Outcomes and Prognostic Factors of Magnetic Resonance-guided Focused Ultrasound Thalamotomy for Essential Tremor at 2-year Follow-up

Abstract

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an effective treatment for essential tremor (ET). However, its long-term outcomes and prognostic factors remain unclear. This study aimed to retrospectively investigate 38 patients with ET who underwent MRgFUS thalamotomy and were followed up for >2 years. The improvement in tremor was evaluated using the Clinical Rating Scale for Tremor (CRST). Adverse events were documented, and correlations with factors, such as skull density ratio (SDR), maximum mean temperature (T-max), and lesion size, were examined. Furthermore, the outcomes were compared between two groups, one that met the cutoff values, which was previously reported (preoperative CRST-B ≤ 25, T-max ≥ 52.5°C, anterior-posterior size of lesion ≥ 3.9 mm, superior-inferior [SI] size of lesion > 5.5 mm), and the other that did not. The improvement rate was 59.4% on average at the 2-year follow-up. Adverse events, such as numbness (15.8%), dysarthria (10.5%), and lower extremity weakness (2.6%), were observed even after 2 years, although these were mild. The factors correlated with tremor improvement were the T-max and SI size of the lesion (p < 0.05), whereas the SDR showed no significance. Patients who met the aforementioned cutoff values demonstrated a 69.8% improvement at the 2-year follow-up, whereas others showed a 43.6% improvement (p < 0.05). In conclusion, MRgFUS is effective even after 2 years. The higher the T-max and the larger the lesion size, the better the tremor control. Previously reported cutoff values clearly predict the 2-year prognosis, indicating the usefulness of MRgFUS.

Keywords: ablation; essential tremor; focused ultrasound; outcome; prognostic factor.

Fig. 1

(A) Flowchart of the study participants. (B) The reasons for missed follow-up of patients, who were eventually excluded from this study. FUS, focused ultrasound surgery; ET, essential tremor; 2Ys F/U, 2-year follow-up; N/A, not attributed (unknown)

Fig. 2

Adverse effects observed at 1-week (gray) and 2-year follow-up (black) after treatment.

Fig. 3

CRST improvement rate of the treated upper extremity (UE) in each period of follow-up. There was no significant difference between 38 patients who achieved 2-year follow-up (2Ys F/U) (A) and 55 patients who were lost to follow-up before 2Ys F/U (B). CRST, Clinical Rating Scale for Tremor

Fig. 4

Relationship between CRST improvement rates and several factors. The Tmax or SI size of the lesion was positively correlated with the improvement rate of CRST (p < 0.05) in the affected upper extremity, although other factors, such as age, SDR, AP, and RL size of the lesion, were not statistically correlated. CRST, Clinical Rating Scale for Tremor; Tmax, maximum mean temperature; SI, superior to inferior; SDR, skull density ratio; AP, anterior to posterior; RL, right to left

Fig. 5

Investigation of the usefulness of the cutoff values of prognostic factors. Patients who met all the cutoff values were classified into group A, and those who did not were classified into group B. There were significant differences between the groups in the postoperative CRST improvement rates at all follow-up periods (p < 0.05). CRST, Clinical Rating Scale for Tremor