Diffuse alveolar hemorrhage secondary to antiphospholipid syndrome presenting as recurrent multifocal pneumonia

Introduction: Diffuse alveolar hemorrhage (DAH) is a rare but life-threatening pulmonary manifestation of antiphospholipid syndrome (APS) that may present with nonspecific symptoms and radiographic findings mimicking infection, leading to delayed diagnosis. Early recognition is critical given its high relapse rates and associated morbidity despite immunosuppressive therapy. Case Report: A 31-year-old woman with APS and chronic pulmonary embolism presented with progressive hypoxemia and recurrent multifocal pulmonary infiltrates, initially treated as pneumonia despite repeatedly negative infectious evaluations. Surgical lung biopsy demonstrated pulmonary capillaritis with hemosiderin-laden macrophages consistent with DAH due to APS, an immune-mediated injury to pulmonary vasculature. The patient initially improved with corticosteroid therapy but experienced relapses during steroid tapering and failed Rituximab despite appropriate CD20 depletion. She subsequently required escalation to cyclophosphamide and adjunctive plasma exchange with clinical stabilization. Conclusion: Antiphospholipid syndrome-associated DAH should be considered in patients with persistent pulmonary infiltrates and unexplained hypoxemic respiratory failure despite antimicrobial therapy. Early diagnosis is essential, as treatment-refractory disease may require escalation beyond corticosteroids to additional immunosuppressive therapies.