Pruritic, polygonal, flat-topped, violaceous papules are seen in

Lichen planus is an inflammatory T cell mediated autoimmune disorder affecting the skin, hair, nail and mucous membranes. Characterised by 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. Close examination of the surface of these papules often reveals a network of gray lines (Wickham's striae). The skin lesions may occur anywhere but have a predilection for the wrists, shins, lower back, and genitalia. Involvement of the scalp (lichen planopilaris) may lead to scarring alopecia, and nail involvement may lead to permanent deformity or loss of fingernails and toenails. Harrison 19e pg: 349