Unveiling Deep Mycoses: Histopathological Challenges in Diagnosing Deep Mycoses as a Neglected Tropical Disease.

Deep mycoses are rare invasive fungal infections involving subcutaneous or systemic tissues and remain underrecognized neglected tropical diseases in Indonesia. This study aims to describe clinicopathological features and highlight histopathological challenges in diagnosing cutaneous deep mycoses at a tertiary hospital in Yogyakarta. A retrospective review of skin biopsies submitted with a differential diagnosis of deep mycosis to the Anatomical Pathology Department, Dr Sardjito Hospital, between 2020 and 2024 was conducted, including cases with demonstrable fungal elements on histopathology and/or histochemistry and complete clinical data. Of 39 suspected cases, 12 were confirmed as deep mycoses, predominantly subcutaneous infections in male patients over 50 years working in agriculture. Chromoblastomycosis was most frequent (8/12), followed by eumycetoma, actinomycetoma, phaeohyphomycosis, and 1 systemic histoplasmosis in an HIV-positive adolescent. Verrucous plaques on the lower extremities predominated clinically, whereas histology showed pseudoepitheliomatous hyperplasia with muriform cells in chromoblastomycosis, pigmented hyphae with necroinflammatory changes in phaeohyphomycosis, characteristic grains with Splendore-Hoeppli phenomenon in eumycetoma, filamentous grains in actinomycetoma, and intracellular yeasts within histiocytes in histoplasmosis. In conclusion, deep mycoses are uncommon but clinically nonspecific, leading to diagnostic delay, and histopathology remains a pivotal, accessible tool for their recognition and differentiation in resource-limited tropical settings.