Tinea incognito due to Trichophyton mentagrophytes: case report.

Tineas are frequent infections caused by dermatophytes that are able to invade keratinized tissue, causing rounded, erythematous, scaly lesions. Nonetheless, in tinea incognito the lesions are modified because of inappropriate use of topical corticosteroids or calcineurin inhibitors, making it difficult to diagnose. We present a case of a 12-year-old male child that presents with erythematous lesions on the right eyebrow, which at first was diagnosed as a contact dermatitis, so corticosteroids were indicated. The lesions became more inflammatory and a fungus culture was requested, which was positive for Tricophyton mentagrophytes. The conclusion of this report is that tineas can mimic other dermatologic conditions therefore caution should be taken when prescribing topical corticosteroids or calcineurin inhibitors without diagnostic certainty because if lesions are caused by tinea, diagnosis and treatment may become more difficult.