Nevus anemicus.

Nevus anemicus (NA) is a congenital localized cutaneous anomaly most often seen on the trunk. It represents a pale-colored irregularly shaped patch of histologically normal-appearing skin in which the pharmacological response to certain mediators may be aberrant, with sympathetic vasoconstriction likely responsible for the pallor. Hence, it has been called a pharmacological nevus. NA may be linked with certain genodermatoses, including neurofibromatosis and phakomatosis pigmentovascularis.