Amyotrophic lateral sclerosis (ALS) and progressive muscular atrophy (PMA) are characterized by a loss of motor units (MUs), reinnervation and, eventually, muscle fibre loss. These three aspects are all reflected in the compound muscle action potential scan (CMAP scan, a high-detail stimulus response curve), which visualizes large MU potentials as 'steps'. We explored changes in the CMAP scan over time, combined the information on steps and CMAP amplitude into a CMAP scan-based progression score (CSPS), and correlated this score with motor unit number estimates (MUNE). Ten patients (three PMA, seven ALS; age 37-77 years) were included. CMAP scan and MUNE measurements were performed five times during a three-month period. Nine patients had additional measurements. The follow-up period was 3-24 months. Results demonstrated that abnormalities in steps preceded a decline in maximum CMAP amplitude during follow-up. Usually, both steps and maximum CMAP amplitude changed between recordings. The correlation between the CSPS and MUNE was-0.80 (p < 0.01). In conclusion, the CMAP scan can be used to visualize and quantify disease progression in a muscle affected by MND. The CSPS is a measure of MU loss that is quick and easy to obtain and that, in contrast to MUNE, has no sample bias.

ALS, CMAP scan, Monitoring, Motor unit, PMA,
Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration
Erasmus MC: University Medical Center Rotterdam

Maathuis, E.M, Drenthen, J, van Doorn, P.A, Visser, G.H, & Blok, J.H. (2013). The CMAP scan as a tool to monitor disease progression in ALS and PMA. Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration, 14(3), 217–223. doi:10.3109/21678421.2012.732079