Albert J. Becker

The clinicopathologic spectrum of focal cortical dysplasias: A consensus classification proposed by an ad hoc Task Force of the ILAE Diagnostic Methods Commission†

Purpose:  Focal cortical dysplasias (FCD) are localized regions of malformed cerebral cortex and are very frequently associated with epilepsy in both children and adults. A broad spectrum of histopathology has been included in the diagnosis of FCD. An ILAE task force proposes an international consensus classification system to better characterize specific clinicopathological FCD entities.

Limbic encephalitis as a precipitating event in adult-onset temporal lobe epilepsy.

Objective: Temporal lobe epilepsy with hippocampal sclerosis (TLE-HS) is the most frequent diagnosis in autopsy and surgical epilepsy series. TLE-HS usually starts during childhood or adolescence. There have been few studies of adult-onset disease. We recognized that some adult individuals have evidence of limbic encephalitis (LE), an autoimmune condition of adult life, which we proposed might lead directly to this syndrome. Methods: We performed a retrospective analysis of history, clinical and paraclinical findings, brain MRI, and outcome of surgical treatment including histopathology (if available) of all patients with TLE-HS presenting to this tertiary center within 6 years of epilepsy onset between 1999 and 2005. Results: Thirty-eight patients were identified, with median age at epilepsy onset of 37.8 years. Eleven patients (29%) were classified as having secondary HS (e.g., after head trauma, febrile seizures). Seven patients (11%) were classified as idiopathic. However, 9 patients (24%) had a diagnosis of definite LE, and another 11 individuals (29%) showed the typical LE pattern of MRI findings with hippocampal swelling evolving into atrophy with continuous FLAIR/T2 signal increase; they were diagnosed as possible LE. Bilateral abnormalities were more frequent in the two LE subgroups (60%) than in the two non-LE subgroups (22%; p = 0.025). Histopathology was performed in one patient with possible LE shortly after disease onset and showed a typical T cell infiltration and loss of hippocampal neurons. Conclusions: Temporal lobe epilepsy with hippocampal sclerosis can manifest in adult life. Around half the patients have evidence consistent with an autoimmune process. If confirmed, this should have implications for diagnosis, prevention, and treatment.

Meningeal hemangiopericytoma and solitary fibrous tumors carry the NAB2-STAT6 fusion and can be diagnosed by nuclear expression of STAT6 protein

Non-central nervous system hemangiopericytoma (HPC) and solitary fibrous tumor (SFT) are considered by pathologists as two variants of a single tumor entity now subsumed under the entity SFT. Recent detection of frequent NAB2-STAT6 fusions in both, HPC and SFT, provided additional support for this view. On the other hand, current neuropathological practice still distinguishes between HPC and SFT. The present study set out to identify genes involved in the formation of meningeal HPC. We performed exome sequencing and detected the NAB2-STAT6 fusion in DNA of 8/10 meningeal HPC thereby providing evidence of close relationship of these tumors with peripheral SFT. Due to the considerable effort required for exome sequencing, we sought to explore surrogate markers for the NAB2-STAT6 fusion protein. We adopted the Duolink proximity ligation assay and demonstrated the presence of NAB2-STAT6 fusion protein in 17/17 HPC and the absence in 15/15 meningiomas. More practical, presence of the NAB2-STAT6 fusion protein resulted in a strong nuclear signal in STAT6 immunohistochemistry. The nuclear reallocation of STAT6 was detected in 35/37 meningeal HPC and 25/25 meningeal SFT but not in 87 meningiomas representing the most important differential diagnosis. Tissues not harboring the NAB2-STAT6 fusion protein presented with nuclear expression of NAB2 and cytoplasmic expression of STAT6 proteins. In conclusion, we provide strong evidence for meningeal HPC and SFT to constitute variants of a single entity which is defined by NAB2-STAT6 fusion. In addition, we demonstrate that this fusion can be rapidly detected by STAT6 immunohistochemistry which shows a consistent nuclear reallocation. This immunohistochemical assay may prove valuable for the differentiation of HPC and SFT from other mesenchymal neoplasms.

Transcriptional Upregulation of Cav3.2 Mediates Epileptogenesis in the Pilocarpine Model of Epilepsy

In both humans and animals, an insult to the brain can lead, after a variable latent period, to the appearance of spontaneous epileptic seizures that persist for life. The underlying processes, collectively referred to as epileptogenesis, include multiple structural and functional neuronal alterations. We have identified the T-type Ca2+ channel Cav3.2 as a central player in epileptogenesis. We show that a transient and selective upregulation of Cav3.2 subunits on the mRNA and protein levels after status epilepticus causes an increase in cellular T-type Ca2+ currents and a transitional increase in intrinsic burst firing. These functional changes are absent in mice lacking Cav3.2 subunits. Intriguingly, the development of neuropathological hallmarks of chronic epilepsy, such as subfield-specific neuron loss in the hippocampal formation and mossy fiber sprouting, was virtually completely absent in Cav3.2−/− mice. In addition, the appearance of spontaneous seizures was dramatically reduced in these mice. Together, these data establish transcriptional induction of Cav3.2 as a critical step in epileptogenesis and neuronal vulnerability.

Focal cortical dysplasia of Taylor's balloon cell type: Mutational analysis of the TSC1 gene indicates a pathogenic relationship to tuberous sclerosis

Focal cortical dysplasia (FCD) is characterized by a localized malformation of the neocortex and underlying white matter. Balloon cells, similar to those observed in tuberous sclerosis, are present in many cases (FCDbc). In these patients, a hyperintense funnel‐shaped subcortical lesion tapering toward the lateral ventricle was the characteristic finding on fluid‐attenuated inversion recovery magnetic resonance imaging scans. Surgical lesionectomy results in complete seizure relief. Although the pathogenesis of FCDbc remains uncertain, histopathological similarities indicate that FCDbc may be related pathogenetically to tuberous sclerosis. Here, we studied alterations of the TSC1 and TSC2 genes in a cohort of patients with chronic, focal epilepsy and histologically documented FCDbc (n = 48). DNA was obtained after microdissection and laser‐assisted isolation of balloon cells, dysplastic neurons, and nonlesional cells from adjacent normal brain tissue. Sequence alterations resulting in amino acid exchange of the TSC1 gene product affecting exons 5 and 17 and silent base exchanges in exons 14 and 22 were increased in patients with FCDbc compared with 200 control individuals (exon 5, 2.3% FCDbc vs 0% C; exon 17, 35% FCDbc vs 1.0% C; exon 14, 37.8% FCDbc vs 15% C; exon 22, 45% FCDbc vs 23.8% C). Sequence alterations could be detected in FCDbc and in adjacent normal cells. In 24 patients, DNA was suitable to study loss of heterozygosity at the TSC1 gene locus in microdissected FCDbc samples compared with control tissue. Eleven FCDbc cases exhibited loss of heterozygosity. In the TSC2 gene, only silent polymorphisms were detected at similar frequencies as in controls. Our findings indicate that FCDbc constitutes a clinicopathological entity with distinct neuroradiological, neuropathological, and molecular genetic features. These data also suggest a role of the TSC1 gene in the development of FCDbc and point toward a pathogenic relationship between FCDbc and the tuberous sclerosis complex.

Characteristics and Surgical Outcomes of Patients With Refractory Magnetic Resonance Imaging–Negative Epilepsies

OBJECTIVE To explore several characteristics of patients with pharmacoresistant epilepsy without distinct lesions on magnetic resonance images (MRI(-)), who account for a relevant proportion of presurgical patient cohorts. DESIGN Retrospective case series. SETTING University epilepsy center. PATIENTS A cohort of 1200 patients who had comprehensive presurgical assessment from January 1, 2000, through December 31, 2006. MAIN OUTCOME MEASURES Frequency of MRI(-) patients in the total presurgical cohort, seizure-free outcome rates in patients who had surgery and those who did not, outcome predictors, and spatial properties of epileptogenic areas in MRI(-) patients with epilepsy. All MRI(-) patients were retrospectively analyzed. Presurgical MRIs were reevaluated for subtle cortical dysplasias by postprocessing and visual reassessment. RESULTS One-hundred ninety MRI(-) patients were identified (16% of all presurgical candidates); 29 (15%) had surgery. Eleven (38%) became seizure free (including those with auras only; 45%). Surgical therapy was more frequently offered to MRI(+) patients (76%; P < .001), and their outcome was also superior (66% seizure-free; P = .001). The seizure-free rate of 16% in MRI(-) patients who did not have surgery was, however, inferior to that of the MRI(-) patients who did (P = .008). Nine MRI(-) patients who had surgery had distinct histopathological lesions, 8 of which turned out to be retrospectively detectable on presurgical MRI. Seven of the MRI(-) but histopathologically lesional patients became seizure free compared with only 4 of 20 patients without histopathological lesions (P = .003). Three-fifths of the histopathologically nonlesional patients had multifocal or extensive epileptogenic areas. CONCLUSIONS Patients with epilepsy who are MRI(-) can be successfully treated with surgery. Improved sensitivity of MRI will improve the outcomes of presurgically studied patients. Surgical failures in patients without histopathological lesions mostly result from extensive epileptogenic areas.

Correlated stage- and subfield-associated hippocampal gene expression patterns in experimental and human temporal lobe epilepsy

Epileptic activity evokes profound alterations of hippocampal organization and function. Genomic responses may reflect immediate consequences of excitatory stimulation as well as sustained molecular processes related to neuronal plasticity and structural remodeling. Using oligonucleotide microarrays with 8799 sequences, we determined subregional gene expression profiles in rats subjected to pilocarpine‐induced epilepsy (U34A arrays, Affymetrix, Santa Clara, CA, USA; P < 0.05, twofold change, n = 3 per stage). Patterns of gene expression corresponded to distinct stages of epilepsy development. The highest number of differentially expressed genes (dentate gyrus, approx. 400 genes and CA1, approx. 700 genes) was observed 3 days after status epilepticus. The majority of up‐regulated genes was associated with mechanisms of cellular stress and injury – 14 days after status epilepticus, numerous transcription factors and genes linked to cytoskeletal and synaptic reorganization were differentially expressed and, in the stage of chronic spontaneous seizures, distinct changes were observed in the transcription of genes involved in various neurotransmission pathways and between animals with low vs. high seizure frequency. A number of genes (n = 18) differentially expressed during the chronic epileptic stage showed corresponding expression patterns in hippocampal subfields of patients with pharmacoresistant temporal lobe epilepsy (n = 5 temporal lobe epilepsy patients; U133A microarrays, Affymetrix; covering 22 284 human sequences). These data provide novel insights into the molecular mechanisms of epileptogenesis and seizure‐associated cellular and structural remodeling of the hippocampus.

Molecular and functional changes in voltage-dependent na+ channels following pilocarpine-induced status epilepticus in rat dentate granule cells

Status epilepticus (S.E.) is known to lead to a large number of changes in the expression of voltage-dependent ion channels and neurotransmitter receptors. In the present study, we examined whether an episode of S.E. induced by pilocarpine in vivo alters functional properties and expression of voltage-gated Na(+) channels in dentate granule cells (DGCs) of the rat hippocampus. Using patch-clamp recordings in isolated DGCs, we show that the voltage-dependent inactivation curve is significantly shifted toward depolarizing potentials following S.E. (half-maximal inactivation at -43.2+/-0.6 mV) when compared with control rats (-48.2+/-0.8 mV, P<0.0001). The voltage-dependent activation curve is significantly shifted to more negative potentials following S.E., with half-maximal activation at -28.6+/-0.8 mV compared with -25.8+/-0.9 mV in control animals (P<0.05). The changes in voltage dependence resulted in an augmented window current due to increased overlap between the activation and inactivation curve. In contrast to Na(+) channel voltage-dependence, S.E. caused no changes in the kinetics of fast or slow recovery from inactivation. The functional changes were accompanied by altered expression of Na(+) channel subunits measured by real-time reverse transcription-polymerase chain reaction in dentate gyrus microslices. We investigated expression of the pore-forming alpha subunits Na(v)1.1-Na(v)1.3 and Na(v)1.5-Na(v)1.6, in addition to the accessory subunits beta(1) and beta(2). The Na(v)1.2 and Na(v)1.6 subunit as well as the beta(1) subunit were persistently down-regulated up to 30 days following S.E. The beta(2) subunit was transiently down-regulated on the first and third day following S.E. These results indicate that differential changes in Na(+) channel subunit expression occur in concert with functional changes. Because coexpression of beta subunits is known to robustly shift the voltage dependence of inactivation in a hyperpolarizing direction, we speculate that a down-regulation of beta-subunit expression may contribute to the depolarizing shift in the inactivation curve following S.E.

Neuronal expression of the drug efflux transporter P-glycoprotein in the rat hippocampus after limbic seizures.

In the brain, the efflux transporter P-glycoprotein (Pgp) is predominantly located on the luminal membrane of endothelial cells lining brain microvessels and forming the blood-brain barrier. Many lipophilic drugs, including antiepileptic drugs, are potential substrates for Pgp. Overexpression of Pgp in endothelial cells of the blood-brain barrier has been determined in patients with drug resistant forms of epilepsy such as temporal lobe epilepsy and rodent models of temporal lobe epilepsy and suggested to lead to reduced penetration of antiepileptic drugs into the brain. Expression of Pgp after seizures has also been described in astrocytes, whereas it is not clear whether neurons can express Pgp. In the present study, Pgp expression was studied by immunohistochemistry in rats 24 h after a status epilepticus induced by either pilocarpine or kainate, widely used models of temporal lobe epilepsy. Unexpectedly, in addition to endothelial Pgp staining, intense Pgp staining was found in neurons in the CA3c/CA4 sectors and hilus of the hippocampus formation, but not in other brain regions examined. The neuronal Pgp staining was confirmed by two different Pgp antibodies. Double immunolabeling and confocal microscopy showed that Pgp was colocalized with the neuronal marker neuronal nuclear antigen, but not with the glial marker glial fibrillary acidic protein. No neuronal Pgp staining was seen in control rats. The expression of Pgp in neurons after limbic seizures was substantiated by determining Pgp encoding genes (mdr1a, mdr1b) in neurons by real time quantitative RT-PCR. Increased Pgp expression in hippocampal neurons is likely to affect the action of drugs with intraneuronal targets and, in view of recent evidence from other cell types, could be associated with prevention of apoptosis which is involved in neuronal damage developing after seizures such as produced by pilocarpine.

Molecular correlates of age-dependent seizures in an inherited neonatal-infantile epilepsy

Many idiopathic epilepsy syndromes have a characteristic age dependence, the underlying molecular mechanisms of which are largely unknown. Here we propose a mechanism that can explain that epileptic spells in benign familial neonatal-infantile seizures occur almost exclusively during the first days to months of life. Benign familial neonatal-infantile seizures are caused by mutations in the gene SCN2A encoding the voltage-gated Na(+) channel Na(V)1.2. We identified two novel SCN2A mutations causing benign familial neonatal-infantile seizures and analysed the functional consequences of these mutations in a neonatal and an adult splice variant of the human Na(+) channel Na(V)1.2 expressed heterologously in tsA201 cells together with beta1 and beta2 subunits. We found significant gating changes leading to a gain-of-function, such as an increased persistent Na(+) current, accelerated recovery from fast inactivation or altered voltage-dependence of steady-state activation. Those were restricted to the neonatal splice variant for one mutation, but more pronounced for the adult form for the other, suggesting that a differential developmental splicing does not provide a general explanation for seizure remission. We therefore analysed the developmental expression of Na(V)1.2 and of another voltage-gated Na(+) channel, Na(V)1.6, using immunohistochemistry and real-time reverse transcription-polymerase chain reaction in mouse brain slices. We found that Na(V)1.2 channels are expressed early in development at axon initial segments of principal neurons in the hippocampus and cortex, but their expression is diminished and they are gradually replaced as the dominant channel type by Na(V)1.6 during maturation. This finding provides a plausible explanation for the transient expression of seizures that occur due to a gain-of-function of mutant Na(V)1.2 channels.