Function of the Normal Neuromuscular Junction in Young Children.

Introduction/aims: The repetitive nerve stimulation (RNS) test is fundamental to test the functional integrity of the neuromuscular junction. RNS data are scarce for newborns and young children, limiting early diagnostic efforts to identify children with neuromuscular diseases. Here, we performed RNS in young children.

Methods: RNS of the axillary nerve was performed in 34 otherwise healthy young children (0 to 48 months of age) undergoing procedural sedation or analgesia. Compound muscle action potentials (CMAP) were recorded over the deltoid muscle. CMAP amplitude and area decrement between the 1st and 4th potential were determined at 3 Hz stimulation. Post-tetanic facilitation, twitch-to-tetanus ratio, and heart rates were recorded.

Results: The largest CMAP amplitude decrement value was 7% at rest, having a median of 1%, and an interquartile range of 1%-3%. There was no correlation between the CMAP amplitude decrement and age. In contrast, a moderate positive correlation was found between the CMAP area decrement and age, occasionally exceeding 10% in infants younger than 6 months. Both post-tetanic facilitation and twitch-to-tetanus ratio exhibited a moderate positive correlation with age.

Discussion: While the CMAP amplitude decrement in young children was within the adult normal range, the area decrement may be higher. Studies of RNS on other nerves in unsedated children are needed to investigate the findings from this study further.