A 17-year-old girl is brought to the office due to a worsening rash on her left upper arm. The rash was the size of a dime when the patient initially noticed it 3 weeks ago, but it has since grown in size, developed a raised edge, and become increasingly itchy. She has applied moisturizing creams without improvement. The patient takes no medications and has no allergies. The rash is shown in the image below: What is the most likely diagnosis for this patient?

Question

A 17-year-old girl is brought to the office due to a worsening rash on her left upper arm.  The rash was the size of a dime when the patient initially noticed it 3 weeks ago, but it has since grown in size, developed a raised edge, and become increasingly itchy.  She has applied moisturizing creams without improvement.  The patient takes no medications and has no allergies.  The rash is shown in the image below:  What is the most likely diagnosis for this patient?

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11ec25c8_d64e_38d2_bc81_3f9abf8b5156_MD0003_00 This patient has an annular, pruritic plaque with a raised, scaly border consistent with tinea corporis (ringworm). Tinea corporis is a cutaneous dermatophyte infection most commonly caused by Trichophyton rubrum. The fungi thrive in warm, moist areas (eg, shower surfaces, pools, gym mats) and can be transmitted by skin-to-skin contact, contact with animals (eg, kittens), or via fomites. Tinea corporis lesions initially present as pruritic plaques that spread centrifugally and may become confluent. The border is typically more erythematous than the center, which may show partial or complete clearing. Individuals with HIV infection or diabetes mellitus may have multiple, widespread lesions. The diagnosis is generally apparent on inspection and can be confirmed with potassium hydroxide examination of skin scrapings in severe, atypical, or refractory cases. Tinea corporis is usually treated with topical antifungals (eg, clotrimazole). (Choice B) Erythema migrans, often described as a bull's-eye rash, is the cardinal manifestation of Lyme disease. The lesions are occasionally pruritic but are not scaly and typically do not have a raised border. Patients frequently have systemic symptoms (eg, myalgias, fatigue) and a history of exposure to ticks in an endemic area. Erythema migrans (Choice C) Psoriasis presents with scaly plaques but typically occurs symmetrically on the extensor surfaces of the elbows and knees. Itching may be present but is usually mild. Psoriasis may occur in adolescents but is more common at age >30. scaly plaques (Choice D) Subacute cutaneous lupus erythematosus can cause annular plaques but typically presents with numerous lesions, predominantly in sun-exposed areas of the upper body. Itching is uncommon. numerous lesions (Choice E) Urticaria presents acutely (minutes to hours) as well-circumscribed, erythematous plaques with intense pruritus and associated edema (ie, wheals). The lesions do not develop scale and typically resolve within 24 hours. Educational objective: Tinea corporis is a superficial fungal infection characterized by pruritic, scaly, erythematous plaques with a raised border and central clearing. The diagnosis is usually apparent on inspection and can be confirmed with potassium hydroxide examination of skin scrapings. Topical antifungals (eg, clotrimazole, terbinafine) are first-line treatment. References: Topical antifungal treatments for tinea cruris and tinea corporis. (http://www.ncbi.nlm.nih.gov/pubmed/25090020)

A 17-Year-Old Girl Is Brought to the Office Due to a Worsening