Food Allergies

Food Allergies - Tiny Trigger Titans

• Definition: Adverse IgE-mediated (Type I hypersensitivity) or non-IgE-mediated immune reaction to specific food proteins.
• Prevalence: Affects ~6-8% of children and ~3-4% of adults; incidence is increasing.
• Common Culprits ("Big 8"): Cow's milk, eggs, peanuts, tree nuts (e.g., walnuts, almonds), soy, wheat, fish, shellfish.
• Clinical Features: Urticaria, angioedema, vomiting, diarrhea, wheezing, anaphylaxis (potentially life-threatening).
• Diagnosis: Detailed history, skin prick tests (SPT), serum specific IgE (sIgE), component-resolved diagnosis (CRD), oral food challenge (OFC) - gold standard.

⭐ Most common food allergy in infants and young children is cow's milk protein allergy (CMPA).

Food Allergies - Immune Mayhem Pathways

• Primary Mechanisms:
  • IgE-Mediated (Type I Hypersensitivity): Rapid onset (minutes to 2 hrs).
    • Sensitization: Allergen → Antigen Presenting Cell (APC) → Th2 cells → IL-4/IL-13 → B cells produce IgE → IgE binds mast cells/basophils.
    • Elicitation: Re-exposure → Allergen cross-links IgE → Mast cell degranulation (histamine, tryptase, leukotrienes).
    • Manifestations: Urticaria, angioedema, anaphylaxis, oral allergy syndrome.
  • Non-IgE-Mediated: Delayed onset (hours to days); T-cell/eosinophil driven.
    • Examples: Food Protein-Induced Enterocolitis Syndrome (FPIES), Food Protein-Induced Allergic Proctocolitis (FPIAP), Eosinophilic Esophagitis (EoE).
  • Mixed IgE & Non-IgE: Features of both mechanisms.
    • Examples: Atopic dermatitis, eosinophilic gastroenteritis.

⭐ Cow's milk protein allergy is the most common food allergy in early childhood, manifesting through IgE-mediated, non-IgE-mediated, or mixed reactions.

Food Allergies - Clinical Clues & Alarms

• IgE-Mediated (Rapid: mins to <2 hrs):
  • Skin: Urticaria, angioedema, flushing, eczema flare.
  • GI: Nausea, vomiting, abdominal pain, diarrhea.
  • Respiratory: Wheeze, stridor, cough, rhinorrhea.
  • Oral: Itching/swelling (lips, tongue) - Oral Allergy Syndrome (OAS).
• Non-IgE-Mediated (Delayed: 2-6 hrs):
  • FPIES: Profuse vomiting, lethargy, pallor, diarrhea (±blood). Triggers: milk, soy, rice.
  • EoE: Dysphagia, food impaction.
• ⚠️ Alarm Signs (Anaphylaxis):
  • Respiratory distress (wheeze, stridor).
  • Hypotension, collapse, dizziness.
  • Altered consciousness.
  • Severe/persistent GI symptoms.

⭐ Biphasic anaphylaxis: recurrence 1-72 hrs (peak 8-12 hrs) post-initial resolution, without re-exposure.

Food Allergies - Testing, Taming & Action

• Testing:
  • Skin Prick Test (SPT): Primary, rapid. Positive: wheal ≥3mm > negative control.
  • Specific IgE (sIgE) blood test: e.g., ImmunoCAP. Useful if skin issues/antihistamines.
  • Oral Food Challenge (OFC): Gold standard, esp. DBPCFC. Confirms diagnosis/tolerance.
• Taming (Management):
  • Strict allergen avoidance: Cornerstone. Educate on label reading.
  • Nutritional counseling: Ensure adequacy, prevent deficiencies.
  • Oral Immunotherapy (OIT): Specialist supervised desensitization. Not routine.
• Action (Emergency Plan):
  • Written anaphylaxis emergency action plan.
  • Epinephrine Auto-Injector (EAI): First-line for anaphylaxis. Dose: 0.01 mg/kg (max 0.3mg child; 0.5mg adult).
    • Administer IM anterolateral thigh. Repeat if needed.
  • Antihistamines (H1 blockers): Adjunct for mild cutaneous/nasal symptoms.
  • Corticosteroids: May prevent protracted/biphasic reactions. Not for acute rescue.

⭐ Biphasic anaphylaxis can occur 1-72 hours (typically within 8-12 hrs) after the initial symptoms resolve, even with initial treatment.

High‑Yield Points - ⚡ Biggest Takeaways

• Most food allergies are IgE-mediated, causing rapid symptoms like urticaria or angioedema.
• Common culprits: cow's milk, egg, peanut, tree nuts, soy, wheat, fish, shellfish.
• Oral Food Challenge (OFC) remains the gold standard for diagnosis.
• Skin Prick Test (SPT) and specific IgE (sIgE) levels support diagnosis.
• Anaphylaxis is life-threatening; epinephrine is the crucial first-line treatment.
• FPIES is a distinct non-IgE mediated allergy with delayed, severe GI symptoms.
• Primary management: strict avoidance of the trigger food and an emergency action plan.