Pictorial Case Study: Pityriasis versicolor

The case: Brenda looked the picture of health after two weeks' holiday on a Greek island. Sun, good food, friends and fun had made the holiday a great success and she was delighted with her new tan. However, she came to the surgery because the appearance of her tan had been ruined by white patches appearing on her back. She wanted to know what had caused this and how it could be treated.

Pityriasis versicolor: hypopigmentation occurs when 'diseased areas' are made obvious by their failure to tan (Photograph: Author Image)
Pityriasis versicolor: hypopigmentation occurs when 'diseased areas' are made obvious by their failure to tan (Photograph: Author Image)

DIAGNOSIS AND MANAGEMENT
The GP quickly made a diagnosis of pityriasis (tinea) versicolor (PV). The presentation is a common one in which hypopigmentation occurs when 'diseased areas' are made obvious by their failure to tan. PV is caused by the yeast, malassezia, which is normally present on the skin but behaves in a pathogenic fashion in certain situations, such as tropical climates where heat and humidity encourage its growth, and in the immunosuppressed or malnourished.

It occurs most commonly after puberty and before the age of 65 years, on the chest, back and abdomen, but can spread to the limbs, neck and face. It can present in two ways; hypopigmented patches that show up more on darkened skin, when they fail to tan, or as hyperpigmented, slightly scaly patches, caused by the organism-inducing enlargement of melanosomes in the basal layer of the dermis. Hypopigmentation results from the action of carboxylic acids.

The diagnosis can be confirmed by microscopy. After mixing with 20% potassium hydroxide solution, a pattern of 'spaghetti and meatballs' is seen. Wood's light may cause some lesions to fluoresce a green/gold colour.

There are a variety of topical treatments that should clear the problem. These include applying selenium sulphide shampoo to affected areas for 10 minutes daily for seven days, avoiding the genitalia, face and any open wounds or scratched lesions, or applying topical azoles for three to five minutes daily before rinsing off, for five days.

Other preparations, such as terbinafine, are effective but more expensive. Occasionally, an oral azole, such as itraconazole or fluconazole, can help in widespread or recurrent cases.

Recurrences are common and sometimes prophylactic treatment with monthly topical preparations or a single dose of itraconazole monthly for six months may help. Patients should be warned that once the disease has been treated, repigmentation might take as long as six months.

POSSIBLE DIFFERENTIAL DIAGNOSES

  • Vitiligo.
  • Pityriasis alba.
  • Seborrhoeic dermatitis.
  • Pityriasis rosea.
  • Guttate psoriasis.

DIFFERENTIAL DIAGNOSIS
Pityriasis alba

  • Cause unknown but thought to be a manifestation of atopic eczema.
  • Usually affects children aged three to 16 years.
  • Initially may display a mild erythema that is usually asymptomatic but might itch.
  • The erythema subsides leaving areas of hypopigmentation that may be covered in fine scales.
  • Can persist for months or longer but resolves spontaneously.
  • In children usually affects the face, especially around the mouth, cheeks, chin and sometimes the limbs.
  • No specific treatment required but emollients may help the scaling.
  • A mild topical steroid (1%) may help the erythema and ease itching.
  • Occasionally photochemotherapy might encourage repigmentation in widespread cases.
  • Dr Watkins is a sessional GP in Hampshire.

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