Incidence of Psoriasis in Patients with Inflammatory Bowel Disease: A Nationwide Population-Based Matched Cohort Study

Background: Emerging data suggest that inflammatory bowel disease (IBD) and psoriasis are associated, sharing common genetic predispositions and immunological mechanisms. However, concrete data on psoriasis risk in IBD patients compared to the general population are limited. Objective: We investigated the risk of developing psoriasis in IBD patients compared to controls without IBD. Methods: Using the Korean National Health Insurance Database, patients diagnosed with Crohn's disease (CD) or ulcerative colitis (UC) between 2005 and 2008 were age- and sex-matched 1:4 to non-IBD subjects from 2003 to 2018. IBD patients were defined by combining the International Classification of Diseases 10th revision code and at least one prescription of IBD-specific medications. Disease phenotypes, including psoriasis severity and psoriatic arthritis, were also identified. We investigated newly diagnosed psoriasis from 2009 to 2018. Incidence rates and risk of psoriasis were assessed with multivariate Cox regression models. Subgroup analyses for age and sex, and sensitivity analysis involving tumor necrosis factor (TNF) inhibitor-naive patients were performed. Results: During nearly a decade of follow-up, 20,152 IBD patients were identified (14,619 [72.54%] UC and 5,533 [27.46%] CD). Among them, 439 patients were newly diagnosed with psoriasis (incidence rate of 217.68 per 100,000 person-years and 228.62 per 100,000 person-years for UC and CD, respectively). The psoriasis risk was higher in IBD patients than in the matched controls (adjusted hazard ratio, aHR, 2.95, 95% confidence interval, CI, 2.60-3.33). Moreover, IBD patients aged <30 years were at an increased risk (aHR 3.35, 95% CI 2.58-4.35), a trend that was unchanged across all psoriasis phenotypes. Sensitivity analysis of TNF inhibitor-naive patients revealed consistent results. Conclusions: IBD patients were more likely to develop psoriasis compared to non-IBD subjects, including younger patients at an elevated risk regardless of TNF inhibitor use. This advocates the interplay between IBD and psoriasis; thus, inspection of cutaneous manifestation and dermatological consultation may be helpful in IBD patients at risk.