An old woman has GAD (General Anxiety Disorder) lesions on the LEFT cheek inside the mouth on the mucosa AND outside on the face, that did NOT cross the midline. What is the diagnosis?

Correct answer: C. Shingles (herpes zoster)

• A. Incorrect. Measles causes bilateral oral Koplik spots and a generalized (not unilateral) facial rash.
• B. Incorrect. Herpetic stomatitis (HSV-1) affects the oral mucosa bilaterally and commonly causes recurrent lip lesions (herpes labialis) — it does NOT follow a strict unilateral dermatomal pattern.
• C. Correct. Lesions on ONE SIDE only (intraoral + extraoral on the same side, NOT crossing the midline) is the hallmark of HERPES ZOSTER (shingles). VZV reactivation causes ulcers following the distribution of a cranial nerve branch (typically V2 or V3), affecting skin and mucosa on the same unilateral side.
• D. Incorrect. Aphthous ulcers are intraoral only, bilateral, and do NOT involve the facial skin or follow dermatomal patterns.