Describe the pseudoallergy.
Description: an IgE-independent reaction that is clinically indistinguishable from type I hypersensitivity
Substances cause direct (or complement-mediated in case of anaphylactoid reaction) mast cell activation and subsequent release of histamine not mediated by immunoglobulin.
In contrast to true anaphylactic reactions, no sensitization to allergens is required (i.e., first contact can already lead to anaphylactic shock)
Clinical features: urticaria, pruritus, edema, hypotension, or even symptoms of anaphylactic shock
Diagnostics: clinical diagnosis
Avoidance of offending drug
Antihistamines for pruritus or urticaria
Describe the infection-induced urticaria.
Viral infections (e.g., rotavirus and rhinovirus)
Bacterial infections (e.g., Mycoplasma pneumoniae, group A streptococcal pharyngitis)
Parasitic infections (e.g., Anisakis simplex infection from eating raw fish and Plasmodium falciparum)
Pathophysiology: mast cell activation and subsequent release of histamine, most likely IgE-independent
Clinical features: See “Urticaria.”
Diagnostics: clinical diagnosis based on physical examination and patient history
Antihistamines may be given for pruritus or urticaria.