Following complete ileal partial jejunal resection, the patient is most likely to have?

Explanation

## Correct Answer: B. Vitamin B12 deficiency Vitamin B12 (cobalamin) is exclusively absorbed in the **terminal ileum** via intrinsic factor-mediated active transport. Complete ileal resection eliminates this sole site of B12 absorption, making B12 deficiency inevitable regardless of dietary intake or gastric intrinsic factor production. The jejunum, though resected, does not absorb B12—it absorbs iron, calcium, and other nutrients. B12 stores in the liver last 3–5 years, so deficiency manifests insidiously as megaloblastic anemia, peripheral neuropathy (subacute combined degeneration), and glossitis. This is a cardinal consequence of ileal surgery in Indian clinical practice, where post-tuberculosis strictures and Crohn's disease requiring ileal resection are common. Patients require lifelong parenteral B12 supplementation (1000 µg IM monthly or 2000 µg IM every 3 months per Indian guidelines) since oral replacement is futile without the ileal absorptive mechanism. ## Why the other options are wrong **A. Gastric ulcer** — Gastric ulcer is not a direct consequence of ileal resection. While Zollinger-Ellison syndrome (gastrin-secreting tumour) can cause refractory ulcers, it is unrelated to small bowel resection. The ileum does not regulate gastric acid secretion or mucosal integrity. This is a distractor that confuses post-surgical complications with acid-related pathology. **C. Constipation** — Ileal resection typically causes **diarrhoea**, not constipation, due to loss of absorptive surface and increased colonic bile acid load (triggering secretory diarrhoea). Constipation is paradoxically seen after proximal small bowel resection with intact colon. This option reverses the expected pathophysiology and traps students who confuse resection site with bowel motility outcome. **D. Folic acid deficiency** — Folic acid is absorbed throughout the small intestine, particularly the **proximal jejunum**. Although jejunal resection occurs here, the ileal resection is complete and the remaining proximal bowel can compensate for folate absorption. B12 has no such redundancy—only the ileum absorbs it. Folate stores last only 3–4 months, but clinical deficiency is less likely than B12 deficiency in this scenario. ## High-Yield Facts - **Terminal ileum** is the exclusive site of vitamin B12 absorption via intrinsic factor-mediated active transport. - B12 deficiency after ileal resection manifests as **megaloblastic anemia** and **subacute combined degeneration** (posterior and lateral column myelopathy). - Hepatic B12 stores last **3–5 years**; deficiency is delayed but inevitable without supplementation. - Ileal resection causes **diarrhoea** (not constipation) due to increased colonic bile acid and fatty acid load. - Lifelong **parenteral B12 supplementation** (1000 µg IM monthly) is mandatory; oral replacement is ineffective without ileal mucosa. - Folic acid absorption occurs throughout the small intestine; proximal bowel can compensate even after jejunal resection. - Common Indian causes of ileal resection: post-TB strictures, Crohn's disease, and intestinal tuberculosis. ## Mnemonics **B12 Absorption Site: TERMINAL** **T**erminal ileum is the **only** site for B12 absorption. **E**xtrinsic factor (B12 in food) + **R**eceptor (intrinsic factor) = **M**egablast if lost. **I**ntrinsic factor needed. **N**o other site works. **A**ctive transport required. **L**ifelong supplementation needed. **Post-Ileal Resection: DIARRHEA (not constipation)** **D**iminished absorption surface. **I**ncreased bile acids reach colon. **A**ccelerates transit. **R**educes water reabsorption. **R**esulting secretory diarrhoea. **H**ealth consequence: malabsorption. **E**xpect loose stools. **A**void constipation trap. ## NBE Trap NBE pairs ileal resection with "constipation" to trap students who confuse proximal small bowel resection (which can cause constipation due to reduced transit) with ileal resection (which causes diarrhoea). The question also tests whether students know B12 has **no redundancy**—unlike folate or iron, which are absorbed throughout the small intestine. ## Clinical Pearl In Indian practice, post-tuberculosis ileal strictures requiring resection are common in endemic regions. Patients often present 2–3 years post-surgery with unexplained anaemia and neuropathy—a classic presentation of B12 deficiency that is preventable with early recognition and lifelong IM supplementation. Always counsel patients undergoing elective ileal resection about mandatory B12 monitoring and supplementation. _Reference: Guyton & Hall Textbook of Medical Physiology (Ch. 65: Secretory and Absorptive Functions); Harrison's Principles of Internal Medicine (Ch. 297: Malabsorption); KD Tripathi Essentials of Medical Pharmacology (B12 metabolism and supplementation)_