Lung vasculitis and alveolar hemorrhage: pathology

Pulmonary vasculitides are a diverse group of limited and systemic disorders associated with inflammation of pulmonary vessels and parenchyma. These diseases often have distinctive clinical, serological, and histopathological features-extrapulmonary sites of involvement, circulating autoantibodies, predispositions for small or large vessels, and others. Some have characteristic inflammatory lesions; others are characterized by the absence of such lesions. Frequently pathological findings overlap, rendering classification, and diagnosis a challenge. The anti-neutrophil cytoplasmic antibody (ANCA)-associated small-vessel diseases constitute the major pulmonary vasculitides. These include Wegener granulomatosis (WG), Churg Strauss syndrome (CSS), and microscopic polyangiitis (MPA). Less frequently, diseases such as polyarteritis nodosa, Takayasu arteritis, Behçet syndrome, and connective tissue diseases may involve pulmonary vessels, but these entities are better associated with extrapulmonary disease. Diffuse alveolar hemorrhage (DAH) is a severe manifestation of pulmonary vasculitis. DAH is most commonly seen in small-vessel vasculitides, specifically MPA and WG. Other syndromes associated with DAH include Goodpasture syndrome, Henoch-Schönlein purpura, and systemic lupus erythematosus. Less commonly, DAH may be secondary to infection or drugs/toxins. Furthermore, in the absence of discernable systemic disease, DAH may be idiopathic-referred to as isolated pulmonary capillaritis (IPC) or idiopathic pulmonary hemosiderosis (IPH), depending on the presence of capillaritis.