Pulmonary Vasculitis

Pulmonary vasculitis involves inflammation and destruction of blood vessel walls in the lungs, mediated by autoantibodies (ANCA), immune complexes, or T-cell-mediated mechanisms. In the ANCA-associated vasculitides (AAVs), pathogenic PR3- or MPO-ANCA activate neutrophils and the complement C5a pathway. The resulting endothelial injury is most dangerous in the delicate pulmonary capillaries and renal glomeruli. The damaged vessels allow blood and inflammatory exudate to leak into alveoli, causing diffuse alveolar hemorrhage and impaired oxygen exchange. Granulomatous inflammation in granulomatosis with polyangiitis (GPA) can also produce pulmonary nodules or cavitary lesions. When the same small-vessel process affects the kidneys, glomerular bleeding and inflammation cause hematuria, proteinuria, and rapidly progressive loss of renal function. The three major AAV patterns are useful, but they are not absolute diagnostic labels: - GPA: PR3-ANCA is commonly associated with a c-ANCA pattern, upper-airway disease, pulmonary nodules, and cavitation. - Microscopic polyangiitis (MPA): MPO-ANCA is commonly associated with a p-ANCA pattern, pulmonary capillaritis, and a pulmonary-renal syndrome without granulomatous nodules. - Eosinophilic granulomatosis with polyangiitis (EGPA): asthma, eosinophilia, sinus disease, and systemic vasculitis point toward EGPA; ANCA is present...