Immediate and Early Postoperative Tremor Fluctuation and 6 to 12-month Tremor Outcomes after Magnetic Resonance-guided Focused Ultrasound for Essential Tremor

While the middle and long-term essential tremor outcome after magnetic resonance-guided focused ultrasound (MRgFUS) is well documented, the immediate and early postoperative tremor outcome is less documented. We aimed to characterize the clinical significance of the immediate and early post-MRgFUS tremor fluctuation in patients with essential tremor. We retrospectively analyzed the consecutive 23 patients with essential tremor who underwent MRgFUS of thalamic ventral intermediate nucleus in our institute. Therapeutic outcomes were scored using clinical rating scale for tremor (CRST) part A and B (part A＋B). We also measured the areas of MR T2-weighted hypointense (zone 1) and peripheral hyperintense (zone 2) on the immediately postoperative MR images. The clinical characteristics, MRgFUS parameters, CRST part A＋B score, and zone 1＋2 area were compared between the group with more than 50% improvement and the group with 50% or less improvement immediately after the MRgFUS. The CRST part A＋B scores were examined from the preoperative to 6-12-month postoperative period using repeated measure analysis of variance (ANOVA). The odds ratio between the early postoperative tremor fluctuation and the 6-12-month postoperative tremor improvement was calculated. Immediately postopertive CRST part A＋B scores improved by more than 50% in 18 patients (78%) and by 50% or less in five patients (22%). The area for the zone 1＋2 was 13.1±4.2mm2 in the patients with improvement and 21.7±8.9mm2 in the patients without immediate improvement (p=0.037). A repeated measure ANOVA demonstrated that the CRST part A＋B scores improved significantly in each postoperative period compared to the preoperative baseline score (p＜0.001). Among the 20 patients with 6-12-month follow-up, eight patients (36%) had deterioration of tremor within the first three months and five of them had ineffective outcome in the postoperative 6-12 months. The odds ratio between tremor fluctuation in 1-3 months and ineffective tremor control in 6-12 months was 8.33 (p=0.046). Patients with ineffective essential tremor control after MRgFUS tend to have a large zone 1＋2 area. Early tremor fluctuation may indicate ineffective tremor control in the middle and long term. Further targeting accuracy is necessary to improve the long-term tremor outcome for patients with essential tremor.