Blastomycosis of Bone

OBJECTIVES: Blastomycosis osteomyelitis is a well-known but infrequently encountered complication of infection with the dimorphic mold, Blastomyces dermatitidis. Oftentimes, the diagnosis is unsuspected, resulting in a delay in making the diagnosis. The role of intraoperative consultation in making a rapid diagnosis has not been discussed previously. METHODS: Retrospective chart review of clinicopathologic information was conducted from all cases of blastomycosis osteomyelitis and arthritis diagnosed at Rush University Medical Center between 2000 and 2010. RESULTS: Fourteen cases of blastomycosis osteomyelitis and/or arthritis were identified, 12 of which clinically and radiologically presented as a bone tumor. The disease most commonly affected the lower extremities, particularly around the knee joint. Septic arthritis generally occurred secondary to osteomyelitis of the adjacent bone. Frozen section was performed in 10 cases, all of which were correctly diagnosed as granulomatous osteomyelitis. Two cases were culture negative, one of which showed many budding yeast forms typical of B dermatitidis on histology. CONCLUSION: Blastomycosis osteomyelitis should be considered in the differential diagnosis of bone tumor, particularly when there is history of residence or travel in endemic areas. This disease can be correctly identified at frozen section, thus offering rapid diagnosis. There is an excellent correlation between morphologic and microbiologic studies.