Disorders of hypopigmentation in children.

The most common disorders of hypopigmentation in children are pityriasis alba, vitiligo, nevus depigmentosus, and tinea versicolor. Pityriasis alba usually presents as ill defined, scaly patches of hypomelanosis on the cheeks of children with an atopic diathesis. The face is also a favored site for vitiligo, but the distribution is periorificial, and the pigment loss is complete because of a destruction of melanocytes. Vitiligo is an acquired, progressive disorder in contrast to nevus depigmentosus, which is a stable, congenital leukoderma. The localized form of nevus depigmentosus must be distinguished from an ash leaf spot, the earliest cutaneous manifestation of tuberous sclerosis, whereas the systematized form may be confused with hypomelanosis of Ito, another neurocutaneous disorder. The lesions of tinea versicolor favor the upper trunk of adolescents, and potassium hydroxide examination of the associated scale reveals hyphal and yeast forms of P. orbiculare. Any inflammatory process in the skin such as dermatitis or psoriasis can resolve with areas of hypopigmentation.