Cats can itch too! Feline pruritic diseases and treatment (Proceedings)

The pruritic cat often poses a challenge for the clinician as there is often no one distinctive pattern that provides the diagnostic criteria leading to a conclusive diagnosis. In fact, the same disease may have varied presentation in different animals. The historical perspective is important but sometimes elusive from the perspective of providing disease specific information. Glucocorticoid response may be somewhat deceiving as refractory pruritus may evolve over time. Licking and compulsive over grooming are mainstays of the pruritic cat and may be misinterpreted by the pet owner. Recognition of parasitism may be limited from the gross dermatologic examination. While secondary bacterial infection or infectious otitis is less common, they may be identified in specific cases with respective treatment included. Routine diagnostics should be performed including cytological examination and fungal culture. Pattern analysis and recognition of relevant lesions is necessary for developing objective differentials. Facial pruritus, +/- otitis externa, should include feline atopy, insect hypersensitivity, adverse reaction to food, dermatophytosis, cutaneous drug reaction, viral dermatitis and parasitism from Notoedres cati and ectopic otoacariasis (Otodectes cynotis).

Integumentary Patterns

Miliary Dermatitis is one of the more common presentations and is characterized by papules that have developed a crust. These are more common on the truncal region and often associated with flea allergy. Some cats with flea allergy will have a military eruption that extends around the cervical region often combined with hypotrichosis or alopecia on the caudal ventral abdomen. Other allergic problems are included such as atopy, food allergy or insect hypersensitivity. Dermatophytosis is a must to rule out with a DTM culture. Antibiotic therapy may be indicated if significant representation of bacteria are found from cytology suggesting a secondary bacterial folliculitis. Less common diseases such as pemphigus foliaceous present with a miliary pattern. Conditions also described with military eruptions include other ectoparasitism, endoparasitisim, and nutritional problems.

Feline Traumatic Alopecia is the consequence of excessive grooming and most often representative of a pruritic etiology although behavioral manifestation may be a differential. Patterns may be variable and most often includes the caudal abdomen. Concurrent erythema may be present although often the skin appears unaffected. In other cases a mild papular eruption may be present. The allergic causes most often associated are feline atopy, adverse food reaction, insect hypersensitivity and flea allergy dermatitis. Demodicosis (D. cati or D. gatoi) has been associated with a pruritic alopecia as are other ectoparasitic causes such as cheyletiellosis, ectopic otodectes or notoedres.

Eosinophilic Dermatoses (aka Eosinophilic Granuloma Complex) are commonly observed in cats with pruritic problems usually caused by ectoparasitism or hypersensitivity reactions. Historically, this syndrome was not related to the common hypersensitivities we consider today. The lesions that have been described include the eosinophilic plaque, indolent ulcer (previously named the rodent ulcer) and the eosinophilic granuloma. The indolent ulcer may require differentiation from neoplastic disease as it often has similar appearance. Indolent ulcers are located on the upper lip appearing as a well circumscribed unilateral or bilateral nodule with an erosive or ulcerative appearing surface. They are most commonly associated with hypersensitivity conditions and have been seen with flea allergy reactivity. The eosinophilic plaques are often well circumscribed and are a common reactive pattern again associated with allergic etiologies and further potentiated by aggressive licking at the lesion. The ventral abdomen is a common site for this problem although other anatomical areas may be seen. The surface of these lesions are usually red to yellow in coloration with a moist surface which reveals eosinophils from their surface by first wiping a lesion, then lightly squeezing it and collecting some of the material for an air dried, rapid stained, microscopic evaluation.

Chin Dermatitis (feline acne) has been touted to be the consequence of older cats, particularly males or neutered males that have become less caring about their grooming habits. While this phenomenon cannot be disputed, there is a prevalence of "chin" lesions in association of allergic dermatoses which often represent progressive furunculosis. Secondary bacterial infection is common and usually requires antibiotic therapy and/or 2% mupirocin ointment on the affected area twice daily for 28 days.

Diagnostic Procedures

A complete history is essential including previous treatments, diet, supplements, parasiticidal therapy, seasonality of the problem, other animals in the household, habitat of the affected animal, concurrent diseases, etc. Skin scrapings should be performed routinely and include both superficial scrapings as well as deep scrapings for demodex mites. A fungal culture (DTM) should be performed to evaluate for dermatophytosis. Evaluation of a trichogram may reveal arthospores or "fuzzy" hair shafts. A Wood's lamp evaluation should be evaluated with caution as non-specific fluorescence may be observed. Cytology of otic exudate should be examined and material collected from lesions evaluated under oil immersion following rapid staining. A CBC and chemistry panel may be indicated depending on age and type/chronicity of therapy. Testing for feline leukemia and feline immunodeficiency is warranted in select cases. Common use of glucocorticoid therapy may have influenced the development of diabetes mellitus. Careful examination for ectoparasites should be performed including aggressive evaluation for fleas. Skin biopsies will often be supportive of an inflammatory (eosinophilic) dermatoses with rule out of neoplastic disease. Biopsies for culture may be necessary when atypical mycobacterial or mycotic infection is suspected. Sterile granulomas would require macerated tissue culture to enable a confirmed diagnosis.

Allergy testing is a prerequisite for allergen immunotherapy. The use of an intradermal procedure is often not feasible as a consequence of intermittent glucocorticoid therapy. Serum allergy testing has been useful in cases and may routinely be applied specifically for the recognition of allergens for inclusion in the treatment solution but should not be used for diagnostic confirmation. Combination of serum allergy testing combined with selected allergens (house dust, house dust mites, flea and miscellaneous insects) for intradermal testing has been very helpful to enhance allergen therapy response.

Diagnostic Trials

Diagnostic trials include dietary elimination trials and parasiticidal trials. There are several options for conducting dietary trials which include commercially available limited ingredient diets, manufactured hydrolysate diets (Hill's Z/D and Royal Canin HP) or home prepared diet. Other than a hydrolysate diet, a dietary history is important to choose a novel protein. Home prepared may be nutritionall enhanced by consulting with Davis Veterinary Medical Consulting, Inc. (BalancelT.com). Restriction inside is necessary for ideal interpretation. A variety of commercial limited ingredient diets exist and the choice should reflect previous protein sources and avoidance of suspected food allergens. Palatability becomes more of an issue with the feline than other species. Some will reject the diet even if it was initially acceptable. All treats must be avoided during the trial. Multi-cat households become a problem as a consequence of peripheral food availability or the extra cost of placing all cats on the same commercial limited ingredient, hydrolysate or home prepared diet. While a total of 8-10 weeks may be required, most cats will have substantial improvement within 3 weeks. Complete cessation of pruritus is not expected as concurrent atopy or insect hypersensitivitymay also be present. Following the dietary trial it is ideal to conduct a dietary challenge with the commercial food that had been given prior to the elimination trial.

Parasiticidal Trials

Ectoparasites and insect induced allergic dermatoses are common in cats and also very difficult to prove in many cases. Cats with flea allergy with no evidence of fleas present. Mosquito or other insect hypersensitivity may occur where the offending agent is not present at the time of examination or by the pet owner. Mosquito bite hypersensitivity has variable clinical signs and is most often observed in the cat with an outdoor exposure. Facial and nasal area is commonly involved and edema may be present with erosive changes developing with eventual crust formation. Progression of the problem may lead ot depigmentation and scarring ultimately with concern for pemphigus foliaceous or lupus. Otitis may be present with periocular dermatitis and hairloss. Pododermatitis also be observed. Multiple insects are usually reactive on an intradermal allergy test with suspicion of varied etiologies of the allergy. Flea allergy remains the most common problem in an environment where fleas are found. Treatment for fleas (whether proven as a problem or only suspected) is for the most part obligatory. The use of the flea allergen test available as a solution in a 1:100 W/V concentration diluted to a 1:1000 concentration (1:10 dilution with saline) provides an immediate response with a wheal & flare reaction in over 75% of the cats tested. The use of a histamine control and saline negative control should be integrated. A delayed reaction may be observed in some cats not showing an immediate reaction. The evidence promotes the acceptance of the disease and often motivates the cat owner that does not accept the "flea allergy theory". Parasiticides useful for a 2 month diagnostic trial includes Imidacloprid ever 14 days, Revolution every 14 days, Vectra for Cats, Advantage Multi every 14 days, Promeris for cats and if concerns about the efficacy of topicals in cats with generalized cutaneous pathology, nitenpyram (Capstar®) may be administered at a standard dosage every other day for 4-6 weeks with modification to other products pending outcome of the trial. Year around treatment is necessary for cats in the southeastern US. Treatment of all incontact animals (dogs & cats) is necessary for maximal control. Flea allergen immunotherapy has not demonstrated sufficient response to be of utility and is not a substitute for a good regimen of flea control. Lime sulfur sprays or rinses varying from 2-3 % may be used for its parasiticidal effect as well as the antipruritic effect. Although undesirable for use it may be very effective and should be done in a well ventilated area where there would be no contact to porcelain,brass, gold or other such objects including the jewelry of the pet owner. The product should be left on and an Elizabethan collar or other mechanical devide applied to prevent licking of the fur which could induce vomiting. Some parasiticides have claims for mosquito control such as dinotefuran, the active ingredient in Vectra for cats. Pet Guard® gel manufactured by Virbac has also been used with some success. Other products such as Skin-So-Soft Bug Guard® by Avon and Bit-blocker organic spray (HOMS) may be employed when biting insects such as mosquitoes are implicated. Trials of combinations may be necessary to provide adequate assessment.

Allergen and Antipruritic Therapy

Antipruritic therapy can be easily summarized as the selection of treatment from 3 areas or in the words of Monty Hall, "Let's Make a Deal". First there are antihistamine products, omega three fatty acids and glucocorticoids. Next is the use of cyclosporine A for more specific immunomodulation therapy and lastly, allergen specific immunotherapy. Antihistamines have a very unpredictable effect in both tolerance in the cat as well as control of the pruritus. Most of the difficulties are met through the administration of the drugs orally since many cats oppose that form of treatment and most antihistamines or antihistamine like drugs require administration 2-3 times per day and must be give consistently to be effective. There are some that may be administered parenterally. A 14 day trial should be followed for sufficient evaluation. Trialing different products is necessary to provide accurate information about the usefulness of the drug. Chlorpheneramine continues to be the standard at 2-4 mg per cat twice daily. Evaluation for lethargy, hyperexcitability, Gl intolerance, or personality change should be conducted while evaluating the efficacy. Zyrtec®, now available as an OTC product has been used with success in some cats. It is cetirizine HCI and represents the active form of hydroxyzine. Tablet sizes are 5 and 10 mg with the dosage of 5 - 10 mg once or twice daily. It is also available in a liquid. Some other antihistamine treatment choices are listed below:

Non-steroidal Treatment for treating Pruritus in the Cat

■  Chlorpheneramine      2-4 mg bid

■  Hydroxyzine              2.2 mg/kg bid

■  Librium                     1/4 of 5 mg tab bid - tid

■  Amitriptyline             5-10 mg bid

■  Cetirizine                  2.5 -5.0 mg qd-bid or 5-10 mg daily for larger cats

■  Cyproheptadine (Periactin) 2 mg/cat or 0.05 mg/kg bid-tid

■  Fexofenadine (Allegra) 10 mg/cat bid

■  Trimeprazine (Temaril) 0.5-1.0 mg/kg bid-tid

Glucocorticoid Therapy in the Cat

Overall glucocorticoids are tolerated betterthan other species although internal adversities may occur without the typical outward signs observed in other species.Polyuria, polydipsia, polyphagia, weight gain and atropy of the shin may all occur even without bilateral symmetrical alopecia. Diabetes mellitus may occur as a consequence of glucocorticoid therapy particularly when using repositol injectable products. Congestive heart failure has been observed in concurrence of cats with chronic glucocorticoid therapy particularly when using methylprednisolone acetate parenterally.

Cats have been estimated to have fewer steroid receptors than dogs which has resulted in a dosage adjustment that is approximately twice that of the dog. Longer acting glucocorticoids have also been used in chronic maintenance therapy of the pruritic cat which would not be used in the dog. Prednisone fails to provide sufficient anti-inflammatory effect at standard dosages because the cat cannot convert prednisone to prednisolone, the active form of the chemical, as well as other species. Therefore, prednisolone or methylprednisolone should be used in the cat and prednisone should be avoided. Blood glucose and urine glucose should be monitored in cases receiving chronic glucocorticoid therapy. Subcutaneous administration of methylprednisolone acetate may result in the development of subcutaneous nodules.

Glucocorticoids - parenteral

     ■Methylprednisolone acetate:

        5 mg/kg SQ or IM (20 mg) repeat twice at 2-3 week intervals

        long term treatment: every 6-8 weeks

     ■ Triamcinolone: .22mg/kg

Glucocorticoids - oral

■ Prednisolone (prednisone much less effective)

    Induction:               2.2-4.4 mg/kg divided bid

    Maintenance         .5-2.2 mg/kg qod

■ Triamcinolone        .5-1.0 mg/kg qd then 2-3 times per week

■ Dexamethasone     .1 -.2 mg/kg qd for 7 days then 2-3 times weekly

Cyclosporine Therapy

Cyclosporine is an immunosuppressant that was developed for veterinary application as Atopica®, so named for the disease being treated in the dog. It is also available as a generic on the human side as a 25 mg and l00mg capsule and a solution containing 100 mg/ml. Both formulations are extra-label in cats with the extrapolation of the dosage from the dog where 5mg/kg is minimal. The regimen recommended includes treatment daily for 4-6 weeks before changing to every other day and eventually to three times weekly depending on clinical signs. Higher doses may be necessary with some reports of 15 mg/kg used. Caution should be followed because of the potency of this immunosuppressant. Associated disease of toxoplasmosis has been observed in cases treated with cyclosporine although direct cause-effect relationship was not determined. Cyclosporine is also compatible with other therapy including antihistamines and glucocorticoids. It has also been used in cases in combination with allergen immunotherapy. Absorption of cyclosporine is variable although the bioavailability seems to be higher in cats compared to dogs. Used rationally, this drug provides an excellent alternative to glucocorticoid therapy or provides more maximal control with lower dosages of glucocorticoid. Monitoring blood levels of cyclosporine provides more specific evaluation of absorption and dosage modification with avoidance of complications. Although ideal levels have not been substantiated, it is believed that trough levels of 250-500ng/ml is recommended.

Allergen Immunotherapy

Allergen immunotherapy for the treatment of feline atopy provides an excellent alternative to other other choices or in conjunction with combined therapy. It is often more appealing than oral therapy because of avoidance of oral administration. Cats are very tolerant of allergen therapy and improvement in at least 50% of the cases treated makes it a worthwhile choice. Modification of allergen not to exceed more than 0.5 ml of maintenance allergen solution at any single injection is recommended. Most cats do well with an injection once a week of 0.3 mis. or 0.15 mis. twice weekly. Allergy testing includes intradermal technique and serum allergy testing to identify allergens. Atopic cats may have reactivity to outside allergens such as pollens from grasses, weeds and trees even when they are restricted inside. Response to allergen immunotherapy may require several months up to a year to achieve optimal success. Modification of the allergen schedule may be necessary in some cases. Rapid induction of allergen (RUSH allergen therapy) may be ideal in fractious cats or in situations where the owner is reluctant or unable to give the injections through the induction protocol. This procedure provides the opportunity to complete the entire induction phase by administering injections according to the protocol every 30 minutes for approximately 6 hrs. Providing monitoring and drugs for an allergic reaction is necessary although highly unlikely of happening. Giving a pretreatment dose of antihistamine or oral glucocorticoid may be helpful. RUSH allergen therapy may not improve either the response time or rate.