Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

Multi-omic strategies applied to the study of pharmacoresistance in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal epilepsy in adults, and hippocampal sclerosis (HS) is a frequent histopathological feature in patients with MTLE. Pharmacoresistance is present in at least one-third of patients with MTLE with HS (MTLE+HS). Several hypotheses have been proposed to explain the mechanisms of pharmacoresistance in epilepsy, including the effect of genetic and molecular factors. In recent years, the increased knowledge generated by high-throughput omic technologies has significantly improved the power of molecular genetic studies to discover new mechanisms leading to disease and response to treatment. In this review, we present and discuss the contribution of different omic modalities to understand the basic mechanisms determining pharmacoresistance in patients with MTLE+HS. We provide an overview and a critical discussion of the findings, limitations, new approaches, and future directions of these studies to improve the understanding of pharmacoresistance in MTLE+HS. However, it is important to point out that, as with other complex traits, pharmacoresistance to anti-seizure medications is likely a multifactorial condition in which gene-gene and gene-environment interactions play an important role. Thus, studies using multidimensional approaches are more likely to unravel these intricate biological processes.

Temporal lobe epilepsy with amygdala enlargement: A systematic review

Temporal lobe epilepsy (TLE) with enlargement of the amygdala (AE) is a distinct clinical entity with contrasting clinical features from TLE with hippocampal sclerosis (HS). The objectives of this systematic analysis were to study the clinical characteristics and treatment outcome of people with TLE with AE. Pubmed, Embase, Cochrane, Web of Science, Scopus, and Medline were searched using the keywords amygdala enlargement, temporal lobe epilepsy, epilepsy, and seizure in November 2020. We found 18 studies that satisfied the inclusion criteria. A total of 361 patients were included in this analysis. The mean age of onset was 36.2 years, and febrile seizure was uncommon compared to TLE with HS subjects. The type of aura and automatism was similar to TLE with HS, though less prevalent. Electroencephalography (EEG) was usually concordant with the side of AE. Anti-seizure medications (ASM), surgical, and immunotherapy were used in different studies. 86 patients underwent surgery with Engel I outcome in 69.7%. Histopathology of the resected samples was predominantly dysplasia and gliosis. A group of patients that responded well to immunotherapy with subsequent reduction of amygdala volume (AMV) purported an autoimmune etiology of AE. Heterogeneity was the main drawback that prevented comparability among the studies. The methods of measurement of AMV also differed widely in the included studies, and standardization of its method is still lacking. This analysis suggests TLE with AE as a distinctive group of patients either due to a developmental anomaly or autoimmune etiology.

The pilocarpine model of mesial temporal lobe epilepsy: Over one decade later, with more rodent species and new investigative approaches

Fundamental work on the mechanisms leading to focal epileptic discharges in mesial temporal lobe epilepsy (MTLE) often rests on the use of rodent models in which an initial status epilepticus (SE) is induced by kainic acid or pilocarpine. In 2008 we reviewed how, following systemic injection of pilocarpine, the main subsequent events are the initial SE, the latent period, and the chronic epileptic state. Up to a decade ago, rats were most often employed and they were frequently analysed only behaviorally. However, the use of transgenic mice has revealed novel information regarding this animal model. Here, we review recent findings showing the existence of specific neuronal events during both latent and chronic states, and how optogenetic activation of specific cell populations modulate spontaneous seizures. We also address neuronal damage induced by pilocarpine treatment, the role of neuroinflammation, and the influence of circadian and estrous cycles. Updating these findings leads us to propose that the rodent pilocarpine model continues to represent a valuable tool for identifying the basic pathophysiology of MTLE.

Global warming and neurological practice: systematic review

Background

Climate change, including global warming, will cause poorer global health and rising numbers of environmental refugees. As neurological disorders account for a major share of morbidity and mortality worldwide, global warming is also destined to alter neurological practice; however, to what extent and by which mechanisms is unknown. We aimed to collect information about the effects of ambient temperatures and human migration on the epidemiology and clinical manifestations of neurological disorders.

Methods

We searched PubMed and Scopus from 01/2000 to 12/2020 for human studies addressing the influence of ambient temperatures and human migration on Alzheimer’s and non-Alzheimer’s dementia, epilepsy, headache/migraine, multiple sclerosis, Parkinson’s disease, stroke, and tick-borne encephalitis (a model disease for neuroinfections). The protocol was pre-registered with PROSPERO (2020 CRD42020147543).

Results

Ninety-three studies met inclusion criteria, 84 of which reported on ambient temperatures and nine on migration. Overall, most temperature studies suggested a relationship between increasing temperatures and higher mortality and/or morbidity, whereas results were more ambiguous for migration studies. However, we were unable to identify a single adequately designed study addressing how global warming and human migration will change neurological practice. Still, extracted data indicated multiple ways by which these aspects might alter neurological morbidity and mortality soon.

Conclusion

Significant heterogeneity exists across studies with respect to methodology, outcome measures, confounders and study design, including lack of data from low-income countries, but the evidence so far suggests that climate change will affect the practice of all major neurological disorders in the near future. Adequately designed studies to address this issue are urgently needed, requiring concerted efforts from the entire neurological community.

Exercise-linked consequences on epilepsy

OBJECTIVE

Epilepsy is a brain disorder that leads to seizures and neurobiological, cognitive, psychological, and social consequences. Physical inactivity can contribute to worse epilepsy pathophysiology. Here, we review how physical exercise affects epilepsy physiopathology.

METHODS

An extensive literature search was performed and the mechanisms of physical exercise on epilepsy were discussed. The search was conducted in Scopus and PubMed. Articles with relevant information were included. Only studies written in English were considered.

RESULTS

The regular practice of physical exercise can be beneficial for individuals with neurodegenerative diseases, such as epilepsy by decreasing the production of pro-inflammatory and stress biomarkers, increasing socialization, and reducing the incidence of epileptic seizures. Physical exercise is also capable of reducing the symptoms of depression and anxiety in epilepsy. Physical exercise can also improve cognitive function in epilepsy. The regular practice of physical exercise enhances the levels of brain-derived neuro factor (BDNF) in the hippocampi, induces neurogenesis, inhibits oxidative stress and reactive gliosis, avoids cognitive impairment, and stimulates the production of dopamine in the epileptic brain.

CONCLUSION

Physical exercise is an excellent non-pharmacological tool that can be used in the treatment of epilepsy.

Let there be light: Inhibitory effect of photic stimulation on spike frequency in patients with mesial temporal lobe epilepsy with hippocampal sclerosis

Inhibition of epileptic discharges and seizures by sensory stimuli is an interesting phenomenon, but highly understudied. Here, we aimed to investigate the modulation of epileptiform discharges in patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) via photic stimulation (PS), based on a hypothesis that light stimulation may activate thalamocortical networks limiting the propagation of interictal epileptiform discharges. In order to do so, all EEGs performed in patients diagnosed with MTLE-HS were reviewed to include available recordings with definite epileptiform abnormalities. These were reevaluated by two clinical neurophysiologists independently, and spikes were counted in a blinded manner to calculate spike index (SI) (spikes per minute-pm) for baseline EEG, hyperventilation (HV), and PS periods. Our final study group consisted of 30 MTLE-HS patients with a mean age of 34.5 (±12.5) years. Mean seizure frequency was 38.1 per year (±46.6), and the mean disease duration was 16.2 years (±12.1). Mean SI during baseline was calculated as 1.17 pm (±1.4), during HV 2.1 pm (±2.8) and during PS 0.8 pm (±2.5). As a result, SI was significantly lower during PS compared to baseline (p = 0.001). Our findings suggest that PS has a remarkable inhibitory effect on epileptiform discharges in MTLE-HS patients, indicating the need for further prospective investigations for clinical translation.

EEG Signal Connectivity for Characterizing Interictal Activity in Patients With Mesial Temporal Lobe Epilepsy

Over the last decade, several methods for analysis of epileptiform signals in electroencephalography (EEG) have been proposed. These methods mainly use EEG signal features in either the time or the frequency domain to separate regular, interictal, and ictal brain activity. The aim of this work was to evaluate the feasibility of using functional connectivity (FC) based feature extraction methods for the analysis of epileptiform discharges in EEG signals. These signals were obtained from EEG-fMRI sessions of 10 patients with mesial temporal lobe epilepsy (MTLE) with unilateral hippocampal atrophy. The connectivity functions investigated were motif synchronization, imaginary coherence, and magnitude squared coherence in the alpha, beta, and gamma bands of the EEG. EEG signals were sectioned into 1-s epochs and classified according to (using neurologist markers): activity far from interictal epileptiform discharges (IED), activity immediately before an IED and, finally, mid-IED activity. Connectivity matrices for each epoch for each FC function were built, and graph theory was used to obtain the following metrics: strength, cluster coefficient, betweenness centrality, eigenvector centrality (both local and global), and global efficiency. The statistical distributions of these metrics were compared among the three classes, using ANOVA, for each FC function. We found significant differences in all global (p < 0.001) and local (p < 0.00002) graph metrics of the far class compared with before and mid for motif synchronization on the beta band; local betweenness centrality also pointed to a degree of lateralization on the frontotemporal structures. This analysis demonstrates the potential of FC measures, computed using motif synchronization, for the characterization of epileptiform activity of MTLE patients. This methodology may be helpful in the analysis of EEG-fMRI data applied to epileptic foci localization. Nonetheless, the methods must be tested with a larger sample and with other epileptic phenotypes.

Astrocytic Ca2+ Signaling in Epilepsy

Epilepsy is one of the most common neurological disorders – estimated to affect at least 65 million worldwide. Most of the epilepsy research has so far focused on how to dampen neuronal discharges and to explain how changes in intrinsic neuronal activity or network function cause seizures. As a result, pharmacological therapy has largely been limited to symptomatic treatment targeted at neurons. Given the expanding spectrum of functions ascribed to the non-neuronal constituents of the brain, in both physiological brain function and in brain disorders, it is natural to closely consider the roles of astrocytes in epilepsy. It is now widely accepted that astrocytes are key controllers of the composition of the extracellular fluids, and may directly interact with neurons by releasing gliotransmitters. A central tenet is that astrocytic intracellular Ca²⁺ signals promote release of such signaling substances, either through synaptic or non-synaptic mechanisms. Accruing evidence suggests that astrocytic Ca²⁺ signals play important roles in both seizures and epilepsy, and this review aims to highlight the current knowledge of the roles of this central astrocytic signaling mechanism in ictogenesis and epileptogenesis.

An inventory of basic research in temporal lobe epilepsy

Temporal lobe epilepsy is a severe neurological disease, characterized by seizure occurrence and invalidating cognitive co-morbidities, which affects up to 1% of the adults. Roughly one third of the patients are resistant to any conventional pharmacological treatments. The last option in that case is the surgical removal of the epileptic focus, with no guarantee for clinical symptom alleviation. This state of affairs requests the identification of cellular or molecular targets for novel therapeutic approaches with limited side effects. Here we review some generalities about the disease as well as some of the most recent discoveries about the cellular and molecular mechanisms of TLE, and the latest perspectives for novel treatments.

Female preponderance in genetic generalized epilepsies

INTRODUCTION

Epilepsy is more prevalent in men but Genetic Generalized Epilepsies (GGE) seem to be more common in women. A predominant maternal inheritance has been previously described in GGE. Our objective was to determine sex and inheritance patterns in a GGE population compared to mesial temporal lobe epilepsy with hippocampal sclerosis (MTLEHS).

METHODS

We performed a prospective observational study including adult GGE and MTLEHS patients followed up at a tertiary epilepsy center from January 2016 to December 2019. Patients' familial history was obtained by a detailed questionnaire. Clinical and demographic data was retrieved from clinical notes.

RESULTS

A cohort of 641 patients, 403 with GGE and 238 with MTLEHS, was analyzed. GGE was more common in women than MTLEHS (58.8% vs 44.5%, OR=1.63, p = 0.004). Compared to MTLEHS patients, more GGE patients had familial history of epilepsy (45.4% vs 25.2%; p<0.001). The GGE group had a higher percentage of female relatives with epilepsy (55% vs 37%; p = 0.006). The prevalence of maternal inheritance was not different between GGE and MTLEHS groups (62.9% vs 57.7%; p = 0.596). Photosensitivity was more common in females than in males (44.7% vs 34.3%, p = 0.036).

CONCLUSION

There is a female preponderance in GGE when compared to MTLEHS, as both GGE patients and their affected relatives are more frequently women. The prevalence of maternal inheritance was not higher in GGE than in MTLEHS.

Granule cell dispersion is associated with hippocampal neuronal cell loss, initial precipitating injury, and other clinical features in mesial temporal lobe epilepsy and hippocampal sclerosis

PURPOSE

To characterize a 10-year series of patients with mesial temporal lobe epilepsy (MTLE) and unilateral hippocampal sclerosis (HS) and determine the histopathological characteristic of the association between granule cell dispersion (GCD) and hippocampal neuronal loss.

METHODS

The study included 108 MTLE/HS patients. Histopathological analyses were performed in NeuN-stained hippocampal sections for HS pattern, neuronal density, dentate gyrus (DG) pathology, and granule cell layer width. Statistical tests investigated the association between DG pathologies and HS patterns, as well as the correlation of DG width with total hippocampal and subfield-specific neuronal densities.

RESULTS

Fifty-six patients (51.9%) presented right HS. All the four ILAE HS patterns were represented (90 Type 1, 11 Type 2, 2 Type 3, and 5 no-HS). Sixty-seven patients (62.0%) presented GCD, 39 (36.1%) normal DG, and 2 (1.9%) narrow DG. GCD was associated with initial precipitating injury, higher numbers of monthly focal seizures and lifetime bilateral tonic-clonic seizures, longer epilepsy duration, and older age at surgery. GCD was prevalent in all HS patterns, except for Type 2 (81.8% normal versus 18.2% GCD, p = 0.005). GCD was associated with total hippocampal and subfield-specific neuronal loss, except for CA1. DG width correlated with total hippocampal (r = -0.201, p = 0.037) and CA4 neuronal densities (r = -0.299, p = 0.002). Patients with HS Type 1 had better surgical outcomes, with 51 (61.4%) seizure-free in the first year post-surgery.

CONCLUSIONS

This study confirmed that seizure control in MTLE/HS patients submitted to surgical treatment is comparable worldwide. Moreover, histopathological analyses showed an association between GCD and hippocampal neuronal loss, especially in the CA4 subfield.

Volumetric and shape analysis of the hippocampus in temporal lobe epilepsy with GAD65 antibodies compared with non-immune epilepsy

Glutamic acid decarboxylase 65 antibodies (anti-GAD65) have been found in patients with late-onset chronic temporal lobe epilepsy (TLE). No prior neuroimaging studies have addressed how they affect hippocampal volume and shape and how they relate to cognitive abnormalities. We aimed to investigate both brain structure and function in patients with isolated TLE and high anti-GAD65 levels (RIA ≥ 2000 U/ml) compared to 8 non-immune mesial TLE (niTLE) and 8 healthy controls (HC). Hippocampal subfield volume properties were correlated with the duration of the disease and cognitive test scores. The affected hippocampus of GAD-TLE patients showed no volume changes to matched HC whereas niTLE volumes were significantly smaller. Epilepsy duration in GAD-TLE patients correlated negatively with volumes in the presubiculum, subiculum, CA1, CA2-3, CA4, molecular layer and granule cell-molecular layer of the dentate nucleus. We found differences by advanced vertex-wise shape analysis in the anterior hippocampus of the left GAD-TLE compared to HC whereas left niTLE showed bilateral posterior hippocampus deformation. Verbal deficits were similar in GAD-TLE and niTLE but did not correlate to volume changes. These data might suggest a distinct expression of hippocampal structural and functional abnormalities based on the immune response.

Brain FDG-PET findings in glutamic acid decarboxylase antibody-associated epilepsy

BACKGROUND AND PURPOSE

Glutamic acid decarboxylase antibodies (GAD-Ab) are sometimes associated with chronic drug-resistant focal epilepsy. Clinically, it may manifest as mesial temporal lobe epilepsy (mTLE), with GAD-Ab patients difficult to distinguish. Therefore, the aim of this study is to compare brain metabolism of patients with mTLE and high serum titers of GAD-Ab (>2000 UI/ml) to those with mTLE and hippocampal sclerosis (HS) and confirmed GAD-ab negativity.

METHODS

Images from PET studies were normalized to an SPM 12 template. Voxel to voxel comparisons were made using a two-sample one-tailed t-test.

RESULTS

In both patients with GAD-Ab and controls (mTLE-HS), hypometabolism in mesial temporal lobe areas was observed. When comparing the two groups, GAD-Ab patients had statistically significant reduced metabolism in both insulae and medial inferior frontal-hypothalamus area (p < 0.001).

CONCLUSIONS

Hypometabolism in mesial temporal lobe areas together with hypometabolism in insulae and medial inferior frontal-hypothalamus may be characteristic of patients with epilepsy and GAD-ab. This PET pattern could be a useful diagnostic tool to identify GAD-Ab patients.

Autobiographical memory in epileptic patients after temporal lobe resection or bitemporal hippocampal sclerosis

The human hippocampus is believed to be a crucial node in the neural network supporting autobiographical memory retrieval. Structural mesial temporal damage associated with temporal lobe epilepsy (TLE) provides an opportunity to systematically investigate and better understand the local and distal functional consequences of mesial temporal damage in the engagement of the autobiographical memory network. We examined 19 TLE patients (49.21 ± 11.55 years; 12 females) with unilateral mesial TLE (MTLE; 12 with anterior temporal lobe resection: 6 right MTLE, 6 left MTLE) or bilateral mesial TLE (7 BMTLE) and 18 matched healthy subjects. We used functional MRI (fMRI) with an adapted autobiographical memory paradigm and a specific neuropsychological test (Autobiographical Memory Interview, AMI). While engaged in the fMRI autobiographical memory paradigm, all groups activated a large fronto-temporo-parietal network. However, while this network was left lateralized for healthy participants and right MTLE patients, left MTLE and patients with BMTLE also showed strong activation in right temporal and frontal regions. Moreover, BMTLE and left MTLE patients also showed significant mild deficits in episodic autobiographical memory performance measured with the AMI test. The right temporal and extra-temporal fMRI activation, along with the impairment in autobiographical memory retrieval found in left MTLE and BMTLE patients suggest that alternate brain areas-other than the hippocampus-may also support this process, possibly due to neuroplastic effects.

Consanguinity in patients with mesial temporal lobe epilepsy due to hippocampal sclerosis in a Saudi population

Objectives:

To investigate if there is an association between consanguinity and hippocampal sclerosis (HS) in the Saudi population.

Methods:

A retrospective case-control study was conducted by assessing the prevalence of consanguinity in patients with pathologically proven HS, who underwent epilepsy surgery at King Faisal Specialist Hospital and Research Center, Jeddah, Saudi Arabia, between January 2004 and December 2015. We reviewed the medical records to extract data, which included; age, gender, duration of epilepsy, history of febrile seizure, family history of epilepsy in a first or second-degree relative, and pathology reports.

Results:

A total of 120 patients, out of which 40 patients (65% male) having mesial temporal lobe epilepsy due to HS, and 80 controls (56% male) with cryptogenic epilepsy, were identified. Twenty-two patients (53.5%) in the HS group had a history of consanguinity. In the control group, 30 patients (37.5%) had a history of consanguinity. The odds ratio was 2.04 (95% confidence interval = 0.94 - 4.4, p = 0.052). A family history of epilepsy was found in 28% of the patients with HS and 32.5% cryptogenic epilepsy. Only 8 patients (19.5%) with HS reported a history of febrile seizure.

Conclusion:

Our retrospective case-control study suggests that consanguinity might increase the likelihood of developing HS.

Identifying Refractory Epilepsy Without Structural Abnormalities by Fusing the Common Spatial Patterns of Functional and Effective EEG Networks

Drug refractory epilepsy (RE) is believed to be associated with structural lesions, but some RE patients show no significant structural abnormalities (RE-no-SA) on conventional magnetic resonance imaging scans. Since most of the medically controlled epilepsy (MCE) patients also do not exhibit structural abnormalities, a reliable assessment needs to be developed to differentiate RE-no-SA patients and MCE patients to avoid misdiagnosis and inappropriate treatment. Using resting-state scalp electroencephalogram (EEG) datasets, we extracted the spatial pattern of network (SPN) features from the functional and effective EEG networks of both RE-no-SA patients and MCE patients. Compared to the performance of traditional resting-state EEG network properties, the SPN features exhibited remarkable superiority in classifying these two groups of epilepsy patients, and accuracy values of 90.00% and 80.00% were obtained for the SPN features of the functional and effective EEG networks, respectively. By further fusing the SPN features of functional and effective networks, we demonstrated that the highest accuracy value of 96.67% could be reached, with a sensitivity of 100% and specificity of 92.86%. Overall, these findings not only indicate that the fused functional and effective SPN features are promising as reliable measurements for distinguishing RE-no-SA patients and MCE patients but also may provide a new perspective to explore the complex neurophysiology of refractory epilepsy.

Hippocampal size did not differ between epileptic and non-epileptic dogs using volumetric and subjective methods

Hippocampal changes in epilepsy may manifest as hippocampal atrophy/sclerosis. A recent human study suggests that the demonstration of hippocampal volume loss is more reliable using quantitative evaluation methods. The aim of the present study was to obtain volumetric data in both epileptic and healthy dogs, to compare hippocampal volumes in both groups, and to compare subjective and volumetric assessment. Volumetric measurements of the hippocampi, lateral ventricles and hemispheria were performed in 31 epileptic and 15 control dogs. There was a positive association between the body weight and the hemispheric volume, as well as between the hemispheric volume and the ipsilateral hippocampal volume. There was no significant correlation between age and the volume of any measured brain structures. There was no statistically significant difference between the hippocampal volumes of the control group and the epileptic group. A statistically significant difference between the two groups for hippocampus/hemispherium ratio or hippocampal asymmetric ratio was not identified. An extrapolated hippocampal volume based on body weight was not possible in this study population.

Resting-state hippocampal networks related to language processing reveal unique patterns in temporal lobe epilepsy

OBJECTIVE

Patients with temporal lobe epilepsy (TLE) commonly experience a broad range of language impairments. These deficits are thought to arise from repeated seizure activity that damages language regions. However, connectivity between the seizure onset region in the hippocampus and regions related to language processing has rarely been studied, and could also have a strong impact on language function. The purpose of this study was to use resting-state functional connectivity (FC) measures to assess hippocampal network patterns and their relation to language abilities in patients with right TLE (RLTE), left TLE (LTLE), and healthy controls.

METHODS

Presurgical resting-state 3T functional MRI data were acquired from 40 patients with mesial TLE (27 RTLE, 13 LTLE) and 54 controls. The regions of interest were the anterior and posterior bilateral hippocampi and eleven regions grouped by frontal or temporo-parietal locations, including large areas of language-related cortex. FC values were computed with the right/left anterior and posterior hippocampi as the seeds and frontal and temporo-parietal regions as targets. Resting-state lateralization indices were also calculated (LI-Rest), and all FC measures were correlated to neuropsychological language scores and measures related to manifestation of epilepsy including age of onset, duration of disease, monthly seizure frequency, and hippocampal volume.

RESULTS

We found significant group differences between the anterior hippocampi and temporo-parietal regions closest to the seizure focus, in which RTLE and LTLE showed stronger connectivity to their contralateral hippocampus, while controls showed similar connectivity to both hippocampi. In addition, LI-Rest demonstrated significantly more right lateralization in LTLE compared to RTLE for temporo-parietal regions only. In LTLE, we found significant associations between stronger hippocampal network resting-state FC and later age of onset and decreased left anterior hippocampal volume.

SIGNIFICANCE

The results of our study indicate that the presence of TLE impacts hippocampal-temporo-parietal networks relevant to language processing.

Application of Optogenetics in Epilepsy Research

Epilepsy is a disease characterized by seizures arising from paroxysmal and self-limited hypersynchrony of neurons. However, the mechanism by which the normal brain develops epilepsy, which involves a chronic process of structural and morphological changes known as epileptogenesis, is not fully understood. Optogenetics involves the use of genetic engineering and optics to monitor or control nerve cell activity. Compared to classical electrophysiological experiments, the application of optogenetics in epilepsy research has many advantages because it allows selective photic stimulation of cell types and electrical observation without introducing artifacts.

Clear and Consistent Imaging of Hippocampal Internal Architecture With High Resolution Multiple Image Co-registration and Averaging (HR-MICRA)

Magnetic resonance imaging of hippocampal internal architecture (HIA) at 3T is challenging. HIA is defined by layers of gray and white matter that are less than 1 mm thick in the coronal plane. To visualize HIA, conventional MRI approaches have relied on sequences with high in-plane resolution (≤0.5 mm) but comparatively thick slices (2–5 mm). However, thicker slices are prone to volume averaging effects that result in loss of HIA clarity and blurring of the borders of the hippocampal subfields in up to 61% of slices as has been reported. In this work we describe an approach to hippocampal imaging that provides consistently high HIA clarity using a commonly available sequence and post-processing techniques that is flexible and may be applicable to any MRI platform. We refer to this approach as High Resolution Multiple Image Co-registration and Averaging (HR-MICRA). This approach uses a variable flip angle turbo spin echo sequence to repeatedly acquire a whole brain T2w image volume with high resolution in three dimensions in a relatively short amount of time, and then co-register the volumes to correct for movement and average the repeated scans to improve SNR. We compared the averages of 4, 9, and 16 individual scans in 20 healthy controls using a published HIA clarity rating scale. In the body of the hippocampus, the proportion of slices with good or excellent HIA clarity was 90%, 83%, and 67% for the 16x, 9x, and 4x HR-MICRA images, respectively. Using the 4x HR-MICRA images as a baseline, the 9x HR-MICRA images were 2.6 times and 16x HR-MICRA images were 3.2 times more likely to have high HIA ratings (p < 0.001) across all hippocampal segments (head, body, and tail). The thin slices of the HR-MICRA images allow reformatting in any plane with clear visualization of hippocampal dentation in the sagittal plane. Clear and consistent visualization of HIA will allow application of this technique to future hippocampal structure research, as well as more precise manual or automated segmentation.

Enrichment of Circular RNA Expression Deregulation at the Transition to Recurrent Spontaneous Seizures in Experimental Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (mTLE) is a common form of epilepsy and is characterized by recurrent spontaneous seizures originating from the temporal lobe. The majority of mTLE patients develop pharmacoresistance to available anti-epileptic drugs (AEDs) while exhibiting severe pathological changes that can include hippocampal atrophy, neuronal death, gliosis and chronic seizures. The molecular mechanisms leading to mTLE remain incompletely understood, but are known to include defects in post-transcriptional gene expression regulation, including in non-coding RNAs (ncRNAs). Circular RNAs (circRNAs) are a class of recently rediscovered ncRNAs with high levels of expression in the brain and proposed roles in diverse neuronal processes. To explore a potential role for circRNAs in epilepsy, RNA-sequencing (RNA-seq) was performed on hippocampal tissue from a rat perforant pathway stimulation (PPS) model of TLE at different post-stimulation time points. This analysis revealed 218 differentially expressed (DE) circRNAs. Remarkably, the majority of these circRNAs were changed at the time of the occurrence of the first spontaneous seizure (DOFS). The expression pattern of two circRNAs, circ_Arhgap4 and circ_Nav3, was further validated and linked to miR-6328 and miR-10b-3p target regulation, respectively. This is the first study to examine the regulation of circRNAs during the development of epilepsy. It reveals an intriguing link between circRNA deregulation and the transition of brain networks into the state of spontaneous seizure activity. Together, our results provide a molecular framework for further understanding the role and mechanism-of-action of circRNAs in TLE.

Initial delta and delayed theta/alpha pattern in the temporal region on ictal EEG suggests purely hippocampal epileptogenicity in patients with mesial temporal lobe epilepsy

OBJECTIVE

To determine whether the ictal scalp EEG findings suggest purely hippocampal epileptogenicity in patients with mesial temporal lobe epilepsy (mTLE) associated with hippocampal sclerosis (HS).

METHODS

Twenty-three patients with mTLE with pathologically confirmed HS were divided into 12 with epileptogenicity only in the hippocampus (HS only group) and 11 with epileptogenicity in both the hippocampus and temporal neocortex or other locations (HS plus group), based on the combination of surgical procedures, postoperative outcome, and pathological findings. Sixteen underwent selective amygdalohippocampectomy (SelAH) and 7 received anterior temporal lobectomy. Ictal scalp EEG findings of 79 focal impaired awareness seizures were compared between the HS only and HS plus groups. We focused on the 1-4 Hz rhythmic delta activity at ictal onset followed by 5-9 Hz rhythmic theta/alpha activity 10-30 s after the onset in the temporal region.

RESULTS

The initial delta and delayed theta/alpha (ID-DT) pattern was observed in 8 of 12 patients in the HS only group, but in none of 11 patients in the HS plus group (p < 0.01).

CONCLUSIONS

ID-DT pattern on ictal EEG suggests purely hippocampal epileptogenicity in mTLE with HS.

SIGNIFICANCE

Patients with the ID-DT pattern are likely to become seizure-free after SelAH.

Complex effects of eslicarbazepine on inhibitory micro networks in chronic experimental epilepsy

OBJECTIVE

Many antiseizure drugs (ASDs) act on voltage-dependent sodium channels, and the molecular basis of these effects is well established. In contrast, how ASDs act on the level of neuronal networks is much less understood.

METHODS

In the present study, we determined the effects of eslicarbazepine (S-Lic) on different types of inhibitory neurons, as well as inhibitory motifs. Experiments were performed in hippocampal slices from both sham-control and chronically epileptic pilocarpine-treated rats.

RESULTS

We found that S-Lic causes an unexpected reduction of feed-forward inhibition in the CA1 region at high concentrations (300 µM), but not at lower concentrations (100 µM). Concurrently, 300 but not 100 μM S-Lic significantly reduced maximal firing rates in putative feed-forward interneurons located in the CA1 stratum radiatum of sham-control and epileptic animals. In contrast, feedback inhibition was not inhibited by S-Lic. Instead, application of S-Lic, in contrast to previous data for other drugs like carbamazepine (CBZ), resulted in a lasting potentiation of feedback inhibitory post-synaptic currents (IPSCs) only in epileptic and not in sham-control animals, which persisted after washout of S-Lic. We hypothesized that this plasticity of inhibition might rely on anti-Hebbian potentiation of excitatory feedback inputs onto oriens-lacunosum moleculare (OLM) interneurons, which is dependent on Ca²⁺ -permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Indeed, we show that blocking Ca²⁺ -permeable AMPA receptors completely prevents upmodulation of feedback inhibition.

SIGNIFICANCE

These results suggest that S-Lic affects inhibitory circuits in the CA1 hippocampal region in unexpected ways. In addition, ASD actions may not be sufficiently explained by acute effects on their target channels, rather, it may be necessary to take plasticity of inhibitory circuits into account.

Epileptic olfactory auras: a clinical spectrum

OBJECTIVE

To investigate the relative frequency of olfactory aura in a large number of patients with focal epilepsy, and examine the full clinical spectrum of epileptic olfactory auras (OAs) and their relationship to hemispheric lateralization and localization of epileptogenic focus.

METHODS

This retrospective study was based on the medical records of 1384 patients with focal epilepsy. Of these, 71 (5.1%) patients were present with OAs, comprising 25 (35.2%) men and 46 (64.8%) women with a mean age of 35.43 ± 12.89 years. These 71 patients were classified according to the clinical features of the OAs, and the electroencephalography and magnetic resonance imaging findings were examined.

RESULTS

The relative frequency of OAs was 5.1% in the focal epileptic patients. The clinical spectrum of OAs in our cases was outlined as follows, complex OAs and elementary OAs. Elementary OAs were divided into three subgroups: elementary neutral OAs, elementary unpleasant OAs, and elementary pleasant OAs. In our cases, there was no difference between the right and left hemispheres in terms of lateralization of the epileptogenic focus. In all the 71 patients, the epileptogenic zone was most commonly localized in the temporal lobe (n = 58; 81.7%).

CONCLUSIONS

The relative frequency of OAs in focal epilepsies is likely to be found higher than expected. Elementary OAs occur much more frequently than complex OAs. Among the elementary OAs, elementary unpleasant OAs and elementary neutral OAs are the most common types, whereas elementary pleasant OAs are extremely rare.

Quantitative brain histogram of canine epilepsy using magnetic resonance imaging

BACKGROUND

Quantitative magnetic resonance imaging (MRI) is used to study the anatomy of the brain in dogs with idiopathic epilepsy.

PURPOSE

To quantitate MRI images in terms of volumetric ratios and histogram analyses of the following regions of interest (ROI) in dogs with idiopathic epilepsy: frontal; parietal; temporal; piriform; thalamic; and hippocampal regions.

MATERIAL AND METHODS

Nine dogs with epilepsy and four healthy controls were evaluated. We examined the volumetric ratios and histogram analyses of six ROIs in all dogs.

RESULTS

MR images, in T1-weighted, T2-weighted, FLAIR, diffusion-weighted imaging, and apparent diffusion coefficient sequences detected changes in 4/9 (44%) epileptic dogs found in 5/6 regions: frontal; parietal; temporal; piriform; and hippocampal regions. However, no such changes were observed in the thalamic region. Interestingly, the frontal and piriform volumetric ratios of epileptic dogs were significantly lower than those of control dogs. The histogram analyses in 4/6 regions were significantly increased in epileptic dogs.

CONCLUSION

Our results demonstrated MRI finding abnormalities in several regions of the brain in several sequences including T1-weighted, T2-weighted, FLAIR, diffusion-weighted imaging, and apparent diffusion coefficient in epileptic dogs. In several regions of the brain, atrophy may exist, and hyperintensity may be present on MR images in epileptic dogs. These findings suggest that the diagnostic yield of MRI, which is an advanced neuroimaging technique, is high in epileptic dogs and has good reliability and sensitivity in detecting abnormal areas in patients.

Evolution of interictal spiking during the latent period in a mouse model of mesial temporal lobe epilepsy

Interictal spikes and high-frequency oscillations (HFOs, ripples: 80–200 ​Hz, fast ripples: 250–500 ​Hz) occur in epileptic patients and in animal models of mesial temporal lobe epilepsy (MTLE). In this study, we explored how type 1 and type 2 interictal spikes as well as ripples and fast ripples evolve during the latent period in the hippocampus of pilocarpine-treated mice. Depth EEG recordings were obtained from the hippocampus CA3 subfield of adult male mice (n ​= ​5, P60–P100) starting one day before pilocarpine-induced status epilepticus up to the first spontaneous seizure, the so-called latent period. We found that rates of type 1 (n ​= ​1 655) and type 2 (n ​= ​2 309) interictal spikes were significantly lower during the late phase of the latent period compared to its early and mid phase (p ​< ​0.001). However, rates of type 1 spikes associated with ripples (n ​= ​266) or fast ripples (n ​= ​106), as well as rates of type 2 interictal spikes associated with ripples (n ​= ​233), were significantly higher during the late phase compared to the early and mid phases (p ​< ​0.05). Our findings reveal that an increase of type 1 interictal spikes co-occurring with ripples or fast ripples and an increase of type 2 interictal spikes co-occurring with ripples mark the end of the latent period. We propose that changes in the occurrence of interictal spike associated with HFOs represent a biomarker of epileptogenicity in this mouse model of MTLE.

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We studied interictal spike types in a model of mesial temporal lobe epilepsy.

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Type 1 and type 2 spike rates were lower in the late phase of the latent period.

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Rates of type 1 spikes with ripples or fast ripples were higher in the late phase.

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Rates of type 2 spikes with fast ripples were also higher during the late phase.

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These changes in interictal spike types mark the end of the latent period.

[Structural heterogeneity of epileptic foci in local drug-resistant epilepsy]

BACKGROUND

To study etiopathogenesis is one of the most important tasks of modern neurology. Various types of structural changes occur in drug-resistant epilepsy (DRE); however, they are described as distinct phenomena.

OBJECTIVE

To provide a comprehensive characterization of structural changes in the cortex and adjacent white matter in the electrophysiological activity zone (in the epileptic focus) in patients undergoing surgery for DRE.

MATERIAL AND METHODS

Biopsy material of fragments of the temporal lobe and hippocampus from 16 patients aged 21 to 54 years (mean age, 25 years) with DRE were intraoperatively obtained at the Prof. A.L. Polenov Russian Research Institute of Neurosurgery. The investigators studied histological sections stained with H&E, toluidine blue according to the Nissl method and the Spielmeyer method, as well as the results of immunohistochemical reactions with glial fibrillary acidic protein (GFAP), vimentin, and neurofilaments (NF) (Dako antibodies, Denmark).

RESULTS

Histological examination revealed a set of heterogeneous changes, reflecting the complex pathogenetic interactions that developed during the formation of an epileptic focus. Structural brain damage involved both gray and white matter. Focal cortical dysplasia was diagnosed in 14 (87.5%) cases; white matter neuronal heterotopia in 100%; neuronal reactive and destructive changes in 100%; epileptic leukoencephalopathy (vascular demyelination, microcysts, sclerosis and dystonia, gliosis) in 100%, cortical atrophy in 12.5%, and hippocampal sclerosis in 20% (in 2 out of the 10 examinees).

CONCLUSION

The morphopathological heterogeneity in the structure of epileptic foci reflects the complexity of etiopathogenetic interactions, the polymorphism of epileptic manifestations, and the individual nature of formation of the epileptic system, which requires an integral approach to understanding the pathogenesis and morphogenesis of formation of the epileptic system and provides a direction for a personalized approach to epilepsy treatment.

A study of medial and lateral temporal lobe epilepsy based on stereoelectroencephalography

BACKGROUND

Patients with temporal lobe epilepsy (TLE) originating from different seizure onset zones had distinct electrophysiological characteristics and surgical outcomes. In this study, we aimed to investigate the relationship between the origin and prognosis of TLE, and the stereoelectroencephalography (SEEG) features.

METHODS

Thirty patients with TLE, who underwent surgical treatment in our functional neurosurgery department from January 2016 to December 2017, were enrolled in this study. All patients underwent anterior temporal lobectomy after an invasive pre-operative evaluation with SEEG. Depending on the epileptic focus location, patients were divided into those with medial temporal lobe seizures (MTLS) and those with lateral temporal lobe seizures (LTLS). The Engel classification was used to evaluate operation effectiveness, and the Kaplan-Meier analysis was used to detect seizure-free duration.

RESULTS

The mean follow-up time was 25.7 ± 4.8 months. Effectiveness was 63.3% for Engel I (n = 19), 13.3% for Engel II, 3.3% for Engel III, and 20.0% for Engel IV. According to the SEEG, 60.0% (n = 18) had MTLS, and 40.0% (n = 12) had LTLS. Compared with the MTLS group, the operation age of those with LTLS was significantly greater (26.9 ± 6.9 vs. 29.9 ± 12.5 years, t = -0.840, P = 0.009) with longer epilepsy duration (11.9 ± 6.0 vs. 17.9 ± 12.1 years, t = -1.801, P = 0.038). Patients with MTLS had a longer time interval between ictal onset to seizure (67.3 ± 59.1 s vs. 29.3 ± 24.4 s, t = 2.017, P = 0.008). The most common SEEG ictal pattern was a sharp/spike-wave rhythm in the MTLS group (55.6%) and low-voltage fast activity in the LTLS group (58.3%). Compared with the LTLS group, patients with MTLS had a more favorable prognosis (41.7% vs. 77.8%, P = 0.049). Post-operative recurrence was more likely to occur within three months after the operation for both groups, and there appeared to be a stable long-term outcome.

CONCLUSION

Patients with MTLS, who accounted for three-fifths of patients with TLE, showed a more favorable surgical outcome.

Differential Glial Activation in Early Epileptogenesis-Insights From Cell-Specific Analysis of DNA Methylation and Gene Expression in the Contralateral Hippocampus

Background and Aims: Morphological changes in mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) are well-characterized. Yet, it remains elusive whether these are a consequence of seizures or originate from a hitherto unknown underlying pathology. We recently published data on changes in gene expression and DNA methylation in the ipsilateral hippocampus (ILH) using the intracortical kainate mouse model of mTLE-HS. In order to explore the effects of epileptic activity alone and also to further disentangle what triggers morphological alterations, we investigated glial and neuronal changes in gene expression and DNA methylation in the contralateral hippocampus (CLH). Methods: The intracortical kainic acid mouse model of mTLE-HS was used to elicit status epilepticus. Hippocampi contralateral to the injection site from eight kainate-injected and eight sham mice were extracted and shock frozen at 24 h post-injection. Glial and neuronal nuclei were sorted by flow cytometry. Alterations in gene expression and DNA methylation were assessed using reduced representation bisulfite sequencing and RNA sequencing. The R package edgeR was used for statistical analysis. Results: The CLH featured substantial, mostly cell-specific changes in both gene expression and DNA methylation in glia and neurons. While changes in gene expression overlapped to a great degree between CLH and ILH, alterations in DNA methylation did not. In the CLH, we found a significantly lower number of glial genes up- and downregulated compared to previous results from the ILH. Furthermore, several genes and pathways potentially involved in anti-epileptogenic effects were upregulated in the CLH. By comparing gene expression data from the CLH to previous results from the ILH (featuring hippocampal sclerosis), we derive potential upstream targets for epileptogenesis, including glial Cox2 and Cxcl10. Conclusion: Despite the absence of morphological changes, the CLH displays substantial changes in gene expression and DNA methylation. We find that gene expression changes related to potential anti-epileptogenic effects seem to dominate compared to the pro-epileptogenic effects in the CLH and speculate whether this imbalance contributes to prevent morphological alterations like neuronal death and reactive gliosis.

Recurrent limbic seizures do not cause hippocampal neuronal loss: A prolonged laboratory study

PURPOSE

It remains controversial whether neuronal damage and synaptic reorganization found in some forms of epilepsy are the result of an initial injury and potentially contributory to the epileptic condition or are the cumulative affect of repeated seizures. A number of reports of human and animal pathology suggest that at least some neuronal loss precedes the onset of seizures, but there is debate over whether there is further damage over time from intermittent seizures. In support of this latter hypothesis are MRI studies in people that show reduced hippocampal volumes and cortical thickness with longer durations of the disease. In this study we addressed the question of neuronal loss from intermittent seizures using kindled rats (no initial injury) and rats with limbic epilepsy (initial injury).

METHODS

Supragranular mossy fiber sprouting, hippocampal neuronal densities, and subfield area measurements were determined in rats with chronic limbic epilepsy (CLE) that developed following an episode of limbic status epilepticus (n = 25), in kindled rats (n = 15), and in age matched controls (n = 20). To determine whether age or seizure frequency played a role in the changes, CLE and kindled rats were further classified by seizure frequency (low/high) and the duration of the seizure disorder (young/old).

RESULTS

Overall there was no evidence for progressive neuronal loss from recurrent seizures. Compared with control and kindled rats, CLE animals showed increased mossy fiber sprouting, decreased neuronal numbers in multiple regions and regional atrophy. In CLE, but not kindled rats: 1) Higher seizure frequency was associated with greater mossy fiber sprouting and granule cell dispersion; and 2) greater age with seizures was associated with decreased hilar densities, and increased hilar areas. There was no evidence for progressive neuronal loss, even with more than 1000 seizures.

CONCLUSION

These findings suggest that the neuronal loss associated with limbic epilepsy precedes the onset of the seizures and is not a consequence of recurrent seizures. However, intermittent seizures do cause other structural changes in the brain, the functional consequences of which are unclear.

Surgical Treatments of Epilepsy

Nearly 30% of epilepsy patients are refractory to medical therapy. Surgical management of epilepsy is an increasingly viable option for these patients. Although surgery has historically been used as a palliative option, improvements in technology and outcomes show its potential in certain subsets of patients. This article reviews the two main categories of surgical epilepsy treatment-resective surgery and neuromodulation. Resective surgery includes temporal lobe resections, extratemporal resections, laser interstitial thermal therapy, and disconnection procedures. We discuss the three main types of neuromodulation-vagal nerve stimulation, responsive neurostimulation, and deep brain stimulation for epilepsy. The history and indications are explored for each type of treatment. Given the myriad types of resection and neuromodulation techniques, patient selection is reviewed in detail, with a discussion on which patients are most likely to benefit from different treatment strategies. We also discuss outcomes with examples of the pertinent landmark trials and their results. Finally, complications and surgical technique are reviewed. As new indications emerge and patient selection is refined, surgical management will continue to evolve as an adjuvant therapy for epileptic patients.

Abnormalities of Cortical Thickness in Pediatric Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

OBJECTIVE

Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is the most common intractable seizure type of pediatric epilepsy, with alterations in the cortex across the whole brain. The aim of this study is to investigate the abnormalities of cortical thickness in pediatric MTLE-HS.

METHODS

Subjects were recruited from Shenzhen Children's Hospital between September 2015 and December 2016. MTLE was confirmed by the experienced neurological physician based on International League Against Epilepsy (ILAE) diagnosis criteria, and structural magnetic resonance imaging (MRI) was performed at 3T for quantitative assessment of cortical thickness. A general linear model with age and gender as covariates was used to examine the vertex-wise differences in cortical thickness between 1) left MTLE-HS (LMTLE-HS) and healthy controls (HC), and 2) right MTLE-HS (RMTLE-HS) and HC. The family-wise error corrected significance threshold was set at P < 0.05. Through a combination of probability and cluster-size thresholding, cluster-wise P values were obtained for the resulting clusters.

RESULTS

13 LMTLE-HS, 6 RMTLE-HS, and 20 age-matched HC were finally enrolled in the study. No significant difference in the mean age (LMTLE-HS vs. HC, p=0.57; RMTLE-HS vs. HC, p=0.39) and gender ratio (LMTLE-HS vs. HC, p=0.24; RMTLE-HS vs. HC, p=0.72) was found between MTLE-HS and HC. In LMTLE-HS, cortical thickness was found significantly decreased in the ipsilateral caudal middle frontal gyrus (p=0.012) and increased in the contralateral inferior temporal gyrus (p=0.020). In RMTLE-HS, cortical thickness significantly decreased in the ipsilateral posterior parietal lobe (superior, p<0.001 and inferior parietal gyrus, p=0.03), the anterior parietal lobe (postcentral gyrus, p=0.006), the posterior frontal lobe (precentral gyrus, p=0.04 and the lateral occipital gyrus, p<0.001), and the contralateral lateral occipital gyrus, middle frontal (p<0.0001) and superior frontal gyrus (p<0.001), and pericalcarine cortex (p=0.020).

CONCLUSION

We detected significant cortical abnormalities in pediatric MTLE-HS patients compared with HC. These cortical abnormalities could be explained by specific pathogenesis in MTLE-HS, and may finally contribute to understanding the intrinsic mechanism of MTLE-HS.

An Excitatory and Epileptogenic Effect of Dentate Gyrus Mossy Cells in a Mouse Model of Epilepsy

The sparse activity of hippocampal dentate gyrus (DG) granule cells (GCs) is thought to be critical for cognition and behavior, whereas excessive DG activity may contribute to disorders such as temporal lobe epilepsy (TLE). Glutamatergic mossy cells (MCs) of the DG are potentially critical to normal and pathological functions of the DG because they can regulate GC activity through innervation of GCs or indirectly through GABAergic neurons. Here, we test the hypothesis that MC excitation of GCs is normally weak, but under pathological conditions, MC excitation of GCs is dramatically strengthened. We show that selectively inhibiting MCs during severe seizures reduced manifestations of those seizures, hippocampal injury, and chronic epilepsy. In contrast, selectively activating MCs was pro-convulsant. Mechanistic in vitro studies using optogenetics further demonstrated the unanticipated ability of MC axons to excite GCs under pathological conditions. These results demonstrate an excitatory and epileptogenic effect of MCs in the DG.

Evaluation of patients with late-onset and medically refractory temporal lobe epilepsy with mesial temporal sclerosis

OBJECTIVES

Our study aims to compare demographics, clinical features and postsurgical outcomes between early and late-onset patients with medically refractory temporal lobe epilepsy (TLE) related to mesial temporal sclerosis (MTS).

PATIENTS AND METHODS

Seventy-one patients admitting to the Epilepsy Clinic of Istanbul University-Cerrahpasa, Cerrahpasa Faculty of Medicine between 1995-2015, who were diagnosed with refractory TLE related to MTS, were included in our study. All of these patients were resistant to medical treatment, and thus candidates for, or underwent surgery, and had no pathology other than MTS in their cranial magnetic resonance imaging (MRI). Based on previous studies, those patients were divided into two categories as "early-onset" and "late-onset", according to the age-onset of afebrile recurrent seizures, where the cutoff was determined as 20 years. Demographics, clinical features, and postsurgical outcomes were compared between both groups.

RESULTS

Fifty-three patients included in our study had early-onset MTS-TLE, and 18 patients had late-onset MTS-TLE. Demographics, clinical features, characteristics of electroencephalography (EEG), MRI, PET MRI/CT, neuropsychometric test (NPT) and postsurgical outcomes were similar in both groups.

CONCLUSION

In both the early-onset and late-onset groups, the presence of similar demographics, clinical features, and postoperative outcomes have suggested that the course of the disease and the success of surgical treatment were not associated with the age-onset of seizures in TLE related to MTS.

The Relationship Between Clinico-Pathological Properties and p-Glycoprotein Expression in Hippocampal Sclerosis Among Patients with Mesial Temporal Lobe Epilepsy Who Undergo Selective Amygdalohippocampectomy Operation

INTRODUCTION

The overproduction of the efflux transporters in the blood-brain barrier is considered to play a role in the development of drug resistance in mesial temporal lobe epilepsy (MTLE) patients. The aim of the present study was to investigate the relationship of clinical features of patients with MTLE accompanied by hippocampal sclerosis (HS) and the p-glycoprotein (p-gp) expression and neuronal loss in the hippocampus.

METHODS

This study included a total of 33 patients who underwent selective amygdala-hippocampectomy operation. A detailed medical history of each patient, including age, side of HS, sex, age of habitual seizure onset, duration of habitual seizures, type and age of initial precipitating injury, presence and duration of latent period, presence and duration of silent period, monthly seizure frequency within 1 year prior to operation, mean age at the time of operation was evaluated retrospectively.

RESULTS

The p-gp expression was significantly higher in the patient group with a seizure frequency of more than 15 days per month and a disease duration of more than 20 years. There was no significant difference between the p-gp expression and the clinical features of the MTLE-HS patients.

CONCLUSION

These results suggest that p-gp expression is affected by disease duration and seizure frequency rather than a patient's clinical and pathological properties. In patients with HS-MTLE, potential use of the p-gp inhibitors as additional therapy and developing novel drugs not carried by multidrug carriers expressed in blood-brain barrier should be regarded as the new treatment targets.

Neuropsychological findings related to the presence of pre-surgical comorbid depression in Latin-American patients with mesial temporal lobe epilepsy and hippocampal sclerosis

PURPOSE

To evaluate the neuropsychological findings related to the presence of pre-surgical comorbid depression in Latin-American patients with mesial temporal lobe epilepsy (MTLE) and unilateral hippocampal sclerosis (HS).

METHOD

Patients with drug-resistant MTLE and unilateral, left (L-) or right (R-) HS were studied. To diagnose depression, psychiatrists with expertise in epilepsy applied a semi-structured interview based on DSM. The depression group (DG) included patients with a psychiatric diagnosis in addition to a Beck Depression Inventory (BDI) score >16 points, and the non-depression group (NDG) included those without this diagnosis and with a BDI score ≤16. We analysed two clusters of neuropsychological tests, which evaluated memory (Complex Rey Figure III, Logical Memory II and RAVLT VII) and attention plus executive functions (Stroop I/II/III and Trail Making A/B). Moreover, we calculated the z-scores (Zs) using a local control group. The DG was compared to the NDG, independently and according to the HS side, using non-parametrical analyses. Due to the multivariate analysis, the p-value was corrected by applyingpost hoc Bonferroni adjustment.

RESULTS

We analysed 65 patients. The NDG included 51 (78.4 %) patients, and the DG included 14 (21.5 %) patients. Pre-surgical comorbid depression occurred in eight patients with L- (n = 29) and in six patients with R-MTLE-HS (n = 36). All of these groups had similar gender, age, IQs, and years of schooling. Compared to the healthy subjects, the L-MTLE-HS patients had lower Zs in verbal episodic memory tests [Logical Memory II (p < 0.001), and RAVLT VII (p < 0.001)], and the R-MTLE-HS patients had lower scores in visual episodic memory [Complex Rey Figure III (p < 0.001)]. In the analysis of the DGvs. NDG, there were no differences in the clusters of tests of memory or in those of attention and executive functions. Moreover, when we analysed the patients according to HS side, no neuropsychological difference was observed in the DG and NDG in terms of L- and R-MTLE-HS.

CONCLUSIONS

The patients with MTLE and unilateral HS in this study showed no differences in memory, attention and executive functions in relation to the presence of pre-surgical comorbid depression and independently of HS side. In this series from Latin-America, this psychiatric comorbidity did not affect cognition more than epilepsy alone.

Focal-to-bilateral motor seizures in temporal lobe epilepsy during video-EEG monitoring: effects on surgical outcome

The aim of this study was to determine whether the occurrence of focal-to-bilateral motor seizures in the course of partial drug withdrawal during video-EEG monitoring (FTBMS-M) had a predictive value for seizure recurrence in surgically treated patients with mesial temporal lobe epilepsy (MTLE). We analyzed the outcomes of 59 patients who underwent temporal lobe resection and had postoperative follow-up from 6 to 58 months. In total, 48 out of 59 patients were rendered seizure free (81.4%). We analyzed seizure recurrence after surgery with reference to: (i) occurrence of seizures after partial drug withdrawal during video-EEG monitoring (FTBMS-M); (ii) history of secondarily generalized seizures during antiepileptic drug treatment prior to presurgical evaluation (FTBMS-H) and (iii) other possible confounding factors (sex, age, epilepsy duration, side of surgery, presence of hippocampal sclerosis, and history of febrile seizures). We found no differences in the frequency of seizure recurrences between patients with FTBMS-M and patients without FTBMS-M (4/20 vs. 7/39; p = 0.848). Conversely, the frequency of seizure recurrence was significantly higher among the patients with FTBMS-H than among the patients without FTBMS-H (7/20 vs. 4/39; p = 0.021). The predictive value of FTBMS-H for postoperative seizure recurrence was confirmed in logistic regression analysis. We found a statistically significant influence of FTBMS-H on poor outcome after surgery, but not of FTBMS-M or other confounding variables, which suggests that withdrawal seizures do not affect post-surgical seizure control.

The morphological characteristics of hippocampus and thalamus in mesial temporal lobe epilepsy

Background

Mesial temporal lobe epilepsy (MTLE) is the most common form of focal epilepsy, which is frequently characterized by hippocampal sclerosis (HS). Accumulating studies have suggested widespread cortico-cortical connections related to MTLE. The role of subcortical structures involved in general epilepsy has been extensively investigated, but it is still limited in MTLE. Our purpose was to determine the specific morphological correlation between sclerotic hippocampal and thalamic sub-regions, using quantitative analysis, in MTLE.

Methods

In this study, 23 MTLE patients with unilateral hippocampal sclerosis and 24 healthy controls were examined with three-dimensional T1 MRI. Volume quantitative analysis in the hippocampus and thalamus was conducted and group-related volumetric difference was assessed. Moreover, vertex analysis was further performed using automated software to delineate detailed morphological patterns of the hippocampus and thalamus. The correlation was used to examine whether there is a relationship between volume changes of two subcortical structures and clinical characteristics.

Results

The patients had a significant volume decrease in the sclerotic hippocampus (p < 0.001). Compared to controls, obvious atrophic patterns were observed in the bilateral hippocampus in MTLE (p < 0.05). Only small patches of shrinkage were noted in the bilateral thalamus (p < 0.05). Moreover, the volume change of the hippocampus had a significant positive correlation with that of the thalamus (P < 0.001). Intriguingly, volume changes of the hippocampus and thalamus were correlated with the duration of epilepsy (hippocampus: P = 0.024; thalamus: P = 0.022). However, only volume changes of thalamus possibly differentiated between two prognostic groups in patients (P = 0.026).

Conclusions

We demonstrated the morphological characteristics of the hippocampus and thalamus in MTLE, providing new insights into the interrelated mechanisms between the hippocampus and thalamus, which have potential clinical significance for refining neuromodulated targets.

Expression of circulating microRNAs as predictors of diagnosis and surgical outcome in patients with mesial temporal lobe epilepsy with hippocampal sclerosis

MicroRNAs have been progressively investigated as post-transcriptional regulators playing important roles in epilepsy pathophysiology. Here we investigate three promising microRNAs (miR-27a-3p, miR-328-3p and miR-654-3p) previously described in the literature as possible peripheral biomarkers for epilepsy diagnose and surgical prognosis. Serum samples from 28 patients with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) were analyzed, 14 with good surgical prognosis (Engel I) and 14 with unfavorable surgical prognosis (Engel III-IV). Serum samples from 11 healthy volunteers were the control group. The microRNAs expression analysis was performed using real-time PCR. The present results did not endorse the role of miR-27a-3p as a peripheral biomarker for epilepsy diagnosis or surgical prognosis. MiR-328-3p, however, presented significant area under the curve (AUC) values when comparing controls to Engel I (90.3%), controls to Engel III-IV (96.8%) and controls to Engel I + Engel III-IV (i.e., epilepsy patients, AUC = 93.5%). Additionally, miR-654-3p displayed AUC = 74.7% when comparing controls to Engel I patients (p = 0.004), and AUC = 73.6% (p = 0.04) in the attempt to discriminate unfavorable from favorable surgical prognosis. In conclusion, the ANOVA and ROC analyzes with the respective AUC, specificity and sensitivity values allows us to conclude that miR-328-3p is the most important peripheral biomarker for the diagnosis of MTLE-HS. In terms of predicting the surgical prognosis of MTLE-HS patients, miR-654-3p proved to be the only microRNA evaluated to present statistical power to differentiate, as a peripheral biomarker, Engel I from Engel III-IV patients.

Heritability of alpha and sensorimotor network changes in temporal lobe epilepsy

OBJECTIVE

Electroencephalography (EEG) features in the alpha band have been shown to differ between people with epilepsy and healthy controls. Here, in a group of patients with mesial temporal lobe epilepsy (mTLE), we seek to confirm these EEG features, and using simultaneous functional magnetic resonance imaging, we investigate whether brain networks related to the alpha rhythm differ between patients and healthy controls. Additionally, we investigate whether alpha abnormalities are found as an inherited endophenotype in asymptomatic relatives.

METHODS

We acquired scalp EEG and simultaneous EEG and functional magnetic resonance imaging in 24 unrelated patients with unilateral mTLE, 23 asymptomatic first-degree relatives of patients with mTLE, and 32 healthy controls. We compared peak alpha power and frequency from electroencephalographic data in patients and relatives to healthy controls. We identified brain networks associated with alpha oscillations and compared these networks in patients and relatives to healthy controls.

RESULTS

Patients had significantly reduced peak alpha frequency (PAF) across all parietal and occipital electrodes. Asymptomatic relatives also had significantly reduced PAF over 14 of 17 parietal and occipital electrodes. Both patients and asymptomatic relatives showed a combination of increased activation and a failure of deactivation in relation to alpha oscillations compared to healthy controls in the sensorimotor network.

INTERPRETATION

Genetic factors may contribute to the shift in PAF and alterations in brain networks related to alpha oscillations. These may not entirely be a consequence of anti-epileptic drugs, seizures or hippocampal sclerosis and deserve further investigation as mechanistic contributors to mTLE.

Hippocampal granule cell dispersion: a non-specific finding in pediatric patients with no history of seizures

Chronic epilepsy has been associated with hippocampal abnormalities like neuronal loss, gliosis and granule cell dispersion. The granule cell layer of a normal human hippocampal dentate gyrus is traditionally regarded as a compact neuron-dense layer. Histopathological studies of surgically resected or autopsied hippocampal samples primarily from temporal lobe epilepsy patients, as well as animal models of epilepsy, describe variable patterns of granule cell dispersion including focal cell clusters, broader thick segments, and bilamination or “tram-tracking”. Although most studies have implicated granule cell dispersion as a specific feature of chronic epilepsy, very few “non-seizure” controls were included in these published investigations. Our retrospective survey of 147 cadaveric pediatric human hippocampi identified identical morphological spectra of granule cell dispersion in both normal and seizure-affected brains. Moreover, sections across the entire antero-posterior axis of a control cadaveric hippocampus revealed repetitive occurrence of different morphologies of the granule cell layer – compact, focally disaggregated and bilaminar. The results indicate that granule cell dispersion is within the spectrum of normal variation and not unique to patients with epilepsy. We speculate that sampling bias has been responsible for an erroneous dogma, which we hope to rectify with this investigation.

Localization of cerebral hypoperfusion in dogs with refractory and non-refractory epilepsy using [99mTc] ethyl cysteinate dimer and single photon emission computed tomography

To evaluate the localization of functional deficit area in epileptogenic zones of the brain in seven refractory and seven non-refractory epilepsy dogs using technetium 99m labeled with ethyl cysteinate dimer and interictal single photon emission computed tomography [^99mTc-ECD SPECT] co-registration with Magnetic Resonance Imaging (MRI). Regions showing perfusion deficits in the SPECT images were analyzed by using the standard semiquantitative evaluation method to compare the level of cortical perfusion to the maximum number of counts within the cerebellum (max C), considered the area of reference. This study showed that SPECT imaging revealed abnormalities in several regions of the brain in both epilepsy groups. The refractory epilepsy dogs showed more frequency area of hypoperfusion in temporal lobe than non-refractory group with not statistically significance (P=0.28). The result suggests the lesion in temporal might be relevance with refractory epilepsy in canine patients.

Granule Cell Dispersion in Human Temporal Lobe Epilepsy: Proteomics Investigation of Neurodevelopmental Migratory Pathways

Granule cell dispersion (GCD) is a common pathological feature observed in the hippocampus of patients with Mesial Temporal Lobe Epilepsy (MTLE). Pathomechanisms underlying GCD remain to be elucidated, but one hypothesis proposes aberrant reactivation of neurodevelopmental migratory pathways, possibly triggered by febrile seizures. This study aims to compare the proteomes of basal and dispersed granule cells in the hippocampus of eight MTLE patients with GCD to identify proteins that may mediate GCD in MTLE. Quantitative proteomics identified 1,882 proteins, of which 29% were found in basal granule cells only, 17% in dispersed only and 54% in both samples. Bioinformatics analyses revealed upregulated proteins in dispersed samples were involved in developmental cellular migratory processes, including cytoskeletal remodeling, axon guidance and signaling by Ras homologous (Rho) family of GTPases (P < 0.01). The expression of two Rho GTPases, RhoA and Rac1, was subsequently explored in immunohistochemical and in situ hybridization studies involving eighteen MTLE cases with or without GCD, and three normal post mortem cases. In cases with GCD, most dispersed granule cells in the outer-granular and molecular layers have an elongated soma and bipolar processes, with intense RhoA immunolabeling at opposite poles of the cell soma, while most granule cells in the basal granule cell layer were devoid of RhoA. A higher percentage of cells expressing RhoA was observed in cases with GCD than without GCD (P < 0.004). In GCD cases, the percentage of cells expressing RhoA was significantly higher in the inner molecular layer than the granule cell layer (P < 0.026), supporting proteomic findings. In situ hybridization studies using probes against RHOA and RAC1 mRNAs revealed fine peri- and nuclear puncta in granule cells of all cases. The density of cells expressing RHOA mRNAs was significantly higher in the inner molecular layer of cases with GCD than without GCD (P = 0.05). In summary, our study has found limited evidence for ongoing adult neurogenesis in the hippocampus of patients with MTLE, but evidence of differential dysmaturation between dispersed and basal granule cells has been demonstrated, and elevated expression of Rho GTPases in dispersed granule cells may contribute to the pathomechanisms underpinning GCD in MTLE.

Multidimensional associations between cognition and connectome organization in temporal lobe epilepsy

OBJECTIVE

Temporal lobe epilepsy (TLE) is known to affect large-scale structural networks and cognitive function in multiple domains. The study of complex relations between structural network organization and cognition requires comprehensive analytical methods and a shift towards multivariate techniques. Here, we sought to identify multidimensional associations between cognitive performance and structural network topology in TLE.

METHODS

We studied 34 drug-resistant adult TLE patients and 24 age- and sex-matched healthy controls. Participants underwent a comprehensive neurocognitive battery and multimodal MRI, allowing for large-scale connectomics, and morphological evaluation of subcortical and neocortical regions. Using canonical correlation analysis, we identified a multivariate mode that links cognitive performance to a brain structural network. Our approach was complemented by bootstrap-based hierarchical clustering to derive cognitive subtypes and associated patterns of macroscale connectome anomalies.

RESULTS

Both methodologies provided converging evidence for a close coupling between cognitive impairments across multiple domains and large-scale structural network compromise. Cognitive classes presented with an increasing gradient of abnormalities (increasing cortical and subcortical atrophy and less efficient white matter connectome organization in patients with increasing degrees of cognitive impairments). Notably, network topology characterized cognitive performance better than morphometric measures did.

CONCLUSIONS

Our multivariate approach emphasized a close coupling of cognitive dysfunction and large-scale network anomalies in TLE. Our findings contribute to understand the complexity of structural connectivity regulating the heterogeneous cognitive deficits found in epilepsy.

Social impairment and stigma in genetic generalized epilepsies

INTRODUCTION

Patients with epilepsy have poor social outcome. Multifactorial factors are usually involved, but among them, stigma features may have an important role. Genetic generalized epilepsies (GGEs) were previously considered "benign" syndromes. The aim of our study was to assess social impairment and stigma in GGE and to evaluate differences between the following GGE subsyndromes: juvenile myoclonic epilepsy (JME), juvenile absence epilepsy (JAE), and generalized tonic-clonic seizures alone (GTCSA). Additionally, we compared these outcomes with outcomes from a cohort of patients with epilepsy with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), a severe and difficult-to-treat syndrome. Results were compared with social data from the general population.

METHODS

Adult patients with epilepsy with a previously classified GGE or MTLE-HS were consecutively invited to fill in a sociodemographic and stigma questionnaire in outpatient clinic. Clinical data and psychiatric comorbidities were retrieved from clinical notes.

RESULTS

Questionnaires from 333 patients were obtained: 226/67% from patients with GGE (JME: 106/31.8%, GTCSA: 74/22.2%, and JAE: 46/13.8%) and 107/32.1% from patients with MTLE-HS. We found that patients with GGE have a good academic achievement but they have increased difficulties in finding a partner, higher rates of divorce, and a reduced number of children per woman and per man when compared with general population. We also observed that patients with GGE have higher rates of unemployment (22.6%) and lower monthly income than general population. Severe problems in housing were only seen in GGEs. Of these, 3 patients (1.3%) were in homeless condition. Over half (52%) of patients with MTLE-HS and over a quarter (28%) of patients with GGE experienced felt stigma. Psychiatric comorbidity was highly prevalent among GGE (34.1%), especially in patients with refractory epilepsy. Mood and anxiety disorders were the most prevalent conditions. No other significant differences were found between GGE subsyndromes.

DISCUSSION

We found an impairment in every social domain assessed (except in level of education) when compared with general population. Most of the social outcome parameters were unexpectedly close or similar to MTLE-HS or even worse as it was the prevalence of homelessness among GGE. Social impairment is underdiagnosed and might be considered in clinical practice even in syndromes for some time considered benign such as GGE.

Modulation of NMDA receptor by miR-219 in the amygdala and hippocampus of patients with mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy with hippocampal sclerosis is the most frequent form of focal epilepsy in adults, and it is often refractory to drug treatment. Regardless of the efforts on developing new antiepileptic drugs for refractory cases, studies suggest a need for better understanding the molecular bases of epilepsy. The microRNAs have been progressively investigated as potential targets for both epilepsy mechanisms elucidation and treatment. Therefore, the goal of this study was to evaluate the differential expression of miR-219, miR-181b, and miR-195, previously described as regulators of the excitatory neurotransmitter receptors NMDA-R1 and AMPA-GluR2 and inhibitory neurotransmitter GABA_A (α2, β3, and γ2 subunits) in the amygdala and hippocampus of patients with mesial temporal lobe epilepsy. Based on genes and miRNAs' quantitative Polymerase Chain Reaction (qPCR) from 18 patients with epilepsy, our results showed an inverse relationship between miR-219 and NMDA-NR1 expression in both the amygdala and hippocampus in comparison to their expression in controls. NR1 and GluR2 were upregulated in the amygdala of epileptic patients. Low miR-195 expression was observed in the amygdala of patients with epilepsy. Our findings indicate that miR-219 has a possible regulatory role in excitatory neurotransmission in patients with epilepsy, contributing to the new avenue of miRNA biology in drug-resistant epilepsy, reserving huge potential for future applications and clinical interventions in conjunction with existing therapies.

Hippocampal microstructural architecture and surgical outcome: Hippocampal diffusivity could predict seizure relapse

PURPOSE

Our aim was to study the microstructural architecture of the contralateral hippocampus to the affected side in patients with temporal lobe epilepsy with hippocampal sclerosis (TLE-HS) and its relation with surgical outcome.

METHOD

We included 33 consecutive patients evaluated in our epilepsy surgery program during a five-year period. They underwent a presurgical MRI with volumetric T1 and diffusion weighted sequences. 22 patients with TLE-HS (13 women, 12 right TLE-HS) were finally selected. Median follow-up after surgery was 6.25 years (4.5-8.83 years). We segmented the hippocampal subfields of the contralateral hippocampus using FreeSurfer and calculated the fractional anisotropy (FA) and the mean diffusivity (MD) of each subfield. We also scanned 18 healthy age-matched controls.

RESULTS

After surgery, 50 % of the patients (n = 11) remained seizure-free (SF) following surgery. Comparing non-SF to SF patients, the MD showed increased values of the CA1 (p = 0.035), the molecular layer (p = 0.010) and the dentate gyrus (p = 0.041) in the healthy hippocampus. Using a cut-off point for a survival analysis, we found that patients with lower values of MD of the molecular layer and the CA1 remained SF during long-term post-operative follow-up (p < 0.0001).

CONCLUSIONS

The contralateral hippocampal internal microstructure may have be implicated in post-surgery seizure freedom in patients with TLE-HS.

Ryanodine receptors drive neuronal loss and regulate synaptic proteins during epileptogenesis

Status epilepticus (SE) is a clinical emergency that can lead to the development of temporal lobe epilepsy (TLE). The development and maintenance of spontaneous seizures in TLE are linked to calcium (Ca⁺²)-dependent processes such as neuronal cell loss and pathological synaptic plasticity. It has been shown that SE produces an increase in ryanodine receptor-dependent intracellular Ca⁺² levels in hippocampal neurons, which remain elevated during the progression of the disease. However, the participation of ryanodine receptors (RyRs) in the neuronal loss and circuitry rewiring that take place in the hippocampus after SE remains unknown. In this context, we first investigated the functional role of RyRs on the expression of synaptic and plasticity-related proteins during epileptogenesis induced by pilocarpine in Wistar rats. Intrahippocampal injection of dantrolene, a selective pharmacological blocker of RyRs, caused the increase of the presynaptic protein synapsin I (SYN) and synaptophysin (SYP) 48 h after SE induction. Specifically, we observed that SYN and SYP were regulated in hippocampal regions known to receive synaptic inputs, revealing that RyRs could be involved in network changes and/or neuronal protection after SE induction. In order to investigate whether the changes in SYN and SYP were related to neuroplastic changes that could contribute to pathological processes that occur after SE, we evaluated the levels of activity-regulated cytoskeleton-associated protein (ARC) and mossy fiber sprouting in the dentate gyrus (DG). Interestingly, we observed that although SE induced the appearance of intense ARC-positive cells, dantrolene treatment did not change the levels of ARC in both western blot and immunofluorescence analyses. Accordingly, in the same experimental conditions, we were not able to detect changes in the levels of both pre- and post-synaptic plasticity-related proteins, growth associated protein-43 (GAP-43) and postsynaptic density protein-95 (PSD-95), respectively. Additionally, the density of mossy fiber sprouting in the DG was not increased by dantrolene treatment. We next examined the effects of intrahippocampal injection of dantrolene on neurodegeneration. Notably, dantrolene promoted neuroprotective effects by decreasing neuronal cell loss in CA1 and CA3, which explains the increased levels of synaptic proteins, and the apparent lack of positive effect on pathological plasticity. Taken together, our results revealed that RyRs may have a major role in the hippocampal neurodegeneration associated to the development of acquired epilepsy.