Sleep scoring in neurodegenerative diseases: Towards new rules

Standard sleep scoring criteria often fail to accurately describe sleep architecture in patients with neurodegenerative diseases, due to disease-related alterations in neurophysiological variables. Although this issue has long been recognised, no specific guidelines or adapted rules to address these challenges has been developed. A more accurate characterisation of sleep structure alterations is essential, as these changes may serve as dynamic and non-invasive biomarkers in patients with neurodegenerative diseases. This review presents a recently proposed alternative sleep scoring system, developed through collaboration between sleep centres in Bologna and Barcelona, specifically tailored to neurodegenerative disorders. The system introduces additional stages-Abnormal Wake, Subwake, Undifferentiated NREM (UNREM), Poorly Structured N2 (P-S N2), REM without low-amplitude mixed-frequency activity (RWL), and REM without rapid eye movements (RWR)- to describe wake and sleep neurophysiological patterns that cannot be classified using conventional international scoring rules. The method was tested on complex video-polysomnography recordings from nine patients with Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, demonstrating excellent interrater agreement. This novel scoring system enables a more detailed and specific analysis of sleep structure in patients with neurodegenerative diseases, and, while it seems promising, it needs to be tested on a larger number of patients.