To assess whether initial ancillary tests (brain magnetic resonance imaging-MRI, electroencephalogram-EEG, and/or cerebrospinal fluid-CSF white blood cell count) are abnormal in children with isolated psychiatric symptoms and anti-NMDA receptor encephalitis.

This multi-center retrospective cohort study from CONNECT (CONquering Neuroinflammation and Epilepsies ConsorTium) from 14 institutions included children under 18 years old who were diagnosed with pNMDARE from January 1, 2008 – September 1, 2022. Psychiatric symptoms were defined as the presence of catatonia, agitation, hallucinations, confusion, behavioral changes, anxiety, and suicidal ideation. Patients who had non-psychiatric symptoms (seizures, movement disorders, autonomic instability, speech changes, and hypoventilation) were excluded. Descriptive statistics using means and medians and comparisons for continuous versus discrete data were performed.

Out of 249 children included, twelve (5%) had only psychiatric symptoms without other typical clinical features of autoimmune encephalitis at presentation. All but one (11/12=92%) had at least one abnormal finding on initial ancillary testing: 8/12 (67%) had an abnormal EEG, 6/12 (50%) had an abnormal MRI, and 5/12 (42%) demonstrated CSF pleocytosis. The single patient with a normal MRI, EEG and CSF profile had low positive CSF NMDA antibody (titer of 1:1) and symptoms improved without immunotherapy.