ABSTRACT
Herpes simplex encephalitis (HSE) is a rare viral encephalitis in adults. A high (70%) mortality rate with serious complications has been reported even after active, appropriate management. The association between HSE and immune suppression is unclear, but there are case reports of cancer patients in which HSE concomitantly developed after whole brain radiation or high-dose steroid treatment. The clinical manifestations and laboratory findings of these patients are atypical compared to the general population. Although brain magnetic resonance images reveal typical HSE findings, cerebrospinal fluid (CSF) analysis might be normal in cancer patients. We report a case of HSE in a 48-year-old male diagnosed with nasopharyngeal cancer and treated with concurrent chemoradiation. This patient had a normal cell count in CSF, but HSE was finally diagnosed from positive polymerase chain reaction test results. After administration of acyclovir and systemic steroid treatment, the patient had a good clinical course with few neurologic sequelae.