Prevalence and characteristics of psoriasis in Denmark: findings from the Danish skin cohort

Background Wide-ranging psoriasis prevalence estimates have been reported, possibly due to methodological differences. Objectives To assess the prevalence of psoriasis in Denmark and to validate the use of questionnaire-based data to identify patients with psoriasis. Methods We used data from the Danish Skin Cohort, a prospective cohort comprising general population adults, as well as patients with dermatologist-verified psoriasis and atopic dermatitis, respectively. The general population cohort was interviewed to assess the psoriasis prevalence in Denmark, and validation of the questions was performed. Results From 3490 general population participants, 7.9% (n=275) were found to have self-reported psoriasis. Of these, 221 (prevalence 6.3%) had their disease diagnosed by a physician (the dermatologist-diagnosed prevalence was 4.3%), whereas 54 (prevalence 1.6%) were not diagnosed by a physician. A total of 176 (5%) had active psoriasis within the last 12 months. More than half of patients had at least one disease flare in the last 12 months, and 44.4% of patients with psoriasis had at least one family member with psoriasis, whereas this was only the case for 13.7% of non-psoriasis individuals. Validation of the psoriasis diagnosis yielded a high sensitivity and specificity, with little incremental value of limiting diagnoses to those diagnosed by a physician. Conclusion The lifetime-prevalence of self-reported psoriasis was found to be 7.9%, whereas the 1-year prevalence (ie, currently active psoriasis) was 5.0%. If used appropriately, questionnaire-based data may accurately identify patients with psoriasis.