Background: Dermatophytosis is a common zoonotic fungal infection in cats, particularly in Persian breeds, which may present diagnostic and therapeutic challenges. Here, we report a ۷-year-old
Persian cat with severe alopecia, extensive scaling, and necrosis of the ear pinnae. The cat was initially misdiagnosed with allergic dermatitis and treated intermittently with dexamethasone and ketoconazole over a prolonged period, without clinical improvement. Methods: Direct microscopic examination of hair and skin samples revealed ectothrix dermatophyte elements. Culture on SCC medium at ۲۸ °C for ۱۴ days produced white, creamy, filamentous colonies with a lemon-yellow reverse, lacking macro- and microconidia. Molecular identification via ITS gene sequencing confirmed the isolate as
Microsporum canis (accession number PX۱۰۶۴۲۹), and phylogenetic analysis placed it within the M. canis clade, closely related to both animal and human reference strains. Results: This case exhibited several unusual findings. The cat was initially misdiagnosed, resulting in delayed initiation of appropriate antifungal therapy. Prolonged administration of corticosteroids appeared to exacerbate and lead to chronicity of the fungal infection. Clinically, ear pinna necrosis represented an uncommon manifestation of M. canis infection. Furthermore, fungal culture revealed atypical colony morphology characterized by the absence of both macroconidia and microconidia. Despite extended antifungal treatment with ketoconazole, only minimal clinical improvement was observed, emphasizing the refractory and persistent nature of deep dermatophytosis in Persian cats. Conclusion: The report underscores the importance of accurate and timely diagnosis of feline dermatophytosis, the risks of prolonged corticosteroid use, and the value of molecular tools for species confirmation and phylogenetic insight. Early recognition and appropriate management are crucial for improving outcomes in chronic M. canis infections, particularly in predisposed breeds such as Persians. To our knowledge, this is the first documented case combining chronic infection, ear necrosis, treatment failure, and molecular/phylogenetic confirmation, emphasizing its diagnostic and clinical significance.