Double lesion MRgFUS treatment of essential tremor targeting the thalamus and posterior sub-thalamic area: preliminary study with two year follow-up.

BACKGROUND: MR-guided focused ultrasound (MRgFUS) is an effective treatment for essential tremor (ET). However, the optimal intracranial target sites remain to be determined.

OBJECTIVE: To assess MRgFUS induced sequential lesions in (anterior-VIM/VOP nuclei) the thalamus and then posterior subthalamic area (PSA) performed during the same procedure for alleviating ET.

METHODS: 14 patients had unilateral MRgFUS lesions placed in anterior-VIM/VOP then PSA. Bain-Findley Spirals were collected during MRgFUS from the treated arm (BFS-TA) and throughout the study from the treated (BFS-TA) and non-treated (BFS-NTA) arms and scored by blinded assessors. Although, the primary outcome was change in the BFS-TA from baseline to 12 months we have highlighted the 24-month data. Secondary outcomes included the Clinical Rating Scale for Tremor (CRST), Quality of Life for ET (QUEST) and PHQ-9 depression scores.

RESULTS: The mean improvement in the BFS-TA from baseline to 24 months was 41.1% ( p  < 0.001) whilst BFS-NTA worsened by 8.8% ( p  < 0.001). Intra-operative BFS scores from the targeted arm showed a mean 27.9% ( p  < 0.001) decrease after anterior-VIM/VOP ablation and an additional 30.1% ( p  < 0.001) reduction from post anterior-VIM/VOP to post-PSA ablation. Mean improvements at 24 month follow-up in the CRST-parts A, B and C were 60.7%, 30.4% and 65.6% respectively and 37.8% in QUEST-tremor score (all p  < 0.05). Unilateral tremor severity scores decreased in the treated arm (UETTS-TA) 72.9% ( p  = 0.001) and non-treated arm (UETTS-NTA) 30.5% ( p  = 0.003). At 24 months residual adverse effects were slight unsteadiness ( n  = 1) and mild hemi-chorea ( n  = 1).

CONCLUSION: Unilateral anterior-VIM/VOP and PSA MRgFUS significantly diminished contralateral arm tremor with improvements in arm function, tremor related disability and quality of life, with an acceptable adverse event profile.