Estimating motor unit numbers from a CMAP scan: Repeatability study on three muscles at 15 centres.
Sørensen DM., Bostock H., Abrahao A., Alaamel A., Alaydin HC., Ballegaard M., Boran E., Cengiz B., de Carvalho M., Dunker Ø., Fuglsang-Frederiksen A., Graffe CC., Jones KE., Kallio M., Kalra S., Krarup C., Krøigård T., Liguori R., Lupescu T., Maitland S., Matamala JM., Moldovan M., Moreno-Roco J., Nilsen KB., Phung L., Santos MO., Themistocleous AC., Uysal H., Vacchiano V., Whittaker RG., Zinman L., Tankisi H.
OBJECTIVE: To assess the repeatability and suitability for multicentre studies of MScanFit motor unit number estimation (MUNE), which involves modelling compound muscle action potential (CMAP) scans. METHODS: Fifteen groups in 9 countries recorded CMAP scans twice, 1-2 weeks apart in healthy subjects from abductor pollicis brevis (APB), abductor digiti minimi (ADM) and tibialis anterior (TA) muscles. The original MScanFit program (MScanFit-1) was compared with a revised version (MScanFit-2), designed to accommodate different muscles and recording conditions by setting the minimal motor unit size as a function of maximum CMAP. RESULTS: Complete sets of 6 recordings were obtained from 148 subjects. CMAP amplitudes differed significantly between centres for all muscles, and the same was true for MScanFit-1 MUNE. With MScanFit-2, MUNE differed less between centres but remained significantly different for APB. Coefficients of variation between repeats were 18.0% for ADM, 16.8% for APB, and 12.1% for TA. CONCLUSIONS: It is recommended for multicentre studies to use MScanFit-2 for analysis. TA provided the least variable MUNE values between subjects and the most repeatable within subjects. SIGNIFICANCE: MScanFit was primarily devised to model the discontinuities in CMAP scans in patients and is less suitable for healthy subjects with smooth scans.