Incidence and prevalence of psoriatic arthritis in Denmark: A nationwide register linkage study

Objectives: To examine the incidence and temporal trends of psoriatic arthritis (PsA) in the general population in Denmark. Methods: Using nationwide registry data, we estimated the number of patients with incident PsA within each 1-year period between 1997 and 2011 and calculated the rate of PsA cases within gender and age subgroups. Incidence rates were presented per 100 000 person-years. Results: There was a female predominance ranging from 50.3% (1998) to 59.2% (2010), and the mean age at time of diagnosis was 47-50 years. We identified a total of 12 719 patients with PsA (prevalence=0.22%), including 9034 patients where the PsA diagnosis was made by a rheumatologist (prevalence=0.16%). Incidence rates of PsA (per 100 000 person-years) increased from 7.3 in 1997 to a peak incidence of 27.3 in 2010. Incidence rates were highest for women and patients aged 50-59 years, respectively. The use of systemic non-biologic agents, that is, methotrexate, leflunomide, ciclosporin or sulfasalazine increased over the 15-year study course and were used in 66.3% of all patients. Biologic agents (etanercept, infliximab, adalimumab, certolizumab pegol, golimumab or ustekinumab) were used in 17.7% of patients with PsA. Conclusions: We found a clear trend of rising PsA incidence on a national level. While the cause remains unclear, our findings might be explained by increased attention by patients and physicians.