Otitis Externa

A lesson about ear problems in dogs and cats from Companion Animal Dermatology
Definition of otitis externa: Otitis externa is defined as inflammation of the external ear canal.

Table of Contents

1. What should I do if my pet has smelly or painful ears?
   
2. What causes otitis externa?
   
3. What should a veterinarian do with a patient with otitis externa?
   
4. How is otitis externa treated?
   

What to do if your pet has smelly or painful ears.

1. First, carefully and gently examine the ears. Try to determine if the odor or pain is originating from the pinnae (external ear), from down in the ear canal, or even from some other body area, like the mouth! Remember, these ears may be so painful that your pet may bite or snap out of fear or pain, so be careful.
   
   
2. Do not try to treat the ears yourself. It is absolutely critical that the ears are careful examined. Treatment without an understanding of the problem could cause serious and permanent damage.
   
   
3. Have your veterinarian examine the ears. Your veterinarian should examine both the outside of the ears and the external ear canal with an otoscope. Normal ears have a smooth, pink lining of skin with minimal accumulation of wax or debris. During the examination, your veterinarian will try to determine if the tympanic membrane (i.e., ear drum) is damaged. This is important in the selection of drugs and dosage schedules to treat ear infections. Be prepared to offer any information that may allow your veterinarian to identify the primary factors that started your pet's problem. (See primary factors)
   
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Pathogenesis of Otitis Externa

Recently, Dr. John August of Texas A & M University classified the causes of otitis externa into three categories.1 This classification helps to understand the clomplexity of this clinical problem. The underlying causes of otitis externa include ("the three Ps") predisposing causes, primary causes, and perpetuating problems.
1. August JR. Otitis Externa: A disease of multifactorial etiology. Vet Clin North Amer 1988:18;731-742.

Predisposing Causes

Predisposing causes of otitis externa are those conditions or behavior that may result in ear problems, but by themselves, do not actually cause inflammation of the ear canal. These causes make the development of otitis externa in a pet more likely.

Conformation of the ear

• Pinnae (floppy vs erect ears): There is no difference in prevelance of otitis externa in erect versus floppy ears, however, the type of ear may make the condition more difficult to treat.
  
  
• Length and conformation of ear canals: Dogs of some breeds have very long and tortuos ear canals. This can make the canal more suitable for primary factors and perpetuating factors to cause inflammation.
  
  
• Stenosis or swelling of the opening of the external ear canal is a real problem in some breeds, such as the Chinese shar-pei. This lack of a significant openig into the canal may reduce air circulation in the external canal. It certainly makes treatment of otitis externa more difficult.

Behavior

• Swimming: Dogs who swim frequently tend to get a lot of water in their ears. This increase moisture facilitate growth of bacteria and yeast in the ear canal.

Environmental factors

• Both heat and humidity will tend to make the microenvironment of the ear canal more suitable for bacterial and yeast growth.

Improper treatment

• Trauma to the ear canal during treatment of the ear canal, necessary or unnecessary, can damage the epithelial lining of the canal and predispose the pet to infections.
  
  
• The use of cotton-tipped applicators and excessive plucking of hair from the ear canal are the most common examples.
  
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Primary Causes

Primary causes of otitis externa are those factors that actually cause or initiate the inflammatory process. In short, they are the reason that the problem begins.

Parasites

• Ectoparasites that cause inflammation of the ear include ear mites (Otodectes cynotis), various forms of mange (e.g. sarcoptic mange), and ticks (e.g., Otobius ...the spinous ear tick).
  
  
• Ear mites are the most common cause of otitis externa in cats!
  

Allergies

• Alliergies are the most common cause of otitis externa in dogs!
  
  
• Allergies include atopy (the allergic disease caused by pollens, molds, and a variety of other substances), flea allergy dermatitis(an extremely itchy condition caused by an allergic reaction to flea bites), and contact allergies (caused by an allergic reaction to topically applied substances, including some ear medications!).
  
  
• Clinical signs of allergies other than repeated episodes of otitis externa include: scratching, licking the feet, rubbing the face (with the paws or against furniture), dragging or scooting the rear end on carpet or rough surfaces, repeated bacterial skin infections, and generalized yeast infections. Allergies may or may not be seasonal. Consider the times of year when your pet has problems and be sure to mention them (if appropirate) to your veterinarian.
  

Foreign bodies

• Many substances accidently or otherwise end up in the external ear canals of dogs and cats. These result in irritation and inflammation. In some cases, the foreings object can damage or perforate the ear drum (tympanic membrane) and result in more serious damage.
  
  
• The most common foreign bodies are plant materials, such as seeds or stickers from grasses or weeds. (e.g. foxtails)
  

Scaling disorders

• Scaling disorders are cutaneous diseases that result in an accumulation of scale (aka, dandruff) or excessive greasiness of the skin or ear canal.
  
  
• Seborrhea is a condition seen most frequently in American cocker spaniels, Irish setters, and other spaniel breeds that results in severe scaling, bacterial skin infections, a heavy accumulation of cebum (ear wax), and severe itchiness.
  
  
• Sebaceous adenitis is a scaling disorder seen in many breeds (e.g., standard poodles, akitas, and others) that results in hair loss and scale accumulation in the ears and all over the rest of the body.
  

Other dermatologic diseases

• Any dermatologic disease that affects the pinnae (aka, ear flaps) can lead to inflammation down in the external ear canal.
  
  
• Autoimmune diseases (e.g., pemphigus foliaceous, pemphigus vulgaris) can cause severe scaling, crusting and ulceration of the pinna and external ear canal.
  
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Perpetuating factors

Perpetuating factors are those factors that allow the inflammaation and irritation to continue, even if and when the primary factor is controlled. These factors are often considered as primary factors....actual causes of otitis externa...however, they rarely start the inflammatory process.

Bacterial and yeast infections

• Bacterial and yeast infections are the most common perpetuating factors. They are often (erroneously) considered as the cause or only important consideration in the treatment of otitis externa!
  
  
• The most common bacteria associated with ear infections are Staphylococcus intermedius, Proteus mirabilis, and Pseudomonas aeruginosa. Pseudomonas spp infections are often notoriously difficult to control. (See treatment)
  
  
• Bacterial infections of the ear result in malodor, excessive exudation (drainage of pus-like material), and ulceration. They frequently make the ear extremly painful to any handling.
  
  
• Malassezia pachydermatis is the yeast found most frequently in association with otitis externa.
  
  
• Malassezia organisms are considered normal inhabitants of the ear canals, although in small numbers.
  
  
• Malassezia infections result in accumulation of a cream-to-dark waxy, odiferous discharge.
  
  
• Malassezia otitis is frequently associated with a generalized cutaneous infection by the same organism.
  

Otitis media

• Otitis media is inflammation of the middle ear. This is the area of the ear that contains the small bones that translate sound waves into nervous impulses. It also contains nerves and is connected to the pharynx by the eustacian tube.
  
  
• Otitis media may result from trauma, cancer in the middle ear, or most commonly, by bacterial or fungal infections.
  
  
• Treatment of otitis media generally requires surgery of some type. (See treatment section)
  

Chronic changes

• Hyperplasia of the ear canal may be caused by repeated episodes of otitis externa and the development of scar tissue in the ear canal. These changes may restrict the size of the ear canal.
  
  
• Calcification of the cartilage of the ear canal results from chronic scarring and inflammation. It is irreversible and may lead to ear abalationas the only viable treatment option in some cases.
  
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What your veterinarian will do when your pet has otitis externa

The following diagnositic tests are always useful to help diagnosis the causes of otitis externa:

Collection of the complete medical history

• This includes any evidence of seasonality, which may indicate allergies of some seasonal parasites.
  
  
• This includes possible exposure of your pet to infectious or contagious diseases, spread through contact with other animals...so, does your pet have contact with any other animals?
  
  
• The pattern of disease: Is it getting worse? Does the problem come and go?
  
  
• Previous treatments: Were they helpful?
  

A complete physical and dermatologic examination

Otoscopic examination of the external ear canal

• This may require sedation if the ears are painful
  

Cytology of the ear canal

• A sample of exudate is taken from the ear and smeared onto a glass microscope slide, stained, and examined microscopically.
  
  
• This test is necessary to identify perpetuating factors, such as bacterial or yeast infections.
  
  
• The test is helpful on follow-up examinations to determine the efficacy of treatment.
  

The following tests may be helpful and necessary to properly diagnose and treat your pet:

Culture of the ear canal

• The test is performed by taking a sample of exudate from the ear as steriley as possible, applying the exudate to an appropriate growth medium for bacteria or yeast, and then incubating the medium for 24 hours or more.
  
  
• More importantly, part of this test helps to identify the antimicrobial agents that will be most effective against the microorganism involved in the otitis externa. Thus, the test allows the veterinarian to choose the most effective treatment for your pet.
  
  
• This test is not necessary in all cases of otitis externa, but is indicated when cytology shows some types of bacteria or when previous treatments have not been completely effective.
  

Radiography (x-rays)

• These tests are indicated when your veterinarian suspects involvment in the middle ear.
  
  
• Heavy sedation or anesthesia is generally required for this procedure.
  

Allergy tests

• These tests are indicated to identify the primary factors in otitis externa.
  
  
• Remember allergies may be to molds or pollens, foods, or medications.
  
  
• The history is the key to identifying possible allergies: season problems and otitis externa seen in conjunction with other signs of allergies (see above) are key points that will lead your veterinarian to consider allergies as the primary factor in your pet's problems.
  
  
• Several types of allergy tests are used to diagnose allergic disease in dogs and catss. Your veterinarian can help select the most appropriate for your pet.
  
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Treatment of otitis externa

Proper and effective treatment of otitis externa requires the following:

• Identification and control of the primary, perpetuating, and predisposing factors
  
  
• Keeping the ears clean and dry
  

Cleaning ears

Ears should be cleaned only when necessary. Excessive cleaning may act as a predisposing factor for otitis externa. Ears should be cleaned regularly (every 2-7 days as needed to keep the ears clean) when they are inflammed.

Ear cleaning technique

1. Obtain a good quality ear cleansing solution from your veterinarian. Human ear cleaning solutions are not formulated properly for use in the ears of the dog or cat. The solution should be kept at room temperature or warmed to room temperature before use.
   
   
2. Supplies needed include the ear cleaning solution, cotton balls, a few gauze sponges, and cotton-tipped applicators.
   
   
3. Fill the entire ear canal with the solution. Allow the solution to overflow from the canal.
   
   
4. Place a cotton ball in the opening of the external ear canal.
   
   
5. Gently massage the ear canal using an upward motion to help pull the solution up into the cotton ball.
   
   
6. Remove the cotton ball and repeat the process until the solution absorbed by the cotton ball is clean.
   
   
7. Repeat the massage with the cotton ball in the opening of the canal...without adding any additional ear cleaning solution...until the majority of the solution has been removed from the ear.
   
   
8. Use the cotton-tipped applicator to clean areas that you can see. Do not clean deep in the canal with the applicators (you will only push exudate deeper into the canal!).
   
   
9. Repeat the process for the opposite ear.
   
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Applying medicine into the ear canal

Sounds easy....but isn't!

• Be sure to have your veterinarian show you the proper way to medicate the ears.
  
  
• Make sure the label for your pet's ear medication indicates how much medicine should be applied at each treatment and the intervals (frequency) for medicating the ears.
  
  
• For drops: pull the pinna (ear flap) up over the head and drop the medication into the lowest opening of the ear canal. Generally 7-9 drops are required to deliver medication into the deeper areas of the ear canal with a liquid medicine. Consult your veterinarian on doses to avoid overdosing with some medications.
  
  
• For ointments: pull the pinna (ear flap) up over the head and gently squeeze the desired amount of medication into the lowest opening of the ear canal. Gently massage the ear after application of the medicine.
  
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For specific questions about ear problems in your pet, consult your veterinarian.