White Matter Alterations Are More Robust Than Gray Matter Differences in Tinnitus and Hearing Loss: An MRI Study of...

Tinnitus and hearing loss are the most prevalent service-related auditory disabilities among American veterans. Previous studies have examined gray matter or white matter alterations in tinnitus and hearing loss relative to healthy controls, but typically in isolation, and none of them have focused specifically on a military-affiliated population.

We employed voxel-based morphometry to assess gray matter differences and diffusion tensor imaging to evaluate white matter integrity in tinnitus and/or hearing loss compared to controls in a sample of 68 military-affiliated adults (56 men, 10 women, two identifying as 'other' gender). Additionally, we conducted an exploratory, hypothesis-generating effect size analysis to describe the magnitude of group differences.

Combined tinnitus and hearing loss was associated with decreased gray matter volume in the thalamus. White matter integrity was reduced in the forceps minor, right superior longitudinal fasciculus, and left inferior longitudinal fasciculus. Hearing loss alone was associated with white matter orientation changes in the right anterior thalamic radiation, left superior longitudinal fasciculus, and right corticospinal tract. Larger effect sizes were noted in white matter comparisons across tinnitus, hearing loss, and combined conditions, suggesting that white matter differences may be of greater magnitude than gray matter alterations.

These findings advance the understanding of the neural correlates of tinnitus and hearing loss in the military population, an understudied group with a high prevalence of tinnitus and hearing loss. They also present preliminary effect size estimates that may inform future studies on the neural correlates of tinnitus and hearing loss, indicating a larger overall magnitude in white matter and more subtle contributions from gray matter.