Abstract
IMPORTANCE: Psoriasis is a heterogeneous disease. Improved understanding of prognosis and long-term outcomes in new-onset psoriasis may improve care. OBJECTIVE: To describe the clinical course of psoriasis and identify possible indicators of long-term outcomes. DESIGN, SETTING, AND PARTICIPANTS: The Stockholm Psoriasis Cohort was a noninterventional inception cohort study enrolling patients between 2001 and 2005. The present study was conducted from January 15, 2019, to February 5, 2021. At enrollment and 10 years, patients were examined by dermatologists and rheumatologists. Data from examinations were complemented by questionnaires, medical records, and registers. A total of 721 patients with recent-onset psoriasis (<12 months duration), 15 years or older were recruited using advertising and referrals from a broad range of health care settings. MAIN OUTCOMES AND MEASURES: Disease severity and psoriatic arthritis (PsA). Recursive partitioning and regression models were implemented to identify probable indicators of long-term outcomes. RESULTS: A total of 721 patients (median [interquartile range] age, 39 [27-55] years; 405 [56%] women), including 542 (75%) with plaque-onset and 174 (24%) with guttate-onset psoriasis, were enrolled. The median follow-up was 9.6 years (interquartile range, 8.8-10.4 years). The cumulative incidence of severe psoriasis at 12 years from enrollment was 21%. Among 509 patients examined clinically after 10 years, 77 of 389 patients (20%) with plaque onset and 56 of 116 (48%) with guttate onset had minimal disease activity without treatment, and 120 of 509 (24%) had PsA. Recursive partitioning identified strata with distinct risks for severe skin disease and PsA: the cumulative incidence of severe disease in patients with plaque phenotype, above-median disease activity, and scalp lesions was 52% (95% CI, 41%-64%), compared with 11% (95% CI, 8%-14%) in patients with below-median disease activity at inclusion; and 48 of 82 patients (59%) with peripheral enthesitis had PsA after 10 years compared with 37 of 304 patients (12%) without initial joint pain (P < .001). Smoking (hazard ratio, 1.70; 95% CI, 1.10-2.63) and activating genes in the interleukin-23 (IL-23) pathway (odds ratio, 1.55; 95% CI, 1.14-2.11) were also significantly associated with a severe disease course. Systemic therapy at or before enrollment was associated with a lower risk for severe disease at 10 years compared with later initiation of systemic therapy (odds ratio, 0.24; 95% CI, 0.06-0.90). CONCLUSIONS AND RELEVANCE: The findings of this cohort study suggest that combinations of clinical characteristics at onset and activating genes in the IL-23 pathway are significantly associated with the clinical course of psoriasis, whereas joint pain and peripheral enthesitis may indicate the probability of PsA. Patients within those categories merit specialist referral and closer follow-up. The possibility of modifying the disease course with early systemic intervention should be tested.