+CANINE ATOPIC DERMATITIS: DETAILED GUIDELINES FOR DIAGNOSIS AND ALLERGEN IDENTIFICATION

: Canine atopic dermatitis (AD) is a common, genetically predisposed, inflammatory and pruritic skin disease. The variation in clinical presentations, due to genetic factors, extent of the lesions, stage of the disease, secondary infections, as well as resemblance to other non-atopic related skin diseases, can complicate a diagnosis of canine AD. A sub-group of the International Committee for Allergic Diseases in Animals (ICADA) was tasked with the development of a set of practical guidelines that can be used to assist practitioners and researchers in the diagnosis of canine AD. Online citation databases and abstracts from international meetings were searched for publications related to the topic, and combined with expert opinion where necessary. The final set of guidelines was approved by the entire committee.


INTRODUCCION
A new tool to assist with the interpretation of the clinical findings when confronted with a pruritic dog is application of clinical criteria known as "Favrot's criteria" (Table 4) [5].These include a set of criteria that have been developed from a large case series of confirmed cases of canine AD.The use of complex statistical analysis allowed a set of clinical features to be identified that had maximum association with canine AD.The analysis revealed two sets of criteria, which yield varying levels of sensitivity and specificity for the condition.Clinicians can use whichever set best serves their needs.For example, use of a set of criteria that yields the highest specificity is more likely to ensure that a particular case actually has canine AD.However, this set would exclude some pruritic dogs that were suffering from the disease.A set yielding the highest sensitivity is more likely to capture cases of canine AD, but it could allow some dogs with other conditions to be classified as atopic when in fact they were not.Further guidance about application of these criteria sets is shown in Table 4.
It is crucial to remember that these criteria should not be used in isolation as a "diagnostic test" for canine AD.They should be applied alongside the other guidelines outlined in this review.In other words, the accuracy of using these criteria will be greatly enhanced if the dog has been subjected to a careful work-up as described in the previous section.Canine atopic-like disease is clinically identical to canine AD, but IgE response to environmental or other allergens cannot be documented [1].However, in a recent study the condition has been associated with a lymphocyte-mediated reaction to food [53].Although it is well known that in people age and season may influence ASIS [54], this information has not been well established in dogs.

Results
A total of 81 publications relevant for this review were identified.The guidelines generated focus on three aspects of the diagnostic approach: 1. 1.
Ruling out of other skin conditions with clinical signs resembling, or overlapping with canine AD.

2.
Detailed interpretation of the historical and clinical features of patients affected by canine AD.

3.
Allergy testing by intradermal versus allergen-specific IgE serum testing.

Conclusions
The .This is due to the diversity of the clinical presentation, which may depend on genetic factors (breed-associated phenotypes) [3,4], extent of the lesions (localised versus generalised), stage of the disease (acute versus chronic), and the presence of secondary microbial infections or other flare factors.Furthermore, some aspects of the disease can resemble other skin conditions that are not related to canine AD.For the above-mentioned reasons, the definitive diagnosis of canine AD can be difficult.
A sub-group of the International Committee for Allergic Diseases in Animals (ICADA) developed, based on extensive searches in online citation databases and abstracts from international meetings, a set of practical guidelines that can be used to assist practitioners and researchers in the diagnosis of canine AD.
These guidelines provide an overview of the diagnosis of canine AD that involves three distinct, but complementary, approaches.These are: Ruling out of other skin conditions with clinical signs that can resemble, or overlap with canine AD.This is traditionally referred to as "the work-up".

2.
Detailed interpretation of the historical and clinical features of the condition.
A new tool to assist with interpretation of these findings is the application of clinical criteria known as "Favrot's criteria" [5].

Assessment of skin reactivity by IntraDermal Testing (IDT) or detection of
IgE by Allergen-Specific IgE Serology (ASIS) testing.This is traditionally referred to as "allergy testing".
Use of any one of these approaches in isolation can result in misdiagnosis, so it is important not to rely on any of them as a sole diagnostic principle.
Ruling out of other skin conditions with clinical signs that can resemble, or overlap with, canine AD The evaluation of a pruritic dog requires a step-by-step thought-process and approach that should lead to a definitive diagnosis.The differential diagnoses and role of complicating factors (Table 1) need to be narrowed down using information derived from the history, the findings on physical examination, diagnostic tests (where necessary), and response to treatment.Basic sampling methods and diagnostic tests, which may be required to rule out most of the common differentials are flea combing, skin scraping, hair plucking and cytological examination of skin and ear samples.
Depending on the complexity of the case, the following steps may be performed over a series of visits, or all at once.
While the clinical signs in a dog with flea infestation are variable, the location of skin lesions and pruritus associated with flea allergy dermatitis (FAD) are most commonly found at the lumbosacral area, tail base and caudomedial thighs (Fig. 1) [6].
A flea infestation is associated with increased flea counts, whereas in dogs with FAD this may not be the case.In addition, clinicians must be aware that many atopic dogs may suffer from concurrent FAD, which may complicate the clinical diagnosis.To exclude FAD or flea infestation as a possible cause of pruritus in a particular case, clinicians should apply the following guidelines: • The prevalence of fleas and associated hypersensitivities depends on the geographical area in which the animal lives.Fleas can be a perennial problem in subtropical and tropical climate zones, seasonal in more tempered climate zones and practically non-existent in arid, high elevation, or cold climates [7,8].Even if fleas are considered to be absent from a particular area, clinicians should consider any recent travel history to flea endemic areas or contact with animals from such areas. • In dogs with pruritus and/or lesions in areas of the body that are not primarily affected by fleas (e.g., the paws or ear canals), FAD may not be the sole cause of pruritus.

•
Clinicians should check all pruritic dogs for fleas or flea faeces on direct examination or brushing the hair coat (flea combing).To exclude FAD when fleas or flea faeces cannot be found, an effective flea control program should be initiated.
Clinicians should be aware that none of the current flea preventatives have an effective repellent effect, and that the fleas in the pupal stage can survive up to 174 days [9].Based on duration of survival it is recommended to maintain consistent flea prevention in flea endemic areas.It is also advised that fast-acting systemic adulticides are used as these may be more effective at reducing pruritus quickly compared to other topically applied flea preventatives [10].

•
Cases that are being entered into a study of canine AD should undergo effective flea control prior to study enrollment.Because the duration of flea control, prior to study inclusion, may influence the outcome of such trials, a recent study suggests that dogs should be on flea prevention for at least 3 months prior to study enrollment [11].In addition, all other dogs and cats in the household need to be on effective flea control as well.
Step 2 -Consider the possibility of other ectoparasites Besides fleas, other ectoparasites may be associated with pruritus (e.g., sarcoptic mange, cheyletiellosis, pediculosis, trombiculiasis, otoacariasis) or can be found as a concurrent disease (e.g., demodicosis).Although the majority of these parasites favour specific body areas (Figs. 2, 3, 4, 5 and 6), they can be difficult to distinguish clinically.Usually Demodex mites are easy to find if multiple affected body areas are sampled.
However, sampling infected feet or in breeds with thick skin (e.g., shar peis) may not always be effective and skin biopsies may sometimes be required [18].from pricked pustules will most likely yield definitive results, while samples from papules and epidermal collarettes may be less rewarding.Aerobic bacterial culture and sensitivity testing is not indicated in every case, but if particular conditions are fulfilled (e.g., previous history of antibiotic treatment, initial appropriate antibacterial treatment has not been effective, high prevalence of meticillin-resistant SP in the area, etc.), a bacterial culture with antibiogram should be performed [25].Bacterial cultures can be performed while the dog is currently being treated with systemic antibiotics Staphylococcal pyoderma is in most cases a secondary problem associated with underlying pruritic and non-pruritic diseases such as canine AD, but also other allergies as well as endocrinopathies.The pyoderma often causes a change in the overall level or distribution pattern of the pruritus.In these cases, eliminating the pyoderma will determine if the primary disease is itself pruritic, and what its severity and distribution pattern may be.In addition to typical pyoderma lesions, dogs with AD can develop bacterial overgrowth that can complicate other lesion types.Hence, it is wise to sample a variety of lesions to characterise the extent of bacterial involvement and manage the infection appropriately.This should certainly be done whenever cases are poorly responsive to "anti-allergy" therapies, or if studies on canine AD are being performed.

Malassezia dermatitis
The most effective diagnostic test for the identification of Malassezia organisms is skin cytology from affected areas such as skin folds, areas with lichenification and oily seborrhea (Fig. 7) [12,24].Malassezia pachydermatis is a budding yeast organism (3-5 µm in diameter) with a characteristic oval, peanut or "Russian doll" shape, allowing easy identification.In general, clinical signs associated with the cytological presence of yeasts reflect a yeast overgrowth or infection.The presence of gastrointestinal signs, such as diarrhoea, vomiting, tenesmus, soft stools, flatulence, and increased number of bowel movements is more typically seen with food-induced canine AD [5,33].In any canine AD case that has year-round clinical signs, CAFR can only be ruled out by effective strict elimination diet trials, since accurate diagnostic commercial tests are not currently available.This is especially important in trials evaluating drugs for the treatment of canine AD since food-induced AD may not respond well to those drugs, as shown for corticosteroids [5].Unfortunately, there are no diets that have been shown to be effective in all cases of CAFR.Therefore in some cases, especially when gastrointestinal signs are present, multiple different diet trials may be needed until a sufficient control of the clinical signs has been achieved.

However, in dogs with
Ideally an elimination diet trial should be performed with a diet to which ingredients the dog has never been exposed before.Unfortunately, most commercially available diets contain a wide range of ingredients and by-products, making the selection of an appropriate diet difficult.Most over the counter diets as well as some  3, Fig. 9) [3].In more chronic stages secondary skin lesions (Table 2) will occur due to self-trauma, chronic inflammation and secondary infections.Typical secondary skin lesions are excoriations, alopecia, lichenification, hyperpigmentation, crusting, and seborrhea (Fig. 10a-c).Common distribution of clinical lesions and pruritus associated with canine AD and food allergy Allergy testingOnce a clinical diagnosis of canine AD has been made several factors may play a role in the decision-making whether an allergy test is necessary or not.Severe clinical signs, duration of clinical signs for more than 3 months per year, and insufficient management with symptomatic therapy, due to side effects to the drugs used and/or poor owner compliance, justify in most cases allergy testing.These can be performed byIDT  and ASIS.Both tests are not recommended as screening tests and should only be used to confirm the clinical diagnosis of canine AD.The results of these tests are also used to identify the offending allergen(s) in order to formulate an allergen-specific immunotherapy (ASIT).Although IDT is considered the preferred diagnostic method among dermatologists, ASIS has several advantages over IDT, such as: no patient risk (no sedation required), less traumatic (no repeated injection required), more convenient (no clipping needed, less time consuming), and lower risk of drugs interfering with test results (concurrent antiinflammatory/antipruritic therapy) [45, 46].However, ASIS only measures circulating allergen-specific IgE, does not take into account other allergic pathways and often shows positive reactions in non-allergic dogs [47, 48].IDT and ASIS are still lacking standardization and it is suspected that false positive and false negative results do occur.It is estimated that between 10 and 30 % of dogs with a clinically confirmed canine AD may show a negative IDT [49, 50].This high percentage of false negative results can be due to several factors including improper technique, too low test concentration of allergens [51, 52], drug interference [46], intrinsic host factors, incorrect selection of allergens, IDT performed too long after (>60 days) or during the peak allergy season, and presence of a condition called atopic-like dermatitis [49].

•
Cheyletiella spp., Trombicula spp.(chiggers), and lice: Microscopic examination of coat brushings, acetate tape impressions and superficial skin scrapings [15].Cheyletiella spp.and lice also produce eggs, which are attached to hair shafts and can be identified by trichography.• Otodectes cynotis: Microscopic examination of aural discharge.The discharge often appears dark brown-black and crumbly (coffee ground-like) and the mites are white, very mobile and light shy.Occasionally ear mites can be found on superficial skin scrapings at other body sites [19].Sarcoptes scabiei var.canis and Cheyletiella spp.can be difficult to find [15, 20].For this reason a response to an antiparasitic trial treatment (e.g., selamectin, moxidectin, ivermectin, amitraz, lime sulfur) may be necessary to rule out these parasites.A positive pinnal pedal reflex has been associated with Sarcoptes and justifies trial therapy [21].Especially in the light that Sarcoptic mites are able to crossreact with house dust mites (HDM) in allergy testing, a trial treatment in very pruritic patients is strongly recommended [22, 23].Step 3 -Consider the possibility of Staphylococcal infection and Malassezia overgrowth Pyoderma Bacterial skin infections caused by Staphylococcus pseudintermedius (SP) are common in dogs with AD.The typical lesions of superficial pyoderma, such as papulo-pustular eruption and epidermal collarettes, are often distinctive enough to make a clinical diagnosis on gross appearance alone.However, the initial diagnosis should be confirmed by examining cytological samples, stained with Diff-Quik®, taken from the skin by impression smears or acetate tape impressions [12, 24].Samples Malassezia hypersensitivity, few organisms may elicit pruritus and associated skin lesions.For this reason a diagnosis of Malassezia dermatitis should be based on the clinical and cytological findings and confirmed by a response to antifungal therapy [27].Fungal culturing can be performed as well, but is not used routinely for the diagnosis of Malassezia dermatitis, because false negative culture results have been reported [28, 29].Therefore, in studies of canine AD, the presence of any number of Malassezia organisms should warrant a trial therapy to determine what role, if any, low numbers of Malassezia are playing in causing the dog's pruritus.

Fig. 9
Fig. 9 Crumbs on the floor and even licking another pet's empty bowl may result in a poor outcome.The client's job is to make sure the dog ingests nothing but the prescribed diet and water.
tooth paste, giving medication in gelatine capsules, using flavoured drugs (e.g., NSAIDs, antibiotics, chewable heartworm or flea preventative), and dogs eating other animals' faeces.Clients need to realize that very small amounts of other foods or food additives ingested, even intermittently, can prevent a favourable response[41].pollen)ornon-seasonal(e.g., dust mites, food)[42].At the beginning the pruritus may be alesional or associated with primary skin lesions such as erythema and occasionally papules (Table2)[43, 44].The face, concave aspect of the ear pinnae, ventrum, axillae, inguinal area, perineal area and distal extremities are most commonly affected in canine AD (Fig.8) [43], but breed-associated variations of body sites affected by canine AD have been identified (Table

Table 2
Key dermatologic features for canine pruritic skin diseases