A 67-year-old man with Parkinson disease has experienced an increasingly dry mouth for the past 3 months, and this interferes with eating and swallowing. He has noted dry eyes as well. On physical examination he has minimal tremor at rest; there are no other abnormal findings. Laboratory studies show no detectable autoantibodies. Which of the following is the most likely cause for his findings?
Alcohol ingestion Anticholinergic drug use Candidiasis Sialadenitis with blockage of salivary duct