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Q. What are your tips for diagnosing and treating atopy in cats? Are cats typically sensitive to some allergens more than others?
RULING OUT OTHER CAUSES OF PRURITUS
Flea allergy dermatitis is the most common cause of feline pruritic disease. Strict flea control on all animals every month is important to rule this out as the sole cause of the pruritus. Other ectoparasitic causes must be ruled out as well (e.g. Cheyletiella, Notoedres, Otodectes, and Demodex species). Whether or not these mites are detected (by evaluating samples obtained by skin scraping, hair plucks, or combing), several treatments are indicated to simply rule these out as causative factors for the pruritic disease. A broad-spectrum topical spot-on parasiticide (selamectin or moxidectin) is usually helpful. Lime sulfur is also an option.
DIAGNOSING FELINE ATOPY
As with dogs, horses, and people, the most common environmental allergens causing clinical signs are house dust or house dust mites. Other common allergens include weeds, grasses, trees, and molds, even if a cat is an indoor cat. Diagnosing feline atopic dermatitis is usually a process of elimination. Allergy testing is not necessarily a diagnostic tool for atopic dermatitis; it is a test that is indicated when a client is interested in immunotherapy. One could make the argument that allergy testing is indicated for avoidance, but this is difficult in many cases.
Serology or intradermal testing can be performed when trying to determine which allergens should be incorporated into the immunotherapy formulation. Skin allergy testing is more challenging in cats as compared with dogs. The reactions seem to be more immediate and less prominent, with variability in erythema and wheal formation. In my opinion, intradermal (skin) testing would usually be the superior option in dogs and horses, while in cats, I usually perform a serology test initially.
Now, the frustration for many is the frequent negative results when allergy testing or the reluctance for clients to choose immunotherapy. A negative test result does not rule out atopic dermatitis. A subset of patients will not have positive results even with multiple intradermal tests or serology tests. For these patients, which are said to have intrinsic atopic dermatitis, immunotherapy is usually not an option. However, there is research looking at regionally specific immunotherapy, or immunotherapy based on the most common allergens in a particular region without relying on allergy test results.
TREATING FELINE ATOPY
Management for environmental allergies does not always need to involve immunotherapy (oral or injectable). In fact, for many cases, it may not be the best option.
Also, dermatophytosis is more common in cats and can mimic allergic skin disease in that a patient with ringworm may be pruritic and have hair loss. This may need to be ruled out (e.g. fungal culture and Wood's lamp examination) and addressed if indicated.
Antihistamines may be considered, and you have several options. Some of the older-generation antihistamine choices such as hydroxyzine and chlorpheniramine can be sedating, which may prove beneficial. While in my experience antihistamines are about 10% to 30% effective, they are still sometimes indicated as an adjunctive treatment.
Essential fatty acids
Essential fatty acids (EFAs) can be helpful as well. Omega-3 EFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid, as well as the omega-6 EFA dihomo-gamma-linolenic acid (DGLA), can decrease skin inflammation via competition with arachidonic acid for metabolic enzymes. EFAs can also modulate leukotriene and prostaglandin synthesis.
Eicosanoids are anti-inflammatory. The goal is a decrease in the inflammatory (arachidonic acid-derived) eicosanoids (inflammatory mediators) and, thus, an increase in more of the "less" inflammatory mediators. Also, EFAs help to restore normal composition of lipids to skin (barrier function) and modulate lymphocyte functions.
Cyclosporine is an excellent option for the management of atopic dermatitis with or without immunotherapy. However, when allergy testing is not elected by the owner because of the reluctance to pursue immunotherapy (injections), cyclosporine is the treatment of choice.
Modified cyclosporine (Atopica—Novartis) is the first oral nonsteroidal treatment approved for the management of feline atopic dermatitis. Atopica is a fat-soluble, cyclic polypeptide fungal product with immunomodulating activity, and it is a calcineurin inhibitor. Cyclosporine targets specific cells (T cells) in the immune system that lead to an allergic reaction. It is well-tolerated and at least 80% effective when used properly. And cyclosporine lacks major adverse effects often associated with corticosteroids.
Infections and parasites must be well-controlled or treated before you incorporate cyclosporine. Also, using the correct dose (7 mg/kg/day in cats) is important. Ideally, the modified formulation (e.g. Atopica) is a better choice than other forms of cyclosporine (compounded and nonmodified forms) as the bioavailability is better understood and less medication is used to achieve the desired effect.1,2
Corticosteroids are usually indicated at some point during the management of allergies. Ideally, corticosteroids are used only when necessary and as infrequently as possible. In my opinion, oral administration is a better option since it allows for a methodical titration and for adjustments to be made, if needed. I think that long-acting injection options are less ideal and that they should be used sparingly (e.g. no more than three methylprednisolone acetate injections yearly). I usually use oral prednisolone, methylprednisolone, dexamethasone, or triamcinolone.
In addition to the aforementioned oral medication options and immunotherapy, topical treatments may be helpful. Some topical antimicrobials target the secondary infections. More recently, products are available that help maintain better barrier function, which is often compromised in allergic patients. Numerous topical anti-inflammatory and antipruritic options are also available.
Topical treatments often complement the other options mentioned above. In some cases, topical treatments are all that is indicated, but cats are not as receptive to this method of treatment as are other species.
A FINAL CONSIDERATION: PSYCHOGENIC ALOPECIA
In rare cases, self-mutilation and overgrooming may be a result of a psychogenic cause. If all of the aforementioned causes are addressed but the problem continues, consider behavior-modifying medications, such as fluoxetine or clomipramine.
Many management options are available for allergic cats. Every patient is different, and every client situation is unique, so the treatment plans are different for all patients. This is where the art of managing the allergic patient comes into play.
Ian B. Spiegel, VMD, MHS, DACVD
Veterinary Specialty and Emergency Center
24 hr Emergency and Referral Hospital
Animerge 24/7 Animal Emergency and Specialty Care
Garden State Veterinary Specialists
Tinton Falls, N.J.
Jersey Shore Veterinary Emergency Service
1. Noli C, Scarampella F. Prospective open pilot study on the use of ciclosporin for feline allergic skin disease. J Small Anim Pract 2006;47(8):434-438.
2. Vercelli A, Raviri B, Cornegliani L. The use of oral cyclosporin to treat feline dermatoses: a retrospective analysis of 23 cases. Vet Dermatol 2006;17(3):201-206.