Abstract
The relationship between sensorineural hearing loss (SNHL) and Diabetes mellitus has been known since more than 150 years. The pathophysiology of diabetes related hearing loss is speculative. Hearing loss is usually, bilateral, gradual onset, affecting higher frequencies. This study aims at knowing the prevalence of SNHL in DM and its relation to age, sex, duration of DM and control of DM. A total of 50 type 2 diabetics of age group 30–65 years were involved in the study. FBS, PPBS, HbA1c of all the subjects were done and later subjected to PTA. The type and severity of hearing loss was noted. Occurrence of SNHL was later compared with age, sex, duration, and control of DM. Sensorineural hearing loss was found in 66 % of type II diabetic patients and 34 % were found normal. Out of 50 diabetes mellitus patients, 33 patients had SNHL. All cases of SNHL detected were of gradual in onset and no one had hearing loss of sudden onset. Normal hearing was found in 34 % of patients, whereas 54 % of patients had mild hearing loss and 12 % of patients had moderate hearing loss. Association of hearing loss of DM patients with sex of the patient is insignificant. However there is significant association between older age group, longer duration and uncontrolled DM with that of SNHL. In subjects with HbA1c more than 8 and duration of diabetes mellitus more than 10 years prevalence of SNHL is more than 85 %, which is statistically significant. Sensorineural hearing loss in diabetes mellitus is gradually progressive involving high frequency thresholds. Hearing threshold increases with increasing age duration of diabetes and also high level of HbA1c greater than 8 %.
Keywords: Diabetes mellitus, Pure tone audiometry, HbA1c, Sensorineural hearing loss, Tuning fork tests
Introduction
Hearing gives us and enriches our day to day life. Hearing enables us to interact with people, work and earn. Hearing is integral part of speech. It helps us to lead our lives happily without any restrictions. Hearing impairment will hamper ones personal and social life and hence quality of life. Our ability to hear has a very great impact on almost every aspect of our lives. The sense of hearing, the perception of sound and its biological purposes is not therefore, a trivial consideration that cannot be lightly dismissed. Diabetes mellitus is a common non communicable metabolic disease that causes various impairments of the body systems. As diabetes mellitus occurs most commonly in general population, the effects caused by it on various organs of our body assume greater importance. Prevalence of diabetes mellitus is increasing worldwide and it is more pronounced in India. According to the estimation, total number of diabetes patients in India is around 40.9 million and by 2025 the number would be around 69.92 million [1, 2]. Chronic complications of diabetes mellitus can be attributed to number of changes occurring at variable time period involving the vascular system, nerves, skin and lens. These complications are the cause of considerable morbidity and mortality and negatively affect the quality of life in individuals with diabetes [4]. A high prevalence of such complications, if documented, will help to convince the physicians of the importance of screening for these complications in all Type 2 diabetics (T2D) at presentation, for appropriate implementation of treatment without delay [3]. One of the known complications of DM is hearing impairment, especially hearing loss and tinnitus, which leads to a decreased quality of life among those affected [4].
Objectives
To evaluate the relation of sensorineural hearing loss with duration of the Diabetes Mellitus. To evaluate the association between the severity of sensorineural deafness with poorly controlled Diabetes Mellitus. To evaluate the result of our study and to compare our data with similarly published studies.
Materials and Methods
This hospital-based cross sectional study was carried out over a period of 1 year from November 2014 to October 2015. This study was conducted at out-patient and in-patient sections of department of ENT and department of Medicine, Dr BR Ambedkar Medical College & Hospital, Bengaluru, Karnataka. After explaining in detail about the study in their own language of subject, informed consent was obtained. The subjects who reported to the department of ENT for evaluation of hearing impairment/loss were enquired for Diabetes Mellitus. The subjects who reported to the department of medicine OPD with Diabetes Mellitus or admitted with Diabetes Mellitus as in-patient were tested for hearing loss. The subjects aged 31–65 years who had Diabetes Mellitus with or without hearing loss were included in the study. The study subjects with hearing loss were categorised after testing with “Tuning fork test, Puretone Audiometry and Impedence Audiometer” as conductive hearing loss, mixed hearing loss and sensorineural hearing loss.
Purposive sampling method was used on 50 study subjects. Data was entered into microsoft excel sheet and analyzed using (Epi data software) descriptive statistics such as percentages and proportions.
The sensorineural hearing loss was categorised using PTA and tuning fork tests as normal, mild hearing loss and moderate hearing loss depending upon PTA value <25, 25–40 and >40 respectively. Secondly, the subjects were tested for FBS, PPBS and HbA1C. The FBS, PPBS and HbA1C results were used for categorising glycemic control. Also other details like onset, duration etc. of Diabetes Mellitus were noted. This process was continued till the intended 50 subjects were obtained (Table 1).
Table 1.
Glycemic control categories
| Glycemic control | FBS (mg/dl) | PPBS (mg/dl) | HbA1C (%) |
|---|---|---|---|
| Well controlled | ≤110 | ≤140 | <7 |
| Moderately controlled | 111–125 | 141–199 | 7–8 |
| Poorly controlled | ≥126 | ≥200 | >8 |
Results
In our study involving 50 type 2 diabetic subjects, 33 subjects (66 %) were found to have sensorineural hearing loss and 17 subjects (34 %) were found normal without SNHL. In these 33 subjects, all had gradual onset of SNHL.
Out of the 33 subjects with hearing deficit, 27 had mild hearing loss and 6 had moderate hearing loss. The SNHL was more among 46–65 age group (64 %) and least among 31–35 age group (4 %). As the age group advances, the SNHL association also increases as confirmed by tests. There is a progressive increase in the percentage of SNHL with the age of the subjects. Presence of SNHL is lowest among 31-35 age group, where no one had hearing loss and highest among 46–65 age group (78.12 %). The percentage of female diabetes having SNHL is more i.e., 71.4 %. But when we analyzed statistically, the p value was not significant (p value 0.495)
In our series, 14 subjects (28 %) had diabetes of duration 5 years or less than 5 years, 16 subjects (32 %) of 6–10 year duration and 20 subjects (40 %) of more than 10 year duration.
In our study 14 subjects with less than 5 year duration of diabetes, 5 developed SNHL (35.71 %) and in 16 subjects with more than 6–10 year duration 11 developed SNHL (68.75 %), and out of 20 subjects with diabetes duration more than 10 years showed significant SNHL amounting to 85 % (affected persons were 17 of 20 in the age group). It is clearly seen that as duration of diabetes increases, the predisposition to SNHL also increases. Association of SNHL with duration of diabetes is significant as p value is significant, which is 0.0114.
Out of the 50 diabetic subjects, 13 had HbA1c level less than 7 indicating good glycemic control, 16 had values between 7 and 8 indicating average glycemic control, whereas 21 subjects had values more than 8 indicating poor glycemic control. In these subjects, SNHL presence and absent is depicted in Table 2.
Table 2.
Distribution of hearing loss and with their HBA1c Levels in the study Subjects
| HBA1c | Sensorineural hearing loss | Total | p value | |
|---|---|---|---|---|
| Absent (%) | Present (%) | |||
| <7 | 9 (69.2) | 4 (30.8) | 13 (26.0) | 0.004336 |
| 7–8 | 5 (31.3) | 11 (68.7) | 16 (32.0) | |
| >8 | 3 (14.3) | 18 (85.7) | 21 (42.0) | |
| Total | 17 (34.0) | 33 (66.0) | 50 (100.0) | |
Chi square value 10.88 for 2 the p value is 0.004336
Of the 50 subjects, 29 subjects had FBS more than 126 mg% and 7 subjects less than 110 mg%. We found that, 23 out of 29 subjects had SNHL who’s FBS is more than 126 mg% and least among subjects who’s FBS less than 110 mg%, only 2 had SNHL out of 7 subjects. Here after statistical analysis, the p value found to be 0.0283 which is an indicator of association of FBS level and SNHL.
We had 6 subjects whose PPBS were less than 140 mg% and 31 subject whose PPBS were more than 200 mg%. In these subjects SNHL was 33.33 and 74.19 % respectively which appears to be more in uncontrolled subjects of PPBS more than 200 mg%. But SNHL among controlled PPBS and uncontrolled PPBS is not statistically significant as shown by p value 0.1426
Discussion
Diabetes mellitus is a common non communicable metabolic disease that impairs all our body systems. Prevalence of Diabetes mellitus is becoming more common in general population, the effects caused by it on various organs of our body needs special attention by the medical fraternity. Prevalence of diabetes mellitus which was seen more in affluent countries, is becoming is increasingly common in our country too.
DM can cause complications to any part of the body to any extent. Hence knowledge about these complications is mandatory for all of us to know so that necessary precautions can be taken to prevent it and help diabetes subjects to lead comparatively satisfactory life.
Hearing is one of the important special sensations which gives us and enriches our day to day life. Hearing enables us to interact with people, work and earn. Hearing is integral part of speech. It helps us to lead our lives happily without any restrictions. Hearing impairment will hamper ones personal and social life and hence quality of life.
In our study involving 50 patients of type 2 diabetics of age 30–65 years from various backgrounds in social life, the percentage of sensorineural hearing loss was found to be 66 % which is of gradual onset and progressive type. From Table 3 it is clear that hearing loss varies from 55 % to as high as 78.2 %. Our study results approximates to those that of Aggarwal (64.86 %) [5].
Table 3.
Percentage of SNHL in diabetes mellitus
Diabetes mellitus is one of the most common metabolic disorders, which affects both the older as well younger individuals and is associated with hearing impairment. Kurien [12] and Cullen [13], stated that there is no correlation between age of the patient and occurrence of SNHL in diabetes mellitus. Our study shows increased percentage of SNHL in diabetics in the older age group (Table 4) and in younger group (31–35) there was no SNHL. In older age group (46–65), SNHL was 78.12 % as compared to 25 % in 36–40 group. Our study of SNHL in this older age group clarifies the strong association between advanced age and SNHL (p value 0.0256), which is contrast to the earlier studies carried out by Friedman [6] and Cullen [13]. It is difficult to distinguish whether hearing loss in diabetes is due to normal process of aging or due to biochemical and the vascular abnormalities associated with diabetes [11].
Table 4.
Percentage of SNHL controlled and uncontrolled subjects (HbA1C)
The factors responsible which influence the worsening of hearing thresholds in diabetics were evaluated. There was significant association between the duration of the diabetes mellitus and SNHL. Less than 5 year duration of DM, 35 % had SNHL compared 85 % whose duration was more than 10 years. It was also noted that there was increase in hearing threshold with increase in duration of diabetes mellitus. It was seen that as duration increases more than 6 years, the percentage of hearing deficit increases to a greater extent. The increase in hearing threshold is attributed to microvascular angiopathy occurring in capillaries of stria vascularis which make these vessels thicker than normal. These changes can occur in vessels supplying other parts of auditory system as well [14]. Older diabetic patients had higher incidence of hearing loss and they had severe grade hearing loss. This result is supported by Virteniemi et al. [15] and Fangcha et al. [16]. However studies done by Kurien et al. [12] and Cullen et al. [13], did not show any correlation between duration of diabetes and hearing loss. (p value for duration of DM and SNHL is 0.0114).
International Expert Committee recommended the use of glycosylated haemoglobin (HbA1c) testing in the diagnosing of this deleterious disease [17]. In present study incidence of SNHL among poorly controlled patients with glycosylated haemoglobin (HbA1c) is 85.71 % where as it is 62 and 38 % among patients in moderately controlled and well controlled with HbA1c 7–8, and <7 respectively (p value 0.004336)
Kurien et al. [12], conclusively demonstrated that poorly controlled diabetics have significant hearing loss in all frequencies. This could be explained by the cumulative effects of advanced glycation end products and their effects on the inner ear [18]. Many studies have been done by various authors to find out the association between Fasting blood sugar and post prandial blood sugar, with that of SNHL [11, 19]. Screening of all patients with diabetes for hearing loss in a multicentric longitudinal study in future may provide a clearer understanding of the relationship between diabetes and hearing loss. Diabetic patients can be advised to keep their glycemic levels under good control to prevent hearing loss.
Conclusion
Our study evidently demonstrated the association between sensorineural hearing loss and uncontrolled diabetes mellitus. SNHL was present in 66 % of type II diabetic patients. Sensorineural hearing loss in diabetes mellitus is usually gradually progressive involving high frequency thresholds. Hearing threshold increases with advanced age and increased duration of diabetes. There was no sex differentiation. Patients with poor control (HbA1c greater than 8 %) of their glycemic status had raised auditory thresholds. We also established the association between the age of the patient and duration of DM and SNHL.
Acknowledgments
The results obtained in this study support the existence of a relationship between SNHL and DM. Hence, the auditory status of DM patients should be thoroughly screened so that complications arising out of uncontrolled diabetes mellitus can be prevented.
Compliance with Ethical Standards
Conflict of interest
Dr. C. V. Srinivas declares that he has no conflict of interest. Dr. Shyamala. V. declares that she has no conflict of interest. Dr. Shivakumar. B. R. declares that he has no conflict of interest.
Ethical Approval
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed Consent
Informed consent was obtained from all individual participants included in the study.
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