The First Case of Phaeohyphomycosis Caused by Exophiala xenobiotica in an Immunocompetent Patient in Korea

Abstract

Phaeohyphomycosis is a rare fungal infection caused by dematiaceous fungi commonly associated with immunocompromised patients. Exophiala (E.) species are linked to phaeohyphomycosis, and in Korea, E. dermatitidis, E. jeanselmei, and E. salmonis were previously isolated from affected patients. Here, we describe a unique instance of phaeohyphomycosis in an immunocompetent patient attributed to E. xenobiotica. A 75-year-old female presented with an asymptomatic erythematous crusted subcutaneous nodule on the dorsum of her left-hand. Her past medical history was negative for immunosuppression or trauma to the affected area. Histopathological examination revealed suppurative granulomatous infiltration, with septate hyphae and spores detected by periodic acid-Schiff staining in the dermis. A fungal culture made from a tissue sample revealed E. xenobiotica, with subsequent confirmation through phylogenetic analyses of the internal transcribed spacer (ITS) and large subunit regions (LSU) of ribosomal ribonucleic acid (rRNA). The patient was diagnosed with phaeohyphomycosis and underwent a 3-week course of terbinafine, followed by 7 weeks of fluconazole. These treatments significantly improved the lesion. To our knowledge, this is the first reported case of phaeohyphomycosis caused by E. xenobiotica in Korea.