Feasibility and reliability of MScanFit motor unit number estimation in peroneus longus muscle

Motor unit number estimation (MUNE) methods may be valuable to detect motor involvement earlier than compound muscle action potential (CMAP) amplitude. The most recent MUNE method, MScanFit, has been shown to have advantages compared with previously described methods. However, MScanFit has only been applied in a few lower extremity muscles. In this study we examined the feasibility and reliability of MScanFit in peroneus longus muscle.

Twenty healthy controls (16 males and 4 females; mean age, 36.05 ± 2.58 years) were examined twice within a 1- to 2-week interval. Fibular nerve was stimulated at the knee and CMAP scans were recorded from peroneus longus muscle. From this, MScanFit MUNE and size parameters were calculated, as was the CMAP amplitude. The reliability was examined using coefficient of variation (CV) and intraclass correlation coefficient (ICC). MUNE was correlated with CMAP amplitude using linear regression analysis.

The CV between sessions was higher for CMAP amplitude (11.63 ± 1.88%) than MScanFit MUNE (3.13 ± 0.78%). Among the size parameters, mean unit amplitude (μV) showed the lowest CV (11.46 ± 1.77%). Using ICC, CMAP amplitude exhibited good reliability (0.787), whereas that of MScanFit MUNE was excellent (0.902). Reliability was good for all size parameters. There was no significant correlation between MScanFit MUNE and CMAP amplitude (R = 0.25, P > .05).

MScanFit MUNE is feasible in the peroneus longus muscle, with high test-retest reliability in healthy subjects. Studies in patients are needed to examine the sensitivity of this muscle in disease.