Beyond the surface: an uncommon case of Microsporum gypseum subcutaneous mycosis induced by an insect bite

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Deep cutaneous and subcutaneous infections caused by dermatophytes are exceptionally uncommon, typically occurring through traumatic inoculation. This clinical report details the complex dermatological journey of a young, immunocompetent 24-year-old girl who reported a rare case of a subcutaneous mycosis caused by Microsporum gypseum. The patient presented with an annular erythematous plaque with centered papules on her left hand, which she referred to as stemming from an insect bite. Initial evaluation at another hospital included a biopsy, which resulted in a preliminary diagnosis of pyoderma gangrenosum. Appropriate treatment with topical steroids and later oral cyclosporine provided no response, leading clinicians to perform a new biopsy and cultural examination; the patient was diagnosed with epidermomycosis and pustular folliculitis caused by Microsporum gypseum, a geophilic dermatophyte. In our patient’s case, terbinafine proved effective, resulting in complete remission. This article aims to emphasize the importance of considering rare conditions such as subcutaneous epidermomycosis when the patient’s medical history provides suggestive clues, particularly if the clinical manifestation aligns with the hypothesis.