Herpes simplex encephalitis and radiotherapy.

The pathogenesis underlying the reactivation of latent herpes simplex virus remains undefined. This article presents the case of a 15-year-old male who developed herpes simplex encephalitis, as proven by a positive cerebrospinal fluid polymerase chain reaction and supported by magnetic resonance imaging findings during radiotherapy for pontine glioma. The temporal relation of radiotherapy to the occurrence of herpes simplex encephalitis suggests that cranial irradiation may play a role in the reactivation of latent herpes simplex virus. This finding suggests that herpes simplex encephalitis should be a part of the differential diagnosis of acute neurologic decline in patients undergoing cranial radiotherapy.