Neuropsychiatric Clues to Herpes Simplex Virus Encephalitis Presenting as Normal Pressure Hydrocephalus.

Herpes simplex virus type 1 (HSV-1) encephalitis can mimic neurodegenerative or structural disorders, particularly in older adults presenting with cognitive or behavioral symptoms. We report the case of a 73-year-old woman with progressive gait instability, urinary incontinence, and cognitive decline, which was initially attributed to normal pressure hydrocephalus (NPH). Despite transient improvement after two lumbar punctures and neuroimaging suggestive of significant ventriculomegaly, the patient's symptoms progressed with increasing paranoia, hallucinations, and agitation. Psychiatric consultation worked up the NPH diagnosis and identified various behavioral abnormalities-such as fluctuating delirium and psychosis-inconsistent with classic NPH. After 20 days of admission, restructuring of the differential and extensive infectious and metabolic testing led to the identification of HSV-1 DNA in cerebrospinal fluid (CSF). The patient improved markedly with prompt acyclovir therapy. This case underscores the diagnostic overlap and mimicry between infectious and neurodegenerative processes and highlights the role of psychiatric input in reframing atypical neurocognitive presentations and expanding the differential of treatment-resistant NPH in the presence of inconsistent symptomatic progression.