OBJECTIVE The role of motor cortex reorganization in the development and maintenance of phantom limb pain (PLP) is still unclear. This study aims to evaluate neurophysiological and structural motor cortex asymmetry in patients with PLP and its relationship with pain intensity. METHODS Cross-sectional analysis of an ongoing randomized-controlled trial. We evaluated the motor cortex asymmetry through two techniques: i) changes in cortical excitability indexed by transcranial magnetic stimulation (motor evoked potential, paired-pulse paradigms and cortical mapping), and ii) voxel-wise grey matter asymmetry analysis by brain magnetic resonance imaging. RESULTS We included 62 unilateral traumatic lower limb amputees with a mean PLP of 5.9 (SD = 1.79). We found, in the affected hemisphere, an anterior shift of the hand area center of gravity (23 mm, 95% CI 6 to 38, p = 0.005) and a disorganized and widespread representation. Regarding voxel-wise grey matter asymmetry analysis, data from 21 participants show a loss of grey matter volume in the motor area of the affected hemisphere. This asymmetry seems negatively associated with time since amputation. For TMS data, only the ICF ratio is negatively correlated with PLP intensity (r = -0.25, p = 0.04). CONCLUSION There is an asymmetrical reorganization of the motor cortex in patients with PLP, characterized by a disorganized, widespread, and shifted hand cortical representation and a loss in grey matter volume in the affected hemisphere. This reorganization seems to reduce across time since amputation. However, it is not associated with pain intensity. SIGNIFICANCE These findings are significant to understand the role of the motor cortex reorganization in patients with PLP, showing that the pain intensity may be related with other neurophysiological factors, not just cortical reorganization.

中文翻译：

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幻肢痛单侧下肢截肢患者的结构和功能运动皮层不对称

目的 运动皮层重组在幻肢痛 (PLP) 的发展和维持中的作用仍不清楚。本研究旨在评估 PLP 患者的神经生理学和结构运动皮层不对称性及其与疼痛强度的关系。方法 一项正在进行的随机对照试验的横断面分析。我们通过两种技术评估了运动皮层的不对称性：i）由经颅磁刺激（运动诱发电位、配对脉冲范式和皮层映射）指示的皮层兴奋性的变化，以及 ii）通过脑磁共振成像进行的体素灰质不对称性分析. 结果 我们纳入了 62 名单侧外伤性下肢截肢者，平均 PLP 为 5.9 (SD = 1.79)。我们发现，在受影响的半球，手部区域重心前移（23 毫米，95% CI 6 到 38，p = 0.005) 和无组织且广泛的代表。关于体素灰质不对称分析，来自 21 名参与者的数据显示受影响半球运动区的灰质体积损失。这种不对称似乎与截肢后的时间呈负相关。对于 TMS 数据，只有 ICF 比率与 PLP 强度呈负相关（r = -0.25，p = 0.04）。结论 PLP 患者的运动皮层存在不对称重组，其特征是手部皮质表现紊乱、分布广泛且移位，以及受影响半球的灰质体积减少。自截肢以来，这种重组似乎随着时间的推移而减少。然而，它与疼痛强度无关。