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.