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.

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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