Foods and additives, inhalants, insect stings, and medications may be triggers. Pathogenesis involves systemic activation of mast cells and basophils resulting in the release of inflammatory mediators. This activation may be immunoglobulin E (IgE) (in the case of classical anaphylaxis) or non-IgE mediated (anaphylactoid reaction). In adults, multiple episodes of anaphylaxis (eg, related to drugs) should lead to a consideration of mastocytosis.
Anaphylactoid reactions mimic anaphylactic reactions and cannot be distinguished clinically aside from the fact that anaphylaxis is IgE mediated and as such requires patient sensitization of the offending trigger. Anaphylactoid reactions are not IgE mediated and occur without sensitization, as the offending trigger causes direct mast cell and basophil activation.
Delayed diagnosis and treatment predict poor prognosis. Immediate management involves removal of the triggering allergen if possible, epinephrine by intramuscular injection, and further evaluation and management.
Related topic: Alpha-gal syndrome
T78.2XXA – Anaphylactic shock, unspecified, initial encounter
39579001 – Anaphylaxis
Differential Diagnosis & Pitfalls
- Other causes of cardiovascular collapse – Massive myocardial infarction, pulmonary embolism, cardiac tamponade, tension pneumothorax, aortic dissection, hemorrhage, or stroke, all of which would typically have other associated symptoms / signs.
- Acute generalized urticaria
- Angioedema (allergic or nonallergic)
- Status asthmaticus
- Vasovagal syncope
- Foreign body aspiration
- Anxiety / panic attacks / panic disorder
- Alpha-gal syndrome
Drug Reaction Data