Widespread hyperpigmented rash present for 1 year.

A 59-year-old woman with type II diabetes mellitus and obesity presented to the clinic for evaluation of a hyperpigmented rash located in her axillae, groin, buttock, umbilicus, and inframammary region (Fig 1, Fig 2, Fig 3, Fig 4, Fig 5, Fig 6) of 1 years' duration. She reported pruritus and occasional fissuring after scratching. She was treated previously with nystatin powder, clotrimazole cream, and oral fluconazole for 4 weeks with minimal improvement.

Fig 1

Fig 2

Fig 3

Fig 4

Fig 5

Fig 6

Question 1: What is the diagnosis?

Mycosis fungoides

Inverse psoriasis

Dermatophytosis

Erythrasma

Candidiasis

Answers:

Mycosis fungoides – Incorrect. Mycosis fungoides classically appears as patches. It takes years to develop and most cases occur in whites (70%; Hispanics, 9%).

Inverse psoriasis – Incorrect. Inverse psoriasis presents with erythematous, shiny, moist plaques in intertriginous areas but with no scale.2, 3

Dermatophytosis – Incorrect. Dermatophytosis often occurs with onychomycosis; lack of response to antifungals makes this diagnosis less likely.

Erythrasma – Correct. Erythrasma presents with erythematous to tan, asymptomatic or pruritic scaly plaques in intertriginous areas and is caused by Corynebacterium minutissimum.5, 6 Risk factors include obesity, poor hygiene, warm climate, and diabetes mellitus.

Candidiasis – Incorrect. Candidiasis has satellite papules and would have improved with antifungals.

Question 2: What does Wood's lamp detect in this patient?

Coproporphyrin III

Melanin

Rhodopsin

Carotenoid

Pyocyanin

Answers:

Coproporphyrin III – Correct. Diagnosis of erythrasma can be made easily by Wood's lamp examination, which characteristically fluoresces coral red due to coproporphyrin III.5, 8

Melanin – Incorrect. Wood's lamp does not detect melanin, the naturally occurring pigment in skin and hair.

Rhodopsin – Incorrect. Wood's lamp does not detect rhodopsin, which is the purple pigment in eyes that helps with sight in dim light.

Carotenoid – Incorrect. Wood's lamp does not detect these red, yellow, or orange pigments, such as carotene, which give color to plant parts such as carrots or fall leaves.

Pyocyanin – Incorrect. Wood's lamp does not detect this blue-green pigment, which gives pseudomonas its characteristic color.

Question 3: How would you treat this patient?

Topical steroids

Macrolide antibiotic

Immunotherapy

Topical antifungals

Barrier cream

Answers:

Topical steroids – Incorrect. Topical steroids would be used for a diagnosis of inverse psoriasis and are not indicated for erythrasma, as it is a bacterial infection.

Macrolide antibiotic – Correct. Erythrasma is treated with topical clindamycin, erythromycin, or antibacterial soaps, such as benzoyl peroxide. For recalcitrant or extensive disease, a 5- to 14-day course of oral erythromycin or clarithromycin is used to eliminate the corynebacterium. For therapeutic failure of intertriginous involvement, topical clindamycin or other antibacterial soaps are added.

Immunotherapy – Incorrect. Immunotherapy can be used for cutaneous malignancies, such as mycosis fungoides; however, immunotherapy is not used for the treatment of erythrasma.

Topical antifungals – Incorrect. The patient has not responded to topical and oral antifungals, and these are not indicated in the treatment of erythrasma.

Barrier cream – Incorrect. Barrier creams are typically used to treat dermatitis and dry skin and work to improve barrier function of the skin and reduce its susceptibility to irritants.

Discussion

This article represents an interesting presentation of extensive erythrasma, which required a biopsy for diagnosis. This case highlights the importance of keeping erythrasma on the differential diagnosis of a rash in the intertriginous areas, especially as it can be easily identified with Wood's Lamp in the office.