A worsening abdominal rash
The confluence of 2 treatments (one appropriate, one not) led to a challenge in diagnosing this worsening rash.
Diagnosis: Tinea incognito
The patient was given a diagnosis of tinea incognito, a form of tinea corporis that is exacerbated by the inappropriate use of corticosteroids in the management of a cutaneous fungal infection.1 Furthermore, this patient’s case was consistent with tinea pseudoimbricata, a variant of tinea incognito. Tinea pseudoimbricata is characterized by striking concentric scaly rings that mimic tinea imbricata, a fungal infection caused by the dermatophyte Trichophyton concentricum, which is commonly found in tropical areas.2
A common infection is alteredby steroid use
Tinea corporis has a relatively high prevalence. Approximately 10% to 20% of the world population is affected by fungal skin infections.3
T rubrum is the most common cause of tinea corporis. Other causes include T tonsurans, T interdigitale, T violaceum, Microsporum canis, M gypseum, and M audouinii.
Tinea corporis can be acquired through direct contact with an infected person, animal, or fomite. It may also be acquired through autoinoculation from another area of the body containing a dermatophyte fungal infection. Tinea corporis lesions are usually pruritic, erythematous, annular plaques with overlying scale and central clearing.
How steroid use can change the picture. Treatment with corticosteroids is ineffective for fungal skin infections and causes immunosuppression, allowing the fungus to thrive. This patient had been treated with a topical steroid (clobetasol) for the abdominal lesion caused by tinea corporis, as well as an oral steroid (prednisone) for an asthma exacerbation. These steroid treatments caused the abdominal lesion to morph from the typical appearance of tinea corporis—classically an annular erythematous plaque with overlying scale and central clearing—to an erythematous plaque with striking concentric scaly rings.
Continue to: Clinical exam can provide clues; KOH examination can reveal the Dx
