Reference range for motor unit number estimation by multiple point stimulation

Objective To examine the technique of multiple point stimulation for motor unit number estimation (MUNE) and to establish the normative value range in Chinese.Methods Surface-recorded motor unit action potentials were measured in 80 healthy subjects.The compound muscle action potential (CMAP) amplitude measured by maximum baseline to negative peak was recorded.The stimuli sites included the wrist, 6 cm above the wrist, elbow and 6 cm above the elbow along median nerve and ulnar nerve.Individual motor unit responses were obtained by adjusting location of the stimulate electrode and isolating threshold responses with distinct morphologies.Then, stimulus intensity was increased gradually to detect single motor unit action potentials (SMUPs).SMUPs were recorded three times.Stimulating was increase again to record another SMUPs set.Total of 12 SMUPs were recorded.Repeat the whole procedure for two times.Results MUNE was 230.0±35.7 in abductor pollieis brevis muscle, and 242.5±30.2 in aductor digiti minimi muscle for multiple point stimulation.Test-retest correlation coefficients and coefficients of variation for mean of two MUNE were 0.88-0.91 and 13.20%-15.24%.Conclusions The multiple point stimulation is a useful and replicable method to asses the MUNE. Key words: Motor neurons;  Amyotrophic lateral sclerosis;  Evoked potentials;  Electric stimulation;  Electromyography;  Reference values