Scratching the Surface of Allergies in Dogs
Pruritus—a classic sign of allergic disease—is a common complaint described by dog owners. The skin is the largest organ of the body and acts as a barrier, offering protection from environmental elements as well as the development of infection. When the skin barrier is disrupted by the allergic process, many secondary problems can develop and increase the pruritus level, further contributing to patients’ discomfort (FIGURE 1).
Allergic skin and ear diseases are common problems in canine patients, and many of the clinical presentations are similar. Sometimes, these problems are not the primary reason for an appointment. For example, clients bringing their dogs in for vaccination may ask to have the skin or ears checked because they have noticed a rash, observed their dog licking or scratching, or smelled an odor from the haircoat or ears.
The types of allergies seen most often in canine patients are flea allergy dermatitis (FAD; hypersensitivity to flea saliva), food hypersensitivity, and atopic dermatitis. These diseases are frustrating for both owners and the veterinary team. To make matters worse, such diseases are only controllable, not curable. The goal is to find the correct therapeutic recommendation to best manage each patient’s condition.
Veterinary technicians are in a unique position to be involved in all aspects of managing these cases, starting with ensuring good client communication at the initial contact, then collecting a complete history, performing the physical examination, and relaying this information to the veterinarian. After the doctor has created the differential diagnosis, technicians often assist with performing diagnostic procedures and providing detailed information to owners. Following up with clients to obtain progress reports and ensuring the scheduling of necessary recheck appointments help the veterinarian with patient management. All of these factors are essential to success.
BEFORE THE DERMATOLOGIC EXAMINATION
Information collected when a client calls to make an appointment can alert veterinary technicians that an animal has a dermatologic condition and will require a longer appointment. It is imperative to communicate that the owner who is most familiar with the dog’s history should be the one present for the examination and to ensure that the owner is aware of the increased appointment length.
Clients should be instructed to bring a list of any current or previous medications and topical products (including over-the-counter preparations) that have been used as well as diets fed. Sending clients a dermatology history questionnaire to fill out before the appointment is a great way to collect important information and gives them time to reflect on their pets’ dermatologic problems, which allows them to provide more accurate details during the appointment. If a client is unable to complete the form in advance, he or she should be asked to arrive early to complete it before the examination. The questionnaire is also a good resource if a dog experiences a recurrence or if different skin problems develop in the future.
DURING THE EXAMINATION
Patient signalment, historical details, and physical examination findings can provide clues to which allergy is the likely culprit. Having the ability to see, touch, and smell the affected body organ is an advantage for both the veterinary staff and owners.
Collecting an accurate patient history is an art and requires excellent communication skills. Technicians who can listen well and guide clients into providing a chronological sequence of the relevant dermatologic details are valuable assets to the veterinary team. Box 1 lists some important questions to ask when obtaining a patient history. A basic diet history should be collected initially; a more thorough diet history can be obtained later if needed. Because many dogs with allergies are pruritic, collecting information regarding the pruritus level is also important. Clients need to be educated that dogs with pruritus may not only scratch but also rub, lick, or chew their skin. For each type of behavior noted, clients should be questioned about how often it occurs, what areas of the body are involved, and how intense it is.
Finally, clients should be asked to provide a total pruritus score using either a numerical scale (0 [no itchiness] to 10 [constant itching]) or a visual analog score, which can be found in many resources.1,2 All observations should be documented in the medical record and can be compared at follow-up appointments to determine changes in pruritus level throughout treatment.
WHICH ALLERGY IS CAUSING THE PROBLEM?
Although collecting historical information can be time consuming, presenting comprehensive patient overviews to veterinarians can help narrow the list of differentials and allow the most efficient and cost-effective diagnostic plan to be implemented. Determining which allergy or combination of allergies is affecting an animal can be a challenging process. Making an accurate diagnosis quickly allows a treatment plan to be initiated sooner and, ideally, provides patient relief (and satisfies clients) earlier. It is critical to inform clients that diagnostic tests and treatment trials do not always provide immediate answers and may be performed to rule out conditions while all possible causes of a problem are being investigated. Owners should understand that each patient is unique and that, once the allergy is identified and being treated, time is needed to determine which therapeutic options are best for their pet.
Because FAD is the most common pruritic skin disease seen in dogs living in warm climates,1 it makes sense to manage potential or existing flea problems before investigating other allergic conditions. Although not all dogs are allergic to fleas, dogs with FAD can become extremely pruritic after just a few fleabites. The most common age of onset is 3 to 5 years, although dogs of any age can be affected. Clinical signs tend to be very typical and are nonseasonal in temperate climates (FIGURE 2).
Food hypersensitivity is typically seen in very young dogs and in older dogs with a first-time skin problem. Older dogs with food hypersensitivity typically become allergic to one or more ingredients in their regular diet or treats after consuming the offending food component(s) for at least 2 years.1 It is usually a nonseasonal condition (most dogs eat the same diet year-round).
Atopic dermatitis is a complex disease estimated to occur in 3% to 27% of the canine population.1 In these patients, environmental allergens such as dust, pollens, and mold spores are absorbed via the respiratory tract or oral mucosa, or percutaneously owing to impairment of the skin’s barrier function, and cause an inflammatory response of the immune system. Clinical signs are usually seen in patients aged 1 to 3 years but can develop in dogs as young as 6 months. Atopic dermatitis is not often diagnosed in patients older than 7 years. Depending on the allergen(s), atopic dermatitis can be a seasonal or nonseasonal condition. Many patients may show seasonal problems initially and progress to nonseasonal signs as they become sensitive to more allergens.
There is a suspicion that atopic dermatitis has a genetic component1; therefore, intact dogs with atopic dermatitis should not be bred. Puppies born during the allergy season may also have more potential to develop atopic dermatitis. Dogs with atopic dermatitis may be more prone to developing a flea allergy, and it has been speculated that foods may be flare factors for dogs with atopic dermatitis.1
Some patients have a combination of food hypersensitivity and atopic dermatitis. The clinical presentations of these two diseases are similar (FIGURE 3). A good history may give clues as to which type of allergy is more likely causing clinical signs; atopic dermatitis is more common.
Although contact dermatitis has been reported in dogs, it is considered a rare cause of pruritic skin disease.1
Flea Allergy Dermatitis
A diagnosis of FAD may be determined after assessing the history (age of onset, duration and seasonality of signs, known or suspected environmental flea exposure) and physical examination findings (pruritus, compatible clinical signs, and lesion type and distribution pattern). Fleas may be found during the physical examination. If not, diagnostic testing options for FAD include combing for fleas, intradermal testing with flea allergen, and measurement of IgE levels through serum testing, although this last test has less sensitivity.1 Because the absence of fleas and/or flea feces does not rule out FAD, the diagnosis is best confirmed by implementing strict flea-control measures and getting a positive patient response.
Although intradermal and serum allergy tests are available, they are not accurate methods for diagnosing food allergies. The ideal test to diagnose or rule out a food allergy is a strict food elimination diet lasting 8 to 10 weeks. After the diet history is reviewed, a novel protein and carbohydrate or a hydrolyzed protein diet should be chosen for the trial. This often means feeding a home-cooked or prescription diet. The switch to the new diet should be gradual to prevent gastrointestinal problems.
While this sounds like a simple test, it actually can be quite difficult. Elimination diets can be expensive, especially for large-breed patients or when multiple dogs must be fed the same diet to ensure a strict trial. Owners must understand that nothing but the elimination diet should pass the affected dog’s lips during these 8 to 10 weeks—which means no treats, no table food, no rawhides, and no flavored chews or toothpastes are allowed. Chewable medications (even monthly heartworm preventives) should be switched to a nonchewable formulation. For the trial to be successful, it is critical that owners follow all instructions properly.
Veterinary technicians are often the ones to educate and support clients throughout the diet trial, starting with an explanation of why such a “test” is necessary. Ideally, veterinary technicians should also contact clients midway through the trial to get patient progress reports, ensure clients are following instructions, answer any questions, and provide support and encouragement to continue the trial. Concerns should be brought to the veterinarian’s attention.
When a patient returns for a recheck at the end of the trial, the next step is based on observed improvement in clinical signs. If a strict trial was performed and there has been no improvement, food hypersensitivity can be ruled out, the dog can return to its normal diet, and other causes of skin problems can be pursued.
For dogs that improve on the elimination diet, the next step is the challenge: the dog is fed the previous diet and observed for recurrence of clinical signs, which typically develop within 2 weeks. Some owners may be unwilling to do the challenge, but it is the step that verifies that improvement was related to the elimination diet, not a change in season, a new medication, or shampoos used to treat secondary infections. Clients should be instructed that their dog does not need to become miserable again. If the dog is truly food allergic, clinical signs will recur; as soon as they do, the diagnosis of food hypersensitivity is confirmed and the test diet is reinstated.
There is no diagnostic test for atopic dermatitis. After ruling out other causes of pruritic skin diseases, the presumptive diagnosis is made based on the patient’s history and clinical signs. Relevant details that aid veterinarians in making a diagnosis include:
- Age of onset
- Pruritus level (pruritus is often present before clinical signs develop)
- Areas affected (face, feet, axillae, ventral neck, ventral abdomen, inguinal area)
- Changing or progressive clinical signs
- Seasonal or year-round signs, with or without seasonal exacerbations
After diagnosis, intradermal (FIGURE 4) or serum allergy tests are used to identify the offending environmental allergens so that they can be avoided (although this is often impractical) or used for therapeutic immunotherapy. To identify all offending allergens, it is often recommended to delay allergy testing until the dog has shown clinical signs for a minimum of 1 year. It may also be beneficial to test dogs that are affected seasonally shortly after their allergic season. Again, these tests are not used for diagnosing atopic dermatitis and should only be performed when clients are willing to use immunotherapy.
TREATING THE ALLERGIC DOG
Flea Allergy Dermatitis
Many flea-control products are available, and veterinary technicians should be knowledgeable about the products offered at their practice, including the mechanism of action and proper administration. The initial goals when treating dogs with FAD are to relieve pruritus, treat secondary infections, and use specific control measures to quickly reduce fleabite exposure. The goals of an ongoing flea-control program include killing adult fleas on dogs, killing immature flea stages in the environment, and preventing reinfestation. Educating clients and setting realistic expectations are critical for success. Ensuring that owners use products as labeled (e.g., not bathing dogs for 48 hours before or after application of spot-on formulations) and demonstrating how to apply products are helpful.
Treatment failures do occur and are often attributed to inadequate treatment of the environment, failure to treat all animals in the household, poor selection of products, and owner noncompliance. Taking the time to educate owners initially and following up throughout treatment should lead to better patient management.
Dogs with food allergies should be fed an appropriate diet, and accidental exposure to any offending allergens must be prevented. Some owners are content with feeding the test diet for maintenance. Others may want to switch to a less expensive over-the-counter diet or to try a homemade diet. This is another opportunity to educate clients about the importance of reading labels to ensure that all ingredients are novel; it may be necessary to contact the manufacturer to determine if the equipment used to produce the diet is dedicated solely to the food in question, eliminating the risk of contamination by other ingredients. If owners choose to prepare a homemade diet, they should be referred to a veterinary nutritionist to formulate a complete and balanced diet.
For dogs with seasonal allergies, owners may choose medical management. Many options exist. Having a good rapport with owners to determine what products will best fit their time, physical, and financial constraints improves client compliance. For patients with year-round atopic dermatitis, clients may be interested in trying allergen-specific immunotherapy. Intradermal testing is still considered the gold standard to identify allergens, although serum testing is more practical in general practice. Some dermatologists perform both tests and choose allergens for immunotherapy after reviewing all test results, taking into account the dog’s history and allergen exposure. Whichever testing methodology is used, proper withdrawal time of medications known or suspected to interfere with test results (e.g., antihistamines, glucocorticoids, cyclosporine, tricyclic antidepressants with antihistaminic properties [doxepin and amitriptyline], antiinflammatories [niacinamide and fatty acids]) should be followed.
Clients can be taught to administer subcutaneous immunotherapy injections at home. Various injection schedule protocols are available, and many have a maintenance schedule of about every 1 to 3 weeks. Although adverse effects are rare and can vary in severity (localized pruritus to anaphylaxis), clients should be made aware of them and instructed to contact the clinic immediately if seen.
Sublingual immunotherapy (SLIT) is an option that has recently become available. This therapy must be administered directly into the oral cavity (not put into food/treats), and dogs should not eat or drink for 10 minutes before or after administration. SLIT may be preferred to injections because of the ease of administration; however, when choosing which type of immunotherapy to try, clients need to understand that oral immunotherapy is given twice daily every day and requires a greater time commitment than subcutaneous injections.
It may take up to a year to determine the level of efficacy of immunotherapy, although patients may show improvement by 6 months. If no or minimal response is seen after 1 year, immunotherapy may be discontinued; symptomatic therapy is the next best option. If the patient improves, immunotherapy is generally continued for life. The mechanism of action of immunotherapy is complex and not completely understood; however, the reported success rate is 50% to 80%.1
To best manage their disease, most dogs benefit from some type of adjunctive therapy in addition to immunotherapy. Selection of adjunctive therapies depends on many factors. Veterinary technicians should be familiar with all the treatment options to discuss with owners after veterinarians have made recommendations.
Topical products such as shampoo therapy are safe and can be very beneficial. Medicated shampoos not only help remove allergens from the skin but also can be prescribed for specific skin conditions. Some shampoos are drying, and a conditioner or rinse can be added if necessary. Frequent bathing (1 to 2 times/week) may be recommended, and it is important that the shampoo be allowed to contact the skin for 10 to 15 minutes before rinsing well.
For dogs with chronic otitis, periodic ear cleaning with a good-quality ear cleaner may be recommended in combination with treatment of existing ear infections and as a preventive against future ear infections. Clients should be taught how to properly clean their dog’s ears according to the veterinarian’s instructions.
Antihistamines (TABLE 1) are another option for dogs with mild pruritus. Many products are available, and in general, they are not expensive and rarely have serious adverse effects. An antihistamine trial can be performed to determine which, if any, will work for the patient. Clients should be instructed to give each antihistamine one at a time for 1 to 2 weeks; they should keep a record of how pruritic their dog is and call the clinic if any side effects are observed. If an antihistamine controls the pruritus, the dog can be maintained on it. Seasonal patients may benefit from starting the antihistamine before the onset of allergen exposure.
|Diphenhydramine||2–4 mg/kg PO q8–12h|
|Chlorpheniramine||4–8 mg/dog (maximum of 0.5 mg/kg) PO q8–12h|
|Clemastine||0.05–1.5 mg/kg PO q12h|
|Amitriptyline||1–2 mg/kg PO q12h|
|Hydroxyzine||2 mg/kg PO q12h|
Essential fatty acids (EFAs) are another safe option and are not too expensive. They may be used to reduce pruritus, decrease production of inflammatory mediators, and improve the skin’s barrier function. To determine the efficacy of EFAs, a treatment trial of 8 to 12 weeks is necessary. Efficacy of EFAs may be enhanced when they are used in conjunction with antihistamines or glucocorticoids. If effective, they may even allow the glucocorticoid dose to be reduced. Another potential benefit of EFA therapy is improved coat quality.
EFAs can be incorporated into the diet or given orally in capsule or liquid form. Although the ideal dosage of EFAs is still unknown, most dermatologists aim for a daily calculated dosage of both eicosapentaenoic acid (EPA; 180 mg/10 lb/day) and docosahexaenoic acid (DHA; 120 mg/10 lb/day)3; many veterinary labeled products are available.
Glucocorticoids are generally inexpensive and usually effective at reducing pruritus. While they may be a great option for dogs with seasonal signs, they should be used cautiously in patients needing year-round therapy. Oral steroids are preferred over injectable agents for several reasons: better dosage control, ease in adjusting dosage, and ability to discontinue administration if severe side effects develop. An every-other-day dosing schedule is preferred to minimize side effects. Clients should be informed of both short- and long-term adverse effects of glucocorticoids and educated about the importance of yearly monitoring. Dogs on year-round steroid therapy have a higher incidence of urinary tract infections4; thus, regular chemistry profile, urinalysis, and urine culture (collected via cystocentesis) tests are recommended.
Cyclosporine is an immunosuppressive drug that may be used as a sole agent for treating atopic dermatitis and may have steroid-sparing benefits. Administration for 4 to 6 weeks may be needed to see results, and the recommended dose range is 3.3 to 6.7 mg/kg PO q24h.3 It is recommended to use the microemulsion form for better absorption of the drug. Reported adverse effects include vomiting, diarrhea, gingival hyperplasia, and hypertrichosis. The disadvantage of cyclosporine is that it is expensive.
Collecting a detailed medication history is important because cyclosporine interacts with a number of other drugs. Concurrently administering ketoconazole can increase cyclosporine blood levels, and this interaction can be used advantageously to decrease the required cyclosporine dose (possibly decreasing cost for owners, especially when treating large breeds). Dogs on year-round cyclosporine therapy have a higher incidence of urinary tract infections,5 and monitoring these patients yearly (as described for glucocorticoids) is suggested.
Oclacitinib is the newest treatment approved for treating canine atopic dermatitis for patients at least 12 months old. It is an immunomodulatory drug that is used to reduce the itch sensation and inflammation. It typically provides a rapid decrease in pruritus with minimal adverse effects (vomiting, diarrhea, decreased appetite, weakness, lethargy). Baseline laboratory work and frequent rechecks with laboratory tests are important to monitor efficacy, side effects, and outcome of long-term treatment with this new therapy.
MANAGING ALLERGIC DOGS
For patients that have multiple allergic conditions, successfully managing one condition may reduce clinical signs. This can alter how the other allergies are treated and may allow medications with lesser side effects to be effective at controlling clinical signs.
It is beneficial to ensure that any secondary infections are identified. Cytology is a great diagnostic test for skin and ear infections. Appropriate antimicrobial therapy should help dogs feel more comfortable, and superficial infections should typically be treated for a minimum of 3 weeks (treatment should be continued for 1 week after resolution of clinical signs3); dogs should be reexamined and cytology performed before discontinuing therapy. Clients should be aware that skin and ear infections are likely to recur until the underlying allergy is identified and controlled.
It is critical that owners understand that their dogs’ allergies will never be cured. The goal is to find the therapeutic combination that controls clinical signs and makes the patient comfortable; however, determining what works best for an individual patient takes time. Educating clients about the specific allergic disease affecting their dog should increase compliance. When veterinary technicians successfully communicate realistic expectations of both the time and financial commitments needed to treat allergic diseases, the end result should be better managed pets and happier clients.
- Miller WH, Griffin CE, Campbell KL. Muller and Kirk’s Small Animal Dermatology. 7th ed. St. Louis: Elsevier; 2013.
- Hill PB. Canine pruritus scale. www.cliniciansbrief.com/sites/default/files/sites/cliniciansbrief.com/files/CaninePruritisScale.pdf. Accessed November 2015.
- Koch SN, Torres SMF, Plumb DC. Canine and Feline Dermatology Drug Handbook. Ames, IA: Wiley-Blackwell; 2012.
- Torres SM, Diaz SF, Nogueira SA, et al. Frequency of urinary tract infection among dogs with pruritic disorders receiving long-term glucocorticoid treatment. JAVMA 2005;227(2):239-243.
- Peterson AL, Torres SM, Rendahl A, Koch SN. Frequency of urinary tract infection in dogs with inflammatory skin disorders treated with oral ciclosporin alone or in combination with glucocorticoid therapy: a retrospective study. Vet Dermatol 2012;23(3):201-205.
This article is no longer available for continuing education credit, but you can still test your knowledge with this quiz.
- When is the ideal time for veterinary technicians to become involved with allergic patients?
- At the initial point of contact by the client
- When diagnostic tests need to be performed
- At the end of the visit, to provide client education
- After the initial visit, contacting clients as a follow-up
- Which fact is helpful when determining the most likely type of allergy in a pruritic patient?
- Age of onset
- Seasonal versus nonseasonal condition
- All of the above
- Which allergic condition is considered to be the most common in warm climates?
- Contact dermatitis
- Flea allergy dermatitis
- Food hypersensitivity
- Atopic dermatitis
- Which of the following conditions would likely present as seasonal pruritus?
- Flea allergy dermatitis in a dog living in Florida
- Food hypersensitivity
- Atopic dermatitis in a dog allergic to trees
- Atopic dermatitis in a dog allergic to house dust
- A 9-year-old dog presents with pruritus and has never had skin or ear problems before. Which allergic condition is most likely in this patient?
- Contact dermatitis
- Flea allergy dermatitis
- Food hypersensitivity
- Atopic dermatitis
- Dogs with environmental allergies do not commonly absorb allergens via the
- Respiratory tract
- Alimentary tract
- Oral mucous membranes
- What is the best way to diagnose atopic dermatitis?
- Perform an intradermal allergy test.
- Perform a serum allergy test.
- Limit the dog’s exposure to the outdoors and look for signs of improvement.
- There is no diagnostic test.
- What is the best way to diagnose food hypersensitivity?
- Perform an intradermal allergy test.
- Perform a serum allergy test.
- Switch the dog to a different commercial diet.
- Perform a food elimination diet trial.
- Which of the following medications does not need routine patient monitoring with laboratory tests?
- When educating the owner of an intact pet, veterinary technicians should advise against breeding a dog with ________, which may have a genetic component.
- contact dermatitis
- flea allergy dermatitis
- food hypersensitivity
- atopic dermatitis