Sleep in essential tremor: A comparison with normal controls and Parkinson's disease patients

Background: Recent studies have shed light on non-motor features of ET, such as depressive symptoms and cognitive changes, which might be attributed to pathophysiological changes in the brains of ET patients. Given these brain changes, we explored sleep abnormalities in ET patients. Methods: Sleep was assessed using the Epworth Sleepiness Scale (ESS) and the Pittsburgh Sleep Quality Index (PSQI) in 120 ET cases, 120 normal controls, and 40 PD cases. Results: The mean ± SD (median) ESS score increased from normal controls (5.7 ± 3.7 (5.0)), to ET cases (6.8 ± 4.6 (6.0)), to PD cases (7.8 ± 4.9 (7.0)), test for trend p=0.03. An ESS score >10 (an indicator of greater than normal levels of daytime sleepiness) was observed in 11 (9.2%) normal controls, compared to 27 (22.5%) ET cases and 10 (25.0%) PD cases (p=0.008 when comparing all three groups, and p=0.005 when comparing ET to normal controls). The global PSQI score was 7.8 ± 2.8 (7.5) in controls, 8.0 ± 3.3 (8.0) in ET cases, and 9.9 ± 3.9 (10.0) in PD cases. The ET case-control difference was not significant (p=0.8), yet in a test for trend, PD cases had the highest PSQI score (most daytime sleepiness), followed by ET (intermediate), and lowest scores in controls (p=0.02). Conclusions: Some sleep scores in ET were intermediate between those of PD cases and normal controls, suggesting that a mild form of sleep dysregulation could be present in ET.