Objective: To test whether efficacy of Deep Brain Stimulation (DBS) in different action tremor syndromes (Essential tremor, ET, ET-plus, or dystonic tremor as per IPMDS criteria) is mediated by stimulation of FGATIR thalamic hypointensity.

Background: DBS of the ventral intermediate nucleus (VIM) and zona incerta (ZI) provides established therapeutic benefit for medically refractory cases. Variability in outcomes of VIM DBS for tremor might depend on indirect targeting of VIM, which is the current approach. Direct anatomical target of thalamic hypointensity by means of Fast Gray Matter Acquisition T1 Inversion Recovery Sequences (FGATIR) has been suggested as useful imaging marker to target in people with ET.

Method: We included subjects who underwent bilateral VIM-ZI stimulation for action tremor syndromes with availability of FGATIR MRI sequences performed before surgery. Each subject was evaluated with Fahn-Tolosa-Marin scale  before DBS and at a minimum of 12 months follow-up (T1). At T1, subjects were assessed both in OFF and ON stimulation. The FGATIR hypointensity was demarcated manually in all individuals and its imaging characteristics quantified. Subsequently, we performed a tractography analysis based off this target and the dentato-rubro-thalamic tract (DRTT). Finally, we compared the results with those from classical lead localisation and connectivity analyses.

Results: Twenty-four subjects were included, four of them were excluded due to incomplete data. Seventeen subjects completed the OFF/ON stimulation challenge. Lead localisation revealed relatively consistent placement at the Vim/Vop junction. We found variability in defining the FGATIR hypointensity between users, reflected in the relatively low Dice co-efficient of 0.44. Tractography revealed that the FGATIR hypointensity was only partially related to the DRTT. Neither DBS proximity nor stimulation of the FGATIR hypointensity was related magnitude of tremor improvement at follow-up. However, both streamline and network-based connectivity analyses were able to reliably predict outcomes.

Conclusion: FGATIR-defined thalamic hypointensity did not predict clinical outcomes in our cohort of patients with different types of action tremors, in contrast to streamline- and network-based connectivity analyses. Analyses on larger samples of patients will confirm whether this imaging biomarker can be used to guide DBS targets in different tremor syndromes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/does-fgatir-hypointensity-predict-outcomes-after-deep-brain-stimulation-for-action-tremors/