Otitis externa is a very common problem, seen in over 10 percent of dogs attending primary care practices (O’Neill et al., 2014). It is an inflammatory condition that affects the external auditory canal, extending from the pinna to the tympanic membrane.
Inflammation of the external ear canal due to otitis externa can be acute or chronic, where persistent or recurring otitis lasts for three months or longer. Changes in the external ear canal caused by inflammation can include glandular hyperplasia, glandular dilation, epithelial hyperplasia and hyperkeratosis, which may increase cerumen production along the external ear canal.
Pathogenesis of this condition is often multifactorial. Therefore, practitioners should investigate and deal with the causes and factors to successfully manage otitis externa cases.
Clinical signs of canine otitis externa
Ears affected by otitis externa are often painful and pruritic, resulting in clinical signs such as head shaking and scratching. If the condition becomes chronic, it is more difficult to control.
Typical clinical signs of otitis externa include:
- Head shaking
- Scratching at/rubbing the ears
- Pain
- Malodour
- Discharge
Clinical signs vary according to the type of otitis present. They can also be unilateral or bilateral, which can provide clues to the underlying causes.
Understanding and diagnosis otitis externa in dogs
The three Ps
Predisposing factors, primary triggers and perpetuating factors, often grouped together as the “three Ps”, are used to describe why otitis occurs in the first place.
Predisposing (risk) factors are factors that increase the likelihood of otitis externa occurring. These can include the conformation of the ear canal, a higher density of ceruminous glands, excess hair in the ear canal, obstructions and increased moisture in the ears (ie in dogs that swim/bathe frequently).
Primary triggers are the underlying causes that act as the initial trigger for inflammation; they can alter the environment in the ear, allowing secondary infection to develop. The three most common primary triggers are:
- Allergies, such as adverse food reactions and atopic dermatitis
- Parasites (eg Demodex species and Otodectes cynotis)
- Foreign bodies, such as grass awns
If the primary causes are not identified and managed, frequent and recurrent otitis externa episodes often occur
Other primary causes include endocrine diseases (hypothyroidism, Cushing’s syndrome) and glandular disorders (sebaceous gland hyperplasia). If the primary causes are not identified and managed, frequent and recurrent otitis externa episodes often occur.
Acute otitis externa can often be treated successfully, but cases of chronic or recurrent otitis externa can be challenging for both vets and owners due to perpetuating factors. These are things that keep the illness in motion, such as stenosis of the ear canal due to epidermal and glandular hyperplasia, fibrosis, and mineralisation of the ear canal cartilage.
Secondary causes
Although canine otitis externa can be associated with bacterial and/or fungal infections, it can occur without the involvement of secondary opportunistic pathogens. This is because the initial inflammation associated with otitis externa changes the environment of the ear canal, which promotes the overgrowth of otic commensals (mainly Staphylococcus spp. and Malassezia spp.). With more chronic cases, a shift to infection with pathogenic Gram-negative bacteria (eg Psuedomonas) can be seen. Dogs may also develop an allergic response to Malassezia spp, leading to even more discomfort and pruritus.
Ear cytology
Ear cytology is one of the most important investigative steps in all otitis externa cases. It is a quick and simple tool to evaluate pruritic ears and is relatively inexpensive. It can, however, be overlooked in practice.
Ear cytology is one of the most important investigative steps in all otitis externa cases
Ear cytology in canine otitis externa cases is a quick and easy diagnosis and management tool that not only improves patient outcomes but will help veterinary practices with their goal of decreasing antimicrobial use for all first-line cases. Cytology not only enables vets to select the most appropriate initial therapy, but during subsequent consultations, it also helps to monitor the success of therapy and provides a subjective assessment of the number of organisms present and whether the infection is changing. There are also client communication benefits to cytology, as it promotes practice experience and increases client confidence in the practice.
Treatment for canine otitis externa
Successful treatment for otitis externa should include the three Ts:
- Think about resolving the acute otitis and resolving the underlying cause and perpetuating factors
- Timing is crucial! Catch it as early as possible, when it is easier to deal with and there are less likely to be chronic changes
- Tailor treatment to the patient’s needs and owner’s situation
The key treatment steps for cases of canine otitis externa are ear cleaning, treating infection if present, treating the inflammation and addressing the underlying causes, followed by continuous maintenance.
New treatment guidelines for canine otitis externa
The British Small Animal Veterinary Association (BSAVA) and its affiliated group, the Small Animal Medicine Society (SAMSoc), has recently updated its PROTECT ME guidelines for “Antibiotic use in our practice” (Figure 1). The new guidelines promote the use of topical steroids and antiseptic cleaners for otitis externa, moving away from using antimicrobials for all first-line cases and encouraging education around antibiotic stewardship.
The new guidelines promote the use of topical steroids and antiseptic cleaners for otitis externa, moving away from using antimicrobials for all first-line cases and encouraging education around antibiotic stewardship
“PROTECTME” stands for:
- Prescribe only when necessary
- Replace with non-antibiotic treatments
- Optimise dosage protocols
- Treat effectively
- Employ narrow spectrum
- Conduct cytology and culture
- Tailor your practice policy
- Monitor
- Educate others
Ongoing management of canine otitis externa
Predisposing factors should ideally be identified and avoided to manage otitis externa in the long term. Some dogs – for example those with hairy ear canals or conformational stenotic ear canals – may require periodic ear cleaning to ensure normal cerumen levels. After treatment of a secondary infection, proactive maintenance therapy could include topical steroids and/or an ear cleanser in some cases. This will ensure normal cerumen levels and control microorganism overgrowth.
