A 62-year-old man comes to the physician for a 3-month history of burning in the throat after meals. He has hypertension and type II diabetes mellitus. Blood pressure is 150/90. HbA1c is 12%. Physical examination shows impairment of pinpoint discrimination up to the knees. He occasionally experiences fainting spells when standing up quickly. Which of the following is the next best step in diagnosis?
24-hour pH monitoring
Barium swallow
Endoscopy
Gastric-emptying scintigraphy
Manometry
