Lichen planus pigmentosus and its variants: review and update.

Lichen planus pigmentosus (LPP) is considered a rare variant of lichen planus (LP). It is characterized by acquired dark brown to gray macular pigmentation located on sun-exposed areas of the face, neck, and flexures, commonly found in dark-skinned patients. In patients with LPP, an inflammatory lichenoid response results in marked pigmentary incontinence. It has been associated with hepatitis C virus, sun exposure, and contactants such as mustard oil and nickel. LPP-inversus affects fair and dark skin, predominantly involving flexural and intertriginous areas, while sun-exposed areas are spared; friction is an associated trigger. LPP along Blaschko's lines has been associated with susceptibility to genetic mosaicisms. LPP can present concomitantly with other variants of LP such as frontal fibrosing alopecia, as well as endocrinopathies, and autoimmune diseases. Treatment is difficult and consists of avoidance of triggers and topical and systemic medications in order to stop the inflammatory reaction and reduce pigmentation, improving aesthetic appearance and quality of life.