Prologue: Evidence Informing the GRAPPA 2021 Treatment Recommendations, by Domain.

Psoriatic arthritis (PsA) is a chronic inflammatory disease that is remarkably diverse in its presentation and course. Important domains of involvement include peripheral arthritis, skin and nail psoriasis, enthesitis, dactylitis, and axial arthritis, along with associated conditions such as inflammatory bowel disease (IBD) and anterior uveitis. 1,2 .