Identifying, managing feline acne, non-parasitic otitis and allergic dermatitis

In DVM Best Practices on Feline Medicine (May, 2002), I wrote about feline ear mites and dermatophytes, two common infectious diseases often seen in feline practice. This month, I would like to discuss other causes of feline otitis, such as ear polyps, tumors, and otitis secondary to allergy. In addition, feline allergic dermatitis and feline acne, two often frustrating and challenging chronic conditions in feline dermatology, will be described. As before, I will try to provide as much practical information as possible to help you in the diagnosis and clinical management of these disorders.

Photo 1: Food intolerance/hypersensitivity in a cat allergic to fish, showing severe facial self-trauma.

Feline non-parasitic causes of otitis and ear masses

Most veterinarians are familiar with the clinical signs and treatment of ear mites in cats and kittens, but what about the feline patient with chronic otitis in which ear mites have been ruled out?

Otitis in cats, other than infection due to ear mites, is uncommon, possibly due to their upright pinna and mostly hairless ear canals. Chronic bilateral recurrent ceruminous otitis, with or without pinnal inflammation and pruritus, is common in cats with underlying food allergy or atopy, and often is resistant to therapy unless the underlying cause is identified and treated. Geriatric cats may develop failure of ear canal epithelial self-cleaning, leading to the formation of large ceruminoliths lodged against the tympanic membrane. Any cat with unilateral, medically resistant otitis externa or otitis media should be evaluated for feline nasopharyngeal polyps or other otic neoplasia.

Feline nasopharyngeal polyps, most common in young cats or kittens, may originate from the pharyngeal mucosa, the middle ear, or the auditory (eustachian) tube. These polyps may be congenital (may be seen in siblings) or secondary to bacterial or viral infections, such as calicivirus. Most polyps are unilateral, in rare cases they can be bilateral. The most common clinical signs include unilateral otic discharge (ceruminous, purulent, or hemorrhagic), head-shaking, and a pink well-encapsulated mass in the horizontal or vertical ear canal. If the mass involves the middle ear, head tilt, nystagmus, Horner's syndrome and ataxia may be seen. Occasionally, the mass can only be visualized by examining the area under the soft palate under sedation. Surgical removal of the polyp, often with bulla osteotomy, is usually needed for complete cure. Simply ripping or pulling out the polyp with a hemostat is traumatic, can cause excessive bleeding and damage to delicate ear canal tissue, and often fails to remove the base of the polyp, leading to regrowth. For these reasons, this procedure is not recommended for ear polyp removal.

Other otic neoplasms seen primarily in older cats include ceruminous gland adenomas and adenocarcinomas. In cats, ear canal tumors are malignant in 50 percent of the cases. Clinical signs include unilateral otic hemorrhage, necrotic odor, secondary bacterial otitis, head-shaking and ear scratching. Swelling with hemorrhage and drainage below the ear in the salivary gland region may be seen. A pink-white often dome-shaped ulcerated and bleeding mass is seen on otoscopic evaluation in the horizontal or vertical canal. The only effective treatment is surgical removal of the mass, and ear canal ablation surgery with bulla osteotomy often gives the best result. Ceruminous gland adenocarcinomas may be locally invasive into regional lymph nodes or parotid glands, and may metastasize to the lungs. Radiotherapy can be used for incompletely excised tumors.

Feline acne

Feline acne, an idiopathic disorder of follicular keratinization, affects cats of any age, gender or breed. The pathogenesis is unknown, but underlying localized seborrhea with the production of abnormal sebum, changes in the hair cycle, viruses (calicivirus, herpes virus), stress, immunosuppression, chin trauma (due to excessive scent marking by rubbing the chin on vertical objects, or from scratching the chin due to underlying food or environmental allergies), plastic food dish contact allergy or bacterial contamination from rubbing the chin in food (especially old dried canned food), or poor grooming habits have all been proposed as possible causes. Most likely, the problem is multi-factorial. Early clinical signs include asymptomatic crusts and comedones on the chin and lower lip. Some cases stay in the comedone stage, while others progress to folliculitis/furunculosis (with formation of papules, pustules and draining cysts/nodules) and in severe cases, cellulitis with painful edematous swelling of the chin and lips. Cats with folliculitis/furunculosis are often pruritic and will rub or scratch the chin. Regional lymphadenopathy may occur. More common organisms isolated in moderate-severe cases of feline acne include Pasteurella, beta-hemolytic Streptococci and Malassezia). Differential diagnoses include dermatophytosis, demodicosis, eosinophilic granuloma (collagenolytic granuloma) and neoplasia. It is important to evaluate cats with feline acne for other signs of allergic dermatitis during your physical examination. Diagnostic tests that should be run in all cases of feline acne include skin scrapings to rule out demodicosis, and fungal culture. In refractory or more severe cases, bacterial culture/sensitivity and biopsy for histopathology should be performed to rule out eosinophilic granuloma/collagenolytic granuloma lesions, underlying allergy, fungal infection and neoplasia. Histopathology results of feline acne include comedo formation with follicular dilatation, keratosis and plugging. Folliculitis, furunculosis and pyogranulomatous dermatitis may be seen in severe cases. Underlying allergy may be diagnosed, and dermatophytosis or other fungal infection can be ruled out. If an underlying allergy is diagnosed, then a flea control trial, an appropriate 10-12 food week elimination diet, and, if nonresponsive to these treatments, intradermal allergy testing should be performed.

Treatment for feline acne varies according to the severity and extent of lesions, and with how much the condition is bothering the cat (and owner)! Cats with only asymptomatic comedones do not require treatment, but may benefit from cleaning the chin once a day with a medicated antibacterial wipe, changing to a dry diet, and feeding out of ceramic or stainless steel bowls that are washed with soap and water daily, rather than plastic. In more severe cases with folliculitis and furunculosis, prolonged oral antibiotic treatment with bactericidal antibiotics used for deep pyoderma treatment should be prescribed. Amoxicillin-clavulanic acid (Clavamox®) enrofloxacin (Baytril®), cephalexin/cefadroxil, clindamycin and metronidazole are recommended and should be continued for six to eight weeks, until all lesions have been resolved for at least two weeks. The chin should be gently washed with anti-seborrheic, antibacterial shampoos such as those containing sulfur-salicylic acid, ethyl lactate, or benzoyl peroxide. Alternatively, moist wipes such as Malacetic® wet wipes are very useful and well-tolerated. The chin should be cleaned once daily initially, then cleaning can be decreased to twice weekly. Topical mupirocin (Bactoderm®) or Zn7 Derm®, a zinc- and L-lysine-containing lotion, applied to the chin every 12 hours is often helpful. In refractory cases, human topical acne treatment products can be prescribed, and are sometimes effective. Examples include Benzamycin® gel, (3 percent erythromycin, 5 percent benzoyl peroxide gel), Metrogel® (0.75 percent metronidazole topical gel), and Retin-A (0.01-0.025 percent cream or gel). Initially these are applied one-two times daily then decreased to every other day. If redness or irritation occurs, reducing the shampoo or cream application frequency or changing to a less drying topical medication is indicated. Omega-6 and Omega-3-containing fatty acid supplementation (DermCaps® liquid) are often helpful as an adjunctive treatment in reducing inflammation and normalizing keratinization. Anecdotal reports of improvement with daily oral low-dose alpha-interferon (30 u orally once a day, seven days on, seven days off) may support a viral etiology.

In cats that are resistant to all forms of oral and topical treatment, isotretinoin (Accutane®) at 2mg/kg/day can be given orally. Response should be evident within four weeks and about one-third of cats respond. Long-term treatment is required, and the dose should be reduced to every two to three days. Periodic chemistry screens and Schirmer tear tests are recommended on cats on isotretinoin. If excessive chin rubbing due to scent marking in multi-cats households is thought to be related to outbreaks of feline acne in one or more cats in the household, Feliway®, a pheromone product, can be applied to the environment to reduce scent marking behavior and may help in some cases.

Photo 2: Atopic cat with extensive truncal alopecia due to over-grooming ("fur mowing").

Feline allergic dermatitis

Evaluating the pruritic/over-grooming cat or the cat with recurrent eosinophilic granuloma complex lesions can be a challenge. Once parasitic mites (Otodectes, Cheyletiellosis, Notoedres, demodicosis), dermatophytosis, and FeLV/FIV infection have been ruled out, a search for possible underlying allergies including flea allergy dermatitis, food intolerance/hypersensitivity and atopy should be undertaken in a logical manner. Cats with allergic dermatitis due to any cause can present in many similar ways, although some presentations are more commonly seen with one particular type of allergy (see Table 1). Generalized miliary dermatitis (multiple small crusted papules) and stubble alopecia, especially over the caudal dorsum, tail base, and caudomedial thighs is most commonly seen with flea allergy dermatitis. Severe head and neck pruritus is most commonly seen in food intolerance/hypersensitivity (Photo 1). Atopy can prevent as generalized over-grooming with non-inflammatory alopecia ("fur mowing") (Photo 2), especially of the insides of the forelimbs, groin and medial thighs, as miliary dermatitis, or as head and neck pruritus and dermatitis due to self-trauma. Blepharitis, chelitis, and ceruminous otitis are most commonly seen with food intolerance/hypersensitivity and atopy. To make matters more complex, cats may have more than one allergy.

Photo 3: Atopic cat with pruritic eosinophilic plaques in the groin area.

Recurrent eosinophilic granuloma complex lesions (indolent ulcer), eosinophilic plaques (Photo 3) and linear/collagenolytic granulomas may be seen with flea allergy dermatitis, food intolerance/hypersensitivity and atopy. Most cases of eosinophilic plaques are associated with underlying allergies, while some cases of indolent ulcers and collagenolytic ulcers, especially in young cats and kittens, are idiopathic or genetically-based. In many cases, recurrent eosinophilic granuloma complex lesions are the only underlying sign of allergic dermatitis and a skin biopsy should be performed of the lesion to rule out neoplasia and fungal infection, and to look for signs of underlying allergy. Skin biopsy may also be helpful early in the work-up of cases of generalized or localized dermatitis or alopecia, to confirm underlying allergy and to rule out infectious or neoplastic disease. Histopathology cannot be used to determine the type of allergy, only to confirm that allergic dermatitis is present.

Table 1: Characteristics of Feline Allergic Dermatitis

Flea allergy dermatitis

All cats with non-seasonal or seasonal pruritus or recurrent eosinophilic granuloma complex lesions should first have a trial of both on-animal and environmental flea treatment to determine if fleabite hypersensitivity (allergy to the saliva of the flea) is the primary underlying cause. Fleas or flea dirt may or may not be present in flea allergic cats. Due to cats' meticulous grooming habits and overgrooming due to pruritus, it is not uncommon to fail to find any evidence of fleas in flea allergic cats. Remember, the more flea allergic the cat, the less likely it is that you will find fleas. If possible, cats that go outdoors should be kept inside during the duration of the trial. Adulticide treatments with either imidacloprid (Advantage®), fipronil (Frontline Top Spot®) or selamectin (Revolution®) applied every two weeks for three or four treatments should be administered to the allergic cat, as well as monthly treatments of all in-contact dogs and cats. The indoor environment should be treated at least once with a household flea spray that contains an adulticide (preferably permethrin) as well as an insect-growth regulator. Remove pets and people from treated areas for at least four to six hours until treated surfaces are dry before re-entering the area. Treated areas should be well-ventilated before pets and people return. If clinical signs in the patient resolve, then flea allergy was the culprit, and flea prevention with year-round monthly flea treatments on all pets, keeping the affected cat indoors, and periodic environmental treatment is needed to prevent recurrences of flea allergy dermatitis.

Table 2: Suitable Feline Commercial Food-Elimination Diets

Food hypersensitivity/food intolerance

If there is no response to flea control, then the allergy work-up should continue with a strict food elimination diet. This is especially important if the cat has severe head and neck pruritus and/or history of gastrointestinal upset (vomiting and diarrhea which may be associated with food intolerance. The most common food allergens in cats are dairy products, beef and fish. A ten-week diet either home-cooked or commercially prepared (see Table 2 for acceptable diets) should be initiated. If a home-cooked diet is used, a nutritionist or nutrition reference should be used to formulate a balanced diet with vitamin and mineral supplementation, including calcium and taurine. All flavored cat treats, table food and chewable medications should be discontinued. It is usually easier to feed all cats in the house the same elimination diet if possible. If not possible, the allergic cat must be fed separately. Access to other pets' food must be prevented. Most food allergic cats will show significant improvement within four to six weeks on a diet, however, some require the full 10 weeks to respond. If the pruritus and dermatitis resolve on the diet, then the owner has two choices. The food allergic cat can continue indefinitely on a strict diet, knowing there is a small chance a new allergy to that food will develop in the future. Alternatively, a dietary rechallenge with the cat's original diet can be performed to prove food hypersensitivity. Most food allergic cats will show worsening of allergic signs within hours to several days of rechallenge, with a few taking 10 to 14 days for pruritus to recur. If the food allergic cat's pruritus worsens with food rechallenge, then the cat is returned to the elimination diet for seven to 14 days until signs abate once more. Then one home-cooked individual protein or carbohydrate ingredient is added one at a time to the elimination diet at weekly intervals. If there is no reaction to the added ingredient after one week, this ingredient is recorded as a "good or safe" ingredient, and the next food is added. If a reaction is seen to that ingredient, it is immediately discontinued, recorded as an "allergic or bad" ingredient, and the plain elimination diet is fed for three to 10 days until allergic signs resolve. It is important to let allergic signs resolve before going on to the next ingredient to avoid confusion over which ingredient is causing the problem. In this way, a list of "good" and "bad" ingredients can be formulated so that a commercially available balanced cat food can be chosen that is free of the patient's allergic ingredients. Some cats are allergic/intolerant to only one ingredient, while others are allergic to multiple ingredients, food additives or dyes. Some cats cannot tolerate any commercial product, and need to stay on a nutritionist-prepared balanced home-cooked diet for life.

Feline atopy

Pruritic cats that have had parasitic mites and fungal infections ruled out, and that fail to respond to flea control and a food elimination diet, most likely are atopic. Feline atopy is caused by a genetic inappropriate immune response involving allergens-specific IgE, to environmental allergens such as house dust mites, molds and grass, tree or weed pollen. Atopy is second only to flea allergy dermatitis as a cause of chronic pruritus in cats. Atopy can occur in any age or breed or cat but is more common in younger cats 6 months to 3 years of age. However, middle aged or older cats can develop the disease. In most cats, the problem is nonseasonal and involves allergies to house dust mites (Dermatophagoides sp.) Some cats may also have mold and pollen allergies. The four most common reaction patterns in atopic cats include: self-induced alopecia (fur-mowing), eosinophilic granuloma complex lesions, miliary dermatitis, and facial otic and neck pruritus and dermatitis. In addition, some cats will have rhinitis, chronic cough, allergic bronchitis, asthma, and chronic blepharoconjunctivitis alone or in addition to their dermatologic signs. Lymphadenopathy and eosinophilia are common in chronic cases with severely inflamed and excoriated skin, miliary dermatitis, or eosinophilic plaques. Cats with atopy may have concurrent food hypersensitivity and fleabite hypersensitivity.

Photo 4: Cat with indolent ulcer of upper lip.

Diagnosis of feline atopy is made by considering the history, physical examination findings and by ruling all other causes of pruritus. Intradermal allergy testing plus/minus serologic testing should only be used to determine which allergens to avoid and to include an immunotherapy vaccine. As normal cats can have positive intradermal allergy tests and serologic test reactions, these tests should not be used alone to diagnose atopy. Intradermal allergy testing is challenging in cats, as cats usually have weak reactions consisting of flat, erythematous wheals that require experience in their interpretation. Some atopic cats will have negative intradermal allergy tests and positive serologic test results. The accuracy of serologic tests in cats has not been proven due to a lack of controlled clinical studies. However, some dermatologists have reported good clinical responses to hyposensitization vaccines based on serologic testing in atopic cats. The use of serologic tests (HESKA, VARL) should be considered if atopy is strongly suspected in cats with negative intradermal allergy test results.

Cats should be off oral corticosteroids for at least one month, injectable corticosteroids for six to eight weeks, and antihistamines, fatty acids and topical corticosteroids including eye and ear medications for two weeks before intradermal allergy testing or serologic testing to avoid false negatives due to drug interference. Response to hyposensitization in cats is approximately 50-75 percent, depending on the study. Most cats respond within three to six months, with some taking eight to 12 months to show signs of improvement.

In addition to hyposensitization, antihistamines (see Table 3), omega-3/omega-6 essential fatty acids, hydrocortisone and oatmeal-containing shampoos/cream rinses, Aveeno oatmeal soaks, Soft Paws® to prevent self-trauma, and topical anti-pruritic agents (Corticalm lotion®, Relief Spray®) can also be tried to reduce pruritus. For moderately severe cases, oral, ophthalmic and otic prednisolone, triamcinolone or dexamethasone may be tried, but should be used in combination with the other treatments listed above to minimize the dose needed (steroid-sparing effect). The lowest possible every other day (prednisolone) and every three and seven day (triamcinolone, dexamethasone) dose should be used. Cats on long-term corticosteroids should have periodic physical examinations, blood work, urinalysis, and urine culture performed to screen for diabetes mellitus, urinary tract infection, and hepatic and renal disease. Cats on chronic corticosteroid therapy are also more prone to demodicosis and dermatophytosis. For refractory cases, chlorambucil or cyclosporine can be tried, but these drugs are expensive and require regular laboratory monitoring, and are best prescribed by a dermatologist.

Table 3: Antihistamines Useful in the Treatment of Feline Atopy (only pure antihistamines, without painkillers or decongestants, should be used to avoid toxicity).

Conclusion

Feline otitis, acne and allergic dermatitis are some of the most common diseases seen in clinical practice. Some cases may be straightforward, while others can be a real challenge to diagnose and treat. Early, accurate diagnosis of the underlying problem is essential to successful long-term management of these often chronic conditions. It is essential to follow a logical and well-organized thought process during the planning of your work-up of these cases. Frequent client communication and patient re-examinations are very important. Referral to a board-certified dermatologist may be needed in refractory cases in order to obtain the best possible outcome for your feline patients.