Investigation of hearing loss in dogs

Diagnosing canine hearing loss, and managing deaf dogs

source: Celia Cox
In Practice vol 24 no 9, October 2002
starts p494, 7 pages long

Dogs can hear sounds up to 67k hertz (Hz) compared with up to 20kHz for humans, though the sensitivity range is similar, which means that dogs' hearing can be tested using similar techniques to those used for humans.

Hearing loss is especially common in certain breeds, such as dalmations, with an estimated 22% affected in the UK and as many as 30% in the US. White bull terriers (19.1%), English setters (14.3%), border collies (10%) and cocker spaniels (6.8%) are also prone to hearing loss.

Hearing loss can be classified into two types: conductive deafness, such as that caused by a damaged ear canal, and sensorineural, where the cochlea is involved. Dogs may inherit conditions which lead to deafness later in life and they may suffer damage from a number of causes, such as from ototoxic drugs.

Behavioural tests involve seeing whether a dog responses to sounds from unseen stimuli, though the dog may not respond out of boredom rather than deafness, or may respond to a visual cue. A brainstem auditory evoked response (BAER) test is considered more reliable and gives more information. Pups can undergo a screening test from four weeks' old. Full hearing tests take longer, from 20-30 minutes, and the dog has to keep still, so a low dose of sedative may be used. Responses to clicks are measured to assess the degree of deafness. Ait and bone conduction tests can be carried out, and the results compared. This helps in assessing whether the problem is conductive or sensorineural.

Other investigations which can help with diagnosis include checking for clinical signs. Deafness is more likely to be noticeable in pups separated from their litters, since they can no longer communicate with their siblings by touch. Dogs deaf in both ears may have a cry that is at a higher pitch, and may show more aggression. It may also be difficult to wake them, and there is no response to loud noises. Dogs deaf in one ear have trouble identifying the location of sounds, and are more difficult to train. Otoscopy checks should be carried out on dogs with conductive hearing loss, to see whether there is a discharge or other sign of an external ear problem. Radiographs can be used to check for middle ear disorders, though magnetic resonance imaging gives more information - and is more expensive. Tympanometry can help in assessing whether deafness is sensorineural or conductive.

Conductive hearing loss can sometimes be successfully treated using surgical or medical methods, but sensorineural hearing loss cannot be treated. Breeders can use BAER tests to check for deafness when selecting breeding animals, and they can test pups before selling them. Working dogs should be tested before a lot of effort is put into training them.

Pet owners can return deaf dogs to breeders, or use special training programmes that involve a lot of body language. Deaf dogs can also benefit from the company of a hearing dog. Some dogs may benefit from hearing aids, so long as the dog has some hearing left, and will allow a hearing aid to be put in and taken out of the ear. Some owners have found vibrating collars to be helpful. The dog has to be trained to know what to do when the collar vibrates.

Deaf dogs should not be bred from, and it is best to neuter dogs with inherited deafness.