Atopic Dermatitis Severity and Risk for Psoriasis: A Nationwide Population-Based Study

<b><i>Introduction:</i></b> As research on the role of the Th17/IL-23 pathway gains importance, the relationship between atopic dermatitis (AD) and psoriasis is becoming elucidated. <b><i>Objective:</i></b> The objective of this study wasto evaluate whether AD and its severity affect the risk for psoriasis. <b><i>Methods:</i></b> This retrospective population-based study used the database from the 2009 National Health Insurance Services-Health Screening Cohort in Korea. A total of 3,957,922 adult subjects were included and observed until 2018. The primary outcome was newly diagnosed psoriasis. <b><i>Results:</i></b> After adjusting for possible confounding factors, the moderate-to-severe AD group had the highest hazard ratio (HR) for psoriasis (HR = 2.50; 95% confidence interval (CI), 2.40–2.61), followed by the mild AD group (HR = 2.31; 95% CI: 2.19–2.44) compared with the non-AD group during a median 8.11 ± 1.19 years of follow-up. <b><i>Limitations:</i></b> It is difficult to define AD, which is not standardized, using a claims database and exclude patients who were misdiagnosed with AD. <b><i>Conclusion:</i></b> Patients with severe AD showed an increased risk for psoriasis compared to controls, and the risk for psoriasis was increased according to AD severity. This suggests that psoriasis and AD could share inflammatory, immune, and genetic features.