title: Subthalamic stimulation for Parkinson disease: determination of electrode location necessary for clinical efficacy.
abstract: OBJECTIVE
  Deep brain stimulation (DBS) of the subthalamic nucleus (STN) performed using intraoperative microelectrode recording (MER) to adjust electrode placement has become a widely used treatment for patients with advanced Parkinson disease (PD). Few studies have been conducted to examine the location of implanted electrodes relative to the intended target, and even fewer have been undertaken to investigate the degree to which variations in the location of these electrodes impacts their clinical efficacy. This study was performed to examine these issues.
  
  
  METHODS
  The authors located 52 bilaterally implanted DBS electrode tips on postoperative magnetic resonance (MR) images obtained in 26 consecutive patients. Postoperative and preoperative planning MR images were merged to determine the DBS electrode tip coordinates relative to the midcommissural point. Surgical records listed the intended target coordinates for each DBS electrode tip. Clinical outcome assessment included the Unified PD Rating Scale (UPDRS) motor score at 1 year, standardized questionnaires, and routine follow-up visits. The mean difference between electrode tip location and intended target for all 52 electrodes was less than 2 mm in all axes. Only one electrode was farther than 3 mm from the intended target, and this was the only electrode that had to be replaced due to lack of clinical efficacy (lack of tremor suppression); its reimplantation 4 mm more medially provided excellent tremor control. High correlation coefficients indicate that the MR imaging analysis accurately determined the anatomical location of the electrode tips. Blinded videotape reviews of UPDRS motor scores comparing effects of stimulation in patients who were "on" and "off" medication identified subgroups in whom there was minimal and maximal stimulation response. Patients in these subgroups had no differences between the MR imaging-determined actual electrode tip location and its intended location. Similarly, improvements of dyskinesias and severity of symptoms encountered during the wearing-off period for the drug did not correlate with variations of electrode tip location.
  
  
  CONCLUSIONS
  The findings in this study lead the authors to suggest that a DBS electrode placed anywhere within a 6-mm-diameter cylinder centered at the presumed middle of the STN (based on stereotactic atlas coordinates) provides similar clinical efficacy. Future studies may be warranted to evaluate prospectively the degree to which MER modification of the anatomically and/or image-determined target improves clinical efficacy of DBS electrodes.
authors.affiliation: Department of Neurological Surgery and Neurology, Columbia University College of Physicians and Surgeons, New York, New York, USA.
authors.forename: Shearwood
authors.initials: S
authors.lastname: McClelland
authors.forename: Blair
authors.initials: B
authors.lastname: Ford
authors.forename: Patrick B
authors.initials: PB
authors.lastname: Senatus
authors.forename: Linda M
authors.initials: LM
authors.lastname: Winfield
authors.forename: Yunling E
authors.initials: YE
authors.lastname: Du
authors.forename: Seth L
authors.initials: SL
authors.lastname: Pullman
authors.forename: Qiping
authors.initials: Q
authors.lastname: Yu
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Frucht
authors.forename: Guy M
authors.initials: GM
authors.lastname: McKhann
authors.forename: Robert R
authors.initials: RR
authors.lastname: Goodman
mesh_terms: D000328:Adult; D000368:Aged; D046690:Deep Brain Stimulation / Q000295:instrumentation* / Q000379:methods; D004567:Electrodes, Implanted; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology / Q000628:therapy*; D018709:Statistics, Nonparametric; D013238:Stereotaxic Techniques / Q000295:instrumentation; D020531:Subthalamic Nucleus / Q000502:physiology