Glymphatic function from diffusion-tensor MRI to predict conversion from mild cognitive impairment to dementia in Parkinson’s disease

Abstract Background Although brain glymphatic dysfunction is a contributing factor to the cognitive deficits in Parkinson’s disease (PD), its role in the longitudinal progression of cognitive dysfunction remains unknown. Objective To investigate the glymphatic function in PD with mild cognitive impairment (MCI) that progresses to dementia (PDD) and to determine its predictive value in identifying individuals at high risk for developing dementia. Methods We included 64 patients with PD meeting criteria for MCI and categorized them as either progressed to PDD (converters) ( n = 29) or did not progress to PDD (nonconverters) ( n = 35), depending on whether they developed dementia during follow-up. Meanwhile, 35 age- and gender-matched healthy controls (HC) were included. Bilateral diffusion-tensor imaging analysis along the perivascular space (DTI-ALPS) indices and enlarged perivascular spaces (EPVS) volume fraction in bilateral centrum semiovale, basal ganglia (BG), and midbrain were compared among the three groups. Correlations among the DTI-ALPS index and EPVS, as well as cognitive performance were analyzed. Additionally, we investigated the mediation effect of EPVS on DTI-ALPS and cognitive function. Results PDD converters had lower cognitive composites scores in the executive domains than did nonconverters ( P < 0.001). Besides, PDD converters had a significantly lower DTI-ALPS index in the left hemisphere ( P < 0.001) and a larger volume fraction of BG-PVS ( P = 0.03) compared to HC and PDD nonconverters. Lower DTI-ALPS index and increased BG-PVS volume fraction were associated with worse performance in the global cognitive performance and executive function. However, there was no significant mediating effect. Receiver operating characteristic analysis revealed that the DTI-ALPS could effectively identify PDD converters with an area under the curve (AUC) of 0.850. Conclusion The reduction of glymphatic activity, measured by the DTI-ALPS, could potentially be used as a non-invasive indicator in forecasting high risk of dementia conversion before the onset of dementia in PD patients.