6th Edition of Neurology World Conference 2026

Abstract

Background Herpes simplex virus type 1 (HSV-1) encephalitis is a well-known trigger of secondary autoimmune encephalitis, particularly anti-NMDA receptor encephalitis. Early recognition is essential, as the clinical course may worsen despite appropriate antiviral therapy. Methods We report a previously healthy 6-year-old girl presenting with fever, altered behavior, and decreased consciousness. Cerebrospinal fluid (CSF) analysis revealed HSV-1 positivity by PCR, and intravenous acyclovir therapy was initiated. Although partial improvement was observed, the patient subsequently developed progressive neuropsychiatric symptoms, including mutism and impaired awareness. Further evaluation demonstrated anti-NMDA receptor antibodies in CSF. Brain MRI showed bilateral cortical and subcortical signal abnormalities, and EEG revealed diffuse slowing. Results Following the diagnosis of secondary anti-NMDA receptor encephalitis, high-dose corticosteroid therapy was initiated. Due to insufficient clinical response, plasmapheresis was subsequently performed, followed by rituximab therapy. Monthly intravenous immunoglobulin (IVIG) was administered as maintenance treatment. The patient showed gradual clinical improvement, with recovery of neurological functions over time. Conclusions/Learning Points This case highlights that anti-NMDA receptor encephalitis may develop following HSV-1 encephalitis and should be suspected in patients with secondary neurological deterioration despite appropriate antiviral treatment. Our patient experienced a severe clinical course requiring intensive care support, followed by marked neurological impairment including mutism, severe ataxia, and inability to walk independently. With timely initiation of immunotherapy, gradual but significant recovery was achieved. The patient regained independent ambulation, ataxia markedly improved, and mutism progressively resolved over time. Early recognition and prompt, stepwise immunotherapy are critical for improving outcomes, even in patients with severe initial presentation.