Cow's-milk protein allergy — branching viva

Opening

Examiner: A four-month-old, exclusively formula-fed infant presents with a two-week history of blood and mucus in the stools, distress on feeds, and an eczema flare. The mother wants to switch to a goat's-milk or A2 formula. How do you frame this? [1]

Candidate: I would frame this as suspected cow's-milk protein allergy, most likely the delayed non-IgE-mediated phenotype given the bloody mucoid stools, feeding distress and eczema, while first clearing the anaphylaxis and red-flag gate — faltering growth, dehydration, signs of FPIES or proctocolitis with systemic compromise. I would take a focused allergy and feeding history, examine growth and hydration, and confirm the diagnosis clinically by eliminating cow's-milk protein for two to four weeks with a planned rechallenge, rather than switching to a goat's-milk or A2 formula, which are not appropriate alternatives because their proteins are broadly cross-reactive. [1] [2]

Branch 1 — phenotype and the anaphylaxis gate

Examiner: Walk me through the two phenotypes and why the distinction matters. [1]

Candidate: There are two phenotypes and the distinction drives the assessment and management. IgE-mediated disease is immediate, within minutes to two hours, driven by specific IgE to cow's-milk proteins, and presents with urticaria, angioedema, vomiting, and the one I must not miss — anaphylaxis. Non-IgE-mediated disease is delayed, hours to days, cell-mediated, and presents with gastrointestinal and dermatological symptoms — blood and mucus in the stools, reflux, distress on feeding, faltering growth, and eczema. The distinction matters because IgE-mediated disease can be anaphylactic and is confirmed with skin-prick testing and specific IgE, while non-IgE-mediated disease is confirmed by elimination and rechallenge and is not detected on allergy testing. [1] [2]

Examiner (probe): Where does anaphylaxis fit in your immediate priorities? [6]

Candidate: First. Any acute reaction with respiratory compromise, stridor, wheeze, hypotension or collapse after milk exposure is anaphylaxis until proven otherwise, and gets intramuscular adrenaline immediately, then assessment and admission, an adrenaline autoinjector, and an anaphylaxis action plan. The EAACI guidelines are explicit that anaphylaxis is a clinical diagnosis and that adrenaline is first-line and underused. [6]

Branch 2 — confirming the diagnosis

Examiner: The mother expects a blood test. How do you actually confirm non-IgE-mediated CMPA? [1]

Candidate: For the non-IgE-mediated phenotype, the diagnosis is clinical and rests on elimination and planned rechallenge. I would remove all cow's-milk protein from the infant's diet — for a formula-fed infant, switch to an extensively hydrolysed formula — for two to four weeks and look for symptom resolution, then reintroduce cow's-milk protein to confirm that symptoms recur. A positive rechallenge confirms CMPA and distinguishes it from coincidental improvement. I would not rely on skin-prick testing or specific IgE for the non-IgE-mediated phenotype, because they are negative in cell-mediated disease. [1]

Examiner (probe): And for the IgE-mediated phenotype — when are tests useful? [2]

Candidate: For the IgE-mediated phenotype, skin-prick testing and serum specific IgE to cow's-milk proteins — casein, beta-lactoglobulin — are useful to support a history consistent with immediate reactions, to stratify severity, and to guide the reintroduction pathway. But a positive test indicates sensitisation, not clinical allergy on its own, so I interpret it alongside the history and the oral food challenge, which remains the gold standard when the diagnosis is uncertain. [2]

Branch 3 — the stepwise elimination ladder

Examiner: He is exclusively formula-fed. Take me through the elimination ladder. [3]

Candidate: First-line for the formula-fed infant with mild to moderate non-IgE-mediated CMPA is an extensively hydrolysed formula — eHF — in which the proteins are broken down sufficiently that most infants tolerate them. The DRACMA and ESPGHAN guidelines place eHF first-line. If symptoms are severe — anaphylaxis, faltering growth, multiple food allergy, or a reaction while on an eHF — or if the infant fails to respond to a two-to-four-week trial of eHF, I escalate to an amino-acid formula, which is hypoallergenic by design. I would not use soy formula before six months because of the risk of co-allergy and its phytoestrogen content. [3] [1]

Examiner (probe): What if the mother is breastfeeding? [1]

Candidate: For the breastfed infant I keep breastfeeding — it is the best source of nutrition — and ask the mother to eliminate all cow's-milk protein, including hidden dairy, from her own diet for two to four weeks, with a planned rechallenge. I arrange dietetic input and calcium and vitamin-D supplementation for the mother, because a maternal dairy-free diet is nutritionally significant. If the breastfed infant is severe or fails a maternal elimination trial, I add an eHF or AAF top-up as indicated. [1]

Branch 4 — tolerance, reintroduction and the long view

Examiner: When does he outgrow it, and how do you build tolerance? [4]

Candidate: The majority outgrow CMPA. For IgE-mediated disease, the Skripak cohort showed about half had resolved by five years and about three-quarters by sixteen, with earlier tolerance in lower IgE and milder reactions. Tolerance is built through the reintroduction ladder — the 'milk ladder' — which starts with extensively baked milk, in which heat and the food matrix denature the conformational epitopes, and progresses stepwise to less-heated and then raw milk. I would reintroduce under specialist guidance for the IgE-mediated phenotype, where reactions can be severe, and more conservatively for those with a history of anaphylaxis. [4] [5]

Examiner (final corner): Tell me about FPIES and proctocolitis — the atypical presentations. [6]

Candidate: Food-protein-induced enterocolitis syndrome — FPIES — is a severe, delayed, non-IgE-mediated reaction, typically one to four hours after cow's-milk ingestion, with repetitive projectile vomiting that can progress to lethargy, pallor and dehydration, and is managed with aggressive intravenous fluid resuscitation; it carries a real risk of shock, so I would admit and observe. Cow's-milk protein-induced proctocolitis is the other end of the spectrum — a well-looking breastfed infant with blood and mucus in the stools, normal growth, and resolution on maternal or infant elimination; it is benign and usually resolves by one year, and I reassure and manage conservatively. Both are part of the non-IgE-mediated family but need very different responses, so the severity of the phenotype dictates the setting of care. [6] [1]