Lower motor neuron involvement in ALS assessed by motor unit number index (MUNIX): Long-term changes and reproducibility

Abstract

Objective: Motor unit number estimation (MUNE) techniques such as motor unit number index (MUNIX) have been used to quantify lower motor neuron loss and disease progression in amyotrophic lateral sclerosis (ALS). We investigated the consistency of reproducibility of MUNIX in 30 ALS-patients during the course of the disorder.

Methods: MUNIX was recorded in abductor pollicis brevis and tibialis anterior muscles bilaterally in ALS-patients by two measurements at the first and at one follow-up visit and once in healthy controls. Intra-rater reproducibility was evaluated by three statistical methods: interclass correlation coefficient (ICC), correlation coefficient analysis (CCA), and coefficient of variation (CV).

Results: We found significant correlation between the first and second measurement of MUNIX in all tested muscles and at the follow-up visit (r⩾0.891, p<0.01) and good statistically significant reproducibility of MUNIX in all four measured muscles at the follow-up visit (ICC⩾0.946, p<0.01). The CV of MUNIX at the follow-up visit ranged from 13.90% to 32.95%.

Conclusions: This study shows good consistency of reproducibility of MUNIX in the course of ALS.

Significance: This study suggests that MUNIX can be used to track the progression of the disorder both in clinical routine and in treatment trials.

Keywords: Amyotrophic lateral sclerosis (ALS); Consistency; Motor unit number index (MUNIX); Reproducibility.