Deafness in cats has long been associated with all-white cats, and there is a known genetic link between a white coat with blue eyes and deafness. Cats that are born deaf have what is called “congenital deafness.”
Cats that become deaf later in life have “acquired deafness,” and this can happen to your cat. We will discuss the ways that cats can go deaf, and help you do everything you can to avoid this outcome for your feline friend. It’s important to note, though, that because eardrums do thicken with age, geriatric hearing loss and deafness are common and often unavoidable.
How Do Cats Hear?
Sound starts as air vibrations that are picked up first by the outermost part of the cat’s ear (pinna), then directed deeper to the ear drum (tympanum). From there, the vibrations move through the middle ear to the inner ear, which is filled with fluid. The air vibrations create waves in this fluid. These waves bend tiny hair cells in the inner ear. This bending biochemically results in neurotransmission along a cranial nerve to the brain, where sound is perceived.
The transmission of sound can be interrupted at any one of these steps. When something blocks the sound from reaching the inner ear it’s called conductive deafness. When there is damage or a defect anywhere from the inner ear to the brain it’s called sensorineural deafness. Conductive deafness is usually acquired. Sensorineural can be congenital or acquired. Causes of congenital deafness include difficulties during birth (dystocia) and toxins encountered by the queen during pregnancy.
Causes of acquired sensorineural deafness include:
- A rare complication of general anesthesia
- Age-related hearing loss (presbycusis)
- Chronic excessive noise exposure
- Head trauma
- Inner ear infection (otitis interna)
- Medications or compounds that damage the inner ear (ototoxins)
- Causes of acquired conductive deafness include:
- Ear canal foreign bodies, polyps, tumors
- External ear infection/inflammation (otitis externa)
- Middle ear infection/inflammation (otitis media)
- Wax impactions
There are no fancy tests for diagnosing deafness available to most veterinarians in general practice. Typically, owners notice behaviors that make them suspect their cat can’t hear:
- Difficult to wake
- Easily startled
- Less interactive
Kittens with congenital deafness are frequently more vocal than their littermates and tend to play much more aggressively, as they can’t hear their siblings’ loud complaints when things get too rough.
Testing by your veterinarian in the exam room usually involves making loud startling noises and assessing the response. This test is rudimentary and, as you can imagine, very subjective.
A definitive objective test is available at some specialty centers like the Cornell University College of Veterinary Medicine. It is called Brain Stem Auditory Evoked Response (BAER) test. The BAER test uses electrodes to record inner ear and brain responses to sound. It usually does not require sedation and only takes a few minutes, but it is not often done.
“The procedure is straightforward,” says Ellis Loew, PhD, professor of physiology at Cornell. “Three stainless steel needle electrodes are placed just under the skin. One is placed on the top of the head between the ears, one below and behind the ear canal, and the other in an earflap or on the midline of the back. A small earpiece is placed into the ear canal and a click stimulus delivered. The signal arising from the click is recorded and displayed on the computer screen.
“This is usually of no problem when doing dogs,” says Dr. Loew, “however, for cats, it is necessary to sedate or even anaesthetize. They do not like needles under the skin or an earpiece in the ear. For this reason, I have only on rare occasions done testing on cats.”
The exception is cats with sudden acute hearing loss, he says. “This can arise after dental procedures, where stretching of the mouth has cut off the blood supply to the inner ear; after an acute ear infection after the taking of some drugs; or idiopathic hearing loss (no known reason).”
What You Can Do
First and foremost, have your cat examined by your veterinarian annually until 10 years of age. After that, every six months is recommended. If your veterinarian does not perform a full otoscopic exam each time, request one. This is the best way to identify most of the causes of acquired conductive deafness outlined above. The earlier problems are identified and rectified, the less likely they are to result in deafness.
If your cat shows any signs that her ears are bothering her, make an appointment with your veterinarian right away. Signs that something is bothering your cat’s ears include head shaking, scratching at the ears, crying or reacting badly if the ears are rubbed or touched, odor or discharge from the ears, head tilt, loss of balance, and loss of appetite.
If medications are prescribed for your cat, ask your veterinarian if the medication is potentially ototoxic. Some of the most common ototoxic medications used in veterinary medicine are aminoglycoside antibiotics (gentamicin, amikacin), other antibiotics (tetracycline, ampicillin, chloramphenicol), some chemotherapy drugs, some diuretics, and a handful of other drugs.
A popular antiseptic used in veterinary medicine, chlorhexidine, has been linked to deafness when instilled in the ear canals of cats.
If a potentially ototoxic medication is deemed necessary for your cat, be sure to follow the directions carefully. Using too much of a topical solution can increase ototoxicity, as can treating for longer than the recommended time.
Monitor your cat carefully during treatment. If there is any suspicion that an adverse event is happening, the sooner you discontinue the medication the better the prognosis for return to normalcy.
Some ototoxins will cause deafness as the only identifiable problem. Others may cause balance issues (vestibular signs) including head tilt, loss of balance, and an abnormal jerking movement of the eyes (nystagmus). If you pick up on any of these signs, discontinue the medication right away and see your veterinarian. Unfortunately, deafness from ototoxicity is frequently permanent. Balance issues will typically resolve.
If your cat becomes deaf for whatever reason, keep him or her indoors! This is paramount for his or her safety.
It is a great kindness to avoid unnecessary startling of deaf cats. One way to do this is by stomping your feet on the floor when approaching, as the vibration will alert them to your presence. Flicking the lights on and off when you get home helps, too, if they are awake at the time.
Nobody wants their cat to go through life unable to hear your voice or hear birds sing. While some of the causes of deafness in cats are not amenable to treatment, many are. Many times, with appropriate treatment, deafness can be avoided. Even in those cases that cannot be cured, though, there are things we can do to make the lives of deaf cats happy, safe, and fulfilling.