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Otitis Externa in Dogs

What is Otitis Externa?

The external ear consists of a tube of skin which extends down to the ear drum. The term otitis externa literally means inflammation of the external ear. There are many reasons for this but generally otitis externa is due to infection (primary or secondary) by either bacteria or yeast organisms or a combination of both.

What causes the symptoms we see?

Inflammation, pain, mucky/dirty ears, bad odour, flicking ears, shaking head. These are all signs which may be seen in a dog with otitis externa. Infection leads to inflammation of the skin and glands of the canal. This inflammation leads to the overproduction of a modified cerumen (ear wax) which leaks out of the canal and has a bad smell. There may also be ulceration of the skin. Pain and irritation from all this leads to shaking & scratching of the ears.

Why do dogs get infections in their ears?

All dogs will have organisms (bacteria & yeast) in their ears when healthy. Generally when otitis occurs there is an upset in the normal balance and populations of these organisms. Sometimes it happens only once every now and then whereas some dogs seem to have continual ear problems.

This generally means that there is possible some factor that is making this dog more susceptible:

• Ear canal shape - a very narrow or irregular shaped canal will not drain or be ventilated as well and this may increase susceptibility to infection
• Chronic build up of 'muck' - if the ears aren't properly cleaned after a about of otitis externa there may be residual infection with the muck which will keep recurring.
• Allergic skin disease - the external ear canal is just an extension of the skin. Any condition effecting the skin will have the same or worse effect in the ear canal
• Hormone disorders - relatively uncommon but we will consider testing for them if we can't identify other reasons for recurrent ear problems (eg Thyroid and Adrenal disorders)
• Foreign body - eg grass seed or dead insect
• Resistant bacteria - some bacteria are resistant to the ear medications we have to use. In such cases we need to perform a culture and sensitivity test on the exudate
• Moisture - some dogs that swim end up with moisture in their ears which increases the chance of infection.

What about hairy ears?

The general thinking is that hair ear canals should not be plucked unless there is infection present or the hairs are actually growing down the canal rather that out. The hair that grows out of the canal acts a bit like a wick and plucking this hair in a normal canal can inflame the hair follicle leading to infection.

Diagnosis

In many cases of otitis it is difficult and painful to pass a scope deep within the ear as it causes too much discomfort. In most ear problems we will make a smear of the material in the ear and view it under the microscope. This will often give us more useful information than looking into the ear. From the smear we can see if an infection is present and, if so, what the predominant infecting agent is (ie yeast or bacteria or both). If we suspect a nasty infection from this test we will sometimes take a special swab to be sent to the lab for culture & sensitivity

Treatment

This will depend on the diagnosis. There are many ointments available which will control the populations of bacteria or yeast or both. It is usually important for the ears to be clean if these ointments are to work properly so we will often prescribe an ear cleaner as well. In severe or painful cases an general anaesthetic may be required for this.

Prevention od Otitis Externa

1. Address underlying cause if one has been diagnosed - this requires a trip to the Vet
2. Regular cleaning and drying using a specific ear cleaner

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Some very useful ear cleaners which can be used in dogs and cats:

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