Glymphatic dysfunction in isolated REM sleep behavior disorder

Objectives This study aimed to evaluate glymphatic‐system function in patients with isolated rapid eye movement sleep behavior disorder (iRBD) in comparison with healthy controls by using diffusion tensor imaging (DTI) along the perivascular space (DTI‐ALPS) method. We hypothesized that patients with iRBD may show glymphatic‐system dysfunction. Methods We retrospectively enrolled 18 patients with iRBD and 18 age‐ and sex‐matched healthy controls. All participants underwent DTI magnetic resonance imaging (MRI) using the same 3T MRI scanner, and the DTI‐ALPS index was calculated using DTI data. We evaluated the differences in the DTI‐ALPS index between patients with iRBD and healthy controls. In addition, we evaluated the correlation between the DTI‐ALPS index and demographic and polysomnographic characteristics. Results The DTI‐ALPS index was significantly different between the groups; it was significantly lower in patients with iRBD than in healthy controls (1.5647 vs. 1.7612, p = .0157). The index did not correlate with demographic and polysomnographic characteristics, including age, Epworth Sleepiness Scale score, total sleep time, sleep efficiency, sleep stage N1 ratio, stage N2 ratio, stage N3 ratio, stage R ratio, and total apnea‐hypopnea index. Conclusion The DTI‐ALPS index was significantly lower in patients with iRBD than in healthy controls, indicating the presence of glymphatic‐system dysfunction in patients with iRBD. Our study also suggests that the DTI‐ALPS index could serve as a biomarker for evaluating glymphatic‐system function in neurological disorders.