Ear Infections
Why does my dog keep getting them?
This is one of the most common questions asked to veterinarians practicing general medicine. The best way to answer that question is to discuss all of the factors that play a role in the development of ear infections.
There are 3 major categories of factors that play a major role in ear infections.
1. Predisposing factors: conformation of the ear (long ears, tight ear canals, hair in canals), behavior of
the patient (swimming, bathing), environment (humidity), Trauma, and immune mediated diseases.
2. Primary factors: parasites (ear mites), foreign bodies (grass awns, dirt), Allergies (inhalant, food
hypersensitivity), systemic immune mediated diseases (pemphigus, seborrhea, sebaceous adenitis)
3. Perpetuating factors: these are the factors that keep inflammation going such as bacteria, and yeast,
fibrosis and calcification of ear canals, polyps and tumors.
The clinical signs of an ear infection are:
- shaking of the head
- redness and/or swelling of the pinna or canals
- odor from the ears
- pain when the ears are touched
Some dogs may have very dramatic clinical signs while others may be very tolerant and show very few signs.
All dogs have the potential to get ear infections.
Let's go over the anatomy of the ear canal. Knowing the anatomy of the ear can help to understand ear structure, which in itself has some inherent problems. In the diagram below, note how the external ear canal has a right angled turn in it. This turn acts to protect the ear drum (tympanic membrane) but it also is the reason why it is very difficult to clean the ear so as to completely remove all debris.
The pinna (ear flap) in dogs can be erect or folded depending on the breed. Floppy eared dogs with a folded over pinna have a closed environment for the ear canal which invites moisture to build up, whereas pointed eared dogs have better air circulation.
However the inside of all dogs' ears consist of an outer ear called the pinna and a vertical and horizontal ear canal and the tympanic membrane (ear drum). They also have a middle ear which consists of tiny bones, the tympanic bulla and the nerves and muscles in this area.
We consider outer ear infections separately from middle and inner ear infection. Outer ear infections are the most common and can lead to inner ear infections. Inner ear infections can develop along with a respiratory infection.
Predisposing factors explain why certain breeds of dogs have recurrent ear problems. Hounds, for example,
have extremely long pinnas with hunting and swimming activity in their life style. Labrador and Golden retrievers have floppy pinnas and love to swim ,creating a moist environment , perpetuating factors to thrive. Sharpei and English Bulldogs have very tight, stenotic ear canals , making it difficult for air to circulate into the canal. Poodles and many Terrier breeds have a tremendous amount of hair growing in the ear canals which plays a role in moisture retention in the canals. These breeds also get groomed frequently which again brings in the moisture factor. Even with the best efforts of owners to maintain healthy ears, these predisposing factors come with the dog.
The primary factors that cause ear infections may or may not be able to be controlled but are the most important factors in discussing why a pet gets recurrent infections. The most important of these factors is allergies. Allergies or Atopy is probably the most frustrating primary factor we deal with in ear disease. Unless we can control the allergies, the ear environment is changed so as to allow perpetuating factors to thrive. Allergic skin disease changes the surface of the skin that lines the ear canal, allowing bacteria and yeast to grow. Other primary factors such as ear mites and grass awns can be controlled or physically removed and the ear can heal completely.
Other systemic diseases such as immune mediated diseases and genetic skin disorders need to be kept under control with proper medication protocols in order to prevent secondary infections.
Realistically all recurrent otitis has an underlying predisposing or primary disorder. These disorders must be identified and properly treated if we are to be successful at curing recurrent ear infections in a particular dog.
The perpetuating factors in ear infections are the bacteria and yeast that invade the unhealthy ear and cause the pain, inflammation and all the smelly discharge. The most common invading organism in ear infections is yeast. One in particular is called Malassezia spp. There are a few other fungal organisms such as Candida spp., Trichophyton spp., and Aspergillus spp. The next most common organism that invades ears are bacteria. The most common bacterial invaders are Staphylococcus Intermedius, Proteus Mirabilis and Pseudomonas Aeruginosa. When these organisms invade the ear, they create severe inflammation, which makes the glands in the skin of the ear canal seep fluid and wax ,which in turn, feed the organism. This is the time that the dog is the most uncomfortable and unable to cure itself.
In order for the veterinarian to diagnose all of the factors involved in an ear infection, some diagnostic procedures are performed. The first procedure is the evaluation of the discharge the dog has created. A sample of the discharge is placed on a slide and the slide is examined under a microscope to identify if bacteria, yeast, mites or all of the above are involved in the infection. Many times there is a mixture of yeast and bacteria. Once the sample is collected, the ear is cleaned or flushed so as to remove as much of the debris as possible. Since the ear canal is deep and angled it is very difficult to effectively clean an ear. Some dogs may require sedation, in order to effectively clean the ear, especially if it would otherwise be painful for the dog. When the ear is clean, the veterinarian will use an canal with an otoscope to look for any foreign bodies, such as grass awns, damage to the canal or polyps or growths. Medication is based on the type of organisms that are seen. Most ear infections are treated topically with the use of ointments or drops that are placed into the ear canal. Most of the ear medications on the market are products that contain multiple medications. These usually include an anti-inflammatory with an antibiotic, and an anti-fungal medication. Effectiveness of the product is dependent on the ability of the owner to apply the medication properly. Some dogs do not allow their owners to do this. In those cases an oral medication will also be administered. The length of time we treat an infection is dependent on the type of infection and the type of predisposing diseases. Care must be given to not to stop treatment too soon. Many ear infections need to be treated for at least 4 weeks. Some need chronic therapy and are treated in some sense forever. The type and length of treatment is customized to each individual dog.
If an ear infection is recurrent, then the dog must be evaluated for an underlying primary or predisposing cause. At times the dog must be seen by the veterinarian as a recheck when the perpetuating factor is under control. Many diagnostic tests may need to be performed to find the underlying disorder that allows the bacteria and yeast to grow. These include thyroid testing, allergy testing, cultures, blood chemistries, and sometimes even biopsies are necessary. The key to understanding recurrent infections is to realize there is a reason that they are occurring and identifying all of the factors involved. Some factors can be altered, while others cannot, but at least we can understand the mechanism of the infections. When we have all of the information, a complete plan can be formulated to keep your dog infection free.
The last consideration in the treatment of recurrent ear infections is dealing with the scaring and fibrosis that occurs in some dogs. Once the ear canal has become filled with scar tissue and calcification occurs then the only option for therapy is surgical. The dogs that have extensive scar tissue built up, with never ending inflammation and infection, are intensely painful, and the only way to improve their life is to surgically remove the entire ear canal. This is radical surgery but if necessary will greatly improve a dog's quality of life. The best case scenario is to control infections and all underlying factors early in a dog's life so that the radical procedures do not need to be done.
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Dr. Ellen Leonhardt
Animal General
East Norwich
(516) 624-7500
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