Dermatophytosis And Other Sup... Health Article

The normal skin is colonized in late childhood and adult life by lipophilic yeasts. Morphologically, these are either oval (most common on the scalp) or round (mainly on the trunk), and they were previously called Pityrosporum ovale and Pityrosporum orbiculare, respectively. These organisms have now been reclassified as members of the genus Malassezia, among which there are seven pathogenic species: Malassezia furfur, M. pachydermatis (not associated with human skin infections), M. sympodialis, M. globosa, M. restricta, M. obtusa, and M. slooffiae. ⁴⁶ Round yeasts, usually M. globosa, are seen in lesions of pityriasis versicolor accompanied by short, stubby hyphae; M. furfur may produce filaments as well but is less common.

The infection is associated with transformation of yeast-phase organisms into hyphal forms, although patients with pityriasis versicolor occasionally have only oval yeasts. The stimulus for this phase change is unknown. Infections are more common in the tropics and may appear after sun exposure, which may therefore be a trigger factor. Patients with Cushings syndrome may also develop this infection, but diseases related to T-lymphocyte suppression are not necessarily associated with pityriasis versicolor. ⁴⁷

A carboxylic acid called azelaic acid, thought to be produced by the organism in the stratum corneum, is believed to lead to the depigmentation seen in lesions. ⁴⁸ Malassezia yeasts grow in the presence of medium-chain-length fatty acids.

Different species of Malassezia obviously play a role in the development of disease, although it is not known why, for instance, M. globosa in particular should be associated with pityriasis versicolor.

Pityriasis versicolor is usually seen on the trunk or proximal portions of the limbs, although more extensive infections involving the face and waist area are seen in the tropics. Lesions may be hypopigmented or hyperpigmented macules that amalgamate to cover the affected area with scaling plaques. The lesions are usually not itchy. In some patients lesions may remit spontaneously.

The diagnosis can be confirmed by direct microscopy of lesions, on which the characteristic round yeast forms and short hyphae can be seen. The scrapings can be viewed after clearing with potassium hydroxide but are seen more clearly after staining with a mixture of Parker Quink ink and potassium hydroxide. Lesions fluoresce yellow-green under Woods light, although this may not be seen on all affected areas. Malassezia yeasts are difficult to culture unless oil is added to the medium. An overlay of Tween 80 encourages growth.

The most appropriate therapy for pityriasis versicolor is a topical azole, terbinafine cream, 2 selenium sulfide lotion, or 20 sodium thiosulfate applied daily for 10 to 14 days. The latter preparations may be irritative. In some cases intermittent applications of 50 propylene glycol in water prevent a relapse. ⁴⁹ In severe cases, oral ketoconazole or itraconazole produces remissions. The exact doses of ketoconazole needed to induce a remission are not clear, but therapy for 5 to 10 days with 200 mg is usually sufficient, although mycologic recovery is not seen for about 30 days because the organisms can still be seen in skin scrapings. In some patients a single dose of 400 mg is effective. The effective dose of itraconazole is 200 mg daily for 5 days.

Patients usually have to be warned that the pigmentary changes may return to normal only after many months, even when the infection has been successfully treated.