Pulmonary Vasculitis

Pulmonary vasculitis is inflammation and destruction of pulmonary blood vessels. The most consequential form for bedside recognition is ANCA-associated vasculitis (AAV), a pauci-immune necrotizing small-vessel vasculitis. Antibodies directed against proteinase 3 (PR3) or myeloperoxidase (MPO) activate primed neutrophils. The neutrophils degranulate, form extracellular traps, and damage the endothelium. In the lung, this injury is called alveolar capillaritis. The capillary wall becomes a damaged filter: red cells escape into the alveoli, while inflammation interferes with gas exchange. The result may be diffuse alveolar haemorrhage (DAH), with rapidly worsening hypoxaemia and a falling haemoglobin concentration. The kidney is affected by the same small-vessel process, producing pauci-immune crescentic glomerulonephritis. Lung haemorrhage plus glomerulonephritis is a pulmonary-renal syndrome and should be treated as an organ-threatening emergency until proved otherwise. The three major AAV phenotypes are not interchangeable: - Granulomatosis with polyangiitis (GPA): granulomatous inflammation of the upper and lower respiratory tract with necrotizing vasculitis. PR3-ANCA is the more characteristic antibody. Chronic sinus disease, otitis or hearing loss, nasal cartilage damage, pulmonary nodules, masses, and cavitation support the pattern. - Microscopic polyangiitis (MPA): non-granulomatous vasculitis,...