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<\/a>FIGURE 1. Pathologic cycle for chronic otitis externa.<\/p><\/div>\n
Primary disorders initiate the inflammatory process within the ear canal and alter the aural environment, allowing secondary complicating factors, such as infections, to develop. The primary cause may be very subtle and often is unrecognized by the owner or even the veterinarian until a secondary complicating factor arises. Most cases have a primary cause. In a retrospective study3<\/sup> of 100 dogs with acute (37%) and chronic-recurrent (63%) otitis externa, the most common primary cause of otitis was allergic dermatitis (43\/100 dogs; Figure 2<\/strong>), followed by grass awns (12\/100) and otoacariasis (7\/100). No primary factor could be identified in 32 of 100 cases. Allergic and hormonal diseases can be associated with unilateral or bilateral otitis, but bilateral otitis is more common. Foreign bodies, neoplasia, and polyps are usually associated with unilateral otitis; however, bilateral problems have been reported.3<\/sup><\/p>\n FIGURE 2. Otitis externa secondary to allergies.<\/p><\/div>\n Secondary causes occur in combination with primary causes or predisposing factors. The most common secondary causes are infections.1\u20133<\/sup> Generally, secondary causes of otitis externa are easy to eliminate once identified. When they are chronic and difficult to treat, it is usually because primary causes or perpetuating factors have not been adequately addressed.<\/p>\n Predisposing factors alone do not cause otitis externa, but they facilitate inflammation by permitting the external ear canal microenvironment to be altered, thereby allowing pathogenic or opportunistic bacteria or yeast to become established.1,2<\/sup> In conjunction with primary or secondary causes, these factors become a significant problem. It is important to eliminate as many of these factors as possible while realizing that some, such as ear conformation, cannot be changed.<\/p>\n Perpetuating factors sustain and aggravate the inflammatory process and prevent resolution of, or worsen existing, otitis externa.1,2<\/sup> Once present, they accentuate or permit the development of secondary causes, such as infection, by providing favorable environments and microscopic niches. In many cases, perpetuating factors prevent the resolution of otitis externa when treatments are directed only at primary and secondary causes. These factors may be subtle at first but can develop into the most severe component of chronic ear disease. They are not disease specific and are most commonly seen in chronic cases. Perpetuating factors are the most common reasons for surgical intervention.<\/p>\n A detailed and complete history is essential to help investigate the underlying cause and associated factors.<\/p>\n The ear examination allows the clinician to evaluate the amount and type of exudate in the ear canals; estimate the amount of otic inflammation; identify hyperplasia (along with palpation of the horizontal and vertical ear canals), masses, and foreign bodies; and determine the status of the tympanic membrane (eg, changes in structure or rupture). These findings help in determining whether medical management or surgery (total ear canal ablation with or without bulla osteotomy) is the best treatment. If the patient\u2019s ears are painful, sedation or general anesthesia may be necessary before otoscopic examination.<\/p>\n Regular (ie, handheld) otoscopes should have a strong light and power source. If available, fiberoptic video-enhanced otoscopy (eg, video-otoscope [Figure 3<\/strong>]) is extremely helpful in improving diagnosis and therapy because it not only allows visualization of fine details that may not be seen with regular otoscopes but also facilitates proper flushing of the ears, determination of disease extent, and discovery of indications for additional diagnostics and treatment (eg, myringotomy, otitis media). However, because of the expense to purchase and maintain this equipment, referral to a dermatologist may be necessary<\/p>\n FIGURE 3. Video otoscopic examination.<\/p><\/div>\n Performing a complete physical examination, including a detailed dermatologic examination, can help in identifying an underlying or primary cause. In patients with otitis media and\/or otitis interna, concurrent neurologic abnormalities (eg, facial paralysis, nystagmus, ataxia, head tilt) may be present; therefore, a detailed neurologic examination is indicated.<\/p>\n Otic cytology establishes whether an infection is present in the ears and assists with the selection of topical therapy. Cytologic samples should be collected gently from the horizontal canal. Exudate samples can be smeared onto a slide with mineral oil to look for mites. The most common type of coccoid bacteria found in the ears of dogs with otitis externa is Staphylococcus<\/em> pseudintermedius<\/em>, and the most common type of rod bacteria is Pseudomonas aeruginosa<\/em>.1\u20136<\/sup> Malassezia<\/em> species are also common organisms1\u20135<\/sup> (Figure 4<\/strong>).<\/p>\n It is important to describe the presence of any inflammatory or neoplastic cells as well as quantify each type of bacteria and yeast per oil immersion field (100\u00d7) to establish severity and allow monitoring at future visits. In one study, mean bacterial counts per high-power dry field of \u226525 and mean Malassezia<\/em> counts per high-power dry field of \u22655 were considered abnormal in the external ear canals of dogs.5<\/sup> Leukocytes are always abnormal, and bacteria in the presence of leukocytes signal infection.<\/p>\n FIGURE 4. Cytologic appearance of Malassezia species (high-power oil immersion field 100\u00d7 objective).<\/p><\/div>\n Culture and sensitivity (C\/S) may be useful in identifying specific otic pathogens and assisting with treatment decisions; however, a limitation is that antibiotic sensitivity data reflect the serum level needed systemically and may not predict true susceptibility of otic topical antibiotics.<\/p>\n Typical indications for bacterial C\/S include the following1\u20134<\/sup>:<\/p>\n FIGURE 5. Cytologic appearance of degenerate neutrophils and cocci (high-power oil immersion field 100\u00d7 objective).<\/p><\/div>\n FIGURE 6. Cytologic appearance of degenerate neutrophils and rods (high-power oil immersion field 100\u00d7 objective).<\/p><\/div>\n Cytology should always be performed before aerobic C\/S to assist with interpretation of results and identification of concurrent problems. In one study,7<\/sup> however, cytologic results agreed with culture results only 68% of the time. The same study7<\/sup> showed that different bacterial organisms were isolated from the same ear in 20% of the cases; therefore, it is important to remember that ear cytology or a single swab submitted for C\/S may not reveal the total population of organisms truly present in the ear canal. This might explain why, in some cases, sensitivity results (in vitro) and response to topical therapy (in vivo) do not always correlate. This study poses questions regarding the true benefit of C\/S for selecting antimicrobials for otic infections; therefore, clinicians should be careful and critical when interpreting otic cytologic and culture results.<\/p>\n Clinicians should sample the middle ear separately if otitis media is confirmed when the tympanic membrane is intact. The types and sensitivity pattern of bacteria isolated from the middle ear may differ from those of bacteria isolated from the external canal.8<\/sup> In one study, different organisms were cultured from the middle and external ear, and even when Pseudomonas<\/em> species were cultured twice from the same ear, different strains were suspected on the basis of the sensitivity pattern exhibited.8<\/sup> Culture results should be interpreted with caution because mixed bacterial flora and light commensal and contaminant bacteria might be present and may not be relevant as pathogens.<\/p>\n Dogs with chronic, recurrent, and severe otitis and those with neurologic signs (eg, vestibular signs or facial nerve paralysis), para-aural swelling, or pain on opening the mouth usually require diagnostic imaging to help identify contributing problems, such as middle ear disease (eg, otitis media, neoplasia) and otitis interna, that cannot be identified with regular otoscopy (Table 2<\/strong>). Patients with an apparently normal tympanic membrane may also have otitis media. Although otitis interna is uncommon in dogs with chronic otitis externa, otitis media is common, with a reported incidence of 50% to 88.9%.8<\/sup> In dogs with recurrent ear infections of 6 months or longer, up to 89% may have concurrent otitis media; about 70% have an intact but abnormal tympanic membrane.8<\/sup><\/p>\n This procedure is very helpful not only as a diagnostic tool but also as part of the treatment plan.9<\/sup> A short course (2 to 3 weeks) of an anti-inflammatory dose of oral and\/or topical glucocorticoids may be needed before deep ear flush in order to decrease inflammation and stenosis of the ear canals. This procedure should be performed under general anesthesia so that the ear can be completely cleaned and the ear canal and tympanic membrane examined. Anesthesia also allows the placement of an endotracheal tube, which precludes the aspiration of fluids that may pass through the middle ear into the auditory tube and then into the posterior pharynx. Ideally, computed tomography of the tympanic bulla should be performed before the flush to stage ear disease and help make the decision to perform myringotomy if otitis media is present.<\/p>\n Several techniques to clean and flush the ears exist.9 <\/sup>Follow-up visits after flushing are very important to monitor response to therapy and evaluate the status of the tympanic membrane. If myringotomy is performed, the tympanic membrane usually heals within 30 days after the procedure. Deep ear flush and myringotomy are best performed by experienced practitioners with a video-otoscope; therefore, referral to a dermatologist might be ideal. For a description of one deep ear flush technique, please see Deep Ear Flush: Step by Step<\/a>.<\/p>\n There are 5 general goals of otitis externa treatment:<\/p>\n In most cases of otitis externa, topical therapy alone is sufficient and is preferred when possible. In contrast, chronic, severe cases of otitis externa and otitis media often require additional systemic therapy. The amount of medication applied is important. Generally, the recommendation is to use about 0.5 to 1 mL (10 to 20 drops) per ear, depending on the size of the dog.<\/p>\n Ear Cleaners<\/em><\/strong><\/p>\n Ear cleaners should be used at home as part of most treatment protocols initially (once daily to twice weekly depending on the severity of the otitis and amount of discharge present) and as maintenance therapy (usually once to twice weekly) to help prevent future infections once the otitis and infection are resolved.10\u201313<\/sup> Removal of debris and purulent material greatly improves the efficacy of topical antimicrobials, especially aminoglycosides and polymyxin B. However, overcleaning should be avoided because it can contribute to maceration and ear disease. Clients should be educated on the proper technique to clean the ears and to avoid using cotton balls and cotton swabs inside the ears. Available ear cleaners include drying agents, antiseptics, ceruminolytics, and combination products.<\/p>\n For a table listing these cleaners, please see Ear Cleaners for Use in Patients with Chronic Otitis<\/a>.<\/p>\n Acaricidals<\/em><\/strong><\/p>\n Many different acaricidal products may be used to treat infections caused by Otodectes cynotis<\/em> (ear mites) and, less commonly, Demodex<\/em> species.10\u201313<\/sup> Veterinary acaricidal products for label and extralabel use include ivermectin, milbemycin, selamectin, fipronil, monosulfiram, permethrin, piperonyl butoxide, pyrethrins, thiabendazole, and rotenone.1<\/sup><\/p>\n Antimicrobials<\/em><\/strong><\/p>\n It is important to always use higher volumes or concentrations of topical antibiotics because they may prove efficacious, even when resistance has been suggested on a susceptibility panel. With topical drugs, concentrations 100 to 1000 times superior to the minimum inhibitory concentration may be reached.13<\/sup> Antimicrobials should be used until 1 week past negative cytologic results for most bacterial and\/or yeast otic infections.10-13<\/sup> Twice-daily applications are usually recommended. For Pseudomonas<\/em> (Figure 7<\/strong>) and multidrug-resistant infections, I recommend treating the patient until 1 week past negative cytologic and culture results.<\/p>\n FIGURE 7. Chronic Pseudomonas<\/em> otitis.<\/p><\/div>\n Antibacterial agents:<\/strong> These products are indicated when infection is present and cleansing solutions are insufficient. Most topical antibacterial products also contain glucocorticoids and antifungals.<\/p>\n Glucocorticoids<\/em><\/strong><\/p>\n Numerous topical preparations of variable potencies are available for use in the external ear canal.10\u201313<\/sup> The frequency of use varies from q6h to q24h, depending on the product and the severity of the otitis. Most cases of chronic otitis externa benefit from topical glucocorticoids. Glucocorticoids have antipruritic, anti-inflammatory effects and decrease exudation and swelling, thereby helping to reduce pain and discomfort. In addition, they cause sebaceous atrophy and decrease glandular secretions. Glucocorticoids may reduce scar tissue and proliferative changes, which helps to promote drainage and ventilation. Most ear products contain various combinations of glucocorticoids, antibiotics, antifungals, and parasiticides.<\/p>\n New Food and Drug Administration\u2013Approved Single-Dose Antimicrobial and Steroid Otic Solutions<\/em><\/strong><\/p>\n Two new veterinarian-administered products containing florfenicol, terbinafine, and mometasone furoate (Claro, bayerdvm.com<\/strong><\/a>) and florfenicol, terbinafine, and betamethasone acetate (Osurnia, osurnia.com<\/strong><\/a>) are indicated as single-dose treatments for canine otitis externa associated with susceptible strains of yeast (Malassezia pachydermatis<\/em>) and bacteria (S pseudintermedius<\/em>). The duration of effect is 30 days for Claro and 7 days for Osurnia. Ears should not be cleaned at home after application. The recommendation is for use in the clinic after ear cleaning, and only with intact tympanic membranes. These are great options for patients that do not allow topical therapy at home and to improve compliance, with potential benefit for acute or mild otitis cases. Their use in chronic severe otitis cases is limited because severe hyperplasia and stenosis preclude ear cleaning and evaluation of the tympanic membrane.<\/p>\n Indications for systemic therapy include the following:<\/p>\n Antibiotics<\/em><\/strong><\/p>\n These drugs may be used in animals with otitis media, moderate or marked proliferative changes with suspected otitis media, or no response to appropriate topical therapy and cleansing. I usually recommend C\/S before a systemic antibiotic is selected. Usually, higher doses are recommended to achieve good penetration in the middle ear. Treatment duration may vary; however, I usually treat for 1 month after resolution of clinical signs and healing of the tympanic membrane (from spontaneous perforation or myringotomy). Fluoroquinolones may be prescribed when Pseudomonas<\/em> species, other relevant gram-negative organisms, or very resistant gram-positive bacteria are isolated and susceptibility is confirmed after culture. Higher doses than usually recommended may be needed.<\/p>\n Oral fluoroquinolones that may be used include enrofloxacin (Baytril) at 10 to 20 mg\/kg q24h, marbofloxacin (Zeniquin, zoetisus.com<\/strong><\/a>) at 5 to 10 mg\/kg q24h, or orbifloxacin (Orbax, merck-animal-health-usa.com<\/strong><\/a>) at 10 mg\/kg q24h. Ciprofloxacin should be avoided in dogs because oral absorption is inconsistent and low (58.4%) with oral tablets,15<\/sup> potentially leading to inefficacy and bacterial resistance. In rare cases, injectable antimicrobials, such as aminoglycosides, carbapenems, and ceftazidime sodium, may be required to treat multidrug-resistant otitis cases. Potential side effects with these therapies need to be considered. Referral of these cases to a dermatologist should be considered, particularly when treatment options are limited.<\/p>\n Antifungals<\/em><\/strong><\/p>\n Antifungal agents can sometimes be used in severe cases of Malassezia<\/em> otitis or cases with poor response to topical agents alone. Oral antifungals commonly used include ketoconazole (Nizoral, nizoral.com<\/strong><\/a>), fluconazole (Diflucan, pfizer.com<\/strong><\/a>), and itraconazole (Sporanox, janssen.com<\/strong><\/a>). All are dosed at 5 to 10 mg\/kg q24h or q12h (divided). Terbinafine (Lamisil, lamisilat.com<\/strong><\/a>) may also be used at 30 mg\/kg q24h.<\/p>\n Glucocorticoids<\/em><\/strong><\/p>\n Glucocorticoids are usually indicated in cases of markedly inflamed and painful otitis with chronic pathologic changes, such as marked hyperplasia and stenosis of the canal. Oral anti-inflammatory dosages of prednisone or prednisolone (0.5 to 1 mg\/kg q24h) can be used initially and then tapered to the minimum alternate-day dosage that controls the clinical signs. I typically recommend oral glucocorticoids for cases of Pseudomonas<\/em> otitis and for dogs that have undergone deep ear flushing. Oral glucocorticoids can also be helpful to reduce pain and discomfort, particularly a few days before the owners clean and medicate the ears. I often combine opioids, such as oral tramadol at 2 to 4 mg\/kg q84 to q12h, with oral glucocorticoids in severely painful cases. When longer-term treatment is expected, alternate-day glucocorticoid therapy may be indicated, with careful monitoring for adverse effects.<\/p>\n<\/a><\/p>\nPrimary Causes<\/h3>\n
<\/a>Secondary Causes<\/h3>\n
Predisposing Factors<\/h3>\n
Perpetuating Factors<\/h3>\n
Important Diagnostic Steps<\/h2>\n
History<\/h3>\n
Otic Examination<\/h3>\n
<\/a>Physical Examination<\/h3>\n
Otic Cytology<\/h3>\n
<\/a>Bacterial Culture and Sensitivity<\/h3>\n
\n
<\/a><\/a>Diagnostic Imaging Techniques<\/h3>\n
<\/a><\/p>\nDeep Ear Flushing<\/h3>\n
Treatment<\/h2>\n
\n
Topical Therapy<\/h3>\n
<\/a>\n
\n
Systemic Therapy<\/h3>\n
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