Mr. D, a 65-year-old man with PD for about 10 years, comes to your outpatient office for re-evaluation. He denies weight loss and pneumonia. A video swallow study 5 years ago showed mild dysphagia, including poor oral control, delayed initiation, and penetration of thin liquids but no aspiration. He complains of a sense of aspiration. What is the most likely cause of his symptoms?
1) Gastroesophageal reflux disease (GERD)
2) Parkinson's disease (PD)
3) Stroke
4) Esophageal cancer