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FPIES is a non-IgE mediated food allergy that primarily affects infants and young children, causing severe gastrointestinal symptoms including projectile vomiting and diarrhea. Unlike typical food allergies, FPIES reactions are delayed, typically occurring 1-4 hours after ingestion of trigger foods, most commonly cow's milk, soy, rice, and oats.
FPIES involves a T-cell mediated immune response in the gastrointestinal tract, leading to increased intestinal permeability and inflammatory cell infiltration. The delayed reaction is caused by activation of T-helper cells and release of inflammatory cytokines, resulting in fluid shifts, electrolyte imbalances, and potential hypovolemic shock.
Diagnosis relies heavily on clinical presentation and dietary history, as standard allergy tests (skin prick tests and serum IgE) are typically negative. The key diagnostic clue is the consistent temporal relationship between food ingestion and symptom onset, along with symptom resolution upon food elimination and recurrence upon rechallenge.