Malabsorption syndromes

Malabsorption - Gut Feeling Gone Wrong

• Pathophysiology: Impaired intestinal absorption of nutrients, leading to steatorrhea, weight loss, and vitamin deficiencies.
• Classification:
  • Pancreatic Insufficiency: ↓ Lipase (e.g., Chronic Pancreatitis, Cystic Fibrosis).
  • Bile Salt Deficiency: ↓ Micelle formation (e.g., Cholestasis, Bacterial Overgrowth).
  • Mucosal Defects: ↓ Surface area (e.g., Celiac Disease, Whipple Disease).

⭐ The D-xylose test distinguishes mucosal from pancreatic causes. Low urinary/serum D-xylose suggests a mucosal defect as its absorption is independent of pancreatic enzymes.

Celiac Disease - Gluten's Arch Nemesis

• Autoimmune-mediated intolerance to gliadin (a gluten protein) found in wheat, barley, and rye.
• Strongly associated with HLA-DQ2 and HLA-DQ8.
• Clinical Features: Chronic diarrhea/steatorrhea, bloating, weight loss, and nutritional deficiencies (e.g., iron deficiency anemia).
• Diagnosis:
  • Initial test: IgA anti-tissue transglutaminase (tTG) antibodies.
  • Gold standard: Small bowel biopsy showing histologic changes.
• Histopathology: Villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes.

⭐ Dermatitis herpetiformis (a pruritic papulovesicular rash on extensor surfaces) is a specific skin manifestation.

• Treatment: Lifelong, strict gluten-free diet.

Key Syndromes - The Usual Suspects

• Celiac Disease

  • Autoimmune reaction to gluten (gliadin) in genetically susceptible individuals (HLA-DQ2/DQ8).
  • Location: Primarily affects duodenum & proximal jejunum.
  • Histology: Blunting/atrophy of villi, crypt hyperplasia, ↑ intraepithelial lymphocytes.
  • Labs: ↑ IgA anti-tissue transglutaminase (tTG), anti-endomysial antibodies.
  • 

  ⭐ Associated with dermatitis herpetiformis, an intensely pruritic papulovesicular rash on extensor surfaces.

• Tropical Sprue

  • Occurs in residents of or visitors to tropical regions; likely infectious etiology.
  • Affects entire small bowel; jejunum & ileum involvement leads to folate & B12 deficiency.
  • Responds to antibiotics (e.g., tetracycline) and folate supplementation.

• Whipple Disease

  • Systemic infection with Tropheryma whipplei.
  • Histology: Lamina propria filled with PAS-positive foamy macrophages.
  • 📌 Mnemonic: Foamy Whipped cream in a CAN (Cardiac, Arthralgias, Neurologic symptoms).

Clinical Workup - Cracking the Code

• Initial Tests: Sudan stain or quantitative fecal fat (>7 g/day) to confirm steatorrhea.
• D-xylose Test: Differentiates pancreatic vs. mucosal causes.

⭐ Low urinary D-xylose points to a mucosal defect (e.g., celiac disease), as the intestine itself cannot absorb the monosaccharide. Normal levels suggest a pancreatic enzyme deficiency is the likely culprit.

High‑Yield Points - ⚡ Biggest Takeaways

• Celiac disease: Autoimmune, HLA-DQ2/DQ8-associated reaction to gluten causing villous atrophy.
• Whipple disease: Systemic infection (T. whipplei) with PAS-positive macrophages in lamina propria.
• Tropical sprue: Affects the entire small bowel (jejunum/ileum) and responds to antibiotics.
• Lactase deficiency: Results in osmotic diarrhea; diagnosed via hydrogen breath test.
• Pancreatic insufficiency: Causes steatorrhea and fat-soluble vitamin (A, D, E, K) deficiency.
• D-xylose test: Distinguishes mucosal damage (impaired absorption) from enzyme deficiency (normal absorption).