A Prospective Cohort Study to Identify Clinical, Biological, and Imaging Features That Predict the Etiology of Acute Encephalitis

Background: New diagnostic tools have been developed to improve the diagnosis of infectious encephalitis. Using a prospective cohort of encephalitis patients, our objective was to identify possible clusters of patients with similar patterns among encephalitis of unknown cause (EUC) and to describe to what extent a patient's initial presentation may be predictive of encephalitis etiology, particularly herpes simplex virus (HSV) and varicella-zoster virus (VZV).

Methods: The National Cohort of Infectious Encephalitis in France is an ongoing prospective cohort study implemented in France in 2016. Patients who present with documented or suspected acute infectious encephalitis were included. Focusing on the variables that describe the initial presentation, we performed a factor analysis of mixed data (FAMD) to investigate a pattern of association between the initial presentation of a patient and the etiologic pathogen.

Results: As of 1 August 2018, data from 349 patients were analyzed. The most frequent pathogens were HSV (25%), VZV (11%), tick-borne encephalitis virus (6%), Listeria (5%), influenza virus (3%), and EUC (34%). Using the FAMD, it was not possible to identify a specific pattern related to the group of EUC. Age, temporal or hemorrhagic lesions, and cerebral spinal fluid lymphocytosis were significantly associated with HSV/VZV encephalitis.

Conclusions: No initial clinical/imaging/biology pattern was identified at admission among EUC, despite the improvement in diagnostic tools. In this context, the recommendation for a universal, early, probabilistic, initial treatment against HSV and VZV is still relevant, regardless of the initial clinical presentation of the encephalitis.