Reproducibility of motor unit number index and MScanFit motor unit number estimation across intrinsic hand muscles

Abstract

Introduction We aimed to evaluate the reproducibility of the motor unit number index (MUNIX) and MScanFit motor unit number estimation (MScan) when recording over intrinsic hand muscles. Methods The compound muscle action potential (CMAP) amplitude, MUNIX and MScan were measured from the abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digit minimi (ADM) muscles from 15 healthy volunteers on three different occasions. Results The reproducibility of CMAP amplitudes was excellent, with intraclass correlation coefficient (ICCs) of 0.86 (APB), 0.90 (FDI), and 0.96 (ADM). MUNIX (ICC_APB 0.73; ICC_FDI 0.85; ICC_ADM 0.85) and MScan (ICC_APB 0.86; ICC_FDI 0.83; ICC_ADM 0.81) were highly reproducible across the three muscles. There were no significant correlations between MUNIX and MScan coefficients of variation (CVs) and CMAP amplitude CVs. Discussion Reproducibility of MUNIX and MScan was not significantly different across the intrinsic hand muscles and was independent on CMAP amplitude variability.