Objective: To evaluate the efficacy and safety of staged bilateral MRgFUS thalamotomy guided by probabilistic tractography.

Background: Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an effective and safe treatment for unilateral essential tremor (ET). In 2023, staged bilateral MRgFUS thalamotomy received regulatory approval. However, key questions remain unresolved, including optimal target selection strategy and the safety of bilateral procedure.

Method: Prospective case series of 43 patients with ET who underwent staged bilateral MRgFUS thalamotomy. The target was individualised in each procedure using probabilistic tractography to identify the dentato-rubro-thalamocortical (DRT) tract.

Results: The median patient age was 71 years (IQR:66.5–76). In 38 patients (88.4%), the right hemisphere was treated first. The median interval between procedures was 419 days (IQR:374.5–497).

Bilateral thalamotomy resulted in a statistically significant improvement of 84.1% in total CRST score [baseline:63 (IQR: 52–69); post-first procedure:29 (IQR: 26–37); post-second procedure:10 (IQR: 5–15); p<0.001]. Functional disability (CRST-C) improved by 97.2% after both procedures [baseline:18 (IQR: 14–21); post-first procedure:6 (IQR: 3–8); post-second procedure:0.5 (IQR: 0–2.25); p<0.001].

Tractography-guided target selection yielded asymmetric coordinates between the two procedures [first treatment—ML:13mm (IQR: 12–14), AP:6mm (IQR: 5.5–7), SI:1mm (IQR: 1–1); second treatment—ML:14mm (IQR: 13–14.25), AP:7.5mm (IQR: 5.86–8), SI:1mm (IQR: 1–1)], reflecting the inherent anatomical asymmetry of the DRT across cerebral hemispheres and underscoring the limitations of symmetric targeting strategies.

Adverse events were recorded in 26 patients (60.5%) at one month, most commonly gait instability (n=17), dysarthria (n=15), and cognitive complaints (n=4). At six months, adverse effects decreased to 10 patients (23.3%), comprising dysarthria (n=6), gait instability (n=5), and cognitive complaints (n=4). All adverse effects were graded as mild.

Conclusion: Bilateral MRgFUS thalamotomy is an effective treatment for essential tremor. Adverse events are common immediate post-procedural period but are mild and diminish substantially by six months. The use of tractography enables specific target selection for each hemisphere, which we propose as a key factor contributing to the sustained efficacy and safety.

References: Cesarano S, Saporito G, Sucapane P, Bruno F, Catalucci A, Pistoia ML, Splendiani A, Ricci A, Di Cesare E, Totaro R, Pistoia F. Staged magnetic resonance-guided focused ultrasound thalamotomy for the treatment of bilateral essential tremor and Parkinson’s disease related tremor: a systematic review and critical appraisal of current knowledge. Front Neurol. 2024 Jun 20;15:1409727. doi: 10.3389/fneur.2024.1409727.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/bilateral-mrgfus-thalamotomy-in-essential-tremor-a-prospective-case-series-using-probabilistic-tractography/