Brain irradiation and antioedematous dexamethasone treatment--risk factors for herpes simplex encephalitis?

Herpes simplex encephalitis (HSE) could result from the reactivation of an endogenous latent herpes simplex virus (HSV) in sensory ganglia or in brain parenchyma. Virus replication and a new lytic virus cycle may be triggered by a wide variety of factors. One of these might be irradiation as suggested by experimental evidence obtained in mouse trigeminal ganglia. Here we report the occurrence of HSE in a 52 years old woman two months after brain irradiation (40 Gray in 20 fractions) and dexamethasone administration for a metastatic brain tumor. HSE has already been observed in a clinical context very similar to that reported here, suggesting that brain irradiation together with corticoid therapy may, in some rare patients, favour the occurrence of HSV reactivation and HSE.