Pulmonary Blastomycosis Masquerading as Metastatic Disease in the Lung: A Case Report

Bobbak Vahid, MD; Bernadette Wildemore, MD; Christopher Nguyen, MD; Niki Sistrun, MD; Paul E. Marik, MD

Disclosures

January 31, 2006

Discussion

Blastomycosis was first described by Gilchrist in 1896 in a patient with cutaneous blastomycosis.[2] The infectious organism, B dermatitidis, is a dimorphic fungus that exists in nature in a mycelial form and converts to yeast at body temperature.[1] The yeast phase presents a very characteristic appearance. Light microscopy shows it to be rounded with a thick, doubly refractile cell wall. Yeast cells usually measure 8-15 mcm in diameter and contain 8-12 nuclei. These yeast cells reproduce by a single, broad-based bud.[1,3] Endemic areas in North America include the Southeastern and South-Central states bordering the Mississippi and Ohio River basins, Midwestern and Canadian provinces that border the Great Lakes, and a small area in New York and Canada along the St. Lawrence River.[1]

Since the first report by Gilchrist, blastomycosis of different organ systems has been described, including pulmonary, genitourinary, cardiac, endocrine, central nervous system, skin, and skeletal.[1] Pulmonary blastomycosis can present as an asymptomatic pulmonary infection, acute pulmonary blastomycosis, chronic pulmonary blastomycosis,[1,4] miliary pulmonary blastomycosis,[5] nonresolving pneumonia,[6] acute lung injury and acute respiratory distress syndrome,[7,8] pulmonary nodule, or tracheal blastomycosis.[9] Underlying immunosuppression is reported in 16% to 25% of patients with blastomycosis.[1,10] The most common reported immunosuppressive conditions are chronic steroid ingestion, malignancy, human immunodeficiency virus infection, organ transplantation, and hematologic malignancies.[11,12,13,14] Jejunoileal bypass surgery[15] and diabetes mellitus[10] are also associated with pulmonary blastomycosis. Serology is not helpful in the diagnosis of blastomycosis,[1,16] although limited data suggest that detection of B dermatitidis antigenuria could be helpful in the diagnosis of acute pulmonary and disseminated blastomycosis.[17] Cytologic examination and culture of the sputum, bronchoscopically obtained samples, needle aspirates, and lung biopsies are the mainstays of diagnosis for pulmonary blastomycosis.[3] Itraconazole and amphotericin B are the treatments of choice.[18] Animal models and in vitro data suggest that voriconazole is a potentially novel treatment option in pulmonary blastomycosis, although human data are lacking.[19,20]

Because different benign pulmonary conditions, including blastomycosis, can be indistinguishable on chest x-ray or chest CT scan from pulmonary malignancies, evaluation of patients with a suspicious pulmonary nodule can be challenging. A PET scan that measures 18F-fluoro-2-deoxy-D-glucose (FDG) uptake based on cellular metabolic activity has been used to evaluate pulmonary nodules. An SUV of more than 2.5 can detect a malignant pulmonary nodule with a sensitivity of 95% and specificity of 80%.[21] False-positive PET scans have been described in coccidiomyocosis, histoplasmosis, tuberculosis, sarcoidosis, Wegener's disease, coal miner's lung, pulmonary hamartoma, bacterial pneumonia, amyloidosis, talc pleurodesis, round atelectasis, and pleural fibrosis secondary to asbestos or beryllium exposure, prior hemothorax, empyema, or thoracotomy.[22,23] To the best of our knowledge, this is the first described case of PET-positive pulmonary blastomycosis appearing as metastatic disease in the lung.

In conclusion, pulmonary blastomycosis presented as a PET-positive pulmonary nodule. Blastomycosis should be considered in the evaluation of pulmonary nodules, especially in endemic areas and in patients with predisposing conditions. Cytologic examination of CT-guided fine-needle aspirates is a practical option to establish the diagnosis of pulmonary blastomycosis.

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