Aspiration Pneumonia with Herpes Simplex Encephalitis in an Elderly Japanese Patient.

A 94-year-old woman residing in a nursing home was admitted with aspiration pneumonia. A sputum culture yielded Klebsiella pneumoniae. Despite appropriate management, the patient's mental status deteriorated. Brain magnetic resonance imaging demonstrated high signal intensity in the right insular cortex on diffusion-weighted images, raising the suspicion of limbic encephalitis. A lumbar puncture revealed clear cerebrospinal fluid (CSF) with normal cell counts and protein levels. On hospital day 5, HSV-1 DNA was detected in the CSF, confirming herpes simplex encephalitis (HSE), and acyclovir was initiated. In elderly patients with unexplained altered consciousness, clinicians should not exclude HSE based on normal CSF findings.