Nevus Depigmentosus

Definition and Cutaneous Features

Photo courtesy of OLIVA Opens in new window

Nevus depigmentosus (also called achromic nevus) is a well circumscribed area of hypopigmentation Opens in new window that may occur as a small isolated (circular or rectangular) patch, or develop in a unilateral segmental distribution or follow the lines of Blaschko, the latter having some clinical resemblance to the pattern seen in hypomelanosis of Ito Opens in new window. In one study, nearly one-half had only one lesion, but a fifth of patients had more than 10 lesions.

Hair within a nevus depigmentosus may also be hypopigmented, and the margins may be irregular or serrated. The isolated form is the most common and the lesions do not usually cross the midline.

In the majority of cases the lesions are present at birth or become evident shortly thereafter, and remain stable in size and shape. Increase in size is in proportion to the growth of the child.

Some lesions may appear after 1 year of age. Under Wood’s lamp Opens in new window, lesions have an off-white accentuation with unilateral lentiginosis and ILVEN has been reported.

Males and females are affected equally and there is no distinct pattern of inheritance. The hypothesis is that during embryogenesis a clone of cells with a reduced melanogenic potential arises via a postzygotic somatic mutation.

The back and buttocks are the most commonly affected sites, followed by the chest and abdomen. Lesions remain stable over time.

Extracutaneous Findings

Systemic manifestations are rare in patients with nevus depigmentosus. Neurologic abnormalities such as seizures Opens in new window and mental retardation Opens in new window have been reported, as well as ipsilateral hypertrophy of the extremities.

In a survey of 50 patients with nevus depigmentosus, none had any extracutaneous features on examination. In two studies involving 29 patients with nevus depigmentosus, extracutaneous abnormalities were present in about 10% of the children.

Occasionally, lentigines can develop within the achromic nevi, and this could be explained by the reversion of a mutation in one of the genes involved in pigmentation.

Pathogenesis

With dopa-staining, normal melanocytes are seen in nevus depigmentosus and electron microscopic studies suggest a reduced synthesis of melanosomes and also a defect in their transfer to the keratinocytes, which could account for the hypopigmentation Opens in new window.

Transfer of melanosomes from melanocytes to keratinocytes is essential for normal pigmentation.

Differential Diagnosis

Other entities with which nevus depigmentosus is sometimes confused include nevus anemicus Opens in new window, segmental vitiligo Opens in new window, hypopigmented lesions of tuberous sclerosis Opens in new window, and hypomelanosis of Ito Opens in new window.

The distinction between nevus depigmentosus and hypomelanosis of Ito Opens in new window may be artificial, as many patients with segmental hypopigmented macules also have linear pigmentary anomalies, similar to those seen in hypomelanosis of Ito, and underlying mosaicism is the common factor.

Patients currently diagnosed with either of these conditions might simply be categorized as having nevoid hypopigmentation with or without extracutaneous anomalies.

Cytogenetic analysis, which entails analysis of peripheral blood lymphocytes and skin fibroblasts, should be considered in all patients with segeental or linear pigmentary abnormalities and extracutaneous abnormalities to look for chromosomal mosaicism.

Therapeutics

One patient with a nevus depigmentosus had partial repigmentation following autologous melanocyte grafting, but otherwise there is no effective treatment. Cosmetic camouflage may be helpful.