A 49-year-old man comes to the office due to a pruritic rash. For the last 6 months he has had an enlarging rash at the groin that causes significant discomfort when he works outdoors in hot weather. The patient has tried over-the-counter diphenhydramine cream, which only partially relieves the itching. Examination findings are shown in the exhibit. The scrotum is not involved, and there is no inguinal adenopathy. Which of the following is the most likely diagnosis of this patient's rash?

Question

A 49-year-old man comes to the office due to a pruritic rash.  For the last 6 months he has had an enlarging rash at the groin that causes significant discomfort when he works outdoors in hot weather.  The patient has tried over-the-counter diphenhydramine cream, which only partially relieves the itching.  Examination findings are shown in the exhibit.  The scrotum is not involved, and there is no inguinal adenopathy.  Which of the following is the most likely diagnosis of this patient's rash?

Quizplus · Accepted Answer

This patient has a pruritic rash at the groin with sparing of the scrotum. The lesions (annular plaques with a raised, scaly border) are consistent with tinea cruris (TC) (ie, jock itch), a common dermatophyte infection caused by Trichophyton rubrum and similar species. Risk of infection is higher in men and in individuals with diabetes or other immune-suppressing conditions. The symptoms are frequently aggravated by heavy sweating and warm ambient temperatures. As with other dermatophyte infections, the diagnosis is often apparent based on historical features and examination findings. It can be confirmed with potassium hydroxide preparation of skin scrapings, especially in severe or atypical cases. Topical antifungals (eg, clotrimazole, tolnaftate) are usually effective, and oral antifungals (eg, fluconazole) can be used for severe or refractory cases; however, nystatin is not effective. Measures recommended to prevent recurrence include good hygiene with thorough drying (and/or desiccant powders) after bathing. Concurrent dermatophyte infection elsewhere on the body (eg, tinea pedis, corporis) should be identified and treated to prevent reinfection via autoinoculation. (Choice A) Like TC, candidal intertrigo affects the warm, occluded skin inside skin folds. However, the rash typically appears moist and macerated (rather than dry and scaly); lacks a clear, raised border; and often shows satellite lesions. satellite lesions (Choice B) Erythrasma is a superficial bacterial infection (Corynebacterium minutissimum) that presents as red or brown patches in intertriginous areas. The border is typically flat, scaling (if present) is fine, and itching is mild. brown patches (Choice C) Unlike common plaque psoriasis, which predominantly affects extensor surfaces, inverse psoriasis affects intertriginous regions. However, this psoriasis variant presents as smooth plaques with minimal to no scaling. smooth plaques (Choice D) Although seborrheic dermatitis can involve the groin and axilla, it is much more common at the head (eg, ears, scalp, eyebrows). The lesions show coarse scaling with a typically greasy appearance, and the plaques usually have a salmon hue. coarse scaling Educational objective: Tinea cruris (ie, jock itch) presents as pruritic, annular plaques with a raised, scaly border. It occurs in the groin but usually spares the scrotum. The diagnosis is often apparent based on clinical findings and can be confirmed with potassium hydroxide preparation of skin scrapings. Topical antifungals (eg, clotrimazole, tolnaftate) are usually effective.

A 49-Year-Old Man Comes to the Office Due to a Pruritic