Secondarily generalized seizures in temporal lobe epilepsy

Altered Metabolic Networks in Mesial Temporal Lobe Epilepsy with Focal to Bilateral Seizures

This study was designed to identify whether the metabolic network changes in mesial temporal lobe epilepsy (MTLE) patients with focal to bilateral tonic-clonic seizures (FBTCS) differ from changes in patients without FBTCS. This retrospective analysis enrolled 30 healthy controls and 54 total MTLE patients, of whom 27 had FBTCS. Fluorodeoxyglucose positron emission tomography (FDG-PET) data and graph theoretical analyses were used to examine metabolic connectivity. The differences in metabolic networks between the three groups were compared. Significant changes in both local and global network topology were evident in FBTCS+ patients as compared to healthy controls, with a lower assortative coefficient and altered betweenness centrality in 15 brain regions. While global network measures did not differ significantly when comparing FBTCS- patients to healthy controls, alterations in betweenness centrality were evident in 13 brain regions. Significantly altered betweenness centrality was also observed in four brain regions when comparing patients with and without FBTCS. The study revealed greater metabolic network abnormalities in MTLE patients with FBTCS as compared to FBTCS- patients, indicating the existence of distinct epileptogenic networks. These findings can provide insight into the pathophysiological basis of FBTCS.

Dynamics of AMPA receptors regulate epileptogenesis in patients with epilepsy

The excitatory glutamate α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) contribute to epileptogenesis. Thirty patients with epilepsy and 31 healthy controls are scanned using positron emission tomography with our recently developed radiotracer for AMPARs, [¹¹C]K-2, which measures the density of cell-surface AMPARs. In patients with focal-onset seizures, an increase in AMPAR trafficking augments the amplitude of abnormal gamma activity detected by electroencephalography. In contrast, patients with generalized-onset seizures exhibit a decrease in AMPARs coupled with increased amplitude of abnormal gamma activity. Patients with epilepsy had reduced AMPAR levels compared with healthy controls, and AMPARs are reduced in larger areas of the cortex in patients with generalized-onset seizures compared with those with focal-onset seizures. Thus, epileptic brain function can be regulated by the enhanced trafficking of AMPAR due to Hebbian plasticity with increased simultaneous neuronal firing and compensational downregulation of cell-surface AMPARs by the synaptic scaling.

Early identification of seizure freedom with medical treatment in patients with mesial temporal lobe epilepsy and hippocampal sclerosis

BACKGROUND

Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is usually associated with a poor response to antiseizure medications. We focused on MTLE-HS patients who were seizure free on medication to: (1) determine the clinical factors associated with seizure freedom and (2) develop a machine-learning classifier to better earlier identify those patients.

METHODS

We performed a retrospective, multicentric study comparing 64 medically treated seizure-free MTLE-HS patients with 200 surgically treated drug-resistant MTLE-HS patients. First, we collected medical history and seizure semiology data. Then, we developed a machine-learning classifier based on clinical data.

RESULTS

Medically treated seizure-free MTLE-HS patients were seizure-free for at least 2 years, and for a median time of 7 years at last follow-up. Compared to drug-resistant MTLE-HS patients, they exhibited: an older age at epilepsy onset (22.5 vs 8.0 years, p < 0.001), a lesser rate of: febrile seizures (39.0% vs 57.5%, p = 0.035), focal aware seizures (previously referred to as aura)(56.7% vs 90.0%, p < 0.001), autonomic focal aware seizures in presence of focal aware seizure (17.6% vs 59.4%, p < 0.001), dystonic posturing of the limbs (9.8% vs 47.0%, p < 0.001), gestural (27.4% vs 94.0%, p < 0.001), oro-alimentary (32.3% vs 75.5%, p < 0.001) or verbal automatisms (12.9% vs 36.0%, p = 0.001). The classifier had a positive predictive value of 0.889, a sensitivity of 0.727, a specificity of 0.962, a negative predictive value of 0.893.

CONCLUSIONS

Medically treated seizure-free MTLE-HS patients exhibit a distinct clinical profile. A classifier built with readily available clinical data can identify them accurately with excellent positive predictive value. This may help to individualize the management of MTLE-HS patients according to their expected pharmacosensitivity.

Temporally Targeted Interactions With Pathologic Oscillations as Therapeutical Targets in Epilepsy and Beyond

Self-organized neuronal oscillations rely on precisely orchestrated ensemble activity in reverberating neuronal networks. Chronic, non-malignant disorders of the brain are often coupled to pathological neuronal activity patterns. In addition to the characteristic behavioral symptoms, these disturbances are giving rise to both transient and persistent changes of various brain rhythms. Increasing evidence support the causal role of these "oscillopathies" in the phenotypic emergence of the disease symptoms, identifying neuronal network oscillations as potential therapeutic targets. While the kinetics of pharmacological therapy is not suitable to compensate the disease related fine-scale disturbances of network oscillations, external biophysical modalities (e.g., electrical stimulation) can alter spike timing in a temporally precise manner. These perturbations can warp rhythmic oscillatory patterns via resonance or entrainment. Properly timed phasic stimuli can even switch between the stable states of networks acting as multistable oscillators, substantially changing the emergent oscillatory patterns. Novel transcranial electric stimulation (TES) approaches offer more reliable neuronal control by allowing higher intensities with tolerable side-effect profiles. This precise temporal steerability combined with the non- or minimally invasive nature of these novel TES interventions make them promising therapeutic candidates for functional disorders of the brain. Here we review the key experimental findings and theoretical background concerning various pathological aspects of neuronal network activity leading to the generation of epileptic seizures. The conceptual and practical state of the art of temporally targeted brain stimulation is discussed focusing on the prevention and early termination of epileptic seizures.

Characterizing Hippocampal Oscillatory Signatures Underlying Seizures in Temporal Lobe Epilepsy

Temporal Lobe Epilepsy (TLE) is a neurological condition characterized by focal brain hyperexcitability, resulting in abnormal neuronal discharge and uncontrollable seizures. The hippocampus, with its inherently highly synchronized firing patterns and relatively high excitability, is prone to epileptic seizures, and it is usually the focus of TLE. Researchers have identified hippocampal high-frequency oscillations (HFOs) as a salient feature in people with TLE and animal models of this disease, arising before or at the onset of the epileptic event. To a certain extent, these pathological HFOs have served as a marker and a potential target for seizure attenuation using electrical or optogenetic interventions. However, many questions remain about whether we can reliably distinguish pathological from non-pathological HFOs and whether they can tell us about the development of the disease. While this would be an arduous task to perform in humans, animal models of TLE provide an excellent opportunity to study the characteristics of HFOs in predicting how epilepsy evolves. This minireview will (1) summarize what we know about the oscillatory disruption in TLE, (2) summarize knowledge about oscillatory changes in the latent period and their role in predicting seizures, and (3) propose future studies essential to uncovering potential treatments based on early detection of pathological HFOs.

Closed-loop stimulation of the medial septum terminates epileptic seizures

Temporal lobe epilepsy with distributed hippocampal seizure foci is often intractable and its secondary generalization might lead to sudden death. Early termination through spatially extensive hippocampal intervention is not feasible directly, because of the large size and irregular shape of the hippocampus. In contrast, the medial septum is a promising target to govern hippocampal oscillations through its divergent connections to both hippocampi. Combining this 'proxy intervention' concept and precisely timed stimulation, we report here that closed-loop medial septum electrical stimulation can quickly terminate intrahippocampal seizures and suppress secondary generalization in a rat kindling model. Precise stimulus timing governed by internal seizure rhythms was essential. Cell type-specific stimulation revealed that the precisely timed activation of medial septum GABAergic neurons underlaid the effects. Our concept of time-targeted proxy stimulation for intervening pathological oscillations can be extrapolated to other neurological and psychiatric disorders, and has potential for clinical translation.

The Medial Septum as a Potential Target for Treating Brain Disorders Associated With Oscillopathies

The medial septum (MS), as part of the basal forebrain, supports many physiological functions, from sensorimotor integration to cognition. With often reciprocal connections with a broad set of peers at all major divisions of the brain, the MS orchestrates oscillatory neuronal activities throughout the brain. These oscillations are critical in generating sensory and emotional salience, locomotion, maintaining mood, supporting innate anxiety, and governing learning and memory. Accumulating evidence points out that the physiological oscillations under septal influence are frequently disrupted or altered in pathological conditions. Therefore, the MS may be a potential target for treating neurological and psychiatric disorders with abnormal oscillations (oscillopathies) to restore healthy patterns or erase undesired ones. Recent studies have revealed that the patterned stimulation of the MS alleviates symptoms of epilepsy. We discuss here that stimulus timing is a critical determinant of treatment efficacy on multiple time scales. On-demand stimulation may dramatically reduce side effects by not interfering with normal physiological functions. A precise pattern-matched stimulation through adaptive timing governed by the ongoing oscillations is essential to effectively terminate pathological oscillations. The time-targeted strategy for the MS stimulation may provide an effective way of treating multiple disorders including Alzheimer's disease, anxiety/fear, schizophrenia, and depression, as well as pain.

SPECT imaging of cerebral blood flow changes induced by acute trigeminal nerve stimulation in drug-resistant epilepsy. A pilot study

OBJECTIVE

To explore the cortical areas targeted by acute transcutaneous trigeminal nerve stimulation (TNS) in patients with drug-resistant epilepsy (DRE) using single photon emission computed tomography (SPECT).

METHODS

Ten patients with DRE underwent brain SPECT at baseline and immediately after a 20-minute TNS (0.25 ms; 120 Hz; 30 s ON and 30 s OFF) applied bilaterally to the infraorbital nerve. The French Color Standard International Scale was used for qualitative analyses and z-scores were used to calculate the Odds Ratio (OR).

RESULTS

At baseline global hypoperfusion (mainly in temporo-mesial, temporo-parietal and fronto-temporal and temporo-occipital areas) was detected in all patients. Following TNS, a global increase in cortical tracer uptake and a significant decrease in median hypoperfusion score were observed. A significant effect favoring a general TNS-induced increase in cortical perfusion (OR = 4.96; p = 0.0005) was detected in 70% of cases, with significant effects in the limbic (p = 0.003) and temporal (p = 0.003) lobes. Quantitative analyses of z-scores confirmed significant TNS-induced increases in perfusion in the temporal (+0.59 SDs; p = 0.001), and limbic (+0.43 SDs; p = 0.03) lobes.

CONCLUSION

Short-term TNS is followed a global increase in cortical perfusion, namely in the temporal and limbic lobes.

SIGNIFICANCE

The TNS-induced perfusion increase may reflect neurons' activity changes in cortical areas implicated in the epilepsy network.

Changes in resting-state cerebral blood flow and its connectivity in patients with focal to bilateral tonic-clonic seizures

Arterial spin labeling (ASL) is an important tool for understanding cerebral perfusion in epilepsy patients. The aim of this study was to explore patterns of change in cerebral blood flow (CBF) and CBF connectivity in patients with focal to bilateral tonic-clonic seizures (FBTCS). High-resolution three-dimensional (3-D) T1-weighted and 3-D pseudo-continuous ASL magnetic resonance imaging (MRI) was collected from 32 patients with FBTCS and 16 healthy volunteers using a 3.0 T MRI scanner. Cerebral blood flow and its connectivity were compared between the FBTCS and control group. Correlation analysis was used to explore relationships of CBF and its connectivity changes with clinical parameters. Cerebral blood flow data of spatial standardization and normalization were used to improve statistical power. Patients with FBTCS exhibited increased CBF in the bilateral thalamus, caudate nucleus, olfactory cortex, and gyrus rectus, but decreased CBF in the bilateral supplementary motor areas (SMA) and middle cingulate cortex (MCC). Patients with FBTCS showed significant positive correlation between CBF and gray matter volume (GMV) in bilateral SMA and MCC. No significant correlations between CBF and clinical parameters were found among FBTCS patients. The anterior cingulate cortex (ACC) showed positive CBF connectivity with the bilateral SMA and MCC, and these CBF connectivity measures differed significantly between groups (cluster-level, FWE-corrected, P < 0.001). These findings suggest that patients with FBTCS have changes in cerebral CBF and CBF connectivity, which may relate to the underlying neuropathology of FBTCS.

Focal to bilateral tonic-clonic seizures are associated with widespread network abnormality in temporal lobe epilepsy

OBJECTIVE

Our objective was to identify whether the whole-brain structural network alterations in patients with temporal lobe epilepsy (TLE) and focal to bilateral tonic-clonic seizures (FBTCS) differ from alterations in patients without FBTCS.

METHODS

We dichotomized a cohort of 83 drug-resistant patients with TLE into those with and without FBTCS and compared each group to 29 healthy controls. For each subject, we used diffusion-weighted magnetic resonance imaging to construct whole-brain structural networks. First, we measured the extent of alterations by performing FBTCS-negative (FBTCS-) versus control and FBTCS-positive (FBTCS+) versus control comparisons, thereby delineating altered subnetworks of the whole-brain structural network. Second, by standardizing each patient's networks using control networks, we measured the subject-specific abnormality at every brain region in the network, thereby quantifying the spatial localization and the amount of abnormality in every patient.

RESULTS

Both FBTCS+ and FBTCS- patient groups had altered subnetworks with reduced fractional anisotropy and increased mean diffusivity compared to controls. The altered subnetwork in FBTCS+ patients was more widespread than in FBTCS- patients (441 connections altered at t > 3, p < .001 in FBTCS+ compared to 21 connections altered at t > 3, p = .01 in FBTCS-). Significantly greater abnormalities-aggregated over the entire brain network as well as assessed at the resolution of individual brain areas-were present in FBTCS+ patients (p < .001, d = .82, 95% confidence interval = .32-1.3). In contrast, the fewer abnormalities present in FBTCS- patients were mainly localized to the temporal and frontal areas.

SIGNIFICANCE

The whole-brain structural network is altered to a greater and more widespread extent in patients with TLE and FBTCS. We suggest that these abnormal networks may serve as an underlying structural basis or consequence of the greater seizure spread observed in FBTCS.

Cortical Excitability in Temporal Lobe Epilepsy with Bilateral Tonic-Clonic Seizures

OBJECTIVE

We investigated motor cortical excitability (CE) in unilateral temporal lobe epilepsy (TLE) and its relationship to bilateral tonic-clonic seizure (BTCS) using paired-pulse transcranial magnetic stimulation (TMS).

METHODS

In this cross-sectional study, we enrolled 46 unilateral TLE patients and 16 age-and sex-matched healthy controls. Resting motor thresholds (RMT); short-interval intracortical inhibition (SICI, GABAA receptor-mediated); facilitation (ICF, glutamatergic-mediated) with interstimulus intervals (ISIs) of 2, 5, 10, and 15 ms; and long-interval intracortical inhibition (LICI, GABAB receptor-mediated) with ISIs of 200-400 ms were measured via paired-pulse TMS. Comparisons were made between controls and patients with TLE, and then among the TLE subgroups (no BTCS, infrequent BTCS and frequent BTCS subgroup).

RESULTS

Compared with controls, TLE patients had higher RMT, lower SICI and higher LICI in both hemispheres, and higher ICF in the ipsilateral hemisphere. In patients with frequent BTCS, cortical hyperexcitability in the ipsilateral hemisphere was found in a parameter-dependent manner (SICI decreased at a stimulation interval of 5 ms, and ICF increased at a stimulation interval of 15 ms) compared with patients with infrequent or no BTCS.

CONCLUSIONS

Our results demonstrate that motor cortical hyper-excitability in the ipsilateral hemisphere underlies the epileptogenic network of patients with active BTCS, which is more extensive than those with infrequent or no BTCS.

Disrupted basal ganglia-thalamocortical loops in focal to bilateral tonic-clonic seizures

Focal to bilateral tonic-clonic seizures are associated with lower quality of life, higher risk of seizure-related injuries, increased chance of sudden unexpected death, and unfavourable treatment outcomes. Achieving greater understanding of their underlying circuitry offers better opportunity to control these seizures. Towards this goal, we provide a network science perspective of the interactive pathways among basal ganglia, thalamus and cortex, to explore the imprinting of secondary seizure generalization on the mesoscale brain network in temporal lobe epilepsy. Specifically, we parameterized the functional organization of both the thalamocortical network and the basal ganglia-thalamus network with resting state functional MRI in three groups of patients with different focal to bilateral tonic-clonic seizure histories. Using the participation coefficient to describe the pattern of thalamocortical connections among different cortical networks, we showed that, compared to patients with no previous history, those with positive histories of focal to bilateral tonic-clonic seizures, including both remote (none for >1 year) and current (within the past year) histories, presented more uniform distribution patterns of thalamocortical connections in the ipsilateral medial-dorsal thalamic nuclei. As a sign of greater thalamus-mediated cortico-cortical communication, this result comports with greater susceptibility to secondary seizure generalization from the epileptogenic temporal lobe to broader brain networks in these patients. Using interregional integration to characterize the functional interaction between basal ganglia and thalamus, we demonstrated that patients with current history presented increased interaction between putamen and globus pallidus internus, and decreased interaction between the latter and the thalamus, compared to the other two patient groups. Importantly, through a series of 'disconnection' simulations, we showed that these changes in interactive profiles of the basal ganglia-thalamus network in the current history group mainly depended upon the direct but not the indirect basal ganglia pathway. It is intuitively plausible that such disruption in the striatum-modulated tonic inhibition of the thalamus from the globus pallidus internus could lead to an under-suppressed thalamus, which in turn may account for their greater vulnerability to secondary seizure generalization. Collectively, these findings suggest that the broken balance between basal ganglia inhibition and thalamus synchronization can inform the presence and effective control of focal to bilateral tonic-clonic seizures. The mechanistic underpinnings we uncover may shed light on the development of new treatment strategies for patients with temporal lobe epilepsy.

Status epilepticus during correction of hyponatremia in a patient with Alzheimer's disease: A case report

An 83-year-old Japanese man with Alzheimer’s disease was admitted to our hospital for treatment of hyponatremia resulting from water intoxication. During hospitalization, the patient developed focal impaired awareness seizures, focal to bilateral tonic-clonic seizures, and subsequent status epilepticus. Electroencephalogram during focal impaired awareness seizures showed rhythmic 5–9 Hz theta activity in the right frontotemporal region. Electroencephalogram during focal to bilateral tonic-clonic seizures showed bilateral polyspikes. Electroencephalogram during an interseizure period revealed sharp waves in the right frontal region. Continuous intravenous administration of midazolam was the only effective treatment for status epilepticus. The patient died of aspiration pneumonia on day 58. Hyponatremia-associated status epilepticus is rare; in the present case, multifocal epileptogenicity resulting from Alzheimer’s disease and hyponatremia-associated elevation of glutamate levels in the synaptic cleft may have contributed to the onset of focal to bilateral tonic-clonic seizures with subsequent status epilepticus.

Effects of Prolonged Seizures on Basal Forebrain Cholinergic Neurons: Evidence and Potential Clinical Relevance

Seizures originating from limbic structures, especially when prolonged for several minutes/hours up to status epilepticus (SE), can cause specific neurodegenerative phenomena in limbic and subcortical structures. The cholinergic nuclei belonging to the basal forebrain (BF) (namely, medial septal nucleus (MSN), diagonal band of Broca (DBB), and nucleus basalis of Meynert (NBM)) belong to the limbic system, while playing a pivotal role in cognition and sleep-waking cycle. Given the strong interconnections linking these limbic nuclei with limbic cortical structures, a persistent effect of SE originating from limbic structures on cBF morphology is plausible. Nonetheless, only a few experimental studies have addressed this issue. In this review, we describe available data and discuss their significance in the scenario of seizure-induced brain damage. In detail, the manuscript moves from a recent study in a model of focally induced limbic SE, in which the pure effects of seizure spreading through the natural anatomical pathways towards the cholinergic nuclei of BF were tracked by neuronal degeneration. In this experimental setting, a loss of cholinergic neurons was measured in all BF nuclei, to various extents depending on the specific nucleus. These findings are discussed in the light of the effects on the very same nuclei following SE induced by systemic injections of kainate or pilocarpine. The various effects including discrepancies among different studies are discussed. Potential implications for human diseases are included.

Oscillotherapeutics - Time-targeted interventions in epilepsy and beyond

Oscillatory brain activities support many physiological functions from motor control to cognition. Disruptions of the normal oscillatory brain activities are commonly observed in neurological and psychiatric disorders including epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, anxiety/trauma-related disorders, major depressive disorders, and drug addiction. Therefore, these disorders can be considered as common oscillation defects despite having distinct behavioral manifestations and genetic causes. Recent technical advances of neuronal activity recording and analysis have allowed us to study the pathological oscillations of each disorder as a possible biomarker of symptoms. Furthermore, recent advances in brain stimulation technologies enable time- and space-targeted interventions of the pathological oscillations of both neurological disorders and psychiatric disorders as possible targets for regulating their symptoms.

Effects of Branched-Chain Amino Acid Supplementation on Spontaneous Seizures and Neuronal Viability in a Model of Mesial Temporal Lobe Epilepsy

BACKGROUND

The essential branched-chain amino acids (BCAAs) leucine, isoleucine, and valine have recently emerged as a potential novel treatment for medically refractory epilepsy. Blood-derived BCAAs can readily enter the brain, where they contribute to glutamate biosynthesis and may either suppress or trigger acute seizures. However, the effects of BCAAs on chronic (ie, spontaneous recurrent) seizures and epilepsy-associated neuron loss are incompletely understood.

MATERIALS AND METHODS

Sixteen rats with mesial temporal lobe epilepsy were randomized into 2 groups that could drink, ad libitum, either a 4% solution of BCAAs in water (n=8) or pure water (n=8). The frequency and relative percent of convulsive and nonconvulsive spontaneous seizures were monitored for a period of 21 days, and the brains were then harvested for immunohistochemical analysis.

RESULTS

Although the frequency of convulsive and nonconvulsive spontaneous recurrent seizures over a 3-week drinking/monitoring period were not different between the groups, there were differences in the relative percent of convulsive seizures in the first and third week of treatment. Moreover, the BCAA-treated rats had over 25% fewer neurons in the dentate hilus of the hippocampus compared with water-treated controls.

CONCLUSIONS

Acute BCAA supplementation reduces seizure propagation, whereas chronic oral supplementation with BCAAs worsens seizure propagation and causes neuron loss in rodents with mesial temporal lobe epilepsy. These findings raise the question of whether such supplementation has a similar effect in humans.

Prognostic factors of postoperative seizure outcome in patients with temporal lobe epilepsy and normal magnetic resonance imaging

PURPOSE

To retrospectively analyse a single-centre consecutive surgical series of patients with temporal lobe epilepsy (TLE) and negative MRI. To identify factors associated with postoperative seizure outcome among several presurgical, surgical and postsurgical variables.

METHODS

Clinical records of 866 patients who received temporal lobe resections and with a minimum follow-up of 12 months were retrospectively searched for MRI-negative cases. Anamnestic, clinical, neurophysiological, surgical, histopathological and postsurgical data were collected. Seizure outcome was categorised as favourable (Engel's class I) and unfavourable (Engel's classes II-IV). Uni- and multivariate statistical analysis was performed to identify variables having a significant association with seizure outcome.

RESULTS

Forty-eight patients matched the inclusion criteria. 26 (54.1%) patients required invasive EEG evaluation with Stereo-electro-encephalography (SEEG) before surgery. Histological evaluation was unremarkable in 34 cases (70.8%), revealed focal cortical dysplasias in 13 cases and hippocampal sclerosis in 2. 28 (58.3%) patients were in Engel's class I after a mean follow-up of 82 months (SD ± 74; range 12-252). Multivariate analysis indicated auditory aura, contralateral diffusion of the discharge at Video-EEG monitoring and use of ¹⁸F-FDG PET as variables independently associated with seizure outcome.

CONCLUSION

Carefully selected patients with MRI-negative TLE can be good candidates for surgery. Surgery should be considered with caution in patients with clinical features of neocortical seizure onset and contralateral propagation of the discharge. Use of ¹⁸F-FDG PET may be helpful to improve SEEG and surgical strategies. The presented data help in optimising the selection of patients with MRI-negative TLE with good chances to benefit from surgery.

Depolarized GABAergic Signaling in Subicular Microcircuits Mediates Generalized Seizure in Temporal Lobe Epilepsy

Secondary generalized seizure (sGS) is a major source of disability in temporal lobe epilepsy (TLE) with unclear cellular/circuit mechanisms. Here we found that clinical TLE patients with sGS showed reduced volume specifically in the subiculum compared with those without sGS. Further, using optogenetics and extracellular electrophysiological recording in mouse models, we found that photoactivation of subicular GABAergic neurons retarded sGS acquisition by inhibiting the firing of pyramidal neurons. Once sGS had been stably acquired, photoactivation of GABAergic neurons aggravated sGS expression via depolarized GABAergic signaling. Subicular parvalbumin, but not somatostatin subtype GABAergic, neurons were easily depolarized in sGS expression. Finally, photostimulation of subicular pyramidal neurons genetically targeted with proton pump Arch, rather than chloride pump NpHR3.0, alleviated sGS expression. These results demonstrated that depolarized GABAergic signaling in subicular microcircuit mediates sGS in TLE. This may be of therapeutic interest in understanding the pathological neuronal circuitry underlying sGS. VIDEO ABSTRACT.

Localized shape abnormalities in the thalamus and pallidum are associated with secondarily generalized seizures in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (mTLE) is a common type of drug-resistant epilepsy and secondarily generalized tonic-clonic seizures (sGTCS) have devastating consequences for patients' safety and quality of life. To probe the mechanism underlying the genesis of sGTCS, we investigated the structural differences between patients with and without sGTCS in a cohort of mTLE with radiologically defined unilateral hippocampal sclerosis. We performed voxel-based morphometric analysis of cortex and vertex-wise shape analysis of subcortical structures (the basal ganglia and thalamus) on MRI of 39 patients (21 with and 18 without sGTCS). Comparisons were initially made between sGTCS and non-sGTCS groups, and subsequently made between uncontrolled-sGTCS and controlled-sGTCS subgroups. Regional atrophy of the ipsilateral ventral pallidum (cluster size=450 voxels, corrected p=0.047, Max voxel coordinate=107, 120, 65), medial thalamus (cluster size=1128 voxels, corrected p=0.049, Max voxel coordinate=107, 93, 67), middle frontal gyrus (cluster size=60 voxels, corrected p<0.05, Max voxel coordinate=-30, 49.5, 6), and contralateral posterior cingulate cortex (cluster size=130 voxels, corrected p<0.05, Max voxel coordinate=16.5, -57, 27) was found in the sGTCS group relative to the non-sGTCS group. Furthermore, the uncontrolled-sGTCS subgroup showed more pronounced atrophy of the ipsilateral medial thalamus (cluster size=1240 voxels, corrected p=0.014, Max voxel coordinate=107, 93, 67) than the controlled-sGTCS subgroup. These findings indicate a central role of thalamus and pallidum in the pathophysiology of sGTCS in mTLE.

Medial temporal lobe epilepsy associated with hippocampal sclerosis is a distinctive syndrome

Epileptic syndromes are distinctive disorders with specific features, which when taken together, permit a specific diagnosis. There is actually a debate on that medial temporal lobe epilepsy with hippocampal sclerosis is an epileptic syndrome. To address this issue, we searched for discriminative semiological features between temporal lobe epilepsy patients with hippocampal sclerosis (TLE-HS patients or group 1), TLE patients with medial structural lesion other than hippocampal sclerosis or in MRI-negative cases with medial onset on further investigations (group 2) and lateral TLE patients (LTLE or group 3). We retrospectively collected data from medical and EEG-video records of 523 TLE patients, referred for surgery to the Pitié-Salpêtrière Epileptology Unit between 1991 and 2014. We identified 389 patients belonging to group 1, 61 patients belonging to group 2, and 73 patients belonging to group 3 and performed a comparative analysis of their clinical data and surgical outcomes. TLE-HS patients (group 1): (1) began epilepsy earlier (11 ± 9 vs. 20 ± 10 vs. 15 ± 9 years); (2) exhibited more frequently early febrile convulsions (FC) (59 vs 7 vs 5%); (3) presented more: ictal gestural automatisms (90 vs 54 vs 67%), dystonic posturing (47 vs 20 vs 23%), and secondary generalized tonic-clonic seizures (GTCS) (70 vs 44% vs 48%) as compared to both groups 2 and 3 patients (all p < 0.001). With respect to auras, abdominal visceral auras were more reported by TLE-HS than by LTLE patients (49 vs 16%). Three cardinal criteria correctly classified 94% of patients into TLE-HS group: history of FC, dystonic posturing, and secondary GTCS. Postoperative outcome was significantly better in TLE-HS group than in the two other groups (p = 0.03 and 0.003). Our study demonstrates that cardinal criteria are reliably helpful to distinguish patients with TLE-HS from those with other TLE and may allow considering TLE-HS as a distinctive syndrome.

Cardiac Asystole Triggered by Temporal Lobe Epilepsy with Amygdala Enlargement

A 25-year-old previously healthy man was hospitalized for syncope. While standing, he suddenly lost consciousness, followed by a generalized tonic clonic seizure. An electrocardiogram demonstrated asystole. No cardiac abnormalities were detected on the echocardiogram, cardiac magnetic resonance imaging (MRI), positron emission tomography, or a coronary angiogram. An electrophysiological study showed normal sinus node and atrioventricular node function. An electroencephalogram revealed small spike waves in the fronto-temporal region. Brain MRI demonstrated a left-sided amygdala enlargement. To the best of our knowledge, this is the first case of temporal lobe epilepsy with an amygdala enlargement that induced cardiac asystole.

Hippocampal sclerosis in feline epilepsy

Hippocampal sclerosis (HS) refers to loss of hippocampal neurons and astrogliosis. In temporal lobe epilepsy (TLE), HS is a key factor for pharmacoresistance, even though the mechanisms are not quite understood. While experimental TLE models are available, there is lack of models reflecting the natural HS development. Among domestic animals, cats may present with TLE-like seizures in natural and experimental settings. With this study on the prevalence, segmental pattern and clinicopathological correlates of feline HS, we evaluated the translational value for human research. Evaluation schemes for human brains were applied to epileptic cats. The loss of neurons was morphometrically assessed and the degree of gliosis was recorded. Hippocampal changes resembling human HS were seen in about one third of epileptic cats. Most of these were associated with infiltrative diseases such as limbic encephalitis. Irrespective of the etiology and semiology of seizures, total hippocampal sclerosis was the most prevalent form seen in epileptic animals. Other HS types also occur at varying frequencies. Segmental differences to human HS can be explained by species-specific synaptic connectivities and a different spectrum of etiologies. All these variables require consideration when translating results from feline studies regarding seizure-associated changes of the temporal lobe and especially HS.

Neurotrophin receptors expression in mesial temporal lobe epilepsy with and without psychiatric comorbidities and their relation with seizure type and surgical outcome

Epilepsy and psychiatric comorbidities are frequently associated, but their common biological substrate is unknown. We have previously reported altered structural elements and neurotrophins (NTs) expression in mesial temporal lobe epilepsy (MTLE) patients with psychiatric comorbidities. NTs receptors can regulate neurotransmission and promote neuroplasticity, being important candidates in the regulation and manifestation of psychopatological states and seizure-related events. MTLE hippocampi of subjects without psychiatric history, MTLE + major depression, MTLE + interictal psychosis derived from epilepsy surgery, and control necropsies were investigated for p75^NTR, TrkB, TrkA, and TrkC immunohistochemistry. Increased expression of p75^NTR, decreased TrkA, unaltered TrkC, and complex alterations involving TrkB expression were seen in MTLE groups. Increased TrkB expression in patients without complete seizure remission and in those with secondarily generalized seizures was seen. Decreased p75^NTR expression associated with interictal psychosis, and increased TrkB in those with psychosis or major depression was also reported, although their p75^NTR/TrkB ratios were lower than in MTLE without psychiatric comorbidities. Our results provide evidence of alterations in expression of NTs receptors in the epileptogenic hippocampus that are differentially modulated in presence of psychiatric comorbidities. As already explored in animal models, even in chronic human MTLE increased TrkB expression, among other NT receptors alterations, may play a major role in seizure type, frequency and surgery outcome.

Ictal spread of medial temporal lobe seizures with and without secondary generalization: an intracranial electroencephalography analysis

OBJECTIVE

Secondary generalization of seizures has devastating consequences for patient safety and quality of life. The aim of this intracranial electroencephalography (icEEG) study was to investigate the differences in onset and propagation patterns of temporal lobe seizures that remained focal versus those with secondary generalization, in order to better understand the mechanism of secondary generalization.

METHODS

A total of 39 seizures were analyzed in nine patients who met the following criteria: (1) icEEG-video monitoring with at least one secondarily generalized tonic-clonic seizure (GTCS), (2) pathologically proven hippocampal sclerosis, and (3) no seizures for at least 1 year after anteromedial temporal lobe resection. Seizures were classified as focal or secondary generalized by behavioral analysis of video. Onset and propagation patterns were compared by analysis of icEEG.

RESULTS

We obtained data from 22 focal seizures without generalization (FS), and 17 GTCS. Seizure-onset patterns did not differ between FS and GTCS, but there were differences in later propagation. All seizures started with low voltage fast activity, except for seven seizures in one patient (six FS, one GTCS), which started with sharply contoured theta activity. Fifteen of 39 seizures started from the hippocampus, and 24 seizures (including six seizures in a patient without hippocampal contacts) started from other medial temporal lobe areas. We observed involvement or more prominent activation of the posterior-lateral temporal regions in GTCS prior to propagation to the other cortical regions, versus FS, which had no involvement or less prominent activation of the posterior lateral temporal cortex. Occipital contacts were not involved at the time of clinical secondary generalization.

SIGNIFICANCE

The posterior-lateral temporal cortex may serve as an important "gateway" controlling propagation of medial temporal lobe seizures to other cortical regions. Identifying the mechanisms of secondary generalization of focal seizures could lead to improved treatments to confine seizure spread.

Does the patient's hand hold the key to preventing secondary generalization in mesial temporal lobe epilepsy?

This study aimed to analyze the impact of ictal dystonic posturing (DP) in postoperative seizure outcome and to assess the influence of DP in generalized tonic-clonic seizure (GTCS) occurrence during video-EEG monitoring of patients with temporal lobe epilepsy with mesial temporal sclerosis. The impact of DP on surgical outcome remains controversial. Moreover, DP has been recently associated with brain networks avoiding GTCS occurrence. Five hundred twenty-seven seizures of 171 patients who were submitted to standard anterior temporal lobectomy (ATL) between 2002 and 2010, with at least one year of post-surgical follow-up, were retrospectively analyzed and classified as with or without DP and as evolving or not to GTCS. The ictal semiologic correlates of DP, timing elapsed since precedent seizure and antiepileptic drug (AED) intake before each seizure were evaluated. Seizure outcome after ATL was assessed according to Engel's scale. Fifty-eight out of 171 patients (34%) exhibited ictal DP, of which 91.5% were always unilateral and contralateral to the operated side. DP was related to shorter seizures (p=0.007) and a much lower likelihood of the seizure evolving to GTCS (p=0.001), even during AED withdrawal (p=0.002). There was no association between DP and prognosis regarding seizure control as the result of the surgical resection, either in patients with shorter or in those with longer period of follow-up. Our data support the hypothesis that DP reflects a brain network activation that helps avoid GTCS, even during AED withdrawal.