Prevalence & clinical outcome of autoimmune encephalitis versus viral encephalitis in children with acute encephalitis syndrome: A prospective observational study

Background & objectives: Acute encephalitic syndrome (AES), encompasses a wide spectrum of potential causes, clinical presentations, and outcomes. While infectious encephalitis is generally considered more prevalent, autoimmune encephalitis is emerging as a significant aetiology. Neuronal autoantibodies have been identified independently or in association with acute viral encephalitis. The primary objective of this study was to ascertain the prevalence and clinical manifestation of autoimmune encephalitis as well as of coexisting viral markers in children with AES. Methods: This study was a prospective observational investigation conducted in a hospital setting. It involved enrolling children with AES who were admitted to specific tertiary hospitals. Children were subjected to examinations to detect the presence of viral markers and neuronal autoantibodies in both their blood and cerebrospinal fluid (CSF). All the participants received treatment based on established guidelines and was followed for six months for outcome assessment. Results: During the study period, 867 children with AES were examined. Among these cases, 37 children (4.2%) were diagnosed with autoimmune encephalitis, and all of them tested positive for anti-NMDAR (N-methyl-D-aspartate receptor) antibodies. Evidence of viral infection was seen in 409 (47.1%) of cases, out of which nearly 254 (29.2%) children had detectable HSV IgM antibodies. Among the 37 children with autoimmune encephalitis, 25 (67.5%) had evidence of a viral trigger, with eight of them tested positive for HSV IgM antibodies. The clinical presentation of autoimmune-associated AES was similar to those with viral aetiology. Interpretation & conclusions: Autoimmune encephalitis triggered by neurotropic (HSV) viral infection was more prevalent in this study than in the earlier reports. Typically, these children show positive responses to immunosuppressive treatments if administered promptly. It is hence advisable to assess children who exhibit behavioural issues and movement disorders for possible autoimmune encephalitis.