Rem Sleep Without Atonia (RSWA) and neuropsychological function in REM sleep Behavior Disorder

Introduction REM sleep Behavior Disorder (RBD) is a parasomnia characterized by the presence of REM Sleep Without Atonia (RSWA) resulting in abnormal and violent behaviors. Evidence from literature demonstrates that Isolated RBD (IRBD) is a prodromal phase of neurodegenerative diseases with high conversion rates in synucleinopathies. The aim of the study is to investigate the relationship between cognitive impairment and RSWA in IRBD patients. Methods 35 IRBD patients and 18 healthy controls (HC) were recruited, underwent a complete polysomnography (PSG) as well as a comprehensive neuropsychological evaluation. Moreover, IRBD patients were divided into two groups based on the presence or absence of Mild Cognitive Impairment (MCI). The PSG were analyzed by a scorer, blind to subjects’ diagnosis, to quantify the RSWA of six different indices of muscle activity extracted by phasic and tonic events recorded in different time series (miniepochs of 2 or 3 seconds, or epochs of 30 seconds) and muscle combinations (flexor digitorum superficialis, mentalis and tibialis muscles). Results Comparative analyses showed that the percentages of RSWA were significantly higher in the IRBD group than HC. The best discriminative power was obtained by the combination of phasic and tonic events recorded in micro epochs of 3 seconds from the mentalis muscle and flexor digitorum superficialis (IRBD 0.787 ±0.195, HC 0.306±0.183, p<0.001; area under the curve=0.952). The correlation analyses between RSWA indices and neuropsychological measures in the IRBD group showed a significant negative correlation (rspearman=-0.374, p=0.029) between the scores at the Mini-Mental State Examination (MMSE) and the phasic events index recorded by the combination of mentalis and bilateral tibialis muscles in micro epochs of 2 seconds. Finally, comparative analyses between MCI and no-MCI with regard to RSWA indices did not demonstrate significant differences. However, MCI indices were systematically higher in comparison to no-MCI for each index taken into account. Conclusion These results suggest an association between RSWA and cognitive functioning that may provide an insight on the relationship between the loss of atonia during REM sleep and neurodegenerative processes.