Double lesion MRgFUS thalamotomy for essential tremor: 4.5-year outcomes and framework for assessing loss of efficacy and tremor progression

Abstract

Background The essential tremor (ET) course to 54 months post-unilateral VIM/PSA magnetic resonance-guided focused ultrasound (MRgFUS) in the treated arm (TA) and non-treated arm (NTA) of 12 patients is reported. Methods Tremor severity was rated using Bain Findley spirography (BFS) scores in the TA and NTA. We divided follow-up into ‘Early’ (0–6 months) and ‘Late’ (6–54 months) phases, to minimise the effect of peri-lesion oedema resolution on the latter. Results The mean baseline BFS score was 6.2 in TA and 5.7 in the NTA. After unilateral VIM/PSA MRgFUS, mean BFS improved in TA at all subsequent time points (p < 0.001), with no significant differences between BFS scores at consecutive assessments or between 1 and 54 months, while the NTA BFS scores worsened between 12 and 24 months (p < 0.003). Three patients showed worsening of their TA BFS scores and an increasing NTA–TA BFS difference, indicating slower tremor worsening in TA compared to NTA, whilst one patient showed a greater rate of worsening in the TA compared to NTA BFS. Conclusion After 54 months, the beneficial effect of MRgFUS is usually maintained with any worsening of BFS scores in TA slower than in NTA. Loss of treatment benefit is rare.