Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

Balloon cells associated with granule cell dispersion in the dentate gyrus in hippocampal sclerosis

Granule cell dispersion (GCD) is a common finding in hippocampal sclerosis in patients with intractable focal epilepsy. It is considered to be an acquired, post-developmental rather than a pre-existing abnormality, involving dispersion of either mature or newborn neurones, but the precise factors regulating it and its relationship to seizures are unknown. We present two cases of GCD with associated CD34-immunopositive balloon cells, a cell phenotype associated with focal cortical dysplasia type IIB, considered to be a developmental cortical lesion promoting epilepsy. This observation opens up the debate regarding the origin of balloon cells and CD34 expression and their temporal relationship to seizures.

History of simple febrile seizures is associated with hippocampal abnormalities in adults

SUMMARY BACKGROUND

It is unclear whether the hippocampal abnormality in temporal lobe epilepsy (TLE) is a consequence or the cause of afebrile or febrile seizures (FSs). We investigated whether hippocampal abnormalities are present in healthy adults>15 years after a simple FS.

METHODS

Eight healthy subjects (5 men) with a history of simple FS (FS+ group) and eight sex- and aged-matched control subjects (FS- group) were investigated by three MR methods: blinded visual inspection of the MRI pictures; automatic voxel-based volumetry; and T2 relaxation time measurements.

RESULTS

The mean total volume of the two hippocampi was 5.36 +/- 1.33 cm(3)in the FS+ group and 6.63 +/- 1.46 cm(3)in the FS- group (p = 0.069). The T2 values in the anterior part of the left hippocampus (p = 0.036) and in the middle part of the right hippocampus (p = 0.025) were elevated in the FS+ subjects. The mean volume of the right hippocampus was 3.05 +/- 0.8 cm(3)in the FS+ men and 4.05 +/- 0.48 cm(3)in the FS- men (p = 0.043). The mean total volume of the two hippocampi was 5.38 +/- 1.4 cm(3)in the FS+ men and 7.48 +/- 1.14 cm(3)in the FS- men (p = 0.043). There were three FS+ men in whom hippocampal abnormalities including hippocampal sclerosis (HS) and dysgenesis were observed on visual inspection.

CONCLUSIONS

A history of simple FS in childhood can be associated with hippocampal abnormalities in adults. These abnormalities are probably more pronounced in men. Simple FS may not be as a benign event as previously thought. Our findings suggest that hippocampal abnormalities associated with FS are not necessarily epileptogenic.

A new potential AED, carisbamate, substantially reduces spontaneous motor seizures in rats with kainate-induced epilepsy

PURPOSE

Animal models with spontaneous epileptic seizures may be useful in the discovery of new antiepileptic drugs (AEDs). The purpose of the present study was to evaluate the efficacy of carisbamate on spontaneous motor seizures in rats with kainate-induced epilepsy.

METHODS

Repeated, low-dose (5 mg/kg), intraperitoneal injections of kainate were administered every hour until each male Sprague-Dawley rat had experienced convulsive status epilepticus for at least 3 h. Five 1-month trials (n = 8-10 rats) assessed the effects of 0.3, 1, 3, 10, and 30 mg/kg carisbamate on spontaneous seizures. Each trial involved six AED-versus-vehicle tests comprised of carisbamate or 10% solutol-HS-15 treatments administered as intraperitoneal injections on alternate days with a recovery day between each treatment day.

RESULTS

Carisbamate significantly reduced motor seizure frequency at doses of 10 and 30 mg/kg, and caused complete seizure cessation during the 6-h postdrug epoch in seven of the eight animals at 30 mg/kg. The effects of carisbamate (0.3-30 mg/kg) on spontaneous motor seizures appeared dose dependent.

CONCLUSIONS

These data support the hypothesis that a repeated-measures, crossover protocol in animal models with spontaneous seizures is an effective method for testing AEDs. Carisbamate reduced the frequency of spontaneous motor seizures in a dose-dependent manner, and was more effective than topiramate at reducing seizures in rats with kainate-induced epilepsy.

Impaired facial emotion recognition in patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS): Side and age at onset matters

To define the determinants of impaired facial emotion recognition (FER) in patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS), we examined 76 patients with unilateral MTLE-HS, 36 prior to antero-mesial temporal lobectomy (AMTL) and 40 after AMTL, and 28 healthy control subjects with a FER test consisting of 60 items (20 each for anger, fear, and happiness). Mean percentages of the accurate responses were calculated for different subgroups: right vs. left MTLE-HS, early (age at onset <6 years) vs. late-onset, and before vs. after AMTL. After controlling for years of education, duration of epilepsy and number of antiepileptic drugs (AEDs) taken, on multivariate analysis, fear recognition was profoundly impaired in early-onset right MTLE-HS patients compared to other MTLE patients and control subjects. Happiness recognition was significantly better in post-AMTL MTLE-HS patients compared to pre-AMTL patients while anger and fear recognition did not differ. We conclude that patients with right MTLE-HS with age at seizure onset <6 years are maximally predisposed to impaired fear recognition. In them, right AMTL does not further worsen FER abilities. Longitudinal studies comparing FER in the same patients before and after AMTL will be required to refine and confirm our cross-sectional observations.

The pilocarpine model of temporal lobe epilepsy

Understanding the pathophysiogenesis of temporal lobe epilepsy (TLE) largely rests on the use of models of status epilepticus (SE), as in the case of the pilocarpine model. The main features of TLE are: (i) epileptic foci in the limbic system; (ii) an “initial precipitating injury”; (iii) the so-called “latent period”; and (iv) the presence of hippocampal sclerosis leading to reorganization of neuronal networks. Many of these characteristics can be reproduced in rodents by systemic injection of pilocarpine; in this animal model, SE is followed by a latent period and later by the appearance of spontaneous recurrent seizures (SRSs). These processes are, however, influenced by experimental conditions such as rodent species, strain, gender, age, doses and routes of pilocarpine administration, as well as combinations with other drugs administered before and/or after SE. In the attempt to limit these sources of variability, we evaluated the methodological procedures used by several investigators in the pilocarpine model; in particular, we have focused on the behavioural, electrophysiological and histopathological findings obtained with different protocols. We addressed the various experimental approaches published to date, by comparing mortality rates, onset of SRSs, neuronal damage, and network reorganization. Based on the evidence reviewed here, we propose that the pilocarpine model can be a valuable tool to investigate the mechanisms involved in TLE, and even more so when standardized to reduce mortality at the time of pilocarpine injection, differences in latent period duration, variability in the lesion extent, and SRS frequency.

[Epileptiform activities generated in vitro by human temporal lobe tissue]

Drug-resistant partial epilepsies, including temporal lobe epilepsies with hippocampal sclerosis and cortical dysplasias, offer the opportunity to study human epileptic activity in vitro since the preferred therapy often consists of the surgical removal of the epileptogenic zone. Slices of this tissue retain functional neuronal networks and may generate epileptic activity. The properties of cells in this tissue do not seem to be significantly changed, but excitatory synaptic characteristics are enhanced and GABAergic inhibition is preserved. Typically, epileptic activity is not generated spontaneously by the neocortex, whether dysplastic or not, but can be induced by convulsants. The initiation of ictal discharges in neocortex depends on both GABAergic signaling and increased extracellular potassium. In contrast, a spontaneous interictal-like activity is generated by tissues from patients with temporal lobe epilepsies associated with hippocampal sclerosis. This activity is initiated not in the hippocampus but in the subiculum, an output region that projects to the entorhinal cortex. Interictal events seem to be triggered by GABAergic cells, which paradoxically excite approximately 20% of subicular pyramidal cells, while simultaneously inhibiting the majority. Interictal discharges are therefore sustained by both GABAergic and glutamatergic signaling. The atypical depolarizing effects of GABA depend on a pathological elevation in the basal levels of chloride in some subicular cells, similar to those of developmentally immature cells. This defect is caused by the perturbation of the expression of the cotransporters regulating the intracellular chloride concentration, the importer NKCC1, and the extruder KCC2. Blockade of excessive NKCC1 by the diuretic bumetanide restores intracellular chloride and thus hyperpolarizing GABAergic actions, suppressing interictal activity.

[Changes in spontaneous epileptic activity after selective intrahippocampal transection in a model of chronic mesial temporal lobe epilepsy]

Drug-resistant mesial temporal lobe epilepsy with hippocampal sclerosis is associated with anatomical, ultrastructural and functional changes that facilitate generation and spread of epileptic seizures. Intrahippocampal circuits are modified in their transversal lamellar and longitudinal translamellar organization. Neuronal death and the neuroplasticity of surviving cells contribute to major phenomena: an increased hyperexcitability of the hippocampal formation and an increased synchronization of its principal cells. Selective disruption of the epileptic networks that are involved in mesial temporal lobe epilepsy may have a therapeutic effect. We present here the preliminary results of a selective intrahippocampal transection in a chronic model of mesial temporal lobe epilepsy after focal injection of kainic acid in adult mice. A complete transection of the hippocampal formation (including dentate gyrus and hippocampus proper, sparing the fimbria) results in a blockade of ictal activities spread from the generator, a reduction in their frequency and an increase in their duration. In contrast, after a transection sparing the dentate gyrus and hilus, no modification was noted. In this model of mesial temporal lobe epilepsy, longitudinally projecting axonal circuits of the dentate gyrus and hilus appear to be implicated in generation, propagation and interruption of ictal activities within hippocampal formation.

Clinicopathological and immunohistochemical findings in an autopsy case of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant, multisystem disorder caused by mutations in either the TSC1 or TSC2 genes and characterized by developmental brain abnormalities. In the present study we discuss the neuropathological findings of a 32-year-old patient with a germ-line mutation in the TSC2 gene. Post mortem MRI combined with histology and immunocytochemical analysis was applied to demonstrate widespread anatomical abnormalities of gray and white matter structure. TSC brain lesions were analyzed for loss of heterozygosity (LOH) on chromosome 16p13. The neuropathological supratentorial abnormalities were represented by multiple subependymal nodules (SENs) and cortical tubers. In addition to cerebral cortical lesions, cerebellar lesions and hippocampal sclerosis were also observed. LOH was not found in the cortical tubers and SENs of this patient. Immunocytochemical analysis of the TSC brain lesions confirmed the cell-specific activation of the mTOR pathway in cortical tubers, SENs and cerebellum, as well as differential cellular localization of hamartin and tuberin, the TSC1 and TSC2 gene products. Examination of the pathological brain regions revealed activated microglial cells and disruption of blood-brain barrier permeability. Predominant intralesional cell-specific distribution was also detected for the multidrug transporter protein P-gp, possibly explaining the mechanisms underlying the pharmacoresistance to antiepileptic drugs. Autopsy findings confirm the complexity of the brain abnormalities encountered in TSC patients and proved useful in clarifying certain aspects of the pathogenesis, epileptogenesis and pharmacoresistance of TSC lesions.

Predictive factors for postoperative outcome in temporal lobe epilepsy according to two different classifications

PURPOSE

The determination of prognostic factors is important for predicting outcome after epilepsy surgery. We investigated the factors related to surgical outcome within a homogeneous group of patients suffering from pathologically proven mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), and compared Engel's outcome classification system with the latest one proposed by the ILAE.

METHOD

We included 109 patients with MTLE-HS who were followed-up for at least 1 year after epilepsy surgery. A retrospective chart review was performed to extract patients' demographic details, and potential pre-postoperative risk factors. Outcome of surgery was defined by the Engel's and ILAE classifications. In addition, the course of prognosis was determined according to the changes in ILAE classifications on an annual basis. Univariate and multivariate logistic regression analyses were used for the latest available outcomes and two different courses of prognosis.

RESULTS

The average duration of follow up was 4.78+/-2.55 years in the 109 patients with MTLE-HS. The univariate and multiple logistic regression analyses showed that the occurrence of seizures during the first month after surgery was a significant risk factor for a poor outcome. A history of trauma was also significant for patients with late recurrence of postsurgical seizures after at least 1-year seizure remission.

CONCLUSION

The occurrence of seizures during the first month after surgery is a significant prognostic factor in patients with MTLE-HS. Ignoring early postoperative seizures in classification systems may result in difficulty in identifying the course of epilepsy after surgery.

Association study between interleukin 1 beta gene and epileptic disorders: a HuGe review and meta-analysis

Previous studies have examined the association of a single nucleotide polymorphism at the promoter region of interleukin 1B (IL-1 beta-511T) with temporal lobe epilepsy and febrile seizures susceptibility, but those studies have been inconclusive. Published studies up to March 2007 of temporal lobe epilepsy, febrile seizures and the IL-1 beta-511T single nucleotide polymorphism were identified by searches of Medline and Embase databases. Meta-analysis of temporal lobe epilepsy and febrile seizures case-control data were performed to assess the association of IL-1 beta-511T with temporal lobe epilepsy, temporal lobe epilepsy with hippocampal sclerosis, febrile seizures, and other epileptic disorders. Pooled odds ratios (OR) were estimated by means of a genetic-model-free approach. The quality of the included studies was assessed by a score. The results show a modest association (OR, 1.48; 95% confidence interval, 1.09-2.00; P = 0.01) between the IL-1 beta-511T polymorphism and temporal lobe epilepsy with hippocampal sclerosis.

Late-onset temporal lobe epilepsy with unilateral mesial temporal sclerosis and cognitive decline: a diagnostic dilemma

We present a patient with new onset temporal lobe epilepsy and cognitive decline in his sixth decade with unilateral hippocampal atrophy on structural brain imaging, compatible with mesial temporal sclerosis. This unusual clinical scenario presented a challenging differential diagnosis since it may overlap with primary cognitive disorders, including early-onset Alzheimer's disease and some forms of frontotemporal dementia, and the recently elucidated syndrome of non-paraneoplastic limbic encephalitis associated with voltage-gated potassium channel antibodies.

The adenosine kinase hypothesis of epileptogenesis

Current therapies for epilepsy are largely symptomatic and do not affect the underlying mechanisms of disease progression, i.e. epileptogenesis. Given the large percentage of pharmacoresistant chronic epilepsies, novel approaches are needed to understand and modify the underlying pathogenetic mechanisms. Although different types of brain injury (e.g. status epilepticus, traumatic brain injury, stroke) can trigger epileptogenesis, astrogliosis appears to be a homotypic response and hallmark of epilepsy. Indeed, recent findings indicate that epilepsy might be a disease of astrocyte dysfunction. This review focuses on the inhibitory neuromodulator and endogenous anticonvulsant adenosine, which is largely regulated by astrocytes and its key metabolic enzyme adenosine kinase (ADK). Recent findings support the "ADK hypothesis of epileptogenesis": (i) Mouse models of epileptogenesis suggest a sequence of events leading from initial downregulation of ADK and elevation of ambient adenosine as an acute protective response, to changes in astrocytic adenosine receptor expression, to astrocyte proliferation and hypertrophy (i.e. astrogliosis), to consequential overexpression of ADK, reduced adenosine and - finally - to spontaneous focal seizure activity restricted to regions of astrogliotic overexpression of ADK. (ii) Transgenic mice overexpressing ADK display increased sensitivity to brain injury and seizures. (iii) Inhibition of ADK prevents seizures in a mouse model of pharmacoresistant epilepsy. (iv) Intrahippocampal implants of stem cells engineered to lack ADK prevent epileptogenesis. Thus, ADK emerges both as a diagnostic marker to predict, as well as a prime therapeutic target to prevent, epileptogenesis.

Is exposure to enriched environment beneficial for functional post-lesional recovery in temporal lobe epilepsy?

Exposure to enriched environment has been shown to induce robust neuronal plasticity in both intact and injured adult central nervous system, including up-regulation of multiple neurotrophic factors, enhanced neurogenesis in the dentate gyrus of the hippocampus, and improved spatial learning and memory function. Neuronal plasticity, though mostly adaptive and abnormal, also occurs during certain neurodegenerative conditions such as the temporal lobe epilepsy (TLE). The TLE is characterized by hippocampal neurodegeneration, aberrant mossy fiber sprouting, spontaneous recurrent motor seizures, cognitive deficits, and abnormally enhanced neurogenesis during the early phase and dramatically declined neurogenesis during the chronic phase of the disease. As environmental enrichment has been found to be beneficial for treating animal models of Alzheimer's, Parkinson's, and Huntington's diseases, there is considerable interest in determining the efficacy of this strategy for preventing or treating chronic TLE after the initial precipitating brain injury. This review first discusses the proof of principle behind the potential application of the environmental enrichment strategy for preventing or treating TLE after brain injury. The subsequent chapters confer the portrayed beneficial effects of enrichment for functional post-lesional recovery in TLE and the possible complications which may arise from housing epilepsy-prone or epileptic rats in enriched environmental conditions. The final segment discusses studies that are essential for further understanding the efficacy of this approach for preventing or treating TLE.

Hyperexcitability of the CA1 hippocampal region during epileptogenesis

Temporal Lobe Epilepsy (TLE) is often preceded by a latent (seizure-free) period during which complex network reorganizations occur. In experimental epilepsy, network hyperexcitability is already present during the latent period, suggesting a modification of information processing. The purpose of this study was to assess the input/output relationship in the hippocampal CA1 region during epileptogenesis. Field recordings in strata pyramidale and radiatum were used to measure the output of CA1 pyramidal cells as a function of the synaptic inputs they receive following the stimulation of Shaffer collaterals in slices obtained from sham and pilocarpine-treated animals during the latent and chronic periods. We show that there is a transient increase of the input and output field responses during the latent period as compared to sham and epileptic animals. The coupling between excitatory inputs and cell firing was also increased during the latent period. This increase persisted in epileptic animals, although to a lesser extent. We also confirm that paired-pulse facilitation occurs before the chronic phase. The present data further support the view that hyperexcitability is present at an early stage of epileptogenesis. Network output is more facilitated during the latent than during the chronic period. Hyperexcitability may participate to epileptogenesis, but it is not sufficient in itself to produce seizures.

The Antiepileptic Drug Levetiracetam Stabilizes the Human Epileptic GABAAReceptors upon Repetitive Activation

PURPOSE

GABAA receptors from the brain of patients afflicted with mesial temporal lobe epilepsy (MTLE) become less efficient (run-down) when repetitively activated by GABA. Experiments were designed to investigate whether the antiepileptic drug, levetiracetam (LEV), which is used as an adjunctive treatment for medically intractable MTLE, counteracts the GABAA receptor run-down.

METHODS

GABAA receptors were microtransplanted from the brains of patients afflicted with MTLE into Xenopus oocytes. The GABA-current run-down, caused by repetitive applications of GABA, was investigated using the standard two-microelectrode voltage-clamp technique. Additionally, the GABA-current run-down was investigated directly on pyramidal neurons in human MTLE cortical slices.

RESULTS

It was found that, in oocytes injected with membranes isolated from the MTLE neocortex, the GABA-current run-down was inhibited by a 3-h pretreatment with 0.5-100 microM LEV. Moreover, the GABAA receptors of pyramidal neurons in human neocortical slices exhibited a current run-down that was significantly reduced by 1 microM LEV. Interestingly, the run-down in oocytes injected with membranes isolated from the MTLE hippocampal subiculum was not affected by LEV.

CONCLUSIONS

We report that the antiepileptic LEV strengthens GABA inhibition of neuronal circuits by blocking the receptor run-down in the cortex whilst leaving the run-down of GABAA receptors in the hippocampal subiculum unaltered. These findings point to the GABAA receptor run-down as an important event in epileptogenesis and as a possible target for testing and screening antiepileptic drugs.

Temporal pole signal abnormality on MR imaging in temporal lobe epilepsy with hippocampal sclerosis: a fluid-attenuated inversion-recovery study

OBJECTIVE: To determine the frequency and regional involvement of temporal pole signal abnormality (TPA) in patients with hippocampal sclerosis (HS) using fluid-attenuated inversion-recovery (FLAIR) MR imaging, and to correlate this feature with history. METHOD: Coronal FLAIR images of the temporal pole were assessed in 120 patients with HS and in 30 normal subjects, to evaluate gray-white matter demarcation. RESULTS: Ninety (75%) of 120 patients had associated TPA. The HS side made difference regarding the presence of TPA, with a left side prevalence (p=0.04, chi2 test). The anteromedial zone of temporal pole was affected in 27 (30%) out of 90 patients. In 63 (70%) patients the lateral zone were also affected. Patients with TPA were younger at seizure onset (p=0.018), but without association with duration of epilepsy. CONCLUSION: Our FLAIR study show temporal pole signal abnormality in 3/4 of patients with HS, mainly seen on the anteromedial region, with a larger prevalence when the left hippocampus was involved.

Innate and adaptive immunity during epileptogenesis and spontaneous seizures: evidence from experimental models and human temporal lobe epilepsy

We investigated the activation of the IL-1 beta system and markers of adaptive immunity in rat brain during epileptogenesis using models of temporal lobe epilepsy (TLE). The same inflammatory markers were studied in rat chronic epileptic tissue and in human TLE with hippocampal sclerosis (HS). IL-1 beta was expressed by both activated microglia and astrocytes within 4 h from the onset of status epilepticus (SE) in forebrain areas recruited in epileptic activity; however, only astrocytes sustained inflammation during epileptogenesis. Activation of the IL-1 beta system during epileptogenesis was associated with neurodegeneration and blood-brain barrier breakdown. In rat and human chronic epileptic tissue, IL-1 beta and IL-1 receptor type 1 were broadly expressed by astrocytes, microglia and neurons. Granulocytes appeared transiently in rat brain during epileptogenesis while monocytes/macrophages were present in the hippocampus from 18 h after SE onset until chronic seizures develop, and they were found also in human TLE hippocampi. In rat and human epileptic tissue, only scarce B- and T-lymphocytes and NK cells were found mainly associated with microvessels. These data show that specific inflammatory pathways are chronically activated during epileptogenesis and they persist in chronic epileptic tissue, suggesting they may contribute to the etiopathogenesis of TLE.

Short-term changes in bilateral hippocampal coherence precede epileptiform events

The mesial temporal lobe epilepsy syndrome (MTLE) is the most common form of focal epilepsies. MTLE patients usually respond very little to pharmacological therapy and surgical resection of temporal brain areas is mandatory. Finding less invasive therapies than resection of the sclerotic hippocampus requires knowledge of the network structures and dynamics involved in seizure generation. Investigation of the time interval immediately preceding seizure onset would help in understanding the initiation mechanisms of the seizure proper and, thereby, possibly improve therapeutical options. Here, we employed the in vivo intrahippocampal kainate model in mice, which is characterized by unilateral histological changes, resembling hippocampal sclerosis observed in human MTLE, and recurrent focal seizures. In these epileptic mice, population spikes occurred during epileptiform events (EEs) in the ipsilateral, histologically changed hippocampus, but also concomitantly in the contralateral, intact hippocampus. We studied synchronization processes between the ipsilateral, sclerotic hippocampus and the contralateral hippocampus immediately preceding the onset of EEs. We show that coherence between the two hippocampi decreased consistently and reliably for all EEs at 8 to 12 s before their onset at high frequencies (>100 Hz), without changes in power in these bands. This early decoupling of the two hippocampi indicates the time range for cellular and network mechanisms leading to increased excitability and/or synchronicity in the tissue and thus ultimately to epileptic seizures.

Bilateral white matter diffusion changes persist after epilepsy surgery

PURPOSE

Bilateral white matter diffusion tensor imaging (DTI) abnormalities have been reported in patients with temporal lobe epilepsy (TLE) and unilateral mesial temporal sclerosis (MTS), but it is unknown whether these are functional or structural changes. We performed a longitudinal study in patients with unilateral MTS who were seizure-free for 1 year after surgery to determine whether the observed presurgical white matter diffusion abnormalities were reversible.

METHODS

Eight TLE patients with unilateral MTS who were seizure-free after anterior temporal resection and 22 healthy subjects were recruited. DTI was performed before surgery and at 1-year follow-up. Tractography and region-of-interest (ROI) analyses were performed in the fornix, cingulum, genu, and splenium of the corpus callosum and external capsules. Diffusion tensor parameters were compared between groups and before and after surgery in the patient group.

RESULTS

The fornix, cingulum, and external capsules showed preoperative bilateral abnormal diffusion parameters (i.e., decreased diffusion anisotropy and increased mean and perpendicular diffusivities). The fornix and cingulum ipsilateral to the resected mesial temporal structures showed signs of wallerian degeneration at 1-year follow-up. The contralateral tracts of the fornix, cingulum, and external capsules, as well as the genu of the corpus callosum, failed to show a normalization of their diffusion parameters.

CONCLUSIONS

The irreversibility of the white matter DTI abnormalities on seizure freedom suggests underlying structural abnormalities (e.g., axonal/myelin degradation) as opposed to functional changes (e.g., fluid shifts due to seizures) in the white matter.

Induction of the Wnt inhibitor, Dickkopf-1, is associated with neurodegeneration related to temporal lobe epilepsy

Inhibition of the Wnt pathway by the secreted glycoprotein, Dickkopf-1 (Dkk-1) has been related to processes of excitotoxic and ischemic neuronal death. We now report that Dkk-1 is induced in neurons of the rat olfactory cortex and hippocampus degenerating in response to seizures produced by systemic injection of kainate (12 mg/kg, i.p.). There was a tight correlation between Dkk-1 expression and neuronal death in both regions, as shown by the different expression profiles in animals classified as "high" and "low" responders to kainate. For example, no induction of Dkk-1 was detected in the hippocampus of low responder rats, in which seizures did not cause neuronal loss. Induction of Dkk-1 always anticipated neuronal death and was associated with a reduction in nuclear levels of beta-catenin, which reflects an ongoing inhibition of the canonical Wnt pathway. Intracerebroventricular injections of Dkk-1 antisense oligonucleotides (12 nmol/2 microL) substantially reduced kainate-induced neuronal damage, as did a pretreatment with lithium ions (1 mEq/kg, i.p.), which rescue the Wnt pathway by acting downstream of the Dkk-1 blockade. Taken collectively, these data suggest that an early inhibition of the Wnt pathway by Dkk-1 contributes to neuronal damage associated with temporal lobe epilepsy. We also examined Dkk-1 expression in the hippocampus of epileptic patients and their controls. A strong Dkk-1 immunolabeling was found in six bioptic samples and in one autoptic sample from patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis. Dkk-1 expression was undetectable or very low in autoptic samples from nonepileptic patients or in bioptic samples from patients with complex partial seizures without neuronal loss and/or reactive gliosis in the hippocampus. Our data raise the attractive possibility that drugs able to rescue the canonical Wnt pathway, such as Dkk-1 antagonists or inhibitors of glycogen synthase kinase-3beta, reduce the development of hippocampal sclerosis in patients with temporal lobe epilepsy.

Cell therapy in models for temporal lobe epilepsy

For patients with refractory epilepsy it is important to search for alternative treatments. One of these potential treatments could be introducing new cells or modulating endogenous neurogenesis to reconstruct damaged epileptic circuits or to bring neurotransmitter function back into balance. In this review the scientific basis of these cell therapy strategies is discussed and the results are critically evaluated. Research on cell transplantation strategies has mainly been performed in animal models for temporal lobe epilepsy, in which seizure foci or seizure propagation pathways are targeted. Promising results have been obtained, although there remains a lot of debate about the relevance of the animal models, the appropriate target for transplantation, the suitable cell source and the proper time point for transplantation. From the presented studies it should be evident that transplanted cells can survive and sometimes even integrate in an epileptic brain and in a brain that is subjected to epileptogenic interventions. There is evidence that transplanted cells can partially restore damaged structures and/or release substances that modulate existent or induced hyperexcitability. Even though several studies show encouraging results, more studies need to be done in animal models with spontaneous seizures in order to have a better comparison to the human situation.

Insertion of subdural strip electrodes for the investigation of temporal lobe epilepsy

✓ Temporal lobe epilepsy (TLE) is the most common type of surgically treatable epilepsy, with a considerable number of patients needing invasive electroencephalography monitoring. The authors describe a surgical technique used in the placement of subdural strip electrodes for coverage of the temporal lobe. The electrodes are inserted through an enlarged temporooccipital bur hole using fluoroscopic guidance. With this technique, subdural electrode strips can be safely placed to cover the mesial, inferior, and lateral temporal surfaces, and the seizure focus can be lateralized and localized within the temporal lobe. The technique does not require the use of a craniotomy, stereotactic frame, or neuronavigation systems. The authors compare this technique with previous descriptions of subdural electrode placement for the evaluation of TLE.

Gene expression profile in temporal lobe epilepsy

Epilepsy is one of the most common neurological disorders. Temporal lobe epilepsy (TLE) represents the most frequent epilepsy syndrome in adult patients with resistance to pharmacological treatment. In TLE, the origin of seizure activity typically involves the hippocampal formation, which displays major neuropathological features, described with the term hippocampal sclerosis (HS). The expansion of neurosurgical epilepsy programs has offered the possibility of disposing of clinically well-characterized hippocampal tissue, so that the analysis of molecular mechanisms underlying the structural and functional reorganization occurring in the hippocampus and neighboring areas in TLE patients can be done on a large scale. The recent development of molecular biological technologies permits the analysis of changes in the expression of a large number of genes. This has opened new perspectives for epilepsy research. However, the hippocampal specimens obtained from patients with TLE most often represent an advanced stage of the pathology. For this reason, animal models that reproduce the clinical and histopathological features of TLE are helpful in detecting the early development of the pathological cascade leading to TLE with HS. An overview of recent data of gene expression profiles in human and experimental TLE is presented along with a discussion of the relevance of functional genomics, to develop new hypotheses and to detect likely candidate genes involved in epileptogenesis, as well as possible target molecules for new therapeutic approaches.

Corpora amylacea in mesial temporal lobe epilepsy: Clinico-pathological correlations

PURPOSE

To investigate the electro-clinical significance of premature accumulation of corpora amylacea (CoA) in the resected hippocampus of patients with medically refractory mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS).

METHODS

We compared the clinical and EEG characteristics, and post-operative seizure outcome of 373 (mean age 29.4 years, range 7-55 years) surgically treated MTLE-HS patients with (MTLE-HS-CoA(+), n=129 [34.5%]) and without (MTLE-HS-CoA(-), n=244 [65.5%]) CoA.

RESULTS

Age at surgery was significantly higher and duration of epilepsy before surgery was significantly longer for MTLE-HS-CoA(+) patients compared to MTLE-HS-CoA(-) patients. Although the distribution of interictal epileptiform EEG abnormalities did not differ, type 1 ictal EEG pattern was more frequent in MTLE-HS-CoA(+) patients. Among the 21 patients with major interictal psychosis detected prior to epilepsy surgery, 19 (90.5%) belonged to MTLE-HS-CoA(+) group. Schizophrenia-like psychosis was most prevalent. The post-operative seizure-free outcome was comparable, but significantly more MTLE-HS-CoA(-) patients were free of antiepileptic drugs.

CONCLUSIONS

Overall, our observations support the hypothesis that the pathological process in MTLE-HS is progressive. MTLE-HS-CoA(+) patients are predisposed to increased psychiatric morbidity. In vivo detection of hippocampal CoA accumulation in the future will help us to understand the neurobiological significance of this phenomenon.

Facial paresis in patients with mesial temporal sclerosis: clinical and quantitative MRI-based evidence of widespread disease

PURPOSE

To assess the frequency and significance of facial paresis (FP) in a well-defined cohort of mesial temporal lobe epilepsy (MTLE) patients.

METHODS

One hundred consecutive patients with MRI findings consistent with mesial temporal sclerosis (MTS) and concordant electroclinical data underwent facial motor examination at rest, with voluntary expression, and with spontaneous smiling. Hippocampal, amygdaloid, and temporopolar (TP) volumetric measures were acquired. Thirty healthy subjects, matched according to age and sex, were taken as controls.

RESULTS

Central-type FP was found in 46 patients. In 41 (89%) of 46, it was visualized at rest, with voluntary and emotional expression characterizing true facial motor paresis. In 33 (72%) of 46 patients, FP was contralateral to the side of MTS. By using a 2-SD cutoff from the mean of normal controls, we found reduction in TP volume ipsilateral to MTS in 61% of patients with FP and in 33% of those without (p = 0.01). Febrile seizures as initial precipitating injury (IPI) were observed in 34% of the patients and were classified as complex in 12 (26%) of 46 of those with FP and in five (9%) of 54 of those without (p = 0.02). The presence of FP was significantly associated with a shorter latent period and younger age at onset of habitual seizures, in particular, with secondarily generalized tonic-clonic seizures.

CONCLUSIONS

Facial paresis is a reliable lateralizing sign in MTLE and was associated with history of complex febrile seizures as IPI, younger age at onset of disease, and atrophy of temporal pole ipsilateral to MTS, indicating more widespread disease.

A new clinico-pathological classification system for mesial temporal sclerosis

We propose a histopathological classification system for hippocampal cell loss in patients suffering from mesial temporal lobe epilepsies (MTLE). One hundred and seventy-eight surgically resected specimens were microscopically examined with respect to neuronal cell loss in hippocampal subfields CA1–CA4 and dentate gyrus. Five distinct patterns were recognized within a consecutive cohort of anatomically well-preserved surgical specimens. The first group comprised hippocampi with neuronal cell densities not significantly different from age matched autopsy controls [no mesial temporal sclerosis (no MTS); n = 34, 19%]. A classical pattern with severe cell loss in CA1 and moderate neuronal loss in all other subfields excluding CA2 was observed in 33 cases (19%), whereas the vast majority of cases showed extensive neuronal cell loss in all hippocampal subfields (n = 94, 53%). Due to considerable similarities of neuronal cell loss patterns and clinical histories, we designated these two groups as MTS type 1a and 1b, respectively. We further distinguished two atypical variants characterized either by severe neuronal loss restricted to sector CA1 (MTS type 2; n = 10, 6%) or to the hilar region (MTS type 3, n = 7, 4%). Correlation with clinical data pointed to an early age of initial precipitating injury (IPI < 3 years) as important predictor of hippocampal pathology, i.e. MTS type 1a and 1b. In MTS type 2, IPIs were documented at a later age (mean 6 years), whereas in MTS type 3 and normal appearing hippocampus (no MTS) the first event appeared beyond the age of 13 and 16 years, respectively. In addition, postsurgical outcome was significantly worse in atypical MTS, especially MTS type 3 with only 28% of patients having seizure relief after 1-year follow-up period, compared to successful seizure control in MTS types 1a and 1b (72 and 73%). Our classification system appears suitable for stratifying the clinically heterogeneous group of MTLE patients also with respect to postsurgical outcome studies.

Complement activation in experimental and human temporal lobe epilepsy

We investigated the involvement of the complement cascade during epileptogenesis in a rat model of temporal lobe epilepsy (TLE), and in the chronic epileptic phase in both experimental as well as human TLE. Previous rat gene expression analysis using microarrays indicated prominent activation of the classical complement pathway which peaked at 1 week after SE in CA3 and entorhinal cortex. Increased expression of C1q, C3 and C4 was confirmed in CA3 tissue using quantitative PCR at 1 day, 1 week and 3-4 months after status epilepticus (SE). Upregulation of C1q and C3d protein expression was confirmed mainly to be present in microglia and in a few hippocampal neurons. In human TLE with hippocampal sclerosis, astroglial, microglial and neuronal (5/8 cases) expression of C1q, C3c and C3d was observed particularly within regions where neuronal cell loss occurs. The membrane attack protein complex (C5b-C9) was predominantly detected in activated microglial cells. The persistence of complement activation could contribute to a sustained inflammatory response and could destabilize neuronal networks involved.

Neurosurgery for the treatment of epilepsy

PURPOSE OF REVIEW

Epilepsy is a common condition that is estimated to afflict 0.5-1.0% of the world's population. Frequently commencing in childhood, it is often associated with life-long disability. Approximately one-third of patients with epilepsy are refractory to antiepileptic drug therapy and many of these patients are candidates for surgical treatment. A growing body of evidence supports the safety and efficacy of surgery for the treatment of selected patients with epilepsy. Little information is available in the anesthesia literature regarding the presurgical assessment of candidates for surgical treatment.

RECENT FINDINGS

The presurgical identification of suitable candidates involves a multidisciplinary approach to assessment. Recent advances, particularly in neuroimaging techniques, are dramatically enhancing the capacity to accurately identify patients who are most likely to benefit from surgery. Epilepsy surgery is underused worldwide and in developed countries. In view of current efforts to increase opportunities to provide surgical treatment to more patients and to offer surgery earlier in the course of the disorder, the number of patients requiring specialized perioperative anesthetic care is expected to increase.

SUMMARY

This article provides anesthesiologists with an overview of the assessment process, investigation techniques and current rationale that influence the selection of appropriate candidates for surgical treatment and the associated need for specialized anesthetic care.

THE SCN2A gene is not a likely candidate for familial mesial temporal lobe epilepsy

A transgenic mouse model carrying a mutation in the Scn2a gene showed chronic focal seizures associated with extensive cell loss and gliosis in the hippocampus, a similar phenotype found in familial mesial temporal lobe epilepsy (FMTLE). Our objective was to test whether the human homolog of the Scn2a gene is responsible for hippocampal abnormalities in FMTLE by linkage analysis. We conclusively ruled out the SCN2A gene as candidate in FMTLE.

Memory guided saccades in mesial temporal lobe epilepsy with hippocampal sclerosis

OBJECTIVE

Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) may involve extrahippocampal areas of structural and functional damage. The incidence and the features of this damage are still a matter of debate and vary depending on the method applied. Memory guided saccades (MGSs) with a memorization delay longer than 20s can be used reliably to evaluate the parahippocampal cortex.

METHODS

MGSs with 3 and 30s memorization delays were recorded with the search coil technique in six patients affected by right MTLE-HS, and in 13 healthy controls.

RESULTS

The patients were not able to reduce the MGSs residual amplitude error after the first saccade with a 30s memorization delay. This finding was more evident with leftward saccades.

CONCLUSIONS

MGS abnormalities suggested the functional involvement of the right parahippocampal cortex in most of the patients with MTLE-HS, and this supports the clinical and anatomopathological heterogeneity of the disease.

SIGNIFICANCE

MGSs can be used in patients with right MTLE-HS to detect a possible functional involvement of the ipsilateral parahippocampal cortex.

Extratemporal White Matter Abnormalities in Mesial Temporal Lobe Epilepsy Demonstrated with Diffusion Tensor Imaging

PURPOSE

Recent studies have demonstrated bilateral white matter abnormalities in temporal lobe epilepsy (TLE) patients with unilateral mesial temporal sclerosis (MTS). The purpose of this project was to determine whether abnormalities of water diffusion are seen in extratemporal white matter of patients with TLE and pathologically confirmed MTS and to determine whether these findings are associated with worse surgical outcome.

METHODS

Eleven patients with TLE and unilateral MTS confirmed in surgical specimens and 14 controls were studied by using cerebrospinal fluid-suppressed diffusion tensor imaging (DTI) and T2 relaxometry.

RESULTS

Hippocampal T2 signal for patients was significantly elevated both ipsilateral (p<0.001) and contralateral (p=0.006) to MTS. DTI demonstrated reduced fractional anisotropy of the genu of the corpus callosum (p=0.003) and external capsule (p=0.02) and elevated mean diffusivity of the genu (p=0.005), splenium (p=0.03), and external capsule (p<0.001). For both the genu and external capsule, parallel diffusion of patients was not different from that of controls (genu, p=0.81; external capsule, p=0.45), whereas perpendicular diffusion was elevated (genu, p=0.001; external capsule, p<0.001). With mean postsurgical follow-up of 18.5 months, eight of 11 patients were entirely seizure free and the remaining three had all experienced a worthwhile reduction in seizure frequency.

CONCLUSIONS

Our findings suggest that although patients with TLE and MTS have extensive bilateral and extratemporal pathology, these findings may not be associated with a worse postsurgical outcome.

Hippocampal neurodegeneration, spontaneous seizures, and mossy fiber sprouting in the F344 rat model of temporal lobe epilepsy

The links among the extent of hippocampal neurodegeneration, the frequency of spontaneous recurrent motor seizures (SRMS), and the degree of aberrant mossy fiber sprouting (MFS) in temporal lobe epilepsy (TLE) are a subject of contention because of variable findings in different animal models and human studies. To understand these issues further, we quantified these parameters at 3-5 months after graded injections of low doses of kainic acid (KA) in adult F344 rats. KA was administered every 1 hr for 4 hr, for a cumulative dose of 10.5 mg/kg bw, to induce continuous stages III-V motor seizures for >3 hr. At 4 days post-KA, the majority of rats (77%) exhibited moderate bilateral neurodegeneration in different regions of the hippocampus; however, 23% of rats exhibited massive neurodegeneration in all hippocampal regions. All KA-treated rats displayed robust SRMS at 3 months post-KA, and the severity of SRMS increased over time. Analyses of surviving neurons at 5 months post-KA revealed two subgroups of rats, one with moderate hippocampal injury (HI; 55% of rats) and another with widespread HI (45%). Rats with widespread HI exhibited greater loss of CA3 pyramidal neurons and robust aberrant MFS than rats with moderate HI. However, the frequency of SRMS (approximately 3/hr) was comparable between rats with moderate and widespread HI. Thus, in comparison with TLE model using Sprague-Dawley rats (Hellier et al. [1998] Epilepsy Res. 31:73-84), a much lower cumulative dose of KA leads to robust chronic epilepsy in F344 rats. Furthermore, the occurrence of SRMS in this model is always associated with considerable bilateral hippocampal neurodegeneration and aberrant MFS. However, more extensive hippocampal CA3 cell loss and aberrant MFS do not appear to increase the frequency of SRMS. Because most of the features are consistent with mesial TLE in humans, the F344 model appears ideal for testing the efficacy of potential treatment strategies for mesial TLE.

Correlations of interictal FDG-PET metabolism and ictal SPECT perfusion changes in human temporal lobe epilepsy with hippocampal sclerosis

BACKGROUND

The pathophysiological role of the extensive interictal cerebral hypometabolism in complex partial seizures (CPS) in refractory mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) is poorly understood. Our aim was to study ictal-interictal SPECT perfusion versus interictal fluorodeoxyglucose (FDG)-PET metabolic patterns.

METHODS

Eleven adults with refractory unilateral mTLE-HS, who were rendered seizure free after epilepsy surgery, were included. All had an interictal FDG-PET and an interictal and ictal perfusion SPECT scan. FDG-PET data were reconstructed using an anatomy-based reconstruction algorithm, which corrected for partial volume effects, and analyzed semi-quantitatively after normalization to white matter activity. Using Statistical Parametric Mapping (SPM), we compared interictal metabolism of the patient group with a control group. We correlated metabolic with ictal perfusion changes in the patient group.

RESULTS

Global cerebral grey matter glucose metabolism in patients was decreased 10-25% compared with control subjects. Interictal PET hypometabolism and ictal SPECT hypoperfusion were maximal in the ipsilateral frontal lobe. Ictal frontal lobe hypoperfusion was associated with crossed cerebellar diaschisis. The ipsilateral temporal lobe showed maximal ictal hyperperfusion and interictal hypometabolism, which was relatively mild compared with the degree of hypometabolism affecting the frontal lobes.

CONCLUSION

Interictal hypometabolism in mTLE-HS was greatest in the ipsilateral frontal lobe and represented a seizure-related dynamic process in view of further ictal decreases. Crossed cerebellar diaschisis suggested that there is a strong ipsilateral frontal lobe inhibition during CPS. We speculate that surround inhibition in the frontal lobe is a dynamic defense mechanism against seizure propagation, and may be responsible for functional deficits observed in mTLE.

Relative localizing value of amygdalo-hippocampal MR biometry in temporal lobe epilepsy

OBJECTIVES

The aims of the study were (i) to examine the localizing value of three MRI quantitative modalities (qMRI) currently used for the analysis of the hippocampus and amygdala in the context of pre-surgical screening and (ii) to propose a step-by-step protocol based on the sensitivity and performance of the different MR techniques.

METHODS

Ninety-two adults with chronic mesial temporal lobe epilepsy (TLE) of which 28 underwent amygdalo-hippocampal resection, and 34 age-matched controls were included in the study. High-resolution qMRI was performed at 1.5 T, including a tilted T1-weighted 3D-dataset for volumetry and four-echoes T2 relaxometry (both for hippocampus and amygdala quantifications) and multi-voxel spectroscopy [NAA/(Cho+Cre)] (exclusively in the hippocampus). Individual qMRI data were compared with electroencephalography regarding the localization of the epileptogenic area, with the neuropathological data and with postoperative outcome. MRI pathology was defined based on 99% confidence ellipses. Ten controls were used to assess the quantitative MRI intra- and inter-observer variability for all variables.

RESULTS

Volumetric measurements revealed unilateral damage in 77% of the patients, T2-relaxometry in 64% and spectroscopy in 53%. Additional measurements of the amygdalae (T2-relaxometry) allowed us to localize pathology that coexists with that of the hippocampus in 34%, and isolated unilateral amygdala damage in 8% of patients. Volumetry and T2-relaxometry (not spectroscopy) were associated with postoperative outcome, but accurate predictive models were computed based on hippocampal measures only. At least at 1-year follow-up, volumetry predicts outcome correctly in 100% of the cases, whilst T2-relaxometry classified 96.4% (27/28) of these patients. All operated patients had hippocampal sclerosis.

CONCLUSIONS

Hippocampal structural damage is equivocally depicted by spectroscopy. For diagnostic and pre-operative evaluation, hippocampal volumetry and T2-relaxometry provide maximal accuracy. Amygdala quantifications are irrelevant in the pre-operative evaluation but may be useful for diagnostic purposes. Of the three qMRI modalities tested, T2-relaxometry provided the best balance between diagnosis accuracy and time-efficiency to lateralize a sclerotic lesion on the majority of the patients. Cases that remain undecided after T2-relaxometry may benefit from additional measurements based on hippocampal volumetry.

Prognostic factors for surgery of neocortical temporal lobe epilepsy

OBJECTIVES

In the current classification of epilepsies two forms of temporal lobe epilepsy (TLE) were included: mesial and lateral (neocortical) TLE. We aimed at identifying prognostic factors for the surgical outcome of lesional neocortical TLE.

METHODS

We included consecutive patients who had undergone presurgical evaluation including ictal video-EEG and high-resolution MRI, who had TLE due to neocortical lateral epileptogenic lesions, who had a lesionectomy and who had >2-year follow-up.

RESULTS

There were 29 patients who met the inclusion criteria. Twenty of them became postoperatively seizure-free. Patients' mean age was 34.8+/-9 years (range 18-52). The age at epilepsy onset was 20.1+/-8 years. We found that left-sided surgery (p=0.048) and focal cortical dysplasia (FCD) on MRI (p=0.005) were associated with non-seizure-free outcome, while lateralized/localized EEG seizure pattern (p=0.032), tumors on the MRI (p=0.013), and a favorable seizure situation at the 6-month postoperative evaluation were associated with 2-year postoperative seizure-freedom (p<0.001). Multivariate analysis indicated that the side of surgery was not an independent predictor.

CONCLUSION

More than two-thirds of the patients with neocortical TLE became seizure-free postoperatively. Lateralized/localized EEG seizure pattern and tumors on the MRI were associated with postoperative seizure-freedom, while FCD were associated with a poor outcome. The 6-month postoperative outcome is a reliable predictor for the long-term outcome.

Epilepsia do lobo temporal mesial associada à esclerose hipocampal

INTRODUÇÃO: A importância clínica da epilepsia do lobo temporal mesial (ELTM) decorre de sua alta prevalência e elevada proporção de pacientes com crises epilépticas refratárias ao tratamento medicamentos; sendo a esclerose mesial a etiologia encontrada em 50-70% dos pacientes com ELTM refratária ao tratamento clínico. OBJETIVO: Revisão, atualização e discussão dos aspectos clínicos, de histologia e fisiopatogenia da ELTM associada à esclerose hipocampal. RESULTADOS: Apesar da relação entre esclerose hippocampal e ELTM já estar bem estabelecida na literatura, o mecanismo exato pelo qual a esclerose hipocampal participa da gênese das crises epilépticas ainda não foi completamente desvendado. CONCLUSÕES: Estudos retrospectivos de centros de cirurgia de epilepsia enfatizam a associação entre esclerose hipocampal e história de injúria precipitante inicial, tais como crises epilépticas, ocorrendo em fase precoce do desenvolvimento cerebral. Apenas recentemente fatores genéticos foram implicados na gênese da esclerose hipocampal.

Serial analysis of gene expression in the hippocampus of patients with mesial temporal lobe epilepsy

Hippocampal sclerosis constitutes the most frequent neuropathological finding in patients with medically intractable mesial temporal lobe epilepsy. Serial analysis of gene expression was used to get a global view of the gene profile in human hippocampus in control condition and in epileptic condition associated with hippocampal sclerosis. Libraries were generated from control hippocampus, obtained by rapid autopsy, and from hippocampal surgical specimens of patients with mesial temporal lobe epilepsy and the classical pattern of hippocampal sclerosis. More than 50,000 tags were analyzed (28,282, control hippocampus; 25,953, hippocampal sclerosis) resulting in 9206 (control hippocampus) and 9599 (hippocampal sclerosis) unique tags (genes), each representing a specific mRNA transcript. Comparison of the two libraries resulted in the identification of 143 transcripts that were differentially expressed. These genes belong to a variety of functional classes, including basic metabolism, transcription regulation, protein synthesis and degradation, signal transduction, structural proteins, regeneration and synaptic plasticity and genes of unknown identity of function. The database generated by this study provides an extensive inventory of genes expressed in human control hippocampus, identifies new high-abundant genes associated with altered hippocampal morphology in patients with mesial temporal lobe epilepsy and serves as a reference for future studies aimed at detecting hippocampal transcriptional responses under various pathological conditions.

Temporo-mesial epilepsy surgery: outcome and complications in 100 consecutive adult patients

BACKGROUND

We studied the surgical outcome, and the complications in a group of 100 consecutive adult patients with medically refractory epilepsy arising from the temporo-mesial structures.

METHODS

Hundred patients were treated surgically between 1994 and 2003 for drug-resistant epilepsy involving the temporo-mesial structures. All of them underwent a comprehensive noninvasive presurgical evaluation. Fourty-eight of them underwent depth electrodes recordings (according to the Talairach's StereoElectroEncephaloGraphic (SEEG) methodology) because the noninvasive investigations were not congruent enough to identify the epileptic zone. The patients presenting with any space-occupying lesion, or with a cavernoma, or with a strictly lateral neocortical epileptic focus, were excluded. The MRI-examination was abnormal in 87 cases, displaying a hippocampal atrophy in 69 cases. The extent of temporal resection was planned according to the results of the presurgical investigation in each particular patient. Consequently, this "tailored" resection varied from selective amygdalo-hippocampectomy (6 cases), to anterior temporal lobectomy (76 cases), or to total temporal lobectomy (18 cases).

FINDINGS

The mean post-operative follow-up period was 53 months. 85 patients were found to be in Engel's class I post-operatively (free of disabling seizures), among them 74 were in class Ia (totally seizure free). Nine patients were in Engel's class II and six were in Engel's class III or IV (failures). There was no surgical mortality. Three patients had a postoperative hematoma; two patients required a shunt insertion; in three patients meningitis occurred; and two patients had postoperative ischaemia of the anterior choroidal artery territory, which resulted in a mild permanent hemiparesis. Neuropsychological complications are not addressed in detail in this article.

CONCLUSIONS

These data indicate that "tailored" resective surgery for temporo-mesial epilepsy can be performed with a low rate of morbidity, and is highly efficacious. The use of invasive presurgical investigation (SEEG) may explain this high rate of success.

Disruption of the neurogenic potential of the dentate gyrus in a mouse model of temporal lobe epilepsy with focal seizures

Adult hippocampal neurogenesis is enhanced in response to multiple stimuli including seizures. However, the relationship between neurogenesis and the development of temporal lobe epilepsy (TLE) remains unclear. Unilateral intrahippocampal injection of kainate in adult mice models the morphological characteristics (e.g. neuronal loss, gliosis, granule cell dispersion and hypertrophy) and occurrence of chronic, spontaneous recurrent partial seizures observed in human TLE. We investigated the influence of a kainate-induced epileptogenic focus on hippocampal neurogenesis, comparing neural stem cell proliferation following status epilepticus and spontaneous recurrent partial seizures. Cell proliferation in the subgranular zone was transiently increased bilaterally after kainate treatment. As a result, neurogenesis was stimulated in the contralateral dentate gyrus. In contrast, the epileptic hippocampus exhibited a strongly reduced neurogenic potential, even after onset of spontaneous recurrent partial seizures, possibly due to an alteration of the neurogenic niche in the subgranular zone. These results show that neurogenesis does not contribute to the formation of the epileptic focus and may be affected when dispersion of dentate gyrus granule cells occurs. Therefore, in patients with TLE, hippocampal sclerosis and granule cell dispersion may play a significant role in disrupting the potential for hippocampal neurogenesis.

Left hippocampal pathology is associated with atypical language lateralization in patients with focal epilepsy

It is well recognized that the incidence of atypical language lateralization is increased in patients with focal epilepsy. The hypothesis that shifts in language dominance are particularly likely when epileptic lesions are located in close vicinity to the so-called language-eloquent areas rather than in more remote brain regions such as the hippocampus has been challenged by recent studies. This study was undertaken to assess the effect of lesions in different parts of the left hemisphere, lesions present during language acquisition, on language lateralization. We investigated 84 adult patients with drug-resistant focal epilepsy with structural lesions and 45 healthy control subjects with an established functional MRI language paradigm. Out of the 84 patients 43 had left hippocampal sclerosis, 13 a left frontal lobe lesion and 28 a left temporal-lateral lesion. All these lesions were likely to have been present during the first years of life during language acquisition. To assess the lateralization of cerebral language representation globally as well as regionally, we calculated lateralization indices derived from activations in four regions of interest (i.e. global, inferior frontal, temporo-parietal and remaining prefrontal). Patients with left hippocampal sclerosis showed less left lateralized language representations than all other groups of subjects (P < 0.005). This effect was independent of the factor of region, indicating that language lateralization was generally affected by a left hippocampal sclerosis. Patients with left frontal lobe or temporal-lateral lesions displayed the same left lateralization of language-related activations as the control subjects. Thus, the hippocampus seems to play an important role in the establishment of language dominance. Possible underlying mechanisms are discussed.

Propagation Dynamics of Epileptiform Activity Acutely Induced by Bicuculline in the Hippocampal-Parahippocampal Region of the Isolated Guinea Pig Brain

PURPOSE

Aim of the study is to investigate the involvement of parahippocampal subregions in the generation and in the propagation of focal epileptiform discharges in an acute model of seizure generation in the temporal lobe induced by arterial application of bicuculline in the in vitro isolated guinea pig brain preparation.

METHODS

Electrophysiological recordings were simultaneously performed with single electrodes and multichannel silicon probes in the entorhinal, perirhinal, and piriform cortices and in the area CA1 of the hippocampus of the in vitro isolated guinea pig brain. Interictal and ictal epileptiform discharges restricted to the temporal region were induced by a brief (3-5 min) arterial perfusion of the GABA(A) receptor antagonist, bicuculline methiodide (50 microM). Current source density analysis of laminar field profiles performed with the silicon probes was carried out at different sites to establish network interactions responsible for the generation of epileptiform potentials. Nonlinear regression analysis was conducted on extracellular recordings during ictal onset in order to quantify the degree of interaction between fast activities generated at different sites, as well as time delays.

RESULTS

Experiments were performed in 31 isolated guinea pig brains. Bicuculline-induced interictal and ictal epileptiform activities that showed variability of spatial propagation and time course in the olfactory-temporal region. The most commonly observed pattern (n = 23) was characterized by the initial appearance of interictal spikes (ISs) in the piriform cortex (PC), which propagated to the lateral entorhinal region. Independent and asynchronous preictal spikes originated in the entorhinal cortex (EC)/hippocampus and progressed into ictal fast discharges (around 25 Hz) restricted to the entorhinal/hippocampal region. The local generation of fast activity was verified and confirmed both by CSD and phase shift analysis performed on laminar profiles. Fast activity was followed by synchronous afterdischarges that propagated to the perirhinal cortex (PRC) (but not to the PC). Within 1-9 min, the ictal discharge ceased and a postictal period of depression occurred, after which periodic ISs in the PC resumed. Unlike preictal ISs, postictal ISs propagated to the PRC.

CONCLUSIONS

Several studies proposed that reciprocal connections between the entorhinal and the PRC are under a very efficient inhibitory control (1). We report that ISs determined by acute bicuculline treatment in the isolated guinea pig brain progress from the PC to the hippocampus/EC just before ictal onset. Ictal discharges are characterized by a peculiar pattern of fast activity that originates from the entorhinal/hippocampal region and only secondarily propagates to the PRC. Postictal propagation of ISs to the PRC occurred exclusively when an ictal discharge was generated in the hippocampal/entorhinal region. The results suggest that reiteration of ictal events may promote changes in propagation pattern of epileptiform discharges that could act as trigger elements in the development of temporal lobe epilepsy.

Epileptogenesis and chronic seizures in a mouse model of temporal lobe epilepsy are associated with distinct EEG patterns and selective neurochemical alterations in the contralateral hippocampus

Major aspects of temporal lobe epilepsy (TLE) can be reproduced in mice following a unilateral injection of kainic acid into the dorsal hippocampus. This treatment induces a non-convulsive status epilepticus and acute lesion of CA1, CA3c and hilar neurons, followed by a latent phase with ongoing ipsilateral neuronal degeneration. Spontaneous focal seizures mark the onset of the chronic phase. In striking contrast, the ventral hippocampus and the contralateral side remain structurally unaffected and seizure-free. In this study, functional and neurochemical alterations of the contralateral side were studied to find candidate mechanisms underlying the lack of a mirror focus in this model of TLE. A quantitative analysis of simultaneous, bilateral EEG recordings revealed a significant decrease of theta oscillations ipsilaterally during the latent phase and bilaterally during the chronic phase. Furthermore, the synchronization of bilateral activity, which is very high in control, was strongly reduced already during the latent phase and the decrease was independent of recurrent seizures. Immunohistochemical analysis performed in the contralateral hippocampus of kainate-treated mice revealed reduced calbindin-labeling of CA1 pyramidal cells; down-regulation of CCK-8 and up-regulation of NPY-labeling in mossy fibers; and a redistribution of galanin immunoreactivity. These changes collectively might limit neuronal excitability in CA1 and dentate gyrus, as well as glutamate release from mossy fiber terminals. Although these functional and neurochemical alterations might not be causally related, they likely reflect long-ranging network alterations underlying the independent evolution of the two hippocampal formations during the development of an epileptic focus in this model of TLE.

Hippocampal sclerosis in severe myoclonic epilepsy in infancy: a retrospective MRI study

PURPOSE

Severe myoclonic epilepsy in infancy (SMEI; Dravet's syndrome) is a malignant epilepsy syndrome characterized by early prolonged febrile convulsions (PFCs) with secondary psychomotor delay and a variety of therapy-resistant seizures. Although the initial symptoms are repeated PFCs, the MRI performed at the onset of disease shows no hippocampal structural abnormalities. We aimed to assess clinical and serial MRI data of patients with SMEI with a special attention to the temporomedial structures. To our knowledge, this is the first systematic MRI study in this disease.

METHODS

Clinical and MRI data of all SMEI patients treated in our hospitals between 1996 and 2004 were reviewed.

RESULTS

Twenty-eight MRIs from 14 children (one to four images/patient) were included. Age at disease onset was between 3 and 9 months; age at initial MRI was 5 months to 13 years. Ten of 14 patients showed hippocampal sclerosis (HS) during the course of the disease (nine unilateral, one bilateral). Six of these 10 had a normal initial MRI. Age at the first verified HS was between 14 months and 13 years. Neither complex partial seizures nor anterior temporal irritative zone was recorded in these children.

CONCLUSIONS

After initially normal structures, in most patients with SMEI, HS develops several months or years after the first PFC. These data support the hypothesis that PFC might be responsible for HS, but other factors and individual sensitivity should play a role in this process.

The temporopolar cortex plays a pivotal role in temporal lobe seizures

We investigated the role of the temporal pole (TP) in 48 consecutive patients with drug-refractory temporal lobe epilepsy (TLE). Chronic depth recordings of TP cortex activity were used in association with video recording of ictal symptoms during 48 spontaneous seizures. In 23 cases (48%, group 1) the TP was involved at the onset of the seizure, before or concurrently with the hippocampus. In the remaining 25 patients (52%, group 2) the TP was involved 16.4 +/- 13.8 s after the hippocampus. A past history of febrile seizures was found in both groups, with no statistical difference. Ictal symptoms did not differentiate TP seizures from seizures originating in the hippocampus but the first clinical sign occurred sooner in group 1 compared with group 2 (respectively 10.56 +/- 9 and 25.7 +/- 19 s, respectively, P = 0.005). Loss of awareness also occurred sooner in the case of TP seizures compared with mesiotemporal lobe (MTL) seizures (22.9 +/- 22.6 versus 42.2 +/- 18.6 s, P = 0.0002). MRI data analysis showed that hippocampal sclerosis was present in both groups of patients, although it was more frequent in patients with MTL onset. Anterior temporal white matter changes were found ipsilateral to the epileptogenic area and tended to be more frequent in patients with TP seizures. All the patients underwent tailored anterior temporal lobectomy that included the TP, the hippocampus, the parahippocampal gyrus and the anterior part of the lateral temporal cortex. A better postoperative outcome was achieved in group 1 compared with group 2 (Engel class 1, 95 and 72% respectively, P = 0.04). We conclude that the frequent TP involvement at the onset of seizures could be a supplementary explanation for some failures of selective amygdalohippocampectomy, which should be addressed preferentially to well-selected patients. Moreover, the involvement of the TP cortex at the onset of the seizures is a good predicting factor for postoperative seizure outcome.