Impaired auditory neural performance, another dimension of hearing loss in type-2 diabetes mellitus

Elsevier

Available online 1 June 2022, 101360

Diabetes & MetabolismHighlights•

Pure-tone audiometry was mildly affected by type-2 diabetes mellitus

An absent middle-ear muscle reflex suggests auditory neuropathy in type-2 DM subjects

Auditory neuropathy affected 40% type-2 DM subjects even with normal audiograms

AbstractAim

to evaluate auditory performance in subjects with poorly controlled type-2 diabetes mellitus, using a simple test battery assessing sensitivity to pure tones and neuronal function.

Methods

Enrolled subjects, aged between 23-79 years, reported several auditory dysfunctions. They were tested using pure-tone audiometry, otoacoustic emissions for cochlear-function evaluation, and measurement of middle-ear muscle-reflex thresholds in search of an auditory neuropathy.

Results

Compared to the standard established for an age-matched normative population, the distribution of averaged pure-tone thresholds in enrolled subjects shifted by about one standard deviation with respect to the normal distribution, in line with past reports of mild sensorineural hearing impairment in diabetes, even though many diabetic subjects fell well within the normative interval of audiometric thresholds. Otoacoustic emissions showed that pure-tone thresholds correctly predicted the status of cochlear sensory cells that, by amplifying sound, ensure normal hearing sensitivity. Whereas the observed hearing losses should not have affected the acoustic levels above which the protective middle-ear muscle reflex is triggered by intense sounds, this reflex was undetectable in around 40% enrolled subjects, a marker of auditory neuropathy.

Conclusion

auditory-neural function should be evaluated to identify diabetic subjects whose hearing is impaired. Simple automatic tests are available for this purpose, for example middle-ear muscle reflex detection, which turns out to be more sensitive than the standard audiogram.

Keywords

Type-2 diabetes mellitus

hearing impairment

pure-tone audiometry

middle-ear muscle reflex

auditory neuropathy

AbbreviationsDPOAE

distortion-product otoacoustic emissions

MNSI

Michigan Neuropathy Screening Instrument

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