4.4 Malabsorption, GI Motility & Clinical Nutrition

Malabsorption, GI Motility & Clinical Nutrition

Malabsorption Syndromes & Celiac Disease

Malabsorption results from mucosal abnormalities, luminal digestion failure, or lymphatic obstruction.

Celiac Disease (Gluten-Sensitive Enteropathy)

Celiac disease is a chronic autoimmune enteropathy triggered by dietary gluten (found in wheat, barley, and rye) in genetically susceptible individuals carrying HLA-DQ2 (90–95%) or HLA-DQ8 (5–10%).

Diagnostic Algorithm

1. Initial Serology: IgA Anti-Tissue Transglutaminase (IgA anti-tTG) antibody AND Total Serum IgA (to exclude selective IgA deficiency, which occurs in 2–3% of celiac patients).
   • If total IgA is deficient, perform IgG anti-tTG or IgG Deamidated Gliadin Peptide (DGP) testing.
   • All serological testing MUST be performed while the patient is consuming a gluten-containing diet (at least 1–2 meals containing gluten daily for 6 weeks).
2. Duodenal Biopsy: Mandatory in adults to confirm diagnosis. Take multiple biopsies (at least 1 from the duodenal bulb and 4 from the distal duodenum).

Modified Marsh Classification of Celiac Duodenal Biopsies

• Complications: Enteropathy-Associated T-Cell Lymphoma (EATL), adenocarcinoma of the small bowel, osteoporosis, hyposplenism (requiring pneumococcal vaccination), and dermatitis herpetiformis (intense pruritic vesicular skin lesions on extensor surfaces displaying granular IgA deposition in dermal papillae).

Differential Diagnosis of Malabsorption

• Whipple's Disease: Multi-system infection caused by Tropheryma whipplei. Features diarrhea, weight loss, arthralgias, hyperpigmentation, lymphadenopathy, and CNS/cardiac signs (culture-negative endocarditis). Duodenal biopsy shows PAS-positive, diastase-resistant macrophages in the lamina propria. Treatment: IV Ceftriaxone 2 g OD for 2 weeks, followed by oral Co-trimoxazole BD for 1 year.
• Tropical Sprue: Chronic malabsorption affecting visitors/residents of tropical regions. Involves both jejunum and ileum (causing megaloblastic anemia from dual B12 and folate deficiency). Treated with Tetracycline 250 mg QDS + Folic acid 5 mg OD for 3–6 months.
• Bile Acid Diarrhea (BAD): Terminal ileal resection (<100 cm) or inflammation (Crohn's) impairs bile acid reabsorption, spilling bile salts into the colon and stimulating secretomotor diarrhea. Diagnosed via ⁷⁵SeHCAT test (7-day retention <10% indicates moderate BAD, <5% severe BAD). Treated with bile acid sequestrants (Colestyramine or Colesevelam).

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Small Intestinal Bacterial Overgrowth (SIBO) & GI Motility

Small Intestinal Bacterial Overgrowth (SIBO)

SIBO occurs when colonic bacteria colonize the small intestine (>10³ CFU/mL aspirate), fermenting carbohydrates and deconjugating bile acids.

• Risk Factors: Anatomic blind loops (Roux-en-Y), ileocecal valve resection, small bowel diverticulosis, diabetes mellitus, scleroderma, and chronic PPI suppression.
• Diagnosis: Hydrogen and Methane Breath Testing using glucose (75 g) or lactulose (10 g).
  • Positive Test: Rise in hydrogen (H₂) ≥20 ppm above baseline OR rise in methane (CH₄) ≥10 ppm within 90 minutes.
• Management: First-line targeted therapy is oral Rifaximin 550 mg TDS for 14 days (add Neomycin or Metronidazole if methane-predominant).

Gastrointestinal Motility Disorders

Diabetic Gastroparesis

• Pathophysiology: Autonomic neuropathy causing delayed gastric emptying in long-standing diabetes mellitus.
• Diagnosis: Upper endoscopy rules out mechanical obstruction. Confirmed by 4-hour Solid-Phase Gastric Emptying Scintigraphy showing >10% meal retention at 4 hours (or >60% retention at 2 hours).
• Management:
  1. Dietary: Small, frequent, low-fat, low-fiber meals.
  2. Prokinetic Pharmacotherapy:
     • Domperidone 10 mg TDS: Peripheral D2 receptor antagonist (does not cross blood-brain barrier). Requires baseline ECG to rule out QTc prolongation.
     • Metoclopramide 10 mg TDS: D2 antagonist. MHRA/EMA limit strictly to 5 days due to extrapyramidal side effects and tardive dyskinesia.
     • Erythromycin 250 mg TDS: Motilin receptor agonist (subject to tachyphylaxis after 2–4 weeks).
     • Prucalopride 2 mg OD: Selective 5-HT4 receptor agonist.

Acute Colonic Pseudo-Obstruction (Ogilvie's Syndrome)

• Massive acute colonic dilation (>9 cm caecum) without mechanical obstruction in hospitalized elderly or postoperative patients.
• Management: Conservative (IV fluids, stop anticholinergics/opioids). If caecal diameter >9–12 cm or fails 24–48h conservative care, administer Neostigmine 2.0 mg IV slowly over 3–5 minutes under cardiac monitoring (atropine at bedside for bradycardia).

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Clinical Nutrition, Refeeding Syndrome & Nutritional Support

Refeeding Syndrome

Refeeding syndrome is a severe, life-threatening metabolic emergency triggered by reintroducing nutrition to severely malnourished or starved patients.

Pathophysiology

Starvation leads to catabolism and intracellular depletion of electrolytes (phosphate, potassium, magnesium). Reintroducing carbohydrates stimulates insulin release, driving glucose, phosphate, potassium, and magnesium into cells and stimulating protein synthesis. The resultant severe hypophosphatemia causes impaired ATP synthesis, muscle weakness, heart failure, arrhythmias, and death.

NICE Criteria for High Risk of Refeeding Syndrome

Patient has one or more of the following:

• BMI <16 kg/m²
• Unintentional weight loss >15% in the preceding 3–6 months
• Little or no nutritional intake for >10 consecutive days
• Low baseline serum levels of phosphate, potassium, or magnesium prior to feeding

OR two or more of the following:

• BMI <18.5 kg/m²
• Unintentional weight loss >10% in the preceding 3–6 months
• Little or no nutritional intake for >5 consecutive days
• History of alcohol abuse or drugs including insulin, chemotherapy, antacids, or diuretics

Refeeding Management Protocol (NICE Guidelines)

1. Immediate Thiamine Supplementation: Administer IV Thiamine (Pabrinex I+II 2 pairs TDS) or oral Thiamine 200–300 mg daily plus Vitamin B co-strong 1–2 tablets TDS at least 30 minutes BEFORE starting nutrition and continue for at least 10 days.
2. Caloric Escalation: Start feeding slowly at 10–15 kcal/kg/day (or 5–10 kcal/kg/day in extreme cases with BMI <14 kg/m²). Gradually increase calories over 4–7 days to full requirements.
3. Proactive Electrolyte Replacement: Replace oral/IV phosphate, potassium, and magnesium proactively before and during refeeding.