University of California Davis School of Medicine, Sacramento, CA, USA.
University of Michigan Medical School, Ann Arbor, MI, USA.
Clin Neurophysiol. 2014 Jan;125(1):142-147. doi: 10.1016/j.clinph.2013.06.187. Epub 2013 Aug 28.
While the standard has been to define motor threshold (MT) using EMG to measure motor cortex response to transcranial magnetic stimulation (TMS), another method of determining MT using visual observation of muscle twitch (OM-MT) has emerged in clinical and research use. We compared these two methods for determining MT.
Left motor cortex MTs were found in 20 healthy subjects. Employing the commonly-used relative frequency procedure and beginning from a clearly suprathreshold intensity, two raters used motor evoked potentials and finger movements respectively to determine EMG-MT and OM-MT.
OM-MT was 11.3% higher than EMG-MT (p<0.001), ranging from 0% to 27.8%. In eight subjects, OM-MT was more than 10% higher than EMG-MT, with two greater than 25%.
These findings suggest using OM yields significantly higher MTs than EMG, and may lead to unsafe TMS in some individuals. In more than half of the subjects in the present study, use of their OM-MT for typical rTMS treatment of depression would have resulted in stimulation beyond safety limits.
For applications that involve stimulation near established safety limits and in the presence of factors that could elevate risk such as concomitant medications, EMG-MT is advisable, given that safety guidelines for TMS parameters were based on EMG-MT.
虽然使用肌电图（EMG）来测量运动皮层对经颅磁刺激（TMS）的反应以定义运动阈值（MT）是标准方法，但另一种使用肌肉抽搐的视觉观察（OM-MT）来确定 MT 的方法已在临床和研究中出现。我们比较了这两种确定 MT 的方法。
在 20 名健康受试者中找到了左运动皮层 MT。采用常用的相对频率程序，从明显的超阈值强度开始，两名评估者分别使用运动诱发电位和手指运动来确定 EMG-MT 和 OM-MT。
OM-MT 比 EMG-MT 高 11.3%（p<0.001），范围为 0%至 27.8%。在 8 名受试者中，OM-MT 比 EMG-MT 高 10%以上，其中 2 名高于 25%。
这些发现表明，使用 OM 会产生明显高于 EMG 的 MT，并且可能会导致某些个体的 TMS 不安全。在本研究的超过一半受试者中，使用 OM-MT 进行典型的 rTMS 治疗抑郁症会导致刺激超出安全限制。
对于涉及在既定安全限制附近进行刺激以及存在可能增加风险的因素（如同时使用药物）的应用，鉴于 TMS 参数的安全性指南是基于 EMG-MT，因此建议使用 EMG-MT。
