Refractory Dermatophytosis Caused by Trichophyton indotineae: A Case Series Highlighting Antifungal Resistance and Management Challenges

Trichophyton indotineae is an emerging dermatophyte responsible for widespread, chronic, and treatment-refractory dermatophytosis worldwide; however, data from China remain limited. This study aimed to characterize the clinical manifestations, antifungal resistance, and management challenges of T. indotineae infections in Chinese patients. Three patients with disseminated dermatophytosis were evaluated clinically. Fungal isolates were identified using multilocus sequence typing and phylogenetic analysis. Antifungal susceptibility testing and sequencing of the squalene epoxidase gene were performed to assess resistance. All patients presented with extensive dermatophytosis accompanied by severe pruritus, and two had a history of residence or work in Malaysia, suggesting imported infection. Elevated serum IgE levels were observed in two cases. Molecular analyses confirmed all isolates as T. indotineae. Antifungal susceptibility testing revealed reduced susceptibility to terbinafine, with two isolates harboring the SQLE F397L mutation and one carrying the F415C mutation. Clinically, all patients showed poor response to standard antifungal regimens. High-dose itraconazole achieved partial improvement; however, relapse occurred after treatment discontinuation in all cases. These findings indicate that T. indotineae infection is characterized by chronicity, extensive involvement, and difficulty in achieving sustained remission. Antifungal resistance, particularly terbinafine resistance, together with host-related factors, may contribute to disease persistence. This study highlights the importance of accurate species identification and resistance-guided therapy, and underscores the need for optimized management strategies for this emerging dermatophyte infection.