Actinomycosis and nocardiosis of the lung.

Actinomyces and Nocardia species are frequently overlooked pulmonary pathogens until their presence is histologically proved. These infections often are not considered in the differential diagnosis of lung disease because of the spectrum of their presentation, the similarity of their appearance to other granulomatous or neoplastic diseases, and coexistence of these infections with other pulmonary conditions. Pulmonary actinomycosis is characterized by pulmonary consolidation, frequently with cavitation and spread to contiguous tissues without regard for normal anatomic barriers. The appearance often is confused with that of bronchogenic carcinoma or other granulomatous infections, especially tuberculosis. Pulmonary nocardiosis most frequently develops in immunocompromised patients, and the incidence of this infection is increasing. The radiographic manifestations of nocardiosis are pleomorphic, but early recognition is essential to initiate appropriate therapy.