DISCUSSION: AAVs are a small group of vasculitides which include granulomatosis with polyangiitis, microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis, and pauci-immune vasculitis. ANCAs trigger a self-perpetuating inflammatory state when they bind to antigens in the cytoplasmic granules of neutrophils. In the lungs, this inflammation results in diffuse alveolar hemorrhage. In our patient, the constellation of p-ANCA and MPO antibodies, hemoptysis, and crescentic glomerulonephritis without granulomas is highly indicative of MPA. This unique presentation of focal hemorrhage demonstrates that although bilateral disease is classic, AAV should not be excluded in cases of unilateral involvement. Furthermore, repeat imaging over the next 48 hours demonstrated progression to bilateral disease, suggesting DAH may begin as focal disease that generalizes in time. Our patient received high dose steroids, plasma exchange, and rituximab. She was discharged home with improving renal function and without further episodes of hemoptysis.