gms | German Medical Science

Objective: Preceding studies found a main influence of the dentato-rubro-thalamic tract (DRTT) in the mechanisms of Essential Tremor. However, the influence of different parts of the DRTT, consisting of a ipsilateral and a decussating part, has not been investigated yet with respect to tremor reduction. Additionally, in only a few studies, probabilistic tractography was used. The aim of this study was to evaluate the influence of the ipsilateral and the intersecting part of the DRTT on clinical tremor improvement in Essential Tremor.

Methods: A cohort of 10 patients having received bilateral DBS of the VIM between 2016 and 2019 was analysed retrospectively. Preoperative DWI scans were performed on patients under general anaesthesia at a 3T MRI scanner with 64 gradient directions. We used a workflow for probabilistic fibre tracking using FSL 6.0.3 (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/). Electrodes were reconstructed using LeadDBS (https://www.lead-dbs.org/). We calculated distance maps from the different parts of the DRTT and correlated distances to the pole coordinates with clinical data on tremor reduction derived from neurological single pole testing.

Results: 3 patients with current-steered systems were excluded from further statistical analysis due to inadequate comparability. Regarding postural tremor, contacts with good clinical response significantly correlated with lower distances to both parts of the DRTT (non-decussating p<0,05; crossing p<0,01). Good contacts were located closer to the crossing part of the DRTT. Bivariate correlation analysis showed significant results for both parts of the DRTT with a higher Pearson-coefficient for the crossing part (Pearson 0,295 vs. 0,429). Regarding intentional tremor, contacts with good clinical response significantly correlated with lower distances to the crossing part (p<0,01). In contrast, the non-decussating part did not show significant results. Bivariate correlation analysis resulted in significant results for both parts of the DRTT with a higher Pearson-coefficient for the crossing part (Pearson 0,356 vs. 0,405).

Conclusion: Pathophysiologically, growing evidence suggests a disruption of cerebellar-thalamic-basal ganglia-motor cortex networks in Essential Tremor. Therefore, the DRTT is considered to play a major role in these mechanisms. Our data suggest an involvement of both parts of the DRTT in tremor reduction indicating mediation of DBS-effects by both fibre bundles, even if the crossing part showed stronger correlations with good clinical responses.