Study objectives: To compare the amounts of REM sleep without atonia (RSWA) between patients with REM sleep behavior disorder (RBD), "isolated loss of REM atonia," narcolepsy, and control subjects and determine if there were threshold values for the amount of RSWA that differentiate each group from controls.
Methods: Retrospective analyses of polysomnography (PSG) records were used employing strict quantitative criteria for the measurement of phasic and tonic EMG activity during REM sleep. The PSG recordings of 47 individuals were analyzed (RBD 16, isolated loss of REM atonia 11, narcolepsy 10, control 10).
Results: Patients with the diagnosis of isolated loss of REM atonia had significantly lower levels of EMG activity during REM sleep than those with RBD but higher than control subjects. RSWA was higher in narcolepsy than in loss of REM atonia but lower than for RBD patients. Receiver operating characteristic (ROC) curves provided threshold values with high specificity and sensitivity in all patient groups with a cutoff value ≥ 1.22% (100% correctly classified) for phasic and ≥ 3.17% for tonic (92% correctly classified) EMG activity in RBD.
Conclusion: Quantification of REM sleep EMG activity can successfully differentiate RBD and isolated loss of REM atonia patients from controls. The consistently increased amount of RSWA in patients with narcolepsy indicates that this can be an additional marker for a diagnosis of narcolepsy. Longitudinal studies of patients with isolated loss of REM atonia are needed to evaluate if these patients are at risk of developing RBD or neurodegenerative disorders.
Keywords: EMG; REM sleep; REM sleep behavior disorder (RBD); narcolepsy; polysomnography.