Transcript Deafness in small animals: a retrospective study of 122 cases.

Deafness in small
animals: a
retrospective study of
122 cases.
Bianchi E., Callegari D., Ravera M., Dondi M.
Unit of Internal Medicine, Animal Health Department
University of Parma - Italy
Introduction
 Auditory abnormalities are common in
companion animals.
 One or both ears affected.
 Complete or partial hearing loss.
 Classification: inherited or acquired,
congenital or later-onset, sensorineural or
conductive.
Mostly inherited congenital sensorineural
(ICS), acquired later-onset sensorineural
(ALS), and acquired later-onset conductive
(ALC).
Introduction
 Objective auditory investigation: Brainstem
auditory-evoked potentials (BAEPs),
impedence audiometry (Tympanometry etc.),
transient evoked otoacustic emissions.
 BAEPs: recording of electrical activity in the
cochlea and auditory pathway evoked by
acoustic or vibratory stimuli.
 The response waveform consists of peaks
produced by the cochlea (I) and nervous
structures of brainstem (II-V).
Introduction: BAEPs
 Light sedation is often required in animals
for obtaining clear tracings.
 BAEPs can be recorded using similar
methodologies in all companion animals.
 Waveforms are similar in different species.
1 uV/Div;
1 ms/Div.
Green Iguana
(Iguana iguana)
0.62 uV/Div;
1 ms/Div.
Bearded Dragon
(Pogona vitticeps)
1 uV/Div;
1 ms/Div.
Aim
 Review medical records and BAEPs
tracings of small animals referred to the
Teaching Hospital for evaluation of
auditory function or with a history of
suspect hearing loss.
 Establish the prevalence of different
types of deafness present in these
animals.
Materials and Methods
 360 dogs, 6 cats and 11 ferrets referred
in the period 1998-2007.
 Medical records and BAEPs evaluated.
 Inclusion criteria: unilateral or bilateral
abnormalities in BAEPs consistent with
partial or complete hearing loss.
 Exclusion criteria: CNS signs, BAEPs as
diagnostic tool for lesion of the
brainstem.
Materials and Methods
 112 dogs, 6 cats and 4 ferrets met the
inclusion criteria.
 All subjects underwent physical and
otoscopic evaluation.
 BAEPs tests were performed under
sedation.
 When needed, laboratory tests and
diagnostic imaging evaluation were also
included.
Materials and Methods:
BAEPs
 Recording: Needle electrodes inserted at the
vertex (non-inverting input), at the level of the
ipsilateral mastoid or of the 2nd cervical
vertebra (inverting input), and at the occipital
protuberance (ground).
 Signal was amplified, filtered (100-3000 Hz)
and averaged 500-1000 times. Artifact rejection
was automatically performed.
 At least 2 trials for each ear were performed to
test waveform consistency.
 Amplitudes and latencies of each wave
measured.
Materials and Methods:
BAEPs
 Stimulation: 90 – 105 dB NHL alternate clicks
delivered monaurally through insert earphones.
The untested ear was masked with a wide
band noise (- 40 dB).
 Bone stimuli were also used if conductive
deafness was suspected.
 Auditory threshold was established when
needed to confirm partial deafness (5-10 dB
steps).
 ALS + ALC: main cause of hearing problems.
Results: dogs
 94/112 (83.9%): ICS deafness.
 Puppies or adults of breeds predisposed to
congenital deafness.
 65 Dalmatians, 7 Eng. Setter, 6 Dogo
Argentino, 3 Eng. Bulldog, 2 Fr. Bulldog, 2
Border Collie etc.
 49 unilateral, 45 bilateral deaf.
Results: dogs
 18/112(16.1%): acquired hearing loss.
 11/112 (9.8%): ALS deafness.
 1 unilateral, 10 bilateral.
 8 partial, 3 complete deafness.
 5 ototoxicity, 6 presbycusis.
 7/112 (6.3%): ALC deafness.
 4 unilateral, 3 bilateral.
 Severe chronic otitis (External/middle ear).
 Partial deafness.
Results: cats
 4/6 (66.6%): ICS deafness
 3 Norvegian Forest, 1 white DSH.
 3 unilateral and 1 bilateral.
 2/6 (33.3%): ALC deafness.
 DSH with inflammatory polyps.
 1 unilateral and 1 bilateral.
Results: ferrets
 All 4 ferrets had ICS deafness.
 2 unilateral and 2 bilateral.
Discussion
 ICS most common type of deafness.
 Assessment of the hearing status: subjects of breeds
affected by hereditary cochleo-saccular degeneration.
 Usually breeds with white pigmentation: dogs (piebald
or merle genes), cats (white gene), ferrets (different
coats).
 Absence of melanocytes in the stria vascularis,
degeneration of the stria vascularis, collapse of
Reissner’s membrane and cochlear duct, degeneration
of hair cells, collapse of the saccule.
Discussion
 ICS deafness easy to recognize.
 Usually complete (unilateral or bilateral).
 Flat waveforms with acoustic and bone
stimuli.
 Sometimes a negative peak (N3
potential) present at high intensities
(vestibular potential?).
ICS deafness
Right
 18 months old male
Ferret.
 Normal right ear.
 Flat tracing in left
ear.
 Dx: cochleo-saccular
degeneration.
 100 dB NHL
 1 uV/Div; 1 ms/Div.
Left
ICS deafness
 60 days old female
Dalmatian puppy.
 Left ear of a
bilaterally deaf.
 105 dB/NHL.
 0.62 uV/Div; 1
ms/Div.
Left
N3 pot.
Discussion
 ALS deafness: 2nd most common type in dogs.
 Not recognised in cats and ferrets.
 Causes: ototoxicity (aminoglycosides etc.),
presbycusis.
 Presbycusis very common in geriatric dogs.
 Partial or complete hearing loss.
 BAEPs: delayed I wave, decreased amplitudes,
increased threshold, increased slope of wave V
latency-intensity curve.
 No improvement with bone stimulation.
ALS deafness
Left
 6 years old, male Pug
dog.
 Treated for 20 days with
Amminosidine for
Leishmaniosis.
 Bilaterally increased
threshold (approx 50 dB
NHL).
 No improvement with
bone stimulation.
 Dx: Ototoxicity.
 0.31 uV/Div; 1 ms/Div.
dB
90
70
50
40
Acoustic
90 dB
Bone
Discussion
 ALC deafness: recognised in
dogs and cats.
 Causes: severe otitis
externa/media in dogs,
inflammatory polyps in cats.
 Usually partial hearing loss.
 BAEPs: delayed I wave,
decreased amplitudes, increased
threshold, wave V latencyintensity curve shifted to the right.
 Marked improvement with bone
stimulation.
ALC deafness
 3 years old, male,
DSH cat.
 Inflammatory polip in
right ear.
 Abnormal waveform
in right ear with
acoustic stimuli.
 Normal waveform in
both ears with bone
stimuli.
Left ac.
Right ac.
Left bone
Right bone
Conclusions
 Hearing loss is a common problem in
companion animals.
 Dogs more affected / Hearing loss easier to
recognize.
 Many breeds affected by congenital deafness.
 Increased average life expectancy
(presbycusis, chronic otitis etc.).
 BAEPs: easy to perform, fast and sensitive
test.
 Normal with cortical deafness!
Conclusions
 Limitations of the study:
 Small number of animals (especially cats and
ferrets).
 Test mainly performed in litters of breeds
predisposed (Dalmatians).
 Future plans:
 Awaken more breeders to congenital deafness.
 New therapies for sensorineural deafness
(cochlear implants).
THANK YOU FOR YOUR
ATTENTION !