Pityriasis rotunda in childhood.

Pityriasis rotunda is a rare disease characterized by round or oval patches, localized mainly on the trunk, arms, and legs. The patches are usually lighter than the surrounding skin, but sometimes may be darker, and are covered by fine, adherent scales. Two types of pityriasis rotunda have been described. Type I has been observed mainly in oriental and black patients older than 60 years of age, and is often associated with systemic disease or malignancy. Type II has been observed in white patients younger than 40 years of age, is often familial, and has never been observed in association with malignancy or internal disease. On Sardinia, a cluster of patients with type II pityriasis rotunda has been described. From 1981 until 1998, 51 cases of this disease have been observed in the Department of Dermatology, University of Sassari; 32 of them were children. The great prevalence of pityriasis rotunda on Sardinia, an island which until 40 years ago had limited contact with the Italian mainland, and the presence of a large number of familial cases suggest that type II pityriasis rotunda should be considered a genetically determined disease. The trend toward spontaneous resolution after the age of 20 years suggests that pityriasis rotunda should be considered a genodermatosis with a temporary phenotypic expression.