MRCP2-1798
A 40-year-old man returns from a significant period abroad working for a tech company in Japan. He reports chronic diarrhoea over the past few months with associated weight loss, fatigue, and now lower limb oedema. Upon examination, he appears pale and has stomatitis and glossitis. His BMI is only 21 and he admits to having lost 5 kg in weight in 2 months. Further investigations reveal megaloblastic anaemia, low albumin levels, positive D-xylose malabsorption test, and elevated faecal fat excretion. Anti-endomysial antibodies are negative. What is the most likely diagnosis for this patient?