Answer: Can you identify this condition?

3. Nevus depigmentosus

Nevus depigmentosus (ND) is an uncommon skin pigmentation disorder characterized by asymptomatic, solitary or multiple, nonprogressive, hypochromic lesions presenting at birth or shortly afterward.^1–4 It most commonly affects the trunk, and the lesions usually remain relatively stable in shape, size, and texture throughout life. In 1967, Coupe¹ proposed the following clinical criteria for diagnosis of ND: leukoderma presenting at, or shortly after, birth; no change in leukoderma distribution, texture, or sensation throughout life; and no surrounding hyperpigmented border.¹ Three patterns of ND have been recognized: an isolated irregular or circular macule involving a small localized part of the body; a unilateral patch or streak presenting in a segment or following the lines of Blaschko; and, rarely, a systemic variant characterized by multiple whorls, although the latter is considered by some to be in part hypomelanosis of Ito.^1–4 The rare systemic variant is commonly associated with extracutaneous manifestations, such as hemihypertrophy, mental retardation, and seizures, which in fact only occur in up to 10% of such cases.^2–4 Our patient had segmental ND, with sharp demarcation at the abdominal midline and no associated systemic abnormalities. In typical cases of ND, results of histologic testing indicate a substantial decrease in the amount of melanin in the lesional skin, while melanocyte counts (usually evaluated using melanocyte markers such as S-100 or Melan-A) might or might not be decreased; these findings were consistent with our patient’s histology results.

The pathogenesis of ND is not completely clear. It occurs sporadically, with no familial tendency. Many believe that it is probably related to a developmental defect of fetal melanocytes, resulting in defective melanosome transfer from melanocytes to keratinocytes.^2–4

Differential diagnosis

Clinical differential diagnosis of ND should include vitiligo, tuberous sclerosis, and nevus anemicus.^2–7 Vitiligo is usually an acquired condition characterized by depigmented macules with discrete borders. The macules commonly involve normally hyperpigmented areas, such as the face, areolae, and intertriginous areas, and areas subject to friction, such as distal acral sites.⁵ On Wood lamp examination, vitiligo lesions commonly show chalky-white accentuation. Histologically, vitiligo lesions are totally devoid of skin pigment and melanocytes.⁵ Unlike ND, tuberous sclerosis is a genodermatosis that can be distinguished clinically based on other associated cutaneous manifestations (eg, facial angiofibromas, shagreen patches, and ungual fibromas) as well as associated systemic involvement (eg, central nervous system, heart, kidneys, and lungs).⁶ Nevus anemicus, a congenital vascular anomaly with localized hypersensitivity to catecholamines, commonly presents as hypopigmented macules or patches, which (unlike ND) fail to show vasodilatation or erythema upon rubbing of the affected area.⁷

Management

Nevus depigmentosus is a benign condition and does not require specific treatment. Management centres on making the correct diagnosis and checking for any associated extracutaneous features, particularly when the patient has the segmental or systemic variant of ND. Our patient had no associated abnormalities.