Background: Although usually simple, the diagnosis of dermatophyte infection is sometimes neglected. An observational study has been realized to evaluate the role of corticosteroid exposure (tinea incognito) and of other primary characteristics of the dermatophytosis that from onset mimic other diseases and mislead an unexperienced physician.
Materials and methods: Between 1990 and 2009, all cases of atypical dermatophytosis mimicking other skin diseases were collected from the more general number of dermatophyte infections diagnosed at the Dermatology Department of Cagliari University, Italy.
Results: One-hundred and fifty-four cases (71 male/83 female, 2-81 years old) were studied, with a median of 7 cases/year. The most observed clinical forms were those mimicking impetigo, eczematous dermatitis, lupus erythematosus, polymorphous light eruption, psoriasis, and rosacea. The identified dermatophytes were: Microsporum canis (70 cases), Trichophyton rubrum (43 cases), Trichophyton mentagrophytes var. mentagrophytes (29 cases), Trichophyton mentagrophytes var. interdigitale (six cases), Microsporum gypseum (three cases), Epidermophyton floccosum (two cases), and Trichophyton verrucosum (one case). Diagnostic difficulties are discussed, with special attention to the origin of the pathomorphosis.
Conclusions: In our experience, clinical atypia is not a mere consequence of corticosteroid therapy but present at the very onset of the illness, due to the variable dermatophyte invasive capacity, the site of invasion, physiological individual, and/or acquired condition, such as excessive washing or sun exposure. Therefore, we suggest using the term "tinea atypica" rather than "tinea incognito" to include all forms of dermatophytosis that do not present the classic features for both primary and secondary pathomorphosis.
© 2012 The International Society of Dermatology.