Diagnosis of blastomycosis in surgical pathology and cytopathology: correlation with microbiologic culture

Blastomycosis, a worldwide disease caused by the inhalation of Blastomyces dermatitidis spores, can be diagnosed by microbiologic culture or morphologic identification in tissue or cytologic material. A retrospective review of cases diagnosed as blastomycosis in surgical pathology and cytopathology was undertaken at a University Medical Center to assess the diagnostic value of morphologic methods and their correlation with microbiologic cultures. Surgical pathology/cytology records were reviewed for the period between January 1998 and April 2007 and 53 cases diagnosed as blastomycosis were retrieved: 38 males, 15 females; age 14 to 77 years, median 48. Twenty-nine cases (54.7%) involved lung, 14 (26.4%) soft tissue/bone, 5 (9.4%) skin, 3 (5.6%) other sites, and 2 (3.7%) involved both lung and skin. Forty-six of the 53 patients (87%) had concomitant cultures: 31 (67.4%) were positive for blastomycosis, 11 (23.9%) negative and 4 (8.7%) showed other fungal organisms. A review of microbiology laboratory results for the same period identified a total of 39 patients who were diagnosed with blastomycosis based on isolation of B. dermatitidis. These included 31 cases (79.5%) that were also diagnosed on histology/cytology specimens, 4 (10.25%) that were not submitted to surgical pathology and 4 (10.25%) cases in which pathologic examination failed to identify Blastomyces. This study shows that blastomycosis encountered in surgical/cytopathology can be reliably diagnosed by morphologic examination allowing for prompt treatment. However, microbiologic cultures still play a major role in clinical management of patients suspected of infection because 10.25% were false negative on morphology in our study.