Background The Disease Activity index for PSoriatic Arthritis (DAPSA) was developed and validated. It is a composite measure of swollen and tender joint counts, patient global and pain assessment and an acute phase reactant. Recently, also DAPSA disease activity states were developed using clinical trial data and observational data (1). However, the validity of these states in regards to important outcomes of the disease has not yet been determined.
Objectives To assess if different DAPSA disease activity states are associated with different degrees of functional impairment and/or different extents of joint damage progression in patients with psoriatic arthritis (PsA).
Methods We used data from two pivotal trials of TNF-inhibitors in PsA, the IMPACT II (n=134) and the GO-REVEAL (n=313) trials. At 4 months, we identified patient in DAPSA remission (REM, ≤4), low disease activity (LDA, ≤14), moderate disease activity (MDA, ≤28), and high disease activity (HDA, >28). We then determined the rate of structural progression (defined as Sharp van der Heijde, SvdH, score increase of >0, >0.5, and >1 point from baseline to end of year 1) across these four disease activity groups. We also correlated DAPSA levels at 4 months with changes in SvdH change scores from baseline to year 1.
We also studied functional construct validity of the DAPSA states by assessing median scores of the Health Assessment Questionnaire Disability Index (HAQ; GO-REVEAL study only), and of the physical component scale of the Short Form-36 (PCS, SF-36; IMPACT II study only), across the different DAPSA states at 6 months.
Results We identified 313 from GO-REVEAL and 134 from IMPACT II, with a mean (SD) baseline DAPSA of 44.7 (17.8) and 48.7 (26.3). The probability of progression according to different DAPSA scores is depicted in panel A of the Figure, separately for three cutpoints of progression. For all three analyses, the link between DAPSA and the probability of progression was significant (progression >0: p=0.039; progression >0.5 and >1.0: p=0.0001 for both). This association was also seen when we compared patients in the four disease activity states at four months for their actual rate of progression, e.g., the proportion of patients with progression of >1 over one year was 3.7% among DAPSA remitters and 15.1% among patients with DAPSA HDA (p=0.0004).
We also confirmed functional construct validity by using HAQ scores in one trial (GO-REVEAL), and the SF-36 PCS in the other (IMPACT II). As can be seen in panel B of the Figure, the HAQ and PCS scores across the four groups were highly significantly different (p<0.0001 for both).
Conclusions The definition of traditional disease activity states on the scale of the DAPSA, a PsA specific disease activity instrument, shows high validity against important constructs in PsA. This is important, and validates these DAPSA endpoints for future use in clinical trials, or as targets in clinical practice.
Schoels M et al. Ann Rheum Dis. 2015 Aug 12. [Epub ahead of print]
Acknowledgement We thank Janssen/Centocor for providing data from their trials for the current analysis.
Disclosure of Interest None declared