Pictorial case study: An uncomfortable and itchy rash

Dr Nigel Stollery explains how to manage this rash.

The presentation

Differential diagnoses
  • Tinea cruris
  • Candida infection
  • Intertrigo
  • Flexural psoriasis
  • Acanthosis nigricans

A 65-year-old diabetic male presented with a few weeks' history of a rash in his groin. Both sides were affected and the area was uncomfortable and itchy. It had initially looked very red, but now looked more brown in appearance and a surface scale was present. The edges were well demarcated, with no difference in the appearance of the skin at the margins.

The patient had no past history of any skin problems, except for eczema as a child. Nowhere else on his body was affected, although he had reported a recent episode of athlete's foot between his toes which he had treated himself with a cream from the local chemist. He had been applying petroleum jelly to his groin and washing daily with soap.

The management

The condition this patient has is erythrasma, a bacterial infection of the skin which is more common in diabetics and obese patients. It tends to occur in the groin and axilla, and under the breasts. It is caused by the Gram-positive bacteria Corynebacterium minutissimum.

If unsure, the diagnosis can be made using a Wood's lamp, which causes the organisms to fluoresce a coral red colour because of the porphyrins released by the bacteria.

It can look similar to a fungal infection, but has no leading edge and is browner. In some cases, fungal or yeast infections may also be present.

Erythrasma is treated with a topical antibacterial such as fusidic acid, along with a topical antifungal to cover any coexisting infections. In severe or persistent cases, an oral antibiotic, such as erythromycin or oxytetracycline, may be required. Antiseptic soaps and lotions can be useful in preventing recurrences.

  • Contributed by Dr Nigel Stollery, a GP in Kibworth, Leicestershire, and clinical assistant in dermatology at Leicester Royal Infirmary.

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