Intraoperative Neurophysiology in DBS for Dystonia
Jerry L. Vitek, MD, PhD,1* Mahlon R. DeLong, MD,2 Philip A. Starr, MD, PhD,3 Marwan I. Hariz, MD, PhD,4
and Leo Verhagen Metman, MD, PhD5
1University of Minnesota, Minneapolis, Minnesota, USA
2Emory University School of Medicine, Atlanta, Georgia, USA
3Division of Neurosurgery, UCSF, San Francisco, California, USA
4Unit of Functional Neurosurgery, UCL Institute for Neurology, Queen Square, London, United Kingdom
5Rush University Medical Center, Chicago, Illinois, USA
ABSTRACT: Deep brain stimulation (DBS) of the in-
ternal segment of the globus pallidus (GPi) has been
demonstrated to be an effective therapy for the treatment
of primary dystonia as well as tardive dystonia. Results
for other forms of secondary dystonia have been less
consistent. Although a number of target sites have been
explored for the treatment of dystonia, most notably the
motor thalamus, the target of choice remains the sensori-
motor portion of the GPi. Although the optimal site within
the GPi has not been determined, most centers agree
that the optimal site involves the posteroventral lateral
‘‘sensorimotor’’ portion of the GPi. Microelectrode re-
cording (MER) can be used to identify boundaries of the
GPi and nearby white matter tracts, including the cortico-
spinal tract and optic tract, and the sensorimotor GPi.
However, whether or not the use of MER leads to
improved outcomes compared with procedures per-
formed without MER has not been determined. Currently,
there is no evidence to support or refute the hypothesis
that mapping structures with MER provides better short-
or long-term outcomes. Centers using MER do not report
a preference of one system over another, but there have
not been any studies to compare the relative benefits or
risks of using more than 1 electrode simultaneously.
Comparison studies of different target structures and tar-
geting techniques in dystonia have not been performed.
Additional research, which includes comparative studies,
is needed to advance our understanding and optimiza-
tion of DBS targets, techniques, and approaches along
with their relative benefits and risks in dystonia. VC 2011
Movement Disorder Society
Key Words: deep brain stimulation; dystonia; GPi;
intraoperative; neurophysiology; microelectrode
recording
Because of its reversibility and adaptability, deep
brain stimulation (DBS) offers an opportunity to more
precisely define existing targets for dystonia and iden-
tify or explore new ones. Although in the past the
choice of target structures for movement disorders has
been based on empirical methods, in more recent years
a rationale-based approach has been developed. This
approach arose out of advances in our understanding
of basal ganglia thalamocortical circuitry and the
changes that occur in this circuitry in patients with
movement disorders.1,2 Methods to target and identify
deep brain structures for implantation of a DBS lead
have been developed that rely on improved imaging
techniques3,4 and may or may not utilize other techno-
logical advances. In this section, we address the target
structures used to treat dystonia and the ongoing
debate5,6 surrounding the decision about whether to
use MER to identify the target structure.
Materials and Methods
Search Strategy
The initial literature search was performed using
PubMed, CINAHL and the Cochrane Collaborative
databases from 1980 to January 2008 using the terms
dystonia AND deep brain stimulation, pallidal stimu-
lation AND dystonia, subthalamic stimulation AND
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* Correspondence to: Jerry L. Vitek, MD., PhD. Department of
Neurology, University of Minnesota, 420 Delaware Street SE,
Minneapolis, MN 55455, USA; vitek004@umn.edu
Relevant conflict of interest: Nothing to report.
Received: 24 April 2010; Revised: 23 November 2010; Accepted: 29
November 2010
Published online in Wiley Online Library (wileyonlinelibrary.com).
DOI: 10.1002/mds.23619
S U P P L E M E N T
Movement Disorders, Vol. 26, No. S1, 2011 S35

dystonia, thalamic stimulation AND dystonia, second-
ary dystonia AND DBS, and neurodegenerative dis-
eases AND DBS. The search was combined with that
used for neuropsychology, neuropsychiatry, microelec-
trode recording, neuroimaging, electrophysiology,
surgical techniques, complications, and targeting.
Only English-language publications involving human
subjects were considered. A total of 235 articles were
retrieved. To facilitate the committee’s work, the
articles were divided into 3 overlapping groups: preop-
erative, intraoperative, and postoperative. A PDF file
was created for each article obtained from the search
and put on a CD that was mailed to members. During
the writing phase, an additional 71 articles were
added to update the search, covering the period from
January 2008 to September 2009.
Process of Generating Clinical
Recommendations
The Consensus Committee members of the Task
Force included neurologists, neurosurgeons, neuro-
physiologists, psychiatrists, neuropsychologists, nurses,
and midlevel practitioners with expertise and experi-
ence in DBS. The experts were also chosen from differ-
ent countries in Asia, Europe, North America, and
South America to provide a more comprehensive con-
tribution to the Task Force. The authors of each chap-
ter were selected taking into account their specific
expertise in the field. The steering committee prepared
a list of questions related to preoperative, intraopera-
tive, and postoperative issues and established 2 chairs
responsible for each of these 3 areas (subcommittees).
These chairs then assigned a few questions to be
addressed by each member of the subcommittees. The
answers to the questions had to be formulated after
reviewing the available literature (provided on CD) and
combining their expertise. Because the level of evidence
for most of the DBS studies for dystonia was low, the
responses were organized according to the template
previously used for the ‘‘Special Supplement on DBS
for Parkinson’s Disease (PD),’’ which included sections
on (1) available data, (2) conclusions, (3) pragmatic
recommendations, and (4) points to be addressed.7 A
preliminary document was prepared from this initial
work that was then reviewed and discussed by the
entire Task Force during a 1-day meeting. During this
meeting, Task Force members provided further feed-
back and agreed on additional refinements of the docu-
ment based on comments and remarks collected during
the meeting. Special attention was paid to formulating
pragmatic recommendations in the absence of available
studies. A second version of the project was sent to the
entire Task Force for final approval. The executive
committee then met again to refine the ‘‘Special Supple-
ment’’ document before submission.
Results
Targets
What is the recommended target structure?
Available Data. Among the 32 centers with 80
reports, the large majority used the internal globus
pallidus (GPi) as the target for primary dystonia. One
class I randomized, controlled clinical trial8 and a pro-
spective single-blind trial9 of GPi DBS have been car-
ried out, both reporting favorable responses. Two
articles described the use of the ventrolateral thalamus
as a target for myoclonus-dystonia.10,11 Two articles
described targeting the ventralis oralis anterior (Voa)
for postanoxic dystonia.12,13 One study described tar-
geting the ventralis intermedius (Vim) with DBS for
paroxysmal dystonia.14 Another article combined Vim
and GPi for tardive dystonia.15 Five studies described
targeting the subthalamic nucleus (STN).16–20 A small
minority of reports did not mention the target at all.
Given the heterogeneous nature of dystonia, with
multiple etiologies, pathophysiological substrates, and
clinical presentations, it may be questionable whether
there is only a single target for dystonia. The postero-
ventral lateral GPi has been a target for ablative
approaches for dystonia since the 1950s, although it
was replaced by the thalamus in the 1960s and into the
1990s. The pallidal target for ablative procedures as
well as DBS was revived, in part, based on the favor-
able experience with pallidotomy for PD, in which the
dystonic features were found to almost universally
improve.21 The STN target has been only recently
explored in small pilot studies.16–20 Thalamic targets,
which were widely employed in the earlier ablative era,
have been largely abandoned for the primary dystonias.
The reasons for this are unclear but may be related to
the marked success of the GPi target, along with the
unclear nature of the specific subnuclei within the thal-
amus that should be targeted. There have been no
head-to-head comparisons of these targets for dystonia.
The optimal target for the secondary dystonias remains
a question because the pallidal target has proven less
satisfactory, except for tardive dystonia15,22–24 and
panthothenate kinase–associated neurodegeneration
(PKAN, formerly Hallervorden-Spatz disease).25,26 A
number of authors targeted the Voa-Vop regions for
secondary dystonia and a variety of other subnuclei in
the thalamus, especially for focal hand dystonia.27,28
Conclusions. The GPi is the currently recommended
target for primary dystonia. The STN is being investi-
gated, but data on this site are limited, and head-to-
head comparisons between the STN and the GPi have
not been performed. For the secondary dystonias, with
the exception of tardive dystonia and PKAN, which
respond to stimulation at the GPi site, the optimal tar-
get is still a matter of uncertainty that may reflect the
V I T E K E T A L .
S36 Movement Disorders, Vol. 26, No. S1, 2011