A 6-week-old girl presents with her parents to the pediatrician for blood-streaked diapers. The patient is breastfed every 2-3 hours and voids 10-12 times daily. The patient previously had several soft stools per day that ranged in color from mustard yellow to dark green. Over the past 2 days, the patient’s stools have become looser and streaked with blood. The patient has also regurgitated several of her feedings in the last few days. Neither the vomit nor bloody stools have seemed to bother the patient. The patient’s weight continues to trend along the 50th percentile. The patient’s temperature is 98.4°F (36.9°C), blood pressure is 66/51 mmHg, pulse is 127/min, and respirations are 26/min. On physical exam, the patient appears well nourished and is cooing. Her abdomen is soft and non-tender. Physical exam reveals the finding seen in Figure A. Which of the following is the most likely etiology of this patient’s presentation?
Congenital enzyme deficiency
Passage of gastric contents into esophagus
Non-IgE-mediated immunologic reaction
Hypertrophy of sphincter muscle
Non-IgE-mediated immunologic reaction
This patient presents with new regurgitation, blood-streaked stools, and eczema, which is consistent with proctocolitis secondary to milk-protein allergy. This type of delayed onset milk-protein allergy is a non-IgE mediated immunologic reaction.

Allergy to cow’s milk is the most common food allergy in children and encompasses both IgE-mediated and non-IgE-mediated reactions. IgE-mediated reactions occur minutes to 2 hours after ingestion of the allergen and range from mild symptoms to anaphylaxis. Milk protein-induced enterocolitis and proctocolitis are non-IgE-mediated reactions that present by 6 months of life with regurgitation or vomiting and bloody stools. Management of milk protein-induced enterocolitis and proctocolitis involves the elimination of cow’s milk and soy from the mother’s diet if the infant is breastfed or switching to a hydrolyzed formula if the infant is formula fed.

Giannetti et al. review the evidence regarding the diagnosis and treatment of milk protein allergy in infants. They discuss how the selective elimination of certain proteins from the diet is usually effective. They recommend considering oral immunotherapy as an adjuvant in the treatment of this disease.

Figure/Illustration A is a clinical photograph demonstrating the physical exam finding of eczema (red circle), which is commonly found in infants with an allergy to milk protein.

Incorrect Answers:
Answer A: Congenital enzyme deficiency describes lactose intolerance, in which there is an absence of lactase activity in the small intestine. Lactose intolerance classically presents with abdominal pain, bloating, flatulence, and diarrhea. Treatment is with diet modification.

Answer C: Hypertrophy of the sphincter muscle describes the pathogenesis of pyloric stenosis, which presents in patients between 3- and 6-weeks of age with non-bilious, projectile vomiting. Treatment is with surgical pyloromyotomy.

Answer D: Passage of gastric contents into the esophagus describes gastroesophageal reflux, which may present with regurgitation or vomiting. Treatment is with positioning but can include proton pump inhibitors in refractory cases.

Answer E: Telescoping of the intestine describes intussusception, which presents with sudden-onset severe, crampy, abdominal pain with non-bilious vomiting and “currant jelly” stools. Intussusception is rare before 3 months of age and presents with intermittent episodes of pain. Initial treatment is with air or contrast enema.

Bullet Summary:
Milk-protein allergy presents in infants between 2- to 8-weeks of age with regurgitation or vomiting, blood-streaked stools, and eczema, and management involves the elimination of cow’s milk and soy from the infant’s diet.