Difficult-to-treat psoriatic arthritis (D2T PsA): a scoping literature review informing a GRAPPA research project.

The definitions and criteria for D2T PsA and for 'active disease' are notably heterogeneous, with considerable variation across sources. The ongoing Group for Research and Assessment of Psoriasis and Psoriatic Arthritis initiative stands to bridge these definitional gaps and aims to provide guidance for clinicians and illuminate a path for pharmaceuticals and regulatory agencies to follow.