Disease activity states of the DAPSA, a psoriatic arthritis specific instrument, are valid against functional status and structural progression

Background Recently, disease activity states were developed for the Disease Activity index for PSoriatic Arthritis (DAPSA). Here, we assess if different DAPSA disease activity states are associated with different degrees of functional impairment and different extents of joint damage progression in patients with psoriatic arthritis (PsA). Methods We used data from two pivotal trials of tumour necrosis factor (TNF) inhibitors in PsA (IMPACT II and GO- REVEAL) and identified patients in DAPSA remission (REM, < 4), and low, moderate or high disease activity (LDA, < 14; MDA, < 28; HDA, > 28) at 6 months. Across these groups we compared the functional scores (Health Assessment Questionnaire Disability Index, HAQ and physical component scale of the Short Form- 36, PCS), and 1- year structural progression (PsA- modified Sharp/van der Heijde Score). Results We identified 310 from GO- REVEAL and 130 from IMPACT II, with a mean (SD) baseline DAPSA of 48.8 (26.4) and 44.6 (17.9), respectively. HAQ scores increased across patients groups in the four DAPSA disease activity states, while PCS decreased (p< 0.001 for both). The mean progression in the combined cohort was- 0.47 for REM,- 0.28 for LDA,- 0.14 for MDA and 0.51 for HDA (p< 0.001). This association was also significant in the individual trial cohorts, and in the subgroups of patients treated with TNF inhibitors or placebo. Higher DAPSA scores were significantly and independently associated with probability of structural progression in multiple analyses. Conclusions Disease activity states of the PsA specific DAPSA score are highly valid for future use as endpoints in clinical trials or as targets in clinical practice.