Darin Dell, DVM, DACVD
Wheat Ridge Animal Hospital, Wheat Ridge, CO
Posted on 2018-10-09 in Dermatology
Patients with otitis externa generally present for head shaking, ear scratching, and odor from their ears. Pet owners may also notice purulent material coming from the ear canal(s), changes in their dog’s behavior, or whining and discomfort. Otoscopic exam typically reveals varying degrees of erythema, edema and debris. These changes can make visualizing the tympanic membrane very difficult or even impossible. Unless the patient is aggressive/dangerous you should try your best to see every tympanic membrane that enters your exam room.
- Otitis externa is most often a clinical sign of underlying skin disease, not a diagnosis in and of itself.
- Identifying and resolving / controlling the underlying cause is essential to long term success in otitis externa.
- Allergy is the most common cause of otitis externa in the canine
- Topical therapy is the most effective therapy for treating otitis externa
- Cytology (clean) – Plan (persuade, purge) – Recheck (re-engage)
Identifying the underlying cause of otitis externa can be difficult. The PSPP system can help you work through the potential causes and also make it easier to discuss otitis with your clients. PSPP stands for Primary, Secondary, Predisposing, Perpetuating. The Primary category includes things that can cause disease in a normal ear. The list includes: allergy, auto-immune disease, foreign objects, mass/polyps, endocrine dysfunction, immune mediated disease, and parasites. The most common primary problem I see is allergy, but in general practice you probably see a fair amount of ear mites and foreign bodies too. Whatever the primary factor, it has to be resolved or controlled before you are going to achieve lasting success. The Secondary category includes things that create disease in an abnormal ear. The secondary list includes: bacteria, yeast (malassezia), fungi, medication reactions, and over-cleaning. Because of the way we commonly communicate about otitis externa it is easy for our clients to misunderstand and think that bacteria or yeast are primary causes of otitis. Sometimes it helps to point out that ear canals are not sterile. There is a normal flora in the ear canal just like on the skin. Infections must be resolved but they are not the root cause. Predisposing factors are fairly simple to understand and are typically what most clients blame for ear disease. Predisposing factors are present prior to otitis but cannot by themselves cause otitis. This list includes: conformation, excess moisture, obstruction, systemic disease, and treatment effects. Sometimes it helps to reassure our clients that there are Cocker Spaniels without ear disease despite their floppy ears and Poodles without ear disease despite their excess ear hair. The last category, Perpetuating, is the one most often neglected in veterinary practice. Perpetuating 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, rupture of the tympanic membrane, and otitis media. I believe that the first three issues in the perpetuating category are most overlooked and least understood in private practice. 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 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 reestablished. 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 which could result in ear pruritus and trauma.
Treatment for 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 check list for any other disease. In most cases you can quickly rule out ear mites, foreign objects, and polyps. You might need to perform blood tests to look for endocrine disease if other suggestive signs are present. Similarly, you might need to perform skin biopsy to look for autoimmune or immune mediated disease if other supportive lesions are present. In the majority of cases you are not going to find any of the problems listed above in this paragraph. The majority of otitis externa in the canine is secondary to allergic dermatitis. In that case, the first question to ask yourself is whether the allergy is controlled or not. 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 un-treated then you will have more work to do. Not the least of which will be convincing the owner that their dog has allergies. Still, you may choose to focus initially on the otitis and address the allergy in two to four weeks. The first step toward treatment is otoscopic exam. You need to assess pain, pruritus, edema, erythema, constriction, and exudate as well as the tympanic membrane. Next you will need to perform ear swab cytology. It is best to collect exudate from both the horizontal and vertical portions of the ear canal. Obviously, you are checking for Malassezia, coccoid bacteria and rod shaped bacteria. But you are also looking for nuclear streaming, white blood cells, red blood cells, and evidence of biofilm. Bacterial culture from the ear canal may also be necessary depending on the situation. Ear cultures are not universally helpful for two reasons. First, you might culture normal flora. Second, MIC’s are usually based on serum levels of antibiotics. In the ear we are concerned about topical / direct exposure to the antibiotic. The essence is of the problem is that some antibiotics to which the bacteria are listed as “Resistant” will actually be “Sensitive.”
Now that you have performed an exam and evaluated cytology you have to choose a therapeutic plan. I want to stress that there isn’t one universal plan for otitis externa. We can’t group treatment into levels such as easy, moderate, and severe either. However, asking yourself the following six questions can help you make better treatment decisions.
- Is there an allergy and are you treating it now?
- How much debris is in the ear canal?
- How is the conformation of the ear canal?
- What type of infection is present?
- How much edema and erythema are present?
- How much pain and anxiety are present?
Now, in more detail:
- 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.
- 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 you will probably want a micellar solution or one with squalene. For mucoid exudate you will probably want a Triz EDTA product with Chlorhexidine.
- 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. Ointments are less likely to travel deep into a constricted or cobblestoned ear canal so you probably want a liquid medication.
- 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. Infection with rod shaped bacteria will also encourage you to use an ear wash with Triz EDTA. Most rod shaped bacteria are gram negative. Triz EDTA damages the gram negative membrane and forms channels which allow antimicrobials into the bacteria.
- How much edema and erythema are present? This will tell you what strength of steroid to use. Topical steroid therapy may be sufficient or you might need oral steroid therapy as well. If the ear canals are completely constricted then you will definitely need help from an oral steroid. Again, you have to know what ingredients are in the products on your shelf! Common steroid ingredients in otic medications, in order or potency are as follows:
- How much pain and anxiety are present? This will tell you if you need to prescribe additional pain relief or anti-anxiety medications. These medications are short term but can really help both the dog and the owner. This might require a prescription of Tramadol, Rimadyl or Xanax. Don’t underestimate the pain or anxiety related to ear infection! How many clients have told you that their dog runs away when they see the ear wash bottle or tube or ear ointment?
Photo credit: Modified and used with permission. By self – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1385225
About the author
Dr. Darin Dell completed two years of undergraduate studies at Iowa State University before being accepted to the University of Illinois College of Veterinary Medicine in 1997. He graduated with honors from the University of Illinois College of Veterinary Medicine in 2001.
Dr. Dell developed a love of dermatology while in veterinary school when he adopted a rough coat collie (Drifter) with food allergies. Dr. Dell worked in small animal general practice for six years and small animal emergency medicine for two years before beginning his residency with Animal Dermatology Clinic. He became a Diplomate of the American College of Veterinary Dermatology in 2012.