Pterygium of the nail occurs at the hyponychium or which other nail fold?

• A. Eponychium
• B. Lunula
• C. Matrix
• D. Nail bed

Answer: (A)

Pterygium of the nail is fibrous scarring that binds the nail folds to the nail plate, leading to distortion as the plate is pulled and cannot lift freely. This process can involve the distal hyponychium or the proximal nail fold, known as the eponychium. The eponychium is the proximal nail fold that covers the matrix area, so involvement of that fold is the other common site besides the hyponychium. The other structures listed are not folds where pterygium typically forms: the lunula is just the visible part of the matrix, the matrix itself is the nail-forming tissue, and the nail bed lies beneath the nail plate.