Chapter 2 Epidemiology of the Antiphospholipid Syndrome

Although much progress has been made in the past 20 years on understanding the clinical features of antiphospholipid syndrome (APS), investigation into its epidemiology has been difficult. The 1999 APS classification criteria made epidemiologic studies practical by providing a common definition for this disease. In this chapter, the classification criteria for the APS will be reviewed, including the 1999 International Sapporo classification criteria and the updated 2006 Sydney criteria. In addition, we will discuss the studies that have been performed to validate both the original and the revised classification criteria for APS. Arterial and venous thromboses are the complications most likely to affect morbidity and mortality in patients with APS. This chapter addresses the prevalence of these thrombotic complications in patients with antiphospholipid antibodies (aPL), as well as the risk factors that promote recurrence of thrombotic events. The prevalence of stroke, myocardial infarction (MI), deep venous thrombosis (DVT), and pregnancy morbidity in patients with aPL will be discussed, as well as non-criteria clinical manifestations of APS, such as chorea, cardiac valvular disease, and pulmonary hypertension. The frequency of aPL in other populations of patients will also be reviewed, including the elderly and those with autoimmune diseases, infections, or malignancy. The lack of adequate standardization of assays to measure aPL and the variety of study designs used to assess these patients has made such estimations of prevalence a challenging task. Nevertheless, analyses of prospective and case-control studies provide valuable information in the investigation of the epidemiology of APS, and we will discuss those along with longitudinal studies of patients with APS.