We describe a child with severe generalized choreoathetosis and anti–N-methyl-d-aspartate receptor encephalitis after herpes simplex virus type 1 encephalitis. Recent evidence supports an autoimmune trigger for anti–N-methyl-d-aspartate receptor encephalitis following a viral infection. This is emerging as a common and potentially treatable autoimmune condition in the pediatric population.

A 6-month-old girl presented with fever, diarrhea, and partial seizures and was subsequently treated for proven herpes simplex virus type 1 encephalitis. Shortly thereafter, she developed irritability, insomnia, dysautonomia, orolingual and facial choreodystonic movements, spontaneous vocalizations, and choreoathetoid movements of her trunk and limbs. Cerebrospinal fluid analysis confirmed anti–N-methyl-d-aspartate receptor antibodies. Management of her movements required titrated doses of clobazam, valproate, tetrabenazine, and immunotherapy. At 3 months' follow-up, her abnormal movements had completely resolved.

Our patient adds to recent evidence linking a viral trigger for brain autoimmunity. Movement disorders appear early, leading to severe patient and family distress, and pose a serious management dilemma because of a paucity of clinical trials assessing treatments in the pediatric population. Abnormal hyperkinetic movements present early and prominently, requiring a combination of symptomatic and immune-modulating therapies for successful treatment.