Abstract

The study of suprathreshold audiometric tests remains relevant in audiology. One of the most informative methods of suprathreshold audiometry for detecting the phenomenon of Loudness Growth Acceleration (LGA) is the determination of the Differential Threshold (DT) of sound intensity perception using Lüscher’s method. This methodology allows for investigating the auditory system’s ability to distinguish minimal changes in sound intensity. The probability of developing sensory hearing disorders in patients with type 2 diabetes is quite significant.

Objective: to evaluate the data of the Differential Threshold of sound intensity perception using Lüscher’s method in patients with type 2 diabetes who have sensorineural hearing disorders.

Materials and methods: We examined a total of ninety-four patients (52 women and 42 men) diagnosed with type 2 diabetes who presented symptoms affecting their auditory system, such as hearing loss, ear congestion and tinnitus. In addition, we included a control group consisting of 15 healthy individuals with normal blood sugar levels for comparison.

Depending on the severity of the disease progression, the patients with type 2 diabetes were divided into groups: group 1 included those without or with isolated microvascular complications, while group 2 comprised individuals diagnosed with triopathies (neuropathy, nephropathy, retinopathy).

We thoroughly examined the medical history, complaints, and conducted a comprehensive clinical and instrumental diagnostic assessment of the auditory system’s condition.

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). The investigation of Differential Thresholds of sound intensity using Lüscher’s method was conducted at frequencies of 0,5, 2, and 4 kHz.

Results and discussion: In the patients with type 2 diabetes that we examined, there was practically no impairment in speech discrimination test results, although some patients did report occasional deterioration in speech clarity and communication difficulties. However, the average thresholds of speech discrimination tests, both for numeral and verbal tests, did not significantly differ from the control values in both studied groups of patients with type 2 diabetes mellitus. Regarding the Differential Thresholds measured by Lüscher’s method, at frequencies of 0,5 and 1 kHz, they did not differ significantly from the control values in either of the studied groups. However, some patients in group 2 exhibited a relative decrease at the 1 kHz frequency. However, at the 4 kHz frequency, the DT were notably low in some patients, particularly in group 2. On average, the DT values at this frequency were significantly lower in the examined patients of group 2 compared to the normal range. Indeed, the DT values at 4 kHz were 1,93±0,04 in group 1 and 1,28±0,03 in group 2, compared to the norm of 1,98±0,04. It is notable that low or relatively decreased DT values at the 4 kHz frequency were observed in 20,3% of patients in group 1 and in 71,4% of those examined in group 2.

Therefore, low DT values at 4 kHz suggest damage to the receptor part of the auditory system in patients with sensorineural hearing impairment associated with type 2 diabetes mellitus. The reductions in DT were more pronounced in patients with advanced type 2 diabetes complications.

Conclusions:

1. According to the Differential Threshold values using Lüscher’s method, patients with type 2 diabetes exhibited low DT values at 4 kHz, indicating impairment of the cochlear function.
2. In patients with complicated type 2 diabetes mellitus, more pronounced reductions in Differential Threshold values are observed compared to those with milder forms, indicating more significant changes in the auditory system’s receptors.
3. Low Differential Thresholds using Lüscher’s method indicate the presence of Loudness Growth Acceleration, suggesting damage to the receptor part of the auditory system. This condition worsens patients’ well-being and is an unfavourable prognostic sign.
4. The Differential Threshold value at 4 kHz using Lüscher’s method is crucial for diagnosing impairment in the receptor structures of the auditory system in patients with type 2 diabetes mellitus (T2DM).

Keywords: diabetes mellitus, sensorineural hearing loss, auditory analyser, suprathreshold audiometry.