Predictors of outcome in HSV encephalitis

This study aims to explore the clinical features, radiological findings, management and the factors influencing prognosis in PCR-confirmed herpes simplex virus encephalitis (HSE). This is a retrospective review of consecutive patients diagnosed with HSE at Mayo Clinic, Rochester, MN, between January 1995 and December 2013. Only HSE cases confirmed by PCR were included. Univariate and multivariate analysis was used to identify factors associated with good (modified Rankin Scale of 0-2) or poor outcome (mRS of 3-6) at hospital discharge and 1-year follow-up. We identified 45 patients with HSE. Median age was 66 (IQR 53.5-78) years. HSE was caused by HSV-1 in 33 cases and by HSV-2 in 9. Nearly half had seizures upon admission or during hospitalization. The most common regions involved on MRI were the temporal lobe in 35 (87.5%), insula in 28 (70.0%), frontal lobe in 27 (67.5%) and thalamus in 11 (27.5%) patients. MRI pattern was quite homogeneous with HSV-1 infection, but much more heterogeneous with HSV-2. Good outcome at discharge and at 6-12 months was seen in 16 (35.6%) and 27 (65.9%) patients, respectively. On multivariate analyses, older age (p = 0.001), coma (p = 0.008), restricted diffusion on MRI (p = 0.005) and acyclovir started after the first day of admission (p = 0.050) were associated with poor outcome at discharge. Older age, development of coma, presence of restricted diffusion on brain MRI and delay in the administration of acyclovir portend poor outcome in HSE. Conversely, presence of seizures, focal neurological deficits, EEG abnormalities and location or extension of FLAIR/T2 abnormalities did not influence functional outcome.