Objective: To report the long-term outcomes in Tremor-Dominant Parkinson Disease (TDPD) after a unilateral Focused Ultrasound (uni-FUS) thalamotomy and explore factors that may predict the outcome.

Background: Uni-FUS thalamotomy is a proven and safe treatment in TDPD.¹ However, in comparison to Essential Tremor the evidence supporting this procedure is relatively scant and individual outcomes are more variable.² Authors have suggested that recurrence of tremor is due to insufficient lesion size,³ but studies confirming this hypothesis have not been performed.

Method: Retrospective blinded pre- and post-operative video assessment of consecutive TDPD patients who underwent a uni-FUS thalamotomy was undertaken. Patients were classified into two groups: ‘responder’ (R) (>50% improvement in Hand Tremor Score at last follow-up) or ‘suboptimal responder’ (SR) (<50% improvement in HTS). Patient and treatment factors were assessed by general linear models, R and SR as the binary outcomes.

Results: From November 2018 to February 2023, 17 patients with TDPD underwent a uni-FUS thalamotomy at our centre. Pre- and post-operative videos were available in 15 patients for analysis. The R group included 7 patients with a HTS of 1.7± 1.5 at the last follow-up (19.7± 13.9 months), compared to 8 patients in the SR group, with a HTS of 16.5± 9.9 at a mean follow-up time of 14.3± 13.7 months. There was a trend for smaller lesion parameters in the R group; lesion volume 160.1± 65.7mm³ vs. 167.9± 63.7mm³, lesion core 14.7± 8.5mm³ vs. 18.3± 4.6mm³, DRTT volume overlap 72.0± 20% vs. 83.6± 9.4%, and DRTT core overlap 25.6± 15.9% vs. 43.0± 7.9%. No baseline patient specific or treatment parameters were identified to predict the outcome. However, an increase in the HTS on the untreated side at the last follow-up was identified as a negative predictor of R’s (OR 0.44, 95% CI 0.21 – 0.93, p<0.05).

Conclusion: In the long-term, uni-FUS thalamotomy for TDPD improved tremor by greater than 50% in approximately a half of patients. Baseline clinical features and treatment parameters, including ablation volume and DRTT overlap did not predict the ‘responder’ from ‘suboptimal responder’ groups. Suboptimal long-term response may be related to progression of PD rather than insufficient lesion size. These findings provide indirect evidence to support the ‘dimmer-switch’ model of tremor in PD.⁴

References: 1. Bond AE, Shah BB, Huss DS, et al. Safety and Efficacy of Focused Ultrasound Thalamotomy for Patients With Medication-Refractory, Tremor-Dominant Parkinson Disease: A Randomized Clinical Trial. JAMA Neurology. 2017;74:1412–1418.
2. Peters J, Maamary J, Kyle K, et al. Outcomes of Focused Ultrasound Thalamotomy in Tremor Syndromes. Mov Disord. Epub 2023 Nov 14.
3. YAMAMOTO K, ITO H, FUKUTAKE S, et al. Focused Ultrasound Thalamotomy for Tremor-dominant Parkinson’s Disease: A Prospective 1-year Follow-up Study. Neurol Med Chir (Tokyo). 2021;61:414–421.
4. Helmich RC, Hallett M, Deuschl G, Toni I, Bloem BR. Cerebral causes and consequences of parkinsonian resting tremor: a tale of two circuits? Brain. 2012;135:3206–3226.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/focused-ultrasound-thalamotomy-for-tremor-dominant-parkinson-disease-ablation-volume-and-dentatorubrothalamic-tract-overlap-does-not-predict-outcome/