P 37 Correlation of intra- and postoperative best active contact and its implication for STN-DBS outcome

Abstract

Objective Deep brain stimulation is a well-established treatment for Parkinson’s Disease. The value of awake DBS to guide the implantation process is an ongoing debate. Intraoperative assessment of symptom control and side effect threshold are considered the gold standard for the decision of the final trajectory. Here we focus on a retrospective analysis of the intraoperative and one year follow up best active contacts and VTA-models. Methods We analyzed 46 patients (15 female) with 92 STN leads who received STN-DBS between 2014-2018. Intraoperative best active contact was defined as the contact with the lowest current to achieve maximum therapeutic effect. To determine stimulation location intraoperative semimacro-teststimulation settings were applied to Guide XT software after fusion of the individual MRi and postoperative CT scan. Same procedure was repeated for the stimulation settings used one year after implantation. Results 96 intraoperative and 96 postoperative leads and VTAs were calculated. Average AC-PC coordinates for the best intraoperative contact were 12.4/2.9/3.1mm (lat./post./inf.) and 12.7/2.2/2mm for the one year follow up. Average vector distance was 2.4mm between intraoperative best contact and chronically used contact (range 0.2 – 7.7mm). The distance between centers of gravity of intra- vs. postoperative VTAs did not show any correlation with motor outcome. Discussion Our findings show a significant location difference between the best contact at intraoperative stimulation and the best active contact at one year follow up. VTA-modelling showed no correlation for the therapeutic effect and the overlap of intra- and postoperative VTAs. Since intraoperative testing is mostly limited to rigidity assessment, a more inferior / caudal stimulation could selectively detect best rigidity control but not achieve the full scope of mobility improvement by STN-DBS. Interestingly, center of gravity for groups lied within the delineations of former published sweet spots. For the implantation process of directional leads, the placement of one directional pole 1-2mm superior to the best intraoperative spot appears advisable.