This consists of a single large irregular-shaped area of completely depigmented or sometimes hypopigmented skin which is strictly unilateral and usually limited to a single neural segment. Sometimes the lesions may be small and multiple but these are still unilateral and segmental.
In contrast to the lesions of segmental vitiligo, the lesion in nevus achromicus 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 anaemicus, 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.
Treatment
The only method of treating such a lesion is to cover it with appropriate cosmetics or to stain the skin with one per cent solution of potassium permanganate. The concentration of potassium permanganate can be altered to exactly match the colour 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.