Atopy
Just as airborne allergy is common in people; it is also
common in dogs and cats. Common allergens are pollens, dander,
grasses, trees, and fabrics; any airborne particle can potentially
become an allergen.
Features of Atopic Dermatitis
- Atopy usually produces a seasonal itchiness
though after several years, the duration of the itchy period
extends. Finally, the pet is itchy nearly all year round.
- Seasonal itchiness due to atopy tends to
begin early in a pet's life (between ages 1 and 3). Flea allergic
dermatitis, the other prime cause of seasonal itchiness, tends to
begin later (between ages 3 and 5).
- Itchiness due to atopy responds rapidly to
cortisone-type medications prednisone , depomedrol, dexamethasone,
azium etc.)
- Atopy may produce characteristic changes on
biopsy samples.
- Atopy is associated with irritation in
certain parts of the body. In dog,s these areas are:
What to do for Atopic Dermatitis?
Prednisone (and other Related Steroids)
These cortisone-type medications tend to be useful as the first
line of defense against itchy skin. A higher dose is used at first
but this is quickly tapered down once the condition is controlled.
Prednisone is given every other day so as to allow the pet one day
of recovery from the prednisone's hormonal actions. An atopic dog
will respond within days. For cats, long-acting cortisone-type
injections are most frequently used as cats are frequently not
amenable to taking pills.
Problems arise when the pet's need for itch
control demands excessive use of prednisone. Prednisone is a
hormone, affecting all body symptoms. Side effects include:
- excess thirst
- excess appetite
- urinary incontinence
- muscle breakdown
- immune suppression
- termination of pregnancy
- inflammation of the pancreas
- lethargy/panting
If your pet has an unacceptable side effect,
you should consider trying alternative therapy for itchy skin.
If your dog requires more than two depomedrol
injections annually or is on every other day prednisone more than 4
months out of the year, you should consider one of the following:
- Alternative therapy
- Further diagnostics
(There may be a more specific treatment for your pet)
- Referral to a specialist
- Continued steroid use but with monitoring
tests
(annual blood panel, re-check exam, and urine checks 3 to 4 times
a year)
Cats are more resistant to the negative
effects of steroid hormones thus they are able to take long acting
injections as frequently as every three months. If a cat seems to
require an injection every other month, efforts should be made to
seek an alternative form of management.
Alternatives to Steroids
There are many alternatives to prednisone; unfortunately, none
produce as reliable a response.
Antihistamines - These are far less harmful than prednisone
but only 10% to 20% of dogs will respond to any given antihistamine.
Our hospital uses a testing protocol using four antihistamines,
showing benefit to approximately 30% of the dogs who try it. Animals
that cannot get by on antihistamines may be able to lower their
prednisone requirement when using antihistamines together with
prednisone. It should be noted that antihistamines are far more
effective in cats than in dogs. Reliable itch control is frequently
obtained but the down side is that the cat in question must take
medication twice a day, potentially indefinately.
Fatty Acid Supplements - These
products are NOT analogous to adding oil to the pet's food. Instead,
these special fatty acids act as medications, disrupting the
production of inflammatory chemicals within the skin. They are often
used in conjunction with antihistamines.
Cyclosporine[AtopicaŽ]) - This is a new
product for dogs (not approved for cats). It is a pill shown to be
as effective as prednisone for the treatment of atopic dermatitis.
This product, which modulates the abnormal immune reaction in atopy,
has been a true breakthrough in reducing the need for steroids. It
is a relatively expensive medication compared with steroids but does
not lead to long term debilitating side effects as steroids can.
Topicals - Dips, soaks, shampoos, and
ointments may also be a helpful addition to one's anti-itch
armament. The disadvantage is that these products must be used two
and three times a week.
Hyposensitization?
Just as people have allergy shots, so can pets; however,
the process is not without difficulty and one should not expect
hyposensitization to end all itchy skin concerns.
- Allergy shots require approximately 6 to 12
months to begin working.
- 25% of atopic dogs will not respond (these
are usually the animals allergic to multiple allergens.)
- 25% will require prednisone at least at
some times.
- You will have to give the allergy shots
yourself.
Is Your Pet a Candidate?
Testing is best done during your pet's non-itchy season (if
there is one) so that the skin responses of the test will not be
clouded by active inflammation. The test involves injections of
small amounts of allergen extracts into the skin. Reactions noted
are compared to reactions produced by two controls: pure histamine
(very inflammatory) and pure saline (very non-inflammatory).
In order to take the test the following
medication withholding scheduled should be followed. Your dog may
not have had:
- Depomedrol injections within 8 weeks
- Vetalog injections within 6 weeks
- Antihistamines within 1 week
- Topical steroids (such as panalog) for 1
week
- Oral steroids (such as prednisone) for 4
weeks
Guidelines for cats are generally more strict.
Check with a specialist for their recommendations.
These requirements come from one board
certified dermatologist; other veterinary dermatologists may have
other requirements. It is often useful to have ruled out food
allergy with an elimination diet trial prior to the skin test as
food allergy/intolerance responds much more rapidly to diet
correction than atopy does to hyposensitization. Food allergy and
atopic dermatitis both present a similar distribution of itchiness
and can be difficult to distinguish.
Allergic skin testing is generally performed
by only by specialists.
You May Hear about Blood Testing
As an alternative to skin testing, several blood tests have
been developed to check for the presence of allergy-type antibodies
in the blood. These tests can be submitted by any veterinarian (no
specialist need be involved) and drugs need not be withheld prior to
testing (though the test may not be valid for animals that have had
hyposensitization in the past). This type of testing is fraught with
controversy. It appears that the results of such tests do not
correlate well with the results of skin testing (our traditional
test). It is difficult to say how this kind of testing will
ultimately fit in to the treatment of atopic dermatitis but seems
best at this time for animals suspected of having inhallant
allergies who simply cannot go without medication, who have negative
skin testing, or for whom skin testing is unavailable due to other
reasons.
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