Objective: To describe a case of dystonic tremor developing after Magnetic Resonance Guided Focused Ultrasound Thalamotomy (MRgFUS) in a patient with essential tremor (ET).

Background: Among other movement disorders such as myoclonus and dystonia, tremor has been reported as potential sequela after thalamic lesions, typically following strokes, tumors, or other tissue disruptions.(1) Case series of thalamic tremor point towards lesions of the posterolateral portions of the thalamus, specifically of the nucleus ventralis intermedius (ViM), ventral caudal nuclei (Vc), and ventral posterolateral nucleus (VPL), causing disruptions of the cerebellothalamic pathway.(2,3) Secondary dystonia has been attributed to lesions of the corticostriatopallidothalamic loop.(4) MRgFUS, approved by the FDA for refractory ET, can lead to lasting tremor suppression, however sensory disturbances and gait abnormalities may persist after intervention. No occurrence of dystonia and/or tremor has been described to our knowledge following MRgFUS thalamotomy.

Methods: We describe a patient who developed a new right hand dystonic tremor two years after left ViM MRgFUS, and will present electrophysiological tremor-studies obtained before and after intervention.

Results: A 71-year old male subject with disabling and treatment-resistant postural and action tremor of the hands, which started at the age of 18 and subsequently diagnosed with ET in the 1990s, was seen at the NIH in 2009, confirming the diagnosis of Definite ET (TRG criteria). A tremor study revealed a central tremor component at 5.6Hz right and 5.7Hz on the left. Following MRgFUS in 2016, the patient reported a dramatic improvement of his right hand tremor. However, at a visit in 2018, a low frequency postural tremor with dystonic posturing of his right hand was noted, which was not present prior to MRgFUS. Tremor physiology showed a 4.8Hz tremor on the (untreated) left hand, as well as a new 3.0 Hz central tremor on the right (treated side).

Conclusions: Clinically and electrophysiologically, the patient exhibited a significant change in the tremor characteristics of his right hand following MRgFUS. We conclude that the low-frequency tremor with dystonic posturing (“thalamic hand”) is compatible with a dystonic tremor secondary to thalamic lesion, a novel observation following MRgFUS in ET. We will present neurophysiological and neuroimaging data to illustrate the case.

References: 1. Krystkowiak P, Martinat P, Cassim F, et al. Thalamic tremor: correlations with three-dimensional magnetic resonance imaging data and pathophysiological mechanisms. Mov Disord 2000;15(5):911-918. 2. Lehericy S, Grand S, Pollak P, et al. Clinical characteristics and topography of lesions in movement disorders due to thalamic lesions. Neurology 2001;57(6):1055-1066. 3. Miwa H, Hatori K, Kondo T, Imai H, Mizuno Y. Thalamic tremor: case reports and implications of the tremor-generating mechanism. Neurology 1996;46(1):75-79. 4. Krystkowiak P, Martinat P, Defebvre L, Pruvo JP, Leys D, Destee A. Dystonia after striatopallidal and thalamic stroke: clinicoradiological correlations and pathophysiological mechanisms. J Neurol Neurosurg Psychiatry 1998;65(5):703-708.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/thalamic-tremor-following-focused-ultrasound-thalamotomy-for-essential-tremor/