Background Four new disease specific composite disease activity measures have been developed for psoriatic arthritis (PsA). Further validation of these measures in interventional trial data is now required.
Objectives The objective of this study was to compare the performance of the Psoriatic Arthritis Disease Activity Score (PASDAS), the Arithmetic Mean of the Desirability Function (AMDF), the Composite Psoriatic Disease Activity Index (CPDAI), and the Disease Activity Index for Psoriatic arthritis (DAPSA) using data from a large (n=324) interventional trial (GO-REVEAL). Thisrandomised, double-blind, study evaluated the safety and efficacy of 2 doses of the TNF inhibitor golimumab in subjects with active PsA. As a comparator the Disease Activity Score for rheumatoid arthritis was used.
Methods Data on various outcomes was excerpted from the GO-REVEAL data set; however, imputation was used to calculate some components (e.g. the PsA quality of life measure: PsAQoL: Domains not addressed in GO- REVEAL (e.g. axial disease) were excluded. The performance of the scores at baseline and follow-up (weeks 14 and 24) was compared and also between the 2 treatment schedules (golimumab 50mg and 100mg 4 weekly). Spearman correlations and stepwise regression analyses were also used.
Results All indices could distinguish response to treatment at 14 and 24 weeks. Effect sizes at 24 weeks for the 50mg (100mg) doses were 2.17 (2.36), 2.08 (2.36), 1.09 (1.41), 1.80 (1.78), and 1.13 (1.18) for PASDAS, AMDF, CPDAI, DAS28 and DAPSA respectively. Comparison of 24 week values across treatment groups by an analysis of covariance using the baseline values as covariates gave the following F statistics for the PASDAS (F = 18.3), AMDF (F = 19.6), CPDAI (F = 9.4), DAS28 (F = 13.6) and DAPSA (F = 7.9). For PASDAS score change was largely predicted by patient and physician global VAS scores, although significant contributions were also made by the physical component summary scale of the SF36, dactylitis and enthesitis scores, the tender joint count and the PASI. Both AMDF and CPDAI reflected a similar range of predictors but DAS28 and DAPSA were largely predicted by articular measures and CRP.
Conclusions All measures are effective in determining treatment response in patients treated with a highly active treatment (the TNF inhibitor golimumab) for active psoriasis and psoriatic arthritis. Joint responses were equally reflected by all composite scores but PASDAS, AMDF and CPDAI better reflect other domains such as skin, enthesitis and dactylitis. PASDAS and AMDF were better able to distinguish between the three treatment groups and had much bigger effect sizes at 24 weeks, an important consideration in trial design and statistical power calculations, particularly when considering other therapeutic approaches.
Acknowledgements We are grateful to Janssen Pharmaceuticals for data from the GO-REVEAL study
Disclosure of Interest P. Helliwell Consultant for: Janssen Pharmaceuticals, A. Kavanaugh Consultant for: Janssen Pharmaceuticals