Abstract

Topicality: Sensorineural hearing loss is a complex disease both in terms of aetiology and pathogenesis. Metabolic disorders and microcirculation disturbances play a significant role in the development of SNHL, which undoubtedly occur in cases of diabetes mellitus. Statistical data indicate a rapid increase in the prevalence of diabetes mellitus, especially type 2, as well as a high percentage of complications. Hearing impairments of varying degrees are often detected in patients with DM. Early diagnosis and prevention of the progression of sensorineural hearing disorders in patients with DM are important tasks.

The purpose of this study is to assess the auditory function based on tonal threshold audiometry data in patients with type 2 diabetes.

Materials and methods: There were examined ninety-four patients with type 2 diabetes complaints related to the auditory system for complaints related to the auditory system (hearing loss, ear congestion, subjective ear noise), along with 15 practically healthy individuals who comprised the control group. The patients with type 2 diabetes were divided into two groups: group 1, consisting of those without or with isolated microvascular complications of diabetes, and group 2, comprising those with diagnosed complications.

The audiometric examination was conducted in a soundproof chamber, with a background noise level not exceeding 30 dB, using clinical audiometers AD 229E and AC 40 of the company “Interacoustics” (Denmark). In the conventional frequency range (0.125-8 kHz), hearing thresholds were determined for bone and air conduction tones. Speech audiometry and Bing and Federici’s tuning fork tests were also performed. Statistical analysis of the obtained results was carried out according to generally accepted methods of mathematical variational statistics.

Results and discussion: In all patients with type 2 diabetes, audiometric examinations revealed sensorineural hearing impairments ranging from mild to severe, corresponding to Grades I-II according to the International Classification. A practically symmetrical sloping audiometric curve was observed.

Comparing the data of tonal threshold audiometry within the conventional (0.125-8 kHz) frequency range of the examined groups with the audiometric indicators of the control group, a significant difference in hearing threshold levels for tones was found at all frequencies within the conventional range (except for the 0.125 kHz frequency for Group 1).

The tonal threshold audiometry results in individuals of Group 2 within the conventional frequency range significantly differed from those in both the control group and Group 1 at all examined frequencies. The most pronounced significant elevation in hearing thresholds was observed in the (4-8) kHz range of the conventional frequency range, both in the first and especially in the second group. Moreover, there was a significant difference in tonal threshold audiometry results between Group 1 and Group 2, starting from 1 kHz. For instance, at the frequency of 4 kHz, the hearing threshold levels for Groups 1 and 2 were (26.72±1.89) and (55.83±3.96) dB, respectively; in the 6 kHz range – (38.72±2.52) and (64.82±3.86) dB; at 8 kHz – (41.52±2.36) and (69.82±4.32) dB, respectively.

The most pronounced significant difference in indicators between groups of patients with different courses of type 2 diabetes was observed in the 4-8 kHz range, especially at the frequency of 4 kHz. This particular observation allowed us to highlight the significance of hearing threshold values in the 4-6 kHz range of the conventional frequency range as a diagnostic criterion for sensorineural hearing impairments in type 2 diabetes mellitus. In the patients we examined with type 2 diabetes, there were practically no impairments in the intelligibility of the speech test. The average statistical thresholds for 50% intelligibility of the number test and 100% intelligibility of the word test did not differ from the norm (P>0.05).

Our studies have shown that in all patients with type 2 diabetes whom we examined and who reported complaints related to the auditory system (hearing loss, ear congestion, subjective ear noise), sensorineural hearing impairments are observed to varying degrees according to subjective audiometry data. Moreover, these impairments were more pronounced in patients with complicated type 2 diabetes.

Conclusions:

1. According to the data from tonal threshold audiometry in patients with type 2 diabetes, symmetric bilateral sensorineural impairments with a sloping audiometric curve were recorded, affecting the basal portion of the cochlea. The most pronounced significant elevation in hearing thresholds was observed in the (4-8) kHz range of the conventional frequency range.
2. In patients with complicated type 2 diabetes mellitus, more pronounced sensorineural hearing impairments are observed based on subjective audiometry data compared to the group of patients with milder course.
3. The conducted research indicates the appropriateness of utilizing tonal threshold audiometry in the examination of patients with diabetes mellitus. This facilitates the early detection of sensorineural hearing impairments and helps prevent the progression of severe hearing disorders in such patients.

Keywords: diabetes mellitus, sensorineural hearing loss, hearing analyser, tonal threshold audiometry.