Objective: To report the occurrence of a thalamic hand as a rare side effect of MR-guided focused ultrasound (MRgFUS) thalamotomy of the right ventral intermediate nucleus (VIM).

Background: MRgFUS thalamotomy of the VIM is an emerging technique to treat patients with drug-resistant-tremor¹. Side effects are frequent but mild in severity, presenting mainly by paresthesias and unbalance². They are largely compensated by the marked benefit on health-related quality of life of patients with essential tremor (ET).

Method: Case report

Results: right MRgFUS thalamotomy (ExAblate Neuro 4000, InSightec). A total of six sonications were performed. The target coordinates were: +14.51 mm, +6.42 mm, and +1.02 mm (AC-PC distance: 25 mm) according to the system x/y/z in relation to the midline, posterior commissure and intercommisural planes, respectively. Two sonications reached the therapeutic temperature with a maximum temperature of 58°C. The tremor immediately decreased by 95%, associated with a slight left-sided ataxia and a tendency to deflect to the left when walking³. Within a month these side effects had significantly decreased. However, the patient reported a progressive difficulty to hold his cigarette between his fingers. Clinical examination showed involuntary metacarpophalangeal flexion of his left index and abduction in fingers 3,4 and 5, resulting in a dystonic posture. A control MRI was performed and showed the expected lesion of the right VIM with minimal hemorrhagic transformation. The final lesion materialized a little more anterior than the theoretical targeted coordinates, i.e. 26% in front of the PC instead of 25%, possibly encroaching on the anterior ventral lateral nuclei of the thalamus (VLa).

Conclusion: This is the first report of the apparition of a thalamic hand after a MRgFUS thalamotomy. Traditionally hand dystonia is related to thalamic lesion⁴ and more precisely to the posterior or posterolateral and the paramedian nuclei⁵ with subsequent reorganization of the dentato-rubro-thalamic tract. Dystonia of our patient could be related to the dysregulation of the underlying network involved in dystonia due to a lesion slightly out of the target.

References: 1. Yamamoto K, Sarica C, Loh A, Vetkas A, Samuel N, Milano V, Zemmar A, Germann J, Cheyuo C, Boutet A, Elias GJ, Ito H, Taira T, Lozano AM. Magnetic resonance-guided focused ultrasound for the treatment of tremor. Expert Rev Neurother. 2022 Oct;22(10):849-861. doi: 10.1080/14737175.2022.2147826. Epub 2022 Dec 5. PMID: 36469578.

2. P.S. Fishman, W.J. Elias, P. Ghanouni, R. Gwinn, N. Lipsman, M. Schwartz, J.W. Chang, T. Taira, V. Krishna, A. Rezai, K. Yamada, K. Igase, R. Cosgrove, H. Kashima, M.G. Kaplitt, T.S. Tierney, H.M. Eisenberg, Neurological adverse event profile of magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor, Mov Disord 33(5) (2018) 843-847.

3. Segar DJ, Lak AM, Lee S, Harary M, Chavakula V, Lauro P, McDannold N, White J, Cosgrove GR. Lesion location and lesion creation affect outcomes after focused ultrasound thalamotomy. Brain. 2021 Nov 29;144(10):3089-3100. doi: 10.1093/brain/awab176. PMID: 34750621.

4. Corp DT, Greenwood CJ, Morrison-Ham J, Pullinen J, McDowall GM, Younger EFP, Jinnah HA, Fox MD, Joutsa J. Clinical and Structural Findings in Patients With Lesion-Induced Dystonia: Descriptive and Quantitative Analysis of Published Cases. Neurology. 2022 Nov 1;99(18):e1957-e1967. doi: 10.1212/WNL.0000000000201042. Epub 2022 Aug 17. PMID: 35977840; PMCID: PMC9651464.

5. Lee MS, Marsden CD. Movement disorders following lesions of the thalamus or subthalamic region. Mov Disord. 1994 Sep;9(5):493-507. doi: 10.1002/mds.870090502. PMID: 7990845.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/apparition-of-a-thalamic-hand-after-focused-ultrasound-thalamotomy/