Non-invasive Cervical Vagus Nerve Stimulation Improves Digital Spiral Tests in Essential Tremor: An Open Label Pilot Study
Massimo Marano1, Rogan Magee4, Francesca Blasi2, Gaia Anzini2, Fioravante Capone2, Riccardo Ricciuti5, Matteo Maria Ottaviani6, Vincenzo Di Lazzaro3
1Operative Research Unit of Neurology, Neurophysiology, Neurobiology and Psychiatry, 2Operative research unit of Neurology, Neurophysiology, Neurobiology and Psychiatry, Università Campus Bio-Medico di Roma, 3Università Campus Bio-Medico di Roma, 4Penn Medicine, 5Department of Neurosurgery, Azienda Ospedaliera San Camillo - Forlanini, 6Università Politecnica delle Marche
Objective:
To explore the potential benefit of non-invasive transcutaneous vagal nerve stimulation in treatment of essential tremor.
Background:
Essential tremor (ET) is the most common cause of action tremor, affecting ~1% of the global population. Medical treatments including propranolol and primidone are limited by dose-related side effects. Preliminary studies have revealed that implantable vagus nerve stimulation (VNS) improves kinematic ET parameters. However, the efficacy and tolerability is limited. Non-invasive options represent a promising alternative.
Design/Methods:
Seventeen subjects (11 female, aged 66.2 ± 13.9 years, disease duration 18.5 ± 12.6 years) with essential tremor were recruited for a pilot study. All subjects were treated with 4 consecutive cycles of 25 Hz GammaCORE cVNS targeting the cervical portion of the left vagus nerve. Total Fahn-Tolosa-Marin scale (FTM) scores were collected before and after treatment. All subjects completed n=10 Archimedes spiral drawings using a digital spiral analysis platform, using both their dominant and non-dominant hands, before and after treatment. Four previously validated spiral metrics (spiral width variability index mean and standard, mean change in radian over change in time, and mean change in radian over change in angle) were collected. Data were analyzed using linear mixed models with subject as a random effect.
Results:
FTM score did not differ after stimulation (log(OR) = 0.03, 95% CI [-1.2,1.2]; ordinal logistic regression). Treatment was associated with significant decreases in spiral width variability indices and delta radian per delta time and delta angle (mean SWVI model: β, 95% CI = -1.4 [-2.0,-0.81]; standard deviation SWVI model: β, 95% CI = -7.3 [-10,-4.6]; mean Δr/Δθ model: β, 95% CI = -0.06 [-0.10,-0.02]; mean (Δr/Δt) model: β, 95% CI = -0.18 [-0.26,-0.10]; linear mixed effects models).
Conclusions:
Treatment with non-invasive cVNS improved previously validated metrics for the analysis of Archimedes spirals. This pilot study highlights the potential benefit of non-invasive cVNS in ET.
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