Straight-up sewer ear: How to improve your outcome in otitis externa cases

October 7, 2016
Adrienne Wagner, Content Marketing Director

The clinical presentation of gnarly otitis externa cases makes it difficult to even see that tympanic membrane. Ask yourself these questions before you tackle your next case, and arrive at a diagnosis and treatment plan swiftly.

[Sniff.] Ah, yes, reminds me of Paris. Imagine you're strolling down a cobblestone street in Paris. The air is scented with coffee and the aroma of baking bread. Sharply dressed Parisians wander past. You turn the corner, and all the sudden you're assaulted … with the obnoxious odor of the sewer below your feet.

And just like that, you're back to reality. Oh, how you know that smell. How many times have you heard, "My dog's ears just stink. What is that?" Or, "My puppy's ears have dark, crumbly stuff in them. What should I do?" What about, "My dog has been rubbing his ears on the carpet. Why is he doing that?" Yup, you've heard it all.

Here's looking at you, tympanic membrane

Patients with otitis externa generally present for head shaking, ear scratching and odor from their ears. Their owners might notice purulent material coming from the ear canal, changes in their dogs' behavior or whining and discomfort. Your otoscopic exam typically reveals varying degrees of erythema, edema and debris.

These changes can make visualizing the tympanic membrane very difficult or even impossible, says Darin Dell, DVM, DACVD, of the Animal Dermatology Clinic in Indianapolis, Indiana. But unless the patient is aggressive or dangerous, you should try your best to see every tympanic membrane that enters your exam room, he says. Don't be afraid to sedate pets if necessary to clearly visualize the ear canal and tympanic membrane. At a recent CVC, Dr. Dell outlined key points to remember when diagnosing otitis externa, and questions to ask yourself before pursuing a treatment plan.

Otitis externa, real quick

1. Otitis externa is most often a clinical sign of underlying skin disease, not a diagnosis in and of itself.

2. Identifying and resolving or controlling the underlying cause is essential to long-term success in otitis externa.

3. Allergy is the most common cause of canine otitis externa.

4. Topical therapy is the most effective therapy for treating otitis externa.

5. Remember CPR

C: Perform cytology, clean the ear

P: Plan your treatment, persuade the client to treat, purge the ear of debris

R: Recheck the ear after treatment to make sure the infection has resolved, re-engage if you still see a problem

Round up the usual suspects

Identifying the underlying cause of otitis externa can be difficult. Try using the PSPP system (that is, primary factors, secondary factors, predisposing factors and perpetuating factors) which can help you work through the potential causes and also make it easier to discuss otitis with your clients.

Primary factors, or things that cause disease in a normal ear, are usually allergy, autoimmune disease and parasites. Secondary factors include things that create disease in an abnormal ear. This means bacteria, yeast (Malassezia species), fungi, medication reactions and over-cleaning.

It's easy for clients to misunderstand veterinarians when they begin to explain otitis externa and to think that bacteria or yeast are primary causes, says Dr. Dell. His tip? Sometimes it helps to point out that ear canals are not sterile. There is normal flora in the ear canal just like on the skin.

Predisposing factors are fairly simple to understand and are typically what most clients blame for ear disease. According to Dr. Dell, predisposing factors are present prior to otitis but cannot by themselves cause otitis. This list includes conformation, excess moisture (let's say from swimming), systemic disease and treatment effects. Another tip: It helps to reassure clients that there are cocker spaniels without ear disease despite their floppy ears and poodles without ear disease despite their excess ear hair.

Perpetuating factors are most often neglected in veterinary practice, says Dr. Dell. These factors occur as a result of the otitis and increase the likelihood of another infection. These factors are excess cerumen production, altered epithelial migration, edema of the ear canal, tympanic membrane rupture and otitis media.


Perpetuating factors: A closer look

Excess cerumen production occurs any time there is inflammation in the ear canal. The body's response is to make more cerumen in an attempt to push out whatever is happening. Unfortunately, this excess cerumen can be a great growth medium for yeast and bacteria.

Cerumen production can continue to be excessive for several weeks after the infectious component of the otitis initially resolves. For this reason, it is beneficial to continue ear cleaning even after the ear infection has resolved.

Altered epithelial migration also develops during otitis externa. Normal otic epithelial migration starts at the tympanic membrane and marches distally out the aural orifice. This too is designed to help move debris out of the ear canals. However, inflammation within the canal disrupts this process, resulting in build-up of debris in the canal. Altered epithelial migration is another reason why stenotic ears and cobblestone ears demonstrate wax build-up. Again, it is necessary to continue ear cleaning until this process is re-established.

Edema in the ear canal is at least a problem you can see through the otoscope. But the importance of edema is often underestimated. Edema will also trap cerumen, which can potentially lead to a better environment for bacteria or yeast growth. Edema can also cause discomfort and pain that could result in ear pruritus and trauma.

Onward to treatment

Treatment of otitis externa starts with the PSPP system. In most cases, you can run through the PSPP list in your mind just like you would a checklist for any other disease, Dr. Dell says. 

The majority of otitis externa in dogs is secondary to allergic dermatitis. If the allergy is generally well controlled and the otitis externa is due to a flare or a dietary indiscretion, then resolving the problem will be easier. Well-controlled allergy patients may still have one or two episodes of otitis externa each year.

If the allergy is unknown or untreated, then you will have more work to do, says Dr. Dell-not the least of which will be convincing the owner that his or her dog has allergies. Still, you may choose to focus initially on the otitis and address the allergy in two to four weeks.


You better have a plan

Dr. Dell stresses that there isn't one universal plan for otitis externa. We can't group treatment into levels such as easy, moderate and severe, either. Dr. Dell recommends asking yourself the following six questions:

1.Is there an allergy and are you treating it now? You may not treat allergy at the first visit for otitis externa. But you should at least start the conversation about allergy.

2. How much debris is in the ear canal? This will help you decide what type of cleaner to use and how often. For thick sticky wax Dr. Dell recommends a micellar solution or one with squalene. For mucoid exudate Dr. Dell says to try a Tris-EDTA product with chlorhexidine.

3. How is the conformation of the ear canal? Is it constricted? Cobblestoned? This too will help you decide what type of ear wash to use and whether to use a topical medication that is a gel, ointment or liquid. The more the canal is constricted, the more you need a wash that is better at dissolving cerumen, says Dr. Dell. Ointments are less likely to travel deep into a constricted or cobblestoned ear canal, so a liquid medication will likely work best.

4. What type of infection is present? This will help you pick a topical treatment. The side note is that you have to know what drugs are in the products on your shelf, says Dr. Dell. Infection with rod-shaped bacteria should encourage you to use an ear wash with Tris-EDTA. Most rod-shaped bacteria are gram negative. Tris-EDTA damages the gram-negative membrane and forms channels that allow antimicrobials into the bacteria.

5. How much edema and erythema are present? This will tell you what strength of corticosteroid to use. Topical corticosteroid therapy may be sufficient or you might need oral therapy as well. If the ear canals are completely constricted, then you will definitely need help from an oral corticosteroid. (Remember when Dr. Dell said to know what's on your shelf?)

6. How much pain and anxiety are present? This will tell you if you need to prescribe additional pain relief or anti-anxiety medications, says Dr. Dell. These medications are short-term but can really help both the dog and the owner. This might require a prescription of tramadol, carprofen or alprazolam. Dr. Dell's takeaway? Don't underestimate the pain or anxiety related to ear infection! After all, how many clients have told you that their dogs run away when they see the ear wash bottle or tube or ear ointment?

So, here's to solving more of those stinky sewer ears. If not, well, we'll always have Paris …

For more on otitis, check out the Veterinary Medicine Essentials, the dvm360 otitis management toolkit and our collection of otitis and dermatology client handouts.