A 58-year-old male with a 40-pack-year smoking history presents with new onset dysphagia to solids, followed by liquids, and significant unintentional weight loss over the past 3 months. He also reports occasional regurgitation of undigested food. Barium swallow shows a 'rat tail' or 'bird's beak' appearance of the distal esophagus. What is the most appropriate next step in diagnosis?

The correct answer to the question "A 58-year-old male with a 40-pack-year smoking history presents with new onset dysphagia to solids, followed by liquids, and significant unintentional weight loss over the past 3 months. He also reports occasional regurgitation of undigested food. Barium swallow shows a 'rat tail' or 'bird's beak' appearance of the distal esophagus. What is the most appropriate next step in diagnosis?" is Option B: Upper endoscopy with biopsy.

The other options — A) Esophageal manometry, C) 24-hour pH monitoring, D) CT scan of the chest and abdomen — are incorrect for this USMLE Exam Prep question. As explained above: While the barium swallow findings suggest achalasia, a patient with a smoking history, dysphagia, and weight loss, especially at this age, has a high risk of esophageal cancer. Upper endoscopy with b…