What is the diagnosis and management for a 6-month-old breastfed female infant with a history of eczema (atopic dermatitis) who develops periocular redness, swelling, and a small rash on the cheeks after ingestion of butter, with normal vital signs and no respiratory distress?

Acute Allergic Reaction (Likely Cow's Milk Protein Allergy)

This 6-month-old infant is experiencing an acute IgE-mediated allergic reaction, most likely to cow's milk protein in the butter, presenting as periocular angioedema and facial urticaria without systemic involvement.

Immediate Management

No treatment is required at this time since the reaction is mild, self-limited, and there are no systemic symptoms or respiratory compromise. 1

• Observe the infant for progression of symptoms, particularly monitoring for respiratory distress, stridor, wheezing, or signs of anaphylaxis over the next 2-4 hours 1
• Oral antihistamines (diphenhydramine or cetirizine) may be considered for symptomatic relief of urticaria and angioedema, though the reaction will likely resolve spontaneously 1
• Document the time of ingestion, foods consumed, timing of symptom onset, and specific symptoms for future reference 1

Diagnosis

This presentation is consistent with IgE-mediated food allergy manifesting as:

• Acute onset (within minutes to 2 hours of ingestion) 1
• Periocular angioedema and facial urticaria 1
• No prior exposure to butter (first exposure can trigger reaction in sensitized infants) 1

The infant's history of eczema significantly increases the risk of food allergy, with up to 35-37% of children under 5 years with moderate-to-severe atopic dermatitis having IgE-mediated food allergy 1. The presence of severe eczema within the first 6 months of life is strongly associated with increased risk of developing milk and egg allergy 2.

Diagnostic Workup

Refer to a pediatric allergist for comprehensive evaluation and confirmatory testing. 1

• Skin prick testing or specific IgE testing for cow's milk protein should be performed to confirm sensitization 1
  • Skin prick test has high negative predictive value (>95%) but lower positive predictive value (40-60%), meaning positive results indicate sensitization but not necessarily clinical allergy 1
• Consider limited food allergy testing for the other common allergens (eggs, wheat, soy, peanuts) given the infant's age (<5 years) and history of eczema 1
• Supervised oral food challenge under allergist guidance is the gold standard to confirm true clinical allergy versus sensitization alone 1

Critical Pitfall to Avoid

Do not start elimination diets based solely on this single reaction or positive testing without allergist confirmation. 1 Prolonged and multiple elimination diets can lead to weight loss, growth delay, calcium deficiency, and other nutritional deficiencies 1.

Ongoing Management

Strict avoidance of cow's milk protein (butter, milk, cheese, yogurt, and hidden sources in processed foods) until allergist evaluation 1

• Prescribe an epinephrine auto-injector (EpiPen Jr 0.15mg for infants 7.5-25kg) and provide emergency action plan training to parents 1
  • While this reaction was mild, the presence of asthma (which often coexists with atopic dermatitis) is a risk factor for severe reactions, and 44% of children with asthma have existing food allergy 2
• Continue breastfeeding, but the mother should eliminate cow's milk protein from her diet, as antigenic food proteins in breast milk can elicit reactions in sensitized infants 3
• Optimize treatment of the underlying atopic dermatitis with appropriate-potency topical corticosteroids and liberal emollient use 1
  • This is crucial because effective treatment of atopic dermatitis remains skin care and topical therapies, even in the presence of confirmed food allergy 1

Follow-up and Prognosis

• Allergist referral for longitudinal care, formulation of emergency anaphylaxis action plan, supervised oral food challenges, and prevention of unnecessary dietary restrictions 1
• Most children with cow's milk allergy develop tolerance over time, and regular re-evaluation is necessary 1
• Keep a food diary to identify consistent correlations between symptoms and food intake, looking for both immediate reactions and delayed effects occurring 2-4 days after exposure 1

Important Consideration

The infant has eaten eggs before without reaction, so this is unlikely to be egg allergy. The temporal relationship with butter (first exposure) strongly implicates cow's milk protein as the culprit allergen 1.