Generalized EEG Slowing Across Phasic REM Sleep, Not Subjective RBD Severity, Predicts Neurodegeneration in Idiopathic RBD

Abstract

Si-Yi Gong,1,* Yun Shen,1,* Han-Ying Gu,1 Sheng Zhuang,1 Xiang Fu,1,2 Qiao-Jun Wang,1 Cheng-Jie Mao,1 Hua Hu,1 Yong-Ping Dai,1 Chun-Feng Liu1– 3 1Department of Neurology and Clinical Research Center of Neurological Disease, The Second Affiliated Hospital of Soochow University, Suzhou, People’s Republic of China; 2Institute of Neuroscience, Soochow University, Suzhou, Jiangsu, 215123, People’s Republic of China; 3Department of Neurology, Suqian First Hospital, Suqian, People’s Republic of China*These authors contributed equally to this workCorrespondence: Chun-Feng Liu; Yong-Ping Dai, Department of Neurology and Clinical Research Center of Neurological Disease, The Second Affiliated Hospital of Soochow University, Suzhou, People’s Republic of China, Tel [phone], Fax [phone], Email [email protected]; [email protected]: Idiopathic rapid eye movement sleep behavior disorder (iRBD) is the prodromal marker of α-synuclein degeneration with markedly high predictive value. We aim to evaluate the value of electroencephalography (EEG) data during rapid eye movement (REM) sleep and subjective RBD severity in predicting the conversion to neurodegenerative diseases in iRBD patients.Methods: At the baseline, iRBD patients underwent clinical assessment and video-polysomnography (PSG). Relative spectral power for nine frequency bands during phasic and tonic REM sleep in three regions of interest, slow-to-fast ratios, clinical and PSG variables were estimated and compared between iRBD patients who converted to neurodegenerative diseases (iRBD-C) and iRBD patients who remained disease-free (iRBD-NC). Receiver operating characteristic (ROC) curves evaluated the predictive performance of slow-to-fast ratios, and subjective RBD severity as assessed with RBD Questionnaire-Hong Kong.Results: Twenty-two (33.8%) patients eventually developed neurodegenerative diseases. The iRBD-C group showed shorter total sleep time (p < 0.001), lower stage 2 sleep percentage (p = 0.044), more periodic leg-movement-related arousal index (p = 0.004), increased tonic chin electromyelographic activity (p = 0.040) and higher REM density in the third REM episode (p = 0.034) than the iRBD-NC group. EEG spectral power analyses revealed that iRBD phenoconverters showed significantly higher delta and lower alpha power, especially in central and occipital regions during the phasic REM state compared to the iRBD-NC group. Significantly higher slow-to-fast ratios were observed in a more generalized way during the phasic state in the iRBD-C group compared to the iRBD-NC group. ROC analyses of the slowing ratio in occipital areas during phasic REM sleep yielded an area under the curve of 0.749 (p = 0.001), while no significant predictive value of subjective RBD severity was observed.Conclusion: Our study shows that EEG slowing, especially in a more generalized manner during the phasic period, may be a promising marker in predicting phenoconversion in iRBD, rather than subjective RBD severity.Keywords: idiopathic rapid eye movement sleep behavior disorder, neurodegenerative diseases, EEG slowing, RBD severity, phenoconversion, neuroprotective therapy

Keywords

• idiopathic rapid eye movement sleep behavior disorder
• neurodegenerative diseases
• eeg slowing
• rbd severity
• phenoconversion
• neuroprotective therapy