Abstract

Diabetes mellitus (DM) is one of the most common systemic disorders, associated with metabolic dysfunction and a high prevalence of complications. Numerous researchers have identified hearing impairments in patients with diabetes using a variety of diagnostic methods.

The purpose of this study is to assess the condition of different parts of the auditory system in patients with type 2 diabetes mellitus and hearing impairment.

Materials and methods: A total of 94 patients with type 2 diabetes mellitus, who reported auditory system complaints, were examined, along with 15 healthy individuals from the control group, all of whom had normal blood glucose levels. The duration of type 2 diabetes was 10,35 ± 1,4 years, and glycated hemoglobin (HbA1c) values ranged from 6,9% to 12,1%. Depending on the severity of the disease, group 1 consisted of 59 patients without complications, while group 2 included 35 patients with diabetes complications and a history of significant fluctuations in blood glucose levels. The audiometric examination was conducted using clinical audiometers AD 229E and AC 40 of the company “Interacoustics” (Denmark). Distortion product otoacoustic emissions (DPOAE), auditory brainstem responses (ABR), and long-latency auditory evoked potentials (LLAEP) were recorded using standardized protocols with the “Eclipse” system (Interacoustics, Denmark)

Results and discussion: According to the results of subjective audiometry, the examined patients with type 2 diabetes mellitus exhibited sensorineural hearing loss (SNHL) characterized by a descending audiometric curve, indicating damage to the basal part of the cochlea. The differential thresholds (DT) measured using the Lüscher method at a frequency of 4 kHz were lower in some patients, particularly in those with a complicated course of type 2 diabetes mellitus. The average values were significantly reduced compared to the control group, reaching 1,28 ± 0,03 dB. Reduced DT in the 4 kHz range were observed in 20,3% of patients without complications and in 71,4% of those with a severe, complicated course of type 2 diabetes.

As for DPOAE data, the presence of a partially positive response or the absence of otoacoustic emission registration in 90,6% of the examined patients with type 2 diabetes mellitus indicates cochlear dysfunction of varying degrees. The emission amplitude at all tested frequencies in patients with type II diabetes was significantly lower compared to the norm (P < 0,01).

The significant prolongation of the latencies of almost all waves in the ABR complex, as well as the interpeak intervals (IPI) I-III and I-V, observed in comparison to the control group, indicates dysfunction of the brainstem structures of the auditory system in patients with type 2 diabetes. Specifically, the IPI I-III in patients with type 2 diabetes exceeded the norm by 0,1 ms, and the IPI I-V by 0,15 ms.

With ipsilateral stimulation using a 1 kHz tone, the examined patients showed a significant (p < 0,01) prolongation of the latency period (LP) of the N2 component to (280,3 ± 3,4) ms and the LP of the P2 component of long-latency auditory evoked potentials (LLAEP) to (176,5 ± 3,1) ms, compared to the norm. This indicates dysfunction of the cortical and subcortical structures of the auditory system in these patients. Similarly, with ipsilateral stimulation using a 4 kHz tone, a significant (p < 0.01) prolongation of the LP of the N2 component of LLAEP to (279,1 ± 2,6) ms and the P2 component to (178,3 ± 2,8) ms was also observed in the patients with type 2 diabetes.

Thus, in patients with type 2 diabetes mellitus and sensorineural hearing loss, both the receptor and central components of the auditory system are affected, as confirmed by objective examination methods. Furthermore, in patients with a more complicated course of type 2 diabetes, the extent of damage to both the receptor and central auditory structures is greater.

Conclusions:

Suprathreshold tests during full subjective audiometry in patients with type 2 diabetes mellitus (T2DM) and sensorineural hearing loss (SNHL) revealed dysfunction of the cochlear structures in these patients. According to the Differential Threshold (DT) data using Lüscher’s method, low DT values at a frequency of 4 kHz were recorded in patients with type 2 diabetes. The application of the DT test using the Lüscher method at a frequency of 4 kHz has important diagnostic value for detecting damage to the receptor structures of the auditory system in patients with type 2 diabetes.

The results of OAE (Otoacoustic Emissions) registration at distortion product frequencies in patients with type 2 diabetes objectively confirm the presence of impairments in the receptor part of the auditory system. In patients with type 2 diabetes, the amplitude of OAE (Otoacoustic Emissions) at distortion product frequencies is significantly lower than normal at all tested frequencies (1-6 kHz), especially at 4 kHz, where the OAE response amplitude was 5,9±0,2 dB, compared to the normal value of 9,4±0,5 dB.

A significant (p<0,01) increase in the latency periods of peaks II, III, and V of the ABR (Auditory Brainstem Response) waves to 2,78±0,03, 3,85±0,04, and 5,83±0,05 ms, respectively, as well as the I-III and I-V interpeak latencies to 2,19±0,03 and 4,13±0,05 ms, respectively, compared to the control group, objectively confirms the presence of impairments in the brainstem region of the auditory system in patients with sensorineural hearing loss due to type 2 diabetes.

The results obtained using the LLEAP method in patients with type 2 diabetes mellitus (DM) and sensorineural hearing loss (SNHL) objectively confirm dysfunction in the central components of the auditory system, including both cortical and subcortical structures. In patients with SNHL on the background of type 2 diabetes mellitus, there is a statistically significant (p < 0,01) prolongation of the LPP components P2 and N2 of the LLEAP compared to the control group – up to (176,5 ± 3,1) ms and (280,3 ± 3,4) ms during 1 kHz tone stimulation, and up to (178,3 ± 2,8) ms and (279,1 ± 2,6) ms during 4 kHz tone stimulation, respectively.

According to subjective and objective audiological assessments, patients with type 2 diabetes mellitus and sensorineural (perceptual) hearing loss exhibit impairments in both the receptor and central components of the auditory system. Moreover, patients with type 2 diabetes mellitus and sensorineural hearing loss who have a complicated disease course, including polyneuropathies and a history of abrupt blood glucose fluctuations, exhibit more profound alterations in both the receptor and central components of the auditory system compared to patients with a milder disease course.

Keywords: diabetes mellitus, hearing system, auditory evoked potentials, otoacoustic emission, hearing function.