Estimating motor unit numbers from a CMAP scan: Repeatability study on three muscles at 15 centres

Area of Science:

• Neurology
• Biomedical Engineering
• Clinical Electrophysiology

Background:

• Motor Unit Number Estimation (MUNE) is crucial for assessing neuromuscular disorders.
• MScanFit software models compound muscle action potential (CMAP) scans for MUNE.
• Previous versions of MScanFit were optimized for patient scans with discontinuities.

Purpose of the Study:

• To evaluate the repeatability and multicenter suitability of MScanFit for MUNE.
• To compare the original MScanFit-1 with a revised MScanFit-2 program.
• To assess MUNE performance across different muscles (APB, ADM, TA) and international research sites.

Main Methods:

• Fifteen international research groups recorded CMAP scans from healthy subjects twice, 1-2 weeks apart.
• MScanFit-1 and MScanFit-2 were used to analyze scans from abductor pollicis brevis (APB), abductor digiti minimi (ADM), and tibialis anterior (TA) muscles.
• MScanFit-2 incorporated a revised method for setting minimal motor unit size based on maximum CMAP amplitude.

Main Results:

• Significant inter-center variability in CMAP amplitudes and MScanFit-1 MUNE was observed.
• MScanFit-2 reduced inter-center MUNE differences, though APB remained significantly different.
• Repeatability coefficients of variation were 18.0% (ADM), 16.8% (APB), and 12.1% (TA).

Conclusions:

• MScanFit-2 is recommended for multicenter MUNE studies.
• The tibialis anterior muscle yielded the most repeatable and least variable MUNE values.
• MScanFit's suitability for healthy subjects with smooth CMAP scans is enhanced by MScanFit-2.