Department of Neurology, Sapporo Medical University School of Medicine, Sapporo, Japan.
Clin Neurophysiol. 2010 Jul;121(7):1051-8. doi: 10.1016/j.clinph.2010.01.036. Epub 2010 Mar 12.
The aim of this study was to elucidate the relationship between the impairment of excitation-contraction (E-C) coupling of masseter and the bite force in patients with myasthenia gravis (MG).
In 20 patients with MG, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRP) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Serial assessments of % decrement in masseteric repetitive nerve stimulation (RNS), ECCT, and bite force were performed before and after corticosteroid therapy alone or in various combinations with FK506, cyclosporin A, intravenous immunoglobulin and immunoabsorption.
Percent amplitude decrement in RNS and ECCT decreased significantly accompanying an increase in bite force after treatment. Simple regression analysis demonstrated a linear correlation among % decrement, ECCT and bite force. However, ECCT shortening accompanying bite force recovery without reduction in % decrement was observed in 4 patients.
Masseteric E-C coupling is impaired in some MG patients, and functional recovery of E-C coupling contributes at least in part to the increase in bite force after treatment.
Impaired E-C coupling contributes to muscle weakness in patients with MG.
本研究旨在阐明重症肌无力（MG）患者咀嚼肌兴奋-收缩（E-C）偶联损伤与咬合力之间的关系。
在 20 例 MG 患者中，用针电极刺激三叉神经运动神经后，同时记录咬肌复合肌肉动作电位（CMAP）和下颌运动相关电位（MRP）。通过 CMAP 和 MRP 之间的潜伏期差异计算 E-C 偶联时间（ECCT）。使用压力敏感片测量咬合力。在单独使用皮质类固醇或与 FK506、环孢素 A、静脉注射免疫球蛋白和免疫吸附联合使用前后，对咀嚼肌重复神经刺激（RNS）、ECCT 和咬合力的%递减进行了连续评估。
治疗后，RNS 和 ECCT 的%幅度递减显著降低，咬合力增加。简单回归分析表明，%递减、ECCT 和咬合力之间存在线性相关性。然而，在 4 例患者中观察到咬合力恢复伴随 ECCT 缩短而无%递减减少。
一些 MG 患者的咀嚼肌 E-C 偶联受损，E-C 偶联的功能恢复至少部分有助于治疗后咬合力的增加。
E-C 偶联受损导致 MG 患者肌肉无力。
