Diagnostic challenges of a spectrum of cases of Phaeohyphomycosis - A histopathological approach of rare dematiaceous (Melanized / pigmented) fungi

Background: Dematiaceous fungi are a group of melanized fungi which imparts light to dark golden brown colour to the cell wall of these fungi on histopathological tissue sections (HPE). Due to lack of clinical suspicion and varied clinico-pathological presentation they are easily mistaken for any chronic swelling. The three common melanized fungi are phaeohyphomycosis, mycetoma, and chromoblastomycosis. Aim: Our study aims at deriving an algorithm for diagnosing these fungi on HPE. Materials and Methods: This is a retrospective study conducted on paraffin blocks of histopathology proven phaeohyphomycosis and mycetoma retrieved from the surgical pathology case files. Special stains for fungus were done for confirmation. Results: Out of 34 cases 29 were phaeohyphomycosis and 5 were mycetoma which included both immunocompromised and immunocompetent patients. Interestingly it was observed that most of the cases presented with a trivial penetrating injury or a minor trauma. These melanized fungi were further distinguished on their clinical presentation and morphological features. Conclusion: Because of their chronicity and localized lesion, most of the cases undergo surgical excision which itself is curative. Clinically and radiologically undiagnosed cases are primarily diagnosed on HPE after surgical excision in many cases. Hence a diagnosis of these melanized fungi on HPE needs an approach which would be beneficial to all practicing pathologists if they come across such rare cases. Keywords: Chromoblastomycosis, Melanized fungi, Mycetoma, Phaeohyphomycosis