Magnetic Resonance–Guided Focused Ultrasound Thalamotomy in a Prospective Cohort of 52 Patients with Parkinson's Disease: A Possible Critical Role of Age and Lesion Volume for Predicting Tremor Relapse

BackgroundMagnetic resonance–guided focused ultrasound (MRgFUS) thalamotomy of ventral intermediate (Vim) nucleus is useful to treat drug‐resistant tremor‐dominant Parkinson's disease (TdPD), but tremor relapse may occur. Predictors of relapse have been poorly investigated so far.ObjectiveThe aim of this study is to evaluate the role of clinico‐demographic, procedural, and neuroradiological variables in determining clinical response, relapse, and adverse events (AEs) in TdPD after MRgFUS Vim‐thalamotomy.MethodsFifty‐two TdPD patients who consecutively underwent unilateral MRgFUS Vim‐thalamotomy were prospectively evaluated at baseline and after 24 hours, 1 month, 6 months, and 12 months using MDS‐UPDRS‐III in off and on medication conditions. AEs were collected at each evaluation. Lesion volume was calculated at 24‐hour magnetic resonance imaging (MRI). Patients with tremor improvement <30% in off medication were considered nonresponders (when detected after 24 hours) or relapsers (if detected from 1‐month visit onward).ResultsAll patients showed tremor improvement >30% at 24 hours. Tremor relapse occurred in 12 patients (23%), exclusively during the first month after thalamotomy. Relapse was associated with younger age (P = 0.030) and smaller lesion volume (P = 0.030). At 1 month, 22 patients (42%) had AEs; at 6 and 12 months, AEs persisted in 19% and 6% of cases. AEs at 6 months were associated with larger lesions (P = 0.018). All AEs were mild.ConclusionsMRgFUS Vim‐thalamotomy is effective in treating tremor in TdPD. Relapse is associated with younger age and smaller lesion volume, but larger lesions make AEs more likely to persist. We suggest that a lesion volume between 145 and 220 mm3 on T1‐weighted MRI may be the therapeutic window that ensures tremor control without long‐lasting AEs. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.