This is a prospective, multicentre, phase IV trial assessing the value of the ultrasound scores PsASon22 and PsASon13 in differentiating between clinically active and inactive patients with psoriatic arthritis, following a treatment with Apremilast for up to 24 months. Additionally, convergent construct validity, inter/intra-reader reliability, sensitivity to change and differences in change in certain patients will be tested for the ultrasound scores.
