Chronic ear problems are some of the most common conditions seen in dogs, and amongst the most mishandled by veterinarians.
These problems are probably the most common chronic conditions that we see. Many clients have either preconceived notions of the causes and treatments based on what is seen with ear infections in people, or they just assume that this is a condition with which their dog has to live.
The most common exam finding in dogs with ear disease is called “otitis”, inflammation of the ear canal.
|Image: Atlas of Veterinary Clinical Anatomy, Hill's Pet Nutrition|
There are a few general areas to the anatomy of the ear. For simplicity’s sake, we can divide the anatomy into the external canal, and the middle and inner ear. In this article we are going to focus on inflammation of the external ear canal – called otitis externa.
There are a few categories of causes for otitis externa:
- Primary causes
- Secondary causes
- Perpetuating factors.
It is very important to note that primary infection (infection with no precipitating cause) is rare in dogs compared to the other causes, as are tumors of the ear canal.
So the most common causes that we see in our practice are atopy, food allergy, and ear mites (with atopy being by far the most common).
How do we distinguish between them?
First, unlike primary infections and tumors, these conditions are bilateral (i.e. occurring in both ears at the same time).
Ear mites are usually seen in younger dogs that have just been adopted, and their ears usually have a very dry, black discharge in the canals. The mites are very easily found by taking some of the discharge and looking at it under the microscope. The mites are easily identified, and can be treated with an ivermectin based medication instilled into the ears. This disease is curable.
With atopy and food allergy the clinician cannot tell the two apart during the first examination, as both these conditions result in otitis externa as part of their presentation.
The first hints for the clinician are obtained by taking a thorough history from the owner.
First, if the dog is on a consistent diet and the signs of otitis are seasonal, food allergy can generally be ruled out as the cause.
If the signs are year round it becomes more difficult to determine the cause initially.
Other historical findings that I’ll focus on is whether or not the patient is itchy elsewhere on their body. Most dogs with atopy and food allergy will itch other area such as the paws, armpits, and face. Many dogs with food allergy will also have perianal itching (their butts!).
Let’s focus on the ears for now.
My preferred first step is to perform a test called otic cytology.
This is where a cotton swab is inserted into the ear canal and then rolled onto a slide to look at the debris with a microscope.
What I am trying to determine is the “secondary offenders” in the canal. In other words, determine if there is bacterial overgrowth or infection (they are different), and/or if there is yeast overgrowth.
This step is very important because these organisms greatly amplify the inflammation and swelling in the ear canal, and must be treated.
Within the bacterial category, I am looking for a few things. First is the shape of the bacteria: if rods are noted I will usually culture the debris to determine the exact species of bacteria because many times rods turn out to be a type called Psuedomonas aeruginosa, which needs very specific therapy for several weeks.
I also want to note if there is a lot of white blood cells in the slide: if noted, this generally indicates that there is true infection present, which MAY necessitate the use of systemic antibiotics. If only bacteria is seen this would generally be categorized as bacterial overgrowth, rather than infection, which is usually treated only with topical medications. If large numbers of yeast are noted, a topical antifungal treatment will be part of the treatment protocol.
After the initial step(s) of otic cytology with or without a culture of the ear, the initial treatment protocol is chosen.
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