Which description best fits lichen planus?

• A. Purple, polygonal, planar, pruritic papules with fine scales & irregular borders on extensor surfaces of extremities, skin, mouth, scalp, genitals, nails, and mucous membranes. May develop Koebner phenomenon (new lesions at site of trauma).
• B. Erythematous scaly plaques on elbows and knees only
• C. Vesicular lesions on mucosa with fever
• D. Nodular lesions on trunk with central necrosis

Answer: (A)

Lichen planus presents with intensely pruritic, violaceous papules that are polygonal and flat-topped, often with fine white lines across the surface (Wickham striae). These lesions can involve skin on various surfaces and frequently affect mucous membranes, nails, and genitals, and trauma can trigger new lesions at the injury site (Koebner phenomenon). The description here captures all of that: purple, polygonal, planar, pruritic papules with fine scales and irregular borders appearing on multiple sites including mucous membranes, with Koebnerization. Other options describe features more typical of psoriasis, viral mucosal vesicles with fever, or nodular lesions with necrosis, which don’t fit lichen planus.