An association of type 1 diabetes mellitus with auditory dysfunction: A systematic review and meta-analysis

Exploring auditory temporal resolution and dichotic listening skills among individuals with type 2 diabetes mellitus

The study aimed to explore the auditory temporal resolution and dichotic listening skills in patients with type 2 diabetes mellitus (T2DM) and identify associated health-related factors. Using a cross-sectional design, 87 adults with T2DM and 48 non-diabetic controls, all with normal hearing, participated. The two central auditory processing (CAP) skills were assessed through the Gaps-In-Noise (GIN) and Dichotic-Digits Listening (DDL) tests. T2DM participants underwent blood tests to measure various health-related factors. In the GIN test, the shortest gap threshold (GapTh) obtained across both ears was significantly higher in the diabetic group (9.1 ± 2.4 ms) compared to the non-diabetic group (7.5 ± 1.5 ms), and the score of correctly identified gaps (GapSc) in the diabetic group (45±11 %) was significantly lower than GapSc in the non-diabetic group (52±9 %), p < 0.001. In the DDL test, the free-recall score (73.8 ± 18.5 %) across both ears and the right-ear advantage (-1.3 ± 20.6 %) in the diabetic group were significantly lower than the free-recall score (85.8 ± 11.9 %) and right-ear advantage (6.9 ± 11.9 %) in the non-diabetic group, p < 0.005. Furthermore, the duration of diabetes, eGFR level, retinopathy, carotid plaque, fasting blood glucose level, and HDL-C (good cholesterol) level were factors significantly associated with performances in the GIN and/or DDL tests for T2DM participants. In conclusion, individuals with T2DM are at risk of reduced auditory processing skills in temporal resolution and dichotic listening, impacting their speech understanding. Six health-related factors were identified as significantly associated with CAP skills in T2DM patients.

L-shaped association of triglyceride glucose index and sensorineural hearing loss: results from a cross-sectional study and Mendelian randomization analysis

Background

The association between the sensorineural hearing loss (SNHL) and triglyceride-glucose (TyG) index remains inadequately understood. This investigation seeks to elucidate the connection between the TyG index and SNHL.

Methods

In this cross-sectional study, we utilized datasets sourced from the National Health and Nutrition Examination Survey (NHANES). A comprehensive analysis was conducted on 1,851 participants aged 20 to 69, utilizing complete audiometry data from the NHANES database spanning from 2007 to 2018. All enrolled participants had accessible hearing data, and the average thresholds were measured and calculated as both low-frequency pure-tone average and high-frequency pure-tone average. Sensorineural hearing loss (SNHL) was defined as an average pure tone of 20 dB or higher in at least one better ear. Our analysis involved the application of multivariate linear regression models to examine the linear relationship between the TyG index and SNHL. To delineate any non-linear associations, we utilized fitted smoothing curves and conducted threshold effect analysis. Furthermore, we conducted a two-sample Mendelian randomization (MR) study, leveraging genetic data from genome-wide association studies (GWAS) on circulating lipids, blood glucose, and SNHL. The primary analytical method for the MR study was the application of the inverse-variance-weighted (IVW) approach.

Results

In our multivariate linear regression analysis, a substantial positive correlation emerged between the TyG index and SNHL [2.10 (1.80-2.44), p < 0.0001]. Furthermore, using a two-segment linear regression model, we found an L-shaped relationship between TyG index, fasting blood glucose and SNHL with an inflection point of 9.07 and 94 mg/dL, respectively. Specifically, TyG index [3.60, (1.42-9.14)] and blood glucose [1.01, (1.00-1.01)] concentration higher than the threshold values was positively associated with SNHL risk. Genetically determined triglyceride levels demonstrated a causal impact on SNHL (OR = 1.092, p = 8.006 × 10-4). In addition, blood glucose was found to have a protective effect on SNHL (OR = 0.886, p = 1.012 × 10-2).

Conclusions

An L-shaped association was identified among the TyG index, fasting blood glucose, and SNHL in the American population. TyG index of more than 9.07 and blood glucose of more than 94 mg/dL were significantly and positively associated with SNHL risk, respectively.

Cardiometabolic diseases according to the type and degree of hearing loss in noise-exposed workers

Background

This study aimed to determine the association between cardiometabolic diseases, including metabolic syndrome, hypertension, and diabetes, and the type and degree of hearing loss in noise-exposed workers.

Methods

A total of 237,028 workers underwent air conduction pure tone audiometry in 2015 to assess their health and diagnose cardiometabolic diseases. The study defined metabolic syndrome, hypertension, and diabetes using blood pressure, fasting blood sugar, cholesterol, and triglyceride levels. Mid-frequency hearing loss was defined as ≥ 30 dB at 2,000 Hz, whereas high-frequency hearing loss was ≥ 40 dB at 4,000 Hz. The average air conduction hearing thresholds at these frequencies were used to determine hearing loss degrees.

Results

The odds ratio (OR) of combined exposure to noise and night-shift work in all cardiometabolic diseases was higher than that of noise exposure alone. The risk of cardiometabolic diseases was dose-response, with higher hearing loss causing higher ORs. The ORs of hypertension compared with the normal group were 1.147 (1.098-1.198), 1.196 (1.127-1.270), and 1.212 (1.124-1.306), and those of diabetes were 1.177 (1.119-1.239), 1.234 (1.154-1.319), and 1.346 (1.241-1.459) for mild, moderate, and moderate-severe hearing loss, respectively.

Conclusions

Workers who are exposed to noise tend to demonstrate high risks of hearing loss and cardiometabolic diseases; thus, bio-monitoring of cardiometabolic diseases, as well as auditory observation, is necessary.

A systematic review of the association of Type I diabetes with sensorineural hearing loss

OBJECTIVES

Type 1 diabetes (T1D) has been associated with several comorbidities such as ocular, renal, and cardiovascular complications. However, the effect of T1D on the auditory system and sensorineural hearing loss (SNHL) is still not clear. The aim of this study was to conduct a systematic review to evaluate whether T1D is associated with hearing impairment.

METHODS

The databases PubMed, Science Direct, Scopus, and EMBASE were searched in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Three reviewers independently screened, selected, and extracted data. The Joanna Briggs Institute (JBI) Critical Appraisal Tools for Analytical cross-sectional and case-control studies were used to perform quality assessment and risk of bias analysis on eligible studies.

RESULTS

After screening a total of 463 studies, 11 eligible original articles were included in the review to analyze the effects of T1D on the auditory system. The included studies comprised cross-sectional and case-control investigations. A total of 5,792 patients were evaluated across the 11 articles included. The majority of the studies showed that T1D was associated with hearing impairment compared to controls, including differences in PTAs and OAEs, increased mean hearing thresholds, altered acoustic reflex thresholds, and problems with the medial olivocochlear (MOC) reflex inhibitory effect. Significant risk factors included older age, increased disease duration, and higher HbA1C levels.

CONCLUSIONS

This systematic review suggests that there is a correlation between T1D and impairment on the auditory system. A multidisciplinary collaboration between endocrinologists, otolaryngologists, and audiologists will lead to early detection of hearing impairment in people with T1D resulting in early intervention and better clinical outcomes in pursuit of improving the quality of life of affected individuals.

REGISTRATION

This systematic review is registered in PROSPERO (CRD42023438576).

Subclinical neural hearing alterations in school children with type 1 diabetes mellitus

BACKGROUND AND OBJECTIVES

Evidence has shown a cause-and-effect relationship between type 1 diabetes mellitus and auditory and cognitive dysfunctions. This study aimed to investigate the effect of type 1 diabetes mellitus (T1DM) on central auditory and cognitive functions in school-age children and adolescents.

METHODS

The study sample consisted of 101 children and adolescents, 50 with T1DM, of both sexes, aged between 7 and 18 years. All participants were selected for a structured interview on hearing, behavioral, and cognitive health and assessment of brainstem auditory evoked potentials (BAEP) and event-related potentials (P300).

RESULTS

Significant differences were observed in memory (p=0.002) and attention (p=0.021) complaints between participants with and without T1DM. In the BAEP responses, there were differences between wave III latencies in the right (p=0.017) and left (p=0.019) ears and in wave V latencies in the left ear (p=0.001) between the evaluated groups. In addition, there was an association between BAEP findings and metabolic control in the T1DM group in the left ear in waves III (p=0.006) and V (p=0.005) and in the right ear in wave V (p=0.026). No differences were observed in the latencies of P300 between the evaluated groups.

CONCLUSION

This study demonstrated the existence of a subclinical finding in the central auditory pathway, offering an increased risk for retrocollear alterations, which may be a consequence of poor metabolic control.

Association between HbA1c and hearing loss: a tertiary care center-based study

The purpose of this study was to investigate the correlation between glycated hemoglobin (HbA1c) levels and hearing loss (HL) using data from a tertiary hospital. Our hypothesis regarding the relationship between HL and HbA1c levels was that elevated HbA1c levels are associated with an increased risk of HL. We retrospectively reviewed the medical charts of patients diagnosed with sensorineural HL or diabetes between 2006 and 2021 at the Catholic Medical Center (CMC). Data were collected from the CMC's Clinical Data Warehouse. Participants were selected from patients who were prescribed pure-tone audiometry and an HbA1c blood test. The survey was completed for 5287 participants. The better ear pure-tone audiometry (PTA) for air conduction thresholds at 500, 1000, 2000, and 4000 Hz was calculated. Sensorineural HL was defined as a better ear PTA of 25 dB or higher. We used the HbA1c level as a diagnostic criterion for diabetes. The following criteria were used to define the HbA1c level: normal, HbA1c level below 5.6%; prediabetes, level between 5.6 and 6.4%; and diabetes, level of 6.5% or more. Among 5287 participants, 1129 were categorized as normal, 2119 as prediabetic, and 2039 as diabetic. The diabetic group was significantly older (p < 0.05). The PTA also significantly deteriorated in the diabetes group (p < 0.05). We analyzed the effects of age, sex, and HbA1c level on frequency-specific hearing using multiple regression. The hearing thresholds at all frequencies deteriorated significantly with increasing age and HbA1c level (p < 0.05). A case-control study was also performed to facilitate a comprehensive comparison between distinct groups. The participants were categorized into two groups: a case (PTA > 25 dB) and control group (PTA ≤ 25 dB), based on their PTA threshold of four frequencies. After adjusting for age and sex, we found no significant odds ratio (OR) of HL between the prediabetes group and the normal group. Notably, the OR of HL was significantly higher in the diabetes group with each PTA threshold and frequency. The 6.3% HbA1c level cutoff value was determined by analyzing the receiver operating characteristic curve for predicting hearing impairment > 25 dB. Diabetes was associated with hearing loss in all frequency ranges, particularly at high frequencies. Screening for HL is strongly recommended for patients with elevated HbA1c levels.

Diabetes mellitus and hearing loss

Diabetes mellitus (DM) is a major disease threatening human health and its incidence is increasing year on year. As a chronic complication of DM, hearing loss mostly occurs undetectably. However, the mechanism of this diabetes-related hearing loss (DRHL) remains unclear and there is no effective clinical treatment. Studies of animal or human pathology show that DM causes damage to the blood vessels, spiral ganglion neurons, afferent nerve fibers, the organ of Corti, and the stria vascularis of the inner ear. In recent years, more advances in pathological research have revealed the possible mechanism of DRHL. In addition, a large number of clinical studies suggest that the duration and severity of DM are closely related to the incidence and severity of DRHL. This review focuses on the relationship between DM and hearing loss. The clinical audiological characteristics of diabetic patients, risk factors for DRHL, typical pathology, and potential interventions of DRHL are summarized. This will help reveal the pathogenesis and intervention approaches for DRHL.

The Role of Metabolic Syndrome Components in Sensorineural Hearing Loss in Adolescents: A Case-Control Study

Introduction  Metabolic syndrome (MetS) and its associated components were reported as a possible cause of inner ear dysfunction. However, research about the influence of cardiovascular risk factors on hearing thresholds are conducted mainly in adult patients. Objective  The aim of the present study was to investigate auditory function in adolescents with MetS compared with healthy controls. Methods  One hundred adolescents with metabolic syndrome and 200 sex- and age-matched controls were recruited from a university pediatric endocrine clinic from May 2018 to July 2020. Hearing loss was defined as hearing level ≥ 15 dB at speech frequency (SFHL) or high frequency (HFHL) in one or both ears. A multivariable conditional logistic regression analysis examined the correlation between MetS components and several important demographic characteristics, and hearing loss. Results  A total of 165 (55.0%) boys and 135 (45.0%) girls participated in this study. The rates of SFHL and HFHL in adolescents with MetS were 32.0% and 51.0%, respectively. Those values for controls were 5.0% and 15.5%, respectively. The regression analysis showed high triglycerides as a significant predictor for SFHL (odds ratio 10.87; 95% confidence interval: 1.98, 59.74). Neither predictor of interest was significant for HFHL. Conclusion  Hypertriglyceridemia may be an important factor in the pathogenesis of SFHL. However, the strength of the association was not significant with a wide confidence interval. Also, we were unable to find an association between predictors and HFHL with the current sample size. Larger and prospective studies are recommended.

Evaluation of the Effects of Dyslipidemia on Hearing in Patients with Type 2 Diabetes Mellitus

Modernization has led to change in life style and physical inactivity which are playing a major role in increasing the number of people with diabetes and dyslipidaemia, Different types of hearing loss in diabetic patients have been reported which shows progressive, gradual, bilateral sensorineural loss. The primary aim of the present study is to evaluate the effects of dyslipidemia on hearing in patients with type 2 diabetes mellitus. A comparative study was conducted where patients were divided into 4 groups-Type II diabetes mellitus with dyslipidemia,Type II diabetes mellitus with normal lipid profile, Only Dyslipidemia,Normal subjects. A total of 128 participants were enrolled in the study. The Diabetes patient was determined by the FBS, PPBS and Hba1c levels. Dyslipidemia determined by LDL,HDL,VLDL.Patients with Type 2 diabetes mellitus and dyslipidaemia was evaluated for the presence of hearing loss with the help of PTA. Prevalence of hearing loss among patients with Diabetes and Dyslipidaemia was 65.7%, 40.6% in Type II DM with normal lipid profile patients, 18.75% in patients with dyslipidaemia. Statistically significant association of hearing loss was noted in patients with diabetes mellitus and dyslipidaemia. Although hearing loss is multifactorial, control of the risk factors like dyslipidaemia in diabetes mellitus definitely halt the process of auditory damage. As observed from this study, poor glycaemic control, associated other co-morbidities were contributing factors for hearing loss. Healthy life style with early recognition of these diseases helps in preventing further damage.

Betahistine prevents development of endolymphatic hydrops in a mouse model of insulin resistance and diabetes

BACKGROUND

Diabetes is associated with inner ear dysfunction. Furthermore, C57BL/6J mice fed high fat diet (HFD), a model for insulin resistance and diabetes, develop endolymphatic hydrops (EH).

AIM

Evaluate if betahistine, spironolactone (aldosterone antagonist) and empagliflozin (sodium -glucose cotransporter2 inhibitor) can prevent EH induced by HFD and explore potential mechanisms.

METHODS

C57BL/6J mice fed HFD were treated with respective drug. The size of the endolymphatic fluid compartment was measured using contrast enhanced MRI. Secondarily, mice treated with cilostamide, a phosphodiesterase3 inhibitor, to induce EH and HEI-OC1 auditory cells were used to study potential cellular mechanisms of betahistine.

RESULTS

HFD-induced EH was prevented by betahistine but not by spironolactone and empagliflozin. Betahistine induced phosphorylation of protein kinaseA substrates but did not prevent cilostamide-induced EH.

CONCLUSIONS

Betahistine prevents the development of EH in mice fed HFD, most likely not involving pathways downstream of phosphodiesterase3, an enzyme with implications for dysfunction in diabetes. The finding that spironolactone did not prevent HFD-induced EH suggests different mechanisms for EH induction/treatment since spironolactone prevents EH induced by vasopressin, as previously observed.

SIGNIFICANCE

This further demonstrates that independent mechanisms can cause hydropic inner ear diseases which suggests different therapeutic approaches and emphazises the need for personalized medicine.

Diabetes Mellitus and Hearing Loss: A Complex Relationship

Background and Objectives: Discussion is open about the relationship between diabetes (DM) and hearing loss (HL). There is a lot of evidence in the literature suggesting a causal link between these conditions, beyond being considered simple comorbidities. The difficulty in identifying populations free from confounding factors makes it difficult to reach definitive conclusions on the pathophysiological mechanisms at play. Nonetheless, there is numerous evidence that demonstrates how the population affected by DM is more affected by sensorineural HL (SNHL) and exhibit a higher prevalence of idiopathic sudden sensorineural HL (ISSNHL). Materials and Methods: Articles reporting potentially relevant information were reviewed, and the most significant results are discussed in this article. Starting from the possible mechanisms relating to auditory impairment in the diabetic condition, this article summarizes the studies on auditory evaluation in subjects with DM1 and DM2 and addresses the relationship between DM and ISSNHL. Results: DM is considered a risk factor for SNHL, although some studies have reported no relationship when the associations were adjusted for age, gender, and hypertension. Macro and microvascular insults that cause decreased blood flow, oxygen exchange, and ion transport are major complications of hypertension and DM and can have a direct effect on the sensory and support cells of the cochlea. Conclusions: Given the difficulty of carrying out studies on populations without confounding factors, new laboratory studies are strongly required to clarify which specific physiopathological mechanisms underlie the diabetic damage caused to the hearing organs and how pharmacological management may contribute to counteracting the pathophysiological effects of the diabetic condition on the auditory system.

Changes in the cochlear and retrocochlear parts of the auditory system in 19-39 and 40-60 years old patients with type 1 diabetes mellitus

Pathophysiological alterations in the cochlea and functional tests of the auditory pathway support that in diabetes both vasculopathy and neural changes could be present. The aim of our research was to study the differential effect of type 1 diabetes mellitus (T1DM) on two different age groups. Audiological investigation was carried out in 42 patients and 25 controls at the same age groups. Investigation of the conductive and sensorineural part of the hearing system by pure tone audiometry, distortion product otoacoustic emission measurement and acoustically evoked brainstem response registration were evaluated. Among the 19-39-year-old people the incidence of hearing impairment was not different in the diabetes and control groups. Among the 40-60-year-old people hearing impairment was more common in the diabetes group (75%) than in the control group (15,4%). Among patients with type 1 diabetes, the mean threshold values were higher in both age groups at all frequencies although significant difference was in 19-39 years old group: 500-4000Hz right ear, 4000Hz left ear, in 40-60 years old group: 4000-8000 Hz both ears. In the 19-39 years old diabetes group only at 8000 Hertz on the left side was a significant (p<0,05) difference in otoacoustic emissions. In the 40-60 years old diabetes group significantly less otoacoustic emissions at 8000 Hz on the right side (p<0,01) and at 4000-6000-8000 Hertz on the left side, (p<0,05, p<0,01, p<0,05 respectively) was present compared to the control group. According to ABR (auditory brainstem response) latencies and wave morphologies, a possible retrocochlear lesion arose in 15% of the 19-39 years old and 25% of the 40-60 years old diabetes group. According to our results, T1DM affects negatively the cochlear function and the neural part of the hearing system. The alterations are more and more detectable with aging.

The effect of increase in blood glucose level on hearing loss

OBJECTIVE

Previous studies have shown that hearing function is also vulnerable to the effects of diabetes mellitus which can be shown by brainstem auditory evoked potential and distortion product otoacoustic emission recordings. This study aimed to investigate the changes of brainstem auditory evoked potential and distortion product otoacoustic emission in hyperglycemia and whether there is a relationship between reactive oxygen substances production and hearing deterioration in the rat model.

METHODS

25 streptozotocin induced diabetic rats were divided into three groups: control, high blood glucose, and diabetes mellitus. Brainstem auditory evoked potential and distortion product otoacoustic emission were recorded, and thiobarbituric acid reactive substances levels were measured in the brainstem tissue.

RESULTS

At 8 kHz, the latencies of I, II, III, IV, and V brainstem auditory evoked potential waves in high blood glucose and diabetes mellitus groups were elongated, at 16 kHz, only these wave latencies of the diabetes mellitus group were prolonged compared with the control group. A significant decrease was also found in distortion product otoacoustic emission amplitudes at 4, 6, 8, and 10 kHz in the high blood glucose and diabetes mellitus groups compared to the control group. There was a significant increase in thiobarbituric acid reactive substances values due to the increase in blood glucose levels in the high blood glucose and diabetes mellitus groups compared to the control group.

CONCLUSION

These results suggested that high blood glucose levels may cause hearing impairment not only in the diabetic state but also in the period of hyperglycemia before the onset of manifest diabetes mellitus and reactive oxygen substances may play an important role in the pathophysiology of diabetes mellitus. We suggest that regulating high glucose levels even before the onset of manifest diabetes mellitus may prevent hazardous effects on hearing function.

LEVEL OF EVIDENCE

Level 3.

Toward a better understanding of nonoccupational sound exposures and associated health impacts: Methods of the Apple Hearing Study

Globally, noise exposure from occupational and nonoccupational sources is common, and, as a result, noise-induced hearing loss affects tens of millions of people. Occupational noise exposures have been studied and regulated for decades, but nonoccupational sound exposures are not well understood. The nationwide Apple Hearing Study, launched using the Apple research app in November 2019 (Apple Inc., Cupertino, CA), is characterizing the levels at which participants listen to headphone audio content, as well as their listening habits. This paper describes the methods of the study, which collects data from several types of hearing tests and uses the Apple Watch noise app to measure environmental sound levels and cardiovascular metrics. Participants, all of whom have consented to participate and share their data, have already contributed nearly 300 × 10⁶ h of sound measurements and 200 000 hearing assessments. The preliminary results indicate that environmental sound levels have been higher, on average, than headphone audio, about 10% of the participants have a diagnosed hearing loss, and nearly 20% of the participants have hearing difficulty. The study's analyses will promote understanding of the overall exposures to sound and associated impacts on hearing and cardiovascular health. This study also demonstrates the feasibility of collecting clinically relevant exposure and health data outside of traditional research settings.

Insulin regulates Nedd4-2 via a PKB-dependent mechanism in HEI-OC1 auditory cells-crosstalks with sphingolipid and cAMP signaling

BACKGROUND

The mechanisms of association between diabetes and inner ear dysfunction are unknown, although endolymphatic hydrops may be involved. We have previously shown that insulin signaling components are expressed in human saccule and that insulin signaling takes place in HEI-OC1 auditory cells.

AIM

To explore Nedd4-2 as a target for insulin signaling.

MATERIALS AND METHODS

Effects of insulin were analyzed using western blot and confocal microscopy in HEI-OC1 auditory cells.

RESULTS

Insulin induced phosphorylation of Nedd4-2 and increased the amount of ENaC at the plasma membrane. Also, protein kinase B (PKB) and NDRG1, a substrate for SGK1 (serum and glucocorticoid stimulated kinase), were phosphorylated in response to insulin. The SGK1 inhibitor GSK650394 prevented insulin-induced phosphorylation of NRDG1, but not of PKB and Nedd4-2, whereas the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin and the PKB inhibitor MK2206 inhibited phosphorylation of all components. Ceramides prevented insulin-induced phosphorylation of PKB and NDRG1, but not of Nedd4-2. The ceramide metabolite sphingosine 1-phosphate induced phosphorylation of Nedd4-2.

CONCLUSIONS

Insulin induces phosphorylation of Nedd4-2, most likely involving PI3K/PKB signaling. Sphingosine 1-phosphate might protect Nedd4-2 against ceramide-induced insulin resistance.

SIGNIFICANCE

Insulin-mediated regulation of Nedd4-2 might impact on inner ear sodium homeostasis with implications for diabetes-induced inner ear damage.

Diabetes mellitus and hearing loss: A review

Diabetes (type 2) and sensorineural hearing loss are common health problems manifested with ageing. While both type 1 and type 2 diabetes have been associated with hearing loss, a causal link has been difficult to establish. Individuals with diabetes have twice the incidence of hearing loss compared to those without diabetes and those with prediabetes have a 30% higher rate of hearing loss. Whether hearing loss is associated with diabetes independent of glycemic control remains to be determined. Hearing loss has its own set of risk factors and shares others with diabetes. This review will summarize the complex relationship between diabetes and sensorineural hearing loss.

Insulin-like Growth Factor 1 Signaling in Mammalian Hearing

Insulin-like growth factor 1 (IGF-1) is a peptide hormone belonging to the insulin family of proteins. Almost all of the biological effects of IGF-1 are mediated through binding to its high-affinity tyrosine kinase receptor (IGF1R), a transmembrane receptor belonging to the insulin receptor family. Factors, receptors and IGF-binding proteins form the IGF system, which has multiple roles in mammalian development, adult tissue homeostasis, and aging. Consequently, mutations in genes of the IGF system, including downstream intracellular targets, underlie multiple common pathologies and are associated with multiple rare human diseases. Here we review the contribution of the IGF system to our understanding of the molecular and genetic basis of human hearing loss by describing, (i) the expression patterns of the IGF system in the mammalian inner ear; (ii) downstream signaling of IGF-1 in the hearing organ; (iii) mouse mutations in the IGF system, including upstream regulators and downstream targets of IGF-1 that inform cochlear pathophysiology; and (iv) human mutations in these genes causing hearing loss.

Hearing impairment and diverse health outcomes : An umbrella review of meta-analyses of observational studies

BACKGROUND

Globally, it is estimated that approximately 1.3 billion people live with some form of hearing impairment. Major causes of hearing loss include infection/disease, age-related factors, and occupational factors. Numerous systematic reviews and meta-analyses have attempted to synthesise literature on these topics. To date there has not been a systematic evaluation of the relationships between hearing impairment and diverse physical, mental, and social outcomes.

OBJECTIVE

We performed an umbrella review of systematic reviews of observational studies with meta-analyses for any physical disease, biomarkers of disease, mental health or cognitive outcomes, and/or modifiable risk factors associated with hearing impairment.

METHODS

For each meta-analytic association, random effects summary effect size, 95% confidence intervals, heterogeneity, evidence for small-study effect, excess significance bias and 95% prediction intervals were calculated, and risk of bias was assessed via the AMSTAR2 tool. These were used to grade significant evidence (p < 0.05) from I to IV, using the recommendations from the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) criteria.

RESULTS

From 3747 studies, 21 were included covering 54 outcomes. Overall, 44/54 outcomes (82%) yielded significant results. Of the highest quality evidence, age-related hearing loss and non-specific hearing impairment were negatively associated with several types of cognitive impairments; pediatric bilateral hearing loss was negatively associated with quality of life, sensorineural hearing loss was positively associated with rheumatoid arthritis and tinnitus was positively associated with temporomandibular disorders.

CONCLUSION AND RELEVANCE

Results show moderate quality evidence for associations between several types of hearing impairments and cognitive difficulties, quality of life and systemic diseases such as rheumatoid arthritis. Practitioners and public health policies should note these findings when developing relevant healthcare policies.

Sensorineural hearing loss and risk of stroke: a systematic review and meta-analysis

The aim of this systematic review and meta-analysis study was to clarify the effects of sensorineural hearing loss (SNHL) on the incidence of stroke. In line with this, PubMed, Scopus, Web of Science, and ScienceDirect databases were searched using related keywords and MeSH terms from inception to March 1, 2020. Out of the 1961 initial records, eight cohort studies comprising 4,564,202 participants were included, and their qualities were assessed using the Newcastle-Ottawa Scale (NOS). Then, the random-effects model was used to pool HR (95% CI) for risk of stroke; and heterogeneity was presented with I² index. Subgroup analysis and publication bias tests were performed, and the pooled HR (95% CI) of stroke in SNHL was estimated as 1.31 (1.08, 1.53) for the unadjusted model and 1.33 (1.18, 1.49) for the adjusted model. Subgroup analysis indicates a significantly higher risk of stroke in patients with sudden SNHL (SSNHL) in comparison to age-related HL (ARHL) both in the unadjusted model, [HR = 1.46; 95% CI (1.08, 1.63)] versus [HR = 1.14; 95% CI (0.64, 1.65)], and in the adjusted model, [HR = 1.44; 95% CI (1.15, 1.74)] versus [HR = 1.29; 95% CI (1.24, 1.34)]. Our study showed that patients with SNHL face a higher risk of stroke than those without SNHL. It is necessary to perform hematologic and neurological examinations to help clinicians detect patients who are potentially at risk for stroke.

High Blood Glucose Levels Affect Auditory Brainstem Responses after Acoustic Overexposure in Rats

INTRODUCTION

Diabetes mellitus (DM) is a systemic disease characterized by hyperglycemia and several pathological changes. DM-related hearing dysfunctions are associated with histological changes. Here, we explore hearing function and synaptic changes in the inner hair cells (IHCs) of rats with streptozotocin (STZ)-induced diabetes.

METHODS

STZ was injected to trigger diabetes. Rats with DM were exposed to narrow-band noise (105 dB SPL) for 2 h, and hearing function was analyzed 1, 3, 7, and 14 days later. Both the hearing threshold and the peak 1 amplitude of the tone auditory brainstem response were assessed. After the last functional test, animals were sacrificed for histological evaluation.

RESULTS

We found no changes in the baseline hearing threshold; however, the peak 1 amplitude at the low frequency (4 kHz) was significantly higher in both DM groups than in the control groups. The hearing threshold had not fully recovered at 14 days after diabetic rats were exposed to noise. The peak 1 amplitude at the higher frequencies (16 and 32 kHz) was significantly larger in both DM groups than in the control groups. The histological analysis revealed that the long-term DM group had significantly more synapses in the 16 kHz region than the other groups.

CONCLUSIONS

We found that high blood glucose levels increased peak 1 amplitudes without changing the hearing threshold. Diabetic rats were less resilient in threshold changes and were less vulnerable to peak 1 amplitude and synaptic damage than control animals.

Diabetes-induced auditory complications: are they preventable? a comprehensive review of interventions

Diabetes mellitus is a chronic metabolic disorder characterized by elevated blood glucose levels, which, over time, lead to major chronic complications in various organs of the body. A growing body of research suggests that diabetes could also result in degenerative changes in the auditory system. To date, several attempts have been made to prevent and reduce diabetes-induced auditory complications. Such attempts have generally focused on disease modifying as well as other pharmacological treatments involving several herbal and non-herbal agents such as vitamins C and E, rutin, resveratrol, coffee, trigonelline, Dioscorea nipponica, red ginseng, Pterostilbene Bofutsushosan, Daisaikoto, tolrestat, ACE inhibitors (enalapril), Ca antagonists (nimodipine), Lipo-prostaglandin E1, methylprednisolone, dexamethasone, and chlorogenic acid and also other strategies like acupuncture. However, there is no consensus about which are the most effective strategies for preventing and reducing auditory complications in diabetic patients with few side effects and maximum efficacy. This paper provides a comprehensive review of interventions for preventing and treating diabetes-induced auditory complications to help therapists.

Factors driving olfactory loss in patients with chronic rhinosinusitis: a case control study

BACKGROUND

Olfactory dysfunction (OD) in chronic rhinosinusitis (CRS) is common. It is likely that numerous factors such as sex, race, age, allergies, asthma, smoking, and other comorbidities play a role in CRS-related OD. In order to determine which aspects of OD are due solely to CRS and which are associated with other confounders, control populations are needed to allow appropriate risk assessments.

METHODS

Prospective, multi-institutional enrollment of patients with CRS and control subjects without CRS was performed. Demographic information, comorbidities, and olfactory testing (Sniffin' Sticks) of threshold (T), discrimination (D), and identification (I) scores (TDI) was collected.

RESULTS

A total of 224 patients with CRS and 164 control subjects were enrolled. Olfaction was worse in CRS patients compared to controls (mean ± standard deviation (SD) TDI = 22.4 ± 9.5 vs 28.8 ± 7.0, respectively, p < 0.001). Only 27% of CRS patients were normosmic compared to 49% of controls (p < 0.001). When stratifying by nasal polyp (NP) status, CRSwNP patients had significant impairments in TDI, T, D, and I compared to controls with mean differences of 11.2, 3.3, 3.5, and 4.4 points, respectively (all p < 0.001). In contrast, CRSsNP patients only had impaired T when compared to controls with a mean difference of 2.2 points (p < 0.001). Multivariate modeling of TDI scoring showed that OD was driven by polyps, asthma, diabetes, and age. CRSsNP was not independently associated with worse TDI scores.

CONCLUSION

OD in CRS patients is multifactorial. Independent drivers appear to be polyp status, asthma, diabetes, and age. OD in patients with CRSsNP is similar to controls with the exception of impaired thresholds.

Type 1 Diabetes Induces Hearing Loss: Functional and Histological Findings in An Akita Mouse Model

The relationship between type 1 diabetes and hearing loss is not well known, although based on many pathological studies, type 2 diabetes induced hearing loss is associated with microcirculation problems in the inner ear. The purpose of this study was to investigate the correlation between type 1 diabetes and hearing loss through hearing function and immunohistochemical analyses using type 1 diabetic Akita or wild-type (WT) mice. The Akita mice had a significant increase in hearing thresholds, blood glucose, and insulin tolerance compared to WT mice. Histological analysis showed that the loss of cells and damage to mitochondria in the spiral ganglion neurons of Akita mice were significantly increased compared to WT. Also, the stria vascularis showed decreased thickness, loss of intermediate cells, and disturbance in blood capillary shape in the Akita mice. Moreover, a reduction in type I, II, and IV fibrocytes and Na⁺/K⁺-ATPase α1 expression in spiral ligament was also observed. Cleaved caspase-3 expression was highly expressed in spiral ganglion neurons. In conclusion, hearing loss in type 1 diabetes is caused not only by ion imbalance and blood flow disorders of cochlear endolymph, but through the degenerative nervous system via apoptosis-mediated cell death.

The Association Between Glycolyzed Hemoglobin A1c and Hearing Loss in Diabetic Patients

Purpose

Our study aimed to determine the correlation between glycated hemoglobin (HbA1c) levels and the audiometric parameters in diabetic patients.

Methods

We included 724 patients (376 male, 348 female) in our outpatient clinic and created four groups by reference to the HbA1c values. The first group was 192 patients with an HbA1c value < 4.5, 176 patients with an HbA1c value between 4.5 - 5 as Group 2, 177 patients with an HbA1c value between 5 - 6 as Group 3, and 179 patients that had an HbA1c value greater than 6 as Group 4. The correlations between HbA1c values and median pure tone thresholds at 250, 500, 1,000, 2,000, 4,000, and 8,000 Hz, the speech recognition thresholds, and the speech discrimination scores were compared.

Results

The median speech recognition thresholds, speech discrimination scores, and the median pure-tone thresholds at 250, 500, 1,000, 2,000, 4,000, and 8,000 MHz in the left ear significantly differed in the fourth group (p < 0.001). Pure-tone thresholds at 500 Hz, 4,000 Hz, speech discrimination scores, and recognition thresholds in the right ear had a significant positive correlation in the fourth group (p < 0.001).

Conclusion

According to HbA1c levels, the severity of diabetes can affect high to all frequencies of hearing functions negatively. The follow-up of patients with higher levels of HbA1c should undergo audiological tests more regularly.

Type 1 diabetes and hearing loss: Audiometric assessment and measurement of circulating levels of soluble receptor for advanced glycation end products

BACKGROUND

We examined the hearing function in adults with and without type 1 diabetes (T1D) to investigate whether an association exists between hearing loss and duration of diabetes, haemoglobin A1C level, diabetes complications and levels of select serum and urinary biomarkers.

METHODS

We measured pure tone audiometry (PTA) thresholds; serum levels of C-reactive protein (CRP), vascular endothelial growth factor (VEGF), soluble receptors for advanced glycation end-product (sRAGE); and urinary isoprostane in 30 adults with T1D (age 43.8 ± 11.4 years). We also measured PTA thresholds in 11 adults without diabetes (age 53 ± 5.5 years).

RESULTS

63.3% of adults with T1D had high-frequency hearing loss. Among adults with T1D, those with hearing loss were older (48.2 vs 36.2 years old, P < .01), had a longer duration of diabetes (30.7 vs 21.2 years, P = .02), a greater prevalence of peripheral neuropathy (57.9 vs 9.1%, P = .02) and significantly lower median levels of sRAGE (1054.27 vs 1306.83 pg/mL, P = .03) compared to those with normal hearing. Adults with T1D between the ages of 40 and 60 years old, who had diabetes for ≥35 years, had significantly higher PTA thresholds at both 500and 8000 Hz than age-matched adults without diabetes.

CONCLUSIONS

A significant proportion of adults with T1D have high-frequency hearing loss before age of 60 that is positively associated with age, duration of diabetes and presence of peripheral neuropathy. Our results are in support of previous studies suggesting a potential protective role of sRAGE against AGE toxicity and diabetes complications.

Inner ear is a target for insulin signaling and insulin resistance: evidence from mice and auditory HEI-OC1 cells

OBJECTIVE

The mechanisms underlying the association between diabetes and inner ear dysfunction are not known yet. The aim of the present study is to evaluate the impact of obesity/insulin resistance on inner ear fluid homeostasis in vivo, and to investigate whether the organ of Corti could be a target tissue for insulin signaling using auditory House Ear Institute-Organ of Corti 1 (HEI-OC1) cells as an in vitro model.

METHODS

High fat diet (HFD) fed C57BL/6J mice were used as a model to study the impact of insulin resistance on the inner ear. In one study, 12 C57BL/6J mice were fed either control diet or HFD and the size of the inner ear endolymphatic fluid compartment (EFC) was measured after 30 days using MRI and gadolinium contrast as a read-out. In another study, the size of the inner ear EFC was evaluated in eight C57BL/6J mice both before and after HFD feeding, with the same techniques. HEI-OC1 auditory cells were used as a model to investigate insulin signaling in organ of Corti cells.

RESULTS

HFD feeding induced an expansion of the EFC in C57BL/6J mice, a hallmark of inner ear dysfunction. Insulin also induced phosphorylation of protein kinase B (PKB/Akt) at Ser473, in a PI3-kinase-dependent manner. The phosphorylation of PKB was inhibited by isoproterenol and IBMX, a general phosphodiesterase (PDE) inhibitor. PDE1B, PDE4D and the insulin-sensitive PDE3B were found expressed and catalytically active in HEI-OC1 cells. Insulin decreased and AICAR, an activator of AMP-activated protein kinase, increased the phosphorylation at the inhibitory Ser79 of acetyl-CoA carboxylase, the rate-limiting enzyme in de novo lipogenesis. Furthermore, the activity of hormone-sensitive lipase, the rate-limiting enzyme in lipolysis, was detected in HEI-OC1 cells.

CONCLUSIONS

The organ of Corti could be a target tissue for insulin action, and inner ear insulin resistance might contribute to the association between diabetes and inner ear dysfunction.

Epidemiology of Diabetes and Hearing Loss

Hearing loss is a highly prevalent chronic condition. In addition to age, sex, noise exposure, and genetic predisposition, cardiovascular disease and its antecedents may precipitate hearing loss. Of emerging interest is the connection between diabetes and auditory dysfunction. Cross-sectional studies consistently suggest that prevalence of hearing loss is higher in persons with diabetes compared with those without diabetes, especially among younger persons. Furthermore, longitudinal studies have demonstrated higher incidence of hearing loss in persons with diabetes compared to those without diabetes. These findings seem to hold for both type 1 and type 2 diabetes, although considerably more population-based evidence is available for type 2 diabetes. Data on gestational diabetes and hearing outcomes are limited, as are data relating diabetes to otologic sequelae such as fungal infection. Here, we examine evidence from epidemiologic studies of diabetes and hearing loss and consider clinical and laboratory data where population-based data are lacking.

Alterations in hearing function of patients with glucose disorders

OBJECTIVE

To study the prevalence of hearing impairment in patients with various glucose disorders.

PATIENTS AND METHODS

A total of 499 individuals were studied, 51 patients with type 1 (TIDM), 188 patients with type 2 diabetes mellitus (T2DM), 39 patients with impaired fasting glucose (IFG), and 221 controls. Measurements were performed, blood was drawn, and a relevant questionnaire was completed. Ηearing function was assessed by pure-tone audiometry (PTA) and distortion product otoacustic emissions (DPOAEs).

RESULTS

Patients with impaired glucose metabolism (IGM: T2DM or IFG) compared to controls had a higher percentage of abnormal PTA and DPOAEs for both the right (70.2 vs. 56.9% and 40.4 vs. 24.2%, respectively, p < 0.001) and the left (74.1 vs. 59.3% and 47.5 vs. 25.4%, respectively, p < 0.001) ear. Patients with TIDM had similar levels for the left ear (54.9 vs. 59.3% and 27.5 vs. 25.4%, respectively, p > 0.05) and lower levels for the right ear (35.3 vs. 56.9% and 13.7 vs. 24.2%, respectively, p < 0.001 and p = 0.044) percentages of abnormal PTA and DPOAEs compared to controls. Logistic regression analysis indicated that independent parameters for abnormal DPOAEs in one or both ears are age, male gender, exposure to noisy environments, and the presence of IGM.

CONCLUSIONS

Hearing impairment was more prevalent in patients with IGM compared to healthy controls, as assessed by PTA and DPOAEs. Age, male gender, and exposure to noise are other factors that can independently affect hearing ability. Physicians should bear in mind possible defects in hearing ability when dealing with such patients.

Hyperglycemia and diabetes mellitus are related to vestibular organs dysfunction: truth or suggestion? A literature review

Diabetes mellitus is an independent risk factor for falling, particularly in the elderly. Due to chronic hyperglycemia and hyperinsulinemia patients with diabetes mellitus may have neurological deficits as peripheral neuropathy that is a debilitating micro-vascular complication affecting the proximal and distal peripheral sensory and motor nerves. Sensory neuropathy is prominent and represents the chief contributor to postural instability in diabetic subjects. Diabetic retinopathy is another complication consequent to a breakdown of the inner blood-retinal barrier with accumulation of extracellular fluids in the macula and growth of new vessels causing retinal detachment. Together peripheral neuropathy and retinopathy contribute to increase the risk of falls in diabetic patients, but a certain vestibular organs impairment should not be underestimated. Nevertheless, the exact mechanism and localization of peripheral vestibular damage consequent to chronic hyperglycemia and hyperinsulinemia are currently not still understood. Moreover it is not defined the possible role of these two blood conditions in worsening the prognosis of typical vestibular pathologies like "benign paroxysmal positional vertigo" and "Meniere disease". The aim of this review was to retrieve all studies investigating about the balance system alterations in patients suffering of diabetes. A search thorough Ovid MEDLINE was performed to enroll all eligible articles. Fourteen studies comprising a total of 1364 patients were included and analyzed in detail. On the basis of data reported in our review it appears plausible to hypothesize a direct connection among chronic hyperglycemic/hyperinsulinemic damage and peripheral vestibular organ dysfunction.

Hearing loss in type 1 diabetes: Are we facing another microvascular disease? A meta-analysis

OBJECTIVE

Evidence shows type 1 diabetes(T1D) leads to vascular damage and neuropathy. The purpose of this study was to perform a systematic review and a meta-analysis to assess the evidence of the effects of T1D on hearing function.

METHODS

Three electronic databases were used. The articles were independently reviewed by two authors using predefined inclusion criteria to identify eligible studies. They were then classified as high or low methodological quality. Meta-analysis was performed on pooled data of hearing loss(HL) prevalence, pure tone audiometry(PTA), otoacoustic emissions(OAE) and auditory brainstem response(ABR).

RESULTS

Twenty-one articles fulfilled the inclusion criteria. In all studies, HL was defined as pure tone greater than 20 dB in at least one frequency. The prevalence of HL ranged between 5.17% and 48% for diabetics, which was higher than in controls which ranged between 0% à 40% (OR = 7.7, 95% CI 3.32-17.98, p < 0.05 and I² = 40%). The tendency of mean thresholds of PTA was higher in diabetics than in controls, with results being statistically significant at 250, 500 and 1000 Hz. OAE were significantly lower in diabetic patients. ABR latencies were longer in T1D group compared to controls and were statistical significant.

CONCLUSIONS

Patients with T1D have a significantly greater prevalence of HL compared to the control group. These damages could be compared to other microvascular diseases. Further studies are needed to assess whether hearing testing should be considered as a part of the screening process in T1D patients and therefore, secondary preventive treatment may be warranted as well.

Association between hearing organ and renal function in young adult type 1 diabetic patients: A cross-sectional study

Type 1 diabetes can lead to impaired function of many organs and tissues. The aim of this study was to evaluate associations between hearing and kidney function in young adult type 1 diabetic patients. 31 patients (9 women) with type 1 diabetes, aged <45, with disease duration <10 years were included. Blood and urine samples for laboratory tests and urinary albumin excretion (UAE) assessment were obtained. eGFR was calculated with CKD-EPI formula. In all patients pure-tone audiometry, transient evoked otoacoustic emissions and auditory brainstem responses were evaluated, also eye fundus was examined. Mean patients' age was 29.5 ± 7.0 years and disease duration 4.6 ± 2.6 years. All patients had eGFR > 60.0 ml/min/1.73 m². In one case microalbuminuria and in 3 patients early retinopathy were revealed. Linear correlation between eGFR and hearing threshold at 4, 6, 8 and 12 kHz was found. Patients with hearing impairment (n = 7) had lower eGFR 108.8 vs. 121.7 ml/min/1.73 m², p = 0.047 compared to normal-hearing subjects. Also patients with absence of otoacoustic emissions in at least one ear had lower eGFR, 103.1 vs. 123.3 ml/min/1.73 m², p < 0.001, compared to the remaining group. In auditory brainstem responses we found significant linear correlation between eGFR and wave III and interval I-III latencies, and between UAE and waves III, V and interval I-III latencies. This study suggests existence of relationship between hearing and kidney function in type 1 diabetic patients. Pathways directly linking hearing and renal function are unknown. Larger studies are necessary to further analyze these relationships.

Susceptibility of Diabetic Mice to Noise Trauma

Diabetes can lead to many end-organ complications. However, the association between diabetes and hearing loss is not well understood. Here, we investigated the effect of noise exposure on diabetic mice compared with wild-type mice. Hearing threshold shifts, histopathologic changes in the cochlea, and inflammatory responses were evaluated over time. After noise exposure, more severe hearing threshold shifts, auditory hair cell loss, and synaptopathies were notable in diabetic mice compared with wild-type mice. Moreover, increased inflammatory responses and reactive oxygen species production were observed in the ears of diabetic mice. The results demonstrated that diabetic mice are more susceptible to noise trauma.

Cochlear dysfunction and microvascular complications in patients with type 1 diabetes mellitus

Sensorineural hearing impairment has been associated with DM, and it is probably linked to the same pathophysiological mechanisms as well-established in microvascular diabetes complications. The study of otoacoustic emissions (OAEs) is useful to identify subclinical cochlear dysfunction. Therefore, the aim of this study was to evaluate the association between abnormal OAEs responses, diabetic kidney disease (DKD) and diabetic cardiac autonomic neuropathy (CAN). We performed a cross-sectional study with 37 type 1 DM patients without auditory symptoms, submitted to the study of Distortion Product Otoacoustic Emissions (DPOAEs) and screened for DKD and CAN. The otoacoustic emissions responses were considered abnormal in 27/37 (73%) patients. A correlation was found between abnormal OAEs responses and presence of DKD (r = 0.36, p < 0.05), and 14/16 (88%) patients with a lower amplitude of OAEs in 8 kHz frequency band presented DKD. Abnormal OAEs responses in the 6 kHz frequency band were correlated with the presence (r = 0.41, p = 0.01) and severity of CAN (r = 0.44, p < 0.001). Additionally, 7/9 (78%) patients with abnormal OAE responses in this frequency also presented abnormal CAN scores. Our results suggest that abnormal otoacoustic emissions responses in high frequency bands are associated with diabetes microvascular complications and could be a risk marker for DKD and CAN, presenting low sensitivity and high specificity. Therefore, assuming that hearing impairment is a pre-clinical stage of hearing loss, performing distortion product otoacoustic emissions in T1DM patients with microvascular complications could be useful to identify those who would be benefit with regular audiologic follow up and tighter diabetes control.