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Brain Stimulation for Torsion Dystonia

Michael D. Fox, MD, PhD1,2,3; Ron L. Alterman, MD4
[+] Author Affiliations
1Berenson-Allen Center for Noninvasive Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
2Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
3Athinoula A. Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, Massachusetts
4Division of Neurosurgery, Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
JAMA Neurol. 2015;72(6):713-719. doi:10.1001/jamaneurol.2015.51.
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Importance  Dystonia is a heterogeneous neurologic disorder characterized by abnormal muscle contractions for which standard medical therapy is often inadequate. For such patients, therapeutic brain stimulation is becoming increasingly used.

Objectives  To review the evidence and effect sizes for treating different types of dystonia with different types of brain stimulation and to discuss recent advances relevant to patient selection, surgical approach, programming, and mechanism of action.

Evidence Review  PubMed was searched for publications on the clinical effect of brain stimulation in dystonia up through December 31, 2014. Recent meta-analyses, consensus statements, and evidence-based guidelines were incorporated. Emphasis was placed on deep brain stimulation (DBS) and randomized clinical trials; however, other stimulation modalities and trial designs were included. For each intervention the mean change in dystonia severity, number of patients studied, and evidence of efficacy based on American Academy of Neurology criteria were determined.

Findings  Strong (level B) evidence supports the use of DBS for the treatment of primary generalized or segmental dystonia, especially when due to mutation in the DYT1 gene, as well as for patients with cervical dystonia. Large effect sizes have also been reported for DBS treatment of tardive dystonia, writer’s cramp, cranial dystonia, myoclonus dystonia, and off-state dystonia associated with Parkinson disease. Lesser benefit is generally seen in dystonia secondary to structural brain damage. Other brain stimulation techniques, including epidural cortical stimulation and noninvasive brain stimulation, have been investigated, but generally report smaller effect sizes in fewer patients.

Conclusions and Relevance  Patients with dystonia that is not adequately controlled with standard medical therapy should be referred for consideration of DBS, especially patients with generalized, segmental, or cervical dystonia. Other less-invasive stimulation modalities require further research before being considered a therapeutic alternative.

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Figure 1.
Illustration of Bilaterally Implanted Deep Brain Stimulation (DBS) Devices

Each DBS device is composed of a stimulating lead in the brain, extension cable, and programmable pulse generator, usually implanted in the chest (used with permission from Medtronic, Inc).

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Figure 2.
Deep Brain Stimulation Target in the Globus Pallidus Based on Retrospective Analysis of the Site of Effective Electrode Contacts and Modeling of Stimulation Fields

Magnetic resonance imaging was used to identify the location of the deep brain stimulation electrode (shown as multicolored rod) in patients with generalized dystonia due to mutation in the DYT1 gene (A) and coregistered into a common atlas space (B). The stimulation field for the effective electrode contact in each patient was modeled (C). A probabilistic volume in the posteroventral aspect of the globus pallidus pars interna was identified that could be used to guide future electrode placement or programming. Colors indicate the proportion of electrodes activating a given voxel location, with hotter colors corresponding with a higher probability of activation (D through F). Modified with permission from Cheung et al.16

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Figure 3.
Evidence of Efficacy for Brain Stimulation in Dystonia

Each bubble represents the evidence that a particular type of brain stimulation is effective for a particular type of dystonia. The position of the bubble along the y-axis indicates the mean improvement in dystonia severity; the size of the bubble, the number of patients studied; and the bubble outline, the quality of the evidence assessed by American Academy of Neurology criteria (level B, thick black outline; level C, thick gray outline; level U, no outline). Treatments with the best evidence of efficacy have larger bubbles higher on the graph and are outlined by darker lines. DBS indicates deep brain stimulation; Dyst, dystonia; DYT-1, generalized dystonia due to mutation in the DYT1 gene; DYT-6, generalized dystonia due to mutation in the DYT6 gene; ECS, epidural cortical stimulation; GM1, GM1 gangliosidosis; Gpi, globus pallidus pars interna; Myo, myoclonus; PD, Parkinson disease; PKAN, panthothenate kinase–associated neurodegeneration; RODP, rapid-onset dystonia parkinsonism; STN, subthalamic nucleus; TD, tardive dyskinesia; tDCS, transcranial direct current stimulation; and TMS, transcranial magnetic stimulation.

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Figure 4.
Location and Functional Relationship Between Invasive and Noninvasive Brain Stimulation Sites in Dystonia

A, The globus pallidus pars interna, the primary target of deep brain stimulation for dystonia, is shown in red. B, Resting-state functional connectivity with this deep brain stimulation site identifies positive and negative correlations on the surface of the brain potentially amenable to noninvasive brain stimulation. Prior targets of noninvasive brain stimulation are identified including primary motor cortex (M1), dorsal premotor cortex (PMd), and supplementary motor area (SMA). Modified with permission from Fox et al.24

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