Download Hearing and Deafness in Dogs

Hearing and Deafness in Dogs
( A presentation made to the New Brunswick Veterinary Medical Association, September, 2007)
Aubrey A. Webb, DVM, PhD
Faculty of Veterinary Medicine
University of Calgary
(www.vet.ucalgary.ca)
And
Western Veterinary Specialist Centre (www.westernvet.ca)
Outline
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Hearing in dogs
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Normal aural (ear) anatomy
How does a dog hear?
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Deafness in dogs
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Deafness – What is it?
Types of deafness
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Sound
Hearing
Sequence of events leading to hearing
Conductive vs. neurologic
Congenital vs. acquired
Diagnosis of Deafness
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Signalment, history, physical and neurologic examinations
Aural examination
Electrodiagnostic examination
Evolution of vestibulocochlear
system
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Thought to have
evolved, in part,
from the inner ear
and lateral line
system seen in fish
(octavolateralis
system)
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Fish detect sounds
and motion through
the inner ear and
lateral line system
3 Compartments of the Ear
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Outer Ear
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Middle Ear
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Inner Ear
Normal Aural Anatomy
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Outer ear
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The outer portion of
the hearing
apparatus
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beginning from the
outside of the ear
and ending at the
level of tympanic
membrane
Function: to capture
and focus sound
into the vertical and
horizontal auditory
canals
From Hills Atlas of Clinical Anatomy
Aural Anatomy
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Middle ear
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An air filled cavity
located in the
temporal bone of the
skull
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Contains three tiny
bones
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Malleus (hammer)
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Incus (anvil)
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Stapes (stirrup)
Function: to conduct
sound waves from the
external environment
to the inner ear
From Hills Atlas of Clinical Anatomy
Aural Anatomy
From Hills Atlas of Clinical Anatomy
From www.hearingaidscentral.com
Normal Aural Anatomy
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Inner ear
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Comprised of the
cochlea
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Found within the
petrous bone of the
skull
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Function: to convert
mechanical energy to
electrical energy that
is then transmitted to
the brain
From Hills Atlas of Clinical Anatomy
How does a dog hear?
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What is sound?
z Our
perception of vibrations (i.e. sound
waves) detected by the hearing apparatus
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What is hearing?
z The
ability to detect sound
How does a dog hear?
From Hills Atlas of Clinical Anatomy
How does a dog hear?
From Hills Atlas of Clinical Anatomy
From Kandel et al, Principles of Neural Science
Organ of Corti:
Contained within the cochlea
Contains hair cells that convert
sound waves into electrical
signals that are transmitted to
the brain
From Kandel et al, Principles of Neural Science
How does a dog hear?
Sound Waves
Movement of bones in
middle ear
Movement of hair cells
in the Inner Ear
Electrical Impulse from
Inner Ear to Brain
Outline
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Hearing in dogs
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Normal aural (ear) anatomy
How does a dog hear?
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Deafness in dogs
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Deafness – What is it?
Types of deafness
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Sound
Hearing
Sequence of events leading to hearing
Conductive vs. neurologic
Congenital vs. acquired
Diagnosis of Deafness
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Signalment, history, physical and neurologic examinations
Aural examination
Electrodiagnostic examination
Pinna
Vertical
Canal
Hammer, anvil,
stirrup
Horizontal
Canal
Cochlea
Tympanic
Membrane
Middle ear
cavity
Deafness
z The
inability to hear
Types of Deafness in Dogs
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Conduction deafness
z Deafness
resulting from failure of conduction of
sound waves to the inner ear
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Neurologic (sensorineural) deafness
z Deafness
resulting from failure of generating or
sending electrical impulses from the inner ear
to the brain
Types of Deafness in Dogs
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Congenital
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Born with deafness or defect leading to deafness
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Inherited
Drug toxicity
Acquired
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Deafness that is acquired after birth
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Ear infections
Neoplasia
Drug toxicity
Loud noise exposure
Presbycusis (old-age)
Congenital Sensorineural Deafness
in Dogs
Coppens et al, 2003
Breeds of Dogs
Strain, Vet J, 2004
Prevalence in particular breeds
Strain, Vet J, 2004
Differences between countries
(dalmatians)
Norway:
3.6% of 1843 dalmatians bilaterally deaf in Norway
Greibrokk, JAAHA, 1994
UK:
Wood, Lakhani, Henley;
Vet J, 2004
Germany:
Juraschko, Vet J, 2003
USA:
Strain, Vet J,
2004
Blue eyes and deafness
(dalmatians)
Reference
Eye colour
Bilateral
deafness
Strain et al. Brown/brown 6.9
1992
Holliday et
al. 1992
Unilateral
deafness
Normal
Number of
dogs
20.3
72.8
915
Brown/blue
18.4
30.3
51.3
76
Blue/blue
12.5
43.8
43.8
32
Brown/brown 5.6
18.8
75.5
799
Brown/blue
15.8
39.5
44.7
76
Blue/blue
22.2
33.3
44.4
27
From Cattanach, jsap, 1999
Effect of parental hearing status
(dalmatians)
Wood, Lakhani, Henley; Vet J, 2004
Congenital Sensorineural Deafness
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Breed predisposition
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Coat colour
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Breeds with spotting, roaning, merling, excessive white
White cats (any colour iris)
Iris colour
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Numerous breeds
Animals with blue eyes (1 or 2) more predisposed
Mode of inheritance
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Unknown
Dogs with one ear deaf as likely to produce deaf puppies as
dogs with deafness in both ears
Breeding Advice
(all predisposed breeds unless proven otherwise)
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Do not breed affected animals (whether they
are unilateral or bilaterally deaf)
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Avoid breeding to blue-eyed animals
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Test all puppies in a litter
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Will give an indication of whether a particular
breeding resulted in a lot of puppies with
deafness
Unaffected ear
Otitis externa
Outline
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Lesson 1. Hearing in dogs
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Normal aural (ear) anatomy
How does a dog hear?
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Lesson 2. Deafness in dogs
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Types of deafness
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Sound
Hearing
Sequence of events leading to hearing
Congenital vs. acquired
Conductive vs. neurologic
Lesson 3. Diagnosis of Deafness
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Signalment, history, physical and neurologic examinations
Aural examination
Electrodiagnostic examination
Diagnosis of Deafness
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How might you determine what form of
deafness a dog has?
Diagnosis of Deafness
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Signalment
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History
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Physical and Neurologic examinations
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External aural (ear) examination
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Electrodiagnostic evaluation
SIGNALMENT and HISTORY
PHYSICAL and NEUROLOGIC
EXAMINATIONS
EXTERNAL AURAL EXAMINATION
http://courses.vetmed.wsu.edu/
http://courses.vetmed.wsu.edu/
http://courses.vetmed.wsu.edu/
ELECTROPHYSIOLOGICAL
TESTING
http://www.geocities.com/Heartland/2169/baer.html
Brainstem Auditory-Evoked
Response (BAER) testing
BAEP Click
1:1 L
RIGHT
LEFT
1:2 R
LEFT
RIGHT
1 (ms)
Hearing in both ears
Hearing only in right ear
For more information on Canine
Hearing and Deafness
z Dr.
George Strain’s (Louisiana State
University) Website:
www.lsu.edu/deafness/deaf.htm
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Lesson 1. Hearing in dogs
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Normal aural (ear) anatomy
How does a dog hear?
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Lesson 2. Deafness in dogs
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Types of deafness
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Sound
Hearing
Sequence of events leading to hearing
Congenital vs. acquired
Conductive vs. neurologic
Lesson 3. Diagnosis of Deafness
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Signalment, history, physical and neurologic examinations
Aural examination
Electrodiagnostic examination
Questions?