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Background:Nowadays,it is widely known that decremental responses in low-frequency repetitive nerve stimulation (LF-RNS) are frequently observed in patients with amyotrophic lateral sclerosis (ALS).The pathological mechanism of this phenomenon remains unknown.This study aimed to illuminate the features of RNS in Chinese patients with ALS.Methods:Clinical and electrophysiological data of 146 probable and definite ALS patients who underwent RNS were retrospectively enrolled and analyzed.LF-RNS (3 Hz) was performed in trapezius,deltoid,abductor digiti minimi (ADM),quadriceps femoris,and tibialis anterior.High-frequency RNS (HF-RNS,10 Hz) was performed only in ADM.The two-sample t-test and Chi-squared test were used for statistical analysis.Results:Decremental responses to LF-RNS (≥10%) in at least one muscle were detected in 83 (56.8%) of the cases and were most commonly seen in trapezius and deltoid.The incidence ofdecremental response was higher in patients with upper limb onset.Incremental responses to HF-RNS (≥60%) in ADM were observed in 6 (5.6%) of the cases.In 106 muscles with decremental response,62 (57.4%) muscles had a continuous decremental patt,more than a U-shape patt (37 cases,34.3%).Nineteen cases showed definite decrements in LF-RNS tests in trapezius,while no abnormalities were found in the electromyography and neurological examination of the stemocleidomastoid muscle,supplied by the accessory nerve as well.Conclusions:Decremental responses in the RNS are commonly observed in ALS patients.The findings regarding the trapezius indicated that some ALS onsets could be initiated by a dying back process,with destruction of neuromuscular junctions (NMJs) before motor neurons.Incremental responses in the ADM implied damage of the NMJs involved both the post and presynaptic membranes.