Background/Purpose: Psoriatic arthritis (PsA) often develops between the 3^rd to 5^th decades of life. However, little is known about PsA activity and prognosis among patients who develop it at an older age. Hence, our aims were: 1) To evaluate disease activity of late onset PsA (LoPsA) patients at presentation and during follow-up, and 2) To evaluate prognosis after several years of follow-up, compared to younger onset PsA patients (YoPsA).

Methods: The study population included patients from a large longitudinal PsA cohort. The patients are followed prospectively according to a standard protocol and all data are stored in a computerized database. Only patients who started their follow up in the PsA clinic within 2 years from diagnosis were included. Patients were divided into two groups: 1) Late onset PsA    (LoPsA) – defined as disease onset after the age of 50, 2) Younger onset PsA (YoPsA) – defined as disease onset before age 50. Disease activity over time was calculated according to the adjusted mean active joint count. Patients were compared at presentation, and after 5 years of follow-up. Descriptive statistics are provided and multivariate logistic regression models were developed to compare the two groups.  

Results: Five hundred and sixty six patients were included at presentation, 177 above the age of 50 years and 389 below 50 years. The LoPsA group included more women (53% vs 41%, p=0.01). The LoPsA had significantly higher BMI (30.7 ± 7.4 vs 28.2 ± 6.1, p<0.001), more clinically damaged joints at presentation (0.9 ± 2.2 vs 0.3 ± 1.6, p=0.001) and higher modified Steinbrocker score (mSS) (4.3 ± 7.9 vs 1.8 ± 1.4, p=0.0001) (Table 1). Multivariate logistic regression analysis showed that the following variables were independently associated with being in the LoPsA group at presentation: less males (OR 0.4, p=0.001), less HLA-C*06 (OR 0.3, p=0.008), longer psoriasis duration (OR 1.04, p=0.0003), higher BMI (OR 1.1, p=0.002) and higher mSS (OR 1.1, p=0.009). After 5 years of follow-up, the LoPsA patients showed a non-significant trend for higher adjusted mean active joint count compared to the YoPsA (7.1 ± 7.3 vs 5± 5.2, p=0.07) as well as higher mean mSS compared to the YoPsA (0.7 ± 1.7 vs 0.3 ± 1.3, p=0.02). Multivariate logistic regression analysis revealed higher adjusted mean active joint count (OR 2.04, p=0.049) and higher mean mSS score (OR 2.4, p=0.009) in the LoSpA group compared to the YoPsA group. .        

Conclusion: The LoPsA patients at presentation are characterized by female predominance, higher BMI, more damage and less HLA-C*06. After 5 years of follow-up the LoPsA patients are associated with worse prognosis manifested by higher disease activity and more damage.