Introduction: High-intensity focused ultrasound (HIFU) targeting the ventral intermediate nucleus (VIM) of the thalamus has been used to alleviate tremor in medication-refractory essential tremor (ET). While unilateral HIFU often improves symptoms, some patients require a second contralateral procedure. However, the safety, efficacy, and optimal parameters for sequential bilateral lesioning remain underexplored.
Methods: We analyzed 194 HIFU patients between March 2022 and July 2024. Inclusion criteria included ET patients who received bilateral HIFU thalamotomy with minimum follow-up criteria. Patient outcomes, adverse effects, and sonication data were assessed. Tremor severity was measured on a scale from 0 to 2 (0 = mild, 1 = moderate, 2 = severe).
Results: Eleven patients underwent bilateral treatment, averaging 397 days between procedures. Bilateral and unilateral groups showed no significant differences in demographic, skull density ratio, number of sonications, peak and average temperature, and energy delivered. The average number of sonications was 8.2 and 7.3 in the first and second sessions, respectively. On the last two sonications, there was a significant decrease between energy delivery (27.1kJ vs 22.6kJ, p=0.02) and no significant differences in average temperature (p=0.26) and peak temperature (p=0.14). Comparison of post-operative day one MRI following each session demonstrated significant reduction in lesion (280.17mm³ vs 157.86 mm³, p=0.014) and edema size (1711.81mm³ vs 1355.10mm³, p< 0.01) in the second session. Adverse effects (p=0.64) and tremor scores at last follow-up (score of 0.45 vs 0.10, p=0.12) showed no significant differences between groups.
Conclusion : This cohort showed that sequential bilateral HIFU thalamotomy for ET demonstrates comparable safety and efficacy to unilateral treatment, with no significant differences in procedural parameters or outcomes. Our initial data indicate that a second contralateral procedure can be safely considered in selected patients. However, due to the small sample size of this study, further research with larger cohorts is necessary to confirm these findings and evaluate long-term effects.
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