Metabolic and functional correlates of age-related hearing loss: Advanced MRI findings and rehabilitation perspectives of the central auditory pathways

BACKGROUND: Presbycusis is the hearing loss (HL) determined by aging mechanisms affecting the inner ear. Auditory cortical hypoperfusion has been shown in the early phases of presbycusis, suggesting a regionally selective metabolic vulnerability secondary to peripheral loss of function. In this study, HL patients were stratified according to the audiogram profiles to possibly enable a finer regional characterization of cortical perfusion changes within the primary auditory cortex. METHODS: Sixty-two HL patients (age range: 47-78 years, PTA <50dB) and thirty-two normal hearing (NH) subjects (age-range 48-78 years) were enrolled in a 3 Tesla MRI study. Two clusters of HL patients were identified, and labeled as low-loss-high-slope (LLHS) and high-losslow-slope (HLLS), according to the audiogram centro-types from an independent data set of fifty-five HL patients (age range: 45-80 years, PTA<50dB). Pseudo-continuous arterial spin labeling (ASL) and T1-weighted MRI were performed to derive cerebral blood flow (CBF) maps and to assess group-level perfusion changes within the primary auditory cortex. RESULT S: The comparison of CBF maps of all HL patients vs. NH controls confirmed a statistically significant CBF reduction in a compact region encompassing the right transverse temporal gyrus. The separate comparisons of LLHS and HLLS patients vs. NH subjects resulted in different localizations of the hypoperfusion region along the transverse temporal gyrus. CONCLUSIONS: Presbycusis is associated with perfusion reductions in the right primary auditory cortex with a different spatial pattern according to the audiogram profile. The observed heterogeneity of central auditory perfusion patterns may underlie different pathogenetic aspects and clinical forms of presbycusis.