Feline Hearing Loss


Have you ever noticed how as we age, people seem to mumble more? It couldn’t be our hearing! I hear just fine -- except for the fact that I have to strain to hear conversations and the television. As we grow older we naturally experience some hearing loss -- a sequel to exposure to loud sounds like music or environmental sounds damaging the hearing mechanism.

Cats can have hearing loss too. Most hearing problems in cats are associated with aging but other less common causes may occur and often very mature cats become completely deaf.

How does hearing loss occur?
In most cases of age-related hearing loss, deafness occurs as a result of damage to the ear system and nerves. It is primarily a degenerative change. Hearing may also be diminished by obstructions in the ear such as debris, infections, masses or even medications. These should all be ruled out before making a diagnosis of degenerative hearing loss.

What are the signs of hearing loss?
Clinical signs of hearing loss in cats can be somewhat subtle and owners are often unaware of changes until they are very advanced. Early signs of deafness may include:

  • A lack of response to everyday sounds that would ordinarily elicit a response (opening a can of food or shaking a bag of treats)
  • Not hearing your footsteps when you come close
  • Being a very sound sleeper
  • Meowing very loudly
  • Failure to respond when called

How can my cat be tested for hearing loss?
Sophisticated tests are available and may be of value when evaluating kittens for the potential of breeding, but they have no bearing on the treatment or outcome. Your vet might administer a test called the Brainstem Auditory Evoked Response (BAER)1. It’s a painless procedure but can be expensive so ask your veterinarian to try other evaluations first. Examples of test include:

  • Tear a piece of paper behind the cat’s head. Make sure you don't touch the cat but he should turn and respond.
  • Crackle a bit of tinfoil or jingle a bunch of keys when he is sleeping or not looking. This tests high frequency hearing.
  • Hiss. This is a universal danger sound. Shield your breath with a tissue or clothes so he can't feel you blowing.
  • Tap a cardboard box or something that makes a drumming noise to test low frequency hearing.

What can you do should your cat go deaf?
Deafness is often insidious, progressive and irreversible. People ask about hearing aids and certainly they have been used successfully in dogs but it is extremely unlikely those would be tolerated by a cat and would be easily lost.

How to protect your deaf cat?
Deaf cats just like deaf people are sometimes at increased risks, especially outdoors. They cannot hear an oncoming car. They cannot hear another cat that may be aggressive or a dog that may pose a threat. For this reason alone it is particularly important that hearing impaired cats be kept indoors unless on a leash.

Similarly, deaf cats cannot hear their owners calling them and should they wander away they can be very difficult to find and return. All cats should be implanted with an identifying microchip but this is particularly critical for deaf or blind cats.

A deaf cat can still be a great pet! He will just need more affection, patience and a few more “I love you” signals.

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.

Resources:


Cochlear Anatomy and Physiology

Understanding mechanisms of deafness begins with a basic knowledge of the normal anatomy and physiology of the auditory pathway. Because the auditory system is complicated with many working parts, there are innumerable potential sources and locations where problems could arise. The first part of this review highlights structural and functional features of the peripheral and central auditory system. This background will provide a context with which to review the pathophysiology of hereditary and acquired deafness.

The cochlea is a spiraled bony tube housing three fluid-filled chambers that spiral along its length ( Fig. 3 ). Highly specialized cells within the cochlea regulate the ionic composition of these chambers. One chamber is folded back at the apex to form two outer chambers (scala tympani and scala vestibuli) that sandwich a middle chamber (scala media). These outer chambers are confluent at the apex and contain perilymph, a filtrate of cerebrospinal fluid of similar composition to extracellular fluid (e.g., high sodium, low potassium). The middle chamber contains endolymph, a high-potassium, low-sodium fluid of similar composition to intracellular fluid. The outer wall of scala media is partially lined by the stria vascularis ( Fig. 3 ). The stria is a vascularized, multilayered epithelial structure formed by three different cell types: marginal, intermediate, and basal cells ( Fig. 4 ). A superficial layer of marginal cells borders the endolymph. Pale-staining basal cells are linked to each other, to intermediate cells, and to fibrocytes of the spiral ligament by gap junctions. This network provides cytoplasmic confluence that allows the free diffusion of K + toward the marginal cells. Intermediate cells are marked by the presence of melanosomes and by deep infoldings of the plasma membrane that are matched by those of the overlying marginal cells. The resulting dense, labyrinthine membrane system of narrow compartments is filled with mitochondria and surround the penetrating capillaries that course longitudinally along the epithelium. The elaborate infoldings of membrane greatly amplify the cell surface in order to transfer K + into marginal cells for secretion into the endolymph [40,41].

Anatomy of the inner ear. (A) view of right hearing and balance apparatus. The cochlea is the coiled structure on the right and the semicircular canals of the vestibular system are on the left. For the cochlea, “A” indicates the apex (low frequencies) and “B” indicates the base (high frequencies). The stapes, a middle ear bone, inserts into the vestibule of the inner ear the round window (RW) is covered by a membrane that relieves the pressure when the stapes “pistons” into the ear. The auditory (AN) and vestibular (VN) nerves bundle together to form the 8 th cranial nerve. (B) A section of the otic capsule has been cut away (indicated in A) to reveal the three chambers of the labyrinth. The sensory organ resides in the scala media (yellow). (C) A rotated view of the cut end of a cochlear turn showing the three chambers, with the scala media (yellow) and the stria vascularis. (D) Enlarged diagram showing a cross-section through the scala media, emphasizing the organ of Corti and the hair cell receptors.

Abbreviations: IHC, inner hair cell OHC, outer hair cells RM, Reissner’s membrane SG, spiral ganglion SM, scala media ST, scala tympani StV, stria vascularis SV, scala vestibuli TM, tectorial membrane. Adapted from Fig. 1 , Eisen and Ryugo, 2007. (Eisen MD, Ryugo DK, Hearing molecules: contributions from genetic deafness, Cell Mol Life Sci 2007 Mar 64(5): 566-80, with permission.)

Schematic drawing of the stria vascularis. Movement of K + ions through the gap junctions and then into the endolymph by way of ion pumps is crucial. This structure is the part of the inner ear that provides the special chemical environment that allows the system to function. (Courtesy of Dr. David K. Ryugo, Garvan Institute of Medical Research, Sydney, Australia.)

As a result of the differences in ionic composition between the compartments, the potential difference between endolymph and perilymph is about +80 mV. This positive potential is the largest found in the body. Since the intracellular resting potential of hair cell receptors is around −70 mV, the potential difference across the hair cell apex is a remarkable 150 mV. This large potential difference represents a tremendous ionic force and serves as the engine driving the mechanoelectrical transduction process of the hair cell [42]. Membrane specializations that feature gap junctions allow free passage of K + ions through fibrocytes and basal cells and into intermediate cells. K + channels and pumps transfer K + from intermediate cells into the intrastrial fluid and then it gets concentrated in the marginal cells. K + is driven into the endolymph down the K + concentration gradient established in the marginal cells. The cycling of K + through the receptor cells and back into the endolymph is key to normal cochlear function.

Gap junctions are channels that allow rapid transport of ions and small molecules between cells. In the stria vascularis, the ion is potassium (K + ).

Connexins are transmembrane proteins that form gap junction channels. Four different connexin molecules have been identified in the cochlea, including connexin 26, 30, 31, and 43 [43].

Mutations that affect internal ear connexins result in hearing impairment and deafness.

Mutations that affect K + transport result in hearing impairment and deafness.

Properties of the cochlea

Sound vibrations are eventually delivered to the stapes, whose footplate serves as a kind of piston and imparts vibrations to the fluids of the scala vestibuli. Specializations within the cochlea decompose the mechanical stimulus of sound into its frequency components. The basilar membrane is a fibrous sheet stretched across the floor of scala media. Its width and thickness vary systematically from the base to the apex of the cochlea in that there is a continuous elasticity gradient from one end to the other. The base is narrow and thick, whereas the apex is wide and thin. This structure functions like a frequency analyzer where it resonates to high frequencies at the base and to progressively lower frequencies along towards the apex.

The organ of Corti is the sensory organ for hearing.

It is a multisensory structure that consists of the following:

Inner hair cells that are the primary sensory receptor

Outer hair cells that modify the activity of the inner hair cells

The organ of Corti rests on top of the basilar membrane ( Fig. 5 ). Inner hair cells synapse onto afferent endings of the myelinated cochlear nerve fibers and are primarily responsible for conveying sensory information to the brain. In contrast, outer hair cells synapse on a small number of unmyelinated cochlear nerve fibers and receive large efferent nerve endings. The outer hair cells also contain contractile machinery that responds to membrane voltage changes. The outer hair cell’s function appears more involved with amplifying and manipulating the sound stimulus. Specialized supporting cells in the organ of Corti complement the hair cells and have a vital role in maintaining the integrity and function of the hair cells. A final component of the cochlea’s functional apparatus is the tectorial membrane, a gelatinous ribbon of extracellular matrix attached medially and contacting the outer hair cell hair bundles.

Components of the organ of Corti. (A) The organ of Corti rests on the basilar membrane, and is composed of the sensory receptor cells (OHCs and IHCs), supporting cells (yellow) and the tectorial membrane (TM). (B) The hair cell receptors are innervated by afferent type I (blue) and type II (green) terminals as well as by efferent (ET, red) terminals whose cell bodies reside in the brain stem. At the apical ends of the receptor cells are stereocilia that form part of the transduction apparatus with tip-links and channels (upper right). Adapted from Fig. 1 , Eisen and Ryugo, 2007. (Eisen MD, Ryugo DK, Hearing molecules: contributions from genetic deafness, Cell Mol Life Sci 2007 Mar 64(5): 566-80, with permission.)

Hair cell anatomy, function, and innervation

Hair cells are polarized in that a bundle of stereocilia protrude from one end of the cell, their apex, which are composed of actin filaments ( Fig. 5 ), whereas afferent innervation occurs only at the opposite end, the base. Interconnecting links from the tip of a shorter stereocilia to the shaft of a longer neighbor, called “tip links”, attach to the mechanoelectric transduction channel [44,45]. Mechanical oscillations of the basilar membrane cause stereocilia within hair bundles to be displaced relative to each other. This displacement puts the tip links under tension and “pulls open” cation channels. Due to the high endocochlear potential, cations flow into the hair bundle and depolarize the hair cell membrane potential. Where the apical end of the cell transduces mechanical energy, the basal end releases neurotransmitter and activates afferent synapses.

The intracellular processes that respond to changes in membrane potential are distinctly different between the two types of auditory hair cells. Inner hair cells form afferent synapses where membrane voltage changes are converted to action potentials in myelinated cochlear nerve fibers outer hair cells, however, contain electromotile elements within their cell membrane and generally serve as mechanical amplifiers of the sound stimuli for inner hair cells [46].

The pre-synaptic machinery of inner hair cells is geared to generate graded release of neurotransmitter along their basolateral surface. Voltage-dependent Ca ++ channels are localized with neurotransmitter release sites that open in response to membrane depolarization, which in turn results in the release of neurotransmitter. The amount of transmitter release is modulated by the magnitude of the membrane voltage change. Neurotransmitter diffuses across the synaptic cleft and binds to postsynaptic receptors on afferent dendrites of cochlear nerve fibers. This process begins the generation and propagation of action potentials along the afferent fibers.

Outer hair cells contain a contractile apparatus that responds to membrane voltage changes with contractions or elongations of the cell proper. This mechanical response appears to be conformational changes in cytoskeletal proteins of the plasma membrane wall that serve to modulate the oscillations transmitted to the inner hair cells’ hair bundles. In addition to the electromotile apparatus within the outer hair cell, a system of efferent auditory feedback innervates the hair cells. Both systems work in concert to tune and amplify the sound source [46].

The spiral ganglion

Spiral ganglion cells reside in Rosenthal’s canal of the cochlea ( Fig. 6 ). Their peripheral processes innervate the hair cell receptors, and their central processes conduct auditory information to the brain. Two types of ganglion cells have been described [47,48].

Type I ganglion cells are large (20–30 µm in diameter), have myelinated processes, represent 90–95% of the population, and innervate inner hair cells.

Type II ganglion cells are small (15–20 µm in diameter), unmyelinated, represent the remainder of the ganglion population, and innervate exclusively outer hair cells.

Receptor innervation by ganglion cells. (Top) drawing that illustrates the segregated innervation of hair cells by the two types of spiral ganglion cells. Type II neurons represent only 5–10% of the population and innervate multiple outer hair cells. In contrast, type I neurons represent the remaining 90–95% and innervate exclusively inner hair cells. Each IHC is innervated by 10–20 ganglion cells. (Bottom) photomicrograph of representative type I and type II ganglion cells as stained by horseradish peroxidase [100] (Kiang, NY-S, Morest, DK, Godfrey, DA, et al. Stimulus coding at caudal levels of the cat's auditory nervous system. I. Response characteristics of single units. In: Basic Mechanisms of Hearing. AR Moller, eds. New York: Academic Press 1973. pp. 455–478.)

Cats have approximately 50,000 ganglion cells in each ear [49]. The central axons of the spiral ganglion cells collect within the central core of the cochlea, called the modiolus, and form the cochlear nerve. The cochlear nerve joins with the vestibular nerve to form the vestibulocochlear nerve, which together, along with the facial nerve, occupies the internal acoustic meatus within the petrous portion of the temporal bone. The vestibulocochlear nerve travels toward the brainstem where the cochlear branch enters and terminates within the cochlear nucleus, whereas the vestibular branch pass beneath and around the cochlear nucleus to arch up to the vestibular nuclei.


Considering adopting a deaf cat or wondering how to tell if your cat is deaf? Here is our guide to caring for them.

Whether you’ve decided to adopt a deaf cat from a rescue centre or are learning to cope with your cat’s diagnosis, there are plenty of ways to help make your feline friend’s life easier. While rehoming a special needs cat can be daunting at first, it is incredibly rewarding and many deaf cats can be very affectionate.

Are cats born deaf?

Some cats are born deaf, while others gradually lose their hearing as they age. For most cats, sudden loss of hearing is normally the result of illness or injury.

Thankfully, deaf cats adapt to their surroundings surprisingly well and easily compensate for their lack of hearing by using their other senses more. In fact, in many cases, it can be difficult for owners to even tell whether their cat is deaf. You can find out more about how to tell if your cat is deaf below.

For cats, there are varying degrees of deafness and a range of different causes, which may or may not be treatable. There are two types of deafness – reversible and permanent.

Reversible deafness in cats

Some types of deafness in cats are reversible by treating the underlying cause. For example, where the sound cannot pass into the ear. This could be due to:

  • polyps
  • tumours
  • outer and middle-ear infections
  • wax build-up
  • ear mites

Permanent deafness in cats

Permanent deafness is usually when the nerves associated with the ear do not function properly, and is usually due to:

  • genetic issues
  • inner ear infections
  • drug toxicity
  • noise trauma
  • age-related degeneration

To find out whether your cat‘s deafness can be treated, it is best to speak to your vet. Like humans, each cat is an individual and has individual needs.

Symptoms of deafness in cats include:

  1. a failure to respond when spoken to or called
  2. being easily startled
  3. signs of dizziness or disorientation
  4. no longer being afraid of the vacuum cleaner or other loud appliances
  5. shaking their head or clawing at their ear
  6. pus or other discharge coming from the ear, or an unpleasant odour coming from the ear

Is my cat deaf or ignoring me?

For most owners, it can be tricky to tell whether your cat is deaf or just has selective hearing. For example, they may ignore you when called but react quickly at the sound of the biscuit box being rattled! One of the biggest indications that your cat may be deaf is to listen to their meows. Some deaf cats call out more often and more loudly as they struggle to regulate their own volume. Other deaf cats will become completely mute.

Caring for a deaf cat

Rehoming a special needs cat, such as a deaf cat, requires a little extra care and patience but most deaf cats are adaptable and can maintain a great quality of life. There are a few things, however, that you can do to help your cat adapt to their environment. When caring for your deaf cat, keep the following tips in mind.

  • Approach your cat with heavy footsteps to make sure they are aware of you approaching. A deaf cat can be easily startled. If you are close to the cat, a sharp hand clap or stamping on the floor might be enough to get their attention
  • Keeping your deaf cat inside is advisable as they are unable to hear danger signals such as cars and other animals. Ensure they are microchipped to identify them in case they escape and if needed, set up a secure section of the garden or outside run for them to safely play in. For cats living indoors, it is vital you keep them stimulated with interactive toys and puzzle feeders to avoid boredom.
  • Deaf cats can learn to recognise hand signals or the flashing of a torch if they can’t hear you calling them. Make sure the signal you choose to call your cat is distinct and consistent so they don’t get confused
  • To wake a sleeping deaf cat, touch the area around them rather than the cat itself. This is less likely to startle them
Find out more about cats and play

Are all white cats deaf?

Interestingly, deaf cats who are white and have blue eyes make up around just 1-1.5% of the total cat population. Due to their genetic make-up, a white cat with blue eyes is 3-5 times more likely to be deaf than a cat with different coloured eyes. While there is no treatment for hereditary deafness in cats, most cats adapt well to their condition.

Do deaf cats meow?

Some deaf cats can be overly noisy, with many crying out in the night when everyone is asleep. Others are quieter, making little to no noise at all. Both are completely normal. For noisy cats, some use their yowling as a way to detect what is going on around them. By making a loud noise, the sound waves travel and are reflected back at them, picked up through their whiskers like a clever cat radar.


Pet Hearing Loss

Many of the same health problems that affect us, including hearing loss, also affect our pets. Fortunately, most pets adapt very well to the disability with a little help from their owners.

What Causes Hearing Loss in Pets?

Some pets are born deaf or hard of hearing, while others develop hearing loss at some point in their lives. Hearing loss can be caused by exposure to heavy metals, such as mercury or lead, or may occur after your pet takes certain medications, including chemotherapy drugs, diuretics or antibiotics.

Tumors in the ear canal or brain may be responsible for hearing loss or deafness. Other potential causes include untreated ear infections, hypothyroidism, distemper, injuries or exposure to toxic household products.

Hearing loss may also occur as part of aging. Deterioration of the nerves used in hearing or thickening of the ear canal can gradually reduce your older pet’s ability to hear.

Are Some Pets More Likely Than Others to Experience Hearing Loss?

Hearing loss is linked to genetics, in some cases. The problem is more likely to occur if the pet has white pigments in its fur. In fact, approximately 80 percent of white cats with two blue eyes will show signs of deafness as early as four days after birth, according to Cornell University College of Veterinary Medicine. The problem occurs due to degeneration in the cochlea in the inner ear. The cochlea turns vibrations into nerve impulses and sends them to the brain, which interprets the nerve impulses as sounds.

Pigment-related deafness in dogs occurs when blood supply to the cochlea is restricted, causing nerve cell death. Although pigment-related hearing loss can occur in any breed, two genes that cause this type of deafness are more commonly found in certain breeds, such as Great Dane, Collie, Old English and Shetland Sheepdogs, Samoyed, Dalmatian and Bull Terriers, according to Louisiana State University veterinarian Dr. George M. Strain

What Are the Signs of Hearing Loss in Pets?

If your pet suffers from hearing loss, you may notice one or more of these signs:

  • Your pet no longer comes when called or exhibits other changes in behavior.
  • Your dog or cat doesn’t react to loud noises.
  • Your pet can suddenly sleep through anything, even loud thunderstorms.
  • Your cat meows constantly, or your dog barks more than normal.
  • Your pet tilts its head to one side.
  • Your dog or cat doesn’t show up the minute you open a can of pet food.

How Can I Help My Pet?

Take your pet to the veterinarian as soon as you notice any signs of deafness. Although treatment is not possible in all cases, if the hearing loss is caused by an inflammation, infection or tumor, medications or surgery may help restore some or all of your pet’s hearing.

If the hearing loss is permanent, it will take a little while for you and your pet to adjust to the new situation. Keep your furry friend safe by using a leash during walks. Getting your pet’s attention can be a little difficult. Pointing a flashlight or laser near your dog or cat (but away from his or her eyes) can be helpful. Teaching your pet some basic hand signals such as come, stay and good job can help create new ways to communicate. In the past, your furry friend may have known that a slamming door meant that you had left the house. If your pet doesn’t see you leave and can’t find you, he or she may become upset. You can prevent confusion by starting a goodbye ritual that you’ll use every time you leave the house.

Are you worried that your pet may be suffering from hearing loss? Call us today to schedule an appointment.

PetMD: Hearing Loss in Dogs

Cornell University College of Veterinary Medicine: Deafness

Orthopedic Foundation for Animals: Genetics and Inheritance of Canine Deafness

Whole Dog Journal: Training the Hearing Impaired Dog Is Not Difficult, 9/03


Why Do Pets Lose Their Hearing?

There are many reasons why a pet can lose their hearing, but it is most often found among older pets. The reason for this is that over time the nerves within the ear degenerate. This can begin in an adult pet, then become more pronounced as they age. This reason for deafness in dogs and cats is similar to the occurrence of hearing loss among older humans.

Other reasons for hearing loss could be a genetic cause resulting in congenital deafness, toxicity, infection, or an injury to the ear canal.


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