Impedance Changes Occur During Threshold Measurements in Deep Brain Stimulation Patients (P7.046)

OBJECTIVE: To test whether electrode impedance varies during the measurement of efficacy and side effect thresholds in DBS patients. BACKGROUND: It has been previously shown that electrode impedance varies in DBS patients (Hemm et al, 2004; Sillay et al, 2010; Cheung et al, 2013). However, it is still unknown whether these impedance changes could have any clinical relevance. Here we report that electrical stimulation in the normal range for measurement of thresholds may result in large and rapid impedance changes. DESIGN/METHODS: The first 7 PD patients in our study, implanted in STN with a current-controlled DBS system for at least 3 months, were stimulated on 3 different electrode combinations, and amplitude was adjusted to measure thresholds. At the beginning and end of threshold measurements, impedance was measured. Mean time stimulation was on was under 20 minutes, and amplitude was increased to 5.5 mA on average. RESULTS: Preliminary analysis reveals that turning stimulation on resulted in an immediate reduction in impedance for 17/21 electrodes, with a maximum decrease of 14% on the active electrode. In this same subject, the inactive electrodes showed a mean impedance decrease of 1.3%. Minimum decrease was 3.2% and mean decrease on the active electrodes was 7.1% across all subjects, as compared to a mean increase of 1.3% on all inactive electrodes. CONCLUSIONS: Impedance changes of this magnitude and time scale may have clinical relevance for some patients. In voltage-controlled systems, the current delivered at each electrode is dependent on impedances. For example, a side effect threshold of 7.1mA would be reached at a voltage of 8.5V when impedance was at 1199ohms. However, with an impedance drop of 14%, that same side effect threshold would be reached with a voltage of 7.3V after only 13 minutes of stimulation. Study Supported by: Boston Scientific Neuromodulation Disclosure: Dr. Carcieri has received personal compensation for activities with Boston Scientific Corporation as an employee. Dr. Reich has nothing to disclose. Dr. Steigerwald has nothing to disclose. Dr. Barbe has nothing to disclose. Dr. Manola has received personal compensation for activities with Boston Scientific Corp. as an employee. Dr. Timmermann has received personal compensation for activities with Medtronic Inc., Boston Scientific Corp., Bayer Pharmaceuticals Corp., and UCB Pharma as a consultant, and with Teva Neuroscience, and Lundbeck Research USA, Inc. as a speaker. Dr. Timmermann has received research support from the German Research Foundation, the German Ministry of Education and Research (BMBF), and the Manfred und Ursula Muller Foundation. Dr. Volkmann has nothing to disclose.