Gastrointestinal system

MCQ NO 1:

An 8-year-old girl is brought to the emergency department with profuse watery diarrhea for 5 days, persistent vomiting, and progressive lethargy. She has a history of chronic abdominal distension, poor weight gain, and intermittent loose stools for the past year. On examination, she appears dehydrated, tachycardic, and hypotensive. She has pedal edema and muscle wasting.

Laboratory investigations reveal:

  • Serum sodium: 124 mEq/L

  • Serum potassium: 2.6 mEq/L

  • Serum bicarbonate: 14 mEq/L

  • Serum albumin: 2.2 g/dL

  • Tissue transglutaminase (tTG-IgA): markedly elevated

Which of the following is the most appropriate immediate management step in this patient?

A. Aggressive intravenous fluid resuscitation with correction of electrolyte imbalance
B. Initiation of gluten-free diet alone
C. Intravenous corticosteroids and parenteral nutrition
D. Oral zinc supplementation and probiotics
E. Rapid correction of hyponatremia with hypertonic saline

 

MCQ NO 2:

A 6-year-old boy presents with recurrent abdominal pain, bloating, flatulence, and watery diarrhea for the past 3 months. His symptoms typically occur 1–2 hours after consuming milk or ice cream and improve when dairy is avoided. There is no weight loss, no blood in stool, and growth parameters are normal. Physical examination is unremarkable.

Stool examination shows acidic pH (5.0) and positive reducing substances. Tissue transglutaminase IgA is negative.

Which of the following is the most appropriate diagnostic test to confirm the suspected condition?

A. Duodenal biopsy demonstrating villous atrophy
B. Hydrogen breath test after oral lactose load
C. Measurement of fecal elastase
D. Serum anti-endomysial antibody testing
E. Sweat chloride test

MCQ NO 3:

An 18-month-old previously healthy boy is brought to the emergency department with 3 days of profuse watery diarrhea and multiple episodes of non-bilious vomiting. He has low-grade fever and decreased oral intake. There is no blood or mucus in stools. On examination, he is irritable, has sunken eyes, dry mucous membranes, delayed capillary refill (3 seconds), and tachycardia.

Laboratory findings:

  • Serum sodium: 150 mEq/L

  • Serum potassium: 3.4 mEq/L

  • Serum bicarbonate: 16 mEq/L

Stool microscopy shows no leukocytes or red blood cells.

Which of the following best explains the primary mechanism of diarrhea in this patient?

A. Direct enterocyte invasion causing mucosal ulceration
B. Enterotoxin-mediated activation of adenylate cyclase
C. Osmotic diarrhea due to lactase deficiency secondary to villous injury
D. Secretory diarrhea due to activation of enteric nervous system by viral NSP4 protein
E. Systemic cytokine-mediated intestinal hypermotility

MCQ NO 4: 

KEYS: 

Gastrointestinal system

MCQ NO1:   Correct Answer: B 

MCQ NO 2:  Correct Answer: B. Hydrogen breath test after oral lactose load

Explanation (Postgraduate Concept)

This child has features suggestive of lactose intolerance, characterized by:

  • Post-dairy abdominal symptoms

  • Normal growth (rules out chronic malabsorption)

  • Acidic stool with reducing substances (carbohydrate malabsorption)

The hydrogen breath test is the gold standard non-invasive diagnostic test. In lactose intolerance, undigested lactose is fermented by colonic bacteria, producing hydrogen, which is measured in expired air.

Why others are incorrect:

  • Duodenal biopsy → for celiac disease

  • Fecal elastase → for pancreatic insufficiency

  • Anti-endomysial antibodies → for celiac disease

  • Sweat chloride test—  cystic fibrosis   

 

  • MCQ NO 3:

  • CORRECT Answer: D. Secretory diarrhea due to activation of enteric nervous system by viral NSP4 protein

  • Postgraduate Discussion

    This presentation is typical of rotavirus gastroenteritis:

    • Age: 6–24 months (most common)

    • Profuse watery diarrhea

    • Vomiting prominent

    • No blood or fecal leukocytes

    • Metabolic acidosis from bicarbonate loss

    • Hypernatremic dehydration possible

    Pathophysiology (PG concept):
    Rotavirus produces NSP4, a viral enterotoxin that:

    • Stimulates chloride secretion

    • Activates the enteric nervous system

    • Causes secretory diarrhea

    • Also leads to villous blunting → secondary lactose malabsorption (osmotic component)

    Thus, diarrhea is primarily secretory, with a secondary osmotic component.

    Why others are incorrect:

    • Direct invasion → seen in Shigella, Salmonella

    • Adenylate cyclase activation → typical of cholera

    • Pure osmotic mechanism → not the primary mechanism

    • Cytokine-mediated hypermotility → not the main mechanism

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