Deafness in small Deafness in small animals: a animals: a

retrospective study retrospective study of 122 cases.of 122 cases.Bianchi E., Callegari D., Ravera M., Dondi M.Bianchi E., Callegari D., Ravera M., Dondi M.

Unit of Internal Medicine, Animal Health DepartmentUnit of Internal Medicine, Animal Health DepartmentUniversity of Parma - ItalyUniversity of Parma - Italy

    

IntroductionIntroduction Auditory abnormalities are common in Auditory abnormalities are common in

companion animals.companion animals. One or both ears affected.One or both ears affected. Complete or partial hearing loss.Complete or partial hearing loss. Classification: inherited or acquired, congenital Classification: inherited or acquired, congenital

or later-onset, sensorineural or conductive.or later-onset, sensorineural or conductive.Mostly inherited congenital sensorineural (ICS), Mostly inherited congenital sensorineural (ICS),

acquired later-onset sensorineural (ALS), and acquired later-onset sensorineural (ALS), and acquired later-onset conductive (ALC). acquired later-onset conductive (ALC).

IntroductionIntroduction Objective auditory investigation: Objective auditory investigation:

Brainstem auditory-evoked potentials Brainstem auditory-evoked potentials (BAEPs)(BAEPs), impedence audiometry , impedence audiometry (Tympanometry etc.), transient evoked (Tympanometry etc.), transient evoked otoacustic emissions.otoacustic emissions.

BAEPs: recording of electrical activity in BAEPs: recording of electrical activity in the cochlea and auditory pathway the cochlea and auditory pathway evoked by acoustic or vibratory stimuli.evoked by acoustic or vibratory stimuli.

The response waveform consists of The response waveform consists of peaks produced by the cochlea (I) and peaks produced by the cochlea (I) and nervous structures of brainstem (II-V). nervous structures of brainstem (II-V).

Introduction: BAEPsIntroduction: BAEPs

Light sedation is often required in animals Light sedation is often required in animals for obtaining clear tracings.for obtaining clear tracings.

BAEPs can be recorded using similar BAEPs can be recorded using similar methodologies in all companion animals.methodologies in all companion animals.

Waveforms are similar in different species.Waveforms are similar in different species.

1 uV/Div;

1 ms/Div.

Green Iguana (Iguana iguana)

Bearded Dragon (Pogona vitticeps)

0.62 uV/Div;

1 ms/Div.

1 uV/Div;

1 ms/Div.

AimAim

Review medical records and BAEPs Review medical records and BAEPs tracings of small animals referred to the tracings of small animals referred to the Teaching Hospital for evaluation of Teaching Hospital for evaluation of auditory function or with a history of auditory function or with a history of suspect hearing loss.suspect hearing loss.

Establish the prevalence of different Establish the prevalence of different types of deafness present in these types of deafness present in these animals. animals.

Materials and Methods Materials and Methods

360 dogs, 6 cats and 11 ferrets referred in 360 dogs, 6 cats and 11 ferrets referred in the period 1998-2007.the period 1998-2007.

Medical records and BAEPs evaluated.Medical records and BAEPs evaluated. Inclusion criteria: unilateral or bilateral Inclusion criteria: unilateral or bilateral

abnormalities in BAEPs consistent with abnormalities in BAEPs consistent with partial or complete hearing loss.partial or complete hearing loss.

Exclusion criteria: CNS signs, BAEPs as Exclusion criteria: CNS signs, BAEPs as diagnostic tool for lesion of the brainstem.diagnostic tool for lesion of the brainstem.

Materials and MethodsMaterials and Methods

112 dogs, 6 cats and 4 ferrets met the 112 dogs, 6 cats and 4 ferrets met the inclusion criteria.inclusion criteria.

All subjects underwent physical and All subjects underwent physical and otoscopic evaluation.otoscopic evaluation.

BAEPs tests were performed under BAEPs tests were performed under sedation.sedation.

When needed, laboratory tests and When needed, laboratory tests and diagnostic imaging evaluation were also diagnostic imaging evaluation were also included. included.

Materials and Methods: Materials and Methods: BAEPsBAEPs

RecordingRecording: Needle electrodes inserted at the : Needle electrodes inserted at the vertex (non-inverting input), at the level of the vertex (non-inverting input), at the level of the ipsilateral mastoid or of the 2nd cervical vertebra ipsilateral mastoid or of the 2nd cervical vertebra (inverting input), and at the occipital protuberance (inverting input), and at the occipital protuberance (ground). (ground).

Signal was amplified, filtered (100-3000 Hz) and Signal was amplified, filtered (100-3000 Hz) and averaged 500-1000 times. Artifact rejection was averaged 500-1000 times. Artifact rejection was automatically performed.automatically performed.

At least 2 trials for each ear were performed to At least 2 trials for each ear were performed to test waveform consistency. test waveform consistency.

Amplitudes and latencies of each wave measured.Amplitudes and latencies of each wave measured.

Materials and Methods: Materials and Methods: BAEPsBAEPs

StimulationStimulation: 90 – 105 dB NHL alternate clicks : 90 – 105 dB NHL alternate clicks delivered monaurally through insert earphones. delivered monaurally through insert earphones. The untested ear was masked with a wide The untested ear was masked with a wide band noise (- 40 dB).band noise (- 40 dB).

Bone stimuli were also used if conductive Bone stimuli were also used if conductive deafness was suspected.deafness was suspected.

Auditory threshold was established when Auditory threshold was established when needed to confirm partial deafnesneeded to confirm partial deafness (5-10 dB s (5-10 dB steps).steps).

ALS + ALC: main cause of hearing problems.ALS + ALC: main cause of hearing problems.

Results: dogsResults: dogs

94/112 (83.9%): ICS deafness.94/112 (83.9%): ICS deafness. Puppies or adults of breeds predisposed to Puppies or adults of breeds predisposed to

congenital deafness.congenital deafness. 65 Dalmatians, 7 Eng. Setter, 6 Dogo 65 Dalmatians, 7 Eng. Setter, 6 Dogo

Argentino, 3 Eng. Bulldog, 2 Fr. Bulldog, 2 Argentino, 3 Eng. Bulldog, 2 Fr. Bulldog, 2 Border Collie etc.Border Collie etc.

49 unilateral, 45 bilateral deaf.49 unilateral, 45 bilateral deaf.

Results: dogsResults: dogs

18/112(16.1%): acquired hearing loss.18/112(16.1%): acquired hearing loss. 11/112 (9.8%): ALS deafness.11/112 (9.8%): ALS deafness.

1 unilateral, 10 bilateral.1 unilateral, 10 bilateral. 8 partial, 3 complete deafness.8 partial, 3 complete deafness. 5 ototoxicity, 6 presbycusis.5 ototoxicity, 6 presbycusis.

7/112 (6.3%): ALC deafness.7/112 (6.3%): ALC deafness. 4 unilateral, 3 bilateral.4 unilateral, 3 bilateral. Severe chronic otitis (External/middle ear).Severe chronic otitis (External/middle ear). Partial deafness.Partial deafness.

Results: catsResults: cats

4/6 (66.6%): ICS deafness 4/6 (66.6%): ICS deafness 3 Norvegian Forest, 1 white DSH.3 Norvegian Forest, 1 white DSH. 3 unilateral and 1 bilateral.3 unilateral and 1 bilateral.

2/6 (33.3%): ALC deafness.2/6 (33.3%): ALC deafness. DSH with inflammatory polyps.DSH with inflammatory polyps. 1 unilateral and 1 bilateral.1 unilateral and 1 bilateral.

Results: ferretsResults: ferrets

All 4 ferrets had ICS deafness.All 4 ferrets had ICS deafness. 2 unilateral and 2 bilateral.2 unilateral and 2 bilateral.

DiscussionDiscussion ICS most common type of deafness.ICS most common type of deafness. Assessment of the hearing status: subjects of Assessment of the hearing status: subjects of

breeds affected by hereditary cochleo-saccular breeds affected by hereditary cochleo-saccular degeneration.degeneration.

Usually breeds with white pigmentation: dogs Usually breeds with white pigmentation: dogs (piebald or merle genes), cats (white gene), (piebald or merle genes), cats (white gene), ferrets (different coats).ferrets (different coats).

Absence of melanocytes in the stria vascularis, Absence of melanocytes in the stria vascularis, degeneration of the stria vascularis, collapse of degeneration of the stria vascularis, collapse of Reissner’s membrane and cochlear duct, Reissner’s membrane and cochlear duct, degeneration of hair cells, collapse of the degeneration of hair cells, collapse of the saccule.saccule.

DiscussionDiscussion

ICS deafness easy to recognize.ICS deafness easy to recognize. Usually complete (unilateral or bilateral).Usually complete (unilateral or bilateral). Flat waveforms with acoustic and bone Flat waveforms with acoustic and bone

stimuli.stimuli. Sometimes a negative peak (N3 Sometimes a negative peak (N3

potential) present at high intensities potential) present at high intensities (vestibular potential?).(vestibular potential?).

ICS deafnessICS deafness

18 months old male 18 months old male Ferret.Ferret.

Normal right ear.Normal right ear. Flat tracing in left Flat tracing in left

ear.ear. Dx: cochleo-saccular Dx: cochleo-saccular

degeneration.degeneration. 100 dB NHL100 dB NHL 1 uV/Div; 1 ms/Div.1 uV/Div; 1 ms/Div.

Right

Left

ICS deafnessICS deafness

60 days old female 60 days old female Dalmatian puppy.Dalmatian puppy.

Left ear of a Left ear of a bilaterally deaf.bilaterally deaf.

105 dB/NHL.105 dB/NHL. 0.62 uV/Div; 1 0.62 uV/Div; 1

ms/Div.ms/Div.

Left

N3 pot.

DiscussionDiscussion ALS deafness: 2nd most common type in dogs.ALS deafness: 2nd most common type in dogs. Not recognised in cats and ferrets.Not recognised in cats and ferrets. Causes: ototoxicity (aminoglycosides etc.), Causes: ototoxicity (aminoglycosides etc.),

presbycusis.presbycusis. Presbycusis very common in geriatric dogs.Presbycusis very common in geriatric dogs. Partial or complete hearing loss.Partial or complete hearing loss. BAEPs: delayed I wave, decreased amplitudes, BAEPs: delayed I wave, decreased amplitudes,

increased threshold, increased slope of wave V increased threshold, increased slope of wave V latency-intensity curve.latency-intensity curve.

No improvement with bone stimulation.No improvement with bone stimulation.

ALS deafnessALS deafness

6 years old, male Pug 6 years old, male Pug dog.dog.

Treated for 20 days with Treated for 20 days with Amminosidine for Amminosidine for Leishmaniosis.Leishmaniosis.

Bilaterally increased Bilaterally increased threshold (approx 50 dB threshold (approx 50 dB NHL).NHL).

No improvement with No improvement with bone stimulation.bone stimulation.

Dx: Ototoxicity.Dx: Ototoxicity. 0.31 uV/Div; 1 ms/Div.0.31 uV/Div; 1 ms/Div.

Left

dB

90

70

50

40

Acoustic

Bone

90 dB

DiscussionDiscussion ALC deafness: recognised in dogs ALC deafness: recognised in dogs

and cats.and cats. Causes: severe otitis externa/media Causes: severe otitis externa/media

in dogs, inflammatory polyps in cats.in dogs, inflammatory polyps in cats. Usually partial hearing loss.Usually partial hearing loss. BAEPs: delayed I wave, decreased BAEPs: delayed I wave, decreased

amplitudes, increased threshold, amplitudes, increased threshold, wave V latency-intensity curve wave V latency-intensity curve shifted to the right.shifted to the right.

Marked improvement with bone Marked improvement with bone stimulation. stimulation.

ALC deafnessALC deafness

3 years old, male, 3 years old, male, DSH cat.DSH cat.

Inflammatory polip in Inflammatory polip in right ear.right ear.

Abnormal waveform Abnormal waveform in right ear with in right ear with acoustic stimuli.acoustic stimuli.

Normal waveform in Normal waveform in both ears with bone both ears with bone stimuli.stimuli.

Left ac.

Right ac.

Left bone

Right bone

ConclusionsConclusions

Hearing loss is a common problem in Hearing loss is a common problem in companion animals. companion animals.

Dogs more affected / Hearing loss easier to Dogs more affected / Hearing loss easier to recognize.recognize.

Many breeds affected by congenital deafness.Many breeds affected by congenital deafness. Increased average life expectancy Increased average life expectancy

(presbycusis, chronic otitis etc.).(presbycusis, chronic otitis etc.). BAEPs: easy to perform, fast and sensitive BAEPs: easy to perform, fast and sensitive

test.test. Normal with cortical deafness!Normal with cortical deafness!

ConclusionsConclusions

Limitations of the study:Limitations of the study: Small number of animals (especially cats and Small number of animals (especially cats and

ferrets).ferrets). Test mainly performed in litters of breeds Test mainly performed in litters of breeds

predisposed (Dalmatians).predisposed (Dalmatians). Future plans:Future plans: Awaken more breeders to congenital deafness.Awaken more breeders to congenital deafness. New therapies for sensorineural deafness New therapies for sensorineural deafness

(cochlear implants).(cochlear implants).

THANK YOU FOR YOUR THANK YOU FOR YOUR ATTENTION !ATTENTION !