Hippocampal Enlargement and White Matter Hyperintensities in Obstructive Sleep Apnea Patients

Abstract

AbstractBackgroundObstructive sleep apnea (OSA), which results from recurrent collapses of the upper airway system, affects around 27% of the geriatric population with mild cognitive impairment (MCI) and causes intermittent hypoxia and sleep fragmentation (Mubashir et al., 2019). Prior research suggests that OSA results in brain ischemic preconditioning, causing hippocampal enlargement due to adaptive hippocampal neurogenesis (Rosenzweig et al., 2013). OSA has also been linked to increased white matter hyperintensities (WMHs) through hypoxic‐ ischemic injury, which contribute to cognitive decline in dementias such as Alzheimer’s disease (Zacharias et al., 2021). Previous research necessitates studying the effects of apnea in an elderly population with MCI.MethodIn the Memories2 study, subjects aged 55‐85 underwent a polysomnography and were assigned to the no OSA (OSA‐) group if their apnea‐hypopnea index (AHI) was <5 events/hour or to the OSA (OSA+) group if their AHI was ≥15. Amnestic MCI status was determined with a neuropsychological battery using standard criteria. The subjects received an optional MRI, in which hippocampal and WMH volumetry were derived from a T1‐weighted structural scan and a whole‐brain fluid‐attenuated inversion recovery (FLAIR) scan, respectively. Statistical analyses (two‐sample t‐tests and Wilcoxon‐Mann‐Whitney test) were performed to understand group differences in hippocampal volume and WMH at baseline. Hippocampal volume data (N = 131) was obtained for 67 OSA+ and 64 OSA‐ subjects. WMH data (N = 129) was obtained for 66 OSA+ and 63 OSA‐ subjects.ResultOSA+ subjects had significantly greater right hippocampal volume (p = 0.0374) and left hippocampal volume (0.0336) than the OSA‐ subjects. OSA+ subjects also had higher levels of white matter hyperintensities as compared to the OSA‐ subjects (p = 0.0340) (Table 1).ConclusionIncreased WMH burden is suggestive of hypoxic‐ischemic injury and supports the hypothesis that hippocampal enlargement may be a response to intermittent hypoxia in OSA. These findings reveal the need for early evaluation for sleep apnea. The future direction of this work includes analyzing the group differences adjusting for covariates, detecting and verifying outliers, and rerunning analyses with the complete baseline data. Future data from the Memories2 study will examine the effects of OSA treatment in MCI patients using continuous positive airway pressure (CPAP).