[Update on Herpes Simplex Encephalitis].

Herpes simplex encephalitis (HSE), which is caused by the herpes simplex virus (HSV), is a severe neuro-infectious disease characterized by high mortality and morbidity. We reviewed the pathomechanism, diagnosis, and treatment of HSE based on recent progress in the field. The highlighted mechanism of HSE in this review is immune-mediated tissue damage caused by host immunity. Major symptoms of HSE include psychiatric alteration, Klüver-Bucy syndrome, and amnesia, caused by frequent involvement of the limbic system. An important differential diagnosis of HSE is autoimmune limbic encephalitis, including anti-N-methyl-D-aspartate receptor encephalitis, and anti-voltage-gated K⁺ channel encephalitis. HSE is definitely diagnosed based on the detection of HSV-DNA by polymerase chain reaction and/or the detection of HSV-IgG antibody in the cerebrospinal fluid (CSF). Repeated CSF examinations are required for the accurate diagnosis of HSE. Acyclovir (ACV) plays a central role in the treatment of HSE, and its early initiation is essential for good outcome in patients with HSE. Acute administration of corticosteroids for HSE is controversial; a randomized, double-blind, placebo-controlled trial to investigate the efficacy of add-on corticosteroids to ACV is ongoing.