Smaller pineal gland is associated with rapid eye movement sleep behavior disorder in Alzheimer’s disease

Background To investigate the association between pineal gland volume and symptoms of rapid eye movement (REM) sleep behavior disorder (RBD) in Alzheimer’s disease (AD) patients without any feature of dementia with Lewy bodies. Methods We enrolled 296 community-dwelling probable AD patients who did not meet the diagnostic criteria for possible or probable dementia with Lewy bodies. Among them, 93 were amyloid beta (Aβ) positive on 18 F-florbetaben amyloid brain positron emission tomography. We measured RBD symptoms using the REM Sleep Behavior Disorder Screening Questionnaire (RBDSQ) and defined probable RBD (pRBD) as the RBDSQ of 5 or higher. We manually segmented pineal gland on 3T structural T1-weighted brain magnetic resonance imaging. Results The participants with pRBD had smaller pineal parenchyma volume (VPP) than those without pRBD ( p < 0.001). The smaller the VPP, the more severe the RBD symptoms ( p < 0.001). VPP was inversely associated with risk of prevalent pRBD (odds ratio = 0.909, 95% confidence interval [CI] = 0.878–0.942, p < 0.001). Area under the receiver operator characteristic curve for pRBD of VPP was 0.80 (95% CI = 0.750–0.844, p < 0.0001). These results were not changed when we analyzed the 93 participants with Aβ-positive AD separately. Conclusions In AD patients, reduced pineal gland volume may be associated with RBD.