**Question:** 30-year old Basanti presents with light brown lesions involving both her cheeks. The lesions had never been erythematous. Which of the following is the most probable diagnosis:

A. Melasma
B. Vitiligo
C. Lichen Planus
D. Dermatitis

**Core Concept:**
Melasma, Vitiligo, Lichen Planus, and Dermatitis are common skin conditions presenting with pigmentary changes. However, distinguishing between them is crucial for appropriate treatment and management.

**Why the Correct Answer is Right:**
The correct answer is **B. Vitiligo** because Basanti's lesions are light brown, non-erythematous (not red), and involve the cheeks. Vitiligo is an autoimmune disorder where the immune system attacks melanocytes, causing hypopigmentation in the affected areas.

**Why Each Wrong Option is Incorrect:**

**A. Melasma:** Melasma is characterized by symmetrical, hyperpigmented macules on sun-exposed areas, with a tendency to worsen in pregnancy and with oral contraceptive use. In Basanti's case, the facial involvement and non-erythematous nature point more towards Vitiligo.

**C. Lichen Planus:** Lichen Planus is a chronic, immune-mediated disorder affecting both skin and mucous membranes. It presents with violaceous, polygonal papules and plaques on the extensor surfaces of extremities, buccal mucosa, and genitalia. The non-erythematous nature and facial involvement in Basanti's case favor Vitiligo over Lichen Planus.

**D. Dermatitis:** Dermatitis refers to inflammation of the skin, which can present with various clinical features, not limited to pigmentary changes. It is unlikely to manifest as non-erythematous, non-inflammatory patches on the cheeks.

**Why Vitiligo is the Correct Answer:**
Vitiligo presents as non-inflammatory, non-erythematous patches on the sun-exposed areas like the face. In this case, the non-erythematous patches on the cheeks and their distribution indicate Vitiligo.

**Clinical Pearls:**
1. Non-erythematous, non-inflammatory patches on the cheeks suggest Vitiligo, which is an autoimmune disorder targeting melanocytes.
2. The face is a common site for Vitiligo presentation due to increased melanin production in the surrounding unaffected skin, creating a contrasting white patch.
3. The non-inflammatory and non-erythematous nature of the lesions in Basanti's case makes Vitiligo more likely than Melasma, Lichen Planus, and Dermatitis.