Tinea incognito is a localized skin infection caused by fungus, just like tinea corporis (ringworm) and tinea capitis (scalp ringworm). It is a skin infectious process that looks very different from other fungal infections, both the shape and the degree of involvement. Topical corticosteroid use is the culprit for the difference.
Fungal infection, most often caused by Trichophyton rubrum, presents initially as a flat, scaly rash that gradually becomes a circular lesion with a raised border and the border is scaly as it advances. While the lesion enlarges, the center becomes brown or less pigmented. These skin findings comprise of the ringworm we typically see on the body. Lesions can be large or small.
At this stage of the disease, if a topical corticosteroid is applied to the lesion, the local inflammation from the fungal infection will be decreased, so to alter the clinical presentation of the typical infection. And this secondary appearance is called tinea incognito.
The most common site for this clinical transformation is the face and the back of the hand. The hand is a popular site for a lot of skin diseases, which is why tinea incognito is hard to diagnose and be differentiated from the others. Altered clinical picture of tinea incognito could resemble eczema, psoriasis and other diseases. What makes the clarification important is the difference in treatment approach. Corticosteroid makes tinea worse but helps the other ones.
The new appearance of tinea incognito is quite different from other fungal infections. Instead of a localized lesion, it becomes much more extensive and loses its original circular shape, which is one of the most important clinical clues to diagnose fungal infection. Sometimes, red rashes show at the edges and the center. On top of everything else, the advancing border might not be present any more. All the features that traditionally associate with fungal infections have been lost in this disease entity.
The clinical cycle is closely related to the use of topical corticosteroids. With initial use, the inflammation caused by the fungi is diminished and lesions appear to be getting better. However, fungi will thrive in the later course of treatment with corticosteroids because of suppressed immune response and result in the clinical picture of tinea incognito. Even though treatment is discontinued at times, lesions are unrecognizable as fungal infection due to the shape change. Most often, patients will try to use the topical medication again to attempt the early response and the cycle continues.
Diagnose can be made by a skin scraping microscopic test. But this should be attempted only after stopping the treatment for a few days to yield the best result quality. Fungal culture is not needed in most situations.
Treatment for tinea incognito is to discontinue the topical corticosteroids. For mild and superficial lesions, they respond well to antifungal creams. Treatment for another week after the resolution of the lesions is important. For more severe forms, oral medications like terbinafine and fluconazole, may be necessary. If open lesions are infected with bacteria, antibiotics should be added to the regimen.
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