The paradoxical impact of periodic limb movements on isolated REM sleep behavior disorder patients

Recently, the α-synuclein origin and connectome model described two types of Parkinson's disease: "brain-first" and "body-first" subtypes. We aimed to investigate the role of periodic limb movements during sleep (PLMS) in identifying these subtypes starting from a prodromal stage of α-synucleinopathies. 191 patients with isolated REM sleep behavior disorder (iRBD) underwent video-polysomnography (vPSG), questionnaires, clinical interview, and neuropsychological battery. Patients who presented PLMS index (PLMSi) > 15 were compared with patients presenting PLMSi ≤ 15 on clinical questionnaires, vPSG, and neuropsychological domains with age as a covariate. Correlations were performed between PLMSi and vPSG and neuropsychological domains in both groups of iRBD. 48.2% of patients presented PLMSi > 15. iRBD subgroup with PLMSi > 15 performed better than the iRBD subgroup with PLMSi ≤ 15 in the executive function domain. In patients with PLMSi > 15 negative correlations were observed between PLMSi and some neuropsychological domains (memory, language, and executive function). Moreover, this subgroup was older and their PLMSi was positively correlated with wake-after-sleep onset and inversely correlated with total sleep time and sleep efficiency, suggesting a detrimental effect of PLM on sleep also in this cohort. Patients with PLMSi > 15 are characterized by a more preserved cognitive status, despite a more disrupted sleep. PLMSi could be explored in longitudinal studies concerning the "brain-first" and "body-first" model.