Hippocampal atrophy in untreated de novo Parkinson's disease with obstructive sleep apnea.

Over the course of Parkinson's disease (PD), there is considerable intersubject variability in gray matter (GM) loss across a wide range of subcortical structures and cortical areas, which is often predictive of the clinical trajectory of the disease. The biological or clinical factors underlying these individual differences are not well understood. Obstructive sleep apnea (OSA) is a sleep-disordered breathing that is associated with an increased risk of cognitive impairment and neurodegeneration. In this study, we investigated whether moderate-to-severe OSA in untreated de novo PD is linked to more severe GM atrophy compared to PD without OSA and a group of controls. High-resolution structural 3 T MRI T1 and T2-weighted scans were used to estimate subcortical GM volumes and hippocampal subfields, and to perform vertex-wise analyses of cortical thickness and cortical surface area. We found that the presence of OSA was associated with a significant bilateral reduction in hippocampal volume, particularly in the CA1, CA3, and subicular regions, an effect specifically observed in PD patients and not in the control group. These findings suggest that the co-occurrence of OSA and PD may be related to early structural brain changes, highlighting the importance of timely OSA diagnosis and management to potentially delay cognitive decline in PD.