What is the diagnosis and treatment for a patient presenting with shortness of breath, wheezing, and generalized body rash after eating peanuts?

Type I Hypersensitivity Reaction to Peanuts: Diagnosis and Management

The 12-year-old boy is experiencing a type I hypersensitivity reaction that involves Immunoglobulin E (IgE) antibodies, which is the correct mechanism for food-induced anaphylaxis presenting with shortness of breath, wheezing, and generalized body rash after peanut ingestion.

Pathophysiology of the Reaction

• This clinical presentation represents a classic IgE-mediated (type I) hypersensitivity reaction, characterized by rapid onset of symptoms following allergen exposure 1, 2
• The reaction involves IgE antibodies binding to Fcε receptors on mast cells and basophils, triggering release of histamine and other inflammatory mediators 2
• Peanut proteins are recognized as foreign by the immune system in sensitized individuals, leading to this potentially life-threatening reaction 3

Clinical Features of Peanut-Induced Anaphylaxis

• Skin manifestations (urticaria, angioedema, generalized rash) occur in approximately 89% of reactions 4
• Respiratory symptoms (wheezing, dyspnea, throat tightness) occur in up to 70% of cases 1
• Gastrointestinal symptoms (vomiting, diarrhea, abdominal pain) occur in up to 40% of cases 1
• Cardiovascular symptoms (hypotension, tachycardia) occur in up to 35% of cases 1
• Symptoms typically develop rapidly, within minutes to 2 hours after exposure 1

Emergency Management

First-Line Treatment

• Administer epinephrine immediately as the first-line treatment for anaphylaxis 1, 5
• For a 12-year-old boy (likely >25 kg), administer 0.3 mg epinephrine via autoinjector or 1:1,000 solution intramuscularly in the anterolateral thigh 1
• Epinephrine doses may need to be repeated every 5-15 minutes if symptoms persist 1

Adjunctive Treatments

• Administer a bronchodilator (albuterol): 4-8 puffs via MDI or 1.5 ml nebulized solution every 20 minutes as needed 1
• Provide H1 antihistamine: diphenhydramine 1-2 mg/kg (maximum 50 mg) orally or IV 1
• Consider H2 antihistamine (ranitidine) 1
• Administer supplemental oxygen therapy if respiratory symptoms are present 1
• Provide IV fluids for hypotension or incomplete response to epinephrine 1
• Position the patient in a recumbent position with lower extremities elevated if tolerated 1

Monitoring and Observation

• Observe the patient for at least 4-6 hours after treatment, as biphasic reactions can occur in 1-20% of anaphylaxis cases 5
• Monitor for recurrence of symptoms, which may develop up to 72 hours after the initial reaction 1
• Be vigilant for signs of persistent or worsening respiratory distress or cardiovascular compromise 1

Risk Factors for Severe Reactions

• Asthma is a significant risk factor for fatal food-induced anaphylaxis, especially in adolescents 1
• Delayed administration of epinephrine increases mortality risk 5
• Previous severe reactions may indicate higher risk, though severity of past reactions does not always predict future reaction severity 1
• Peanuts and tree nuts cause the majority of fatalities from food-induced anaphylaxis 5

Discharge Planning

• Prescribe two doses of epinephrine autoinjector for the patient to carry at all times 5
• Create an anaphylaxis emergency action plan 5
• Arrange follow-up evaluation with an allergist-immunologist 5
• Educate about strict avoidance of peanuts and potential cross-reactive foods 6
• Warn about potential for accidental exposures, which occur in approximately 55% of peanut-allergic children 4

Long-Term Considerations

• Peanut allergy is usually persistent, with only about 20% of affected individuals outgrowing it 3
• Patients with peanut allergy have a high likelihood of sensitization (92%) to other tree nuts, though clinical reactivity to multiple nuts is lower (12-37%) 6
• Allergen-specific immunotherapy is being investigated but is not currently recommended as standard treatment 1

Common Pitfalls to Avoid

• Delaying epinephrine administration in favor of antihistamines alone, which can lead to increased mortality 5
• Failing to recognize that absence of skin symptoms does not rule out anaphylaxis 1
• Discharging patients too early without adequate observation for biphasic reactions 5
• Neglecting to provide comprehensive education about avoidance strategies and emergency treatment 5