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Introduction: Drug-resistant essential tremor (ET) can benefit from open standard stereotactic procedures, such as deep-brain stimulation or radiofrequency thalamotomy. Non-surgical candidates can be offered either high-focused ultrasound (HIFU) or radiosurgery (RS). All procedures aim to target the same thalamic site, the ventro-intermediate nucleus (e.g., Vim). The mechanisms by which tremor stops after Vim RS or HIFU remain unknown. We used voxel-based morphometry (VBM) on pretherapeutic neuroimaging data and assessed which anatomical site would best correlate with tremor arrest 1 year after Vim RS.Methods: Fifty-two patients (30 male, 22 female; mean age 71.6 years, range 49–82) with right-sided ET benefited from left unilateral Vim RS in Marseille, France. Targeting was performed in a uniform manner, using 130 Gy and a single 4-mm collimator. Neurological (pretherapeutic and 1 year after) and neuroimaging (baseline) assessments were completed. Tremor score on the treated hand (TSTH) at 1 year after Vim RS was included in a statistical parametric mapping analysis of variance (ANOVA) model as a continuous variable with pretherapeutic neuroimaging data. Pretherapeutic gray matter density (GMD) was further correlated with TSTH improvement. No a priori hypothesis was used in the statistical model.Results: The only statistically significant region was right Brodmann area (BA) 18 (visual association area V2, p = 0.05, cluster size Kc = 71). Higher baseline GMD correlated with better TSTH improvement at 1 year after Vim RS (Spearman’s rank correlation coefficient = 0.002).Conclusions: Routine baseline structural neuroimaging predicts TSTH improvement 1 year after Vim RS. The relevant anatomical area is the right visual association cortex (BA 18, V2). The question whether visual areas should be included in the targeting remains open. [ABSTRACT FROM AUTHOR]

Background: Tremor is a main feature of two different movement disorders, Parkinson's disease (PD) and essential tremor (ET), for which previously published data suggested functionally different underlying brain circuitry. Objectives: We analyzed resting-state fMRI data of 16 patients: 8 with tremor-dominant PD, and 8 with ET (mean age 74 years). Tremor was predominant in the right upper limb in all patients. In PD, 7 out of 8 were under Levodopa medication at the time of scanning, with a mean dose of 525 mg (range 0-800). Methods: The functional connectivity of the tremor network has been probed using a seed-to-voxel (further referred to as seed connectivity analysis) and ROI-wise (further referred to as network analysis) approach. Four seeds (dentate nucleus, red nucleus, thalamus, precentral gyrus) in both hemispheres were investigated. Results: We report exclusive negative functional connectivity (FC) during resting-state in ET between the right dentate and left red nucleus towards the left precentral gyrus. Furthermore, the same connectivity is consistently positive in PD (independent of the medication levels). Conclusion: The major differences in FC between two groups suggest an altered tremor network in PD and ET and further point toward the involvement of the putamen and globus pallidus (both internal and external) on one side, as well as the right ventral anterior thalamic nuclei, on the other side. In summary, our findings suggest that rs-fMRI could be used as an additional confirmation test, beside the clinical history and examination and the eventual adding of a DAT scan, in the differential diagnosis between PD and ET. [ABSTRACT FROM AUTHOR]

Objective: To assess for the first time structural brain changes, by voxel-based morphometry (VBM), before and after unilateral Gamma Knife thalamotomy (GKT) for drug-resistant tremor. To identify differences between clinical responders and nonresponders to GKT. Methods: Thirty-eight patients (mean age 71.8 years) with severe refractory right essential tremor (ET) were treated with unilateral left GKT. Targeting of ventro-intermediate nucleus (Vim) was performed with Leksell Gamma Knife using a single 4- mm collimator and 130 Gy. Neurological, neuropsychological and neuroimaging (3 Tesla, including 3D T1 weighted) assessment had been done at baseline and 1 year after GKT. Clinical responders were considered those improved in tremor score (Fahn-Tolosa-Marin) with at least 45%. Results: Thirty-one (81.6%) patients were responders (R) and 7 (18.4%) non-responders (NR). With regard to GM changes after GKT, independently of clinical answer, atrophy was present in extensive areas (right globus pallidus, left putamen, left thalamus, right anterior and medio-dorsal thalamus, cerebellar, right premotor and supplementary motor area, left and right visual association cortex, right ventral temporal, left parahippocampal and posterior cingulate gyrus). The interaction between R - NR with time showed brain plasticity in R remote areas, within left temporal pole (BA 38) and cluster including left occipital cortex (BA 19), visual areas V4 and V5, parahippocampal place area (punc<0.005, k>120). Conclusions: Our results show brain plasticity after unilateral left GKT. Responders present changes in areas involved in motion, mainly locomotor monitoring towards the local and distant environment, suggesting the requirement to recruit in the targeting specific visuomotor networks. [ABSTRACT FROM AUTHOR]