Persistent and chronic diarrhoea — formative SAQs

SAQ 1 — The thriving toddler with loose stools (20 marks, ~15 minutes)

A 2-year-old is brought in by anxious parents with a three-month history of four to six loose stools a day that often contain recognisable undigested food such as peas and carrots. The first stool of the day is the largest and they become looser as the day goes on. There is no blood and no night-time diarrhoea. The child is active and well, and the growth chart shows steady tracking along the 50th centile for weight and height. The parents have switched to a low-fat diet and the child drinks about a litre of fruit juice and squash a day. [4]

Questions

1. Give the most likely diagnosis and the three features of this history that support it. (5 marks) [4]
2. Explain the two dietary contributors and the physiology by which each produces loose stools. (5 marks) [5]
3. State what investigations, if any, you would perform and justify your answer. (4 marks) [1]
4. Outline your management and the advice you would give the parents. (4 marks) [4]
5. State the features that, if present, would change your diagnosis and prompt investigation. (2 marks) [1]

Model answer (must-hit)

1. The most likely diagnosis is chronic nonspecific diarrhoea of childhood (toddler's diarrhoea). The three supporting features are the normal growth and thriving state of the child, the presence of recognisable undigested food in the stool with the stools becoming looser through the day, and the complete absence of red flags — no blood, no weight loss and no nocturnal diarrhoea. It is a positive clinical diagnosis in a well, growing child. [4]
2. The first contributor is the excessive fruit juice and squash: the fructose and sorbitol they contain exceed the small bowel's absorptive capacity, remain in the lumen and act as an osmotic load that draws water into the colon and produces loose stools. The second is the low-fat diet the parents have adopted, which paradoxically worsens the problem by speeding intestinal transit and reducing the contact time for water absorption; adequate dietary fat slows transit and firms the stool. [5] [4]
3. In a thriving child with this classic history, no investigations are required. The diagnosis is clinical, and a battery of tests risks harm and anxiety without benefit. A three-day stool and food diary to quantify the juice and fat intake is the most useful step, and coeliac serology may be considered if there is any doubt, taken while the child is still eating gluten. [1] [6]
4. Management is dietary and reassuring: reduce the fruit juice and sorbitol-containing drinks, ensure an adequate normal fat intake, avoid the counterproductive low-fat diet, and maintain a balanced fibre and fluid intake. Give firm reassurance that the child is well, is growing normally and will grow out of the condition, usually by school age, and that no medication or antidiarrhoeal is needed. Arrange follow-up to confirm continued normal growth. [4]
5. Any of blood in the stool, weight loss or faltering growth, nocturnal diarrhoea that wakes the child, dehydration, or onset in early infancy would exclude toddler's diarrhoea and mandate investigation for an organic cause. [1]

SAQ 2 — The school-age child with chronic bloody diarrhoea (20 marks, ~15 minutes)

An 11-year-old presents with a four-month history of loose stools, now up to eight a day, containing blood and mucus and sometimes waking him at night. He has lost 4 kg, has abdominal pain and mouth ulcers, and looks pale and tired. His height and weight have fallen across two centiles. Blood tests show a microcytic anaemia, a raised C-reactive protein and erythrocyte sedimentation rate, a low albumin, and a markedly elevated faecal calprotectin. [7]

Questions

1. Give the most likely diagnosis and the features that support it. (5 marks) [7]
2. State how you would confirm the diagnosis, naming the criteria and the investigations required. (6 marks) [7]
3. This child had coeliac serology sent by the general practitioner after starting a gluten-free diet two weeks ago; it was negative. Explain why this result cannot be relied upon. (3 marks) [6]
4. Outline the principles of management. (4 marks) [7]
5. State two adjuncts to supportive care in persistent diarrhoea and their rationale. (2 marks) [12]

Model answer (must-hit)

1. The most likely diagnosis is inflammatory bowel disease. The supporting features are chronic bloody, mucoid diarrhoea with nocturnal symptoms, weight loss and faltering growth across two centiles, abdominal pain, mouth ulcers as an extraintestinal feature, and the laboratory picture of microcytic anaemia, raised inflammatory markers, hypoalbuminaemia from protein loss, and a markedly elevated faecal calprotectin indicating mucosal inflammation. This combination is inflammatory bowel disease until proven otherwise. [7]
2. Confirmation follows the revised Porto criteria: referral to paediatric gastroenterology for ileocolonoscopy and upper gastrointestinal endoscopy with multiple biopsies from all segments, together with small-bowel imaging by magnetic resonance enterography to assess disease extent. Stool cultures and infective screens exclude an infective mimic. The histology, endoscopic appearance and imaging together distinguish Crohn disease from ulcerative colitis and define disease location and severity. [7]
3. Coeliac serology depends on the immune response to ingested gluten, so it must be taken while the child is still eating a gluten-containing diet. Starting a gluten-free diet normalises the anti-tissue-transglutaminase and endomysial antibodies within weeks, so a negative result taken after gluten withdrawal is uninterpretable and cannot exclude coeliac disease; a formal gluten challenge with repeat serology would be required to test for it properly. [6]
4. Management is specialist and staged: induce remission (exclusive enteral nutrition or corticosteroids in Crohn disease), then maintain it with aminosalicylates, immunomodulators or biologics tailored to disease type, location and severity. The goals are mucosal healing, resolution of symptoms, correction of anaemia and nutritional deficiencies, restoration of normal growth and pubertal progression, and monitoring with faecal calprotectin and growth, with planned transition to adult services in adolescence. [7]
5. Two adjuncts are zinc supplementation, which shortens the duration and severity of persistent diarrhoea, and correction of micronutrient deficiencies (iron, folate and fat-soluble vitamins) together with continued feeding and nutritional rehabilitation to reverse the malnutrition that persistent diarrhoea causes. [12]