**Core Concept:** Lichen planus is a chronic, systemic, immune-mediated disorder affecting the skin, mucous membranes, and nails. It is characterized by the presence of a specific pattern of nail changes.

**Why the Correct Answer is Right:** Lichen planus affecting the nails (onych lichen planus) presents with a characteristic pattern of changes, including:

1. **Option C - Subungual hyperkeratosis (off-white, dusky, or yellowish discoloration under the nail:** This is due to the thickening of the nail bed caused by the abnormal keratinization.
2. **Option D - Nail matrix involvement:** Onych lichen planus affects the nail matrix, leading to deformation and irregularities in nail growth.
3. **Option A - Hyponychium involvement (the area between the nail plate and the nail bed):** Onych lichen planus may extend into this area, causing hyponychium pigmentation or discoloration.
4. **Option B - Sudden, painless subungual hemorrhage (bleeding under the nail):** This is a rare manifestation of onych lichen planus, often associated with the underlying disease activity.

**Why Each Wrong Option is Incorrect:**

- Option A (Hyponychium involvement) is not the only nail change in onych lichen planus; it is a less common manifestation.
- Option B (Sudden, painless subungual hemorrhage) is a rare symptom of onych lichen planus and not a characteristic feature.
- Option D (Nail bed involvement) is not specific to onych lichen planus and can be seen in other nail disorders.
- Option E (Onycholysis) is a rare manifestation of onych lichen planus and is not a consistent feature.

**Clinical Pearl:** Lichen planus affects the nail plate, matrix, and nail bed, presenting with a combination of nail changes. Sudden, painless subungual hemorrhage is a rare manifestation and should raise suspicion for underlying disease activity. Monitoring the nail changes over time can help differentiate lichen planus from other nail disorders.