Abstract
ObjectiveSegmented deep brain stimulation leads in the subthalamic nucleus have shown to increase therapeutic window using directional stimulation. However, it is not fully understood how these segmented leads with reduced electrode size modify the volume of tissue activated (VTA) and how this in turn relates with clinically observed therapeutic and side effect currents. Here, we investigated the differences between directional and omnidirectional stimulation and associated VTAs with patient-specific therapeutic and side effect currents for the two stimulation modes.ApproachNine patients with Parkinson’s disease underwent DBS implantation in the subthalamic nucleus. Therapeutic and side effect currents were identified intraoperatively with a segmented lead using directional and omnidirectional stimulation (these current thresholds were assessed in a blinded fashion). The electric field around the lead was simulated with a finite-element model for a range of stimulation currents for both stimulation modes. VTAs were estimated from the electric field by numerical differentiation and thresholding. Then for each patient, the VTAs for given therapeutic and side effect currents were projected onto the patient-specific subthalamic nucleus and lead position.ResultsStimulation with segmented leads with reduced electrode size was associated with a significant reduction of VTA and a significant increase of radial distance in the best direction of stimulation. While beneficial effects were associated with activation volumes confined within the anatomical boundaries of the subthalamic nucleus at therapeutic currents, side effects were associated with activation volumes spreading beyond the nucleus’ boundaries.SignificanceThe clinical benefits of segmented leads are likely to be obtained by a VTA confined within the subthalamic nucleus and a larger radial distance in the best stimulation direction, while steering the VTA away from unwanted fiber tracts outside the nucleus. Applying the same concepts at a larger scale and in chronically implanted patients may help to predict the best stimulation area.
Highlights
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has demonstrated efficacy in treating motor symptoms of Parkinson’s disease [1,2]
While beneficial effects were associated with activation volumes confined within the anatomical boundaries of the subthalamic nucleus at therapeutic currents, side effects were associated with activation volumes spreading beyond the nucleus’ boundaries
Though we were not able to show statistically significant results regarding the correlation between therapeutic, side effect currents and therapeutic window, we found it useful to show the correlation between the volume of tissue activated (VTA) and the anatomical boundaries of the STN in patient-specific situations
Summary
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has demonstrated efficacy in treating motor symptoms of Parkinson’s disease [1,2]. It delivers electrical pulses at high stimulation frequencies to pathogenic brain areas using leads with four (Medtronic Activa, Abbott St Jude Libra) to eight (Boston Scientific Vercise) ring electrodes. Most implanted DBS systems provide current delivery in all directions around the electrode This omnidirectional mode has shown to significantly improve motor symptoms, but unintended stimulation of surrounding anatomical structures can induce disabling side effects such as tonic muscular contraction, dysarthria, conjugate eye deviation, paresthesia, or gait imbalance [3,4,5]. This typically reduces treatment efficacy as less stimulation is directed towards the target structure, which is the dorsolateral, or motor part, of the STN [2]
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