Question category: Gastroenterology
A 55 year old gentleman presents to his GP with intermittent abdominal pain and diarrhoea which is sometimes difficult to flush away. He has also had a cough, fever and has noticed aches and pains in his joints. A biopsy of the duodenum reveals periodic acid Schiff stain positive macrophages with intracellular clumps. What is the most likely diagnosis?