Objectives

Mechanisms of analgesic efficacy related to motor cortex stimulation (MCS) remain poorly understood. Specifically, it is unclear whether pain relief is somatotopically driven or not. We present three illustrative case-reports of MCS in which unintentional stimulation setting errors occurred, leading to differential (and reversible) pain relief outcomes across the hemi-body.

Methods

After successful preoperative rTMS trials, three patients suffering from post-stroke pain were selected for MCS. Stimulation was set with the aim of activating two epidural electrodes over the somatotopic representation of the lower and upper limbs. Data regarding pain relief were prospectively collected.

Results

At the first follow-up, all three patients complained of a lack of pain relief in the lower limb, contrasting with good outcome in the upper limb. In fact, for each of them we diagnosed the same stimulation setting error, to which they were “blinded”, i.e., the parasagittal electrode over the somatotopic representation of the lower limb was inadvertently turned off. Subsequently, six months after having the electrode turned on (still in a “blinded” fashion), all three patients described substantial pain relief in the lower limb, with a median improvement of 50% (range: 40–70%).

Discussion

These incidental case reports argue in favor of a genuine and at least partly somatotopically-driven analgesic efficacy of MCS. Therefore, the parasagittal electrode seems crucial when treating lower limb pain with MCS.

中文翻译：

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运动皮层刺激的镇痛作用是否由躯体驱动？

目标

与运动皮层刺激（MCS）有关的镇痛功效机制仍知之甚少。具体而言，尚不清楚是否通过体位驱动止痛。我们提出了MCS的三个说明性病例报告，其中发生了意外的刺激设置错误，导致整个半身疼痛的缓解效果不同（且可逆）。

方法

在成功的术前rTMS试验之后，选择了三名患有中风后疼痛的患者进行MCS治疗。设置刺激的目的是激活下肢和上肢的体位表征上方的两个硬膜外电极。前瞻性收集有关缓解疼痛的数据。

结果

在第一次随访中，所有三名患者均抱怨下肢疼痛没有缓解，而上肢预后良好。实际上，对于他们中的每一个，我们都诊断出了相同的刺激设置错误，他们被“盲目”了，即下肢体位表征上方的旁矢状电极被意外关闭。随后，在打开电极六个月后（仍然以“盲”方式），所有三名患者的下肢疼痛均得到了缓解，中位数改善了50％（范围：40-70％）。

讨论区

这些偶然的病例报道认为，MCS具有真正的且至少部分是由体位驱动的镇痛效果。因此，用MCS治疗下肢疼痛时，矢状旁电极似乎至关重要。