A dog with an ear infection is uncomfortable; its ear canals are sensitive. It shakes its head trying to get the debris and fluid out, and it scratches its ears. The ears often become red and inflamed and develop an offensive odor. A black or yellowish discharge commonly occurs. 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 internal ear infections and thickening and closing of the ear canal.
Ear mites can cause several of these symptoms, including a black discharge, scratching, and head shaking. However, ear mite infections generally occur most commonly in cats. Ear mites in adult dogs occur most frequently after a cat 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). It is far more common for a dog showing the above symptoms to have a bacterial or yeast infection of the ear.
DIAGNOSIS
There are several kinds of bacteria and at least one type of fungus (yeast) which might cause an ear infection. In some cases, the ear infection may be caused by a foreign body or tumour in the ear canal. 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. Not all medicines treat all types of infection. The type of medicine is determined by the veterinarian and must be done in the office so ear medication is not sold over-the-counter.
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 us to determine whether the eardrum is intact and if there is any foreign material in the canal.
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 veterinarian can determine whether yeast or bacteria are causing the infection and sometimes get an idea as to the type of bacteria. A culture may be done to determine the exact bacteria involved.
TREATMENT
If there is a foreign body or tick lodged in the ear canal, the dog is sedated so that it can be removed. Some dogs have such a heavy buildup of debris that sedation is needed to clean 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. Medication can in the form of pills or ear drops.
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. If 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 favorable response to treatment or recurrence.
