Which symptom is most characteristic of rosacea and supports using topical metronidazole as treatment?

• A. Flaky scalp
• B. Pustular acne on trunk
• C. Eye irritation without facial redness
• D. Persistent facial redness with visible blood vessels

Answer: (D)

Rosacea is defined by chronic facial redness with visible blood vessels (telangiectasia) and a low-threshold to inflammatory flares. This persistent facial erythema with visible vasculature is the feature most characteristic of rosacea and is what topical metronidazole is intended to treat, since it has anti-inflammatory effects that help reduce both redness and inflammatory papules/pustules on the face. The other symptoms point to different conditions: flaky scalp suggests seborrheic dermatitis, pustular acne on the trunk is not rosacea, and eye irritation without facial redness could be unrelated ocular irritation or a different diagnosis. Thus, the presence of persistent facial redness with visible blood vessels best supports using topical metronidazole.