This is known as the Koebner phenomenon. The oral mucosa is involved in about 50 percent of the cases. Nails are involved in 10 percent of cases.
It is important to rule out other causes of parallel, streak-like skin lesions, such as Koebner phenomenon due to inflammatory, infectious, or self-inflicted processes, or
phenomenon (development of typical lesions at the site of trauma); keys to diagnosis are purple color and distribution of lesions 20 Skin biopsy is diagnostic and often done