Lichen planus may involve mucous membranes in addition to skin; which sites are commonly involved?

• A. Extensor surfaces of extremities, mouth, scalp, genitals, nails, mucous membranes
• B. Palms only
• C. Molds on nails
• D. Oral ulcers only

Answer: (A)

Lichen planus is a mucocutaneous inflammatory condition, meaning it can affect both the skin and mucous membranes. A hallmark pattern is involvement beyond the skin, especially the oral mucosa, which is the most common mucosal site, and it can extend to genital mucosa. It can also involve the scalp, leading to scarring alopecia, and the nails, causing changes such as ridging or thinning. Because this option lists mouth, scalp, genitals, nails, and mucous membranes alongside skin involvement, it best reflects the typical distribution of lichen planus. Other choices are too limited or describe non-applicable findings (like molds on nails or only oral ulcers).