Mechanical vibration does not systematically reduce the tremor in essential tremor patients

Essential tremor (ET) is a major cause of disability and is not efectively managed in half of the patients. We investigated whether mechanical vibration could reduce tremor in ET by selectively recruiting aferent pathways. We used piezoelectric actuators to deliver vibratory stimuli to the hand and forearm during long trials (4min), while we monitored the tremor using inertial sensors. We analyzed the efect of four stimulation strategies, including diferent constant and variable vibration frequencies, in 18 ET patients. Although there was not a clear homogeneous response to vibration across patients and strategies, in most cases (50–72%) mechanical vibration was associated with an increase in the amplitude of their tremor. In contrast, the tremor was reduced in 5–22% of the patients, depending on the strategy. However, these results are hard to interpret given the intrinsic variability of the tremor: during equally long trials without vibration, the tremor changed signifcantly in 67% of the patients (increased in 45%; decreased in 22%). We conclude that mechanical vibration of the limb does not have a systematic efect on tremor in ET. Moreover, the observed intrinsic variability of the tremor should be taken into account when designing future experiments to assess tremor in ET and how it responds to any intervention.

Tis work was funded by the projects ESSENTIAL (DPI2015-72638-EXP) and NeuroMOD (DPI2015-68664-C4-1-R), fnanced by the Spanish Ministry of Economy, Industry and Competitiveness, and by RoboCity2030- DIH-CM, Madrid Robotics Digital Innovation Hub, S2018/NMT-4331, funded by “Programas de Actividades I+D en la Comunidad de Madrid” and cofunded by Structural Funds of the EU. Julio S. Lora-Millan was in receipt of a Training Program for Academic Staf fellowship (FPU16/01313) by the Ministry of Science, Innovation and Universities of the Government of Spain. Juan A. Gallego received funding from the EU Commission (FP7- PEOPLE-2013-IOF-627384) and from the Community of Madrid (Atracción de Talento Grant 2017-T2/TIC5263).