Anaphylaxis: The Severe Hypersensitivity Reaction That Produces an Allergic Response
The correct answer is D. Anaphylaxis, which is a severe, life-threatening, generalized or systemic hypersensitivity reaction that produces an allergic response.
Understanding Hypersensitivity Reactions
Hypersensitivity reactions are categorized according to the Gell and Coombs classification:
- Type I (IgE antibody-mediated): Includes anaphylaxis, which is characterized by IgE-mediated mast cell and basophil degranulation 1
- Type II (Antibody-mediated cytotoxic): Includes hemolytic anemia, thrombocytopenia, and blood transfusion reactions 1
- Type III (Immune complex-mediated): Includes serum sickness and vasculitis 1
- Type IV (Delayed T cell-mediated): Includes allergic contact dermatitis, psoriasis, and other delayed reactions 1
Defining Anaphylaxis
Anaphylaxis is specifically defined as:
- A severe, life-threatening, generalized or systemic hypersensitivity reaction 1
- Characterized by rapid onset and potentially fatal outcomes without appropriate intervention 1
- Can be divided into "allergic anaphylaxis" (immune-mediated) and "non-allergic anaphylaxis" (non-immune-mediated) 1
Clinical Manifestations of Anaphylaxis
Anaphylaxis typically presents with multi-system involvement:
- Respiratory symptoms: Dyspnea, wheeze, bronchospasm, stridor, reduced peak expiratory flow, hypoxemia 1
- Cardiovascular symptoms: Hypotension, tachycardia, shock, cardiac arrest 1, 2
- Cutaneous symptoms: Urticaria, flushing, angioedema, pruritus 2, 3
- Gastrointestinal symptoms: Abdominal pain, vomiting, diarrhea 1, 2
Diagnostic Criteria for Anaphylaxis
Anaphylaxis is highly likely when any one of these criteria is met:
- Acute onset with skin/mucous membrane involvement PLUS respiratory compromise OR reduced blood pressure 1
- Two or more of the following occurring rapidly after allergen exposure: skin/mucous membrane involvement, respiratory compromise, reduced blood pressure, persistent gastrointestinal symptoms 1
- Reduced blood pressure after exposure to a known allergen 1
Triggers of Anaphylaxis
Common triggers include:
- Foods (especially nuts, peanuts, fish, shellfish) 4, 3
- Medications (particularly antibiotics like penicillin) 4, 5
- Insect stings/venom 2, 3
- Diagnostic agents and contrast media 1, 4
Management of Anaphylaxis
First-line treatment is:
- Epinephrine (adrenaline) administered intramuscularly in the mid-outer thigh at a dose of 0.01 mg/kg (maximum 0.5 mg in adults, 0.3 mg in children) 1
- Epinephrine is the cornerstone of anaphylaxis management and should not be delayed 1
- Additional treatments may include antihistamines, corticosteroids, bronchodilators, and IV fluids, but these should not replace or delay epinephrine administration 1
Distinguishing from Other Options in the Question
- Systemic erythematosus: Not a hypersensitivity reaction classification; likely referring to systemic lupus erythematosus, which is an autoimmune disease 6
- Hemolytic shock: Related to Type II hypersensitivity reactions causing hemolysis, not the immediate allergic response seen in anaphylaxis 1
- Necrotizing vasculitis: Can be associated with Type III hypersensitivity reactions but is not the immediate allergic response 1
Prevention and Long-term Management
- Identification and avoidance of triggers 5, 7
- Prescription of epinephrine auto-injectors for at-risk patients 1, 5
- Patient education on recognition and management of anaphylaxis 1
- Referral to an allergist for comprehensive evaluation 1, 5
Understanding anaphylaxis as the severe hypersensitivity reaction that produces an allergic response is crucial for prompt recognition and appropriate management to reduce morbidity and mortality.