A Practical Approach to Diagnosing and Managing Ear Disease in Dogs

SERIES EDITOR Craig E. Griffin, DVM, DACVD Animal Dermatology Clinic, San Diego, California SERIES EDITOR Wayne S. Rosenkrantz, DVM, DACVD Animal Dermatology Clinic, Tustin, California

❯❯ Paul Bloom, DVM, DACVD, DAVBP (Canine and Feline) Allergy, Skin and Ear Clinic For Pets Livonia, Michigan

ntire books have been written on the subject of canine ear mendations for primary causes (e.g., parasiti- Edisease. Rather than attempt to present all the available cidal treatment, food trial) is beyond the scope of this article. information here, I am providing an overview of how I diag- Predisposing factors must also be addressed nose and manage ear disease in dogs. It is critical to appreciate if possible. Although predisposing factors do that ear disease is only a clinical problem (no more specific not cause ear disease, they increase the risk than pruritus)1 and that steps must be taken to prevent otitis for its development and may make successful treatment more difficult.1–4 Anatomic fac- externa from progressing to proliferative otitis. Box 1 summa- tors (such as the long pendulous ears of basset rizes step-by-step approaches to specific clinical scenarios. hounds), excessive moisture in the ears (from swimming), and iatrogenic trauma (plucking Identification of Primary Causes and hairs from the ear canals) are examples of pre- At a Glance Predisposing and Perpetuating Factors disposing factors. Identification and treatment of the primary Perpetuating factors do not cause otitis Identification of (underlying) cause(s) of ear disease are impor- externa, but clinicians often consider them to Primary Causes and tant to determining the appropriate manage- be the reasons for disease when the problem Predisposing and ment approach.1–4 The most common primary is that the primary cause has not been identi- Perpetuating Factors causes of otitis externa are: fied or treated. Even if the primary cause is Page E1 eliminated, perpetuating factors may cause Specific Scenarios: Hypersensitivities (atopy and cutaneous ad- the ear disease to continue. Examples of per- Step by Step verse food reaction); unilateral ear disease petuating factors include: Page E2 may be the only clinical sign of an underly- Diagnosis ing hypersensitivity Bacteria Page E3 Parasites (Otodectes and Demodex spp) Yeast (Malassezia pachydermatis) T r e a t m e n t Foreign bodies (e.g., grass awns) Progressive pathologic changes Page E4 Autoimmune or immune-mediated diseases Otitis media (e.g., pemphigus foliaceus) Undertreatment (dose or duration)—a very common problem aDr. Bloom discloses that he If the primary cause of otitis externa is not has received financial support from Novartis Animal Health addressed, the ear disease will likely recur; These factors must also be identified and and Pfizer Animal Health. however, a discussion of the treatment recom- treated or corrected. The treatment section of

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Acute and/or Infrequent Otitis Externa table 1 Patient Factors and Therapy Ascertain whether this is a first-time at Initial Presentation for Acute Otitis episode, a recurrence, or an unresolved previous infection (acute-on-chronic Patient Factor Therapy otitis). Unfortunately, differentiating between Only yeast present Azole (for miconazole, add 3 mL of dexamethasone sodium phosphate [4 mg/mL concentration] to 30 mL recurrence and unresolved infection is often of miconazole) difficult because of the lack of good follow- Cocci present ± rods Neomycin or gentamicin up, which emphasizes the importance of performing follow-up examinations on all Only rods present TrisEDTA + gentamicin otitis externa cases. The absence of clinical Dog is in pain Add systemic glucocorticoids ± analgesics (tramadol, 2–5 mg/kg bid–tid and/or acetaminophen with codeine signs is not synonymous with resolution [codeine, 2 mg/kg bid–tid]); do not mix systemic of disease. For dogs experiencing their first glucocorticoids and NSAIDs. episode of otitis, educate the owners about the Tympanic membrane not Add topical fluocinolone acetonide + dimethyl sulfoxide possible primary cause(s) and predisposing initially visualized (because of + oral glucocorticoids (prednisone, 0.50–0.75 mg/kg PO and perpetuating factors and outline the ear canal swelling) q12h for 10–14 days); recheck dog in 10–14 days workups that may be necessary.

Eliminate easily diagnosed primary table 2 causes (e.g., foreign bodies, parasites, Patient Factors and Therapy masses) and perform a thorough otoscopic at Recheck for Acute Otitis examination, including evaluation of the Patient Factor Therapy tympanic membrane. Tympanic membrane visible and Discontinue prednisone; continue other therapy Diagnose and treat secondary infection(s) swelling resolved and inflammation. My first line of treatment Tympanic membrane not visible Perform ear lavage, using a standard otoscope or, for inflammation is a topical glucocorticoid but swelling resolved preferably, a fiber-enhanced video otoscope with patient under general anesthesia ointment; I base other treatment choices on the patient factors outlined in Table 1. Tympanic membrane not visible Continue prednisone for another 10–14 days and recheck and swelling not resolved Recheck the patient after 7–14 days of If the ear canals are still narrowed at recheck, consider referring patient to a dermatologist before treatment. This is critical in the proper contemplating ear ablation management of ear disease (Table 2). Continue treatment for 7–14 days beyond resolution of clinical signs. table 3 Patient Factors and Therapy at Presentation for Chronic Otitis Chronic Otitis (Recurrent and/or Patient Factor Therapy Unresolved) Only yeast present Depending on what products have already been used, switch to 1% clotrimazole, 1% miconazole, or Follow the steps outlined for acute otitis compounded 2% ketoconazole lotion externa. Add topical steroids either by mixing dexamethasone Identify and treat the primary cause, any sodium phosphate to a final concentration of 0.1% predisposing factors (if possible), and with current product or by concurrent use of a product containing fluocinolone acetonide perpetuating factors. If drops are dispensed Cleanse ear Treatment (Table 3) should last for a minimum of 30 days. In patients with severe ear inflammation, use a mild cleanser Cocci ± rods TrisEDTA (with or without 0.15% chlorhexidine) + either Chronic Pseudomonas Infections gentamicin or polymyxin B (depending on which antibiotics have already been used). Note: I rarely use These infections are especially challenging, and fluoroquinolones in these cases unless the infection a discussion of the required therapy is beyond fails to respond to therapy. This means a follow-up the scope of this article. examination is essential.

E2 Compendium: Continuing Education for Veterinarians® | May 2009 | CompendiumVet.com this article generally addresses perpetuating To avoid missing abnormalities, the otic factors; however, if the primary cause is not examination should be performed systemati- identified and managed, treatment of the per- cally, beginning with the pinna. Any alope- petuating cause will not eliminate ear disease. cia, erythema, ulceration, crusting, scaling, or swelling should be noted and the ear canals Diagnosis palpated to identify pain, calcification, or History thickening. External ear disease is a form of skin disease, Because the presence of pain can limit and, as with any skin problem, a detailed his- proper evaluation of the ear canal, the dog tory must be gathered. History taking for an should be evaluated for pain and sedated as otic problem is similar to that for any general needed before the otoscopic examination is medicine problem. Two key points to discuss performed. The presence, degree, and loca- with the pet owner are the age of the dog tion of inflammation, ulceration, and prolifera- when ear disease first appeared and whether tive changes of the ear canals should be noted. the dog has been treated for skin or ear dis- Likewise, it should be noted whether the tym- ease in the past. panic membrane is visible and, if so, whether Owners should be questioned about the it appears normal. A ruptured or abnormal first episode of ear disease in the dog’s life (bulging, necrotic, or thickened) tympanic and not just when the current episode was first membrane may indicate the presence of otitis noticed. Determining the dog’s age at onset media2,3,5; however, the tympanic membrane helps narrow the possible primary causes of may thicken in cases of chronic otitis externa otitis externa. For example, if the first epi- without the presence of otitis media. If the QuickNotes sode developed when the dog was between tympanic membrane cannot be visualized, an 6 months and 5 years of age, atopic dermati- attempt should be made to identify the reason. If the primary cause tis or cutaneous adverse food reactions would Potential causes include a ruptured membrane, of ear disease is not be a likely cause; however, if the dog was swelling or debris in the ear canal, or a false identified and man- older than 7 years when it first developed oti- middle ear (a condition in which the tympanic aged, treatment of tis externa, cutaneous adverse food reactions membrane is diseased and flaccid or partially the perpetuating would still be a reasonable cause, but atopic forced into the tympanic cavity and bulla; the cause will not elimi- dermatitis would be much less likely. membrane is present but out of view). nate the disease. Another goal of the history taking is to iden- The next step is to determine whether con- tify whether ear disease is a seasonal problem; current middle or inner ear disease is present. if so, atopic dermatitis is the more likely cause. Because of the close association of sympa- It is also important to ask about any therapy thetic and parasympathetic nerves with the used previously, the outcome of treatment, middle ear, Horner’s syndrome, keratocon- and how the outcome was determined. If the junctivitis sicca, and facial nerve paralysis may owner reports that otitis externa resolved, be be present in cases of otitis media. Conduction sure to establish whether this was confirmed (not neurologic) deafness may also be present. by a follow-up otoscopic examination or is Inner ear disease may cause peripheral ves- merely the owner’s observation that clinical tibular signs such as head tilt (to the affected signs resolved (as opposed to resolution of side), circling (to the affected side), and nys- infection). If resolution of previous ear disease tagmus (with the fast phase away from the was not confirmed by a veterinary examination, affected side). establishing seasonality becomes impossible. As a time saver, some veterinarians have samples collected for ear cytology before they Clinical Examination perform the clinical examination, but I believe After a thorough history has been obtained, a that this practice makes it difficult to evaluate complete dermatologic examination should be the true appearance of the ear canal. In addi- performed. Dogs with ear disease frequently tion, debris may be pushed and compacted have concurrent skin disease that also needs to into the horizontal canal, thereby limiting be identified and treated. The pattern of gener- visualization of the tympanic membrane. I rec- alized skin disease can help identify an appro- ommend collecting samples after completing priate differential diagnosis for the ear disease. the otoscopic examination.

CompendiumVet.com | May 2009 | Compendium: Continuing Education for Veterinarians® E3 Laboratory Tests part of the treatment protocol. I find that many Laboratory tests are a necessary component of owners have enough trouble just medicating the proper diagnostic workup for canine ear the ear and that adding ear cleaning decreases disease. Cytologic examination of a roll swab compliance. This experience is supported by sample of any otic exudate—including quan- a recent study11 in which dogs were assigned tification of the number and type of bacteria, to one of two ear cleanser groups (reference yeast, and inflammatory cells present—is indi- cleanser and test cleanser); the authors noted cated.4,6 In my opinion, any organism seen that 38.1% of dogs in the reference cleanser on ear cytology in a dog with signs of otitis group and 37.5% of dogs in the test cleanser externa is potentially significant. A recent study group exhibited “a moderate to marked avoid- reported that cytologic samples from normal ance reaction.”11 The reaction was attributed dogs have ver y few yeast or cocci and no rods.7 to animal irritability or to the cleanser itself. Because small numbers of yeast or bacteria An additional drawback to ear cleaners is that can cause a hypersensitivity reaction, I believe many have a low pH, leading to discomfort if that treatment is warranted in such cases if the used in an inflamed ear and decreasing the dog shows clinical signs. effectiveness of certain antibiotics (aminogly- I do not routinely conduct bacterial culture cosides and fluoroquinolones). and susceptibility testing, but if such tests are used, they should always be done in Topical Treatment conjunction with cytology.8,9 I submit sam- Topical therapy is the foundation of treating ples for bacterial culture when proliferative otitis externa. Most topical products contain a QuickNotes changes are present along with neutrophils combination of glucocorticoids and antibacterial and rods on cytology and the dog has failed and/or antifungal agents. I prefer otic ointments Topical therapy to respond to appropriate empirical antimicro- because they usually contain mineral oil, which is the foundation bial therapy or in cases in which cocci bacteria has ceruminolytic-like properties and seems of treating otitis persist despite appropriate therapy. Methicillin- to keep the ear clean during treatment with- externa. resistant Staphylococcus spp exist in veterinary out additional cleaning. Also, I think that the medicine and should be considered in resis- drugs get to the region of the tympanic mem- tant cases.10 Skin biopsies may be necessary brane better with ointments than with liquid depending on the differential diagnosis. formulations (although this may be related more to volume than formulation). Treatment I commonly use the following agents: Ear Cleaning Ear cleaning is the first step in the treatment Aminoglycosides (neomycin or gentamicin): of otitis externa. Cleaning agents contain These have good activity against gram-posi- substances that soften and emulsify wax, as tive and gram-negative bacteria; gentamicin well as lipids that are helpful in removing has better activity than neomycin against otic debris. Removing this debris is important gram-negative organisms. because it may be inflammatory (e.g., bacterial Enrofloxacin:This agent is effective against toxins) and interfere with the effectiveness of gram-positive and gram-negative organisms. topical agents. I clean the patient’s ears in the However, I reserve it for primarily culture- clinic using a bulb syringe or by retrograde resistant gram-negative infections. tube flushing (with the patient anesthetized). I Polymyxin B: This is one of the more effec- may delay cleaning if the ears are very swol- tive antibiotics against gram-negative organ- len or painful, in which case I use topical— isms, especially Pseudomonas spp. and possibly systemic—glucocorticoids for 10 Silver sulfadiazine: This agent is effective to 14 days to decrease the swelling and pain. against gram-negative organisms, especially Tramadol and/or acetaminophen with or with- Pseudomonas spp; it is a thick cream that out codeine may also be dispensed for pain. must be mixed with equal parts of water or NSAIDs are contraindicated if systemic ste- mineral oil to be instilled in the ear. roids are used. Antifungal agents: Nystatin (mixed efficacy Unlike some dermatologists, I usually do against Malassezia spp), clotrimazole 1%, micon- not instruct owners to clean their dogs’ ears as azole 1%, and ketoconazole 0.1% are effective.

E4 Compendium: Continuing Education for Veterinarians® | May 2009 | CompendiumVet.com When gram-negative organisms are the absorbed and may lower thyroid hormone con- only (or primary) organisms found on cytol- centrations,13,14 elevate liver enzymes, and even ogy, EDTA should be added to the treatment. cause polyuria/polydipsia.15 Topical EDTA solution has a direct bactericidal action against gram-negative bacteria.11,12 Systemic Agents EDTA products that contain 0.1% keto- I use systemic antibiotics or antifungal agents conazole are available and can be used if a only in patients that test positive for bacteria Malassezia sp is concurrently present; how- or Malassezia spp on cytology and that have ever, I have two concerns about such com- (1) evidence of otitis media or (2) severe pro- bination products: (1) whether resistance to liferative changes in the ear canals that failed ketoconazole will develop with long-term to respond to topical treatment. Empirical use and (2) their alkalinizing effect on the ear choices for cocci include cephalosporins, when it is actually desirable to acidify the ear amoxicillin–clavulanic acid, and clindamy- canal while treating Malassezia otitis. cin. Empirical choices for rods include cepha- Successful treatment of otitis externa fre- losporins, amoxicillin–clavulanic acid (dose quently requires topical glucocorticoids, and I tid versus bid for gram-positive organisms), have seen cases resolve once topical glucocor- and potentiated sulfonamides. I reserve fluo- ticoids were added to the treatment regimen. roquinolones for culture-proven resistant Glucocorticoids are antipruritic and antiinflam- gram-negative rods because the overuse of matory, and they decrease glandular secretions fluoroquinolones has been associated with (cerumen), pain, swelling, and glandular hyper- the emergence of antibiotic-resistant bacteria. plasia—all properties that can help restore the The antifungal agents I use include ketocon- QuickNotes normal barrier function to the epithelium of the azole (5 to 10 mg/kg sid, given with food to ear canal. When using topical glucocorticoids, enhance absorption), fluconazole (10 mg/kg Successful treat- it is best to begin with the most potent form; sid), and itraconazole (5 mg/kg sid). ment of otitis however, if long-term therapy is needed, a less I dispense systemic glucocorticoids (predni- externa frequently potent agent should be used. The following sone, 0.50 to 0.75 mg/kg q12h for 7–14 days) if requires topical topical steroids are listed in decreasing order the ear canals are edematous or stenotic. The glucocorticoids. of potency: mometasone, betamethasone, fluo- appearance of the ear canals at the 7- to 14-day cinolone, triamcinolone, dexamethasone, pred- recheck dictates whether the prednisone is nisolone, and hydrocortisone. It is important to continued for another 7 to 14 days at the same remember that topical steroids are systemically or a decreased dose or is discontinued.

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