Anti-N-methyl-D-aspartate receptor encephalitis presenting as isolated first-episode psychosis in a 16-year-old girl, complicated by neuroleptic malignant syndrome

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a rare but increasingly recognized autoimmune disorder that predominantly affects adolescents and young adults. It often presents with prominent psychiatric symptoms at onset, leading to frequent misdiagnosis as a primary psychiatric disorder. We report the case of a 16-year-old girl who presented with acute psychiatric symptoms, including mood lability, hallucinations, and aggression, initially diagnosed as first-episode psychosis. Her condition rapidly deteriorated under antipsychotic treatment, progressing to neuroleptic malignant syndrome, followed by the emergence of cerebellar ataxia, which raised strong suspicion of an underlying organic aetiology. Subsequent investigations confirmed the diagnosis of anti-NMDAR encephalitis. The patient was successfully treated with intravenous immunoglobulin, achieving complete recovery. This case underscores the diagnostic challenges posed by isolated psychiatric presentations of anti-NMDAR encephalitis in adolescents. Early recognition and prompt initiation of immunotherapy are crucial for favourable outcomes, particularly in cases presenting with antipsychotic intolerance or atypical clinical progression.