Abstract:

Objective: To summarize the electrophysiological and muscle pathological characteristics of Lambert-Eaton myasthenic syndrome (LEMS). Methods and Results: Twelve LEMS patients referred to China-Japan Friendship Hospital between January 2010 and December 2021 were included. Clinically, they all showed proximal muscle weakness and reduced or disappeared tendon reflexes. Electrophysiologically, all 12 patients showed decreased compound muscle action potential (CMAP) amplitudes, normal distal motor latency (DML), and normal motor and sensory conduction velocities. Ten patients underwent repetitive nerve stimulation (RNS) test: all had amplitude increments of more than 100% at high-frequency RNS, and 8 had amplitude decrements of more than 15% at low-frequency RNS. Three patients completed the post-exercise facilitation (PEF) test: the ulnar nerve CMAP amplitude reached a peak immediately after maximum voluntary contraction of the abductor digiti minimi for 5-10 s and then gradually decreased to near baseline level after contraction for 60 s; the ulnar nerve CMAP amplitude reached a peak immediately after maximum voluntary contraction for 10 s, and then rapidly decreased to near baseline level after 15 s. On needle EMG, 8 patients showed normal motor unit action potential (MUAP), 3 showed short-duration MUAP mimicking myopathy, and one showed long-duration MUAP mimicking neuropathy. Two patients with normal MUAP underwent biceps biopsy, which showed selective type Ⅱ fiber atrophy. Conclusions: Electrophysiologically, CMAP amplitudes of LEMS patients are usually diffusely low or borderline. LEMS patients have amplitude increments of more than 100% at high-frequency RNS, and some have amplitude decrements of more than 15% at low-frequency RNS. PEF test shows a transient but significant CMAP amplitude increase after 5-10 s maximum voluntary contraction. Needle EMG is usually normal, but some show myogenic lesions, and some show neurogenic lesions. Muscle biopsy shows selective type Ⅱ fiber atrophy. Needle EMG myogenic lesion may not be associated with pathologically selective type Ⅱ fiber atrophy.

Key words: Lambert-Eaton myasthenic syndrome, Electrophysiology, Pathology

摘要：

目的: 总结Lambert-Eaton肌无力综合征的神经电生理学和肌肉病理学特点。方法与结果: 纳入2010年1月至2021年12月中日友好医院诊断与治疗的12例Lambert-Eaton肌无力综合征患者，临床均表现为四肢无力，以近端肌无力为著，腱反射减弱或消失。神经电生理检测，12例复合肌肉动作电位（CMAP）波幅均不同程度降低，远端运动潜伏期、运动和感觉神经传导速度正常；10例行重复神经刺激，均呈高频递增阳性，其中8例低频递减阳性；3例行运动后易化检查均阳性，小指展肌最大用力收缩5~10 s后尺神经CMAP波幅达峰值，此后逐渐下降，最大用力收缩60 s后波幅降至接近基线水平，最大用力收缩10 s后即刻尺神经CMAP波幅达峰值，此后迅速下降，至15 s波幅降至接近基线水平；8例针极肌电图正常，3例呈肌源性损害，1例呈神经源性损害。2例针极肌电图正常患者行肱二头肌组织活检术，均表现为选择性Ⅱ型肌纤维萎缩。结论: Lambert-Eaton肌无力综合征患者CMAP波幅降低，存在高频递增现象，部分患者存在低频递减现象；运动后易化检查最大用力收缩5~10 s后CMAP波幅达峰值；针极肌电图多正常，部分呈肌源性损害，小部分呈神经源性损害；肌肉组织活检可见选择性Ⅱ型肌纤维萎缩；针极肌电图肌源性损害与肌肉病理选择性Ⅱ型肌纤维萎缩可能不相关。

关键词: 郎伯综合征, 电生理学, 病理学