CASE #1: Tinea incognito

The atypical lesions referred to as tinea incognito are the result of morphologic changes induced by topical corticosteroid treatment of tinea corporis. The changes may include loss of the raised, scaly, advancing border that is characteristic of tinea corporis lesions and a more widespread eruption.

A superficial dermatophyte infection, tinea corporis can involve the skin of the trunk and extremities, while excluding the scalp, beard area, face, hands, feet, and groin. Commonly seen in tropical regions, tinea corporis can be found worldwide. Its most common global cause is Trichophyton rubrum, followed by Trichophyton mentagrophytes; however, tinea corporis can be caused by any of the dermatophytes. The organisms are transmitted from human to human, animal to human, or soil to human. Domestic animals are common carriers of the zoophilic dermatophyte species.1

Tinea corporis is most commonly characterized by one or more circular, slightly scaly, erythematous plaques with central clearing and a prominent advancing edge, creating an annular outline and leading to the lay term “ringworm.” These lesions are generally associated with pruritus or burning. Widespread lesions of tinea corporis can occur in immunodeficient states and may be the presenting sign of AIDS.2

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Tinea corporis can mimic many dermatoses, including nummular eczema, contact dermatitis, psoriasis, granuloma annulare, parapsoriasis, and pityriasis rosea. The atypical appearance of tinea incognito is more likely than classic tinea corporis to be confused with other entities, and not uncommonly, biopsy of a chronic refractory dermatosis will reveal tinea incognito.2

Classic lesions of tinea corporis can be easily recognized clinically; however, the diagnosis can be easily confirmed by visualizing fungal elements microscopically in skin scrapings.2 Microscopic examination is performed by scraping scale from the lesion onto a glass slide with either a scalpel blade or the side of another glass slide. A 10% KOH solution is added to the scrapings to dissolve cellular components while leaving fungal hyphae intact. This process can be accelerated by gently heating the slide with a flame. The slide is covered with a cover slip and viewed under the microscope. The presence of fungal hyphae is considered a positive result. Additionally, tinea corporis and tinea incognito may be diagnosed with fungal culture or skin biopsy using appropriate fungal stains.
Localized lesions of tinea corporis can be treated with topical antifungals once or twice daily for at least four weeks and for at least one week after symptoms resolve. Topical antifungal therapies include terbinafine, ketoconazole, miconazole, clotrimazole, tolnaftate, ciclopirox, naftifine, econazole, oxiconazole, butenafine, or sulconazole.3 Oral terbinafine, fluconazole, or itraconazole may be required for recalcitrant or extensive lesions.1

In our patient with recalcitrant lesions, oral terbinafine 250 mg daily for four weeks resulted in complete resolution of symptoms. No scaly lesions were noted at the follow-up examination, and the patient did not complain of persistent pruritus.