Pictorial case study - A purple lesion

Further lesions developed in this otherwise well patient, explains Dr Jean Watkins.

Presentation

This 50-year-old woman was concerned about symptomless patches that had developed, mainly on her trunk. This semicircular, purplish lesion with small papules around the edges was the first to appear close to the axilla. More had developed on her abdomen in the ensuing weeks. Some were circular with a clear centre, which coalesced with others as they enlarged. The patient was otherwise fit and well.

Diagnosis

The diagnosis was generalised granuloma annulare (GA), a benign inflammatory condition that tends to occur in children aged under 10 and adults aged 30-60. Generalised GA differs from the more common localised GA, which more often occurs under the age of 30.

The cause is unknown, although a number of trigger factors, such as trauma, malignancy, viral infections and insect bites, have been suggested. There is possibly an association with diabetes.

Diagnosis is normally clinical, based on the appearance of the rash.

Management

Treatment is usually unnecessary and the rash should clear within a few months. Sometimes it will be more persistent, especially in generalised GA. Localised GA may respond to an intralesional or potent topical corticosteroid or cryotherapy, but with these methods, there is a risk of subsequent scarring and/or atrophy. There is no reliable cure for generalised GA, but oral steroids, psoralen UVA therapy or immunosuppressants are suggested.

Differential diagnosis

  • Pityriasis rosea
  • Tinea corporis
  • Erythema annulare centrifugum
  • Lichen planus
  • Lyme disease (erythema migrans)

Dr Watkins is a retired GP in Hampshire.

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