Nevus Depigmentosus

A nevus depigmentosus (ND) is a common, well-circumscribed hypopigmented patch that can be seen at birth or becomes apparent later infancy or early childhood as the surrounding skin pigmentation increases.
Although the name implies absence of pigment, ND are usually hypopigmented and have reduced pigment but not a total lack of pigment.
ND are usually an isolated finding.

Presents as a solitary, hypopigmented (flat) macule or patch with well-defined irregular borders (Fig. 1.31).
ND can occur anywhere on the skin but are typically seen on the trunk and grow proportionately with child.
Persists lifelong, remains unchanged.
Occasionally, can present as multiple lesions or as a linear and/or segmental lesion (Fig. 1.32).
When more extensive, the term pigmentary mosaicism or segmental pigmentation disorder is applied.
If multiple small lesions are present, ND must be distinguished from an ash leaf macule that is associated with the neurocutaneous genetic disorder, tuberous sclerosis (see Chapter 11: Neurocutaneous Syndromes).

Hypopigmentation at birth sometimes presents in a more widespread, patterned distribution such as block-like or a checkerboard pattern; or as streaks and swirls along the lines of Blaschko (Fig. 1.33).
This type of patterned pigmentation was previously termed hypomelanosis of Ito but now pigmentary mosaicism or segmental pigmentation disorder are the preferred terms.
Alternatively, there can be patterned hyperpigmentation on the skin at birth or developing shortly thereafter (also called linear and whorled nevoid hypermelanosis) (Fig. 1.34).
Although programmed in utero, sometimes these birthmarks do not become apparent until the first few years of life when pigmentation increases.
Parents are often frightened because the pigment alteration can be extensive.
Cells within the hypo- or hyperpigmented area of skin reflect genetic mosaicism whereby a clone of cells were programmed during embryologic development to make more or less pigment.
Associated systemic findings usually of the neurologic, musculoskeletal, or cardiac system are found in a minority of patients with pigment alterations along Blaschko lines and workup should be symptom-directed.
In the vast majority of patients this patterned hypo- or hyperpigmentation is merely a cosmetic issue.

Differential Diagnosis

Vitiligo

Ash-leaf Macule

Hypopigmented oval or leaf-shaped macules and patches; usually multiple are present.
Other clinical features of tuberous sclerosis may be present.

Pityriasis Alba (P. alba) or Postinflammatory Hypopigmentation (PIH)

In older children, P. alba may be confused for ND.
P. alba or PIH presents as ill-defined areas of hypopigmentation on the face or arms often associated with background xerosis or atopic dermatitis.

Management

Patients with ND should have a complete physical examination to determine extent of lesion and presence of other skin findings.
ND are benign and nonprogressive and parents can be reassured.
Specific treatment is not necessary.
For lesions in cosmetically sensitive areas or for those who desire treatment, autologous skin grafting and transfer with melanocyte-rich suspensions have been successful in some cases.
There are also reports of improvement with excimer laser (308 nm) treatments.
Cosmetic cover-up is also an effective albeit temporary treatment.

Helpful Hint

When in doubt the use of a Wood lamp will help distinguish an ND which will appear milky white, from vitiligo which will appear chalk white.

Points to Remember

Large and patterned areas of hypo- or hyperpigmentation (aka pigmentary mosaicism) is a relatively common birthmark that sometimes does not become apparent until later in infancy and is usually only a cosmetic issue.
Although the name implies lack of pigment, ND are hypopigmented.