Abstract
This study proposes and clinically tests intramuscular electrical stimulation below motor threshold to achieve prolonged reduction of wrist flexion/extension tremor in Essential Tremor (ET) patients. The developed system consisted of an intramuscular thin-film electrode structure that included both stimulation and electromyography (EMG) recording electrodes, and a control algorithm for the timing of intramuscular stimulation based on EMG (closed-loop stimulation). Data were recorded from nine ET patients with wrist flexion/extension tremor recruited from the Gregorio Marañón Hospital (Madrid, Spain). Patients participated in two experimental sessions comprising: 1) sensory stimulation of wrist flexors/extensors via thin-film multichannel intramuscular electrodes; and 2) surface stimulation of the nerves innervating the same target muscles. For each session, four of these patients underwent random 60-s trials of two stimulation strategies for each target muscle: 1) selective and adaptive timely stimulation (SATS) - based on EMG of the antagonist muscle; and 2) continuous stimulation (CON) of target muscles. Two patients underwent SATS stimulation trials alone while the other three underwent CON stimulation trials alone in each session. Kinematics of wrist, elbow, and shoulder, together with clinical scales, were used to assess tremor before, right after, and 24 h after each session. Intramuscular SATS achieved, on average, 32% acute (during stimulation) tremor reduction on each trial, while continuous stimulation augmented tremorgenic activity. Furthermore, tremor reduction was significantly higher using intramuscular than surface stimulation. Prolonged reduction of tremor amplitude (24 h after the experiment) was observed in four patients. These results showed acute and prolonged (24 h) tremor reduction using a minimally invasive neurostimulation technology based on SATS of primary sensory afferents of wrist muscles. This strategy might open the possibility of an alternative therapeutic approach for ET patients.
Highlights
P ATHOLOGICAL tremor is the most prevalent movement disorder globally and the fundamental clinical sign of Essential Tremor (ET), a medical disorder with an estimated prevalence of 4% of the population over 65 years [1]
This study demonstrates the feasibility of modulating muscle afferents through intramuscular (IntraStim) selective and adaptive timely stimulation (SATS) to decrease tremor
Short-term effects were observed for all six patients who underwent SATS IntraStim trials (P01-P06). We conclude that these effects are not attributed to a placebo effect due to four main reasons: 1) tremor reduction was significantly higher using intramuscular than surface stimulation; 2) SATS IntraStim was the only condition achieving significant acute tremor reduction; 3) non-specific stimulation usually led to tremor aggravation; 4) patients were blinded to the stimulation strategy applied and, in some cases, they did not feel any sensation when stimulation was delivered
Summary
P ATHOLOGICAL tremor is the most prevalent movement disorder globally and the fundamental clinical sign of Essential Tremor (ET), a medical disorder with an estimated prevalence of 4% of the population over 65 years [1]. PASCUAL-VALDUNCIEL et al.: INTRAMUSCULAR STIMULATION OF MUSCLE AFFERENTS ATTAINS PROLONGED TREMOR REDUCTION and primidone [4], the average reduction of tremor using these medications is only approximately 50%, and one in three patients ends up discontinuing treatment [4], [5]. For these cases, there are second-line therapies, such as deep brain stimulation (DBS) or high-intensity focused ultrasound (HIFU) [6]. A potential alternative that has been explored is peripheral electrical stimulation
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