Anaphylaxis refers to a
rapidly developing and serious allergic reaction that affects
a number of different areas of the body at one time. Severe
anaphylactic reactions can be fatal. Most people experience
allergy symptoms only as a minor annoyance. However, a small
number of people are susceptible to a reaction that can lead
to shock or even death.
Anaphylaxis is often
triggered by substances that are injected or ingested and
thereby gain access into the blood stream. An explosive
reaction involving the skin, lungs, nose, throat, and
gastrointestinal tract can then result. Although severe cases
of anaphylaxis can occur within seconds or minutes of exposure
and be fatal if untreated, many reactions are milder and can
be ended with prompt medical therapy.
What does anaphylaxis
mean?
To fully understand this
term, we need to go back almost 100 years. The story begins on
a cruise aboard Prince Albert I of Monaco's yacht. The Prince
had invited two Parisian scientists to perform studies on the
toxin produced by the tentacles of a local jellyfish, the
Portuguese Man of War. Charles Richet and Paul Portier were
able to isolate the toxin and tried to vaccinate dogs in the
hope of obtaining protection, or "prophylaxis," against the
toxin. They were horrified to find that subsequent very small
doses of the toxin unexpectedly resulted in a new dramatic
illness that involved the rapid onset of breathing difficulty
and resulted in death within 30 minutes. Richet and Portier
termed this "anaphylaxis" or "against protection." They
rightly concluded that the immune system first becomes
sensitized to the allergen over several weeks and upon
re–exposure to the same allergen may result in a severe
reaction. An allergen is a substance that is foreign to the
body and can cause an allergic reaction in certain
people.
Allergy Facts
- The first documented
case of presumed anaphylaxis occurred in 2641 B.C. when
Menes, an Egyptian pharaoh, died mysteriously following a
wasp or hornet sting. Later, in Babylonian times, there
are two distinct references to deaths due to wasp stings.
- Charles Richet was
awarded the Nobel Prize in 1913 for his work on
anaphylaxis.
Richet went on to suggest
that the allergen must result in the production of a
substance, which then sensitized the dogs to react in such a
way upon re–exposure. This substance turned out to be
IgE.
In the first part of the
20th century, anaphylactic reactions were most commonly caused
by tetanus diphtheria vaccinations made from horse serum.
Today, human serum is used for tetanus prevention, and the
most common causes of anaphylaxis are now penicillin and other
antibiotics, insect stings, and certain
foods.
Allergy Fact
In
1956, Mary Hewitt Loveless showed that the injection of wasp
venoms could cause anaphylaxis in individuals allergic to
wasps. She subsequently used wasp extracts to successfully
immunize such individuals.
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.
What are the signs of
anaphylaxis?
It is worth mentioning a
few general observations regarding the features of
anaphylactic reactions. Be aware, however, that these
guidelines are not always consistent or reliable for a
particular individual.
- The severity of the
reaction varies from person to
person.
- Subsequent reactions
to the same trigger are typically similar in
nature.
- The more rapid the
onset of symptoms, the more severe the reaction is likely to
be.
- A history of allergic
disease (rhinitis, eczema, asthma) does not increase the
risk of developing IgE mediated anaphylaxis, but it does
incline the person to a non–IgE mediated
reaction.
- Underlying asthma may
result in a more severe reaction and can be more difficult
to treat.
- The risk of
anaphylaxis may diminish over time if there are no repeated
exposures or reactions. However, a person at risk should
always expect the worst and be prepared.
What are anaphylaxis
symptoms?
The symptoms of an
anaphylactic reaction may occur within seconds of exposure, or
be delayed 15 to 30 minutes, or even an hour or more after
exposure (typical of reactions to aspirin and similar drugs).
Early symptoms are often related to the skin and
include:
- Flushing (warmth and
redness of the skin),
- itching (often in the
groin or armpits), and
- hives.
These symptoms are often
accompanied by:
- a feeling of
"impending doom,"
- anxiety, and
- sometimes a rapid,
irregular pulse.
Frequently following the
above symptoms, throat and tongue swelling results in
hoarseness, difficulty swallowing, and difficulty breathing.
Symptoms of rhinitis (hay
fever) or asthma may occur causing:
- a runny nose,
- sneezing, and
wheezing, which may worsen the breathing difficulty,
- vomiting, diarrhea,
and stomach cramps may develop.
About 25% of the time,
the mediators flooding the blood stream cause a generalized
opening of capillaries (tiny blood vessels) which results in a
drop in blood pressure, lightheadedness, or even loss of
consciousness. These are the typical features of anaphylactic
shock.
What happens after the symptoms
begin?
There are three possible
outcomes:
- The signs and symptoms
may be mild and fade spontaneously or be quickly ended by
administering emergency medication. In this outcome, the
symptoms do not subsequently recur from this particular
exposure.
- After initial
improvement, the symptoms may recur within 4 to 12 hours
(late phase reaction) and require additional treatment and
close observation. Recent evidence suggests that a late
phase reaction occurs in fewer than 10% of cases.
- Lastly, the reaction
may be persistent and more severe, thus requiring intensive
medical treatment and hospitalization. This may occur up to
20% of the time with certain exposures.
Epinephrine, which is
also known as "adrenaline," is a drug that acts immediately to
cause the blood vessels to contract, thereby preventing fluid
leakage. It is one of the medications frequently used to treat
anaphylaxis. Epinephrine also helps relax the bronchial tubes,
thus relieving breathing difficulty. It also lessens stomach
cramps and stops itching and hives. More importantly,
epinephrine helps prevent the release of more mediators of the
allergic reaction. In addition to epinephrine, other
medications and IV fluids and oxygen will probably be
administered as well. The choice of interventions will depend
on the severity of the reaction the patient
experiences.
Are there any disorders that
appear similar to anaphylaxis?
Several disorders may
appear similar to anaphylaxis. Fainting (vaso–vagal reaction)
is the reaction that is most likely to be confused with
anaphylaxis. The key differences are that in a fainting
episode, the affected person has a slow pulse, cool and pale
skin, and no hives or difficulty breathing. Other conditions,
such as heart attacks, blood clots to the lungs, septic shock,
and panic attacks can also be confused with
anaphylaxis.
How is anaphylaxis
diagnosed?
Once you think that you
might have had an anaphylactic reaction, the first order of
business is to seek emergency care. Once the acute reaction
has been treated you should follow–up with your doctor who
will probably recommend seeing an allergist. The allergist
will assess whether or not the reaction was indeed allergic in
nature. Usually, a careful and detailed medical history and
selected blood or skin tests can identify the cause. Be
prepared to recall your activities before the event, the food
and medications you ingested, and whether or not you had any
contact with rubber products.
Table 1: The Common
Causes of Anaphylaxis
