MRgFUS of the nucleus ventralis intermedius in essential tremor modulates functional connectivity within the classical tremor network and beyond

MR-guided focused ultrasound thalamotomy modulates cerebello-thalamo-cortical tremor network in essential tremor patients

Objectives

To advance the mechanistic understanding of changes occurring to brain connectivity after successful MR-guided Focused Ultrasound ventral intermediate nucleus (VIM) thalamotomy for essential tremor (ET).

Methods

This retrospective study included fifteen right-handed ET patients, who underwent successful unilateral VIM ablation and experienced improved hand tremor on their dominant hand. Resting-state fMRI scans were conducted both before and 1-year post-treatment for all participants. A seed-based whole brain resting-state functional connectivity (FC) analysis was performed, centering on tremor-related regions within the cerebello-thalamo-cortical (CTC) network, including the left and right ventral intermediate nucleus (VIM), primary motor cortex (M1H), and dentate nucleus (DN). The study examined both the changes in FC and their correlation with clinical outcomes evaluated using the Clinical Rating Scale for Tremor (CRST) at the 1-year post-treatment.

Results

ET patients demonstrated significant tremor improvement at the treated hand, which persisted throughout the 1-year study period. Compared with the baseline, FC of both left VIM and right VIM decreased in precentral gyrus and postcentral gyrus; FC of left M1 hand area increased in premotor cortex and supplemental motor area (SMA); and FC of left DN also increased in premotor cortex, SMA, M1, and anterior cingulate cortex (ACC). Association analysis between changes in left VIM functional connectivity and contralateral hand tremor scores revealed a significant negative correlation in the bilateral precentral gyrus, superior parietal lobule, precuneus, occipital cortex, and middle prefrontal cortex. Conversely, a significant positive correlation was observed in the frontal orbital cortex, right insular cortex, temporal pole, hippocampus, left lingual gyrus, right cerebellar lobules IV/V, left cerebellar lobule VI, and vermis IV/V.

Conclusion

Our findings of altered functional connectivity within the cerebello-thalamo-cortical network, encompassing regions involved in motor, sensory, attention, visual, and visuospatial functions, and its association with hand tremor improvement suggest that targeting functional connectivity abnormalities may be a potential approach for alleviating tremor symptoms in ET patients.

Beyond the cerebello-thalamo-cortical tract: Remote structural changes after VIM-MRgFUS in essential tremor

INTRODUCTION

Essential tremor (ET) is a progressive disorder characterized by altered network connectivity between the cerebellum, thalamus, and cortical regions. Magnetic Resonance-guided Focused Ultrasound (MRgFUS) of the ventral intermediate nucleus (VIM) is an effective, minimally invasive treatment for ET. The impact of MRgFUS interventions on regional Gray Matter Volume (GMV) are as yet not well understood.

METHODS

Forty-six patients with medication-resistant ET underwent unilateral VIM-MRgFUS. Voxel-based morphometry was applied to investigate GMV changes over a time span of 6 months in the whole brain and the thalamus in particular to investigate local and distant effects.

RESULTS

Clinically, contralateral tremor significantly decreased by 68 % at 6 months following MRgFUS. In addition to local GMV decreases in thalamic nuclei (VIM, ventral lateral posterior, centromedian thalamus and pulvinar), VBM revealed remote GMV decreases in the ipsilesional insula and the anterior cingulate cortex as well as the contralesional middle occipital gyrus. Increased GMV was found in the right superior and middle temporal gyrus, as well as in the left inferior temporal gyrus. There was no significant correlation between regional GMV declines and tremor improvement. However, temporal volume increases were associated with improved motor-related functional abilities and quality of life outcomes.

CONCLUSION

Our findings implicate distributed structural changes following unilateral VIM-MRgFUS. Structural losses could reflect Wallerian degeneration of VIM output neurons or plasticity due to decreased sensory input following tremor improvement.

Profiling functional networks identify activation of corticostriatal connectivity in ET patients after MRgFUS thalamotomy

BACKGROUND

MR-guided focused ultrasound (MRgFUS) thalamotomy is a novel and effective treatment for medication-refractory tremor in essential tremor (ET), but how the brain responds to this deliberate lesion is not clear.

OBJECTIVE

The current study aimed to evaluate the immediate and longitudinal alterations of functional networks after MRgFUS thalamotomy.

METHODS

We retrospectively obtained preoperative and postoperative 30-day, 90-day, and 180-day data of 31 ET patients subjected with MRgFUS thalamotomy from 2018 to 2020. Their archived resting-state functional MRI data were used for functional network comparison as well as graph-theory metrics analysis. Both partial least squares (PLS) regression and linear regression were conducted to associate functional features to tremor symptoms.

RESULTS

MRgFUS thalamotomy dramatically abolished tremors, while global functional network only sustained immediate fluctuation within one week after the surgery. Network-based statistics have identified a long-term enhanced corticostriatal subnetwork by comparison between 180-day and preoperative data (P = 0.019). Within this subnetwork, network degree, global efficiency and transitivity were significantly recovered in ET patients right after MRgFUS thalamotomy compared to the pre-operative timepoint (P < 0.05), as well as hemisphere lateralization (P < 0.001). The PLS main component significantly accounted for 33.68 % and 34.16 % of the total variances of hand tremor score and clinical rating scale for tremor (CRST)-total score (P = 0.037 and 0.027). Network transitivity of this subnetwork could serve as a reliable biomarker for hand tremor score control prediction at 180-day after the surgery (β = 2.94, P = 0.03).

CONCLUSION

MRgFUS thalamotomy promoted corticostriatal connectivity activation correlated with tremor improvement in ET patient after MRgFUS thalamotomy.