Objective: To investigate the effectiveness of closed-loop sensory-specific peripheral electrical stimulation (CLS) in reducing tremor and modulating tremorogenic neural drive.

Background: Sensory peripheral electrical stimulation is a promising approach for suppressing hand tremors in Essential Tremor (ET). Our group developed CLS, which adaptively targets the antagonist muscle based on real-time electromyographic (EMG) activity (Fig 1). When delivered percutaneously, CLS has shown tremor reduction lasting up to 24 hours.[1] However, the neuromuscular mechanisms underlying CLS remain unclear.

Method: A 78-year-old male with ET underwent CLS and control (CON, no stimulation) interventions, with a three-week washout between sessions. CLS was delivered transcutaneously at the wrist for 40 minutes. Pre-, post-, and 24 hours post-intervention, the participant completed spiral drawing and handwriting tasks, with tremor severity assessed by a blinded movement disorder specialist using TETRAS.[2] High-density EMG was also recorded from the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) of the tremorogenic arm during two postural tasks (arms extended forward and flexed close to the chest) to extract motor unit firing patterns. Cumulative spike trains (CSTs) of FCR and ECR motor units were computed to estimate neural drives. Intermuscular coherence in the tremor band (4–12 Hz) and phase differences between tremorogenic neural drives were analyzed using CSTs.

Results: TETRAS scores indicated that CLS resulted in the greater reduction in tremor severity immediately after stimulation. Tremor intensity increased at 24 hours but remained lower than pre-stimulation levels (Fig 2). A total of 123 motor units were analyzed. Following CLS, peak intermuscular coherence in the tremor band decreased, whereas it increased after CON (Table 1). Up to 24 hours post-intervention, CLS shifted the phase difference of tremorogenic neural drives toward an in-phase pattern, similar to that previously observed in ET patients at rest. [3] In contrast, CON resulted in out-of-phase neural drives, a pattern typically seen in ET patients during postural tasks.[3]

Conclusion: Transcutaneous CLS effectively suppressed tremor for up to 24 hours, likely due to neuroplastic changes at the spinal level that modulate both the magnitude and phase of tremorogenic neural drives between wrist flexors and extensors.

Table 1

Figure 1

Figure 2

References: 1. Pascual-Valdunciel A, Gonzalez-Sanchez M, Muceli S, Adan-Barrientos B, Escobar-Segura V, Perez-Sanchez JR, Jung MK, Schneider A, Hoffmann K-P, Moreno JC, Grandas F, Farina D, Pons JL, Barroso FO. Intramuscular Stimulation of Muscle Afferents Attains Prolonged Tremor Reduction in Essential Tremor Patients. IEEE Trans Biomed Eng 68: 1768–1776, 2021. doi: 10.1109/TBME.2020.3015572.
2. Elble RJ. The Essential Tremor Rating Assessment Scale. .
3. Gallego JA, Dideriksen JL, Holobar A, Ibanez J, Glaser V, Romero JP, Benito-Leon J, Pons JL, Rocon E, Farina D. The Phase Difference Between Neural Drives to Antagonist Muscles in Essential Tremor Is Associated with the Relative Strength of Supraspinal and Afferent Input. J Neurosci 35: 8925–8937, 2015. doi: 10.1523/JNEUROSCI.0106-15.2015.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/closed-loop-electrical-stimulation-reduces-tremor-and-decreases-tremorogenic-neural-drives-in-essential-tremor-a-case-report/