Phaeohyphomycosis in a Solid Organ Transplant Recipient: Case Report of a New Pathogenic Species of Kirschsteiniothelia.

Phaeohyphomycoses are rare infections caused by melanin-pigmented, saprophytic fungi commonly found in soil and on decaying plant matter. Infections typically affect immunocompromised individuals and present a wide clinical spectrum. Here, we report the case of a 63-year-old immunocompromised patient, with a history of combined heart-lung transplantation, who consulted in 2022 due to the appearance of a subcutaneous lesion on the thigh. A complete surgical debridement was performed and histopathological examination concluded the presence of a deep fungal infection. Three years later, relapse occurred. A spindle biopsy of the lesion was performed for microbiological and histopathological analysis. Mycological examination confirmed the diagnosis of phaeohyphomycosis caused by a dematiaceous fungus unknown as human pathogen before which belonged to the Kirschsteiniothelia genus. Retrospective analysis of formalin-fixed biopsies from 2022 found the same undescribed dematiaceous fungus, confirming the chronic and progressive nature of the fungal infection for 3 years. This case highlights how an integrated histological and mycological diagnosis improves patient care and outcomes.