Lichen planus.

Lichen planus is an inflammatory mucocutaneous condition with characteristic violaceous polygonal flat-topped papules and plaques. Pruritus is often severe. Skin lesions may be disfiguring, and involvement of the oral mucosa or genital mucosa in severe cases may be debilitating. Oral lichen planus may predispose to the development of squamous cell carcinoma within lesions. Involvement of the scalp and the nails may also occur. While most cases of lichen planus are idiopathic, some may be caused by the ingestion of certain medications (e.g., gold, antimalarial agents, penicillamine, thiazide diuretics, beta blockers, nonsteroidal anti-inflammatory drugs, quinidine and angiotensin-converting enzyme inhibitors) or linked to hepatitis C virus infection. Patients with localized lichen planus are usually treated with potent topical steroids, while systemic steroids are used to treat patients with generalized lichen planus.