Persistent and chronic diarrhoea — branching viva

Station opening

Examiner: "Define persistent and chronic diarrhoea, and explain how you would frame your approach to a child referred with diarrhoea that will not settle." [1]

Strong candidate (must-hit)

• Defines persistent diarrhoea as an episode lasting fourteen days or more and chronic diarrhoea as loose or frequent stools continuing for four weeks or more; explains that the duration shifts the differential away from self-limiting infection towards an underlying cause; frames the approach around three lines — the duration, the stool type (watery osmotic or secretory, fatty, inflammatory) and the age — and states that the first decision is whether the child is thriving, which points to a functional or dietary cause, or failing to grow or passing blood, which points to an organic enteropathy. [1]

Weak candidate

• "Diarrhoea is chronic if it goes on a long time, and I would send off some stool tests." [1]

Branch A — The thriving two-year-old

Examiner: "A well, thriving two-year-old passes loose stools with recognisable undigested food, worse through the day, with no blood and no weight loss. What is the diagnosis and what do you do?" [4]

Strong

• Makes the positive clinical diagnosis of chronic nonspecific (toddler's) diarrhoea on the basis of normal growth, undigested food in the stool worsening through the day, and the absence of red flags; identifies excessive fruit juice with its fructose and sorbitol as an osmotic contributor and the counterproductive low-fat diet as another; manages with a dietary review — cut the juice, ensure adequate fat, balance fibre and fluid — and firm reassurance that the child will grow out of it by school age; resists over-investigation and avoids antidiarrhoeals. [4]

Weak

• "I would arrange a full malabsorption screen, endoscopy and imaging to be safe." [4]

Branch B — The six-month-old with blood and mucus

Examiner: "A six-month-old, otherwise well and breastfed, has blood and mucus in the stool with some loose stools. The mother is still breastfeeding. What is the likely diagnosis and how do you manage it?" [8]

Strong

• Diagnoses non-IgE-mediated cow's milk protein allergy (allergic proctocolitis) as the likely cause of blood and mucus in an otherwise well infant; manages the breastfed infant with maternal exclusion of cow's milk protein, and the formula-fed infant with an extensively hydrolysed formula, escalating to an amino-acid formula if symptoms persist; confirms the diagnosis by resolution on elimination and recurrence on a supervised reintroduction; and explains that tolerance usually develops by early childhood, so reintroduction is planned. [8]

Weak

• "Blood in the stool means I should start antibiotics for infective colitis." [8]

Branch C — The nine-year-old with faltering growth

Examiner: "A nine-year-old has a two-year history of loose stools, a distended abdomen, iron-deficiency anaemia and a fall across the growth centiles. What is your leading diagnosis and how do you confirm it?" [6]

Strong

• Puts coeliac disease at the top of the differential for faltering growth, iron-deficiency anaemia and chronic diarrhoea; confirms with immunoglobulin A anti-tissue-transglutaminase antibody plus a total immunoglobulin A to exclude deficiency, taken while the child is still eating gluten; applies the ESPGHAN 2020 no-biopsy route only when the anti-transglutaminase titre is at or above ten times the upper limit of normal with a positive endomysial antibody on a separate sample, and otherwise proceeds to duodenal biopsy; and manages with a strict lifelong gluten-free diet with dietitian support, monitoring falling antibody titres and catch-up growth. [6]

Weak

• "I would start a gluten-free diet now and check the coeliac antibodies afterwards." [6]

Branch D — The fifteen-year-old with bloody diarrhoea

Examiner: "A fifteen-year-old has bloody diarrhoea, weight loss, nocturnal symptoms and a raised faecal calprotectin. How do you confirm the diagnosis, and what distinguishes the osmotic from the secretory diarrhoeas you considered earlier?" [7]

Strong

• Diagnoses inflammatory bowel disease and confirms it under the revised Porto criteria with ileocolonoscopy, upper gastrointestinal endoscopy and multiple biopsies plus small-bowel imaging, excluding an infective mimic with stool studies; explains the earlier osmotic-versus-secretory distinction using Field's ion-transport model — osmotic diarrhoea depends on an unabsorbed luminal solute and stops with fasting, whereas secretory diarrhoea is driven by active enterocyte chloride and water secretion and persists through a fast; outlines induction with exclusive enteral nutrition or steroids and maintenance with immunomodulators or biologics. [7] [3]

Weak

• "It's probably irritable bowel syndrome; I would reassure him and review in a few months." [7]

Close

Examiner: "Summarise your approach to the child with chronic diarrhoea in one sentence." [1]

Strong

• "Persistent diarrhoea lasts fourteen days or more and chronic diarrhoea four weeks or more: I classify it by duration, stool type and age, decide first whether the child is thriving or failing, distinguish osmotic from secretory diarrhoea by the response to fasting, work up with stool studies, coeliac serology on a gluten-containing diet and faecal calprotectin, and manage by rehydrating, continuing to feed, giving zinc and treating the specific cause." [1] [6]