Nonallergic hypersensitivity

Description: an IgE-independent reaction that is clinically indistinguishable from type I hypersensitivity

Etiology

• Radiocontrast media

• Narcotics

• Vancomycin, NSAIDs

Pathophysiology

• 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

Treatment

• Minor reactions

  • Avoidance of offending drug

  • Antihistamines for pruritus or urticaria

Etiology

• 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

Treatment

• Usually self-limited

• Antihistamines may be given for pruritus or urticaria.