Herpes simplex encephalitis in patients receiving chemotherapy and whole-brain radiation therapy

Herpes simplex encephalitis (HSE) is a very severe infection of the central nervous system (CNS) caused mainly by herpes simplex virus type 1 (HSV-1) and occasionally by herpes simplex virus type 2 (HSV-2). After relapse or drug-resistant to chemotherapy, whole-brain radiation therapy (WBRT) is a mainstay of treatment in patients with both identifiable brain metastases and CNS lymphoma. Although HSV-1 encephalitis predominantly affects immunocompetent host, HSV encephalitis may be more common in immune-suppressed patients than is currently recognized. Disease presentation may be atypical including lack of pleocytosis in cerebrospinal fluid (CSF). We report four patients diagnosed with HSE following chemotherapy and WBRT. The occurrence of HSE in patients with cancer seems not to be increased compared to the general population, but as our case series shows, a high level of suspicion is needed by the treating physician to diagnose HSE early in patients presenting with new neurological symptoms following WBRT.