presentation for ent cpd meeting

1. PRESBYCUSIS

2. INTRODUCTION
• Presbycusis refers to sensorineural hearing
impairment in elderly
• Most common otolaryngologic problem of elderly
• Involves bilateral high – frequency hearing loss
associated with difficulty in speech discrimination
and central auditory processing of information
• Association between advanced age and high tone
deafness was first described by Zwaardemaker in
1899

3. • Occurs in elderly population that relies on
special senses to compensate for other age
associated disabilities
• elderly patients may rely of hearing to
overcome limitations of impaired vision as well
as slowed reaction time
• In addition, age associated decline in
concentration and memory contribute to
difficulty in understanding speech in noisy evn

4. • Hearing loss may contribute to the isolation of
elderly people by restricting their usage of
phone, causing them to forfeit social events
such as concerts and social gatherings and
amplifying their sense of disability

5. Epidemiology
• No race, sex differences. Increases with age
• 25 – 30% of people aged 65 – 75 are estimated to
have impaired hearing
• For people aged 75 or older incidence is thought
to be 40 – 50%
• Westernized countries and primitive civilisations
have very different patterns of hearing loss
• Rosen et al study in Sudanese tribe called
mabaans revealed significantly less hearing loss in
elderly people than those of urban society

6. Physiologic property
Urged to read and revise from Dr C Favara’s presentation titled:
Ultrastructure of the cochlea

7. • Cochlear duct = coiled duct filled with fluid
• Ectodermal origin
• Walls are lined with cells that constitute the
membranous labyrinth
• Constitutes of hair (sensory cells) and auxiliary
and supportive cells
• Membranous labyrinth is surrounded by
additional fluid space filled with perilymph
and lined by cells of mesodermal origin

8. • Role of cochlea is to transduce complex sound
waves into electrical activity to transmit to
brain via auditory nerve
• Inner hair cells of organ of corti perform the
transduction and initiate the depolarisation of
spiral ganglion neurons
• Outer hair cells are accessory sensory cells
that enhance the sensitivity and selectivity of
cochlea

9. Basic anatomy of cochlea

10. Endolymph vs perilymph
Endolymph
• In scala media
• Extracellular fluid
• Ionic composition similar to
intracellular fluid
• High [K +] , low [Na +]
• Electric potential of
endolymph +80mV =
endolymphatic potential
perilymph
• In scala tympani and scala
vestibuli
• Ionic composition similar to
CSF or plasma
• Rich in Na and low in K +
• Weakly positive electrical
potential
• 5 – 7 mV

11. • Only possible ion
communication with
spaces beyond scala
media is through the
ion channels situated in
the stereo cilia of the
sensory hair cells of the
organ of corti

12. • The stria vascularis generates the end cochlear
potential and maintains the ionic composition of the
endolymph.
• The mechanical characteristics of the basilar
membrane and its related structures further enhance
the frequency selectivity of the auditory transduction
mechanism.
• The tectorial membrane is an extracellular matrix,
which provides mass loading on top of the organ of
Corti, facilitating deflection of the stereo cilia.

13. • Stria vascularis = 3
layers of cells
• Marginal cells
• Intermediate cells
• Basal cells
• Stria vascularis and
spiral ligament are
richly supplied by blood
vessels

14. Spiral ligament
• Located between stria vascularis and otic
capsule
• Reaches beyond the limits of stria vascularis
and perilymphatic spaces of scala vestibuli
and scala tympani
• Anchors the lateral aspect of the basilar
membrane
• Has prominent capillary bed for the supply
and drainage of cochlea

15. • Essential structure for maintaining the ionic
balance in scala media
• K+ absorbed via gap junctions
• K+ ion pumps K+ from scala tympani and
organ of corti and reroutes to the basal cells of
stria vascularis
• Implicated in presbycusis ( pathological
changes of the fibrocytes of spiral ligament)

16. • Base of cochlea is the region where higher sound
frequencies are transduced
• Lower frequencies are transduced at apical end
• Range of frequencies is tonotopically distributed
along the cochlear duct from base to apex

17. the organ of Corti

18. • Sensorineural
end organ of hearing
• Contains both sensory and supporting cells
• Sensory cells are hair cells which have active
process in their stereocilliar bundles
• Receive both afferent and efferent innervation
• Coupled with tectorial membrane

19. • Hair cells are supporting cells are spatially organised
in an orderly pattern that extend repetitively for the 2
and half turns of cochlea
• Every sensory cell is surrounded by four supporting
cells
• Sensory cells have no contact with each other

20. • Inner hair cells are true sensory cells, able to
send impulses via auditory nerve
• Outer hair cells enhance the performance of
the cochlea’s selectivity and sensitivity
• The sensory cells do not reach the basilar
membrane, only supporting cells do
• All cells are differentiated, thus no turnover of
cells
• If sensory cells are lost, they are irreplacable

21. • Inner hair cells:
– Pear shaped
– Central nucleus
– Apical tight junction
– No desmosomes
– At apical surface stereo cilia implanted on cuticular
plate
– Stereo cilia and reticular lamina are in endolymph,
rest of cell surrounded by perilymph
– Base – synaptic connection with afferent nerve
terminals

22. • Outer hair cells
– 3 rows on lateral side
– Cylindrical in shape, nucleus in base
– Supported by Deiter’s cells
– Apical surface part of reticular lamina
– Surrounded by and make tight junction at the upper
junction with 4 different deiters cells
– Hair bundle is W shaped with multiple rows of
stereocilia
– Apical surface endolymph, body on all sides except
base by perilymph (space of Nuel)

24. • Outer hair cells are stiff and motile
• Movement modulates distance between
reticular lamina and basilar membrane
• Require presence of protein, prestin in cell
membrane to move
• Prestin can change it’s conformation at
microseconds rates dependence of changes in
electrical voltage

25. Summary of essential physiology

26. pathophysiology
• Histologic changes associated with aging occur
throughout the auditory system from the hair
cells of the cochlea to the auditory cortex in
temporal lobe of the brain
• Elucidation of pathophysiology of presbycusis
is still incomplete

27. • Crowe and associates
• Saxen and Gacke and Schuknecht
– Studied histologic changes in cochlea of human
ears with presbycusis
– Identified 4 sites of aging in cochlea and divided
presbycusis into 4 types based on these sites
– Histologic changes correlated approximately with
symptoms and auditory test results

28. Sensory presbycusis
• Epithelial atrophy with loss of sensory hair cells
as well as supporting cells in the organ of corti
• Originates in basal turn of cochlea and slowly
progress towards the apex
• sharp drop in high frequency threshold, begins
after middle age
• Abrupt downward slope of audiogram begins
above speech frequency, speech discrimination is
preserved

29. • Histologically atrophy may be limited to only
the first few millimetres of basal end of
cochlea
• Process is slowly progressive over time
• ? Due to accumulation of lipofuscin pigment
granules at the basal end of cochlea

30. Neural presbycusis
• Atrophy of nerve cells in the cochlea and central
neural pathways
– Schuknecht estimated that 2100/35000 neurons are
lost every decade. Loss begins early in life and may be
genetically predetermined
– Effects not noticeable until old age because PTA not
affected until 90% of neurons are gone
• Atrophy occurs throughout the cochlea
• Basilar region slightly more predisposed than the
remainder of cochlea

31. • No precipitous drop in high frequency
threshold observed
• A disproportionally severe decrease in speech
discrimination is a clinical correlate of neural
presbycusis
• May be observed before hearing loss is noted
because fewer neurons are required to
maintain speech thresholds than speech
discrimination

32. Metabolic (strial)
• Results as atrophy of stria vascularis
• Normally maintains the chemical and
bioelectrical balance and metabolic health of
cochlea
• Hearing is represented by a flat hearing curve
because entire cochlea is affected
• Speech discrimination is preserved
• Process in younger population (30 – 60 years)
with slow progression and may be familial

33. Mechanical (i.e. cochlear conductive)
• Results from thickening and secondary stiffening
of the basilar membrane of the cochlea
• Thickening is more severe in the basal turn of the
cochlea where the basilar membrane is narrow
• Correlates with gradually sloping high frequency
sensorineural hearing loss that is slowly
progressive
• Speech discrimination is
average for the given PTA

34. • Changes associated with presbycusis is rarely
found exclusively at one site
• Development typically involves simultaneous
changes at multiple sites
• Explained by the difficulty of associating
specific clinical symptoms or signs with
specific anatomical location

35. • Large volume of current research is being
conducted to determine the exact underlying
cause of presbycusis
• Much of the research focuses on finding
underlying genetic abnormalities that may
cause, contribute to or predispose to
presbycusis

36. • Genetic mutation of mitochondrial
DNA
– Reduced perfusion of the cochlea
associated with age may contribute
to the formation of reactive oxygen
metabolites
– Affect the inner ear neural structures
and cause damage to mitochondrial
DNA
– Damaged mitochondrial DNA =
reduced oxidative phosphorylation =
disruption in ATP production =
disruption of K+ channels = neural
dysfunction

37. • Damaged mitochondrial DNA may lead to
anatomic changes of the inner ear
– Narrowing of the vaso nervorum In the auditory
meatus in temporal bone (Dai et al 2006)
– Greater rates of apoptosis of supporting cells in inner
ear (pickles et al 2004)
• 2 specific deletions
– mtDNA4834 and mtDNA4977 have been linked to age
related hearing loss in rodents
– Han et al and Dai et al have demonstrated
mtDNA4977 deletion with archived human temporal
bones from patients with presbycusis

38. Other causes
• Nutritional and anatomic
– Berner et al investigated the relation between
vitamin B12 and Folate - not significant
relationship
– Martin Villares et al found positive relation ship
between high cholesterol levels and hearing loss
– Statin users had no improvement in rate of
presbycusis

39. The Patient….
• Presentation varies
• Patients typically have more difficulty
understanding rapidly spoken language,
vocabulary that is less familiar or more
complex as well as speech within a noisy,
distracting environment
• Localising sound is difficult for patient

40. aetiology
• Arteriosclerosis
– Cause diminished perfusion and oxygenation of
cochlea
• Diet and metabolism
– DM accelerates process of arteriosclerosis
– Diffuse proliferation and hypertrophy of intimal
endothelium which may also interfere with
perfusion of cochlea
– Brainstem neuropathy in DM

41. • Accumulated exposure to noise
• Drug and environmental chemical exposure
• Genetics
• stress

42. workup
• Blood tests for autoimmune
• Audiology with PTA and speech discrimination
– Need for additional testing can be determined
from the audiometric plus physical examination of
the patient

43. treatment
• Presbycusis is not curable
– Effects of disease on patients lives can be
managed
– Amplification devices – properly fitted hearing
aids
– Older patients with arthritis and visual difficulties
need extra help on learning to use hearing aids
– Patients using hearing aids may still experience
difficulties with speech discrimination in noisy
situations

44. • Lip reading
– May help patients with diminished speech
discrimination and hearing aid users who have
difficulty in noisy evns
– Assistive listening devices
• Range from amplification of telephone signal to sound
transmitters
– Cochlear implants
• Patients with cochlear changes and intact spiral ganglia
and central candidates are best candidates

45. Future of treatment…
• Researchers proposing
treatments that address
underlying genetic cause
• Medications that block
production of reactive oxygen
metabolites (carnitine) may treat
presbycusis at molecular level
• Stem cell transplant into the
cochlea to attempt to regenerate
sensory cells….