Objective To determine the frequency, age and sex associations for autoimmune encephalitis antibody biomarkers (AE-Abs).

Methods There were 42032 patients tested in the Mayo Clinic Neuroimmunology Laboratory between January 2018-December 2019 for AE-Abs in serum and/or cerebrospinal fluid (CSF) including; NMDA-R-IgG, AMPA-R-IgG, GABAB-R-IgG, CASPR2-IgG, LGI1-IgG, GAD65-IgG, CRMP5-IgG, amphiphysin-IgG, PCA1/2/Tr-IgGs, ANNA1/2/3-IgGs, GFAP-α-IgG, mGluR1-IgG, DPPX-IgG, MOG-IgG1, were examined to determine frequency of antibody positivity. Age and sex associations were examined using multivariable logistic regression.

Results Adult serum analysis (22,472 patients; 56% female) revealed 814 (4%) were positive: NMDA-R-IgG (25%) > GAD65-IgG (22%) > LGI1-IgG (21%) > others. Of children (5,649; 50% female), 250 (4%) were positive: NMDA-R-IgG (53%) > MOG-IgG1 (32%) > GAD65-IgG (7%) > others.

Adult CSF analysis (18,745 patients; 54% female) revealed 709 (4%) were positive; NMDA-R-IgG (45%) > GAD65-IgG (19%) > LGI1-IgG (13%) > others. Of children (5136; 50% female), 276 (5%) were positive: NMDA-R-IgG (90%) > GAD65-IgG (7%) > others.

Age <20 years was associated with NMDA-R-IgG and MOG-IgG1 (OR=8.11 and 7.73 respectively, p<0.001). Age >65 years was associated with GABAB-R-IgG, LGI1-IgG, CASPR2-IgG and ANNA1-IgG (OR=7.33, 14.98, 3.67, 14.53, p<0.001). Women accounted for 60% of NMDA-R-IgG (CSF) and 78% of GAD65-IgG (CSF/serum) cohorts (OR=1.32, p=0.002, OR=2.78, p<0.001, respectively). Men accounted for 62% of the LGI1-IgG cohort (OR=1.87, p <0.001). Age and sex interacted for NMDA-R-IgG, particularly in females <20 years (OR=7.72, p <0.001).

Conclusion The most frequently detected were NMDA-R-IgG, LGI1-IgG, GAD65-IgG and MOG-IgG1. Age and sex associations may suggest paraneoplastic, endocrinological or aging influences on neurological autoimmunity.