Epidemiology of antiphospholipid syndrome: macro- and microvascular manifestations

Antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by thrombotic and non-thrombotic macro- and microvascular manifestations and pregnancy complications in the setting of persistent antiphospholipid antibodies (aPL), namely anticardiolipin antibodies, anti-β2 glycoprotein-I antibodies and lupus anticoagulant. Four decades after its first description, APS prevalence and incidence are still not completely understood due to the limited number of well-designed, population-based multi-ethnic studies. Furthermore, despite decades of efforts to standardise aPL immunoassays, considerable intraassay and interlaboratory variances in aPL measures still exist. Large multicentre APS cohorts have shown a 10-year survival of ∼91% and the presence of catastrophic APS occurs in about 1% of the entire population, associated with a 50% mortality rate. Clinically, any organ can be affected in the context of large, medium or small vessel (artery and/or vein) thrombosis. Macrovascular thrombosis is the hallmark of the disease and veins are more frequently affected than arteries. Deep vein thrombosis/pulmonary embolism thromboembolic disease is the most common APS manifestation, while stroke and transient ischaemic attack are the most frequent arterial thrombosis events. Myocardial infarction can also occur and contributes to increased mortality in APS. A minority of patients present with thrombosis affecting the intraabdominal organs, including the liver, spleen, small and large bowel, and the kidneys. Microvascular thrombosis, including APS nephropathy, chronic skin ulcers and livedoid vasculopathy represent a diagnostic challenge requiring histologic confirmation. In this narrative review we summarize the available evidence on APS epidemiology, focusing on the description of the prevalence of macro- and microvascular manifestations of the disease.