Inferring seizure frequency from brief EEG recordings.

Routine EEGs remain a cornerstone test in caring for people with epilepsy. Although rare, a self-limited seizure (clinical or electrographic only) may be observed during such brief EEGs. The implications of observing a seizure in this situation, especially with respect to inferring the underlying seizure frequency, are unclear. The issue is complicated by the inaccuracy of patient-reported estimations of seizure frequency. The treating clinician is often left to wonder whether the single seizure indicates very frequent seizures, or if it is of lesser significance. We applied standard concepts of probabilistic inference to a simple model of seizure incidence to provide some guidance for clinicians facing this situation. Our analysis establishes upper and lower bounds on the seizure rate implied by observing a single seizure during routine EEG. Not surprisingly, with additional information regarding the expected seizure rate, these bounds can be further constrained. This framework should aid the clinician in applying a more principled approach toward decision making in the setting of a single seizure on a routine EEG.

Predictors of clamp-induced electroencephalographic changes during carotid endarterectomies.

OBJECTIVE: Electroencephalograms (EEGs) detect clamp-induced cerebral ischemia during carotid endarterectomy (CEA) and thus impact management and minimize the risk of perioperative stroke. We hypothesized that age, preoperative neurologic symptoms, ≥70% contralateral carotid and bilateral vertebral stenosis increase the probability of clamp-induced EEG changes, whereas ≥70% unilateral carotid stenosis does not. METHODS: This is an observational cohort study of 299 patients who underwent CEA with EEG monitoring at a single large urban academic medical center in 2009. Univariate and multivariate logistic regression were used. RESULTS: Seventy percent or greater ipsilateral carotid stenosis decreases the odds of clamp-induced neurophysiologic dysfunction (odds ratio [OR] = 0.43, 95% confidence interval [CI] [0.18, 0.99], P = 0.04) after adjustment for symptomatic status, degree contralateral carotid or vertebral stenosis, and age. Preoperative neurologic symptoms, ≥70% contralateral carotid stenosis, and bilateral extracranial vertebral stenosis independently increase these odds (OR 2.62, 95% CI [1.32, 5.18], P = 0.005; OR 2.84, 95% CI [1.27, 6.34], P = 0.01; and OR 3.58, 95% CI [1.02, 12.53], P = 0.04, respectively), after adjustment for the other factors. Age ≥70 years has no significant impact. CONCLUSIONS: Preoperative neurologic symptoms, ≥70% contralateral carotid, and bilateral vertebral stenosis increase the probability of clamp-induced ischemia as detected by intraoperative EEG, while ≥70% ipsilateral carotid stenosis decreases it.

The utility of routine EEG in the diagnosis of sleep disordered breathing.

Sleep disordered breathing (SDB) is a common medical condition. Its manifestations of snoring, nocturnal choking, arousals, and sleep fragmentation can lead to excessive daytime sleepiness, neuropsychological slowing, lapses of consciousness, and accidents that can be misinterpreted as epileptic phenomena. Moreover, patients with documented epilepsy commonly exhibit similar symptomatology because of the undiagnosed coexistence of sleep apnea. Therefore, a large proportion of patients referred to the electroencephalogram (EEG) laboratory primarily to confirm or refute the diagnosis of epilepsy could suffer from latent sleep apnea and the routine EEG has the potential to divulge it. We retrospectively evaluated the reporting of sleep apnea symptomatology (snoring, choking, gasping/deep breath, apnea, desaturation, excessive drowsiness) in routine inpatient and outpatient adult EEG studies performed in our institution over the past 12 years (39,130 studies, approximately half of which recorded at least early stages of sleep). Comparisons were performed with the medical records to ascertain the coexistence of objectively diagnosed SDB with polysomnography before or after the EEG study and the importance of reporting variations in assisting with the diagnosis. Two illustrative examples are provided. Sixty-nine EEG studies were identified, performed primarily to confirm, or refute the diagnosis of epilepsy. The mean age of the subjects at EEG was 64 years (range 30-89), and 55 (80%) were male. 36% of them suffered from known epilepsy. Snoring was the most commonly reported sign in 48 (70%) of the studies, followed by arousals in 29 (42%), apnea in 16 (23%), excessive drowsiness in 13 (19%), gasping/deep breath in 9 (13%), and desaturation in 7 (10%). A sleep disorder was suggested in 25 (36%) of the interpretations and a direct recommendation for a sleep study was made in 22 of them (32%). This interpretation was included in the impression of the report in 21 (30%) of the cases, in the detail in 20 (30%) of the cases and in both in 28 (40%). Only 14 (20%) patients underwent polysomnography, and all of them were formally diagnosed with SDB. Seven (50%) of them were diagnosed with obstructive sleep apnea, 2 (14%) with central sleep apnea, 3 (22%) with both, 1 (7%) with upper airways resistance syndrome, and 1 (7%) with primary snoring. From these 14 patients, 9 (64%) were diagnosed with a sleep study performed after the EEG, 4 (29%) before the EEG interpretation, and 1 (7%) had a repeat study after the EEG. In the logistic regression model applied, with the exception of the presence of arousals (odds ratio = 4.63, P = 0.033), none of the aforementioned symptomatology or the reporting of suspicion for SDB or the location (impression vs. detail) of the reporting showed a statistically significant association with the completion of a sleep study. Routine EEG offers a unique opportunity of direct clinical observation along with electrophysiologic and cardiorespiratory monitoring. When sleep is recorded, it can help identify clinical and electrographic features of sleep apnea and prompt confirmation with a polysomnogram in the appropriate clinical context. It can therefore serve as a valuable, adjunctive tool for the diagnosis of SDB. Our data highlight that potential but unveil its decreased use in the neurology community. Increased awareness is required by the EEG technologists, interpreting neurologists, and referring physicians, regarding reporting and using sleep apnea features on the EEG.

Phase reversal of somatosensory evoked potentials triggered by gracilis tract stimulation: case report of a new technique for neurophysiologic dorsal column mapping.

BACKGROUND AND IMPORTANCE: : Reliable visual identification of the median raphae, essential for the preservation of function of the posterior dorsal columns during intramedullary spinal cord tumor resection, is not possible in many cases, because of distorted local anatomy. In such cases, intraoperative neurophysiologic mapping of the dorsal columns offers invaluable information to the surgeon, and guides the myelotomy. We hereby describe such a new technique. CLINICAL PRESENTATION: : A 41-year-old man with a C3-C4 intramedullary spinal cord tumor underwent successful myelotomy and tumor resection. Dorsal column mapping was performed by use of an 8-contact minielectrode strip placed on the dorsal spinal cord. Direct electrical stimulation was applied via 2 adjacent contacts of the strip at a time, in an attempt to stimulate in succession the left and right dorsal columns. Somatosensory evoked potentials (SSEPs) were recorded after each stimulation, via scalp electrodes. A sharp change in polarity of the recorded scalp SSEPs (phase reversal) indicated when the stimulation of the opposite dorsal column occurred. Myelotomy was performed in between the minielectrode contacts identified as being situated closest to the raphe. The posterior tibial SSEPs were continuously monitored during and after myelotomy and until the dura closure. No changes from premyelotomy SSEPs were present. Postoperatively, the patient had preservation of the posterior column function. CONCLUSION: : SSEP phase-reversal technique is a promising new method to identify the neurophysiologic midline in intramedullary tumor resection. Fast and easy to perform, its final role in neurophysiologic dorsal column mapping awaits confirmation in future applications.

The variability of stimulus thresholds in electrophysiologic cortical language mapping.

The aim of this study was to investigate the variability of electrical stimulation threshold in cortical language mapping in relationship to the lobar location of the mapped eloquent cortex and the distance between the latter and the location of the cortical lesion. A multivariate linear regression analysis was performed in a sample of 39 patients who underwent standardized successful language cortical mapping. Estimated stimulus threshold for temporal language cortex was 1.45 times higher than the estimated threshold for frontal language cortex, after adjusting for the other variables (P = 0.017). Stimulation of the mapped cortex in close proximity to the lesion or to the lesional edema increased the estimated threshold 2.6 or 1.8 times, respectively, compared with stimulation in other areas, after adjusting for the other variables (P < 0.0001, P = 0.0017). In concordance with prior findings, our results show that stimulus threshold in cortical language mapping is dependent on the lobar location of the mapped cortex. In addition, stimulus threshold is increased when the mapped cortex is in close proximity to the location of the lesion or perilesional edema.

Cerebral embolism during elective carotid endarterectomy treated with tissue plasminogen activator: utility of intraoperative EEG monitoring.

Electroencephalography (EEG) is routinely used during elective carotid endarterectomy (CEA) for monitoring cerebral perfusion. The period most frequently associated with cerebral hypoperfusion is the one during the clamping of the carotid artery. We present a case whereby acute hypoperfusion, as detected by ipsilateral hemispheric slowing and attenuation of the fast frequencies on EEG, was detected in the period prior to clamping of the carotid artery. The acute changes were caused by a cerebral embolism. Following emergent treatment with intraoperative thrombolytic therapy with intra-arterial tissue plasminogen activator (t-PA) the EEG changes reversed fully. We discuss the utility of intraoperative EEG monitoring in the detection and treatment of cerebral embolism. The ability of EEG to intraoperatively measure the function of the at-risk cerebral cortex makes it not only a useful tool in detecting acute changes such as from a large embolism, but also in guiding necessary treatment by offering direct feedback in the absence of reliable imaging and clinical examination.

The effects of EEG suppression and anesthetics on stimulus thresholds in functional cortical motor mapping.

OBJECTIVE: To investigate the effects of EEG suppression and anesthetics on variability of electrical stimulus thresholds during functional cortical motor mapping, and the possible influences of age, lesion location and pathology. METHODS: Multivariate regression analysis was performed to study these relationships in 60 cases of successful mapping using the monopolar multipulse train technique. RESULTS: An increase in the length of EEG "flats" by 1s produced an increase in stimulus threshold by 1.08 mA (p=0.0004). Administration of TIVA (total intravenous anesthesia) or inhalational agents produced an additional increase in threshold by 1.27 mA (p=0.38) or 4.84 mA (p=0.04) respectively, when compared to awake patients. CONCLUSIONS: Depth of cortical suppression impacts the stimulus thresholds. The effect of TIVA on thresholds is mediated by its effect on cortical excitability. The effects of inhalational agents on thresholds involve their influence on excitability at other levels of the neuraxis. SIGNIFICANCE: The study represents an important step towards building a predictive model for stimulus thresholds. It also improves our understanding of the relationships of anesthetics, EEG burst suppression pattern and age with cortical excitability.

Propofol and the electroencephalogram.

Propofol is an emulsion formulation of 2,6 diisopropylphenol developed in 1975. Widely recognized, it offers beneficial effects compared with other sedative drugs. Propofol is used in several clinical situations including multiple surgical procedures and critical-care medical conditions. Since technological advances over recent years have allowed an ever-increasing number of patients undergoing propofol therapy to be monitored by using continuous digital EEG, it is important to have a complete understanding of the effects of propofol on EEG in diverse clinical scenarios. This paper presents a review of the effects of propofol in electroencephalograms and discusses proconvulsive, anticonvulsive proprieties and the EEG findings in different medical conditions.

Prognostic implications of periodic epileptiform discharges.

BACKGROUND: Periodic epileptiform discharges (PEDs) are an abnormal finding on electroencephalograms (EEGs), the significance of which is uncertain. OBJECTIVE: To investigate long-term outcome in patients with PEDs. DESIGN: We retrospectively analyzed the outcomes of patients who had PEDs diagnosed during a 7-year period. We abstracted and tabulated clinical parameters from the time of EEG, imaging findings, EEG measurements, and subsequent clinical outcome from medical records. We used descriptive, inferential, and logistic regression analysis to determine the factors associated with clinical outcomes in patients with PEDs. We divided PEDs into the following subgroups: periodic lateralized epileptiform discharges (PLEDs), generalized PEDs, and bilateral PEDs and analyzed these subgroups individually. SETTING: University-affiliated teaching hospital. Subjects One hundred sixty-two patients with PEDs. RESULTS: We obtained complete clinical, neuroimaging, neurophysiologic, and long-term outcome data in 118 patients. In the subgroup of patients with PLEDs, absence of seizures at onset (odds ratio, 0.21 per point; 95% confidence interval, 0.04-0.97) and an acute etiology for the PLEDs (odds ratio, 0.14 per point; 95% confidence interval, 0.03-0.72) were associated with death. A nonneoplastic cause for PLEDs was associated with independent functionality (odds ratio, 0.45 per point; 95% confidence interval, 0.3-0.67). CONCLUSION: In patients with PLEDs, the absence of clinical seizures at the time of detection and presumed acute etiology are associated with death, whereas a nonneoplastic etiology was associated with a good clinical outcome.

Progressive myoclonus epilepsy with demyelinating peripheral neuropathy and preserved intellect: a novel syndrome.

BACKGROUND: The progressive myoclonic epilepsies (PMEs) are a disparate group of syndromes whose common features include disabling myoclonus, progressive cognitive decline, and seizures, typically with a relentless deterioration over time. OBJECTIVE: To report a novel PME syndrome. DESIGN: Case report. SETTING: Epilepsy service in a tertiary care urban medical center. PATIENT: A 24-year-old man with progressive myoclonus, seizures, and unique features of preserved intellect and demyelinating peripheral neuropathy. MAIN OUTCOME MEASURE: Detailed clinical assessment, electrophysiologic studies, and survey of the literature. RESULTS: We characterize an unusual PME phenotype with unique features of preserved intellect and electrophysiologic evidence of a generalized demyelinating peripheral neuropathic condition. An extensive diagnostic evaluation did not reveal an underlying cause, and a literature survey did not identify other, similar clinical reports. CONCLUSION: We describe a novel PME syndrome with preserved intellect and demyelinating peripheral neuropathy.

How seizure detection by continuous electroencephalographic monitoring affects the prescribing of antiepileptic medications.

OBJECTIVES: To assess the effect of continuous electroencephalographic monitoring on the decision to treat seizures in the inpatient setting, particularly in the intensive care unit. DESIGN: Retrospective cohort study. SETTING: Medical and neuroscience intensive care units and neurological wards. PATIENTS: Three hundred consecutive nonelective continuous electroencephalographic monitoring studies, performed on 287 individual inpatients over a 27-month period. MAIN OUTCOME MEASURES: Epileptiform electroencephalographic abnormalities and changes in antiepileptic drug (AED) therapy based on the electroencephalographic findings. RESULTS: The findings from the continuous electroencephalographic monitoring led to a change in AED prescribing in 52% of all studies with initiation of an AED therapy in 14%, modification of AED therapy in 33%, and discontinuation of AED therapy in 5% of all studies. Specifically, the detection of electrographic seizures led to a change in AED therapy in 28% of all studies. CONCLUSIONS: The findings of continuous electroencephalographic monitoring resulted in a change in AED prescribing during or after half of the studies performed. Most AED changes were made as a result of the detection of electrographic seizures.

Transcranial magnetic stimulation during voluntary action: directional facilitation of outputs and relationships to force generation.

Single-pulse transcranial magnetic stimulation (TMS) of the human motor cortex evokes simple muscle jerks whose physiological significance is unclear. Indeed, in subjects performing a motor task, there is uncertainty as to whether TMS-evoked outputs reflect the ongoing behavior or, alternatively, a disrupted motor plan. Considering force direction and magnitude to reflect qualitative and quantitative features of the motor plan respectively, we studied the relationships between voluntary forces and those evoked by TMS. In five healthy adults, we recorded the isometric forces acting a hand joint and the electromyographic activity in the first dorsal interosseous (FDI) muscle. Responses obtained at rest were highly invariant. Evoked responses obtained while subjects generated static and dynamic contractions were highly codirectional with the voluntary forces. Such directional relationships were independent of stimulation intensity, stimulated cortical volume, or magnitude of voluntary force exerted. Dynamic force generation was associated with a marked increase in the magnitude of the evoked force that was linearly related to the rate of force generation. The timing of central conduction was different depending on functional role of the target muscle, as either agonist or joint fixator. These results indicate that the architecture of motor plans remain grossly undisrupted by cortical stimulation applied during voluntary motor behavior. The significant magnitude modulation of responses during dynamic force generation suggests an essential role of the corticospinal system in the specification of force changes. Finally, the corticospinal activation depends on the functional role assumed by the target muscle, either postural or agonist.

Efficacy of surgical treatment of de novo, adult-onset, cryptogenic, refractory focal status epilepticus.

BACKGROUND: There have been few published reports of successful surgical treatment of focal status epilepticus. Surgical intervention is considered a last resort after medical strategies have been exhausted. OBJECTIVE: To report a case of an adult who was initially seen with de novo, medically refractory, cryptogenic focal status epilepticus and underwent resection of an electrographically defined portion of the left middle frontal gyrus with multiple subpial transections of the adjacent cortex resulting in termination of the electroclinical seizure activity. DESIGN: Report of a case of successful surgical treatment of cryptogenic focal status epilepticus. INTERVENTION: After an initial 35 days of oral antiepileptic drug therapy and subsequent 16 days of continuous electroencephalography-guided intravenous antiepileptic drug therapy in an intensive care unit setting, and after extensive preoperative and intraoperative characterization of the epileptogenic zone, a tailored resection of the left middle frontal gyrus with multiple subpial transections of the surrounding cortex was performed. RESULTS: The restricted surgical resection and multiple subpial transections terminated the seizure activity. Neuropathological examination of the resected tissue revealed moderate inflammatory changes and a few abnormally located neurons without any definitive evidence of dysplasia, which was suspected preoperatively. CONCLUSIONS: We suggest that focal cortical resection may be an appropriate intervention in medically refractory focal status epilepticus even when an overt structural etiology is not evident preoperatively and should be considered as an option at the onset of intractability.

Motion and ballistocardiogram artifact removal for interleaved recording of EEG and EPs during MRI.

Artifacts generated by motion (e.g., ballistocardiac) of the head inside a high magnetic field corrupt recordings of EEG and EPs. This paper introduces a method for motion artifact cancellation. This method is based on adaptive filtering and takes advantage of piezoelectric motion sensor information to estimate the motion artifact noise. This filter estimates the mapping between motion sensor and EEG space, subtracting the motion-related noise from the raw EEG signal. Due to possible subject motion and changes in electrode impedance, a time-varying mapping of the motion versus EEG is required. We show that this filter is capable of removing both ballistocardiogram and gross motion artifacts, restoring EEG alpha waves (8-13 Hz), and visual evoked potentials (VEPs). This adaptive filter outperforms the simple band-pass filter for alpha detection because it is also capable of reducing noise within the frequency band of interest. In addition, this filter also removes the transient responses normally visible in the EEG window after echo planar image acquisition, observed during interleaved EEG/fMRI recordings. Our adaptive filter approach can be implemented in real-time to allow for continuous monitoring of EEG and fMRI during clinical and cognitive studies.