Two-year experience of magnetic resonance-guided focused ultrasound(MRGFUS) surgery for patients with essential tremor(ET) and tremor dominant Parkinson’s disease(TDPD) in Show Chwan Hospital

BACKGROUND: Since the approval of MRgFUS technology for ET and TDPD, MRGFUS offers feasible results in unilateral thalamotomy with non-incisional surgery and optimized accuracy in targeting. We describe here the two-year results of MRgFUS surgery for patients with ET and TDPD in single-center experience in Show Chwan Memorial Hospital.
METHODS: The authors describe the results of MRgFUS in 66 patients during the period from June 2017 to December 2019. Total 71 treatments for unilateral ventralis intermedius (VIM) thalamotomy were performed in patients with dominant hand tremors and medications refractory ET and TDPD patients. In all treatments, a 1.5-T MRI scanner was used for planning and monitoring. The target was defined real-time with the patient’s subjective statements during low power sonication. Primary relief symptoms were evaluated with the subjective statements and intra-operative tremography. Adverse effects (AE) were evaluated in post-operative Day-0, 1, 7 and Month-1, 3, 6,12, 24. The Clinical Rating Scale for tremor (CRST) and the MR examinations were performed before the treatment and immediately, 3 6 and 12 months after the operation. Post-operative Day-1 MRI T2-weighted images (T2WI) defined the degrees of brain edema from grade 0 to 5( the condition of zone 1 and 2 invading into the internal capsule and surrounding tissues). The relationship between the edema degree and AE were also surveyed.
RESULTS: During the study period, a total of 66 patients with 47 males and 19 females were evaluated before and after the treatment with a clinical control of the treatment effectiveness. Patients’ age were from 27 to 90 (61±14) year-old and symptoms persisted from 3 to 67 (21.12±14.76) years. A total of 71 treatments with ET and PD were successfully undergone MRgFUS unilateral VIM thalamotomy (59 left VIMs and 12 right VIMs). The skull density ratio (SDR) was from 0.26 to 0.7 (0.45±0.09). The lengths of anterior commissure to posterior commissure (AC-PC) were from 21.60 to 26.93mm (23.89±1.45). As a consequence, the treatment protocol was adapted by applying the repetition of the final temperatures 52°C to 61°C (56.44±3.24). Five patients had the second operation because of recurrence within six months. MRI showed thermal lesions on VIM in T2WI after sonications. Two patients with low SDR (0.26 and 0.3) and one patient with high skull thickness (average 11.3mm and SDR:0.38) achieved only 52°C with maximal energies had initial decreased tremor but symptoms come back within one month. The 63 treated patients who completed the procedure showed immediately free from tremor , with no intra- operation severe permanent side effects. Five patients had second treatment because of tremor recurrence after 3-6 months. The radius of ablated lesions were from 1.08 to 5.88mm (3.86±0.96). Grades of post-operative brain edema were defined from grade 0 to 5 (1.72±1.46). The common post-operative Day-1 AEs were dysmetria(75%), ataxia(65%), numbness over lip or tongue (34%), and weakness over hand (12.5%). 16.7% of patients had lip or tongue numbness post-operative 6-month and 8.3% of patients persisted numbness in post-operative 24-months. The other AEs were subsided in post-operative 3-6 months. Ablated lesions were diminished in post-operative MRI T2WI in 3-6 months. AEs were statistical significance related to the highest temperature achieved (p=0.029), the superior-inferior location of ablated lesion(p=0.045), grade 4 and 5 edema grade (p=0.037 and 0.021), PC to AC-PC ratio (p=0.045) .
CONCLUSIONS: This is the first experience in Taiwan of a unilateral thalamotomy using the MRgFUS. Our experience demonstrated the feasibility, safety, and accuracy of the MRgFUS thalamotomy in treating ET and TDPD. Treatment for patients with low SDR (lower than 0.35) and high skull thickness (thicker than 11mm) are still technical issues. Patients with post-operative tremors, either inadequate thermal ablation or tremor recurrence, MRGFUS is still a promising choice of technique for tremor control. AEs are related to high edema grades ablated lesions. Surgeons should take great care in each sonication especially with high power and long periods in high energies. In the treatment of movement disorders, the MRgFUS may be an alternative choice.

References

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