Version October 2024
| Mechanism | Known or presumed pathophysiology | Examples |
| Activation of mast cells Clinical characteristics – Often associated with pruritus and urticaria. May present as part of an allergic reaction or anaphylaxis. | IgE-mediated mast cell activation (type I hypersensitivity) | Allergic reactions to foods, drugs, latex, insect stings, other allergens |
| Direct mast cell activation | Opioids, radiocontrast agents | |
| Perturbations in arachidonic acid metabolism | Aspirin and other NSAIDs | |
| Immunologic and other non-IgE-mediated mast cell activation | Idiopathic histaminergic angioedema, often associated with chronic spontaneous urticaria or inducible urticaria | |
| Generation of bradykinin Clinical characteristics – Not associated with pruritus or urticaria. May present with abdominal symptoms due to bowel wall edema. | Inhibition of enzymes involved in degradation of bradykinin | ACE inhibitors, DPP-4 inhibitors, NEP inhibitors (eg, neprilysin inhibitors) |
| Deficiency or dysfunction of complement C1 inhibitor due to mutation | Hereditary angioedema (also known as hereditary C1 inhibitor deficiency or dysfunction) | |
| Deficiency or dysfunction of complement C1 inhibitor often due to anti-C1 inhibitor antibody or an underlying malignancy | Acquired C1 inhibitor deficiency | |
| Defects in several genes have been implicated, including those for coagulation factor XII, plasminogen, and angiopoietin-1. Other cases are idiopathic. | Hereditary angioedema with normal C1 inhibitor | |
| Unknown pathophysiology Clinical characteristics – Variable. Sometimes associated with urticaria. | Idiopathic nonhistaminergic angioedema | |
| Infections (especially in children) | ||
| Drugs – Calcium channel blockers, fibrinolytic agents, herbal medicines | ||
| Hypereosinophilic syndrome | ||
| Gleich syndrome | ||
| Urticarial vasculitis |
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