A 45-year-old woman comes to the office for evaluation of a rash. The rash started 3 weeks ago under her breasts and has gradually spread to her chest. There is no associated pruritus. The patient has a history of diabetes, hypertension, and gastroesophageal reflux disease. Her medications include hydrochlorothiazide, metformin, and omeprazole. She has no history of tobacco or alcohol use. The patient's vital signs are within normal limits. Her BMI is 38 kg/m². Skin examination is shown in the image below. There is no warmth or tenderness around the lesions. Which of the following is the most likely organism causing this patient's rash?

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Explanation: 11ec2b69_be7c_99d3_8f63_f5c4b7cd47df_MD0005_00 This patient's presentation is consistent with severe intertrigo, an inflammatory skin disorder affecting the intertriginous areas (inguinal, perineal, genital, intergluteal, axillary, or inframammary). Risk factors include conditions that increase skin friction (eg, obesity), increase moisture (eg, tight clothing, hyperhidrosis), or promote fungal overgrowth (eg, diabetes, immunosuppression). Candidal intertrigo (primarily Candida albicans) is the most common etiology as the fungus grows well under the warm, moist environment of the skinfolds. Patients typically develop erythematous plaques and erosions, sometimes with satellite papules (black arrows above) and significant inflammation (white arrows above). The lesions can be pruritic or painful if there is significant skin breakdown. The diagnosis is made clinically but can be confirmed with KOH examination. Topical antifungals (eg, miconazole, nystatin, terbinafine) are the preferred first-line treatment for intertrigo. After antifungal treatment, the use of skin-drying agents and correction of any underlying predisposing conditions can reduce the risk of recurrence. (Choice B) Corynebacterium minutissimum is a gram-positive bacillus found in normal skin flora that can cause erythrasma, a superficial skin infection affecting the intertriginous areas. Erythrasma causes well-defined erythematous patches or thin plaques with fine wrinkling in the groin, axillae, inframammary region, or umbilicus. erythrasma (Choice C) Staphylococcus aureus can cause cellulitis, which usually presents with acute-onset erythema, edema, and warmth. The duration of the rash and absence of warmth make this less likely. cellulitis (Choice D) Trichophyton rubrum causes tinea cruris, which presents as erythematous patches with sharply demarcated borders, most commonly on the inner thighs. The patch typically spreads with partial central clearing and can be slightly elevated. tinea cruris (Choice E) Varicella zoster virus causes herpes zoster (shingles), which presents as erythematous papules that quickly evolve into painful vesicles in a dermatomal distribution. This patient's bilateral, non-dermatomal distribution makes this less likely. herpes zoster (shingles) Educational objective: Intertrigo is most commonly due to Candida infection and causes erythematous plaques and erosions in intertriginous regions (eg, inguinal, perineal, genital, intergluteal). Topical antifungals are the preferred initial therapy. References: Intertrigo and secondary skin infections. (http://www.ncbi.nlm.nih.gov/pubmed/24695603)

A 45-Year-Old Woman Comes to the Office for Evaluation of a Rash