Fig 1.
Preferred reporting items for systematic reviews and meta-analyses (PRISMA) flowchart showing the article selection process.
Fig 2.
A schematic representation of potential molecular mechanisms underlying diabetes-induced hearing loss.
The hyperglycemia prevalent during diabetes initiates a cascade of pathological events, leading to microangiopathy, oxidative stress, and neuropathy. These molecular events can cause damage to the sensory structures such as stria vascularis, spiral ganglion neurons and hair cells leading to hearing impairment. This damage is measurable through two key auditory tests: distortion product otoacoustic emissions (DPOAE) and auditory brainstem responses (ABRs). DPOAE assesses the function of outer hair cells in the cochlea. A probe with two speakers is inserted into the external ear canal to deliver two different frequency tones (f1 and f2). These tones travel through the ear, reaching the cochlear receptor and generating mechanical distortions at various basilar membrane positions, including the prominent 2f1-f2 location. The interaction of these tones depends on the normal function of outer hair cells, which amplify sound through electromotility. The resulting distortions travel back to the external ear and are recorded by a sensitive microphone, measured as DPOAEs in terms of frequency and amplitude in dB SPL. On the other hand, ABRs is an electrophysiological test that evaluates the integrity of the central auditory pathway from the cochlea to the brainstem. Electrodes placed on the scalp capture electrical activity generated by the auditory nerve and brainstem in response to sound stimuli, usually clicks or tone bursts, delivered through earphones. The recorded neural responses form a characteristic waveform, with several peaks corresponding to different points in the central auditory pathway. The central auditory pathway image was taken from Wikimedia Commons uploaded by Jonathan E. Peelle from https://osf.io/u2gxc/ under the Creative Commons Attribution 4.0 International license. Created with BioRender.com.
Fig 3.
Assessment of risk of bias using the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) tool.
Table 1.
A summary of studies included in this systematic review.