Melanosis of the Dermis Degenerative

Dermal degenerative melanosis, or melanocytic metaplasia, is a group of pigmented dermatoses characterized by increased proliferation of melanin-forming cells in the basal layer of the epidermis and the appearance of dysmorphic melanocytes containing atypical melanosomes. These include raceleform nevus, pigmented nevus type OIV, melanoma from pigmented nevus, borderline pigmentary melasma, xeroderma pigmentosum, focal intraepithelial paraneoplastic melanorrhea, vitiligo-like leukedysplastic melanosis. The pathogenesis of melanosis is as follows. Mild irritation of the basal layer of the epidermis leads to the differentiation of poorly differentiated hyperchromic cells along the path of keratinocyte precursors in the basal layers of the epidermis (Raven's syndrome). Increased differentiation of progenitor cells turns into syncytial cutaneous melanomatosis. When it is incompletely removed, islands of melanogenous epidermis remain in the pigmentary type of pigmentary dystrophy (melana) or areas of cellular melanin degeneration (vitiliga). Borderline melasma pigmentosa is characterized by increased exposure to UV radiation and an autoimmune mechanism. Pathological proliferation of epidermal melanocytes and the appearance of abnormal melanocytes contribute to hyperpigmentation.