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Allergy
Respiratory allergies affect approximately 20% of
the population and contribute to numerous medical disorders of the
ears, nose and throat. Symptoms
can include:
What
causes allergies?
Airborne pollens produced by trees, grasses, and
weeds usually cause seasonal hayfever symptoms.
Year round symptoms can be caused by pets, dust and insects
such as cockroaches and dust mites.
Molds are frequently an under recognized and therefore under
treated source of allergies. Recent
studies have demonstrated that even low level mold allergies may be a
significant cause of chronic sinus disorders.
Allergies are caused by tiny particles called
antigens which react with our immune systems.
Antigens are found on pollens, pet danders, dust, molds and
other substances. The
immune system may react by producing a variety of antibodies.
IgE
antibodies are the most relevant to allergies.
In allergy, an abnormal quantity of
IgE antibodies are produced
in response to common antigens. This
results in an abnormally reactive immune system.
When an antigen attaches to an IgE antibody, inflammatory
mediators are released. These
inflammatory mediators cause localized reactions such as swelling,
irritation, inflammation and wheezing.
If the allergic reaction is severe enough, life threatening
systemic anaphylactic reactions can occur which require immediate
medical attention.
Allergy
treatment
Avoidance of
the offending allergen is the obvious and most simple treatment
option. Air filters will
remove pollens from the air. Mattress covers and special pillow cases will protect against
dust mites. Avoidance is
often impossible or impractical.
Most patients will get rid of their allergist before they part
with their dog or cat which they’re allergic to.
Antihistamines can
be taken as pills or as nasal spray or eye drops.
Histamine is one of the most important inflammatory mediators
involved in allergies. It
causes swelling, inflammation and irritation.
Antihistamines block the effect of histamine.
Nasal Sprays The
nose is the organ most commonly affected by allergies.
Nasal sprays administer either corticosteroids or cromolyn
sodium into the nose. Corticosteroids
are potent anti-inflammatory drugs which reduce the effects of
inflammatory mediators. Cromolyn
sodium prevents release of the inflammatory mediators in response to
offending antigens.
Leukotriene
Inhibitors are a new class of drugs which block the effect of
inflammatory mediators.
Immunotherapy is
used to repair the immune system so that fewer IgE antibodies are
produced and the offending antigens are blocked by blocking
antibodies. Once the
offending antigens have been determined, serums of those antigens are
administered by injection on a weekly basis.
These serums result in the production of antibodies of a
different type known as IgG. These
antibodies block the antigens from reacting with the IgE antibodies.
By gradually increasing the dose of antigen injected, the
number of blocking antibodies is slowly increased without causing a
dangerous anaphylactic reaction. Eventually, the blocking antibodies reduce the stimulation of
the immune system to the point that fewer IgE antibodies are produced.
The dose of antigen serum is increased until an optimum symptom
relieving dose is reached. This
maintenance doses is continued for several years and shots may be
stopped after about five years. At
this point,
the symptom relieving effect of immunotherapy usually continues after the
shots are stopped.
How do we
test for allergies?
Testing for allergies involves various methods of
testing for the presence of IgE antibodies specific for offending
antigens. In allergic
individuals, IgE antibodies will be present in the blood and blood
tests may be used to determine the presence of allergies.
IgE antibodies are also found in the skin.
Skin testing is more sensitive in determining the presence of
allergies and has the additional advantage that the degree of allergy
to each antigen can be accurately determined.
The degree of allergy or sensitivity is important because
knowing this allows us to tailor the treatment to the individual
patient so that it is both safe and effective.
The most common methods of allergy testing
include prick testing and
intradermal testing. In
prick testing, a needle is dipped in a solution containing a small
amount of the substance (antigen) which is suspected to be causing the
allergic reactions. The
skin is then pricked with the needle and observed for a reaction.
This technique is not very sensitive and will identify the
offending allergen only if the patient is highly allergic.
Because of this, prick testing is usually combined with
intradermal testing.
In intradermal
testing, a small amount of the antigen is injected into the skin
which is observed for a reaction.
Typically, a larger amount of the antigen is injected with this
technique than with prick testing.
This test is typically performed when prick testing is negative
and is used to look for allergies to substances to which the patient
is less sensitive. Even in conjunction with prick testing, this technique has
the disadvantage of not quantifying the sensitivity to the antigen.
In other words, it cannot tell us how allergic the patient is.
Skin
endpoint titration (SET) is the most accurate and sensitive test
for allergies. It can
tell both what the allergy is and how sensitive the patient is.
A very dilute solution of each antigen is injected into the
skin like in standard intradermal testing.
This is followed by a series of injections of progressively
increasing concentration of each antigen until a local skin reaction
starts to occur. This tells us how much antigen to start with in administering
immunotherapy shots.
SET results in a precise starting point for
beginning immunotherapy. It
avoids starting with too high a dose and running the risk of a life
threatening anaphylactic reaction.
It also allows us to start with the highest safe dose so that
we can get a response to treatment as soon as possible.
SET has been proven to be both effective and safer than other
methods of initiating immunotherapy. In fact, it is worthwhile noting that the United States Food
and Drug Administration (FDA) uses skin endpoint titration as its
definitive test of allergenic extracts.
The disadvantages of SET include: It is more time consuming
and, like other skin tests, is inaccurate in patients taking
antihistamines and steroids.
Blood tests such as RAST
are used to evaluate for the presence of allergies in situations
where it is impractical to use skin tests.
Blood tests do not quantitate the degree of sensitivity as
accurately as skin tests do. Therefore
the optimal starting dose for immunotherapy is more difficult to
determine which results in a more conservative initial dose for
immunotherapy, hence the optimal dose for relief of symptoms is not
reached as quickly. We use RAST technology when SET is
impractical. |
