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Terbinafine-Resistant Tinea — SCE Dermatology MCQ

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HardCutaneous InfectionTerbinafine-Resistant TineaSCE Dermatology

A 30-year-old man has widespread tinea corporis not responding to topical antifungals. His dermatologist suspects Trichophyton indotineae (previously T. mentagrophytes genotype VIII). This is an emerging concern. Why is this strain clinically significant?

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Correct answer: B — T. indotineae carries acquired resistance to Terbinafine (via mutations in squalene epoxidase gene) and may require alternative antifungals such as Itraconazole

The correct answer is B, T. indotineae carries acquired resistance to Terbinafine (via mutations in squalene epoxidase gene) and may require alternative antifungals such as Itraconazole. Terbinafine acts by inhibiting squalene epoxidase, an enzyme in ergosterol biosynthesis, and point mutations in the SQLE gene abolish drug binding, producing high-level in vitro and clinical resistance. This explains the exact clinical scenario in the stem: widespread tinea corporis failing standard topical and, by extension, oral terbinafine therapy. UK surveillance data confirm that most T. indotineae isolates remain susceptible to itraconazole, making it the recommended alternative when resistance is suspected or confirmed on susceptibility testing.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/skin-conditions