Surface-Based Morphometric Changes of The Hippocampus At Global and Subfield Levels Of Early-Stage Parkinson’s Disease

Parkinson’s Disease (PD) is a prevalent and progressive neurodegenerative condition. Previous research has primarily identified the hippocampus as a key affected brain region in PD, with or without dementia, and even in cases without cognitive impairment. However, most earlier studies have treated the hippocampus as a singular global structure, focusing mainly on its overall volume or surface area alterations. There is a notable gap in detailed research on local morphological changes in the hippocampus during the early stages of PD. Our study involved T1-weighted MRI scans of forty-eight early-stage PD patients and forty-eight age-and sex-matched healthy controls. Initially, we assessed the global volume and surface area of the bilateral hippocam-pus. Subsequently, we delved into the detailed morphometric changes at the subfield scale of the bilateral hippocampus using a novel surface-based morphometric approach. Our findings indicate no significant global differences, except in the surface area ratio between the left and right hippocampus. However, significant deformations, primarily atrophic regions, were observed at the subfield level, particularly in the CA1 subfield, followed by the CA2-CA3 and Subiculum subfields. In summary, our study reveals that the CA1 sub-field is most vulnerable in early-stage PD, with atrophy likely progressing from CA1 to other subfields. This study also underscores that global metrics, such as volume or surface area, lack the sensitivity to accurately detect hippocampal deformations in early-stage PD.