Objective: The aim of this study was to determine the discrepancies between the final location of the contacts in the GPi and the targets that had been previously chosen by magnetic resonance imaging (MRI). The second aim was to compare the location of the contacts being used for stimulation in patients with dystonia and to correlate the results with clinical outcomes to identify an optimal target. 

Background: Factors that may influence the clinical outcomes of GPi DBS include clinical variables such as patient characteristics and types of dystonia, surgical variables such as electrode contact location, and electrical stimulation parameters such as pulse width, amplitude, and rate. Unlike the case for DBS of the subthalamic nucleus (STN), the correlation between the electrode location and the clinical outcome for GPi DBS has not been fully elucidated. 

Methods: Thirty-six patients who underwent GPi DBS for dystonia were included in this retrospective study. The Burke-Fahn-Marsden dystonia scale (BFMDRS) for movement assessment and a disability score for functional assessment were recorded. Patients were assessed preoperatively and at defined follow-up examinations postoperatively, at 3, 6, 12, 24, 36, 60, and 84 months. The mean follow-up duration was 47.50 ± 23.67 months (range, 6–84 months). The pre- and postoperative images taken 6 months after GPi DBS were fused by using a mutual information technique. With this fusion method, we were able to locate the center of the electrode’s MRI artifact, which we presumed to be the center of the electrode. The distances between the target and midcommissural point, midline, and intercommissural line were measured on the fused image. The X coordinate was defined as the lateral distance from the midline, the Y coordinate as the anterior distance from the midcommissural point, and the Z coordinate as the inferior distance from the intercommissural line. 

Results:

All coordinates showed a significant difference between theoretical and actual values for all electrode locations (P<0.05). The left-side actual electrode tended to locate more laterally, posteriorly, and inferiorly than the theoretical target, and the right-side actual electrode more medially, posteriorly, and inferiorly than the theoretical target. In particular, greater differences were exhibited for Y than for X and Z coordinates. There was no significant difference in the accuracy of the localization of the left-side versus the right-side electrode for any coordinates. The patients whose electrodes were located within or near the posteroventral GPi showed better clinical outcomes. 

Conclusions:

This study demonstrates the differences between target and actual electrode locations and the relationship with clinical outcomes. The actual electrode location was slightly more posterior to the theoretically planned target. Electrodes concentrated near the posteroventral GPi tended to yield favorable outcomes. Future work will be required to heighten the accuracy of DBS and elucidate the GPi structure.   

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MDS Abstracts - https://www.mdsabstracts.org/abstract/correlation-of-electrode-position-and-clinical-outcomes-in-globus-pallidus-stimulation-for-dystonia/