Are These Pale Patches Vitiligo-or Something More Benign?

Case:  The parents of this 8-year-old girl have brought her for evaluation of areas of loss of pigment on her face. They are worried that these might represent the beginnings of vitiligo.

What morphological features can help you sort through the differential diagnosis of this girl's condition and either rule out or confirm her parents' fears of vitiligo?

 (Answer on next page)

It is common for the parents of darkly pigmented children to be frightened by a loss of skin pigment in their child; it seems that everyone knows someone who has lost all of their skin pigment to vitiligo. However, this child has pityriasis alba, the skin condition most commonly confused with vitiligo.

In vitiligo, there is complete loss of the pigment in the skin but no other skin changes. Clues that pityriasis alba is the correct diagnosis are an incomplete loss of pigment, commonly associated with subtle skin changes of erythema and scaling within the hypopigmented patches, as seen in this patient. Also, the borders of the hypopigmented areas are less distinct than in vitiligo, in which the hypopigmented areas are typically sharply demarcated.

Pathophysiology of pityriasis alba. Pityriasis alba represents postinflammatory hypopigmentation secondary to a very subtle eczema of the skin. It is most common on the cheeks but can also appear on the upper outer arms in association with keratosis pilaris. It is typically first noticed during the summer months, when the contrast between normal skin and the area of hypopigmentation increases. However, the condition almost certainly begins during the winter months, when a reduction in relative humidity, washing with soap and water, and an absence of emollients result in the development of a mild eczema. This eczema disturbs the transfer of melanosomes from the melanocyte to the keratinocyte, which is revealed when the UV light of summer stimulates pigmentation.

Treatment of pityriasis alba. Therapy for pityriasis alba consists of treatment of its eczematous component. A low-potency topical corticosteroid will reduce the inflammatory component, and emollients will repair the skin barrier. Once the eczema is treated, pigmentation will slowly return. Advise parents that it takes many months for the pigment to return to the skin and that the condition is likely to recur throughout childhood and early adolescence.