A 60-year-old man with chronic diarrhoea, bloating and macrocytic anaemia has a Stage II Schilling test showing low vitamin B12 excretion that corrects when the test is repeated after a 5-day course of tetracycline. Which is the most likely diagnosis?
- A Pernicious anaemia
- B Blind loop syndrome with bacterial overgrowth ✓
- C Terminal ileal Crohn disease
- D Pancreatic exocrine insufficiency
Correct answer: B. Blind loop syndrome with bacterial overgrowth
Explanation
In bacterial overgrowth, bacteria deconjugate bile salts and consume cobalamin, so radiolabelled B12 bound to intrinsic factor is not absorbed, giving an abnormal Stage II Schilling test. Eradication of bacteria with antibiotics normalises excretion, which is diagnostic. In pernicious anaemia the abnormality persists despite antibiotics because intrinsic factor is absent, and in ileal disease correction cannot occur because the absorptive site itself is damaged.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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