BACKGROUND: Magnetic 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. OBJECTIVE: The 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. METHODS: Fifty-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). RESULTS: All 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. CONCLUSIONS: MRgFUS 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 mm