Reproducibility of statistical motor unit number estimates in amyotrophic lateral sclerosis: comparisons between size- and number-weighted modifications.

Motor unit number estimations (MUNEs) can directly assess motor unit populations in muscle and quantify the degree of physiological or pathological motor unit degeneration. A high degree of reproducibility and reliability is required of any effective quantitative tool. MUNE is being increasingly applied clinically, and statistical MUNE has several advantages over alternative techniques. Nevertheless, the optimal method of applying statistical MUNE with respect to its reproducibility has not been established. We performed statistical MUNE by selecting the most compensated compound muscle action potential (CMAP) area as a test area and modified the results obtained by using the weighted mean surface-recorded motor unit potential (SMUP). MUNE measurements made in patients with amyotrophic lateral sclerosis (ALS) showed better reproducibility after incorporating the size-weighted modification. Therefore, we suggest that the size-weighted MUNE in combination with the selection of testing "neurogenically compensated" CMAP areas is a more reliable method of statistical MUNE analysis in ALS patients.