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of conductive hearing loss in OI.
22,27
Some apparently
do not feel it is directly related to OI and do not include
the data.
29,30
In adults the inclusion criteria are easier to
classify because the conductive hearing loss is almost
always due to ossicular chain problems. Even though the
ear drum is usually thin, it seems to function normally.
The malleus, incus and stapes crura can be thin and frag-
ile. Breaks in them have been reported with minimal
trauma. The stapes footplate is the usual site of pathol-
ogy though with thickening and fixation of the footplate
in the oval window.
11
Sensorineural hearing loss is common in OI, especially
in type I OI.
22
This is inner ear hearing loss not associ-
ated with any other cause such as head trauma, ototoxic
drugs or aging. Most people with OI who develop senso-
rineural loss will see this start by the age of 40. The exact
mechanism of the loss is not clear. It has been postulated
that the bony turnover and changes in collagen in the
inner ear make the inner ear environment less friendly
to the health of the inner ear sensory hair cells and the
supporting stria vascularis.
15
COL1A2 is expressed in
moderate to high levels in membranous cochlear cells
31
the function of which remains unknown. Interestingly,
no relationship has been seen between the gene mutation
and the degree or type of hearing loss found.
7,32
Mixed hearing loss is seen commonly in older
patients with OI and may be present in as many as 55%
of patients over the age of 20 years.
22
While younger
patients may start out with a purely conductive hearing
loss, they can develop the additional sensorineural loss
with aging and the factors alluded to above. Separation
of the extent of conductive versus sensorineural involve-
ment can be done through audiologic testing.
Hearing loss is a major clinical feature of OI. In sur-
veys of hearing loss in OI, prevalence rates of hear-
ing loss range from 46%
29
to 62%.
22
Methodological or
definitional differences of what constitutes significant
hearing loss may account for some of the variability
of results.
27
As noted previously, some investigators
exclude cases of conductive hearing loss believed to
be secondary to otitis media with effusion in younger
patients with OI - thus lowering the prevalence
reported.
29,30
The age distribution of the sample sur-
veyed is also a major factor in prevalence studies of
hearing loss in patients with OI.
Hearing loss in OI generally appears initially as a
conductive hearing loss and is commonly described
as occurring in the second or third decade of life,
33,34
although significant conductive hearing loss
35
or senso-
rineural hearing loss
27
can occur much earlier. In a study
consisting of 22 children ranging in age from 3 to 19
years, 14 (63.6%) were diagnosed with conductive hear-
ing loss and three (16.6%) with sensorineural hearing
loss.
27
On the other hand, following a national survey in
Finland, only 3/42 (6.7%) of children age 16 or younger
with OI were found to have hearing loss.
36
Some inves-
tigators have reported that sensorineural hearing loss
is frequently found in patients with OI in both younger
and older age groups.
37
Hearing loss overall is more
common with increasing age in patients with OI. Across
all types of OI, 50% of patients in large-scale surveys
have hearing loss by 50 years of age.
33
The prevalence of hearing loss varies significantly
with type of OI. Patients with type I OI are significantly
more likely to have hearing loss than patients with
type III or IV OI.
33
Hearing loss of all types was reported
in 60.4% of patients with type I OI and 42.3% of type IV
patients with OI in one population study.
38
In addition,
sensorineural involvement is more common in type I OI
than in type IV OI.
38
Hearing loss occurred with a fre-
quency of only 4% in a population study
38
and 0% in a
recent small clinic sample
8
in patients with type IV OI.
Hearing loss has not been reported in types V through
XI, but that may be because of very small numbers.
Thus, the mix of types of OI in the data being reported
will cause some variability in the prevalence seen. In a
recent study, 67% of 49 adult patients with type I OI had
hearing loss which was predominantly of mixed origin.
8
Other associated features of OI such as skull fractures,
seizures and brain stem compression from basilar invagi-
nation that can cause hearing loss are included in some
reports
22,27
and excluded in others.
38
Whatever the inclu-
sion or exclusion criteria are though, there is clearly a sig-
nificantly increased loss when compared to the general
population.
VESTI
BULAR DYSFUNCTION A
ND OI
Since OI affects so many with hearing loss, there is
concern that it also affects the other inner ear function -
balance. This is also the case for individuals with otoscle-
rosis who have a relatively high prevalence of vertigo
39
which in some cases is related to surgical intervention.
40
In the case of OI, in one study, 43.8% of 42 adult patients
with type I, III and IV OI reported experiencing recur-
rent or continuous vertigo.
41
Of the patients with vertigo,
approximately half was attributable to inner ear causation
on the basis of case history information.
41
Balance prob-
lems have been reported in patients with basilar impres-
sion which is seen in as many as 25% of adult patients
with OI
41
due to brainstem compression. Despite the
high prevalence of vertigo in OI, no correlation has been
shown between the severity of OI and degree of hear-
ing loss in studies comparing hearing loss, auditory
brainstem response (ABR) and electronystagmography
(ENG).
41
It should be noted that the prevalence of vertigo
overall was greater in the patients with hearing loss.
41
The numbers are small, however, leaving the issue still
unresolved.
