Abstract
Objective Prior incidence estimates of psoriatic arthritis (PsA) vary considerably. We aimed to assess the annual incidence of clinically diagnosed PsA among adults in Sweden 2014-2016, overall and stratified by age/sex/education/geography, and to investigate potential time-trends in incidence 2006-2018. Disease-modifying anti-rheumatic drug (DMARD) use during 2 years (y) from diagnosis was also examined.
Methods Patients (≥18y) with incident clinically diagnosed PsA in Sweden were identified from the National Patient Register (NPR) and/or the Swedish Rheumatology Quality register (SRQ). Population statistics, stratification parameters and DMARD information were retrieved from other nationwide registers. Incidence was estimated according to a base case (BC) definition (i.e., ≥1 main ICD-10 diagnosis of PsA [L40.5/M07.0-M07.3] from rheumatology/internal medicine in NPR, or a PsA diagnosis in SRQ during the relevant year, and no prior such diagnoses) and four different sensitivity analysis case definitions.
Results The mean annual incidence of clinically diagnosed PsA among adults in Sweden 2014-2016 was estimated at 21.77/100 000 person-years at risk (PY), according to the BC definition; 17.41/100 000 PY after accounting for diagnostic misclassification; and 15.78-28.83/100 000 PY across all sensitivity analyses. Incidence was slightly higher in females, lower in individuals with higher education (>12y) and peaked in the age-span 50-59y. No apparent increasing/decreasing time-trend was observed 2006-2018. Within 2y from diagnosis, 71.03% of patients had received DMARD-therapy (22.37% biologic/targeted synthetic DMARDs).
Conclusion During 2014-2016, the annual incidence of clinically diagnosed PsA in the adult Swedish population was around 20/100 000 PY. Two years after diagnosis, almost 3/4 had received DMARD-therapy.
