A 58-year-old man is brought to the office by his family with a pruritic rash on his feet. He lives in a group home due to intellectual disability, and his family members noted the rash while visiting him on his birthday. Medical history is notable for hypertension and type 2 diabetes. When the patient's socks are removed for examination, a large quantity of skin flakes falls onto the examination table. Skin examination findings are as shown in the exhibit. Examination also shows erythema and excoriations at the medial and lateral aspects of both heels. Which of the following is the most appropriate next step in evaluation of this patient's skin condition?

Question

A 58-year-old man is brought to the office by his family with a pruritic rash on his feet.  He lives in a group home due to intellectual disability, and his family members noted the rash while visiting him on his birthday.  Medical history is notable for hypertension and type 2 diabetes.  When the patient's socks are removed for examination, a large quantity of skin flakes falls onto the examination table.  Skin examination findings are as shown in the exhibit.  Examination also shows erythema and excoriations at the medial and lateral aspects of both heels.  Which of the following is the most appropriate next step in evaluation of this patient's skin condition?

Quizplus · Accepted Answer

11ec25c8_d38e_a2eb_bc81_974c9e0d139e_MD0003_00 This patient has a pruritic rash involving the feet, which likely represents tinea pedis (TP). Early/mild TP is often limited to the skin between the toes (interdigital pattern), but in more extensive or chronic cases it can extend to involve the soles and sides of the feet (moccasin pattern), often with significant hyperkeratosis and flaking. TP is primarily caused by dermatophytes, especially Trichophyton rubrum and similar species. The organisms are widespread and are often acquired following exposure to public places while barefoot (eg, athletic facilities, public swimming pools). Mild cases of interdigital TP are often treated empirically with topical antifungals (eg, miconazole, tolnaftate). However, more extensive or persistent/recurrent cases (such as in this patient) warrant confirmation to exclude other hyperkeratotic disorders. A potassium hydroxide (KOH) preparation of skin scrapings showing branched, segmented hyphae is diagnostic. TP can be treated with a variety of topical antifungals (eg, miconazole, terbinafine, tolnaftate). hyphae (Choice A) Allergen patch testing is used in the diagnosis of allergic contact dermatitis, which can cause erythema and pruritus but typically occurs in exposed skin (eg, hands, face) and is not associated with significant skin flaking. Allergic reactions to leather or rubber (or related chemicals) in shoes can occur in the feet, but typically affect the dorsa rather than the soles. (Choice B) Gram stain and bacterial culture can be considered for cases of TP complicated by secondary bacterial cellulitis, but this would typically present with acute erythema, warmth, tenderness, and possibly fever. (Choice D) Punch biopsy is useful in evaluating bullous or eczematous disorders and in some cases of suspected malignancy. It is less likely to be helpful in diffuse scaling and flaking of the feet. (Choice E) Serum immunoglobulin E assays are useful in evaluation of allergic bronchopulmonary aspergillosis but are not indicated in dermatophyte infections and generally have low specificity in dermal conditions. (Choice F) Wood's lamp examination can help visualize infection with Microsporum species in patients with tinea capitis. It is less helpful in evaluation of tinea pedis, and KOH microscopy would still be required for confirmation. Educational objective: Tinea pedis most commonly involves the skin between the toes but can extend to involve the soles and sides of the feet (moccasin pattern), often with significant hyperkeratosis and flaking. A potassium hydroxide preparation of skin scrapings showing branched, segmented hyphae is diagnostic. Treatment includes topical antifungals (eg, miconazole, terbinafine, tolnaftate).

A 58-Year-Old Man Is Brought to the Office by His