Auditory acuity in type 2 diabetes mellitus

BACKGROUND AND OBJECTIVES: The relationship between diabetes and hearing loss has been debated for many years. Hyperglycemia appears to have an effect on hearing loss and the proposed mechanisms are microangiopathy, neuropathy or a combination of both. The objective of this study was to evaluate a cross section of hyperglycemic subjects with ageand sex-matched normoglycemic controls with pure tone audiometry and compare the differences. MATERIAlS AND METHODS: Forty-one type 2 diabetes mellitus subjects and 41 ageand sex-matched normoglycemic controls were subjected to a pure tone audiometric assessment followed by evaluation of their glycemic status and degree of glycemic control. The resulting data was statistically analyzed. RESUlTS: The auditory thresholds in hyperglycemic subjects were higher in all age groups in all the frequencies suggestive of sensorineural hearing loss. The hyperglycemic subjects with poor control of their blood sugar levels (HbA1C > 8%) had elevated auditory thresholds in all the test frequencies. The fasting blood sugar level in hyperglycemic subjects showed a trend towards significant difference at higher frequencies, the postprandial blood sugar levels showed significant differences at higher frequencies. There was no effect of duration of diabetes mellitus on the hearing thresholds in hyperglycemic subjects. CONClUSION: Subjects with hyperglycemia have a sensorineural hearing loss when evaluated with a pure tone audiometer in all frequencies than a normoglycemic control group. The study showed that post prandial blood sugar levels and HbA1C levels had a direct bearing on the auditory acuity of the hyperglycemic subjects.


BACKGROUND AND OBJECTIVES:
The relationship between diabetes and hearing loss has been debated for many years.Hyperglycemia appears to have an effect on hearing loss and the proposed mechanisms are microangiopathy, neuropathy or a combination of both.The objective of this study was to evaluate a cross section of hyperglycemic subjects with age-and sex-matched normoglycemic controls with pure tone audiometry and compare the differences.MATERIAlS AND METHODS: Forty-one type 2 diabetes mellitus subjects and 41 age-and sex-matched normoglycemic controls were subjected to a pure tone audiometric assessment followed by evaluation of their glycemic status and degree of glycemic control.The resulting data was statistically analyzed.RESUlTS: The auditory thresholds in hyperglycemic subjects were higher in all age groups in all the frequencies suggestive of sensorineural hearing loss.The hyperglycemic subjects with poor control of their blood sugar levels (HbA1C > 8%) had elevated auditory thresholds in all the test frequencies.The fasting blood sugar level in hyperglycemic subjects showed a trend towards significant difference at higher frequencies, the postprandial blood sugar levels showed significant differences at higher frequencies.There was no effect of duration of diabetes mellitus on the hearing thresholds in hyperglycemic subjects.CONClUSION: Subjects with hyperglycemia have a sensorineural hearing loss when evaluated with a pure tone audiometer in all frequencies than a normoglycemic control group.The study showed that post prandial blood sugar levels and HbA1C levels had a direct bearing on the auditory acuity of the hyperglycemic subjects.

Introduction
Hearing loss is a functional disability which affects a person's day-to-day activities in subtle ways.Sensorineural hearing loss involving the inner ear and its central connections is irreversible.The prevalence of hearing loss in diabetes has been shown in many studies [1][2][3][4][5][6][7][8][9][10][11] to be moderately high, progressive and bilateral.The predominant mechanism of hearing loss in diabetes appears to be related to microangiopathy of the inner ear. [12]The prevalence of hearing loss in diabetics in Indian population has not been studied extensively. [7]e present study is undertaken to compare auditory acuity in normoglycemic and hyperglycemic subjects to find out the effect of hyperglycemia on auditory acuity.
Diagnostic audiometry comprises tests that detect conductive and sensorineural hearing losses.Pure tone audiometry involves the estimation of the threshold of hearing for certain standardized stimuli via the air and bone conduction routes. [13]An audiometer, being a fundamental tool in the diagnosis of auditory capacities, has been employed in this study.

Source of data
The study was conducted in a sample of 82 subjects in Bangalore.The study was approved by the institutional ethics committee of Bangalore Medical College and Rajiv Gandhi University of Health Sciences, Bangalore, India.They have been divided into two groups of 41 subjects each.
Group 1 comprises of 41 normal, healthy subjects of either sex selected from the patient attenders in Victoria hospital belonging to the ages between 35 and 55 years.Group 2 comprises of 41 type 2 diabetic patients of either sex selected from the Department of Medicine Victoria Hospital, belonging to the ages between 35 and 55 years.The sample size was determined after taking into consideration the methods used in other studies.Many published studies on the prevalence of hearing loss in diabetics used a similar sample size between 20 and 45 diabetic subjects. [1,3,6,7,10,11]

Method of collection of data
The study comprising of 41 type 2 diabetics and 41 nondiabetics, matched with respect to age and sex are selected based on inclusion and exclusion criteria.

Inclusion criteria [group 1]
Forty-one normal healthy subjects of either sex between 35 and 55 years who had given written consent and who were nonhypertensive were included.

Inclusion criteria [group 2]
Forty-one type 2 diabetic patients between the ages 35 and 55 years who had given written consent and who were nonhypertensive were included.Both groups were matched with respect to age and sex.

Exclusion criteria [group 1]
1. Hypertension 2. Diabetes mellitus 3. History of consumption of ototoxic drugs in past three months.4. History of ear surgeries performed in the past. 5. History of ear infections in the past.6. History of recent infections in the nose, throat or ear.7. Patients having a noise induced hearing loss (as shown by pure tone audiometry at 4000 Hz.)

Exclusion criteria [group 2]
1. History of consumption of ototoxic drugs in past three months.2. History of ear surgeries performed in the past.3. History of ear infections in the past.4. History of recent infections in the nose, throat or ear. 5. Patients having a noise induced hearing loss (as shown by pure tone audiometry at 4000 Hz.)

Pure tone audiometer Instrument: ARPHI [500 MK I] audiometer
Ear phones are used to test hearing by air conduction and a small vibrator placed over the mastoid is used test hearing by bone conduction.All audiometers incorporate a calibration circuit, which allows the output sound level to be set at each frequency.The signals presented to the subject by an audiometer are characterized by its frequency, sound pressure level and wave form which are all controlled. [13]thodology Protocol All the subjects included in this study are given a prepared questionnaire to answer.This questionnaire was designed to reveal the patients' assessment of hearing ability.
An assessment of the hearings status using a pure tone audiometer [ARPHI 500 MK 1] is done.

Pure tone audiometry
Principle: [13] An audiometer [ARPHI 500 MK 1] is an electronic device that produces pure tones, the intensity of which can be increased or decreased in 5-Db steps.Air conduction thresholds are measured for tones of 250, 500, 1000, 1500, 2000, 4000 6000 and 8000 Hertz.Bone conduction thresholds and measured for 250, 500, 1000, 1500, 2000, 4000 Hertz.The amount of intensity that has to be raised above the normal level is a measure of the degree of hearing impairment at that frequency.It is charted in form of a graph called the "audiogram."The thresholds of bone conduction are a measure of the cochlear function.The difference in the thresholds of air and bone conduction (A-B gap) is a measure of a degree of conductive deafness.The audiometer is so calibrated that hearing of a normal person, both of air and bone conduction is at 0 db and there is no A-B gap.

Methodology of pure tone audiometry
The method is based on American Society for Speech and Hearing Association [ASHA] 1978 guidelines for manual pure tone audiometry (PTA).Masked pure tone audiometry is done if there is a difference of more than 40 dB between air conduction threshold of the test ear and the bone conduction threshold of the opposite ear, or when the air bone gap of the poorer ear under test is more than 10 dB.
Statistical methods [14,15] Student t test (unpaired and two tailed) has been used to find the significance of auditory thresholds (dB) between various categories of parameters.Analysis of variance [ANOVA] has been used to find the significance of auditory thresholds in different age groups.The effect size (d) has been used to find the effect of DM on auditory thresholds (dB).

Statistical software:
The statistical soft ware namely SPSS 11.0 and Systat 8.0 were used for the analysis of the data and Microsoft Word and Microsoft Excel have been used to generate graphs, tables, etc.

Results
Tables 1 and 2 show the age and sex distribution of the control group and the diabetics.
Differences in the fasting blood sugar and post-prandial blood sugar level between the cases and controls were statistically significant at 1% as seen in Table 3.
As shown in Table 4, there was a significant difference in the auditory thresholds at all frequencies from 250 Hz to 8000 Hz between type 2 diabetic subjects and control group and all the hyperglycemic subjects showed sensorineural hearing loss changes on audiogram.The effect size was large to very large.The controls, all had normal hearing thresholds, whereas the cases showed a gradual increase in hearing loss starting at 250 Hz and becoming pronounced as the frequency increased.This difference is highly statistically significant at 1% confidence interval.As shown in Table 5, there was no statistically significant difference in auditory thresholds among type 2 diabetic patients and control group when analyzed according to their age groups, yet all type 2 diabetic patients' auditory thresholds were higher than the control groups' thresholds.
As shown in Table 6, from a frequency of 250 Hz to 8000 Hz, there was a significant difference between diabetic type 2 patients with good control of their blood sugars [HbA1c values between 6% and 8%] versus type 2 diabetic patients with poor control [HbA1c values greater than 8%].The number of patients in the good control group was 20 and in the poor control group was 21.The significance levels are at 1%.
Table 7 shows that there was no significant difference in the hearing thresholds between patients with short duration of type 2 diabetes [less than 10 years] versus long duration [greater than 10 years].
Table 8 shows that there is a trend towards a difference which is noted at higher frequencies (6000 Hz and 8000 Hz) when the effect of fasting blood sugar levels on auditory thresholds is considered.Table 9 shows that there is a 5% significant difference at 3000, 4000, and 8000 Hz and a 1% significant difference at 6000 Hz when the effect of post prandial blood sugar levels on the auditory thresholds is considered.

Discussion
The relationship between diabetes mellitus and hearing loss is controversial, primarily because the pathogenic mechanism remains obscure.This is a case control study investigating this relationship using pure tone audiometer.
Diabetes has been shown to affect hearing loss by many studies.Many have tried to identify the cause, and based on their conclusions, the probable mechanisms are microangiopathy of the inner ear, neuropathy of the cochlear nerve, a combination of both, outer hair dysfunction and disruption of endolymphatic potential.
This study a significant hearing loss in diabetes in all the frequencies tested.This could be  Panchu: Auditory acuity in diabetes explained by microangiopathy of the vessels to the inner ear as proposed by Wackym. [16]e effect of age on auditory thresholds in diabetic subjects was found to be clinically and statistically insignificant.Kakarlapudi [4] and Dalton [8] both showed similar findings in their study, but Taylor and Irwin [3] found a correlation between hearing levels and age of the subjects in the diabetic group and concluded that any hearing loss due to diabetes will be additional to that due to age alone.Similar conclusions were drawn by Axelson. [5]ck of glycemic control shows a positive correlation with extent of hearing loss when compared to those diabetics with good glycemic control.This is noted in all the frequencies tested.Both Kurien [7] and Lasisi [2] show similar findings.A possible mechanism to explain this observation could be the cumulative effects of advanced glycation end products on the inner ear.High postprandial blood sugar levels cause a significant alteration in high frequency hearing thresholds in diabetics.Damage to outer hair cells by sustained hyperglycemia

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1. To assess the degree of auditory acuity in type 2 diabetes mellitus patients using pure tone audiometry [evaluating the frequency and intensity of hearing acuity] 2. To compare pure tone audiometric results between diabetic type 2 patients [hyperglycemic group] and a matched control group [normoglycemic group].[