30th July 2023

A 42-year-old man attends his GP complaining of a three-week history of non-bloody diarrhoea

A 42-year-old man attends his GP complaining of a three-week history of non-bloody diarrhoea, described as loose and foul-smelling stools. He has lost around 4kg in weight. He recently returned from Vietnam following a placement teaching at a local school.

On examination, you note an enlarged and erythematous tongue.

Blood tests reveal a macrocytosis, but nil else of note.

What is the most likely cause of his symptoms and investigation results?

Select the SINGLE most appropriate option from the list below. Select ONE option only.