Pityriasis versicolor

Pityriasis versicolor is a skin eruption that usually develops after sun exposure with white macules on the tanned skin but pale brown patches on the covered areas, hence the name versicolor, or variable colour. The lesions are: (a) flat; (b) only partially depigmented—areas of vitiligo are totally white; and (c) do not show inflammation or vesicles.

The causative organism is a yeast, Pityrosporum orbiculare, that takes advantage of some unknown change in the epidermis and develops a proliferative, stubby, mycelial form, Malassezia furfur. This otherwise incidental information can be simply put to practical use by taking a superficial scraping from a lesion on to a microscope slide—add a drop of potassium hydroxide or water with a coverslip. The organisms are readily seen under the microscope as spherical yeast forms and mycelial rods, resembling "grapes and bananas" ("spaghetti and meatballs" in the United States).

Treatment is simple: selenium sulphide shampoo applied regularly with ample water while showering or bathing will clear the infection. The colour change may take some time to clear.

A mica scale pityriasis lichenoides

Pityriasis versicolor skin lesions

Ketoconazole shampoo is an effective alternative. Oral terbinafine, which is very effective in other fungal infections, has no effect.

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