Otitis externa means inflammation of the external part of the ear. The external part of the ear extends from the tympanic membrane (ear drum), along the ear canal to the ear pinna (ear flap). While we often see patients with ear infections, otitis externa does not always mean an infection in the ear is present. However, the presence of an ear infection is very common and is a perpetuating factor in ear disease which prevents the ear disease from resolving. In order to understand how otitis externa can be treated and managed, it is important to know that this is a multifactorial disease, meaning that many factors contribute to the disease process and these underlying factors must be addressed, especially for chronic or recurrent bouts of otitis externa.
The causes of otitis externa can be divided into predisposing, primary and perpetuating factors.
The primary causes are those responsible for initiating the inflammatory process in the ear. The most common primary factors include:
- Allergies (atopy, contact allergy, adverse food reaction)
- Endocrine diseases
- Ectoparasites (ear and skin mites)
- Foreign bodies (grass seeds)
- Keratinisation disorders (diseases of the skin lining the ear canal)
- Masses within the ear (polyps, cysts, tumours).
For successful treatment of otitis externa, the primary causes must be identified and managed. This is especially important for chronic or recurrent ear infections, as failure to control the underlying inflammation will lead to repeated flares of otitis externa and possible secondary infections.
Predisposing factors will contribute to otitis externa by making the ear more susceptible to ear disease. These factors, however, will not cause ear disease on their own. A primary cause will need to be present to initiate the inflammation. However, predisposing factors can make it more difficult to treat these patients and can promote recurrence of infections and inflammation. Examples of predisposing factors are:
- Conformation (hairy ear canals, pendulous ears, stenotic or narrowed ear canals)
- Moisture within the ear (humidity, swimming, water-based ear cleaners and medication)
- Treatment effects (irritant ear cleaners, traumatic physical cleaning of ears, overuse of topical medications)
Perpetuating factors exacerbate the inflammatory process and maintain disease, even if the primary factor is addressed. Perpetuating factors include:
- Secondary infections (bacteria and/or yeast)
- Middle ear disease
- Chronic changes in the ear from repeated infections
Clinical signs of otitis externa include scratching at the ears, shaking the head, painful ears, red and inflamed ear pinna, discharge in the ear and malodour. The most common presentation that vets see is when the ear is infected which is often when the ear has discharge, is red and painful and can have a bad smell. Depending on what organisms are present the discharge may be a thick brown waxy discharge or a purulent (pus) discharge.
The diagnostic tests performed will be to identify the perpetuating factors and to address any primary causes.
An otoscope can be used to look into your pet’s ear. A lot of information can be obtained from this simple test – changes to the ear canal such as redness and narrowing, foreign bodies and masses within the ear can be visualised, the ear drum can be assessed and the amount of discharge within the ear can be determined.
The next step is usually to take a sample of the discharge present and to view it under a microscope. This will enable your vet to determine what type of organisms (if present) have proliferated in your pet’s ear and to help guide treatment.
Further tests to help identify the primary condition include blood tests, skin tests and even using an otoscope while your pet is under general anaesthetic.
The treatment of otitis externa ultimately depends on what the underlying causes are. For example, a patient with a grass seed in its ear may need a general anaesthetic to flush the ear and topical medication to treat the secondary infection if present. However, a patient with atopic dermatitis and recurrent flares of otitis may need long term medication to treat the allergy along with frequent ear cleaning to reduce the amount of discharge and micro-organisms present in the ear. Treatment will be individual for each patient and a plan will need to be made with your veterinarian.