We highlight a case of hemiballismus after MRI-guided Focused Ultrasound (MRIgFUS) targeting the ventral intermediate nucleus(VIM) of the thalamus in Essential Tremor(ET) Management.

An 80-year-old man with ET presented to our clinic for involuntary left-hand movements in October 2022. He  had undergone Neuravive MRIgFUS targeting the right VIM in December 2021 at an outside facility. His left-hand tremor resolved with the procedure . Two days after the procedure, he developed new involuntary movements in the left arm that progressively worsened. Ten months following symptom onset, he could not use his left hand for any purposeful activities. Neurological examination at the time of our initial evaluation was notable for ballistic movements and chorea of the left upper extremity and lower face, and residual postural and kinetic tremor in the right hand. MRI showed a T2 bright lesion in the right thalamus adjacent to the subthalamic nucleus (STN) post-MRIgFUS. The STN was not visualized on MRI due to the slice thickness. He was treated with deutetrabenazine, titrated to 12 mg BID, which led to notable improvement of ballismus and choreiform movements at a one-month follow-up.

Our patient presented with hemichorea and hemiballismus 2 days after his procedure, which did not abate with time. Given the temporal and anatomical proximity of his symptoms to the procedure, we concluded that his hyperkinetic movements were an adverse effect related to MRIgFUS. Also notable about this patient’s presentation was the delayed onset of these symptoms, meaning that these adverse effects may be missed during tissue targeting before the ablation is performed. The pivotal MRIgFUS trial reported adverse events such as gait disturbance, paresthesia, and hemiparesis in a fraction of patients at 12 months. Hyperkinetic movements such as chorea or ballismus were not reported.