Pictorial case study: Facial rash

Dr Jean Watkins investigates a rash on a concerned teenager.

Annular and oval, scaly lesions (Photograph: CNRI/Science Photo Library)
Annular and oval, scaly lesions (Photograph: CNRI/Science Photo Library)

Case study

This teenager was concerned about the rash that was spreading from her neck up to her face. It had started with itchy, inflamed patches and pustules, which had first developed on her neck and quickly spread to form these annular and oval, scaly lesions, which then appeared to clear centrally.

Her mother was blaming the new Persian cat that they had just acquired from a rescue centre.

On examination, there were no signs of any other skin problems, but judging by the appearance of the lesions, it was thought to be ringworm (tinea corporis). A skin scraping was taken at the advancing edge of a lesion and sent to the laboratory for culture and sensitivity.  

Aetiology

Ringworm is a superficial fungal infection of the skin, most often caused by a dermatophyte, Trichophyton rubrum, Epidermophyton floccosum or Microsporum canis.

It is transmitted by direct contact with a lesion and the incubation period is about two weeks.

Some animals, particularly long-haired cats and dogs, may be affected and are a common source of infection of humans.

Ringworm can affect other parts such as the feet, flexures, scalp, hands and nails, and may present with different features. The immunosuppressed, patients with diabetes or those with problems such as leukaemia are more vulnerable to the condition.

Management

The diagnosis and the fungus involved are confirmed by microscopy and culture of skin scrapings in the laboratory. It is advisable to start treatment quickly, so a microscopic check in the surgery may be helpful. Full examination of the patient should be undertaken. The finding of ringworm at other sites might alter the approach to treatment.

Localised infections should respond to the application of an imidazole topical antifungal agent, such as clotrimazole, miconazole, ketoconazole or econazole; terbinafine is also effective, but more expensive. If the ringworm is more widespread, where topical treatment has failed and/or it is affecting other sites, an oral antifungal agent can be used.

The infection is often acquired from a family pet, which may or may not show signs of skin disease, so pets should be checked and treated if necessary by their vet.

According to the Health Protection Agency, school exclusion is not usually necessary, but some recommend exclusion until treatment has been started. Sharing of clothing with an infected person is best avoided.  

Differential diagnosis

  • Impetigo
  • Psoriasis
  • Discoid eczema
  • Pityriasis rosea
  • Contact allergic dermatitis
  • Mycosis fungoides

Dr Watkins is a retired GP in Hampshire

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