Ear Disease in Dogs - Part I

By David Prydie BVMS, CertSAO, CCRT, MRCVS

Why do dogs get bad ears?

In part 1 I look at the anatomy of a dog’s ear and how this affects the disease process. In part 2 I look at treatment of ear disease in the dog from cleaners and medicated drops through to surgery.

Anatomy

To answer this we must first look at the anatomy of a dog’s ear. Fig. 1 shows a model of a dog’s ear. As you can see there is a hole at the top of the trumpet or ear canal. This is the hole you can see on your dog and where you put any eardrops. If you follow the trumpet or ear canal down, it narrows and then does 45 degree bend before ending up at the eardrum. In people the ear canal runs horizontally inwards straight to the eardrum. In the dog, this means that the only place for drainage is at the top of the vertical canal – which is not the best place to put a drain hole. On the other side of the eardrums are the bones or ossicles associated with hearing. Also on the inside of the eardrum is the bulla, a hollow sphere of bone that is filled with air. This connects to the back of the throat via the Eustachian tube. The function of the bulla and Eustachian tube is to keep the air pressure on both sides of the eardrum the same.

The ear canal is line with skin, so ears cannot be thought of in isolation. Skin disease elsewhere on the dog, may also affect the ears. If the ears become inflamed or if skin somewhere else on the body becomes inflamed, the skin lining the ears can also become inflamed. This then causes a narrowing of the ear canal and making it even more difficult for any debris to escape. (Fig.2.) It also creates a warm moist environment perfect for the proliferation of bacteria, yeasts and mites. Infection and inflammation
can also spread to the bulla, middle and inner ears. In these cases the eardrum is often ruptured. Pus and debris collect in the bulla. These dogs will have pain although they may hide it. They will often have a head tilt. Often skin changes can result in a chronic thickening of the ear canal. Once this happens the skin will never return to normal and treatment is aimed at managing these cases medically. The more severe cases may require surgery.

Causes of ear problems in dogs

1. Bacteria
There are many bacteria that normally live down a dog’s ear. However, pathogenic bacteria may become established and multiply in an inflamed ear canal. The use of antibiotic ointments will usually kill these bacteria but in chronic cases bacteria may become resistant to many of the common antibiotics used to treat ear infections. All chronic cases or acute cases that fail to respond satisfactorily should have swabs taken for culture and sensitivity to determine what bacteria are there and to which antibiotic they are susceptible.

2. Yeasts
Yeasts are often found down the normal ears in dogs. However, if the environment down the ear canal becomes very moist and warm, the yeasts can proliferate and become part of the problem.

3. Ear Mites
Dog’s ears have wax gland in then similar to ours. They wax helps maintain the health of the ear canal as well as discouraging flying insects from entering the ear canal. However, dogs can pick up ear mites that actually live off the earwax. The ear mites irritate the wax glands and instead of producing a nice golden wax they produce black or dark brown crumbly wax.

4. Foreign Bodies
Grass seeds are a common foreign body to find down dog’s ears. This usually occurs in the summer months and presents as a sudden onset irritation sometimes with a head tilt and often with signs of pain. As mentioned earlier, the ear canal is lined with skin and often there is hair growing on the skin down the ear particularly in certain breeds such as Poodle and Bichons. The hair can block the ear canal and can form into a lump causing a foreign body reaction.

Ear Disease in Dogs