Neuroimaging correlates of cognitive stages in Parkinson's disease: A multimodal MRI study

OBJECTIVE: Cognitive impairment in Parkinson's disease (PD) ranges from mild executive deficits to dementia. This exploratory study aimed to characterize neuroanatomical correlates of cognitive subtypes to improve understanding of disease-related cognitive heterogeneity. Structural and diffusion-weighted MRI were used to examine preliminary patterns of brain-behavior relationships across PD cognitive stages.

METHODS: 38 patients with PD and 10 healthy controls underwent neuropsychological testing, structural MRI, and diffusion-weighted imaging (dMRI). Patients with PD were classified as cognitively intact (PDi), mild cognitive impairment (PD-MCI), or dementia (PDD) using Movement Disorder Society guidelines. Volumetric and dMRI analyses focused on hippocampal volume and white matter integrity in key tracts.

RESULTS: Volumetric analyses revealed smaller hippocampi in PDD (Left M = 3.71 cm³, Right M = 3.69 cm³) compared to PD-MCI and PDi (p < .03). Patients with PDD had significantly larger lateral ventricles (Left M = 21.17 cm³, p = .05). dMRI analyses showed reduced fractional anisotropy (FA) in the left posterior limb of the internal capsule (p = .002) and increased apparent diffusion coefficient (ADC) in the same region (p = .003). These findings reflect stage-related correlates of cognitive impairment rather than predictive markers of future decline. Cognitive domains correlated with FA and ADC values in the internal capsule and splenium.

CONCLUSIONS: Present findings revealed isolated regions of volume loss and white matter abnormalities in patients with PDD as compared to other cognitive subtypes. Hippocampal atrophy and white matter disruption were observed in patients with PDD and should be interpreted as correlates of advanced cognitive impairment rather than predictive biomarkers. Longitudinal studies are needed to determine whether these imaging features track or precede cognitive decline.