Towards optimizing single pulse electrical stimulation: High current intensity, short pulse width stimulation most effectively elicits evoked potentials

BACKGROUND

While single pulse electrical stimulation (SPES) is increasingly used to study effective connectivity, the effects of varying stimulation parameters on the resulting cortico-cortical evoked potentials (CCEPs) have not been systematically explored.

OBJECTIVE

We sought to understand the interacting effects of stimulation pulse width, current intensity, and charge on CCEPs through an extensive testing of this parameter space and analysis of several response metrics.

METHODS

We conducted SPES in 11 patients undergoing intracranial EEG monitoring using five combinations of current intensity (1.5, 2.0, 3.0, 5.0, and 7.5 mA) and pulse width at each of three charges (0.750, 1.125, and 1.500 μC/phase) to study how CCEP amplitude, distribution, latency, morphology, and stimulus artifact amplitude vary with each parameter.

RESULTS

Stimulations with a greater charge or a greater current intensity and shorter pulse width at a given charge generally resulted in greater CCEP amplitudes and spatial distributions, shorter latencies, and increased waveform correlation. These effects interacted such that stimulations with the lowest charge and highest current intensities resulted in greater response amplitudes and spatial distributions than stimulations with the highest charge and lowest current intensities. Stimulus artifact amplitude increased with charge, but this could be mitigated by using shorter pulse widths.

CONCLUSIONS

Our results indicate that individual combinations of current intensity and pulse width, in addition to charge, are important determinants of CCEP magnitude, morphology, and spatial extent. Together, these findings suggest that high current intensity, short pulse width stimulations are optimal SPES settings for eliciting strong and consistent responses while minimizing charge.

Deep Brain Stimulation of the Centromedian Nucleus of the Thalamus for Lennox-Gastaut Syndrome: A Systematic Review and Individual Patient Data Analysis

BACKGROUND

Lennox-Gastaut syndrome (LGS) is a severe childhood-onset pharmacoresistant epilepsy. Deep brain stimulation (DBS) of the centromedian nucleus of the thalamus (CMN) has been utilized.

OBJECTIVE

To conduct a systematic review and individual patient data (IPD) analysis to characterize outcomes of DBS of CMN in LGS.

METHODS

PubMed, Embase, and Scopus were searched per Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Articles were screened by title/abstract then full text. Included articles were reviewed for bibliographic, demographic, and outcome data. IPD were extracted from studies providing IPD for all patients.

RESULTS

Of 72 resultant articles, 10 studies (114 patients) were included. Six of 7 studies reporting the outcome of ≥50% seizure reduction indicated that ≥50% of patients achieved this, with improved functional ability. Seizure freedom rate was generally <10%. Six studies with 47 patients provided IPD. The mean ages at epilepsy onset and CMN DBS were 3.9 ± 4.5 years and 17.4 ± 8.8 years, respectively. Nineteen of 41 (46.3%) patients had positive MRI findings. Seizure types included atypical absence in 39 (83.0%) patients, generalized tonic-clonic in 32 (68.1%), tonic in 22 (46.8%), and atonic in 20 (42.6%). Thirty-eight (80.9%) patients experienced ≥50% reduction in seizure frequency, and only 3 (6.4%) experienced seizure freedom. The mean seizure reduction was 62.9% ± 31.2% overall. Quality of life improved in 30/34 (88.2%) and was unchanged in the remainder (11.8%). The complication rate was 2/41 (4.9%). The mean length of follow-up was 19.8 ± 26.1 months (IQR: 4-18 months).

CONCLUSION

Limited data indicate that DBS of the CMN may be effective and safe for people with LGS.

Functional anomaly mapping lateralizes temporal lobe epilepsy with high accuracy in individual patients

Mesial temporal lobe epilepsy (mTLE) is associated with variable dysfunction beyond the temporal lobe. We used functional anomaly mapping (FAM), a multivariate machine learning approach to resting state fMRI analysis to measure subcortical and cortical functional aberrations in patients with mTLE. We also examined the value of individual FAM in lateralizing the hemisphere of seizure onset in mTLE patients. Methods: Patients and controls were selected from an existing imaging and clinical database. After standard preprocessing of resting state fMRI, time-series were extracted from 400 cortical and 32 subcortical regions of interest (ROIs) defined by atlases derived from functional brain organization. Group-level aberrations were measured by contrasting right (RTLE) and left (LTLE) patient groups to controls in a support vector regression models, and tested for statistical reliability using permutation analysis. Individualized functional anomaly maps (FAMs) were generated by contrasting individual patients to the control group. Half of patients were used for training a classification model, and the other half for estimating the accuracy to lateralize mTLE based on individual FAMs. Results: Thirty-two right and 14 left mTLE patients (33 with evidence of hippocampal sclerosis on MRI) and 94 controls were included. At group levels, cortical regions affiliated with limbic and somatomotor networks were prominent in distinguishing RTLE and LTLE from controls. At individual levels, most TLE patients had high anomaly in bilateral mesial temporal and medial parietooccipital default mode regions. A linear support vector machine trained on 50% of patients could accurately lateralize mTLE in remaining patients (median AUC =1.0 [range 0.97-1.0], median accuracy = 96.87% [85.71-100Significance: Functional anomaly mapping confirms widespread aberrations in function, and accurately lateralizes mTLE from resting state fMRI. Future studies will evaluate FAM as a non-invasive localization method in larger datasets, and explore possible correlations with clinical characteristics and disease course.

Low-frequency stimulation of a fiber tract in bilateral temporal lobe epilepsy

OBJECTIVE

Pharmacoresistant bilateral mesial temporal lobe epilepsy often implies poor resective surgical candidacy. Low-frequency stimulation of a fiber tract connected to bilateral hippocampi, the fornicodorsocommissural tract, has been shown to be safe and efficacious in reducing seizures in a previous short-term study. Here, we report a single-blinded, within-subject control, long-term deep-brain stimulation trial of low-frequency stimulation of the fornicodorsocommissural tract in bilateral mesial temporal lobe epilepsy. Outcomes of interest included safety with respect to verbal memory scores and reduction of seizure frequency.

METHODS

Our enrollment goal was 16 adult subjects to be randomized to 2-Hz or 5-Hz low-frequency stimulation of the fornicodorsocommissural tract starting at 2 mA. The study design consisted of four two-month blocks of stimulation with a 50%-duty cycle, alternating with two-month blocks of no stimulation.

RESULTS

We terminated the study after enrollment of five subjects due to slow accrual. Fornicodorsocommissural tract stimulation elicited bilateral hippocampal evoked responses in all subjects. Three subjects underwent implantation of pulse generators and long-term low-frequency stimulation with mean monthly seizures of 3.14 ± 2.67 (median 3.0 [IQR 1-4.0]) during stimulation-off blocks, compared with 0.96 ± 1.23 (median 1.0 [IQR 0-1.0]) during stimulation-on blocks (p = 0.0005) during the blinded phase. Generalized Estimating Equations showed that low-frequency stimulation reduced monthly seizure-frequency by 0.71 per mA (p < 0.001). Verbal memory scores were stable with no psychiatric complications or other adverse events.

SIGNIFICANCE

The results demonstrate feasibility of stimulating both hippocampi using a single deep-brain stimulation electrode in the fornicodorsocommissural tract, efficacy of low-frequency stimulation in reducing seizures, and safety as regards verbal memory.

The Temporal Lobe as a Symptomatogenic Zone in Medial Parietal Lobe Epilepsy

Some surgical failures after temporal lobe epilepsy surgery may be due to the presence of an extratemporal epileptogenic zone. Of particular interest is the medial parietal lobe due to its robust connectivity with mesial temporal structures. Seizures in that area may be clinically silent before propagating to the symptomatogenic temporal lobe. In this paper, we present an overview of the anatomical connectivity, semiology, radiology, electroencephalography, neuropsychology, and outcomes in medial parietal lobe epilepsy. We also present two illustrative cases of seizures originating from the precuneus and the posterior cingulate cortex. We conclude that the medial parietal lobe should be strongly considered for sampling by intracranial electrodes in individuals with nonlesional temporal lobe epilepsy, especially if scrutinizing the presurgical data produces discordant findings.

Common functional connectivity alterations in focal epilepsies identified by machine learning

OBJECTIVE

This study was undertaken to identify shared functional network characteristics among focal epilepsies of different etiologies, to distinguish epilepsy patients from controls, and to lateralize seizure focus using functional connectivity (FC) measures derived from resting state functional magnetic resonance imaging (MRI).

METHODS

Data were taken from 103 adult and 65 pediatric focal epilepsy patients (with or without lesion on MRI) and 109 controls across four epilepsy centers. We used three whole-brain FC measures: parcelwise connectivity matrix, mean FC, and degree of FC. We trained support vector machine models with fivefold cross-validation (1) to distinguish patients from controls and (2) to lateralize the hemisphere of seizure onset in patients. We reported the regions and connections with the highest importance from each model as the common FC differences between the compared groups.

RESULTS

FC measures related to the default mode and limbic networks had higher importance relative to other networks for distinguishing epilepsy patients from controls. In lateralization models, regions related to somatosensory, visual, default mode, and basal ganglia showed higher importance. The epilepsy versus control classification model trained using a 400-parcel connectivity matrix achieved a median testing accuracy of 75.6% (median area under the curve [AUC] = .83) in repeated independent testing. Lateralization accuracy using the 400-parcel connectivity matrix reached a median accuracy of 64.0% (median AUC = .69).

SIGNIFICANCE

Machine learning models revealed common FC alterations in a heterogeneous group of patients with focal epilepsies. The distribution of the most altered regions supports the hypothesis that shared functional alteration exists beyond the seizure onset zone and its epileptic network. We showed that FC measures can distinguish patients from controls, and further lateralize focal epilepsies. Future studies are needed to confirm these findings by using larger numbers of epilepsy patients.

Multifocal myoclonus as a presentation of levetiracetam toxicity

•

Levetiracetam (LEV) is a widely used antiseizure medication, but LEV toxicity is not commonly reported.

•

We report a patient with chronic kidney disease who developed multifocal myoclonus after treatment with LEV.

•

The findings suggest the possibility of an inverted U-shaped dose–response of the anti-myoclonic effect of LEV.

Background

Levetiracetam (LEV) is widely used for treatment of focal and myoclonic seizures, but reports of LEV toxicity are scarce. Here, we report a rare case of multifocal myoclonus due to LEV toxicity in a patient with chronic renal insufficiency.

Case presentation

A 52-year-old woman with history of chronic kidney disease was admitted to the ICU for sedation and intubation after a cardiac arrest. She developed nonconvulsive status epilepticus that resolved after administration of propofol while receiving LEV 1500 mg twice a day. After holding the propofol infusion, the patient started having multifocal myoclonic jerks, documented on video-EEG recordings with a supratherapeutic level of LEV. After discontinuation of LEV, the myoclonus resolved.

Conclusion

This is a unique manifestation of LEV toxicity, which has been scarce in the literature. It suggests an inverted U-shaped dose–response of the antimyoclonic effect of LEV.

Clinical and genomic analysis of a large Chinese family with familial cortical myoclonic tremor with epilepsy and SAMD12 intronic repeat expansion

Objective

Our goal was to perform detailed clinical and genomic analysis of a large multigenerational Chinese family with 21 individuals showing symptoms of Familial Cortical Myoclonic Tremor with Epilepsy (FCMTE) that we have followed for over 20 years.

Methods

Patients were subjected to clinical evaluation, routine EEG, and structural magnetic resonance imaging. Whole exome sequencing, repeat-primed PCR, long-range PCR, and PacBio sequencing were performed to characterize the disease-causing mutation in this family.

Results

All evaluated patients manifested adult-onset seizures and presented with progressive myoclonic postural tremors starting after the third or fourth decade of life. Seizures typically diminished markedly in frequency with implementation of antiseizure medications but did not completely cease. The electroencephalogram of affected individuals showed generalized or multifocal spikes and slow wave complexes. An expansion of TTTTA motifs with addition of TTTCA motifs in intron 4 of SAMD12 was identified to segregate with the disease phenotype in this family. Furthermore, we found that the mutant allele is unstable and can undergo both contraction and expansion by changes in the number of repeat motifs each time it is passed to the next generation. The size of mutant allele varied from 5 to 5.5 kb with 549-603 copies of TTTTA and 287-343 copies of TTTCA repeat motifs in this family.

Significance

Our study provides a detailed description of clinical progression of FCMTE symptoms and its management with antiseizure medications. Our method of repeat analysis by PacBio sequencing of long-range PCR products does not require high-quality DNA and hence can be easily applied to other families to elucidate any correlation between the repeat size and phenotypic variables, such as, age of onset, and severity of symptoms.

Human hippocampal connectivity is stronger in olfaction than other sensory systems

During mammalian evolution, primate neocortex expanded, shifting hippocampal functional networks away from primary sensory cortices, towards association cortices. Reflecting this rerouting, human resting hippocampal functional networks preferentially include higher association cortices, while those in rodents retained primary sensory cortices. Research on human visual, auditory and somatosensory systems shows evidence of this rerouting. Olfaction, however, is unique among sensory systems in its relative structural conservation throughout mammalian evolution, and it is unknown whether human primary olfactory cortex was subject to the same rerouting. We combined functional neuroimaging and intracranial electrophysiology to directly compare hippocampal functional networks across human sensory systems. We show that human primary olfactory cortex-including the anterior olfactory nucleus, olfactory tubercle and piriform cortex-has stronger functional connectivity with hippocampal networks at rest, compared to other sensory systems. This suggests that unlike other sensory systems, olfactory-hippocampal connectivity may have been retained in mammalian evolution. We further show that olfactory-hippocampal connectivity oscillates with nasal breathing. Our findings suggest olfaction might provide insight into how memory and cognition depend on hippocampal interactions.

Epileptogenesis-induced changes of hippocampal-piriform connectivity

OBJECTIVE

Tissue remodeling has been described in brain circuits that are involved in the generation and propagation of epileptic seizures. Human and animal studies suggest that the anterior piriform cortex (aPC) is crucial for seizure expression in focal epilepsies. Here, we investigate the effect of kainic-acid (KA)-induced seizures on the effective connectivity of the aPC with bilateral hippocampal CA3 regions using cerebro-cerebral evoked potentials (CCEPs).

METHODS

Adult male Sprague-Dawley rats were implanted with a tripolar electrode in the left aPC for stimulation and recording, and with unipolar recording electrodes in bilateral CA3 regions. Single pulse stimulations were given to the aPC and CCEPs were averaged before KA injections and after the emergence of spontaneous recurrent seizures (SRS). Similar recordings at equivalent time intervals were obtained from animals that received saline injections instead of KA (controls).

RESULTS

In the experimental group, the percentage change of increased amplitude of the contralateral (but not ipsilateral) CA3 CCEPs between pre-KA injection and after the emergence of SRS was significantly greater than in controls. No significant single-pulse-induced spectral change responses were observed in either epileptic or control rats when comparing pre- and post-stimulus time intervals. Also, we found no correlation between seizure frequency and the extent of amplitude changes in the CCEPs.

CONCLUSIONS

In the KA model, epileptogenesis results in plastic changes that manifest as an amplification of evoked potential amplitudes recorded in the contralateral hippocampus in response to single-pulse stimulation of the aPC. These results suggest epileptogenesis-induced facilitation of interhemispheric connectivity between the aPC and the hippocampus. Since the amplitude increase of the contralateral CCEP is a possible in vivo biomarker of epilepsy, any intervention (e.g. neuromodulatory) that can reverse this phenomenon may hold a potential antiepileptic efficacy.

Anticipation-induced delta phase reset improves human olfactory perception

Anticipating an odor improves detection and perception, yet the underlying neural mechanisms of olfactory anticipation are not well understood. In this study, we used human intracranial electroencephalography (iEEG) to show that anticipation resets the phase of delta oscillations in piriform cortex prior to odor arrival. Anticipatory phase reset correlates with ensuing odor-evoked theta power and improvements in perceptual accuracy. These effects were consistently present in each individual subject and were not driven by potential confounds of pre-inhale motor preparation or power changes. Together, these findings suggest that states of anticipation enhance olfactory perception through phase resetting of delta oscillations in piriform cortex.

Use of human intracranial electroencephalography methods, including rare direct recordings from human olfactory cortex, shows that anticipation of odor resets the phase of delta oscillations prior to the arrival of an odor.

The effects of ammonia stimulation on kainate-induced status epilepticus and anterior piriform cortex electrophysiology

OBJECTIVE

Strong olfactory stimulation (OS) with such substances as toluene or ammonia has been reported to suppress seizures. We aimed to investigate the role of ammonia stimulation on acute kainic acid (KA)-induced seizures. We also investigated any possible effects of ammonia stimulation on the electrophysiology of the anterior piriform cortex (APC).

METHODS

Adult male Sprague-Dawley rats were implanted with bilateral hippocampal electrodes and an electrode in the left APC. Animals were exposed to either distilled water (control) or ammonia stimulation for 20 s every 5 min during KA induction of status epilepticus (SE). The electroencephalogram (EEG) was analyzed for seizure frequency, duration, severity, and total KA doses given prior to reaching SE. Seizure-free EEG epochs that coincided with OS were chosen and analyzed via wavelet analysis for any spectral changes.

RESULTS

We found no significant differences in seizure frequency, duration, severity, or administered KA doses before SE between the groups. In the experimental group, a wavelet analysis of variance (WANOVA) revealed a significant stimulation-induced increase of power in the delta and alpha bands prior to the first KA injection and higher power in the delta and theta bands after KA injection.

CONCLUSIONS

Whereas the spectral analysis of the APC revealed specific OS-induced changes, our findings suggest that OS with ammonia does not result in altering the threshold of attaining KA-induced SE. This does not rule out a potential role for OS in reducing recurrent seizures in the KA or other epilepsy models.

Electroencephalography in Epilepsy Evaluation

PURPOSE OF REVIEW

Epilepsy is a heterogeneous disorder that is often associated with abnormal electroencephalogram (EEG) findings. This article provides an overview of common EEG findings in epileptic disorders. The physiologic basis of EEG and intracranial EEG studies is also discussed.

RECENT FINDINGS

EEG is widely used in clinical practice. Because of the paroxysmal nature of seizure disorders, interictal epileptiform discharges, such as spikes and sharp waves, are often used to support the diagnosis of epilepsy when a habitual seizure is not captured by EEG. Interictal and ictal EEG findings also underlie the classification of seizures and epilepsy. Continuous critical care EEG monitoring has become an invaluable study in the diagnosis and treatment of subclinical seizures and nonconvulsive status epilepticus. Intracranial EEG with subdural or intraparenchymal electrodes is warranted when localization of the seizure focus and mapping of eloquent brain areas are required to plan epilepsy surgery.

SUMMARY

The EEG is a key tool in the diagnosis of epilepsy. Interictal and ictal EEG findings are crucial for the confirmation and classification of seizure disorders. Intracranial EEG monitoring is also indispensable for planning surgery for some patients.

The Claustrum in Relation to Seizures and Electrical Stimulation

The neural mechanisms of altered consciousness that accompanies most epileptic seizures are not known. We have reported alteration of consciousness resulting from electrical stimulation of the claustrum via a depth electrode in a woman with refractory focal epilepsy. Additionally, there are reports that suggest possible claustral involvement in focal epilepsy, including MRI findings of bilaterally increased T2 signal intensity in patients with status epilepticus (SE). Although its cytoarchitecture and connectivity have been studied extensively, the precise role of the claustrum in consciousness processing, and, thus, its contribution to the semiology of dyscognitive seizures are still elusive. To investigate the role of the claustrum in rats, we studied the effect of high-frequency stimulation (HFS) of the claustrum on performance in the operant chamber. We also studied the inter-claustral and the claustro-hippocampal connectivity through cerebro-cerebral evoked potentials (CCEPs), and investigated the involvement of the claustrum in kainate (KA)-induced seizures. We found that HFS of the claustrum decreased the performance in the operant task in a manner that was proportional to the current intensity used. In this article, we present previously unpublished data about the effect of stimulating extra-claustral regions in the operant chamber task as a control experiment. In these animals, stimulation of the corpus callosum, the largest interhemispheric commissure, as well as the orbitofrontal cortex in the vicinity of the claustrum did not produce that same effect as with claustral stimulation. Additionally, CCEPs established the presence of effective connectivity between both claustra, as well as between the claustrum and bilateral hippocampi indicating that these connections may be part of the circuitry involved in alteration of consciousness in limbic seizures. Lastly, some seizures induced by KA injections showed an early involvement of the claustrum with later propagation to the hippocampi. Further work is needed to clarify the exact role of the claustrum in mediating alteration of consciousness during epileptic seizures.

Uncertainties from a worldwide survey on antiepileptic drug withdrawal after seizure remission

Background

We sought to determine differences in practice for discontinuation of antiepileptic drugs (AEDs) after seizure remission and stimulate the planning and conduction of withdrawal trials.

Methods

We utilized a worldwide electronic survey that included questions about AED discontinuation for 3 paradigmatic cases in remission: (1) focal epilepsy of unknown etiology, (2) temporal lobe epilepsy after surgery, and (3) juvenile myoclonic epilepsy. We analyzed 466 complete questionnaires from 53 countries, including the United States. Statistical analysis included χ² and multivariate logistic regression.

Results

Case 1: responders in practice for <10 years were less likely to taper AEDs: odds ratio (OR) (95% confidence interval [CI]) 0.52 (0.32-0.85), p = 0.02. The likelihood of stopping AEDs was higher among doctors treating children: OR (95% CI): 11.41 (2.51-40.13), p = 0.002. Doctors treating children were also more likely to stop after 2 years or less of remission: OR (95% CI): 6.91 (2.62-19.31), p = 0.002, and the same was observed for US physicians: OR (95% CI): 1.61 (1.01-2.57), p = 0.0049. Case 2: responders treating children were more likely to taper after 1 year or less of postoperative remission, with the goal of discontinuing all medications: OR (95% CI): 1.91 (1.09-3.12), p = 0.015, and so were US-based responders: OR (95% CI): 1.73 (1.21-2.41), p = 0.003. Case 3: epileptologists were less likely to withdraw the medication: OR (95% CI): 0.56 (0.39-0.82), p = 0.003, and so were those in practice for 10 or more years: OR (95% CI): 0.54 (0.31-0.95), p = 0.025.

Conclusions

We observed several differences in practice for AED withdrawal after seizure remission that highlight global uncertainty. Trials of AED discontinuation are needed to provide evidence-based guidance.

Acute and spontaneous seizure onset zones in the intraperitoneal kainic acid model

OBJECTIVE

Hippocampal monitoring is often used in the intraperitoneal kainic acid (KA) seizure model for detection and quantification of early ictal activity. Here, we investigated extra-hippocampal seizure onset zones (SOZs) in this model.

METHODS

Eight male Sprague Dawley rats implanted with depth electrodes were continuously recorded during intraperitoneal KA injections until status epilepticus (SE) was induced. Another group of four rats was monitored chronically up to two weeks after emergence of spontaneous recurrent seizures. All rats had hippocampal electrodes. Other sampled brain regions included, among others, the claustrum, piriform cortex, and orbital cortex. Seizures recorded with video-EEG were visually analyzed.

RESULTS

In the 58 seizures recorded during KA injections, the SOZ was extrahippocampal in 7 (12%), diffuse in 29 (50%), and hippocampal in 22 (38%). Of the 14 spontaneous seizures recorded, none were solely extrahippocampal, 10 (71%) were diffuse, and 4 (29%) were of hippocampal onset. All extra-hippocampal seizures propagated to the hippocampus within 4 to 50s (mean=14, n=7). No distinctive semiological manifestations correlated with the SOZs.

SIGNIFICANCE

We conclude that seizures can have multifocal SOZs in the KA model. This finding is important to consider when using this model, among other purposes, to screen for new therapies, study pharmacoresistance, or investigate comorbidities of epilepsy.

Yawning induced by focal electrical stimulation in the human brain

The primary function of yawning is not fully understood. We report a case in which electrical stimulation of the putamen in the human brain consistently elicited yawning. A 46-year-old woman with intractable epilepsy had invasive depth electrode monitoring and cortical stimulation mapping as part of her presurgical epilepsy evaluation. The first two contacts of a depth electrode that was intended to sample the left insula were in contact with the putamen. Stimulation of these contacts at 6mA and 8mA consistently elicited yawning on two separate days. Engagement in arithmetic and motor tasks during stimulation did not result in yawning. When considering the role of the putamen in motor control and its extensive connectivity to cortical and brainstem regions, our findings suggest that it plays a key role in the execution of motor movements necessitated by yawning. Furthermore, given the role of the anterior insula in attention and focused tasks, activation of this area while engaged in arithmetic and motor tasks could inhibit the putaminal processing necessary for yawning. Many have hypothesized the function of yawning; however, it remains debatable whether yawning serves a primarily physiological or communicative function or perhaps both.

Multiple hippocampal transections for intractable hippocampal epilepsy: Seizure outcome

PURPOSE

The purpose of this study was to evaluate the seizure outcomes after transverse multiple hippocampal transections (MHTs) in 13 patients with intractable TLE.

METHODS

Thirteen patients with normal memory scores, including 8 with nonlesional hippocampi on MRI, had temporal lobe epilepsy (TLE) necessitating depth electrode implantation. After confirming hippocampal seizure onset, they underwent MHT. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at approximately 1-cm intervals and spike counting for 5-8min before each cut. The number of transections ranged between 4 and 7. Neuropsychological assessment was completed preoperatively and postoperatively for all patients and will be reported separately.

RESULTS

Duration of epilepsy ranged between 5 and 55years. There were no complications. Intraoperatively, MHT resulted in marked spike reduction (p=0.003, paired t-test). Ten patients (77%) are seizure-free (average follow-up was 33months, range 20-65months) without medication changes. One of the 3 patients with persistent seizures had an MRI revealing incomplete transections, another had an additional neocortical seizure focus (as suggested by pure aphasic seizures), and the third had only 2 seizures in 4years, one of which occurred during antiseizure medication withdrawal. Verbal and visual memory outcomes will be reported separately. Right and left hippocampal volumes were not different preoperatively (n=12, p=0.64, Wilcoxon signed-rank test), but the transected hippocampal volume decreased postoperatively (p=0.0173).

CONCLUSIONS

Multiple hippocampal transections provide an effective intervention and a safe alternative to temporal lobectomy in patients with hippocampal epilepsy.

A white matter tract mediating awareness of speech

OBJECTIVE

To investigate the effects of extraoperative electrical stimulation of fiber tracts connecting the language territories.

METHODS

We describe results of extraoperative electrical stimulation of stereotactic electrodes in 3 patients with epilepsy who underwent presurgical evaluation for epilepsy surgery. Contacts of these electrodes sampled, among other structures, the suprainsular white matter of the left hemisphere.

RESULTS

Aside from speech disturbance and speech arrest, subcortical electrical stimulation of white matter tracts directly superior to the insula representing the anterior part of the arcuate fascicle, reproducibly induced complex verbal auditory phenomena including (1) hearing one's own voice in the absence of overt speech, and (2) lack of perception of arrest or alteration in ongoing repetition of words.

CONCLUSION

These results represent direct evidence that the anterior part of the arcuate fascicle is part of a network that is important in the mediation of speech planning and awareness likely by linking the language areas of the inferior parietal and posterior inferior frontal cortices. More specifically, our observations suggest that this structure may be relevant to the pathophysiology of thought disorders and auditory verbal hallucinations.

Levetiracetam-induced pancytopenia

Pancytopenia is a rare side effect of levetiracetam (LEV) that is associated with severe morbidity that requires hospitalization. Here, we report a patient with a right temporoparietal tumor who underwent a temporal craniotomy with resection of the mass and was started on LEV for seizure prophylaxis per the neurosurgery local protocol. The patient developed LEV-induced pancytopenia, which was successfully managed by discontinuation of this medication. Our report aims to increase awareness of this rare cause of pancytopenia among clinicians.

The piriform, perirhinal, and entorhinal cortex in seizure generation

Understanding neural network behavior is essential to shed light on epileptogenesis and seizure propagation. The interconnectivity and plasticity of mammalian limbic and neocortical brain regions provide the substrate for the hypersynchrony and hyperexcitability associated with seizure activity. Recurrent unprovoked seizures are the hallmark of epilepsy, and limbic epilepsy is the most common type of medically-intractable focal epilepsy in adolescents and adults that necessitates surgical evaluation. In this review, we describe the role and relationships among the piriform (PIRC), perirhinal (PRC), and entorhinal cortex (ERC) in seizure-generation and epilepsy. The inherent function, anatomy, and histological composition of these cortical regions are discussed. In addition, the neurotransmitters, intrinsic and extrinsic connections, and the interaction of these regions are described. Furthermore, we provide evidence based on clinical research and animal models that suggest that these cortical regions may act as key seizure-trigger zones and, even, epileptogenesis.

Electrical stimulation of a small brain area reversibly disrupts consciousness

The neural mechanisms that underlie consciousness are not fully understood. We describe a region in the human brain where electrical stimulation reproducibly disrupted consciousness. A 54-year-old woman with intractable epilepsy underwent depth electrode implantation and electrical stimulation mapping. The electrode whose stimulation disrupted consciousness was between the left claustrum and anterior-dorsal insula. Stimulation of electrodes within 5mm did not affect consciousness. We studied the interdependencies among depth recording signals as a function of time by nonlinear regression analysis (h(2) coefficient) during stimulations that altered consciousness and stimulations of the same electrode at lower current intensities that were asymptomatic. Stimulation of the claustral electrode reproducibly resulted in a complete arrest of volitional behavior, unresponsiveness, and amnesia without negative motor symptoms or mere aphasia. The disruption of consciousness did not outlast the stimulation and occurred without any epileptiform discharges. We found a significant increase in correlation for interactions affecting medial parietal and posterior frontal channels during stimulations that disrupted consciousness compared with those that did not. Our findings suggest that the left claustrum/anterior insula is an important part of a network that subserves consciousness and that disruption of consciousness is related to increased EEG signal synchrony within frontal-parietal networks.

Accuracy of frame-based stereotactic depth electrode implantation during craniotomy for subdural grid placement

BACKGROUND

Frame-based stereotaxy and open craniotomy may seem mutually exclusive, but invasive electrophysiological monitoring can require broad sampling of the cortex and precise targeting of deeper structures.

OBJECTIVES

The purpose of this study is to describe simultaneous frame-based insertion of depth electrodes and craniotomy for placement of subdural grids through a single surgical field and to determine the accuracy of depth electrodes placed using this technique.

METHODS

A total of 6 patients with intractable epilepsy underwent placement of a stereotactic frame with the center of the planned cranial flap equidistant from the fixation posts. After volumetric imaging, craniotomy for placement of subdural grids was performed. Depth electrodes were placed using frame-based stereotaxy. Postoperative CT determined the accuracy of electrode placement.

RESULTS

A total of 31 depth electrodes were placed. Mean distance of distal electrode contact from the target was 1.0 ± 0.15 mm. Error was correlated to distance to target, with an additional 0.35 mm error for each centimeter (r = 0.635, p < 0.001); when corrected, there was no difference in accuracy based on target structure or method of placement (prior to craniotomy vs. through grid, p = 0.23).

CONCLUSION

The described technique for craniotomy through a stereotactic frame allows placement of subdural grids and depth electrodes without sacrificing the accuracy of a frame or requiring staged procedures.

Low-frequency electrical stimulation of a fiber tract in temporal lobe epilepsy

OBJECTIVE

Surgical resection of the temporal lobe is an effective treatment for medically intractable temporal lobe epilepsy, but can cause memory impairment. Deep brain stimulation in epilepsy has targeted gray matter structures using high frequencies, but achieved limited success. We tested the hypothesis that low-frequency stimulation of the fornix reduces interictal epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy, without affecting memory.

METHODS

We implanted depth electrodes in 11 patients for surgical evaluation of intractable epilepsy. Low-frequency stimulation of the fornix occurred in 4-hour sessions in the video-electroencephalography unit. Mental status assessment was performed at baseline and during stimulation. We studied the effect of stimulation on hippocampal spikes and seizures.

RESULTS

There were no complications, and the patients were unaware of the stimulation. Fornix stimulation elicited evoked responses in the hippocampus and the posterior cingulate gyrus. Hourly Mini-Mental Status Examination (MMSE) scores showed an increase during stimulation when compared to prestimulation MMSE, largely due to improvement in recall, possibly representing a practice effect. Hippocampal spikes were significantly reduced during and outlasting each stimulation session. Seizure odds (n = 7) were reduced by 92% in the 2 days that followed stimulation.

INTERPRETATION

Low-frequency stimulation of the fornix activates the hippocampus and other areas of the declarative memory circuit. The results of this preliminary study suggest that low-frequency stimulation is tolerable and reduces epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy. A controlled clinical trial may be warranted.

Risk factors associated with death in in-hospital pediatric convulsive status epilepticus

Objective

To evaluate in-patient mortality and predictors of death associated with convulsive status epilepticus (SE) in a large, multi-center, pediatric cohort.

Patients and Methods

We identified our cohort from the KID Inpatient Database for the years 1997, 2000, 2003 and 2006. We queried the database for convulsive SE, associated diagnoses, and for inpatient death. Univariate logistic testing was used to screen for potential risk factors. These risk factors were then entered into a stepwise backwards conditional multivariable logistic regression procedure. P-values less than 0.05 were taken as significant.

Results

We identified 12,365 (5,541 female) patients with convulsive SE aged 0–20 years (mean age 6.2 years, standard deviation 5.5 years, median 5 years) among 14,965,571 pediatric inpatients (0.08%). Of these, 117 died while in the hospital (0.9%). The most frequent additional admission ICD-9 code diagnoses in addition to SE were cerebral palsy, pneumonia, and respiratory failure.

Independent risk factors for death in patients with SE, assessed by multivariate calculation, included near drowning (Odds ratio [OR] 43.2; Confidence Interval [CI] 4.4–426.8), hemorrhagic shock (OR 17.83; CI 6.5–49.1), sepsis (OR 10.14; CI 4.0–25.6), massive aspiration (OR 9.1; CI 1.8–47), mechanical ventilation >96 hours (OR9; 5.6–14.6), transfusion (OR 8.25; CI 4.3–15.8), structural brain lesion (OR7.0; CI 3.1–16), hypoglycemia (OR5.8; CI 1.75–19.2), sepsis with liver failure (OR 14.4; CI 5–41.9), and admission in December (OR3.4; CI 1.6–4.1). African American ethnicity (OR 0.4; CI 0.2–0.8) was associated with a decreased risk of death in SE.

Conclusion

Pediatric convulsive SE occurs in up to 0.08% of pediatric inpatient admissions with a mortality of up to 1%. There appear to be several risk factors that can predict mortality. These may warrant additional monitoring and aggressive management.

Requirement of longitudinal synchrony of epileptiform discharges in the hippocampus for seizure generation: a pilot study

OBJECT

The goal in this study was to assess the role of longitudinal hippocampal circuits in the generation of interictal and ictal activity in temporal lobe epilepsy (TLE) and to evaluate the effects of multiple hippocampal transections (MHT).

METHODS

In 6 patients with TLE, the authors evaluated the synchrony of hippocampal interictal and ictal epileptiform discharges by using a cross-correlation analysis, and the effect of MHT on hippocampal interictal spikes was studied. Five of the 6 patients were studied with depth electrodes, and epilepsy surgery was performed in 4 patients (anterior temporal lobectomy in 1 and MHT in 3).

RESULTS

Four hundred eighty-two (95.1%) of 507 hippocampal spikes showed an anterior-to-posterior propagation within the hippocampus, with a fixed peak-to-peak interval. During seizures, a significant increase of synchronization between different hippocampal regions and between the hippocampus and the ipsilateral anterior parahippocampal gyrus was observed in all seizures. An ictal increase in synchronization between the hippocampus and ipsilateral amygdala was seen in only 24.1% of the seizures. No changes in synchronization were noticed during seizures between the hippocampi and the amygdala on either side. The structure leading the epileptic seizures varied over time during a given seizure and also from one seizure to another. Spike analysis during MHT demonstrated that there were two spike populations that reacted differently to this procedure--namely, 1) spikes that showed maximum amplitude at the head of the hippocampus (type H); and 2) spikes that showed the highest amplitude at the hippocampal body (type B). A striking decrease in amplitude and frequency of type B spikes was noticed in all 3 patients after transections at the head or anterior portion of the hippocampal body. Type H spikes were seen in 2 cases and did not change in amplitude and frequency throughout MHT. Type B spikes showed constantly high cross-correlation values in different derivations and a relatively fixed peak-to-peak interval before MHT. This fixed interpeak delay disappeared after the first transection, although high cross-correlation values persisted unchanged. All patients who underwent MHT remained seizure free for more than 2 years.

CONCLUSIONS

These data suggest that synchronized discharges involving the complete anterior-posterior axis of the hippocampal/parahippocampal (H/P) formation underlie the spread of epileptiform discharges outside the H/P structures and, therefore, for the generation of epileptic seizures originating in the H/P structures. This conclusion is supported by the following observations. 1) Hippocampal spikes are consistently synchronized in the whole hippocampal structures, with a fixed delay between the different hippocampal areas. 2) One or two transections between the head and body of the hippocampal formation are sufficient to abolish hippocampal spikes that are synchronized along the anterior-posterior axis of the hippocampus. 3) Treatment with MHT leads to seizure freedom in patients with H/P epilepsy.

Transection of CA3 does not affect memory performance in rats

Longitudinal hippocampal pathways are needed for seizure synchronization, and there is evidence that their transection may abolish seizures. However, the effect of such transection on memory is unknown. In this study, we investigated the effect of transverse CA3 transections on memory function in Sprague-Dawley rats. With a stereotactic knife, a single CA3 transection was made unilaterally (n=5) or bilaterally (n=5). Sham surgery was done in another group (n=4). Morris water maze and novel object recognition tests were started 18 days later and revealed no significant differences between transected animals and controls. Cresyl-violet brain staining confirmed the locations of transections in the CA3 region. We conclude that normal performances in Morris water maze and novel object recognition tests do not appear to require intact transmission throughout the whole length of CA3, supporting the hypothesis that CA3 transections may be used in temporal lobe epilepsy to interrupt seizure circuitry while preserving memory.

Connectivity between perisylvian and bilateral basal temporal cortices

Language processing requires the orchestrated action of different neuronal populations, and some studies suggest that the role of the basal temporal (BT) cortex in language processing is bilaterally distributed. Our aim was to demonstrate connectivity between perisylvian cortex and both BT areas. We recorded corticocortical evoked potentials (CCEPs) in 8 patients with subdural electrodes implanted for surgical evaluation of intractable epilepsy. Four patients had subdural grids over dominant perisylvian and BT areas, and 4 had electrode strips over both BT areas and left posterior superior temporal gyrus (LPSTG). After electrocortical mapping, patients with grids had 1-Hz stimulation of language areas. Patients with strips did not undergo mapping but had 1-Hz stimulation of the LPSTG. Posterior language area stimulation elicited CCEPs in ipsilateral BT cortex in 3/4 patients with left hemispheric grids. CCEPs were recorded in bilateral BT cortices in 3/4 patients with strips upon stimulation of the LPSTG, and in the LPSTG in the fourth patient upon stimulation of either BT area. This is the first in vivo demonstration of connectivity between LPSTG and both BT cortices. The role of BT cortex in language processing may be bilaterally distributed and related to linking visual information with phonological representations stored in the LPSTG.

Efficacy and safety of intravenous lacosamide in refractory nonconvulsive status epilepticus

BACKGROUND

Lacosamide (LCM) is a novel antiepileptic drug (AED) recently approved as an adjunctive therapy in the treatment of partial seizures in adults. LCM is available in oral and intravenous formulations, has linear pharmacokinetics and a unique mechanism of action.

THE AIM OF THIS STUDY

To evaluate the safety and efficacy of intravenous LCM in the treatment of nonconvulsive status epilepticus (NCSE) after failure of conventional therapy.

METHODS

We retrospectively reviewed all patients with NCSE treated with LCM. We reviewed the clinical and electrographic changes before and after LCM administration. We also noted any reported side effects including electrocardiographic changes.

RESULTS

We report four cases of NCSE that were refractory to conventional treatment, but readily responsive to LCM. No side effects attributable to LCM were identified.

CONCLUSIONS

Intravenous LCM may be safe and efficacious as an add-on AED for the treatment of NCSE when standard therapy fails.

Triple pathology in epilepsy: coexistence of cavernous angiomas and cortical dysplasias with other lesions

Coexistence of cortical dysplasias (CD) with cavernomas has rarely been reported. We reviewed our surgical specimens from patients who underwent surgery for pharmacoresistant epilepsy between 2003 and 2008, and identified seven cases with cavernoma, of whom two had overlying CD. In addition, each of these patients had a third form of a potentially epileptogenic lesion: hippocampal sclerosis in one, and venous angioma in the other. We conclude that CD is heterogeneous, with milder forms appearing to co-exist with other pathologies, including vascular abnormalities and hippocampal sclerosis.

Analysis of dynamics and propagation of parietal cingulate seizures with secondary mesial temporal involvement

Cingulate-onset seizures, particularly those originating from parietal cingulate regions, are inadequately described and confounded by patterns of propagation. We analyzed scalp and depth electrode recordings in a patient whose seizures originated from a lesion in the right posterior cingulate region and produced secondary seizure activity in ipsilateral mesial temporal structures. Analyses included the matching pursuit (MP) method of time-frequency decomposition and the Gabor atom density (GAD) measure of signal complexity. Although scalp recordings suggested a right temporal onset, seizures recorded with depth electrodes clearly began in the parietal cingulate region before producing a secondary discharge in ipsilateral mesial structures. GAD revealed a significant increase in complexity during ictal cingulate activity and a consistent pattern of subsequent complexity changes in the hippocampus 30 seconds later. MP and GAD measures were valuable supplements to confirm the stereotyped pattern of both time-frequency changes and complexity. This provides additional evidence for pathways between the parietal cingulate region and mesial temporal structures and raises questions as to whether parietal cingulate seizures can produce clinical symptoms independent of regional or remote propagation.

Being with virtual others: studying social cognition in temporal lobe epilepsy

Social cognitive neuroscience has highlighted the importance of frontotemporal neurocircuitry for social cognition. Temporal lobe epilepsy (TLE) impacts these brain areas and their functional connections and might therefore specifically affect social perceptual and cognitive skills. In the study described here, an established paradigm was used to evaluate the social cognitive skills of female patients with left TLE. Study participants were shown dynamic animations in which virtual characters either looked at the human observer directly or looked away toward someone else, thus manipulating self-involvement. The virtual characters then exhibited different facial expressions that were either socially relevant or arbitrary. Participants were asked to rate the communicative intentions of the virtual character. Patients' ratings of communicative intent appeared to be linked to their own self-involvement in the interaction, whereas healthy volunteers' ratings of facial expressions were independent of self-involvement. Potential mechanisms for the observed differences are discussed.

Cerebellar and thalamic stimulation treatment for epilepsy

The present chapter describes the most important available experimental and clinical evidence on the role of electrical stimulation of the cerebellum or the thalamus in the control of epilepsy. Cerebellum serves as an integrator of sensory information and regulator of motor coordinating and training. The sole output of the cerebellum is inhibitory Purkinje cell projections to deep cerebellar nuclei in the brainstem. Cerebellar stimulation in animal models of epilepsy has given mixed results. Nevertheless, more than 130 epileptic patients have been subjected to cerebellar stimulation and the results from uncontrolled studies have been encouraging. The anterior thalamic nucleus (ATN) is part of the Papez circuit, a group of limbic structures with demonstrated role in epilepsy. The centromedian thalamic nucleus (CMN) is considered part of the thalamic reticular system. Stimulation of either of these nuclei in experimental animals has been associated with considerable antiepileptic effects. On the basis of the research evidence, numerous studies have been done on humans, which gave promising results. Currently, a multicenter trial on stimulation of the ATN, the SANTE trial is in progress in the USA. On the basis of the reported studies, the authors aim to provide insights into how the electrical stimulation of the above structures exerts an antiepileptic effect and also provide suggestions regarding the future progress in this field.

Seizures manifesting as an urge to defecate, with an ictal discharge in the right hemisphere

We report a 47-year-old right-handed woman with simple partial seizures manifesting in part as an urge to defecate shortly after a visual distortion. On at least one occasion, this was followed by head deviation to the left and a secondarily generalized tonic-clonic seizure. The ictal electroencephalogram lateralized to the right hemisphere, suggesting that the ictal urge to defecate may lateralize to this side.