Tsuneyama Atsuko, Shibuya Kazumoto, Misawa Sonoko, Suzuki Yo-Ichi, Suichi Tomoki, Kojima Yuta, Nakamura Keigo, Kano Hiroki, Prado Mario J, Kuwabara Satoshi
Department of Neurology, Graduate School of Medicine, Chiba University Chiba, Japan.
Clin Neurophysiol Pract. 2022 Mar 2;7:71-77. doi: 10.1016/j.cnp.2022.02.003. eCollection 2022.
Fatigue is a major disabling problem in patients with neuromuscular disorders. Both nerve demyelination and increased axonal branching associated with collateral sprouting reduce the safety factor for impulse transmission and could cause activity-dependent hyperpolarization and conduction block during voluntary contraction, and thus fatigue. This study aimed to investigate whether activity-dependent conduction block is associated with fatigue in demyelinating neuropathies and lower motor neuron disorders.
This study included 31 patients (17 with chronic inflammatory demyelinating polyneuropathy [CIDP] and 14 with spinal and bulbar muscular atrophy [SBMA]). Sixteen healthy subjects served as normal controls. Fatigue was assessed using the Fatigue Scale for Motor and Cognitive Functions (FSMC). Compound muscle action potential (CMAP) recording and nerve excitability testing after median nerve stimulation in the wrist were performed before and after maximal voluntary contraction of the abductor pollicis brevis for 1 min.
Patients with CIDP/SBMA had prominent fatigue with higher FSMC motor scores (P < 0.0001) than normal controls. After voluntary contractions, CMAP amplitudes decreased significantly in four of the 17 patients with CIDP and one of the 14 patients with SBMA. The reduction in CMAP amplitude was associated with the fatigue score in the motor but not in the cognitive domain. After voluntary contraction, excitability testing showed axonal hyperpolarization in the normal and CIDP/SBMA groups.
In CIDP or SBMA, fatigue is caused by voluntary contraction-induced membrane hyperpolarization and conduction block, presumably due to the critically lowered safety factor due to demyelination or increased axonal branching.
Peripheral fatigue can be objectively assessed using CMAP amplitudes and nerve excitability testing.
疲劳是神经肌肉疾病患者的一个主要致残问题。神经脱髓鞘以及与侧支发芽相关的轴突分支增加都会降低冲动传递的安全系数，并可能在自主收缩过程中导致活动依赖性超极化和传导阻滞，进而引起疲劳。本研究旨在调查活动依赖性传导阻滞是否与脱髓鞘性神经病和下运动神经元疾病中的疲劳相关。
本研究纳入了31例患者（17例慢性炎症性脱髓鞘性多发性神经病[CIDP]患者和14例脊髓性延髓肌萎缩症[SBMA]患者）。16名健康受试者作为正常对照。使用运动和认知功能疲劳量表（FSMC）评估疲劳情况。在拇短展肌进行1分钟最大自主收缩前后，对手腕部正中神经刺激后的复合肌肉动作电位（CMAP）进行记录，并进行神经兴奋性测试。
CIDP/SBMA患者存在明显疲劳，其FSMC运动评分高于正常对照（P<0.0001）。自主收缩后，17例CIDP患者中有4例以及14例SBMA患者中有1例的CMAP波幅显著降低。CMAP波幅降低与运动领域而非认知领域的疲劳评分相关。自主收缩后，兴奋性测试显示正常组和CIDP/SBMA组均出现轴突超极化。
在CIDP或SBMA中，疲劳是由自主收缩诱导的膜超极化和传导阻滞引起的，推测这是由于脱髓鞘或轴突分支增加导致安全系数严重降低所致。
可使用CMAP波幅和神经兴奋性测试客观评估周围性疲劳。
