Objective Action tremors affect many Parkinson’s disease (PD) patients and can significantly impair daily functioning. These tremors often persist despite dopaminergic therapy, while stereotactic surgery, though effective, is invasive and not suitable for all. Alternative treatment options are therefore needed. The STIL Orthosis is a wearable device developed to reduce forearm tremor. Its effectiveness has been shown in essential tremor, but its impact on PD-related action tremors remains unknown. This pilot study evaluates its effect in a small PD sample.

Methods: Three PD patients with action tremor participated in a sham-controlled, single-blind, crossover pilot study. Tremor severity was assessed in three conditions: baseline, sham, and STIL Orthosis. The primary outcome was the TETRAS score. Secondary outcomes included MDS-UPDRS tremor scores, tremor power (accelerometry and sEMG), and patient satisfaction (PGI-I).

Results: Although effects did not reach statistical significance (for n=3), a consistent trend toward tremor reduction was observed across clinical and accelerometry-based measures when comparing the STIL Orthosis to baseline. TETRAS scores decreased from baseline \(13 \pm 4.0\) and sham \(11 \pm 5.2\) to orthosis \(8.0 \pm 2.1\). MDS-UPDRS tremor scores similarly declined (baseline: \(7.3 \pm 0.9\), sham: \(5.3 \pm 1.7\), orthosis: \(3.3 \pm 0.9\)). Two participants showed reduced tremor power (up to \(55\%\) compared to baseline). EMG tremor power of the ECR and FCR muscles decreased by \(15\%\) and \(58\%\), respectively. All three participants reported slight improvement with the orthosis (PGI-I).

Conclusion: This pilot study indicates that the STIL Orthosis influences action tremor in PD. Larger studies are needed to assess its clinical significance.