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

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

Jun 01, 2002

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

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.