Axial spondyloarthritis and axial psoriatic arthritis: similar or different disease spectrum?

Aims: First, to compare clinical features and biological disease modifying anti-rheumatic drugs (bDMARDs) response in patients with axial spondyloarthritis (axSpA) and axial psoriatic arthritis (axPsA). Second, to identify possible predictors of treatment response in both entities. Methods: One-year follow-up, observational, single-center study including all patients with axSpA or axPsA who started bDMARDs therapy. Clinical features were collected at baseline while disease activity was measured at baseline, 6 and 12 months by the Ankylosing Spondylitis Disease Activity Score and the Physician Global Assessment. The frequency of patients achieving inactive disease (ID), low disease activity (LDA), high or very high disease activity and clinical improvement were compared between axSpA and axPsA. Baseline predictor factors for achieving treatment response were identified through regression models, using odds ratio (OR) as an estimate. Results: In total, 352 patients were included: 287 (81.5%) axSpA and 65 (18.5%) axPsA. No significant differences at baseline were observed between the two diseases for most of the characteristics. While HLA-B27 positivity was associated with axSpA (OR = 5.4; p < 0.001), peripheral manifestations were associated with axPsA (OR = 4.7; p < 0.001). The frequency of patients with axSpA and axPsA achieving ID/LDA after 6 and 12 months of bDMARDs was comparable: 53% versus 58%, p = 0.5; and 58% versus 60%, p = 0.9, respectively. Both diseases also presented similar clinical improvement. In axSpA and axPsA, male gender seemed to be associated with achieving LDA [OR at 12 months visit = 2.8 (p < 0.01) and 2.7 (p = 0.09)]. Conclusion: In clinical practice, patients with axSpA and axPsA present numerous similarities, including comparable medium-term clinical response to bDMARDs. Male gender could be a predictor of treatment response in both diseases.