**Question:** Recurrent erythematous plaques on glans penis in a 21 yrs old sexually active male which heals with residual hyperpigmentation, is suggestive of ?

**Core Concept:** Lichen Planus is a chronic inflammatory disease of the skin, mucous membranes, and sometimes internal organs, characterized by the formation of flat, reddish-brown, or violaceous, well-demarcated, papular lesions, with a characteristic "target" appearance. These lesions are typically asymptomatic but can cause pruritus occasionally. Lichen Planus usually affects adults and is more common in females. The exact etiology is unknown, but it is believed to be an immune-mediated reaction involving T-cells and antigen-presenting cells.

**Why the Correct Answer is Right:** The correct answer (C) is suggestive of Lichen Planus because:

1. **Relevant Clinical Presentation**: The patient presents with recurrent erythematous plaques on the glans penis, which is a common site for involvement in Lichen Planus.
2. **Healing with Residual Hyperpigmentation**: Lichen Planus typically results in the formation of well-demarcated, flat, and violaceous papules that heal without scarring. Residual hyperpigmentation is a common feature of Lichen Planus and helps to differentiate it from other skin conditions.
3. **Immune-mediated reaction**: Lichen Planus is an immune-mediated reaction involving T-cells and antigen-presenting cells, which aligns with the correct answer choice (C).

**Why Each Wrong Option is Incorrect:**

**Option A:** Lichen Planus does not typically cause pruritus, as it is usually asymptomatic. This makes option A incorrect.

**Option B:** Lichen Planus presents with characteristic "target" lesions, not "nail changes" as seen in the wrong answer choice (B).

**Option D:** Lichen Planus primarily affects adults, while the patient in question is a 21-year-old male, making option D less likely.

**Option E:** Lichen Planus does not involve the oral mucosa, which is a common site for involvement in this case, making option E incorrect.

**Clinical Pearl:** Lichen Planus is a chronic inflammatory disease with a complex etiology involving T-cells and antigen-presenting cells. Lichen Planus can affect various sites, including the genitalia, and may present with asymptomatic lesions or mild pruritus. Understanding the clinical presentation, histopathology, and the age range can help differentiate Lichen Planus from other skin conditions.