65-year-old man with long-standing diabetes presents with chronic constipation. What is the most likely diagnosis explaining his bowel symptoms?

• A. Diabetic autonomic neuropathy affecting the bowel via pelvic splanchnic nerves, causing loss of parasympathetic pro-peristalsis.
• B. Hypercalcemia-related constipation due to calcium excess.
• C. Mechanical obstruction from diverticulosis.
• D. Primary intestinal obstruction due to valvular disease.

Answer: (A)