Chronic encephalitis associated with epilepsy: immunohistochemical and ultrastructural studies

Diagnosis and staging of Rasmussen's encephalitis by serial MRI and histopathology

OBJECTIVE

To correlate MRI and histopathologic findings in patients with Rasmussen's encephalitis (RE).

PATIENTS AND METHODS

MRI features of 10 patients with RE were studied on serial scans. In surgical specimens from these patients, densities of T lymphocytes, microglial cells and nodules, and reactive astrocytes were evaluated.

RESULTS

Densities of T cells, microglial nodules, and astrocytes were inversely correlated to disease duration. MRI abnormalities had a focal onset and spread across one hemisphere. The following course of MRI abnormalities in a given brain region was observed: on very early scans, the cortex was swollen and showed a hyperintense T2/fluid-attenuated inversion recovery signal. Consecutively, progressive atrophy of the affected hemisphere occurred. Correlation of MRI features with quantitative histopathology revealed that there was a higher number of T cells and reactive astrocytes in the earlier MRI stages compared with the late (merely atrophic) stage.

CONCLUSION

These data suggest a disease course in RE with the highest inflammatory intensity in the early stages and a subsequent decrease in inflammation. The MRI abnormalities and their characteristic sequence may help to identify patients with RE and to obtain informative biopsies.

Selective introduction of antisense oligonucleotides into single adult CNS progenitor cells using electroporation demonstrates the requirement of STAT3 activation for CNTF-induced gliogenesis

We have developed a novel method in which antisense DNA is selectively electroporated into individual adult neural progenitor cells. By electroporation of antisense oligonucleotides against signal transducer and activator of transcription 3 (STAT3) we demonstrate that ciliary neurotrophic factor (CNTF) is an instructive signal for astroglial type 2 cell fate specifically mediated via activation of STAT3. Activation of the mitogen-activated protein kinase (MAPK) signaling pathway induced only a transient increase in glial fibrillary acidic protein (GFAP) expression, and inhibition of this signaling pathway did not block the induction by CNTF of glial differentiation in progenitor cells. In addition we show that microelectroporation is a new powerful method for introducing antisense agents into single cells in complex cellular networks.

Surgical pathologic findings of extratemporal-based intractable epilepsy: a study of 133 consecutive resections

BACKGROUND

Surgical management of intractable epilepsy continues to be important in select cases to achieve seizure control.

DESIGN

This study retrospectively reviews the pathologic findings in 133 consecutive cases of extratemporal lobe epilepsy experienced during a 17-year period.

RESULTS

The study group consists of 133 patients (78 males) who underwent extratemporal lobe resection for epilepsy at a mean age of 21.1 years (range, 3 months to 57 years). In 50 patients (37.6%), cortical dysplasia (neuronal migration abnormalities) was identified. The most common patterns of dysplasia observed included diffuse architectural disorganization in 46 cases, neuronal cytomegaly in 30 cases, increased numbers of molecular layer neurons in 30 cases, and balloon cells in 18 cases. Tumors were identified in 37 cases (27.8%) and included 13 astrocytomas, 7 gangliogliomas, 6 dysembryoplastic neuroepithelial tumors, 6 glioneuronal hamartomas, 4 oligodendrogliomas, and 1 oligoastrocytoma (mixed glioma). Twenty-four resections (18%) showed evidence of remote ischemic damage or infarct. Neuronal heterotopia was identified in 59 resection specimens (44.4%). Other less common findings included vascular malformations in 4 patients (3.0%), Sturge-Weber malformations in 3 patients (2.3%), and Rasmussen encephalitis in 2 patients (1.5%). Two patients were known to have tuberous sclerosis. In 23 resection specimens (17.3%), no significant pathologic finding was identified. Coexistent cortical dysplasia and tumor were seen in 10 cases and coexistent dysplasia and infarct or remote ischemic damage in 11 cases.

CONCLUSION

This series demonstrates that most patients with extratemporal lobe epilepsy have significant histopathologic findings, which most frequently include cortical dysplasia, tumor, or evidence of remote ischemic damage or infarct. Coexistent pathologic findings were present in a significant minority of cases (16.5%).

Immunoglobulin G and complement immunoreactivity in the cerebral cortex of patients with Rasmussen's encephalitis

OBJECTIVE

To provide evidence that complement (C')-dependent processes may be involved in Rasmussen's encephalitis (RE).

BACKGROUND

RE is a rare, progressive, childhood epilepsy syndrome associated with inflammation and neuronal cell loss in a single cerebral hemisphere. Recent work suggests an autoimmune immunoglobulin (Ig) G-mediated process is important in disease pathogenesis.

METHODS

Brain samples from RE and complex partial epilepsy control patients were analyzed immunohistochemically. Sections were stained for IgG and the C' factors C4, C8, and the membrane attack complex (MAC).

RESULTS

Brain samples from three of five patients with active, progressive RE but neither of two chronic RE nor five control epilepsy patients demonstrated immunoreactivity for IgG, C4, C8, and MAC on discrete patches of cerebrocortical neurons. Intensely activated glial fibrillary acid protein-positive astrocytes were found in areas overlapping these patches.

CONCLUSION

Focally distributed IgG- and C'-positive neurons were found to colocalize with activated astrocytes, suggesting focal IgG-dependent classical C' cascade pathway activation with attendant tissue damage in this subset of RE patients. Intraparenchymal C' activation triggered by pathogenic antibodies may contribute to the development of focal inflammation, neuronal cell loss, and pharmacoresistant seizures in some patients with this disease. This process may be an important component in the initial, active phase of RE.

Autoimmunity to the glutamate receptor in mice--a model for Rasmussen's encephalitis?

We investigated the in vivo pathogenic potential of murine autoimmunity to peptides of the glutamate/AMPA receptor subunit 3 (GluR3). Antibodies to GluR3 are found in human epilepsy, Rasmussen's encephalitis (RE). In our accompanying paper in this issue we found that murine antibodies to the GluR3B peptide (amino acids 372-395) bind neurons in culture, evoke GluR channel activity, and kill neurons in a complement-independent excitotoxic manner, mimicking the pathophysiologic effects of excess of glutamate. In the present study, we immunized four mouse strains (BALB/c, C3H/HeJ, SJL/J and C57BL/6) with the GluR3B peptide, and investigated the development of (1) anti-GluR3B antibodies; (2) anti-GluR3 T cells; (3) clinical symptoms and abnormal behaviour; (4) brain pathology. We found that BALB/c, C3H/HeJ and SJL/J mice strains developed high titres of anti-GluR3B antibodies. The low levels anti-GluR3B antibodies raised in C57BL/6 mice suggest that the genetic background of mice influences their ability to mount a humoral autoimmune response towards the GluR3B peptide. The GluR3B-immunized mice also developed anti-GluR3B T cells, and their splenocytes showed significantly biased frequencies of particular (Vbeta11, Vbeta7 and Vbeta8) TCR Vbeta families. Surprisingly, GluR3B-immunized mice also raised high anti-ssDNA humoral immunoreactivity. GluR3B-immunized mice exhibited multiple brain pathology, partially resembling that observed in RE, and subclinical behavioral abnormalities, but no epilepsy, even upon facilitating the entry of the autoreactive antibodies into the brain, by weakening the blood-brain barrier. Taken together, these results suggest that autoimmunity to the GluR3B epitope may account for the neuronal death and brain pathology seen in neurodegenerative diseases like RE, but may not be sufficient to underly epilepsy, at least not in mice.

Histopathologic findings in 37 cases of functional hemispherectomy

Hemispherectomy procedures are performed in patients for whom focal cortical resection would be predicted to produce a significant reduction in seizures. The functional hemispherectomy procedure consists of disconnecting the hemispheres while attempting, in some cases, to preserve parenchyma. This study retrospectively reviews the histopathologic findings in 37 cases of functional hemispherectomy performed between 1990 and 1998 at a major epilepsy center. Procedures were performed in 20 males and 17 females who ranged in age from 3 months to 37 years (mean age, 9.6 years). In all but two cases, more than half or all the material submitted for pathologic testing was examined histologically. Cortical dysplasias or hemimegalencephaly were identified in 14 patients. The most common patterns of dysplasia observed included architectural disorganization (n = 13), increased molecular layer neurons (n = 11), and neuronal cytomegaly (n = 11). One patient was known to have epidermal nevus syndrome. Six patients had Sturge-Weber syndrome. Remote infarct/ischemic damage was identified as the etiology of seizures in six patients; four of these patients had mild associated secondary cortical architectural abnormalities. Three patients demonstrated pathology consistent with Rasmussen's encephalitis; one additional patient had chronic encephalitis changes, not otherwise specified. In two cases, changes consistent with hippocampal sclerosis were identified; additionally, hippocampal neuronal loss and gliosis was focally identified in three patients. Most of these patients had coexistent cortical dysplasia or radiographic evidence of remote infarct. One specimen demonstrated areas of infarct following resection of an arteriovenous malformation. In two specimens, significant histopathologic findings were not identified; both of these patients had radiographic evidence of remote infarct. The spectrum of pathologic conditions that may be encountered in the setting of a functional hemispherectomy is varied and in this study most frequently included cortical dysplasia, Sturge-Weber syndrome remote infarct, and Rasmussen's encephalitis.

Autoimmunity and neurological disease: antibody modulation of synaptic transmission

Over the past three decades, compelling evidence has emerged that the immune system can attack the nervous system with devastating consequences for human health. Either cell-mediated or humoral (antibody-mediated) autoimmune mechanisms may predominate in effecting a given disease, and either glia or neurons may fall under immune attack. A subset of these diseases has been particularly useful for understanding fundamental neuroscience as well as mechanisms of human disease. This subset involves humoral autoimmune attack on cell surface molecules subserving transmembrane signaling of excitable cells; special emphasis is placed here on proteins involved in synaptic transmission. We begin by reviewing the prototypic humoral autoimmune disease of synaptic transmission, myasthenia gravis. This provides a context for insights obtained from the study of diseases targeting molecules that regulate synaptic transmission at the neuromuscular junction and in the central nervous system. We also explore a disease where autoimmunity produces agonist antibodies acting at two distinct G-protein-coupled receptors. We conclude with an exploration of the vital issue of access of antibodies to targets within the central nervous system and the implications that such access may have in the pathogenesis of poorly understood idiopathic central nervous system diseases.

Improvement in adult-onset Rasmussen's encephalitis with long-term immunomodulatory therapy

OBJECTIVE

To study the immediate and chronic effects of high-dose, long-term human i.v. immunoglobulin (h i.v.Ig) therapy in two patients with advanced adult-onset Rasmussen's encephalitis (RE).

BACKGROUND

Despite advances in our understanding of the autoimmune pathogenesis of RE, medical options for chronic treatment are limited.

METHODS

In an open-label treatment trial, treatment started with monthly cycles of high-dose h i.v.Ig (0.4 g/kg/d for 5 days) followed by maintenance therapy (0.4 g/kg 1 day each month) after the patients' conditions began to improve. Outcome measures included clinical, psychological, functional, and laboratory assessments before and at relevant intervals throughout 1 year of treatment.

RESULTS

In both patients, unrelenting pretreatment deterioration halted, and after this they displayed striking improvements in seizure control, hemiparesis, and cognition that produced useful recovery of function. Improvements were delayed until after 2 to 4 monthly cycles of high-dose h i.v.Ig and continued when patients switched to maintenance treatment. Their recoveries were accompanied by increased cerebral perfusion on interictal SPECT and suppression of inflammatory markers in CSF.

CONCLUSIONS

h i.v.Ig can be a useful, possibly disease-modifying, long-term therapy for adult-onset RE that should be considered before radical surgery is performed. Because improvements can be delayed, we propose guidelines for intensive and prolonged trials of immunomodulatory therapy in adults with this syndrome.

Glutamate receptor GluR3 antibodies and death of cortical cells

Rasmussen's encephalitis (RE), a childhood disease characterized by epileptic seizures associated with progressive destruction of a single cerebral hemisphere, is an autoimmune disease in which one of the autoantigens is a glutamate receptor, GluR3. The improvement of some affected children following plasma exchange that removed circulating GluR3 antibodies (anti-GluR3) suggested that anti-GluR3 gained access to the central nervous system where it exerted deleterious effects. Here, we demonstrate that a subset of rabbits immunized with a GluR3 fusion protein develops a neurological disorder mimicking RE. Anti-GluR3 IgG isolated from serum of both ill and healthy GluR3-immunized animals promoted death of cultured cortical cells by a complement-dependent mechanism. IgG immunoreactivity decorated neurons and their processes in neocortex and hippocampus in ill but not in healthy rabbits. Moreover, both IgG and complement membrane attack complex (MAC) immunoreactivity was evident on neurons and their processes in the cortex of a subset of patients with RE. We suggest that access of IgG to epitopes in the central nervous system triggers complement-mediated neuronal damage and contributes to the pathogenesis of both this animal model and RE.

Plasma exchange in Rasmussen's encephalitis

The authors observed a 4-year-old girl who has Rasmussen's encephalitis. She started with frequent localized and generalized seizures. Standard antiepileptic treatment was almost ineffective. The frequency of the generalized seizures decreased, but the myoclonic jerks of the left part of the body persisted. An EEG showed partial status epilepticus. The results of the CT scan were normal. Antibodies to viruses were absent from the blood and cerebrospinal fluid. An MR scan showed a T2-weighted hypersignal zone in the right frontal region. Intravenous bolus injections of corticosteroids and drips of immunoglobulins were inefficient, and we started plasma exchanges which have continued for 9 months. The clinical state stabilized, and the images on the MR scan improved, but the results of the EEG did not improve. The authors discuss the effect of the plasma exchange, the use of which is questionable in this disease.

Rasmussen's encephalitis: an autoimmune disorder?

Rasmussen's encephalitis is a rare progressive pediatric epileptic syndrome. Recent evidence from experimental animals and patients with the disease suggests an important role for both humoral and cell-mediated immune mechanisms in the pathogenesis of this disease. The glutamate receptor subunit GluR3 may be an important autoantigen in the disease. (This review has been modified from a review published in Current Opinion in Neurology 1996, 9:141-145.)