Often pleura based, the infection may extend directly into the pleural space, ribs, and chest wall to produce empyemas, osteomyelitis, and draining fistulous tracts. Less frequently, thoracic actinomycosis can extend to the mediastinum and present as pericarditis. The differential diagnosis includes carcinoma, tuberculosis, bacterial infections, nocardiosis, and systemic mycosis. In the presence of pleural or chest wall involvement, the correct diagnosis of actinomycosis should not be problematic. Because A. israelii is part of the normal oral flora, culturing the organism from sputum or bronchoscopic washings is not diagnostic.
Diagnosis often requires percutaneous needle aspiration, bronchoscopic biopsy, or open lung biopsy.
The disease can spread to the omentum, the mesenteric lymph nodes, and the intra-abdominal viscera and can produce fistulous invasions of the abdominal wall or perineum. Carcinoma, tuberculosis, and Crohn's disease are prominent considerations in the differential diagnosis. Unless draining sinus tracts are present, surgery is required for diagnosis. If the bladder is involved, sulfur granules may be present in the urine. A careful pathologic search may be needed to establish the diagnosis, even when excisional biopsy is performed.