Pictorial case study: Itchy rash with a large lesion

This is thought to be a viral infection mainly affecting young patients. By Dr Jean Watkins.

The patient was fine except for a slightly itchy rash (Photograph: Dr P Marazzi/SPL)

The presentation

This 13-year-old boy was fine apart from a slightly itchy rash that had developed on his chest and back over the past week. His mother was concerned. On examination, the rash consisted of pink, mostly oval, slightly scaly macules. A single, larger, pink lesion, with a collarette of fine scale inside its edge, had appeared on the upper abdomen about 10 days before the main rash.

The management

The diagnosis of pityriasis rosea (PR) was confirmed on the basis of the herald patch on the boy’s stomach. The patient can be reassured the rash will clear spontaneously. Antihistamines and a topical corticosteroid may be used if necessary for itching. UV light may ease itching in troublesome cases. Exclusion from school and work is unnecessary because the risk of transmitting the disease is small.

The discussion

PR is a mild, self-limiting condition that usually resolves within about six weeks. Some patients report headache and feeling ‘off colour’ for a few days before the rash appears. Further investigations are usually unnecessary unless there are concerns that syphilis could be a problem, or in cases where the rash persists for more than three months, when skin biopsy may be taken.

When the rash fades, the patient may be left with some hypo- or hyperpigmentation. In about 20% of cases, symptoms may vary and the patient develops a lymphadenopathy, photosensitivity, or the rash may occur in the groins, axillae, face and distal extremities.

 Possible differential diagnoses

  • Lichen planus
  • Pityriasis lichenoides
  • Guttate psoriasis
  • Syphilis
  • Tinea corporis
  • Seborrhoeic dermatitis

Dr Jean Watkins is a retired GP in Hampshire

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