Although the ear may seem like a very simple structure, it is actually a complex organ that can become irritated because of a whole host of primary causes and contributing factors. In cats and dogs, the external part of the ear consists of the pinna, the ear canal, and the eardrum. The ear canal consists of a vertical part (the part you can see when you look inside the ear) and a horizontal part, which extends deeper to the eardrum. Dr. John Angus, a resident in veterinary dermatology at the University of Illinois Veterinary Teaching Hospital in Urbana, says, "This abrupt angle in the ear canal is a normal anatomical feature that makes cleaning difficult and can help trap debris and wax inside the ear." Many factors can make ear infection more likely. Things that increase moisture and decrease ventilation can contribute to infection. Animals that like to swim or that have a naturally narrow ear canal can be at risk. Excessive hair or floppy ears can also trap moisture inside the ear. While these factors may predispose your pet to infection or make a current infection worse, by themselves they do not cause infection. If your animal's ear problem has been treated several times with little improvement, it may be time for your veterinarian to dig a little deeper for the root of the problem. Dr. Angus says, "Unless you stop the cause of the problem, the infection may never go away."
Technically, otitis externa is an inflammation of the external ear, but the term is more commonly used to refer specifically to inflammation of the external ear canal. Otitis externa has numerous causes, including anything that results in irritation, such as allergies, excessive earwax, excessive moisture in the ear, and bacterial infections, which are most commonly caused by Staphylococcus and Streptococcus. In addition, yeast infections, ringworm, parasitic mites and ticks, injuries, foreign bodies, tumors, poor ear drainage, infections spreading from other areas of the body, hormone imbalances, ear mites, ticks, vitamin deficiencies, and skin diseases have all been implicated in the development of ear infections.
The inside of a dog's ear is normally light pink and dry. When ear infections are present, the lining of the ear appears wet, swollen, red, and sometimes ulcerated. Crusts and brownish or pus-like discharge may be seen, and the odor is frequently offensive. If the condition has been present for some time, the lining of the ear will be thickened and tough, and no discharge may be present. As any ear disease in dogs is painful and irritating, pawing at the ear, shaking the head, and scratching the ear are the most obvious diagnostic signs to both the owner and the veterinarian. The disease is diagnosed based on clinical signs, physical examination, and tests on the discharge of debris in the ear canal. Eear mites, if present, can be observed with a magnifying glass as white moving specks among the black debris. Ticks are readily visible to the naked eye.
If parasites are not causing the dog's ear problem, the veterinarian will need to examine the ear canal with an otoscope and, depending on the dog's temperament, this may require the use of a tranquilizer or even full anesthesia. A sample of the discharge will be examined under a microscope, which will reveal the cause of the ear problem in most instances. If the cause is a bacterial or fungal infection, a culture of the organism will need to be grown, and then sensitivity testing will be done to determine which drugs will be effective. Occasionally, a biopsy or surgical exploration will be needed to make a diagnosis. Because veterinary practitioners see so many cases of otitis externa in dogs, they often treat them initially without conducting all these tests in order to save their clients' added expenses. This is called diagnostic treatment, but if it is not successful, then diagnostic tests will be needed. Treatment of otitis involves cleaning out the ear canal, preferably by a veterinarian. Foreign bodies can then be readily seen and removed, if they are the cause of the ear problem. Ointments containing antibiotics, cortisone, enzymes, insecticides, mineral oil, or wax-dissolving products are then used for follow-up treatment. Acute cases may require antibiotics by injection or by mouth. Tranquilizers, pain killers, and a restraint collar may be required in dogs that continue to mutilate their ears by scratching. If ear mites are the problem, other pets in the household will need to be checked and treated if infected.
The most common cause of failure in treatment of ear disease in dogs is inadequate home follow-up treatment when the owner stops the ear or oral medication prematurely. In many cases, this results in relapse and can lead to a chronic condition. Failure also results if the medication is ineffective. If this is the case, the dog owner should contact the veterinarian. Each time an infection recurs or is inadequately treated, the ear canal thickens and becomes narrower, and successful treatment by medication is more difficult. Surgical treatment involving partial or complete removal of the ear canal will then be the only approach available to cure the problem.
In addition, owners sometimes make infections worse by using water or irritating substances such as straight rubbing alcohol or vinegar to clean the ear, or by causing trauma to the ear canal by over-aggressive cleaning. Water increases moisture within the ear and does not evaporate adequately deep in the canal. Irritating substances can damage the fragile lining of the ear canal, making it more susceptible to bacterial infections. Only gentle cleansers designed for use in the ear canal should be used. Prescription ear cleansers available from a veterinarian may be used to treat specific disorders or infections. Use of cotton swabs is not recommended because they tend to pack the earwax into the ear canal, making it more difficult to remove.
An infection of the external ear is almost always a sign of an underlying disease." Changes in the ear canal resulting from the underlying cause allow normal bacteria and yeast to overpopulate. Eventually the overgrowth becomes infection and results in ongoing disease even after the initial cause has resolved. The most common underlying cause of ear problems in dogs is allergic reactions. The pollens and molds that cause hay fever symptoms in people are the principal causes of skin and ear disease in dogs. Dogs can also become allergic to an ingredient in their food, even after they have been eating that food for years. (If you suspect your dog has an allergy, contact your veterinarian for directions on managing these conditions.)