Magnetic resonance-guided focused ultrasound thalamotomy in essential tremor subtypes: a phenotype-based insight into gait and balance.

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an established treatment for medication-refractory essential tremor (ET). However, evidence regarding its efficacy and safety in ET with imbalance (ET-I) and dystonic tremor (DT) remains limited, particularly with respect to gait outcomes. We prospectively evaluated whether tremor control and gait stability after unilateral MRgFUS ventral intermediate nucleus (VIM) thalamotomy differed according to tremor phenotype and baseline gait status. Eighty-one patients were enrolled (40 ET, 11 ET-I, 30 DT; 59.3% male; median age 73 years) and assessed with the clinical rating scale for tremor, Berg balance scale, and tandem gait performance at baseline, 6 months and 12 months. Phenotypes were assigned by two movement disorder specialists with substantial inter-rater agreement (κ & 0.72). Seventy-six patients achieved at least one effective sonication (≥55°C) and were included in outcome analyses. At 6 months, treated hand tremor score improved by 80% in ET, 70% in ET-I, and 71% in DT. At 12 months, a sustained improvement of 50% or greater was maintained in 94% of ET patients, 71% of ET-I patients, and 82% of DT patients. While ET patients maintained stable tremor benefit at 12 months (78% improvement), ET-I and DT showed a modest decline (63% and 63%, respectively). Disability scores followed similar trajectories. Tandem gait remained stable in 87% of patients at 12 months, with gait worsening being infrequent and generally mild (15.7% at 6 months; 13.3% at 12 months) and not associated with phenotype, baseline instability or age. Notably, some ET-I and DT patients improved from moderate to mild impairment, and only two patients developed severe gait disturbances at 12 months. Adverse events, systematically assessed at 1, 6 and 12 months, were mild and transient, and no DT patient exhibited worsening of dystonia. These findings indicate that MRgFUS VIM thalamotomy is a relatively safe and effective option across tremor phenotypes, including patients with mild baseline imbalance, with most individuals achieving durable tremor benefit and preserved gait function. Our results support phenotype-based patient selection and reinforce the value of long-term, individualized follow-up, particularly in older or clinically complex cases.