Objective: To study long term clinical outcome of patients <18 years old with anti-NMDAR encephalitis.

Anti-N-Methyl-D-Aspartate Receptor (anti-NMDAR) encephalitis is an acute, autoimmune neurologic pathology with variable presentations that are often severe. The short-term prognosis is well known but its long-term evolution is poorly described especially in children.

Methods: In this French multicenter retrospective cohort study, patients <18 years old, diagnosed with anti-NMDAR encephalitis between 2007 and 2015 with a minimum follow-up of 2 years were included. Clinical, paraclinical and therapeutical data as well as cognitive evaluations, information concerning schooling, psychological and re-educational follow-up were collected.

Results: Eighty-one patients were included, fifty-seven were girls, with a median age at diagnosis of 10,6 ± 5 years. The mean time of follow-up is 45±22 months. Nine (11%) patients relapsed. Thirty (37%) patients have cognitive impairment. The mean mRankin score was 1,3±1,5, at the last follow up. Patients having fewer symptoms at diagnosis have less cognitive sequelae (p = 0.01) and higher mRankin score (≥ 2) (p = 0.01) and abnormal electroencephalogram (EEG) (p = 0.01) at onset are associated with cognitive difficulties.

Conclusion: Despite careful monitoring, we demonstrated that 37% of patients had cognitive sequelae. Initial severity of the symptoms and abnormal EEG has an impact on cognitive difficulties. Earlier management of these factors may help to limit their impact on cognition.