Study on the relationship between cognitive function and sleep structure in patients with idiopathic rapid eye movement sleep behavior disorder

Objective To summarize the characteristics of cognitive function and sleep structure in patients with idiopathic rapid eye movement sleep behavior disorder (iRBD) and to explore the correlation between them. Methods Total 73 patients with iRBD who visited Fujian Medical University Union Hospital from August 2018 to August 2021 were included, all of whom underwent neuropsychological tests and polysomnography monitoring. Pearson and partial correlation analyses were used to explore correlation between cognitive function and sleep structure parameters. Results 1) Neuropsychological tests: iRBD patients had lower Mini ⁃ Mental State Examination (MMSE; t = ⁃ 3.703, P = 0.000), Montreal Cognitive Assessment (MoCA; t = ⁃ 4.811, P = 0.000), Verbal Fluency Test (VFT)⁃number of correct words (t = ⁃ 2.171, P = 0.032) than control group. Trail Making Test (TMT)⁃A (t = 2.500, P = 0.014), TMT⁃B (t = 2.430, P = 0.016) and Stroop Color Word Test (SCWT)⁃A (t = 2.507, P = 0.013), SCWT⁃B (t = 15.042, P = 0.000), SCWT⁃ C (t = 27.228, P = 0.000) completion times were longer than control group. 2) Polysomnography monitoring: total sleep time (t = 2.699, P = 0.008), sleep efficiency (Z = ⁃ 2.103, P = 0.035), number of sleep stage transitions (t = 3.965, P = 0.000), proportion of non⁃rapid eye movement sleep stage 1 (N1 stage) to total sleep time (t = 2.887, P = 0.005), periodic limb movement of sleep index (PLMSI; t = ⁃ 2.917, P = 0.004), periodic limb movement⁃related arousal index (Z = ⁃ 2.291, P = 0.022), and total arousal index (Z = ⁃ 2.609, P = 0.009) were higher than those in control group, and the time of wakefulness after sleep was less than those in control group (t = ⁃ 2.230, P = 0.027). 3) Correlation between cognitive function and sleep structure parameters: MoCA score was negatively correlated with the percentage of N1 stage (r = ⁃ 0.184, P = 0.035), and positively correlated with the percentage of N2 stage (r = 0.173, P = 0.049); SCWT⁃B completion time was negatively correlated with the number of awakenings (r = ⁃ 0.186, P = 0.033); SCWT⁃C completion time was positively correlated with the number of sleep phase transitions (r = 0.212, P = 0.015) and the percentage of N1 stage (r = 0.181, P = 0.039); VFT⁃number of correct words was negatively correlated with the periodic limb movement of wake index (PLMWI; r = ⁃ 0.216, P = 0.018); the number of correct China⁃Rey Auditory Verbal Learning Test (C⁃RAVLT) immediate recall was positively correlated with the rapid eye movement (REM) sleep latency (r = 0.183, P = 0.045); the number of correct C⁃RAVLT delay recall was negatively correlated with the PLMWI (r = ⁃ 0.196, P = 0.032) and PLMSI (r = ⁃ 0.180, P = 0.049); the Clock Drawing Test was positively correlated with sleep latency (r = 0.192, P = 0.035) and REM sleep latency (r = 0.199, P = 0.029), and negatively correlated with the percentage of REM sleep (r = ⁃ 0.189, P = 0.038). The Beck Depression Inventory (BDI) score was positively correlated with total sleep time (r = 0.347, P = 0.000), sleep efficiency (r = 0.319, P = 0.000) and the percentage of REM sleep (r = 0.204, P = 0.026), and negatively correlated with the time of wakefulness after sleep (r = ⁃ 0.280, P = 0.002) and the percentage of N1 stage (r = ⁃ 0.299, P = 0.001). Conclusions Patients with iRBD have cognitive dysfunction mainly manifested by decreased attention, executive function and language function, and sleep structural disorders may affect the cognitive function of such patients.