Virus in brain of child with hemiplegia, hemiconvulsions, and epilepsy

Fundamental mechanistic insights from rare but paradigmatic neuroimmunological diseases

The pathophysiology of complex neuroimmunological diseases, such as multiple sclerosis and autoimmune encephalitis, remains puzzling - various mechanisms that are difficult to dissect seem to contribute, hampering the understanding of the processes involved. Some rare neuroimmunological diseases are easier to study because their presentation and pathogenesis are more homogeneous. The investigation of these diseases can provide fundamental insights into neuroimmunological pathomechanisms that can in turn be applied to more complex diseases. In this Review, we summarize key mechanistic insights into three such rare but paradigmatic neuroimmunological diseases - Susac syndrome, Rasmussen encephalitis and narcolepsy type 1 - and consider the implications of these insights for the study of other neuroimmunological diseases. In these diseases, the combination of findings in humans, different modalities of investigation and animal models has enabled the triangulation of evidence to validate and consolidate the pathomechanistic features and to develop diagnostic and therapeutic strategies; this approach has provided insights that are directly relevant to other neuroimmunological diseases and applicable in other contexts. We also outline how next-generation technologies and refined animal models can further improve our understanding of pathomechanisms, including cell-specific and antigen-specific CNS immune responses, thereby paving the way for the development of targeted therapeutic approaches.

Proliferative hippocampal activity in a group of patients with Rasmussen's encephalitis: Neuronal, glial, and BDNF tissue expression correlations

Rasmussen's encephalitis (RE) is a rare and devastating unilateral inflammatory brain disease that causes severe and intractable partial epilepsy. It has been shown that epilepsy and subsequent inflammation have deleterious influence on hippocampal cell survival and neurogenesis, but this still has not been systematically explored in human tissue. In this study, we investigated the correlation between inflammation and epilepsy as well as the rates of hippocampal gliogenesis and neurogenesis in a pediatric group of six patients with RE and six control cases. The dentate gyrus (DG) samples were obtained from patients who underwent surgery for intractable RE. Sections were processed for immunohistochemistry using antibodies against sex determining region Y-box 2 (Sox2), nestin, human protein encoded by MKI67 gen (Ki67), and brain-derived neurotrophic factor (BDNF). There was an increase in the number of Ki67-positive granule cells in the DG of patients with RE in comparison with the autopsy control group, but no statistical difference for Sox2-positive cells was observed between these groups. Nestin immunolabeling was less intense in the RE group while BDNF expression was increased. Neurons that were BDNF-positive were found in DG from patients with RE but not in the control group. In patients with RE, few nestin-positive cells in DG were also positive for BDNF, unlike in controls which showed no colocalization for these two markers. These results suggest a proliferation activity in the DG subfield of patients with RE, and also future studies are necessary to address the role of new cells in the hippocampus of patients with RE.

Elevated expression of EBV and TLRs in the brain is associated with Rasmussen's encephalitis

Rasmussen's encephalitis (RE) is a rare pediatric neurological disorder, the etiology of which remains unclear. It has been speculated that the immunopathogenesis of RE involves damage to neurons, which eventually leads to the occurrence of RE. Viral infection may be a critical factor in triggering RE immunopathogenesis. In this study, we analyzed the expression of Epstein-Barr virus (EBV) antigens as well as of Toll-like receptor 3 (TLR3), TLR9, and downstream adapter TIRdomain-containing adapter-inducing interferon-β (TRIF) in the brain tissues of 26 patients with RE and 16 control individuals using immunohistochemistry (IHC). In the RE group, EBV antigens were detected in 53% of individuals at various expression levels. In contrast, there was no detectable EBV antigen expression in control brain tissues. Moreover, we found marked increases in the expression of TLR3, TLR9, and TRIF in the brain tissues of RE patients compared with levels in the control group. Furthermore, among RE cases, EBV expression and high TLR3 expression were associated with more severe brain atrophy. Our results suggest that the elevated expression of EBV and TLRs may be involved in RE occurrence through the activation of downstream molecules.

Autoimmune encephalitis and its relation to infection

Encephalitis, an inflammatory condition of the brain that results in substantial morbidity and mortality, has numerous causes. Over the past decade, it has become increasingly recognized that autoimmune conditions contribute significantly to the spectrum of encephalitis causes. Clinical suspicion and early diagnosis of autoimmune etiologies are of particular importance due to the need for early institution of immune suppressive therapies to improve outcome. Emerging clinical observations suggest that the most commonly recognized cause of antibody-mediated autoimmune encephalitis, anti-N-methyl-D-aspartate (NMDA) receptor encephalitis, may in some cases be triggered by herpes virus infection. Other conditions such as Rasmussen's encephalitis (RE) and febrile infection-related epilepsy syndrome (FIRES) have also been posited to be autoimmune conditions triggered by infectious agents. This review focuses on emerging concepts in central nervous system autoimmunity and addresses clinical and mechanistic findings linking autoimmune encephalitis and infections. Particular consideration will be given to anti-NMDA receptor encephalitis and its relation to herpes simplex encephalitis.

Rasmussen's encephalitis: clinical features, pathobiology, and treatment advances

Rasmussen's encephalitis is a rare chronic neurological disorder, characterised by unilateral inflammation of the cerebral cortex, drug-resistant epilepsy, and progressive neurological and cognitive deterioration. Neuropathological and immunological studies support the notion that Rasmussen's encephalitis is probably driven by a T-cell response to one or more antigenic epitopes, with potential additional contribution by autoantibodies. Careful analysis of the association between histopathology and clinical presentation suggests that initial damage to the brain is mediated by T cells and microglia, suggesting a window for treatment if Rasmussen's encephalitis can be diagnosed early. Advances in neuroimaging suggest that progression of the inflammatory process seen with MRI might be a good biomarker in Rasmussen's encephalitis. For many patients, families, and doctors, choosing the right time to move from medical management to surgery is a real therapeutic dilemma. Cerebral hemispherectomy remains the only cure for seizures, but there are inevitable functional compromises. Decisions of whether or when surgery should be undertaken are challenging in the absence of a dense neurological deficit, and vary by institutional experience. Further, the optimum time for surgery, to give the best language and cognitive outcome, is not yet well understood. Immunomodulatory treatments seem to slow rather than halt disease progression in Rasmussen's encephalitis, without changing the eventual outcome.

Neuroprotective intervention by interferon-γ blockade prevents CD8+ T cell-mediated dendrite and synapse loss

Neurons are postmitotic and thus irreplaceable cells of the central nervous system (CNS). Accordingly, CNS inflammation with resulting neuronal damage can have devastating consequences. We investigated molecular mediators and structural consequences of CD8(+) T lymphocyte (CTL) attack on neurons in vivo. In a viral encephalitis model in mice, disease depended on CTL-derived interferon-γ (IFN-γ) and neuronal IFN-γ signaling. Downstream STAT1 phosphorylation and nuclear translocation in neurons were associated with dendrite and synapse loss (deafferentation). Analogous molecular and structural alterations were also found in human Rasmussen encephalitis, a CTL-mediated human autoimmune disorder of the CNS. Importantly, therapeutic intervention by IFN-γ blocking antibody prevented neuronal deafferentation and clinical disease without reducing CTL responses or CNS infiltration. These findings identify neuronal IFN-γ signaling as a novel target for neuroprotective interventions in CTL-mediated CNS disease.

Focal Chronic Inflammatory Epileptic Encephalopathy in a Patient with Malformations of Cortical Development, with a Review of the Spectrum of Chronic Inflammatory Epileptic Encephalopathy

PURPOSE

Chronic cellular inflammation closely associated with epilepsy without an active infection is a hallmark of Rasmussen encephalitis (RE). RE has typical and defining features lacking in other rare epilepsy patients who also have neocortical lymphocytes without an identifiable cause. A patient with malformations of cortical development had an abrupt change in frequency and epileptic focus after 22 years of a stable seizure disorder. Functional neurosurgery yielded a specimen showing a mixed cellular meningoencephalitis in the absence of a demonstrable infection.

METHODS

Historical, neurologic, electroencephalographic, pathologic, and literature data were correlated.

RESULTS

There was a subarachnoid mixed infiltrate including evidence of dendritic cells in our patient and also cytotoxic T lymphocytes adjacent to karyolytic neurons that corresponded to cells previously demonstrated to damage neurons in RE. Literature review disclosed 42 other cases similar to RE but with heterogeneous findings. The course was more protracted and often more benign than in RE. The inflammation that would have markedly decreased or disappeared in RE over that period was generally still well represented.

CONCLUSIONS

Our patient has heterogeneous features similar to, yet with differences from, RE. Literature review of chronic cellular inflammatory epileptic encephalopathy cases also similar to RE discloses important differences that may reflect idiosyncratic reactions and pace of the disease rather than a different disease. Comorbidity factors, genetic population traits, and secondary effects of the seizure disorder may lead to an expansion of the initial site of damage by an autoimmune reaction. These cases might best be grouped, probably along with RE, as secondary autoimmune diseases.

[Recent advances in pathogenic concepts and therapeutic strategies in Rasmussen's encephalitis]

Rasmussen's encephalitis (RE) is a rare inflammatory brain disease mainly affecting children and characterised by intractable epilepsy involving a single hemisphere that undergoes progressive atrophy. RE is characterized by refractory focal seizures, often associated with epilepsia partialis continua, progressive unilateral motor defect, slow EEG activity over the entire contralateral hemisphere, with focal white matter hyperintensity and insular cortical atrophy on neuroimaging. Surgical exclusion of the affected hemisphere is the only treatment that interrupts progression of the disease. Pathogenic concepts have considered viruses, autoimmune antibodies and autoimmune cytotoxic T lymphocytes that might contribute to the initiating or perpetuating events in the central nervous system. Based on these concepts, different therapeutic strategies have been pursued, such as antiviral agents, plasmapheresis, immuno-adsorption, immunosuppression or immunomodulation with intravenous immunoglobulins. However, due to the lack of large studies, to date there is no established therapeutic strategy for this devastating condition. In this review, we give an overview of the current state of immunopathogenic concepts for Rasmussen's encephalitis and discuss the different therapeutic options for future perspectives.

Advances in pathogenic concepts and therapeutic agents in Rasmussen's encephalitis

Rasmussen's encephalitis is a rare inflammatory brain disease which occurs mainly in children and is characterised by affection of only one hemisphere. Pathogenetic concepts have considered three different, not mutually exclusive, key factors contributing to the initiating or perpetuating events in the central nervous system. These include viruses, autoimmune antibodies and autoimmune cytotoxic T lymphocytes. Based on these concepts, different therapeutic strategies have been pursued, such as antiviral agents, plasmapheresis, immuno-adsorption, immunosuppression or immunomodulation with intravenous immunoglobulins. However, due to the lack of larger studies, to date there is no established therapeutic strategy of this devastating disease. An overview of the current state of immunepathogenic concepts for Rasmussen's encephalitis is given and past and present treatment attempts are discussed, including an outline of future perspectives. An opinion on symptomatic treatment with anticonvulsive drugs is included.

Rasmussen's encephalitis: a role for autoimmune cytotoxic T lymphocytes

The present review describes advances in Rasmussen's encephalitis (also known as Rasmussen's syndrome), an unihemispheric intractable epileptic disease with persistent inflammation. Specific attention is given to the recent recognition of cytotoxicity by CD8+/granzyme-B-positive T lymphocytes as a new pathogenic mechanism of neuronal damage.

Rasmussen's syndrome: intractable epilepsy and progressive neurological deterioration from a unilateral central nervous system

Rasmussen's syndrome (chronic encephalitis with epilepsy) is a rare neurological disorder of unknown cause characterized by severe epilepsy, hemiplegia, dementia, and inflammation of the brain, and progressive functional and structural destruction of a single cerebral hemisphere. While one mechanism underlying the pathogenesis of Rasmussen's encephalitis has been hypothesized to be mediated by production of excitotoxic GluR3 autoantibodies to the a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor, other neuropathological etiologies have also been indicated. Proposed therapies have included antiepileptics, steroids, antiviral agents, alpha-interferon, and immunoglobulin. The mainstay of therapy is surgical hemispherectomy. To date, no medical therapies have permanently halted neurologic deterioration.

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.)

Chronic encephalitis associated with epilepsy: immunohistochemical and ultrastructural studies

Chronic encephalitis has been recognized as a cause of epilepsy since the work of Rasmussen et al. in the late 1950s. Despite this, few immunohistochemical studies of the affected brain tissue have been attempted. We have studied specimens of brain tissue from seven patients with this condition who underwent therapeutic multilobar cortical resection or hemispherectomy. Immunohistochemical studies were carried out using antibodies to glial fibrillary acidic protein (GFAP), proliferating cell nuclear antigen (PCNA, PC10), T lymphocytes (UCHL-1), B lymphocytes (L26), macrophages and microglia (HAM-56), and major histocompatibility complex molecules (LN3 and beta 2-microglobulin). Additionally, the results of preliminary immunohistochemical and ultrastructural investigation of possible immune complex deposition in blood vessel walls of affected brain tissue are presented. The pattern of GFAP immunoreactivity suggested a patchy and/or laminar disease process in most patients. GFAP immunoreactive cells were especially prominent around microvessels in some cases, suggesting an abnormality and perivascular collections of inflammatory cells, seen to a variable extent in all cases, contained abundant cells immunolabelled with UCHL-1, LN3 and beta 2-microglobulin. L26-labelled B lymphocytes were extremely sparse. Anti-PCNA frequently labelled microvascular endothelial cells, rare pericytes and occasional cells with microglial/macrophage morphology. The data suggest that chronic encephalitis found in patients with epilepsy results from patchy but widespread parenchymal brain injury, in the course of which cells of both microglial and lymphocyte series accumulate or proliferate within brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Partially successful treatment of Rasmussen's encephalitis with zidovudine: symptomatic improvement followed by involvement of the contralateral hemisphere

An 18-year-old woman with a 4-year history of Rasmussen's encephalitis (RE) manifested by progressive aphasia, right hemiparesis, and nearly continuous intractable simple partial seizures that frequently secondarily generalized was treated with zidovudine (AZT). Seizures had not responded to any of the major antiepileptic drugs (AEDs) administered to high and toxic levels, or to ACTH. AZT was given for 62 days and discontinued because of granulocytopenia. Within 6 weeks of AZT initiation, seizure stopped and neurologic deterioration was arrested for approximately 21 months. Subsequently, partial somatomotor seizures developed, affecting the previously uninvolved left hemibody. A 2-week repeat course of AZT was attempted, but unremitting fever and gastrointestinal (GI) side effects precluded continuation of AZT treatment. Spontaneous, sustained remission of seizures has not been reported in untreated RE. Seizure control and arrest of neurologic deterioration in this case outlasted use of AZT by 19 months. Because of the apparent response of this patient to AZT, clinical studies designed to assess long-term palliative/curative properties of antiviral agents, particularly in patients with involvement of the hemisphere dominant for language, appear warranted.

Herpesviruses in chronic encephalitis associated with intractable childhood epilepsy

Herpesviruses (especially cytomegalovirus [CMV] and Epstein-Barr virus [EBV]) have been implicated in the pathogenesis of chronic (Rasmussen) encephalitis associated with epilepsy. To assess the presence of herpesvirus genes in brain tissue from epileptic children with chronic (usually Rasmussen type) encephalitis, DNA was extracted from surgically resected brain tissue and studied by the polymerase chain reaction using primers specific for CMV, varicella zoster virus, herpes simplex virus, EBV, and human herpesvirus 6 genes. By this technique evidence for the presence of low levels of CMV and EBV genes was detected in most brain specimens from encephalitis patients and in several brain specimens from patients without encephalitis (eg, cortical dysplasia, gliosis, or encephalomalacia) who also had intractable epilepsy. Occasionally, both EBV and CMV genes were found in the same brain. Signal strength for both CMV and EBV was much lower in epileptic brains than in the brains of acquired immunodeficiency syndrome patients with CMV encephalitis or brain lymphoma. We found evidence for infection of the brain by human herpesvirus 6 in only one patient with encephalitis. Polymerase chain reaction technology applied to resected brain tissue from epileptic patients may provide evidence for or against viral-mediated pathogenesis of Rasmussen encephalitis or other types of encephalitis. The small amounts of EBV and CMV genes found suggest that herpesvirus infection of the brain does not directly cause Rasmussen encephalitis.

Rasmussen's encephalitis in surgery for epilepsy

Nineteen patients with Rasmussen's encephalitis were studied, using light-microscopy, immunohistochemistry and in some cases electron-microscopy. Although there was inflammation, no causative agent was identified. 10 patients underwent hemispherectomy and with one exception did well, while local resection for seven produced little or no improvement. For two patients biopsy with subpial transection was beneficial, although a third had a poor response, necessitating subsequent hemispherectomy. Surgical treatment of these patients is justified by a beneficial outcome. Neuropathological study of the resected material is essential for diagnosis and management of this condition.

Cytomegalovirus and Rasmussen's encephalitis

In-situ hybridisation with a biotinylated cytomegalovirus (CMV) DNA probe was done on brain biopsy specimens from 10 patients with Rasmussen's encephalitis (RE) and 46 age-matched control patients with other neurological diseases. All 10 patients with RE had intractable epilepsy and focal neurological deficits, and there was perivascular cuffing, microglial nodules, astrogliosis, and neuronal loss. CMV genomic material was demonstrated in 7 of the 10 patients with RE (in neurons, astrocytes, oligodendrocytes, and endothelial cells) and in 2 of the 46 control patients. Probes for herpes simplex virus and hepatitis B virus were negative in all patients and in fibroblast controls. The results suggest that CMV is a likely cause of Rasmussen's encephalitis.

Rasmussen encephalitis: epilepsia partialis continua secondary to chronic encephalitis

Rasmussen encephalitis is a disease consisting of chronic encephalitis with progressive neurologic deficits and focal intractable seizure activity. The etiology is unknown, but pathologic specimens revealed changes consistent with viral encephalitis. Even though neuro-imaging techniques, such as positron emission tomography and magnetic resonance imaging, offer the prospect of specific, presurgical diagnostic criteria, the initial diagnosis usually is made on a clinical basis. Treatment modalities, including a wide variety of antiepileptic drug therapies and surgical interventions, may result in significant physical and mental impairments. We summarize the clinical presentation, diagnostic considerations, and different treatment protocols in a patient with this rare and debilitating disorder.

Chaos, balance, and development: thoughts on selected childhood epilepsy syndromes

Age-specific epilepsy syndromes raise important questions about developmental susceptibility to seizures and epileptogenesis and about the effect of seizures on function. The diagnosis and treatment of these syndromes has been enhanced by the use of modern science and technology. Epidemiologic studies have changed our approach to febrile convulsions. This developmental seizure disorder is benign and self-limited. We have been forced to think carefully about threshold, therapy, and whether other seizures in childhood may be equally benign. This framework of developmental specificity can also be applied to West syndrome, especially with respect to neurophysiology, neurochemistry, neuroimaging, and epidemiology--the types of seizures, clustering, variations associated with sleep, PET scans, and therapy. Rasmussen's syndrome and other unilateral developmental epilepsies are progressive but remain confined to a single hemisphere. However, they usually are devastating to global neurologic function. They are models for examining the impact of epilepsy in one pathologic hemisphere on the function of the entire brain. Current therapy for this condition is hemispherectomy. Recovery of function after this major surgery is striking and provides clues to brain organization. The analysis of these three syndromes provides windows on the dynamic, changing central nervous system of the child and may lead to better understanding and therapy for other seizure disorders.

Chronic focal encephalitis (Rasmussen syndrome): six cases

Six of 81 (7.4%) patients with medically intractable epilepsy treated by selective cortical excision at The Hospital for Sick Children, Toronto, Canada, since 1974 were found to have inflammatory changes in the excised specimens of cerebral cortex. The clinical and histopathological findings in these cases resemble the chronic encephalitic syndrome described by Rasmussen. We confirm the unsatisfactory seizure control and the guarded neurological and intellectual prognosis that has been associated with Rasmussen syndrome.

Chronic localised encephalitis (Rasmussen's) in an adult with epilepsia partialis continua

A 29 year old male presented with epileptic fits, progressive left sided focal seizures and epilepsia partialis continua, increasing left hemiparesis and mental slowing. Death occurred 2 years after the onset of the illness. Lesions were limited to the right cerebral hemisphere. Hypertrophic astrocytosis was diffuse throughout the gray and white matter but was more severe in the deep cortical layers and U fibres, where it was associated with vacuolar changes and capillary proliferation. Sparse perivascular lymphocytic cuffs, rod shaped microglia and microglial nodules were present. No inclusion bodies were found. These clinico-pathologic features were similar to the cases described by Rasmussen. Only five necropsy cases of this rare disease have been reported previously, all in children. The aetiology is unknown.