Albinos have defects in melanin production. Vitiligo is due to focal destruction of melanocytes by auto-immune processes. Melanocytes migrate to the skin from the neural crest at the 13th week of embryonic life. Blue naevi are accumulations of dendritic melanocytes in the dermis thought to be due to arrested migration. An increase in numbers of dendritic melanocytes along the dermo-epidermal junction is a lentigo .
Proper name is melanocarcinoma.
Consists of melanocytes which are non-dendritic and malignant. Most occur in the skin but some in the eyes and some in many other sites. They metastasise early and there is no treatment that affects survival when they have metastasised. They metastasis widely including lymph nodes, skin, brain and liver - the only effective treatment is complete excision before they metastasise. Summary Pigments may arise as a part of metabolism or from external sources.