Background/Purpose: There is limited information on the epidemiology of psoriasis and psoriatic arthritis (PsA) in North America. The aims of this study were to estimate the prevalence and incidence rates of psoriasis and PsA and their temporal trends in Ontario, Canada.

Methods: A retrospective cohort analysis was performed in Ontario health administrative databases. The following validated algorithms were used for case definition: 1) Psoriasis: diagnosis in hospitalization records or at least 2 psoriasis diagnostic codes assigned by any physician (specificity 99%, sensitivity 52%, PPV 62%); 2) PsA: diagnosis in hospitalization records or a combination of: [1 psoriasis code by any physician or 1 prescription of topical anti-psoriatic treatment] and 2 diagnostic codes of spondyloarthritis at least 1 by a rheumatologist (specificity 100%, sensitivity 52%, PPV 66%). The crude and age and sex-standardized prevalence and incidence rates of psoriasis were calculated from 2000 to 2015 in the general population. For PsA, results are reported from 2008 onwards due to a change in billing code in 2006.

Results: Among the 10,757,627 individuals aged 20 years and older living in Ontario in 2015, we identified 263,586 and 16,144 patients with psoriasis, and PsA, respectively, resulting in overall crude psoriasis and PsA cumulative prevalence of 2.25% and 0.14%, respectively. For psoriasis, the age and sex-standardized prevalence increased from 1.43% in 2000 to 2.24% in 2015 (Figure 1). For PsA, the age and sex-standardized prevalence increased from 0.07% in 2008 to 0.13% in 2015 (Figure 2). In contrast, the incidence rates of both diseases remained relatively stable.

Conclusion: These findings enhance our understanding of the Canadian epidemiology of psoriatic disease and burden for healthcare resources planning. Although our previous validation work showed that administrative data under captures psoriatic disease the prevalence and incidence rates of psoriasis and PsA in Ontario were comparable to European populations. The steady increase in the prevalence of psoriasis and PsA over the past decade may be attributable to population growth, an aging demographic, and increase in patients seeking medical care.