Infection appears to be acquired by inhalation of fungus from soil, decomposed vegetation, or rotting wood. The skin appears to be the portal of entry in some cases, with infections commonly following cutaneous injuries. In the skin, cutaneous abscesses develop beneath the epidermis and are surrounded by a granulomatous reaction. Clinically, it may resemble a skin neoplasms. Similar lesions may be encountered in the lungs.
Infection subsequently can spread to bones, viscera, and lymph nodes.
The bones may be affected in as many as 50 per cent of patients with disseminated disease. Skeletal changes can occur from hematogenous seeding or by direct extension from overlying cutaneous lesions. One or several osseous sites can be affected, especially the vertebrae, the ribs, the tibia, and the carpus and tarsus. The radiologic features of blastomycotic osteomyelitis are not specific. In the carpal and tarsal areas, cystic foci or diffuse, moth-eaten bony destruction can be seen, associated with osteoporosis and periostitis.