Instrument selection for the assessment of peripheral arthritis in axial and peripheral spondyloarthritis: an ASAS...

To identify the most appropriate instrument to assess disease activity related to peripheral arthritis in axial spondyloarthritis (axSpA) and peripheral spondyloarthritis (pSpA) in clinical research.

This Assessment of Spondyloarthritis International Society (ASAS) project followed the Outcome Measures in Rheumatology (OMERACT) framework. Candidate instruments were identified through a systematic literature review (SLR). Domain match and feasibility were assessed by a working group (WG). A second SLR evaluated measurement properties (construct validity, test-retest reliability, responsiveness, clinical trial discrimination, and thresholds of meaning). Additional analyses were performed using individual patient data from randomised controlled trials (RCTs). Evidence was synthesised in summary of measurement properties tables, followed by a WG discussion and ASAS consensus voting.

Composite disease activity instruments consistently outperformed single-item measures. Evidence from the second SLR was limited, particularly for axSpA with peripheral arthritis, but analyses of 13 RCTs strengthened the evidence. In both axSpA and pSpA, composite instruments, particularly the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Axial Spondyloarthritis Disease Activity Score (ASDAS), and Disease Activity index for Psoriatic Arthritis based on 44 joints (DAPSA44), showed better construct validity, responsiveness, and clinical trial discrimination than joint counts alone. Clinical trial discrimination was particularly better for DAPSA44, making it the best-performing instrument across all measurement properties. Following ASAS voting, DAPSA44 was the preferred instrument, receiving 92% agreement for axSpA and 97% for pSpA.

DAPSA44 demonstrated the most adequate measurement performance across axSpA and pSpA and was endorsed by ASAS as the recommended instrument for assessing disease activity related to peripheral arthritis in pSpA clinical research. Future clinical trials and research studies should report DAPSA44 when analysing disease activity related to peripheral arthritis in SpA.