Bilateral deep brain stimulation of the subthalamic nucleus: Targeting differences between the first and second side

Introduction and objectives

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a recognized treatment for drug-refractory Parkinson's disease (PD). However, the therapeutic success depends on the accuracy of targeting. This study aimed to evaluate potential accuracy differences in the placement of the first and second electrodes implanted, by comparing chosen electrode trajectories, STN activity detected during microelectrode recording (MER), and the mismatch between the initially planned and final electrode positions on each side.

Materials and methods

In this retrospective cohort study, we analyzed data from 30 patients who underwent one-stage bilateral DBS. For most patients, three arrays of microelectrodes were used to determine the physiological location of the STN. Final target location depended also on the results of intraoperative stimulation. The choice of central versus non-central channels was compared. The Euclidean vector deviation was calculated using the initially planned coordinates and the final position of the tip of the electrode according to a CT scan taken at least a month after the surgery.

Results

The central channel was chosen in 70% of cases on the first side and 40% of cases on the second side. The mean length of high-quality STN activity recorded in the central channel was longer on the first side than the second (3.07 ± 1.85 mm vs. 2.75 ± 1.94 mm), while in the anterior channel there were better MER recordings on the second side (1.59 ± 2.07 mm on the first side vs. 2.78 ± 2.14 mm on the second). Regarding the mismatch between planned versus final electrode position, electrodes on the first side were placed on average 0.178 ± 0.917 mm lateral, 0.126 ± 1.10 mm posterior and 1.48 ± 1.64 mm inferior to the planned target, while the electrodes placed on the second side were 0.251 ± 1.08 mm medial, 0.355 ± 1.29 mm anterior and 2.26 ± 1.47 mm inferior to the planned target.

Conclusion

There was a tendency for the anterior trajectory to be chosen more frequently than the central on the second side. There was also a statistically significant deviation of the second electrodes in the anterior and inferior directions, when compared to the electrodes on the first side, suggesting that another cause other than brain shift may be responsible. We should therefore factor this during planning for the second implanted side. It might be useful to plan the second side more anteriorly, possibly reducing the number of MER trajectories tested and the duration of surgery.