PMC6134173_01
Neurophysiological tests in LEMS. Representative neurophysiological diagnostic approach in patients with LEMS. (A) the baseline low amplitude of the median nerve compound muscle action potential (CMAP) from right abductor pollicis brevis (APB) was significantly increased after brief isometric exercise; (B) in the same muscle, low- (LF) and C) high-frequency (HF) repetitive stimulation test (RST) showed significant decremental (B) and incremental response (C), respectively.
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Extended neurophysiological testing revealed an increase of the median nerve CMAP basal amplitude after brief (10 s) isometric contraction (4.4   12.7 mV, increase of 288%) (Fig. 1A), a decremental response of CMAP amplitude at LF-RST (3 Hz) (-22.7%) and incremental response at HF-RST (30 Hz) (227%) (Fig. 1B-C), recording from right abductor pollicis brevis (APB).
Frequency-dependent neuromuscular jitter in LEMS. Stimulated single-fiber electromyography (sSFEMG) demonstrated a frequency-dependent reduction of the neuromuscular jitter values at the increase of the stimulation rate.
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In contrast, sSFEMG showed the typical rate-dependent reduction of the neuromuscular jitter and blocking: neuromuscular jitter and the percentage of blocks were significantly reduced at the increase of the stimulation rate (jitter: 166.5   90.5   50.3 mus; percentage of blocks: 24   13   2% at 10, 20, and 50 Hz, respectively) (Fig. 2).