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ALLERGIC OTITIS


What is allergic otitis?
Otitis is inflammation (redness, heat, pain, and swelling) of the ear. 

What causes allergic otitis?
There are three basic causes of the allergies: parasites, atopy (allergic reactions  
brought on by normally harmless substances like grass, mold spores, house dust 
mites, and other environmental allergens), and food. 

Allergic otitis is a common disease of the ear canal of dogs. Otitis can be externa 
(of the outer ear canal alone), media (involving the middle ear), or interna 
(involving the inner ear and associated structures). Unlike ear infections humans 
suffer (children, especially) in which the middle ear is typically affected, this disease is one that usually only affects the external ear canal.

The typical disease process is as follows: Irritation to the skin lining the ear canal 
causes inflammation, which results in excess wax production and a comfortable 
environment for yeast and bacteria (normal residents of the ear canal) to 
overgrow. These microbes cause significant itchiness and more inflammation, 
which lead to an itch-scratch cycle conducive to self-trauma via headshaking, 
pawing, and rubbing of the ears.

Any dog can develop an ear infection regardless of ear shape, exposure to water 
(swimming), or the amount of hair inside the ear canal. That’s because the 
underlying cause of the irritation that initiates the disease process is typically 
allergic. 

The most common cause of allergies in our area is flea hypersensitivity. Your 
dog or cat may not have visible fleas because when it grooms, it usually eats the 
fleas. However, even a few bites can cause significant allergies in some pets. 
Environmental allergies (atopy) and food allergies can cause allergic skin 
disease, which is a common reason for otitis externa. Allergic skin disease may 
also be influenced by the presence of thyroid disease or adrenal gland disease 
(Cushing’s disease).

Other less common causes of otitis externa in dogs include:
          • Polyps or other growths in the ear canal
          • Foreign bodies in the ears, including dirt, sand, or plant material (foxtails and
             grass awns)
          • External parasites (like ear mites)

The most severely affected patients often get stuck in a cycle of inflammation, 
infection, and thickening of the tissues lining the ear canal (fibrosis), which 
eventually leads to narrowing of the ear canals, ruptured eardrums, and debris 
and infection within the middle ear.

Over time, scar tissue occludes the canals, preventing medications from reaching 
the diseased portions of the canal. The occluded canals also prevent the natural 
sloughing of the canal’s skin cells, sebum (wax), and hair, which accumulate in 
both the canal and middle ear, thereby intensifying the infection.
Considering the potential long-term nature of this condition, allergic otitis is a 
frustrating disease for both owners and veterinarians. But for patients, the 
disease is much more critical, given that they typically suffer significant pain. 

What signs are associated with allergic otitis?
Affected dogs typically experience recurrent bouts of malodorous discharge, 
pain, and itchiness. But a significant subset will suffer these symptoms on a 
constant basis with no relief from their profound discomfort. Some pets may even 
try to bite someone who attempts to touch their ears or head.

The clinical signs of otitis depend on the severity of the inflammation but may 
include:
            • Shaking the head or rubbing the head and ears on the floor or furniture
            • Scratching at the ears
            • Discharge from the ears, which can sometimes have a foul odor
            • Redness of the ear canal and earflap (the ears may also feel warm when 
               touched)
            • Ear hematoma, evidenced by a grossly swollen earflap
            • Aggression whenever the head is approached

Some dogs with severe otitis may cry or groan as they rub and scratch their ears. 
Others will scratch so severely that their nails create wounds on the skin around 
their face, neck, and ears. If the otitis is severe or chronic, the outer ear canal 
can begin to thicken and become deformed. This thickening can make the ear 
opening very narrow, so cleaning the ears becomes more difficult. Ulcerations on 
the inside of the ear canal can also result from infection and self-trauma.

As mentioned above, otitis that begins in the outer ear canal can ultimately 
rupture the eardrum, ending in otitis media and otitis interna. Progression of this 
infection into the middle and inner ear can be associated with more severe 
clinical signs, including development of a head tilt, incoordination, inability to 
stand or walk, hearing loss, and severe, unrelenting pain.

A medical history and physical examination findings can provide valuable 
information for your veterinarian when trying to diagnose an ear infection. The 
medical history may include trying to determine how long the ear infection has 
been going on, whether it has occurred before and whether any other signs of 
illness have been observed. Physical examination findings may reveal evidence 
of underlying illness, such as thyroid disease and Cushing’s disease.

How is allergic otitis diagnosed?
Diagnosis of otitis is usually based on a history of previous ear infections and 
physical examination findings. Redness, inflammation, discharge, and other 
changes within the ear will readily indicate the presence of an ear infection. 
That’s the easy part. The hard part is finding out a) what kinds of microorganisms 
are taking advantage of the dog’s inflamed ears and b) what’s causing the 
inflammation in the first place. Determining both a) and b) generally requires 
diagnostic testing. In the case of identifying microorganisms, these are the tests 
most commonly used:

Microscopy: The most common test used to identify the presence of mites, 
bacteria, and yeast is a simple evaluation of the discharge obtained from 
the ear under a microscope. Mites are readily identified in this way. With 
special staining techniques, yeast and bacteria can also be identified and 
their characteristics evaluated.

Culture and sensitivity testing: Testing the debris inside a dog’s ear using 
simple microscopy isn’t always enough when the otitis has been stubborn 
or severe. Obtaining a sample of the discharge using a sterile swab and 
submitting it to a diagnostic laboratory will help determine exactly which 
bacteria and/or yeast are present. This information helps veterinarians 
devise the ideal drug strategy to treat the infection.

Underlying illnesses leading to the overgrowth of microorganisms will require a 
different approach. Here are the most common tests:
Otoscopy: An otoscope is a tool used to help a veterinarian visualize the ear 
canal. This is the ideal tool to help identify the presence of an eardrum 
rupture, a polyp, or a mass in the ear canal. Unfortunately, most dogs 
require sedation — if not anesthesia — before they’ll submit to this kind of 
examination.

Thyroid testing: This determines if thyroid disease may be playing a role.
Adrenal gland testing: Tests to explore the possibility of Cushing’s disease are 
sometimes required in dogs with otitis externa.
Allergy testing: A blood test can help identify allergens causing the clinical 
signs. Once allergens are identified, a solution is formulated so that 
injections can be given at home to desensitize the pet to the allergens.
Food trial: Since food allergies are such a common feature in the chronic otitis 
landscape, food trials are perhaps even more important than blood 
testing. Most food allergic dogs are allergic to the primary protein source 
in their food. A food trial’s goal is to change the proteins the patient eats 
to those it has never been exposed to before. If the otitis resolves when 
the diet is changed, a food allergy may be the underlying cause of the 
condition. A 12- to 16-week period in which the diet is restricted is 
considered the ideal approach to undertaking food trials.

How is allergic otitis treated?
Treatment of chronic otitis is a multistep process. First, the bacterial and fungal 
(yeast) component must be addressed along with the inflammation. The following 
strategies are typically used: 
          • Cleansing the ear canal is always recommended to clear accumulated debris. If              the otitis is painful and/or an extensive process, cleansing should ideally 
             be undertaken with the pet under sedation or anesthesia. Otoscopy is 
             often recommended as an aid in this process.
          • Topical medication tailored to treat the specific bacteria, yeast, or mites                         present is typically used (these are usually available as either ear drops                           or ointments). These include antibiotics, antifungals (to kill yeast), anti-                             inflammatory drugs (like cortisone), and topical anesthetics.
          • Systemic antimicrobials (antibiotic given by mouth or injection) are indicated                  in some cases, such as if the eardrum is ruptured. Ideally, antibiotic therapy 
             is based on the results of culture and sensitivity testing.
          • Systemic anti-inflammatory medications, such as corticosteroids, are 
            sometimes employed to reduce the pain, redness, and swelling. 
            Antihistamines may also be prescribed.

How do you prevent it?
The key to preventing allergic otitis is to reduce the pet’s allergies as much as 
possible. The cornerstone of that plan is monthly flea control with an effective 
flea control medication. Regular checks for internal parasites are important. If 
parasite control does not prevent recurrence, food trials and allergy testing often 
reduce or completely prevent the return of clinical signs.

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University Veterinary Center
1716 West Glenoaks Ave
    Anaheim, CA 92801 
     

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