Microelectrode recording: lead point in STN-DBS surgery M. S. Kim

Acta Neurochir Suppl (2006) 99: 37–42

# Springer-Verlag 2006 Printed in Austria

Microelectrode recording: lead point in STN-DBS surgery

M. S. Kim

, Y. T. Jung

, J. H. Sim

, S. J. Kim

, J. W. Kim

, and K. J. Burchiel

1

Department of Neurosurgery, Inje University Busan Paik Hospital, Busan, Korea

2

Department of Neurology, Inje University Busan Paik Hospital, Busan, Korea

3

Department of Neurology, Dong A University, OHSU, Busan, Korea

4

Department of Neurosurgery, OHSU, Portland, OR, USA

Summary

Background. Microelectrode recording is an integral part of many surgical procedures for movement disorders. We evaluate the Lead point compared to the NeuroTrek system. We used NeuroTrek in 18 Parkinsonian patients, Lead point-4 in 12 patients, during STN- DBS surgery. We compared MR-Stir image with Microelectrode recording.

Method. The MicroGuide system with its integrated screen display provides the user with all the information needed during the sur- gery on its screen. Microelectrode recordings showed characteristic neuronal discharges on a long trajectory (5–6 mm), intraoperative stimulation induces dramatic improvement of Parkinsonian motor symptoms.

Findings. Microrecording data of the Leadpoint showed high back- ground activity, and firing rate of 14–50 Hz. The discharge pattern is typically chaotic, with frequent irregular bursts and pauses.

Discussion. The microelectrode recording of the neuroTrek and Lead- point-4 showed unique results of the typical STN spike. The DBS effect is maximized associated by MER mapping.

Keywords: Parkinsonian; microelectrode recording; STN-DBS;

intraoperative stimulation.

Introduction

Microelectrode recording is an integral part of many surgical procedures for movement disorder. In the past, clinicians and researchers had to create their own mi- crorecording systems from separately purchased compo- nents. This practice resulted in a variety of setups, and many clinical centers are still using these ‘‘home made’’

systems [16]. Most of the commercially available micro- recording devices are Neurotrek (MicroGuide), Lead point 2 =Lead point 4, NeuroMap, Guideline system 3000A, Iso-X cell 3 þ=Iso Pulsar=micro Targeting, etc [16].

We used the Lead point-4 and Neurotrek (MicroGuide) in STN-DBS surgery of the Parkinsonism. I analysed

microelectrode findings in subthalamic nucleus and sub- stania nigra.

Materials and methods

Eighteen Parkinsonism patients for treatment with neuroTrek were enrolled between September, 2001 and August, 2002. in Oregon Health

& Sciences University, Portland, OR, USA, and twelve Parkinsonism patients for Lead point-2 =4 treatment between November, 2004 and March, 2005 in Busan Paik Hospital, Busan, Korea.

Bilateral electrodes were implanted stereotactically under local anesthesia in a single operation. Magnetic resonance imaging (T1, fast spin echo inversion recovery, Stir) was used to determine initial targets.

Although there is considerable variation, an approximate target for the central region of the STN nucleus is usually at about 12 mm lateral to the midline, 2–4 mm posterior to the mid-commissural point and 3 mm below the AC-PC line, with Stealth station (Medtronic, Sofamor, Mineapolis, USA) or Gamma-Plan (Elekta, Atlanta, USA). In our pro- cedure, microelectrode recording tracks starts 10 mm above target in the STN. Depending on the 55–60

angle in the sagittal plane, recording usually starts in the thalamic reticular nucleus or in the anterior thalamus Voa, Vop.

In this region there are cells with spontaneous burst discharge [13, 14].

The entry into the subthalamic nucleus is apparent when high amplitude spikes with firing rates of 25–45 Hz are found [8].

Tremor cells have also been identified in the human subthalamic

nucleus. Since subthalalmic nucleus-like cells may be found in the ad-

jacent, superiorly located zona incerta, the dorsal border of the subtha-

lamic nucleus should be defined by a continuous, cell-dense region,

populated by neurons showing movement-related activity [8]. Typically,

subthalamic spike is chaotic with frequent irregular bursts and pauses

[8]. Below the STN, the substantia nigra, is located whose characteristic

features are a high (60–90 Hz) and regular firing rate, but there may be

another group with lower rates around 30 Hz [3–5, 7]. The ideal target is

defined as one showing clinical benefit and minimal adverse effects after

stimulation through the DBS electrode. The position of the Medtronic

3387 quadripolar DBS electrode is chosen so that the 4 electrodes con-

tracts span the 5–6 mm of the subthalamic nucleus [8]. This means that

one contact is usually placed in the substantia nigra, two contacts within

the subthalamic nucleus, and the superior contact in the zona incerta [8].

Postoperatively, thin section brain CT was checked and DBS location confirmed.

Results

In our study, the spikes of the subthalamic nucleus showed high-amplitude spikes with firing rates of 14–

52 Hz (Fig .1). This is similar to other studies (Table 1).

Discussion

Bressand et al. [1] showed that there can be remark- able improvement of motor symptoms in Parkinsonism with bilateral deep brain stimulation of the subthalamic nucleus.

The most compact of all commercially available microrecording systems is developed and commonly used machine is Microguide. Lead point (Medtronic, Skovlundae, Denmark, and Shoreview, MN) is designed for single and multiple microelectrode recording capable of single-cell isolation and FDA cleared [16].

Fig. 1. Subthalamic nucleus microelectrode finding in Neurotrek

Table 1. Characteristic mean firing rates of subthalamic regions encountered during microelectrode recordings

STN mean discharge rate (Hz)

STN cells recorded

SNr mean discharge rate (Hz)

SNr cells

Theodosopoulos et al. [17]

34 102 86 6

Hutchison et al. [8] 37 248 71 56

Pidoux et al. [19] 39 45 50–60

Magnin et al. [10] 41 24

Lozano et al. [7] 46 213

Rodriguez et al. [15] 33 200 71 27

Magarinos-Ascone et al. [9]

59–69 190

Kim et al. [our study] 14–52

Gielen FLH [5], described 5 channels tracing of the Lead-point Micro- electrode recording and the spikes of the center, lateral, posterior spikes showed excellent view (Figs. 2, 3). Usually, I used 3–5 channels for microelectrode recording. In our study, the mean depth of the sub- thalamic nucleus was 6–7 mm and our microelectrode recording of the Lead point-4 showed excellent view in center, posterior, laterial, anterior order (Fig. 4).

The follow-up is between 6 and 48 months, with a median 28 months.

There were no permanent complications from the procedure.

38 M. S. Kim et al.

The system is delivered in two versions: Lead point 2 accommodates two microelectrodes, and Lead point 4 may simultaneously record from four electrodes, with the fifth electrode being switchable.

Lead point 4.0 is available in Europe now, and will soon be available to U.S. users [16]. For microelec- trode navigation Lead point uses the microTargeting drive by Frederick Haer & Co. From a nonacademic user point of view, the system is a very good choice because it is compact, easy to use, has good quality of recording =amplification, and is less expensive than its competitors. Another advantage of Lead point is its potential integration with frameless navigation systems that may effectively eliminate the need for multiple instrumentation racks in an already crowded operating room [16].

Anatomic studies have shown somatotopically orga- nized projections to the subthalamic nucleus from various parts of the frontal cortex. An autoradiographic tracer study in macaque monkeys showed motor cortex projec-

tions representing the face, arm, and leg arranged lateral to medial within the dorsolateral part of the nucleus [11].

More recently, a study of anterograde tracer injection after intracortical microstimulation mapping in macaque monkeys showed that the facial, forelimb, and hindlimb primary motor cortex projected to the lateral subthala- mic nucleus in a lateral to medial arrangement [12].

Similar parts of the supplementary motor area project- ed in an inverse order into a more medial part of the nucleus [12].

Electrophysiological studies in the normal monkey reveal a predominance of cells responsive to somatosen- sory examination in the dorsolateral part of the STN [3, 18]. Cells representing the hindlimb are located cen- trally within this part of the nucleus, whereas forelimb cells are primarily encountered laterally and at the ros- tral and caudal poles. In a study of Parkinsonian humans undergoing STN surgery, leg-related cells were medial, arm-related cells were lateral, and orofacial cells were located in an intermediate zone [15].

Fig. 2. Subthalamic nucleus microelectrode finding in Lead point 2

Lead point in STN-DBS surgery 39

Theodosopoulos et al. [17] studied the location of 303 cells during 15 procedures for STN-DBS for Parkinson’s disease. The dorsolateral part of the nucleus was the pre- dominant location of the movement-related cells. Within this part of the nucleus, leg- and arm-related cells ex- hibited different locations. Leg-related cells occupied a relatively central location, whereas arm-related cells tended to populate the lateral part and the rostral and caudal poles of the nucleus.

The somatotopic organization of the skeletomotor ter- ritory of SNr is unclear. DeLong et al. [2] showed that five of seven arm-related cells recorded in a primate study were located ventrally and posteriorly with respect to orofacial cells. Leg-related activity has not been iden- tified. There is little information on movement-related activity in the human substantia nigra [17]. On a para- sagittal approach to the subthalamic nucleus at 55–60 degrees from the AC-PC plane, the typical operative tra- jectory passes along the anterior part of the thalamus, transverses the zona incerta, enters the subthalamic nucleus, and encounters the substantia nigra past the

nucleus’s ventral border. Thalamic cells recorded on this trajectory may demonstrate bursting or non bursting patters, with mean discharge rates of 15  19 Hz and 28  19 Hz, respectively [6]. High background activity, frequent multicellular recordings, and firing rates of 30–50 Hz are characteristic of subthalamic nucleus cells [17]. The discharge pattern is typically chaotic, with fre- quent irregular bursts and pauses [17]. The finding of movement-related activity confirms that the microelec- trode is within the dorsolateral subthalamic nucleus, the presumed target area for subthalamic nucleus-Deep Brain Stimulation. In our study, the firing rate of 14–50 Hz was seen in subthalamic nucleus and finding of movement related activity of the dorsolateral subthalamic nucleus was checked. Motor symptoms are improved by the

‘‘micro lesion’’ effect associated with microelectrode re- cording mapping or DBS lead insertion [17].

In conclusion, the microelectrode recording of Neuro Trek and Lead point showed unique results of the typi- cal subthalamic nucleus spike. Interest in the electro- physiology of the subthalamic nucleus is prompted by

Fig. 3. Continuous microelectrode recording in Lead point 2

40 M. S. Kim et al.

its increasing importance in the surgical treatment of Parkinsonism.

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Correspondence: Moo Seong Kim, Department of Neurosurgery, Busan Paik Hospital, Kaekeumdong, Jin Koo, Busan 614-735, Korea.

e-mail: kinmmo@yahoo.co.kr

42 M. S. Kim et al.: Lead point in STN-DBS surgery