Discussion Author: Greg J Hardin
Blastomycosis is a systemic pyogranulomatous infection derived from the inhalation of Blastomyces dermatitidis, a thermally dimorphic fungus. B. dermatitidis may involve multiple organs, but the lungs are the most common site of infection followed by the skin, bones, and genitourinary system. Up to 50% of B. dermatitidis infections are asymptomatic. Diagnosis is often delayed for more than one month, even when patients seek medical attention within seven days of illness onset.
The presenting symptoms for Blastomycosis may include: cough, fever, sputum production, chest pain, shortness of air, weight loss, night sweats, chills, and hemoptysis.
Chest radiography usually reveals alveolar infiltrates or a mass lesion; however, a miliary or reticulonodular pattern can occur. Small pleural effusions are common. The absence of obvious hilar adenopathy can help distinguish blastomycosis from histoplasmosis. Cavitation occurs less commonly in patients with blastomycosis than in patients with tuberculosis or chronic histoplasmosis. The reported incidence of cavitation is 15-20%.
Definitive diagnosis necessitates organism culture. Presumptive diagnosis may be derived by visualization of the novel yeast form from clinical specimens. Serology is unhelpful. In cases of pulmonary blastomycosis, sputum culture has a high yield (75% per single sample, 86% per patient). Specimens obtained for culture by bronchoscopy are positive 92% of the time. Care should be taken to include chloramphenicol in the medium to exclude extraneous bacterial growth.
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