CASE #1: Pityriasis alba
A common disorder of the skin, pityriasis alba occurs primarily in children between the ages of 3 and 18 years. The condition usually manifests as dry, fine-scaled, pale patches 0.5 to 6 cm in diameter. In 50% of cases, the rash is limited to the face, particularly the mid-forehead, malar ridges, and the area around the eyes and mouth; involvement of the shoulders, neck, back, and upper chest occurs as well. The rash is symmetrical in distribution. Pityriasis alba typically begins as a pale pink or light brown macule with indistinct margins. Over a period of weeks, the subtle erythema fades, leaving an off-white to tan-white macule with a powdery scale. Macules typically vary from 5 to 30 mm in size, but some patients present with as many as 20 larger hypopigmented lesions that are ill-defined and range in size from 1 to 4 cm. The borders of the rash are not clearly visible, as the light-colored patches seem to blend gradually into normal-appearing skin.
The condition derives its name from the Latin words pityriasis, meaning scaly, and alba, meaning white. More males are affected than females. Pityriasis alba seems to occur more frequently in those with light skin, but it is more apparent in those of darker complexion, as seen in our case. The dry scaling appearance is most noticeable during the winter because of the dry air inside people’s homes. During the summer, tanning of the surrounding normal skin makes the pale patches more apparent, as the affected skin fails to tan as much as the surrounding skin. Various studies have reported prevalence rates from 1% to 31% of schoolchildren.
There is no specific known cause for pityriasis alba; however, studies seem to suggest at least four possible causes for the condition: absence of normal skin-protective substances, sunlight-sensitive melanocytes, damaged melanocytes, and a possible depigmenting factor. The incidence of pityriasis alba is increased in individuals who bathe excessively, defined as showering more than once daily. This could infer that removal of normal epidermal defensins and other natural protective substances from the skin surface increases susceptibility to this condition. Certainly, any inflammation of the skin may affect pigment-cell function. Indeed, many consider the disease to be a mild form of eczema.
Photosensitivity may also play a role. The peak incidence of pityriasis alba coincides with the age at which children begin to spend more time in outdoor activities, and lesions typically occur in sun-exposed areas. In addition, prolonged sun exposure, i.e., several hours, also increases an individual’s chances of developing the condition. All this suggests that the melanocytes in these patients are sensitive to sunlight.
Hypopigmentation can also be explained by damage to melanocytes and inhibition of tyrosinase by decarboxylic acid, azelaic acid (a competitive inhibitor of tyrosinase), and/or tryptophan-derived metabolites produced by normal yeast, namely Malassezia furfur, one of the organisms that comprise the normal flora found on the skin’s surface. Thus, some pityriasis alba patients may have a sensitivity to the by-products of this fungus.
The fourth possible cause is a hypothetical depigmenting factor that some suggest is produced by Propionibacterium acnes bacteria, which live in the hair follicles.
Pityriasis alba is not contagious. It is self-limited but can last for a few months to several years before resolving. The condition is usually asymptomatic, but some patients complain of burning or itching.
The diagnosis of pityriasis alba is made clinically; biopsies are rarely necessary or helpful because pathological findings are nonspecific. Sometimes pityriasis alba is confused with tinea versicolor. While tinea versicolor is characterized by overgrowth of M. furfur in the epidermis, the number of organisms in pityriasis alba is not increased. The diagnosis of tinea versicolor can be ruled out by KOH examination of the scaly skin. In this examination, a small amount of the surface flakes is scraped off the skin onto a glass slide. KOH is added to the scraping, and the slide is viewed under the microscope. Fungal elements can be seen readily with tinea versicolor but not with pityriasis alba.
Another disorder resembling pityriasis alba is vitiligo. The two diseases can be distinguished visually, as the rash of vitiligo has a very distinct border with a sharp line between normal and lighter-colored skin. The patches in pityriasis alba are not totally depigmented as they are in vitiligo. Pityriasis alba is due to reduced activity of melanocytes as well as fewer and smaller melanosomes; in vitiligo, there is total loss of both melanocytes and melanosomes. In terms of distribution, vitiligo also occurs around the mouth and on the distal extremities. Wood’s light examination can be helpful to distinguish between these two entities.
When evaluating a possible case of pityriasis alba, be sure to consider any previous condition that leaves postinflammatory hypopigmentation. Additionally, similar lesions may occur secondary to topical medications, such as retinoic acid, benzoyl peroxide, and steroids. Mycosis fungoides can also present with hypopigmentation.
Treatment of pityriasis alba is not necessary; moreover, no treatment has been shown to speed resolution. Routine use of a moisturizer is helpful, as is avoiding overwashing of affected skin. Since the patches of pityriasis alba do not darken normally in sunlight, effective sun protection helps minimize the discrepancy in coloration against the surrounding normal skin. Although the current textbook management of pityriasis alba consists of low- or moderate-potency topical corticosteroids, these agents may be inadvisable for long-term use because of the potential for skin atrophy and further hypopigmentation, especially on the face. In addition, these corticosteroids have limited efficacy for pityriasis alba. In some patients, cosmetic camouflage may be required. Tacrolimus has also been reported to assist resolution. I prefer using a topical antifungal/antiyeast medication, such as ketoconazole or ciclopirox cream, as it moisturizes the skin and reduces fungal elements that may be generating by-products.
This patient was placed on ciclopirox cream twice daily, and resolution occurred over the ensuing six months. As an aside, his mother was told that his condition was not life-threatening and that he was not contagious and could return to school.
Dr. Burkhart is clinical professor of dermatology at the University of Toledo College of Medicine and clinical assistant professor of dermatology at Ohio University College of Osteopathic Medicine in Athens, Ohio. He has no relationships to disclose relating to the content of this article.