VOLUME 10 NUMBER 4 • NOVEMBER 2013
127
SA JOURNAL OF DIABETES & VASCULAR DISEASE
RESEARCH ARTICLE
Correspondence to: Prof Katijah Khoza-Shangase
Speech and Hearing Clinic, Witwatersrand University,
Johannesburg
Tel: +27 0(11) 717-4565
Fax: 086 553 6055
e-mail:
D Pillay, A Moolla
Speech and Hearing Clinic, Witwatersrand University,
Johannesburg
S Afr J Diabetes Vasc Dis
2013;
10
: 127–133
Diabetes and the audiologist: is there need for concern
regarding hearing function in diabetic adults?
K KHOZA-SHANGASE, D PILLAY, A MOOLLA
Abstract
Background:
The main aim of the current pilot study was to
describe the auditory function of individuals diagnosed with
type 1 diabetes mellitus (T1DM) in Johannesburg, Gauteng.
Methods:
A quasi-experimental, non-equivalent control-group
design was used. A non-probability purposive sample of nine
adults with T1DM and nine healthy adults with normal hearing
were recruited and assessed at the University’s Speech and
Hearing Clinic (USHC). Data collection involved detailed case
history taking, otoscopic examination, tympanometry, pure-
tone audiometry, speech audiometry and diagnostic distortion
product otoacoustic emissions (DPOAE) testing. Findings
were analysed descriptively and through inferential statistics
(Fisher’s exact test and the independent samples
t
-test).
Results:
Individuals with T1DM presented with normal middle
ear function and no middle ear pathology, as suggested by the
otoscopic examination and impedance audiometry. Hearing
levels were within normal limits even though thresholds were
elevated at 6 000 Hz. Speech audiometry results were found
to be elevated in this group, with reduced DPOAE amplitudes
in the high frequencies.
Conclusion:
Current findings imply that microvascular
complications of T1DM may cause damage to the outer hair
cells, resulting in reduced DPOAE amplitudes and elevated
thresholds in thehigh frequencies aswell as in speech reception
and discrimination levels. These findings highlight the need
for future studies on a larger sample size for generalisability,
with inclusion of older participants with T1DM
.
Keywords:
type 1 diabetes mellitus, distortion product
otoacoustic emissions, cochleovestibular, pure tones, microvascular
Background
The causes of hearing loss vary widely, and dysfunctions in the
metabolism of carbohydrates, thyroid disturbances and other
metabolic disorders have been listed as some of the frequent
causes of vestibular and auditory abnormality. Among the
glucose metabolism disorders, type 1 diabetes mellitus (T1DM)
is most commonly related to auditory disorders.
1
Regardless of
the cause of hearing loss, documented consequences of hearing
loss include a profound negative impact on speech and language
development, educational achievement, vocational performance,
social interactions and psychological well-being.
Although there is a lack of good data on T1DM prevalence
in developing countries, and in particular in sub-Saharan Africa,
epidemiologically, developing countries have a lower incidence of
T1DM compared to developed countries. The incidence of T1DM
in developing countries is reported to be limited but accounts for
approximately 0.9 to 5% of all diabetics in these countries.
2
The
low prevalence of the condition may reflect inaccessible and/or
unaffordable healthcare that may result in the misdiagnosis or lack
of diagnosis of T1DM, poor prognosis as well as low incidence. The
low prevalence could also be explained by factors such as quality of
diabetes care and survival rates.
Despite a low recounted T1DM incidence, prevalence of diabetes
has been documented to be increasing in Africa, specifically South
Africa, estimated to be home to 841 000 affected people.
3
This raises
concerns for the assessment and management of individuals with this
condition, as changes in diets as well as management may change
the presentation of the disease, including audiological presentation.
Diabetic microangiopathy is one morphological aspect that
is common in diabetes mellitus. It is defined as diffuse thickness
of the basal membrane, which may also occur with the vascular
endothelium.
1,4
It may lead to microvascular complications, which
result in retinopathy, nephropathy and neuropathy.
5
Diabetic
neuropathy is known to affect the sensory and motor nerves in
a distal to proximal pattern, producing diabetic polyneuropathy,
which is a common complication of T1DM.
6
Examinations of
temporal bones in patients with T1DM have revealed cochlear
damage, characterised by microangiopathy of the inner ear vessels,
stria vascularis atrophy and spiral ligament and hair cell loss.
Researchers believe this may result in hearing loss.
7
A number of international research studies have confirmed a
relationship between diabetes mellitus and sensorineural hearing
loss but with conflicting findings.
8-13
More specifically, research
by Lisowska
et al
.
4
concluded that individuals with T1DM may
have alterations in both the cochlear and retrocochlear auditory
pathway and that the hearing impairment is mild and subclinical,
which can only be detected by accurate and objective audiometric
methods. The motivation for inclusion of a combination of the
basic audiometric and physiological testing (using a combination
of audiometric testing procedures such as pure-tone audiometry,
tympanometry, otoacoustic emissions and auditory brainstem
responses) assisted us to determine if the auditory alteration in
individuals with T1DM indicate impairment at the cochlear level or
in the acoustic neural pathways.
10
Despite the aforementioned studies, which used a combination
of audiometric testing with large sample sizes and inclusion and
exclusion criteria that varied widely, generalisation of findings to
the whole diabetic population becomes a challenge. The majority of
these studies were conducted internationally with very little evidence
