Pigmentary mosaicism.

Pigmentary mosaicism refers to patterned hypo- and/or hyperpigmentation that results from genetic heterogeneity of skin cells. The most common clinical patterns are streaks and swirls following Blaschko's lines in narrow or broad bands and a block-like distribution. This contribution provides an update on the diverse genetic etiologies, cutaneous findings, potential associated extracutaneous abnormalities, and management of various forms of pigmentary mosaicism. Current terminology, the recent reappraisal of the classic patterns based on scientific advances, and distinct clinicogenetic entities are highlighted. A practical approach to the diagnosis and evaluation of patients with pigmentary mosaicism is provided, including clues to distinguish other conditions in the differential diagnosis and applications of advances in genetic testing technology.