Longitudinal MRI study of hippocampal subfields Morphometry in early Parkinson's disease

Parkinson's Disease (PD) is a neurodegenerative disorder characterised by motor and non-motor symptoms. Cognitive impairment is a prominent non-motor feature.

This study investigated hippocampal subfield shape deformation and atrophy in early-stage PD using spherical harmonic-based shape analysis.

Our cohort of early PD patients (n = 146; disease duration = 14.9 ± 9.5 months; 44% Female) and matched healthy controls (HC) (n = 59; 56% Female) underwent magnetic resonance imaging (MRI) and cognitive assessments at baseline and 2-year follow-up. Hippocampal subfields were segmented in FreeSurfer; shape analysed with SPHARM-PDM.

Baseline shape analysis identified morphological changes in Cornu Ammonis 1 (CA1), CA3, subiculum, and fimbria in early PD patients compared to HCs, despite no baseline volumetric differences. Longitudinally, volume decline/atrophy was observed in the right whole hippocampus, right CA1, and left fimbria. In the PD-Mild Cognitive Impairment (PD-MCI) subgroup, localised shape deformations in CA1, CA3, Granule Cell Layer and Molecular Layer of the Dentate Gyrus (GC-ML-DG), and fimbria were observed at baseline when compared to PD-Normal Cognition (PD-NC), with longitudinal left fimbria decline observed and associated with cognitive deterioration in this cohort, especially with visuospatial and executive function domains.

These findings suggest that, in this cohort, shape analysis may capture baseline subfield differences that are not apparent using volumetric measures in early-stage PD. This study suggests hippocampal subfield shape analysis may help characterize early structural differences related to cognition in PD. The left fimbria warrants further study as a candidate imaging marker of cognitive vulnerability in PD.