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Otitis Externa in Dogs

By T. Mark Neer, DVM, DACVIM, Professor and Hospital Director, Center for Veterinary Health Sciences, Oklahoma State University ; Michele R. Rosenbaum, VMD, DACVD ; Patricia D. White, DVM, MS, DACVD

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The tubular portion of the outer ear that carries sound to the eardrum is called the ear canal. The most common disorder of the ear canal in dogs is called otitis externa. This condition occurs when the layer of cells that line the external ear canal becomes inflamed. Signs include redness of the skin, swelling, itchiness, increased discharge, and scaly skin. The ear canal may be painful or itchy depending on the cause or duration of the condition. Otitis externa can be caused by many different factors. Some of these factors (such as parasites, foreign objects, and allergies) appear to directly cause the inflammation, while others (such as certain bacteria and yeasts) perpetuate the condition. To complicate things further, the shape or form of the pinnae or ear canals can predispose dogs to developing otitis externa. Identifying these factors is key to successful control of the inflammation. Unless all the causes are identified and treated, the condition may return.

Otitis externa, the most common ear disease in dogs, can be caused by many factors.

A detailed history and thorough physical and skin examination can provide clues as to the cause of otitis externa. The pinnae and regions near the ear may show evidence of self-trauma (from scratching, for example), redness of skin, and primary and secondary skin abnormalities. Deformities of the pinnae, an abnormal growth of tissue in the canal, and head-shaking suggest chronic ear discomfort.

Your dog may require sedation or anesthesia to allow a thorough examination using an otoscope. This is especially true if the ear is painful, if the canal is obstructed with discharge or widespread inflammatory tissue, or if the animal is uncooperative. An examination using an otoscope will allow identification of foreign objects deep in the ear, impacted debris, low-grade infections with ear mites, and ruptured or abnormal eardrums. Tissues for culture (to identify any infection-causing microbes) are usually taken at the same time that the examination of the ear canal using an otoscope is being conducted.

Sometimes a smear taken using a cotton-tipped applicator can provide immediate diagnostic information. The external ear canals of most dogs and cats harbor small numbers of harmless microorganisms. These organisms may cause disease if the environment of the ear changes in a way that allows them to multiply. Microscopic examination of a smear can quickly determine if this type of overgrowth is present.

A dark discharge in the canal usually signals the presence of either a yeast infection or a parasite such as ear mites, but may also be seen with a bacterial or mixed infection. Your veterinarian will examine the discharge for eggs, larvae, or adults of ear mites.

Additional tests are sometimes needed to identify the factors causing the inflammation. Allergy testing may be recommended. Biopsies from animals with long-term, obstructive, inflammation of the external ear canal in only one ear may reveal whether tumors are present. X-rays may be taken when better visualization of the eardrum is needed, when inflammation of the middle ear is suspected, or when neurologic signs (such as loss of balance) are present.

Treatment

To treat these conditions, your veterinarian will need to identify and correct any underlying causes. Usually, the area around the ear is clipped of fur, and hair is removed from the ear canal. This improves the movement of air and eases cleaning and drying of the canals.

Most commercial topical products contain a combination of antibiotic/antifungal drugs and glucocorticoids. Products that are water-based or those that have a thin film should be used; ointments should be avoided.

Irritating medications (eg, home remedies and vinegar dilutions) should be avoided. They cause swelling of the lining of the ear canal and an increase in glandular secretions, which predispose to bacterial or yeast infections. Substances that are usually not irritating in normal ear canals may cause irritation in an ear that is already inflamed. This is particularly true of propylene glycol. Powders, such as those used after plucking hair from the canal, can form irritating concretions within the ear canal and should not be used.

Because topical medications can be inactivated by discharge from the ears or excessive earwax, your veterinarian will probably clean the ears gently and then dry them before treatment is started. In animals with painful ears, proper cleaning requires general anesthesia.

When properly applied, the ideal medication will coat the layer of cells lining the external ear canal as a thin film. Medication given by mouth or injection will probably be included in the treatment regimen in most cases of longterm inflammation of the ear canal and in any case in which inflammation of the middle ear is suspected.

When severe bacterial infection of the external ear canal is the cause of inflammation, antibacterial drugs in combination with corticosteroids may be used to reduce discharges, pain, and swelling, and to decrease glandular secretions. Dogs that have recurring bacterial inflammation of the external ear and a history of infection with ear mites should be treated with a topical product that contains antibacterial and antiparasitic drugs to ensure that any parasitic infections are eliminated.

The treatment should continue until the infection is completely gone. For dogs with bacterial and yeast infections, you should expect weekly or bi-weekly physical examinations and tests until there is no evidence of infection. For most cases, this takes 2 to 4 weeks. Longterm cases may take months to resolve, and in some instances, treatment must be continued indefinitely. Follow your veterinarian’s recommended treatment program carefully and fully for the best result for your pet.

Preventive Care

The best treatment of inflammation of the outer ear is prevention. Be sure to inspect your dog’s ears regularly and note any unusual temperature changes, changes in skin color or condition, sudden increases in moisture, or other changes. When you notice changes in your pet’s ears, it is time for a prompt checkup.

Your veterinarian can show you how to properly clean your dog’s ears, if necessary. The frequency of cleaning usually decreases over time from daily to once or twice weekly as a preventive maintenance procedure. The ear canals should be kept dry and well ventilated. Using drying agents in the ears of dogs that swim frequently and preventing water from entering the ear canals during bathing should minimize softening of the ear canal and decrease the frequency of bac-terial or fungal infections in moist ear canals. (Softening impairs the barrier function of the skin, which makes it easier for infection to start.) In some cases, clipping or plucking hair from the inside of the pinna and around the ear canal improves ventilation and decreases humid-ity in the ears. However, you should check with your veterinarian before removing any hair. If such a step is warranted, be sure to get a demonstration of how to do this correctly.

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