[Pathogenesis of acute encephalitis and acute encephalopathy].

Many aspects of the pathogenesis of acute encephalitis and acute encephalopathy have been clarified in this decade, although many unknown mechanisms remain to be elucidated. According to progress of MRI and neuroimmunological analysis and the observation of clinical findings, many new syndromes were found, which enhanced our understanding of acute encephalitis and acute encephalopathy. The pathogenesis of encephalitis is divided into infection and immune mediated mechanisms. The antibodies to neuronal surface antigens(NSA) such as NMDA receptors, leucin-rich glioma inactivated 1 (LGI1) and aquaporin 4 were demonstrated in specific encephalitis, limbic encephalitis and neuromyelitis optica. Anti-NSA antibody encephalitis should be treated by immunotherapy such as corticosteroid and plasmapheresis. Acute encephalitis with refractory repetitive partial seizures (AERRPS) is a devastating postinfectious disease in children and adults, although the pathogenesis of AERRPS is poorly understood. Influenza associated encephalopathy(IAE) is characterized by it's high incidence in Japanese children between 1 year and 5 years of age, its onset in the first or the second day of illness and its high mortality (15-30%) and morbidity (25-40%). We proposed the classification of IAE with poor prognosis from the neuroradiological findings. Four types of encephalopathy seem to be differentiated from each other, acute necrotizing encephalopathy (ANE) type, hemorrhagic shock and encephalopathy syndrome (HSES) type, acute brain swelling (ABS) type, febrile convulsive status epilepticus (FCSE) type. The notable radiological features are thalamic lesions in ANE, diffuse cerebral cortical cytotoxic edema in HSES, reversible cerebral swelling in ABS which sometimes reaches lethal brain herniation, and in FCSE type, dendritic high signal in subcortical white matter by DWI ("bright tree appearance") appears simultaneously with the later onset of repetitive focal seizure. These four types are not specific to IAE but are noticed in another encephalopathies caused by HHV6, rotavirus, etc.