Abstract
Successful deep brain stimulation (DBS) in Parkinson's disease (PD) requires optimal electrode placement. One technique of intraoperative electrode testing is determination of stimulation thresholds inducing corticospinal/corticobulbar tracts (CSBT) motor contractions. This study aims to analyze correlations between DBS electrode distance to CSBT and contraction thresholds, with either visual or electromyography (EMG) detection, to establish an intraoperative tool devoted to ensure safe distance of the electrode to the CSBT. Twelve PD patients with subthalamic nucleus DBS participated. Thresholds of muscular contractions were assessed clinically and with EMG, for three different sets of stimulation parameters, all monopolar: 130 Hz high-frequency stimulation (HFS); 2 Hz low-frequency stimulation with either 60 or 210 µs (LFS-60, LFS-210). The anatomical distance of electrode contacts to CSBT was measured from fused CT-MRI. The best linear correlation was found for thresholds of visually detected contractions with HFS (r2 = 0.63, p < 0.0001) when estimated stimulation currents rather than voltages were used. This correlation was found in agreement with an accepted model of electrical spatial extent of activation (r2 = 0.50). When using LFS, the correlation found remained lower than for HFS but increased when EMG was used. Indeed, the detection of contraction thresholds with EMG versus visual inspection did allow more frequent detection of face contractions, contributing to improve that correlation. The correlation between electrode distance to the CSBT and contraction thresholds was found better when estimated with currents rather than voltage, eliminating the variance due to electrode impedance. Using LFS did not improve the precision of that evaluation, but EMG did. This technique provides a prediction band to ensure minimum distance of the electrode contacts to the CSBT, integrating the variance that can be encountered between prediction of models and practice.
Highlights
Deep brain stimulation (DBS) is an established procedure to treat motor symptoms of patients with Parkinson’s disease (PD)
Significant correlation was found between the distance of the DBS electrode to the corticospinal/corticobulbar tracts (CSBT) and the stimulation threshold of contractions for high-frequency stimulation (HFS) and low-frequency stimulation (LFS) (Table 1)
This study found a significant linear correlation between the distance of the DBS electrode contact to the CSBT and the stimulation amplitude
Summary
Deep brain stimulation (DBS) is an established procedure to treat motor symptoms of patients with Parkinson’s disease (PD). In the DBS field, a linear correlation between the stimulation thresholds of CSBT side effects and the distance to CSBT has been found, allowing for the assessment of the position between CSBT to DBS electrodes [7] In this initial study, the stimulation amplitudes were described with voltages, and stimulation thresholds were determined visually. Aims of the present study are (i) to analyze the correlation between the distance of DBS contacts to CSBT and the amplitude of stimulation expressed with both voltage (volts) and estimated current (milliamperes), to establish an intraoperative tool devoted to ensure safe distance of the electrode to the CSBT; (ii) to determine if this correlation was stronger using low-frequency stimulation (LFS) or high-frequency stimulation (HFS) (i.e., 2 versus 130 Hz) and for pulse durations of 60 versus 210 μs, as used in centers intraoperatively; and (iii) to examine whether this correlation could be stronger using EMG beyond visually detected muscle contractions. One technique of intraoperative electrode testing is determination of stimulation thresholds inducing corticospinal/corticobulbar tracts (CSBT) motor contractions
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