A patient undergoing chemotherapy presents with painful, diffuse ulceration and erythema of the oral mucosa. Fungal infection has been ruled out. What is the MOST likely diagnosis?

Correct answer: A. Oral mucositis

• A. Correct. Oral mucositis is the most common and most debilitating oral complication of cytotoxic chemotherapy. Rapidly dividing basal epithelial cells are killed, producing atrophy, erythema and painful confluent ulceration of non-keratinized mucosa (buccal, labial, ventral tongue, soft palate), typically beginning 5–10 days after infusion. Management is supportive: bland rinses, topical anesthetics, oral cryotherapy, systemic analgesia.
• B. NUG produces punched-out interdental papillae, fetor and pseudomembrane, and is localized to the gingiva rather than diffuse across the mucosa.
• C. Erythema multiforme is an immune-mediated reaction classically triggered by HSV or drugs, with target lesions and crusted hemorrhagic lips — not the expected chemotherapy sequela.
• D. Osteoradionecrosis follows head-and-neck RADIATION therapy and involves exposed necrotic bone, not diffuse mucosal ulceration.