**Question:** Differential diagnosis of rosacea includes all of the following except?

A. Eczema
B. Psoriasis
C. Acne vulgaris
D. Lichen planus

**Core Concept:** Rosacea is a chronic inflammatory skin disorder predominantly affecting the face, characterized by persistent facial redness, papules, and pustules. It is distinct from eczema, psoriasis, acne vulgaris, and lichen planus.

**Why the Correct Answer is Right:** Rosacea is distinct from the other options due to its specific clinical features and course. Eczema (atopic dermatitis) is a chronic inflammatory skin disorder with a distinct clinical appearance and different distribution patterns. Psoriasis is a different inflammatory skin disorder characterized by scaly plaques on extensor surfaces and scalp. Acne vulgaris is a condition specific to the skin appendages, with comedones, papules, and pustules concentrated in the pilosebaceous units, while rosacea affects the central face. Lichen planus is a different inflammatory skin disorder affecting the skin and oral mucosa, with a distinct clinical appearance, different distribution, and distinct pathogenesis.

**Why Each Wrong Option is Incorrect:**

A. Eczema: Eczema is characterized by a distinct clinical appearance, distribution, and pathogenesis compared to rosacea.
B. Psoriasis: Psoriasis is a different inflammatory skin disorder with distinct clinical features and distribution patterns, not involving the central face like rosacea.
C. Acne vulgaris: Acne is a condition specific to the skin appendages with comedones, papules, and pustules concentrated in the pilosebaceous units, while rosacea affects the central face.
D. Lichen planus: Lichen planus is a different inflammatory skin disorder affecting the skin and oral mucosa, with a distinct clinical appearance, distribution, and pathogenesis compared to rosacea.

**Core Concept:** It is essential for medical students and practitioners to accurately differentiate between these skin disorders to provide appropriate management and avoid unnecessary treatments or misdiagnosis. Differentiating clinical features, distribution, and pathogenesis are critical for accurate diagnosis and treatment planning.