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.