Tibial Nerve Somatosensory Evoked Potentials Research Articles

Intraoperative Neurophysiological Monitoring in Tethered Cord Syndrome Surgery: Predictive Values and Clinical Outcome.

"Tethered cord syndrome" (TCS) refers to a congenital abnormality associated with neurological signs and symptoms. The aim of surgery is to prevent or arrest their progression. This study reports a retrospective case series of tethered cord syndrome surgeries, supported by intraoperative neurophysiological monitoring. The case series comprises 50 surgeries for tethered cord syndrome in which multimodal intraoperative neurophysiological monitoring was performed using motor evoked potentials (transcranial motor evoked potentials [TcMEPs]), tibial nerve somatosensory evoked potentials (TNSEPs), and pudendal-anal reflex (PAR). The intraoperative neurophysiological monitoring results are reported and correlated with clinical outcomes. Sensitivity, specificity, and negative predictive value were high for TcMEPs and TNSEPs, while PAR exhibited low sensitivity and positive predictive value but high specificity and negative predictive value. Fisher's exact test revealed a significant correlation between changes in TcMEPs, TNSEPs, and clinical outcome ( P < 0.000 and P = 0.049 respectively), but no correlation was detected between PAR and urinary/anal function ( P = 0.497). While TcMEPs and TNSEPs were found to be reliable intraoperative neurophysiological monitoring parameters during tethered cord syndrome surgery, PAR had low sensitivity and positive predictive value probably because the reflex is not directly related to bladder function and because its multisynaptic pathway may be sensitive to anesthetics. New onset muscle weakness and sensory deficits were related to postoperative changes in TcMEPs and TNSEPs, whereas changes in PAR did not predict bladder/urinary impairment. Urinary deficits may be predicted and prevented with other neurophysiological techniques, such as the bladder-anal reflex.

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.

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.

Utility of the tibial nerve somatosensory evoked potentials in differentiating between neuromyelitis optica spectrum disorders and multiple sclerosis.

Somatosensory evoked potentials (SEPs) are widely used for the diagnosis and evaluation of neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS). However, whether the parameters of tibial nerve SEPs can help to distinguish NMOSD from MS remains unclear. Thus, the aim of this study was to investigate the utility of tibial nerve SEP parameters in differentiating patients with NMOSD and MS. The clinical data of patients with NMOSD or MS treated in our institution between 2005 and 2021 were retrospectively extracted from our electronic database. Additional inclusion criteria were presentation with sensory symptoms in the lower extremities with corresponding lesions in the magnetic resonance images as well as available data on anti-aquaporin-4 antibodies and tibial nerve SEPs. The Z-scores of the N21-P38 interval (central sensory conduction time), P38 latency, and P38 amplitude were compared between the patients with NMOSD and MS. The relationship of disease severity with the parameters of the tibial nerve SEPs was also evaluated. Twenty patients with NMOSD and 13 patients with MS were enrolled. The Z-scores of the N21-P38 interval and P38 latency were significantly higher in the MS group than in the NMOSD group (p < 0.05 and p < 0.01, respectively), whereas there was no difference in the Z-scores of the P38 amplitude between the two groups. In the MS group, only the N21-P38 interval and P38 latency were significantly correlated with disease severity (p < 0.05 and p < 0.01, respectively). In contrast, none of the tibial nerve SEP parameters were significantly correlated with disease severity in the NMOSD group. Evaluation of the N21-P38 interval and P38 latency in tibial nerve SEPs potentially helps in differentiating between NMOSD and MS.

Tibial nerve SEPs in diagnosing lumbar spinal stenosis: The utility of segmental evaluation using P15 and N21

ObjectiveTo establish the utility of the additional evaluation of the P15 potential generated at the greater sciatic foramen in the tibial nerve somatosensory evoked potentials (SEPs) in diagnosing lumbar spinal stenosis (LSS). MethodsWe retrospectively reviewed tibial nerve SEP findings in patients having MRI-confirmed LSS at the cauda equina or conus/epiconus region. P15 and N21 potentials were recorded and the following findings were defined as localizing abnormalities: 1) normal P15 latency either with prolonged P15-N21 interval or with absent N21; 2) decreased ratio of the N21 amplitude to P15 amplitude. As non-localizing abnormalities, N21 and P38 latencies were also evaluated. Tibial nerve F-wave findings were also investigated. ResultsAccording to the entry criteria, 18 patients were included, 15 with cauda equina lesions and 3 with conus/epiconus lesions. Localizing abnormalities in SEPs were found in 67% of patients, achieving significantly higher sensitivity than delayed P38 latency (28%), and higher sensitivity than N21 abnormalities (39%), though this was not significant. Localizing abnormalities were observed even in 6 out of 11 patients lacking both sensory symptoms and signs. Tibial nerve F-wave was abnormal in 36% of 14 patients with F-wave examinations, whereas the localizing abnormalities in SEPs were found in 64% of the same patient population. P15 amplitude was depressed in 4 patients (22%), which may indicate the involvement of the dorsal root ganglion in LSS, although its latency was normal even for these patients. ConclusionsTibial nerve SEPs with the recording of P15 and N21 potentials achieved sufficiently high sensitivity in diagnosing LSS. They have the advantage over F-wave in that they can localize the lesion at the cauda equina or conus/epiconus level. SignificanceTibial nerve SEPs are promising in evaluating LSS, especially in documenting sensory tract involvement in cases lacking sensory symptoms/signs.

Misconceptions in IONM Part II: Does Anodal Blocking Occur and Is Bipolar Stimulation Necessary with Intraoperative Somatosensory Evoked Potentials?

ABSTRACT Current intraoperative somatosensory evoked potential (SSEP) guidelines recommend bipolar stimulation with the anode at or near the crease of the wrist and the cathode 2–4 cm proximal to the anode for median nerve SSEPs. The rationale for this cathode proximal bipolar configuration appears to be the avoidance of anodal blocking; however, there is a paucity of experimental support for the existence of anodal blocking. Evidence that bipolar stimulation preferentially drives stimulation from the cathode better than monopolar cathodal or monopolar anodal in peripheral nerves in human neurophysiology is also lacking. This study compared anode proximal to anode distal bipolar stimulation of median nerve SSEPs and the efficacy of monopolar cathode to monopolar anode stimulation in generating median, ulnar, and tibial nerve SSEPs. No difference in median nerve cortical SSEP amplitude was observed between anode proximal and anode distal bipolar stimulation at supramaximal stimulation suggesting cathode proximal bipolar is equal to anode proximal bipolar stimulation at supramaximal intensity. This data suggests that anodal blocking does not occur inintraoperative SSEPs. Furthermore, no differences were observed in ulnar, median, and tibial nerve SSEP cortical or subcortical amplitudes and latencies between monopolar cathodal or monopolar anodal stimulation suggesting monopolar cathode and anode stimulation are equally effective at evincing intraoperative SSEPs at supramaximal intensity.

The influence of right-left error in the placement of the Cc electrode in tibial nerve somatosensory evoked potentials (SEPs)

ObjectiveAt our laboratory, we routinely record tibial nerve somatosensory evoked potentials (SEPs) using 5 channels including the second cervical vertebra (C2S)-contralateral central area (Cc) and Cz’ (2 cm posterior to Cz)–Cc derivations. In a man with lumbar spondylotic myelopathy, symptoms improved after surgery, although the N21-P38 interval was markedly prolonged in comparison with that before surgery. We presumed that the Cc electrode was actually placed on the ipsilateral central area (Ci) at the second examination. Inspired by this episode, we investigated the influence of the right-left error in the placement of the Cc electrode. MethodsSubjects were 20 healthy volunteers. Tibial nerve SEPs were recorded with 8 leads including Cz’–Cc, Cz’-Ci, C2S-Cc and C2S-Ci. ResultsFor the Cz’-Ci lead, the P38 potential diminished in amplitude, was absent or became negative. For the C2S-Ci lead, a large negative potential corresponding to the phase reversal of P38 was frequently observed. ConclusionsTibial nerve SEPs using the Cz’–Cc or C2S-Cc lead are distorted if the Cc electrode is placed on the opposite side. SignificanceWhen a strange result is obtained in tibial nerve SEPs, we should check for a right-left error in the Cc electrode placement.

Imagined paralysis alters somatosensory evoked-potentials

ABSTRACT Recent studies employing body illusions have shown that multisensory conflict can alter body representations and modulate low-level sensory processing. One defining feature of these body illusions is that they are sensory driven and thus passive on behalf of the participant. Thus, it remained to establish whether explicit alteration of own-body representations modulates low-level sensory processing. We investigated whether tibial nerve somatosensory-evoked potentials were modulated when participants imagined paralysis of their legs and arms. Imagined paralysis of the legs decreased P40 amplitude, but not imagined paralysis of the arms. These results show modulation of early somatosensory processing via explicit, top-down alteration to the internal representation of the body. Interestingly, P40 suppression positively correlated with bodily awareness scores whereas it negatively correlated with body dissociation scores. This suggests that the ability to actively alter own-body representation and its corresponding sensory processing depends upon dispositions to attend to and focus on bodily sensations.

Evaluation of Neurological Examination, SEP Results, MRI Results, and Lesion Levels in Patients Who Had Been Operated for Myelomeningocele.

Objective:Myelomeningocele is the most severe and the most frequent form of spina bifida. Most of the myelomeningocele patients undergo operations in new-born age. In terms of life quality and rehabilitation, follow-up’s of these patients in the growth and development period after the operation is critical. In our study, our aim is to emphasize the correlation of SEP results with MRI results and clinical features of the myelomeningocele patients.Materials and Methods:In our study, we included 36 patients who had undergone myelomeningocele operation and have been followed-up in Istanbul Bilim University Florence Nightingale Hospital, Spina Bifida Research and Treatment Centre. Posterior tibial nerve SEP was performed on each patient and neurological examinations were done in the same session. Results were compared with clinical functional lesion levels, levels of fusion defect and ambulation levels. In order to evaluate SEP results, we used age-related reference values from Boor et al.’s study in 2008. Patients were grouped as normal, unilaterally prolonged, bilaterally prolonged, unilaterally lost, and bilaterally lost.Results:The correlations of posterior tibial nerve SEP results were significant with ambulation levels (r = 0.428, P < 0.01), clinical functional lesion levels (r = 0.477, P < 0.01) and fusion defect levels (r = −0.528 P < 0.05). The lumbar SEP results were only significantly correlated with functional lesion levels (r = 0.443 P < 0.05).Conclusions:Radiological studies are insufficient when evaluating the functionality of the central nervous system. To fully evaluate the functionality and watch the neurological development with accuracy, especially in operated patients, electrophysiological studies should be an indispensable part of myelomeningocele follow-ups.

Utility of motor evoked potentials to diagnose and reduce lower extremity motor nerve root injuries during 4,386 extradural posterior lumbosacral spine procedures

BACKGROUND CONTEXTMotor evoked potentials (MEPs) have excellent sensitivity for monitoring the functional integrity of the lateral corticospinal tract of the spinal cord. The sensitivity for nerve root function, however, is not as well established; consequently, MEPs are often not utilized for posterior extradural spine procedures distal to the conus. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) are often included for these procedures, but their limited sensitivity has been well documented. Given the risk of motor nerve root injuries during spine procedures, and specifically increased vulnerability of the L4 and L5 nerves, the sensitivity of MEPs was evaluated for diagnostic accuracy and therapeutic impact. PURPOSETo determine the diagnostic sensitivity of MEPs during lumbosacral spine procedures and the potential therapeutic impact of the resolution of MEP alerts. STUDY DESIGNA total of 4,386 posterior extradural lumbosacral spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) with sEMG, SSEPs, and MEPs were abstracted from a multi-institutional database. All cases took place between October 2015 and October 2017. No external funding was provided. OUTCOME MEASURESSensitivity and specificity, as well as positive and negative likelihood ratios for new postoperative neurologic deficits were calculated for each modality individually as well as when combined (multimodality). PATIENT SAMPLEAge 18 and older METHODSData entered in the electronic medical record were analyzed. Alerts to sEMG activity, decreases in SSEP amplitude, or decreases in MEP amplitude were documented as well as the status of the alerts at closure: resolved or unresolved. The presence of an sEMG alert or an unresolved MEP or SSEP alert at closure was considered a positive diagnostic result, and these results were assessed relative to presence of new immediate onset neurologic deficits as documented in the electronic record. RESULTSThe sensitivity and specificity of multimodality IONM for new immediate-onset lower extremity motor deficits were 100.0% (95% confidence interval: [64.6, 100.0]) and 92.2% (91.1, 93.1), respectively. Looking at the modalities in isolation, the sensitivity of MEPs was considerably better than either lower extremity sEMG or posterior tibial nerve SSEPs: 100.0% (78.5, 100.0) versus just 14.3% (4.0, 39.9) and 28.6% (8.2, 64.1), respectively. Surprisingly, the specificity of lower extremity MEPs was better than sEMG, 97.9% (97.5, 98.3) versus 95.4% (94.7, 96.0) (χ2=43.0, p<.001). The specificity of lower extremity SSEPs was 99.0% (98.5, 99.3). Only 4.4% of all procedures had a lower extremity MEP alert. There were 14 significant new nerve root injuries and all 14 had unresolved MEPs at closure. Total 85.7% of those nerve root injuries were dorsiflexion foot drop injuries and all had unresolved tibialis anterior MEP alerts. Although the overall rate of nerve root injuries was 0.32% (14/4,386), the rate for procedures with unresolved isolated tibialis anterior MEP alerts was 44.4% (12/27). The therapeutic impact is evident in the 2.0% of cases (87/4,386) with lower extremity MEP alerts that were able to be fully resolved by closure and for which the rate of injury was zero. CONCLUSIONSThe diagnostic accuracy of MEPs for anterior tibialis-related nerve root dysfunction supports the inclusion of this modality during routine posterior extradural lumbosacral procedures, especially when the L4 or L5 nerve roots are at risk. Moreover, therapeutic interventions that lead to the resolution of MEP alerts avert postoperative neurologic injuries.

P2-08-01. The influence of right-left error of the placement of Cc electrode in tibial nerve SEPs

P2-08-01. The influence of right-left error of the placement of Cc electrode in tibial nerve SEPs

Lower Extremity Somatosensory Evoked Potential P37 Waveform Optimization

ABSTRACTSomatosensory evoked potentials (SEPs) using tibial nerve stimulation are used during neurophysiologic intraoperative monitoring (NIOM). These SEPs produce a P37 waveform that is recorded from scalp electrodes. In this study, we attempted to determine the best derivation for recording the P37 waveform. Surgical cases using tibial nerve SEP NIOM were reviewed. Only cases in which the P37 was recorded using all of the following derivations were analyzed: centroparietal ipsilateral–centroparietal contralateral (CPi-CPc), centroparietal midline–frontopolar midline (CPz-Fpz), and CPz-CPc. The amplitude of the P37 waveform was measured in each derivation. Descriptive statistics were obtained for the P37 waveform amplitude. The mean amplitude in each of the derivations was compared using a chi-square test. Data from 39 patients (78 lower limbs) were available for analysis. The mean age of the patients was 49.64 years (range: 4–87 years); 18 were female. The highest amplitude P37 waveform was recorded from the CPz-Fpz derivation in 29 (35.4%) limbs, whereas the CPz-CPc and CPi-CPc derivations showed the highest amplitude in 29 (35.4%) and 20 (24.4%) limbs, respectively. The mean amplitudes were not significantly different between the various derivations. In only 10 (24.4%) of patients was the best derivation the same for both left and right limbs. A single best derivation was not found for recording the P37 waveform. Multiple derivations should be used to record cortical channels whenever possible. If the number of available channels is limited, using at least the CPz-Fpz and CPz-CPc derivations is recommended.

S79. The utility of tibial nerve SEPs in diagnosing lumbar spinal stenosis, comparison with NCS and F-Waves

Introduction Lumbar spinal stenosis (LSS) is a popular cause of lower limb motor and sensory impairments and gait disturbance. SEPs can be a tool to evaluate LSS, and there have been considerable number of studies investigating the utility of dermatomal SEP in evaluating LSS or lumbar radiculopathy. However, few studies investigated the utility of tibial nerve SEPs. Tibial nerve SEPs have an advantage that they can evaluate plural points along the whole course of the peripheral nerve and can localize the lesion site. Three segments of ankle-knee, knee-pelvis, and pelvis-spinal entry can be evaluated by N8o latency, N8o-P15 interval, and P15-N21 interval. In this study, we compared the utility of tibial nerve SEPs with nerve conduction studies (NCS) and F-waves. Methods We searched our EMG database from 2012 to 2017 with the keyword of “LSS” or “lumbar” and SEP examinations. For extracted cases, we retrospectively reviewed clinical and EMG records and MRI images. The entry criteria were as follows: (1) presence of sensory, motor, or gait (typically, intermittent claucication) complaints, (2) unequivocal LSS in lumbar MRI, (3) final diagnosis that the chief complaint was caused by the MRI-documented LSS, (4) Tibial nerve SEPs, motor conduction study (MCS) and F waves of the tibial nerve, and sensory conduction study (SCS) of the sural nerve were conducted for the same lower-limb that was the more affected, (5) no other causes that can explain his or her symptoms, especially neuropathies and diabetes, (6) no prior lumbar surgery. Results Among 39 patients initially extracted, many have been excluded by the strict inclusion criteria. Finally enrolled were 8 patients (53–82 years, all men). The clinical features of these patients were as follows. Weakness was present in 7 (absent in 1). Sensory symptoms or signs were present in 4 (absent in 4). Intermittent claucication was present in 3 patients. Tibial nerve SEPs were abnormal in 7, and could localize the lesion at the lumbar segment (P15-N21) in 6. Notably, in 3 out of 4 patients without sensory symptoms or signs, tibial nerve SEPs localized the lesion at lumbar segment. The amplitude of the compound muscle action potential (CMAP) of the tibial MCS was reduced in 2 cases, and F-wave latency was prolonged in the same 2 cases. In no cases, F-waves were abnormal despite normal SEPs. Sural SCS was normal for all cases. In two patients in which tibial nerve SEPs could not localize the lesion, needle EMG confirmed the diagnosis of LSS. Conclusion Tibial nerve SEPs are useful in diagnosing LSS by localizing the lesion at the lumbar segments. Especially the fact that they documented lumbar lesions in patients lacking sensory symptoms or signs would contribute to the differentiation from amyotrophic lateral sclerosis. The sensitivity of F-waves was much lower than tibial nerve SEPs and added no value to the amplitude of the tibial CMAP.

Platform Session – Evoked potentials & NIOM: Somatosensory evoked potentials and central motor conduction times help predict outcomes from deep brain stimulation (DBS) in children with dystonia

DBS of the Globus pallidus internus has dramatic benefits in primary dystonia. Responsiveness of secondary dystonia is more modest and varies markedly between individuals. Predictive markers are lacking and the underlying pathophysiology of secondary dystonia is poorly understood. We report Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) in children with dystonia and test the hypothesis that these parameters relate to outcome from DBS. Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary DBS assessment (mean age 10 years; range 2.5–19). Transcranial Magnetic Stimulation was applied to motor cortex and Motor Evoked Potentials were recorded in the activated contralateral hand and foot muscles. CMCT to each limb was calculated using the F-wave method. Median nerve SEPs were recorded over ipsilateral Erb’s point, 7th and 2nd cervical vertebrae and contralateral centroparietal scalp. Posterior tibial nerve SEPs were recorded over ipsilateral popliteal fossa and midline centroparietal scalp. A mid-frontal reference was used. Electrical stimuli of 0.2millisecond duration were applied at 2.1 Hz, just above motor threshold. SEPs were classed as abnormal if delayed, absent or of abnormal waveform. Technically unsatisfactory recordings 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). Of the 146 children with satisfactory CMCT data, 28(19%) had an abnormal CMCT to at least one limb. Of the 100 children with satisfactory cortical SEP data, 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: 22% vs. 9%, SEP: 53% vs. 24%). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney p = 0.002) and in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney p = 0.001). On sub-group analysis, these relationships were preserved regardless of aetiology (primary versus secondary) or cranial imaging (normal vs abnormal MRI). CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia. Abnormal CMCTs and SEPs relate to DBS outcome, therefore contributing to patient selection and counselling of families about potential benefit from neuromodulation.

Somatosensory Evoked Potentials and Central Motor Conduction Times in children with dystonia and their correlation with outcomes from Deep Brain Stimulation of the Globus pallidus internus

ObjectivesTo report Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) in children with dystonia and to test the hypothesis that these parameters predict outcome from Deep Brain Stimulation (DBS). Methods180 children with dystonia underwent assessment for Globus pallidus internus (GPi) DBS, mean age 10 years (range 2.5–19). CMCT to each limb was calculated using Transcranial Magnetic Stimulation. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Structural abnormalities were assessed with cranial MRI. One-year outcome from DBS was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). ResultsAbnormal CMCTs and SEPs were found in 19% and 47% of children respectively and were observed more frequently in secondary than primary dystonia. Of children proceeding to DBS, better outcome was seen in those with normal (n = 78/89) versus abnormal CMCT (n = 11/89) (p = 0.002) and those with normal (n = 35/51) versus abnormal SEPs (n = 16/51) (p = 0.001). These relationships were independent of dystonia aetiology and cranial MRI findings. ConclusionsCMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome. SignificanceCMCTs and SEPs can contribute to patient selection and counselling of families about potential benefit from neuromodulation for dystonia.

Somatosensory evoked potentials in patients with high-grade aneurysmal subarachnoid hemorrhage.

OBJECTIVE The aim of this prospective study was to investigate the value of somatosensory evoked potentials (SEPs) in predicting outcome in patients with high-grade aneurysmal subarachnoid hemorrhage (SAH). METHODS Between January 2013 and January 2015, 48 patients with high-grade SAH (Hunt and Hess Grade III, IV, or V) who were admitted within 3 days after hemorrhage were enrolled in the study. Right and left median and tibial nerve SEPs were recorded on Day 3 after hemorrhage and recorded again 2 weeks later. Glasgow Outcome Scale (GOS) scores were determined 6 months after hemorrhage and dichotomized as poor (Scores 1-3) or good (Scores 4-5). Results of SEP measurements were dichotomized (present or missing cortical responses or normal or prolonged latencies) for each nerve and side. These variables were summed and tested using logistic regression and a receiver operating characteristic curve to assess the value of SEPs in predicting long-term outcome. RESULTS At the 6-month follow-up visit, 29 (60.4%) patients had a good outcome, and 19 (39.6%) had a poor outcome. The first SEP measurement did not correlate with clinical outcome (area under the curve [AUC] 0.69, p = 0.52). At the second measurement of median nerve SEPs, all patients with a good outcome had cortical responses present bilaterally, and none of them had bilateral prolonged latencies (p = 0.014 and 0.003, respectively). In tibial nerve SEPs, 7.7% of the patients with a good GOS score had one or more missing cortical responses, and bilateral prolonged latencies were found in 23% (p = 0.001 and 0.034, respectively). The second measurement correlated with the outcome regarding each of the median and tibial nerve SEPs and the combination of both (AUC 0.75 [p = 0.010], 0.793 [p = 0.003], and 0.81 [p = 0.001], respectively). CONCLUSIONS Early SEP measurement after SAH did not correlate with clinical outcome, but measurement of median and tibial nerve SEPs 2 weeks after a hemorrhage did predict long-term outcome in patients with high-grade SAH.

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.

A Comparison of Interside Asymmetries of Lower Extremity Somatosensory Evoked Potentials in Anesthetized Patients with Unilateral Lumbosacral Radiculopathy.

Study DesignProspective cohort study.PurposeThis study was to investigate interside asymmetries of three lower extremity somatosensory evoked potentials (SSEPs) in anesthetized patients with unilateral lumbosacral radiculopathy.Overview of LiteratureAlthough interside asymmetry is an established criterion of abnormal SSEP, little is known which of the lower SSEPs is more sensitive in detecting interside asymmetry in anesthetized patients.MethodsSuperficial peroneal nerve SSEP (SPN-SSEP), posterior tibial nerve SSEP (PTN-SSEP), and sural nerve SSEP were obtained in 31 lumbosacral surgery patients with unilateral lumbosacral radiculopathy, and compared with a group of 22 control subjects.ResultsThe lumbosacral group showed significant larger interside asymmetry ratios of P37 latencies in SPN-SSEP and PTN-SSEP, and significant larger interside asymmetry ratio of P37-N45 amplitude in SPN-SSEP, when comparing with the control group. Within the lumbosacral group but not the control group, SPN-SSEP displayed significant larger interside asymmetry ratio in P37 latency. When referencing to the control group, more patients in the lumbosacral group displayed abnormal interside SPN-SSEP latency asymmetries which corroborated the symptom laterality.ConclusionsThe data suggested that SPN-SSEP was more sensitive in detecting interside latency asymmetry in anesthetized patients.

24. Dorsal column nuclei evoked activity recorded from the human Pedunculopontine nucleus

This study aimed to verify the hypothesis that somatosensory activity recorded from the Pedunculopontine nucleus (PPTg) comes from the dorsal column nuclei (DCN) (Insola et al., 2015). In one parkinsonian patient implanted in the PPTg for DBS, both tibial and median nerve SEPs were recorded from the PPTg electrode. The finding obtained from this patient was compared with that issued from another patient implanted with an epidural electrode at Cv2 level for pain relief. The triphasic waform and HFOs recorded from the PPTg after tibial nerve stimulation were very similar to the low- and high-frequency components recorded from the Cv2 epidural electrode, known to be generated in the DCN (Insola et al., 2010). Therefore, the present results suggest that both the low-frequency triphasic waveform and the HFOs recorded from the PPTg are generated from the DCN.

Evaluation of Electrophysiological Effects of Melatonin and Alpha Lipoic Acid in Rats with Streptozotocine Induced Diabetic Neuropathy

Neuropathy is a common complication of diabetes mellitus and is closely related to quality of life. There are many studies in which biological ingredients, such as alpha lipoic acid (ALA), that may inhibit or reduce the generation of diabetic neuropathy were investigated. Another biological agent that may reduce the generation of diabetic neuropathy is melatonin and there are a few studies that investigate the effects of melatonin on diabetic neuropathy. In this study we aimed to examine the effect of melatonin on experimentally induced diabetic neuropathy by comparing it with both ALA and control groups. We included 24 male Wistar rats. Tibial motor nerve conduction and cortical tibial nerve somatosensory evoked potentials (SEP) studies were performed before and after diabetes mellitus (DM) for all rats. Rats were divided into 3 (ALA, melatonin and control) groups. After 2 weeks of treatment period, tibial motor nerve conduction and cortical tibial SEP studies were repeated. Our data showed that ALA significantly increased nerve conduction velocity and amplitude in rats with diabetic neuropathy (p=0,001; p=0,002). Also, melatonin significantly increased nerve conduction velocity and amplitude in rats with diabetic neuropathy (p=0.002; p=0.002). There was no significant difference between the electrophysiological effects of ALA and melatonin. Besides, neither ALA nor melatonin did significantly affect P1 and N1 latency values on cortical tibial nerve SEP studies. Our study is the study in which both tibial nerve conduction and cortical tibial SEP studies were performed to compare effects of ALA and melatonin on experimental diabetic neuropathy. Lack of significant difference on cortical tibial SEP study would be attributed to the involvement of other central nervous system pathways which do not include ALA or melatonin in the pathogenesis. RESULTS of ALA group are important by means of giving objective evidences for results of biochemical studies about the role of ALA in the pathogenesis of diabetic neuropathy. However, there is not enough information about the effect of melatonin in the pathogenesis of diabetic neuropathy. Consequently, results of our study may anticipate further biochemical and clinic studies which investigate the about the role of melatonin in diabetic neuropathy.