Herpes Simplex Encephalitis in a Patient With Recurrent Pituitary Adenoma Receiving Radiation Therapy

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A 61-year-old male initially presented with decreased libido and right visual field loss. Evaluation revealed an elevated prolactin level and a pituitary mass consistent with a secretory pituitary adenoma. His tumor progressed on cabergoline and he subsequently underwent transphenoidal tumor debulking. Four years later, his tumor recurred, and a second resection was performed. Postoperatively his dexamethasone was tapered from 16 to 4 mg/d and stereotactic radiation therapy (180 cGy per day to a planned dose of 5040 cGy) was initiated. Two weeks into his radiation, he suddenly began to speak incoherently and had a witnessed seizure with bowel and bladder incontinence while at home. He was evaluated in the hospital where he was found to be dyspneic and febrile to 38.7°C with fluent but nonsensical speech. His baseline bitemporal hemianopsia, right-sided ptosis, and facial droop with incomplete adduction of the right eye were stable. Admission studies revealed a white cell count of 7600/mL and a CD4 count of 104/mm3. Magnetic resonance imaging of the brain demonstrated an unchanged 2.0 × 2.2 × 2.5 cm pituitary mass (Fig. 1). Diffusion-weighted magnetic resonance imaging demonstrated a new area of restricted diffusion in the left mesial temporal lobe with corresponding hyperintensity on FLAIR (Fig. 2). The cerebrospinal fluid (CSF) contained 62 white cells/µL of which 95% were neutrophils, 53 RBC/µL, a protein of 45 mg/dL, and glucose of 81 mg/dL. Phenytoin was prescribed for his witnessed seizure, dexamethasone was increased for peritumoral edema, and given his fevers and CSF findings ceftriaxone, vancomycin and acyclovir were initiated. By day 3 of admission all bacterial and fungal cultures were negative, the CSF herpes simplex virus (HSV) polymerase chain reaction was positive, and other viral polymerase chain reactions were negative. The patient completed a 14-day course of acyclovir and returned to his baseline status, which was fully oriented, conversant, and able to care for himself. He had no further fevers or seizures and continued with the planned radiation therapy.