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celiac disease child chronic diarrhea diagnosis investigations pediatric

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celiac disease villous atrophy duodenal biopsy histology

Scenario 3: Chronic Diarrhea, Growth Failure, Buttock Wasting in a 7-Year-Old

This is a classic presentation of malabsorption in childhood.

1. Most likely diagnosis

Coeliac disease (gluten-sensitive enteropathy)
The combination of chronic diarrhea (>4 months), bulky/pale/offensive stools (steatorrhoea), abdominal distension, poor weight gain, growth faltering (height below the 10th percentile), mild pallor (from iron/folate deficiency anaemia), and wasting of the buttocks (loss of subcutaneous fat/muscle from malnutrition) is the textbook description of paediatric coeliac disease presenting with malabsorption. It remains "the most common cause of malabsorption" in children in many populations, presenting with steatorrhoea and growth retardation - Bailey and Love's Short Practice of Surgery, p. 1336.
Differentials to keep in mind (worth excluding, but less likely given this exact constellation): cystic fibrosis, cow's milk protein intolerance, giardiasis, and other causes of chronic malabsorptive diarrhea - but the age, chronicity, and growth failure pattern point most strongly to coeliac disease.

2. Mechanism causing the diarrhea

Coeliac disease is an immune-mediated enteropathy triggered by gluten (gliadin) in genetically susceptible individuals (associated with HLA-DQ2/DQ8, and HLA-B8 has also been described). Ingested gluten peptides are deamidated by tissue transglutaminase and presented to CD4+ T cells in the lamina propria, driving an inflammatory response that damages the small bowel mucosa.
This produces the characteristic histological picture: a hypertrophic mucosa with atrophic (flattened) villi and deep, elongated crypts, along with increased intraepithelial lymphocytes. The loss of villous surface area and brush-border enzymes (e.g., lactase) causes malabsorption of fat, carbohydrate, and protein - Bailey and Love's Short Practice of Surgery, p. 1336.
The diarrhea itself is therefore predominantly:
  • Osmotic - unabsorbed nutrients (sugars, fats) draw water into the bowel lumen
  • Steatorrhoeic - fat malabsorption from reduced absorptive surface and bile-salt/enzyme dysfunction produces bulky, pale, foul-smelling stools
  • Compounded by secondary lactase deficiency from brush-border enzyme loss, worsening osmotic diarrhea after dairy intake
The proximal small bowel (duodenum/jejunum, the site of greatest gluten exposure) is affected most severely, which is why malabsorption of iron, folate, calcium, and fat-soluble vitamins is prominent and explains the pallor (anaemia) and growth failure.

3. Investigations to confirm the diagnosis

Serology (first-line screen):
  • IgA tissue transglutaminase antibody (IgA-tTG) - the preferred, most sensitive/specific screening test
  • IgA endomysial antibody (IgA-EMA) - used as a confirmatory test
  • Total serum IgA level - must be checked, since IgA deficiency (paradoxically more common in coeliac disease) causes false-negative IgA-based serology; if IgA-deficient, use IgG-tTG or IgG-EMA instead
  • The child should be on a normal gluten-containing diet for several weeks before testing, as serology reverts to negative on a gluten-free diet
Small bowel biopsy (gold standard):
  • Endoscopic duodenal/jejunal biopsy showing villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes confirms the diagnosis - Scott-Brown's Otorhinolaryngology Head & Neck Surgery, p. 201; Grainger & Allison's Diagnostic Radiology
  • In some current paediatric guidelines (ESPGHAN), biopsy can be omitted in symptomatic children with very high tTG titres (>10x upper limit of normal) plus positive EMA and appropriate HLA type, but biopsy remains standard confirmatory practice in most settings
Supportive investigations:
  • HLA-DQ2/DQ8 typing (high negative predictive value; presence doesn't confirm but absence essentially excludes coeliac disease)
  • FBC and blood film (microcytic or macrocytic anaemia from iron/folate deficiency), ferritin, folate, vitamin D, calcium
  • Response of symptoms and antibody titres to a gluten-free diet supports the diagnosis retrospectively
  • Stool studies/fat estimation (72-hour faecal fat) can demonstrate steatorrhoea but aren't diagnostic of coeliac disease specifically
Together, positive coeliac serology plus villous atrophy on duodenal biopsy, with subsequent clinical improvement on a gluten-free diet, confirms the diagnosis.
Recent evidence check: A quick literature check did not surface any 2-year systematic reviews/meta-analyses that contradict this standard diagnostic approach; the ESPGHAN 2020 no-biopsy pathway for select high-titre cases remains the main active area of guideline evolution, which I've noted above.
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  1. Diagnosis: Lactose intolerance (lactase deficiency)
  2. Type of diarrhea: Osmotic diarrhea
  3. Mechanism: Deficiency of brush-border lactase means lactose isn't hydrolyzed into glucose and galactose in the small intestine. Undigested lactose passes into the colon, where it draws water osmotically into the lumen (causing watery diarrhea/bloating) and is fermented by colonic bacteria into gas and short-chain fatty acids (causing cramps and bloating). Symptoms resolve when milk/lactose is removed, and growth remains normal since it's a digestive enzyme issue, not a structural/immune mucosal disease like coeliac disease.
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