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PA23.5-7 | Intestinal TB, Appendicitis, IBD & Malabsorption — SDL Guide (Part 4)

Coeliac Disease — Pathology and India Context

A three-panel medical diagram compares normal and coeliac duodenal biopsy findings, explains gliadin-mediated immune injury, and highlights North Indian epidemiology with gross changes and complications. — **Panel A:** Normal duodenal villi, normal crypts, absorptive surface, coeliac total villous atrophy, flat mucosa, crypt hyperplasia, intraepithelial lymphocytes >25 per 100 enterocytes, lamina propria plasma cells and lymphocytes, Marsh 0 to Marsh 3 grading strip. **Panel B:** Dietary gliadin peptide, tissue transglutaminase tTG, deamidated gliadin, HLA-DQ2/DQ8 antigen presentation, CD4+ T cell, Th1 response, cytotoxic T-cell epithelial injury, local antibody production. **Panel C:** North India map highlight for Punjab and Haryana, wheat staple icon, scalloping of duodenal folds, loss of Kerckring folds, gluten-free diet mucosal recovery, refractory coeliac disease, enteropathy-associated T-cell lymphoma EATL, small bowel adenocarcinoma, osteoporosis, infertility.

Coeliac disease deserves focused attention because its incidence in North India (Punjab, Haryana) rivals European rates — wheat is the dietary staple.

Pathogenesis: Dietary gliadin peptides are deamidated by tissue transglutaminase (tTG) → presented via HLA-DQ2/DQ8 to CD4+ T cells → Th1 response → villous destruction by cytotoxic T cells and local antibody production.

Biopsy findings — duodenum/proximal jejunum (Marsh classification):
• Villous atrophy — partial to total flattening of villi → loss of absorptive surface ('flat mucosa').
• Crypt hyperplasia — crypts elongate (compensatory proliferation).
• Intraepithelial lymphocytes (IELs) > 25 per 100 enterocytes — earliest, most sensitive change.
• Lamina propria plasma cell and lymphocyte infiltration.

Gross: Scalloping of duodenal folds on endoscopy; loss of Kerckring folds.

Response: Gluten-free diet → mucosal recovery within months.

Complications: Refractory coeliac disease, enteropathy-associated T-cell lymphoma (EATL) (rare but serious), small bowel adenocarcinoma, osteoporosis, infertility.

A multi-panel medical diagram compares normal duodenal villi with coeliac villous atrophy, shows Marsh grading, highlights intraepithelial lymphocytes, and links biopsy findings to laboratory diagnosis. — **Panel A:** Normal duodenal villi, villous architecture, crypts of Lieberkuhn, lamina propria, enterocytes, goblet cells, coeliac total villous atrophy, crypt hyperplasia, increased intraepithelial lymphocytes. **Panel B:** Marsh 0 normal mucosa, Marsh 1 increased intraepithelial lymphocytes, Marsh 2 crypt hyperplasia, Marsh 3a partial villous atrophy, Marsh 3b subtotal villous atrophy, Marsh 3c total villous atrophy. **Panel C:** Enterocytes, brush border region, intraepithelial lymphocytes, lamina propria lymphocytes, IEL count greater than 25 per 100 enterocytes. **Panel D:** Faecal fat estimation, Sudan III stain, D-xylose absorption test, anti-tTG IgA, total IgA, anti-endomysial antibody, duodenal biopsy, Marsh lesion confirmation.

Malabsorption Syndrome — Laboratory Diagnosis

A four-panel diagnostic infographic shows the stepwise laboratory workup of malabsorption syndrome using faecal fat testing, D-xylose localisation, and cause-specific tests. — **Panel A:** Three-step laboratory algorithm: confirm fat malabsorption, localise luminal versus mucosal defect, and identify specific cause.. **Panel B:** Faecal fat estimation, 72-hour stool collection on 100 g/day fat diet, >7 g/day steatorrhoea, Sudan III-positive fat globules.. **Panel C:** D-xylose absorption test with low D-xylose indicating mucosal disease and normal D-xylose indicating pancreatic or luminal problem.. **Panel D:** Cause-specific tests including anti-tTG IgA, total IgA, EMA, small bowel biopsy, PAS stain, Schilling test concept, hydrogen breath test, and faecal elastase-1..

A systematic laboratory approach confirms malabsorption, localises it, and identifies the cause.

Step 1 — Confirm fat malabsorption:
• Faecal fat estimation (72-hour stool collection on 100 g/day fat diet) — >7 g/day = steatorrhoea; gold standard quantitative test.
• Sudan III stain of fresh stool — qualitative screen (fat globules).

Step 2 — Localise the defect (luminal vs mucosal):
• D-xylose absorption test — oral 25 g D-xylose → measure urine (5-hour) and/or serum (1-hour) levels.
- Low D-xylose → mucosal disease (coeliac, tropical sprue) — xylose requires mucosal transport.
- Normal D-xylose → pancreatic insufficiency or luminal problem (xylose absorbed without pancreatic enzymes).

Step 3 — Identify specific cause:
• Anti-tTG IgA (and total IgA) — highly sensitive/specific for coeliac disease; first-line serological test.
• Anti-endomysial antibody (EMA) — high specificity, operator-dependent; confirmatory.
• Small bowel biopsy (duodenal/jejunal) — definitive for coeliac, tropical sprue, Whipple (PAS stain).
• Schilling test — tests B12 absorption at each step (intrinsic factor, ileal mucosa, bacterial overgrowth); now largely replaced by serum B12 + methylmalonic acid but still asked in exams.
• Hydrogen breath test — lactase deficiency (lactose challenge), SIBO (glucose challenge).
• Faecal elastase-1 — screen for pancreatic exocrine insufficiency (low in chronic pancreatitis).
• Endoscopy + biopsy — gold standard for mucosal causes.

A colour-coded diagnostic flowchart shows confirmation of steatorrhoea, D-xylose testing, and branching into mucosal versus luminal causes of malabsorption with specific confirmatory tests. — **Panel A:** Main algorithm: chronic diarrhoea/steatorrhoea → stool fat confirmation → D-xylose test → low urinary D-xylose versus normal urinary D-xylose branches.. **Panel B:** Mucosal malabsorption branch: damaged intestinal mucosa, low D-xylose absorption, anti-tTG IgA, duodenal biopsy, villous atrophy, crypt hyperplasia, coeliac disease.. **Panel C:** Luminal malabsorption branch: intact intestinal mucosa, normal D-xylose absorption, Schilling test, hydrogen breath test, pancreatic insufficiency, bile salt problems, bacterial overgrowth..

SELF-CHECK

A 19-year-old presents with steatorrhoea and iron-deficiency anaemia. Serum anti-tTG IgA is markedly elevated. D-xylose test shows low urinary excretion at 5 hours. Duodenal biopsy shows total villous atrophy with crypt hyperplasia. Which statement best explains why D-xylose excretion is low in this patient?

A. D-xylose requires pancreatic lipase for absorption

B. D-xylose requires bile salt micelles for uptake

C. D-xylose is metabolised before reaching the kidney

D. D-xylose is absorbed passively by intestinal mucosa, which is destroyed in coeliac disease

Reveal Answer

Answer: D. D-xylose is absorbed passively by intestinal mucosa, which is destroyed in coeliac disease

D-xylose is a pentose sugar absorbed passively by the intestinal mucosa without requiring pancreatic enzymes or bile salts. In coeliac disease, villous atrophy destroys the absorptive mucosa, directly reducing D-xylose uptake and urinary excretion. This contrasts with pancreatic insufficiency, where the mucosa is intact and D-xylose absorption is normal or near-normal, making the D-xylose test the key discriminator between mucosal and luminal causes of malabsorption.

CLINICAL PEARL

The India malabsorption differential: When you see a young adult from a tropical region with chronic diarrhoea, steatorrhoea, and folate/B12 deficiency, consider tropical sprue before coeliac disease — especially if anti-tTG is negative. Tropical sprue responds dramatically to tetracycline + folic acid supplementation for 3-6 months. Missing it means unnecessary gluten-free diet counselling and delayed cure.