Tremor suppression following treatment with MRgFUS: skull density ratio consistency and degree of posterior dentatorubrothalamic tract lesioning predicts long-term clinical outcomes in essential tremor

Abstract

ObjectivesMagnetic resonance-guided focussed ultrasound (MRgFUS) is an incisionless ablative procedure, widely used for treatment of Parkinsonian and Essential Tremor (ET). Enhanced understanding of the patient- and treatment-specific factors that influence sustained long-term tremor suppression could help clinicians achieve superior outcomes via improved patient screening and treatment strategy.MethodsWe retrospectively analysed data from 31 subjects with ET, treated with MRgFUS at a single centre. Tremor severity was assessed with parts A, B and C of the Clinical Rating Scale for Tremor (CRST) as well as the combined CRST. Tremor in the dominant and non-dominant hand was assessed with Hand Tremor Scores (HTS), derived from the CRST. Pre- and post-treatment imaging data were analysed to determine ablation volume overlap with automated thalamic segmentations, and the dentatorubrothalamic tract (DRTT) and compared with percentage change in CRST and HTS following treatment.ResultsTremor symptoms were significantly reduced following treatment. Combined pre-treatment CRST (mean: 60.7 ± 17.3) and HTS (mean: 19.2 ± 5.7) improved by an average of 45.5 and 62.6%, respectively. Percentage change in CRST was found to be significantly negatively associated with age (β = −0.375, p = 0.015), and SDR standard deviation (SDRSD; β = −0.324, p = 0.006), and positively associated with ablation overlap with the posterior DRTT (β = 0.535, p < 0.001). Percentage HTS improvement in the dominant hand decreased significantly with older age (β = −0.576, p < 0.01).ConclusionOur results suggest that increased lesioning of the posterior region of the DRTT could result in greater improvements in combined CRST and non-dominant hand HTS, and that subjects with lower SDR standard deviation tended to experience greater improvement in combined CRST.

Magnetic Resonance–Guided Focused Ultrasound for Treatment of Essential Tremor: Ventral Intermediate Nucleus Ablation Alone or Additional Posterior Subthalamic Area Lesioning?

“…This is consistent with the growing body of evidence that Vim lesions with more posterior extension may provide improved tremor suppression in patients with ET. 14 , 24 , 26 The COG coordinates of the Vim ablation in the single‐target group were about 25% of the AC–PC distance, anterior to the PC, consistent with the coordinates conventionally used to target the Vim, compared with 28% in patients who required a lesion in the PSA. This finding was confirmed by analysis of the Vim ablation overlap with the tractography‐derived DRTT, where patients who required lesioning of the PSA had significantly lower Vim ablation overlap with the DRTT, particularly in the posterior fibers, and on average greater overlap between the PSA ablation and the DRTT.…”

“… 23 The pretreatment dMRI data were processed to reconstruct the dentatorubrothalamic tract (DRTT) for retrospective analysis. DRTT fiber bundles representing the anterior, middle, and posterior DRTT components in an unbiased template space, as described previously, 24 were also generated and used for tractography analysis of the Vim ablation location.…”