Case study: Diagnosing a persistent rash

This patient was worried by a rash not responding to treatment, writes Dr Suneeta Kochhar.

The rash was increasing in size (Dr Suneeta Kochhar)


This 60-year-old woman presented with a seven-month history of a dark rash in the axillae and under both breasts. She was concerned about it and worried because the area affected was increasing. The appearance of the rash was unchanged. It was not itchy, but had been in preceding months. There was no travel history and no contacts had similar symptoms.

The patient had been seen by a GP who prescribed clotrimazole, which gave minimal improvement. She mentioned that the slight itching had improved. She attended a couple of months later and was prescribed clotrimazole and hydrocortisone, which did not clear the rash.

There was no significant medical history, no history of skin problems and no evidence of immunosuppression. She was not overweight.

Clinical examination revealed a well-demarcated area of brown discoloration in both axillae, and in the inframammary folds, brown macules with fine scaling.

There were also areas of postinflammatory hyperpigmentation. There were no areas of central clearing, maceration or fissures. The skin was otherwise normal.

The clinical appearance was suggestive of erythrasma. Differential diagnoses included dermatophytosis, candidiasis, psoriasis, seborrhoeic dermatitis and contact dermatitis. A swab was taken for microscopy and culture to confirm the diagnosis.

Erythrasma fluoresces coral-pink when exposed to Wood's light, because of porphyrin production by Corynebacterium minutissimum, which may confirm the diagnosis.


The patient was treated with a course of erythromycin because of the extensive area affected and advised to use an antibacterial soap. The treatment of choice is erythromycin 250mg four times a day for two weeks. A tetracycline may be used second line.1

The swab confirmed the presence of C minutissimum.

The patient attended for review at three weeks and her symptoms had significantly improved.

In the case of intertriginous involvement or failure of treatment, there is some evidence for the use of topical solutions, such as clindamycin and Whitfield's ointment.1

Whitfield's ointment contains benzoic acid 6% and salicylic acid 3% in emulsifying ointment and is applied twice daily. Antibacterial soap may be used in the treatment and prophylaxis of erythrasma.1

Erythrasma, a superficial bacterial infection caused by C minutissimum, may coexist with a fungal infection, dermatophyte or Candida albicans.

It occurs more often in patients with diabetes. It may be seen in the inframammary areas, crural area and intergluteal folds. The discoloration is usually evident in intertriginous areas. It is often asymptomatic, but pruritus may be present.

Corynebacterium may cause other infections, such as trichomycosis axillaris, which is often associated with hyperhidrosis.2,3

  • Dr Kochhar is a GP principal in Bexhill, East Sussex


1. Holdiness MR. Drugs 2002; 62: 1131-41.

2. O'Dell ML. Am Fam Physician 1998; 57: 2424-32.

3. Blaise G, Nikkels AF, Hermanns-Le T et al. Int J Dermatol 2008; 47: 884-90.

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