The clinical characteristics of acute encephalitis

In a review of 198 cases, the principal etiologies were viral infection and autoimmune disease; outcomes were good in about 50%.

Due to its relatively low incidence, acute encephalitis remains poorly studied. To better define the etiology, clinical presentation, and outcomes of this condition, investigators retrospectively analyzed all cases seen at a tertiary care medical center in Minnesota between 2000 and 2012.

A total of 198 patients were identified (51% male; mean age, 58). Viral encephalitis accounted for 95 cases (48%): herpes simplex virus in 19%, varicella zoster virus in 11%, West Nile virus in 9%, Epstein-Barr virus in 3%, HIV in 2%, and other viral pathogens in 5%. Autoimmune disease was responsible for 22% of cases, with disease mainly due to anti–N-methyl-D-aspartate receptor or voltage-gated potassium channel antibodies. Etiology was unidentified in 30% of cases.

Overall, outcomes were good (i.e., mild or no disability) in 49% of patients at discharge and — among those with available follow-up information — approximately 60% at 1 year. Mortality rates were 9% during hospitalization and 17% at 1 year. Factors associated with poor outcome (i.e., moderate to severe disability or death) were age ≥65, immunocompromise, coma, acute thrombocytopenia, and need for mechanical ventilation.

Although viral etiologies account for the majority of acute encephalitis cases for which an etiology is identified, never forget to check for autoimmune encephalitis (e.g., anti-NMDA and anti-VGKC antibodies) and paraneoplastic etiologies (e.g., anti-Hu, anti-Yo, anti-Ma, and anti-Amphiphysin antibodies)


  1. Singh TD et al. The spectrum of acute encephalitis: Causes, management, and predictors of outcome. Neurology 2015 Jan 2784:1.
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Tags: autoimmune encephalitis, encephalitis, HPC updates, paraneoplastic encephalitis, viral encephalitis

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