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.