Association of reduced DTI-ALPS index and increased free water with glymphatic system alterations in noise-induced hearing loss: a neuroimaging study

To investigate diffusion changes suggestive of possible glymphatic alterations in patients with noise-induced hearing loss (NIHL), and to evaluate their relationships with free water (FW) and clinical characteristics. DTI scans were acquired from 48 NIHL patients and 40 healthy controls (HCs). The diffusion tensor imaging along perivascular spaces (DTI-ALPS) technique and FW diffusion model were used to calculate DTI-ALPS and FW values. Between-group differences were assessed using ANCOVA. Spearman correlation analysis was conducted between DTI-ALPS, FW, Hamilton Anxiety Scale (HAMA), and better-ear monaural threshold weighted value (MTWV). Compared with HCs, NIHL patients exhibited significantly reduced DTI-ALPS indices (mean: β = - 0.073, p = 0.008; left: β = - 0.081, p = 0.006; right: β = - 0.068, p = 0.026) and increased FW (β = 0.017, p = 0.019). Within the NIHL group, the left DTI-ALPS index was significantly lower than the right DTI-ALPS index (p < 0.001). Significant negative correlations were observed: mean DTI-ALPS with HAMA (r = - 0.406, p = 0.004) and FW (r = - 0.510, p < 0.001); left DTI-ALPS with HAMA (r = - 0.463, p < 0.001) and FW (r = - 0.459, p = 0.001); and right DTI-ALPS with FW (r = - 0.488, p < 0.001). All above results remained significant after FDR correction. Correlations of DTI-ALPS with MTWV (mean: r = - 0.311, p = 0.031; left: r = - 0.295, p = 0.042; right: r = - 0.287, p = 0.048) and right DTI-ALPS with HAMA (r = -0.308, p = 0.033) did not survive FDR correction. Patients with NIHL exhibited altered diffusion patterns suggestive of possible glymphatic alterations. These cross-sectional, correlational findings do not permit causal inferences. Longitudinal studies in larger and more diverse cohorts are needed for validation.