Background:Although pts with axial PsA and axial SpA share some common clinical characteristics, there are also potential differences that may influence disease assessment and treatment response. Identifying differences between the two pt populations is important for assessment of disease characteristics and severity as well as informing treatment decisions. There has been little comparative characterization of these conditions in a US population.Objectives:To compare characteristics of pts with axial PsA and axial SpA.Methods:Pts ≥18 years of age diagnosed with axial PsA or axial SpA at enrollment in the prospective, multicenter, observational Corrona PsA/SpA Registry between March 2013 and August 2020 were included. Enrollment visit demographics, clinical characteristics, treatment history, disease activity measures, and PROs were compared between disease groups. Continuous measures were reported using means and standard deviations; means for disease groups were compared using two-sample t tests or Wilcoxon rank sum tests. Categorical measures were reported as frequencies and percentages; frequencies in disease groups were compared using chi-square or Fisher exact tests.Results:A total of 1044 pts (470 with axial PsA and 574 with axial SpA) were identified (Table). Pts with axial PsA were older with a higher percentage being female vs pts with axial SpA. Time since symptom onset and diagnosis were shorter for pts with axial PsA vs axial SpA (12.0 vs 15.6 years [P<0.001] and 6.8 vs 8.3 years [P=0.01]). Pts with axial PsA were less likely than pts with axial SpA to have current or historical uveitis (4% vs 14% [P<0.001]) or inflammatory bowel disease (5% vs 10% [P=0.005]). Prior biologic synthetic disease-modifying antirheumatic drug (bDMARD) and conventional synthetic DMARD use was more prevalent in the axial PsA vs axial SpA groups (64% vs 52% [P<0.001]/59% vs 32% [P<0.001]), while mean dactylitis (measured by Dactylitis Count) and enthesitis (measured by Spondyloarthritis Research Consortium of Canada [SPARCC] Enthesitis Index) counts were higher (0.4 vs 0.1 [P<0.001]/1.7 vs 1.2 [P<0.001]). Mean pt-reported pain and spinal pain were lower in pts with axial PsA vs axial SpA (49.4 vs 53.9 [P=0.015]/40.8 vs 49.7 [P<0.001]) (Figure). The proportion of pts with morning stiffness along with mean fatigue and work impairment scores were similar between disease groups.Table.Baseline demographics and clinical characteristicsAxial PsAN=470Axial SpAN=574P valueAge (years), mean ± SD51.6 ± 13.247.7 ± 14.0<0.001Female, n (%)265 (57)248 (44)<0.001White, n (%)428 (94)507 (91)0.089Years since symptom onset, mean ± SD12.0 ± 11.615.6 ± 12.1<0.001Years since diagnosis, mean ± SD6.8 ± 9.08.3 ± 10.50.010HLA-B27 positive status, n/n (%)52/189 (28)214/295 (73)<0.001Abnormal CRP, n (%)88 (19)140 (24)0.033Uveitis, n (%)20 (4)80 (14)<0.001IBD, n (%)25 (5)59 (10)0.005Dactylitis count, mean ± SD0.4 ± 1.50.1 ± 0.7<0.001SPARCC enthesitis count, mean ± SD1.7 ± 2.91.2 ± 2.4<0.001Morning stiffness, n (%)439 (95)537 (96)0.923BASDAI (0–10), mean ± SD4.8 ± 2.54.9 ± 2.40.463BASDAI Q2 (0–10): spinal pain, mean ± SD5.0 ± 2.95.7 ± 2.9<0.001BASDAI Q3 (0–10): peripheral pain/swelling, mean ± SD4.5 ± 2.94.0 ± 3.10.010Modified BASDAI (0–10), mean ± SD5.0 ± 2.55.4 ± 2.40.013Prior bDMARDs, n (%)300 (64)299 (52)<0.001Prior csDMARDs, n (%)275 (59)181 (32)<0.001Prior prednisone use, n (%)54 (12)73 (13)0.611Prior NSAID use, n (%)52 (11)46 (8)0.115Conclusion:Findings from this descriptive real-world analysis suggest there may be meaningful differences between pts with axial SpA and axial PsA but future studies are needed to better understand these differences.Acknowledgements:Medical writing services provided by Alan Saltzman of Fishawack Facilitate Ltd, part of Fishawack Health, and funded by AbbVie.This study was sponsored by Corrona, LLC. Corrona has been supported through contracted subscriptions in the last 2 years by AbbVie, Amgen, Boehringer Ingelheim, Bristol Myers Squibb, Celgene, Crescendo, Eli Lilly and Company, Genentech, Gilead, GSK, Janssen, Merck, Momenta Pharmaceuticals, Novartis, Pfizer, Regeneron, Roche, Sun, UCB, and Valeant. The design, study conduct, and financial support for the study were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the abstract. No honoraria or payments were made for authorship.Disclosure of Interests:Philip J Mease Speakers bureau: AbbVie, Amgen, Janssen, Lilly, Novartis, Pfizer, and UCB, Consultant of: AbbVie, Amgen, BMS, Boehringer Ingelheim, Celgene, Galapagos, Gilead, GlaxoSmithKline, Janssen, Lilly, Novartis, Pfizer, Sun, and UCB, Grant/research support from: AbbVie, Amgen, BMS, Galapagos, Gilead, Janssen, Lilly, Novartis, Pfizer, Sun, and UCB, Maya Marchese Employee of: Corrona, Robert McLean Employee of: Corrona, Taylor Blachley Employee of: Corrona, Laura Anatale-Tardiff Employee of: Corrona, Christopher Saffore Shareholder of: AbbVie, Employee of: AbbVie, Elizabeth Lesser Shareholder of: AbbVie, Employee of: AbbVie, Alexis Ogdie Consultant of: Amgen, AbbVie, BMS, Celgene, Corrona, Gilead, Janssen, Lilly, Novartis, Pfizer, and UCB, Grant/research support from: National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases, Rheumatology Research Foundation, National Psoriasis Foundation, Pfizer, and Novartis