Seronegative herpes simplex virus (HSV) encephalitis causing temporal lobe epilepsy resulting in new-onset psychosis: a case report and literature review.

Background: Herpes simplex virus (HSV) encephalitis is the most common nonepidemic encephalitis and can result in temporal lobe necrosis. Inflammation of the temporal lobe can result in temporal lobe epilepsy which is known to cause psychiatric symptoms. Case Description: We describe the case of a geriatric male patient who was admitted for new-onset visual hallucinations and other neuropsychiatric symptoms which began five days prior to admission. His lab work was unremarkable, and a computed tomography (CT) scan of the brain demonstrated small vessel ischemic disease. There was clinical suspicion for seizures, and electroencephalogram (EEG) monitoring showed focal seizure activity in the right hemisphere. He received a brain magnetic resonance imaging (MRI) which was suspicious for encephalitis. Various etiologies were considered, and he received an extensive workup including cerebrospinal fluid evaluation. Ultimately, he improved with empiric antiviral treatment added alongside multiple antiepileptic agents. The seizure control and resolution of symptoms with antiviral treatment, in addition to the findings of his central nervous system (CNS) workup, confirmed the presumptive diagnosis of HSV encephalitis. Conclusions: Understanding the multifactorial causes of neuropsychiatric symptoms is important in determining an appropriate workup. The acute onset of specific symptoms in our patient increased suspicion for a structural neurological process. His initial presentation could largely be explained by the vascular dementia and epileptiform activity that were discovered during hospitalization. However, his refractory seizures were suggestive of another underlying etiology. The localization of his seizures and MRI findings were suggestive of HSV encephalitis despite negative HSV polymerase chain reaction (PCR). A patient may benefit from antiviral treatment when the clinical picture is consistent with HSV encephalitis even in the setting of negative serological studies. Clinicians should also be mindful of false negatives on serological tests.