Objective: To assess the prevalence and characteristics of video-polysomnography (PSG) confirmed REM sleep behaviour disorder (RBD) in patients with Essential Tremor (ET).

Background: ET has classically been defined by the presence of tremor in the absence of other neurological symptoms or signs. This notion has been challenged by studies suggesting the presence of non-tremor signs in ET patients. A recent questionnaire based investigation [1] showed a high prevalence of probable RBD, a parasomnia closely linked with α-synucleinopathies. This finding remains to be confirmed by polysomnography.

Method: 49 consecutive patients fulfilling the 2017 MDS Consensus Statement criteria for ET  were screened with the REM sleep behavior disorder symptom questionnaire (RBDSQ) and underwent PSG if they score above cut off (>4). Tremor features were collected from patient clinical files. Another 6 ET patients, who had undergone PSG for spontaneous complaints of RBD, were added to this population. RBD was diagnosed based in the ICSD criteria. Sleep structure, sleep breathing disturbance, muscular activity and motor events during REM sleep (ME) data were collected from PSG files and compared to that of patients with Parkinson’s Disease and RBD (PD-RBD) and idiopathic RBD (iRBD).

Results: 13 patients (26.5%) presented with RBDSQ score  > 4: 3 refused PSG, 5  had RBD (ET-RBD), and in 3 patients PGS was inconclusive for lack of REM sleep. The final prevalence of PSG confirmed RBD was 11.6%. Compared to ET-non-RBD, ET-RBD presented with a higher prevalence of rest tremor component (5 (100%) vs 14 (34.2%) , p=0.009) (no other significant differences regarding tremor features). PSG was positive for RBD in 3 of the patients who underwent PSG for RBD spontaneous  complaints and inconclusive in 1. In PSG, ET-RBD presented with less total sleep time, longer sleep latency and lower ME global severity (compared to iRBD, p=0.038,  p=0.005 and p=0.04 respectively) shorter N2 duration (compared to iRBD, p=0.036 and PDRBD, p=0.024).

Conclusion: Prevalence of RBD in ET was higher than what was described in the general population. An higher prevalence of rest tremor in ET-RBD patients could signify a significant relation between this sub-group of ET patients and Parkinson’s Disease. ET-RBD PSG parameters were closer to PD-RBD than to iRBD, suggesting that sub-group of ET patients to be an intermediate state between iRBD and full blown PD.

References: [1] Barbosa R, Mendonça M, Ladeira F, Miguel R, Bugalho P. Probable REM-Sleep Behavior Disorder and Dysautonomic Symptoms in Essential Tremor. Tremor Other Hyperkinet Mov (N Y). 2017 Dec 29;7:522. doi: 10.7916/D8Z61VW5

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-prevalence-and-features-of-rem-sleep-behaviour-disorder-in-essential-tremor-a-polysomnography-study/