Objective: To investigate the effectiveness of MRI-guided cerebellar transcranial ultrasound stimulation (TUS) for the treatment of primary orthostatic tremor (POT).

Background: POT is a rare movement disorder manifested through high frequency (13 – 18 Hz) tremor of the weight bearing limb. POT has been linked to abnormal cerebellar activity in previous studies. TUS is a novel non-invasive brain stimulation technique that permits stimulation with high spatial focality and can accurately reach deep brain structure. Therefore, TUS can precisely target the cerebellum and can be a superior technique for the management of POT. We investigate the effects of TUS targeting the dentate nucleus (DN) of the cerebellum on POT symptoms.

Method: Preliminary data from 3 POT patients are presented. Patients underwent an anatomical MRI scan to allow MRI guided TUS and modelling of the ultrasound beam. In the second visit, patients underwent baseline assessments that consisted of the Orthostatic Tremor Severity Scale, electromyography (EMG) recordings, and posturography. Patients then received 120 s of theta burst TUS, an excitatory protocol, on each hemisphere while sitting. Assessments were conducted at 5, 15 and 30 mins after the stimulation together with the patient’s Global Impression of Severity. The tremor frequency, derived from EMG, was measured using power spectrum analysis. The change in amplitude was estimated by the variation in power of the peak frequency.

Results: Baseline measurements from the tibialis anterior (TA) muscles from 3 patients show peak tremor frequency consistent with OT (median = 15.49 Hz) with high degree of coherence between left and right TA muscles (coherence = 1). No changes in median peak frequency and frequency range relative to baseline was found following TUS.  However, there was a trend toward increased peak frequency power in TA, relative to baseline, as a function of time after TUS (Post 5 mins = 1.30; Post 10 mins = 1.88; Post 30 mins =1.67; values represent ratio to baseline).

Conclusion: Although preliminary, our results show a potential effect of TUS in increasing the power of peak frequency up to 30 mins after stimulation.  The increase in power is likely due to the excitatory protocol used and reflects higher amplitude of the tremor in the TA muscle. Data collection is ongoing. This study is the first stage in developing a therapeutic protocol for the management of POT using TUS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/preliminary-report-of-cerebellar-transcranial-focused-ultrasound-for-primary-orthostatic-tremor/