Antiphospholipid syndrome (APS) is a rare immune-mediated acquired thrombophilia mainly affecting young adults. It is characterized by a heterogeneous clinical picture due to arterial and/or venous thrombosis and pregnancy morbidity, giving rise to potentially devastating and life-threatening manifestations [[1], [2], [3]]. Despite the standard of care based on long-term anticoagulant therapy, approximately 44.2% and 20–30% of patients, respectively, experience recurrent thrombosis or loss of pregnancy [4,5]. This recurring course of the disease leads to potential damage accrual, negatively impacting quality of life [5,6]. Even though the acute manifestations of the disease are well known, this is not the case for the long-term outcome and damage accrual. Limited data derive from mixed cohorts of secondary APS (SAPS) and primary APS (PAPS). In the early 2000, in a small cohort of APS patients followed for up ten years, 38.9% developed organ damage. One-fifth of those had functional problems, being unable to carry out daily activities [7]. Almost one decade later, damage accrual was described in approximately 29% of APS patients in two small cohorts of APS populations [5,8]. Neurologic damage determined the highest morbidity with an estimated rate of 18.71 events/1000 person-years (5). Damage accrual, evaluated by Systemic Lupus Erythematosus (SLE) International College of Rheumatology/American College of Rheumatology damage index (SDI) score as a surrogate marker of damage determined a 1.3-fold increased mortality rate for a 1-unit increase [5,9].

In the last decade, efforts have been made to quantify the damage in APS. In 2015, a group of experts from Mexico developed for the first time the disease Damage Index in APS (DIAPS) [10]. DIAPS showed a high correlation with SDI in a cross-sectional study of 50 patients with PAPS, 50 SLE patients, and 50 with SAPS [11]. However, the damage pattern differed between groups; PAPS patients presented a higher score early in the disease course. Recently, Gaspar et al. [12] showed that thrombotic APS patients already presented organ damage six months after disease onset, and a one-point increase in DIAPS in the first five years was associated with about a 5-fold mortality risk. Few studies [5,8,[12], [13], [14]] have addressed the risk factor associated with damage accrual in APS patients with contradictory results. Moreover, the major populations in these studies also consist of SAPS patients for the most SLE patients.

In this study, we aimed to identify risk factors predicting damage accrual in PAPS patients. We also assessed the damage accrual rate and its association with laboratory and clinical APS subsets.