Dr. T. Balasubramanian M.S.
Synonyms: Otospongiosis, Ankylosis of foot
plate of stapes.
is a hereditary localised disease of the bone derived from the
otic capsule characterised by alternating phases of bone resorption
and new bone formation. The mature lamellar bone is removed by
osteoclasis and replaced by woven bone of greater thickness,
cellularity and vascularity.
History: In 1741
Antonio Valsalva described ankylosis of stapes while doing a
postmortem on the body of a deaf patient.
1894, Adam Politzer introduced the term "otosclerosis" and described
the histopathology of the disease for the first time.
In 1912 Siebenmann introduced the
term otospongiosis to denote active otosclerotic foci.
The primary pathological change occurs in the bony labyrinth with
secondary effects upon middle ear and inner ear function.
The otosclerotic focus may be asymptomatic, or if present in
the area of foot plate of stapes it may give rise to ankylosis
of foot plate with resultant conductive deafness. Otosclerotic
foci may involve other portions of labyrinth causing sensori
neural hearing loss and vestibular
combination of effects are possible in otosclerosis. They
Histological otosclerosis: Otosclerotic foci doesnot cause
any symptoms and hence known as histological
Stapedial otosclerosis: is the classical
otosclerosis with fixation of stapedial foot plate causing
Cochlear otosclerosis: The foci involves the
cochlea causing sensorineural deafness.
otosclerosis: Here in addition to fixation of foot plate of
stapes there is also associated sensorineural hearing loss due to
involvement of cochlea.
European otologists prefer to use this term to indicate the active
phase of otosclerosis.
Incidence: Otosclerosis is common in
caucasian races. It is rarely found in Mongoloid and Negro
incidence: In clinical practice otosclerosis is seen more
often in women than in men. The ratio was found to be
2:1. Nowadays the authors believe the apparent female
preponderance may be due to the fact that unilateral otosclerotic
deafness is less common in women than in men. Noticeable
deterioration in hearing also occur during pregnancy due to hormonal
changes. Deafness due to otosclerosis may be initiated or made
worse by pregnancy.
Causative factors / etiology: Many
theories have been proposed to explain the etiological factors of
otosclerosis. They are:
3. Vascular disease
(Measles) currently accepted
5. Trauma : The petrous bone
doesnot have regenerative capacity. This is because of the
fact that the enzymes released during reparative phase are very
toxic to the inner ear hair cells.
Pockets of tissue capable of regeneration may be sequestered in various portions of labyrinthine bone. These tissue could be activated by the presence of regenerative enzymes in the blood following bone fracture elsewhere in the body.
Temporal bone abnormalities
predisposing to otosclerosis: The tendency for otosclerosis to
run in families has been documented. Authors have postulated an
autosomal dominant mode of inheritance with varying degrees of
Otosclerosis is associated with osteogenesis
imperfecta in 0.15 % of cases. This is known as Van der
Hoeve syndrome or Adair - Dighton syndrome.
Sites affected by
otosclerosis: The commonest site for apperance of otosclerotic
bone is fissula ante fenestrum. This fissula
is constantly seen in the labyrinthine capsule lying in front
of the oval window. This area may contain unossified cartilage
persisting even in adults. This area was referred to as
Cozzolino's zone by Perozzi in memory of his teacher.
Otosclerosis may occur in this area due to bony ossification of the
Residual cartilage may be present in the
following areas of labyrinth:
1. Fissula ante fenestram
Fissula post fenestram
4. Round window
6. Petrosquamous suture
7. Base of styloid
In normal development the fissula appears as fibrous
connective tissue bundle joining the vestibule with the tympanic
cavity. This fibrous tissue is encased in primary cartilage
which later gets replaced by bone. From the fissula the bone
acquires a connective tissue lining which later becomes converted
into perichondrium. The fissula is reduced in size by the
production of new secondary cartilage from the perichondrium.
These changes are completed by birth. The secondary
cartilage remains throughout life as a stable, dormant cartilage and
hence may even be considered as normal structure. It is only
when this secondary cartilage gets ossified otosclerosis occur (Bast
representation of fissula ante
changes may appear as a result of interaction between bone growth
promoting substances circulating in the blood stream, and the
unstable cartilagenous elements in the capsule of the
labyrinth. Otosclerosis is often seen at times when the bone
growth promoting substances are circulating in the blood as in
pregnancy and following fractures of other
endochondral bone of labyrinthine capsule in which otosclerotic
focus begins is compact in type. Ultrastructurally, lamellae
composed of fine fibrils lying in a ground substance are
concentrically disposed around haversian canals containing blood
vessels and connective tissue. In otosclerosis there is
sharply defined new bone formations that could be differentiated
from normal bone by their deep carmine stain and by marked
enlargement of bone spaces and haversian canals. The following
are the changes which occur in a otosclerotic foci:
Focal / diffuse replacement of normal compact bone by irregular,
loose cancellous bone with more deeply staining
2. There is an associated increase in size of
Haversian canals, cell spaces and marrow spaces with corresponding
increase in vascularity. The blood vessels are frequently
surrounded by a narrow margin of blue staining material that
Manassee described first as Blue Mantle zone.
in osteocytes, and appearance of osteoblasts and osteoclast
Histologically otosclerosis may be classified
1. Early focal otosclerosis
2. Diffuse active
3. Quiescent otosclerosis
Early focal otosclerosis: In this type the
abnormalities are localised to one or two small areas of an
otherwise normal foot plate section. The abnormal areas show
an enlarged marrow space surrounded by a blue staining area on
Diffuse active otosclerosis: In this
type there is abnormal vascularity with a great increase in size and
number of marrow spaces. Most of these spaces are lined by
osteoblasts. In places around the circumference of the marrow
spaces there is a scalloped appearance where bone has been recently
absorbed. The number of osteocytes are greatly
Quiescent otosclerosis: Here eventhough
there may be some increase in the size and number of marrow spaces
there is no evidence of bone formation or bone destruction.
Osteoblasts and osteoclasts are only occasionally seen. This
could be considered as a burnt out phase of the disease
Cochlear otosclerosis: This condition causes
pure sensorineural deafness without stapes fixation.
Otosclerotic foci may occur in the otic capsule without the
involvement of stapedial foot plate. The process of bone
erosion and new bone formation which occur in otosclerosis releases
enzymes like amylase, SGOT, SGPT etc which can enter into the
endolymph via the round window membrane. These enzymes are
toxic to the sensitive hair cells of the cochlea causing
sensorineural hearing loss.
Clinical types of
otosclerosis: Classification of various clinical types of
otosclerosis is based on microscopic appearances of the diseased
Rim fixation: Here the otosclerotic foci
starts from the anterior portion of the oval window niche. It
gradually expands to involve the anterior portion of the foot plate
causing fixation of the anterior portion of the foot plate only
leaving the centre of the plate free.
representation of various clinical types of
Biscuit foot plate: This type occur less
frequently. The focus originates in the foot plate itself and
as it expands it gives rise to the biscuit or rice grain foot plate
with delineated margins.
Obliterative otosclerosis: Rarely a
large mass of otosclerotic new bone fills up the oval window niche
obscuring the entire foot plate. This condition is known as
obliterative otosclerosis. It is a difficult condition to
Deafness: Typically deafness in otosclerosis
is bilateral and gradually increasing in nature.
Unilateral otosclerosis occur in 15% of patients.
Frequently it occurs between third and fifth decades of
life. In majority of cases the deafness is conductive in
nature. The deafness will not be noticed by the patient till
the loss reaches 30 dB level. This is the deafness level in
which understanding speech becomes difficult. These patients
may hear better in noisy environment because the speaker has a
tendency to raise his voice because of excessive ambient
noise. This phenomenon a feature of otosclerosis is known as
otosclerosis the deafness is purely sensorineural in nature.
Some patients may have both conductive and sensorineural hearing
loss (mixed deafness) because of the tendency of bone reparative
enzymes to damage the inner hair cells.
Patients with otosclerosis have
characteristically quiet voice with good tone and the change in
speech pattern may be detected only by close relatives.
Tinnitus: is a common symptom and occasionally
could be the only presenting feature. The presence of tinnitus
should alert the physician about the presence of cochlear
otosclerosis. It could also be seen in some patients without
cochlear degeneration due to abnormally increased vascularity of the
otosclerotic bone. Mostly tinnitus indicates sensorineural
degeneration. Tinnitus may be unilateral or bilateral.
It is usually roaring in nature.
attacks of vertigo is not uncommon in patients with
otoslerosis. This could be due to the action of toxic enzymes
released by the lesion into the vestibular labyrinth. These
patients may even have coexisting Meniere's disease.
Clinical examination: The ear drum in these patients
is normal (mint condition). Rarely during active phase of the
disease the increased vascularity of the promontory may be seen
through the ear drum. This sign is known as Flemingo's flush
sign or Schwartz's sign. This indicates otospongiosis (active
Hearing assessment can be done using
tuning forks. For detailed description of tuning fork tests
read the chapter titled clinical examination of the ear.
auditometry will show precisely the amount and type of hearing
loss. The presence of Carhart's notch is a classic audiometric
feature in these patients. This Carhart's notch is
present in bone condution. There is a dip centered around 2000
Hz. This is actually an artifact. In cochlear
otosclerosis audiometry reveals sensorineural hearing loss.
Stapes fixation causes an elevation in the bone conduction
thresholds of 5dB at 500Hz, 10dB at 1000 Hz, 15 dB at 2000 Hz, and 5
dB at 4000 Hz. In the audiogram this creates a peculiar
pattern known as Cookie bite audiogram. The bone conduction
audiogram appears like a cookie having been
Fig showing a
cookie bite audiogram
showing audiogram with carhart's notch
Impedence audiometry is an useful investigation to diagnose
otosclerosis. Middle ear compliance is often reduced.
When stapes is fixed stapedial reflex is absent. The typical
impedence curve is As curve.
All these patients with
pure conductive deafness have excellent speech discrimination
Medical: The aim
of medical management is to convert an active otosclerotic foci into
an inactive or quiscent foci. Fluride is the drug of
Indications of fluride therapy:
Patients with surgically confirmed otosclerosis who show
progressive sensorineural deafness disproportionate to
2. Patients with pure sensorineural loss with family
history, age of onset, audiometric pattern and good auditory
discrimination indicate the possibility of cochlear
3. Patients with radiological demonstration by
CT scan of spongiotic changes in the cochlear capsule
Patients with positive Schwartz sign.
5. Post op treatment:
If patients are found to have an active focus during surgery,
fluride therapy is prescribed for 2 years.
of fluride therapy:
1. Patients with chronic nephritis
and nitrogen retention
2. Patients with chronic
3. Patient who are pregnant /
4. In children before skeletal growth has
5. Patients who show allergy for the
6. Patients with skeletal flurosis
act on otosclerotic foci by reducing osteoclastic bone resorption
with a corresponding increase in osteoblastic bone formation.
Fluride also has antienzymatic action thereby it can neutralise the
toxic enzymes released from the otospongiotic
Dose: A daily dose of 50 mg of sodium fluride is
given for a period of 2 years. In patients with positive
Schwartz's sign the dose can be increased up to 75 mg per day.
Adverse effects of sodium fluride therapy:
Hearing aids: These patients will benefit
from the use of hearing aids if surgery is not acceptable to the
patient or if it is risky. There is always a 1% risk of
producing a dead ear during surgery even in the best of hands.
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