Objective: To describe a case of chorea after magnetic resonance guided focused ultrasound (MRgFUS) for the treatment of essential tremor (ET).

Background: ET can provide substantial impairment of activities of daily living and affect social interaction in some patients. It is estimated that 25-55% of patients with ET are refractory to medical treatment.(1) MRgFUS is an effective, recent and non-invasive procedure in this particular case

Method: We present a 75 year-old patient who underwent MRgFUS targeting the ventralis intermedius (VIM) nucleus of the thalamus to treat disabling right hand tremor. After the procedure she reported a worsening of tremor severity; therefore a consecutive FUS was performed one year later. Albeit there was a significant improvement in tremor, she exhibited chorea in her right upper extremity immediately after the procedure which became disabling and has persisted for more than two years. An MRI was perfomed showing a lesion on the VIM nucleus without extension to the subthalamic region or other surrounding areas that could explain the advent of chorea.

Results: MRgFUS is a useful approach for the treatment of ET non responsive to oral medications. The complication rate of thalamotomy has been estimated to be 15-20%, with an incidence of disability of 2-4% (2). The most common adverse effects reported among studies and case series are paresthesias and gait disturbances (3). Nonetheless, hemichorea/hemiballism has a low incidence of 0.1-0.2% and an underlying lesion in the subthalamic area has not always been encountered.

Conclusion: We describe a case of persistent chorea after a second MRgFUS thalamotomy. Although choreo-ballistic movements have been reported as a complication of thalamotomy, it is extremely rare, most have a remitting course and the underlying mechanism is still unclear.

References: 1. Louis ED, Barnes L, Albert SM, et al. Correlates of functional disability in essential tremor. Mov Disord. 2001;16:914–20.

2. T. Saitoh, R. Enatsu, M. Kitagawa et al., Choreo-ballistic movement after thalamotomy in a patient with Lewy body dementia, Journal of Clinical Neuroscience. 2019; 66:264-266

3. Elias WJ, Lipsman N, Ondo WG, et al. A randomized trial of focused ultrasound thalamotomy for essential tremor. N Engl J Med. 2016;375:730–9

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MDS Abstracts - https://www.mdsabstracts.org/abstract/chorea-after-mrgfus-for-the-treatment-of-essential-tremor-a-case-report/