From the Guidelines
In an anaphylactoid reaction, what's missing is the involvement of IgE antibodies and prior sensitization to an allergen. Unlike true anaphylaxis, which requires previous exposure to an allergen that triggers IgE antibody production and subsequent mast cell sensitization, anaphylactoid reactions occur without this immunological memory. Instead, these reactions involve direct activation of mast cells and basophils by certain substances, causing the release of histamine and other inflammatory mediators. Common triggers include radiocontrast media, NSAIDs like aspirin, and opioid medications. Despite this mechanistic difference, anaphylactoid reactions produce clinically identical symptoms to anaphylaxis, including urticaria, angioedema, bronchospasm, hypotension, and potentially life-threatening shock. Treatment remains the same as for anaphylaxis, with epinephrine (0.3-0.5mg IM for adults, 0.15mg for small children) as first-line therapy, followed by antihistamines, corticosteroids, and supportive care. Understanding this distinction is important because anaphylactoid reactions can occur on first exposure to a substance, without requiring prior sensitization, as noted in the study by 1.
Some key points to consider in the management of anaphylactoid reactions include:
- The importance of prompt recognition and treatment, as delayed administration of epinephrine can lead to severe consequences, including fatalities, as highlighted in the study by 1.
- The use of epinephrine as the first-line treatment, with a recommended dose of 0.01 mg/kg of a 1:1000 solution, up to a maximum of 0.5 mg in adults and 0.3 mg in children, as stated in the study by 1.
- The potential for anaphylactoid reactions to occur in response to a wide range of substances, including radiocontrast media, medications, and other agents, as discussed in the study by 1.
- The need for individualized management and prevention strategies, taking into account factors such as the patient's medical history, age, and occupation, as emphasized in the study by 1.
Overall, the management of anaphylactoid reactions requires a comprehensive approach that takes into account the underlying mechanisms, clinical presentation, and potential triggers, as well as the need for prompt and effective treatment, as outlined in the study by 1.
From the Research
Anaphylactoid Reaction
- Anaphylactoid reactions resemble anaphylaxis but are not caused by an IgE-mediated immune response 2
- These reactions are immediate systemic reactions that are not caused by antigen-specific cross-linking of IgE molecules or complement proteins on the surface of tissue mast cells and peripheral blood basophils
- The key difference between anaphylaxis and anaphylactoid reactions is the presence of an IgE-mediated immune response in anaphylaxis, which is missing in anaphylactoid reactions
Mechanisms of Anaphylactoid Reactions
- Anaphylactoid reactions involve the release of mediators from mast cells and basophils, but the mechanism is not IgE-mediated 3
- These reactions can be triggered by various factors, including medications, foods, and other substances
- The pathophysiology of anaphylactoid reactions is complex and involves multiple interrelated pathways, including the release of preformed and newly formed mediators, as well as the generation of cytokines and chemokines 4
Clinical Presentation
- Anaphylactoid reactions can present with symptoms similar to anaphylaxis, including urticaria, difficulty breathing, and mucosal swelling 5, 6
- The clinical presentation can vary widely, and the diagnosis is often based on a combination of symptoms and signs
- Prompt recognition and treatment of anaphylactoid reactions are crucial to prevent severe consequences, including cardiovascular collapse and respiratory failure 4