Clinical Study Stereotact Funct Neurosurg 2015;93:122–126 DOI: 10.1159/000369355
Received: May 20, 2014 Accepted after revision: October 26, 2014 Published online: February 18, 2015
The Influence of Positioning and Muscle Activity on Motor Threshold during Motor Cortex Stimulation Programming Stephano Chang a Manish Ranjan b Philipp J. Slotty a, c Christopher R. Honey a
a Division of Neurosurgery, University of British Columbia, Vancouver, B.C., Canada; b Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, India; c Department of Stereotactic and Functional Neurosurgery, Heinrich Heine University, Duesseldorf, Germany
Abstract 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
© 2015 S. Karger AG, Basel 1011–6125/15/0932–0122$39.50/0 E-Mail [email protected] www.karger.com/sfn
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
Introduction
Motor cortex stimulation (MCS) was first described in the treatment of post-stroke pain and thalamic pain syndromes by Tsubokawa et al. [1, 2] in the early 1990s. Today its indications have grown steadily as a treatment modality for many forms of refractory neuropathic pain syndromes, including trigeminal neuropathic pain, post-stroke pain, phantom limb pain, postherpetic neuralgia, spinal cord injury pain and pain related to multiple sclerosis [1–4]. Several systematic reviews and meta-analyses have demonstrated an efficacy between 55 and 84% in the treatment of refractory neuropathic pain, with enduring long-term results [4–6]. Despite this, controversy over MCS as a therapeutic modality remains, and although the mechanism of action of MCS appears to include thalamocortical, corticocortical and corticospinal inhibition of pain signals, a precise understanding remains to be uncovered [7–10]. Christopher R. Honey, MD, DPhil, FRCS(C) Gordon and Leslie Diamond Health Care Centre Vancouver General Hospital, 8105-775 Laurel Street Vancouver, BC V5Z 1M9 (Canada) E-Mail chris.honey @ telus.net
Downloaded by: Emory University 198.143.47.65 - 1/26/2016 7:28:22 PM
Key Words Motor cortex stimulation · Deafferentation pain · Neuromodulation
Color version available online
10 n.s.
*
*
8
6 MT (V)
Like other neuromodulatory techniques, the delivery of stimulation itself involves numerous parameters, including frequency, amplitude, pulse width, dipole configuration and daily stimulation duration and frequency. During MCS, motor threshold (MT) is defined as the lowest current (or voltage) at which contraction of a target muscle occurs and is routinely elicited during the initial MCS programming sessions to provide a baseline measurement upon which a safe and effective stimulation amplitude can be determined. The MT most likely resembles the seizure threshold, and amplitudes above it should therefore be avoided. Despite the importance of this baseline measurement, there is no standardized or widely agreed upon protocol by which the MT should be measured, and specifically the effects of patient position and activity on MT measurements have not previously been studied in the literature. We hypothesized that patient position and activity each have direct and independent effects on MT measurement.
4
2
19 0
MT1
MT2
MT3
MT4
Methods Fig. 1. Boxplot with median MT values in different resting states,
whiskers representing min./max. values; * p < 0.001: highly significant; n.s. = not significant; ⚪ = outlier.
Results
Statistical Analysis A Shapiro-Wilks test resulted in normal distribution for all data sets, a paired 1-tailed t test was used for differences between pairs of MT measurements. In this way we were able to determine whether or not there was a difference between MT measurements when one of either patient position or patient activity was varied. A 1-way ANOVA was performed to determine differences in MT between the patients to determine whether individual differences in susceptibility exist. Based on the sample size, p values of
Received: May 20, 2014 Accepted after revision: October 26, 2014 Published online: February 18, 2015
The Influence of Positioning and Muscle Activity on Motor Threshold during Motor Cortex Stimulation Programming Stephano Chang a Manish Ranjan b Philipp J. Slotty a, c Christopher R. Honey a
a Division of Neurosurgery, University of British Columbia, Vancouver, B.C., Canada; b Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, India; c Department of Stereotactic and Functional Neurosurgery, Heinrich Heine University, Duesseldorf, Germany
Abstract 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
© 2015 S. Karger AG, Basel 1011–6125/15/0932–0122$39.50/0 E-Mail [email protected] www.karger.com/sfn
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
Introduction
Motor cortex stimulation (MCS) was first described in the treatment of post-stroke pain and thalamic pain syndromes by Tsubokawa et al. [1, 2] in the early 1990s. Today its indications have grown steadily as a treatment modality for many forms of refractory neuropathic pain syndromes, including trigeminal neuropathic pain, post-stroke pain, phantom limb pain, postherpetic neuralgia, spinal cord injury pain and pain related to multiple sclerosis [1–4]. Several systematic reviews and meta-analyses have demonstrated an efficacy between 55 and 84% in the treatment of refractory neuropathic pain, with enduring long-term results [4–6]. Despite this, controversy over MCS as a therapeutic modality remains, and although the mechanism of action of MCS appears to include thalamocortical, corticocortical and corticospinal inhibition of pain signals, a precise understanding remains to be uncovered [7–10]. Christopher R. Honey, MD, DPhil, FRCS(C) Gordon and Leslie Diamond Health Care Centre Vancouver General Hospital, 8105-775 Laurel Street Vancouver, BC V5Z 1M9 (Canada) E-Mail chris.honey @ telus.net
Downloaded by: Emory University 198.143.47.65 - 1/26/2016 7:28:22 PM
Key Words Motor cortex stimulation · Deafferentation pain · Neuromodulation
Color version available online
10 n.s.
*
*
8
6 MT (V)
Like other neuromodulatory techniques, the delivery of stimulation itself involves numerous parameters, including frequency, amplitude, pulse width, dipole configuration and daily stimulation duration and frequency. During MCS, motor threshold (MT) is defined as the lowest current (or voltage) at which contraction of a target muscle occurs and is routinely elicited during the initial MCS programming sessions to provide a baseline measurement upon which a safe and effective stimulation amplitude can be determined. The MT most likely resembles the seizure threshold, and amplitudes above it should therefore be avoided. Despite the importance of this baseline measurement, there is no standardized or widely agreed upon protocol by which the MT should be measured, and specifically the effects of patient position and activity on MT measurements have not previously been studied in the literature. We hypothesized that patient position and activity each have direct and independent effects on MT measurement.
4
2
19 0
MT1
MT2
MT3
MT4
Methods Fig. 1. Boxplot with median MT values in different resting states,
whiskers representing min./max. values; * p < 0.001: highly significant; n.s. = not significant; ⚪ = outlier.
Results
Statistical Analysis A Shapiro-Wilks test resulted in normal distribution for all data sets, a paired 1-tailed t test was used for differences between pairs of MT measurements. In this way we were able to determine whether or not there was a difference between MT measurements when one of either patient position or patient activity was varied. A 1-way ANOVA was performed to determine differences in MT between the patients to determine whether individual differences in susceptibility exist. Based on the sample size, p values of
