Objective: To investigate the non-motor profiles of essential tremor (ET) and essential tremor-plus (ET-plus) syndromes.

Background: The recently established concept of differentiating ET from ET-plus syndrome has brought many controversies since it was based solely on clinical grounds with no differences in etiology, pathology, or prognosis. Motor phenotypes of the disease could be indicative of a different etiopathological process and a solid ground to reclassify ET patients.

Method: We conducted a retrospective study in a tertiary Neurology referral center including ET patients. We categorized our patients into ET syndrome as defined by the movement disorder society 2017 classification of tremors and into ET-plus syndrome defined by the association of other motor signs to bilateral upper limbs action tremor. We assessed non-motor signs (NMS) using the non-motor severity scale (NMSS), a large battery of cognitive tests, clinical and electrophysiological study of the autonomic nervous system along with the evaluation of sleep disturbances.

Results: A total of 163 patients were included (sex-ratio of 0.94, mean disease duration=13.7±11 years). One third were classified into the ET-plus syndrome (rest tremor 23%, bradykinesia 14%, rigidity 9%, parkinsonism 4%, questionable dystonic posture in 9 % and one case of ataxia). Mean NMSS was higher within the ET-plus group (50 vs. 32 points, p=0.052). Comparing ET and ET-plus showed no statistically significant differences while assessing cognitive function. However, ET-plus presented more with cognitive dysfunction (62% vs. 53%, p=0.264), executive dysfunction (52% vs. 38%, p=0.308), attention problems (47% vs. 44%, p=0.799), episodic memory impairment (44% vs 42%, p=0.712) and depression (50% vs 49 %, p=0,386). Finally, no significant differences were noted while comparing sleep dysautonomic features and sleep disturbances between both groups.

Conclusion: The absence of significant differences of the non-motor profile between ET and ET-plus implies a probable common etiopathogenic process centered around cerebellar dysfunction and supported further by the cognitive profile of both groups is in line with the features of the cerebellar cognitive affective syndrome. Genetic and anatomopathological studies are required to further investigate and reclassify the ET spectrum.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/non-motor-signs-in-essential-tremor-and-essential-tremor-plus-syndromes/