Diagnostic tests are performed to establish the diagnosis of deafness and help identify the cause. Some of the testing for bilateral and complete deafness can be done at home as frightened or uncooperative animals may be impossible to evaluate in the veterinary clinic. Your veterinarian can make recommendation for treatment and lifestyle modifications based on the findings of the examinations and tests.
Testing at Home
You can easily assess whether your pet is bilaterally and completely deaf. This testing method requires two people, the "observer" and the "noisemaker." This method avoids some of the mistakes people can make in evaluating hearing. The first step is to wait until your pet is lying down either asleep or very quiet. The observer should be in the same room as your pet. The noisemaker should be in an adjoining room but out of sight from the pet. The noisemaker begins by making low decibel sounds such as clapping or whistling. The observer should watch for a reaction from the pet to the sound. Reactions are usually lifting of the head (alerting) and turning towards the sound. The noisemaker should increase the volume of the sound until a reaction is observed.
By testing this way, you avoid giving your pet visual cues and decrease the chance of misdiagnosing your pet's deafness. The noisemaker should be aware that vibrations through air and surfaces can be felt by mechanoreceptors not associated with the ear. For example, an animal may alert to feeling a vibration from a slammed door rather than actually hearing the sound of the slamming door.
Testing At the Veterinarian's Office
Your veterinarian will take a complete medical history and perform a thorough general physical examination. Previous medications and any illness your pet has had should be brought to your veterinarian's attention in the case of a youngster suspected of being deaf. It would be helpful to know the hearing status of the animal's parents. A thorough ear (otic) exam. The otic exam will consist of looking at the ear, ear canal and eardrum. This is done with an otoscope. It may be necessary to sedate or even anesthetize a painful animal in order to thoroughly evaluate the ear structures.
Other important information your veterinarian will need is the age at which you first noticed the deafness, what alerted you to the suspected deafness, and any signs associated with the problem such as head shaking, ear scratching or discharge from the ears.
Your veterinarian may repeat some of the hearing tests you have done. Remember, it can be difficult to assess frightened or uncooperative animals. After assessing for deafness in your dog, your veterinarian may perform the following tests:
Neurological assessment. Because it is important to determine if your pet's deafness is related to other deficits in the brain or central nervous system, your veterinarian will want to perform a neurological exam.
Radiographs of the skull may be indicated in the case of suspected ear infection or masses. Where available, a CT or MRI may be an alternative to skull radiographs. These test help assess the severity of the infection, as well as help establish the best treatment for the condition.
Cultures of ear discharge may be taken to help determine the best antibiotic to use in cases of ear infections.
If other neurologic deficits are detected with a neurologic examination, additional diagnostic tests such as cerebrospinal fluid (CSF) analysis, titers on blood and CSF, and computed tomography or magnetic resonance imaging of the head may need to be performed.
Impedence audiometry and brainstem auditory-evoked response (BAER) testing may be recommended to determine the type (conduction versus sensorineural), degree (partial versus complete) and symmetry (unilateral versus bilateral) of the deafness. These tests require specialized equipment, which may require referral to neurologic specialty centers.
Electrodiagnostic testing is generally available at specialty or university hospitals. Using electrodiagnostic testing, specialists can determine the type, degree, and symmetry of dysfunction. The equipment required is specialized and expensive (>$25,000). Depending on the equipment and the tests to be performed, the pet may need to be sedated or anesthetized. A brain stem auditory evoked response (BAER) test can determine if complete sensorineural deafness is present in either one ear or both. Potential breeding pairs and all puppies from dog breeds with a high incidence of deafness should be BAER tested.
In the case of conduction deafness caused by ear infections and wax accumulation, treatment is aimed at removing the infection or blockage. Cleaning should be done only by well-trained people to prevent further hearing damage. In some cases of severe ear infections or presence of a large foreign body, your pet may need to be anesthetized by your veterinarian. Hearing can be restored as long as the damage is not too severe. Other treatments may include: Infections may be treated with topical medications placed in the ear canals and systemically with injectable or oral antibiotics. When a culture of the ear discharge is taken, your veterinarian may change the antibiotics you are giving your pet if the test indicates a more effective antibiotic.
Sensorineural deafness is not treatable since it either involves the nerves or the organ of hearing. Future treatment for sensorineural deafness may include cochlear implants.
Hearing aids that fit in the ear canal only amplify sound so partially deaf animals are helped by these devices. Complete hearing deficits such as seen with congenital sensorineural deafness are therefore not helped with these devices. Animals generally do not tolerate hearing aids; to test if your animals will accept a hearing aid in their ear canal, you can place a $2 foam earplug in your pet's ear. If he can tolerate the presence of an earplug for several hours, he may be a candidate for a $1000 hearing aid.