Transcriptomic and genetic analyses reveal potential causal drivers for intractable partial epilepsy.

Mesial temporal lobe epilepsy with hippocampal sclerosis represents the most common epilepsy syndrome in adult patients with medically intractable partial epilepsy. Mesial temporal lobe epilepsy is usually regarded as a polygenic and complex disorder, still poorly understood but probably caused and perpetuated by dysregulation of numerous biological networks and cellular functions. The study of gene expression changes by single nucleotide polymorphisms in regulatory elements (expression quantitative trait loci, eQTLs) has been shown to be a powerful complementary approach to the detection and understanding of risk loci by genome-wide association studies. We performed a whole (gene and exon-level) transcriptome analysis on cortical tissue samples (Brodmann areas 20 and 21) from 86 patients with mesial temporal lobe epilepsy with hippocampal sclerosis and 75 neurologically healthy controls. Genome-wide genotyping data from the same individuals (patients and controls) were analysed and paired with the transcriptome data. We report potential epilepsy-risk eQTLs, some of which are specific to tissue from patients with mesial temporal lobe epilepsy with hippocampal sclerosis. We also found large transcriptional and splicing deregulation in mesial temporal lobe epilepsy with hippocampal sclerosis tissue as well as gene networks involving neuronal and glial mechanisms that provide new insights into the cause and maintenance of the seizures. These data (available via the 'Seizubraineac' web-tool resource, www.seizubraineac.org) will facilitate the identification of new therapeutic targets and biomarkers as well as genetic risk variants that could influence epilepsy and pharmacoresistance.

The lifelong course of chronic epilepsy: the Chalfont experience.

The long-term outcome of chronic epilepsy remains largely unknown, despite a long historical experience. We report the lifelong course of epilepsy of an historical cohort of 235 subjects who were in residential care at the Chalfont Centre for Epilepsy: 122 had comprehensive post-mortem examination. The populations admitted as resident to the centre over time followed the evolution of society's perception of epilepsy. 'Early residents' (before 1972) were admitted for sheltered employment, escaping stigmatization, whereas 'later' residents with more severe epilepsies were admitted for care. Subjects admitted before 1972 were similar to subjects followed nowadays as outpatients, whereas patients admitted later with a higher burden of disabilities are often those in residential care. This long follow-up allowed exploration of a wide spectrum of epilepsies, affecting both subjects who were otherwise healthy and those with co-morbidities. Age at death showed a bimodal distribution with an early peak of mortality between 45-50 years old, whilst the remainder had life expectancy comparable to the general population. As a group, subjects who had post-mortem examination were not significantly different from patients who did not have post-mortem examination, but post-mortem examination provided data that were otherwise unavailable. For those who had post-mortem examination, sudden unexpected death in epilepsy (SUDEP, 18% of all deaths) did not fully explain the early mortality, to which co-morbidities contributed. High seizure frequency was a significant independent predictor of early death even after excluding SUDEP (e.g. reduction in years of life for those who had >4 seizures/month compared with those who had <1 seizure/month: 13 years; 95% confidence interval: 6-19; overall P = 0.0006). Those who survived to older age increasingly went into spontaneous remission lasting until death (in the whole cohort, 38/166, 23% of those who died in or after sixth decade). In subjects who had post-mortem examination, older age (odds ratio = 1.13; 95% confidence interval: 1.06-1.20) and presence of neuropathologically confirmed degenerative changes (that were not the cause of epilepsy) (odds ratio 7.14; 1.95-26.2) were independent predictors of terminal remission. Epilepsy may cause premature death indirectly through co-morbid conditions. Terminal remission occurs even without prior remissions; ageing may improve epilepsy drug responsiveness although unknown factors related to the natural history may also play a role.

Regional thalamic neuropathology in patients with hippocampal sclerosis and epilepsy: a postmortem study.

PURPOSE: Clinical, experimental, and neuroimaging data all indicate that the thalamus is involved in the network of changes associated with temporal lobe epilepsy (TLE), particularly in association with hippocampal sclerosis (HS), with potential roles in seizure initiation and propagation. Pathologic changes in the thalamus may be a result of an initial insult, ongoing seizures, or retrograde degeneration through reciprocal connections between thalamic and limbic regions. Our aim was to carry out a neuropathologic analysis of the thalamus in a postmortem (PM) epilepsy series, to assess the distribution, severity, and nature of pathologic changes and its association with HS. METHODS: Twenty-four epilepsy PM cases (age range 25-87 years) and eight controls (age range 38-85 years) were studied. HS was classified as unilateral (UHS, 11 cases), bilateral (BHS, 4 cases) or absent (No-HS, 9 cases). Samples from the left and right sides of the thalamus were stained with cresyl violet (CV), and for glial firbillary acidic protein (GFAP) and synaptophysin. Using image analysis, neuronal densities (NDs) or field fraction staining values (GFAP, synaptophysin) were measured in four thalamic nuclei: anteroventral nucleus (AV), lateral dorsal nucleus (LD), mediodorsal nucleus (MD), and ventrolateral nucleus (VL). The results were compared within and between cases. KEY FINDINGS: The severity, nature, and distribution of thalamic pathology varied between cases. A pattern that emerged was a preferential involvement of the MD in UHS cases with a reduction in mean ND ipsilateral to the side of HS (p = 0.05). In UHS cases, greater field fraction values for GFAP and lower values for synaptophysin and ND were seen in the majority of cases in the MD ipsilateral to the side of sclerosis compared to other thalamic nuclei. In addition, differences in the mean ND between classical HS, atypical HS, and No-HS cases were noted in the ipsilateral MD (p < 0.05), with lower values observed in HS. SIGNIFICANCE: Our study demonstrates that stereotypical pathologic changes, as seen in HS, are not clearly defined in the thalamus. This may be partly explained by the heterogeneity of our PM study group. With quantitation, there is some evidence for preferential involvement of the MD, suggesting a potential role in TLE, which requires further investigation.

A quantitative study of white matter hypomyelination and oligodendroglial maturation in focal cortical dysplasia type II.

PURPOSE: A diagnostic feature of focal cortical dysplasia (FCD) type II on magnetic resonance imaging (MRI) is increased subcortical white matter (WM) signal on T2 sequences corresponding to hypomyelination, the cause of which is unknown. We aimed to quantify WM pathology in FCD type II and any deficiency in the numbers and differentiation of oligodendroglial (OL) cell types within the dysplasia. METHODS: In 19 cases we defined four regions of interests (ROIs): ROI1 = abnormal WM beneath dysplasia, ROI2 =dysplastic cortex, ROI3 = normal WM, and ROI4 = normal cortex. We quantified axonal and myelin density using immunohistochemistry for neurofilament, myelin basic protein and quantified mature OL with NogoA, cyclic nucleotide 3-phosphodiesterase (CNPase) and OL precursor cell (OPC) densities with platelet derived growth factor receptor (PDGFR)α, ß and NG-2 in each region. KEY FINDINGS: We observed a significant reduction in myelin and axons in the WM beneath dysplasia relative to normal WM and there was a correlation between relative reduction of myelin and neurofilament in each case. OL and OPC were present in the WM beneath dysplasia and although present in lower numbers with most markers, were not significantly different from normal WM. Neurofilament and myelin labeling highlighted disorganized orientation of fibers in dysplastic cortex but there were no significant quantitative differences compared to normal cortex. Clinical correlations showed an association between the severity of reduction of myelin and axons in the WM of FCD and duration of epilepsy. SIGNIFICANCE: These findings indicate a reduction of myelinated axons in the WM of FCD type II rather than dysmyelination as the primary pathologic process underlying WM abnormalities, possibly influenced by duration of seizures. The range of OPC to OL present in FCD type II does not implicate a primary failure of cell recruitment and differentiation of these cell types in this pathology.

Neuropathology of the blood-brain barrier and pharmaco-resistance in human epilepsy.

Blood-brain barrier dysfunction is implicated in various neurological conditions. Modulating the blood-brain barrier may have therapeutic value. Progress is hindered by our limited understanding of the pathophysiology of the blood-brain barrier in humans, partly due to restricted availability of human tissue, and because human tissue can only provide limited data about temporal patterns of change. We addressed these important challenges by examining surgically resected brain tissue with various lengths of interval between intracranial depth electrode-related injury and resection, and post-mortem whole brain from patients with drug-sensitive or drug-resistant chronic epilepsy and controls. In this valuable set of resources, we found that: (i) there is a highly localized overexpression of P-glycoprotein in the epileptogenic hippocampus of patients with drug-resistant epilepsy; (ii) this overexpression appears specific to P-glycoprotein and does not affect other transporters; (iii) P-glycoprotein is expressed on the vascular endothelium and end-feet of vascular glia (forming a 'double cuff') in drug-resistant epileptic cases but not in post-mortem controls or surgical epilepsy tissue with electrode-related injuries; (iv) an acute insult from intracranial electrode recording causes localized inflammation, increased blood-brain barrier permeability and structural changes to vasculature detectable for up to at least 330 days and (v) chronic epilepsy is associated with inflammation, enhanced blood-brain barrier permeability and increased P-glycoprotein expression. The occurrence of seizures appears central to P-glycoprotein overexpression. Our findings have potential clinical impact because they directly improve our understanding of blood-brain barrier disruption and transporter expression in humans. In particular, our findings show that the expression of P-glycoprotein in humans is compatible with the inherent assumptions of one current hypothesis of multidrug resistance, and that the specific upregulation of P-glycoprotein expression is likely to be associated with ongoing chronic seizures. There may be a therapeutic window after initial acute injury for the prevention of P-glycoprotein overexpression, and thus this one potential component of drug resistance. Our findings add to the need for careful consideration of the benefit and risks of invasive electroencephalographic recording in surgical evaluation of drug-resistant epilepsy.

Investigation of hypoxia-inducible factor-1α in hippocampal sclerosis: a postmortem study.

PURPOSE: Hypoxia-inducible factor-1α (HIF-1α) is involved in critical aspects of cell survival in response to hypoxia and regulates vascular endothelial growth factor (VEGF) expression. Previous experimental and human studies in epilepsy show up-regulation of VEGF following seizures, although expression of HIF-1α as its potential regulator has not been explored. We used a postmortem (PM) series from patients with epilepsy and hippocampal sclerosis (HS) to investigate patterns of expression of HIF-1α and VEGF and their potential contribution to neuroprotection. METHOD: In 33 PMs (17 cases with unilateral HS, 3 with bilateral HS, 3 with No-HS, and 10 controls), we quantified neuronal immunolabeling for HIF-1α and VEGF in hippocampal subfields. KEY FINDINGS: HIF-1α- and VEGF-immunopositive hippocampal neurones were observed in HS, No-HS, and also in control cases; there was no significant difference in overall labeling between epilepsy cases and controls. In positive cases, HIF-1α and VEGF neuronal labeling localized primarily in CA1, CA4, and CA3 subfields in all groups; significantly more positive neurons were seen in the entorhinal cortex in epilepsy cases (p < 0.05). Labeling lateralized to the side of sclerosis in unilateral HS cases, with significant differences between hemispheres (p < 0.05). There was a trend for high HIF-1α labeling scores in patients with Dravet syndrome without HS and sudden unexpected death in epilepsy (SUDEP) cases, and lower scores with long seizure-free periods prior to death. Hippocampal HIF-1α and VEGF labeling showed a significant correlation. There was neuronal colocalization of HIF-1α and VEGF. SIGNIFICANCE: Regional expression patterns are in keeping with seizure-related activation of HIF-1α and VEGF. The prominent expression in non-HS cases could support an overall neuroprotective effect. Correlation between HIF-1α and VEGF neuronal immunolabeling supports HIF-1α-mediated induction of VEGF in epilepsy.

In vivo monitoring of neuronal loss in traumatic brain injury: a microdialysis study.

Traumatic brain injury causes diffuse axonal injury and loss of cortical neurons. These features are well recognized histologically, but their in vivo monitoring remains challenging. In vivo cortical microdialysis samples the extracellular fluid adjacent to neurons and axons. Here, we describe a novel neuronal proteolytic pathway and demonstrate the exclusive neuro-axonal expression of Pavlov's enterokinase. Enterokinase is membrane bound and cleaves the neurofilament heavy chain at positions 476 and 986. Using a 100 kDa microdialysis cut-off membrane the two proteolytic breakdown products, extracellular fluid neurofilament heavy chains NfH(476-986) and NfH(476-1026), can be quantified with a relative recovery of 20%. In a prospective clinical in vivo study, we included 10 patients with traumatic brain injury with a median Glasgow Coma Score of 9, providing 640 cortical extracellular fluid samples for longitudinal data analysis. Following high-velocity impact traumatic brain injury, microdialysate extracellular fluid neurofilament heavy chain levels were significantly higher (6.18 ± 2.94 ng/ml) and detectable for longer (> 4 days) compared with traumatic brain injury secondary to falls (0.84 ± 1.77 ng/ml, < 2 days). During the initial 16 h following traumatic brain injury, strong correlations were found between extracellular fluid neurofilament heavy chain levels and physiological parameters (systemic blood pressure, anaerobic cerebral metabolism, excessive brain tissue oxygenation, elevated brain temperature). Finally, extracellular fluid neurofilament heavy chain levels were of prognostic value, predicting mortality with an odds ratio of 7.68 (confidence interval 2.15-27.46, P = 0.001). In conclusion, this study describes the discovery of Pavlov's enterokinase in the human brain, a novel neuronal proteolytic pathway that gives rise to specific protein biomarkers (NfH(476-986) and Nf(H476-1026)) applicable to in vivo monitoring of diffuse axonal injury and neuronal loss in traumatic brain injury.

Neurofibrillary tangle pathology and Braak staging in chronic epilepsy in relation to traumatic brain injury and hippocampal sclerosis: a post-mortem study.

The long-term pathological effects of chronic epilepsy on normal brain ageing are unknown. Previous clinical and epidemiological studies show progressive cognitive decline in subsets of patients and an increased prevalence of Alzheimer's disease in epilepsy. In a post-mortem series of 138 patients with long-term, mainly drug-resistant epilepsy, we carried out Braak staging for Alzheimer's disease neurofibrillary pathology using tau protein immunohistochemistry. The stages were compared with clinicopathological factors, including seizure history and presence of old traumatic brain injury. Overall, 31% of cases were Braak Stage 0, 36% Stage I/II, 31% Stage III/IV and 2% Stage V/VI. The mean age at death was 56.5 years and correlated with Braak stage (P < 0.001). Analysis of Braak stages within age groups showed a significant increase in mid-Braak stages (III/IV), in middle age (40-65 years) compared with data from an ageing non-epilepsy series (P < 0.01). There was no clear relationship between seizure type (generalized or complex partial), seizure frequency, age of onset and duration of epilepsy with Braak stage although higher Braak stages were noted with focal more than with generalized epilepsy syndromes (P < 0.01). In 30% of patients, there was pathological evidence of traumatic brain injury that was significantly associated with higher Braak stages (P < 0.001). Cerebrovascular disease present in 40.3% and cortical malformations in 11.3% were not significantly associated with Braak stage. Astrocytic-tau protein correlated with the presence of both traumatic brain injury (P < 0.01) and high Braak stage (P < 0.001). Hippocampal sclerosis, identified in 40% (bilateral in 48%), was not associated with higher Braak stages, but asymmetrical patterns of tau protein accumulation within the sclerotic hippocampus were noted. In over half of patients with cognitive decline, the Braak stage was low indicating causes other than Alzheimer's disease pathology. In summary, there is evidence of accelerated brain ageing in severe chronic epilepsy although progression to high Braak stages was infrequent. Traumatic brain injury, but not seizures, was associated with tau protein accumulation in this series. It is likely that Alzheimer's disease pathology is not the sole explanation for cognitive decline associated with epilepsy.

Dravet syndrome as epileptic encephalopathy: evidence from long-term course and neuropathology.

Dravet syndrome is an epilepsy syndrome of infantile onset, frequently caused by SCN1A mutations or deletions. Its prevalence, long-term evolution in adults and neuropathology are not well known. We identified a series of 22 adult patients, including three adult post-mortem cases with Dravet syndrome. For all patients, we reviewed the clinical history, seizure types and frequency, antiepileptic drugs, cognitive, social and functional outcome and results of investigations. A systematic neuropathology study was performed, with post-mortem material from three adult cases with Dravet syndrome, in comparison with controls and a range of relevant paediatric tissue. Twenty-two adults with Dravet syndrome, 10 female, were included, median age 39 years (range 20-66). SCN1A structural variation was found in 60% of the adult Dravet patients tested, including one post-mortem case with DNA extracted from brain tissue. Novel mutations were described for 11 adult patients; one patient had three SCN1A mutations. Features of Dravet syndrome in adulthood include multiple seizure types despite polytherapy, and age-dependent evolution in seizure semiology and electroencephalographic pattern. Fever sensitivity persisted through adulthood in 11 cases. Neurological decline occurred in adulthood with cognitive and motor deterioration. Dysphagia may develop in or after the fourth decade of life, leading to significant morbidity, or death. The correct diagnosis at an older age made an impact at several levels. Treatment changes improved seizure control even after years of drug resistance in all three cases with sufficient follow-up after drug changes were instituted; better control led to significant improvement in cognitive performance and quality of life in adulthood in two cases. There was no histopathological hallmark feature of Dravet syndrome in this series. Strikingly, there was remarkable preservation of neurons and interneurons in the neocortex and hippocampi of Dravet adult post-mortem cases. Our study provides evidence that Dravet syndrome is at least in part an epileptic encephalopathy.

Investigation of widespread neocortical pathology associated with hippocampal sclerosis in epilepsy: a postmortem study.

PURPOSE: One possible cause for surgical failure following temporal lobectomy for the treatment of epilepsy due to classical hippocampal sclerosis (CHS) is the presence of more widespread cortical changes. Neocortical changes in CHS shown by quantitative neuroimaging studies may involve hippocampal projection pathways. Our aim was to quantitate neocortical pathology using a postmortem series of brains from patients with epilepsy and CHS. METHODS: Sections from 13 cortical regions from both left and right hemispheres, including hippocampal projection pathways, were examined from nine epilepsy patients with unilateral CHS (4), bilateral CHS (2), non-CHS (3), and non-epilepsy controls (4). Using GFAP, CD68, and NPY immunohistochemistry as markers of acquired neocortical pathology, quantitative analysis of the staining fractions in the cortex and white matter was carried out. KEY FINDINGS: Higher staining fractions were observed for all markers in both cortex and white matter in CHS patients, which was significantly different for CD68 and NPY compared to controls (p < 0.05) but not to non-CHS epilepsy cases. There was no significant difference between staining fractions in left and right hemispheres for unilateral CHS cases. Regional analysis showed preferential gliosis and microgliosis of temporal poles, frontal poles, and orbitofrontal cortex in epilepsy cases. SIGNIFICANCE: This study supports acquired neocortical pathology in epilepsy patients both with and without CHS. Cortical pathology does not show lateralization to the side of CHS. Preferential involvement of the temporal and frontal poles may relate to other factors, such as cortical injury associated with seizures, rather than involvement through hippocampal pathways.

Genomic microdeletions associated with epilepsy: not a contraindication to resective surgery.

PURPOSE: Several recent reports of genomic microdeletions in epilepsy will generate further research; discovery of more microdeletions and other important classes of variants may follow. Detection of such genetic abnormalities in patients being evaluated for surgical treatment might raise concern that a genetic defect, possibly widely expressed in the brain, will affect surgical outcome. METHODS: A reevaluation was undertaken of clinical presurgical data, histopathology of surgical specimen, and postsurgical outcome in patients with mesial temporal lobe epilepsy (MTLE) who have had surgical treatment for their drug-resistant seizures, and who have been found to have particular genomic microdeletions. KEY FINDINGS: Three thousand eight hundred twelve patients with epilepsy were genotyped and had a genome-wide screen to identify copy number variation. Ten patients with MTLE, who had resective epilepsy surgery, were found to have 16p13.11 microdeletions or other microdeletions >1 Mb. On histopathology, eight had classical hippocampal sclerosis (HS), one had nonspecific findings, and one had a hamartoma. Median postsurgical follow-up time was 48 months (range 10-156 months). All patients with HS were seizure-free after surgery, International League Against Epilepsy (ILAE) outcome class 1, at last follow-up; the patient with nonspecific pathology had recurrence of infrequent seizures after 7 years of seizure freedom. The patient with a hamartoma never became seizure-free. SIGNIFICANCE: Large microdeletions can be found in patients with "typical" MTLE. In this small series, patients with MTLE who meet criteria for resective surgery and harbor large microdeletions, at least those we have detected, can have a good postsurgical outcome. Our findings add to the spectrum of causal heterogeneity of MTLE + HS.

The application of cortical layer markers in the evaluation of cortical dysplasias in epilepsy.

The diagnostic criteria for focal cortical dysplasia type I (FCD I) remain to be well and consistently defined. Cortical layer-specific markers (CLM) provide a potential tool for the objective assessment of any dyslamination. We studied expression patterns of recognised CLM using immunohistochemistry for N200, ER81, Otx1, Map1b (subsets of V/VI projection neurones), Pax6, Tbr1, Tbr2 (differentially expressed in cortical neurones from intermediate progenitor cells), Cux 1 (outer cortical layers) and MASH1 (ventricular zone progenitors). Dysplasia subtypes included FCD I and II, dysplasias adjacent to hippocampal sclerosis (HS) or dysembryoplastic neuroepithelial tumours (DNTs); all were compared to neonatal and adult controls. Laminar expression patterns in normal cortex were observed with Tbr1, Map1b, N200 and Otx1. FCDI cases in younger patients were characterised by abnormal expression in layer II for Tbr1 and Otx1. FCDII showed distinct labelling of balloon cells (Pax6, ER81 and Otx1) and dysmorphic neurones (Tbr 1, N200 and Map1b) supporting origins from radial glia and intermediate progenitor cells, respectively. In temporal lobe sclerosis cases with dysplasia adjacent to HS, Tbr1 and Map1b highlighted abnormal orientation of neurones in layer II. Dyslamination was not confirmed in the perilesional cortex of DNT with CLM. Finally, immature cell types (Otx1, Pax6 and Tbr2) were noted in varied pathologies. One possibility is activation of progenitor cell populations which could contribute to the pathophysiology of these lesions.

Reliability of patterns of hippocampal sclerosis as predictors of postsurgical outcome.

PURPOSE: Around one-third of patients undergoing temporal lobe surgery for the treatment of intractable temporal lobe epilepsy with hippocampal sclerosis (HS) fail to become seizure-free. Identifying reliable predictors of poor surgical outcome would be helpful in management. Atypical patterns of HS may be associated with poorer outcomes. Our aim was to identify atypical HS cases from a large surgical series and to correlate pathology with clinical and outcome data. METHODS: Quantitative neuropathologic evaluation on 165 hippocampal surgical specimens and 21 control hippocampi was carried out on NeuN-stained sections. Neuronal densities (NDs) were measured in CA4, CA3, CA2, and CA1 subfields. The severity of granule cell dispersion (GCD) was assessed. RESULTS: Comparison with control ND values identified the following patterns based on the severity and distribution of neuronal loss: classical HS (CHS; n = 60) and total HS (THS; n = 39). Atypical patterns were present in 30% of cases, including end-folium sclerosis (EFS; n = 5), CA1 predominant pattern (CA1p; n = 9), and indeterminate HS (IHS, n = 35). No HS was noted in 17 cases. Poorest outcomes were noted for no-HS, and CA1p groups with 33-44% International League Against Epilepsy (ILAE) class I at up to 2 years follow-up compared to 69% for CHS (p < 0.05). GCD associated with HS type (p < 0.01), but not with outcome. CONCLUSIONS: These findings support the identification and delineation of atypical patterns of HS using quantitative methods. Atypical patterns may represent distinct clinicopathologic subtypes and may have predictive value following epilepsy surgery.

Multi-focal occurrence of cortical dysplasia in epilepsy patients.

This study describes the existence and the clinical and electrophysiological features of multi-focal cortical dysplasia in epilepsy patients. Five patients with intractable focal epilepsy are reported. All patients underwent invasive presurgical video-electroencephalography monitoring. Localization of dysplastic areas was based on high-resolution magnetic resonance scanning, surface and intracranial electroencephalography. Four patients underwent epilepsy surgery. Histological findings in focal cortical dysplasia (FCD) were classified according to Palmini. In addition, genetic examinations were performed in order to assess possible mutations in the genes for tuberous sclerosis complex. In four patients, FCDs were located in the same hemisphere. One case presented with bilateral FCDs. In three patients seizures arose from two separate dysplastic areas and in one patient, one lesion showed only interictal activity. In one further patient, seizures started exclusively from the hippocampus. In two of three patients with removal of the FCDs, the histological subtype was identical (Palmini type 2) and in one patient, histology differed between the lesions. All operated patients became seizure-free. In patients with FCD type 2, germ-line mutations in the tuberous sclerosis complex genes were not detectable. Dysplastic brain regions may not be restricted to a single brain region. Areas of FCD can have different degrees of epileptogenicity, ranging from electrographic silence to interictal epileptic discharges and initial involvement in seizure generation. Based on genetic analysis and clinical features, multi-FCD in this patient series was not likely to be related to tuberous sclerosis.

Temporal lobe sclerosis associated with hippocampal sclerosis in temporal lobe epilepsy: neuropathological features.

Widespread changes involving neocortical and mesial temporal lobe structures can be present in patients with temporal lobe epilepsy and hippocampal sclerosis. The incidence, pathology, and clinical significance of neocortical temporal lobe sclerosis (TLS) are not well characterized. We identified TLS in 30 of 272 surgically treated cases of hippocampal sclerosis. Temporal lobe sclerosis was defined by variable reduction of neurons from cortical layers II/III and laminar gliosis; it was typically accompanied by additional architectural abnormalities of layer II, that is, abnormal neuronal orientation and aggregation. Quantitative analysis including tessellation methods for the distribution of layer II neurons supported these observations. In 40% of cases, there was a gradient of TLS with more severe involvement toward the temporal pole, possibly signifying involvement of hippocampal projection pathways. There was a history of a febrile seizure as an initial precipitating injury in 73% of patients with TLS compared with 36% without TLS; no other clinical differences between TLS and non-TLS cases were identified. Temporal lobe sclerosis was not evident preoperatively by neuroimaging. No obvious effect of TLS on seizure outcome was noted after temporal lobe resection; 73% became seizure-free at 2-year follow-up. In conclusion, approximately 11% of surgically treated hippocampal sclerosis is accompanied by TLS. Temporal lobe sclerosis is likely an acquired process with accompanying reorganizational dysplasia and an extension of mesial temporal sclerosis rather than a separate pathological entity.

Cortical neuronal loss and hippocampal sclerosis are not detected by voxel-based morphometry in individual epilepsy surgery patients.

Voxel-based morphometry (VBM) has detected differences between brains of groups of patients with epilepsy and controls, but the sensitivity for detecting subtle pathological changes in single subjects has not been established. The aim of the study was to test the sensitivity of VBM using statistical parametric mapping (SPM5) to detect hippocampal sclerosis (HS) and cortical neuronal loss in individual patients. T1-weighted volumetric 1.5 T MR images from 13 patients with HS and laminar cortical neuronal loss were segmented, normalised and smoothed using SPM5. Both modulated and non-modulated analyses were performed. Comparisons of one control subject against the rest (n = 23) were first performed to ascertain the smoothing level with the lowest number of SPM changes in controls. Each patient was then compared against the whole control group. The lowest number of SPM changes in control subjects was found at a smoothing level of 10 mm full width half maximum for modulated and non-modulated data. In the patient group, no SPM abnormalities were found in the affected temporal lobe or hippocampus at this smoothing level. At lower smoothing levels there were numerous SPM findings in controls and patients. VBM did not detect any abnormalities associated with either laminar cortical neuronal loss or HS. This may be due to normalisation and smoothing of images and low statistical power in areas with larger inter-individual differences. This suggests that the methodology may currently not be suitable to detect particular occult abnormalities possibly associated with seizure onset zone in individual epilepsy patients with unremarkable standard structural MRI.

Doublecortin expression in focal cortical dysplasia in epilepsy.

PURPOSE: Doublecortin (DCX) is a microtubule-associated protein with regulatory roles in radial and tangential migration of neurons during cortical development. In normal adult cortex there is restricted expression, and DCX is widely used as a marker of neurogenesis. Imperfect corticogenesis is thought to underpin many focal cortical pathologies in epilepsy surgical series, including focal cortical dysplasia (FCD). The aim was to study DCX expression patterns in such lesions compared to normal developing and mature cortex. METHOD: Cases of FCD types Ia (13) and IIb (4), pediatric hippocampal sclerosis (HS) (5), temporal lobe sclerosis (5), glioneuronal tumors (5), gray matter heterotopia (3), and control tissues (16) from a wide age range [20 gestational weeks (GW) to 85 years] were studied using immunohistochemistry to DCX. RESULTS: In controls and all epilepsy cases, perinuclear labeling of small round cells (SRCs) and satellite perineuronal cells was observed in both postmortem and surgical tissues. In FCD Ia up to the age of 4 years, prominent DCX-positive (DCX(+)), immature cells were present along the junction of layers I and II, with processes extending into the molecular layer. These cell types were not a significant feature in other pathologies, which showed multipolar DCX(+) cells or labeling of dysmorphic cells throughout the cortex. DISCUSSION: Persistent cellular DCX expression is confirmed in normal adult cortex. Characteristic expression patterns in layer II of FCD Ia could indicate delayed or abnormal cortical maturation rather than ongoing cytogenesis. This could be indicative of enhanced local cortical plasticity as well as a potential diagnostic feature of this type of pathology.

An investigation of the expression of G1-phase cell cycle proteins in focal cortical dysplasia type IIB.

Balloon cells (BCs) are the pathologic hallmark of focal cortical dysplasia type IIB, a common cause of pharmacoresistent epilepsy. Expression of markers of cell immaturity and of the proliferation marker minichromosome maintenance protein 2 (mcm2) have been previously shown in BCs, suggesting that these cells might represent a pool of less-differentiated cells licensed for replication. An alternative explanation is that these cells are the remnants of early cortical plate cells that have failed to differentiate or to be eliminated during development and are arrested in the cell cycle, a hypothesis that this study aims to explore. Using immunohistochemical methods and semiquantitative analysis in 19 cases of focal cortical dysplasia (ages 1-81 years), we studied the expression of cell cycle proteins important either in regulating progression through the G1 phase or inducing cell arrest and promoting premature senescence. Only a small fraction of BCs expressed geminin, suggesting that few BCs enter the S phase or complete the cell cycle. Variable expression of nonphosphorylated retinoblastoma protein (Rb), cdk4, and p53 was noted in BCs. Cyclin E, D1, cdk2, phosphorylated Rb (795 and 807/811), and checkpoint 2 expression levels were low in BCs. These findings suggest early rather than late G1 arrest. Cell senescence could be induced by an undefined cerebral insult during development or alternatively represent a physiologic replicative senescence. These findings also suggest that dysregulation of cell cycle pathways may occur in focal cortical dysplasia, which opens further areas for exploration as potential new treatment avenues.

Increased immunoreactivity of cdk5 activators in hippocampal sclerosis.

Cyclin-dependent kinase 5 is important in several in-vitro neurodegeneration paradigms. Whether cyclin-dependent kinase 5 contributes to cell death in human neurodegenerative diseases remains uncertain, particularly because post-mortem delay and other extrinsic factors might influence cyclin-dependent kinase 5 activity. Here we demonstrate increased immunoreactivity for the activators of cyclin-dependent kinase 5 in post-mortem human hippocampi affected by the neurodegenerative condition hippocampal sclerosis, but not in histologically normal hippocampi. Moreover, in post-mortem brain tissue from patients with unilateral hippocampal sclerosis, increased immunoreactivity for cyclin-dependent kinase 5 activators was detected in the hippocampus with sclerosis, but not in the contralateral hippocampus, suggesting that extrinsic factors are unlikely to account for the differential staining observed. Our findings suggest that deregulation of cyclin-dependent kinase 5 might contribute to the pathogenesis of hippocampal sclerosis.

Increased NKCC1 expression in refractory human epilepsy.

Cation-chloride co-transporters (CCTs), particularly NKCC1, may be important in epileptogenesis. We have performed a detailed histological examination of NKCC1 in large samples of patients with hippocampal sclerosis (HS) or focal cortical dysplasia (FCD), pathologies both commonly associated with pharmacoresistant epilepsy. We consistently found increased immunoreactivity for NKCC1 in HS and FCD, but not in adjacent histologically normal cortex. Our results suggest that NKCC1 might contribute to the pathogenesis or pathophysiology of HS and FCD, thereby potentially offering a new therapeutic target in the treatment of pharmacoresistant epilepsy.