Oral Lichen Planus Associated With Lichen Planus Pigmentosus and Lichen Sclerosus in Monozygotic Twins.

Lichen planus (LP) is a mucocutaneous immune-mediated disease of unknown etiology. It is more prevalent in women and usually occurs between the third and sixth decades of life. Oral lesions may or may not be associated with skin and genital lesions. Although the role of genetic factors is still undetermined, reports of LP in more than one family member are not uncommon. However, the occurrence of LP in monozygotic twins is rare. We report a rare case of 42-year-old female monozygotic twins presenting oral LP. This report is even rarer because one of the patients had cutaneous lesions of an unusual variant of LP (LP pigmentosus) and the other had an uncommon association with lichen sclerosus. The etiology and pathogenesis of LP are still uncertain. However, despite being rare, its occurrence in family members and monozygotic twins suggests that genetic factors are involved in its development.