Anaphylaxis, urticaria, and angioedema frequently share a common pathophysiology
in that these conditions most commonly result from IgE-mediated
mast cell activation resulting in the release of histamine, leukotrienes,
and other mast cell mediators. Urticaria and angioedema are isolated
to mucocutaneous symptoms whereas anaphylaxis is an acute systemic
reaction that may rapidly lead to cardiopulmonary collapse.
Anaphylaxis is an acute systemic type I (IgE-mediated) hypersensitivity
reaction mediated by histamine, leukotrienes, and other mast cell–derived
mediators.1 The estimated overall lifetime prevalence
of anaphylaxis from all causes is 0.5% to 2%,
and 0.7% to 2% of anaphylactic reactions are fatal.
Rapid recognition, diagnosis, and therapy of anaphylaxis are imperative to
prevent morbidity and mortality.
Although anaphylaxis can occur at any age, adolescents and young
adults are most at risk for serious anaphylaxis. Preexisting asthma
is a primary risk factor for fatal anaphylaxis, and delay in epinephrine
therapy has been strongly associated with anaphylaxis mortality.
Additional risk factors for poor outcomes with the occurrence of
anaphylaxis include concomitant therapy with β-adrenergic
or α-adrenergic antagonists, which blunts the effects
of epinephrine treatment, and angiotensin-converting enzyme inhibitors,
which interfere with physiologic compensatory mechanisms, thereby
leading to severe or protracted anaphylaxis.
Risk factors for anaphylaxis include parenteral antigen exposure
(ie, IV medications) and repeated, interrupted antigen exposure
(ie, medication or food ingestion). The most common causes of anaphylaxis
include (1) medications, (2) foods, (3) stinging insects, (4) latex,
and (5) blood products. Of these causes, medications and foods account
for the majority of serious anaphylactic reactions resulting in
emergency room visits or causing anaphylaxis mortality. The most
commonly implicated causative medications are β-lactam antibiotics
(penicillins and cephalosporins), other antibiotics, radiocontrast
agents (through direct mast cell stimulation), and neuromuscular
blocking agents. Among foods, peanuts, tree nuts, cow’s
milk, egg, and seafood (crustaceans, mollusks, fish) most commonly cause
anaphylaxis.2 Rarely, the temporal combination
of food ingestion and exercise may trigger anaphylaxis.3 This
food-dependent, exercise-induced anaphylaxis is best evaluated by
an allergy specialist. Other uncommon causes of anaphylaxis include
physical factors such as cold, heat, or ultraviolet light exposure.
Finally, idiopathic anaphylaxis occurs when no inciting allergen
can be identified by considering the patient’s history
or by diagnostic testing.
In the pediatric population, anaphylactic reactions to vaccines
are a concern. True IgE-mediated anaphylaxis to immunizations is
rare and more commonly involves IgE to vaccine components rather
than the immunizing antigen itself. Gelatin, added to vaccines as
a stabilizing agent, has been implicated in anaphylactic reactions
to measles, mumps, and rubella (MMR), varicella, influenza, and Japanese
encephalitis vaccines. Children with a history of allergy to egg
should be seen by an allergy specialist prior to receiving influenza and
yellow-fever vaccines, as egg protein used in these vaccines has
been implicated in anaphylactic reactions to these immunizations. IgE-mediated
reactions to the specific vaccine antigen is exceedingly rare, but
has been reported for diphtheria and tetanus.