Pulmonary Capillaritis
Fabio R. Tavora, M.D., Ph.D.
Allen P. Burke, M.D.
Background
Pulmonary vasculitis denotes inflammation of the capillaries of the alveolar septa (small-vessel vasculitis), a condition that often causes diffuse alveolar hemorrhage (DAH).1,2 Vasculitis involving muscular arteries may occur with granulomatosis with polyangiitis and secondarily with infections, and vasculitis of elastic pulmonary arteries may occur in Takayasu disease and Behçet disease (Chapter 51).3
Pulmonary capillaritis is only one cause of DAH (see Chapter 29). While DAH is usually a clinical and radiologic diagnosis, largely based on the finding of blood in the bronchoalveolar lavage, pulmonary capillaritis is by definition diagnosed histologically. In most cases, it is associated with systemic, especially renal disease.4,5
The most common entities associated with pulmonary capillaritis are granulomatosis with polyangiitis (Wegener disease) and microscopic polyangiitis (MPA), both discussed in Chapter 48, and anti-glomerular basement membrane (GBM) disease (Chapter 50). Other collagen vascular diseases, especially systemic lupus erythematosus, may manifest as capillaritis. A list of causes of pulmonary capillaritis is presented in Table 47.1.
Pathogenesis
The deposition of immune complexes along the capillary vasculature plays an important role in the pathogenesis of pulmonary capillaritis. Furthermore, a genetic basis is suspected for cases of autoimmune disease-associated DAH, especially in cases of MPA.6,7 Serum antinuclear cytoplasmic autoantibodies (ANCA) directly activate neutrophils, causing injury to the capillary endothelium, chemotaxis, and release of myeloperoxidase (MPO) that damages the endothelium resulting in hemorrhage. Increased vascular permeability also contributes to acute hemorrhage.
TABLE 47.1 Conditions Associated with Pulmonary Capillaritis | ||||||||||||||||||
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Clinical Findings
Although most cases of biopsy-proven capillaritis occur in patients with DAH, many patients with DAH have other causes (see Chapter 29).8 Hypoxemic respiratory failure accompanied by a decline of hemoglobin without hemolysis is suggestive of DAH. The diagnosis is confirmed by bronchoalveolar lavage retrieving bright red fluid, or increasing blood in the fluid, with negative cultures and the appearance of hemosiderin macrophages.
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