Melanocytic Naevi and Malignant Melanoma

Abstract

Alterations in the melanin pigmentation of the skin produce abnormal duskiness or whiteness and may be due to many factors. Lightening of the skin may be due to a deficiency of melanin, or a reduction in the number of melanocytes. In albinism there are normal numbers of melanocytes, whereas in vitiligo the number of melanocytes is reduced or absent. This change is difficult to judge in ordinarily stained histological sections but can be assessed by quantitative electron-microscopic studies1, or by performing a DOPA oxidase histochemical test. In a similar fashion, darkening of the skin may be caused by an increase in epidermal or subepidermal melanin or an increase in the number of melanocytes. Thus in Addison’s disease there is an increase of activity of the cutaneous melanocytes without an alteration in their number, whereas in naevi and melanoma the abnormal pigmentation is associated with melanocytic hyperplasia.