A case of blastomycosis is reported involving the mediastinum and comp
romising the plexus brachialis. The pathology, pathophysiology, and tr
eatment of this patient and of a previously reported patient are discu
ssed and compared with the characteristics of extrapulmonary thoracic
disease caused by histoplasmosis. Because of the favorable response of
these patients to prolonged antifungal therapy, blastomycosis should
be considered in the differential diagnosis of invasive extrapulmonary
thoracic disease.