Itchy cat: Don't want that! (Proceedings)

Where to Start?

Pruritus in cats, like other species, can be caused by a multitude of diseases. Identifying the condition may be a frustrating process requiring a compliant and understanding pet owner. As with any dermatologic disease, a detailed history is essential before creating an appropriate list of differential diagnoses. A systematic diagnostic approach is necessary to avoid oversight of an important disease and should be performed on all cases. This should include the minimal database (MDB) of skin scrapings, fungal culture (DTM) and cytology. Further diagnostics are performed pending the history, clinical examination and differential diagnosis.

Examination should include detailed observation of lesions and distribution patterns. A general examination should also be included. Rule-outs should routinely be performed and therapeutic trials may be required. Perception of endemic diseases commonly seen in your geographic region should be prioritized. The history of the cat's current habitat and previous locations may be helpful and included in the history. Previous therapy and response should be acquired.

Pruritic habits are usually described and represent the owners chief complaint. Some cases where symmetrical alopecia is the most prominent clinical sign may not be perceived as an itchy problem. Pet owners may accept the cat's excessive compulsive grooming as within "normal limits" or the cat is a "closet hair-puller."

Clinical manifestations are variable in the pruritic cat. Presentations commonly seen include miliary dermatitis characterized by a papular–crusting dermatitis. The descriptive term meaning "seed-like" represents a wide variety of diseases and is only a reaction pattern of the skin. Feline symmetrical alopecia is another clinical presentation characterized, as the name implies, by a symmetrical pattern of hairloss. This is also a descriptive term and represents a number of disease possibilities. Hairloss in the cat is most commonly self-inflicted. The cause of the compulsive over grooming is most often the result of a pruritic condition although psychogenic hair pulling and excessive licking is observed.

Eosinophilic lesions are also observed in the pruritic cat. These have been commonly referred to as the "eosinophilic granuloma complex." While idiopathic hypereosinophilic syndromes exist, the most common association is hypersensitivity reactions. Some animals will present with regionalized or generalized dermatitis although when inflammation is present, papules and crusts are often observed with characteristic features of "miliary dermatitis." In other words, regionalized or generalized erythema without papules is rare.

Diseases To Consider In The Pruritic Cat

Hypersensitivity Reactions

Flea allergy dermatitis is probably the most common allergic condition observed in flea infested areas. This condition may be observed with the classical miliary dermatitis regionalized over the pelvic region. Caudal abdominal alopecia is often seen and a circumferential miliary dermatitis is observed around the neck.

Adverse reaction to food was considered to be a more common problem than recognized now. It is typically characterized by severe pruritus with excoriations and evidence of self mutilation. Miliary dermatitis, multifocal to symmetrical alopecia, eosinophilic ulcers or plaques and erythroderma may be seen. Facial pruritus is a hallmark of this problem.

Feline atopy is a pruritic disease of cats that is underestimated in frequency of occurrence. The characteristics are similar to those of adverse reaction to food ("food allergy") and may have an assortment of lesions. Pruritus may be seasonal or non-seasonal and does not require routine outdoor exposure. In fact, cats with restrictive inside habitats have been observed with seasonal pruritus and cats restricted inside have demonstrated reactivity to pollen aeroallergens through intradermal testing. Facial pruritus should elicit feline atopy as a differential. Symmetrical alopecia is frequently observed with common distribution in the medial aspect of the forelegs, caudal abdomen and lateral regions of the trunk. Otitis externa may be present and often complicated by yeast or bacterial infection. Eosinophilic lesions may be observed, particularly affecting the head and thorax. The age of onset for feline atopy is not as restrictive as canine atopy and may occur later in life beyond seven years of age. While canine atopy is usually steroid responsive, feline atopy may be refractory.

Insect hypersensitivity is often a component of feline atopy but may be observed as a separate entity. The allergens I include in this category are: cockroach, mosquito, house fly, deer fly, horse fly, moth, black ant, fire ant, etc. The clinical features may be similar to those observed for atopy. Steroid responsiveness may be limited and the condition may be generalized although the face and head are usually affected.

Infectious Diseases

Dermatophytosis is more prevalent in the southeast United States among infectious skin diseases in the cat. Consideration of this infection should always be considered in the pruritic cat, and in particular those that have been treated aggressively with glucocorticoids or megestrol acetate. Classical appearing lesions may be present. The infection may be (and often is) a secondary complication of an underlying problem particularly if seen in an adult cat. The long coated breeds like the Persian may be an exception. Fungal culture (DTM) should be acquired on all cases.

Cutaneous malassezia is far less common in the cat than the dog but is intermittently observed as a secondary complication potentiating the pruritus. Cytologic evaluation of the skin surface should be included with the minimum database.

Bacterial folliculitis has been associated with pruritic miliary dermatitis although less common than canine bacterial folliculitis, staphylococcal pyoderma may be present as a complicating problem. Cytology may be helpful in evaluating for bacterial infection, although surface bacterial colonization may be present without overt infectious folliculitis or dermatitis.

Viral infection may be associated with facial pruritus. Herpes virus tends to affect the nasal and facial area and have historical or concurrent upper respiratory signs, conjunctivitis and/ or oral ulcers. FeLV and FIV positive cats have been observed with pruritic dermatitis (miliary dermatitis) and concurrent systemic illness.

Parasitic Causes of Feline Pruritus

The flea is definitely the most common ectoparasite of the cat, but is associated with hypersensitivity when noticeable pruritus and lesions are found.

Otodectes cynotis is not commonly observed as a cause of pruritic dermatitis but is occasionally observed as ectopic otoacariasis. The mite has a reputation of migrating from the ear canal with a population found on the skin. Hypersensitivity reaction is probably involved.

Notoedres cati is the scabies mite of cats and often referred to in layman's terms as "head mange." This parasite is regionally endemic and may not be observed at your location. Unlike canine scabies, Notoedres cati is usually easy to diagnose by skin scraping or tape examination. The disease classically involves head, face and pinnae initially but may lead to generalized pruritus and dermatitis. Miliary lesions are frequently found.

Demodex gatoi is also a parasite with regional geographic influence. This demodex mite is a surface dweller and poses a contagious element with concern for transmission in multi-cat households. Demodex cati is not usually pruritic unless associated with a secondary infection.

Cheyletiella is another pruritic disease with regional endemic characteristics. It is associated with excessive scale and has been referred to as "Walking dandruff." Skin scrapings and tape examinations will usually demonstrate organisms.

Miscellaneous Causes o Pruritus

Miscellaneous causes of pruritus include autoimmune disease (pemphigus foliacious), cutaneous drug reaction, hypereosinophilic syndrome, epitheliotrophic lymphoma, cutaneous mastocytosis and idiopathic dermatoses (Persian cat facial pruritus, sterile granuloma, miliary dermatitis)

Diagnostic Approach

Diagnostic testing should always include the MBD. Skin scrapings from representative lesions to evaluate for ectoparasites. Fungal culture (DTM) for evaluation of dermatophytoisis. Tape preps for cytology and smears from ears, exudate or moist lesions should be performed. Nodules and plaques should include fine needle aspirates for cytology. Skin biopsies of pruritic cats usually only substantiate the presence of mast cells and eosinophils characteristic of a hypersensitivity reaction although dermatophytosis or diseases such as pemphigus foliaceous, mast cell tumor may be identified.

Allergy testing may be integrated in the diagnostic plan depending on the index of suspicion and the preliminary rule out of other problems. Intradermal allergy testing for environmental allergens should be reserved for cases where allergen specific immunotherapy is intended. Serum allergy testing is may be best option since many cats are presented with a long background of steroid therapy or have generalized miliary lesions making intradermal testing impossible. A combination of limited skin testing and serum allergy testing are included by some as a routine work-up for allergy. Elimination trials are often included with the assessment of the pruritic cat. The first and most obvious is diet elimination trial utilizing an exclusive diet with a limited ingredient food, a hydrosylate food or home prepared food for 8-10 weeks. Cats should be restricted to being inside the house to avoid obscure consumption of animals through predation. The intermittent evaluations are necessary. Response is usually observed in 4 weeks. Dietary challenge should be used to validate that the response was a consequence of the dietary change.

Infectious diseases should be treated the appropriate amount of time with reputable drugs. Antibiotics routinely used include amoxicillin-clavulanic acid 22mg/kg BID, clindamycin 11mg/kg QD, cefadroxil 20mg/kg BID, enrofloxacin 5mg/kg QD, cephalexin 20-30mg/kg BID. Antifungal systemic treatment includes itraconazole 5-10mg/kg daily or 3 consecutive days per week. Fluconazole has become affordable as a generic now available. The dosage is 5-10mg/kg daily or 3 days per week. Terbinafine may be used at 30 mg/kg once daily. Griseofulvin is still used by some but caution should be exercised and cats should be tested for FeLV and FIV infection. Irreversible myelosuppression may occur particularly in those cats that are FeLV and FIV positive. With so many other ideal medications available, I do not use griseofulvin in the cat. Topical antimicrobial therapy includes lime sulfur 2.5-3.0% as a pour-on for parasiticidal activity and antifungal effect. Miconazole is available as a shampoo, spray, leave-on rinse and leave–on conditioner. While systemic ketoconazole should not be used in cats, shampoos containing it may be incorporated.

Parasiticidal treatment trials include both insecticides and acaricides. Therapeutic trials for flea control are commonly performed. A standard parasiticidal trial is the application of imidacloprid (Advantage, Bayer Animal Health) every 14 days for four treatments with evaluation at the conclusion of the trial and midway. Selamectin (Revolution, Pfizer Animal Health) may be incorporated particularly if mites are considered a component of the problem. Reapplication every 14 days for three treatments is used for treating feline scabies. Lime sulfur rinses (LymDip, DVM Pharmaceuticals) provide acaricidal activity as well as fungicidal effect. It is the treatment of choice for Demodex gatoi and is applied weekly to affect. It is also anti-pruritic. Lufenuron (Program, Novartis) may be integrated in a flea control program by using the injectable product every 6 months as an insect development inhibitor. Ivermectin has been used in cats at 250 ug/kg once weekly for feline scabies or every other day for Demodex cati. Screening for circulating microfilaria of D. imitis may be considered before ivermectin therapy in heartworm endemic areas.

Symptomatic Anti-Pruritic Therapy

Symptomatic therapy is commonly used for antipruritic effect. Glucocorticoids are commonly used in cats. Methylprednisolone acetate is a routine treatment and unfortunately become an option in lieu of performing the necessary diagnostics. Subcutaneous injections may result in SQ nodules and/or focal alopecia over the injection site. Cats are known to be more steroid tolerant than other species although systemic and cutaneous pathology may occur from overzealous steroid therapy. Dermatopyhtosis in the adult cat is often the consequence of chronic glucocorticoid therapy. In contrast to the dog, oral dexamethasone may be used for maintenance therapy in cats. Where prednisone and prednisolone seem to have similar affect in the dog, prednisolone appears to be more effective in the cat then prednisone. Prednisolone may be acquired in a 20 mg tablet for easier administration. Compounding may also be performed for use of a liquid if it enhances the ease of administration. A local pharmacy advises me that one of the more favorite flavors of cats is butterscotch! Go figure. Antihistamine drugs are often utilized in the cat combined with allergen specific immunotherapy for treating atopy. Their tolerance and beneficial effect is variable in the cat but of value for trialing. Adversities of antihistamines may include lethargy or in contrast, hyperexcitability. Pet owners should be advised of the possible expectations before electing the use of antihistamine. Topical gels for percutaneous absorption has gained some popularity because of the ease of topical application rather than oral treatment. Antihistamine therapy has a poor track record of eliciting a dramatic affect. Cyclosporine A (Atopica, Novartis) has also been used in atopic cats and cats with eosinophilic lesions. The dosage is 5-10 mg/kg daily for one month then every other day with eventual reduction in frequency to the least frequent administration. The average dose for cats is 25 mg. and may be integrated with glucocorticoid therapy. It is certainly more expensive then other modalities and may have gastrointestinal side effects. In SE United States, most cats require therapy every other day on maintenance while some require a daily dose. Allergen immunotherapy response is approximated to be 60% and should be less expensive with fewer side effects. Cyclosporine A (CsA) has also been used in conjunction with allergen immunotherapy. Evaluation for FeLV and FIV should be considered before implementing a potent immunosuppressant. A list of commonly used drugs is provided for consideration as symptomatic therapy. Megestrol acetate should not be considered in treating the pruitic cat.

Non-Steroidal Systemic Treatment for Cats

Chlorpheneramine.......................2-4 mg b.i.d.

Librium.......................¼ of 5 mg tab b.i.d-t.i.d.

Amitriptyline.......................5-10 mg b.i.d.

Citirizine.......................2.5-5.0 mg qd - b.i.d.

Hydroxyzine.......................5-10 mg/cat or 2.2 mg/kg every 8-12 hours

Clemastine.......................0.125 mg/kg b.i.d.

Cyproheptadine (Periactin)...............2 mg/cat or 0.05 mg/kg every 12 hours

Fexofenadine (Allegra).......................10 mg/cat every 12 hours

Trimeprazine (Temaril).......................0.5-1.0 mg/kg every 8-12 hours

Diphenhydramine.......................2-4 mg/cat every 8-12 hours

Systemic Glucorticoid Treatment for Cats

Parenteral

Methylprednisolone acetate

5 mg/kg SQ or IM (usual dosage is 20 mg/cat)

Repeat twice at 2-3 week intervals

Long term treatment: every 6-8 weeks

Triamcinolone: .22 mg/kg

Oral

Prednisolone

Induction: 2.2-4.4 mg/kg divided b.i.d.

Maintenance: .5-2.2 mg/kg qod

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

Dexamethasone: .1 mg/kg qd for 7 days then twice weekly

References

Scott, WS, Miller, WH, Griffin, CE, Muller & Kirk's Small Animal Dermatology, 6th Ed., WB Saunders, Philadelphia, 2001

Guaguere, E, Prelaud, P, A Practical Guide to Feline Dermatology, Merial, 1999