Insomnia and somnolence in idiopathic RBD: a prospective cohort study

Although some sleep disorders are markers of prodromal Parkinson's disease and dementia with Lewy bodies, it is unclear whether insomnia and somnolence can predict disease. We assessed a large cohort of patients with idiopathic rapid eye movement sleep behavior disorder and age/sex matched controls, comparing the Epworth sleepiness scale, the Insomnia Severity Index, the Pittsburgh Sleep Quality Index, and polysomnographic variables. In those with repeated scales, we assessed change over time. Finally, we assessed whether sleep abnormalities predicted defined neurodegenerative disease. The 151 patients (age = 65.9, 75% male) completed sleep scales and were included. Epworth scores were similar between patients and controls (7.0+/-4.6 vs. 7.2 +/-4.7, p = 0.77), and did not progress with time (change = + 0.46+/-2.1, p = 0.45). Epworth scores were similar between those who developed neurodegenerative disease and those remaining disease-free (6.7+/-4.4 vs. 7.1+/-4.7, p = 0.70). Pittsburgh Index scores were higher in patients than controls (7.2+/-3.8 vs. 4.9+/-3.4, p = 0.004), mainly driven by the sleep disturbance/medication components (reflecting rapid eye movement sleep behavior disorder symptoms/treatment). Baseline Pittsburgh scores did not predict conversion to neurodegeneration, although sleep duration increased over time in those converting to neurodegenerative disease (+ 0.88+/-1.32 h, p = 0.014). Insomnia index scores were higher in patients than controls (10.0+/-5.5 vs. 6.35+/-4.66, p < 0.001), but declined over time (-1.43+/-5.09, p = 0.029) particularly in those converting to neurodegenerative disease. Finally, on polysomnogram, those with increased tonic rapid eye movement had higher risk of developing defined neurodegenerative disease (HR = 1.88, p = 0.039). In summary, we found that somnolence and insomnia do not predict neurodegeneration in idiopathic rapid eye movement sleep behavior disorder. As neurodegeneration progresses through prodromal stages, patients may have increasing sleep drive and duration.