Diffuse alveolar hemorrhage and Libman-Sacks endocarditis as a manifestation of possible primary antiphospholipid syndrome.

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of circulating autoantibodies against phospholipid-binding plasma proteins, leading to an increased risk of thrombosis and pregnancy loss. The most common manifestation of lung disease in APS is pulmonary embolism, which may often be the presenting symptom. We present a 30-year-old man with probable primary APS (with no history of thromboses) presenting with diffuse alveolar hemorrhage, an uncommon presentation.