Cognitive study on Chinese patients with idiopathic REM sleep behavior disorder

Aims: We investigated cognitive abnormalities using standard tests in Chinese patients with idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) compared with those in normal controls.

Methods: Twenty-three patients with iRBD and 23 normal controls were included in this study. All of the participants underwent one night of video-polysomnography (PSG) monitoring to certify REM sleep without atonia or abnormal behaviors. The cognitive assessments were administered and scored according to a standard procedure, including global cognitive screening and attention/processing speed, executive function, memory, language, and visuospatial ability testing.

Results: Patients with iRBD had similar scores of the Mini Mental State Examination (MMSE) but lower Montreal Cognitive Assessment (MoCA) scores compared with controls (p>0.05, p=0.013). The iRBD patients performed poorly on verbal memory tests, which included immediate recall (p<0.001), delayed recall (p<0.001), and false recognitions (p=0.002) of the Rey Auditory Verbal Learning Test (RAVLT). The visual memory and visuospatial abilities were also impaired in iRBD patients, as reflected by the copy (p=0.005) and immediate (p=0.004) and delayed (p=0.003) recall of the Rey-Osterrieth complex figure, although no difference was found after Bonferroni correction. The duration of RBD was 6.98±8.10years. After controlling for age, the duration of RBD was only correlated with the Trail Making Test B (r=0.613, p=0.045) and block design (r=-0.667, p=0.025).

Conclusions: Impaired verbal memory was observed in iRBD patients who identified as Chinese. MoCA could detect cognitive abnormalities and serve as a screening scale. The present study further confirmed cognitive deficits in iRBD as an early clinical marker in the prodromal stage of synucleinopathy.