Quantitative REM Sleep without Atonia in Parkinson's Disease and Essential Tremor

Background: Rapid eye movement (REM) sleep behavior disorder (RBD) occurs occasionally in essential tremor (ET), but polysomnographic REM sleep without atonia (RSWA) analyses have been sparse. Objective: To characterize the amount and distribution of polysomnographic RSWA, the electrophysiologic substrate of RBD, in patients with Parkinson's disease (PD) and ET. Methods: We analyzed quantitative RSWA in 73 patients: PD (23), ET (23), and age-sex-matched controls (27). None had dream-enactment behavior history or received antidepressants. Phasic, tonic, "any," and phasic-burst duration RSWA measures were calculated in the submentalis (SM) and anterior tibialis (AT) muscles. The automated REM atonia index (RAI) was also determined. Statistical analysis was performed by Kruskal-Wallis rank-sum and Mann-Whitney tests. Results: SM phasic RSWA was significantly greater for PD than ET patients and controls (12.5% +/- 12.8% vs. 4.9% +/- 6.7%, 3.9% +/- 2.6%), as was SM "any" (13.54% +/- 14.30% vs. 5.2% +/- 7.6%, 4.2% +/- 2.6%). RAI was significantly lower in PD than in ET and controls (0.78 +/- 0.23 vs. 0.92 +/- 0.09 vs. 0.90 +/- 0.17, P <= 0.005), but no different between ET and controls. AT phasic and "any" RSWA was similar between the 3 groups. ET and control RSWA was similar in all measures. Two ET patients (8.7%) had SM RSWA similar to PD patients. Conclusions: Elevated SM RSWA distinguished PD from ET in patients without dream-enactment symptoms and occurs frequently in PD patients, and in isolated tremor suggests underlying synucleinopathy. Prospective studies will further validate these findings.