OBJECTIVE
To study the effect of magnetic resonance imaging-guided focused ultrasound (MR-FUS) on the motor and non-motor symptoms of essential tremor (ET) (cognitive functions, anxiety, depression, apathy, sleep disorders), as well as to establish association between adverse events (AEs) and the technical parameters of the surgery, postablation neuroimaging changes in the brain matter, and clinical and demographic factors.
MATERIAL AND METHODS
Twenty-two patients with disabling drug-resistant ET were prospectively evaluated prior to unilateral ventral intermediate nucleus (Vim) FUS thalamotomy, and at 24 hours, 3, 6, and 12 months postoperatively.
The change of tremor was assessed using the Clinical Rating Scale for Tremor (CRST). Non-motor symptoms were assessed using the Montreal Cognitive Assessment (MoCA), the Beck Depression Inventory (BDI) and Beck Anxiety Inventory (BAI), the Apathy Scale, and the Epworth Sleepiness Scale. The Tinetti test was used to assess balance and gait. The quality of life for patients with ET was assessed using the Quality of Life in Essential Tremor Questionnaire (QUEST). MRI with a magnetic field strength of 3.0 T was performed immediately after surgery, as well as at 24 hours, 3, 6, and 12 months post-surgery.
RESULTS
MR-FUS led to a significant reduction in tremor in the extremities of the contralateral thalamotomy site; the mean total CRST and hemi-CRST scores decreased by 78% and 80% (p<0.0001), respectively, with a significant persistence of the improvement at 12 months after surgery by 63% and 64% (p=0.012), respectively. The quality of life of patients with ET significantly improved at 6 and 12 months after surgery by 38% (p=0.017) and 45% (p=0.012), respectively. MR-FUS had no statistically significant impact on cognitive function, severity of apathy, anxiety, depression, or daytime sleepiness (p>0.05). Mild adverse events occurred in 45% of patients immediately after surgery, and most of the AEs regressed by Month 3 of follow-up. The lesion volume and postoperative edema were significantly correlated with a decrease in the total CRST score at 6 and 12 months postoperatively (r=–1, p=0.01). The results of the correlation analysis showed that patients with AEs after FUS-thalamotomy had larger foci of necrosis and postoperative edema, and also had a significantly shorter duration of surgery (p=0.042). However, the number of sonications (both verification and therapeutic), the power of ultrasound waves, and the maximum exposure temperatures in the patients of the compared groups did not differ significantly.
CONCLUSION
The results of an open prospective study confirmed the effectiveness of unilateral FUS thalamotomy of the Vim nucleus of the thalamus for the treatment of ET. There was no significant effect on the non-motor manifestations of ET. All reported AEs were mild and transient. The risk of AEs was determined by the volume of the lesion and postoperative edema, as well as the duration of surgery.
