Background:Axial involvement affects 25-70% of psoriatic arthritis (PsA) patients, depending on the criteria used for its definition. Efforts are underway to clarify the similarities and differences between axial-PsA and ankylosing spondylitis (AS).Objectives:We aimed to compare, in a real-world setting, axial-PsA and AS, in terms of demographic, radiologic and clinical (musculoskeletal and extra-articular) characteristics, with a focus on comorbidities.Methods:All AS (New York criteria, n=128) and PsA patients (CASPAR criteria, n=78) with axial involvement who were regularly followed-up in the outpatients’ rheumatology clinics from two tertiary hospitals (December 2018-July 2020) were included. Axial-PsA was defined when both of the following were ever present: inflammatory axial symptoms and radiological findings in X-ray or MRI of the sacroiliac joints or the spine. The following findings were considered: sacroiliitis (unilateral ≥ grade 3 or bilateral ≥ grade 2), corner lesions or squaring in the vertebrae, syndesmophytes (marginal or para-marginal) and facet joints arthritis.Demographic, radiologic and clinical characteristics including comorbidities were compared between AS and axial-PsA. For comorbidities (Major Adverse Cardiovascular Events [MACE: combined coronary disease and cerebrovascular accidents], hypertension, diabetes mellitus, dyslipidemia, depression, osteoporosis, and malignancies), adjustments were made for relevant confounders as follows: MACE were adjusted for: age, gender, smoking, hypertension, dyslipidemia, disease duration, DM and non-steroidal anti-inflammatory drugs [NSAIDs] use; depression for: age, gender and disease duration; malignancy for: age, gender, disease duration; hypertension for: age, sex, BMI, NSAIDs use, smoking for; DM: age, sex, BMI, glucocorticoids treatment; osteoporosis for: age, sex, glucocorticoids treatment. Statistical significance is considered for p-values less than 0.05 and 0.1 in univariate and multivariate analyses, respectively.Results:AS patients were younger (p=0.05) and were diagnosed at a younger age (p=0.002), more frequently of male gender (p=0.04), had lower BMI (p=0.006) and they were more frequently HLA-B27-positive (p=0.006). In AS patients, peripheral arthritis, dactylitis and nail involvement were less common (p=0.001 for all), in contrast to eye (p=0.001) and bowel involvement (p=0.004). Frequency of radiologic abnormalities in the spine was similar between the two groups while sacroiliitis was more often bilateral in AS and unilateral in axial-PsA (p<0.001 for both) Comorbidities, including MACE, were comparable between AS and axial-PsA, apart from depression which was more frequent in axial-PsA (Table 1. next page).Table 1.Comorbidities. Comparison between axial-PsA and AS. OR: odds ratio, MACE: Major cardiovascular events. * adjustments are reported in the textComorbiditiesaxial-PsA (n=79)AS(n=129)Crude OR(95%CI)Adjusted OR (95%CI)p-valueMACE* n (%)4 (5.1)6 (4.6)0.91 (0.25-3.34)1.73 (0.32-9.34)0.526Dyslipidemia n (%)37 (46.8)45 (34.9)0.61 (0.34-1.07)NA0.108Hypertension* n (%)27 (34.2)24 (18.6)0.44 (0.23-0.83)1.11 (0.38-3.21)0.843Diabetes mellitus* n (%)12 (15.2)10 (7.7)0.47 (0.19-1.14)1.65 (0.43-6.29)0.463Depression* n (%)19 (24.1)16 (12.4)0.44 (0.21-0.93)0.48 (0.22-1.07)0.07Osteoporosis* n (%)3 (3.8)10 (7.7)2.13 (0.57-7.98)2.40 (0.56-10.18)0.235Malignancies* n (%)3 (3.8)3 (2.3)0.60 (0.12-3.06)0.87 (0.16-4.70)0.870Conclusion:AS and axial-PsA have certain clinical and radiologic differences. Comorbidities were comparable, while depression was more common in axial-PsA.Disclosure of Interests:George E. Fragoulis: None declared, Maria Pappa: None declared, Gerasimos Evangelatos: None declared, Alexios Iliopoulos: None declared, Petros Sfikakis Grant/research support from: AbbVie, Pfizer, MSD, Roche, UCB, GSK, Novartis, Maria Tektonidou Grant/research support from: AbbVie, GSK, Genesis, MSD, Novartis, Pfizer, UCB.