Ear Infections

Ear Infection:

Why & What to Do

T The ear canal anatomy in a dog and cat starts with the outer flap called the pinna. The pinna can either cover the ear canal or stand up. Its functions are to protect from things going in or when standing up allow airflow and oil evaporation. The pinna meets the outer ear at an area referred to as the ear base. The outer ear canals have several functions. One is to conduct sound to the tympanic membrane (eardrum) and protect the tympanic membrane (TM). The canals are lined with hair, sebaceous glands, and ceruminous glands, and epithelial cells. The hair catches debris and keeps insects from being able to crawl in. Sebaceous and ceruminous glands produce oils that coat the epithelial cells and protect them from water and bacterial damage. Airflow through the canal leads to evaporation of oil and carries the oil out. If the canal is obstructed

by the pinna, hair, or debris, the oil is not removed and builds up. Excess production occurs in response to infection, parasites, and irritation due to allergies. Too much oil leads to the transformation into wax that builds up and acts as a growth medium for bacteria and yeast. Studies have shown 65-80% of dogs with food allergies will develop ear infections; the technical term is otitis externa (OE). Epithelial cells line the ear canal and exfoliate, starting at the TM and work their way up the canals to the opening at the top of the canals. This is referred to as epithelial migration. This allows wax and other debris: i.e., dirt, pollen, dust, and exfoliated cells, to be removed. If obstructed, then wax and debris accumulate, further clogging the canal. Obstructions can consist of plant material, hair, tumors, polyps, swelling of clogged glands, and scar tissue.

The tympanic membrane is made of skin covering fibrous tissue. It separates the outer ear from the middle ear. When sound waves hit it, it vibrates and passes the vibration to 3 tiny bones that conduct the vibrations to the vestibule window in the inner ear, creating movement in the cochlea fluid. This leads to sound receptor activation. The middle ear consists of the bulla, a thin-walled boney structure that houses the incus, malleolus, and stapes; three tiny bones previously mentioned. The middle ear connects to the Eustachian tube. The eustachian tube connects the middle ear to the throat. This maintains air pressure and prevents the TM from rupturing when going up and down elevations. It also allows drainage from the middle ear helping to control pressure in the middle ear again. It’s also is a way to drain an infection from the middle ear or allow fluid to pass if theTM ruptures. There are three main categories that cause OE: Allergies, Mechanical obstruction, and Trauma. Allergies can be caused by either one or all three reasons: food, contact, or inhalant. Allergies can lead to excessive epithelial production along with excessive oil production. In the case of contact, we see hives or swelling in the canal. This can lead to mechanical obstruction. As previously mentioned, obstruction can lead to blocked epithelial migration, causing a build-up of material in the canals and resulting in infection. Trauma can be induced by excessive cleaning, which can irritate or with allergies cause itching and scratching that can lead to a break in the skin of the ear and open it to infection. Parasites such as ear mites can induce trauma and lead to infection. Fleas can cause scratching and trauma to pinna or allergic reactions and waxy build-up. Otitis externa can consist of either bacterial or fungal or a combination of both. The most common bacteria are staphylococcal psuedointermedius, a cocci bacteria, and pseudomonas aeruginosa, a rod bacteria. Pseudomonas aeruginosa can be very difficult to treat because of its ability to change DNA and become resistant to antibiotics. The most common fungal is Malassezia, which is an overgrowth of the normal inhabitant of the skin. Now that we know the causes, how do we treat? We do it in steps. The first step is finding the underlying cause. A detailed medical history will help tell if allergies are involved, if activities such as swimming or bathing have led to the problem, there is a hormonal problem such as hypothyroid, and if this is a chronic versus acute ear infection. A second step is a thorough exam of the ear canal. This will help determine if a mechanical obstruction is present; a growth, foreign material, excessive waxy build-up, glandular swelling, or scar tissue. We sometimes can see mites moving. Also, noting if the ear canal flow is narrow or makes a sharp bend like an "L" or a soft bend like an "S" and acts like a sink drain trap. This can inhibit airflow and lead to impaired oil evaporation; hence chronic waxy ears. A lot of times, we find one good ear and one bad ear. The third step is microscopy, Looking under the microscope at oil preps and stained slides. Oil preps

will allow us to see ear mites and eggs. Stained slides make it possible to see the type of bacteria—cocci versus rod and if Malassezia (fungi) are present in higher-than-normal numbers. We also see white blood cells and red blood cells telling us weeping and bleeding in severe cases. Treatment can be done based on history, exam, and microscopy. If inhalant or contact allergies are suspected, we treat them with an antihistamine, steroid, or janus kinase inhibitor such as Apoquel. For food allergies, if the dog is not on one, change to a hypoallergenic diet. I always recommend hydrolyzed food since studies have shown that 100% of commercial diets have contamination that is not listed on the label. Clean the pinna and ear canal with an appropriate ear cleaner. Your veterinarian can dispense one this to you. Most veterinary ear cleaners have some astringent to them to dry the ear canal out. Therefore, after a bath or at the end of a day of swimming, we recommend cleaning the ears out. Sometimes with severe excessive waxy build-up, a cerumenolytic ear cleanser is needed to be used first to soften wax, then follow with ear cleaner. With the cerumenolytic cleanser, leave in 5 minutes, then clean afterward. Cleaning can be irritating; doing so too frequently can lead to soreness and being vulnerable to infection. To clean the ear, position the bottle to squeeze a portion of the cleaner into the ear canal opening at the ear base. Be sure not to touch the bottle tip to the ear canal because it can contaminate the bottle with bacteria. Message the ear canal moving the fluid up in down. You should hear a swishing noise. Do this for 30- 60 seconds. Let the pet shake the head. Then using a cotton ball, remove the fluid and debris. Repeat till clear. I recommend cleaning the ear every one to two weeks if it's not infected but prone to waxy build-up. If treating an ear infection, I will have clients clean the ear(s) every three days during treatment then go to every 1-2 weeks. Treat with appropriate antiparasitic or antibiotics based on microscopy. For mild cases, topicals may be all that is needed, but for severe infections, a combination of oral and topical are usually required. Culture of the ear is an optional fourth step that the use of antibiotics can be based on. Antiparasitics consist of flea and tick control and ear mite meds. Flea medications can be either oral or topical. One topical used to treat both fleas and ear mites is selamectin (Revolution). It works by being absorbed through the skin into the bloodstream then distributed systemically. Topical antibiotic medications without culture can be done initially. A general first-line medication usually consists of an aminoglycoside (gentamicin or neomycin) in conjunction with steroid and antifungal. We must be sure the eardrum is intact, or this can cause deafness if not. Even with what was thought to be intact eardrums, I have seen some dogs go

acutely deaf with it. Common orals are in the cephalexin family for cocci and fluoroquinolones for rods. A culture is needed for those that have had chronic issues to see what the bacteria is and what it is sensitive to. Treatment with orals can be up to 4-6 weeks. If severe inflammation and excess wax build-up are noted, oral steroids should be added in and weaned down over time. The length of time they are used is based on the severity of irritation and infection. Steroids work by decreasing oil secretion and inflammation. Taking down inflammation helps provide relief for those tender ears. Also, with glandular swelling, it helps take that down and reduce obstruction. If a growth is present, surgical removal can be done to open the canal. A total ear canal ablation can be performed if severe scar tissue has built up, filling the whole ear canal. Only IF in the vertical canal, a lateral ear canal resection can open the horizontal canal to breathe better. OE can be a frustrating disease process, but taking these steps will give you the best chance at success and prevention of OE in the future.

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