[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.