A patient presents with painful unilateral vesicular lesions on the hard palate. The lesions do not cross the midline. What is the most likely diagnosis?

Correct answer: B. Herpes zoster (VZV reactivation)

• A. Aphthous stomatitis does not produce vesicles — it starts as erythematous macules that develop into ulcers. It occurs on non-keratinized mucosa and is bilateral.
• B. CORRECT. Herpes zoster (shingles) is caused by reactivation of varicella-zoster virus (VZV) and characteristically follows a single dermatomal/neural distribution — it does NOT cross the midline. Intraoral zoster follows the distribution of branches of the trigeminal nerve (V2 = maxillary = palate). Unilateral palatal vesicles that respect the midline are classic for HZ.
• C. Recurrent intraoral herpes simplex occurs on keratinized mucosa (hard palate, attached gingiva) but is typically a small cluster; it does cross the midline and is rarely as widespread. VZV is the better answer for the strict unilateral pattern.
• D. Primary herpetic stomatitis (initial HSV-1 infection) causes widespread vesicles and ulcers bilaterally on both keratinized and non-keratinized mucosa, with fever and systemic symptoms.