Nail Lichen Planus — SCE Dermatology MCQ

Correct answer: B — Pterygium

The correct answer is B, pterygium. Dorsal pterygium (pterygium unguis) refers to the permanent scarring destruction of the nail matrix seen in advanced nail lichen planus, where the proximal nail fold fuses to the nail bed and extends as a V-shaped wedge over the nail plate, splitting it in two. This occurs because the lichenoid inflammatory infiltrate destroys the matrix irreversibly, so once pterygium forms it cannot be reversed with treatment, unlike the earlier reversible changes of ridging and thinning described in this patient. Because of this irreversibility, nail lichen planus with early pterygium formation is treated as a dermatological emergency requiring prompt, aggressive immunosuppression (potent topical, intralesional or systemic corticosteroids) to prevent further matrix scarring. Why the other options are wrong: E. Beau lines: these are transverse grooves across the nail plate caused by a temporary interruption of nail matrix growth (eg severe illness), not permanent matrix destruction or fold fusion. D. Onycholysis: this is separation of the nail plate from the underlying nail bed distally, a nail bed problem rather than matrix scarring, and it is often reversible once the cause resolves. A. Koilonychia: this describes spoon shaped concave nail plates, classically from iron deficiency, and reflects a growth abnormality rather than matrix destruction or fold adhesion. C. Onychomadesis: this is complete shedding of the nail plate from the matrix, usually following a severe systemic illness, but the matrix itself typically survives and can regrow a nail, unlike the permanent scarring in pterygium. Key point: Dorsal pterygium, permanent fusion of the proximal nail fold to the nail bed from matrix scarring, is the pathognomonic and irreversible hallmark of advanced nail lichen planus.

Reference: Primary Care Dermatology Society (PCDS), Nail disorders / Lichen planus clinical guidance, pcds.org.uk (accessed 2025), which states that destructive nail lichen planus should be referred urgently to dermatology as early intervention may prevent long-term nail damage including pterygium formation