A 22-year-old dental student presents to the clinic with a 2-day history of a painful sore on the inside of her lower lip. She notes that these sores occur two or three times a year, usually during final exams. She denies any fever, malaise, or skin rashes. On physical examination, there is a single, 5-mm, well-circumscribed ulcer on the labial mucosa. The ulcer has a yellow-gray necrotic center surrounded by a prominent erythematous halo. There is no associated lymphadenopathy.
Which of the following is the most likely diagnosis?
The correct answer is:
A) Aphthous ulcer
The patient is presenting with a canker sore, or aphthous ulcer. This is a very common, non-infectious inflammatory condition of the oral mucosa. While the exact etiology is unknown, it is thought to be T-cell mediated and is often triggered by stress, local trauma, or certain foods. The classic presentation is a painful, shallow, round-to-oval ulcer with a yellow-gray pseudomembrane and a peripheral red halo. Aphthous ulcers occur on non-keratinized mucosa (e.g., labial mucosa, buccal mucosa, ventral tongue) and are not preceded by vesicles.
Answer choice B: Behcet syndrome, is incorrect. While Behcet syndrome presents with recurrent aphthous ulcers, it is a systemic vasculitis that also requires the presence of recurrent genital ulcers and uveitis (or other skin/joint involvement) for diagnosis. A single recurrent oral ulcer in an otherwise healthy student is much more likely to be simple aphthosis.
Answer choice C: Herpetic gingivostomatitis, is incorrect. This is caused by HSV-1 and typically presents with a prodrome of fever and lymphadenopathy. The lesions begin as vesicles that later rupture into ulcers. Unlike aphthous ulcers, herpetic lesions commonly involve keratinized mucosa such as the gingiva (gums) and the hard palate.
Answer choice D: Oral candidiasis, is incorrect. Also known as thrush, oral candidiasis presents as white, curd-like plaques that can be scraped off to reveal an erythematous base. It is common in immunocompromised patients or those using inhaled corticosteroids, and it does not typically present as a discrete, circumscribed ulcer.
Answer choice E: Squamous cell carcinoma, is incorrect. While oral squamous cell carcinoma can present as an ulcer, it typically appears as a persistent, non-healing lesion with indurated (hardened) borders, often in patients with a significant history of tobacco or alcohol use. A recurrent, painful lesion that heals within 1–2 weeks in a young patient is highly characteristic of a benign aphthous ulcer.
Key Learning Point
Aphthous ulcers are painful, recurrent oral sores characterized by a yellow-gray center and erythematous halo. They occur exclusively on non-keratinized mucosa, distinguishing them from herpetic lesions. Treatment is primarily symptomatic with topical corticosteroids (e.g., triamcinolone acetonide in dental paste) or topical anesthetics (e.g., lidocaine).
