Dr. T. Balasubramanian M.S.
of the elderly, Age related deafness.
Presbyacusis is defined as a progressive bilateral symmetrical age
related sensorineural hearing loss. The hearing loss is confined to
Presbyacusis is an added problem
for the elderly who have a tendency to compensate for their loss of
vision through their intact sense of hearing. They even tend to get
isolated and become a social recluse due to this problem.
Factors responsible for
presbyacusis: Various factors have been postulated as
causes of presbyacusis. They are:
1. Hereditary: Features like early
aging of the cochlea and susceptiblility of the cochlea for drug
insults are genetically determined.
2. Atherosclerosis: May diminish
vascularity of the cochlea there by reducing its oxygen supply.
3. Dietary habits: Increased intake
of fatty diet may accelerate atherosclerotic changes in old age.
4. Diabetes: May cause vasculitis
and endothelial proliferation in the blood vessels of the cochlea
there by reducing its blood supply.
5. Noise trauma: Exposure to loud
noise on a continuing basis stresses the already hypoxic cochlea
hastening the presbyacusis process.
6. Smoking: Is postulated to
accentuate atherosclerotic changes in blood vessels aggravating
7. Hypertension: Causes potent
vascular changes, like reduction in blood supply to the cochlea
thereby aggravating presbyacusis.
8. Ototoxic drugs: Ingestion of
ototoxic drugs like aspirin may hasten the process of
Cochlear pathology seen in
Depending on the pathology seen in
the cochlea, 4 different types of presbyacusis have been identified.
They are Sensory presbyacusis, neural presbyacusis, strial
presbyacusis and cochlear conductive presbyacusis. The aging cochlea
present disorders that are symmetric in paired ears; but the extent
of involvement at the cellular level may be uneven. Hence
presbyacusis can occur in 4 differing pathological types, or in
combination ther of. A study of pure tone audiograms and
1. Abrupt high freqency hearing
loss (attributed to sensory cell pathology (loss).
2. Flat threshold hearing loss
(seen in cases with strial atrophy)
3. Diminised speech discrimination
(due to loss of cochlear neurons)
4. Gradual descending audiometric
pattern (due to inner ear conductive disorder)
Patients with presbyacusis
uniformly have poor threshold for frequncies in 8 Khz range. Infact
the threshold was as low as 60% in most of the patients.
is caused by loss of hair cells at the basal end of the
cochlea. This commonly occurs in an aging cochlea. The area of
involvement may extend to involve even the speech frequency area of
the cochlea. These changes cause a rapid decrease in the threshold
for high freqency sounds.
The earliest changes occurring in
the cochlea is the loss of stereocilia, which can be identified only
on electronmicroscopy. The second change to occur is distortion or
flattening of the organ of corti followed by loss of supporting
cells. Finally the organ of corti appears as an undifferentiated
mound of tissue on a basement membrane. There is a gradual reduction
in the number of outer hair cells in the elderly more so in the
basal area of the cochlea. This occurs to a lesser extent at the
apex of the cochlea. The apical loss of outer hair cells is seen
only in individuals of more than 70 years of age. The loss of inner
hair cells is less marked, but follows the same pattern as the outer
The wear and tear pigment
lipofuscin is known to accumulate in the apical cytoplasm of the
hair cells. The lipofuscin is assumed to be a waste product of
presbyacusis: Is caused by a loss in the population of
cochlear neurons, but the end organs are still functional causing
severe loss in speech discrimintion. Pure tone thresholds are nearly
normal. Gaeth used the term Phonemic
regression to describe this phenomenon. Studies have shown
that speech discrimination scores are slightly better in the left
ear when compared to the right, this has been attributed to the left
cerebral dominence becoming manifest due to the degenerative changes
affecting the auditory pathway. The loss of cochlear neurons is the
most consistent pathologic change seen in these patients. It has
been calculated that loss of cochlear neurons occur at the rate of
2,100 (Schuknecht) neurons every
decade. There are roughly about 35,000 cochlear neurons in a normal
ear. The loss of cochlear neurons may be genetically determined. The
atrophy occurs throughout the cochlea, but is more pronounced in the
basal turn of the cochlea.
Strial Presbyacusis:( Also
known as Metabolic presbyacusis) Atrophy of stria
vascularis is commonly seen in this condition. Hearing loss in these
patients is insidious in onset occurring during the 3rd - 6th
decades of life. It progresses slowly. The clinical feature that
identifies this condition from the other types of presbyacusis is
the presence of a flat or a slightly descending audiometric curve.
These patients respond well to the amplification produced by hearing
aids. This type of presbyacusis carries the best prognosis because
of this feature. Takahashi demonstrated two types of atrophy in
Type I: a patchy type more severe
in the apical and extreme basal regions of the cochlea.
Type II: A diffuse type often
showing normal strial thickness with large intercellular spaces that
may not be visible under light microscopy.
All 3 layers of stria are involved
in various degrees. The loss of strial tissue may cause changes in
the composition of the endolymphatic fluid causing further damage to
the cochlear hair cells.
Pure tone audiometry shows a flat
curve because the pathology involves the whole of the cochlea.
Speech discrimination is preserved. This type of presbyacusis is
considered by many to be familial.
(Mechanical) presbyacusis: This type of presbyacusis is
differentiated from others by a linear descending audiogram. This is
postulated to be caused due to stiffening of the basilar membrane of
the cochlea. The thickening has been found to be more severe in the
basilar turn of the cochlea where the basilar membrane is thin.
Speech discrimination is average for the given frequency.
Has been recently introduced to describe conditions which
features of either two or all of the types of presbyacusis discussed
above. These patients have been clubbed under this mixed catergory
to account for their varied manifestations.
Presbyacusis is a diagnosis of
exclusion. All the other causes of sensorineural hearing loss must
be ruled out before declaring the patient to be suffering from
Amplification of the sounds with the use of hearing aids
(with proper features) must be considered in all these patients.
Administration of placebo drugs like neurotropic vitamins may make
the patient feel something is being done to allieviate his problem.
In rare patients cochlear implants may be considered.
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