Objective: To describe the clinical course of younger children with Anti-N-methyl-D-aspartate Receptor (Anti-NMDAR) encephalitis.

Methods: Retrospective chart review of children with Anti-NMDAR encephalitis at a pediatric tertiary hospital during 2015-2018.

Results: 6 children younger than 7 years (age range: 18 months to 4 years at time of presentation; 3 girls) were admitted with Anti-NMDAR encephalitis (all positive CSF Antibody). All presented with altered sensorium, acute developmental regression and abnormal movements. Seizures occurred in only one child. Two had documented viral infections prior to anti-NMDAR symptoms (one with severe HSV encephalitis, another with EBV). All received therapy per standardized institutional protocol (corticosteroids, Intravenous Immunoglobulin [IVIG], rituximab). Three additionally underwent plasmapheresis. All children were functionally impaired initially (non-verbal, non-ambulatory; mRS=4-5) with improvement to mRS= 3 only in one by discharge. All had neurodevelopmental gains at follow up (duration 6-30 months). Three children have minimal deficits (mRS 0-1) while three have moderate-severe deficits (mRS 2-3; including one with HSV and one with a cerebellar stroke). All have continued to make gains, even beyond 18 months with outpatient rehabilitation programs.

Discussion: Our young anti-NMDAR patients presented with acute regression and movement disorders and not seizures as do older children. Even with early diagnosis and aggressive immunomodulation all young children were significantly impaired at discharge. With rehabilitation, there has been gradual and sustained gains in recovery. It is unclear if deficits will continue to improve with age.