Failure to Thrive and Chronic Diarrhea in a 15-Month-Old
A 15-month-old girl presents with a 4-month history of chronic diarrhea, 3–5 loose, foul-smelling stools per day, and poor weight gain. Her weight is 8.2 kg (below the 3rd percentile for age, down from the 25th percentile at 12 months), and length is 72 cm (3rd percentile). She was breastfed until 12 months and then transitioned to whole cow's milk. She has been eating table foods but with a poor appetite. Physical exam reveals a protuberant abdomen, decreased subcutaneous fat, and mild muscle wasting. She is irritable but consolable. Laboratory tests show a microcytic anemia (hemoglobin 9.8 g/dL, MCV 72 fL), low ferritin, and a normal CBC otherwise. Stool studies show increased fecal fat (steatorrhea) but no pathogens. Sweat chloride test is normal. Celiac serology (tTG-IgA) is pending.
1. What is the most likely diagnosis, and what is the pathophysiologic mechanism?
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The most likely diagnosis is cow's milk protein intolerance (CMPI) leading to malabsorption and failure to thrive. The chronic diarrhea, steatorrhea, and weight loss after introduction of cow's milk at 12 months are classic. The mechanism is an immune-mediated reaction to cow's milk proteins causing villous atrophy and increased intestinal permeability, leading to malabsorption of nutrients, including fat and iron. The microcytic anemia is likely due to iron deficiency from malabsorption and possible chronic blood loss. Celiac disease is also a strong consideration, but the temporal relationship with cow's milk introduction and the improvement often seen with elimination diet support CMPI. Other causes like cystic fibrosis are less likely given the normal sweat chloride. The steatorrhea indicates fat malabsorption, which can occur in CMPI due to mucosal damage.
2. How would you manage this patient, and what follow-up is essential?
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The management is a cow's milk protein-free diet using an extensively hydrolyzed formula or a soy-based formula (if tolerated) for at least 2–4 weeks to assess response. In older children, a strict elimination of all cow's milk products is necessary. Breastfeeding should continue if possible, with maternal elimination of cow's milk. Monitor weight, stool frequency, and consistency. Follow-up in 2–4 weeks to assess weight gain and symptom improvement. If no improvement, consider other diagnoses like celiac disease (await serology and consider small bowel biopsy) or other food protein intolerances. Iron supplementation is needed for the anemia. A dietitian should be involved to ensure adequate nutrition. If symptoms resolve, a gradual reintroduction may be attempted later, but often avoidance is long-term.