Herpes simplex encephalitis.

Herpes simplex encephalitis (HSE) is a life-threatening condition with high mortality as well as significant morbidity in survivors. In most cases herpes simplex virus type 1 (HSV-1) is responsible for the diseases, however, the type 2 virus (HSV-2) is involved in 4-6% of cases. Primary HSV infection is identified in only one-third of patients with HSE. The majority of cases are recorded in adults with recurrent HSV infection who are already seropositive for HSV at the onset of symptoms, but only 6-10% of these patients have a history of labial herpes. Acute focal, necrotizing encephalitis with inflammation and swelling of the brain tissue are consistent features of the pathology of HSE. HSV-induced cytolysis certainly damages neurones, oligodendrocytes and astrocytes, but the role of cellular and humoral immunopathology is important. A complex network of cytokines seems to be active in regulating the local immune response and inflammation during and after HSE. Brain biopsy, serological analysis of intrathecal HSV antibodies and detection of HSV-DNA in the cerebrospinal fluid (CSF) are all useful techniques to confirm the aetiology of HSE. Neurodiagnostic tests which support a presumptive diagnosis of HSE include: CSF analysis, electroencephalography, computer-assisted tomography and magnetic resonance imaging. Although aciclovir is the treatment of choice in HSE, mortality and morbidity still remain problematic. Long-term follow-up indicates that intrathecal cellular and humoral activation persist in HSE.