132
VOLUME 10 NUMBER 4 • NOVEMBER 2013
RESEARCH ARTICLE
SA JOURNAL OF DIABETES & VASCULAR DISEASE
this epitomises human contact. Provision of aural rehabilitation in
the form of amplification and/or communication strategies would
ensure enhanced communication functioning for the individual
with T1DM.
The mean DPOAE amplitude values were notably reduced in the
experimental group compared to the control group. These changes
in the experimental group were significantly reduced in the high
frequencies: 6 000 and 8 000 Hz. These finding indicate that there
was outer hair cell dysfunction in the inner ear, as DPOAEs provide
information on the OHCs located in the cochlear,
34,35
and can detect
when the function of the cochlear amplifier is impaired.
36
DPOAEs
are also known to be more sensitive to subclinical hearing changes
long before they can be detected on the audiogram.
Microangiopathy of the inner ear vessels, stria vascularis atrophy,
and spiral ligament and hair cell loss are likely to result in hearing
loss.
7,36
Moreover the ear-specific microvascular complications of
the inner ear have been reported to be the source of the hearing
loss related to T1DM.
7
All of these factors could alter the OHCs
function and consequently the DPOAE, as evidenced in the current
sample.
The reduced DPOAE amplitudes in this study are consistent with
previous literature that indicated reduced amplitudes for the mid to
high frequencies on this phenomenon.
11-13
DPOAEs are known to
be an excellent physiological measure to identify hearing loss, and
the identification of hearing loss is better at mid to high frequencies
than at lower frequencies.
36
A comparison of the DPOAE amplitudes and auditory thresholds
at each frequency indicated that DPOAEs are more sensitive in
detecting the early signs of cochlear dysfunction in individuals
with T1DM compared to pure-tone audiometry. DPOAEs are more
sensitive as the DPOAE amplitudes at the high frequencies, 6 000
and 8 000 Hz, were significantly reduced, indicating damage to the
OHCs. However, the auditory thresholds on pure-tone assessment
only showed an increase in threshold at 6 000 Hz. An increase in
threshold was also noted at 8 000 Hz but this was not as notable
when compared to the increased threshold at 6 000 Hz.
This finding is consistent with previous literature. For example,
Ottaviani
et al.
13
also found that the use of DPAOEs demonstrated
alterations of the cochlear function despite the participants having
normal pure auditory thresholds.
The current findings on the reduced DPOAE amplitudes in
individuals with T1DM as well as DPOAEs being more sensitive in
detecting the early signs of cochlear dysfunction have implications
for audiologists who are assessing individuals with T1DM. They
indicate that the audiologist should ensure that DPOAEs form part
of the protocol when assessing the hearing status of individuals
with T1DM.
Results of the auditory function and its relationship with T1DM
and age of onset indicated that the PTAs were highest for an
individual who had had T1DM for 20 years. However, the PTA
decreased for individuals who had had T1DM for 21 years and
longer. These results are inconclusive, possibly due to the small
sample size. Ferrer
et al.
29
concluded that the duration of T1DM is
significantly correlated with the auditory thresholds at 1 000, 2 000
and 8 000 Hz.
In summary, results from the current study revealed that tinnitus
and vertigo were prevalent cochleovestibular symptoms in T1DM.
The otoscopic and immittance findings were within normal limits
for the experimental and control groups. Additionally, the pure-
tone audiometry results indicated the absence of hearing loss.
However, auditory thresholds were elevated at 6 000 Hz in the
experimental group. Speech audiometry results were found to be
not statistically significantly different between the two groups but
the SRT and SD results were elevated in the experimental group.
DPOAEs amplitudes were reduced in the experimental group at
all frequencies but were most statistically significantly reduced at
6 000 and 8 000 Hz. DPOAEs were found to be more sensitive than
the pure-tone assessment battery in detecting the early signs of
cochlear dysfunction in individuals with T1DM.
Limitations of the study
Due to the small sample size, the current study is presented as a
pilot study. Therefore its results need to be considered in relation to
the identified limitations. Firstly, the small sample size. The results
could have been more conclusive and generalisable had there
been a larger sample size, with a wider age range cohort, which
is an indication for future studies. Secondly, ultra-high frequency
audiometry testing did not form part of the test protocol due to a
lack of equipment. The use of high-frequency audiometry testing
at 10 000 and 12 000 Hz could have identified the high-frequency
hearing loss that is characteristic of T1DM, which may have been
missed in the current sample. Finally, a larger sample size would
have allowed for more powerful statistical analysis to be conducted
to support the current findings.
The findings of this study have important implications for
the assessment and management of individuals with T1DM by
audiologists. Despite the fact that the low prevalence and high
cost mean that T1DM is likely to be low on the list of priorities for
the ministry of health in South Africa, all efforts should be made
to improve the quality of life of individuals diagnosed with this
condition, and that might include audiological management. The
key findings of this study suggest the importance of incorporating
audiological assessment for individuals with T1DM.
When assessing individuals with T1DM, the assessment
should include the basic audiometric test battery as well DPOAEs.
Importantly, hearing loss may be present with DPOAE assessment
but absent with pure-tone audiometry. The use of DPOAEs as a test
procedure in any basic audiometric test battery is paramount as it is
able to detect early signs of cochlear dysfunction.
The elevated thresholds at 6 000 Hz in individuals with T1DM can
reasonably be ascribed to T1DM itself due to the strict inclusion and
exclusion criteria that were adhered to. Finally, further replicated
research with the same protocol and a larger sample is required to
obtain more conclusive and generalisable results.
Conclusion
This study provides preliminary understanding of the concerns
regarding hearing function in people living with T1DM in South
Africa. The main conclusion drawn from the study was that
microvascular complications of T1DM may cause damage to
the OHCs, resulting in reduced DPOAE amplitudes in the high
frequencies. This may also result in elevated auditory thresholds at
6 000Hz. Furthermore, individualswith T1DMappear to have normal
middle ear function and no middle ear pathology, as suggested
by the otoscopic examination and impedance audiometry. Such
individuals identify speech sounds at an elevated threshold.
These study findings provide valuable information about the
assessments necessary for long-term management of persons with
T1DM. Because of the small sample size in the current study as well as
