Unveiling axial involvement in psoriatic arthritis: an ancillary analysis of the ASAS-perSpA study

Abstract Objective To determine the clinical profile of axial psoriatic arthritis (PsA) in a worldwide setting. Secondly, to identify factors associated with the development of axial involvement in patients with PsA. Methods Data from 3684 patients with axial spondyloarthritis (axSpA) or PsA from the ASAS-perSpA study were analysed. The ASAS-perSpA is a cross-sectional study that recruited consecutive patients with SpA (as diagnosed by their rheumatologist) from 68 centers worldwide and collected patient and disease data. First, 2651 axSpA patients and 367 PsA patients with any history of axial involvement (axPsA) were compared using logistic regression to later identify predictive factors for rheumatologist diagnosis of axPsA. Secondly, 367 axPsA patients were compared with 666 PsA patients lacking axial involvement (peripheral PsA [pPsA]) and the characteristics associated with axial manifestations were explored by logistic regression analysis. Results Patients with axPsA were older and less frequently males or HLA*B27 positive in comparison with axSpA patients. Additionally, while patients with axPsA had more peripheral manifestations and psoriasis, other extra-musculoskeletal manifestations (IBD and uveitis) were more frequent in those with axSpA. In the multivariable analysis, older age at diagnosis (OR = 1.04), peripheral arthritis (OR = 7.32) and dactylitis (OR = 2.82) were significantly associated with the diagnosis of axPsA. However, uveitis (OR = 0.22), IBD (OR = 0.12), HLA*B27 carriership (OR = 0.26) or sacroiliitis on imaging (OR = 0.5) were inversely associated with axPsA diagnosis as compared to axSpA. Axial involvement in patients with PsA was significantly associated with male gender (OR = 1.68), elevated CRP (OR = 2.87) and the absence of psoriasis (OR = 0.33). Conclusion In this worldwide setting axPsA was defined by rheumatologists as a unique phenotype, with disease features lying between axSpA and pure pPsA.