## **Core Concept**
Lichen planus is a chronic inflammatory condition that affects the skin, mucous membranes, and other areas, including the nails. The condition can manifest in various ways, including skin lesions, oral lesions, and nail changes. Nail involvement in lichen planus can lead to several characteristic changes.

## **Why the Correct Answer is Right**
The correct answer, **Pterygium formation**, is a characteristic nail finding in lichen planus. Pterygium formation refers to the scarring process that leads to the formation of a band of fibrotic tissue in the proximal nail fold, which can cause the nail plate to become adherent to the overlying tissue or result in the obliteration of the nail plate. This occurs due to the inflammatory process and scarring associated with lichen planus. The condition can lead to permanent damage and deformation of the nail.

## **Why Each Wrong Option is Incorrect**
- **Option A: Subungual hyperkeratosis** is more commonly associated with conditions like psoriasis or fungal infections rather than lichen planus.
- **Option B: Splinter hemorrhages** are typically seen in conditions like endocarditis or vasculitis, not lichen planus.
- **Option C: Onycholysis** (separation of the nail from the nail bed) can occur in various conditions, including psoriasis and trauma, but is not the most characteristic feature of lichen planus.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl for lichen planus involving the nails is that **pterygium formation and nail plate thinning** are highly suggestive of the condition. Lichen planus can cause significant morbidity, and early recognition of its manifestations, including nail changes, is crucial for management.

## **Correct Answer:** D. Pterygium formation