Objectives: To estimate the incidence of anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis.
Methods: We conducted a retrospective cohort study of >10 million person-years of observation from members of Kaiser Permanente Southern California, 2011-2022. The electronic health record of individuals with text-string mention of NMDA and encephalitis were reviewed to identify persons who met diagnostic criteria for anti-NMDAR encephalitis. Age-standardized and sex-standardized incidences stratified by race and ethnicity were estimated according to the 2020 US Census population.
Results: We identified 70 patients who met diagnostic criteria for anti-NMDAR encephalitis. The median age at onset was 23.7 years (IQR = 14.2-31.0 years), and 45 (64%) were female patients. The age-standardized and sex-standardized incidence of anti-NMDAR encephalitis per 1 million person-years was significantly higher in Black (2.94, 95% CI 1.27-4.61), Hispanic (2.17, 95% CI 1.51-2.83), and Asian/Pacific Island persons (2.02, 95% CI 0.77-3.28) compared with White persons (0.40, 95% CI 0.08-0.72). Ovarian teratomas were found in 58.3% of Black female individuals and 10%-28.6% in other groups.
Discussion: Anti-NMDA receptor encephalitis disproportionately affected Black, Hispanic, or Asian/Pacific Island persons. Ovarian teratomas were a particularly common trigger in Black female individuals. Future research should seek to identify environmental and biological risk factors that disproportionately affect minoritized individuals residing in the United States.