Anaphylaxis (cont.)
How common is anaphylaxis?
The exact prevalence of anaphylaxis is unknown. The
available statistics probably underestimate the true
frequency because reactions are not always reported.
Milder reactions may be attributed to an asthma attack or a
sudden episode of hives. More serious, fatal episodes
might be reported as a heart attack since the indicative
signs of hives, swollen throat, and asthma can fade
quickly. Thus, it is quite possible that even the true
incidence of fatalities due to anaphylaxis is both under-
recognized and under-reported. The importance of awareness, early
recognition, and prompt treatment of this disorder must be
stressed.
What are common causes of anaphylaxis?
The causes of anaphylaxis are divided into two major
groups:
- IgE mediated: This form is the true anaphylaxis that requires an initial sensitizing exposure, the coating of mast cells and basophils (cells in the blood and tissue that secrete the substances that cause allergic reactions, known as mediators) by IgE, and the explosive release of chemical mediators upon re-exposure.
- Non-IgE mediated: These reactions, the so
called "anaphylactoid" reactions, are similar to those of
true anaphylaxis, but do not require an IgE immune
reaction. They are usually caused by the direct stimulation
of the mast cells and basophils. The same mediators as
occur with true anaphylaxis are released and the same
effects are produced. This reaction can happen, and often
does, on initial as well as subsequent exposures, since no
sensitization is required.
The terms anaphylaxis and anaphylactoid (meaning "like anaphylaxis") are both used to describe this severe, allergic reaction. Anaphylaxis is used to describe reactions that are initiated by IgE and anaphylactoid is used in reference to reactions that are not caused by IgE. The effects of the reactions are the same, however, and are generally treated in the same manner. Often, they can not be distinguished initially.
Although it may appear that IgE mediated anaphylaxis occurs upon a first exposure to a food, drug, or insect sting, there must have been a prior, and probably unwitting, sensitization from a previous exposure. You may not remember an uneventful sting or be aware of "hidden" allergens in foods.
Next: What are the signs of anaphylaxis? »
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