Correlations between slow-rate repetitive nerve stimulation and characteristics associated with amyotrophic lateral sclerosis in Chinese patients

[Purpose] To clarify the features associated with decrements in compound muscle action potentials (CMAP) during slow-rate repetitive nerve stimulation (RNS) of muscles involved in amyotrophic lateral sclerosis (ALS) in mainland China. [Subjects and Methods] A retrospective study of decremental responses to slow-rate RNS was performed to compare patients with ALS to those with myasthenia gravis (MG). [Results] A significant decrement (>5%) was observed in at least one muscle in 54% of ALS patients. The trapezius muscle was the most commonly affected (67%). In the ALS group, the CMAP amplitude evoked by the first stimulus was negatively correlated with the CMAP decrement in ulnar but not accessory nerves. Additionally, a positive decrement was associated with disease progression but not gender, age at onset, disease duration, region of onset, ALSFRS-R scores, or ALS diagnostic subgroup in ALS. Furthermore, the incidence of positive decrements and the decremental percentages were significantly higher in myasthenia gravis (MG) than in ALS. [Conclusions] The lower CMAP amplitude by the first RNS stimulus was more likely to induce a positive decrement in the ulnar nerve in ALS patients. The positive decremental responses to RNS observed in ALS indicate the faster progress of the disease, which is helpful for evaluating prognoses.