Similar DTI-ALPS metrics in Parkinson's disease and essential tremor: a cross-sectional comparative analysis

Purpose This study investigated glymphatic function in tremor disorders using the diffusion tensor imaging-derived ALPS (analysis-along-the-perivascular-space) index, a non-invasive surrogate of perivascular fluid movement. Materials and Methods Fourty-three patients with tremor-dominant Parkinson's disease (PD, n=22) or essential tremor (ET, n=21), aged 50-75, were retrospectively compared with 18 age-matched healthy controls (HC) imaged with the same 3 T MRI protocol. Subjects with significant cognitive impairment, white matter disease, other CNS disorders, or poor-quality diffusion data were excluded. ALPS indices were calculated from projection and association fibre regions. Results Both PD (mean ALPS = 1.34 +/- 0.19) and ET ( 1.31 +/- 0.13) groups exhibited 12 significantly lower ALPS values than HC ( 1.54 +/- 0.11 P < 0.05), but no difference was 13 found between PD and ET. In PD, lower ALPS correlated with greater tremor severity and older age, particularly in the right hemisphere (R-2=0.80, p=0.003). ET showed weaker clinical associations though MoCA correlated positively with right-hemisphere ALPS (rho=0.462, p=0.018). Conclusion The findings indicate perivascular diffusivity is reduced in both tremor-dominant PD and ET, supporting a role for glymphatic dysfunction in their pathophysiology, though larger, prospective studies are needed to validate this observation.