Otitis externa is the painful, smelly, head-shaking cause of misery for many companion animals and their owners. It is a particularly common problem in dogs. The ear canal is lined with epithelium, or skin. The causes of ear disease can be divided into the categories of primary, secondary, and perpetuating factors.
Primary causes include anatomical abnormalities (narrow canals, hair-filled canals, and floppy ears), allergy, parasites (ear mites), foreign bodies (foxtails), obstructions (polyps, growths), and other problems to produce an irritated canal.
Secondary causes develop as a result of primary causes and worsen ear disease. These are primarily infections: bacterial and yeast. Some infections, particularly the gram-negative bacteria, can be very resistant to antibiotics and very difficult to treat.
Perpetuating factors are the result of chronic ear infection and inflammation. Chronic disease stimulates the lining of the ear to thicken, resulting in a narrow and more tortuous canal. This prevents medications and cleansers from getting into the ear, and keeps debris from getting out of the canal, keeping the canal waxy, moist, and warm – an ideal environment for continued infection. Chronic inflammation can also stimulate the enlargement of wax glands and polyps, further obstructing the canal. In severe cases, the cartilage that surrounds the canal can accumulate calcium (become calcified) making it firm and the ear permanently scarred and closed. In these cases, surgical removal of the ear canals may be the only option to provide the patient comfort.
External ear disease and infection can rapidly spread through the eardrum and into the middle ear (otitis media). This increases the severity of the infection and can result in equilibrium problems as well as deafness.
Treatment of otitis externa requires a two-pronged approach. The first is to treat the current ear infection. The veterinary dermatologist will obtain a sample of debris from the ear canal and examine it under the microscope to determine the types and numbers of bacteria and the presence or absence of yeast. If bacteria are noted, a sample may be sent to the laboratory for culture to identify the organism causing the infection and to determine which antibiotics might be most affective in combating it.
Once a sample has been obtained, the ear canal must be cleaned and cleared of debris so that it can be examined and treated. Cleaning may require sedation. Sometimes treatment with medications to reduce swelling and pain may be necessary prior to cleaning so that the canal becomes more accessible. Multiple visits for sedation and cleaning may be necessary before the infection is controlled. Once the canal is cleaned, topical therapy with anti-inflammatory and antibiotic medications is used. Systemic therapy may also be necessary in severe cases.
The second approach to the treatment of ear disease is identifying the underlying cause. Obviously, if a foreign body, such as a foxtail awn, can be found and removed, the infection should heal. Most often, and especially if both ears are affected, a more generalized cause of the ear infections is present. This must be identified and controlled. The most common cause of ear disease is allergy -- which the veterinary dermatologist is especially trained to identify and treat.
The veterinary dermatologist is the primary referral specialist for the diagnosis and treatment of this frustrating and chronic condition. It takes a coordinated effort on the part of the dermatologist and the animal owner (and cooperation from the patient) to control this difficult problem.