Objective: This study seeks to better characterize postural tremor in ET and to investigate the effect of intention and visual input on the amplitude and frequency of the postural tremor.

Background: Patients with ET exhibit several different types of action hand tremor, including postural tremor (while voluntarily maintaining a position against gravity) and kinetic tremor (during voluntary movement in space) [1,2]. The current classification scheme does not include an intention component of postural tremor. Intention tremor is a subcategory of kinetic tremor and is defined as an increase in tremor amplitude as the patient approaches a visual target [1,3]. However, it is not known whether the postural tremor in ET can have an intention component. Characterization of the presence of intention component of postural tremor in ET is essential for genotype-phenotype correlations. Furthermore, different types of tremor in ET may respond differently to treatment modalities such as neuromodulation, therefore identifying the different types of tremor is essential for prediction of treatment response.

Method: Adults aged 18 and older with essential tremor are currently recruited from the movement disorders clinic at the University of Utah. Tremor measurements are obtained using accelerometry on the dorsal aspect of the hand, and EMG on the wrist flexors and extensors. Each subject’s tremor is recorded for a duration of forty seconds during several different tasks that included pointing towards a target or pointing forward without a target with eyes open or with eyes closed. The data is analyzed with custom-made MATLAB® scripts. The primary outcome is the change of tremor amplitude in different conditions (eyes open with target, eyes open without target and eyes closed without target). Data collection is currently ongoing.

Results: Preliminary analysis of 4 subjects shows that the mean tremor amplitude of the postural tremor is reduced when eyes are closed without a target (compared to eyes open without target) and increases when eyes are open with target (compared to eyes open without target). These changes are independent of the position of the hand (which is the same in all conditions). Formal statistical comparisons are pending.

Conclusion: An intention component may be present in postural tremor in ET. Further work is required to clarify whether the intention postural and intention kinetic tremor are pathophysiologically related.

References: [1] K. P. Bhatia et al., “Consensus statement on the classification of tremors. from the task force on tremor of the international parkinson and movement disorder society,” Movement Disorders, vol. 33, no. 1, pp. 75–87, 2017, doi: 10.1002/mds.27121.
[2] A. Lenka and E. D. Louis, “Revisiting the Clinical Phenomenology of ‘Cerebellar Tremor’: Beyond the Intention Tremor,” The Cerebellum, vol. 18, no. 3, pp. 565–574, Dec. 2018, doi: 10.1007/s12311-018-0994-6.
[3] E. J. Sternberg, R. N. Alcalay, O. A. Levy, and E. D. Louis, “Postural and Intention Tremors: A Detailed Clinical Study of Essential Tremor vs. Parkinson’s Disease,” Frontiers in Neurology, vol. 4, 2013, doi: 10.3389/fneur.2013.00051.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-intention-component-of-postural-tremor-in-essential-tremor/