Linear and whorled nevoid hypermelanosis.

A case of hyperpigmentation distributed in streaks and whorls was recently delineated and separated from a confusing number of pigmentary disorders. A 13-year-old boy had hyperpigmented, reticulate spots on his trunk and neck in a linear and whorled distribution following the lines of Blaschko. Onset was at age 1 year. Histologically, the spots showed increased melanin in the basal layer of the epidermis, but no increase in melanocytes, incontinence of pigment, or melanophages were seen in the dermis. The karyotype was 46,XY and there was no evidence of chromosomal mosaicism or chimerism. This entity represents a disorder separated recently from other pigmentary alterations that follow Blaschko lines, such as Bloch-Sulzberger incontinentia pigmenti, hypomelanosis of Ito, early systematized epidermal nevus, and chimerism.