Correlation between fractional anisotropy changes in the targeted ventral intermediate nucleus and clinical outcome after transcranial MR-guided focused ultrasound thalamotomy for essential tremor: results of a pilot study

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OBJECTIVE

This study evaluated changes of fractional anisotropy (FA) in the ventral intermediate nucleus (VIM) of the thalamus after transcranial MR-guided focused ultrasound (TcMRgFUS) thalamotomy and their associations with clinical outcome.

METHODS

Clinical and radiological data of 12 patients with medically refractory essential tremor (mean age 76.5 years) who underwent TcMRgFUS thalamotomy with VIM targeting were analyzed retrospectively. The Clinical Rating Scale for Tremor (CRST) score was calculated before and at 1 year after treatment. Measurements of the relative FA (rFA) values, defined as ratio of the FA value in the targeted VIM to the FA value in the contralateral VIM, were performed before thalamotomy, and 1 day and 1 year thereafter.

RESULTS

TcMRgFUS thalamotomy was well tolerated and no long-term complications were noted. At 1-year follow-up, 8 patients demonstrated relief of tremor (improvement group), whereas in 4 others persistent tremor was noted (recurrence group). In the entire cohort, mean rFA values in the targeted VIM before treatment, and at 1 day and 1 year after treatment, were 1.12 ± 0.15, 0.44 ± 0.13, and 0.82 ± 0.22, respectively (p < 0.001). rFA values were consistently higher in the recurrence group compared with the improvement group, and the difference reached statistical significance at 1 day (p < 0.05) and 1 year (p < 0.01) after treatment. There was a statistically significant (p < 0.01) positive correlation between rFA values in the targeted VIM at 1 day after thalamotomy and CRST score at 1 year after treatment. Receiver operating characteristic curve analysis revealed that the optimal cutoff value of rFA at 1 day after thalamotomy for prediction of symptomatic improvement at 1-year follow-up is 0.54.

CONCLUSIONS

TcMRgFUS thalamotomy results in significant decrease of rFA in the targeted VIM, at both 1 day and 1 year after treatment. Relative FA values at 1 day after treatment showed significant correlation with CRST score at 1-year follow-up. Therefore, FA may be considered a possible imaging biomarker for early prediction of clinical outcome after TcMRgFUS thalamotomy for essential tremor.

ABBREVIATIONS AC-PC = anterior commissure–posterior commissure; AUC = area under the curve; CRST = Clinical Rating Scale for Tremor; DTI = diffusion tensor imaging; FA = fractional anisotropy; FOV = field of view; rFA = relative FA; ROC = receiver operating characteristic; ROI = region of interest; SDR = skull density ratio; TcMRgFUS = transcranial MR-guided focused ultrasound; VIM = ventral intermediate nucleus.

Article Information

Correspondence Yoshihiro Muragaki: Institute of Advanced Biomedical Engineering and Science, Tokyo Women’s Medical University, Tokyo, Japan. ymuragaki@twmu.ac.jp.

INCLUDE WHEN CITING Published online February 15, 2019; DOI: 10.3171/2018.10.JNS18993.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Location of the ROI for posttreatment FA measurements in the VIM of both thalami using axial isotropic DTI (A) and a color-coded vector map (B) at the level of the AC-PC line. Of note, ROI was set at the presumed VIM in vicinity to the pyramidal tract (PT), but not at the thalamotomy lesion itself. Figure is available in color online only.

  • View in gallery

    Graph of dynamic changes in rFA in the targeted VIM after TcMRgFUS thalamotomy in cases with clinical improvement (circles) and recurrence of tremor (squares) at 1 year after treatment. Horizontal bars indicate median values for each group.

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    Correlation between rFA values in the targeted VIM at 1 day after TcMRgFUS thalamotomy, and CRST improvement ratio at 1 year after treatment. Dashed line defines the cutoff value of 0.54 suggested by ROC analysis for prediction of good and durable symptomatic relief. Cases with clinical improvement (circles) and recurrence of tremor (squares) at 1-year follow-up are shown.

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