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<h5 class="section-title" id="d1772784e260">Objectives</h5>
<p id="P1">We evaluate incidence and prevalence of autoimmune encephalitis and compare
the epidemiology
of autoimmune and infectious encephalitis.
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<h5 class="section-title" id="d1772784e265">Methods</h5>
<p id="P2">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 subgroups were defined by 2016 diagnostic criteria and infectious encephalitis
diagnosis required a confirmed infectious pathogen. Age- and sex-adjusted prevalence
and incidence rates were calculated. Patients with encephalitis of uncertain etiology
were excluded.
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<h5 class="section-title" id="d1772784e270">Results</h5>
<p id="P3">The prevalence of autoimmune encephalitis on January 1, 2014 of 13.7/100,000
was not
significantly different from that of all infectious encephalitides (11.6/100,000;
p=0.63) or the viral subcategory (8.3/100,000; p=0.17). 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=0.03). 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 (2.8 vs 0.7/100,000 person-years; p=0.01) and prevalence (38.3
vs 13.7/100,000; p=0.04) of autoimmune encephalitis was higher among African-Americans
than Caucasians. The prevalence of specific neural autoantibodies was: myelin-oligodendrocyte-glycoprotein
(MOG) (1.9/100,000); glutamic acid decarboxylase-65 (GAD65) (1.9/100,000); unclassified
neural autoantibody (1.4/100,000); 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).
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<h5 class="section-title" id="d1772784e275">Interpretation</h5>
<p id="P4">This study shows that the prevalence and incidence of autoimmune encephalitis
is comparable
to infectious encephalitis and its detection is increasing over time.
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