a primary disorder of the skin resulting in violaceous, polygonal, flat skin lesions that often pruritic (itchy). Seen commonly on the wrists, shins, lower back and genitalia. Involvement of the scalp may lead to hair loss. The cause of lichen planus is unknown, but may occur after the use of a drug (thiazide diuretics, phenothiazines, antimalarials). Treatment with topical corticosteroids is common. In most patients, spontaneous regression of the disease will be seen 6 months to 2 years after onset.