Tinea incognita B35.8

Tinea incognita (TI) is a term first used by IVE and Marks in 1968 to describe the condition caused by steroid ingestion that results in an atypical presentation of dermatophyte infections (Ive Fa et al. 1968). The term "tinea atypica" may sometimes be used instead of TI. The term TI is used accurately for drug-induced conditions, but atypical tinea occurs in immunocompetent individuals who are not using topical and systemic immunosuppressants.

Clinically asymptomatic dermatomycosis that does not have the classic (usual) appearance (see tinea below). Tinea incognito is probably the most common clinical manifestation of tinea corporis.

The prevalence of the pathogens was given as follows: Trichophyton rubrum (40 %), Trichophyton mentagrophytes (24 %), Microsporum canis (19 %).

Exact epidemiological data are unknown (Ghaderi A et al. 2023).

TI is usually caused by the misuse of topical or systemic corticosteroids. Clobetasol propionate and betamethasone valerate are the most common causative agents. It is usually a diagnostic challenge for dermatologists as this infection does not present with the classic symptoms and can mimic other diseases (Khurana A et al. (2020). Immunomodulators such as calcineurin inhibitors (including tacrolimus and pimecrolimus) or treatment with tumor necrosis factor inhibitors (Eichhoff G 2021) can also cause TI, but are observed less frequently than corticosteroid extenders (Chang P et al. 2016). Fumaric acid esters can also cause TI (Nenoff P et al. 2017).

Discrete, mostly skin-colored skin lesions characterized peripherally by delicate scales. The sharply marked border typical of tinea corporis is absent. The recurrent itching is usually treated with a glucocorticoid externum, which masks the characteristic picture of dermatomycosis. Often an incidental finding. Various clinical patterns of tinea incognita are described. Eczema-like lesions were found in 50 % of cases, followed by psoriasiform lesions and lesions similar to parapsoriasis. Rosaceous and pyodermic lesions were rarer (Ghaderi A et al. 2023).

The question of pre-treatment, especially after a glucocorticoid externum, is often negated by many patients.

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