Clinical and Audiometric Assessment of Hearing Loss in Diabetes Mellitus

Abstract

Hyperglycemia has been reported to cause hearing loss. We evaluated hyperglycemic subjects with controls undergoing pure tone audiometry. Hundred subjects were divided into case (n = 50, diabetes mellitus patients) and control (n = 50, non DM subjects). Pure tone audiometry was performed for subjects. Degree of hearing loss was categorized as mild, moderate, moderately severe, severe and profound hearing loss. Out of 50 cases, 26% had normal hearing, 20% had moderately and 28% had moderately severe hearing loss. Longer duration of diabetes (p = 0.031) was significant predictor of moderately severe, severe and profound SNHL. Profound SNHL was more common in those with > 200 fasting blood sugar (p = 0.001) and severe and profound SNHL was common in those having > 300 random blood sugar (p = 0.004). To conclude age, duration and severity of diabetes was the significant predictor of hearing loss in patients of diabetes mellitus.

Introduction

A person’s day-to-day activities affected with the presence of hearing defects in subtle ways. Sensorineural hearing loss involving the inner ear and its central connections is irreversible. Several previous authors have reported moderately high, progressive and bilateral hearing loss in patients with diabetes mellitus [17, 20].

But attention has not been given to hearing loss in diabetes and more research needs to be done in this area. It is important to determine the magnitude of the problem, establish a cause and effect relationship and to increase awareness among health care providers and laypersons about hearing loss and diabetes mellitus.

A post mortem examination of 8 temporal bones of diabetics who have been known to have worse hearing as compared to age and sex matched controls revealed microangiopathy as the most common cause. Histologically other studies showed atherosclerotic changes in the cochlea as the cause of hearing loss. Marked similarity has been found between Cochlear stria vascularis and the renal nephrons. Hence the vasculopathy that leads to renal failure could also be responsible for hearing loss in diabetics [5, 15].

In present study we tried to assess and identify hearing loss by clinical and audiometric examination in diabetics.

Materials and Methods

Fifty cases attending diagnosed with diabetes mellitus (as per American Diabetes Association) without any ear complaint (case group) were studied in the Department of Otorhinolaryngology and head and neck surgery at Gandhi Medical College and Hamidia Hospital from March 2017 to August 2018.

Age-matched 50 non diabetic without any ear complaints subjects (control group) presented to outpatient clinics of Otorhinolaryngology were also reviewed.

Patients diagnosed with diabetes as per The National Diabetes Data Group and World Health Organization issued diagnostic criteria having random blood glucose concentration > 200 mg/dl or fasting plasma glucose ≥ 126 mg/dl or 2-h plasma glucose ≥ 200 mg/dl during an oral glucose tolerance test and age greater than 18 years were included in case group. Whereas age and sex matched non diabetic subjects having age greater than 18 years were included in control group.

Subjects with history of chronic noise exposure, with history of ear discharge, perforated tympanic membrane or any other chronic ear disease, with the history of intake of ototoxic drugs in the past 2 months, with family history of hearing loss, on central nervous system sedatives and subjects with trauma to the ear were excluded from the present study.

All patients were subjected to thorough ENT examination with special emphasis on detailed examination of ear, pinna, preauricular area, external auditory canal and tympanic membrane was done. Cranial nerves of the subjects were examined. Acuity of hearing was tested bedside (Rinne’s test, Weber’s test, modified Schwabach’s test, fistula test) and anterior rhinoscopy, posterior rhinoscopy, oropharynx examination were also done. Furthermore audiometry tests were also done (PTA, TDT, SISI, SDS).

Pure tone audiometry was performed on all the subjects in a sound proof room, using a calibrated Interacoustics Clinical audiometer-AC-40 (Denmark). The transducers used were TDH 39 Supra Aural Head phones and Radio Ear B 71 bone vibrator. Modified Hughson-Westlake procedure (ASHA [3]) was used for the threshold estimation. The threshold was determined based on the American National Standard Institute (ANSI). According to ANSI S3.21, threshold is determined as the “lowest hearing level at which responses occur in at least one half of a series of ascending trials, with a minimum of two responses out of three required at a single level” (ANSI 1978, 1986). The threshold was obtained across all the frequency octaves from 250 to 8000 Hz. The thresholds obtained were used for the quantitative assessment of degree of hearing loss based on the Clark [7] modification of Goodman Classification of severity of hearing loss (1965). Categories of degrees of hearing loss, based on air conduction pure-tone average at 500, 1000, and 2000 Hz.

Degree of Hearing Loss was categorized as mild hearing loss (26 dB HL to 40 dB HL), moderate hearing loss (41 dB HL to 55 dB HL), moderately severe hearing loss (56 dB HL to 70 dB HL), severe hearing loss (71 dB HL to 90 dB HL) and profound hearing loss > 91 dB HL.

The data obtained was subjected to statistical analysis using Statistical Package of Social Science (SPSS Version 20; Chicago Inc., USA). Quantitative variables were compared using mean values and qualitative variables using proportions. Chi square test was used to compare the categorical data. Significance level was fixed at p < 0.05.

Results

When Audiometric assessment was done, 37 (74%) cases were having sensorineural hearing loss and 13 (26%) cases were having normal hearing. Only 9 (18%) control were having sensorineural hearing loss and 41 (82%) control were having normal hearing. There was statistically significant association found between diabetes and sensorineural hearing loss (p = 0.001).

Sensorineural hearing loss was found in less number of young cases and it was found in most of old age patients. It showed that as age increases, frequency of SNHL is also increased. There was statistically significant association was found between age and sensorineural hearing loss among cases (p = 0.050) while among control no significant difference found in SNHL according to age (p = 0.706).

Out of 37 cases of SNHL, 18 (48.64%) were male and 19 (51.35%) were female. While among 9 controls, 4 (8%) were male and 5 (10%) were female. Statistically insignificant difference was found in sensorineural hearing loss according to gender among both cases (p = 0.264) and controls (p = 0.814).

Comparing Speech Increment Sensitivity Index (SISI) with hearing loss among cases and controls showed that SISI was less than 70% among 16 (32%) and 47 (94%) case and controls while it was 70–100% among 34 (68%) and 3 (6%) can and controls respectively (p = 0.001).

Discussion

The hearing loss seen in diabetes mellitus is bilaterally symmetrical, gradual in onset and progressive in nature. Complex relationship between diabetes mellitus and sensorineural hearing loss has not been dealt with complete explanations. Some debatable opinion occurs in various studies whether there is strong association or no relation between diabetes mellitus and sensorineural hearing loss. The two factors that are found to affect hearing in diabetic patients are—Diabetic angiopathy and Diabetic neuropathy [4].

Edgar in 1915 was the first to report a high frequency sensorineural hearing loss in diabetic patient (Jordao [14]. In present study, majority (74%) of the cases were having sensorineural hearing loss. Whereas in control only 18% were having sensorineural hearing loss (p = 0.001) (Table 1). The hearing loss is more common in higher frequencies in the study done by Kurien et al. [16] and Dalton et al. [9]. Another study by Saini et al. [19] reported that 30% of cases had sensorineural hearing loss and only 4% in control group had sensorineural hearing loss, Bhaskar et al. [6] in 2014 reported the association of SNHL with diabetes with an incidence of 78.2% as compared to 38% among non diabetics. Rajendran et al. [18] reported sensorineural deafness among the diabetics is 73.3% when compared to that of the controls 6.7%, which is highly significant (p = 0.001).Others studies like Friedman et al. [12] had (55%) hearing loss and Agarwal et al. [1] had (64.86%) hearing loss.

Table 1.

Comparing different patient’s characteristic with sensorineural hearing loss

Characteristic	Mild	Moderate	Moderately severe	Severe	Profound	p value
Duration of DM (years)
1–3	1 (2)	0 (0)	0 (0)	0 (0)	0 (0)	0.031
4–6	2 (4)	2 (4)	1 (2)	0 (0)	0 (0)
7–9	3 (6)	4 (8)	1 (2)	0 (0)	0 (0)
10–12	0 (0)	3 (6)	4 (8)	0 (0)	0 (0)
13–15	0 (0)	1 (2)	5 (10)	3 (6)	1 (2)
> 15	0 (0)	0 (0)	3 (6)	1 (2)	2 (4)
FBS (mg/dl)
< 150	6 (12)	2 (4)	3 (6)	0 (0)	0 (0)	< 0.001
150–200	0 (0)	8 (16)	9 (18)	2 (4)	0 (0)
> 200	0 (0)	0 (0)	2 (4)	2 (4)	3 (6)
RBS (mg/dl)
< 200	4 (8)	2 (4)	0 (0)	0 (0)	0 (0)	0.004
200–300	2 (4)	7 (14)	9 (18)	1 (2)	1 (2)
> 300	0 (0)	1(2)	5 (10)	3 (6)	2 (4)
Serum creatinine (mg/dl)
< 1.5	4 (8)	3 (6)	7 (14)	0 (0)	1 (2)	0.583
1.5–3.0	2 (4)	4 (8)	4 (8)	2 (4)	1 (2)
> 3.0	0 (0)	3 (6)	3 (6)	2 (4)	1 (2)

In present study, out of 37 cases of SNHL, most of the patients were 51–65 years (32%) and more than 66 year old (24%) (Table 1). Sensorineural hearing loss was found in less in young cases and it was found in most of old age patients. It shows as age increases, frequency of SNHL is also increased. In agreement to present study findings study by Bhaskaar et al. [6] also observed that as age of the subjects increases, the percentage of severe and profound hearing loss increases. Normal hearing or minimal hearing loss was not observed in age group 66–75 years. In age group 56–65 years (41.7%), and more than 66 years old, 25% were noted for SNHL with increasing degree of hearing loss. Our study is consistent with the finding of Bhaskaar et al. [6] that as the age of diabetic patient increases, prevalence of sensorineural hearing loss and degree of hearing loss (SNHL) also increases.

In present study, out of 37 cases diagnosed with SNHL, 18 were male and 19 were female. While among 9 controls diagnosed with SNHL, 4 were male and 5 were female (Table 1). Saini et al. [19] studied that among the Cases (diabetics) there were 23 (46%) males and 27 (54%) females. Out of total 15 cases of SNHL in DM, 7 (46%) were males and 8 (54%) were females. Present study did not show any strong correlation between hearing loss and sex of the patients. However study done by Kurien et al. [16] showed that male diabetics had slightly worse hearing when compared to female diabetic patients and Taylor and Irwin [22] observed that female patients with diabetes had significantly greater hearing loss than male patients with diabetes. Majority of the study did not show any variation in sex with hearing.

Present study showed that mild and moderate SNHL was more in patients with less than 9 year of diabetes while moderately severe, severe and profound SNHL were found more in patients with longer duration of diabetes (Table 1). It indicates that as duration of diabetes was increasing, severity of sensorineural hearing loss also increases (p = 0.031). In a study conducted by Saini et al. [19], it was observed that the patients who were suffering from DM from less than 9 years of duration had SNHL of mild degree, while who were having DM more than 9 years of DM had moderate degree of SNHL. Only one patient was found with DM with period more than 15 years and he was having severe degree of SNHL. This result is supported by Virteniemi et al. [23] and Fangcha et al. [10]. However studies done by Kurien et al. [16] and Dalton et al. [9] did not show any correlation between duration of diabetes and hearing loss probably it could be due to the lower age group selected. Kurien et al. [16] included only patients less than 50 years. Age is a confounding factor for hearing loss, but in diabetics as duration of diabetes increases the decreasing in hearing is more rapid.

Our study revealed that patients with less than 200 mg/dl fasting blood sugar were having more prevalence of mild to moderate SNHL while profound SNHL was found only in those patients who were having more than 200 mg/dl FBS (Table 1). It indicates as FBS increases, degree or severity of sensorineural hearing loss increases (p = 0.001). Similar results were seen in study done by Asma et al. [4] However Kurien et al. [16], Dalton et al. [9] and Tay et al. [21] concluded that good control of diabetics reduces the incidence of sensorineural hearing loss.

Our study found no association of serum creatinine levels with degree of sensorineural hearing loss. All types of sensorineural hearing loss were equally distributed in all the levels of serum creatinine (p = 0.583) (Table 1). Bhaskar et al. [6] also found no significant association with the increasing levels of serum creatinine with degree of sensorineural hearing loss. However Kakarlapudi et al. [15] advocated the association of SNHL with worsening serum creatinine in diabetic patients which was attributed to micro vascular disease. The possible reason for insignificant results in our study was may be due to smaller sample size as compared to study done by Kakarlapudi et al. [15] and also we were not having many patients whose serum creatinine w as greater than 3 mg/dl.

Present study association of Speech Discrimination Score (SDS) with hearing loss revealed that most of (58%) cases had 80–90% SDS score while most of the (82%) controls had 90–100% SDS score (p = 0.001) (Table 2). In a study conducted by Curhan et al. [8] found that diabetes had a negative effect on auditory function in aged Type 2 diabetic subjects [8]. The speech discrimination test that measures both the peripheral and central auditory systems also showed a decline in diabetics. Although the differences in SDS between the diabetics and controls were not significant, these results might be dependent on the study design, which excluded participants with serious health problems or neurological conditions due to diabetic complications.

Table 2.

Association of speech discrimination score (SDS) with hearing loss

SDS (%)	Cases	Controls	Total	p value
< 80	8 (16)	6 (12)	14 (14)	0.001
80–90	29 (58)	3 (6)	32 (32)
90–100	13 (26)	41 (82)	54 (54)

Data is expressed as number of patients (%)

SDS speech discrimination score

But our study showed the significant association between SDS values and hearing loss suggesting diabetes is involving cochlea and affecting cochlear hearing. Speech discrimination, as opposed to speech sensitivity, is the person’s ability not only to hear words but also to identify them (Table 3).

Table 3.

Association of tone decay test (TDT) with hearing loss

TDT (db/hl)	Cases	Controls	Total	p value
> 25	5 (10)	7 (14)	12 (12)	0.001
15–20	32 (64)	2 (4)	34 (34)
< 5	13 (26)	41 (82)	54 (54)

Data is expressed as number of patients (%)

TDT tone decay test

In present study we found that most of 64% cases had 15–20 db/hl TDT while most of 82% controls had less than 5 db/hl TDT (p = 0.001) (Table 2). In present study SISI was less than 70% among 16 (32%) and 47 (94%) subjects in Cases and controls while it was 70–100% among 34 (68%) and 3 (6%) subjects in Cases and controls (p = 0.001). In a similar study by Fransen et al. [11], Gatland et al. [13] and Wackym and Linthicum [24] reported similar findings as compared to present study.

Present study had few limitations; cross-sectional nature was one of them because of that present study findings cannot be applied to large population. Sample size was another; a large randomized clinical trial is required to strengthen the present study findings.

Conclusion

Based on the findings of present study we concluded that cochlear dysfunction is an important complication of diabetes mellitus. Sensorineural type of hearing loss is the result of microangiopathic process affecting the vessels of internal ear. Age, duration, severity of diabetes correlate very well with the degree of hearing loss and may be considered important determining factors for hearing loss. Based on this study we could recommend to screen all newly diagnosed diabetic patients with pure tone audiometry, annual pure tone audiometry to be done routinely even if patient does not report hearing deficit, hearing aid to be advised before hearing loss becomes of severe grade and early diagnosis and prompt treatment will improves the quality of life of the patient.

Compliance with Ethical Standards

Conflict of interest

Both authors declare that they have no conflict of interests.

Informed Consent

Informed consent was obtained from all individual participants included in the study.