CMAP scan discontinuities: automated detection and relation to motor unit loss.

Abstract Objective To evaluate an automated method that extracts motor unit (MU) information from the CMAP scan, a high-detail stimulus–response curve recorded with surface EMG. Discontinuities in the CMAP scan are hypothesized to result from MU loss and reinnervation. Methods We introduce the parameter D50 to quantify CMAP scan discontinuities. D50 was compared with a previously developed manual score in 253 CMAP scans and with a simultaneously obtained motor unit number estimate (MUNE) in 173 CMAP scans. The effect of MU loss on D50 was determined with a simulation model. Results We found a high agreement (sensitivity = 86.8%, specificity = 96.6%) between D50 and the manual score. D50 and MUNE were significantly correlated below 80 MUs ( r  = 0.65, n  = 68, p r  = 0.23, n  = 59, p  = 0.08). Conclusions Discontinuities in the CMAP scan as expressed by a decreased D50 are related to significant MU loss. The determination of D50 is objective, quantitative, and less time-consuming than both manual scoring and many existing MUNE methods. Significance D50 is potentially useful to monitor neurogenic disorders and moderate to severe MU loss.