Can diabetes cause hearing loss? A focus on auditory ossicles

Studies have shown a link between diabetes and changes in the inner ear. A new study is now investigating whether ossicles in the middle ear also contribute to hearing loss.

Diabetes and Hearing

• Diabetes mellitus is associated with a three-fold increased risk of hearing loss compared to healthy individuals.
• Previous otopathological studies have identified various changes in the inner ear in diabetics, including hair cell loss and blood vessel abnormalities.
• Furthermore, chondrocytes in cartilage are sensitive to changes in glucose levels, leading to abnormal glucose uptake and oxidative stress.
• However, the exact pathophysiological mechanisms of hearing loss in patients with type 2 diabetes remain unclear.

For their study, the researchers used 47 middle ears from 25 deceased individuals with type 2 diabetes from the temporal bone collection of the University of Minnesota Ear Pathology Laboratory, as well as controls from the same collection. Hearing function was assessed using audiograms from the donors' medical records, although the results were available for only nine individuals.

Significant cartilage changes in diabetics

Histopathological examination revealed significant thickening of the hyaline cartilage of the malleus (34.17 ± 9.71 μm vs. control: 21.96 ± 4.16 μm) and incus (35.11 ± 10.12 μm vs. control: 22.42 ± 4.368 μm). At the same time, the joint space was significantly widened in diabetics compared to the control group (266.72 ± 59.11 vs. 239.81 ± 35.56 μm), while the distance between the articular discs was smaller (96.84 ± 36.80 μm vs. control: 113.63 ± 23.81 μm).

The few available audiograms did not show a significant increase in hearing impairment. However, all patients with diabetes had reported auditory symptoms such as subjective hearing loss, ear pressure, or tinnitus during their lifetime.

Is there a connection between ossicular anomalies and hearing function?

The authors believe that the identified ossicular chain anomalies could be related to the self-reported hearing symptoms of diabetics and possibly also to objective hearing function. It is theoretically conceivable that increased compliance of the middle ear leads to the absorption of mechanical energy and a reduction in frequency transmission. However, given the limited number of hearing tests available and the overall small number of cases, this hypothesis cannot be proven.

This small study provides evidence that degenerative changes in type 2 diabetes may also affect the microjoints in the middle ear.