The Influence of Positioning and Muscle Activity on Motor Threshold during Motor Cortex Stimulation Programming

Background: Stimulation parameters are crucial for the efficacy and safety of motor cortex stimulation (MCS). Motor threshold (MT) can be defined as the lowest voltage that produces motor contraction. The final stimulation parameters are always a smaller percentage of MT in order to avoid seizures. We determined how patient position and activity affect MT. Methods: Prospective MT measurements were made while patients were either lying down or sitting up, and in a resting state or while actively contracting the target muscle. Paired 1-tailed t tests were performed to assess for statistically significant differences between MT measurements made under the 4 different combinations of position and activity. Results: The MT was lower when the target muscle was being actively contracted compared to resting in both supine and upright positions (both p < 0.001). The MT was also lower when upright compared to supine in both resting and active states of muscle contraction (both p < 0.001). The mean difference between supine resting and upright active states is 0.79 V. Conclusion: When selecting final stimulation parameters for MCS, clinicians should be aware that the lowest MT is elicited while patients are seated upright and actively contracting the target muscle. Using this method of determining the MT when calculating the final stimulation parameters could reduce the chance of MCS-induced seizures. © 2015 S. Karger AG, Basel.