Frequency and characteristics of axial involvement in psoriatic arthritis

Objectives: The Axial Involvement in Psoriatic Arthritis (AXIS) cohort aimed at evaluating the frequency of and clinical and imaging features of axial involvement in psoriatic arthritis (PsA). Methods: AXIS (NCT04434885) is a prospective, multicentre, cross-sectional study conducted in 19 countries, by the Assessment of SpondyloArthritis International Society and the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis. Participants with a diagnosis of PsA meeting ClASsification criteria for Psoriatic ARthritis with musculoskeletal symptom duration ≤10 years and no prior exposure to biological or targeted synthetic disease-modifying antirheumatic drugs were consecutively included. Standardised clinical, laboratory, and imaging assessments (radiography and magnetic resonance imaging of the axial skeleton, including sacroiliac joints [SIJs] and spine), were performed. Imaging was reviewed locally and centrally to detect axial involvement. The presence of axial involvement was determined by local investigator judgement before and after central-imaging review. Results: Among 409 participants, axial involvement was identified in 153 (37.4%) based on the investigator’s initial assessment and was decreased to 112 (27.4%) in the final evaluation after incorporating central-imaging review. Participants with axial involvement were younger (45.2 ± 13.8 vs 47.6 ± 12.6 years), more often male (56.3% vs 51.5%), and had a higher frequency of human leukocyte antigen (HLA)-B*27 positivity (22.4% vs 10.8%), inflammatory back pain (IBP) (74.7% vs 43.4%), and elevated C-reactive protein (CRP) (52.7% vs 37.4%). Active inflammatory and structural imaging changes were highly discriminative between participants with and without axial involvement. The central review identified imaging signs of axial involvement (active inflammation or structural lesions) in 95 participants (23.2%). Conclusions: Axial involvement was identified in 27.4% of participants with PsA after final diagnostic assessment, with associated features including HLA-B*27 positivity, IBP, elevated CRP, and imaging changes in SIJ or spine.