When the infant's immature gut cannot adequately digest a food protein, the body may mount an immunologic response against it, usually by forming immunoglobulin E (IgE) antibodies. Alternatively, food antigens can cause a non–IgE-mediated reaction.
Of these less common types of GI allergic manifestations, the most common are immediate GI hypersensitivity and oral allergy syndrome. The former typically involves nausea, abdominal pain, and emesis within 1 to 2 hours of exposure to the allergen, diarrhea within 2 to 6 hours, and often a history of atopy. Treatment is strict elimination of the implicated food allergen—which is generally milk, soy, egg, peanuts, shellfish, or wheat.
Oral allergy syndrome is characterized by immediate onset of burning and swelling of the lips, itching, and erythema, and a history of pollen sensitivity, particularly to ragweed or birch. These pollens cross-react with certain fresh fruit and vegetables, which the child should either avoid or eat only when cooked.
"Mixed" GI allergy syndromes, involving some IgE components and some non-IgE components, include allergic eosinophilic esophagitis and allergic eosinophilic gastritis/enterocolitis.
Non–IgE-mediated allergic GI disorders include dietary protein enteropathy, enterocolitis, and proctitis. The classic dietary protein enteropathy involves diarrhea, malabsorption, failure to thrive, vomiting, abdominal distension, and early satiety. Anemia, edema, hypoproteinemia, and protein-losing enteropathy are all characteristic. An x-ray reveals small bowel edema. Serum IgE is normal, and no peripheral eosinophils are evident. Onset is early and depends on exposure to the responsible antigen, usually cow's milk, soy, gluten, egg, or cod.
The pathology is marked by patchy subtotal villous injury, many intraepithelial lymphocytes, and few eosinophils. Strict elimination of the offending protein clears symptoms in 10 to 21 days. The condition resolves by 3 to 5 years of age.
Dietary protein enterocolitis can appear from birth to 1 year of age. It involves bloody diarrhea and anemia, emesis, abdominal distension, failure to thrive, protein-losing enteropathy, hypotension, and fecal polymorphonuclear neutrophil leukocytes. The primary responsible proteins are cow's milk, soy, ovalbumin, and casein and whey hydrolysates. Chronic inflammatory colitis with moderate enteropathy is characteristic. Stool exam reveals red blood cells, eosinophils, polymorphonuclear neutrophil leukocytes, and positive reducing substances. About 90% of patients respond within 3 to 5 days to hydrolyzed protein formula.
Dietary protein-induced proctitis is a common benign condition marked by blood-streaked soft to loose stools and sometimes constipation. Fecal leukocytes, mild peripheral eosinophilia, and hypoalbuminemia are characteristic. Age of onset is from 1 day after birth to 6 months of age. About 60% of infants with proctitis are exclusively breastfed; cow's milk, soy, and hydrolyzed protein also can cause the condition. Treatment with casein hydrolysate formula usually clears symptoms in 72 hours. The mother can resume breastfeeding but should first identify and eliminate the responsible antigen from her diet. The condition generally resolves by 9 months to a year.