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ATOPY
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Provet for educational purposes only.
You should seek the advice of
your veterinarian if your pet is ill as only he or she can correctly advise
on the diagnosis and recommend the treatment that is most appropriate for
your pet.
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Description
Atopy, also called atopic dermatitis, or allergic inhalant dermatitis is an
allergic disorder to environmental factors that are inhaled, or sometimes
absorbed across the skin, or swallowed..
Cause
Dogs that develop atopy are
thought to have an inherited predisposition to develop IgE antibodies,
and/or IgG antibodies, to environmental factors - called allergens.
Affected animals develop a Type I hypersensitivity reaction. However, the
full, complex aetiopathogenesis of this condition in animals has still to be
determined. It has been suggested that dogs are most susceptible to develop
inhalant allergy if they are exposed to the allergen (eg pollen) within the
first 4 months of life. In
cats the immunological cause has yet to be identified. In
humans atopic dermatitis is associated with several changes to the immune
system including the following:
- Poor cell-mediated immune
responses
- Overproduction of IgE by
B-cells - although 20% of atopic humans have low IgE levels
- T-lymphocyte activation
- Overstimulation of
Langerhans cells
- Release of inflammatory
mediators from eosinophils, mast cells and monocytes.
- Abnormal biochemical
responses in the skin
Breed Occurrence
Several breeds have been recognised as having a higher
risk of developing the disease including the following which are reported in the
literature :
- Beaucerons
- Beagles
- Belgian Tervurens
- Boston Terriers
- Boxers
- Cairn Terriers
- Chinese SharPeis
- Cocker Spaniels
- Dalmatians
- English Bulldogs
- English Setters
- German Shepherd Dogs
- Golden Retrievers
- Irish Setters
- Labrador Retrievers
- Lhasa Apsos
- Miniature Schnauzers
- Newfoundlands
- Pugs
- Scottish Terriers
- Shih Tzus
- Springer Spaniels
- West Highland White Terriers
- Wire-haired Fox Terriers
Signs
Clinical signs usually occur in dogs 6 mths - 7 years of
age, with most occurring between 1-3 years of age and they consist of :
- Itchiness (pruritus) - resulting in scratching,
biting or rubbing
- Reddening of the skin
- Hair loss (alopecia)
- Sites usually involved include:
- The pinnae of the ears - and chronic otitis
externa is a common complication
- The face - around the eyes, sometimes the
lips
- The underside (ventrum) of the body
- Under tail - the perineum
- Under the front leg (the axillae)
- Between the toes - cysts
In cats signs usually occur between 6 mths - 2
years of age and include :
- Itchiness (pruritus)
- Hairloss (alopecia)
- Hairballs
- Self-trauma - biting excessive grooming, broken
hairs
- Sites affected include the face, pinnae of the
ears and neck.
In addition cats with atopy may also have other
skin lesions including :
- Eosinophilic complex lesions (red plaques)
- Miliary dermatitis
AND
- Sneezing and coughing - in some cases
- Many other signs
Atopy is more difficult to diagnose in cats than
dogs because of the wide variety of signs reported.
Signs may be seasonal (eg pollen allergies) or
non-seasonal (eg allergies to household products or house dust mites). In
cats most (90%+) of cases are non-seasonal. If
there is self-trauma the skin may be broken and secondary infection may
occur:
- Organisms involved include Staphylococcus
intermedius or Malassezia pachydermatis
- Spots may result - firm swelling (papules) or
pus-filled swelling (pustules)
- Crusts may form
- Patchy hair loss may occur with scale around the
bald spot
If the condition has been present for some time
secondary changes may occur in the skin, including :
- Thickening
- Black pigmentation
Complications
Complications include :
- Secondary infections
- Chronic otitis externa
Diagnosis
Diagnosis is often based upon
the presenting history and signs Confirmation
of the diagnosis can be made sometimes by:
1. Intradermal
skin testing - challenging the skin by injecting into it common
allergens. Care has to be taken not to over-interpret positive reactions.
For example, many dogs have been exposed to housedust mite in their
environment and so they may show a positive reaction when injected
with housedust mite allergen. However, this does not necessarily mean that
allergy to housedust mite is the cause of an episode of acute dermatitis.
Positive dogs often react to several allergens eg housedust mite and
pollens.False negatives may occur if :
- The allergen to which the animal is reacting is
not included in the test solutions. Exposure to types of pollens varies
greatly from one geographical region to another.
- The animal has been treated with an
anti-inflammatory drug prior to the test. So, corticosteroids and
antihistamines or non-steroidal anti-inflammatory drugs should be
discontinued for at least 3 weeks prior to testing, and longer if
long-acting depot drugs have been given.
2. Serology testing - these tests (RAST,
ELISA, Immunoenzyme assays) measure allergen-specific IgE in blood .
However, false positives are common with many normal dogs showing positives,
so interpretation of results can be difficult and many veterinary
dermatologists consider reliance on these tests for diagnosis to be
controversial.
3. Basophil degranulation test is reported
to be a useful test but it is confined to research laboratories at this
time.
NB Skin biopsies are NOT diagnostic for atopy in
cats or dogs.
Treatment
Apart from avoiding contact with known allergens -
which is possible in some cases:
- Removing houseplants from the animals environment
- Hoovering up house dust
- Ban smoking in rooms occupied by the pet
There are basically 2 forms of treatment:
- Hyposensitisation to reduce the immune reaction to
allergens in the environment, and
- Treatment to relieve the signs of the disease
1. Hyposensitisation (also called immunotherapy)
Many (50%+) dogs can be hyposensitised by giving
increasing doses of allergens (antigens) that the animal is sensitive to by
injection. This theoretically results in the production of circulating IgM
antibodies in the blood which bind to the environmental allergens and blocks
them before they stimulate local IgE or IgG antibody production in the skin. In
addition, the animal becomes tolerant to the allergen.
2. Symptomatic treatment
Most dogs with atopy (c90%) can be controlled ,
although treatment may need to be given for life. Some of the drugs that are
used may have undesirable side-effects so the choice of drug therapy must be
based upon consideration of the individual animal. The clinical objective is to
give therapy at as low a dose as possible, and as infrequently as possible to
control the signs.
Drugs that are used include :
- Corticosteroids - most widely used, but can have
serious side-effects.
- Antihistamines - effective at preventing the onset
of pruritus in some individuals, but not in others. Not so effective
when pruritus is already present.
- Amitriptyline
- Chlorpheniramine
- Clemastine
- Diphenhydramine
- Hydroxyzine
- Non-steroidal antinflammatory drugs
- Other drugs - few reports confirm that they are
effective.
- Orgotein
- Tranquillizers
- Barbiturates
- Levamisole
- Nutritional modification - essential fatty acid
supplementation eg evening primrose oil (gamma-linolenic acid), omega3/6
mixtures..
Prognosis
A large number of atopic dogs (c80%) will go on to
develop non-seasonal pruritus.
Long term problems
Chronic treatment with corticosteroids can lead to
complications such as diabetes or liver disease
Last updated : March 2008
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