Skin Disorders Guide

Diagnostic Hallmarks

1. Distribution: chest, back, and shoulders
2. Sharp margination
3. Confluence of central lesions; peripheral satellite macules
4. Fine scale visible only with scraping
5. Positive potassium hydroxide (KOH) preparations

Clinical Presentation

The word “versicolor” means various colors. On sun-exposed surfaces the lesions are usually white, but on covered areas they are often light brown or brown-red. The initial lesions of tinea versicolor are sharply marginated macules 3 or 4 mm in diameter. Centrifugal growth leads to enlargement and subsequent coalescence of adjacent lesions. Rather large patches may be formed. Small, isolated satellite manlles are characteristically found at the periphery of the large patches. Scale is neither visible nor palpable, but when the lesions are scraped with the edge of a scalpel blade, fine (pityriasis-type) scale can be demonstrated.

Lesions are most commonly found on the central area of the upper chest and back, but when the disease is extensive, lesions can also occur on the upper arms, antecubital fossae, lower trunk, and groin. The face is almost always spared. This distribution pattern together with the sharp margination of the lesions helps to clinically distinguish pityriasis versicolor from pityriasis alba.

A clinical diagnosis should be confirmed by use of a KOH preparation. The microscopic appearance of the KOH preparation in pityriasis versicolor is described . Culture of the organism in ordinary clinical laboratories is not possible.

Course and Prognosis

Pityriasis versicolor occurs at any age, but it is found most commonly in teenagers and young adults. Left untreated, the infection persists indefinitely with varying degrees of exacerbation and remission. When the lesions are treated, scale formation stops and the KOH becomes negative. The white color present at the site of the lesions remains for several months, however, before normal skin color gradually returns. Patients should be forewarned that this persistence of hypopigmentation is not necessarily an indication of treatment failure. The disease has a marked tendency for recurrence even after adequate treatment has been administered.

Pathogenesis

Pityriasis versicolor is caused by the mycelial form of the yeast Pityrosporum orbicular. This organism, in its spore phase, is a normal inhabitant of the stratum corneum of human skin. The trigger that converts the spore phase to mycelial growth is unknown, but environmental factors are probably important. For instance, the prevalence of the disease correlates well with climatic conditions of high heat and high humidity and also correlates with work environments that favor the production of copious sweating. Other factors such as pH and variations in skin lipid formation, which may be genetic, may also playa role. Treatment presumably reconverts growth of the organism to the spore phase without eradicating it from the skin. This probably explains the great predilection for periodic recrudescence of the disease. The cause of the hypopigmentation in this disease is not known, but the presence of fungal products such as dicarboxylic acids are hypothesized to influence melanin production.

Therapy

Pityriasis versicolor responds to a variety of different treatment programs. Selenium sulfide shampoo (Exsel and Selsun), used as a soap daily for 3 weeks, is commonly prescribed. Imidazole preparations such as clotrimazole (Lotrimin) or miconazole (Micatin, Monistat), although more expensive, are also quite effective when they are applied twice daily for several weeks. Ketoconazole, in a dose of 200 mg each morning for as little as 2 to 7 days, is increasingly used because of convenience; fluconazole, a related drug, may also be effective. Orally administered griseofulvin and topically applied tolnaftate (Tinactin, Aftate) are not effective in the treatment of this disease. Patients should be forewarned that the whiteness will remain for months following treatment. Since the recurrence rate is very high, patients are well advised to re-treat themselves each spring prior to the “tanning season.”