Etiologies of intra-alveolar hemorrhage are often divided into diseases causing intra-alveolar hemorrhage associated with vasculitis, including capillaritis, and diseases causing intra-alveolar hemorrhage unassociated with vasculitis. Diseases causing intra-alveolar hemorrhage associated with vasculitis/capillaritis include Churg-Strauss syndrome, microscopic polyarteritis, Goodpasture syndrome, Wegener granulomatosis, and connective tissue diseases including rheumatoid arthritis, scleroderma, and polymyositis/dermatomyositis, among many others. Goodpasture syndrome may be diagnosed by the presence of circulating antibodies alone or with immunofluorescent staining of kidney or lung biopsies. Intra-alveolar hemorrhage may occur in patients with systemic lupus erythematosus, and it is associated with reduced serum complement levels and the presence of serum antinuclear antibodies. Wegener granulomatosis is associated with the presence of C-antineutrophil cytoplasmic antibodies and characterized by necrotizing granulomatous vasculitis that may also involve the kidneys and/or the upper respiratory tract.

Diseases causing intra-alveolar hemorrhage unassociated with capillaritis include diffuse alveolar damage, pulmonary hypertension, infections, mitral stenosis, aspiration, and idiopathic pulmonary hemosiderosis, among others. Intra-alveolar hemorrhage may be caused by a large number of drugs and toxins as well, including warfarin, sulfonamides, cocaine, estrogens, and many others. Intra-alveolar hemorrhage may occur in autologous or allogenic bone marrow transplant patients, generally in older patients with preexisting lung disease, and may be fatal. Intra-alveolar hemorrhage may also occur in patients with HIV infection, associated with opportunistic infections (Table 21-1).