What is Otitis Externa and structure of the ear
Otitis externa is inflammation of the external ear canal. The ear is divided into the outer, middle and inner ear. The outer ear includes the region from the ear flap (pinna) to the eardrum. The middle ear contains a number of bones required for transmitting sound waves, and the inner ear contains the organs required for hearing (cochlea) and balance (vestibular system)
What causes ear infection in dogs and how does it develop?
Most dogs with otitis externa have a primary underlying disease such as a food or pollen allergy, parasites (ear mites), hormonal disease, foreign body or tumour. These disrupt the normal structure and function of the ear canal. Not only can the primary conditions cause otitis externa directly, but they also increase the likelihood of yeast and bacteria (such as Staphylococcus spp.) to cause a secondary infection in the ear canal. Otitis externa should be addressed immediately, as inflammation can progress into the middle and inner ears (otitis media and otitis interna) and ultimately affect the dog’s hearing and balance.
Symptoms of otitis externa
Dogs with otitis externa may show one or more of the following symptoms:
- Itchy or painful ears
- Head rubbing, shaking or tilting (with the affected ear down)
- Yellow or black ear discharge that may be smelly
- Hair loss in the ear
- Redness, swelling and/or crusts on the pinna and ear canal
- Reduced hearing
Why are some dogs more prone to ear infection?
Some dogs are more prone to ear infections due to environmental or physical factors that make the skin more susceptible to overgrowth of yeast and/or bacteria. These factors can include long and floppy ears (such as in the Cocker Spaniel) and excessive swimming, which lead to warm, moist environments ideal for bacterial/fungal growth. Excessive ear cleaning can also damage the protective structure of normal skin, potentially allowing invasion of these agents. Hairy or narrowed ear canals, and excessive wax production can entrap bacteria/fungi, making their overgrowth more likely. Dogs with diseases that suppress the immune system are also more likely to develop otitis externa.
Treatment and management
Full remission and prevention of future ear infections relies on identification and treatment of the underlying cause, therefore the treatment plan varies from case to case depending on what might be the underlying cause. However, the general treatment approach usually includes cytology (identification of the organisms present in the ear canal under the microscope), cleaning of the ears and medication.
- Cytology is vital to identify the type of microbes causing the infection. This is performed by obtaining an ear swab and examining a stained sample under the microscope.
- Cleaning and/or flushing of infected ears removes excess debris which may prevent topical medication from contacting affected areas. It is done by instilling cleaning agents into the canal, followed by massaging of the ear, and removing excess solution with cotton balls. Cleaning agents used by veterinarians include Ilium Oticlean and PAW Blackmores Gentle Ear Cleaner. In severe cases, sedation or even anaesthesia may be required for a full ear flushing.
- Topical medication applied to the ear canal will target the infection as well as reduce inflammation, and will differ depending on the type of microbe. They can include antifungal or antibiotic agents, steroids (“cortisone”), or combination products that are effective against yeast and some bacteria in one solution. To ensure effective administration of medication, the veterinarian will show owners how to apply treatment.
The predisposing factors for otitis externa (such as underlying allergies) should be identified and managed as best as possible. Where possible, contributing factors should be limited or managed also. This may include limiting swimming and regular (but not over-zealous) cleaning of the ears. Some predisposing factors may not easily be avoided, and so close monitoring for otitis externa symptoms should always be ensured.