Cerebellum crus II cortical thickness as a cognitive brain reserve in Parkinson's disease

Although the cerebellum plays a role in the pathophysiology of motor symptoms in Parkinson's disease (PD), its association with cognition remains unclear. We investigated whether the cognition-related cerebellar lobules are associated with baseline and longitudinal cognition in PD.

In this retrospective cohort study, we enrolled 203 drug-naïve patients with PD who underwent dopamine transporter (DAT) scans, high-resolution brain magnetic resonance imaging, and detailed neuropsychological testing at baseline. We analyzed the association of cerebellar lobular volume and cortical thickness with baseline cognitive domain composite scores and future PD dementia (PDD) conversion using multivariable linear regression analysis and the Cox proportional hazards model, respectively. We further tested whether striatal DAT availability moderated the cerebellar-cognitive associations.

The volumes of cognitive cerebellar lobules were not significantly associated with cognitive domain scores. However, the cortical thickness of Crus II was positively associated with the baseline visuospatial score (β = 0.208, p = 0.004). Greater Crus II cortical thickness was also associated with lower risk of PDD conversion (hazard ratio [HR], 0.197; 95% confidence interval [CI], 0.071-0.544; p = 0.002). A Crus II x striatal DAT interaction was significant for both the baseline visuospatial score (β = -0.255, p = 0.001) and PDD conversion (HR = 0.61, p = 0.016). The effect of Crus II cortical thickness on PDD conversion was not mediated by the baseline visuospatial score.

The cortical thickness of Crus II may serve as a cognitive brain reserve and be useful for predicting the risk of dementia conversion in PD.