Feline Health Topics for veterinarians

July-September Volume 13, Number 3

The Itchy Cat

William H. Miller, Jr., VMD, DACVD

Editor's Note: This article is excerpted from Dr. and profound eosinophilic response than do dogs. William Miller's presentation at the Tenth Annual The major basic protein found in eosinophils can Fred Scott Feline Symposium on July 17-19 at the dampen an allergic reaction by breaking down hista­ Veterinary Education Center on the Cornell Univer­ mine, but it can also accelerate the reaction by dam­ sity campus in Ithaca, New York. The seminar was aging collagen and by causing mast cell degranula­ sponsored by the Cornell Feline Health Center, tion. In normal cats, the number of mast cells around Cornell University College of Veterinary Medicine the superficial dermal blood vessels can be nearly Continuing Education Department, and several cor­ double the number found in dogs (20/hpf vs 12/hpf). porate sponsors. The number in allergic cats is usually even greater. Consequently, the pruritus is often well out of propor­ Pruritus, the sensation which evokes the desire to tion to the allergic stimulus. At the initial allergic itch, is a complex process which can be mediated event, some mast cells degranulate and attract eosi­ centrally, peripherally, or peripherally with signifi­ nophils into the area. Pressure on the skin caused by cant central modification. For years, psychogenic licking or scratching causes additional mast cell pruritus was thought to be important in the cat. Today degranulation, initiating a vicious cycle. As a result we know that the vast majority of itchy cats are of this amplification process, itchy cats usually re­ perfectly sane; their skin tingles, tickles, bums, or quire a longer course of steroids than do dogs. itches and they simply respond in the expected fash­ Cats have fewer steroid receptors than do dogs, so ion by licking or scratching. The premature diagnosis they require higher doses of drug to control the same of psychogenic pruritus does the cat and owner a level of pruritus. The attack dose of prednisolone for great disservice. the cat is 2.2 mg/kg/day; most itchy cats will require For some unknown reason, cat skin appears to be a minimum of 10 to 14 days of treatment before the programmed to itch. Cats have a much more rapid fire is taken out of the skin. ALLERGIC DISORDERS

Allergic diseases are the most common reasons for Inside this issu e ... cats to itch, and they appear to be increasing in The Itchy Cat page 1 frequency. As in dogs, some cats have more than one allergic disorder (e.g., flea bite hypersensitivity and Research Briefs page 7 atopy), so the diagnostic evaluation must continue until the cat is itch-free. Feline Health Topics 2

Unlike dogs, allergic cats have no predictable tal antigens that are normally innocuous. Atopy is pattern of pruritus. Atopic cats can have miliary considered to be uncommon in cats, but it appears to dermatitis, facial pruritus, anterior body pruritus, be increasing in frequency. With the exception of whole body pruritus, traumatic alopecia on any part purebred cats (where signs may occur early in life), of the body, eosinophilic plaques, or eosinophilic most atopic cats begin to itch when between three to granulomas. five years-of-age. Over 85% of atopic cats itch during warm weather. Atopic dogs commonly Flea Bite Hypersensitivity progress from seasonal to non-seasonal pruritus, but Worldwide, flea bite hypersensitivity (FBH) is the most atopic cats stay seasonal for long periods of most common allergic skin disease of cats. FBH is time. fairly easy to diagnose but often difficult to control. Clinical signs are quite variable and their severity Products like Program®, Advantage®, and Frontline® often determines when the cat is presented for treat­ have made treatment much more effective and easier ment. Intensely pruritic cats are usually presented for most owners. However, the expense of these shortly after the itching starts. Cats who just groom products may preclude their use i n multiple-cat house­ excessively may not be presented for weeks to months holds where only one cat has clinical disease. In such after the onset of signs. As a result of the variability cases, environmental infestation should be mini­ of signs and timing to presentation, it can be difficult mized by means of household sprays or growth to offer the tentative diagnosis of atopy based upon regulator “flea” collars, and the allergic cat should be the owner’s perception of the onset of pruritus. Good treated with the most aggressive control program records are necessary to document the seasonally available. Purified flea saliva may soon be available, recurrent nature of the cat’s problem. so it may be possible to address FBH in a more specific manner within the next few years. The physical findings in atopic cats are mini­ mally specific, and include facial pruritus, recurrent Atopy otitis externa, head and neck pruritus, miliary derma­ Atopy is a genetically influenced disorder which titis, whole body pruritus, traumatic alopecia, eosino­ causes the animal to become allergic to environmen- philic plaques, and eosinophilic granulomas with collagen degeneration. The steroid response test is / \ very helpful in ruling out atopy. An uncomplicated The ultimate purpose of the Cornell Feline Health Center is to improve atopic cat routinely stops itching when the appropri­ the health of cats everywhere by developing methods to prevent or cure feline diseases, and by providing continuing education to veteri­ ate dose (2.2 mg/kg/day) of prednisolone is given; a narians and cat owners. All contributions are tax-deductible. poor response indicates that the cat is not atopic. Director: James R. Richards, D.V.M. Administrator: Iva Heim (Bear in mind that bacterial folliculitis and Malassezia Secretaries:Gwendolyn M.Frost dermatitis may be confounding disorders, especially Kathleen M. Mospan Pamela E. Sackett if steroids have been used previously.) However, a Sheryl A. Thomas positive response does not invariably mean that the

©1998 by Cornell University on behalf of the cat is atopic. Cornell Feline Health Center, College of Veterinary Medicine, Ithaca, NY 14853. Phone: Excluding other causes of pruritus is the most (607) 253-3414 Fax: (607) 253-3419 All rights reserved. Permission to reprint se­ practical method of supporting the diagnosis of atopy, lected portions must be obtained in writing. but allergy testing is the most specific. Allergy Cornell University is an equal opportunity, af­ firmative action educator and employer. testing not only confirms the diagnosis, but it also Printed on recycled paper. defines the specific allergens so immunotherapy can be formulated. First generation serologic allergy 3

tests have such poor sensitivity and specificity that only one of many mediators of pruritus, antihistaminic they are of questionable value in the cat. However, agents are not uniformly effective. However, in some several companies (Heska, VARL) have modified patients, the results with antihistamines are as good the tests in order to bypass some technical problems as they are with corticosteroids. Antihistamines associated with ELISA testing. These improved tests should be avoided or used with caution in pregnant appear to have reduced or eliminated the incidence of animals or those with glaucoma, seizure disorders, false positive results previously due to flaws in the fluid-retentive disorders, heart disease, or known test. Because ELISA tests are capable of measuring allergies to antihistamines. Antihistamine overdose very low levels of IgE, they will detect clinically can be fatal. Since ketoconazole is known to alter the insignificant antibody levels. Accordingly, all posi­ hepatic metabolism of antihistamines in humans, it is tive test results must be carefully evaluated in light of prudent to avoid concurrent administration of the patient’s history. Intradermal testing is the gold ketoconazole and antihistamines to dogs and cats. If standard of allergy testing, and is associated with a both agents need to be used simultaneously, the very low incidence of false positive reactions. It patient should be monitored carefully. Of the hun­ rarely, if ever, detects clinically insignificant reac­ dreds of antihistamines available, the following have tions. proved to be effective in cats.

Treatment:

Corticosteroids Drug Dosage

Cats are resistant to steroid side effects, so these Chlorpheniramine 2-4 mg/cat q 12h drugs are used with regularity in atopic felines. For Clemastine 0.68 mg/cat ql2h cats with a short allergy season, DepoMedrol® injec­ tions (4-5 mg/kg) are commonly administered. If a Cyproheptadine 2 mg/cat q 12h young healthy cat requires no more than 3 or 4 injections per year, the margin of safety of this method of treatment is wide. If more frequent injec­ Fatty Acid Supplements tions are required or if the cat is old, oral steroids are safer. Prednisone (2.2 mg/kg/day) and The first report on the antipruritic effects of specially- methylprednisone (1.8 mg/kg/day) are safest but some formulated fatty acid supplements appeared in the cats do not respond. The drug is initially given daily veterinary literature in 1988. That report and others to heal the rash, followed by alternate day administra­ prompted intense study of these agents. These spe­ tion to keep things under control. Dexamethasone cial supplements can control pruritus in some ani­ (0.2 mg/kg/day) or triamcinolone (0.2 mg/kg/day) mals, but the best formulation and the optimum usually work in prednisone-resistant cats, but these dosage is not known. Several studies have shown that drugs are not as safe because of their longer duration dogs are very individualistic in their response to these of action. The latter two drugs should be used every supplements, suggesting that there is no one best third day if possible. When steroids are not an option, formulation. The same is probably true in cats as nonsteroidal drugs or immunotherapy vaccines may well. If one supplement does not work, another with be beneficial. a different formulation should be tried. If a supple­ ment is to be effective, results will be seen within 21 Antihistamines days after the initiation of treatment. Antihistamines can minimize the impact of hista­ mine on the animal’s pruritus. Since histamine is (continued on next page) Feline Health Topics 4

Supplement Dosage Food Hypersensitivity

DermCaps® Per label Food allergy can occur in any cat and can occur at any age. Kittens and geriatric patients appear to be EfaVet® Per label equally susceptible. Signs are variable and are non- Gamma linolenic acid >8 mg/kg q24h seasonal provided the cat eats the offending “food” year-round. Cats can develop allergies to commer­ Drug Combinations cial diets, water, snacks, rodents, or anything else that enters its mouth. Accordingly, simply switching the Because of the vast number of mediators of pruritus cat to a different commercial diet is of limited value and the narrow focus of nonsteroidal agents, simulta­ in the diagnosis and treatment of food allergy. The neous administration of two or more drugs, each with cat’s (and owner’s!!) whole lifestyle needs to be a different target mediator, can improve the response modified to prevent accidental ingestion of the aller­ to treatment. The steroid-sparing effects of antihista­ gen. mines and DermCaps® have been proven, as has been the additive benefit of administering DermCaps® Young cats or geriatric patients with a sudden with antihistamines. The author routinely dispenses onset of a steroid non-responsive, intensely pruritic DermCaps® with antihistamines; if the combination disease are prime candidates for a food allergy. If the proves to be effective, the antihistamine is discontin­ signs start in the dead of winter, atopy easily can be ued to determine if the DermCaps®, the antihista­ dismissed. Food sensitivity can be steroid respon­ mine, or the combination of both, are responsible for sive, can start in the middle of the summer, and can the patient’s improvement. occur in middle-aged cats, so the only way to confirm or dismiss food allergy is to investigate it. Unfortu­ Immunotherapy nately, first-generation serologic and intradermal al­ Immunotherapy is the most specific form of treat­ lergy tests are of little or no use in the diagnosis of ment for atopy. Additionally, some veterinary aller­ food allergy. Second generation serologic testing gists believe that effective immunotherapy prevents may play a role in the diagnostic procedure by help­ the development of new allergies. Clinical response ing the clinician select the appropriate diet. How­ is allergen-specific, so an allergy test must be per­ ever, dietary change is the only reliable test. Al­ formed to formulate a specific vaccine. The response though there are various “hypoallergenic” cat foods rate in cats is approximately 75%, and adverse reac­ which appear to be very good in a large number of tions rarely, if ever, are reported. cats, there are no 100% effective commercial foods, so homecooking is still advised. If a response is to be Immunosuppressive Treatments seen, it will be noticeable within 30 days after initiat­ ing the diet change. Complete response may take 10 Simplistically speaking, allergy is an overactive im­ or more weeks. mune response to an allergen. Unfortunately, if the allergen cannot be avoided or if the pruritus cannot be Treatment involves avoiding the offending food. controlled with immunotherapy, corticosteroids, or The author directs owners to challenge the cat with nonsteroidal agents, the cat owner may opt for eutha­ individual “pure” foods to facilitate identification of nasia. For the extra-special patient and client, immu­ the specific allergen. Once the allergen or allergens nosuppressive treatment may be beneficial, but this are identified, the owner should then be able to select form of treatment is untested in the cat. An agent a commercial food which agrees with the cat. Rarely, which might be effective is Chlorambucil (2-6 mg/m2 homecooking must be continued and the diet must be BSA q24h). 5

balanced with fatty acids, taurine, vitamins, and min­ skin disease associated with roundworm or hook­ erals. worm infection. Feces should be examined for para­ sites, and the parasite treatment history of all pruritic Insect and Arachnid Hypersensitivity cats should be reviewed. House dust mites and fleas are well known problems Heartworm Hypersensitivity: for allergic cats. In dogs, skin test reactions to insects (ants, black flies, moths, etc.) are commonplace and Heartworm hypersensitivity is currently a rare condi­ may be of significance to some atopic dogs. Informa­ tion, but if heartworm infection becomes more com­ tion on the significance of most of these insects in cats mon in cats, this disorder will be seen more fre­ is lacking but they can play an important role in quently. allergic pruritus. Miscellaneous Hypersensitivities Mite Hypersensitivity: Contact Hypersensitivity: Mite hypersensitivity is a common disorder in which Contact hypersensitivity is considered to be a rare to the cat itches well out of proportion to the number of non-existent condition in cats. mites present. Hypersensitivity makes the diagnosis of mite infestation more difficult than usual since Drug Hypersensitivity: some/many mites are killed by the allergic reaction. Pruritus can persist for several weeks after all the Cats with cutaneous drug allergies rarely develop mites are killed. non-lesional pruritus. More commonly, primary lesions develop and the cat responds to them. No Mosquito Bite Hypersensitivity: diagnostic tests are available to confirm the suspi­ Mosquito bite hypersensitivity is an uncommon sea- cion, but improvement within 14 days after drug sonally-pruritic disorder. Signs initially develop withdrawal supports the diagnosis. during warm weather and become significantly worse Bacterial Hypersensitivity: at each subsequent exposure. The diagnosis is made by documenting a seasonal eosinophilic dermatitis Bacterial hypersensitivity is a rare to non-existent which resolves spontaneously with mosquito con­ condition in cats. trol. Corticosteroids accelerate healing. Skin testing Malassezia Hypersensitivity: and immunotherapy may be beneficial. The pruritus seen in dogs infected with Malassezia Parasitic Hypersensitivity appears to be mediated by a hypersensitivity reaction IgE is both the antiparasitic and anti-allergen anti­ to the organism. Although the yeast can infect body and some animals become clinically allergic to allergic cats, the hypersensitivity component may or their parasites. Antiparasitic IgE has the potential to may not exist. interfere with the kinetics of the routine serologic Hormonal Hypersensitivity: allergy test. All atopic cats should be free of parasites for thirty or more days before serologic tests are Hormonal hypersensitivity is very rare to non-exis­ performed. tent in cats.

Intestinal Parasite Hypersensitivity:

Intestinal parasite hypersensitivity is a rare pruritic (continued on next page) Feline Health Topics 6

NON-ALLERGIC PRURITIC DISORDERS

Demodicosis Anal Sac Disease

Two different types of demodex mites can infect cats. Anal sac disease is uncommon in cats and rarely Demodexfelis infection is indicative of an underlying results in the clinical signs seen in dogs. If cutaneous immunosuppressive disorder. The second type is an signs are present, they usually are due to excessive unnamed species which resembles the demodex mite licking near the tail base. The diagnosis is made by seen in some rodents. A common history is that the palpation, and expression of the distended anal sacs cat ran away from home and started to itch shortly should be curative. after returning. The mite appears to be contagious Endocrine Disorders from cat to cat, so the point source may be another cat or the environment. Diagnosis is confirmed by For unknown reasons, some hyperthyroid cats lick visualizing the mite in skin scrapings examined un­ their skin excessively. Overall, skin lesions resulting der a lOx or 40x objective. Treatment with lime from endocrine disease are uncommon in cats, and sulfur dips or ivermectin should be curative. when they do occur, they usually are not pruritic.

Dermatophytosis Hyperesthesia Syndrome

Ringworm in most cats results in focal skin lesions Hyperesthesia syndrome is a rare, poorly understood which are minimally pruritic. With widespread in­ condition which probably is mediated centrally. fection, especially with organisms other then M. Rarely, the disorder is due to spinal cord disease canis, pruritus can be significant. Pruritic cats may cranial to the area involved. Diagnosis is by exclu­ groom away the typical scale, scruff, and broken sion, and optimal methods of treatment are not known. hairs; the absence of these features may lessen the suspicion of dermatophytosis. Trichography or fun­ Psychogenic Alopecia gal culture confirms the diagnosis. Psychogenic alopecia is a rare condition in which Staphylococcal Infection excessive grooming is thought to be due to an under­ lying behavior abnormality. The diagnosis is made Staphylococcal skin infections are uncommon in by excluding all other causes of excessive grooming. cats. However, allergic cats-either because of the The optimum therapy is not known, but it often immunologic abnormalities associated with the al­ includes trials of various psychotropic medications. lergy, or as a result of repeated use of corticosteroids- appear to be more prone to infection than non-allergic Dr. William H. Miller is a professor o f Clinical Sciences at Cornell's College of Veterinary Medicine. cats. When infection is superimposed on the under­ lying allergy, the cat’s response to steroids disap­ pears and the skin disease may worsen as a result of corticosteroid administration. Diagnosis is made by cytological examination and by response to appropri­ ate antimicrobial therapy. Superficial infections re­ quire 14 to 21 days of treatment; deeper lesions require a longer course. 7

Research Briefs

Prevalence of Heartworm Infection in Cats with Cough or dyspnea may indicate heartworm dis­ Signs of Cardiorespiratory Abnormalities ease in cats; serologic tests, echocardiography, and (Authors— C.E. Atkins, T.C. Defrancesco, M.W. radiography are most useful diagnostic procedures. Miller, K.M. Meurs, and B. Keene)—The study was Although living indoors is protective, it may not to determine prevalence of heartworm infection in a preclude heartworm infection in cats. (Resource: J population of pet cats with cardiorespiratory abnor­ Am Vet Med Assoc 212:517, 1998) malities and to determine relative usefulness of clini­ Feline Chronic Renal Failure: Calcium Homeo­ cal signs and tests in diagnosis of heartworm disease. stasis in 80 Cases Diagnosed Between 1992 and One hundred client-owned cats with clinical signs 1995. of cardiorespiratory abnormalities were evaluated (Authors— P.J. Barber and J. Elliott)—Eighty using CBC, modified Knott test, ELISA for serologic cats with chronic renal failure (CRF) were evaluated detection of heartworm antigen and antibodies to in a prospective study to investigate the prevalence heartworms, thoracic radiography, and and etiopathogenesis of renal secondary hyperpar­ echocardiography. Cats were considered infected if athyroidism (RHPTH), using routine plasma bio­ they had circulating microfilaria, heartworm anti­ chemistry and assays of parathyroid hormone (PTH), gens in serum, or if heartworms were detected by blood ionized calcium and 1,25 echocardiography or on necropsy. Cats were consid­ dihydroxycholecalciferol (1,25[OH]2D3). Hyperpar­ ered suspicious for infection if they had 2 of the athyroidism was a frequent sequela of CRF, affecting following: serum antibodies to heartworms, eosino­ 84 percent of cats with CRF, the severity and preva­ philia or basophilia, or indicative radiographic find­ lence of RHPTH increasing with the degree of renal ings. dysfunction. Compared with an age-matched control population, plasma concentrations of phosphate and Nine cats were infected with heartworms, result­ PTH were significantly higher and 1,25(OH)2D3 con­ ing in a prevalence of 9%; 26 cats had evidence of centrations were significantly lower in the two groups heartworm exposure (ie, serum antibodies to heart­ of cats presenting with clinical signs of CRF. Signifi­ worms). Twenty cats were considered suspicious for cant ionised hypocalcaemia was present only in cats heartworm infection. Some outdoor exposure was with end- stage renal failure. However, a number of reported twice as often in heartworm-infected cats, cats were hyperparathyroid in the absence of abnor­ compared with non-infected and suspicious cats. malities in the parameters of calcium homeostasis However, a third of infected cats were reportedly measured in this study. There was a significant housed totally indoors. Cough and dyspnea were correlation between plasma phosphate and PTH con­ strong indicators of heartworm disease. Eight of 9 centrations. (Resource: J Small Anim Pract 39:108- infected cats had serum antibodies to heartworms and 116, 1998) heartworm antigen in serum. Thoracic radiography and echocardiography indicated heartworm infection Feline Chronic Renal Failure: Clinical Findings in 6 and 7 of the 9 cats, respectively. in 80 Cases Diagnosed Between 1992 and 1995. (continued on next page) Feline Health Topics 8

(Authors—J. Elliott and P.J. Barber)— Clinical with or without ill-defined pulmonary nodules and/or and laboratory findings at the time of first diagnosis pleural effusion. More cats presented with pulmo­ in 80 cats with chronic renal failure (CRF) were nary metastatic disease in the category of either ill- examined in a prospective study to determine the defined nodules (n = 10) or a diffuse pattern (n = 7). survival time of these animals and identify possible Within this group, the most commonly represented factors contributing to the progression of feline CRF. primary tumor was mammary gland adenocarcinoma. On the basis of clinical presentation, animals were (Resource: Vet Radiol Ultrasound 39:4-8, 1998). assigned to one of three groups; compensated (n= 15), uremic (n=39) and end-stage (n=26) CRF. Loss of Cutaneous Mast Cell Ttimors in Cats: 32 renal concentrating ability was a common finding, Cases (1991-1994). even before clinical signs of renal disease were evi­ (Authors—H. Molander-McCrary, C.J. Henry, dent. The plasma creatinine concentration at initial K. Potter, J.W. Tyler, and M.S. Buss)— Case records presentation was a poor predictor of survival time and of 32 cats with cutaneous mast cell tumors (CMCTs) the presence of significant anemia was indicative of were reviewed. Using the Patnaik system for grading a poor prognosis. The study demonstrated the highly canine mast cell tumors, the relationships between variable degree of renal impairment present at the histopathological grade and patient survival time and time of diagnosis and the potentially long survival tumor recurrence were examined. Tumor histologi­ time of many compensated and uremic cases. (Re­ cal grade had no prognostic significance. One-, source: J Small Anim Practice 39:78-85, 1998) two-, and three-year tumor recurrence rates follow­ ing surgical excision were 16%, 19%, and 13%, Radiographic Patterns of Pulmonary Me­ respectively incomplete excision was not associated tastasis in 25 Cats. with a higher rate of tumor recurrence. (Resource: J (Authors—L.J. Forrest and C.A. Gray bush)— Amer Anim Hosp Assn 34:281-284, 1998) Thoracic radiographs of 25 cats with pulmonary

metastatic disease and confirmed primary tumors Photocopies of the above article can be obtained for a were reviewed retrospectively. Pulmonary patterns small fee from the Flower-Sprecher Library, College of Veteri­ of metastasis were divided into three categories, nary Medicine, Ithaca, NY 14853. Telephone: (607) 253- 3510. Fax: (607) 253-3080. The total charged is based on the described as well-defined interstitial nodules, ill- number of pages copied, NYS sales tax (if applicable), and the defined interstitial nodules or a diffuse pulmonary method of delivery. pattern. The latter consisted of an alveolar pattern

Cornell Feline Health Center Cornell University College of Veterinary Medicine Ithaca, New York 14853