Acyclovir Encephalopathy in HSV Encephalitis Elderly With Normal Renal Function

Herpes simplex virus (HSV) encephalitis is a disease treated with acyclovir (ACV). However, the neurotoxicity of ACV can lead to the development of ACV encephalopathy. While ACV is used to treat HSV encephalitis, the treatment for ACV encephalopathy is to discontinue the use of ACV. Electroencephalography (EEG) is useful for distinguishing ACV encephalopathy from HSV encephalitis. An 83-year-old male presented with fever and fatigue. He had no decline of renal function. By the fourth day, he experienced tonic-clonic seizures, right-sided conjugate deviation, and loss of consciousness, leading to a diagnosis of HSV encephalitis. He was treated with ACV, which resulted in acute kidney injury (AKI) and loss of consciousness. A diagnosis of ACV encephalopathy with AKI was confirmed by EEG. His treatment continued by vidarabine instead of ACV. His AKI improved after discontinuing ACV and performing plasma exchange, and his level of consciousness fully returned to normal. This case highlights the utility of EEG for distinguishing HSV encephalitis from ACV encephalopathy. We conducted the literature review, and AKI is considered as a risk factor for ACV encephalopathy in elderly patient using ACV or valacyclovir. However, we could not identify a cause for AKI in our case apart from the use of ACV.