Letting go of the dichotomy between psoriasis and psoriatic arthritis

Psoriasis and PsA have predominantly shared genetic background
and overlapping immunologic signature, confirming their denomination as falling
within a spectrum of one single disease. Local tissue factors induce a primary
inflammatory response, followed by a persistent inflammatory environment that
hosts innate and adaptive immune cells with overlapping functional effects. The
local inflammatory process of the tissue is capable of determining the phenotype:
where psoriasis and/or arthritis can occur in an independent fashion both from
clinical and pathophysiological point of view. In the circulating compartment we
detected only subtle changes between patients with psoriasis compared to PsA,
indicating that if cross-tissue contamination occurs, this is a chronic and subtle
process not readily detectible by cross-sectional screening. The result from the clinical work presented in this thesis indicate that screening questionnaires for PsA should be implemented in care for psoriasis patients attending dermatology clinics. Our results indicate major phenotypic manifestation should drive the choice of therapy, with methotrexate as preferred option over sulfasalazine for treating arthritis. Main phenotypic manifestations should drive study participant selection for both clinical and basic research questions, without the need to dichotomize PsA versus psoriasis. Future work should examine if the inflammatory response at the primary tissue site is capable of priming distant tissue sites for a secondary inflammatory response, in order to better understand and better treat PsA.