presbycusis and noise induced gearing loss.

1. Presenter-Dr Utpal Sarmah
Moderator-Dr(Prof)Gul Motwani
Co-Moderator-Dr Nihar Topno
VMMC and Safdarjung Hospital ,New Delhi

2. Noise induced hearing loss

3. Definition
 Reduction in auditory acuity associated with noise
exposure.
 Typical NIHL is of a sensorineural type
 Involves injury to the inner ear.
 Usually bilateral and symmetrical.
 affects the higher frequencies (3k, 4k or 6k Hz) and
then spreading to the lower frequencies (0.5k, 1k or 2k Hz).

4. TYPES
 Temporary described as Temporary Threshold Shift
(TTS), or
 Permanent described as Permanent Threshold Shift
(PTS)
 Acoustic trauma where a single exposure to an intense
sound leads to an immediate hearing loss.

5. Incidence
 About 10% of the world population work in hazardous levels of
noise
 Worldwide, 16% of the disabling hearing loss in adults is
attributed to occupational noise.
 NIHL is the 2nd most common form of acquired hearing loss
after age-related loss (presbyacusis).
 Studies showing that people who are exposed to noise levels
higher than 85 db suffered from NIHL
 Its one of the most common military occupational disabilities.

6.  In India, occupational permissible exposure limit for 8
h time weighted average is 90 dB
 Male preponderance

7. Pathophysiology
 Metabolic
 Structural
METABOLIC
Acoustic overstimulation
Excessive neurotransmitter release(? Glutamate)
Transduction

8.  Stimulation with sound of moderate intensity increases
cochlear blood flow, whereas sound of high intensity
decreases cochlear blood flow
 Outer hair cell (OHC) plasma membrane fluidity
 Role of glucocorticoid receptors
 Recent studies shown the presence of glucocorticoid
signaling pathways in the cochlea and their protective
roles against noise-induced hearing loss

9.  Oxidative stress:
overstimulation of tissues by noise causes excess
production of reactive oxygen species, including
superoxide and hydroxyl radicals which oxidize
cellular targets such as lipids, proteins and DNA by
virtue of a highly reactive unpaired electron therby
causing necrotic changes or apoptotic cell death

11.  Activity of ROS is antagonized by the antioxidant system
consisting of small molecules (e.g. glutathione, vitamin C,
vitamin E) and protective enzymes (e.g. glutathione
peroxidase, superoxide dismutase).
 The balance determines the cellular redox status.
 Overstimulation by noise can increase the production of
ROS resulting in a shift of the redox balance and triggering
the activation of signalling pathways and gene expression.
 Depending on the severity of the insult, the cell may activate
survival pathways (e.g. synthesis of antioxidant enzymes) or
invoke death pathways of necrosis or apoptosis.

12.  Acoustic overstimulation activates multiple transcription
factors in the cochlea, including the transcription factor AP-l
and thus potentially apoptotic pathways via jun kinase
 Greatest area of injury in occupational NIHL appears to be to
that portion of a cochlea sensitive to frequencies of about 4k Hz
 Continuous stimuli are more damaging than interrupted
stimuli.
 Intermittent noise defined as loudness levels that fluctuate
more than 20 dB is more protective for apical lesions induced by
low frequencies than for basal lesions induced by high
frequencies.

13. Structural
 Changes to the micro mechanical structures
like depolymerization of actin filaments in stereocilia.
 Changes to nonsensory elements of the cochlea
1. swelling of the stria vascularis.
2. swelling of afferent nerve endings.
3. destruction of the intercilial bridges
4. rupture of the Reissner membrane

14.  Outer hair cells are more susceptible to noise exposure
than inner hair cells.
 Temporary threshold shifts (TTS) decreased stiffness of the
stereocilia of outer hair cells. The stereocilia become
disarrayed and floppy and they respond poorly.
 Permanent threshold shifts (PTS) are associated with
fusion of adjacent stereocilia and loss of stereocilia.

15.  gene association study for NIHL in 2 independent
noise-exposed populations revealed
that PCDH15 and MYH14 may be NIHL susceptibility
genes

16. Acoustic trauma
 Caused by an extremely loud noise usually resulting in
immediate, permanent hearing loss.
 Such transient noise stimuli are generally less than 0.2 seconds
in duration.
TYPES OF TRANSIENT NOISE
 Impulse noise usually due to blast effect and the rapid
expansion of gases
 Impact noise which results from a collision (usually metal on
metal). Impact noises are often associated with echoes and
reverberations, which produce acoustic peaks and troughs.

17.  The sound stimuli generally exceed 140 dB
 Mechanical tearing of membranes and physical
disruption of cell walls with mixing of perilymph and
endolymph.
 Damage from impulse noise appears to be a direct
mechanical disruption of inner ear tissues because their
elastic limit is exceeded

18. Predisposing factors
 Genetic basis:Ahl gene.
 Smoking
 Diabetes
 Cardiovascular disease
 Recreational drug
 Exposure to ototoxic agents use
 Industrial solvents
 Blue eye colour

19. Clinical presentation:Symptoms
and signs
 Male patient in early middle age
 If young patient c/o:tinnitus>>>hearing loss
 Women frequently presents with acoustic shock.
 h/o:hearing difficulty in background noise
 Trouble in normal and telephone conversation
 Turning up the radio/television volume
 Tinnitus
Many patients experience tinnitus associated with
both TTS and PTS. Postexposure tinnitus and TTS
serve as warning signs of impending permanent NIHL.

20.  NIHL, is generally symmetrical.
 Occasionally, a work environment results in
asymmetrical noise exposure, as seen in tractor drivers.

21.  The most common cause of asymmetric NIHL is
exposure to firearms, particularly long guns.
 Right-handed shooters have a more severe hearing
loss in the left ear because the left ear faces the barrel
while the right ear is tucked into the shoulder and is in
the acoustic shadow of the head.(The SHADOW
EFFECT)
 Reduced Transiently evoked otoacoustic emission
(TEOAE )levels in soldiers exposed to noise may be the
first sign of potential hearing loss.

22.  (TEOAE) reduction was registered predominantly
at 2, 3, and 4 kHz, with greatest decrease at 2 kHz
(P < 0.02).

23. Symtoms specific to acoustic shock
 Objective hearing loss is rarely a feature but high levels of
psychological distress are common.
 Common symptoms include
 Otalgia
 Tinnitus
 Hyperacuisis
 Dizziness
 Headache
 Sleep disturbance
 Poor concentration

24. Natural history of disease process
 NIHL begins with a temporary threshold shift (TTS)
which recovers almost completely once the noxious
stimulus is removed. The amount of time over which
recovery occurs is unclear and controversial, but a 24
hr period is generally considered.
 extent of a NIHL (TTS/PTS) is predictable on
1. Intensity
2. Spectral pattern of the noise(Frequency content)
3. Temporal pattern of exposure (intermittent or
continuous)

25.  Duration of exposure to the noise (time weighted average
[TWA])
 Individual susceptibility to the noise
In occupational situations, TTSs are almost always greatest
between 3000-6000 Hz and are often quite narrowly focused
at 4000 Hz.

26.  The 4k HZ notch in audiogram appears to be a
consequence of several factors:
1.The fact that human hearing is more sensitive at 1-5 kHz
2.The fact that the acoustic reflex attenuates loud noises
below 2 kHz (as demonstrated by Borg)
3.Nonlinear middle ear function as a result of increased
intensities.

27. Diagnosis
 No specific test available
 History:H/O unprotected exposure to excessive noise.
 No evidence of other otological pathology.
 Separate effects of ageing from the effects of noise.(use of standarized table:NPL
table,ISO7029, ISO 1999
 Audiometry
1. Classical audiometric pattern is of a high-tone hearing loss with a notched
appearance centred on 4 or 6 kHz, with some recovery at 8 kHz. However, the
notch is often absent
2. Significant audiometric loss at frequencies below 2 kHz is extremely uncommon.
 Tympanometry :to confirm normal middle ear functioning.
 Cortically evoked reflex audiometry may be required in those individuals in whom a
significant nonorganic component (feigned thresholds) is suspected
 MRI to r/o vestibular schwannoma.(in case of significant asymmetry)

28.  In a possible case of noise induced hearing loss,the
individual will have a hearing loss composed of 3 parts:
Age related component
Noise induced component
Idiopathic degenerative component
The clinician task is to separate and calculate the relative
contribution ( if any )from three sources.

30.  From the audiogram,the average of the thresholds of
hearing for frequencies of 500, 1000, 2000, 4000 and
6000 Hz is calculated
 25 dB is deducted from the value (as there is no
impairment up to 25 dB).
 1.5 is then multiplied to it.
 This is the percentage of hearing impairment for one ear
 Percentage handicap= (Better ear%×5)+(worse ear%)
6
CALCULATION OF THE HEARING IMPAIRMENT

31. Differential diagnosis
 Inner ear
1. Autoimmune disease
2. Genetic SNHL
3. Autotoxicity
4. Presbycussis
5. Sudden hearing loss
 Middle ear
1. Otosclerosis

32. PREVENTION:
 PERSONAL HEARING PROTECTION:
 Ear plugs
 Ear muffs
 Active noise reduction
 NON SPECIFIC MANAGEMENT:
 Optimisation of acoustic environment.(background noise reduction)
 Increase face to face communication.
 Rehabilitation programme (psychological counselling)
 Lip reading classes.
 SPECIFIC MANAGEMENT:Hearing Aids,tinnitus management.

33. Prevention cont:
 Therapeutic intervention should target early parts of
the toxic molecular cascades.
 The protectant must be present in the inner ear in
sufficiently high amounts at the time of noise trauma.
 Protective medication should not have any side
effects of its own.

34. Antioxidant therapy
 Glutathione
 sodium thiosulphate
 Mannitol
 WR-2721
 desferoxamine,
 2,3-dihydroxybenzoic acid
 Salicylate
 N-acetyl cysteine
 D-methionine
 Alpha tocophero1

35. Neurotrophic factors
 Noise trauma may affect the spiral ganglion cells
 Viability of the spiral ganglion cells is required for
the success of cochlear implant in the profoundly
deaf.
 Neurotrophic factors regulate cellular homeostasis
including the cellular redox state and modulate gene
transcription and cell cycle activities.
 Brain-derived neurotrophic factor, neurotrophin-3
and glial-derived neurotrophic factor

36. OCCUPATIONAL NIHL
( Indian scenario)
 Studies of NIHL in India are limited.
 Study was conducted in heavy engineering industry,
which included machines shop and press divisions. The
sound levels ranged from 83 to 116 dBA. Hearing
impairment was progressive in all the study groups.
 In a textile mill weavers study, the sound levels were
around 102-104 dBA . NIHL at 4000 Hz was as high as 30
dB in the age range 25-29 years, 40 dB in the age range 30-
34 years and 45 dB in the age range 35-39 years

37.  Noise pollution on traffic policemen in the city of
Hyderabad, India, was carried out by the Society to
Aid the Hearing Impaired, revealed that 76% had
NIHL
 The National institute of miners’ health (NIMH) has
carried out NIHL studies in various mines. NIHL was
prevalent among 12.8% of the employees. Moderate
NIHL was detected in 10.2% and severe NIHL was
observed in 2.6% of the employees.

38. Compensation
 In India, NIHL has been a compensable disease since 1948
under the Employees State Insurance Act (1948) and the
Workmen's Compensation Act (1923). But still there is very
little awareness regarding this fact.
 Nearly 3 billion dollars has been paid as compensation for
NIHL in the USA in the last two decades.
 In India, it was only in 1996 that the first case got
compensation
 About 250 workers are receiving compensation for NIHL

39. PURSUING A CLAIM
 The common option is to pursue a civil claim where the
burden of proof is on the claimant. For such a case to
succeed the claimant must demonstrate “on the balance of
probabilities” (i.e. more likely than not) that:
1. There has been exposure to excessive noise levels;
2. The hearing loss has been a consequence of that
exposure;
3. There was a forseeable risk of injury from the exposure;
4. The case was brought in time.
 The claimant must retain a solicitor to coordinate the case.

41. INTRODUCTION
 Mid to late adult onset,B/L progressive sensorineural
hearing loss,where underlying causes have been excluded.
 Exclude hearing loss caused by primary factors including
loud noise exposure,underlying medical condition
 Most common otolaryngologic problem of elderly
 Involves bilateral high – frequency hearing loss associated
with difficulty in speech discrimination and central auditory
processing of information

43. 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%

44. 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

45. Saxen , 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

46. 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.

47.  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

48. Neural presbycusis
 Atrophy of nerve cells in the cochlea(cochlear ganglion
cells)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
 Most common type.

49.  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

50. 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

51. 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

52. INTERMEDIATE
 Change in characteristics of the cochlear duct that are
not evident on light microscopy but alter function at
sub microscopic level.
 Changes in intracellular organalles involved in cell
metabolism,decrease in synapse numbers and changes
in endolymph composition have all been implicated in
this category.

53. MIXED
 Some combination of other five.

54. GENETICS
 Genetic studies of mice have made an important
contribution to the field of deafness and conclusively
indicate that genetic factors can be important in age
related hearing loss.
 Many different inbred mouse strain show accelerated
age related hearing loss ,and in atleast ten of these the
gene involved is ahl,which maps to mouse
chromosome 10.

55.  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

56.  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

57. 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

58. Environmental factors and
presbycusis
 Noise exposure
 Cigarette smoking
 Alcohol use
 Systolic BP
 Blood hyperviscosity
May all exacerbate age related hearing loss.

59. Clinical features
 Presentation varies
 Old patient normally at least in their fifties.
 H/O :Slow and insidious hearing problem
 Description involves loss of clarity rather than loss of volume.
 Difficulty in hearing conversation particularly in presence of
background noise.
 Sometimes tinnitus may be the only presenting
feature.

60. EXAMINATION
 Otological examination will be normal.

61. INVESTIGATION
 Audiology with PTA and speech discrimination
 Need for additional testing can be determined from the
audiometric plus physical examination of the patient .
 Most commonly though,the
audiogram show a hearing loss
which tend to be worse at higher
frequency.
As the condition advances there tends to be progressive loss of
be loss of middle( 1 and 2 KHz) and
even low frequencies.(250 & 500hz).

62. DIAGNOSIS
 Age >60yrs.
 Normal examination finding.
 Symmetrical
 High frequency hearing loss.

63. MANAGEMENT
 NON SPECIFIC:PSYCHOLOGICAL AND PRACTICAL
MEASURES.
 SPECIFIC

64. NON SPECIFIC
Hearing aids tend to provide little benefit
• Optimizataion of acoustic environment.
Psychological counselling
practical measures
• Infrared headphones/bluetooth headphones
• Volume controllable telephone.
• Louder doorbells.
• Lip reading classes.

65. Specific management
Binaural hearing aids.
Tinnitus management.
Tinnnitus retraining therapy
Cognitive directive counselling.
Sound therapy

66. Future of treatment…
 Researchers are proposing treatment underlying genetic
cause(gene therapy)
 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.