Chapter 19 · Malabsorption & Small Intestine Disorders

Celiac disease · Food allergy · Postenteritis enteropathy · Congenital & autoimmune enteropathy · Protein-losing enteropathy · Intestinal lymphangiectasia · Immune deficiency & gut · Short gut syndrome · Inborn errors (carbohydrate, lipid, protein, electrolyte/mineral) · Investigations (radiology, biopsy, capsule endoscopy, breath tests, stool chromatography, duodenal intubation)

📌 Core principles: Celiac disease = immune-mediated enteropathy triggered by gluten; IgA tTG + biopsy gold standard. Short gut syndrome leads to malabsorption; requires parenteral nutrition and intestinal adaptation. Disaccharidase deficiencies cause osmotic diarrhoea. Investigation algorithm: stool studies, breath tests, endoscopy with biopsy, radiology.

📖 Malabsorption & Small Intestine – Key Concepts

🌾 Celiac disease
Autoimmune enteropathy triggered by gluten (wheat, barley, rye). HLA-DQ2/DQ8. Serology: IgA anti-tTG, EMA. Diagnosis: duodenal biopsy (Marsh grade ≥2). Treatment: lifelong gluten-free diet. Complications: anemia, osteoporosis, lymphoma risk.
🥛 Food allergy (non-IgE & mixed)
Eosinophilic gastroenteropathy, FPIES (food protein-induced enterocolitis). Cow’s milk, soy, egg. Symptoms: vomiting, diarrhea, FTT, bloody stools. Diagnosis: elimination diet + challenge; endoscopy with eosinophilia.
🩻 Postenteritis enteropathy & congenital enteropathies
Postinfectious (rotavirus, giardia) – transient lactase deficiency. Congenital: microvillus inclusion disease, tufting enteropathy (intractable diarrhea, PN dependent). Autoimmune enteropathy (IPEX syndrome, anti-enterocyte antibodies).
💧 Protein-losing enteropathy (PLE)
Excessive protein loss into gut lumen. Causes: lymphangiectasia, IBD, Menetrier disease, congenital heart disease (Fontan). Diagnosis: fecal alpha-1 antitrypsin clearance. Treat underlying cause, medium-chain triglycerides (MCT) diet.
🔪 Short gut syndrome (SGS)
After massive resection (NEC, atresia, volvulus). Malabsorption, dependence on PN. Adaptation promoted by enteral feeding (continuous infusion), teduglutide (GLP-2 analogue), manage SIBO, liver protection.
🧪 Inborn errors of digestion/absorption
Carbohydrate: lactase (primary/secondary), sucrase-isomaltase deficiency (stool pH low, breath H2). Lipid: abetalipoproteinemia (acanthocytes, fat-soluble vitamin deficiency). Protein: enterokinase deficiency, trypsinogen deficiency. Electrolyte: congenital chloride diarrhoea (CLCN2/SLC26A3), congenital sodium diarrhoea.
🔍 Investigations of small intestine
Radiology (barium follow-through, MR enterography). Small bowel biopsy (endoscopic or capsule). Capsule endoscopy (visualize entire mucosa). Breath hydrogen (lactose/fructose malabsorption). Stool chromatography (reducing sugars, fat). Duodenal intubation (aspirate for culture, disaccharidases).

🔎 Symptom-based approach: chronic diarrhoea, malabsorption, PLE

1️⃣

Chronic diarrhoea + faltering growth + abdominal distension – Celiac disease, cystic fibrosis, tropical sprue. Check IgA tTG, fecal elastase, sweat test. Upper endoscopy with duodenal biopsies.

2️⃣

Watery diarrhoea after milk ingestion + reducing substances in stool + low pH – Lactose intolerance (primary or secondary). Breath hydrogen test; trial of lactose-free diet.

3️⃣

Hypoalbuminemia, edema, and no proteinuria; normal LFTs – Protein-losing enteropathy. Measure fecal alpha-1 antitrypsin clearance. Investigate lymphangiectasia (endoscopy with biopsies), IBD, Fontan circulation.

4️⃣

Intractable diarrhoea starting in first days of life, requiring parenteral nutrition – Congenital enteropathies (microvillus inclusion disease, tufting enteropathy). Small bowel biopsy (electron microscopy). Autoimmune enteropathy (IPEX, FOXP3 mutation).

5️⃣

Fatty stools (steatorrhoea), acanthocytes, low cholesterol, retinitis pigmentosa – Abetalipoproteinemia (MTTP mutation). Fat-soluble vitamin deficiencies (A, D, E, K).

📌 Red flags in malabsorption: Severe failure to thrive, perianal fistulas (Crohn), clubbing (CF, IBD), unexplained bleeding (vitamin K deficiency), neuro symptoms (vitamin E deficiency).

📋 Management algorithms: Celiac, Short gut, PLE, Inborn errors

🌾

Celiac disease – management
▪️ Lifelong strict gluten-free diet (GFD).
▪️ Nutritional rehabilitation (iron, folate, calcium, vitamin D).
▪️ Monitor weight, tTG titres, bone density, thyroid function (associated AI).
▪️ Dietitian support; screen first-degree relatives.

🔪

Short gut syndrome – staged management
▪️ Phase 1 (post-resection): parenteral nutrition (PN), small-volume continuous enteral feeds (trophic).
▪️ Phase 2 (adaptation): increase enteral feeds, monitor for bacterial overgrowth (SIBO – treat with cyclic antibiotics).
▪️ Phase 3 (weaning from PN): use GLP-2 analogue (teduglutide) if refractory; surgical lengthening procedures in selected.
▪️ Prevent cholestasis (cyclic PN, omega-3 lipids).

💧

Protein-losing enteropathy – workup and therapy
▪️ Treat underlying condition (IBD: immunomodulators; lymphangiectasia: MCT diet, medium-chain triglycerides).
▪️ Replace albumin losses, diuretics for edema.
▪️ Octreotide in refractory lymphangiectasia.

🧪

Inborn error of disaccharide digestion – e.g. sucrase-isomaltase deficiency
▪️ Dietary restriction of sucrose and starch; enzyme replacement (sacrosidase).
▪️ Breath hydrogen test after sucrose load for diagnosis.

🔬

Investigation pathway for suspected malabsorption
▪️ Step 1: stool microscopy, fecal fat, elastase, reducing substances, calprotectin.
▪️ Step 2: breath tests (lactose, fructose, glucose H2).
▪️ Step 3: upper endoscopy with duodenal biopsies (villous atrophy, disaccharidase assay).
▪️ Step 4: capsule endoscopy, MR enterography (small bowel Crohn, tumours).

💡 Reflex prompts – Malabsorption & small intestine

🌾 A 5-year-old with chronic diarrhoea, iron deficiency, and IgA tTG >100 U/mL. Next diagnostic test?
Upper endoscopy with duodenal biopsies (Marsh classification). Celiac disease.
🧪 A child with chronic diarrhoea, stool pH 5.5, reducing substances 2+. Most likely diagnosis?
Carbohydrate malabsorption (lactose intolerance). Breath hydrogen test.
💊 A child with short gut syndrome develops abdominal distension, foul-smelling diarrhoea, and B12 deficiency. Likely complication?
Small intestinal bacterial overgrowth (SIBO). Treat with rotating antibiotics (metronidazole, rifaximin).
📉 A 2-year-old with edema, hypoalbuminemia, and no liver/kidney disease. Fecal alpha-1 antitrypsin elevated. Diagnosis?
Protein-losing enteropathy – causes: lymphangiectasia, IBD, Menetrier disease.
🔬 What is the gold standard for diagnosing microvillus inclusion disease?
Transmission electron microscopy of small bowel biopsy (microvillus atrophy, inclusions).
🩺 A child with known Fontan circulation develops edema, ascites, and low albumin. Diagnosis?
Fontan-associated protein-losing enteropathy due to elevated central venous pressure; manage with high PEEP, MCT diet, budesonide.
🍞 Non-invasive screening test for celiac disease when IgA deficient?
IgG deamidated gliadin peptide (IgG-DGP) or IgG anti-tTG.
📊 A child with steatorrhoea, acanthocytes, and ataxia. Vitamin E level low. Diagnosis?
Abetalipoproteinemia (MTP deficiency) – fat-soluble vitamin replacement essential.
⚙️ Which study assesses small bowel motility and detects bacterial overgrowth?
Hydrogen breath test using lactulose (fast transit, early peak suggests SIBO).
🔍 Most accurate method to visualise entire small bowel mucosa in suspected Crohn?
Capsule endoscopy (if no strictures) or MR enterography.