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

Abstract

Essential tremor (ET) is a major cause of disability and is not effectively managed in half of the patients. We investigated whether mechanical vibration could reduce tremor in ET by selectively recruiting afferent pathways. We used piezoelectric actuators to deliver vibratory stimuli to the hand and forearm during long trials (4 min), while we monitored the tremor using inertial sensors. We analyzed the effect of four stimulation strategies, including different 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 significantly in 67% of the patients (increased in 45%; decreased in 22%). We conclude that mechanical vibration of the limb does not have a systematic effect 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.

Peripheral electrical stimulation to reduce pathological tremor: a review

“…Selectively timed activation of Ia afferents and cutaneous afferents through electrical stimulation in synchronization with tremorgenic electrophysiological activity should be further explored to better understand and exploit spinal reflex mechanisms and inhibitory pathways for tremorgenic activity reduction [16,27,36,42]. It is worth mentioning that one study, out of the scope of this review, proposed mechanical vibration as an alternative method to acutely suppress tremor via stimulation of afferent fibers [64]. No tremor reduction was achieved for the patients with ET, which might imply that electrical stimulation is more suitable than mechanical vibration to selectively activate afferent fibers interacting with tremorgenic circuitries.…”

A Review on Wearable Technologies for Tremor Suppression

“…Based on the results obtained by these electrical afferent stimulation devices, Lora-Millan et al ( 87 ) evaluated a new hypothesis to suppress tremorous movements in ET patients by using mechanical afferent stimulation instead of low-level electrical stimulation. Their work was based on the hypothesis that sensory responses from Pacinian corpuscles could provide a pathway to modulate the circuits that mediate tremor in ET.…”

The Validation of Tremor-Cancelling Technologies Needs a Multidisciplinary Consensus Statement

“…We would also like to underline the lack of independent testing outside the initial ones and also the scant publications of negative studies, which are crucial to understand important methodological and technological issues that could surely result in the improved development of otherwise encouraging solutions. 4,5 Finally, in this review, some methodological aspects are discussed, such as the body location, the clinical outcomes used and some technological features of certain tremor-cancelation prototypes. However, in our opinion, the authors missed a key methodological issue, which is the inherent variability of tremor intensity during testing.…”

“…6 This is something that we have consistently observed in various research studies related to tremor-cancelling systems even after modifying the test length and the temporal windows used in the analyses. 7-11 Importantly, nonstimulation periods may even show greater tremor-intensity fluctuations when testing a novel device 4 as compared to those used for stimulation. This issue can confound the interpretation of testing protocols that do not include long enough nonstimulation periods, although their ideal duration also remains to be defined.…”