Dr Martin Briggs B.Sc, B.V.Sc, M.Sc(Med), FRCVS, Registered Specialist In Veterinary Dermatology 028 316 2297 firstname.lastname@example.org
Reviewed by Dr Heidi Schroeder
Otitis externa (Fig 1), inflammation of the external ear canal, is one of the most commonly diagnosed skin conditions in dogs. There are a number of predisposing factors which render individual pets susceptible to chronic and recurrent otitis. Otitis media is inflammation of the middle ear.
Otitis externa is usually easily recognised by the clinician, while otitis media may be less apparent. It is important to manage otitis externa thoroughly in order to prevent the development of otitis media.
There is no recognised sex distribution for otitis externa. Young animals may be more commonly affected. There are clear breed predispositions for otitis, which directly reflect the breed predispositions for skin disease (e.g. allergic skin disease in retrievers and terriers, food allergies in German Shepherd dogs ). The most common historical findings are headshaking and aural pruritus. Predisposing factors, primary causes and perpetuating factors are all implicated in the development of otitis.
These include defective anatomical conformation, excessive moisture, irritant topical products, and systemic disease. Conformation defects in dogs include
Figure 1. Typical appearance of otitis externa.
a hirsute (Fig 2a,b) or stenotic meatus, and pendulous pinnae. Excessive moisture occurs in dogs that swim. Systemic disease such as immunosuppression, renal disease, hepatic disease, and in cats, FeLV and FIV infection, may predispose to otitis.
These include parasites, foreign material, hypersensitivity, neoplasia, polyps, keratinization disorders, and endocrine disorders. Hypersensitivity is a very common underlying cause of otits externa, even if only one ear is affected. Animals such as golden retreivers and German Shepherd dogs have the most perfect anatomy – wide open canals, minimal hair in the canal and in GSDs’ upright ears –
yet they are predisposed to otitis. It’s because they are predisposed to allergic disease: atopy or food allergic dermatitis. Often just managing this underlying cause will cause resolution of the otitis. Without managing
Without managing the allergic disease the otitis will be recurrent and chronic changes will develop in the ear canals which will perpetuate the problem. Parasites include mites (Otodectes, Demodex, Sarcoptes), ticks (Otobius) and biting flies (Stomoxys calcitrans). Otodectes cynotis (Fig 3) the ear mite of dogs and cats, spend their entire 3-week life-cycle deep in the ear canal of the host.
Otoscopic examination reveals these long-legged mites. The mites produce a marked reaction which is probably allergic in origin. Dogs shake their heads, which may lead to the formation of othaematomas. The tympanic membrane may perforate, leading to otitis media and nervous symptoms. A roll smear of ear canal debris often reveals pathogenic organisms. Demodex infestation may intra- or peri-aural. Acaricides (e.g. benzyl benzoate and thiabendazole) can be inserted into the ear canal. Spot-ons containing acaricides (e.g. moxidectin, milbemycin, eprinomectin or selamectin) are advised concurrently, since the mite will often be found in the peri-auricular regions. Otobius megnini, the spinose ear tick, may occasionally invade cats’ ears. Management is as for O. cynotis.
Foreign material may be grass awns, grass seeds or ticks as well as certain irritant topical agents. Atopy, cutaneous adverse food reactions, and contact hypersensitivities frequently play a mayor role.
Sensitivity to otic preparations may occur, although this is rare. Keratinization disorders include seborrhoea and endocrine disorders causing otitis include hypothyroidism, hyperadrenocorticism and sex hormone imbalance. Auditory polyps occur in both the canine and the feline, although they are extremely rare in dogs.
There is increased risk for tumours in pets with a history of chronic otitis. Benign or malignant tumours can develop in the external ear canal of dogs and cats, and arise from the apocrine or ceruminous glands that line the ear canal. The most commonly encountered tumour is the ceruminous gland adenocarcinoma and is more commonly seen than adenomas in both dogs and cats.
Figure 2a. Schnauzers and Poodles typically have a lot of hair lining the ear canal.
Figure 2b. Otoscopic view of an ear canal with a lot of hair showing how plugs form within the ear canal.
Figure 3. Otodectes cynotis on low power magnification
Bacteria, yeasts, otitis media, swimming, sensitivity to ceruminolytics, and progressive pathological changes such as narrowing of the ear canal due to chronic changes in the epidermis.
The first step in the management of chronic otitis is to determine the severity of pain. This can be done by gentle palpation or petting of the animal. If the ear is painful or the degree of discomfort is high, the animal should be sedated before performing any further diagnostic testing. The second step is gentle palpation to determine the presence of swelling, pruritus, fibrosis, or calcification since these findings will determine whether imaging is necessary.
The outside of the ear should be examined, noting erythema, oedema, crusts, scales, ulceration, lichenification, hyperpigmentation, or the presence of exudate. The pinnae and peri-auricular regions should be examined for evidence of self-trauma and demodicosis (Fig 4), erythema, and primary and secondary skin lesions. Pinnal deformities, hyperplastic tissue in the ear canal, and headshaking suggest a chronic condition.
If the otitis is unilateral, the unaffected ear should be examined first to prevent iatrogenic contamination of the unaffected ear with organisms (e.g. Pseudomonas aeruginosa or Proteus mirabilis) that may be present in the diseased ear. The clinically unaffected ear may, in fact, be diseased, meaning that the differential diagnosis list should also include causes of bilateral otitis. Otoscopic examination often requires sedation.
Hyperplasia of the ear canal may prevent tympanic membrane visualisation. In some cases, where there is severe inflammation, swelling and pain it may be appropriate to treat with glucocorticoid anti-inflammatories for a few days prior to performing and otoscopic examination, even if a GA will be given. This allows the swelling to decrease facilitating vvisualisationof structures within the ear canal The epidermis is also less friable and bleeds and oozes less serum.
Radiographs are normal in many otitis media cases. CT or MRI, if available, should be performed for cases of severe, chronic otitis. Radiographic abnormalities include calcification of the walls of the ear canal, fluid opacity with in the bulla and thickening and sclerosis of the bulla wall. Roll smears should be prepared using a cotton wool bud to retrieve debris and this applied to a microscope
slide. Low power examination (parasites) and high power examination (stained, for pathogens) is necessary.
Selecting appropriate topical treatment
Antimicrobials should be narrow spectrum products to minimise antimicrobial resistance. Whereas culture is necessary for specific identification of causative organisms, the key to determining successful antimicrobial therapy is ear cytology. Repeated cytology is necessary to evaluate the response to therapy. Owner compliance requires careful instruction. Pets should be suitably restrained so that insertion of medication is successful and reaches the target organisms.
Accurate quantities of medication for insertion may be provided by the manufacturer, or correct amounts can be inserted using a syringe. This is especially relevant for ceruminolytics. Separate syringes for each ear prevent cross-contamination.
Since purulent material decreases the efficacy of antimicrobial therapy, ceruminolyitic therapy is an essential part of successful management; purulent exudate is hyperosmolar, and results in a hypoxic, acidic environment within the ear canal.
Prophylactic use of ceruminolytics is indicated in chronic and recurring otitis. Ceruminolytics have surfactant and detergent action and help soften, emulsify and dissolve cerumen and debris. Dioctyl sodium succinate and triethanolamine polypeptide oleate condensate are potent ceruminolytics. In the presence of a ruptured tympanic membrane saline solution only should be used. Irrigation with a bulb syringe under sedation or anaesthesia may be necessary prior to topical antibacterial therapy. Although irritation of the ear canal can occur, the author has found that diluting ceruminolytics with water can reduce irritation to the ear canal.
Astringents (drying agents) assist in preventing maceration
Figure 4. In many cases of otitis externa the skin of the pinna and face can also be severley affected and need specific treatment
of the ear canal, and include isopropyl alcohol and mild acids such as benzoic, acetic, boric, salicylic, malic and lactic acids. If the ear canal is ulcerated avoid the use of products containing alcohol or acid. Acetic, malic, boric, benzoic, salicylic and lactic acid also have antibacterial action, however a lower pH inactivates aminoglycosides and fluoroquinolones.
Malassezia spp are a normal commensal inhabitant of the ear. Increases in numbers is a secondary change treatment off the underlying cause will normally reduce numbers to normal. In true infections Malassezia pachydermatitis is the species routinely involved and this usually responds to azole antifungals. Azoles include clotrimazole and miconazole. However, recently developed triazole antifungals such as variconazole (Vfend®) and posaconazole may be more effective. Candida, although a common cause of fungal disease in humans, is rarely encountered in companion
animal otitis. In these cases, polyene macrolides, such as nystatin is advised
Otomax® contains clotrimazole, gentamycin and betamethasone, and Surolan® contains miconazole, polymixin and prednisolone. Fluoroquinolones are broadspectrum and Posatex® is a new product not yet available here which contains posaconazole and orbifloxacin. Panalog® contains neomycin, triamcinolone and nystatin. Caution is necessary, since ototoxicity can occur in the event of a ruptured tympanic.
Coccoid organisms routinely incriminated in bacterial otitis externa include Staphylococcus, Streptococcus and Enterococcus. Rods (pseudomonads) are often encountered in chronic and recurrent otitis externa. Where Gram negative rods are found, culture and
Approach to managing chronic otitis
Owners should be informed of correct ear cleaning procedures. Frequency of cleaning usually decreases over time to once or twice weekly as a preventive maintenance procedure. Owners should be warned to keep the pet as dry as possible, and avoid swimming. Dogs with confirmation defects such as hirsute or pendulous ears may need to have regular clipping of the pinnae. The ear canals should be kept dry and well ventilated. Topical astringents prevent water from entering the ear canals in dogs that swim frequently, minimizing maceration of the ear canal. Chronic maceration impairs the barrier function of the skin, which predisposes to opportunistic infection. Preventative otic astringents may decrease the frequency of bacterial or fungal infections in moist ear canals.
Clipping hair from the inside of the pinna and around the external auditory meatus, and plucking it from hirsute ear canals, improves ventilation and decreases humidity in the ears. Hair, however should not routinely be removed from the ear canal if it is not causing a problem, because doing so can induce an acute inflammatory reaction. Owners will have to be instructed as to the correct procedure for instilling ceruminolytics and astringents. Since pets predisposed to chronic otitis may require life-long ceruminolytic application, minimising discomfort to the pet during this procedure is necessary. Warming the solution to body temperature in a water bath also minimises the discomfort felt by the patient and controlled “dribbling” administration rather than a rapid squirt may be better.
Control of inflammation minimises discomfort from ceruminolytics, and corticosteroids may be required in the early stages. Non-steroidal anti-inflammatories are not as effective otic analgesics as opiods and should not be used concurrently with corticosteroids. NSAIDS may have to be supplied to the owner for administration prior to instilling the ceruminolytic. Occasionally sedatives may be necessary until the pet has become accustomed to the procedure. The pet should be suitably restrained, as this allows for speedy instillation of otic products. For dogs, restraint may include a muzzle and cats may need to be wrapped in a towel. The author advises that dogs and cats should be accustomed to a collar, and dogs should have the lead attached while the ears are treated. Dogs should be trained to sit during application of otic products. A treat given afterwards encourages compliance. Pets may want to irritate (rub or scratch at) the ear and if a collar and lead has been applied they can be taken for a walk immediately afterwards as a distraction and reward for compliance.
Rinsing products should be inserted by holding the container vertical and upside down. The owner holds the ear pinnae with one hand, and the solution is instilled along the grooves of the inner pinnal surface into the canal. This avoids the container tip contacting an inflamed ear. The owner maintains their hold on the ear pinna to prevent the pet shaking the product out of the canal, and gently massages the base of the ear canal to promote the action. Cotton wool or tissue paper can be used to wipe away excess solution since cats, especially, are averse to topically applied liquids. The owner may not be 100% successful at first, but should be encouraged to persist on a regular basis. Discuss with the owner the suspected cause of the otitis, emphasising that treatment should be long term or even lifelong. All primary and secondary causes and predisposing factors should be identified and managed. Pain or pruritus should be controlled. Otitis externa is one of the few dermatologic conditions in which glucocorticoids concurrently with antimicrobial use are beneficial. Glucocorticoids such as prednisolone and triamcinolone decrease swelling of the ear canal – a key to successful treatment.
Duration depends on the severity. Ear hygiene is important; in particular, the hair in the peri-auricular area should be clipped as well as hair on the inner surface of the pinnae. This facilitates cleaning and medication. Plucking hair from the canal is controversial but may be necessary, under anaesthesia, to adequately resolve the infection. The first ear cleaning should be performed in the clinic, and owners should refrain from topical administration until rechecked in 5–7 days since they may be too aggressive, causing further damage. Owners can administer systemic drugs and then begin to clean the ears after the first recheck, provided the otitis is resolving. Topical medications are inactivated by exudates, and excessive cerumen may prevent medications from reaching the epithelium. Thick, dry, or waxy material requires a ceruminolytic solution such as carbamide peroxide, dioctyl sodium sulfosuccinate (DSS) or combinations of weak acids. If the tympanic membrane is ruptured, detergents and DSS are contraindicated; milder cleansers (eg, saline, saline plus povidone iodine, the Triz EDTA formulation) should be used to flush the ear.
Effective treatment may require both topical and systemic antimicrobial therapy, along with pain medications and glucocorticoids. In the management of acute bacterial otitis, the administration of corticosteroids in combination with antibacterial agents causes as reduction in exudation, pain, swelling, and glandular secretions. The least potent glucocorticoid at the lowest effective dose should be used. Most topical products contain a combination of an antibiotic or antifungal and glucocorticoids. Most dogs require the instillation of at least one ml twice daily for effective therapy. Products with an aqueous base are preferable, however, vinegar dilutions and propylene glycol should be used with caution since swelling of the lining of the ear canal and increased glandular secretions may result. Substances that do not usually irritate the normal ear may result in irritation and inflammation. Powders, such as those used after plucking hair from the canal, can form irritating concretions within the ear canal and should be avoided. It is important to demonstrate to the owner into which “hole” the ointment must be placed – holding the pinna upright and placing the tip into (not necessarily deeply) the most outer opening – which is the meatus of the ear canal. It is not necessary to fill the canal with ointment – a drop or two with a good ear massage, if possible, is required.
Systemic antibiotics should be used when neutrophils or rod-type bacteria are found on cytology, in cases of therapeutic failure with topical antimicrobial agents, in chronic recurring ear infections, and in all cases of otitis media. The most common cause of recurrent otitis externa is undiagnosed otitis media. Failure to use systemic antimicrobial therapy is an important cause of chronic ear disease in dogs. Yeast infections can be treated with oral ketoconazole 5 mg/kg/day, per os, for 15–30 days. In cats, itraconazole at 2–3 mg/kg/day for 15–30 days or one week on/one week off, is recommended. The best treatment of chronic otitis is prevention. In addition to identifying the cause of acute otitis, topical and/or systemic medications should be chosen based on cytology or culture. They should have a narrow spectrum and be specific for the current condition.
Aminoglycoside and fluoroquinolone antibiotics should not be used unless absolutely required for successful treatment but are the most common ingredients in topical otic medications. Because many topical products contain a combination of glucocorticoid, antibiotic, and antifungal medications, it is imperative to educate the owner on the frequency and duration of administration. Polymyxin B and fluoroquinolone antibiotics have shown the best success in controlling Pseudomonas infections in cases in which resistance has been identified through culture. Methicillin-resistant Staphylococcus pseudintermedius and Pseudomonas aeruginosa have emerged as frustrating causes of otitis and resistance is developing to fluoroquinolones. Duration of treatment will vary depending on the individual case but should continue until the infection is resolved based on re-examination and repeat cytology and culture. Animals with bacterial and yeast infections should be physically examined, with roll smears examined every other week until there is no evidence of infection. In some chronic cases a therapeutic
Figure 5. Chronic hyperplastic changes of the external ear canal. Surgery is now the only option
r egimen must be continued indefinitely. Infections are often chronic in course and associated with marked suppurative exudation, severe epithelial ulceration, pain, and oedema. Successful treatment is multifaceted and should include the following steps: 1. Identify the primary cause of the otitis and manage it. 2. Remove the exudate via irrigation of the ear canal 3. Identify and treat concurrent otitis media. 4. Select an appropriate antibiotic from the results of culture and mean inhibitory concentration and use it at an effective dosage for an appropriate duration. 5. Treat topically and systemically until the infection resolves (weeks to months). Non-responsive cases may require surgery. Lateral ear canal resection may be necessary to allow resection of neoplasia or polyps, and may assist in hyperplasia of vertical canal, also known as proliferative otitis externa (Fig 5.).
The keys to successful management of chronic otitisexterna include early recognition and management ofof predisposing factors, client education, and the formulationof a consistent management regime. Regularre-evaluation by the veterinary surgeon is essentialto prevent hyperplasia of the ear canal, also known asproliferative otitis externa.
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