26th April 2024

A 65-year-old man presents with a 6-month history of progressively worsening constipation.

A 65-year-old man presents with a 6-month history of progressively worsening constipation. He reports having bowel movements less than twice a week, often with straining and a sensation of incomplete evacuation. He has tried increasing his fibre intake and using over-the-counter laxatives, with minimal improvement. He denies any abdominal pain, blood in stool, or significant weight loss. His past medical history is unremarkable, and he is not on any medications.

On examination, his abdomen is soft, non-tender with normal bowel sounds. Rectal examination reveals hard stool in the rectal vault.

Investigations:

Complete blood count: Normal

Thyroid function tests: Normal

Serum electrolytes: Normal

Colonoscopy: Unremarkable

Which is the most likely cause of his presentation?