McKay Owen M, Krishnan Arun V, Davis Mark, Kiernan Matthew C
Faculty of Science, Australian National University, Canberra, Australia.
Clin Neurophysiol. 2006 Sep;117(9):2064-8. doi: 10.1016/j.clinph.2006.05.014. Epub 2006 Jul 18.
To investigate the cause of the transient weakness that occurs in recessive myotonia congenita (RMC) following sustained muscle contraction.
Nerve excitability studies were performed on a 35-year-old male with RMC due to a novel 696+1G>A CLCN1 mutation. The median nerve was stimulated at the wrist and compound muscle action potentials (CMAPs) were recorded from abductor pollicis brevis (APB). Stimulus-response behaviour using two stimulus durations, threshold electrotonus to 100-ms polarizing currents, a current threshold relationship and the recovery of excitability following supramaximal stimulation were recorded at rest. Excitability parameters were also recorded before and after maximal voluntary contraction (MVC) of APB against resistance for 60s. Results were compared to data obtained from 12 normal controls.
Baseline axonal excitability parameters were all normal, indicating that axonal function was normal at the point of stimulation. Following one minute of MVC, excitability parameters demonstrated a significant increase in threshold when compared to controls (RMC 54.9%; controls 15.5+/-3.1%). In the RMC patient, this increase in threshold was associated with a 39% reduction in the amplitude of the maximal CMAP, which remained unaffected in controls.
The reduction in maximal CMAP is likely to represent muscle activation failure due to depolarization block, with the increase in threshold possibly reflecting a compensatory attempt by motor axons to overcome prolonged contraction-induced changes in the muscle membrane.
The prolonged recovery of excitability following sustained muscle contraction is likely to be a contributing factor to symptoms of weakness and fatigue experienced by RMC patients.
研究先天性隐性肌强直（RMC）患者在肌肉持续收缩后出现短暂肌无力的原因。
对一名因新型696 + 1G>A CLCN1突变导致RMC的35岁男性进行神经兴奋性研究。在腕部刺激正中神经，并从拇短展肌（APB）记录复合肌肉动作电位（CMAP）。记录静息状态下使用两种刺激持续时间的刺激-反应行为、对100毫秒极化电流的阈下电紧张、电流阈值关系以及超强刺激后兴奋性的恢复情况。还记录了APB对抗阻力进行60秒最大自主收缩（MVC）前后的兴奋性参数。将结果与12名正常对照者的数据进行比较。
基线轴突兴奋性参数均正常，表明在刺激时轴突功能正常。在进行一分钟的MVC后，与对照组相比，兴奋性参数显示阈值显著增加（RMC为54.9%；对照组为15.5±3.1%）。在RMC患者中，这种阈值增加与最大CMAP幅度降低39%相关，而对照组中该幅度未受影响。
最大CMAP降低可能代表由于去极化阻滞导致的肌肉激活失败，阈值增加可能反映运动轴突试图补偿因长时间收缩引起的肌膜变化。
肌肉持续收缩后兴奋性恢复延长可能是RMC患者出现肌无力和疲劳症状的一个促成因素。
