Relapsing herpes simplex encephalitis: pathological confirmation of viral reactivation

This case is reported to raise awareness of herpes simplex encephalitis as a persisting brain disorder. A 66 year old immunocompetent man developed status epilepticus and died of pneumonia in the course of progressive hemiparesis, cognitive decline, and atrophy of the brain over a five year period after herpes simplex encephalitis. In addition to a completely destroyed left temporal lobe, necropsy revealed active encephalitis consisting of necrosis and lymphocyte infiltration with a large number of intranuclear inclusions in the neurones and glial cells in the markedly oedematous parenchyma of the right frontal and parietal lobes. Herpes simplex virus type 1 (HSV-1) antigen was detected by immunohistochemistry, HSV-1 DNA by in situ hybridisation, and herpes simplex virus nucleocapsids by electronmicroscopy. These clinical and pathological findings suggest that direct viral reactivation might result in a relapse of herpes simplex encephalitis, causing progressive clinical deterioration associated with the persistence of HSV-1 in the brain. This is the first case report demonstrating HSV-1 antigen, HSV-1 DNA, and herpes simplex virus nucleocapsids in a case of relapsing herpes simplex encephalitis.