Primary orthostatic tremor: is deep brain stimulation better than spinal cord stimulation?

Clinical neurophysiology in the treatment of movement disorders: IFCN handbook chapter

In this review, different aspects of the use of clinical neurophysiology techniques for the treatment of movement disorders are addressed. First of all, these techniques can be used to guide neuromodulation techniques or to perform therapeutic neuromodulation as such. Neuromodulation includes invasive techniques based on the surgical implantation of electrodes and a pulse generator, such as deep brain stimulation (DBS) or spinal cord stimulation (SCS) on the one hand, and non-invasive techniques aimed at modulating or even lesioning neural structures by transcranial application. Movement disorders are one of the main areas of indication for the various neuromodulation techniques. This review focuses on the following techniques: DBS, repetitive transcranial magnetic stimulation (rTMS), low-intensity transcranial electrical stimulation, including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), and focused ultrasound (FUS), including high-intensity magnetic resonance-guided FUS (MRgFUS), and pulsed mode low-intensity transcranial FUS stimulation (TUS). The main clinical conditions in which neuromodulation has proven its efficacy are Parkinson's disease, dystonia, and essential tremor, mainly using DBS or MRgFUS. There is also some evidence for Tourette syndrome (DBS), Huntington's disease (DBS), cerebellar ataxia (tDCS), and axial signs (SCS) and depression (rTMS) in PD. The development of non-invasive transcranial neuromodulation techniques is limited by the short-term clinical impact of these techniques, especially rTMS, in the context of very chronic diseases. However, at-home use (tDCS) or current advances in the design of closed-loop stimulation (tACS) may open new perspectives for the application of these techniques in patients, favored by their easier use and lower rate of adverse effects compared to invasive or lesioning methods. Finally, this review summarizes the evidence for keeping the use of electromyography to optimize the identification of muscles to be treated with botulinum toxin injection, which is indicated and widely performed for the treatment of various movement disorders.

Deep Brain Stimulation for Orthostatic Tremor: An Observational Study

BACKGROUND

Primary orthostatic tremor (OT) can affect patients' life. Treatment of OT with deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (Vim) is described in a limited number of patients. The Vim and posterior subthalamic area (PSA) can be targeted in a single trajectory, allowing both stimulation of the Vim and/or dentatorubrothalamic tract (DRT). In essential tremor this is currently often used with positive effects.

OBJECTIVE

To evaluate the efficacy of Vim/DRT-DBS in OT-patients, based on standing time and Quality of Life (QoL), also on the long-term. Furthermore, to relate stimulation of the Vim and DRT, medial lemniscus (ML) and pyramidal tract (PT) to beneficial clinical and side-effects.

METHODS

Nine severely affected OT-patients received bilateral Vim/DRT-DBS. Primary outcome measure was standing time; secondary measures included self-reported measures, neurophysiological measures, structural analyses, surgical complications, stimulation-induced side-effects, and QoL up to 56 months. Stimulation of volume of tissue activated (VTA) were related to outcome measures.

RESULTS

Average maximum standing time increased from 41.0 s ± 51.0 s to 109.3 s ± 65.0 s after 18 months, with improvements measured in seven of nine patients. VTA (n = 7) overlapped with the DRT in six patients and with the ML and/or PT in six patients. All patients experienced side-effects and QoL worsened during the first year after surgery, which improved again during long-term follow-up, although remaining below age-related normal values. Most patients reported a positive effect of DBS.

CONCLUSION

Vim/DRT-DBS improved standing time in patients with severe OT. Observed side-effects are possibly related to stimulation of the ML and PT.

Deep brain stimulation and spinal cord stimulation for orthostatic tremor: A systematic review

BACKGROUND

Orthostatic tremor is a rare and debilitating movement disorder. Its first-line treatment is pharmacological. For pharmaco-refractory patients, surgical treatment options such as deep brain stimulation (DBS) and spinal cord stimulation (SCS) have been investigated recently.

OBJECTIVES

We conducted a systematic review of all published outcome and safety data on DBS and SCS for orthostatic tremor patients.

METHODS

We searched Pubmed and Embase for studies describing orthostatic tremor patients treated with DBS or SCS. We collected all available outcome and safety data and our primary endpoint was the change in unsupported stance duration 1 year postoperatively (±6 months).

RESULTS

We included 15 studies, reporting on 32 orthostatic tremor patients who underwent DBS, 4 patients SCS and 2 both. The ventral intermediate nucleus and the zona incerta were targeted in 25/34 and 9/34 DBS cases, respectively. The median stance time at 1 year follow-up was 240 s compared to 30 s pre-operatively (p < 0.001). Stimulation-induced side effects occurred in the majority of patients, but were often transient. Bilateral stimulation appeared more effective than unilateral and stimulation settings were comparable to thalamic DBS for essential tremor. There were insufficient data available to draw meaningful conclusions on the long-term effects of DBS. Due to insufficient data, no conclusions could be drawn on the effects of SCS on orthostatic tremor.

CONCLUSION

DBS may be effective to increase stance time in orthostatic tremor patients in the first year, but further research is necessary to evaluate the long-term effects and the role of spinal cord stimulation.

The Top 50 Most-Cited Articles in Orthostatic Tremor: A Bibliometric Review

Background

Article-level citation count is a hallmark indicating scientific impact. We aimed to pinpoint and evaluate the top 50 most-cited articles in orthostatic tremor (OT).

Methods

The ISI Web of Knowledge database and 2017 Journal Citation Report Science Edition were used to retrieve the 50 top-cited OT articles published from 1984 to April 2019. Information was collected by the Analyze Tool on the Web of Science, including number of citations, publication title, journal name, publication year, and country and institution of origin. Supplementary analyses were undertaken to clarify authorship, study design, level of evidence, and category.

Results

Up to 66% of manuscripts were recovered from five journals: Movement Disorders (n = 18), Brain (n = 4), Journal of Clinical Neurophysiology (n = 4), Neurology (n = 4), and Clinical Neurophysiology (n = 3). Articles were published between 1984 and 2018, with expert opinion as the predominant design (n = 22) and review as category (n = 17). Most articles had level 5 evidence (n = 26). According to their countries of origin, 34% of articles belonged to the United States (n = 17) leading the list, followed by United Kingdom (n = 15). University College London yielded the greater number of articles (n = 12), followed by the University of Kiel (n = 9). Most popular authors were G. Deuschl (n = 10), C.D. Marsden (n = 6), J. Jankovic (n = 5), P.D. Thompson (n = 5), J.C. Rothwell (n = 5), L.J. Findley (n = 4), and P. Brown (n = 4), who together accounted for 48% of them. All papers were in English.

Discussion

Publishing high-cited OT articles could be facilitated by source journal, study design, category, publication language, and country and institution of origin.

Proprioceptive muscle tendon stimulation reduces symptoms in primary orthostatic tremor

INTRODUCTION

Primary orthostatic tremor (OT) is characterized by high-frequency lower limb muscle contractions and a disabling sense of unsteadiness while standing. To date, therapeutic options for OT are limited. Here, we examined the effects of proprioceptive leg muscle stimulation via muscle tendon vibration (MTV) on tremor and balance control in patients with primary OT.

METHODS

Tremor in nine patients with primary OT was examined during four conditions: standing (1), standing with MTV on the bilateral soleus muscles (2), lying (3), and lying with MTV (4). Tremor characteristics were assessed by frequency domain analysis of surface EMG recordings from four leg muscles. Body sway was analyzed using posturographic recordings.

RESULTS

During standing, all patients showed a coherent high-frequency tremor in leg muscles and body sway that was absent during lying (p < 0.001). MTV during standing did not reset tremor frequency, but resulted in a decreased tremor intensity (p < 0.001; mean reduction: 32.5 ± 7.1%) and body sway (p = 0.032; mean reduction: 37.2 ± 6.8%). MTV did not affect muscle activity during lying. Four patients further reported a noticeable relief from unsteadiness during stimulation.

CONCLUSION

Proprioceptive stimulation did not reset tremor frequency consistent with the presumed central origin of OT. However, continuous MTV influenced the emergence of OT symptoms resulting in reduced tremor intensity, improved posture, and a relief from unsteadiness in half of the examined patients. These findings indicate that MTV either directly interferes with the peripheral manifestation of the central oscillatory pattern or prevents proprioceptive afferent feedback from becoming extensively synchronized at the tremor frequency.

Health-Related Quality of Life Is Severely Affected in Primary Orthostatic Tremor

Background

Primary orthostatic tremor (POT) is a movement disorder characterized by unsteadiness upon standing still due to a tremor affecting the legs. It is a gradually progressive condition with limited treatment options. Impairments in health-related quality of life (HQoL) seem to far exceed the physical disability associated with the condition.

Methods

A multi-center, mixed-methodology study was undertaken to investigate 40 consecutive patients presenting with POT to four movement disorder centers in France. HQoL was investigated using eight quantitative scales and a qualitative study which employed semi-structured interviews. Qualitative data were analyzed with a combination of grounded-theory approach.

Results

Our results confirm that HQoL in POT is severely affected. Fear of falling was identified as the main predictor of HQoL. The qualitative arm of our study explored our initial results in greater depth and uncovered themes not identified by the quantitative approach.

Conclusion

Our results illustrate the huge potential of mixed methodology in identifying issues influencing HQoL in POT. Our work paves the way for enhanced patient care and improved HQoL in POT and is paradigmatic of this modern approach for investigating HQoL issues in chronic neurological disorders.

Tremor

Tremor is a phenomenon observed in a broad spectrum of diseases with different pathophysiologies. While patients with tremor may not complain in the clinic of symptoms of imbalance, gait difficulties, or falls, laboratory research studies using quantitative analysis of gait and posture and neurophysiologic techniques have demonstrated impaired gait and balance across a variety of tremor etiologies. These findings have been supported by careful epidemiologic studies assessing symptoms of imbalance. Imaging and neurophysiologic studies have identified cerebellar networks as important mediators of tremor, and therefore a likely common site of dysfunction to explain the phenomenologic overlap between impaired postural and gait control with tremor. Further understanding of these mechanisms and networks is of crucial importance in the development of new treatments, particularly surgical or minimally invasive lesional therapies.