Chronic ear problems are common conditions in dogs and among the most mishandled by veterinarians.
These problems are probably the most common chronic conditions that we see. Many clients have preconceived notions of the causes and treatments. They draw on what ear infections are like in people. Or they assume that this is a condition with which their dog has to live.
The most common exam finding in dogs with ear disease is “otitis”, inflammation of the ear canal.
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.
Common primary causes include:
- environmental/seasonal allergies(atopy)
- ear mites, food allergy
- primary bacterial or fungal infections,
- and tumors of the ear canal.
It is essential 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.
Most common causes
So the most common causes that we see in our practice are
- 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 prevalent in younger dogs that have just been adopted. Their ears usually have a very dry, black discharge in the canals. The mites show up by taking some of the discharge and looking at it under the microscope. The mites are easy to identify, and treatment involves 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. Both these conditions result in otitis externa as part of their presentation.
The first hints for the clinician come from taking a thorough history from the owner.
Is the dog is on a consistent diet and the signs of otitis are seasonal? Then you can generally rule out food allergy as a cause.
Year-round ear problems
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 areas such as the paws, armpits, and face. Many dogs with a food allergy will also have perianal itching (their butts!).
Let’s focus on the ears for now.
Examining the ears
My preferred first step is to perform a test called otic cytology. Cytology involves the insertion of a cotton swab into the ear canal to sample the content. Then I roll the swab onto a slide to examine the debris under 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 important because these organisms greatly amplify the inflammation and swelling in the ear canal; it is essential to treat them.
Within the bacterial category, I am looking for a few things:
The shape of the bacteria—if I see rods, I will culture the debris to determine the exact species of bacteria. Often rods turn out to be a type called Psuedomonas aeruginosa, which needs very specific therapy for several weeks.
If there is a lot of white blood cells in the slide it usually indicates the presence of true infection.. The dog MAY need systemic antibiotics.
If I see only bacteria, this would generally be categorized as bacterial overgrowth, rather than infection. That 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, I decide on the initial treatment.
More than meets the eye
By now, you might realize that not all ear diseases are from infection alone. Rather, each dog may have multiple problems occurring at the same time.
After the examination (which includes an examination of the rest of the body, otic cytology, +/- a culture of the ear, and hopefully an examination of the ear canal with an otoscope – if the patient allows it), I formulate a treatment plan and discuss it with the client.
In addition to the underlying medical problem, the temperament of the patient and the ability of the owner to administer treatment is a consideration when deciding the best approach. However, for the sake of this discussion, let’s assume that the patient will allow therapy and the owner can administer treatment as directed.
If the extent of the presenting signs is confined to the ears, the first thing that I consider is whether both ears are affected. Because if both ears are affected—as is usually the case—the primary cause is not likely infectious. Developing infections in both ears at the same time is not common.
If infections or overgrowth of bacteria or yeast is present, it is likely secondary to another underlying disorder.
The significance of symmetry
Remember, when it comes to dermatologic/skin diseases (ears are many times included with these.), SYMMETRY = SYSTEMIC disease!
The most common systemic conditions that we see affecting the ears are hypersensitivities, such as environmental or food allergies. Other conditions can cause symmetrical ear disease. However, those are less common.
Okay….on to treatment.
If the ear canals are swollen to the point that cleaning would be difficult and painful, I may consider oral steroids for several days to make topical therapy easier.
If cytology revealed yeast, I will use a cleanser with an antifungal such as ketoconazole. I will fill the ear canal with the cleanser, massage the ear canals and allow the dog to shake her head. I will not clean the ears out for 5-10 minutes in order to allow sufficient contact time for the antifungal to kill the yeast.
Next, I will apply a light coat of an ointment based medication that has an antifungal and a steroid. I will have the owners administer the therapy once daily and have them come back for a follow-up examination in a week or so.
- If the dog improves, I will continue the treatment for another week and then decrease therapy to every second or third day for another 1-2 weeks.
- If there is no improvement, I would consider either a diet trial with a hypoallergenic diet for at least 12 weeks and/or just discontinue the topical therapy, as some dogs may have a hypersensitivity reaction to the topical medications.
- In cases with bacterial overgrowth only, I will choose one of a few cleansers to apply based on what type of bacteria are found. I may or may not use topical steroids in these dogs initially.
Treating secondary infection first
My priority in these cases is to treat the secondary infections first. Then I follow up on the underlying conditions, such as allergies, once the overgrowth or infections are cleared.
That approach should be taken with all dermatologic cases, not only otitis. If the otitis occurs for a few weeks during the height of allergy season, and the dog is normal the rest of the year, this is a very reasonable approach.
If however, the signs occur during most or all of the year, a more aggressive approach is needed.
This may include diet trials with a hypoallergenic diet, allergy testing, or other medications that would be safer for long-term use. In some cases, by the time these dogs are brought to us, the changes in the ear canal are so severe that no medical approach will work. In these dogs, the pain is so severe and they cannot usually hear well at this point, those surgical procedures are recommended to provide comfort. The ability to hear may not return, but the dog (and the owner) are usually very happy due to the pain relief.
An important thing to note is that when there is a primary infection present, oral therapy used alone will not work!
A strong topical antibiotic solution must be infused into the ear canal daily, sometimes for several weeks depending on the type of infection. In fact, I usually do not prescribe an oral antibiotic for these cases unless there are generalized skin infections present.
Chronic Otitis in Dogs