Deafness in cats – causes, diagnosis and management plus dog info. too

This article covers the causes, the breeds most commonly concerned, diagnosis and management of deafness in cats (plus info on dog breeds predisposed to deafness). It is closely based on a research paper called: AETIOLOGY, PREVALENCE AND DIAGNOSIS OF DEAFNESS IN DOGS AND CATS by George M Strain published in this instance by Science Direct (the study). I have focused on cats and I have been selective. I have also simplified and summarised without, I hope, changing the meaning. It is quite scientific but I have broken it down to make it more understandable, I hope.

The word “aetiology” means: the study of causation, or origination. It can also be spelled: etiology. In other words what causes deafness in cats and dogs in this instance.

Having skimmed the study document the most intriguing thing for me is that one cause is “ototoxic agents”. In this instance it means drugs, specifically certain antibiotics, which are toxins, that damage the ear (oto-), specifically the cochlea or auditory nerve and sometimes the vestibular system. I discuss that more later in the article.

Deafness in cats – commonly occurring types

I’ll start with a definition: “Peripheral deafness”. This means hearing loss. The word “peripheral” in day-to-day use means: relating to the outside at the edge of things. In this instance it means abnormalities outside the central nervous system.

There are three types of peripheral deafness that are commonly seen in cats and dogs:

1. Inherited congenital sensorineural. “Congenital” means a condition that is present at birth. “Sensorineural” means of or relating to the neural process of sensation¹.
2. Acquired later-onset conductive: “Acquired” means anything that is not present at birth but develops sometime later. “Later-onset” means a condition that happens later in the life of the cat or dog. “Conductive” in this context means the process of transmission of sound in the form of pressure waves to something that we can hear.
3. Acquired later-onset conductive.

Causes of deafness in cats

Inherited congenital sensorineural peripheral deafness is usually caused by the presence of “pigmentation genes responsible for white in the coat”. The gene concerned is the white (W) gene. It is autosomal (not sex-linked) dominant over colour. It is not related to albinism. Homozygous white cats are more prone to having blue eyes (iris) and deafness. The deafness can be one ear or both ears. Sometimes white cats have odd eye colour. If both eyes are blue there is an increased chance of deafness.

Longhaired white cats are more likely to be deaf than shorthaired ones.

However, white cats that have the underlying c^s Siamese dilution pigment gene can have blue eyes without deafness. This may be why purebred white cats are less often deaf than random bred cats (moggies).

The research says that there is no report of deafness in cats who carry the piebald gene or white spotting gene. This gene produces cats with white areas. However, my research indicates to me that the piebald gene can cause deafness in cats.

Studies on the prevalence of deafness in 256 white mixed-breed cats (random-bred) indicate the following:

• 12.1% were deaf in one ear;
• 37.9% were deaf in both ears
• 50% in total were affected
• The occurrence of either being deaf in one or both ears in offspring of parents who were both white cats was between 52 and 96%
• White cats with two blue eyes have an 85% – 64.9% chance of being deaf in both or one ear
• White cats with one blue eye have about a 40% chance of being deaf in both or one ear and
• White cats with no blue eyes have about a 19% chance of being deaf in both or one ear.

White cats of the following breeds carrying the white (W) coat pigment gene and which are at risk of congenital deafness are:

• Cornish Rex
• Devon Rex
• Manx
• Persian
• Scottish Fold
• Turkish Angora
• American Wirehair
• American Shorthair
• British Shorthair
• Exotic Shorthair
• Oriental Shorthair

(Note: the study also refers to “White”, “European White” and “Foreign White” but these don’t make sense to me as cat breeds). You can read about all these breeds by initially clicking on this link and going from there.

Conductive deafness is most often caused by “chronic otitis externa” and media. Chronic otitis externa means chronic inflammation of the skin lining the external ear canal leading to the ear drum. This results in stenosis and closing of the ear canal. “Stenosis” is an abnormal narrowing in a blood vessel or other tubular organ or structure². It may also lead to ossification of the external ear canal.

Another cause is excess production of ear wax (cerumen).

Hearing loss or deafness can also be caused by ototoxic agents as mentioned. I am referring to certain antibiotics (see list below). These can have a direct effect on the cochlear and/or vestibular hair cells or they may damage the stria vascularis causing secondary hair cell loss. The cochlear is the auditory portion of the inner ear². The stria vascularis is numerous capillary loops and small blood vessels in the cochlear.

Tinnitus can accompany deafness caused by ototoxity. Tinnitus is a persistent ringing in the ears. This may result in changes in behavior. Over 180 compounds are ototoxic. Here is a selected list:

Aminoglycside antibiotics	Non-aminoglycodide antibiotics	Misc. agents
Amikacin	Amphotericin B	Aresenic compounds
Dibekacin	Bacitracin	Ceruminolytic agents
Framycetin	Chloramphenicol	Cyclophospamide
Gentamicin	Chlortetracyline	Danazolol
Kanamycin	Colistin	Dapsone
Neomycin	Erythromycin	Detergents
Netilmicin	Griseofulvin	Digoxin
Sisomicin	Hygromycin B	Dimethylsulphoxide
Streptomycin	Minocycline	Gold salts
Tobramycin	Polymixin	Insulin
	Tetracyclines	Lead
	Vancomycin	Mercury
		Potassium bromide
		Prednisolone
		Propylene glycol
		Triethyl & trimethyl tin
		Quinine
		Quinidine
		Salicylates

Other ototoxic agents that can cause deafness in cats are:

Diuretics: Bumetanide, Furosemide, Ethacrynic acid

Antineoplastic agents: Actiomycin C&D, Cisplatin, Nitrogen mustard, Vinblastine, Vincristine.

Antiseptics: Benzalkonium chloride, Benzethonium chloride, Centrimide, Chlorhexidine, Ethanol, Iodine & iodophors.

Old age can also cause deafness in cats. The condition is called “Presbycusis” (age-related hearing loss). Cats normally compensate and so hide it. This gives the impression that it has suddenly occurred when in fact hearing has degenerated to a level where compensation is no longer possible. Hearing aids can be used with dogs. They have not been tried with cats as far as I am aware. This is probably due to the difficulty in training the cat to accept it and the fact that cats compensate so well in using their other skills and senses.

Excessive Noise can cause hearing loss and deafness in cats. It can damage the tympanum (ear drum) and ossicles (bones in middle ear transmitting the sound). It can also break the hair cell cilia.

Other causes of deafness in cats include: meningitis, anoxia (an absence of oxygen supply to an organ or a tissue), malformations and trauma (being hit)

Diagnosis of deafness in cats

Subjective assessments are difficult because, as mentioned, cats compensate well. If there is unilateral deafness (in one ear) the technique of behavioral testing with sound stimuli will fail. Bilateral deafness can be detected by “sound stimuli outside the visual field”. The response should be at least a twitch of the ears. A better response is the cat turning towards the sound source.

A so called “objective assessment”, which means being pure science based, is called the BAER or auditory brain stem response (ABR). The machinery detects signals in the cochlea and auditory pathway like an ECG test to check the heart.

Management of deafness in cats

Importantly, cats who are deaf make excellent companions; no less a companion that a cat with hearing. It might be argued that the disability helps create a closer human/cat bond. As it is usually the white gene that results in deafness in cats they should be prevented from breeding. Indeed, all domestic cats other than cats kept by breeders should be neutered.

A deaf cat should be left to adapt but precautions taken to avoid injury from cars and routines adopted. Also, the study says that precautions should be taken to prevent “bite injuries to humans, especially children, when deaf dogs are startled.”

Deaf cats place emphasis on visual and vibratory (whiskers and paw pads) senses to cope.  A deaf cat’s life is not substantially diminished. The brain’s “plasticity” (ability to learn anew) enables the cat to continue much as before.

Deafness in Dogs

Now for a bit about dogs. Dog breeds reported with congenital deafness are as follows (bold indicates breed specific deafness in dogs as presented in the study). Two pigmentation genes are commonly associated with deafness in dogs: the merle (dapple) gene (indicated by “M” in the table below) and the piebald or extreme piebald gene (indicated by “P” in the table – this is not the true genetic ID). The merle gene is dominant so that heterozygous dogs show the pattern.  The canine piebald gene is recessive. See table below to match these to the breeds.

Akita	Dogo Argentino	Norwegian Dunkerhound (P)
American Staffordshire Terrier	English Bulldog	Old English Sheepdog (P)
Australian Cattle Dog (2.9% deaf in both ears and 8.5% deaf in one ear)	English Cocker Spaniel (1.8% are deaf in both ears and 7% deaf in both ears)</stron g>	Papillon
Australian Shepherd	English Setter (2.4% are deaf in both ears and 12.7% deaf in one ear) (M)	Pit Bull Terrier
Beagle (M)	Foxhound	Pointer
Bichon Frist	Fox Terrier	Rhodesian Ridgeback
Border Collie	French Bulldog	Rottweiler
Boston Terrier	German Shepherd	Saint Bernard
Boxer	Great Dane	Schnauzer
Bulldog (M)	Great Pyrenees (M)	Scottish Terrier
Bull Terrier (0.8% are deaf in both ears and 10.3% deaf in both ears)	Ibizan Hound	Sealyhan Terrier (M)
Catahoula Leopard Dog	Italian Greyhound	Shetland Sheepdog (P)
Chow Chow	Jack Russell Terrier	Shropshire Terrier
Cocker Spaniel	Kuvasz	Siberian Huskie
Collie (P)	Labrador Retriever	Springer Spaniel
Dalmatian (8% are deaf in both ears and 21.8% are deaf in one ear) (M)	Maltese	Toy Poodle
Dappled Dachshund (P)	Miniature Pinscher	Walker American Foxhound
Doberman Pinscher	Miniature Poodle mongrel

Overall prevalence of bilateral deafness in dogs in studies varies:

• 0.065%
• 0.025%
• 0.875%

The author of the study says these figures are low by a factor of 4.

Deafness in cats – Notes:

1. audioenglish.net

2. Wikipedia authors