lichen planus, a nonmalignant, chronic, pruritic skin disease of unknown cause that is characterized by small flat purplish polygonal papules or plaques with fine gray lines on the surface. Common sites are flexor surfaces of wrists, forearms, ankles, abdomen, sacrum, and genitalia. On mucous membranes the lesions appear gray and lacy. Nails may have longitudinal ridges. Episodes of disease activity vary but may last for months and may recur. Treatment with topical corticosteroids is common.
