By Matthew Kearns, DVM
“Ooooooh … those itchy ears. My dog or cat is constantly scratching or shaking its head. I feel terrible for them and it sometimes keeps me up at night. My vet calls it an ear infection. It clears up on the medication but once finished it keeps coming back. Why does this happen?”
That is the million dollar question (actually, I’m sure millions of dollars are spent on ear infections every year). To call every dog or cat that comes in with itchy ears an ear infection is misleading.
These pets have otitis externa, and “otitis externa” literally means inflammation (not infection) of the external ear canal. Although we veterinarians commonly dispense medications with antibiotics and antifungals in them, the bacteria and yeast we are treating are considered natural flora (in the ear canal at all times in lower numbers).
So why do we get “flora gone wild”? Usually some other primary trigger is involved and the infection is secondary overgrowth. Examples are parasitic infections (ear mites), pets that swim or get baths and get water (and shampoo) in their ears, ear tumors (both benign polyps and cancerous tumors) etc. However, the most common cause of recurrent otitis externa is allergies. I consulted with a veterinary dermatologist, and she estimated that between 80 and 90 percent of all recurrent otitis externa in dogs is related to allergies.
To understand why an allergy would cause such problems in the canine and feline ear canal we first have to describe the anatomy. Unlike a human ear canal, which has a shorter external component in a horizontal direction only, the canine and feline external ear canal is much longer and has both a vertical and horizontal component. Therefore, there is a much greater distance from the opening of the ear canal to the ear drum. This shape and extra distance plays a critical role in otitis externa.
Also, the healthy ear canal is lined with three types of cells: epithelial cells (those similar to skin), ceruminous cells and apocrine cells (cells that produce earwax). Just like the epithelial cells of the skin, these cells will be replaced every few days. The new cells push the old (dead) cells out to the entrance of the canal, and the small amount of earwax produced in the healthy ear migrates out with the dead epithelial cells.
However, if the lining of the ear canal becomes inflamed, it narrows due to swelling and excessive earwax is produced. This not only overwhelms the ability to clear the wax, it also leads to a warm, dark and moist environment and allows the normal bacteria and yeast to overgrow and a true ear infection is produced.
This will clear up with medication but, if your pet is exposed to the same trigger, it will come back again. Certain breeds such as Labrador retrievers, golden retrievers, cocker spaniels, shar-peis and many others may have complicating factors such as hair in the ear canal, floppy ears, narrow ear canals or a combination of these things. Now, this does not mean that every member of these breeds is guaranteed to have chronic ear infections, rather it means that if you have a member of these breeds and they have even low-grade allergies the ears can spiral out of control quickly.
In my next article I will describe how to manage chronic or recurrent otitis externa.
Dr. Kearns has been in practice for 16 years and is pictured with his son, Matthew, and his dog, Jasmine.