Introduction Idiopathic rapid eye movement behaviour disorder (iRBD) is a strong predictor for the development of alpha-synucleinopathies. Electroencephalographic (EEG) oscillations known as sleep spindles are found during non-rapid eye movement sleep. These bursts of neural oscillatory activity are known to decrease in patients with alpha-synucleinopathies. We hypothesized that that sleep spindle density would differ in patients with iRBD with and without an alpha-synucleinopathy.
Methods This was a retrospective cohort study comprised of sixty male participants, all of whom were diagnosed with RBD. Sleep spindles were manually identified by an experienced technologist at a central scalp location (C3-A2) in 20 patients with iRBD who converted to an alpha-synucleinopathy, 20 age-matched patients with secondary RBD and 20 patients with a diagnosis of iRBD who had not converted.
Results Patients who phenoconverted showed a significant decrease in sleep spindle activity compared to patients with secondary RBD (p<0.05) at time of diagnosis. Spindle density was lower in patients who had phenoconverted. Sleep spindle density reduction was significant in patients with PD; there were too few patients with MSA and DLB to determine differences in spindle density counts.
Discussion This is the first study to look into multiple alpha-synucleinopathies to investigate sleep spindle density changes. As a statistical significance was found between the spindle density of patients who had gone on to develop a neurodegenerative disorder and those who had secondary RBD, when examining spindle density in the second half of the night (p=0.026) (figure 1). It follows that sleep spindle density may have the potential to be a prodromal marker for phenoconversion and underlying alterations in sleep networks that lead to a clinical diagnosis of an alpha-synucleinopathy.
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