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Deafness in dogs and cats can have many causes
I have had many a pet owner come to me and wonder if their dog or cat is deaf. Most times it is said somewhat tongue-in-cheek and followed up with a statement similar to, "well no one else in the house listens to me either, so why should the dog?" But there are times that the owners are concerned. What causes deafness in pets? How do we diagnose if deafness is present?
Before we discuss deafness it would be best to briefly review how sound travels through a healthy ear to the brain. Sound waves travel down the external ear canal to the tympanum (ear drum) causing it to vibrate. The vibration continues through some small bones in the middle ear and into a snail shaped organ of the inner ear called the cochlea. The cochlea contains highly specialized hair cells that convert sound vibrations into nerve impulses. The impulses travel through a nerve called the vestibulocochlear, up the brainstem and finally reaching the auditory portion of the higher brain (the cerebral cortex).
If a pet is deaf there are two types of deafness: acquired and congenital (genetic). It is true that dogs and cats will lose their hearing (sometimes going completely deaf) as they age due to degeneration of cells that line the inner ear (that is a benign congenital cause of deafness).
Other conditions that can cause acquired deafness include: chronic infections of the outer or middle ear, tumors (benign or malignant) and secondary to certain medications.
Congenital deafness can be more difficult to diagnose early on because like human infants, even healthy puppies and kittens are still developing the sense of sight and sound in the early stages of life. The first hearing of sound is estimated at six to eight weeks but can take months to fully develop.
Coloring can help, as all white puppies and kittens have been shown to have an increased risk for deafness, as well as certain breeds (e.g. dalmations).
How do we test for deafness? A good breeder may notice signs early on but not always. Dogs and cats will respond to vibratory cues (stomping feet, a shutting door), as well as visual cues (clapping hands). This can make it difficult for both you (at home) and your veterinarian (with an exam) to assess. It can also be difficult to assess if the deafness is one-sided or in both ears.
There is a test called a BAER, or Brainstem Auditory Evoked Response, test to definitively diagnose deafness in pets. The BAER test can be performed on awake, sedated or anesthetized animals. It relies on specialized ear plugs in conjunction with electrodes arranged in a specific pattern on the scalp. Sound waves are delivered at a specific frequency in a series of clicks in the stimulated ear and "white noise" in the nonstimulated ear. As the clicks or tones are delivered a series of waves that represent electrical activity in the brain are recorded. These waves will represent the ability to hear. The BAER test needs to be performed and interpreted by a specialist but there are many great referral hospitals right here on Long Island.
Dogs and cats born deaf can live long, healthy lives with certain modifications in their lifestyles. I personally feel keeping deaf cats inside, only walking deaf dogs on a leash or letting them play in fenced-in backyards, etc. is a small price to pay on our part. Therefore, if you are concerned with your dog or cat's deafness, discuss it with your veterinarian right away.
Dr. Kearns has been in practice for 14 years.