Malabsorption Syndrome
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Direct answer
Malabsorption is the failure of digestion or absorption producing weight loss, chronic diarrhoea, steatorrhoea (pale, bulky, floating, offensive stools) and deficiency states — iron and folate lost first, fat-soluble vitamins A, D, E and K next, and vitamin B12 last when the terminal ileum or pancreas fails. Indian aetiology is dominated by tropical sprue, coeliac disease, giardiasis, chronic pancreatitis and blind-loop syndromes, a ladder quite different from Western lists. Discriminating mucosal from pancreatic disease is the diagnostic axis: the D-xylose test (absorbed normally in pancreatic disease, impaired in mucosal disease) and faecal elastase (low in pancreatic insufficiency) do the work in one out-patient visit. Correct deficiencies with folate given before B12 and treat the cause — tetracycline and folate for tropical sprue, a gluten-free diet for coeliac, metronidazole for giardia, enzymes for the pancreas.
What you must remember
- Presentation cluster: weight loss with a good appetite (classic in coeliac children), steatorrhoea, glossitis, anaemia, osteomalacia, night blindness, easy bruising, peripheral neuropathy — deficiency patterns localise the lesion.
- Site-based deficiency logic: iron, folate and disaccharidases go with proximal jejunal disease; B12 and bile salts with terminal ileal disease; all fat-soluble vitamins with cholestasis and pancreatic insufficiency.
- D-xylose test: 25 g orally, urine recovery under 4-5 g in 5 hours (or low blood level at 1-2 hours) indicates mucosal disease such as sprue or coeliac; normal in pancreatic insufficiency.
- Coeliac package: tissue transglutaminase IgA (sensitivity above 90 percent) with total IgA to exclude deficiency, confirmed by Marsh-graded duodenal biopsy (villous atrophy, crypt hyperplasia) on a gluten-containing diet; HLA-DQ2 in about 90 percent, DQ8 in most of the rest.
- Tropical sprue: megaloblastic anaemia from folate and B12 deficiency, villous atrophy throughout the small bowel, responds to folic acid 5 mg daily plus tetracycline 250 mg four times daily for 3-6 months; by definition occurs in, or after travel to, the tropics including India.
- Giardiasis: stinky steatorrhoea without blood, cysts on stool microscopy or trophozoites on duodenal aspirate; treat with metronidazole 400 mg thrice daily for 5-7 days or tinidazole 2 g single dose.
- Chronic pancreatitis markers: faecal elastase below 200 microgram/g, low faecal chymotrypsin, plain radiograph pancreatic calcification — enzyme replacement with lipase 25,000-40,000 units per main meal.
- Correction order: always give folate with, or before, B12 in combined deficiency to avoid precipitating subacute combined degeneration; parenteral vitamin K for prolonged prothrombin.
A diagnostic pathway in practice
A 34-year-old man from a village near Lucknow reports eight months of bulky stools, 8 kg weight loss, glossitis and pallor; he has been treated twice as "amoebiasis" without benefit. Examination shows angular stomatitis and pigmented shins consistent with scurvy-like dermatitis. The pathway starts with confirmation: stool for fat globules and parasites (giardia cysts are found on a single sample in many cases), haemoglobin with peripheral smear showing macrocytosis and hypersegmented neutrophils, and a D-xylose test that returns low — mucosal disease. Serology comes next: tTG IgA positive, total IgA normal, so duodenal biopsy is planned. If biopsy showed villous atrophy with crypt hyperplasia and increased intraepithelial lymphocytes in a tTG-positive patient, coeliac disease is confirmed and a lifelong gluten-free diet begins with repeat serology at 6-12 months.
But suppose the biopsy showed subtotal villous atrophy with tTG negative and a tropical-residence history — tropical sprue now leads, and the prescription becomes folic acid 5 mg daily with tetracycline for months, with haematological recovery within weeks as the teaching point. If instead the D-xylose had been normal with low faecal elastase and pancreatic calcification, the same patient would be on pancreatic enzymes with fat-soluble vitamin replacement. Three outcomes from one complaint, separated by two cheap tests and one biopsy — the whole architecture of malabsorption questions.
How the exam frames malabsorption
NBE constructs diagnostic ladders: a stem with steatorrhoea plus a discriminating detail (apthous ulcers and dermatitis herpetiformis pointing to coeliac, tropical residence pointing to sprue, alcohol and calcification pointing to pancreas, previous surgery pointing to blind loop), then asks for the single best investigation or the drug. Classical one-liners include which vitamin deficiency appears first, which test separates mucosal from pancreatic disease, and why folate precedes B12. The Indian convention is that tropical sprue stays high-yield precisely because Indian textbooks and NBE question writers keep it alive, while Western exams have retired it. Viva examiners ask for the D-xylose logic in one sentence.
Frequently asked questions
Which test distinguishes mucosal from pancreatic causes of malabsorption?
The D-xylose absorption test, which is abnormal in mucosal disease (sprue, coeliac) and normal in pancreatic insufficiency, complemented by faecal elastase for the pancreas.
How is coeliac disease confirmed?
Tissue transglutaminase IgA serology with total IgA, followed by duodenal biopsy showing villous atrophy, crypt hyperplasia and intraepithelial lymphocytosis while on a gluten-containing diet.
What is the treatment of tropical sprue?
Folic acid 5 mg daily (with B12 if deficient) plus tetracycline 250 mg four times daily for 3-6 months, with nutritional rehabilitation.
Why must folate be given before or with B12 in combined deficiency?
Folate alone can precipitate subacute combined degeneration of the cord by fueling myelin synthesis while B12 remains deficient.
Which parasitic cause of malabsorption is commonest in India and how is it treated?
Giardia lamblia, diagnosed by stool microscopy or duodenal aspirate, treated with metronidazole or tinidazole.