Multipoint incremental motor unit number estimation versus amyotrophic lateral sclerosis functional rating scale and the medical research council sum score as an outcome measure in amyotrophic lateral sclerosis

Introduction: Monitoring the disease progression in amyotrophic lateral sclerosis (ALS) is a challenge due to different rates of progression between patients. Besides clinical methods to monitor disease progression, such as the ALS functional rating scale (ALSFRS) and the medical research council (MRC) sum score, quantitative methods like motor unit number estimation (MUNE) are of interest.

Objective: The objective of the present study is to evaluate the rate of progression in ALS using multipoint incremental MUNE and to compare MUNE, ALSFRS and MRC sum score at baseline and at 6 months for progression of the disease.

Materials and methods: Multipoint incremental MUNE using median nerve, ALS-FRS and MRC sum score was carried out in 29 ALS patients at baseline and then at 6 months.

Results: Of the 29 ALS patients studied, the mean MUNE at baseline was 21.80 (standard deviation [SD]: 19.46, range 4-73), 15.9 in the spinal onset group (SD: 14.60) and 30.16 (SD: 22.89) in the bulbar onset group. Spinal onset patients had 74.02% of baseline MUNE value while bulbar onset patients had only 24.74% baseline value MUNE at 6 months follow-up (Unpaired t-test, P = 0.001). ALSFRS and MRC sum score showed statistically significant decline (P < 0.001) at 6 months follow-up. MUNE had the highest sensitivity for progression of the disease when compared to the ALS FRS and MRC sum score.

Conclusion: Multipoint incremental MUNE is a valuable tool for outcome measure in ALS and other diseases characterized by motor unit loss. The rate of decline of multipoint incremental MUNE is more sensitive than that of MRC sum score and ALSFRS-R, when expressed as the percentage change from baseline.