Corticosteroid-responsive focal granulomatous herpes simplex type-1 encephalitis in adults

We describe corticosteroid-responsive focal granulomatous encephalitis as a manifestation of herpes simplex virus (HSV) type 1 disease in the brain: something easily missed and easily treated. Two adult cases presented with cognitive symptoms progressing over weeks, despite aciclovir treatment. Brain imaging showed temporal lobe abnormalities, with gadolinium enhancement but no abnormal diffusion restriction. HSV-1 PCR analysis was negative in cerebrospinal fluid (CSF) but positive in brain biopsies, which showed vasocentric granulomatous inflammation. Paired blood and CSF samples showed intrathecal synthesis of HSV-1 type-specific IgG. The patients improved clinically only after immunosuppression. Despite profound cognitive impairment at their clinical nadir, both patients recovered fully. We suggest that, at least in a subset of patients with HSV-1 encephalitis, adjunctive corticosteroid treatment is critical to improve the outcome of the disease.