Differential diagnoses: Pityriasis

Dr Nigel Stollery compares four presentations and offers clues for their diagnosis including pityriasis rosea, pityriasis versicolor, pityriasis alba, pityriasis capitis

Pityriasis rosea

Presentation

  • Common condition, occurs more in autumn and winter
  • Cause thought to be reaction to a virus (69% have preceding URTI)
  • Starts with herald patch, followed one to two weeks later by rash
  • Usually lasts six to eight weeks, but may last up to 12 weeks
  • ild to severe itching in 25% of cases
  • Scale usually seen on most lesions as a collarette

Management

  • Diagnosis usually clinical
  • Herald patch may be mistaken for ringworm
  • Treatment not required, but if itchy, an oral antihistamine or moderately potent topical steroid may help

Pityriasis versicolor

Presentation

  • Affects 1% of people in UK; more common in humid, warm climates
  • Usually asymptomatic, may be present for years
  • Discoloration more apparent after tanning, with superficial scale
  • Caused by proliferation of Malassezia furfur

Management

  • Investigations not usually necessary
  • Yellow green fluorescence seen under Wood's light
  • Treatment with topical antifungals, especially imidazoles, usually adequate, although more severe cases may require oral antifungal (itraconazole 200mg daily for seven days)

Pityriasis alba

Presentation

  • Occurs in children and young adults
  • Hypopigmented round or oval scaly macules on face
  • More apparent in summer and on darker-skinned individuals
  • Mild form of dermatitis
  • No link with vitiligo, which may concern parents

Management

  • Treatment not usually required
  • Usually clears in a few months, but may last two to three years
  • Emollients can be helpful if skin is dry
  • Where there is erythema, a mild topical steroid may help

Pityriasis capitis

Presentation

  • Affects more than half of the population
  • Often associated with itching
  • Dandruff scale is cluster of corneocytes which have separated from stratum corneum

Management

  • Usually diagnosed clinically
  • May be associated with other conditions, such as psoriasis, eczema, seborrhoeic dermatitis
  • No cure, but most cases can be controlled with medicated shampoo
  • Antifungal or coal tar shampoos usually most effective
  • Dr Stollery is a GP in Kibworth, Leicestershire, and clinical assistant in dermatology at Leicester Royal Infirmary

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