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VOLUME 10 NUMBER 4 • NOVEMBER 2013
RESEARCH ARTICLE
SA JOURNAL OF DIABETES & VASCULAR DISEASE
from developing countries where the diagnosis, presentation and
management of the disease may be different from that in developed
countries, hence the importance of the current study.
In addition to individuals with T1DM having a mild high-
frequency sensorineural hearing loss, the literature also suggests
that they may also present with cochleovestibular symptoms such
as tinnitus, which precedes the hearing loss, as well as vertigo.
8,14
Lasisi, Nwaorgu and Bella’s study
15
on diabetic subjects further
confirmed this. A prevalence of cochleovestibular dysfunction
(benign paroxysmal positional vertigo, tinnitus and sensorineural
hearing loss) was evident. However, the prevalence of these
symptoms specifically for T1DM was not specified.
Diabetic neuropathy caused by diabetic microangiopathy may
cause damage to the inner ear, resulting in a hearing impairment.
It is therefore important that audiologists recognise and manage
the microvascular complications of diabetes in order to provide
optimal care and treatment for this growing population. Moreover,
audiologists should have a clear understanding of the disease
process, which will allow them to be able to conduct appropriate
assessment and management of individuals who present with T1DM.
Currently, there is a dearth of research in South Africa regarding
auditory function in individuals diagnosed with T1DM. Therefore, the
current study aimed at describing the auditory function of individuals
diagnosed with T1DM in Gauteng, South Africa.
This pilot study proposed to answer the following research
questions:
• What is the prevalence of cochleovestibular symptoms such as
tinnitus and vertigo in T1DM?
• How can the results of the basic audiological assessment for
the individuals diagnosed with T1DM and the control group be
described?
• What are the DPOAE characteristics of both groups?
• Are DPOAE measures more sensitive in detecting the early
signs of cochlear dysfunction in individuals with T1DM, when
compared to the pure tone test battery?
• Is there a relationship between the auditory function in
individuals with T1DM and duration of T1DM?
Methods
A quasi-experimental, non-equivalent control-group research design
was used, with the aim of determining the relationship between
T1DM and auditory function. The study setting was an out-patient
clinic at the University’s Speech and Hearing Clinic (USHC) in
Johannesburg, Gauteng. Participants were recruited through a non-
probability purposive sampling technique. Participants were invited
to participate if they had medical confirmation of the diagnosis of
T1DM, were between the ages of 19 and 40 years of age, and were
able to provide informed consent.
Participants who had a congenital/family history of hearing
impairment, head and/or neck trauma, including ear operations,
and participants who had been or were at the time of the study
on ototoxic medication were excluded from participating in the
study. Participants with an occupational/personal history of noise
exposure were also excluded.
The participants responded to poster advertisements that were
placed at various diabetes centres as well as to word of mouth
in Gauteng. Prior to recruitment, consent and information letters
were sent to all relevant authorities to obtain permission to conduct
the study.
Measurements
A structured test battery was used that included a questionnaire
and audiology tests. The following section briefly describes the
measurements used in this study.
The testing procedure commenced with a detailed case history
taking for each participant using a questionnaire. The questionnaire
consisted of a biographical information section, medical history and
hearing history section. The questionnaire provided background
information and cochleovestibular symptoms which could relate to
a hearing loss such as tinnitus and vertigo; information that when
used together with the audiometric results could contribute to the
interpretation of the results and guide treatment planning.
15
The audiological test battery consisted of the following.
Otoscopic examination:
this was conducted using a Welch Allyn
Pocket otoscope to allow the audiologist to detect middle and
outer ear pathology.
16
In addition, malformations of the auricle
or the external auditory canal, signs of trauma or infection and
cerumen obstruction or collapse of the external auditory canal were
observed.
16
Impedance audiometry:
tympanometry and acoustic reflexes
(both ipsilateral and contralateral) were conducted using a Grason
Stadler Inc, 38 Version 4 tympanometer on all participants. The
single-frequency 226-Hz probe tone was used. The tympanogram
results were analysed according to the types of tympanograms: A,
B, C, As and Ad. Type A tympanograms were recorded as normal
and all other types were considered abnormal.
17
Acoustic reflexes
were recorded as normal if elicited between 70 and 110 dB at 500,
1 000, 2 000 and 4 000 Hz.
18
Pure-tone audiometry:
air- and bone-conduction testing was
conducted on each participant using an AC 40 audiometer. Air
conduction was done at 250, 500, 1 000, 2 000, 3 000, 4 000,
6 000 and 8 000 Hz bilaterally. A pure-tone average (PTA) was
obtained for the right and left ear, respectively. Pure-tone averages
below 26 dB were regarded as indicative of hearing function
within normal limits.
19
Bone conduction was done at 250, 500,
1 000, 2 000 and 4 000 Hz bilaterally. This was only conducted in
participants who had air-conduction thresholds greater than 25 dB
at any of the frequencies. As air- and bone-conduction testing was
done together, it was possible to differentiate between the types of
hearing loss: conductive, sensorineural or mixed.
20
Speech audiometry:
speech reception threshold (SRT), and
speech discrimination (SD) testing was performed using an AC
40 audiometer. SRT was used to verify the pure-tone audiometry
results.
21
The Central Institute for the Deaf version 1 (CID W-1)
word list was used for SRT testing, while speech discrimination was
carried out bilaterally at 5 and 25 dB SL and at TD-10, using the
NAL AB word list with monitored live voice if hearing thresholds
were not within normal limits.
21
If the hearing thresholds were
within normal limits, it was carried out at 25 dB SL.
21
For interpretation, a good correlation between SRT and PTA was
considered to exist if they were within 6 dB of each other, a fair
correlation existed if the scores were between ± 7 and ± 12 dB of
each other, and a poor correlation existed if the scores differed by
± 13 dB or more.
21
It is acknowledged that the use of monitored
live voice and a word list that is not South African normed were
limitations in the current study.
