Ear
Diseases




Ear disease is very common
in the dog.  Early action is very
important in order to keep the
infection from becoming permanent.




Ear disease is very common in dogs, and much less common in cats.  Ear infections in dogs and cats really do not have much in common with ear infections in people.  A review of the anatomy is a good place to start in our quest to understand ear disease in pets.

The part of the ear that does the hearing is called the inner ear.  It is very delicate, and is buried deep inside the skull for protection.  It is not well-labled in the image at the right, but the inner ear is the Cochlea. 

The Inner Ear is run by some mechanical parts that are contained in the middle ear.  The middle ear is an air-filled, drum-like hollow space.  There are some bones present, called the auditory ossicles, that transmit sound vibrations from the ear drum, or tympanic membrane, to the inner ear. 

The rest of the ear is a collecting funnel that collects sound and funnels it down to the tympanic mambrane.  The ear canal is a tube that runs from the outside to the inside and ends at the tympanic membrane.  In dogs and cats, the ear canal has two parts.  The vertical canal runs up and down, then makes a right angle bend and becomes the horizontal canal.

The ear canals are lined with a special type of skin.  This skin has special glands in it that make ear wax, also called cerumen by the medical types.  The skin also has billions of microscopic cilia.  Cilia are tiny hairs that beat in waves, kind of like sports fans sitting in a stadium.  This wave action is what keeps the cerumen from collecting in and plugging up the ear canal.  The cilia wave the ear wax towards the outside.

Living happily inside the ear canal along with the cilia and the cerumen are various bacteria and also some yeast.  These bacteria and yeast are normal, and are present in all dogs and cats.  They are there in low numbers, because the ear is healthy and happy, the cilia are working, and the cerumen galnds are doing their job too.

Something has to happen to upset the balance for an ear infection to occur.  There are many things that can do this.  A partial list follows:
Allergies                                                   Grass Awns

Water in the ears                                     Bad Genetics

Ear Mites                                                 Bad Luck
Sometimes it is a combination of two or more things.  Sometimes we are not able to identify the cause.


What dogs most commonly end up with is an infection in the ear canal.  This is called otitis externa, and is quite different from the ear infections children get.  Children get infections on the other side of the ear drum, in the middle ear.  Otitis externa is itchy and may even burn, but I do not believe dogs feel the pressure and pain (in the middle of the night!)  that children feel with ear aches.  Not that otitis externa is fun.  It really bothers dogs, and they show their discomfort by shaking their heads, scratching their ears (sometimes to the point of bleeding), carrying one ear low, etc. 
In the images, normal is on the right, infected is on the left.

To treat otitis externa, it is important to know the enemy.  There are three main types of things rhat can grow in infected ears:  Round bacteria,  rod-shaped bacteroa, and yeast.  It is important to know what we have, because it can take different medications to kill each type of problem.  To find out what is growing in your dog's ears, we take a swab of the goo in the ear, put it under the microscope, and look at it under high magnification.  Then an appropriate drug can be prescribed.

If ear infections are not treated promptly, they get worse.  If an ear is infected for months, the infection can cross the ear drum and enter the middle ear.  If this happens, ear drops are not going to solve the problem because they can't get across the ear drum.  Also, pus builds up in the middle ear, and unless it is removed, the infection will never go away. And that's not all.  If an ear stays infected for months, the special skin that lines the ear canal changes in response to the infection.  While it would be convenient if the skin would change in a way that made it better able to fight the infection, that is the opposite of what really happens.  The canals swell, sometimes completely shut.  The cilia disappear.  The cerumen glands get hyperactive.  This leads to poor drainage, accumulation of cerumen, and the bacteria and yeast just go wild in that environment.  If the infection stays long enough, these changes become permanent, and the ear may never be totally healthy again.

One of the worst things you can do to your dog's ears is under-diagnose and over-treat.  This usually happens in dogs that have recurring ear problems.  Many owners just want to get some more of the same old medicine and put that in whenever the ears flare up, rather than address the underlying problems.  We see quite a few dogs as second (or third or fourth) opinions who have been on Otomax (a commonly prescribed ear drop that I hate) for years.  Many of them have underlying allergy problems.  Others have middle ear infections.  Others have just plain bad genetics.  But the point is that by the time I see them, their ears are end-stage, meaning that the canals have undergone permanent changes, meaning that nobody can fix those ears medically.  Click here for a link to a discussion of surgical ear treatments.

If your dog has more than two episodes of ear problems a year, or even if he or she has only two episodes a year but has them every year, we need to address the underlying problems before the ear infections become permanent.  Allergy medication, ear washes, and or middlle ear lavage can all help restore your dog's ears to health, but only if done in time.