WVC 2017: Dealing with Chronic Ear Infections in Dogs

At the 2017 Western Veterinary Conference this week, James Noxon, DVM, DACVIM (SAIM) discussed the often difficult issue of chronic ear infections in dogs.

Dr. Noxon pointed out that a 2010 Banfield report ranked otitis externa as the third most common diagnosis among dogs. He also noted that the condition has many inciting causes and is often a concurrent disease state.

According to Dr. Noxon, treatment failure in patients with otitis commonly is secondary to improper treatment (wrong medication), inadequate treatment of underlying disease (missed disease), and/or poor client compliance. Acute ear infections should be addressed aggressively at the first visit; the infection should not be allowed to become more chronic in nature. Thorough client communication is key to getting buy-in and appropriate understanding from pet parents. Extensive communication that includes drawings and models and may help clients fully understand the severity of the disease and the importance of their role in treating it.

Appropriate knowledge of the patient and ear are vital. Information that is missed in the history or physical examination can be detrimental; ear cytology must be performed on initial examination and with each recheck. Recheck exams and cytologies are needed to ensure total resolution of the infection. Partially treated infections can become chronic or, worse, resistant to treatment. Some ear infections may require more than 14 days of treatment despite many medications being labeled for 7- or 14-day regimens.

Shortsightedness by the veterinarian can lead to insufficient treatment. Veterinarians “must prevent relapse or recurrence while searching for the underlying cause,” said Dr. Noxon, as chronic infections are often initiated by parasites, foreign bodies, hypersensitivities, keratinization disorders, or irritant reactions. These inciting causes can then allow disease states to build with problems such as atopy, Staphyloccoccus or Malassezia infection, or dry skin, worsening any original problem. Because of these multifaceted disease states, it is important to treat all components involved while educating the client appropriately.

Ear cytology is the key to the examination. Dr. Noxon recommends collecting 2 cytology slides, always from both ears. He stains with Diff-Quik on one slide and, if rod bacteria are noted, he may follow up with a Gram’s stain. Culture and sensitivity testing are needed less commonly unless the patient has an insufficient response to treatment or has had exposure to numerous antibiotics. If a culture is performed, it is important to wait at least 1 or 2 days after administration of the last topical treatment to ensure the most accurate results.

Ear cleaning is the key to treatment. Without a thorough cleaning, any topical medication is less likely to be effective. While healthy ears are “self-cleaning,” diseased ears are not, and earwax alone is irritating. Additionally, ear cleaning helps to remove biofilm, purulent discharge, and debris that may block movement of the medication into the horizontal canal. It is important to extend the ears when cleaning or treating to elongate and straighten the horizontal and vertical canals; there is a small U-shaped “trap” between the canals that may harbor debris. It is vital to use sufficient volumes of cleaner as well as medication; the ears of a medium-sized dog may hold a 4 to 6 mL; therefore, 1 mL of medication is insufficient.

Biofilm is often a concurrent problem. Biofilm is a matrix of proteins in a gel-like substance that may contain sugars, allowing bacteria to live in clusters. Tunnels separate the bacterial clusters in the matrix. Bacterial isolation allows for bacterial growth and provides protection from antibiotics and phagocytes. Ear cleaning is the most effective way to break down the biofilm, allowing medication to then reach the bacterial clusters. Topical medication is most effective, and enrofloxacin/silver sulfadiazine (Baytril Otic) may be used in cases of a missing or damaged tympanum.

Amanda Landis-Hanna, DVM, graduated from Auburn University in 2002. Since then, she has practiced small animal, exotic, shelter, and relief medicine. She was a VCA medical director for 7 years in California and Virginia, and she served as director of veterinary medicine for Voyce from 2013 to 2016. Dr. Landis-Hanna resides in Virginia with her family and rescue Labrador, Sophie.