N-methyl-D-aspartate receptor antibodies in pediatric dyskinetic encephalitis lethargica.

Encephalitis lethargica (EL) describes an encephalitis with psychiatric, sleep, and extrapyramidal movement disorders. Dyskinetic and parkinsonian forms have been described. EL shares clinical features with the anti-N-methyl-D-aspartate receptor (NMDAR-Ab) encephalitis. We studied 20 sera from pediatric patients with contemporary EL. Ten sera (from 2 males and 8 females, aged 1.3-13 years) and 6/6 cerebrospinal fluid samples were positive for NMDAR-Ab. NMDAR-Ab-positive patients had dyskinesias, agitation, seizures, and insomnia, whereas parkinsonism and somnolence dominated in the NMDAR-Ab-negative children. We were unable to identify any tumors. The dyskinetic form of EL is an NMDAR-Ab encephalitis and can affect very young children.