Objective: To compare the efficacy of stimulation in VIM versus PSA on tremor suppression we conducted a randomized, double-blind crossover trial.

Background: DBS of the thalamic VIM nucleus is established as an effective treatment for upper limb (UL) action tremor, but in published case series the posterior subthalamic area (PSA) may seem even more effective.

Method: This trial took place at Oslo University Hospital, Norway, in collaboration with Wuerzburg University Hospital, Germany. Key inclusion criteria were severe, medically intractable UL action tremor as a symptom of various common tremor disorders, and age 18-80 years. Included patients were implanted with 4-level DBS leads bilaterally or unilaterally as indicated clinically, so that the two upper contact levels should cover the VIM nucleus and the two lower the PSA. Post-surgery, patients were randomly assigned in a 1:1 ratio, in an AB:BA crossover design. Thus, half the patients were randomized to be stimulated in the VIM during the first three months postoperatively, then in the PSA the next three months (Sequence 1), and the other half in PSA first, then VIM (Sequence 2). Blinded study evaluations were performed at the end of each 3-month randomized treatment period (period 1: 0-3 months post-surgery, period 2: 4-6 months). Primary endpoint was the difference in improvement from baseline to the end of the period with VIM versus PSA stimulation, in the Sum score of UL tremor items of the Fahn-Tolosa-Marin Tremor Rating Scale (FTMTRS) for the dominant arm (FTMTRS items 5/6 + 10-14).

Results: Between April 2014 and Dec 2018, 45 patients were enrolled, operated and randomised to sequence 1 (n=23) or sequence 2 (n=22). In the per protocol analysis of the primary endpoint (mixed model, n=40), the difference in mean improvement from baseline of Sum FTMTRS items for dominant UL between the VIM and the PSA period was -2.65 points (95% CI -4.33 to -0.97, p=0.002). This difference in favour of PSA-stimulation was highly significant in period 2 (4-6 months post-surgery), but not in period 1 (0-3 months post-surgery).

Conclusion: This double-blind, randomised crossover trial provides class 1 evidence that stimulation in PSA provides better tremor suppression than in VIM.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/deep-brain-stimulation-dbs-of-the-ventral-intermediate-thalamic-nucleus-vim-compared-to-the-posterior-subthalamic-area-psa-for-upper-limb-action-tremor-a-single-center-randomized-double-blind/