|Year : 2013 | Volume
| Issue : 1 | Page : 13-17
Pure tone audiometry and otoacoustic emissions for the assessment of hearing loss in diabetic patients
Ashish C Agarwal1, Kailesh Pujary1, Kanaka Ganapathy2, R Balakrishnan1, Dipak R Nayak1, Faisal Hasan3
1 Department of ENT, Kasturba Medical College, Manipal University, Karnataka, India
2 Department of Speech and Hearing, Manipal College of Allied Health Sciences, Manipal University, Karnataka, India
3 Department of Medicine, Kasturba Medical College, Manipal University, Karnataka, India
|Date of Web Publication||6-Mar-2013|
Ashish C Agarwal
Department of ENT, Kasturba Medical College, Manipal University, Manipal - 576 104, Karnataka
Source of Support: None, Conflict of Interest: None
Context: Evaluation of hearing loss with diabetic control. Aims: The aim of this study was to profile the audiologic findings of diabetic patients by assessing the degree of hearing loss and the presence/absence of otoacoustic emissions (OAEs); to correlate the factors, namely, age, gender, glycemic status, and duration of diabetes mellitus with hearing loss. Settings and Design: The study was done at a tertiary care hospital and a cross-sectional study design was employed. Materials and Methods: Forty known diabetic patients who satisfied the selection criteria and consented were included in the study. Three tests were carried out, namely, pure tone audiometry, immittance audiometry, and OAEs. Statistical Analysis Used: Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 11.5. For the current study, median, interquartile range (IQR), frequency, and percentage were considered. Results: Majority of the patients had bilateral sensorineural hearing loss ranging in severity from minimal to mild degree. Median pure tone average (PTA) values were less in patients with good glycemic status as compared to those with poor glycemic status. OAEs were absent in 30% of the subjects. Age had a contributing effect on raising the hearing threshold but gender and duration of diabetes did not show such an effect. Conclusion: Diabetic patients are at an increased risk of developing sensorineural hearing loss.
Keywords: Diabetes mellitus, Glycosylated hemoglobin, Otoacoustic emissions, Pure tone average
|How to cite this article:|
Agarwal AC, Pujary K, Ganapathy K, Balakrishnan R, Nayak DR, Hasan F. Pure tone audiometry and otoacoustic emissions for the assessment of hearing loss in diabetic patients. Indian J Otol 2013;19:13-7
|How to cite this URL:|
Agarwal AC, Pujary K, Ganapathy K, Balakrishnan R, Nayak DR, Hasan F. Pure tone audiometry and otoacoustic emissions for the assessment of hearing loss in diabetic patients. Indian J Otol [serial online] 2013 [cited 2020 Feb 26];19:13-7. Available from: http://www.indianjotol.org/text.asp?2013/19/1/13/108154
| Introduction|| |
Diabetes mellitus (DM) is a syndrome of chronic hyperglycemia due to relative deficiency of insulin, resistance to insulin, or both. Its prevalence has been estimated to be more than 285 million people worldwide and 51 million people in India.  DM produces complications which are vascular and/or neurologic. Though there is disagreement among researchers regarding the existence of hearing loss secondary to DM, ,, there is some evidence that elderly diabetic patients have progressive, bilateral, sensorineural hearing impairment with gradual onset, predominantly affecting the higher frequencies. 
El-Tabal, et al. reported that the hearing threshold in diabetic patients and controls in all age groups had no significant differences, except for high frequencies, that is, ≥4,000 Hz in the age group of 40 years or older. In addition, it has been suggested that the severity of DM or the serum glucose level maybe related to hearing loss. A few studies have examined the potential link between hearing loss and the severity of diabetes. Panchu  found that all the frequencies (250 to 8,000 Hz) were affected in poorly controlled diabetics, that is, glycosylated hemoglobin (HbA1c) >8 %, while examining the auditory acuity in type II DM in an Indian population. Asma, et al. failed to establish any association between the type of treatment given and the effect on hearing thresholds in their study on conventional oral hypoglycemic agents versus insulin therapy on pure tone average (PTA). Individuals with significant cochlear hearing loss have no measurable otoacoustic emissions (OAEs).  A study by Simoncelli, et al. on diabetic patients with normal hearing showed that mean OAE intensity and amplitude by 100 Hz frequency band was significantly lower in diabetic patients that in control groups, thus indicating an alteration in cochlear biomechanics in diabetics.
Thus, the current study aimed to document the degree of hearing loss and the presence/absence of OAEs in diabetic patients. The second objective was to correlate the audiological findings with factors such as age, gender, glycemic status, and duration of DM.
| Materials and Methods|| |
A cross-sectional study was carried out from November 2010 to October 2011 on 40 consecutive diabetic patients visiting the departments of Ear, nose, and throat (ENT) and medicine of a tertiary care hospital. Subjects included in the study were diabetic patients (type I and II) of either gender, between 18 and 50 years of age, with no past history of head injury, ear surgery, ear discharge, meningitis/encephalitis, exposure to acute/chronic noise, otitis media, treatment with ototoxic drugs, and family history of deafness. Patients with tympanic membrane lesions like perforation, thinning, tympanosclerotic patch, retraction/congestion, and impaired mobility on Valsalva maneuver/siegelisation on otoscopy were also excluded from this study. The patients who were diagnosed to have DM according to the criteria given by the American Diabetes Association  were included as a part of the study. An otoscopic examination was performed by a qualified ENT doctor prior to selection of the subject. A clearance from the Institutional Ethics Committee (IEC) was obtained prior to the start of the study. Informed written consent was taken from all the subjects.
After consent, the demographic data, clinical characteristics, and audiological symptoms were noted down for further analysis. All the subjects underwent biochemical and routine urine investigations such as postprandial blood sugar (PPBS), fasting blood sugar (FBS), serum urea and creatinine, HbA1c, and urine for sugar, protein, ketones, and microalbuminuria. All the levels were noted for further analysis.
The audiological investigations were performed by a qualified audiologist at our institute. PTA and OAEs, as measures, were carried out on all the subjects in a sound-treated room.
PTA was carried out for the estimation of hearing thresholds using a duly calibrated [American National Standards Institute (ANSI) S3.6; 1996]  double-channel clinical audiometer, GSI 61 coupled with TDH-50P earphones and MX41R ear cushions to obtain air conduction thresholds. Bone conduction was obtained using Radioear B-71 bone vibrator. Pure tone thresholds were obtained at an octave between frequencies of 250 and 8,000 Hz for air conduction and 250 and 4,000 Hz for bone conduction, using the modified Hughson-Westlake procedure as recommended by ANSI 1997.  PTA was calculated and classified according to Goodman's classification (as cited by Aguila-Vinson  ).
Immittance audiometry was performed to rule out any middle ear pathology prior to performing the OAE test. This was carried out using the equipment GSI Tympstar audiometer with a probe tone frequency of 226 Hz.
Measurement of Transient OAEs (TEOAEs) was done to check the function of outer hair cells (OHCs). This was carried out using software Scout OAE version 1.63, Biologic System Corp. TEOAEs were evoked using clicks presented at 80 dB peak sound pressure level (peSPL). Its presence indicates a normal function of OHCs, whereas its absence suggests that the OHCs have been affected by the disease process.
The main outcome variable was to profile the PTA and OAE findings in diabetic subjects. However, there were many independent variables such as age (≤40 years, >40 years), gender (male, female), duration of disease (newly diagnosed, ≤5 years, >5 years), and HbA1c levels (≤7.5%, >7.5%).
Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 11.5. For the current study, median, interquartile range (IQR), frequency, and percentage were considered.
| Results|| |
A total of 40 subjects consented and completed the study. The male-to-female ratio was approximately 2:1, with 85% of the subjects being more than 40 years old. Among the subjects, 82.5% were known diabetics of whom 95% had type II diabetes. The duration of the disease was ≤ 5 years in 47.5 % the patients; 42.5% patients had good glycemic control and 57.5% had poorly controlled diabetes. [Table 1] depicts the demographic and clinical characteristics of the subjects.
|Table 1: Demographic and clinical characteristicsof diabetes mellitus subjects|
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The audiological characteristics of the subjects with respect to PTA and OAE are depicted in [Table 2] and [Table 3], respectively. From the case history, it was noted that only one subject experienced vertigo (2.5%) and eight (20%) had reported tinnitus; of them, 7.5% had unilateral tinnitus. [Table 2] indicates that the majority of them had minimal hearing loss (right ear: 42.5%; left ear: 37.5%). This was followed by mild loss (right ear: 20%; left ear: 27.5 %). Thirty percent patients had normal hearing in both the ears. However, none of the patients had a severe or profound loss. From [Table 3], it is seen that OAEs were present bilaterally in 28 (70%) subjects, unilaterally present in six (15%) subjects, and was absent in 15%.
[Table 4] indicates the hearing level/PTA (dB HL) and IQR across factors such as age, gender, HbA1c values, and duration of diabetes for both the ears. From [Table 4], it is seen that age wise, 15% patients were aged below 40 years with a median PTA of 15 (IQR: 5.41) in the right ear (i.e., within normal range) and PTA of 18.33 (IQR: 2.08) in the left ear, that is, the category of minimal hearing loss. For those who were aged above 40 years, both the right and left PTA were in the category of minimal hearing loss (right ear IQR: 14.16; left ear IQR: 16.67).
|Table 4: Hearing level (dB HL) and interquartile range across various factors|
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Gender wise, it is seen that the median PTA values of both males and females were in the category of minimal hearing loss, that is, 18.33 dB and 20 dB, respectively. The IQR in males for the right ear was 15 and for the left ear it was 16.67. For females, the IQR for the right ear was 7.50 and left ear was 10.48. From [Table 4], it is also indicated that the patients with good HbA1c level (HbA1c ≤ 7.5) had a better PTA (16.67) in both the ears (IQR: 10 in right ear and 05 in left ear) as compared to those with poor glycemic control (median PTA: 21.67; IQR: 18.33 for the right side and median PTA 25; IQR: 15 for the left side).
Duration wise, the newly diagnosed diabetics and those with known diabetes whose duration of illness was ≤5 years had a median PTA value in the category of minimal hearing loss, as compared to those with the diabetes duration of >5 years, who had mild hearing loss. For those who were newly diagnosed, the median PTA for right ear was 21.67 (IQR: 1.66) and for the left ear it was 25 (IQR: 6.6). For patients having a history of diabetes of less than five years, the median PTA was 16.67 in both the ears with IQR 6.67 in the right ear and 3.33 in the left ear. For those who had a history of diabetes >5 years, the median PTA was 26.6 in both the ears with an IQR of 28.8 for the right ear and 23.74 for the left ear.
| Discussion|| |
Overall, it is seen that only 67.5% of DM individuals had sensorineural hearing loss. As stated earlier, a few of the patients exhibited hearing-related symptoms such as vertigo and tinnitus. These changes in the hearing status can be attributed to the changes within the cochlea that include thickened vessels of stria vascularis, atrophy of stria vascularis, and loss of OHCs, but no loss of spiral ganglion cells. These findings were established by Fukushima, et al. and could be attributed to this study too. Previous studies done in India too have drawn a positive relationship between DM and hearing acuity. ,
To rule out the influence of age-related changes in the hearing status, this study was carried out in DM subjects aged between 18 and 50 years only. In the current study, it was seen that the younger age group did have better hearing thresholds as compared to those above 40 years. The presence of hearing loss ranged from normal (30% subjects) to mild (60% subjects), and only 5% had moderate or moderately severe hearing loss. These subtle changes in the hearing could be due to DM alone rather than the result of presbycusis. Studies on DM and hearing loss in the past have indicated evidence of elderly diabetic patients having a gradual onset of progressive, bilateral, sensorineural hearing impairment predominantly affecting the higher frequencies.  Suggested pathogenesis for this DM-associated sensorineural hearing loss has included cochlear microangiopathy, hyperglycemia of cerebrospinal fluid or perilymph, auditory neuropathy, and diabetic encephalopathy, even though there is disagreement among researchers regarding the existence of hearing loss secondary to diabetes. , This necessitates carrying out screening for hearing loss as a routine procedure for every individual diagnosed with DM. Apart from exhibiting obvious hearing loss, these individuals exhibit central auditory processing deficits or auditory neuropathy, as stated above, which results in speech-understanding difficulties even when the hearing thresholds maybe within normal limits.
This study also tried to understand the relationship of DM with factors such as age, gender, HbA1c level, and duration of diabetes, and the effect on the hearing thresholds. Though the sample size of the current study was small, a few conclusions could be drawn. Analysis of our results show that patients with good glycemic control (HbA1c ≤ 7.5) had a median PTA of 16.67 for either ear, whereas those with poor glycemic control had a median PTA of 21.67 for the right side and 25 for the left side [Table 4]. Though all the above values were in the range of minimal hearing loss, a difference of 8.33 (25-16.67) signifies that a well-controlled diabetic has a better hearing acuity than a poorly controlled diabetic. In the current study and past literature, ,, HbA1c value was used as a measure and correlated with the hearing status. However, various researchers have used different parameters of blood sugar status while correlating the hearing thresholds, such as fasting plasma glucose , and fructosamine levels.  A need for a controlled study is warranted in identifying those values that may have a positive influence on hearing thresholds.
Age also had an effect, however, with the large differences in the size of the sample among the categories of age. Only six patients were aged ≤40 years as against 34 aged >40 years; so, it will be inappropriate to comment on the effect of age on hearing threshold of diabetics. In the literature, a correlation was found between hearing levels and age of the subjects in the diabetic group. The hearing loss due to diabetes could be attributed to age alone.  However, a study done by Panchu  showed that the effect of age on auditory thresholds of diabetic patients was statistically insignificant. A future study is warranted, focussing on these areas.
From this study, it is noted that gender and duration of diabetes did not have an effect on hearing status. Relationship between hearing threshold and gender has been quoted differently by various studies. No correlation between hearing impairment and gender was seen in some studies. , However, in one study,  female diabetics had a higher hearing threshold as compared to the males. With respect to the effect of the duration of diabetes on hearing threshold, different authors have shown variable associations. Some found a positive correlation between duration of diabetes and hearing loss, ,, and others found no association. ,,, In the current study, patients with newly diagnosed diabetes and those known diabetics whose duration of illness was ≤5 years had a median PTA value in the category of minimal hearing loss, whereas those patients who were known diabetics for more than five years had a median PTA value in the category of mild hearing loss [Table 4]. As the PTA of the ≤5-year duration group (16.67) was less than that of newly diagnosed patients (21.67 right, 25 left), any significance of duration of disease on hearing acuity is difficult to comment on.
Influence of the type of diabetes (type I or type II) could not be commented upon as only two patients in this study had type I DM. Most of the past literature also established the association between type II DM and hearing loss, ,, with few studies considering both the types of DM.  With respect to glycemic status, some studies found no correlation between severity of diabetes and hearing loss, ,, whereas some of them have demonstrated a positive correlation between severity of diabetes and hearing loss. ,,,
OAEs, which indicate the functioning of OHCs, were found to be affected in 30% of the DM subjects. Even though DM may cause loss of function of OHCs, the presence of OAEs in most of the subjects correlates with the degree of loss in the DM subjects, as OAEs are obtained for hearing loss less than 40 dB with normal functioning of the middle ear. Studies indicate that individuals with significant hearing loss have no measureable OAEs.  A study by Simoncelli, et al. on diabetic patients with normal hearing showed that mean OAE intensity and amplitude by 100 Hz frequency band was significantly lower in diabetic patients than in control groups, thus indicating an alteration in cochlear biomechanics in diabetics.
| Conclusions|| |
Though the sample size considered in this study was small, the study offers significant clinical implications. From the study, it was seen that majority of the DM patients had subclinical hearing loss. The age of the patient and degree of glycemic control had a positive correlation with hearing loss. Gender and duration of diabetes did not have any effect on the hearing status. Health-care providers need to be aware of the coexistence of hearing symptoms and incorporate audiological referral as a routine practice in future for every patient with DM. Future studies are needed to understand the existence of central auditory processing deficits or auditory neuropathy in these individuals and to note the change in hearing threshold with an improvement in glycemic control.
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[Table 1], [Table 2], [Table 3], [Table 4]
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