The Incidence and Prevalence of Autoimmune Encephalitis and a comparison to Infectious Encephalitis: A Population-Based Study (P5.401)

Objective: We evaluate incidence and prevalence of autoimmune encephalitis and compare the epidemiology of autoimmune and infectious encephalitis. Background: Population-based studies of autoimmune encephalitis incidence and prevalence are lacking. Awareness of its epidemiology is essential for allocation of resources and health care planning. Design/Methods: We performed a population-based comparative study of the incidence and prevalence of autoimmune and infectious encephalitis in Olmsted County, USA. Autoimmune encephalitis diagnosis and its subgroups were defined by recently published diagnostic criteria. Age- and sex-adjusted prevalence and incidence rates were calculated, and compared using Poisson regression. Results: The prevalence of autoimmune encephalitis on January 1, 2014 of 13.2/100,000 was not significantly different from that of all infectious encephalitides (11.6/100,000; p=0.75) or the viral subcategory (8.3/100,000; p=0.23). The incidence rates (1995–2015) of autoimmune and infectious encephalitis were 0.8/100,000 and 1.0/100,000 person-years respectively (p=0.58). The number of relapses or recurrent hospitalizations was higher for autoimmune than infectious encephalitis (p=0.04). The incidence of autoimmune encephalitis increased over time from 0.4/100,000 person-years (1995–2005) to 1.2/100,000 person-years (2006–2015) (p=0.02), attributable to increased recognition of autoantibody-positive cases. The incidence (2.3 vs 0.7/100,000 person-years; p=0.01) and prevalence (38.3 vs 12.9/100,000; p=0.03) of autoimmune encephalitis was higher among African-Americans than Caucasians. Additionally, males had a significantly higher prevalence of autoimmune encephalitis than females (19.0 vs 7.2/100,000, p=0.04). The prevalence of specific neural autoantibody biomarkers among the definite autoimmune encephalitis category was: glutamic acid decarboxylase-65 (GAD65) (1.9/100,000); unclassified neural autoantibody (1.4/100,000); myelin-oligodendrocyte-glycoprotein (MOG) (1.3/100,000); leucine-rich glioma-inactivated-protein-1 (LGI1) (0.7/100,000); collapsin response-mediator protein-5 (CRMP5) (0.7/100,000); N-methyl-D-aspartate-receptor (NMDAR) (0.6/100,000); anti-neuronal nuclear antibody-2 (ANNA-2/anti-Ri) (0.6/100,000) and glial fibrillary acidic protein-α (GFAPα) (0.6/100,000). Conclusions: This study shows that the prevalence and incidence of autoimmune encephalitis is comparable to infectious encephalitis and its recognition is increasing over time. Disclosure: Dr. Dubey has nothing to disclose. Dr. Pittock has nothing to disclose. Dr. Kelly has nothing to disclose. Dr. McKeon has received research support from Medimmune, Euroimmun, Grifols and Alexion. Dr. Lopez has nothing to disclose. Dr. Lennon has received royalty, license fees, or contractual rights payments from RSR, royalties from sale kits for AQP4 IgG detetction and from clinical service assays performed outside Mayo clinic. Dr. Gadoth has nothing to disclose. Dr. Smith has nothing to disclose. Dr. Bryant has nothing to disclose. Dr. Klein has nothing to disclose. Dr Aksamit has nothing to disclose. Dr. Toledano has nothing to disclose. Dr. Boeve has received research support from GE Heathcare and Axovant. Dr. Tillema has nothing to disclose. Dr Flanagan has nothing to disclose.