Methods Design: the ReFlaP (Remission/Flare in PsA) study is a prospective, multicentric international, longitudinal, observational study. It will take place in 2017-18 in 25 centers across Europe, North and South America and Asia. Investigators plan to include a total of 450 patients. The inclusion period will last 6 months; each center will include around 20 patients. Each patient is seen twice at baseline and at 1-6 months (follow-up visit) in the context of usual care.