Mrgfus Thalamotomy versus DBS for Medically-refractory Essential Tremor: A Case Report

Introduction: Essential tremor (ET) is a prevalent movement disorder with high rates of resistance to first-line management. Techniques such as stereotactic deep brain stimulation (DBS) and magnetic resonance-guided focused ultrasound (MRgFUS) have emerged as promising treatment options.

Methods: A 67-year-old right-handed male with a 37-year history of medically-refractory ET presented with disabling tremor symptoms. Four years prior, he underwent DBS of bilateral ventral intermediate (VIM) nuclei, resulting in significant symptom improvement. The patient’s postoperative course was complicated by hardware infection requiring total explantation. The patient experienced recurrence of disabling tremor and elected to undergo left MRgFUS thalamotomy. Pre- and post-MRgFUS T2-FLAIR imaging and post-DBS CT imaging from his original DBS surgery were co-registered in BrainLab. A region-of-interest was constructed around the immediate post-operative MRI lesion from MRgFUS.

Results: Combined imaging illustrated overlap of the MRgFUS lesion in the left thalamus with the left decussating and non-decussating dentato-rubro-thalamic tracts (DRTTc and DRTTi, respectively), while avoiding the left medial lemniscus (ML) and corticospinal tract (CRT). However, the postoperative lesion was slightly anterolateral to the patient’s original DBS lead. The patient reported 90% subjective tremor reduction at his post-MRgFUS follow-up visit, and his clinical rating scale for tremor (CRST) dropped from 48 immediately pre-procedure to 11. However, he noted that his tremor had not improved as much as after his initial DBS implant at which time he reported 100% subjective reduction.

Conclusion : These findings have several possible explanations. Firstly, it is possible that unilateral hand tremor is influenced by bilateral VIM pathology or truncal tremor, both of which were not addressed with unilateral MRgFUS thalamotomy. Alternatively, the MRgFUS lesion did not exactly overlap with his original left VIM DBS electrode, indicating need for more extensive sonication. Further insight into the efficacy of MRgFUS vs. VIM DBS is critical as focused ultrasound finds its place in functional neurosurgery.