Deep Fungal Infections of Skin and Role of Histopathology in Diagnosis

Introduction: Deep mycoses acquired by penetrating trauma to the skin can have varied and sometimes atypical morphological presentations resulting in diagnostic dilemmas and delay in treatment onset. Histopathology can be a useful tool in not only diagnosing but also differentiating various deep mycoses.

Aims and objectives: To observe various morphological presentations and histopathological features of deep fungal infections.

Materials and methods: A retrospective multi-centric study was conducted from 2010 to 2020 at 16 centres. The cases with diagnoses of various deep mycoses were included in the study. The patients presenting with cutaneous manifestations were included in the study. Their demographic details, history, presenting signs and symptoms, morphological presentations, histopathological features and treatment details were collected from the case sheets.

Results: A total of 124 cases were found from the case records. The most common type was chromoblastomycosis (42) followed by mycetoma (28) and rhinosporidiosis (17). The mean age was 43.76 ± 5.44 years. The average duration of symptoms before presentation was between 2 months to 10 years (average 2.5 ± 1.33 years). Male to female ratio was 1:0.7. Prior history of trauma was recorded in 36% of cases. Chromoblastomycosis cases presented with verrucous to atrophic plaques with black dots on the surface and histopathology findings included pesudoepitheliomatous hyperplasia, epithelioid cell granulomas, copper penny bodies within granulomas and abscesses. Rhinosporidiosis cases had polypoid grape-like lesions in the nose and eyes most commonly with histopathology findings of abundant thick-walled sporangia in dermis packed with thousands of spores. Eumycetoma patients had pigmented, indurated swelling with multiple sinuses discharging black granules and histopathology showed dermal abscesses and foreign body granulomatous reaction with PAS-positive hyphae. Histoplasmosis patients presented with few to multiple nodulo-pustular lesions on skin and palatal ulcers while small basophilic bodies packed in the cytoplasm of histiocytes were noted in histopathology. Phaeohyphomycosis cases presented as deep-seated cystic lesions and biopsy revealed deepithelialized cysts in the dermis or hypodermis with lumen showing necro inflammatory debris and fungal hyphae. Sporotrichosis cases had erythematous, tender nodules and papules either as single lesions or as multiple lesions arranged in a linear fashion and histopathology showed pseudoepitheliomatous hyperplasia of epidermis, loose to well-defined epithelioid cell granulomas and microabscesses. Spores were found in two cases. Cryptococcosis patient had multiple umbilicated lesions resembling giant molluscum contagiosum loose epithelioid cell granulomas and medium-sized spores lying in both intra and extracellularly on histopathology. Penicilliosis patients had nodulo-pustular lesions and histopathology showed an admixture of histiocytes, epithelioid cells, plasma cells, lymphocytes and polymorphs in the dermis with the presence of yeast-like spores in the cytoplasm of histiocytes and epithelioid cells. Entomophthoromycosis cases presented with asymptomatic subcutaneous firm swelling with loss of skin pinchability.

Conclusion: Though clinical findings of deep fungal infections are characteristic similar morphology and atypical presentations can be sometimes confusing. Histopathology is useful for confirming the diagnosis.