M furfur is now the most commonly accepted name for the etiologic agent of tinea versicolor. Thus, P orbiculare, P ovale, and Malassezia ovalis are synonyms .
M furfur is a dimorphic lipophilic organism that is cultured only in media enriched with C12-sized or C14-sized fatty acids. Malassezia is able to exist in both yeast and mycelial forms, with yeast most commonly associated with saprofital form (P ovale). Historically, the name M furfur was used to designate the fungal pathogen of tinea versicolor before it is grown in culture. M furfur is not a dermatophyte, does not grow on dermatophyte test media (DTM), and does not respond to griseofulvin therapy.
With the advent of DNA sequencing, numerous pathogenic and nonpathogenic species were found. Some of them appear to be more common in certain areas of the world, and some are more likely to be pathogenic in one area and not in another. Much of the confusion was resolved with the taxonomic revision in 1996, based on sequencing of the large-subunit rRNA and nuclear DNA of more than 100 isolates of Malassezia species. [3] The genus Malassezia was revised to include 7 species: Malassezia globosa, Malassezia sympodialis, M furfur, Malassezia slooffiae, Malassezia pachydermatis, Malassezia restricta, and Malassezia obtusa. The clinical significance of each of these species is under investigation. A study of the epidemiology of Malassezia yeasts associated with pityriasis (tinea) versicolor in Canada revealed the most frequently isolated species included M sympodialis, M globosa, and M furfur.
One study found M globosa in 97% of patients with tinea versicolor; it was found alone in 60% of cases, was associated with M sympodialis in 29% of cases, and was associated with M slooffiae in 7% of cases. [3] M sympodialis and M slooffiae were found in similar percentages on clinically uninvolved skin of the trunk, whereas M globosa was not isolated at other sites. Thus, some authors suggest that M globosa in its mycelial phase is the causative agent of tinea versicolor. [3, 4]
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In patients with lighter skin color, lesions frequently are a light tan or salmon color.
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Upon potassium hydroxide (KOH) examination, hyphae are visible and grow into strands within clumps of keratinocytes. Thick-walled spores frequently occur in grapelike clumps. Individual spores and short stubby hyphae float in the clear areas between clumps of keratinocytes. Many of the short hyphae are dystrophic.
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Scale is frequently difficult to appreciate upon clinical examination.
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This individual developed skin discoloration and mild itching every summer for the past few years. These patients should be instructed on the prophylactic use of topical therapy.
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This superficial plaque of tinea versicolor is located in the right antecubital fossa of an adult. This appearance and distribution is uncommon but not rare. A potassium hydroxide (KOH) preparation confirmed the diagnosis.
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Although tinea versicolor is uncommon in children in temperate climates, when it does occur, it is more likely to be atypical in distribution. This 7-year-old boy had areas of tinea versicolor across the forehead and both temples. He was in good health and lived in Washington state when he was diagnosed.
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In some patients, the areas affected by tinea versicolor are not always obvious. In this patient, the abnormal areas are hypopigmented.
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Clear adhesive tape can be pressed onto areas of tinea versicolor to collect hyphae and spores. The tape is then lightly pressed onto a glass slide, and a drop of methylene blue is placed at the edge of the tape. The methylene blue is allowed to run under the tape staining Malassezia furfur. The spores and hyphae easily are seen against a background clutter of keratinocytes and glue.
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Some patients present with extensive tinea versicolor. This patient related that his discoloration had been present for more than 20 years. The light-colored areas on the abdomen are the normal areas of skin. Although topical therapy alone is usually effective, this patient may benefit from initial therapy with oral ketoconazole, followed by selenium sulfide applications in the shower 2-3 times a month.
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Significant hyperpigmentation caused by a tinea versicolor infection.
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Confluent and reticulated Gougerot and Carteaud papillomatosis.
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Mycelium strands and numerous spores observed on a potassium hydroxide (KOH) preparation of tinea versicolor. This combination is commonly referred to as "spaghetti and meatballs."
