The CMAP idealizes the summation of a group of almost simultaneous action potentials from several muscle fibers in the same area. These are usually evoked by stimulation of the peripheral motor nerve.
Scientists wanted to determine which compound muscle action potential (CMAP) scan-derived electrophysiological markers are most sensitive for monitoring disease progression in amyotrophic lateral sclerosis (ALS), and whether they hold value for clinical trials.
Theye used four independent patient cohorts to assess longitudinal patterns of a comprehensive set of electrophysiological markers including their association with the ALS functional rating scale (ALSFRS-R).
The scientists recorded 225 thenar CMAP scan in 65 patients.
Electrophysiological markers showed extensive variation in their longitudinal trajectories. Expressed as standard deviations per month, motor unit number estimation (MUNE) values declined by 0.09, D50, a measure that quantifies CMAP scan discontinuities, declined by 0.09 and maximum CMAP by 0.05.
ALSFRS-R declined fastest, however the between-patient variability was larger compared to electrophysiological markers, resulting in larger sample sizes. MUNE reduced the sample size by 19.1% (n = 388 vs n = 314) for a 6-month study compared to the ALSFRS-R.
Conclusions: CMAP scan-derived markers show promise in monitoring disease progression in ALS patients, where MUNE may be its most suitable derivate.
Yet this study is weird, as it is known that electrophysiology (an very indirect measure of lower motor neuron activity done on muscle surface) is not accurate as it relies much on interpretation by the practitioner. In addition comparing electrophysiological markers to the unreliable ALSFRS-R looks like a very bad idea.