Pityriasis versicolor

Pityriasis versicolor

Cause

The old name, tinea versicolor, should be dropped as the disorder is caused by commensal yeasts (Pityro-sporum orbiculare) and not by dermatophyte fungi.Overgrowth of these yeasts, particularly in hot humid conditions, is responsible for the clinical lesions.

Carboxylic acids released by the organisms inhibit the increase in pigment production by melanocytes that occurs normally after exposure to sunlight. The term ‘versicolor’ refers to the way in which the super-ficial scaly patches, fawn or pink on non-tanned skin (Fig. 14.49), become paler than the surrounding skin after exposure to sunlight (Fig. 14.50). The condition should be regarded as non-infectious.

Presentation and course

The fawn or depigmented areas, with their slightly branny scaling and fine wrinkling, look ugly. Other- wise they are symptom-free or only slightly itchy. Lesions are most common on the upper trunk but can become widespread. Untreated lesions persist, and depigmented areas, even after adequate treatment, are slow to regain their former colour. Recurrences are common.

Differential diagnosis

In vitiligo, the border is clearly defined, scal-ing is absent, lesions are larger, the limbs and face are often affected, and depigmentation is more complete; however, it may sometimes be hard to distinguish vitiligo from the pale non-scaly areas of treated versi-color. Seborrhoeic eczema of the trunk tends to be more erythematous, and is often confined to the presternal or interscapular areas. Pityriasis alba often affects the cheeks. Pityriasis rosea, tinea corporis, secondary syphilis and erythrasma seldom cause real confusion.

Investigations

Scrapings, prepared and examined as for a dermato-phyte infection, show a mixture of short branched hyphae and spores (a ‘spaghetti and meat-balls’ appearance). Culture is not helpful.

Treatment

A topical preparation of one of the imidazole group of antifungal drugs (Formulary 1) can be applied at night to all affected areas for 2– 4 weeks. Equally effective, but messier and more irritant, is a 2.5% selenium sulphide mixture in a detergent base (Selsun shampoo). This should be lathered on to the patches after an evening bath, and allowed to dry. Next morning it should be washed off. Three applica-tions at weekly intervals are adequate. A shampoo containing ketoconazole is now available (Formulary 1) and is less messy, but just as effective as the selenium ones. Alternatively, selenium sulphide lotion (USA) can be applied for 10 min, rinsed off and re-applied daily for 1 week. For widespread or stub-born infections systemic itraconazole (200 mg daily for 7 days) has been shown to be curative, but interac-tions with other drugs must be avoided (Formulary 2). Recurrence is common after any treatment.