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Veterinarian Technician April 2006 (Vol 27, No 4) Focus: Dermatology

All About Itch: Atopy in Dogs and Cats

by Mindy Cohan, VMD

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    Key Points

    • Atopic dogs and cats develop pruritus following exposure to ordinary environmental substances.
    • Atopy cannot be cured; it must be managed through immunotherapy, medical treatment, or avoidance of the offending substance.
    • Many diseases have clinical presentations similar to that of atopy.

    Atopy, an allergic condition that results from ex­posure to common airborne particles such as molds, pollen, and dander,1 can affect both people and pets. Humans with atopic disease are prone to asthma, hay fever, and der­matitis.2 Atopy in dogs and cats is characterized primarily by pruritic dermatitis.2

    Atopy is a frustrating condition for pet owners and veterinary health care team members alike. Owners must be accurately informed about the time and financial commitment necessary to diagnose and treat atopic pets. Veterinary technicians and clinicians must clearly explain to clients that atopic pets cannot be cured; the disease is merely managed. Technicians play a vital role in the diagnosis of atopy and in helping pet owners understand the available treatment options.

    Pathogenesis

    Dogs and cats with atopy are genetically predisposed to developing IgE-mediated responses following exposure to airborne allergens.1 The basis for atopy is believed to involve both biologic and environmental factors. The nature/genetic theories are supported by the predisposition toward atopy in certain dog breeds. The nurture/environmental theories are reinforced by findings of atopy in unrelated dogs of various breeds living within the same household.2 The environmental influence is supported by a study that found an increased likelihood of atopy in dogs born in the midst of pollen season.3

    Signalment

    It is estimated that 3% to 15% of the canine population is affected by atopic disease.2 Some breeds that are predisposed to the condition include Boston terriers, cairn terriers, West Highland white terriers, pugs, shar-peis, Lhasa apsos, shih tzus, golden retrievers, Labrador retrievers, boxers, and cocker spaniels. Although some reports state that females are more prone to atopy, other studies have failed to confirm a sex predilection.3 Atopic dogs can exhibit clinical signs between 4 months and 7 years of age; however, most dogs become symptomatic before 3 years of age.3

    Cats also begin to show clinical signs of atopy at a young age. The onset of pruritus typically occurs before 2 years of age, yet some cats can develop signs as late as 8 years of age.2 No breed or sex predilections for cats have been established.3

    Clinical Signs

    Pruritus is considered the hallmark sign for both dogs and cats with atopic disease.2 The most commonly affected areas on dogs include the face, feet, ventrum, and axillae. While some dogs exhibit signs on a seasonal basis, others are affected throughout the year. Depending on their sensitivities, many dogs initially affected during certain times of the year will eventually develop nonseasonal clinical signs.3 Atopic pruritus can be exacerbated by secondary bacterial or Malassezia pachydermatis infections.3

    Although feline atopy holds many unanswered questions, dermatologists have recognized four cutaneous reaction patterns associated with the condition. These patterns include eosinophilic granuloma complex lesions, miliary dermatitis (crusted papular eruption), self-induced alopecia, and pruritus of the face, neck, and ears that may not necessarily result in skin changes.3 Many areas of the body can be affected. Common sites include the abdominal and inguinal areas, lateral chest, legs, head, and neck.3

    Dermatologic clinical signs that are shared by both canine and feline populations include pododermatitis, pruritic ears with secondary otitis externa, and alopecia and erythema of the limbs and ventrum.4 Both species can also develop noncutaneous signs. Dogs have been reported to exhibit respiratory signs such as rhinitis, allergic bronchitis, and reverse sneezing, while cats have been noted to sneeze and cough with asthmatic signs.3

    Diagnosis

    A tentative diagnosis of canine or feline atopy relies on a thorough physical examination, a detailed patient history, and the exclusion of other medical conditions.3 Taking a thorough history for suspected atopic patients can be time-consuming. Technicians familiar with the appropriate clinical questions are an invaluable aid to busy veterinarians.

    Differential Diagnosis

    If a patient's history is suggestive of atopy, physical examination findings and dermatologic tests should be evaluated. Several tests are required to rule out diseases with clinical signs similar to atopy. Fungal cultures, skin impression smears, fecal flotation tests, and occasionally skin biopsies are recommended for patients with pruritus and skin changes.2 Once infectious, parasitic, neoplastic, and autoimmune causes have been eliminated, food allergies should be investigated. An elimination diet trial and subsequent challenge will help to determine the existence of food hypersensitivity. Because of their limited reliability, skin testing and serum tests are not recommended in the diagnosis of canine and feline food hypersensitivity.2

    Allergy Testing

    Although intradermal skin testing is not dependable for diagnosing food hypersensitivity, it is the preferred test to diagnose atopy.3 Intradermal testing can be conducted on both dogs and cats, but feline skin can make evaluation difficult. The procedure involves shaving an area on the patient's flank, followed by intradermal injection of small samples of allergens indigenous to the local environment. A trained clinician then evaluates the patient's reaction based on visual and palpable changes. Chemical restraint is recommended for anxious or fractious dogs. All cats that are otherwise healthy should be sedated. Chemical restraint enables smooth and quick intradermal testing and minimizes the release of endogenous cortisol, which could affect the results.5

    Despite the widespread use of intradermal testing among veterinary dermatologists, this diagnostic tool is not infallible. There are many factors that can lead to both false-positive and false-negative results. False-positive results can be due to contaminated test allergens, poor technique, irritable skin, or scabies infection. One of the most common reasons for a false-negative result is failure to discontinue certain medications in the pet before testing.3 Although further studies are needed to definitively establish appropriate withdrawal times, some general guidelines are accepted. Oral and topical glucocorticoids should not be used within 4 weeks of testing, and injectable steroids should be avoided for at least 8 weeks. Both antihistamines and products containing omega-3/omega-6 fatty acids should be discontinued at least 10 days before testing.3

    The reliability of in vitro (serologic) tests is still under debate and not universally accepted. Although commercial serologic tests have been more thoroughly evaluated for dogs, further studies are needed for both the canine and feline populations. Until more feline studies are conducted, serologic tests should not be relied on to definitively diagnose feline atopy. Serologic tests can, however, aid in the selection of allergens for hyposensitization, or immunotherapy.3 Serologic testing also has several advantages over intradermal testing, including3:

    • Increased patient safety (no sedation needed, no chance of an anaphylactic reaction)
    • Less chance of a false-negative result due to the prior use of therapeutic agents
    • Convenience for owner (no fur needs to be shaved, drawing blood takes less time than intradermal testing)
    • No complications related to severe dermatitis

    Intradermal and serum tests help to identify the problematic allergens for an individual patient. Although these tests are costly, the results can be used to formulate accurate immunotherapy protocols.

    Management

    The three options available for atopy management are symptomatic therapy, immunotherapy, and avoidance.2 Although avoidance is the preferred method, it is the least practical in terms of inhalant allergens.2 Avoidance measures can be taken to lessen clinical signs, but significant improvement in patient comfort usually depends on immunotherapy and medical management.

    Immunotherapy

    The goal of immunotherapy is to lessen the atopic patient's sensitivity to specific allergens. This is achieved by gradual exposure to the aggravating substance in increasing doses.2 The success rate of immunotherapy is regarded as 50% to 80%.3 Immunotherapy should be considered in patients that are intolerant of the side effects of glucocorticoids and in those that have clinical signs at least 4 to 6 months of the year.3

    Symptomatic Therapies

    Many atopic patients benefit from systemic and topical medications either alone or in conjunction with immunotherapy. The primary route of allergen exposure is thought to be absorption through either mucous membranes or skin. It is therefore not surprising to observe the therapeutic benefit of medicated shampoos and conditioners.3 Products generally provide relief by removing the offending allergen from the skin. Warm water should be avoided when bathing pruritic animals.

    Although considered the "silver bullet" for atopy treatment, glucocorticoids can result in many undesirable side effects. The severity of the side effects depends on the specific drug (i.e., its potency, length of action), dosage, and frequency of use as well as the patient's metabolic status.2 Owners of atopic dogs must understand that despite a quick decrease in itchiness, pets will likely experience an increase in thirst, urination, appetite, and panting. Personality changes such as aggression have also been observed in dogs receiving glucocorticoids.2

    Cats are more resistant than dogs to the effects of oral glucocorticoids; however, cats are sensitive to injectable steroids such as methylprednisolone acetate (Depo-Medrol, Pfizer). Long-term effects of steroid use in cats include diabetes mellitus, fragile skin, weight gain, urinary tract infections, and iatrogenic Cushing's syndrome.4 The veterinary team must explain to pet owners the inherent risks of steroid use and the dangers of abrupt cessation. The risks of using steroids can sometimes be minimized with concurrent use of nonsteroidal therapies.

    Although antihistamines are more effective in curbing atopy symptoms in humans, they can provide relief to atopic animals by inhibiting the actions of mast cells. Antihistamines are generally regarded as safe but should be avoided or used with caution in pregnant patients and those with liver disease, central nervous system disorders, glaucoma, or cardiac arrhythmias.2 Some patients may experience drowsiness from antihistamines, but the effect is usually transient.2

    Studies have shown the benefits of cyclosporine in the treatment of canine atopic dermatitis.6 Cyclosporine is generally well tolerated but can result in gastrointestinal problems for some patients.6 Cats suffering from eosinophilic granuloma complex lesions have shown improvement with cyclosporine treatment.6 As is seen in dogs, gastrointestinal upset is the most common adverse reaction for cats receiving cyclosporine. Intolerant cats typically develop anorexia and vomiting. Because of its immunosuppressive effects, cyclosporine should be avoided in cats that test positive for FIV, FeLV, and Toxoplasma sp infection.4

    The Role of the Technician

    Veterinary technicians have many important responsibilities surrounding the diagnosis and treatment of canine and feline atopy. Technicians who are thorough and accurate historians are a great asset to veterinarians. By conducting tests to identify endoparasites and ectoparasites, they help to rule out diagnostic differentials for atopy. Technicians play an important role both before and during intradermal testing. They should be able to prepare and maintain fresh allergen test kits, restrain the patient during the test, and record the patient's skin reactions. In addition to the specific therapies discussed here, successful treatment of atopy relies on client education and consistent communication. Veterinary technicians can help pet owners to understand the lifelong nature of this incurable disease and be instrumental in maintaining the well-being of their patients.

    1. Benjamini E, Leskowitz S: Immunology: A Short Course. New York, Alan R. Liss, 1989, p 207.

    2. Reedy LM, Miller WH, Willemse T: Allergic Skin Diseases of Dogs and Cats. Philadelphia, WB Saunders, 1997, pp 25-172.

    3. Scott DW, Miller WH, Griffin CE: Small Animal Dermatology, ed 6. Philadelphia, WB Saunders, 2001, pp 563-608.

    4. Foster AP: Diagnosing and treating feline atopy. Vet Med 97(3):226-240, 2002.

    5. Bettenay SV: Feline atopy, in Bonagura JD (ed): Kirk's Current Veterinary Therapy XIII: Small Animal Practice. Philadelphia, WB Saunders, 2000, pp 564-569.

    6. Robson DC, Burton GV: Cyclosporin: Applications in small animal dermatology. Vet Dermatol 14(1):1-9, 2003.

    References »

    NEXT: Case Report: "Bovine Anesthesia During Mastectomy"

    CETEST This course is approved for 0.5 CE credits

    Start Test

    didyouknow

    Did you know... Typically, dogs with atopic dermatitis begin to show clinical signs between 1 and 3 years of age.Read More

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