A 58-year-old man with multiple jejunal diverticula and previous limited bowel resections develops weight loss, steatorrhoea, and macrocytic anaemia. Vitamin B12 level is low, folate is normal, and serum folate breakdown products are raised. His anaemia improves after a course of oral tetracycline. What is the underlying mechanism?
- A Bacterial overgrowth in stagnant segments consuming B12 and deconjugating bile salts ✓
- B Ileal receptor destruction by chronic inflammation
- C Autoimmune gastritis reducing intrinsic factor secretion
- D Pancreatic exocrine insufficiency impairing B12 release from R-protein
Correct answer: A. Bacterial overgrowth in stagnant segments consuming B12 and deconjugating bile salts
Explanation
Jejunal diverticula create stagnant loops permitting bacterial overgrowth (blind loop syndrome). Anaerobic bacteria consume luminal vitamin B12 and deconjugate bile salts, causing steatorrhoea, while bacterial metabolism raises serum folate. Response to a broad-spectrum antibiotic confirms the diagnosis. Autoimmune gastritis and ileal disease would not respond to tetracycline, and pancreatic insufficiency does not raise folate breakdown products.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.