A 52-year-old man comes to the office due to an enlarging rash at the left ankle and upper back. The rash began 6 weeks ago and is associated with significant itching. The patient has tried topical antihistamines and calamine lotion without relief. Medical history is otherwise unremarkable. Temperature is 36.9 C (98.4 F), blood pressure is 135/82 mm Hg, pulse is 76/min, and respirations are 12/min. BMI is 25 kg/m². Examination shows a rash at the ankle, as seen in the image below, and a similar rash is noted at the upper back. Which of the following is the most likely diagnosis in this patient?

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11ec25c8_d38e_06aa_bc81_774b04542491_MD0003_00 This patient has a pruritic rash with a scaly, erythematous border and partial central clearing consistent with tinea corporis (ringworm). Tinea corporis is a cutaneous dermatophyte infection most commonly caused by Trichophyton rubrum. Patches of tinea corporis are typically annular but may become confluent to form a "flower petal" shape. Patients with tinea corporis often have concurrent infection elsewhere on the body, hands (tinea manuum), groin (tinea cruris), or between the toes or sides of the feet (tinea pedis). Those with immunocompromising conditions (eg, HIV, diabetes mellitus) can have severe or widespread disease. Other risk factors include exposure to warm, moist areas (eg, public showers, swimming pools), contact with infected animals or people (eg, during sports participation), and wearing tight or occlusive clothing. The diagnosis is confirmed using potassium hydroxide (KOH) preparation of skin scrapings. Most cases can be treated with topical antifungals (eg, terbinafine, clotrimazole); patients who fail topical therapy or have extensive disease may need systemic therapy (eg, oral terbinafine, fluconazole). (Choice A) Erythema marginatum is a manifestation of acute rheumatic fever characterized by numerous, widespread plaques with a sharp annular or serpiginous border and central clearing. It is transient, nonpruritic, and most common in children. annular or serpiginous border (Choice B) Erythema migrans is a target-shaped rash that is the cardinal manifestation of Lyme disease. The lesions are not scaly and do not have a raised border. Patients frequently have systemic symptoms (eg, myalgias, fatigue) and history of exposure to ticks in an endemic area. Erythema migrans (Choice C) Nummular eczema is a chronic, relapsing/remitting condition that presents with erythematous, pruritic, coin-shaped patches on the extremities. The lesions may initially have a scant exudate and are uncommon on the back and upper trunk. Nummular eczema (Choice D) Pityriasis rosea is characterized by numerous small, oval, scaly plaques, often with an initial lesion (herald patch) that is much larger than the later lesions. It is typically seen in children and young adults, and usually occurs on the trunk and proximal (not distal) extremities. In addition, the rash typically resolves within 6 weeks of presentation. Pityriasis rosea Educational objective: Tinea corporis is a cutaneous dermatophyte infection that causes a pruritic rash with a scaly, erythematous border and central clearing. Patients often have concurrent infection elsewhere on the body, hands, groin, or feet. Those with immunocompromising conditions (eg, HIV, diabetes mellitus) can have severe or widespread disease. References: Mycology - an update. Part 1: dermatomycoses: causative agents, epidemiology and pathogenesis. (http://www.ncbi.nlm.nih.gov/pubmed/24533779)

A 52-Year-Old Man Comes to the Office Due to an Enlarging