Trauma as triggering factor for development of melanocytic nevi.

The mechanisms for the development of acquired melanocytic nevi remain mostly unclear. Here we report a case of eruptive nevi that developed after localized superficial trauma, and review the currently known cellular and triggering factors for acquired melanocytic nevi. A 66-year-old woman presented a linear arrangement of pigmented macules on her left calf that developed after a bloodless skin erosion on the same spot, resulting from friction with the lining of a ski boot. Dermatopathology identified multiple junctional proliferations of single or small nest-forming melanocytes with bridging, pigment incontinence and moderate cellular atypia. The number of a person's nevi correlates with age, race and genetics, but blistering diseases, scarring processes, light exposure and immunosuppression can contribute to nevocellular growth as well. Damaged keratinocytes and inflammatory cells can release growth factors inducing nevus cell proliferation, and immunosuppression could end cellular surveillance keeping preexisting nevus cell nests in check. We conclude that in predisposed patients, the trigger for eruptive nevi can be reduced to a simple localized minor trauma.