Tinea incognita: causes, symptoms, diagnosis, and treatment

Tinea incognita is a tinea with loss of typical clinical features due to various causes, mostly topical glucocorticoids and scratches.


Causes

HIV infection, organ transplantation, immunosuppressive agents, and glucocorticoids causing immunodeficiency and chronic diabetes is the main cause. Studies have shown that clinical symptoms subside and the fungi in the stratum corneum are eliminated when the body develops cellular immunity, mainly delayed type hypersensitivity (DTH) reaction, against dermatophyte infection. If the body lacks cellular immunity or cannot produce effective cellular immune responses, chronic infections or relapses may occur, which result in expansion of tinea in size, aggravated symptoms and signs, protracted duration, loss of typical characteristics, and presence of atypical skin lesions.

Long-term scratches can cause hypertrophy, expansion, pigmentation, and loss of typical marginal development and central regression.

Treatment with topical glucocorticoids are the most common cause. Large amounts of clinical evidence indicate that topical glucocorticoids alone can aggravate superficial fungal infections. Glucocorticoids can inhibit the skin's cellular immune response against dermatophytes, and in vitro studies have found hydrocortisone obviously stimulates the growth of trichophyton rubrum and dose-dependent effects are present.

Various dermatophytes can cause different skin lesions.


Signs and Symptoms

Dermatitis-like lesions

Skin lesions are erythema, papules, and vesicles, as well as eczema in severe cases, without typical marginal development and central regression characteristics, with no scales or little scales, with rapid development, with obvious pruritus, and are often misdiagnosed as contact dermatitis. When the skin lesion spreads, the illness is even misdiagnosed as a drug eruption. The disease is caused mostly by topical glucocorticoids, as well as immunodeficiency.

Figure 1 tinea incognita

Figure 2 tinea incognita

Chronic lichenoid lesions

Appearances and predilection sites are similar to those of lichen simplex chronicus. Skin lesions are sharply demarcated and lichenoid, and are often caused by trichophyton rubrum. Disseminated neurodermatitis-like manifestations can also occur if without prompt treatment or with scratches.

Concentric lesions

Skin lesions are concentric and may be caused by trichophyton rubrum, microsporum canis, and microsporum gypseum.

Scutulum-like lesions

Skin lesions are yellow, thickened crusts, with obvious inflammation in the stratum basale, and are caused by microsporum gypseum.


Diagnosis

The diagnosis of tinea incognita is mainly based on the positive fungal examination. KOH examination can assist in the diagnosis.


Treatment

Topical medications include resorcinol cream, econazole cream, clotrimazole cream, miconazole cream, bifonazole cream, ketoconazole cream, sertaconazole cream, butenafine cream, and terbinafine cream.

Systemic medications are mainly fluconazole, itraconazole, and terbinafine.