SN6 SHORT NOTE 5M ★ High-yield

Classify malabsorption syndromes. Differentiate coeliac disease from tropical sprue.

Pathology · 2nd Professional — Para-Clinical

Definition

Malabsorption is defective absorption of one or more dietary constituents, resulting from impaired digestion (maldigestion), impaired mucosal absorption, or impaired transport from the gut.

Classification BY Mechanism

Mechanism	Causes
Defective intraluminal digestion	Chronic pancreatitis, cystic fibrosis, pancreatic carcinoma; bile salt deficiency from obstructive jaundice, ileal resection or bacterial overgrowth
Primary mucosal defect	Coeliac disease, tropical sprue, Crohn disease, Whipple disease, lactase deficiency, abetalipoproteinaemia
Reduced absorptive surface	Extensive resection (short bowel syndrome), gastrojejunostomy
Infection and infestation	Giardiasis, intestinal tuberculosis, strongyloidiasis, HIV enteropathy
Lymphatic obstruction	Intestinal lymphangiectasia, lymphoma, tuberculosis of mesenteric nodes — causes loss of fat and protein
Bacterial overgrowth	Blind loops, strictures, diverticula, hypomotility — bacteria deconjugate bile salts and consume B12

Coeliac Disease and Tropical Sprue

Feature	Coeliac disease	Tropical sprue
Cause	Immune reaction to gliadin in wheat, barley and rye	Unknown; probably an infective agent; follows residence in the tropics
Genetics	HLA-DQ2 (95%) and DQ8	None
Site affected	Proximal small bowel — duodenum and jejunum	The whole small bowel, including the ileum
Histology	Villous atrophy, crypt hyperplasia, increased intraepithelial lymphocytes; Marsh grading	Similar but usually less severe
Antibodies	Anti-tissue transglutaminase, anti-endomysial (IgA)	Absent
Deficiencies	Iron and folate (proximal)	Folate and B12 (ileal involvement)
Treatment	Lifelong gluten-free diet	Tetracycline and folic acid for 3–6 months
Associations	Dermatitis herpetiformis; type 1 diabetes; thyroid disease; enteropathy-associated T cell lymphoma; small bowel adenocarcinoma	None

CLINICAL PEARL

The site of involvement predicts the deficiency, and that distinguishes the two. Coeliac disease attacks the proximal bowel, where iron and folate are absorbed, so B12 is usually spared. Tropical sprue involves the ileum as well, so B12 is also deficient. Reasoning from anatomy answers the question without memorising it.

Clinical Features

Steatorrhoea — bulky, pale, greasy, offensive stools that float and are difficult to flush
Chronic diarrhoea, abdominal distension, flatulence, weight loss despite adequate intake; failure to thrive in children
Consequences of specific deficiencies — anaemia (iron, folate, B12); bone pain and tetany (calcium and vitamin D); bleeding (vitamin K); night blindness (vitamin A); oedema (protein); glossitis and cheilosis (B vitamins); neuropathy

Investigation and Applied Aspects

Confirm malabsorption — faecal fat estimation (over 7 g a day on a 100 g fat diet); D-xylose test distinguishes mucosal disease from pancreatic causes
Small bowel biopsy is the key investigation for mucosal disease, taken endoscopically from the second part of the duodenum
Serology for coeliac disease — anti-tissue transglutaminase, with total IgA measured alongside, since IgA deficiency gives false negatives
Test for giardia and for intestinal tuberculosis in India, both of which are common and treatable causes
Coeliac disease must be diagnosed before starting a gluten-free diet, since both the serology and the histology normalise on treatment and the opportunity is lost
Lactose intolerance is very common in Indian and East Asian adults, is a normal genetic state rather than a disease, and requires only dietary adjustment

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