The prevalence and incidence of thrombotic primary antiphospholipid syndrome in adults aged 18-49 years: A population-based study in a mountain community in northern Italy

Objective: To estimate prevalence and incidence of thrombotic Primary Antiphospholipid Syndrome (PAPS) in the general population aged 18-49 years. Methods: The study was carried out in Valtrompia, a valley in northern Italy, in 2011-2015. The identification of PAPS cases leveraged three integrated sources: 1) Rheumatology Unit at the University Hospital; 2) General Practitioners; 3) hospital discharge codes of patients admitted for thrombotic events. Results: Prevalence and incidence were estimated as 22.9 (95% C.I. 11.4-41.0) and 5.0 (2.6-8.7) cases per 100,000 individuals, respectively. The estimates were 28.3 and 4.8, and 17.2 and 5.1 in males and females, respectively. The type of disease onset was mainly of arterial type in men and venous in women. Conclusions: Thrombotic PAPS was found to be a rare disease in this population-based study. Prevalence and incidence were not significantly different between males and females aged 18-49 years, but a different type of onset was observed.