Download Outline for a Lecture on Presbycusis

Geriatric Otolaryngology
August 2007
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Presbycusis
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Definition: Older hearing (Greek presby – old man; ackousis – hearing)
a. Refers to all the conditions that lead to hearing loss with age
i. Aging
ii. Genetic susceptibility
iii. Noise exposure
iv. Otological disorders (e.g., Meniere’s disease, otosclerosis)
v. Ototoxic agents
1. Estimated as an important contributor in up to 30% of
elderly patients presenting with hearing impairment
a. Aminoglycosides, quinine, β-blockers, loop
diuretics, NSAIDs, salicylates, tricyclic
antidepressants
Characteristics
a. Reduced hearing sensitivity
b. Reduced speech understanding, particularly in noisy environments
c. Reduced dynamic range
d. Slowed central processing of auditory information
e. Impaired sound localization of sound sources
f. Progressive
Disability
a. Hearing impairment
i. Conversations, telephone use, music appreciation, etc.
ii. Social isolation
1. Depression
2. Loss of self-esteem
iii. Difficulty orienting to alarms
iv. Difficulty integrating with other sensory modalities
v. Particularly limiting in the face of co-morbidities such as cognitive
dysfunction (e.g., dementia)
Incidence
a. >65 years of age
i. 40% have hearing loss great enough to impair communication
b. Varies according to societal factors
i. For example, hearing levels are poorer in industrial vs. isolated,
agrarian societies
Progression
a. Begins with loss of sensitivity in high frequencies
i. Adverse effect on understanding speech in noisy or reverberant
environments
ii. High-frequency alarms not heard
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b. Progresses toward low frequencies
i. Once it reaches range of 2-4 kHz, speech understanding in any
situation is affected (difficulty hearing voiceless consonants t, p, k,
f, s, and ch)
ii. With further progression speech detection is affected
Pathophysiology
a. Outer and middle ears
i. Flaccidity of cartilaginous external auditory canal
ii. Stiffening of the tympanic membrane
iii. Difficulty clearing cerumen
iv. Cerumen impaction aside, relatively small impact on function
b. Inner ear
i. Degeneration of stria vascularis and loss of Na+-K+ ATPase
1. Microvasculature diminished
2. Starts in base and apex and extends to mid-cochlear regions
with age
3. Inability to maintain direct current endolymphatic resting
potential (80-90 mV) – impairs cochlear amplifier
ii. Hair cells
1. Human temporal bone pathology suggest primarily outer
hair-cell loss, followed by inner hair-cell loss
2. Starts in the base and progresses to the apex
3. Some argue that hair-cell losses are a manifestation of noise
exposure, rather than aging per se
iii. Ganglion cells/auditory nerve
1. Thought to be secondary to loss of sensory cells
2. Asynchronous activity in auditory nerve
a. Impacts temporal resolution of conveyed signal
c. Central nervous system
i. Decrease in number and size of neurons in the central nuclei, as
well as changes in neurochemical makeup of cells with age
ii. Diminished function of neurons projecting to the cochlea
iii. Known as neural or central presbycusis, age-related auditory
processing disorder
iv. Secondary degeneration of central pathways after loss of peripheral
input
v. Can limit rehabilitation
1. Affects speed of speech processing and result in poorer
speech understanding in noise or with rapid or degraded
speech
Schuknecht’s classification of presbycusis
a. Sensory (outer hair-cell loss) – The most common
i. Associated with high- to low-frequency progressive
threshold elevation
ii. Audiogram: abruptly sloping high-frequency loss above speechfrequency range
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b. Neural (ganglion-cell loss)
i. Progressive loss of speech discrimination, relatively stable
audiogram
c. Metabolic (strial atrophy)
i. Associated with gradual elevation of thresholds across frequencies
ii. Audiogram – flattened, relatively good speech discrimination
d. Cochlear conductive
i. Theoretical – Stiffness of basilar membrane, changes in resonance
of the cochlear duct
ii. Audiogram – Linear descending pattern
e. Intermediate
i. No pathological correlate
ii. Audiogram – Flat and/or abrupt high-tone hearing loss
f. Mixed
i. Audiogram – Mild to moderate high-frequency hearing loss
Hereditability
a. High index
i. Particularly for strial and sensory types of presbycusis
ii. May involve mitochondrial DNA
Molecular mechanisms
a. Mitochondrial clock theory ( = membrane hypothesis) – aging renders
mitochondria bioenergetically inefficient
i. Hypoperfusion of cochlear tissue with aging
1. Production of ischemia and reactive oxygen species
ii. ROS damage mitochondrial DNA
1. mtDNA deletions
2. Reduction of mitochondrial membrane potential
Diagnosis
a. History
i. Global question: “Do you have a hearing problem now?”
1. More effective than the 10-item Hearing Handicap Inventor
for Elderly-Screening (HHIE-S) questionnaire
ii. Not all patients with hearing loss present with a complaint
1. Often presbycusis is identified when patient presents with
another ENT complaint
2. Tinnitus is an important attribute to be kept in mind
iii. Risk factors
1. Noise exposure
a. Occupational
b. Recreational
2. Smoking
3. Medication
4. Family history
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iv. Co-morbidities
1. Hypertension
2. Stroke
3. Diabetes
4. Atherosclerosis
5. Myocardial infarction
6. Hyperlipidemia
7. Kidney disease
8. Alzheimer’s disease
9. Metabolic bone disease
10. Plasma hyperviscosity
11. Hypothyroidism
12. Immune dysfunction/Autoimmune phenomena
b. Physical examination
i. Aside from cerumen, normal
c. Screening
i. Do you have a hearing problem now?
ii. Audiogram
Coming next: Rehabilitation
a. Barriers to rehabilitation
i. Only 20% of patient who might benefit from amplification actually
purchase hearing aids
ii. 25%-40% of those who purchase hearing aids underuse or
abandon them
Key references:
Gates GA, Mills JH. Presbycusis. Lancet. 2005, 366:1111-1120.
Howarth A, Shone GR. Ageing and the auditory system. Postgrad Med J.
2006;86:166-171.
Jennings CR, Jones NS. Presbyacusis. J Laryngol Otol. 2001,115:171-178.
Ohlemiller KK. Age-related hearing loss: the status of Schuknecht’s typology. Curr
Opin Otolaryngol Head Neck Surg. 2004,14:439-443.
Seidman MD, Ahmad N, Joshi D, Seidman J, Thawani S, Quirk WS. Age-related hearing
loss and its association with reactive oxygen species and mitochondrial DNA
damage. Acta Otolaryngol Suppl. 2004 (552):16-24.