A 63-year-old man presents to the office with a 2-year history of episodic swallowing problems...

This presentation is classic for Zenker diverticulum , characterized by progressive dysphagia, regurgitation of undigested food, coughing, and halitosis due to food retention in a pharyngoesophageal pouch. Symptoms are chronic and episodic, often involving regurgitation hours after eating. MCCQE objectives emphasize selecting the safest and most appropriate diagnostic test. The best initial test is a barium swallow (contrast esophagram) , which clearly visualizes the posterior outpouching above the upper esophageal sphincter.

Endoscopy is not the first step because there is a risk of perforation if a large diverticulum is present. pH monitoring and PPI trials are used for gastroesophageal reflux disease, which does not explain regurgitation of undigested food and halitosis. CT chest is unnecessary for diagnosis.

Therefore, a barium swallow is the safest and most informative investigation to confirm suspected Zenker diverticulum before considering surgical or endoscopic management.