Objective: To investigate the effects of transcutaneous spinal cord stimulation (tSCS) in patients with essential and dystonic tremor, and to assess whether baseline spectral regularity predicts response to stimulation.

Background: Essential tremor (ET) syndrome is clinically and pathophysiologically heterogeneous, and the distinction from dystonic tremor is not always clear. This heterogeneity likely contributes to variable therapeutic responses and reflects the limited understanding of tremor mechanisms. We previously showed that tSCS delivered at each patient’s tremor frequency (TF-tSCS) could reduce tremor amplitude in a subgroup of patients with ET.

Method: Fifteen patients with postural tremor (8 ET, 3 ET plus, 4 dystonic tremor) underwent postural tremor recordings during TF-tSCS. Tremor amplitude was quantified from accelerometry and compared with baseline. Responses were defined by percent change in tremor amplitude relative to baseline. Baseline EMG recordings were analyzed to derive spectral metrics of tremor regularity, including peak prominence, harmonic content, peak width, and tremor frequency variability. Associations between baseline spectral features and stimulation-induced amplitude changes were assessed.

Results: At the group level, TF-tSCS did not reduce tremor amplitude and a non-significant increase was observed during the second half of stimulation. Individual responses were heterogeneous: four patients showed >15% tremor reduction (two statistically significant), all with ET or ET plus. Four patients showed >15% tremor increase, predominantly in dystonic tremor, including two with significant worsening. Two patients (one dystonic tremor, one ET plus) showed phase entrainment between tremor and stimulation, accompanied by increased tremor amplitude. Baseline tremor regularity metrics did not appear to predict amplitude response.

Conclusion: Responses to TF-tSCS were heterogeneous and bidirectional across tremor syndromes. Tremor reduction was observed mainly in ET and ET plus, whereas worsening was more frequent in dystonic tremor. Baseline spectral regularity metrics did not predict stimulation response. These findings highlight the heterogeneity of tremor syndromes and the need for improved physiological or clinical stratification to guide neuromodulation therapies.

References: Pascual-Valdunciel A et al. Frequency-Selective Suppression of Essential Tremor via Transcutaneous Spinal Cord Stimulation. Movement Disorders. 2024.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/differential-tremor-responses-to-transcutaneous-spinal-cord-stimulation-across-tremor-syndromes/