Infections of the external ear canal (outer ear) by bacteria or yeast, are one of the most common types of infections seen in dogs and is called otitis externa.

Some breeds, seem more prone to ear infections but they may occur in any breed.

A dog with an ear infection is uncomfortable; his ear canals are sensitive. He shakes his head trying to get the debris and fluid out, and scratches his ears. The ears often become red and inflamed and develop an offensive odour. A black or yellowish discharge commonly occurs.

Ear mites can cause several of these symptoms, including a black discharge, scratching, and head shaking. Ear mite infections generally occur most commonly in puppies. Ear mites in adult dogs occur most frequently after a puppy carrying mites is introduced into the household. Sometimes ear mites will create an environment within the ear canal which leads to a secondary infection with bacteria and yeast (fungus). By the time the dog is presented to the veterinarian, the mites may be gone, but a significant ear infection remains.

There are several kinds of bacteria and at least one type of fungus which might cause an ear infection. Without knowing the kind of infection present, your veterinarian will not know which drug to use. In some cases the ear infection may be caused by a foreign body or tumour in the ear canal. Treatment with medication alone will not resolve these problems. Also, the dog must be examined to be sure that the eardrum is intact. Administration of certain medications can result in loss of hearing if the eardrum is ruptured. This determination is made by the veterinarian and must be done in the office.

First, the ear canal is examined with an otoscope, an instrument that provides magnification and light. This permits a good view of the ear canal. This examination allows veterinarians to determine whether the eardrum is intact and if there is any foreign material in the canal. When a dog is in extreme pain and refuses to allow the examination, he must sometimes be completed under sedation or anesthesia.

The next step is to examine a sample of the material from the ear canal to determine which organism is causing the infection. This is called cytology. Examination of that material under the microscope is very important in helping the veterinarian choose the right medication to treat the inflamed ear canal.

The results of the otoscopic examination and cytology tell the veterinarian what to do. If there is a foreign body or tick lodged in the ear canal, the dog is sedated so that it can be removed. As stated previously, some dogs have such a heavy build-up of debris that sedation is needed to cleanse the canal and examine it completely.

Cytological study of debris from the ear canal dictates which drug to use. Sometimes it reveals the presence of more than one type of infection (i.e., a bacterium and a fungus, or two kinds of bacteria); this situation usually requires the use of multiple medications or a broad-spectrum medication.

An important part of the evaluation of the patient is the identification of underlying disease. Many dogs with chronic or recurrent ear infections have allergy problems or low thyroid function (hypothyroidism). If a underlying disease is found, it must be diagnosed and treated, if at all possible. If this cannot be done, the dog is less likely to have a favourable response to treatment. Also, the dog might respond temporarily, but the infection will relapse at a later time (usually when ear medication is discontinued).

Nearly all ear infections that are properly diagnosed and treated can be cured. If an underlying cause remains unidentified and untreated, the outcome will be less favourable. A progress check may be needed before the process is completed.

Dogs with ear infections are miserable. Their ears are a source of constant pain resulting in head shaking and scratching. However, that is not the only problem. Head shaking and scratching can also cause broken blood vessels in the ear flap, requiring surgery, and chronic ear infections can penetrate the ear drum and result in an internal ear infection.

The ear canal being almost closed is another result of a chronic ear infection. There are medications that can shrink the swollen tissues and open the canal in some dogs. Some cases will eventually require surgery.

The surgery for a closed ear canal is called a lateral ear resection. Its purposes are to remove the vertical part of the ear canal and to remove swollen tissue from the horizontal canal. Removing the vertical canal should be successful, but removal of large amounts of tissue from the horizontal canal is more difficult. In some cases, the ear canal is surgically obliterated. This solves the canal problem, but it leaves the dog deaf on that side.

The most severe consequence of a chronic ear infection is total closure and hardening of the ear canal. When this occurs, the lateral ear resection will no longer be helpful. The appropriate surgery for this situation is an ear canal obliteration. The entire ear canal is surgically removed. Since severe scarring and calcification occur, this can be a lengthy surgical procedure requiring a skilled veterinary surgeon.

It is important to get the medication into the horizontal part of the ear canal. Be aware that the dog’s external ear canal is "L" shaped. The vertical canal connects with the outside of the ear; the horizontal canal lies deeper in the canal and terminates at the eardrum. The ear canal may be medicated by following these steps:

When all medications have been applied, clean the outer part of the ear canal and the inside of the ear flap with a cotton ball soaked with a small amount of rubbing (isopropyl) alcohol. Do not use cotton tipped applicators to do this as they tend to push debris back into the vertical ear canal.