The National Prevalence of Clinically Diagnosed Psoriatic Arthritis in Sweden 2017.

OBJECTIVE: Psoriatic arthritis (PsA) prevalence estimates vary across studies; studies based on national data are few. We aimed to estimate the prevalence of clinically diagnosed PsA in Sweden in 2017, overall and stratified by sex/age/education/geography, and to quantify disease-modifying anti-rheumatic drug (DMARD) use among those in contact with specialized rheumatology care 2015-2017.

METHODS: Individuals, 18-79 years (y), alive, residing in Sweden on December 31, 2017, with a prior PsA diagnosis were identified from the National Patient Register (NPR) and/or the Swedish Rheumatology Quality Register (SRQ). The PsA prevalence was estimated according to a base case (BC) definition (≥1 main PsA ICD-code from rheumatology or internal medicine departments in NPR, or a PsA diagnosis in SRQ), four sensitivity analysis definitions, and for those seen in specialized rheumatology care 2015-2017. In the latter group, DMARD use during 2017 was also assessed. Data for stratifications were retrieved from national registers.

RESULTS: The crude national prevalence of PsA (18-79y) was estimated at 0.39% (BC), 0.34% after accounting for diagnostic misclassification and 0.32-0.50% across all sensitivity analyses. The prevalence was lower in males and in those with higher level of education. The prevalence for those seen in specialized rheumatology care 2015-2017 was estimated at 0.24%. In this population, 32% received biologic or targeted synthetic DMARDs, and 41% conventional synthetic DMARDs only, during 2017.

CONCLUSION: The prevalence of clinically diagnosed PsA (18-79y) in Sweden in 2017 was around 0.35%. Among PsA cases in recent contact with specialized rheumatology care, almost 3/4 received DMARD therapy in 2017.