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

## TL;DR

This study found similar reduced glymphatic function in Parkinson’s disease and essential tremor, suggesting a shared underlying mechanism.

## Contribution

The study introduces DTI-ALPS as a non-invasive metric to compare glymphatic function in tremor disorders.

## Key findings

- Both PD and ET groups had significantly lower ALPS values than healthy controls.
- Lower ALPS in PD correlated with tremor severity and age, especially in the right hemisphere.
- ET showed weaker clinical correlations, but ALPS in the right hemisphere linked to cognitive function.

## Abstract

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.

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.

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 (R²=0.80, p=0.003). ET showed weaker clinical associations though MoCA correlated positively with right-hemisphere ALPS (ρ=0.462, p=0.018).

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.

The online version contains supplementary material available at 10.1007/s00234-025-03840-6.