Balancing the scales

February 1, 2008

Tinea incognito is a dermatophyte infection that has been altered by use of topical or systemic corticosteroids. It lacks the classic features of a ringworm infection due to corticosteroid suppression of inflammation and altered local immune response.

Dermatology: What's your Dx?

Tinea incognito is a dermatophyte infection that has been altered by use of topical or systemic corticosteroids. It lacks the classic features of a ringworm infection due to corticosteroid suppression of inflammation and altered local immune response. Tinea incognito often takes on atypical or even bizarre morphologies.1,2

Clinical findings

Dermatophyte infections of non-hair-bearing skin are typically well demarcated annular patches, or plaques with central clearing. The appearance may vary by location, and may start as a simple papule. The characteristic lesion subsequently develops with an expanding elevated, red scaly border. Vesicles, pustules, and/or crusts may be present within the border when inflammation is intense.3

A number of clinical patterns have been described with tinea capitis:4

Symptoms of tinea capitis depend on the clinical pattern, and can vary from minimal pruritis and no alopecia to diffuse tenderness with purulence and scarring alopecia.4

However, treatment with topical or systemic steroids may suppress local immunity and inflammation, resulting in unusual clinical presentations and a delay in diagnosis. Tinea capitis and tinea corporis must be considered in this setting, even when the clinical pattern is not typical.

Differential diagnosis

The differential diagnosis for tinea incognito includes seborrheic dermatitis, atopic dermatitis, alopecia areata, telogen effluvium, bacterial folliculitis, and psoriasis.4,5 The presence of tinea at other body sites and in other family members should increase the index of suspicion for tinea. A potassium hydroxide preparation is usually positive and allows for immediate confirmation of dermatophyte infection. However, a fungal culture is still the gold standard for diagnosis, and should be sent especially when a patient's infection involves the scalp.

Treatment

Effective treatment of tinea incognito requires discontinuation of steroids. This may result in an increase in inflammation, as well as symptoms that can be managed with a slower taper to lower potency and less frequent applications of the topical steroid. Warning parents of this rebound phenomenon should minimize the risk of prolonged additional use of steroids.1,2