Objectives: Diabetes mellitus (DM) is associated with a variety of sensory complications. Very little attention has been given to auditory neuropathic complications in DM. The aim of this study was to determine whether type 1 DM (T1DM) affects neural coding of the rapid temporal fluctuations of sounds, and how any deficits may impact on behavioral performance.
Design: Participants were 30 young normal-hearing T1DM patients, and 30 age-, sex-, and audiogram-matched healthy controls. Measurements included: electrophysiological measures of auditory nerve and brainstem function using the click-evoked auditory brainstem response (ABR), and of brainstem neural temporal coding using the sustained frequency-following response (FFR); behavioral tests of temporal coding (interaural phase difference, IPD, discrimination and the frequency difference limen, FDL); tests of speech perception in noise; and self-report measures of auditory disability measures using the Speech, Spatial and Qualities (SSQ) hearing scale.
Results: There were no significant differences between T1DM patients and controls in the ABR. However, the T1DM group showed significantly reduced FFRs to both temporal envelope and temporal fine structure. The T1DM group also showed significantly higher IPD and FDL thresholds, worse speech-in-noise performance, as well as lower overall SSQ scores than the control group.
Conclusions: These findings suggest that T1DM is associated with degraded neural temporal coding in the brainstem in the absence of an elevation in audiometric threshold, and that the FFR may provide an early indicator of neural damage in T1DM, before any abnormalities can be identified using standard clinical tests. However, the relation between the neural deficits and the behavioral deficits is uncertain.