Fontana-Masson stain in fungal infections

Background: Fontana-Masson (FM) staining is a histopathology technique used to identify dematiaceous fungi. The result often guides initial species identification and antifungal treatment; however, there is evidence that nondematiaceous fungi might react with this stain. Few studies in the current literature address this issue. Objective: Our aim was to classify the FM staining patterns of common fungal pathogens for use by pathologists attempting to accurately identify fungi on histopathologic examination. Methods: In total, 132 cases of culture proven mycoses were identified. We stained tissue with 2 different FM protocols and recorded the intensity and distribution of results. Results: There was variability in staining, and many nondematiaceous fungi showed positivity, including Zygomycetes, Aspergillus, and Fusarium spp. Limitations: The study was limited by the number of cases. Of 132 cases identified, 112 cases had adequate tissue left after sectioning deeper into the block. Conclusion: Nondematiaceous fungi frequently stained positive with FM. The course of treatment should not be based on the result of this stain alone. Histopathology should be examined in multiple tissue sections, and therapy should be determined on the basis of clinical context and culture results.