MSRA-0647

A 68-year-old man comes to the clinic complaining of intermittent swallowing difficulties for the past two years. His wife has noticed that he has bad breath and coughs at night. He has a history of type 2 diabetes mellitus but reports that he is generally healthy. Despite having a good appetite, his weight has remained stable. Upon clinical examination, no abnormalities are found. What is the probable diagnosis?