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Veterinarian Technician April 2005 (Vol 26, No 4)

Basics of Ear Infections in Dogs

by Oreta M. Samples, AAS, BS

    Key Points

    • Ear disorders are frequently painful and may cause problems with maintaining balance.
    • Any disorder that affects the ears has the potential to cause irreparable damage to the patient's hearing.
    • The type of ear problem can sometimes be determined by noting characteristic odors and the color and consistency of the discharge.

    The ears play an important role in both hearing and equilibri­um.1 These special sense organs are especially significant in service and herding dogs, which rely on their acute auditory sense to be successful in their work. Any disorder of the ears, regardless of the etiology, can be painful and may cause irreparable damage. Therefore, technicians should educate dog owners to be particularly attentive to signs of impending ear problems.

    Anatomy of the Ear

    The Outer or External Ear

    The external ear consists of the pinna (earflap), external auditory canal (meatus), and the tympanic membrane (eardrum). The external ear is L-shaped and begins with a cartilaginous landmark known as the tragus. There is a long vertical canal and a horizontal canal ending at the tympanic membrane.

    The pinna is the funnel-like part of the ear that can be seen from the outside. The pinna can be pendulous (as in flop-eared dogs [e.g., retrievers]) or erect (as in prick-eared dogs [e.g., German shepherds]). Animals with pendulous ears are predisposed to ear infections because of poor ventilation of the external ear canal. The type of pinna an animal possesses relates to the amount of damage that can be done during vigorous head shaking. During violent head shaking, the plate of cartilage that lends support and rigidity to the earflap may break or the tips of pendulous ears may become damaged.

    The pinna is commonly involved in a variety of dermatologic disorders, such as hypothyroidism and atopic dermatitis; it has a rich blood supply, and profuse bleeding can occur from trauma of any kind. The inner pinna and the external ear canal contain abundant ceruminous glands. These glands excrete sebum, a thin waxy, pale yellow substance, which is perfectly normal (similar to earwax found in humans) and not to be confused with infectious exudates. The tympanic membrane is very fragile and can be easily ruptured by disease processes or improper ear cleaning.

    The Middle Ear

    The middle ear is encased by the temporal bone and begins at the tympanic membrane. The middle ear is composed of the tympanic cavity; the three small bones of the middle ear (ossicles), which transmit sound from the tympanum to the internal ear; the tympanic bulla; and the eustachian tubes (auditory tubes), which connect the middle ear to the nasal pharynx.2

    The Inner Ear

    The inner ear is also embedded in the temporal bone and is the most well-protected and inaccessible part of the organ. Although encased in bone, the inner ear is susceptible to various disorders, many of which can cause disabling problems with equilibrium as well as hearing loss. Anatomically, the inner ear consists of the semicircular canals, the cochlea, and the vestibular and cochlear nerves.

    Clinical Signs of Ear Problems

    Typical signs of an ear problem include head shaking, head tilt, pawing at the ears, or rubbing the ears on the ground. Patients may exhibit pain when the ears are palpated, and odors or discharge may be apparent. Involvement of the middle and inner ear are signaled by head tilt, circling, uncoordinated gait, loss of balance, unequal pupil size, or abnormal eye movements (nystagmus).

    Physical Examination

    Once a technician has a good understanding of the anatomy of the canine ear, he or she will be capable of conducting a safe yet thorough examination of the ear. It is important for technicians to be aware of the potential for doing harm, such as causing pain or puncturing the eardrum, if examinations or cleanings are performed roughly.

    When performing a physical examination of the ear, it is important to first note if there is an abnormal odor from the ear; a clean, noninfected ear should have no odor. Next, a visual assessment should be done. The technician should begin at the outermost edge of the pinna looking for evidence of fly bites or other injuries to the tips of the ears. Fly strike is quite common in dogs that spend much time outdoors, especially in areas in which biting flies are prevalent. The tips or outer margins and folds of the ears may be painful or inflamed or show crusted blood from the bleeding insect bites. When examining the inner side of the pinna, evidence of inflammation (e.g., redness, swelling, pain), presence of dirt, excessive sebum, or other exudates should be noted. If discharge is present, the consistency should be recorded and samples obtained using a cotton-tipped swab so that they can be examined later.

    After an external inspection is complete, an otoscope can be used to visualize the horizontal and vertical portions of the external ear canal. Depending on the size and breed of the dog, a human pediatric otoscope cone/speculum may be more appropriate than an adult model.3 While gently inspecting the area with this instrument, the technician should look for signs of inflammation, parasites, exudates, hair, or other foreign bodies. Findings may include redness, also known as erythema, sebum accumulation, bleeding, discharge, and the presence of polyps, tumors, or ulcers. Discoveries such as these may warrant further investigation by the veterinarian. It is important to note that at this point the technician should report findings directly to the vet­erinarian for diagnosis so that a treatment plan can be ­developed.

    Exudates may often signify a problem within the ear; often, the type of exudate is indicative of the problem. Technicians should pay particular attention to the color and consistency of such material. All exudates should be described and noted on the examination form. Sufficient samples of any material noted should be collected in case further laboratory analysis is required. Yeast infections typically have a dry, waxy, yellow or brown discharge with a musty odor; bacterial infections typically have thinner, purulent, or hemorrhagic-purulent exudates with foul odors. Ear mites typically cause a dry, brown, flaky discharge that resembles coffee grounds.

    Common Conditions

    Otitis Externa

    Otitis externa is an acute or chronic inflammation of the soft tissue components of the external auditory meatus, which sometimes involves the pinna.4,5 There are many factors that can contribute to otitis, both of a physical and biologic nature. Some of these causes may include bacteria (e.g., Proteus mirabilis, Staphylococcus intermedius), yeasts (e.g., Malassezia pachydermatis), parasites, foreign bodies, congenital factors (e.g., hair in the ear canal), tumors, and environmental factors.4,5 Anatomically, the conformation of the ear with regard to the size and shape can contribute to ear infections. Animals with droopy, nonerect ears, which have a tendency to be dark, warm, and moist because of no circulating air, are more prone to ear infections than animals with erect ears. Outside circumstances can also contribute to the presence of otitis. Trauma caused during cleaning of the ear as well as cleaning solutions left in the ear from improper rinsing can lead to not only moisture but also caustic burns to sensitive skin as deep as the middle ear.

    The ectoparasites of importance are the spinose ear tick (Otobius megnini) and the ear mite (Otodectes cynotis). Biting flies can also be worrisome pests because they take blood meals by biting the outer edges of the ear, leaving dry crusts that are inflamed and very irritating to the animal. These pruritic lesions have the potential to become excoriated and infected as the animal scratches and paws at the earflap and can be worsened by head shaking.

    There are many other causes of otitis that may not be as easily recognized, including endocrine imbalances, nutritional disorders, dermatologic disorders, and excessive water in the ear. Obtaining a thorough health history and performing a physical examination at presentation can help the veterinary staff determine if any of these possibilities should be considered.2

    Otitis Media and Otitis Interna

    Although the external ear is prone to otitis externa, the middle and inner ear can also be affected by similar conditions of otitis media and otitis interna. Otitis media is often a result of otitis externa that has extended through a ruptured tympanic membrane or ascended from the pharynx by way of the eustachian tubes into the middle ear. Signs may include pharyngitis or tonsillitis. It is important to note that the prolonged presence of otitis media can lead to deafness or loss of equilibrium, which may be indicated by head tilt, abnormal eye movements, staggering, or walking with an uneven gait.2-4

    Otitis interna, which is also referred to as labyrinthitis, is somewhat uncommon in dogs.2 This may be because of the general inaccessibility to the inner ear by outside irritants. Again, just as with otitis media, otitis interna may occur as a direct result of an existing otitis externa or media. This condition also has the potential to cause damage to such auditory organs as the semicircular canals. Because of the proximity of the vestibular connections to the emetic centers of the brain stem, vomiting and increased salivation may be observed in addition to lack of coordination.2,3 It is interesting to note that the sympathetic nerve supply to the face passes very near to the tympanic bulla. Middle ear infections can affect this nerve and cause a partial loss of sympathetic innervation known as Horner's Syndrome.


    Cotton-tipped swabs should be used to collect samples from the pinna and external ear canal. The sample should be transferred to a microscope slide using the technique known as a roll prep. Once the material is gently rolled off the swab onto a microscope slide, the slide can be pro­cessed as desired.

    A common examination to detect ear mites (Otodectes cynotis) involves examining exudates swabbed onto a microscope slide that has been prepared with a drop of mineral oil. The presence of ear mites can be easily confirmed if live mites are observed clinging to the exudates or moving about sluggishly.

    Smears for microbiologic or cytologic examination may be made by rolling the swab onto slides, effectively smearing the exudates in a thin layer on the glass.4 Once the slide has been allowed to air dry, it may be stained with modified Wright's or Giemsa stain to detect cells and yeasts or Gram's stain for bacteria.


    Once a diagnosis has been made by the veterinarian, a treatment plan can be prescribed. Treatment of any type of otitic condition should begin with clean, dry ears. Therapeutic agents are rendered ineffective if applied to dirty pinnas or ear canals; therefore, a major role of the technician is to perform a preliminary ear cleaning. This may require sedation or anesthesia. In addition, clients should be taught proper cleaning procedures and how to properly apply prescribed medications. Clients should be advised about the importance of noninterrupted treatment regimens and finishing all medications. Environmental or other predisposing conditions that may contribute to the problem should be addressed and eradicated. Therapeutic agents should be chosen for their effectiveness and ease of use. The pharmaceutical agents used should reflect the specific problems to be treated. A mixture of agents such as an antibacterial agent combined with a parasitic agent for ear mites and a corticosteroid (e.g., hydrocortisone) for treatment of pain and inflammation is often required.


    It is not uncommon for otitis to be difficult to treat and resolve. This may be because the infection has been present for a while before the animal began to exhibit signs or was presented for treatment. There are many underlying causes and circumstances that predispose a patient to chronic or recurring otitis. Although an acute case of otitis externa may require treatment over the course of 2 to 4 weeks, extreme cases of otitis media or interna may require extensive treatment of 6 weeks to several months. In cases of long-term treatment, it is imperative for owners to recognize the importance of continual uninterrupted care because a partially treated infection can recur. Otitis in any form can be remedied only through the collaborative efforts of a dedicated veterinary team and owners who are diligent in at-home therapy.

    1. Colville T: Sense organs, in Colville T, Bassert JM (eds): Clinical Anatomy & Physiology for Veterinary Technicians. St. Louis, Mosby, 2002, pp 269-287.

    2. Blakemore JC: Diseases of the ear, in Catcott EJ (ed): Canine Medicine. Santa Barbara, CA, American Veterinary Publications, 1979, pp 1335-1360.

    3. Shell LG: Otitis media and otitis externa, in Birchard SJ, Sherding RG (eds): Saunders Manual of Small Animal Practice, ed 2. Philadelphia, WB Saunders, 2000, pp 435-438.

    4. Logas D, Neer M: Eye and ear, in Aiello S, Mays A (eds): The Merck Veterinary Manual, ed 8. Whitehouse Station, NJ, 1998, pp 372-375.

    5. Noxon JO: Otitis externa, in Birchard SJ, Sherding RG (eds): Saunders Manual of Small Animal Practice, ed 2. Philadelphia, WB Saunders, 2000, pp 419-423.

    References »

    NEXT: Editorial: Aiming for Excellence


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