INTRODUCTION
Atopic dermatitis in
dogs is defined as: “A genetically-predisposed inflammatory and pruritic
allergic skin disease with characteristic clinical features”. It is associated
most commonly with Ig E antibodies specific for environmental allergens such as
house dust mites and grass pollen”
Canine Atopic Dermatitis (CAD) is a frequent disease
of skin associated with release of inflammatory mediators with estimated
prevalence of around 10% (Hillier et al., 2001). Though the exact cause
is unknown, it is commonly associated with IgE antibodies to environmental
allergens. The primary clinical signs, erythema and pruritus is associated with
lesions at ear pinna, paws, ventral abdomen, inguinal and axillary regions
(Herbert et al., 2006). Though the diagnosis of atopic dermatitis is
based on ruling out other etiological causes, Intra dermal allergic skin test
(IDST) is still the gold standard diagnostic procedure. Though the literature
on canine atopy is available, reports on long term research particularly on
diagnosis using Intra dermal allergic skin test (IDST) and therapy is dearth in
India. Hence, the present paper puts on record for the first of its kind
clinical study from India.
Cutaneous adverse food reaction (CAFR) and CAD have
been historically considered as two different conditions. In fact, CAFR
includes both immune mediated and non-immune-mediated food intolerances and may
be associated with a wide range of clinical signs such as gastro-intestinal
disturbances, urticaria, angioedema, and signs mimicking those of atopic
dermatitis. The present article will consequently describe the clinical
features and diagnostic methods of dogs affected by CAD from whatever cause.
The clinical signs and diagnostic methods of food allergy are however beyond the
scope of this article.
SIGNALMENT OF
CAD DOGS
Some studies reported predisposition for male,
female or for neither sex. However, some sex predispositions were detected in
some breed such as golden or Labrador retrievers (more female) or Boxer (more
male). The typical age at onset of CAD is reported to be between 6 months and 3
years. We have however recently shown that about 78% of CAD present with
clinical signs before three years of age. It does mean that every fifth CAD dog
develops the first clinical signs later in life.
HISTORY OF CAD
DOGS
Information regarding the history of the affected
dog should be recorded carefully. Some important questions have already been mentioned
(age at onset, breed, familial predisposition) but some others such as
seasonality, presence of “pruritus sine material” (pruritus with no skin
changes) at onset, efficacy of previous treatment, should be asked before any
clinical examination. Clinical signs of CAD may be seasonal or not but
seasonality is often present at onset (42-75%). Approximately 80% of dogs with seasonal signs
are symptomatic in spring or summer while the others exhibit signs in winter or
autumn. It should be mentioned that some dogs with non-seasonal disease do exhibit
worsening of clinical signs during one specific season. Pruritus must be
present and its absence rules out the diagnosis CAD.
In fact, some CAD dogs do exhibit initially pruritus.
This feature was recorded in 61% of affected dogs in recent study. As well, 43%
of CAD dogs presented first with an episode of otitis externa. In comparison,
associated conjunctivitis blepharitis is very much rarer. CAD dogs are often treated
with glucocorticoids and responses to such therapy should be evaluated carefully.
It is also
shown in the study that 78% of CAD dogs responded adequately to such treatment.
In the first stages of the disease, the pruritus responds well and readily to
the administration of reduced amount of glucocorticoid (i.e. 0.3-0.5mg/kg Prednisolone
daily). In chronic cases however, the development of secondary bacterial or
yeast infections usually corresponds with a poorer response to such treatment. Last
but not least, we have also showed that 82% of atopic dogs spend most of their
time indoor. This suggests that prolonged exposure to house dust mites may
trigger or worsen CAD clinical signs.
CLINICAL SIGNS
OF CAD
Although very frequent, CAD may be difficult to
diagnose owing to the lack of pathognomonic signs and the protean clinical picture.
Erythema and pruritus are however virtually always present and often represent
the first clinical signs. However, mild pruritus may remain unrecognized by the
owner and the veterinarian may sometimes rely on indirect proofs of pruritus
such as the presence of excoriations or saliva-coloured hairs. Most of the
signs are actually due to self-trauma and/or secondary infections. In fact,
small erythematous papules, which are considered the primary lesion of CAD, are
rarely observed in CAD dogs.
The practitioner will usually observe the
consequences of the inflammation and pruritus, namely excoriations and
self-induced alopecia and/or the signs of the secondary bacterial infection
(papules, pustules, crusts, erosions) and/or the symptoms of secondary yeast
dermatitis (epidermal hyperplasia, hyperpigmentation, lichenification).
Recurrent or chronic
skin or ear infections are very frequently observed in CAD Most of these signs
are however not specific at all and the distribution of these lesions is
consequently more helpful. The most often affected areas are the pinnae (58%),
the axillae (62%), the abdomen (66%), the front (79%) and hind feet (75%), the
lips (42%) and the perineal area (43%). Unfortunately, all these areas are
rarely simultaneously affected in the same individual, except in chronic
cases. Dermatological (pyotraumatic dermatitis,
interdigital fi stulae) and non
dermatological signs are sometimes associated with CAD and their presence should
reinforce the suspicion. Spring/summer conjunctivitis, for example, is
presented in approximatively 20% of CAD dogs while gastro-intestinal signs (soft
stools, diarrhea, vomiting) are recognized in 26% of FIAD dogs.
Clinical signs of FIAD dogs differ very slightly
from those of classical, environment-induced AD. In fact, in our study, statistically
significant differences were only uncovered for gastro-intestinal signs,
seasonality, cortico-sensible pruritus and pruritus sine material (less frequent
in FIAD dogs). As well, more FIAD dogs show the fi rst clinical signs early in
life (less than one year) or, on the contrary, rather late (more than 6 years
of age).
DIAGNOSIS OF CAD
The diagnosis of CAD is based on the history (age at
onset, seasonality, pruritus sine material at onset, familial or breed predisposition,
previous response to glucocorticoids), the development of the disease
(seasonality, “wax and wane” character, development of secondary skin
infections) and the lesional pattern.
A diagnosis of CAD should however never been made,
as long as resembling diseases such as fleas, ectoparasites (sarcoptic mange)
and primary skin infections have not been ruled out. Depending on the clinical
presentation and the age of the affected dog, some other differentials,
i.e.demodicosis, dermatophytosis, cheyletiellosis, cutaneous lymphoma should be
properly ruled out. It should also be mentioned that the histological aspect of
allergic skin is usually not specific and that his test is consequently not
adequate to make the diagnosis.
It may be indicated, however, to perform skin
biopsies in some instances, to rule out some differentials such as cutaneous lymphoma,
for example. As well, allergy testing (serological evaluation of
allergen-specific Ig E and intradermal skin testing) are not regarded as
criteria for the diagnosis of CAD. This is because numerous healthy dogs are
sensitized to environmental allergens and are consequently positive (poor
specificity of this criterion) and ALD and some FIAD dogs are deemed negative. These
tests should consequently be only carried out to identify the offending
allergens (i.e. to choose the allergens for allergen specific immune therapy:
desensitization). In the same way, in order to identify FIAD dogs, a 6-to
8-week elimination diet and a subsequent challenge with the previous food
should be carried out in all dogs with clinical signs of CAD. Several sets of
criteria have been proposed for the diagnosis of CAD.
CRITERIA FOR THE DIAGNOSIS OF CANINE ATOPIC DERMATITIS AND ASSOCIATED SENSITIVITY AND SPECIFICITY.
1.
Age at onset < 3years
2.
Mostly indoor
3.
Corticosteroid-responsive pruritus
4.
Chronic or recurrent yeast infections
5.
Affected front feet
6.
Affected ear pinnae
7.
Non –affected ear margins
8.
Non-affected dorso-lumbar area
Sensitivity
when 5 criteria are fulfilled: 85%
Specificity
when 5 criteria are fulfilled: 79%
Sensitivity
when 6 criteria are fulfilled: 58%
Specificity
when 6 criteria are fulfilled: 88 %
SUMMARY
Canine Atopic Dermatitis (CAD) is the most frequent
canine dermatosis. It has been defined by the International Task Force on
Canine Atopic Dermatitis (ITFCAD) as a “genetically predisposed inflammatory
and pruritic allergic skin disease with characteristic clinical features
associated with IgE antibodies most commonly directed against environmental
allergens”. ITFCAD-revised nomenclature
for veterinary allergy also takes into account dogs with clinical signs of
atopic dermatitis but no demonstrable allergen-specific IgE (Intradermal tests
and/or serology).
REFERENCES
1. Favrot, C., Steffan, J., Seewald, W., &
Picco, F. (2010). A prospective study on the clinical features of chronic
canine atopic dermatitis and its diagnosis.Veterinary dermatology, 21(1),
23-31.
2. DeBoer, D. J., & Hillier, A. (2001). The
ACVD task force on canine atopic dermatitis (XV): fundamental concepts in clinical
diagnosis. Veterinary
immunology and immunopathology, 81(3), 271-276
3. Nambi, A. P., & Kavitha, S. (2013).
Canine atopic dermatitis. Intas
Polivet,14(2), 236-24
4. Bensignor, E. (2010). [Canine atopic
dermatitis]. Bulletin de
l'Academie nationale de medecine, 194(7), 1357-1364.
5. Olivry, T., & Mueller, R. S. (2003). Evidence‐based veterinary dermatology: a systematic
review of the pharmacotherapy of canine atopic dermatitis.Veterinary
dermatology, 14(3), 121-146.
