Deafness in Dogs and Cats

Oct 25, 2023

Deafness, or an inability to hear sounds, affects dogs and cats as well as humans. It may be difficult to recognize and diagnose in pets due to their lack of ability to communicate hearing difficulty, the struggle to identify true hearing loss from inattentiveness, and the remarkable ability of cats and dogs to compensate for deficits in special senses.

When compared to humans, healthy dogs and cats have a much different range of hearing. Most humans can hear sounds in the 30 Hz (low frequency) to 20 kHz (high frequency) range. By comparison, a cat has a range of about 50 Hz to 80 kHz, and a dog has a range of about 40 Hz to 45 KHz (though references vary significantly and are based on age, breed, and a variety of other factors).

In order for an animal to hear, sound must travel through the air, and be channeled by the pinna (the large external portion of the ear) into the ear canal. In veterinary species, this is divided into the vertical and horizontal components. Sound is directed through this canal and contacts the eardrum, which vibrates in response to this sound. This vibration is conducted through the “middle ear” by three bones (or “ossicles”); the incus (anvil); malleus (hammer); and stapes (stirrup). These translate the vibration to the cochlea in the inner ear. The cochlea is a snail-shell shaped organ that contains fluid and is lined by small hair like projections called “cilia”. These cilia vibrate back and forth in response to movements of the fluid generated by the action of the ossicles; the exact cilia that vibrate depend on the frequency or pitch of the sound. Vibrations of cilia are transformed into electrical signals which travel down nerves to the brain, which registers them as sound.

Deafness in dogs and cats (as in other species) can be broadly divided into two primary types: conductive or sensorineural. If sounds cannot travel properly from the air, through the external or middle ear, the problem is said to be conductive. This can occur when there is an ear infection, a ruptured eardrum, blocked ear canals, fluid, tumors or polyps in the ear, or any other disruption to conduction. Anything that happens between the outside environment and the cochlea causing deafness is considered conductive. Usually, in these patients, hearing loss is only partial and treatment involves medical or surgical correction. While hearing does not always recover, it carries a better prognosis. If this is the case with your dog, a veterinarian may be able to resolve your pet's deafness with appropriate diagnosis and treatment.

If the deafness is sensorineural, the issue occurs somewhere between the cochlea and the brain and generally involves deficits to nerves or the brain. Sensorineural deafness is often due to nerve abnormalities or problems with the hydrodynamics or physics of the inner ear. This type of deafness is more difficult to treat and is more often complete. It is more often congenital but may also occur as a result of aging – the deafness associated with age in humans (and likely dogs) appears to be sensorineural in nature.

Deafness can be hereditary in many breeds of both dogs and cats. It may occur in a wide variety of breeds due to several genetic or other congenital issues. Perhaps the most common congenital deafness in veterinary medicine is that associated with blue eyes, as the counterpart to human Waardenburg syndrome. In this condition, animals with white coats and blue eyes may have sensorineural deafness on the same side (or sides) as the blue eye(s). This is due to a failure of development of components of the middle ear. It occurs in color point cats and Merle coated dogs.

Deafness is difficult to evaluate in both dogs and cats, especially if only one ear is involved or if there is only partial deafness. In many cases deafness is not appreciated in animals until it is very progressed. Congenital deafness may never be recognized in many cases, and animals may be written off by owners as “difficult to train” or unintelligent. This is a classic condition in Dalmatian dogs, in whom deafness is often dismissed as stubbornness or difficulty in training.

Definitively determining the hearing status of dogs and cats may be very difficult. Often a response to sound is used to determine if an animal can hear. Care must be taken to ensure an animal is not responding to the motion of a hand moving (ie to snap fingers) or changes to facial expression. In many cases, pets will display an involuntary flicking or twitching of the ears (called Pryor's reflex) in response to a sound.

Definitive diagnosis of deafness in animals relies on an electrodiagnostic test called a “Brainstem Auditory Evoked Response” or “BAER”. This is a relatively simple test that involves placing earplugs in an animal’s ear canals and small electrodes on the head and measuring changes in brain waves in response to a noise. Access to this test is, however, limited and often only available in veterinary teaching hospitals.

Suspected deafness in dogs and cats should be promptly investigated by a veterinarian, especially if it is new onset. It may reflect more serious underlying disease, represent simple aging changes, or be an unrecognized congenital issue.

References

Ryugo DK, Menotti-Raymond M. Feline deafness. Vet Clin North Am Small Anim Pract. 2012 Nov;42(6):1179-207. doi: 10.1016/j.cvsm.2012.08.008. Epub 2012 Oct 9. PMID: 23122176; PMCID: PMC3490225.
Strain GM. Canine deafness. Vet Clin North Am Small Anim Pract. 2012 Nov;42(6):1209-24. doi: 10.1016/j.cvsm.2012.08.010. Epub 2012 Oct 10. PMID: 23122177.
Strain GM. The Genetics of Deafness in Domestic Animals. Front Vet Sci. 2015 Sep 8;2:29. doi: 10.3389/fvets.2015.00029. PMID: 26664958; PMCID: PMC4672198.

Author

Matthew Kornya, BSc, DVM, ABVP (Feline) Residency Trained, Resident ACVIM (SAIM)
Consulting Editor

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