What is pityriasis versicolor?
Pityriasis versicolor is a common yeast infection of the skin, in which flaky discoloured patches appear on the chest and back.
The term pityriasis is used to describe skin conditions in which the scale appears similar to bran. The multiple colours of pityriasis versicolor give rise to the second part of the name, versicolor. Pityriasis versicolor is sometimes called tinea versicolor, although the term tinea should strictly be used for dermatophyte fungus infections.
Who gets pityriasis versicolor?
Pityriasis versicolor most frequently affects young adults and is slightly more common in men than in women. It can also affect children, adolescents and older adults.
Pityriasis versicolor is more common in hot, humid climates than in cool, dry climates. It often affects people that perspire heavily. It may clear in the winter months and recur each summer.
Although it is not considered infectious in the conventional sense, pityriasis versicolor sometimes affects more than one member of a family.
What are the clinical features of pityriasis versicolor?
Pityriasis versicolor affects the trunk, neck, and/or arms, and is uncommon on other parts of the body. The patches may be coppery brown, paler than surrounding skin, or pink. Pale patches may be more common in darker skin; this appearance is known as pityriasis versicolor alba. Sometimes the patches start scaly and brown, and then resolve through a non-scaly and white stage.
Pityriasis versicolor is usually asymptomatic, but in some people it is mildly itchy.
In general, pale or dark patches due to pityriasis versicolor do not tend to be more or less prone to sunburn than surrounding skin.
What is the cause of pityriasis versicolor?
Pityriasis versicolor is caused by mycelial growth of fungi of the genus Malassezia.
Malassezia are part of the microbiota (microorganisms found on normal skin). They are dependent on lipid for survival. Fourteen different species of malassezia have been identified. The most common species cultured from pityriasis versicolor are M globosa,M restricta and M sympodialis.
Usually malassezia grow sparsely in the seborrhoeic areas (scalp, face and chest) without causing a rash. It is not known why they grow more actively on the skin surface of patients prone to pityriasis versicolor. One theory implicates a tryptophan-dependent metabolic pathway.
The yeasts induce enlarged melanosomes (pigment granules) within basal melanocytes in the brown type of pityriasis versicolor. It is easier to demonstrate the yeasts in scrapings taken from this type of pityriasis versicolor than in those taken from the white type.
The white or hypopigmented type of pityriasis versicolor is thought to be due to a chemical produced by malassezia that diffuses into the epidermis and impairs the function of the melanocytes.
The pink type of pityriasis versicolor is mildly inflamed, due to dermatiits induced by malassezia or its metabolites. Pink pityriasis versicolor and seborrhoeic dermatitis may co-exist, as both are associated with malassezia.
Hyperpigmented, hypopigmented and inflamed pityriasis versicolor are usually seen as distinct variants but may sometimes co-exist.
How is pityriasis versicolor diagnosed?
Pityriasis versicolor is usually diagnosed clinically. However, the following tests may be useful.
- Wood lamp (black light) examination— yellow-green fluorescence may be observed in affected areas
- Microscopy using potassium hydroxide (KOH) to remove skin cells—hyphae and yeast cells that resemble spaghetti and meatballs are observed
- Fungal culture—this is usually reported to be negative, as it is quite difficult to persuade the yeasts to grow in a laboratory
- Skin biopsy—fungal elements may be seen within the outer cells of the skin (stratum corneum) on histopathology. Special stains may be required.
What is the treatment of pityriasis versicolor?
Mild pityriasis versicolor is treated with topical antifungal agents.
- Topical azole cream/shampoo (econazole, ketoconazole)
- Selenium sulfide
- Terbinafine gel
- Ciclopirox cream/solution
- Propylene glycol solution
- Sodium thiosulphate solution
The medicine should be applied widely to all the affected areas before bedtime for as long as directed (usually between 3 days and about two weeks, depending on extent of the rash).
Oral antifungal agents, itraconazole and fluconazole, are used to treat pityriasis versicolor when extensive or if topical agents have failed. Oral terbinafine, an antifungal agent used to treat dermatophyte infections, is not effective for malassezia infections such as pityriasis versicolor.
Vigorous exercise an hour after taking the medication may help sweat it onto the skin surface, where it can effectively eradicate the fungus. Bathing should be avoided for a few hours. A few days' treatment will clear many cases of pityriasis long term, or at least for several months.
Recurrences of pityriasis versicolor
Pityriasis versicolor generally clears satisfactorily with treatment but often recurs when conditions are right for malassezia to proliferate. When the scaly component of pityriasis versicolor recurs, antifungal treatment should be repeated.
In those who have frequent recurrences, antifungal shampoo or oral antifungal treatment may be prescribed for one to three days each month.
Occasionally white marks persist long after the scaling and yeasts have gone and despite exposure to the sun. In such cases, further antifungal treatment is unhelpful.