Impaired cerebrovascular-cerebrospinal fluid coupling is associated with non-motor features of Lewy body disease

The temporal coupling between cortical blood-oxygen-level-dependent (BOLD) activity and CSF inflow has recently been proposed as a non-invasive marker of glymphatic function, a brain-wide clearance system closely linked to sleep, neuromodulatory regulation and neurodegeneration. Reduced BOLD-CSF coupling has been previously reported in Parkinsons disease but its characterization in dementia with Lewy bodies, regional specificity and relevance to shared neuropsychiatric symptoms remain unclear. Using resting-state functional MRI, we quantified global and regional BOLD-CSF coupling in 39 participants, including 17 with Parkinsons disease (mean age 61.4 years), 10 with dementia with Lewy bodies (mean age 72.8 years) and 12 healthy controls (mean age 66.2 years), and examined the relationship with clinical and cognitive measures, as well as volumetric measures of the subcortical ascending arousal network. Parkinsons disease and dementia with Lewy bodies patients both demonstrated weaker global BOLD-CSF coupling compared to controls, with no detectable difference between patient groups. Coupling reductions were most pronounced within the unimodal and attentional networks, encompassing regions that are particularly vulnerable in Lewy body disease. Weaker coupling was associated with the severity of hallucinations and cognitive fluctuations, poorer nocturnal sleep quality and impaired attentional working memory, but not overall motor symptom burden. Associations between BOLD-CSF coupling and basal forebrain and brainstem volumes were observed, though partially age-dependent, suggesting a complex interaction between neuromodulatory system degeneration, ageing and brain-fluid dynamics. Our results provide preliminary evidence that disrupted temporal coordination between cerebrovascular activity and CSF inflow may contribute to the fluctuating neuropsychiatric features of Lewy body disease and highlight the utility of BOLD-CSF coupling as a dynamic in vivo proxy of glymphatic function. Replication in larger cohorts incorporating multimodal imaging and biomarkers of pathology will be essential to validate these findings and determine whether brain-fluid dysregulation represents a potentially modifiable therapeutic target.