Canine otitis externa is certainly one of the most common problems veterinarians are dealing with in small animal practice.
However, recurrent ear diseases can be very challenging to manage and be quite frustrating for the practitioner as well as
for the pet owner. To be successful in the treatment of ear infections, especially in recurrent cases, it is important to
understand the different aspects of primary, predisposing and secondary factors which may contribute to the disease. Causes
such as ectoparasites (e.g. ear mites, ticks), auto-immune diseases (e.g. Pemphigus foliaceus), foreign body (e.g. grass awn),
keratinization defects (e.g. idiopathic seborrhea, hypothyroidism), neoplasia, and most importantly allergies, are responsible
for directly inducing an otitis. Ear conformation and breed (e.g. Cocker Spaniel, Shar Pei), environmental factors (e.g. increased
humidity), or excessive ear cleaning are considered predisposing factors. Secondary or perpetuating factors such as irreversible
anatomical changes, otitis media and especially infections with bacteria and Malassezia will lead to chronicity.
Inflammation within the ear canal, caused for example by trauma or hypersensitivity, is probably the most important process
in the pathomechanism of otitis. This is characterized by increased humidity, temperature, pH and edema, as well as apocrine
hyperplasia, fibrosis, and hyperkeratosis, resulting in stenosis, decreased ventilation and perfect environment for secondary
Common reasons for failure to successfully managing otitis externa are multifaceted, and may include: too much focus on symptomatic
therapy without indentifying underlying problems, insufficient ear cleaning, resistant bacteria and poor antibiotic selection,
side effects, treatment duration and treatment discontinuation without follow-up exams.
Before treatment can be initiated it is important to obtain a thorough history and to perform an in-depth ear examination.
However, it is not unusual that the tympanic membrane cannot be assessed at the initial visit due to the debris and pathological
changes (e.g. pain, stenosis) within the ear canal. Before affected ears are flushed samples for ear cytology and eventually
culture should be obtained to determine what organisms are involved and to pick the right treatment. It is important to remember
that cytology is much more reliable for the quantitative assessment of the microorganisms involved than bacterial cultures.
However bacterial cultures are valuable in cases of otitis which will be treated with oral antibiotics.
The main purpose of a thorough ear flush is the removal of excessive cerumen, foreign body material, microorganism and their
toxins, and inflammatory mediators. The goal should be to obtain a clean ear canal so that topical ear medication is able
to directly interact with the epithelium. Treating ear infections without removing the excessive debris will often result
in treatment failures. Initial ear cleaning should be performed by the veterinarian, under heavy sedation or even general
anesthesia, because affected ears are commonly painful, irritated and the debris may sit deep in the horizontal ear canal.
Severely inflamed, swollen and painful ear canals are difficult to assess and even under full anesthesia a proper cleaning
and evaluation may not be possible. I such cases it is recommended to postpone the procedure and to treat the patient with
oral steroids (e.g. 1mg/kg every 12-24 hours for 3-7 days). This will allow the ear canal to open up, to reduce cerumen formation
and inflammation and to evaluate the condition of the tympanic membrane. The owner should be advised before the procedure
that a fragile intact ear drum may rupture and that temporary side effects, such as head tilt, nystagmus, and deafness may
Because many topical ear products contain potentially ototoxic compounds, the use of them without knowing whether the ear
drum is intact or not is discussed controversially among veterinarians. However, using an effective ear cleaner will help
with loosing up debris resulting in shorter ear flushing time and so irritation. To minimize potential ototoxic effect the
ear canals should be flushed thoroughly with saline after using an ear cleaner.
Many ear cleaners are available, but their efficacy, especially regarding their cerumenolytic activity, varies. The following
cerumenolytic components can be found in ear cleaners.
- Organic oils
- Solvents: propylene glycol (Cerulytic; Virbac), lanolin, glycerin, squalene (e.g. Cerumene; Evsco), butylated hydroxytoluene,
cocamidopropyl betaine (e.g. OtiFoam; DVM Pharm or Tricide; Molecular Therapeutics), isopropanol (Nolvasan Otic; Fort Dodge),
- Surfactants: dioctyl sodium, sulfosuccinate, calcium sulfosuccinate