Reliability of MScanFit Motor Unit Number Estimation in the Trapezius Muscle

MScanFit motor unit number estimation (MUNE) is the most recent MUNE method which has shown promising results in extremity muscles, but it has not been applied to bulbar muscles. Bulbar muscles are particularly important in the diagnosis of amyotrophic lateral sclerosis (ALS). This study aimed to investigate the feasibility and reliability of MScanFit MUNE in the accessory nerve and trapezius muscles.

A total of twenty healthy participants were examined twice within 1-2 weeks. We extracted the MScanFit MUNE and size parameter, and compound muscle action potential (CMAP) amplitude values. The reliability of these parameters was assessed using the intra-rater coefficient of variation (CoV), intraclass correlation coefficient (ICC), and Bland-Altman plots. We also correlated MUNE values with CMAP amplitudes using correlation coefficients.

Mean MUNE values (Day 1 = 132.1 and Day 2 = 137.4), CMAP amplitudes (Day 1 = 9.71 mV and Day 2 = 10.10 mV) and size parameters did not differ between the two sessions (p > 0.05). CoV showed excellent reliability for MUNE values, size parameters, and CMAP amplitudes (CoV < 7%) whereas ICCs showed moderate reliability for MUNE values (ICC = 0.619), poor to moderate reliability for size parameters (between 0.393 and 0.689), and good reliability for CMAP amplitude (ICC = 0.864) There was no correlation between MUNE values and CMAP amplitudes.

MScanFit MUNE is applicable and mostly reliable in the trapezius muscle. Further studies in patients are needed to investigate the sensitivity of MScanFit in this muscle in detecting motor unit loss, particularly in ALS.