Overview of Chronic Ear Infections in Dogs
Otitis is an inflammation of the ear and it is one of the most frequent reasons for owners to seek a veterinarian’s help for their dog. The prevalence of otitis externa, or inflammation of the external ear, in dogs has been reported to be between 10 to 20 percent although in more tropical climates it is probably closer to 30 to 40 percent.
The term otitis does not refer to a specific disease, but it is a symptom of many diseases and not a specific diagnosis.
Causes of Chronic Ear Infections in Dogs
Allergies, such as inhalant allergy and food allergy
Parasites such as ear mites
Endocrine diseases such as hypothyroidism
Auto-immune diseases like lupus
Chronic inflammation stimulates the proliferation of the skin lining the ear canal. As a consequence, thickening of the canal occurs and leads to narrowing of the canal. More importantly the skin is thrown into numerous folds, and this inhibits effective cleaning and the application of medications. These folds act as a site for the perpetuation and protection of secondary micro-organisms like bacteria.
Inflammation of the middle ear (otitis media) results from chronic inflammation of the external part of the ear canal, rupture of the ear drum and establishment of infection in the middle part of the ear. Discharge in the tympanic cavity is difficult to treat with topical therapy and often remains as a source for infection. Otitis media is usually bacterial in origin. Clinical signs suggestive of otitis media include head shyness and pain on palpation of the ears. Some cases of otitis media might experience head tilt, circling and dry eyes, but the vast majority do not have neurological abnormalities.
As the ear drum quickly grows back after rupture, otitis media may also be present, even if an intact membrane is seen on otoscopic examination. Radiography cannot be used to completely rule out the presence of otitis media since 25 percent of confirmed cases had no radiographic evidence of the disease. In one study, otitis media was present in 80 percent of cases of chronic, relapsing otitis externa, so it must be considered as a possible cause of any refractory or relapsing otitis externa. Treatment of otitis media is based on bacterial culture and sensitivity results. Most cases require long term antibiotic therapy, a minimum of 2 months, and aggressive topical therapy.
Diagnosis for Possible Ear Problems in Dogs
The identification of the underlying disease responsible for the chronic ear disease is of crucial importance. In order to do this it is important for your veterinarian to:
Take a complete history that includes information concerning the age of onset, progression of the disease, and response to previous treatments.
Perform a thorough physical examination of the ears to detect the presence and condition of tympanic membrane, the severity of changes in the ear canal, and also the rest of the body to detect signs of concurrent skin or internal disease
Examine the ear discharge under the microscope to identify the organisms that are perpetuating the infection. Bacterial culture may be necessary in cases that have been treated by numerous drugs with only moderate improvement, because some of the bacteria tend to become rapidly resistant to commonly used antibiotics.
Treat the secondary infections aggressively. Antibiotics and antifungal drugs may be prescribed for extended periods of time, up to two months, in cases in which the infection has progressed in the deep part of the ear canal (otitis media). This happens in over 80 percent of cases of animals with chronic ear disease.
Thoroughly clean the ear canals. Topical therapy is vitally important for successful management of otitis. Ear flushing under sedation or general anesthesia is required in most cases to remove the discharge that is present in the deep part of the ear (bulla). Failure to remove this material will result in poor response to treatment and relapse of infection as soon as therapy is discontinued. Wax, oil, and cellular debris may be irritating, prevent medication from contacting the canal epithelium, and produce a favorable environment for microorganisms to proliferate and inactivate certain antibiotics.
Home Care for Dogs with Ear Problems
Regular cleaning at home is an important part of the therapy. Several products can be used.
A mixture of vinegar and water (1/10) is a good degreasing solution to remove wax (cerumen) and dry the excessive moisture in the ear canal. The liquid should be applied gently in the canal, the ear massaged to allow breakage of the cerumen and cotton balls used to remove the cerumen and wipe out the excess liquid. Extreme care should be used when mechanically cleaning the ears. The use of cotton applicators should be avoided or limited as they may cause rupture of the tympanic membrane. Also powders should not be applied in the canal as they build up, predisposing the ears to the development of secondary infections.
Several products are available on the market and they should be used as directed by a veterinarian as some of them may interfere with the efficacy of the topical medications. These products are usually classified as either ceruminolytic or drying agents. Gentle massage improves their effect. Most of these products are contraindicated with a ruptured ear drum. However, frequently the condition of the ear drum cannot be determined until after the canal has been cleaned. In those cases the probability of ear toxicity may be decreased by flushing with water after the application of such agents.
More Causes of Chronic Ear Infections in Dogs
Inhalant allergy is extremely common in dogs and is the most common underlying cause for recurrent otitis externa. Clinical signs are initially seasonal. Progressive worsening with time is also typical. At least 50 percent of these dogs have bilateral otitis externa. In up to 5 percent of cases, otitis may be the only complaint. These dogs tend to have itchy feet, itchy face and itchy ears. They are predisposed to secondary skin and ear infections that tend to recur after treatment unless the underlying allergy is well controlled.
Food allergy. Over 20 percent of these cases start with just otitis externa and ear disease is present in 80 percent of the cases. It should be considered as a top differential for otitis externa in any dog less than one year of age. Food allergy, however, can occur at any age and may mimic clinical signs of inhalant allergy. These animals tend to have recurrent skin and ear infections unless the underlying allergy is identified and addressed.
Foreign bodies. Plant material (fox tails) dirt, sand, impacted wax, loose hair and dried medications are frequently responsible for ear infections. In most cases this is a unilateral otitis, which means it only affects one ear.
Diseases of keratinization, such as primary seborrhea of cocker spaniels. Follicular casts and scales are found on physical exam and secondary skin infections occur commonly as the excessive amount of lipids is an optimal medium for bacteria and yeast to proliferate.
Endocrine disorders. Hypothyroidism and Cushing’s disease are the most common endocrine diseases that can cause otitis externa. If a middle-aged dog keeps relapsing with otitis externa and is not itchy, then endocrine disease should be considered as a possible underlying cause.
The ear mite (Otodectes cynotis). In dogs, the incidence is controversial but most veterinarians agree that it is responsible for 5 to 10 percent of cases. In recurrent cases it is possible that others in contact with animals can act as asymptomatic carriers. It is hypothesized that hypersensitivity may induce severe inflammation that is sometimes seen in some cases, especially when few or no mites are found.
Information In-depth on Chronic Canine Ear Problems
Most cases (over 80 percent) of chronic or relapsing otitis externa have otitis media. This results from chronic inflammation of the external part of the ear canal, rupture of the tympanic membrane and establishment of infection in the middle part of the ear.
Discharge in the middle ear cavity is difficult to treat with topical therapy and often remains a source of infection. Otitis media is usually bacterial in origin.
Treatment of otitis media is based on bacterial culture and sensitivity results. Most cases require long term antibiotic therapy (minimum of two months) and aggressive topical therapy.
Most causes of otitis externa are associated with generalized dermatologic conditions. A complete dermatologic history and work-up may therefore be necessary in the diagnosis of many primary otitis externa cases. The most common causes seen in dermatology are atopy (inhalant allergies), food allergy, diseases of keratinization (e.g. primary seborrhea of cocker spaniels), and ear mites. It is critical to long term management of otitis externa that a primary cause can be found.
Related Symptoms to Ear Infections
Clinical signs suggestive of otitis media in dogs include head shyness and pain on palpation of the ears. Some cases of otitis media might present with head tilt, circling and dry eyes, but the vast majority do not have neurological abnormalities.
As the ear drum quickly grows back after rupture, otitis media may also be present even if an intact membrane is seen on otoscopic examination. X-rays cannot be used to completely rule out the presence of otitis media since 25 percent of confirmed cases had no radiographic evidence of the disease.
In most cases of chronic otitis externa/media bacteria such as Staphylococcus and Pseudomonas are present. The color, texture and odor of the exudate from a diseased ear can provide clues regarding the underlying primary cause of the otitis and the perpetuating factors that may be involved. A dark, moist brown discharge tends to be associated with bacteria and yeast infections. Purulent creamy to yellow exudates are most often seen with bacteria such as Pseudomonas.
Diagnosis In-depth for Chronic Ear Infections in Dogs
In cases of ear inflammation, your veterinarian will want to identify and correct the primary underlying cause as well as the perpetuating cause (e.g. bacterial infection).
Diagnosis of atopy is based on history (age of onset, progressive worsening overtime), clinical signs (pruritus on face, feet and ears), exclusion of other pruritic diseases, intradermal skin test, and serology testing for allergen-specific IgE.
Food allergy is diagnosed by appropriate food trial in which a source of protein is selected based on the individual history and used for a minimum of two months. The food is then discontinued, and if signs clear up, the food will be given again to see if symptoms recur.
Diagnosis of a primary disease of keratinization is made based on history of very young age of onset, lack of pruritus (itchiness) at least initially, and skin biopsy.
Diagnosis of an underlying endocrine disease is based on clinical signs, compatible changes on CBC and chemistry panel and specific tests for either thyroid or adrenal function.
Diagnosis of ear mites is made by cytology and identification of mites under the microscope.
In most cases of chronic otitis externa/media bacteria are present. Although bacteria are not a primary cause of otitis, once the infection is established, they can cause significant inflammation and damage. Diagnosis is based on cytology of the exudate, bacterial culture and sensitivity. Aggressive treatment is warranted as resistance to antibiotic may easily occur especially in cases when Pseudomonas is cultured.
Any time that rods are detected on cytology, a bacterial culture/sensitivity test is warranted to investigate whether Pseudomonas is present and what the sensitivity is.
Thorough ear cleaning is a vital part of the treatment of chronic otitis. The reasons are multiple. The exudate is irritating and provides a good environment for bacteria and yeast to proliferate. In addition, the exudate may inactivate antibiotics and thus cause treatment failure.
When flushing an ear with a ruptured ear drum, the use of saline or 1:1 or 1:3 dilutions of 5 percent white vinegar are recommended. The fluid is discarded with every flush and suck cycle and the canal is filled again with clean saline. This is repeated multiple times using a fair amount of saline. The best results for deep ear cleaning or flushing are obtained with the patient under general anesthesia.
Cleaning cannot be done on very swollen, narrowed, ulcerated or painful ears. Such cases need to be treated symptomatically at first and cleaned at a later date when the inflammation has been reduced and the canals have opened. Systemic anti-inflammatory doses of prednisone for 10 days and topical glucocorticoids like Synotic® may be used to decrease inflammation, swelling and pain.
Pseudomonas infections are extremely frustrating and difficult to treat. Most effective treatments include:
Topical Polymyxin B. This medication is rapidly inactivated by the exudate and aggressive cleaning is an essential part of therapy.
Acetic acid (vinegar/water 1:1)
Silver sulfadiazine (1gm of silver sulfadiazine is mixed with 100ml of sterile water). 0.5 ml of the mixture is applied twice daily.
Pre-soaking the ear with edetate trisodium (tris-EDTA) 15 minutes prior to application of the antibiotic increases the efficacy of aminoglycosides.
Injectable enrofloxacin has been used topically with DMSO (1/1). The stability of this mixture has never been evaluated in controlled studies but in clinical situations it seems to be stable and effective for at least 7 days.
Systemic enrofloxacin or ciprofloxacin twice daily for a minimum of 2 months.
If Staphylococcus is the cause of infection, cephalexin or trimethoprim-sulfa are used.
Topical therapy is usually sufficient and miconazole and clortrimazole are the most commonly used ingredients. In rare cases of otitis media due to *Malassezia**, systemic treatment is necessary and oral ketoconazole (Nizoral) is used twice daily for 3-4 weeks. Side effects include anorexia, vomiting and diarrhea. In animals that have adverse reaction to ketoconazole, itraconazole (Sporonox®) may be used once daily. It comes in capsules or in a suspension.
Therapy for ear mites can be topical or systemic. Topical treatments include thiabendazole (Tresaderm®) in the ears or selamectin (Revolution®) as a spot on treatment to be applied in between the shoulder blades. Treatment should cover the cycle of the mites, which is three weeks. One single application of selamectin is usually sufficient to eradicate the infestation. Systemic treatment includes the use of oral or injectable ivermectin once every two weeks for three times.
Follow-up for Dogs with Chronic Ear Infections
Cytology and culture should be performed monthly throughout the therapy and before discontinuation of antibiotic therapy. Early identification of the underlying cause and aggressive treatment of the infection are the only ways to prevent more serious and permanent damage in the ear canal.
In hunting dogs, ears should be checked regularly for the presence of foreign bodies. Excessive swimming should be avoided.
In breeds with a lot of hair like poodles, gentle hair plucking may prevent the occurrence of infections.