ABSTRACT
The clinical criteria for distinguishing primary antiphospholipid syndrome (APS) from secondary APS are controversial. The clinical manifestations of primary and secondary APS are diverse and may involve virtually every organ-system in the body. Vaso-occlusive disease (VOD) is the pathologic basis of all known complications of primary and secondary APS. Large-vessel VOD in APS may be arterial or venous, or both, and it may occur virtually anywhere in the body. Small vessel VOD in APS is microvascular thrombosis. In the lungs, small-vessel VOD may present as the diffuse alveolar hemorrhage syndrome with pulmonary capillaritis and recurrent microvascular thrombosis. Vasculitis may be associated with APS in two possible situations. The first is vasculitis of an independent underlying disease, such as systemic lupus erythematosus, coincidental with the APS and the second is microvascular injury, known as "capillaritis". Microvascular thrombosis is an important cause of cutaneous necrosis and peripheral gangrene associated with APS.
