Normal 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.

Positive effect of microvascular proliferation on functional recovery in experimental cervical spondylotic myelopathy.

Cervical Spondylotic Myelopathy (CSM), the most common cause of spinal cord dysfunction globally, is a degenerative disease that results in non-violent, gradual, and long-lasting compression of the cervical spinal cord. The objective of this study was to investigate whether microvascular proliferation could positively affect neural function recovery in experimental cervical spondylotic myelopathy (CSM). A total of 60 male adult Sprague-Dawley (SD) were randomly divided into four groups: Control (CON), Compression (COM), Angiostasis (AS), and Angiogenesis (A G),with 15 rats in each group. Rats in the AS group received SU5416 to inhibit angiogenesis, while rats in the AG group received Deferoxamine (DFO) to promote angiogenesis. Motor and sensory functions were assessed using the Basso Beattie Bresnahan (BBB) scale and somatosensory evoked potential (SEP) examination. Neuropathological degeneration was evaluated by the number of neurons, Nissl bodies (NB), and the de-myelination of white matter detected by Hematoxylin & Eosin(HE), Toluidine Blue (TB), and Luxol Fast Blue (LFB) staining. Immunohistochemical (IHC) staining was used to observe the Neurovascular Unit (NVU). Rats in the CON group exhibited normal locomotor function with full BBB score, normal SEP latency and amplitude. Among the other three groups, the AG group had the highest BBB score and the shortest SEP latency, while the AS group had the lowest BBB score and the most prolonged SEP latency. The SEP amplitude showed an opposite performance to the latency. Compared to the COM and AS groups, the AG group demonstrated significant neuronal restoration in gray matter and axonal remyelination in white matter. DFO promoted microvascular proliferation, especially in gray matter, and improved the survival of neuroglial cells. In contrast, SU-5416 inhibited the viability of neuroglial cells by reducing micro vessels. The microvascular status was closely related to NVU remodeling an-d functional recovery. Therefore, proliferation of micro vessels contributed to function -al recovery in experimental CSM, which may be associated with NVU remodeling.

Usefulness of the H-Reflex for Intraoperative Monitoring of Thoracoabdominal Aneurysms.

Intraoperative neurophysiologic monitoring in thoracoabdominal aneurysms (TAAA) is essential to avoid intraoperative spinal cord injury). Motor and somatosensory evoked potentials may be considered intraoperative tools for detecting spinal cord injury. H-reflex is a well-known neurophysiologic technique to evaluate L5-S1 root. Current evidence supports the observation that H-reflex changes may occur with spinal cord damage as high as the cervical level. This study aimed to evaluate the usefulness of the H-reflex in these surgeries. The use of intraoperative H-reflex in TAAA monitoring was evaluated in 12 patients undergoing open or endovascular repair of TAAA for a period of four years (2016-2020) using somatosensory evoked potentials (SSEPs) and transcranial motor evoked potentials (TcMEPs) and bilateral H-reflex. Six neurophysiologic alarms were recorded in five of the 12 patients. Summarizing the neurophysiologic changes of our series, we considered a peripheral change when we detected a unilateral loss of SSEPs, TcMEPs, and H-reflex. Instead, we assumed a central change when we detected a unilateral or bilateral loss of TcMEPs and H-reflex with normal SSEPs, which we considered a sign of spinal cord ischemia. Interestingly H-reflex always changed significantly in combination with TcMEPs in the same fashion. According to our series, H-reflex can detect intraoperative changes with the same sensitivity as TcMEPs in TAAA surgeries. With the support of other techniques, it can be useful to localize the origin of the lesion (peripheral or central spinal cord), to help in surgical decision-making to avoid postoperative neurologic damage. Based on our results, we recommend the systematic use of H-reflex in TAAA surgeries.

Correlation of urodynamic studies and somatosensory evoked potential and their prognostic value in children with closed spinal dysraphism

Somatosensory evoked potential (SSEP) and urodynamic studies (UD) are valuable tools for assessing patients with closed spinal dysraphism (CSD) before neurosurgical intervention. No studies have correlated their findings in this cohort and our aim is to study their correlation and prognostic value in pediatric patients with closed spinal dysraphism. Retrospective review of all patients referred to a multidisciplinary clinic in a tertiary pediatric surgical center over a 17 years period between April 2004 to September 2021 was performed. Inclusion criteria were <18 years old, diagnosed with CSD, with SSEP and UD done within 1 year of each other. Demographics data collected include age at presentation/at referral/at neurosurgical operation, gender, symptoms at presentation and intra-operative diagnoses. Pre-operative SSEP and UD findings were documented. Primary outcome was UD results in the group with normal and abnormal SSEP. Secondary outcome was urological and bowel function outcome in 4 groups of patients (Group A-both normal SSEP and UD, Group B- abnormal SSEP only, Group C - abnormal UD only and Group D-both abnormal SSEP and UD). A total of 45 patients were included for analysis. Mean follow up time was 118.9 months (24-216 months, SD 55.8 months). SSEP was normal in 20 patients and abnormal in 25 patients. Baseline demographics, preoperative symptoms and imaging were similar between 2 groups. Primary outcome Patients with abnormal SSEP were more likely to have abnormal UD results with a statistically significant difference (84% vs 40%, p<0.05). They have a significantly higher end-fill detrusor pressure (12% vs 0%, p<0.05), abnormal bladder compliance (20% vs 0%, p<0.05), abnormal cystometric capacity (48% vs 10%, p<0.05), poor emptying efficiency (24% vs 5%, p<0.05) and sphincter incompetence (8% vs 0%, p<0.05). Secondary outcome When compared to Groups A to C, patients in group D were more likely to be on anti-cholinergic (33.3% vs 4.3%, p<0.05), required clean intermittent catheterization (42.9% vs 4.3%, p<0.05) and had intravesical botulinum injection (19% vs 0%, p<0.05). All the patients who had augmentation cystoplasty were in this group as well. Bowel function in terms of regular enema use was also statistically significantly higher in this group (33.4% p<0.05). Pre-operative SSEP and UD results correlate well in patients with closed spinal dysraphism. Patients with abnormal SSEP and UD preoperatively have higher risk of urological deterioration over time. Close monitoring in this group is warranted.

A translational study of somatosensory evoked potential time-frequency components in rats, goats, and humans.

Somatosensory evoked potentials (SEPs) have been widely used to assess neurological function in clinical practice. A good understanding of the association between SEP signals and neurological function is helpful for precise diagnosis of impairment location. Previous studies on SEPs have been reported in animal models. However, few studies have reported the relationships between SEP waveforms in animals and those in humans. In this study, we collected normal SEP waveforms and decomposed them into specific time-frequency components (TFCs). Our results showed three stable TFC distribution regions in intact goats and rats and in humans. After we induced spinal cord injury in the animal models, a greater number of small TFC distribution regions were observed in the injured goat and rat groups than in the normal group. Moreover, there were significant correlations (P < 0.05) and linear relationships between the main SEP TFCs of the human group and those of the goat and rat groups. A stable TFC distribution of SEP components was observed in the human, goat and rat groups, and the TFC distribution modes were similar between the three groups. Results in various animal models in this study could be translated to future clinical studies based on SEP TFC analysis. Human studies were approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (approval No. UM 05-312 T/975) on December 5, 2005. Rat experiments were approved by the Committee on the Use of Live Animals in Teaching and Research of Li Ka Shing Faculty of Medicine of the University of Hong Kong (approval No. CULART 2912-12) on January 28, 2013. Goat experiments were approved by the Animal Ethics Committee of Affiliated Hospital of Guangdong Medical University (approval No. GDY2002132) on March 5, 2018.

T87. EEG and simultaneously recorded SEPs in evaluation of newborns with hypoxic ischemic encephalopathy or stroke in the NICU

Introduction Differential diagnostics and outcome prediction in newborns presenting with seizures or encephalopathy remain difficult in the bedside. The objectives of the present study were (i) to determine the accuracy of simultaneously recorded EEG and somatosensory evoked potentials (SEPs) in differentiating between hypoxic-ischemic encephalopathy (HIE) and stroke as the underlying etiology of neonatal seizures or encephalopathy and (ii) to determine the accuracy of EEG and SEPs and their combination for predicting outcome in newborns with HIE or stroke. Methods The study comprised of 133 newborns (gestational age > 34 weeks) that underwent a clinically indicated EEG and simultaneous SEPs in the acute phase of their illness. 102 of the newborns had HIE and 31 had stroke. EEG background was scored as continuous (sleep stages identifiable and EEG continuous at least in active sleep or awake state) or discontinuous (sleep stages not identifiable and EEG not continuous at any time during the recording). The SEPs were classified as bilaterally absent, unilaterally absent, or bilaterally present. Outcome was evaluated from medical records at approximately 1–1.5 years age. Death, cerebral palsy, severe mental retardation, and epilepsy were considered as unfavorable outcomes. Normal or mildly abnormal development (e.g. mild motor or language delay) were considered as favorable outcomes. Results The combinations of EEG and SEP abnormalities were indicative of etiology (HIE vs stroke) and predictive of outcome. If the EEG was discontinuous, the etiology was always HIE (33 newborns) regardless of SEPs. Furthermore, if the EEG was continuous, but SEPs were uni- (9 newborns) or bilaterally (1 newborn) absent, the etiology was always stroke. Normal SEPs and continuous EEG occurred in 69 newborns with HIE and 21 newborns with stroke, and hence in these newborns the distinction between the etiologies could not be made with the present EEG-SEP criteria. This combination was, however, highly predictive of a favorable outcome regardless of the etiology: The outcome was favorable in 67/69 of those HIE and 20/21 of those with stroke. On the contrary, bi- or unilaterally absent SEPs were associated with poor outcome in all newborns with HIE (22/22) and all but two newborns with stroke (8/10). Furthermore, in newborns with HIE, even if the EEG was discontinuous but SEPs were bilaterally present, the outcome was likely to be favorable (8/11 newborns). Conclusion EEG-SEP is useful in bedside differential diagnostics between HIE and stroke in newborns presenting with seizures or general signs of encephalopathy. Furthermore, EEG-SEP is accurate in outcome prediction in both etiologies.

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.

P 92 The prognostic value of somatosensory evoked potentials in patients with severe traumatic brain injury

Objective The prognosis after traumatic coma is often unclear. It can be difficult to predict the neurological outcome using clinical criteria or imaging techniques alone. In patients with severe traumatic brain injury (TBI) median somatosensory evoked potentials (SSEPs) serve as an accepted prognostic tool. They are widely available electrophysiological tests. We evaluated the prognostic value of SSEPs in comatous patients in the intensive care unit regarding longterm outcome. Methods We retrospectively analyzed 50 patients (18–75 years) with severe brain trauma (GCS Results Preliminary results demonstrate that 90% of the patients with bilaterally absent or abnormal SSEP results had fatal prognosis or severe neurological deficits. Unilaterally absent SSEP had a negative predictive value with a rather poor GOS. Patients with GOS 4 and 5 could be predicted by bilateral normal SSEP. Conclusion Somatosensory evoked potentials are widely available electrophysiological tests and can provide an objective biomarker of a neurological outcome and assist in reliable predicting of the prognosis in patients with TBI. They should therefore be used more often for intensive care unit patients.

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.

Neonatal somatosensory evoked potentials persist during hypothermia.

Treatment with therapeutic hypothermia has challenged the use of amplitude-integrated electroencephalography in predicting outcomes after perinatal asphyxia. In this study, we assessed the feasibility and gain of somatosensory evoked potentials (SEP) during hypothermia. This retrospective study comprised neonates from 35+6 to 42+2 gestational weeks and treated for asphyxia or hypoxic-ischaemic encephalopathy at Helsinki University Hospital between 14 February 2007 and 23 December 2009. This period was partly before the introduction of routine therapeutic hypothermia, which enabled us to include normothermic neonates who would these days receive hypothermia treatment. We analysed SEPs from 47 asphyxiated neonates and compared the results between 23 normothermic and 24 hypothermic neonates. Our data showed that hypothermia led to SEP latencies lengthening by a few milliseconds, but the essential gain for predicting outcomes by SEPs was preserved during hypothermia. Of the 24 hypothermic neonates, bilaterally absent SEPs were associated with poor outcome in 2/2 neonates, normal SEPs were associated with good outcomes in 13/15 neonates and 5/7 neonates with unilaterally absent or grossly delayed SEPs had a poor outcome. Our findings indicated that SEPs were a reliable tool for evaluating the somatosensory system in asphyxiated neonates in both normothermic and hypothermic conditions.

Somatosensory evoked potentials as a screening tool for diagnosis of spinal pathologies in children with treatment refractory overactive bladder.

To evaluate the usefulness of somatosensory evoked potential as a screening tool for spinal pathologies in patients with treatment refractory overactive bladder. This prospective study was performed between January 2011 and January 2014. Children >5years old with treatment refractory overactive bladder were enrolled after exclusion of anatomical and neurological causes of incontinence. All patients underwent urodynamic studies, spinal MRI, and somatosensory evoked potential (SEP). Sensitivity, specificity, PPV, and NPV were calculated for SEP. Thirty-one children (average age 8.3±2.9years) were included in the study. SEP was abnormal in 13 (41.9%), and MRI was abnormal in 8 (25.8%) patients. SEP was found to have a sensitivity of 87.5%, a specificity of 73.9%, positive predictive value of 53.85%, and negative predictive value (NPV) of 94.4%. In patients with treatment refractory OAB, SEP is an important tool for the screening of tethered cord/spinal pathologies. Our results suggest that a child with a normal SEP study in this group of patients may not require further investigation with MRI.

21. Habituation of somatosensory evoked potentials in patients with dementia

Habituation is defined as “a response decrement with repeated stimulation”. In normal cerebral cortex repetitive stimulation delivered with various sensory modalities elicits responses characterized by habituation, presumably owing to mechanisms that alter synaptic effectiveness. Habituation may represent an early, pre-clinical marker of synaptic dysfunction. In dementia, evidence of changes in synaptic functioning in sensory cortices is lacking. We investigated somatosensory evoked potentials (SEPs) habituation in 29 patients with mild dementia, grouped according to clinical, neuropsychological, and neuroimaging features. We recorded median-nerve SEPs in 15 AD-type and 14 VD-type, mild dementia, and 15 controls. We measured N20-P25 amplitudes from 3 blocks of 200 sweeps, and assessed amplitude of block 1, and habituation from amplitude changes between the 3 sequential blocks. ANOVA showed a main effect of factor group (F = 3.43 p = 0.042). AD-type patients, had normal block1 SEP amplitudes, but abnormal habituation (p = 0.036). VD-type patients had normal SEP amplitudes and habituation (p = 0.58). SEP habituation is altered in AD-type dementia suggesting hyperresponsivity of the somatosensory cortex. This abnormality is not found in patients with VD-type mild dementia, which manifest normal synaptic function to repetitive stimulation. Further investigation is deserved to see whether abnormal SEP habituation may represent a neurophysiological marker of degenerative dementia.

20. Habituation of somatosensory evoked potentials in dystonia

Dystonia is a disorder of both motor and sensory function, clinically characterized by involuntary movements, abnormal postures, and abnormal sensory discrimination. Whereas most data on the physiology of motor cortices are consistent with a general frame of reduced inhibition and maladaptative plasticity, electrophysiological data in sensory cortices are controversial. Habituation refers to response decrement with repeated stimulation, and reflects mechanisms that alter synaptic effectiveness in the stimulated cortex through LTD or LTP-like phenomena. We investigated somatosensory evoked potentials (SEPs) habituation in patients with dystonia and hemifacial spasm (HSF). We recorded median-nerve SEPs in 28 patients (8 cranial, 4 cervical, 1 cranial-cervical dystonia, 15 HSF) and 18 age-matched controls. We measured N20-P25 amplitudes from 3 blocks of 200 sweeps, and assessed amplitude of block 1, and habituation from amplitude changes between the 3 sequential blocks. ANOVA showed a main effect of factor group ( F =4.4 p =0.015). In patients with dystonia, SEP amplitudes were normal in block 1, but thereafter failed to habituate ( p =0.03). Patients with hemifacial spasm had normal SEP amplitudes and habituation ( p =0.98). SEP habituation is altered in dystonia indicating that somatosensory cortex becomes hyperresponsive. This abnormality is not the result of involuntary movements because in patients with HSF SEPs habituate normally.

NEUROPHYSIOLOGICAL ASSESSMENT OF SPINAL FUNCTION IN SURGICAL TREATMENT OF PATIENTS WITH CERVICAL SPONDYLOGENIC MYELOPATHY

SummaryThe aim of the study is to improve diagnosis of spinal disorders in patients with cervical spondylogenic myelopathy (CSM) using complex neurophysiological (NPh) methods of diagnostics, development of Nph criteria...

Quantitative assessment of somatosensory-evoked potentials after cardiac arrest in rats: Prognostication of functional outcomes*

High incidence of poor neurologic sequelae after resuscitation from cardiac arrest underscores the need for objective electrophysiological markers for assessment and prognosis. This study aims to develop a novel marker based on somatosensory evoked potentials (SSEPs). Normal SSEPs involve thalamocortical circuits suggested to play a role in arousal. Due to the vulnerability of these circuits to hypoxic-ischemic insults, we hypothesize that quantitative SSEP markers may indicate future neurologic status. Laboratory investigation. University Medical School and Animal Research Facility. : Sixteen adult male Wistar rats. None. SSEPs were recorded during baseline, during the first 4 hrs, and at 24, 48, and 72 hrs postasphyxia from animals subjected to asphyxia-induced cardiac arrest for 7 or 9 mins (n = 8/group). Functional evaluation was performed using the Neurologic Deficit Score (NDS). For quantitative analysis, the phase space representation of the SSEPs-a plot of the signal vs. its slope-was used to compute the phase space area bounded by the waveforms recorded after injury and recovery. Phase space areas during the first 85-190 mins postasphyxia were significantly different between rats with good (72 hr NDS >or=50) and poor (72 hr NDS <50) outcomes (p = .02). Phase space area not only had a high outcome prediction accuracy (80-93%, p < .05) during 85-190 mins postasphyxia but also offered 78% sensitivity to good outcomes without compromising specificity (83-100%). A very early peak of SSEPs that precedes the primary somatosensory response was found to have a modest correlation with the 72 hr NDS subscores for thalamic and brainstem function (p = .066) and not with sensory-motor function (p = .30). Phase space area, a quantitative measure of the entire SSEP morphology, was shown to robustly track neurologic recovery after cardiac arrest. SSEPs are among the most reliable predictors of poor outcome after cardiac arrest; however, phase space area values early after resuscitation can enhance the ability to prognosticate not only poor but also good long-term neurologic outcomes.

Thalamic stroke: correlation of clinical symptoms, somatosensory evoked potentials, and CT findings.

We studied 18 patients with a single ischemic thalamic lesion, who had somatosensory disturbances and/or central pain in the opposite hemibody, by correlating their clinical symptoms, somatosensory evoked potentials (SEPs), and computed tomography (CT) findings. Patients were divided into three groups: (1) those with somatosensory deficits, central pain, and abnormal SEPs, which comprised two thirds of the patients (classic thalamic pain syndrome), (2) those with somatosensory deficits, no central pain, and abnormal SEPs (analgetic thalamic syndrome), and (3) those with almost normal sense perception, central pain, and normal SEPs (pure algetic thalamic syndrome). CT evidence of a paramedian or anterolateral thalamic lesion might be an indicator for the development of central pain, because these types of infarctions occurred only in patients with the classic thalamic syndrome or the pure algetic thalamic syndrome. The differentiation of the thalamic syndrome into three subtypes is of prognostic value, because patients with a loss of cortical SEPs and a posterolateral ischemic thalamic lesion on the CT scan probably will not exhibit central pain.

Utility of somatosensory evoked potentials in chronic acquired demyelinating neuropathy

Chronic acquired demyelinating polyneuropathy (CADP) is a heterogeneous syndrome that may be classified into a number of subtypes. Somatosensory evoked potentials (SSEPs) assess proximal segments of sensory nerves, inadequately assessed by routine nerve conduction studies (NCSs). The aim of the present study was to determine the utility of SSEPs in diagnosing and classifying different CADP subtypes. Forty-seven patients with CADP were studied and classified in five groups based on conventional NCSs and SSEPs. Some patients in Group 1 were initially misdiagnosed as having either motor neuron disease or multifocal motor neuropathy due to normal sensory NCSs, but they exhibited abnormal tibial and median nerve SSEPs, as evidenced by marked prolongation or absence of peripheral potentials (N9-median nerve, and N20-tibial nerve). These were reclassified as having chronic inflammatory demyelinating neuropathy (CIDP). In CIDP patients (Group 2), SSEPs were abnormal, thereby confirming the presence of demyelination in the proximal peripheral nerves. Patients with distal acquired demyelinating neuropathy (DADS) (Group 3), as defined by conventional NCS, exhibited abnormal SSEPs when anti-MAG antibodies were present. Anti-MAG-negative DADS patients (Group 3) had normal SSEPs. In the pure sensory ataxic group (Group 4), SSEP studies disclosed poorly formed and delayed cortical potentials with absent lumbar (N20) potentials, thereby suggesting the presence of proximal demyelination. SSEPs were normal in the pure motor CIDP and multifocal motor neuropathy patients (MMN) (Group 5), thereby differentiating asymmetric forms of CIDP from MMN. These findings suggest that SSEPs may be an important complementary investigation to conventional NCSs in the diagnosis of CADP.

Analysis of motor and somatosensory evoked potentials during thoracic and thoracoabdominal aortic aneurysm repair

Use of motor evoked potentials (MEP) and somatosensory evoked potentials (SSEP) monitoring during thoracic and thoracoabdominal aortic surgery is controversial. This study evaluated the intraoperative use of SSEP and MEP during thoracoabdominal repair and assessed their role in decreasing the risk of spinal cord ischemia and paralysis. We conducted paired SSEP and MEP monitoring to assess agreement between the methods and their ability to predict neurologic outcome in 233 patients. Changes in SSEP and MEP monitoring were classified as no change, reversible change, or irreversible change during the intraoperative period and by the conclusion of surgery. Agreement between the methods was computed using the Cohen kappa statistic. Sensitivity, specificity, and positive and negative predictive values were computed for each method on the immediate and delayed neurologic deficit. Immediate neurologic deficit, determined immediately upon awakening from anesthesia and confirmed by a neurologist, occurred in eight of 233 (3.4%) patients. For any change (reversible plus irreversible), agreement between MEP and SSEP was relatively low (kappa = 0.53), despite being highly statistically significant (P < .001). MEP tended to overestimate SSEP for immediate neurologic deficit, demonstrating a 53% false-positive rate, compared with a 33% false-positive rate for SSEP (specificity ratio, 1.42; P < .0001). With irreversible change, agreement between the methods was 90% (kappa = 0.896, P < .0001). Only irreversible change was significantly associated with neurologic outcome (odds ratio, 21.9; P < .00001 for SSEP; 60.8, P < .0001 for MEP), but sensitivity and positive predictive values were low (37% and 33% for SSEP; 22% and 45% for MEP, respectively). Reversible changes in neurophysiologic monitoring were not significantly associated with immediate neurologic deficit. Negative predictive values for all negative evoked potential findings were >98% for immediate deficit. No evoked potential variables were associated with delayed deficit. SSEP and MEP monitoring were highly correlated only when intraoperative changes were irreversible. Reversible changes were not significantly associated with immediate neurologic deficit. Irreversible changes were significantly associated with immediate neurologic deficit, and the findings were identical for SSEP and MEP in this variable, indicating that the more complex MEP measures do not add further information to that obtained from SSEP. Normal SSEP and MEP findings had a strong negative predictive value, indicating that patients without signal loss are unlikely to awake with neurologic deficit.

Prognostic Value of Somatosensory-Evoked Potentials in the Surgical Management of Cervical Spondylotic Myelopathy

Preoperative somatosensory-evoked potentials (SEPs) were retrospectively analyzed and classified, and compared with surgical outcome. To evaluate the value of the preoperative SEP waveform in predicting the clinical outcome after surgical management of cervical spondylotic myelopathy (CSM). SEPs have played an important role in spinal surgery. However, the value of SEPs in predicting the outcome of surgery for CSM remains controversial. This study enrolled 76 CSM patients who underwent surgical intervention. Median nerve SEPs were recorded before surgery. The Japanese Orthopedic Association (JOA) scoring system was used to evaluate the neurologic function before surgery and at postoperative follow-up at 1, 3, 6, 12, and 24 months. Patients were divided into 5 groups according to the classification of their preoperative SEP waveforms. Group I patients had normal SEPs, group IIa had normal latency and abnormal amplitude, group IIb had abnormal latency and normal amplitude, group III had abnormal latency and amplitude, and group IV had immeasurable waveforms. The myelopathic disability scores and surgical outcomes in different groups were compared by the Kruskal-Wallis test. The SEP classification was found to be significantly associated with the JOA score (Pearson's chi test, chi = 53.9, P < 0.05). There were no significant differences in JOA score recovery at different follow-up times within any SEP group. At 24 months after surgery, there was no significant difference in the recovery ratio between groups I and IIa, or between groups IIb and III (Kruskal-Wallis test, P > 0.05). However, the recovery ratio was significantly higher in groups I and IIa than in all the other groups (Kruskal-Wallis test, P < 0.05), and in groups IIb and III than in group IV (Kruskal-Wallis test, P < 0.05). SEP classification correlates well with CSM disability and postoperative recovery ratio. Median nerve SEP recordings would be a valuable and practical tool for the diagnosis and prognosis of myelopathy.