OBJECTIVE To assess excitability differences between motor and sensory axons of affected nerves in patients with multifocal motor neuropathy (MMN). METHODS We performed motor and sensory excitability tests in affected median nerves of 20 MMN patients and in 20 age-matched normal subjects. CMAPs were recorded from the thenar and SNAPs from the 3rd digit. Clinical tests included assessment of muscle strength, two-point discrimination and joint position. RESULTS All MMN patients had weakness of the thenar muscle and normal sensory tests. Motor excitability testing in MMN showed an increased threshold for a 50% CMAP, increased rheobase, decreased stimulus-response slope, fanning-out of threshold electrotonus, decreased resting I/V slope, shortened refractory period, and more pronounced superexcitability. Sensory excitability testing in MMN revealed decreased accommodation half-time and S2-accommodation and less pronounced subexcitability. Mathematical modeling indicated increased Barrett-Barrett conductance for motor fibers and increase in internodal fast potassium conductance for sensory fibers. CONCLUSIONS Excitability findings in MMN suggest myelin sheath or paranodal seal involvement in motor fibers and, possibly, paranodal detachment in sensory fibers. SIGNIFICANCE Excitability properties of affected nerves in MMN differ between motor and sensory nerve fibers.

中文翻译：

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多灶性运动神经病中运动和感觉轴突的兴奋性

目的 评估多灶性运动神经病 (MMN) 患者受累神经的运动和感觉轴突之间的兴奋性差异。方法 我们对 20 名 MMN 患者和 20 名年龄匹配的正常受试者的受影响正中神经进行了运动和感觉兴奋性测试。CMAP 是从鱼际记录的，SNAP 从第 3 位开始记录。临床测试包括​​评估肌肉力量、两点辨别力和关节位置。结果所有MMN患者的鱼际肌无力，感觉检查正常。MMN 中的运动兴奋性测试显示 50% CMAP 的阈值增加、rheobase 增加、刺激反应斜率降低、阈值电张力散开、静息 I/V 斜率降低、不应期缩短以及更明显的超兴奋性。MMN 中的感觉兴奋性测试显示调节半时间和 S2 调节减少，亚兴奋性较不明显。数学模型表明运动纤维的 Barrett-Barrett 电导增加，感觉纤维的节间快钾电导增加。结论 MMN 中的兴奋性发现表明运动纤维中的髓鞘或副结节密封受累，并且可能是感觉纤维中的副结节脱离。意义 MMN 中受影响神经的兴奋性特性在运动神经纤维和感觉神经纤维之间不同。结论 MMN 中的兴奋性发现表明运动纤维中的髓鞘或副结节密封受累，并且可能是感觉纤维中的副结节脱离。意义 MMN 中受影响神经的兴奋性特性在运动神经纤维和感觉神经纤维之间不同。结论 MMN 中的兴奋性发现表明运动纤维中的髓鞘或副结节密封受累，并且可能是感觉纤维中的副结节脱离。意义 MMN 中受影响神经的兴奋性特性在运动神经纤维和感觉神经纤维之间不同。