Lichen planus is a chronic, itchy skin disease of unknown cause, characterized by small, purplish bumps or patches of skin having fine, gray lines on the surface.

Common sites of involvement are the flexor surfaces of wrists, forearms, ankles, abdomen, and sacrum. Nails may have ridges running lengthwise. On mucous membranes (e.g., the mouth), the membranes appear gray and lacy.

Episodes of disease activity, of which there are numerous variations, may last for months and may recur. In more...