Nevus depigmentosus or nevus achromicus consists of a single large irregular-shaped area of completely depigmented or sometimes hypopigmented skin which is strictly unilateral and is usually limited to a single neural segment. Sometimes the lesions may be small and multiple but these are still unilateral and segmental.
Nevus depigmentosus is uncommon, appears mostly as a unilateral hypopigmented macular patch with irregular, serrated borders, and as a rule, the lesions do not cross the midline. Unilateral hypertrophy of the extremities on the same side of nevus depigmentosus has been described.
Types of Nevus Depigmentosus
There are three clinical variants
- Single, circumscribed, rounded or oval lesion – the commonest form
- Segmental (dermatomal) nevus depigmentosus
- Systematized form with whorls or streaks predominantly in a unilateral fashion. Resembles hypomelanosis of Ito
Types Based on Size
Type I nevus depigmentosus (ND)
Lesion is <10 cm. It is the most common localized depigmentation seen in healthy newborns. May be confused with nevus anemicus
Type II ND simplex
Lesion is >10 cm. It develops during early childhood and presents with a checkerboard or a linear pattern. It should be differentiated from segmental vitiligo.
Cause and pathogenesis of nevus depigmentosus are not fully understood. Light microscopy shows either a normal number or a decreased number of melanocytes.
On electron microscopy, a large reduction in the number of melanosomes and aggregated melanosomes is visible.
Clinical Diagnostic Criteria
- Hypopigmentation which presents at birth or has an onset early in life
- No alteration in the distribution of hypopigmentation throughout life
- No alteration in texture, or change of sensation, in the affected area
- No hyperpigmented border around the achromic area.
- The hypopigmentation is permanent and enlarges in proportion with the growth of the person
- Nevus anemicus
- Ash leaf spot
- Hypomelanosis of Ito.
In contrast to the lesions of segmental vitiligo, the lesion in nevus depigementosus is usually present at birth or may appear early in life but it does not increase in size later. It may also be mistaken for nevus anemicus, but it does not lack the erythema response following friction.
The melanocytes in nevus achromicus are normal and have normally pigmented melanosomes but these are unable to transfer their melanosomes to the keratinocytes.
No effective treatment is available yet.
The only method of treating such a lesion is to cover it with appropriate cosmetics or to stain the skin with one percent solution of potassium permanganate. The concentration of potassium permanganate can be altered to exactly match the color of the skin of the individual.
The stain with potassium permanganate lasts for nearly 24 hours and the application has to be repeated every day. Alternatively, the lesion can be excised surgically to be followed by skin grafting, if necessary. Otherwise, the lesion can be left alone.