Voxel-Based Morphometry before and after Gamma Knife Thalamotomy of the Ventro-Intermediate Nucleus for Tremor could help Discriminating Clinical Responders from Non-Responders

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 non-responders 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 toward the local and distant environment, suggesting the requirement to recruit in the targeting specific visuomotor networks.