Deafness—the absence of perception of sound—and decreased hearing are common in dogs and cats, and to a lesser extent in other species. The condition can be hereditary or acquired, congenital or later onset, and sensorineural (due to loss of cochlear cells) or conductive (due to sound being unable to reach the cochlea as a result of infection, obstruction, or damage). Deafness in dogs and cats is usually congenital and hereditary and is associated with white pigmentation. Deafness can be mild, moderate, severe, or complete. In adult and geriatric animals, deafness may be the result of otitis, drug toxicosis, noise trauma, or age-related hearing loss.
Hereditary deafness, usually congenital, can be either cochleosaccular or neuroepithelial in origin. Cochleosaccular deafness is most common in dogs with the piebald or merle pigmentation genes and in cats with white coats. It can be unilateral or bilateral and is often associated with blue eyes and white pigmentation. Affected ears are totally deaf. Pigment-associated deafness also occurs in equine, bovine, porcine, and other species. Hereditary deafness is the most common type of deafness in dogs and cats and should be the first diagnosis considered in an animal with any white pigmentation.
Cochleosaccular deafness develops within 1–3 weeks after birth, secondary to stria vascularis degeneration that results from melanocyte suppression by the pigmentation gene, leading to cochleosaccular neuronal degeneration. Unilateral deafness in animals may go undetected without brainstem auditory evoked response (BAER) testing (see BAER testing dog image); however, animals with unilateral deafness will pass on an increased deafness risk to offspring if bred. Inheritance is not simple autosomal.
Courtesy of Dr. Peter M. Scheifele.
Neuroepithelial deafness is not associated with pigment patterns, is usually bilateral, and results from primary hair cell loss within 1–3 weeks after birth but without affecting the stria vascularis. Vestibular signs may also be present (eg, in Doberman Pinschers).
Hereditary deafness occurring in midlife has been documented in several dog breeds (Border Collie, Rhodesian Ridgeback); however, the pathology and mechanism of inheritance have not been documented.
Congenital deafness, usually hereditary, affects more than 100 dog breeds and is especially prevalent in piebald gene–carrying breeds (Dalmatian, Dogo Argentino, Catahoula Leopard Dog, Bull Terrier, Australian Cattle Dog, English Setter, English Cocker Spaniel, Boston Terrier, and Parson Russell Terrier) and merle gene–carrying breeds. Congenital deafness is highly prevalent in white cats (dominant white pigmentation gene), especially those with blue eyes; however, some blue-eyed cats (Siamese and related breeds) do not appear to be affected.
DNA testing is available only for some forms of genetic deafness, such as nonsyndromic deafness in Rottweilers (LOXHD1 mutation) and hereditary deafness in Doberman Pinschers (PTPRQ mutation).(Two causative genetic mutations have been identified in Doberman Pinschers [1].) Consequently, BAER testing and informed selective breeding are often the best available screening tools for lowering prevalence within breeds.
Conduction (or conductive) deafness occurs when sound cannot effectively reach the cochlea because of infection, obstruction, or damage. It usually results from otitis media, chronic otitis externa, or excess cerumen, and less commonly from tympanum rupture or ossicle damage. Resolution of the obstruction or tissue damage usually restores hearing. Recovery after otitis media can take weeks while the body phagocytizes the infection residue and hearing is progressively restored. Primary secretory otitis media (glue ear), especially in Cavalier King Charles Spaniels, produces a persistent conduction deafness that can be treated by myringotomy, bulla osteotomy, or tympanostomy tubes. Ear canal resection results in decreased hearing but does not necessarily lead to complete deafness.
Sensorineural deafness results from loss of cochlear nerve (hair) cells and is not reversible in mammals. Clinical experience indicates that hearing aids have limited effect. Acquired sensorineural deafness may be due to intrauterine infection or toxins, otitis interna or meningitis, mechanical or noise trauma, ototoxic effects, anesthesia, neoplasms, or aging (presbycusis). Loss can be bilateral or unilateral, and partial or complete. Otitis interna is often accompanied by vestibular signs, such as head tilt and circling. Hunting, police, or military dogs exposed to loud percussive sounds (eg, gunfire) experience cumulative losses that may initially go unnoticed. When hunting dogs experience sensorineural deafness from noise trauma, the distance from which the dog is able to respond to commands shrinks by half or more. Hearing protection devices are available.
A variety of drugs and chemicals are potentially ototoxic and vestibulotoxic, especially aminoglycoside antimicrobials (gentamicin, amikacin), antineoplastic drugs (cisplatin), salicylates, loop diuretics (furosemide), and antiseptics (chlorhexidine). The damage from toxicosis is usually permanent. Aminoglycoside toxicosis is the most common. The ability to hear high frequencies, well above the range of human auditory perception, is affected first, slowing pet owners' recognition of hearing loss; consequently, the loss may not be detected until weeks after drug treatment has been discontinued.
Pearls & Pitfalls
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Dogs or cats undergoing general anesthesia for teeth or ear cleaning occasionally awaken bilaterally deaf; however, the mechanisms, which can be conductive or sensorineural, are unknown. Few cases of postanesthesia bilateral deafness have been reported for procedures on body regions other than the mouth and ear, and there are no known cases of unilateral deafness resulting from anesthetic procedures.
Many geriatric animals develop presbycusis (age-related hearing loss). Middle to high frequencies are affected first, followed by progressive loss of hearing at all frequencies. The loss may appear acute in onset but reflects the animal’s eventual inability to compensate for progressive loss that has been developing for some time. Sex of the animal does not appear to affect prevalence. Onset of presbycusis is typically in the last third of a breed’s typical lifespan and progresses to complete deafness if the animal lives long enough.
Unilaterally deaf animals show few clinical signs. The main signs may be an inability to localize sound origins and a tendency to orient toward the good ear; however, many animals compensate and show no clinical signs. Bilateral orienting pinnae movements persist in unilaterally deaf animals. Bilaterally deaf animals do not respond to sound stimuli but become adept at paying increased attention to other senses, such as vision and vibration. Affected animals take cues from the behavior of littermates or from other household pets responding to sounds.
Breeders of dog breeds highly prone to deafness often choose to euthanize bilaterally deaf (and spay/neuter unilaterally deaf) animals because of the potential for a deaf dog to have poor quality of life and for its owner to have increased liability from the dog's unpredictable behaviors, such as startle biting. Bilaterally deaf dogs can be successfully raised; however, more dedication than normal is required. Dog owners have used obedience hand signals and sign language successfully to improve communication with deaf dogs. Owners of deaf dogs should be counseled to protect their pets against undetected dangers, such as motor vehicles.
Dogs that lose hearing later in life appear to cope well but occasionally exhibit transient behaviors suggestive of auditory sensations similar to subjective tinnitus in humans. Such transient behaviors include not attending to vocal commands or sounds in general and routinely staying where they can see their owners. There is no evidence that deaf animals otherwise experience pain or discomfort from the condition.
Identification of deafness is most accurate with BAER testing at referral centers (see normal BAER testing output and abnormal BAER testing output images; however, behavioral testing is typically used in the clinical setting. Behavioral testing for deafness involves observing an animal's response to a sound stimulus outside its visual field. This approach is limited by several factors, including the inability to identify unilateral deafness, stimulus detection through other senses, blunted responses in stressed animals, and failed responses from expired novelty of a repeated stimulus. In the home environment, failure of a sleeping animal to waken to an auditory stimulus that does not activate other senses is a suggestive indicator of bilateral deafness.
Courtesy of Dr. Peter M. Scheifele.
Courtesy of Peter M. Scheifele.
A thorough evaluation to determine hearing threshold and middle ear function consists of BAER threshold testing and otoacoustic emissions testing (testing that measures faint sounds produced by vibration of cochlear hair cells in response to sound to determine hair cell function).
Otoscopic examination of the external ear and tympanum, radiographic or CT evaluation of the tympanic bullae, and neurological examination may reveal the cause of deafness, especially in cases of conduction deafness, which usually respond to appropriate medical or surgical treatment. Early intervention in patients with ototoxic effects may decrease or reverse hearing loss but usually is not successful. Once developed, sensorineural deafness cannot be reversed, and its cause cannot be determined. Congenital deafness in breeds with white pigmentation is nearly always of genetic origin.
Key Points
Most deafness in dogs and cats is congenital and hereditary and is associated with white pigmentation and blue eyes.
Deafness can be mild, moderate, severe, or complete, as well as unilateral or bilateral.
Sensorineural deafness is irreversible, whereas conduction deafness frequently resolves.
Hearing loss in middle to late life usually results from otitis, ototoxic effects, noise trauma, or presbycusis.
BAER and otoacoustic emissions testing can be used to confirm and characterize deafness in animals.
For More Information
University of Cincinnati: FETCHLAB animal hearing and bioacoustics laboratory.
Also see pet owner content regarding deafness in dogs, deafness in cats, and deafness in horses.
References
Webb AA, Ruhe AL, Neff MW. A missense mutation in MYO7A is associated with bilateral deafness and vestibular dysfunction in the Doberman pinscher breed. Can J Vet Res. 2019;83(2):142-148.
