Write a short note on chronic diarrhoea and malabsorption.

Definitions

Diarrhoea is the passage of loose or watery stools three or more times daily, or more frequently than is normal for the individual, and is more precisely defined by a stool weight exceeding 200 g/day. Chronic diarrhoea persists for more than 4 weeks.

Malabsorption is impaired absorption of nutrients, resulting from defects in digestion (maldigestion), mucosal absorption, or transport of absorbed nutrients.

Classification of Chronic Diarrhoea

Causes of Malabsorption

Clinical Features

• Diarrhoea with steatorrhoea — bulky, pale, offensive, greasy stools that float and are difficult to flush.
• Weight loss despite adequate intake; failure to thrive in children.
• Abdominal bloating, distension, flatulence and cramps.
• Consequences of specific deficiencies — worth reciting in an answer as they demonstrate understanding:
• Iron, folate, B12 → anaemia (microcytic, macrocytic or dimorphic)
• Vitamin D and calcium → osteomalacia, bone pain, proximal myopathy, tetany
• Vitamin K → bruising and prolonged prothrombin time
• Vitamin A → night blindness, xerophthalmia
• Protein → oedema and hypoalbuminaemia
• Zinc → dermatitis, poor wound healing; B-complex → glossitis, angular stomatitis, neuropathy
• Red flags requiring urgent investigation: nocturnal diarrhoea, rectal bleeding, weight loss, anaemia, fever, onset over the age of 50, and a family history of malignancy or inflammatory bowel disease. Their absence, with a long history and stable weight, points towards irritable bowel syndrome.

Investigations — a Stepwise Approach

Step 1 — basic:

CBC (anaemia and its type), ESR and CRP, renal function and electrolytes, liver function and albumin, calcium and phosphate, INR, thyroid function, iron studies, vitamin B12 and folate, and blood glucose.

Step 2 — stool:

Microscopy for ova, cysts and parasites (particularly *Giardia*, which requires multiple samples or duodenal aspirate), stool culture, *C. difficile* toxin, faecal fat estimation or a qualitative Sudan stain, faecal calprotectin (raised in inflammatory, normal in functional disease — a valuable discriminator), and faecal elastase (low in pancreatic insufficiency).

Step 3 — targeted:

• Coeliac serology — IgA anti-tissue transglutaminase (tTG) with total IgA (to exclude IgA deficiency, which causes false negatives). The patient must be eating gluten at the time of testing.
• Hydrogen breath tests — for lactose intolerance and small intestinal bacterial overgrowth.
• Upper GI endoscopy with duodenal biopsy — for coeliac disease, tropical sprue, giardiasis and Whipple's disease.
• Colonoscopy with ileoscopy and biopsies — for inflammatory bowel disease, intestinal tuberculosis, malignancy, and microscopic colitis (which requires biopsy of macroscopically normal mucosa).
• Imaging — CT or MR enterography, barium follow-through; CT abdomen for pancreatic disease and lymphadenopathy.
• Gut hormone profile (VIP, gastrin, chromogranin A, urinary 5-HIAA) for suspected neuroendocrine tumour.

COELIAC DISEASE AND TROPICAL SPRUE — the two key mucosal diseases

Coeliac disease is a T-cell-mediated immune reaction to gluten in genetically susceptible individuals (HLA-DQ2/DQ8), causing villous atrophy, crypt hyperplasia and intraepithelial lymphocytosis in the proximal small bowel. It is considerably more common in India than was once thought, particularly in the wheat-eating north.

• Features: diarrhoea, steatorrhoea, weight loss and anaemia; but also silent or atypical presentations — isolated iron deficiency anaemia, short stature, delayed puberty, infertility, osteoporosis, unexplained transaminitis, and neurological symptoms.
• Dermatitis herpetiformis — an intensely itchy, blistering rash on the extensor surfaces — is its cutaneous manifestation.
• Associations: type 1 diabetes, autoimmune thyroid disease, Down syndrome, IgA deficiency.
• Diagnosis: serology followed by duodenal biopsy (Marsh classification), both while on a gluten-containing diet.
• Treatment: a STRICT, LIFELONG GLUTEN-FREE DIET — excluding wheat, barley and rye (oats are usually tolerated). Involve a dietitian; correct nutritional deficiencies; monitor with serology and repeat biopsy where response is poor. Non-adherence is the commonest cause of persistent symptoms; refractory disease raises the possibility of enteropathy-associated T-cell lymphoma.

Tropical sprue — a malabsorption syndrome of unknown aetiology (probably post-infective with bacterial overgrowth), occurring in residents of and visitors to the tropics, including large parts of India. It causes diarrhoea, steatorrhoea, weight loss, and megaloblastic anaemia from B12 AND folate deficiency. Biopsy shows partial villous atrophy affecting the entire small bowel (unlike the proximal predominance of coeliac disease). It responds to prolonged tetracycline with folic acid and vitamin B12 — a distinction of considerable practical importance, since it is treatable with antibiotics rather than dietary exclusion.

Management Principles

1. Treat the specific cause — gluten-free diet, antibiotics for bacterial overgrowth and tropical sprue, pancreatic enzyme replacement for pancreatic insufficiency, antimicrobials for giardiasis and tuberculosis, immunosuppression for inflammatory bowel disease.

2. Correct nutritional deficiencies — iron, folate, B12, fat-soluble vitamins (A, D, E, K), calcium, magnesium and zinc.

3. Nutritional support and dietetic input; lactose avoidance where secondary lactase deficiency is present.

4. Symptomatic — antidiarrhoeals only when infection and inflammation have been excluded; bile acid sequestrants for bile acid diarrhoea.

5. Monitor weight, nutritional markers, and bone density.