**Core Concept:** Lichen planus is a chronic immune-mediated disease affecting the skin, oral mucosa, and internal organs. It presents with polymorphic lesions, including white papules and plaques with leukonychia (white nail plates) due to melanin pigment release. Lichen planus is characterized by an abnormal activation of T-cells against basal cells, leading to keratinocyte apoptosis and inflammation.

**Why the Correct Answer is Right:** The correct answer is "D," which refers to the clinical picture described in the question. Lichen planus presents with polymorphic lesions, which include white papules and plaques with leukonychia (white nail plates) due to melanin pigment release. These lesions are typically found on the skin, oral mucosa, and nails, as seen in the presented case.

**Why Each Wrong Option is Incorrect:**
A. Lichen planus does not exclusively present with bilateral lesions and lacks the characteristic nail changes, making it an incorrect choice.
B. Lichen planus does not exclusively present with lesions on the buttocks and anogenital region, while the case described presents with lesions on the skin and oral mucosa.
C. Lichen planus is not characterized by the presence of "red papules" and lacks the nail changes described in the case, making it an incorrect choice.

**Clinical Pearl:** Lichen planus is an important clinical diagnosis to consider for patients presenting with white papules and plaques, particularly when associated with nail changes. Early recognition and referral to a dermatologist are crucial for proper diagnosis and management, as lichen planus can progress to oral mucosa and can lead to complications like mucosal ulceration and malignant change.