Pigmentary mosaicism This condition is characterized by areas of hypopigmentation following the lines of Blaschko. These are present from birth or evolve during early childhood. The lesions may be generalized, with individual areas of hypopigmentation assuming blotchy, whorled, or streaked patterns.

A very small number of patients with this pigmentary disorder have central nervous system disease, usually manifest as seizures or mental retardation. Other reported abnormalities include skeletal and ocular defects. This condition was formerly called hypomelanosis of Ito or incontinentia pigmenti achromians.

Pigmentary mosaicism In this form of mosaicism, there are lines of hyperpigmentation that follows lines of Blaschko. In this patient, there is a linear pattern on the extremities and a whorled pattern on the trunk. This condition was formerly referred to as “linear and whorled nevoid hypermelanosis.” The hyperpigmentation may be present at birth or develops shortly thereafter, spreading during the first 2 years of life, at which time it stabilizes.

Nevus depigmentosus (achromicus) These are localized areas of hypopigmentation that are usually present at birth. The lesions may be irregular in size and shape and occasionally follow a linear or segmental pattern. Electron microscopic study of these areas suggests that melanosomes are not being transferred from melanocytes into surrounding keratinocytes. There are no associated abnormalities. It is best considered as a more subtle form of pigmentary mosaicism, also resulting from a somatic mutation during embryogenesis.

Nevus anemicus This benign lesion develops at birth or in early childhood. Rubbing the area causes the surrounding skin to turn red, while the area itself maintains its white color. Nevus anemicus does not represent a loss of pigment, but rather a constriction of blood vessels, due to a local increased sensitivity to catecholamines.

Carotenemia The vegetable pigment carotene is widely distributed in carrots, lettuce, squash, and many other vegetables and fruits. A diet that is very rich in these foods results in a yellowish-orange discoloration of the skin. This appearance is usually localized to the palms and soles (note the hand on the left in Fig. 27-6) but may also involve the skin of the face. The presence of normal sclera distinguishes the clinical appearance of this condition from that of jaundice. Return to normal skin color follows a reduction in dietary intake of carotene.

Waardenburg syndrome This genetic disorder is transmitted as an autosomal dominant, with variable penetrance. It is characterized grossly by partial albinism in the form of a white forelock (Fig. 27-7), broad nasal root (Figs. 27-7 and 27-8), hypertrichosis of the inner portions of the eyebrows, lateral displacement of the medial canthi (Figs. 27-7 and 27-8), partial or complete heterochromia of the irides (Fig. 27-8), and complete or unilateral deafness. In children with skin of color, blue irides, vitiligo, and pigmentary changes in the fundi may be seen. There are no other constitutional symptoms, but the hearing loss and unusual appearance may pose handicaps.