Case Report on Deep Brain Stimulation Rescue After Suboptimal MR-Guided Focused Ultrasound Thalamotomy for Essential Tremor: A Tractography-Based Investigation

Abstract

Essential tremor (ET) is the most prevalent movement disorder in adults, and can often be medically refractory, requiring surgical intervention. MRI-guided focused ultrasound (MRgFUS) is a less invasive procedure that uses ultrasonic waves to induce lesions in the ventralis intermedius nucleus (VIM) to treat refractory ET. As with all procedures for treating ET, optimal targeting during MRgFUS is essential for efficacy and durability. Various studies have reported cases of tremor recurrence following MRgFUS and long-term outcome data is limited to 3-4 years. We present a tractography-based investigation on a case of DBS rescue for medically refractory ET that was treated with MRgFUS that was interrupted due to the development of dysarthria during the procedure. After initial improvement, her hand tremor started to recur within 6 months after treatment, and bilateral DBS was performed targeting the VIM 24 months after MRgFUS. DBS induced long-term tremor control with monopolar stimulation. Diffusion MRI tractography was used to reconstruct the dentatorubrothalamic (DRTT) and corticothalmic (CTT) tracts being modulated by the procedures to understand the variability in efficacy between MRgFUS and DBS in treating ET in our patient. By comparing the MRgFUS lesion and DBS volume of activated tissue (VAT), we found that the MRgFUS lesion was located ventromedially to the VAT, and was less than 10% of the size of the VAT. While the lesion encompassed the same proportion of DRTT streamlines, it encompassed fewer CTT streamlines than the VAT. Our findings indicate the need for further investigation of targeting the CTT when using neuromodulatory procedures to treat refractory ET for more permanent tremor relief.

Diffusion tensor imaging‐based magnetic resonance imaging‐guided focused ultrasound thalamotomy for tremor recurrence after radiofrequency thalamotomy: A case report

“…The best therapeutic option for tremor recurrence has not been elucidated. Three cases of Vim‐DBS for tremor recurrence after MRgFUS Vim thalamotomy have been reported 11‐13 . On the contrary, this is the first report of MRgFUS Vim thalamotomy for tremor recurrence after RF Vim thalamotomy.…”

“…Three cases of Vim-DBS for tremor recurrence after MRgFUS Vim thalamotomy have been reported. [11][12][13] On the contrary, this is the first report of MRgFUS Vim thalamotomy for tremor recurrence after RF Vim thalamotomy. Further studies with a larger number of patients are needed; however, MRgFUS Vim thalamotomy could become one of the therapeutic options for tremor recurrence.…”

Feasibility of Magnetic Resonance–Compatible Accelerometers to Monitor Tremor Fluctuations During Magnetic Resonance–Guided Focused Ultrasound Thalamotomy: Technical Note

“…18 The volume and shape of sonicated tissue likely do not correspond very well with the volume of tissue activation with electrical stimulation during DBS. 19,20,21,22 Still, depending on the patient's skull density ratio and other factors, the focus of the ultrasound energy can be constrained enough to cover a muscle group that is undertreated. Although we know that these initial results must be interpreted with caution and that further validation with more treatment data is needed, we believe that the challenges presented by interpatient variability should not limit further investigation into the use of accelerometers to refine coordinates in an attempt to improve treatment effectiveness.…”

Update in the clinical application of focused ultrasound

“…The experience of our team (with around 5% of essential tremor patients presenting tremor relapse, data not published) corroborates this suggestion. Otherwise, thalamic DBS rescue can also be contemplated in case of ultrasound thalamotomy failure [38,39]. Finally, alternative approaches, such as cerebellothalamic tractotomy [40] or a combined Vim and posterior subthalamic area double lesion approach [41] have been successfully tested.…”