Chang Ming-Hong, Wei Shiew-Jue, Chiang Hui-Ling, Wang Hui-Mei, Hsieh Peiyuan F, Huang San-Yong
Section of Neurology, Taichung Veterans General Hospital, No. 160, Chung-Kang Road, Section 3, Taiwan, ROC.
Clin Neurophysiol. 2002 Jul;113(7):1072-6. doi: 10.1016/s1388-2457(02)00117-7.
To elucidate the etiopathogenesis of decreased forearm median motor conduction velocity (FMMCV) in carpal tunnel syndrome (CTS), we used segmental stimulation at the palm, wrist and antecubital fossa to determine conduction block at wrist and calculate and compare the segmental median motor conduction velocity (MMCV) to determine the pathogenesis.
The cause of the decreased FMMCV in CTS remains unclear. Animal models have supported retrograde axonal atrophy as the cause. Some authors believe standard FMMCV, calculated by subtracting the distal latency, may not represent an exact assessment of FMMCV but rather the velocity of small fibers that persist throughout the carpal tunnel.
Patients with clinical symptoms and signs of CTS which had been confirmed with standard electrodiagnosis, were included. The patients were divided into two groups: one with reduced FMMCV <50m/s (Group I, n=20) and the other with normal FMMCV>50m/s (Group II, n=40). Age-matched volunteers served as controls (n=60). We used palm, wrist and antecubital stimulation, and recorded compound muscle action potential (CMAP) amplitudes at the abductor pollicis brevis (APB) muscle. Based on a ratio of the CMAP amplitudes obtained from wrist and palm stimulation (W/P ratio) and the latency differences, we calculated the W/P ratio and the across wrist MMCV (AWMMCV) and FMMCV and compared and correlated them between two patient groups.
There was no difference in median motor and sensory distal latency between Groups I and II. CMAP and sensory nerve action potential amplitudes were reduced in Group I compared with Group II, but the difference was only marginally significant. Four patients had a significant reduction of the W/P ratio in Group I, compared with 7 patients in Group II, which did not reach a significance. Sixteen patients (80%) in Group I demonstrated no conduction block. Furthermore, Group I showed significantly decreased FMMCV when compared with Group II; however, AWMMCV was not significantly reduced in Group I, suggesting that decreased FMMCV does not result from a decrease in AWMMCV.
There was no significant motor conduction block and no correlation of the FMMCV and AWMMCV in CTS patients with a decrease of FMMCV, suggesting retrograde axonal atrophy, and not selective conduction block of the large fibers at the wrist, is the direct cause of decreased FMMCV in CTS.
为阐明腕管综合征（CTS）患者前臂正中神经运动传导速度（FMMCV）降低的病因，我们通过在手掌、腕部和肘前窝进行节段性刺激，以确定腕部的传导阻滞，并计算和比较节段性正中神经运动传导速度（MMCV）来确定发病机制。
CTS患者FMMCV降低的原因尚不清楚。动物模型支持逆行性轴索萎缩为其病因。一些作者认为，通过减去远端潜伏期计算得出的标准FMMCV可能并不代表对FMMCV的准确评估，而更像是贯穿腕管的小纤维的速度。
纳入有CTS临床症状和体征且经标准电诊断确诊的患者。患者分为两组：一组FMMCV降低<50m/s（I组，n = 20），另一组FMMCV正常>50m/s（II组，n = 40）。年龄匹配的志愿者作为对照（n = 60）。我们采用手掌、腕部和肘前窝刺激，并记录拇短展肌（APB）处的复合肌肉动作电位（CMAP）波幅。根据腕部和手掌刺激获得的CMAP波幅比值（W/P比值）以及潜伏期差异，我们计算W/P比值、跨腕部MMCV（AWMMCV）和FMMCV，并在两组患者之间进行比较和关联分析。
I组和II组之间正中神经运动和感觉远端潜伏期无差异。与II组相比，I组的CMAP和感觉神经动作电位波幅降低，但差异仅为边缘显著。I组有4例患者W/P比值显著降低，II组有7例，差异无统计学意义。I组16例患者（80%）未表现出传导阻滞。此外，与II组相比，I组的FMMCV显著降低；然而，I组的AWMMCV未显著降低，提示FMMCV降低并非由AWMMCV降低所致。
FMMCV降低的CTS患者中，未发现明显的运动传导阻滞，FMMCV与AWMMCV也无相关性，提示逆行性轴索萎缩而非腕部大纤维的选择性传导阻滞是CTS患者FMMCV降低的直接原因。
