Herpes simplex encephalitis.

This is an acute necrotizing encephalitis with a high mortality rate. It is thought to occur by the reactivation of herpes simplex virus type 1 from latently infected trigeminal ganglia, with subsequent centripetal spread and fulminant growth in tissue of the central nervous system. Prompt diagnosis and antiviral therapy are required because of the rapidly progressive nature and severe consequences of this disease. The physician must understand the pathophysiology to fully appreciate the need for early diagnosis and the gravity of mismanagement.