Risk of psoriasis in patients with childhood asthma: a Danish nationwide cohort study

Background Psoriasis and asthma are disorders driven by inflammation. Psoriasis may carry an increased risk of asthma, but the reverse relationship has not been investigated. Objectives To investigate the risk of psoriasis in subjects with childhood asthma in a nationwide Danish cohort. Methods Data on all Danish individuals aged 6-14 years at study entry between 1 January 1997 and 31 December 2011 (n = 1 478 110) were linked at an individual level in nationwide registers. Incidence rates per 10 000 person-years were calculated, and incidence rate ratios (IRRs) adjusted for age, sex, concomitant medication and comorbidity were estimated by Poisson regression models. Results There were 21 725 cases of childhood asthma and 6586 incident cases of psoriasis. There were 5697 and 889 incident cases of mild and severe psoriasis, respectively. The incidence rates of overall, mild and severe psoriasis were 4.49, 3.88 and 0.61 for the reference population, and 5.95, 5.18 and 0.83 for subjects with childhood asthma, respectively. The IRRs for overall, mild and severe psoriasis were 3.94 [95% confidence interval (CI) 2.16-7.17], 5.03 (95% CI 2.48-10.21) and 2.27 (95% CI 0.61-8.42) for patients with childhood asthma. Conclusions Childhood asthma was associated with a significantly increased risk of psoriasis. Further studies are warranted to determine the clinical significance and effects of therapeutic interventions on this association.