Psoriatic arthritis phenotype may vary depending on whether the skin or joint domain appears first or whether both...

We aimed to analyse psoriatic arthritis (PsA) features based on psoriasis-arthritis lag times: simultaneous (S), psoriasis first (PF), arthritis first (AF).

We carried out an inception cohort study involving 340 PsA patients. Phenotypic differences between patients were analysed based on the three disease latency models identified in the study. A post-hoc correction of significant p-values was applied by the Benjamini-Hochberg method.

Forty-five (13.2%) patients had S onset, 97 (28.5%) manifested AF, while in 198 (58.2%) psoriasis appeared first. Lag times were markedly different between PF (16.3 ±12.4 years) and AF (5.4 ±2.8 years) groups, p<0.001. The AF group presented less frequently the classic arthritogenic psoriasis pattern: nail (18.8%, p<0.001), scalp (28.1%, p=0.001), folds (10.9%, p=0.009), and ≥3 psoriasis body areas (18.8%, p<0.001), but showed more psoriasis family history (67.6%, p=0.001) and a milder overall joint phenotype. The S group associated a worse cardiometabolic profile and developed more dactylitis (44%, p=0.012) during follow-up. The PF group was younger at psoriasis onset (p<0.001), had more extensive psoriasis (p<0.001), and higher frequency of HLA-Cw6 positivity (43.2%). Within the PF group, patients with axial onset [median 19.0 years (IQR: 10.5-25.5)] had a longer psoriasis-arthritis latency compared to other onset forms [median 14.0 years (IQR: 5-24)].

In this study, substantial phenotypic differences were identified based on the three PsA lag time models. In addition, the classic pattern of arthritogenic psoriasis did not prevail in the same way between these groups, which was novel.