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?

• A.Mycosis fungoides
• B.Inverse psoriasis
• C.Dermatophytosis
• D.Erythrasma
• E.Candidiasis

Answers:

• A.Mycosis fungoides – Incorrect. Mycosis fungoides classically appears as patches. It takes years to develop and most cases occur in whites (70%; Hispanics, 9%).¹
• B.Inverse psoriasis – Incorrect. Inverse psoriasis presents with erythematous, shiny, moist plaques in intertriginous areas but with no scale.2, 3
• C.Dermatophytosis – Incorrect. Dermatophytosis often occurs with onychomycosis; lack of response to antifungals makes this diagnosis less likely.⁴
• D.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.⁷
• E.Candidiasis – Incorrect. Candidiasis has satellite papules and would have improved with antifungals.

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

• A.Coproporphyrin III
• B.Melanin
• C.Rhodopsin
• D.Carotenoid
• E.Pyocyanin

Answers:

• A.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
• B.Melanin – Incorrect. Wood's lamp does not detect melanin, the naturally occurring pigment in skin and hair.
• C.Rhodopsin – Incorrect. Wood's lamp does not detect rhodopsin, which is the purple pigment in eyes that helps with sight in dim light.
• D.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.
• E.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?

• A.Topical steroids
• B.Macrolide antibiotic
• C.Immunotherapy
• D.Topical antifungals
• E.Barrier cream

Answers:

• A.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.²
• B.Macrolide antibiotic – Correct. Erythrasma is treated with topical clindamycin, erythromycin, or antibacterial soaps, such as benzoyl peroxide.⁷ 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.
• C.Immunotherapy – Incorrect. Immunotherapy can be used for cutaneous malignancies, such as mycosis fungoides; however, immunotherapy is not used for the treatment of erythrasma.¹
• D.Topical antifungals – Incorrect. The patient has not responded to topical and oral antifungals, and these are not indicated in the treatment of erythrasma.
• E.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.⁹

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.