This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Papulosquamous disorders, Subject name: Dental
Characterstic nail finding in lichen planus - 
Select and explain. 
A. Pitting, B. pterygium, C. Beau's Lines, D. Hyperpigmentation of nails
B: pterygium
Answer: B: pterygium 
Explanation: NAIL CHANGES IN LICHEN PLANUS: 1.Early change- bluish red discolouration of proximal nail fold. 2.thinning of nail plate, koilonychia, longtudinal ridging, splitting(onychoschizia) 3. pterygium formation-wing shaped growth of proximal nail fold across the nail plate due to severe nail matrix involvement. it is a characteristic nail change in lichen planus 4. pup tent sign: proximal onycholysis with elevation of nail plate and longitudinal splitting ue to involvement of nail bed. 5. anonychia 6. melanonychia IADVL textbook of dermatology, page 1075