Comparative analysis of instruments measuring peripheral arthritis activity in Spondyloarthritis: a measurement properties study in 13 RCTs
Dafne Capelusnik, Clementina López-Medina, Casper Webers, Augusta Ortolan, Désirée van der Heijde, Robert Landewé, Philip J Mease, Anna Molto, Sofia RamiroObjectives
Using randomised controlled trial (RCT) data, this study evaluated the measurement properties of selected instruments to assess peripheral arthritis in axial and peripheral spondyloarthritis (axSpA/pSpA) and to inform selection of the best-performing instrument.
Methods
Eligible studies were RCTs in axSpA or pSpA with individual patient data available to calculate Patient Global Assessment (PGA), swollen/tender joint counts (44 or 66/68 joints), C reactive protein, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Axial Spondyloarthritis Disease Activity Score, Disease Activity Index for Psoriatic Arthritis/Disease Activity in Psoriatic Arthritis with 44 joint count (DAPSA44) and 44-joint Disease Activity Score at baseline and timing of primary endpoint. In axSpA, analyses were restricted to patients with peripheral arthritis at baseline. Measurement properties assessed included construct validity, test–retest reliability, longitudinal construct validity, trial discrimination and thresholds of meaning. Risk of bias (RoB) was evaluated and evidence was synthesised using Outcome Measures in Rheumatology-based GREEN/AMBER/RED ratings (low/uncertain/high RoB and good/adequate/poor performance, respectively).
Results
13 RCTs were included (10 axSpA and 3 pSpA). In axSpA trials, 25–51% of patients had peripheral arthritis at baseline (median swollen joint count of 44 joints (SJC44) across studies: 2–3); in pSpA trials, median SJC44 ranged 2–5. In axSpA, construct validity and thresholds of meaning were rated AMBER/GREEN for all instruments, while test–retest reliability was RED only for PGA. Responsiveness was consistently GREEN. Clinical trial discrimination was RED for single-item instruments but consistently GREEN for composite scores. In pSpA, most instruments showed AMBER/GREEN performance, although SJC44 demonstrated RED discrimination.
Conclusions
This study provides the first comprehensive, trial-based evaluation of measurement properties for instruments assessing peripheral arthritis activity in axSpA and pSpA. Composite scores, such as BASDAI, ASDAS and DAPSA44, generally demonstrated more robust performance than single-item instruments, expanding the evidence base for the final instrument-selection phase.