To assess the epidemiology of pediatric autoimmune encephalitis and acute disseminated encephalomyelitis (ADEM) at a national clinical laboratory.

As cases of autoimmune encephalitis are rare, it is difficult to ascertain the relative incidence of the different types of encephalitis in children. A previous study from an individual institution examined the frequency of pediatric autoimmune encephalitis; however, sample size was limited. By examining data from a national laboratory, the relative incidence of different encephalitides in the pediatric population can be better assessed. As ADEM is frequently similar to autoimmune encephalitis and diagnosed in children when examining for autoimmune encephalitis, it is included in this study.

This observational study assessed positivity rates for NR1, GAD-65, VGKC, Hu, CV2, LGI1, CASPR2, Ma-Ta, Amphiphysin, Neuromyelitis Optica (NMO), and myelin oligodendrocyte glycoprotein (MOG) for tests performed January 2020 through September 2022, at Quest Diagnostics and Athena Diagnostics.

Since 2020, children <18 tested for encephalitis and ADEM were examined for the above antibodies. Of this cohort, 694 tests have reported a positive outcome and 57.93% (402) were positive for NR1, 25.94% (180) for NMO, 5.76% (40) for GAD-65, 3.46% (24) for VGKC, 2.74% (19) for MOG, 1.59% (11) for Hu, 1.44% (10) for CV2, 0.57% (4) for LGI1, 0.29% (2) for CASPR2, 0.14% (1) for MaTa, and 0.14% (1) for Amphiphysin.

These findings from a national clinical laboratory suggest that since 2020 the highest incidence of pediatric autoimmune encephalitis is defined by the NR1 antibody, which makes up 57.93% of total positive test count. The MOG antibody, which is associated with ADEM in children, had the highest positivity rate when ordered as an individual test, suggesting that the clinical picture suggested MOG-associated ADEM.