Small Bowel Pathology
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Direct answer
Villous atrophy with crypt hyperplasia on a duodenal biopsy taken while the patient is still eating gluten defines coeliac disease — the gluten-sensitive enteropathy of the proximal small bowel, associated with HLA-DQ2 or DQ8 and diagnosed by IgA anti-tissue transglutaminase antibody. Tropical sprue, endemic in the Indian subcontinent, affects the whole length of the bowel, produces folate and B12 deficiency together, and responds to folic acid with tetracycline — the pair of facts that separates it from coeliac disease at the bedside. Mechanical catastrophes complete the chapter: Meckel diverticulum with its rule of twos, intussusception, volvulus and mesenteric ischaemia with its pain out of proportion to findings.
What you must remember
- Coeliac disease: deamidated gliadin peptides presented on HLA-DQ2/DQ8; IgA anti-tissue transglutaminase is the screening test (check total IgA concurrently); histology — flat mucosa with crypt hyperplasia and intraepithelial lymphocytosis; strict gluten-free diet is the treatment.
- Coeliac associations and complications: dermatitis herpetiformis with granular IgA at the dermal papillae; hyposplenism; type 1 diabetes and thyroid disease; long-term risks of refractory sprue, ulcerative jejunitis and enteropathy-associated T-cell lymphoma.
- Tropical sprue: whole-bowel malabsorption in the tropics including India; partial villous atrophy with folate and B12 deficiency (B12 falls because the terminal ileum too is involved); treated with folic acid plus tetracycline for months; gluten exclusion does nothing.
- Whipple disease: Tropheryma whipplei; foamy PAS-positive macrophages in the lamina propria; migratory arthralgia, diarrhoea, weight loss, neurological and cardiac involvement; long-term antibiotics.
- Meckel diverticulum — rule of twos: present in about 2 per cent, 2 feet (60 centimetres) from the ileocaecal valve, about 2 inches long, with two ectopic tissue types (gastric and pancreatic); gastric mucosa acidifies the adjacent ileum, causing painless lower gastrointestinal bleeding in children; diagnosed by technetium-99m pertechnetate scan, which visualises gastric mucosa.
- Intussusception: infant 3 months to 2 years, idiopathic (viral lymphoid hyperplasia as lead point); colicky pain, red-currant-jelly stools, sausage-shaped mass, target sign on ultrasound; pneumatic or hydrostatic reduction, surgery if signs of peritonism.
- Volvulus and malrotation: midgut volvulus in the neonate with bilious vomiting is a malrotation emergency; sigmoid volvulus of the elderly gives the coffee-bean sign and enormous dilatation.
- Mesenteric ischaemia: superior mesenteric artery territory; pain out of proportion to physical findings; watershed zones at the splenic flexure and rectosigmoid junction injured first in global hypoperfusion.
Chronic diarrhoea and anaemia, reasoned through
A 30-year-old presents with six months of bulky stools, weight loss and a haemoglobin of 9 with a mean corpuscular volume of 102. The first fork is geographic: in India, both coeliac disease and tropical sprue sit high on the list, and the discriminator set is worth writing down. Coeliac disease tests positive for anti-tissue transglutaminase IgA, involves the duodenum and proximal jejunum most severely (the site of first contact with gluten), produces iron deficiency at least as often as folate deficiency, and normalises histologically on gluten withdrawal. Tropical sprue tests negative, involves jejunum and ileum alike, therefore producing B12 deficiency with folate deficiency and often a neuropathy or glossitis, and responds not to diet but to folic acid with a prolonged tetracycline course.
The second fork is anatomical. Painless recurrent bleeding in a six-year-old is Meckel diverticulum with ectopic gastric mucosa, demonstrated by the pertechnetate scan. An infant drawing up the legs with screaming episodes and a right-sided mass has intussusception, confirmed by the ultrasound target sign and reduced by air enema. And in the elderly diabetic with severe pain and an unremarkable abdomen, mesenteric ischaemia must be diagnosed early: lactate rises late, so a normal lactate never reassures.
Where students slip
Two errors recur in orals. First, duodenal biopsies are ordered after the patient has already stopped gluten — the villi regrow, the histology normalises, and the diagnosis is lost; serology and biopsy both belong to the gluten-eating phase. Second, coeliac disease is framed as a childhood malabsorption only, when adult presentations with iron deficiency, osteoporosis or infertility are routine.
Frequently asked questions
Which antibody screens for coeliac disease?
IgA anti-tissue transglutaminase, with total IgA measured concurrently because IgA deficiency causes false-negative results; diagnosis is confirmed by duodenal biopsy on a gluten-containing diet.
How does tropical sprue differ from coeliac disease?
Whole-bowel involvement with both folate and B12 deficiency, negative coeliac serology, occurrence in the tropics including India, and response to folic acid with tetracycline rather than gluten exclusion.
What is the rule of twos for Meckel diverticulum?
About 2 per cent prevalence, 2 feet from the ileocaecal valve, 2 inches long, and two ectopic tissues — gastric and pancreatic; gastric mucosa causes painless bleeding, demonstrated on pertechnetate scanning.
Which scan diagnoses bleeding Meckel diverticulum and why?
Technetium-99m pertechnetate, which is taken up by ectopic gastric mucosa.
What is the classic triad of intussusception?
Intermittent colicky pain with drawing up of the legs, red-currant-jelly stools and a sausage-shaped abdominal mass; ultrasound shows the target sign.
Why does mesenteric ischaemia show pain out of proportion to signs?
Early ischaemia injures the mucosa and visceral afferents while the serosa and parietal peritoneum remain intact, so examination findings lag behind the severity of pain until transmural infarction supervenes.