Linear and whorled nevoid hypermelanosis.

Two cases are presented of congenital linear and whorled hypermelanosis. Hyperpigmented macules in streaky configurations along Blaschko's lines appeared gradually after birth. Histologic examination revealed prominent epidermal melanocytes and irregular basal layer hyperpigmentation with normal melanosomes. This condition must be differentiated from incontinentia pigmenti, early systematized epidermal nevus, extensive hypomelanosis of Ito, and chimerism. Other similar case reports from the literature suggest that incidence is sporadic and may be associated with more serious congenital anomalies. The patterning is the inverse to that found in hypomelanosis of Ito. Developmental somatic mosaicism may be responsible for this patterned hypermelanosis.