Objective: Identify network alterations in essential tremor (ET) after magnetic resonance–guided focused ultrasound (MRgFUS) treatment using independent component analysis (ICA).

Background: MRgFUS has been approved by the FDA to treat patients with “medication-refractory tremor by thermal ablation of the designated area in the brain responsible for the movement disorder symptoms (ventralis intermedius, VIM)” of the thalamus. Whether it is indeed a lesion of the VIM or the cerebello-thalamo-cortical tract (CTT) or both is difficult to decipher and has not been fully explored yet. Resting-state fMRI (rs-fMRI) is a neuroimaging technique to explore functional networks. ICA is a robust data driven approach to explore functional networks without a priory hypothesis.

Method: We enrolled 12 consecutive patients with medication-refractory right-sided tremor, treated with contralateral MRgFUS. The ExAblate Neuro device creates a precise temperature zone within the thalamus: temperatures of ~50C will inactivate the tremor sensitive zone only briefly. The treatment procedure was started using standard stereotaxic coordinates (14mm lateral to midline, 1 mm above AC-PC, 0,25(AC-PC) anterior) but a permanent lesion was created in the location which was identified by the patient as being most efficacious and devoid of side effects. For each patient among others, demographic data, tremor severity (Fahn-Tolosa-tremor rating scale, TRS) and 3T rs-fMRI were acquired one day prior and three days after treatment. Rs-fMRI images were preprocessed and analysed using the FMRIB Software Library (www.fmrib.ox.ac.uk/fsl). Group-level ICA was implemented to explore functional networks across all participants before and after MRgFUS; a paired t-test was applied across all networks to investigate brain connectivity alterations after MRgFUS (P < 0.05).

Results: All patients showed reduced tremor amplitude immediately after treatment. Improvement in tremor severity ranged from 42 to 62% (TRS). ICA across all networks revealed decreased resting-state functional connectivity mainly restricted to the CTT (e.g. thalamus, primary motor cortex, dorsolateral prefrontal cortex and contralateral cerebellum). Other networks showed no alterations in functional connectivity.

Conclusion: The preliminary results suggest that treatment with MRgFUS affects mainly the CTT, while other networks remained unaffected.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/resting-state-fmri-in-essential-tremor-after-mrgfus-treatment/