Effect of lead trajectory on the response of essential head tremor to deep brain stimulation

https://doi.org/10.1016/j.parkreldis.2013.03.015Get rights and content

Abstract

Background

Essential tremor (ET) is one of the most common movement disorders. Normally ET affects the distal upper extremities, but it can also be accompanied by midline symptoms. Ventralis intermedius (VIM) thalamic deep brain stimulation (DBS) has been shown to be effective in reducing hand tremor, but its effects on head tremor have been inconsistent.

Methods

Twenty-nine DBS patients with a diagnosis of ET met inclusion criteria. All implantations targeted VIM. The factors examined included age, gender, disease duration, presence or absence of head tremor, handedness, and the Fahn-Tolosa-Marin rating scale (TRS). This analysis specifically focused on TRS head tremor sub-scores at baseline, 6 months and 12 months post-DBS. Additionally, DBS lead entry angles were examined.

Results

Twenty-three ET patients underwent unilateral DBS and six underwent staged bilateral DBS. At both 6 and 12 months following DBS, stimulation resulted in diminished head tremor (ON vs OFF; p < 0.0001). The most important predictor of head tremor suppression was the entry angle of the DBS lead in the sagittal projection relative to the AC–PC axial plane (AC–PC angle). Head tremor reduction was greater among more vertical AC–PC angles.

Conclusion

A more vertical AC–PC angle of the DBS lead trajectory was associated with improved head tremor suppression. Further studies will be necessary to confirm this potentially important finding.

Introduction

Essential tremor (ET) is one of the most common movement disorders encountered in the general population [1], [2], [3]. ET typically presents as a predominantly postural and action tremor that progresses slowly over many years [1]. The prevalence of essential tremor has been estimated to be between 0.4% and 5% of the population [2]. ET most commonly affects the distal, but can also affect the proximal upper extremities. ET can symptomatically manifest in the head, voice, face and trunk [4]. Previous studies have revealed that over 90% of sufferers have hand tremor, but head tremor has also been observed in a significant proportion of cases (approximately 40–60%) [5]. Head tremor may rarely occur without the presence of hand tremor, however some of these more unusual cases may actually be manifesting dystonic or other tremor-related diagnoses [5]. Pharmacological management of moderate to severe head and voice tremor has, in general, been less effective than it has been for hand tremor [1].

Deep brain stimulation (DBS) of the thalamic ventralis intermedius nucleus (VIM) has become an important option for select cases of medication refractory ET. VIM DBS has been shown to be particularly effective in reducing hand tremor [2], [3], [4], [6], [7], [8]. The effects of DBS on head tremor, however, have been inconsistent and seem to be less predictable [3], [9], [10], [11]. Many physicians believe that bilateral VIM stimulation is necessary to effectively treat head tremor, however this clinical impression remains to be substantiated by more data. We have observed that some Vim DBS head tremor patients do not seem to respond to unilateral or to bilateral DBS. On the other hand, some head tremor patients respond to unilateral DBS alone. The potential effects of DBS lead location or DBS lead trajectory on head tremor suppression have yet to be elucidated [12]. Although it is clear that a suboptimal lead position may result in a less than satisfactory long-term outcome, the optimal lead trajectory and position for head tremor response remains mostly unexplored [13]. We aimed to evaluate factors, including surgical techniques such as the DBS lead trajectory, that potentially contribute to head tremor improvement in VIM ET DBS.

Section snippets

Study design

A retrospective chart review was performed utilizing a prospectively maintained IRB-approved Movements Disorders Database (INFORM) in accordance with University protocols. Informed consent was signed by all patients. The database was queried for patients with ET and Vim DBS (with and without head tremor) from the period spanning July 2002 to May 2011. The diagnosis of ET was made based on the Louis criteria [14]. For inclusion in the study, the required surgical target was the VIM thalamic

Demographics and unilateral vs. bilateral DBS

Forty-nine patients with ET underwent VIM DBS at the University of Florida and returned for 6 and 12-month follow-up evaluations. Twenty-nine of 49 patients met the inclusion criteria presenting with head tremor. Examination of demographic characteristics indicated that at the time of the first surgery the mean age was 73 (13.4 SD), and the group was predominantly female (52%). The mean duration of tremor symptoms was 33 years (19.1 SD). The baseline head tremor scores as well as the mean

Active DBS contacts

The active DBS contact was calculated for all study participants. Contact 0 (deep) was activated in 32.5% of the leads. Contact 1 and 2 were activated in 45% and 22.5% of the leads, respectively. There were nine electrodes with multiple active contacts, and the number of the active contacts was counted separately. The improvement in head tremor in each group is described in Supplemental Table 2. There were no statistically significant differences between these groups, however, there was a

Surgery related complication

Side effects were carefully documented and none of the patients in the cohort had a hemorrhage. During surgery the surface vessels are meticulously avoided. In our case series transient confusion was the major complication and was present in 5 patients with unilateral DBS and in 1 patient with bilateral DBS.

Discussion

VIM DBS has been well established as an effective treatment for appropriately selected patients with severe, medication refractory essential tremor [6], [7], [10], [19], however, predictors of head tremor improvement have not been extensively studied. We aimed to examine the potential factors that might influence head tremor suppression with VIM thalamic DBS. The results revealed that patient characteristics (ex. age, gender, etc.) and other disease factors had little impact on head tremor

Conclusion

A larger (more vertical) AC–PC angle may be more effective for capture of head tremor in VIM thalamic DBS for essential tremor. More data from multiple DBS practitioners with varying methodologies and approaches will likely be required to confirm these observations. In addition to the DBS target, the trajectory of the DBS lead may be important to individual patients who report head tremor as disabling or bothersome.

Copyright license statement

The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive license (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd, and its Licensees to permit this article (if accepted) to be published in the Journal of Neurology, Neurosurgery and Psychiatry and any other BMJPGL products and to exploit all subsidiary rights, as set out in our license.

Authorship and contributorship

Mariana Moscovich was responsible for acquisition of data, interpretation of data, drafting of the manuscript and final approval of the version to be published. Takashi Morishita was responsible for analysis and interpretation of data and manuscript revision. Christopher Favilla was responsible for statistical analysis, interpretation of data and manuscript revision. ZhongxingPeng Chen was responsible for manuscript revision, interpretation of data and drawing. Kelly Foote was responsible for

Financial disclosure

The authors report no relevant financial disclosures. Dr. Okun serves as a consultant for the National Parkinson Foundation, and has received research grants from NIH, NPF, the Michael J. Fox Foundation, the Parkinson Alliance, Smallwood Foundation, and the UF Foundation. Dr. Okun has previously received honoraria, but in the past >36 months has received no support from industry including travel. Dr. Okun has received royalties for publications with Demos, Manson, and Cambridge (movement

Conflict of interest

The authors have no conflicts of interest to report.

Acknowledgments

This work was support by Grant-in Aid for Clinical Research from St. Luke's Life Science Institute of Japan, Japan Society for Promotion of Science, the UF INFORM database, and the University of Florida Foundation.

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    Drs. Moscovich and Morishita equally contributed to the manuscript.

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