Subcutaneous hyalohyphomycosis in a domestic cat caused by Flavodon flavus, an under-recognized fungal pathogen.

Abstract

This report describes the first documented case of subcutaneous hyalohyphomycosis caused by Flavodon flavus in a domestic cat. A 3-year-old spayed indoor cat presented with progressive cutaneous nodules on all four limbs. Histopathology revealed a pyogranulomatous inflammatory response with fungal elements, and fungal culture followed by molecular identification confirmed F. flavus as the etiologic agent. The cat tested negative for FIV and FeLV. Initial treatment with oral itraconazole (5 mg/kg/day) resulted in partial improvement. Due to stagnation in clinical response by day 90, oral potassium iodide (5 mg/kg/day) was added. Combined therapy led to complete resolution of lesions by day 135, and treatment was extended for an additional 60 days. No recurrence has been observed to date. This case highlights the emerging role of F. flavus-an environmental basidiomycete previously unrecognized as a feline pathogen-as a potential cause of subcutaneous mycoses in cats. Long-term antifungal treatment and close monitoring are recommended due to the risk of relapse.