Other Superficial Mycoses
Pityriasis (tinea) versicolor occurs in tropical and temperate climates; it is characterizedby discrete areas of hypopigmentation or hyperpigmentation associated with induration and scaling. Lesions are found on the trunk and arms; some assume pigments ranging from pink to yellow-brown, hence the term versicolor. Members of the genus Malassezia, of which M. furfur is the most common, are the cause; these organisms can be seen in skin scrapings as clusters of budding yeast cells mixed with hyphae. They grow in the yeast form in culture media enriched with lipids.
Tinea nigra, another tropical infection, is characterized by brown to black macular le-sions, usually on the palms or soles. There is little inflammation or scaling, and the infection is confined to the stratum corneum. The cause, Hortaea werneckii, is a black-pigmented fungus found in soil and other environmental sites. Scrapings of the lesion show brown–black-pigmented septate hyphae. In culture initial growth is in the yeast form, with slow development of hyphal elements.
Piedra is an infection of the hair characterized by black or white nodules attached tothe hair shaft. White piedra (caused by Trichosporon cutaneum) infects the shaft in hy-phal forms, which fragment with occasional buds. Black piedra (caused by Piedraia hor-tae) shows branched hyphae and ascospores in sections of the hair.