Abnormal excitability of a spinal motoneuron in patients with amyotrophic lateral sclerosis.

为探讨肌萎缩侧索硬化症(ALS)皮质脊髓束退行性变的病理生理学机制，研究了经颅磁刺激对自发激活时单个运动单位放电特性的影响。对12例ALS患者、14例健康人、12例上运动神经元病变者和9例单纯下运动神经元病患者的第一骨间背肌记录了运动单位。在最小的肌肉收缩期间，超过100个磁刺激被传递到头皮上。运动单位放电的发生被绘制在刺激前时间直方图中。在正常单位，在20-30毫秒的潜伏期，代表单突触激活(主峰)的放电概率增加。病程短的肌萎缩侧索硬化症患者的运动单位在主峰时放电概率显著增加(p&lt；0.01)。4例有上运动神经元体征的肌萎缩侧索硬化症患者的运动单位均为双峰，先同步后分散。后者被归因于缓慢的皮质脊髓通路，在健康受试者中仍未被检测到或功能上微不足道。我们的结论是ALS患者存活的皮质脊髓束通路的兴奋性异常增加，尤其是在早期。

The pathophysiology of corticospinal tract degeneration in amyotrophic lateral sclerosis (ALS) was investigated by studying the effect of transcranial magnetic stimulation on discharge characteristics of single motor units during voluntary activation. The motor units were recorded from the first dorsal interosseus muscles of 12 patients with ALS,14 healthy subjects, 12 patients with upper motor neuron lesions and 9 with pure lower motor neuron diseases. More than 100 magnetic stimuli were delivered over the scalp during minimal muscle contraction. The occurrence of motor unit discharges was plotted in a peristimulus time histogram. An increase in discharge probability at latencies of 20-30 msec, that represents monosynaptic activation (primary peak) was found in normal units. Motor units from ALS patients with short disease durations had significantly increased discharge probabilities in the primary peak (p<0.01). Motor units from 4 ALS patients with upper motor neuron signs showed double primary peaks ; an initial synchronized peak followed by a dispersed peak. The latter was ascribed to a slow corticospinal pathway, which remains undetected or is functionally insignificant in healthy subjects. We conclude that the excitabilities of the surviving corticospinal tract pathways ate abnormally increased in ALS,especially in the early stage.