Defining Low Disease Activity States in Psoriatic Arthritis using Novel Composite Disease Instruments

OBJECTIVE: To explore the relationship between minimal disease activity (MDA) and the low disease activity cutoffs of the Psoriatic ArthritiS Disease Activity Score (PASDAS) and the Composite Psoriatic Disease Activity Index (CPDAI). METHODS: Data from the GRAPPA (Group for Research and Assessment of Psoriasis and Psoriatic Arthritis) composite exercise (GRACE) study were used for these analyses. Alternative definitions of low disease activity were used with 6/7 and 7/7 of MDA items, and a criteria set mandating the 2 articular items and 3/5 alternate items (MDA-joints). Two reference questions were used as anchors: physician's global opinion of MDA, and patient's opinion on their disease control. RESULTS: Substantial agreement was found between MDA, MDA-joints, PASDAS, and CPDAI. Compared to the 2 reference questions, the various definitions of low disease activity gave sensitivities that were generally worse than specificities, the latter being high (> 0.9) in most cases. Both PASDAS and CPDAI demonstrated good discrimination between the "low" and "high" disease activity states by all the MDA definitions. Using these data, with an MDA of 7/7 to define a very low disease cutoff, the corresponding values for PASDAS and CPDAI were 1.9 and 2, respectively. CONCLUSION: An MDA score of 7/7 is proposed as very low disease activity in psoriatic arthritis. Using this definition, the equivalent cutoffs for PASDAS and CPDAI are 1.9 and 2, respectively.