Diabetic Otopathy

Abstract

Introduction

Diabetes mellitus is a multisystemic disease with both microvascular and macrovascular chronic complications, having an increased prevalence worldwide. Diabetic otopathy is defined by the presence of symptoms and signs of vestibular and auditory disorders in patients with diabetes mellitus after the exclusion of other causes. Its clinical manifestations include dizziness, vertigo, tinnitus, and hearing loss. The prevalence of auditory disorders in diabetic patients was between 67.5%-72.22% for high-frequency sounds and 27.78% for low and medium frequency sounds.

 

Material and method

We reviewed the literature by searching the MEDLINE database for the most representative articles published so far. The studies that we selected were observational studies that hypothesise a link between diabetes mellitus and premature hearing loss. Those studies included patients with type 2 diabetes, type 1 diabetes and prediabetes.

 

Conclusions

There is an insufficiently described link between diabetes mellitus and otopathy through microvascular lesions, atherosclerotic lesions of the great vessels and linear lesions of the cochlear and vestibular nerve. It is necessary to establish a screening and monitoring strategy for patients with diabetes to prevent diabetic otopathy and its consequences on patients’ life quality. Also, representative cohort studies are needed to identify the link between diabetes and hearing loss.

 

Table of Contents:

1. Introduction

2. Physiopathological mechanisms

3. Materials and method

4. The link between diabetic otopathy and other diabetic complications

5. Other factors involved

6. Conclusions

 

1. Introduction

Diabetes mellitus (DM) is a multisystemic disease with both microvascular and macrovascular chronic complications. Its global prevalence is in continuous growth, the effect being the rise in mortality and morbidity [1, 2]. Observational studies raise the hypotheses that hearing loss and vestibular disorders are complications of diabetes mellitus, with physiological and pathological mechanisms yet unknown [3].

Diabetic otopathy is defined by the presence of symptoms and signs of vestibular and auditory disorders in patients with diabetes mellitus after the exclusion of other causes. Its clinical manifestations include dizziness, vertigo, tinnitus, and hearing loss [4]. It is a complication with early onset in the natural evolution of diabetes mellitus, being in correlation with the duration of diabetes and the level of glycemic control. Diabetic otopathy has an essential impact on the quality of life, affecting the communication, cognitive and relation processes with other people.

Comparing with the control groups, diabetic patients have a higher auditory threshold for each frequency, mostly for the sounds with a wavelength between 2-8 Hz [5].

The prevalence of auditory disorders in diabetic patients was between 67.5%-72.22% for high-frequency sounds and 27.78% for low and medium frequency sounds [5].

 

2. Physiopathological mechanisms

Besides noise pollution, it is known that other risk factors contribute to deafness including the metabolic syndrome through its components – arterial hypertension, hyperlipemia or low HDL-cholesterol. A cross-sectional study recently published done on a large sample of the Iranian population demonstrated a correlation between BMI change (body mass index) and hearing loss [6].

Its pathogenesis was explained by the onset of auditory neuropathy, cochlear microangiopathy and encephalopathy. Hyperglycemia raises intracellular accumulation of sorbitol (a component of polyol pathway), slowing down nervous conductivity. These modifications can be the result of the immune, ischemic or metabolic changes caused by diabetes [4].

The cochlea contains Na/K/ATP-ase, an enzyme that is down-regulated by hyperglycemia. This change causes an increase in intracellular Na+, and also extracellular K+ and Ca2+, the final result being excitotoxicity. NO plays an essential role in the modulation of the vascular endothelium of the auditory system. The metabolic changes in diabetes disturb the production of NO leading to vasodilation which limits the influx of blood in some areas of the auditory system. Also, a correlation has been reported between lipid disorders and diabetic otopathy as a result of hyperinsulinemia and insulin-resistance [4].

 

3. Materials and method

We made a review of the literature by searching the MEDLINE database for the most representative articles published since 1970. The search terms that we used were “diabetes otopathy” and “diabetes hearing loss”. Eighteen articles published in medical journals were selected.

We considered some investigative methods for assessing the sensory function used in the studies: tone audiometric tests to evaluating aerial and bone conduction of sounds; logoaudiometric tests to assess speech reception threshold (SRT) and speech recognition index (SRI); acoustic impedance tests (to analyse tympanometry and the acoustic reflex).

The relation between diabetes mellitus and otopathy – is otopathy an early-onset disorder or is it associated with a reduced long-term glycemic control?

Since 1970 there have been made observational studies which raised the hypothesis of a relation between diabetes mellitus and premature hearing loss. These studies included patients with type 2 diabetes [7], type 1 diabetes [8], pre-diabetes [9] and control groups from a general population. These initial studies had the disadvantage of a small number of patients included, in general, fewer than 50 in each group.

The study done by Jin Lin has shown that a significant number of type 2 diabetes patients suffered hearing loss, in comparison with pre-diabetes patients or the control group. Even though pre-diabetes is not necessarily associated with a significant hearing loss, there can be a cochlear malfunction, indicated by the otoacustic emissions (DPOAE) generated by the external ciliary cells of the healthy cochlea.

These can be measured by putting in the ear canal a sound source that produces the stimulus and a microphone for the recording of the response. The obtained information is usually specific and can be correlated with other tests results to define the sensory deficit. The absence of the otoacustic emissions indicates early damage to the cochlea, which is found in pre-diabetes patients [9].

Also, in favour of early disruption theory is the prospective cohort study published by Kim MB. It was performed on a large group of young adults and middle-aged men and women with regular auditory tests results which participated in regular screenings between 2002-2014. The study demonstrated that the participants with normal glucose levels, pre-diabetes and diabetes mellitus have a rate of hearing loss of 1.8, 3.1 and 9.2 to 1000 person-years. Also, in regression analysis, the risk of hearing loss was proportional to HbA1c levels [10].

On the other hand, in some studies, there weren’t any associations between high levels of HbA1c >7% (suggesting a poor glycemic control) and the onset of hearing loss. However, Cruickshank et al., reported that auditory sensibility loss is more commonly found in patients with HbA1 >12.5%, which show the necessity of a severe glycemic imbalance to generate the auditory disorders. The duration of diabetes and the use of normoglycemic treatment weren’t associated with a higher risk of acoustic complications onset [11-12].

 

4. The link between diabetic otopathy and other diabetic complications

There have been published several studies and reviews that analyse the link between diabetes complications and otopathy [13]. In the survey conducted by Tay, hearing impairment was correlated with the duration of diabetes, but not with other complications of the disease such as retinopathy [14].

Bayazit analysed hearing disturbance in patients with complications of diabetes in comparison with a group of patients without complications and concluded that diabetic neuropathy and encephalopathy are involved in aetiology [15]. The theory of cochlear microvascular damage, as in the other diabetic complications, was proposed in 2008 by Loader after formerly Fukushima conducted a morphological study which confirms the affection of small vessels of the cochlea, dysplasia of vascular striatum cells and cochlear hair cells [16, 17].

The relationship between otopathy and diabetic kidney disease has a particular place. Dalton et al., showed an association between severe diabetic nephropathy (patients with proteinuria, kidney transplant or dialysis) and hearing loss. The glomerular filtration rate was used as an indicator of renal function, and thus it was shown that hearing loss occurs from the early stages of chronic kidney disease. This observation comes to complement the data from a study conducted in Korea, which indicates that patients with chronic renal disease stage 2 (eGFR 60-90ml/min/1.73m2) had a severe auditory disorder. Independent of diabetes, lowering the glomerular filtration rate is associated with hearing loss of moderate severity among the analysed population. Severely reduced kidney function is not associated with hearing loss of mild or elevated seriousness, which can be explained by the increased mortality rate of these patients who fail to develop hearing impairment [18, 19].

The atherosclerosis of large vessels may result in consecutive ischaemia in hearing impairment as demonstrated by Gutmann et al., using ultrasonography in diabetic patients [20].

 

5. Other factors involved

There has been demonstrated a positive association between increased levels of triglycerides and hearing loss for medium and low frequencies. Identifying the association between atherogenic potential risk factors such as smoking and high levels of triglycerides and the risk of injury of auditory sensitivity has led to the hypothesis that this association is based on a vascular aetiology.

This hypothesis can be explained by the fact that atherogenic dyslipidemia points in time to a thinning of the capillaries and sclerosis the internal auditory artery among diabetic patients. Also, obesity alters the expression of cytokines, causes gastroesophageal reflux and lipid accumulation, which can cause otitis media with effusion [3]. Hyperlipidemia also inhibits the morphological and functional development of the cochlea [6].

Arterial hypertension also participates in the occurrence or worsening of hearing disorders, both directly (through a less known mechanism), and indirectly by association with diabetes [3].

Moderate alcohol consumption is associated with a low risk of hearing impairment, but increased use is positively associated with a much higher risk of hearing impairment. In the study conducted by Bainbridge [12], patients were divided into chronic alcohol users and patients in withdrawal, thus obtaining a J-shaped association curve between alcohol consumption and hearing loss.

Active smoking is not associated with hearing loss, but together with diabetes causes the incidence of auditory disorders to be much higher among the population studied [12]. This risk factor increases the risk of head and neck neoplasms, that account for 2% of all cancers [21, 22].

 

6. Conclusions

There is an insufficient description of the relationship between diabetes mellitus and hearing impairment. Studies have shown that microvascular lesions, atherosclerosis of the large vessels and even direct damage of the acoustic-vestibular nerve can contribute to the development of hearing loss in diabetes. Concerning other complications of DM, an association between hearing loss and diabetic nephropathy has been demonstrated. Other elements that correlate with hearing impairment in DM are hypertriglyceridemia, increased alcohol consumption and hypertension.

Shreds of evidence involving the influence of glycemic control (HbA1c) on hearing and balance disturbances are uncertain. It is necessary to establish a screening and monitoring strategy for patients with diabetes mellitus to prevent the development of diabetic otopathy and its consequences on life quality. Representative cohort studies are also necessary to identify a possible link between diabetes and hearing loss.

 

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Contribution selected by Filodiritto among those published in the Proceedings “National ENT, Head and Neck Surgery Conference - 2018”

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