after each IVIG cycle.ConclusionsThe correlation between the neurophysiological data and the INCAT-ODSS scores has allowed the modulation of IVIG cycles with a significant reduction of the clinical fluctuations and disability. SSEPs may therefore represent an useful and recommended additional aid for the treatment schedule of this rare clinical form.

Laser and somatosensory evoked potentials in amyotrophic lateral sclerosis.

Mild involvement of sensory nerves has been reported in previous studies in ALS patients. In this study, we assessed sensory pathways in ALS patients using laser evoked potentials (LEPs) and somatosensory evoked potentials (SSEPs). We recruited 18 ALS patients and 31 healthy subjects. Neodymium-doped yttrium aluminium perovskite (Nd:YAP)-laser was used to evoke LEPs in upper (UE) and lower (LE) extremities. N1 and N2P2 potentials were obtained from contralateral insular cortex (T3 or T4) and vertex (Cz), respectively. Median SSEPs were recorded from C3' or C4' and tibial SSEPs from Cz'. Compared to controls, ALS patients had longer N2 and P2 latencies, and smaller N2P2 amplitudes in both UE- and LE-LEPs (p<0.05), and longer latencies for median and tibial SSEPs (p<0.05). LEPs and SSEPs were abnormal in 72.2% and 56.6% patients, respectively. Cortical potentials showed that A-beta or A-delta sensory fibres, or both, were impaired in more than half of the ALS patients. The findings support that ALS is a multi-systemic disorder involving, although to a lesser degree, other systems than the motor.

Causal factors for position-related SSEP changes in spinal surgery.

Somatosensory evoked potentials (SSEPs) are effective in detecting upper extremity positional injuries; however, causal factors for which patient population is most at risk are not well established. To review causal factors for intraoperative SSEP changes due to patient positioning. A case series with retrospective chart analysis was performed. 398 patient charts and intraoperative neurophysiological monitoring data from patients who underwent thoracolumbar and lumbosacral spine surgery were reviewed in a consecutive sequence from 2012 to 2013. Adverse events (AE) with the upper extremity SSEP recordings were compared to the independent variables, sex, positioning, length of procedure, and body habitus. Thoracolumbar and lumbosacral spine surgeries using contemporaneous ulnar and median nerve SSEPs were reviewed. The one-way analysis of variance (ANOVA) test, Chi-square, and independent samples t test were used to determine statistical significance in having an upper extremity SSEP AE to the aforementioned independent variables. The sample consisted of 209 males (52.5%) and 189 females (47.5%) (n=398). AE to the upper extremity SSEP was seen in 44 patients. Sex was found to be statistically significant for isolated ulnar nerve AE (P≤0.001) with males being most at risk (87.5%). AE for isolated median nerve SSEP was statistically significant for supine and prone positions (P=0.043). Length of procedure was statically significant for isolated ulnar nerve SSEP AE (P=0.039). BMI was statistically significant for generalized upper extremity SSEP AE (P=0.016), as well as isolated ulnar SSEP AE (P=0.006), isolated median SSEP AE (P≤0.001) and contemporaneous median and ulnar SSEP AE of the same limb (P≤0.001). Sex, patient positioning, length of procedure, and BMI are determinants for upper extremity neural compromise during thoracolumbar and lumbosacral spine surgeries.

ID 377 – Somatosensory evoked potentials as a predictor of clinical outcome after emergent recanalization of internal carotid artery occlusion

Objectives Median somatosensory evoked potential (SEP) amplitude monitoring is reliable tool for early cerebral ischemia detection. Aim of the study Set feasibility of routine SEP monitoring in emergent internal carotid artery (ICA) recanalization. Material and methods 05/2013 to 02/2015 were performed 12 emergent ICA recanalisations after acute ischaemic stroke (AIS). Mean age 72.7; ICA occlusion: 6 (50%), 90-99% stenosis: 6 (50%). Inclusion criteria: AIS or crescendo TIA 24 hours, ICA occlusion or stenosis, functional independence before stroke. Exclusion criteria: hemorhagic stroke, ischaemia on CT scan. Median SEP were monitored during carotid surgery. Clinical finding was evaluated 3 months after surgery. Results N20/P25 amplitude was decreased in 5 (41.7%) at symptomatic side (in 1 by > 50%) comparing to asymptomatic. Successful recanalisation: 11 (91.7%), intraluminal shunt was placed in 1 according SEP amplitude decrease intraoperatively. Mean muscle strength: arm: 2.4, leg: 3.3, speech disorder: 8 (66.7%). 3 month outcome: muscle strength: 3.9, 4.4 respectively, speech disorder: 3 (25.0%). Modified Rankin Score 0-1: 8 (66.7%), mRS 2: 3 (25.0%), mRS 6: 1 (8.3%). Conclusion Median SEP is feasible to monitor in emergent ICA recanalizations. Median SEP amplitude seems to be promising marker of good clinical outcome.

ID 36 – Somatosensory evoked potentials in juvenile myoclonic epilepsy with tremor and essential tremor

Objective Many clinicians may encounter juvenile myoclonic epilepsy (JME) patients complaining of tremor. The etiology and generators of this tremor are not clear. We aimed to evaluate if there were differences or similarities between JME tremor and ET by using somatosensory evoked potentials (SEP). Methods We analyzed the median SEPs of 14 patients with JME complaining of hand tremor, 14 patients with ET, and 14 healthy volunteers. Tremors were also assessed by accelerometric recordings. Results The N20-P25 and P25-N35 amplitudes were significantly higher in the JME group as compared to other groups. In three siblings in the JME group “giant SEPs” were observed. Moreover left N20, P25 latencies were significantly longer in ET group. Tremor frequencies of both groups showed some overlap but ET had a distinctive pattern whereas JME patients had mild interrupting myoclonus. Ten JME patients were using VPA, but their tremor had started earlier. Conclusions The SEP amplitudes of two patient groups are different even though they have the tremor as a common symptom. Our findings might be interpreted as there are two different pathophysiological mechanisms associated with this similar symptom in JME and ET patients. Key message Same complaint, different SEP findings.

Prolonged central sensory conduction time in patients with chronic arsenic exposure

BackgroundMany patients from Toroku, Japan, who have chronic arsenic exposure demonstrate whole-body sensory disturbance that is slightly more pronounced in the extremities. Although previous research in this population showed a mild peripheral neuropathy, it is unknown whether these patients have central nervous system impairment. To investigate the lesion sites underlying sensory disturbance related to chronic arsenic poisoning, we analyzed somatosensory evoked potentials (SEP). MethodsClinical features, nerve conduction study results, and median and/or tibial SEP were analyzed in patients with chronic arsenic exposure (total, 13 patients; median & tibial, 4; median, 5; tibial, 4) retrospectively. The SEP findings in patients were compared with those in normal controls. ResultsThe median SEP results indicated a conduction delay between the proximal brachial plexus and the primary sensory cortex, and tibial SEP findings indicated a delay between the dorsal gray matter of the lumbosacral cord and the primary sensory cortex. ConclusionThis is the first study to identify an impairment of the central somatosensory pathway in patients with chronic arsenic exposure. Sensory disturbance in these patients is related not only to peripheral neuropathy but also to impairment of the central nervous system.

33. Intraoperative neurophysiological monitoring of brain perfusion during cardiac surgery in patients with asymptomatic internal carotid stenosis

Introduction Asymptomatic internal carotid (ICA) stenosis is one of documented risk factors of perioperative ischemic stroke (IS) in cardiac surgery. There is no strict consensus in benefit of prophylactic carotid endarterectomy (CEA) in asymptomatic ICA stenosis to reduce intraoperative IS. Median somatosensory evoked potentials (SEP) is reliable tool for intraoperative neurophysiological monitoring (IONM) of brain perfusion during CEA. Aim of study Determine safety of median SEP monitoring in intraoperative IS prevention. Material and methods From 1st Jan 2013 to 31st Aug 2014 were enrolled 26 patients (20 males (76.9%), 6 females (23.1%) age range 59–84, average 71.9 ± 6.47 years). All patients underwent cardiosurgical procedure in extracorporal perfusion (EC) with IONM of cerebral perfusion. Inclusion criteria: ICA stenosis ⩾50% on one or more sides, asymptomatic >6 months. Unilateral stenosis was detected in 10 (38.5%), bilateral in 13 (50.0%), occlusion with contralateral stenosis was in 3 patients (11.5%). IONM consisted of median SEP and brainstem auditory evoked potentials (BAEP), near infrared spectroscopy (NIRS) were monitored synchronously. Warning and alarm were always directed at anaesthesiologist or perfusionist. Significant changes were defined as: >50% of N20/P25 amplitude decrease in SEP and/or “V” wave in BAEP and or “V” latency prolongation >1 ms. NIRS decrease ⩽40. Coronary bypass was performed in 22 patients (86.4%), aortic valve replacement in 10 (38.5%), mitral valve replacement in 6 (23.1%). Cardiac compartments were opened in 17 cases (65.4%). Results SEP amplitude decrease was detected in 5 (19.2%). In 4 of them (80%) was asymmetrical relevant to higher grade of ICA stenosis. Mean arterial pressure (MAP) increase was most effective manoeuvre in all cases. Full SEP restoration (>50% baseline amplitude) appeared in 3, partial in remaining 2 patients. Decrease of NIRS was recorded in 4 (15.4%) and always bilateral, symmetrical. Both NIRS and SEP decrease was only marginal, and in 1 case only. BAEP changed nonsignificantly. No new neurological deficit appeared in 25 (96.2%) within 24 h. 1 patient could not be clinically evaluated. 3 patients (11.5%) died within 7 days (1 – ileus, 2 circulation failure). Perioperative IS was not recorded. In all surviving 23 patients neither neurological deficit nor TIA/IS within 3 months period after surgery. Conclusion Intraoperative brain hypoperfusion in SEP was detected in about 19% of cases. MAP elevation caused in SEP restitution. No false negative SEP changes were recorded. No new neurological deficit developed during and after surgery. NIRS changes were neither consistent with SEP changes nor neurological outcome.

Is Lack of Habituation of Evoked Potential a Biological Marker of Migraine?

The aim of this study was to evaluate sensitization and habituation of median somatosensory-evoked potential (MSEP) and correlate with migraine characteristics and allodynia. A total of 100 migraineurs were included; their demographic features, migraine characteristics, and the presence of allodynia were noted. The patients were grouped into episodic migraine (EM), chronic migraine (CM), and medication overuse headache (MOH). Three consecutive MSEPs averaging 100 epochs each were recorded. The N19 amplitude of block 1 was considered for sensitization, and amplitudes of block 2 and 3 compared with block 1 were considered for habituation and augmentation. MSEP was also evaluated in 29 controls. Seventy-one percent of migraineurs had a lack of habituation as opposed to 27.6% of controls (P<0.001). The lack of habituation was observed in all subtypes of migraine, and patients with EM (76.1%) had greater lack of habituation compared with patients with MOH (61.3%; P=0.03). Augmentation was present in 61% migraineurs and was more frequent in CM (73.9%) compared with EM (63%) and MOH (48%). Sensitization was not significantly different in migraineurs compared with controls (8.23±4.07 vs.7.99±2.84 μV; P=0.72), but patients with allodynia had greater sensitization compared with those without allodynia (8.57±4.32 vs. 6.89±2.55 μV; P=0.03). The sensitization was also related to age and duration of migraine. The migraineurs have impaired cortical inhibition to somatosensory stimuli, and sensitization may be a feature of chronicity.