Herpes Simplex Encephalitis as a Complication of Whole-Brain Radiotherapy: A Case Report and Review of the Literature

A 55-year-old male recently diagnosed with stage IV lung adenocarcinoma presented with altered mental status approximately 1 week after the completion of 14 fractions of whole-brain radiotherapy (WBRT) for brain metastases. On admission, he was somnolent but oriented and without focal neurological deficits. Brain imaging revealed marked regression of his brain metastases. Laboratory values were only significant for hyponatremia with urine hyperosmolality consistent with syndrome of inappropriate antidiuretic hormone secretion. The patient developed seizures 3 days after admission, at which time cerebrospinal fluid was significant for positive herpes simplex virus (HSV)-1 PCR but with a negative cell count, and acyclovir was started for HSV encephalitis (HSE). After 3 weeks of acyclovir 10 mg/dl i.v. 3 times per day, he had significant neurological recovery and was discharged. Although HSE is a relatively rare condition, it is the most common cause of sporadic encephalitis in Western countries. Since the pathogenesis is believed to be due to the reactivation of latent HSV, it is possible that patients who are immunosuppressed are at higher risk for HSE. In addition, patients who are immunosuppressed or immunocompromised often present atypically, which may delay time to diagnosis and treatment, thus significantly worsening prognosis. This case report intends to raise awareness of this severe condition in the context of patients who have received WBRT and immunosuppressive therapy. In addition, important considerations of diagnosis and treatment of HSE in this patient population are discussed.