Pediatric Allergy and Immunology
This domain tests anaphylaxis management, the recognition of primary immunodeficiency, and the distinction between IgE-mediated and non-IgE-mediated food reactions.
Anaphylaxis
- Give intramuscular epinephrine 0.01 mg/kg of 1:1000 solution (maximum 0.5 mg) into the lateral thigh immediately; repeat every 5-15 minutes if needed.
- Antihistamines and corticosteroids are adjuncts only; they never replace epinephrine.
- Observe 4-6 hours for biphasic reactions.
Primary immunodeficiency red flags
- Two or more pneumonias per year, eight or more ear infections per year, failure to thrive, recurrent deep abscesses, persistent thrush, or a family history of immunodeficiency.
- Severe combined immunodeficiency: lymphopenia, absent thymus, low TREC on newborn screening; live vaccines are absolutely contraindicated.
- X-linked agammaglobulinemia (Bruton): boys with absent tonsils, undetectable immunoglobulins, absent B cells, and pyogenic infections after maternal IgG wanes at about 6 months.
- Chronic granulomatous disease: catalase-positive organisms (Staphylococcus aureus, Aspergillus, Serratia, Nocardia); abnormal dihydrorhodamine test.
- Leukocyte adhesion deficiency: delayed cord separation, marked leukocytosis, no pus formation.
- Terminal complement deficiency: recurrent Neisseria infections.
Food allergy
- IgE-mediated reactions are diagnosed by skin prick testing or specific IgE; the oral food challenge is the gold standard.
- Milk, egg, soy and wheat allergies usually resolve; peanut, tree nut and shellfish allergy often persists.
- FPIES is a non-IgE entity with delayed repetitive vomiting and pallor, not urticaria.
Worked example
A 3-year-old develops urticaria, wheeze and hypotension minutes after eating peanut. Reasoning: this is anaphylaxis with respiratory and circulatory involvement. Give intramuscular epinephrine into the thigh first; antihistamines come after.
Traps
Giving an antihistamine before epinephrine; interpreting immunoglobulin levels before 6 months of age (maternal IgG persists); and ordering skin tests during an acute reaction.