Phenotypic differences and treatment persistence in a large multicenter cohort of axial psoriatic arthritis

Objective: To compare clinical features across three axial psoriatic arthritis (PsA) phenotypes: (i) isolated axial PsA, (ii) axial PsA with oligoarticular involvement (axial PsA+oligo), and (iii) axial PsA with polyarticular disease (axial PsA+poly), and assess persistence of first-line biologic and targeted synthetic DMARDs (b/tsDMARDs). Methods: Baseline demographic, clinical, therapeutic, laboratory, and imaging data were retrospectively collected. Kaplan-Meier analysis evaluated treatment persistence, and LASSO Cox regression identified baseline factors associated with discontinuation. Results: Among 621 patients, 175 (28.2%) had isolated axial PsA, 252 (40.6%) axial PsA+oligo, and 194 (31.2%) axial PsA+poly. Psoriasis was more frequent in isolated axial PsA and axial PsA+oligo than in axial PsA+poly (82.3% and 82.1% vs 66.1%; p< 0.001), with lower HLA-B27 positivity in axial PsA+poly (10.9% vs 18.9% in isolated axial PsA and 21.6% in axial PsA+oligo; p= 0.02). Sacroiliitis was more frequent in isolated axial PsA (70.3%) and axial PsA+oligo (65.7%) than in axial PsA+poly (53.6%, p< 0.001), whereas spondylitis was more frequent in axial PsA+poly (15.0% vs 8.3% in axial PsA+oligo and 6.3% in isolated axial PsA; p< 0.001). Treatment persistence was longest in axial PsA+oligo (62 months, 95% CI 43-67) and shortest in axial PsA+poly (38 months, 95% CI 24-49) (p= 0.006). Higher VAS global pain was associated with shorter persistence (aHR 1.010, 95% CI 1.003-1.018, p= 0.009), whereas HLA-B27 positivity (aHR 0.56, 95% CI 0.32-0.99, p= 0.045) with longer persistence. Conclusion: Treatment persistence in axial PsA varies according to clinical phenotypes, HLA-B27 status and pain, supporting the relevance of phenotypic stratification in clinical practice