Mechanism of recurrence of pigmented nevi following dermabrasion.

A study was made of pigment freckles which recur after skin abrasion of spotted grouped pigmented nevi, according to the lapse of time, chiefly by means of the fluorescence method of Falck and Hillarp. The mechanism of recurrence is summarized as follows. Nearly simultaneously with the epidermal regeneration, dendritic melanin-producing cells derived from hair follicles and eccrine sweat ducts appear in the basal and prickle-cell layers of epidermis. These cells then create junction activity in the basal layer of epidermis, in the hair follicles and in the eccrine sweat duct walls. Finally, these nevus cells drop off into the underlying layer of scar tissue along the epidermal appendages. The dendritic melanin-producing cells seen in the early regenerative pigment freckles were thought to be incompletely differentiated nevus cells in the pre-stage of junction nevus formation. Appearance of dendritic melanin-producing cells and formation of junction activity in the eccrine sweat duct walls suggest the following possibilities. (1) In the cases of spotted grouped pigmented nevus which we studied, nevus cell proliferation also occurred eccrine-centrically on pathogenesis. (2) An important role is played by the eccrine sweat ducts in the recurrence of ordinary pigmented nevi after incomplete removal. (3) Eccrine-centered nevus cells are derived from nevoblasts in the eccrine sweat duct walls.