Otitis Externa

Vol.18, No. 7

July 1996

V

Continuing Education Article

Otitis Externa FOCAL POINT ★ Otitis externa occurs secondary to predisposing factors or other diseases and is also a primary condition caused by microorganisms and parasites.

KEY FACTS ■ Atopic dermatitis is the most common disease predisposing to otitis externa. ■ Cytologic evaluation of otitic exudate should be performed in every case to determine the types of microorganisms present. ■ Otitic ears should be thoroughly cleaned of exudate, wax, and debris so that appropriate medication can reach diseased tissue. ■ Detailed client education concerning the correct methods of cleaning and applying medication is necessary for successful management of otitis externa.

University of Minnesota

Patrick J. McKeever, DVM, MS

O

titis externa is inflammation of the epithelium that lines the external auditory canal. Diagnosis of the condition can be frustrating and challenging, as a number of causative agents can be responsible for its development. Failure to diagnose and treat the primary cause (whether attributable to disease or environment) may lead to less than satisfactory results. The incidence of otitis externa in the canine population has been reported to be from 4% to 16% of hospital admissions and up to 20% of the general population.1 In cats, the incidence has been reported to be from 2% to 6.6% of hospital admissions.2 Such factors as time of year when the surveys were taken, breed popularity in a given area, and varying diagnostic criteria may be responsible for the wide range of reported incidence.

ANATOMY OF THE EXTERNAL EAR The funnel-shaped pinna, which is formed from distal flaring of the auricular cartilage, receives air vibrations and transmits them by way of the ear canal to the tympanic membrane. The pinna is covered on both sides with skin that is tightly attached to the periochondrium. The skin that lines the inner surface of the pinna generally contains fewer hairs. Each pinna functions independently of the other and is very mobile.3 The shape of the pinna is breed specific. The diameter of the ear canal or external acoustic meatus formed from the auricular and annular cartilages ranges from 5 to 10 mm, depending on the age, breed, and size of the dog. The canal is approximately 2 cm in length and ends proximally with the tympanic membrane or eardrum.4 The tympanic membrane is thin, semitransparent, and elliptical (Figure 1). It serves as a wall between the tympanic cavity and the external acoustic meatus. The membrane is thinnest in the center and becomes progressively thicker toward its periphery. At the periphery, the membrane is attached to a fibrocartilaginous circular pad that is fastened to a collar of bone in the external acoustic meatus.4 The manubrium of the malleus is a white fingerlike projection that extends into the tympanic membrane. The epithelial lining is thinnest on the deep, or proximal, portion of the ear canal. The lining becomes thicker as it progresses to the distal or superficial part of the canal and reaches its greatest thickness on the distal third of the concave surface of the pinna.5 Close to the tympanic membrane, the epithelial lining is aglandular. In short-haired breeds, no hair follicles may be found. In long-haired dogs, however, very fine hairs are present.5 In the dermis of the ear canal and especially the more distal or superficial areas of the canal, sebaceous

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glands form the superficial glandular bed. Apocrine glands, which form below the sebaceous glands in the deeper dermis, open directly to the skin surface either immediately adjacent to the opening of an associated hair follicle or at some distance from it.6 The number of sebaceous and apocrine glands varies. In long-haired and fine-haired breeds (e.g., Irish setters or spaniels), the glands are more developed and numerous than in short-haired breeds.5

primary condition from parasites. In dogs, various factors may be involved:6,8–11 • Foreign bodies (weed awns, seeds, excess hair, and dried wax) • Parasites (mites, ticks, chiggers, and biting flies) • Physiologic disturbances (nutritional deficiencies and concomitant disease) • Trauma (iatrogenic or self-induced) • Abnormally small or restrictive ear canals • Adverse reaction to food • Ear canal tumors • Excessive moisture in the ear (dogs that swim frequently, dogs with pendulous ears [which results in poor air circulation], and dogs exposed to increased environmental humidity).

PATHOPHYSIOLOGY OF OTITIS EXTERNA In the early acute stages of otitis, irritation caused by the inciting or predisposing factors results in hyperplasia of both the epidermis and sebaceous glands as well as hyperkeratinization of the infundibulum of the hair follicle. An infiltrate of lymphocytes, plasma cells, polymorphonuclear leukocytes, and histiocytes develops in the superficial dermis.7 Atopic Dermatitis. Otitis externa is more likely to be Chronic otitis is characterized by extensive epidermal secondary to atopic dermatitis than to other diseases.12 About 55% of cases of atopic dermatitis develop conhyperplasia (five to six times normal epidermal thickcurrent otitis; in 3% of the cases, ness) with or without formation otitis is the only clinical sign of of distinct retepegs extending the disease. 13 When associated between the dermal papillae. 6 Ulceration of the epidermis is with atopic dermatitis, inflamfrequently observed in chronicalmation of the pinna causes hyly affected ears, especially if perplasia of the epidermis, dermis, Pseudomonas or Proteus organisms and sebaceous and apocrine are present. Sebaceous glands are glands.10,14 The decrease in ventilation that occurs when the ear usually smaller and less active in canal narrows as well as the incases of chronic otitis and are crease in secretions create an ideal displaced in the superficial derenvironment for bacteria and mis by the apocrine glands, yeast to grow and reproduce. Otiwhich become hyperplastic and tis secondary to atopic dermatitis dilated. Changes in the apocrine most often develops in conjuncglands further narrow the ear tion with the pruritic skin discanal. If the cystic apocrine ease. Initially, the condition glands rupture, they become surrounded by a dense infiltrate of Figure 1—Normal ear canal and tympanic mem- appears as erythema and/or hyhistiocytes, polymorphonuclear brane of dogs. The manubrium of the malleus is perplasia with minimal exudaleukocytes, mast cells, giant cells, the white, curved, fingerlike projection extending tion; however, some animals may have excessive wax producand fibroblasts. Narrowing of into the tympanic membrane. tion by glands of the ear canal the ear canal is further exacerand pinna. Ear lesions respond bated by fibroplasia of the derto topical or systemic steroids or hyposensitization. mis.6 Ossification of the external ear canal and associated cartilage may develop in long-term, very severe Endocrine-Related Disorders. The pathogenesis surcases. rounding the development of endocrine-related otitis is unknown. Changes in glandular activity and keraEXTERNAL FACTORS AND CONDITIONS tinization are probably involved, as most animals with PREDISPOSING TO OTITIS EXTERNA otitis externa related to an endocrine disorder also have Originally, otitis externa was believed to be a primary seborrhea. Some conditions that may be associated with condition caused by microorganisms and parasites. Today, chronic otitis externa are hypothyroidism, male feminizotitis externa is known to occur secondary to predisposing syndrome, Sertoli cell tumor, and ovarian imbaling factors or other disease states in addition to being a ances.3,9 Of these, hypothyroidism is encountered most PATHOPHYSIOLOGY ■ ENDOCRINE-RELATED OTITIS ■ ATOPIC DERMATITIS

The Compendium July 1996

frequently. In two reported cases of hypothyroidism, otitis was the only clinical sign noted.9 Immune-Mediated Conditions. Diseases of the pemphigus complex and both systemic or discoid lupus erythematosus can cause vesicular, pustular, ulcerative, or crusting lesions of the pinna and ear canal.3,9,10 Pemphigus foliaceus and pemphigus erythematosus are associated with ear lesions and otitis more often than other diseases of the pemphigus complex. Lesions almost always involve other parts of the body as well, although cases of pemphigus foliaceus involving only the ear have been reported.9 Clinical signs of systemic lupus erythematosus vary considerably. If ear lesions are observed by the clinician, they are usually associated with one or more of the following: concomitant skin lesions, polyarthritis, fever, proteinuria, anemia, or thrombocytopenia. Although drug eruptions that result in ear lesions are uncommon, they can occur if the animal is on topical or systemic medication. If the reaction is to a topical otic preparation, lesions are confined to the ears. Lesions, however, also may occur on the skin of other areas of the body and at mucocutaneous junctions. Obtaining a history of recent drug use and drug withdrawal response can confirm a diagnosis.3 Foreign Bodies. Such foreign bodies as plant material, dirt, sand, and dried medications can cause otitis externa.9,15 The most common cause of foreign body otitis in some geographic areas is a variety of grass awns (Figure 2). In most cases, the otitis externa is acute and unilateral; however, many dogs in areas with a high density of grass awns may develop chronic bilateral disease. Penetration of the tympanic membrane by grass awns can occur. Otoacariasis. Otoacariasis, which is also called parasitic otitis, is an infection of the ears of cats and dogs with ear mites, chiefly Otodectes cynotis. These mites are large, white, and free moving. They live on the surface of the epithelial lining of the ear canal or, in rare instances, on the skin surface. Parasitic otitis is highly transmissible. Studies have shown that Otodectes mites lack specificity among carnivore hosts.16 Ear mites are responsible for about 10% of the cases of otitis in dogs and 50% in cats.9,17,18 The actual incidence, however, may be higher, as otitis can be produced by only two or three mites, which would be difficult to demonstrate.9 In addition, if severe inflammation occurs and a purulent bacterial or yeast infection develops, the mites often abandon the ear canal.17 Mites feed on lymph and whole blood and thus expose the host to mite antigens. Animals may develop a hypersensitivity reaction and produce reagins that are immunoglobulin E (IgE) antibodies. 19 Immediate

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wheal and flare responses to mite antigens are found in 87% of random source cats. This response is unrelated to infestation with mites.20 It has been proposed that almost all cats are exposed to a small number of mites at a very young age. Some cats develop immune responses that promote a hostile environment, which, in turn, prevents mite colonization in the ears and clinical disease. Other cats may have defective or lesser immune reactions, thereby fostering mite colonization and subseExternal Factors and quent clinical disease.19 Diseases that Tumors. Tumors should be Predispose an Animal included in the differential dito Otitis Externa agnosis when the clinician is confronted with a chronic case of otitis externa that does ■ Atopic dermatitis not respond to appropriate ■ Parasites (Otodectes therapy. Ear canal tumors can cynotis, ticks, chiggers, develop in the skin or its adand biting flies) nexal structures. Various epithelial and dermal tumors ■ Foreign bodies (weed have been reported, including awns, seeds, excess squamous cell carcinoma, hishair, and dried wax) tiocytoma, sebaceous gland ■ Excessive moisture in adenoma and adenocarcinothe ear ma, basal cell carcinoma, mastocytoma, chondroma, ■ Adverse reaction to chondrosarcoma, trichoepifood thelioma, apocrine gland ■ Abnormally small or adenocarcinoma, fibroma, firestrictive ear canals brosarcoma, and papillo3,9,10,21 Ear canal tumors ■ Ear canal tumors ma. generally occur more often in ■ Immune-mediated dogs than in cats; however, conditions the tumors in dogs tend not to be malignant.22 One excep- ■ Endocrine-related tion is squamous cell carcinodisorders ma, which occurs more often ■ Physiologic in cats than dogs. These tudisturbances mors are frequently found on (nutritional the pinnal margins of the ears of white-haired cats. deficiencies and Another type of ear canal concomitant disease) tumor that is common yet unique to cats is the inflammatory polyp. The stroma of this tumor comprises either myxomatous or dense fibrous connective tissue, which contains inflammatory cells and dilated capillaries. The stroma is covered either by ciliated or nonciliated columnar epithelium or by stratified squamous, nonkeratinizing epithelium. Inflammatory polyps have been diagnosed in cats ranging in age from three months to five years of age. About 45% of the cats with

IMMUNE-MEDIATED CONDITIONS ■ FOREIGN BODIES ■ OTOACARIASIS ■ TUMORS

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inflammatory polyps are youngtypically have exudates that are er than two years of age. Sex or light brown or yellow (Figure 5). breed predisposition has not Exudates produced as a result of been reported. If the tumor is copopulation of Streptococcus are extensive, it may occupy the usually light in color, whereas external ear canal, middle ear, exudates resulting from copopueustachian tube, and nasopharlation of Malassezia are brown to ynx.23 dark brown.10,27,28 Bacteria and Yeast. If the When data are averaged from presence of bacteria and yeast in several studies, it is found that the ear canal is confirmed, cliniStreptococcus can be isolated cians should not automatically asfrom about 16% of normal ears sume these organisms are playing and 10% of ears with otitis exa causative role in the pathogene- Figure 2—Grass awn lodged in the ear canal of a terna.24,26 In some cases, the environment of otitis may be less sis of otitis. A low number of dog. favorable for Streptococcus growth commensal bacteria and yeast than the environment of the northat have pathogenic potential mal ear. If present, Streptococcus can be present in the ear canal of exudate is usually light yellow to normal dogs.24 These organisms, however, can quickly proliferate if light brown. the lining or microclimate of the Malassezia pachydermatis ear canal changes.17 Their growth (formerly called Pityrosporum then exacerbates and perpetuates pachydermatis) is a nonlipophilic the inflammatory reaction.17 Alspecies that forms a part of the though these bacteria and yeast normal flora of animals. Malasmay not be the principal caussezia is an oval or peanut-shaped, ative agents, there is a high probgram-positive, nonmycelial ability that they are involved in yeastlike organism. Malassezia any subsequent disease process has been frequently isolated (Figure 3). from both normal and otitic Pseudomonas aeruginosa has Figure 3—Gram’s stain of exudate from an ear show- ears, which has created controbeen isolated from normal ears ing yeast, gram-positive cocci, and gram-negative versy as to the role it plays in in only 0.4% of dogs studied.11 rods. perpetuating otitis. There is no In contrast, Pseudomonas has general agreement between varibeen isolated in 20% of otitic ous studies as to its incidence eiears.17 The organism is isolated frequently from dogs ther in normal (15% to 49%) or otitic (2% to 80%) with recurrent chronic otitis and from dogs undergoing ears. If data are averaged, the incidence in normal and long-term treatment with topical antibacterial drugs.17 otitic ears would be 17% and 24%, respectively. I conOtitic ears populated with Pseudomonas are generally cur with others who have found the incidence of painful and have copious amounts of a pale or light yelMalassezia in otitic ear canals to be about 50%.2 The 25 frequency of Malassezia in relation to the amount of low secretion (Figure 4). Ulceration of the ear canal epithelium is also commonly associated with this orwax within the ear canal has been investigated and it ganism and may be extensive. was concluded that the organism is most easily demonProteus organisms have not been cultured from norstrated in ears with excess wax.2 One investigator suggested that Malassezia is a nonmal ears and have been reported in only 11% of otitic pathogenic, normal commensal because its incidence ears.14 Proteus is often found in cases of chronic ulcerated otitis with light yellow secretions.15 was the same for both normal and otitic ears.2 Another In one study, coagulase-positive Staphylococcus organstudy, however, showed that Malassezia may be isms were isolated from 9.6% of dogs with normal or pathogenic because clinical cures for otitis were obclean ears, 14% with waxy ears, and 22% of dogs with tained in cases in which Malassezia was isolated in otitis externa.26 Other studies show that Staphylococcus monoculture and topical nystatin was the only treatis present in about 20% of normal ears and 40% of ears ment.29 It was concluded that although Malassezia is 24 usually commensal, it may become pathogenic, thereby with otitis externa. Ears populated with Staphylococcus PSEUDOMONAS ■ PROTEUS ■ STAPHYLOCOCCUS ■ STREPTOCOCCUS

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contributing to the development of lesions if the aural microclimate is favorable. Ears with a high population of Malassezia have copious amounts of chocolate-brown waxy discharge (Figure 6).

unilateral otitis is frequently associated with foreign bodies, especially grass awns. Unilateral otitis of gradual onset is more suggestive of a neoplastic process. Bilateral otitis is frequently associated with parasitic infestation or often occurs secondary to some other disease. Finally, based on the differential diagnosis developed, appropriate diagnostic plans can be formed for any primary disease.

DIAGNOSIS AND MANAGEMENT History A complete history with emphasis on dermatology and a complete physical examination are the initial steps for develop- Figure 4—Pseudomonas otitis with a light yellow Physical Examination As with a general physical exing a differential diagnosis of secretion. amination of other body sysprimary diseases and predispostems, examination of the ears ing environmental factors. should be done in a systematic The history often provides as fashion and the findings recordmany clues to the cause as any ed. To minimize the time necesother diagnostic procedure. Besary for recording the findings, it cause of time restraints of a busy is very helpful to have an ear expractice schedule, however, cliniamination form. cians may be unable to devote Equipment. The standard adequate time to obtain a deotoscope is the preferred piece tailed history. This problem can of equipment for routine exambe avoided by having the owner ination of the vertical and horicomplete a history form either at zontal ear canals and the tymhome or in the waiting room. panic membrane. A halogen This form then can be scanned light source is desirable, as it is by the attending clinician to obtain pertinent information. Only Figure 5—Staphylococcus otitis with pale yellow bright enough to reach to the depths of the long canine ear clarifying questions or questions exudate. canal. I suggest using an operatspecific to the ears would have to ing head because it accommobe asked of the owner. Informadates obser vation when the tion pertaining to any previously clinician removes foreign matter used medication and the pet’s refrom the ear or aspirates the ear sponse to the drug also should be with suction. Cones for the vetobtained. After the animal has erinary otoscope are needed in a been evaluated generally, focus variety of lengths, diameters, can be directed to the ears. and shapes to fit the various Environment can be imporshapes and sizes of canine and tant, as animals that have free feline ears. Because the lumina access to fields are more likely to of the ear canals are often narhave foreign bodies, such as rowed by hyperplastic tissue, I grass awns, causing ear proboften use a cone that is 4 mm in lems. Animals that swim frediameter and 5.5 cm in length. quently are predisposed to otitis Cones designed for examining attributable to the maceration Figure 6—Malassezia otitis with chocolate-brown the human ear are unsatisfactocaused by continual presence of waxy discharge. ry for use, as they are too short water in the ear. for adequate viewing of the horChronicity and whether the izontal ear canal and tympanic membrane. otitis is unilateral or bilateral also are important. Acute, DIFFERENTIAL DIAGNOSIS ■ EXAMINATION EQUIPMENT

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Restraint. For examination of even-tempered dogs with minimal problems and for cursory examination of most other animals, physical restraint may be the only measure necessary. When conducting a complete, thorough examination of the horizontal canal and tympanic membrane, however, almost all animals require chemical restraint. In addition, chemical restraint allows the clinician to clean the ear, a procedure often necessary in order to visualize the horizontal canal and tympanic membrane. In dogs, ketamine (1.36 to 2.2 mg/kg) combined with diazepam (0.045 mg/kg) and acepromazine (0.023 mg/kg) mixed in the same syringe and given intravenously has been successful for restraint during the examination and cleaning of ears. The higher dose of ketamine (2.2 mg/kg) is preferred, as it results in sufficient restraint for about 20 minutes. Examination of the Ear Canal and Tympanic Membrane. To visualize the ear canal with an otoscope properly, the pinna should be pulled up and away from the head so that the canal is straight. While the clinician looks into the otoscope, the cone should be slowly inserted to the depth necessary for examination of the horizontal canal and tympanic membrane. The normal ear canal may contain small amounts of pale yellow or yellow-brown wax. Some breeds of dogs, such as the poodle, schnauzer, and terriers (Airedale, wirehaired, and fox) typically have hair growing in the canals. Any hair may have to be removed using an alligator forceps before complete examination is possible. The normal tympanic membrane is translucent, glistening, pearl-gray, and slightly concave. Cloudiness, opacity, color changes, or bulging are generally indicative of pathologic changes in the middle ear. Rupture of the tympanic membrane may appear as a small tear in its surface or may be so complete that the clinician has difficulty determining where the horizontal canal ends and the middle ear begins.

Establishing a Diagnosis Primary Disease. Appropriate diagnostic and laboratory procedures can be conducted to rule out the various primary diseases that are potentially responsible for or predispose an animal to otitis. Cytology. Cytologic evaluation of otitic exudate provides immediate diagnostic information about the inflammatory response as well as determines the types of microorganisms and ectoparasites present within the ear canal. Smears stained with modified Wright’s stain or Gram’s stain should be examined carefully for the number and morphology of bacteria, yeast, leukocytes, and neoplastic cells. Generally, the presence of gram-

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positive cocci on smears is indicative of either Staphylococcus or Streptococcus; gram-negative rods usually indicate either Pseudomonas or Proteus. Yeast is typically Malassezia, but Candida is a possibility. In addition to obtaining information from stained smears, debris from the ear canal can be mixed with mineral oil and examined for ectoparasites and their eggs or larvae. Cultures. Although cytologic evaluation provides clues as to the organisms present, culture and sensitivity tests are still very appropriate because a greater proportion of bacteria is becoming resistant to routine antibacterials used for treatment of otitis.30 If gram-negative rods (which have a high probability of being Pseudomonas) are present on the smears, culture and sensitivity testing is mandatory because Pseudomonas organisms are often resistant to many antibacterials. Biopsy. To diagnose a tumor or confirm proliferative tissue in the ear canal, a small pinch biopsy can be obtained by passing an endoscopic biopsy forceps through the otoscope cone.

Initial Management Successful treatment of otitis externa is based on four fundamental principles: 1. Diagnosing and treating or correcting the primary disease or environmental factors predisposing to the otitis 2. Accurately identifying specific bacteria, yeast, parasites, or foreign bodies in the ears (see the section on Establishing a Diagnosis) 3. Thoroughly cleaning all debris, exudate, and wax from the pinna and the vertical and horizontal ear canals 4. Educating the owner about the cause of the otitis and reviewing the anatomy of the ear as well as instructing the owner on proper ear-cleaning techniques and application of medications at home.

Ear Cleaning All hair, wax, debris, exudate, and foreign matter must be removed from the horizontal and vertical ear canals to allow complete examination of the ear canal and tympanic membrane as well as penetration of topical medications to affected tissue (see the box In-Hospital Cleaning Technique). Any debris that may serve as a focus for reinfection and any bacterial toxins, degenerating cells, and free fatty acids that may stimulate renewed inflammation should be removed. Equipment. The use of a bulb syringe or a dental water-propulsion device to flush the ears has been advocated.27,31 In my experience, however, this technique can be messy, is more time-consuming, and fails to clean the

PHYSICAL & CHEMICAL RESTRAINT ■ CYTOLOGY ■ CULTURE & SENSITIVITY ■ BIOPSY

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ears as well as the suction techminute to loosen any debris. nique. If the veterinary facility The carbamide peroxide has a has a suction apparatus for foaming action that helps to In-Hospital Cleaning surgery, this can be used. As an break down larger clumps of Technique for the External alternative, a device can be easily debris and float them to the and inexpensively made from canal opening. After the canal Ear Canal supplies found in hardware has been massaged, excess ■ Sedate the animal. stores. Three nipples that are 1⁄4 cleaning solution as well as exu■ Coat the pinna and fill the ear canal inch in diameter (two that are 1date and debris that have floatwith a cleaning solution of docusate inch long and one that is 2 inches ed to the surface should be wiped sodium, carbamide peroxide, and long) and six 1⁄4-inch locknuts can away with a cottonball. Using a tetracaine. be purchased from the hardware bulb syringe, the ear canal ■ For ears in which the tympanic store. First, the 2-inch nipple is should then be flushed twice membrane is ruptured, fill the placed through a hole drilled in a with warm water. While the external and middle ear with a No. 6 rubber stopper and secured clinician is observing through solution of either propylene glycol, with a locknut on each side of an operating head otoscope, the malic acid, benzoic acid, and salicylic the stopper. Next, holes that are 8-French urinary catheter atacid or of diluted povidone-iodine 1 ⁄4 inch in diameter are made on tached to a suction apparatus solution (l part povidone-iodine to opposite sides of the snap-on lid should be used to remove loos3 parts water). of a one-liter plastic container. ened debris, exudate, and any ■ Fold the pinna on itself and massage The 1-inch nipples should be water that remains. The clinithe ear canal for 2 minutes to loosen threaded halfway through the lid cian should examine the ear to and dissolve debris. and a locknut placed on either verify that it is completely ■ Use a cottonball to remove excess side of the lid. The lid is reatclean. If the ear is not clean, the cleaning solution as well as exudate tached to the container, and a process should be repeated. and debris that have floated to the 2- to 2.5-meter piece of appropriThis procedure should be folsurface of the ear canal. ately sized plastic tubing is placed lowed for the other ear as nec■ Flush the ear canal twice with warm over each nipple. An 8-French essary. After this technique has water using a bulb syringe. urinary catheter that has been cut been mastered, both ears can ■ Use an 8-French urinary catheter (cut to a length of 12 cm should be be completely cleaned in fewer to a length of 12 cm and attached to attached to one free end of plastic than 20 minutes. If, however, one free end of plastic tubing) that is tubing. The other free end of the tissue lining the ear canal is attached to a suction apparatus to plastic tubing is attached to the so hyperplastic that the canal remove loosened debris, exudate, and nipple protruding from the outer cannot be completely cleaned, any remaining water; this step should side of the rubber stopper. The surgical intervention may be be done while the clinician observes stopper can be placed into a hose necessary. through an operating head otoscope. of any household vacuum cleanIf the tympanic membrane is ■ Examine the ear to verify that it is er. The suction control device on ruptured, a cleaning solution completely clean. the vacuum cleaner hose can be of propylene glycol, malic acid, ■ Repeat the process if the ear is not adjusted to obtain the desired debenzoic acid, and salicylic acid or completely clean. gree of suction. Other necessary of diluted povidone-iodine equipment includes a bulb sysolution (one part povidoneringe plus mosquito and alligator iodine to three parts water) can forceps for plucking hair and forbe used for cleaning both the eign objects from the ears. external and middle ear.15 The cleaning technique is the same as previously described. A short-term head tilt or Technique. With the animal sedated and in lateral transient ataxia has been observed in about 1% of cases recumbency, the upper ear should be filled with a soluwhen the middle ear is flushed.31 Owners of animals tion containing docusate sodium, carbamide peroxide, with a ruptured tympanic membrane should be and tetracaine. warned that some animals may swallow or cough when The canal should then be massaged for two minutes. liquid solutions are instilled in their ears. This reaction If the pinna has exudate or wax on its surface, the occurs because the solution is flowing through the cleaning solution should be applied to it also. The pinruptured tympanum, to the middle ear, and down na then can be folded on itself and massaged for one EAR CLEANING EQUIPMENT ■ SUCTION DEVICE CONSTRUCTION

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the eustachian tube into the pharynx. Although a ruptured tympanum increases the likelihood of middle ear infection, it is not a serious problem in a clean ear and heals in 5 to 10 days.17,31 Although cotton swabs are useful for cleaning the folds of the anthelix, the practice of using cotton swabs to clean the ear canal should be abandoned. This technique invariably packs exudate and debris further down the canal next to the tympanum, regardless of how careful the clinician is. If the tympanic membrane is diseased, pressure caused by packed debris may rupture the membrane. If the tympanum is ruptured, the debris can be pushed by the swab into the middle ear, where it can promote development of otitis media. The physical presence of the swab in the canal also tends to traumatize and often ulcerate the epithelial lining.

Treatment Initial treatment should be based on the results of the stained smears of exudate. If gram-positive cocci are present, neomycin, gentamicin, or chloramphenicol would be appropriate. If gram-negative rods are present, gentamicin, polymyxin B, enrofloxacin, or amikacin would be the antibacterials of choice. Because of their ototoxicity, the aminoglycosides (neomycin, polymyxin, amikacin, and gentamicin) should not be used for treatment of otitis if the tympanic membrane is ruptured. If yeast is found, such topicals as miconazole or clotrimazole should be used. After culture and sensitivity findings are known, treatment can be changed, if necessary, to more appropriate antibacterial or antifungal agents. If at any point response to therapy is not as anticipated, additional culture and sensitivity testing should be conducted. Another approach to treatment is use of 2% to 5% solutions of acetic acid to lower the pH within the ear canal. This treatment is especially beneficial against Pseudomonas infection if the organism becomes resistant to antibacterials. Inflammation, sometimes severe, is an occasional side effect of otic treatment with acetic acid. The inflammation is more likely to occur when a 5% solution is used. Silver sulfadiazine is another antibacterial frequently used for the treatment of otitis caused by Pseudomonas. A 1% solution of silver sulfadiazine is made by combining 1 gram of silver sulfadiazine powder and 100 ml of water and shaking well. Depending on the size of the ear canal, from 4 to 12 drops should be instilled twice daily. I have used this solution to treat animals with ruptured tympanic membranes, and no adverse effects have been noted. In most cases of otitis, topical glucocorticoids reduce

tissue inflammation in the ear canal, resulting in less pruritus, swelling, exudation, and tissue proliferation. Fluocinolone acetonide in 60% dimethyl sulfoxide is especially beneficial for treatment because the dimethyl sulfoxide allows penetration of fluocinolone into the tissue. This treatment often reduces the tissue hyperplasia associated with chronic otitis externa. Owners should be instructed to fill the affected ear canal with the solution and massage the canal for 30 to 60 seconds two to three times daily. This treatment has also been beneficial in decreasing wax buildup, which often results in concomitant Malassezia infection. Even if an infected ear is completely cleaned and treated with appropriate medication, small amounts of exudate or wax may persist. Owners can prevent wax or exudate from accumulating and interfering with successful treatment by performing in-home cleaning. Ear cleaners can be dispensed to the owner, who should be instructed to clean the animal’s ears by filling the canal with cleanser, massaging the ear canal for one to two minutes, and then using a cottonball to wipe the cleansing solution and debris from the outer ear and pinna. The interval between cleanings will vary from three to seven days, depending on the state of the ears and the rate of wax or exudate accumulation. If Otodectes cynotis infestation is diagnosed, the ears should be cleaned and treated for 20 days with a mixture containing 1 ml of rotenone and 10 ml of a solution containing procaine penicillin G, neomycin sulfate, polymyxin B, and glucocorticoids. Alternatively, a 300 µg/kg dose of ivermectin can be given subcutaneously and repeated two weeks later.32 All contact animals, both dogs and cats, should be treated because asymptomatic carriers may often be sources for reinfection.

Client Education Regardless of how thorough the clinician is throughout the diagnosis and treatment procedures, successful management of otitis depends on owner cooperation. The owner must be prepared to complete home treatment measures. To ensure owner compliance, the clinician should carefully explain and demonstrate the cleaning and treatment methods and then watch the owner repeat the process. All instructions pertaining to the cleaning and treatment of the ears should be typed or clearly printed for the owner. To save time, the instructions can be printed on a form so the clinician only has to fill in the names, amounts, and frequency of medications to be used. Finally, reexaminations should be scheduled so that treatment progress can be monitored and any problems with home cleaning or treatment measures can be addressed.

OTODECTES CYNOTIS ■ CLIENT INSTRUCTIONS

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The Compendium July 1996

About the Author Dr. McKeever is Professor of Veterinary Comparative Dermatology, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota. He is a Diplomate of the American College of Veterinary Dermatology.

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