Objective: To describe the prevalence of rapid eye movement disorder (RBD) among essential tremor (ET) patients and its correlates in terms of associated motor and non-motor signs.

Background: With the emergence of the new classification of tremors, ET represents a spectrum of phenotypes that may overlap with other neurodegenerative disorders such as Parkinson’s disease (PD). RBD is an established marker of synucleinopathy and a potential marker of conversion to PD among ET patients.

Method: We recruited patients diagnosed with ET and ET-plus syndrome based on the latest classification of tremors by the Movement Disorder Society. We assessed associated motor signs including extrapyramidal and cerebellar features. As for the non-motor signs, we evaluated cognitive functions by using a large battery of tests. We assessed the presence of RBD via the RBD-SQ. SCOPA-AUT score was used to evaluate clinical dysautonomia.

Results: We have included 163 patients. The mean disease duration was 13.7 years with a sex ratio equal to 0.94. RBD was noted in 14.5% of cases. Regarding associated motor signs, the presence of RBD correlated with bradykinesia (p=0.046) and rest tremor (0.032). As for the non-motor signs, RBD correlated with the presence of attention impairment (p=0.026) and clinical dysautonomia (p=0.001): urinary dysfunction (p=0.042), cardiovascular dysfunction (p=0.028) and sexual dysfunction (p=0.045).

Conclusion: The prevalence of RBD lines with previous studies with a rate ranging from 13% to 43.5%. Such dissimilarity could be explained by the variability of the assessment method. In line with previous literature, we have established that RBD was associated to the presence of extrapyramidal signs and dysautonomic features which do all represent established prodromal markers of phenoconversion to PD. This may indicate an underlying synucleionopathy among RBD-ET patients. In fact, the main efferent connections of the locus coeruleus (LC), where Lewy bodies aggregate, are directed towards Purkinje cells helping to maintain their inhibitory output. Thus, Lewy body pathology among RBD-ET is closely intertwined with the main pathological hallmark of cerebellar dysfunction in ET which is purkinjopathy.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/phenotypic-presentation-of-essential-tremor-patients-with-rapid-eye-movement-disorder/